EP4731164A1

EP4731164A1 - Composite material of bismuth oxycarbonate and organosilicon compounds for filtering ultraviolet radiation

Info

Publication number: EP4731164A1
Application number: EP24736417.7A
Authority: EP
Inventors: Clément LARQUET
Original assignee: LOreal SA
Current assignee: LOreal SA
Priority date: 2023-06-22
Filing date: 2024-06-21
Publication date: 2026-04-29
Also published as: CN121398779A; WO2024261324A1; FR3150104A1

Abstract

The present invention relates to a composite material comprising at least one particle of bismuth oxycarbonate of empirical formula (BiO)2-x(CO3), and solvates thereof such as hydrates thereof, in which -0.4 < x < 0.6, the largest mean dimension of said particles being less than 400 nm; and at least one organosilicon compound, to the process for preparing them, and also to cosmetic compositions and uses using said composite materials.

Description

Description Title: Composite material of bismuth oxycarbonate and organosilicon compounds for filtering ultraviolet radiation Technical field The present invention relates to the field of sun protection and more particularly to composite materials of bismuth oxycarbonate, and solvates thereof, such as hydrates thereof, and of organosilicon compounds, for their use in filtering ultraviolet radiation. The invention also relates to a composition, in particular a cosmetic composition, notably comprising composite materials of bismuth oxycarbonate, and solvates thereof, such as hydrates thereof, and of organosilicon compounds. Keratin materials are exposed daily to sunlight. It is known that light radiation with wavelengths of between 280 nm and 400 nm makes it possible to tan the human epidermis. However, rays with wavelengths of between 280 and 320 nm, referred to as UV-B rays, are detrimental to the development of a natural tan. This exposure is also liable to induce impairment of the biomechanical properties of the epidermis, which is reflected by the appearance of wrinkles, leading to premature ageing of the skin. It is also known that UV-A rays with wavelengths of between 320 and 400 nm penetrate more deeply into the skin than UV-B rays. UV-A rays promote rapid and persistent pigmentation of the skin. Under normal conditions, daily exposure to UV-A radiation, even of short duration, can also cause damage to collagen and elastin fibers, which is reflected by a modification to the microrelief of the skin, the appearance of wrinkles and uneven pigmentation (i.e. liver spots, non-uniformity of the complexion, etc.). Furthermore, prolonged exposure to the sun can also dry out the hair, making it brittle. Consequently, it is of utmost importance to protect keratin materials, notably human keratin materials such as the skin. Prior art In order to counteract these undesirable effects, it is common practice to formulate organic and/or inorganic anti-UV-A and/or anti-UV-B screening agents in compositions intended to provide sun protection. Many photoprotective cosmetic compositions for the skin have been proposed to date. They generally contain organic UV-screening agents and/or inorganic UV-screening agents, which act according to their own chemical nature and according to their own physical properties by absorption, reflection or scattering of the UV radiation. They generally contain combinations of oil-soluble organic UV-screening agents and/or of water-soluble organic UV-screening agents combined with metal oxide pigments, such as titanium dioxide (TiO2) or zinc oxide (ZnO). As regards customary organic screening agents, they must have acceptable cosmetic properties, good solubility in the customary solvents, notably in oils, and also good photostability, alone and in combination. They must also be colorless or have a color that is cosmetically acceptable to consumers. These organic screening agents are generally used as mixtures and such combinations of screening agents can limit the formulation range. In addition, nowadays, photoprotection using inorganic UV-screening agents is a highly important expectation of consumers, because they consider mineral sunscreens to be safer. TiO₂ and ZnO are the most commonly used mineral UV-screening agents. However, one of the major drawbacks of such mineral screening agents is that, once applied to the skin, they cause a whitening effect thereon which is cosmetically undesirable and generally not particularly appreciated by users. This effect is all the more pronounced when the concentration of mineral screening agents in the composition is high, which limits the concentration thereof in sun formulations. To avoid this problem, it would of course be possible to use reduced amounts of inorganic screening agent(s), but the resulting compositions, which would certainly result in films having acceptable transparency on the skin, would then no longer offer suitable protection in the UV range, which greatly limits the advantage of such an option. Furthermore, aside from significant whitening, using large amounts of these UV-screening agents leads to unpleasant sensations after application to the skin, and notably causes sensations of roughness and dryness on the skin, in the case of significant and regular use of the products. Consumers are increasingly seeking products which are effective but are also very easy to apply, are comfortable for longer and have satisfactory sensory properties. Disclosure of the invention There is thus still a need for inorganic UV-screening agents that afford efficient photoprotection and that do not have the drawbacks presented above. In particular, there is still a need for inorganic UV-screening agents that are capable of efficiently blocking UV rays, in particular in the UV-A and UV-B range, and notably UV-B rays, which have high transparency to visible light, which do not whiten the keratin materials to which they are applied, and which have good cosmetic properties. There is notably still a need for mineral UV-screening agents other than titanium dioxide or zinc oxide, which prove just as effective, which are transparent, which do not cause sensations of roughness and dryness on the skin, and which are easy to formulate, notably at high concentrations. The present invention is specifically directed towards proposing novel mineral UV- screening agents which can meet these expectations. Summary of the invention Thus, according to a first of its aspects, the present invention relates to a composite material comprising: a) at least one particle of bismuth oxycarbonate of empirical formula (I) (BiO)_2-x(CO₃), and solvates thereof, such as hydrates thereof, in which -0.4 < x < 0.6, the largest mean dimension of said particles being less than 400 nm; and b) at least one organosilicon compound. Preferably, the present invention relates to a composite material comprising: - a core comprising at least a) at least one particle of bismuth oxycarbonate of empirical formula (I) (BiO)2-x(CO3), and solvates thereof, such as hydrates thereof, in which -0.4 < x < 0.6, the largest mean dimension of said particles being less than 400 nm; and - at least one layer continuously or discontinuously surrounding said core and comprising b) at least one organosilicon compound. Preferably, the present invention relates to a composite material comprising: a) at least one particle of bismuth oxycarbonate in the form of tubes, platelets and/or rods, preferably in the form of platelets and/or rods and of empirical formula (I) (BiO)2- _x(CO₃), and solvates thereof, such as hydrates thereof, in which -0.4 < x < 0.6, the largest mean dimension of said particles being less than 400 nm; and b) at least one organosilicon compound. Preferably, the composite material according to the invention has a mean size of the largest dimension of the composite material particle ranging from 0.005 µm to 10 µm. Preferably, the mean size of the largest dimension of the composite material particle ranges from 0.01 µm to 1 µm. According to one embodiment, the composite material according to the invention also comprises one or more inorganic compounds c) other than said bismuth oxycarbonate particles a), and solvates thereof, such as hydrates thereof, preferably chosen from inorganic oxides or hydrated forms thereof, more preferentially chosen from Al(OH)₃, Al₂O₃, SiO₂, TiO2 and ZnO, and even more preferentially chosen from Al(OH)3 or SiO2. Surprisingly, and as emerges from the examples below, the inventors discovered that the composite materials according to the invention have excellent efficacy for filtering ultraviolet radiation, and in particular UV-B rays, and also high transparency in the visible range, and make it possible to afford the composition containing them cosmetic properties that are satisfactory to consumers. For the purposes of the present invention, the term "composite material" means a heterogeneous particulate solid material comprising at least two immiscible components, the components of which are linked via physical and/or chemical interactions. For the purposes of the present invention, the term “high transparency in the visible range” means particles having a high transmission of rays between 400 and 780 nm. For the purposes of the present invention, the term “efficacy for filtering ultraviolet radiation” means particles having a threshold absorbance in the UV range, in the dispersion medium comprising said particles in a mass fraction of 0.005%, of greater than 0.23, preferably greater than or equal to 0.25, preferably greater than or equal to 0.30, and even more preferentially greater than or equal to 0.35. The higher the threshold absorbance, the greater the efficacy for filtering UV radiation. UV-B radiation means the wavelength range extending from 280 to 320 nm. UV-A radiation means the wavelength range extending from 320 to 400 nm. Visible light means the wavelength range extending from 400 to 780 nm. Thus, for the purposes of the present invention, the term “UV-screening agent” is intended to denote any compound which screens out ultraviolet (UV) radiation in the wavelength range extending from 280 nm to 400 nm. The term “UV-B screening agent” is intended to denote any compound which screens out ultraviolet (UV) radiation in the wavelength range extending from 280 nm to 320 nm. The term “UV-A screening agent” is intended to denote any compound which screens out ultraviolet (UV) radiation in the wavelength range extending from 320 nm to 400 nm. This efficacy of the composite materials according to the invention is, to the inventors’ knowledge, characterized for the first time. It has never been proposed to use composite materials of bismuth oxycarbonate, and solvates thereof, such as hydrates thereof, and of organosilicon compounds in cosmetic compositions intended for the efficient screening of UV radiation, in particular UV-B radiation. The composite materials according to the invention are notably intended for protecting keratin materials, in particular the skin and the hair, against UV radiation, in particular in cosmetic compositions for the fields of sun protection, haircare, hair treatment and makeup. Thus, according to another aspect, the present invention also relates to the non-therapeutic cosmetic use of a composite material according to the invention, for filtering UV radiation, preferably UV-B, comprising at least the application to keratin materials of a composition comprising a composite material according to the invention. The present invention also relates to a non-therapeutic cosmetic process for filtering UV radiation, preferably UV-B, comprising at least the application to keratin materials of a composition comprising composite materials of bismuth oxycarbonate, and solvates thereof, such as hydrates thereof, and of organosilicon compounds as defined above. The present invention also relates to processes for preparing the composite materials according to the invention. The term “keratin materials” notably means the skin, including the scalp, the lips, and also keratin fibers such as the hair, the eyelashes, the eyebrows, in particular the skin and/or the hair, and preferably the skin. The term “at least one” is equivalent to “one or more”. The expressions “of between ... and ...”, “comprises from ... to ...”, “formed from ... to ...” and “ranging from ... to ...” should be understood as being inclusive of the limits, unless otherwise specified. Other characteristics, variants and advantages of the compositions according to the invention will emerge more clearly on reading the description and the examples that follow. Brief description of the drawings [Fig 1] depicts the absorbance spectrum obtained by UV-visible spectrophotometry on dispersions of composite material A at 0.005% by mass in isododecane. [Fig 2] depicts the absorbance spectrum obtained by UV-visible spectrophotometry on dispersions of composite material B at 0.005% by mass in isododecane. [Fig 3] depicts the absorbance spectrum obtained by UV-visible spectrophotometry on dispersions of composite material C at 0.005% by mass in a water/propylene glycol/polysorbate 20 mixture with respective mass fractions of 49.85/49.85/0.30. [Fig 4] depicts the absorbance spectrum obtained by UV-visible spectrophotometry on dispersions of composite material D at 0.005% by mass in a water/propylene glycol/polysorbate 20 mixture with respective mass fractions of 49.85/49.85/0.30. [Fig 5] depicts the absorbance spectrum obtained by UV-visible spectrophotometry on dispersions of composite material E at 0.005% by mass in a water/propylene glycol/polysorbate 20 mixture with respective mass fractions of 49.85/49.85/0.30. [Fig 6] depicts the absorbance spectrum obtained by UV-visible spectrophotometry on dispersions of composite material F at 0.005% by mass in a water/propylene glycol/polysorbate 20 mixture with respective mass fractions of 49.85/49.85/0.30. [Fig 7] depicts the absorbance spectrum obtained by UV-visible spectrophotometry on dispersions of composite material G at 0.005% by mass in isododecane. [Fig 8] depicts the absorbance spectrum obtained by UV-visible spectrophotometry on dispersions of composite material H at 0.005% by mass in isododecane. [Fig 9] depicts the absorbance spectrum obtained by UV-visible spectrophotometry on dispersions of composite material I at 0.005% by mass in isododecane. [Fig 10] depicts the absorbance spectrum obtained by UV-visible spectrophotometry on dispersions of composite material Z at 0.005% by mass in isododecane. [Fig 11] depicts the absorbance spectrum obtained by UV-visible spectrophotometry on dispersions of composite material J at 0.005% by weight in isododecane. [Fig 12] depicts the absorbance spectrum obtained by UV-visible spectrophotometry on dispersions of composite material K at 0.005% by weight in isododecane. [Fig 13] depicts the absorbance spectrum obtained by UV-visible spectrophotometry on dispersion A1 of composite material A at 0.005% by weight in caprylic capric triglyceride. [Fig 14] depicts the absorbance spectrum obtained by UV-visible spectrophotometry on dispersion A2 of composite material A at 0.005% by weight in propylene carbonate. [Fig 15] depicts the absorbance spectrum obtained by UV-visible spectrophotometry on composition A7 at 0.005% by weight of composite material A in water. [Fig 16] depicts the absorbance spectrum obtained by UV-visible spectrophotometry on composition A8 at 0.005% by weight of composite material A in water. Detailed description The invention relates to a composite material comprising a) of formula (I) (BiO)_2-x(CO₃), and solvates thereof, such as hydrates thereof, in which -0.4 < x < 0.6, the largest mean dimension of said particles being less than 400 nm; and at least one organosilicon compound b). C^{OMPOSITE MATERIAL} As indicated previously, the composite material comprises at least a) a bismuth oxycarbonate particle, and solvates thereof, such as hydrates thereof, and at least b) an organosilicon compound. The composite materials according to the invention are nanometric and/or micrometric in size. In particular, the mean size of the largest dimension of the composite material particle ranges from 0.005 µm to 10 µm. Preferably, the mean size of the largest dimension of the composite material particle ranges from 0.01 µm to 1 µm. The term “mean dimension” is intended to denote the number-average value of the dimensions of the primary particles. The dimensions of the particles can be determined by transmission electron microscopy, for example using a Hitachi HT 7700 microscope, notably at an acceleration voltage of 100 kV, by scanning electron microscopy, or else by measuring the specific surface area via the BET method, or else using a laser particle size analyzer. Preferably, the dimensions of the particles are determined by transmission electron microscopy, for example using a Hitachi HT 7700 microscope, notably at an acceleration voltage of 100 kV, or by scanning electron microscopy. Preferentially, the measurement is performed on the smallest individualized or individualizable objects. The number-average value may be calculated by analyzing the images obtained using software, such as the ImageJ software (C.A. Schneider, W.S. Rasband, K.W. Eliceiri, NIH Image to ImageJ: 25 years of image analysis, Nat. Methods. 9 (2012) 671–675). The mean dimension is chosen from the mean length L, the mean width l, the mean thickness e, or the mean diameter d. The term “mean size of the largest dimension” or “largest mean dimension” of the composite materials or the particles is intended to denote the largest mean dimension of a surface, such as a face, that it is possible to measure between two diametrically opposed points on an individual particle. The “length” L of a composite material or of a particle is the largest dimension thereof which can be observed in an image taken in a direction perpendicular to the plane on which said composite material or said particle rests. The “width” l and the “thickness” e of a composite material or of a particle are the lengths of the long and short axes, respectively, of the smallest possible ellipse in which the median cross section of said composite material or of said particle can be inscribed. The “diameter” d of a composite material or of a particle is the largest dimension that can be observed along a line which passes through the center of a circle or a sphere. The composite materials according to the invention may be of various shapes and structures. The composite materials according to the invention may notably be spherical, cubic, platelet- shaped, cylindrical or tubular. The shape of said composite materials will notably depend on the process for preparing them and on the operating conditions. In particular, the composite materials according to the invention may be in the form of tubes, platelets, sheets, rods, spheres, flowers, pompoms, threads, filaments, fibers, needles, cubes or any mixture thereof. The composite materials according to the invention may also aggregate in the form of superstructures. For example, platelets, tubes and/or rods can aggregate in the form of spheres, flowers or pompoms. In one particular embodiment, the composite materials according to the invention are in the form of spheres. According to a particular embodiment, the composite materials according to the invention are in the form of tubes, platelets and/or rods. Even more preferentially, the composite materials according to the invention are in the form of platelets and/or rods. The composite materials in the form of platelets or rods or tubes thus differ notably from spherical or fibrous forms or flowers, pompoms, threads, filaments, needles or cubes. It is understood that the composite materials according to the invention can be used in the form of a mixture. In particular, the composite materials according to the invention can be used in a mixture in any proportion of platelets and/or of rods and/or of tubes. According to a preferred embodiment, the composite materials used according to the invention are predominantly or exclusively in the form of platelets. A composite material in “platelet” form has a length greater than the width thereof, and a width greater than the thickness thereof. According to a preferred embodiment, the composite materials are predominantly or exclusively in the form of rods. A composite material in “rod” form has a solid cylindrical form and the length thereof L is greater than the diameter thereof d, or has a prism form, the base of which is solid and polygonal, preferably triangular or hexagonal, and the diameter d of the circle within which this polygonal base is circumscribed is less than the length L of the prism. According to a preferred embodiment, the composite materials are predominantly or exclusively in the form of tubes. A composite material in “tube” form has a hollow cylindrical form and the length thereof L is greater than the diameter thereof d. For the purposes of the present invention, the term “predominantly in the form of platelets/rods/tubes” is intended to denote that at least 50% by number, in particular at least 70% by number, or even at least 90% by number of the composite materials are in the form of platelets/rods/tubes, respectively. The bismuth oxycarbonate particle(s) a), and solvates thereof, such as the hydrates thereof, and the organosilicon compound(s) b) may be arranged in different ways within the composite material. According to one embodiment, the composite material may have at least one core and at least one coating as a layer or layers surrounding said core. Thus, they may comprise at least one coating as a layer or layers surrounding a core that is chemically different from said coating. The coating may be formed of one or more layers. The core of the composite materials may consist of at least a) one or more particle of bismuth oxycarbonate of empirical formula (BiO)2-x(CO3), and solvates thereof, such as hydrates thereof, in which -0.4 < x < 0.6, the largest mean dimension of said particles being less than 400 nm. According to a particular embodiment, the core of the composite materials may consist of at least one inorganic compound c) different from said bismuth oxycarbonate particles a), and solvates thereof, such as hydrates thereof. The composite material may contain bismuth oxycarbonate particles a), and solvates thereof, such as hydrates thereof, as defined above in the core and/or in the layer(s) forming the coating. According to a particular embodiment, the material contains at least one bismuth oxycarbonate particle, and solvates thereof, such as hydrates thereof, as defined above in the core. According to another particular embodiment, the material contains bismuth oxycarbonate particles a), and solvates thereof, such as hydrates thereof, as defined above in the coating. According to one embodiment, the inorganic compound(s) c), when they are present, may cover all or some of at least one bismuth oxycarbonate particle a), and solvates thereof, such as hydrates thereof. According to another embodiment, the inorganic compound(s) c), when they are present, may be totally or partially covered with at least one bismuth oxycarbonate particle a), and solvates thereof, such as hydrates thereof. In particular, the molar ratio between the number of moles of coating compound(s) and the number of moles of core compound(s) ranges from 0.0001 to 20, preferably from 0.005 to 10, better still from 0.01 to 5, and even more preferentially from 0.05 to 3. According to a particular embodiment, the composite materials according to the invention contain at least one layer surrounding the core. Thus, according to a particular embodiment, the composite materials according to the invention comprise a core comprising at least a) particles of bismuth oxycarbonate of empirical formula (BiO)2-x(CO3), and solvates thereof, such as hydrates thereof, in which - 0.4 < x < 0.6, the largest mean dimension of said particles being less than 400 nm, said core being covered on the surface, continuously or discontinuously, with a coating comprising at least one organosilicon compound b). According to a first variant of the invention, the composite materials according to the invention include a coating, also called a shell or envelope, which is continuous, i.e. surrounding the entire surface of the core. According to a second variant of the invention, the composite materials in accordance with the invention include a coating, also known as a shell or envelope, which is discontinuous, i.e. discontinuously surrounding the core surface. Preferably, from 10% to 90%, more particularly from 10% to 70%, and even more particularly from 30% to 50% of the core surface is covered with the coating. According to one embodiment, the coating is a multilayer coating, i.e. comprising one or more inner layers and an outer layer, in other words several totally or partially superimposed layers, each of which may be continuous or discontinuous. In a multilayer coating, the term "inner layer" means any layer which is not an outer layer. This may be the layer directly superimposed on the core, or any intermediate layer between the core and the outer layer. In a multilayer coating, the term "outer layer" means the layer forming the last layer of the coating which is not adjacent to the core. The outer layer is separated from the core by at least one inner layer. The outer layer has no coating. In a multilayer coating consisting of two layers, the inner layer is the layer adjacent to the core and the outer layer is the layer adjacent to the inner layer and not adjacent to the core. In a multilayer coating consisting of more than two layers, the inner layers are the core- adjacent layer and the intermediate layer(s) between the core-adjacent layer and the outer layer. The inner layer(s) forming the multilayer coating of the composite material and the single outer layer of the composite material may be formed from identical or different compounds. Each layer may consist of a single compound or a mixture of compounds. In particular, the layer(s) may extend concentrically relative to the core. In particular, the composite materials according to the invention have a double layer surrounding the core, in other words an inner layer and an outer layer. According to a preferred embodiment, the composite materials according to the invention have at least one layer, preferably comprising at least one organosilicon compound b). According to a preferred embodiment, the composite materials according to the invention comprise: - a core comprising at least a) at least one particle of bismuth oxycarbonate of empirical formula (BiO)2-x(CO3), and solvates thereof, such as hydrates thereof, in which -0.4 < x < 0.6, the largest mean dimension of said particles being less than 400 nm, and - at least one layer continuously or discontinuously surrounding said core and comprising b) at least one organosilicon compound. Preferably, the composite materials according to the invention comprise: - a core comprising at least a) at least one particle of bismuth oxycarbonate of formula (I) (BiO)_2-x(CO₃), and solvates thereof, such as hydrates thereof, in which -0.4 < x < 0.6, the largest mean dimension of said particles being less than 400 nm, - a single layer adjacent to said core and comprising b) at least one organosilicon compound. According to another preferred embodiment, the composite materials according to the invention comprise: - a core comprising at least a) at least one particle of bismuth oxycarbonate of formula (I) (BiO)_2-x(CO₃), and solvates thereof, such as hydrates thereof, in which -0.4 < x < 0.6, the largest mean dimension of said particles being less than 400 nm, and b) at least one organosilicon compound, - at least one layer surrounding said core and comprising b) at least one organosilicon compound. According to a preferred embodiment, the composite materials according to the invention comprise: - a core comprising a) at least one particle of bismuth oxycarbonate of formula (I) (BiO)_2- x(CO3), and solvates thereof, such as hydrates thereof, in which -0.4 < x < 0.6, the largest mean dimension of said particles being less than 400 nm, and b) at least one organosilicon compound, - a single layer adjacent to said core and comprising b) at least one organosilicon compound. According to a particular embodiment, the composite materials according to the invention comprise: - a core comprising at least a) at least one particle of bismuth oxycarbonate of formula (I) (BiO)2-x(CO3), and solvates thereof, such as hydrates thereof, in which -0.4 < x < 0.6, the largest mean dimension of said particles being less than 400 nm, - an inner layer adjacent to said core, comprising b) at least one organosilicon compound. - an outer layer adjacent to said inner layer and comprising at least a) at least one particle of bismuth oxycarbonate of formula (I) (BiO)2-x(CO3), in which -0.4 < x < 0.6, and solvates thereof, such as hydrates thereof, the largest mean dimension of said particles being less than 400 nm, and b) at least one organosilicon compound. According to another preferred embodiment, the composite materials according to the invention comprise: - a core comprising at least a) at least one particle of bismuth oxycarbonate of formula (I) (BiO)_2-x(CO₃), and solvates thereof, such as hydrates thereof, in which -0.4 < x < 0.6, the largest mean dimension of said particles being less than 400 nm, and at least one inorganic compound c) different from said bismuth oxycarbonate particles a), - at least one layer surrounding said core and comprising b) at least one organosilicon compound. According to a preferred embodiment, the composite materials according to the invention comprise: - a core comprising at least a) at least one particle of bismuth oxycarbonate of formula (I) (BiO)2-x(CO3), and solvates thereof, such as hydrates thereof, in which -0.4 < x < 0.6, the largest mean dimension of said particles being less than 400 nm, and at least one inorganic compound c) different from said bismuth oxycarbonate particles a), - a single layer adjacent to said core and comprising b) at least one organosilicon compound. According to a particular embodiment, the composite materials according to the invention comprise: - a core comprising at least a) at least one particle of bismuth oxycarbonate of formula (I) (BiO)2-x(CO3), and solvates thereof, such as hydrates thereof, in which -0.4 < x < 0.6, the largest mean dimension of said particles being less than 400 nm, - an inner layer adjacent to said core, comprising at least one inorganic compound c) different from said bismuth oxycarbonate particles a), - an outer layer adjacent to said inner layer and comprising b) at least one organosilicon compound. a) Bismuth oxycarbonate particles The bismuth oxycarbonate particles a) according to the invention are of formula (I) (BiO)_2- x(CO3), and solvates thereof, such as hydrates thereof, in which -0.4 < x < 0.6, the largest mean dimension of said particles being less than 400 nm. The value of x may notably be determined by elemental analysis. Preferably, x is equal to 0 and the empirical formula of the bismuth oxycarbonate particles is (BiO)₂(CO₃). The bismuth oxycarbonate particles, and the solvates thereof, such as the hydrates thereof, according to the invention may be crystalline or amorphous. According to one embodiment of the invention, the bismuth oxycarbonate particles are amorphous. According to a preferred embodiment of the invention, the bismuth oxycarbonate particles are crystalline. It will be appreciated that the bismuth oxycarbonate particles may consist of a mixture of several bismuth oxycarbonate particles, and solvates thereof, such as hydrates thereof, having different empirical formulae and/or different shapes. Thus, the bismuth oxycarbonate particles, and solvates thereof, such as hydrates thereof, may be a mixture of amorphous particles and of crystalline particles. For the purposes of the present invention, “crystalline” means that the atoms forming the bismuth oxycarbonate particles are arranged in an ordered manner. In other words, the crystalline bismuth oxycarbonate particles are organized materials. In contrast, “amorphous” particles are those in which the atoms are disordered. The atoms of such particles do not exhibit any organization at the microscopic level. Preferably, the crystalline particles required according to the invention have the crystal phase of the natural ore bismutite, referred to as lamellar, and which has alternating layers of [Bi2O2]²⁺ and [CO3]^2-. Such particles crystallize in an orthorhombic system with the space group Imm2. The bismutite crystal structure of bismuth oxycarbonate may have the following lattice parameters: a = 3.865 Å; b = 3.862 Å; c = 13.675 Å and Vlattice = 0.204 nm³. This particular arrangement of atoms notably enables the growth of anisotropic objects. A particle is considered to be “anisotropic” when the elongation factor R between the length thereof L and the thickness thereof e, i.e. R = L / e, is greater than 2. According to the invention, the largest mean dimension of the crystalline or amorphous, preferably crystalline, bismuth oxycarbonate particles of formula (I) (BiO)_2-x(CO₃), and solvates thereof, such as hydrates thereof, in which -0.4 < x < 0.6, the largest mean dimension of said particles being less than 400 nm. Preferably, the largest mean dimension of said particles is less than or equal to 300 nm. In particular, the largest mean dimension of said particles ranges from 10 nm to 300 nm, preferably from 25 nm to 250 nm, and more preferentially from 25 nm to 200 nm. According to the invention, the particles of bismuth oxycarbonate of empirical formula (BiO)_2-x(CO₃), in which -0.4 < x < 0.6, can be of any shape. The shape of said particles will notably depend on the process for preparing them and on the operating conditions. In particular, the particles according to the invention may be in the form of tubes, platelets, sheets, rods, spheres, flowers, pompoms, threads, filaments, fibers, needles, cubes or any mixture thereof. The particles according to the invention may also aggregate in the form of superstructures. For example, platelets, tubes and/or rods can aggregate in the form of spheres, flowers or pompoms. According to a preferred embodiment, the particles according to the invention are in the form of tubes, platelets and/or rods. Even more preferentially, the particles according to the invention are in the form of platelets and/or rods. The particles in the form of platelets or rods or tubes thus differ notably from spherical or fibrous forms or flowers, pompoms, threads, filaments, needles or cubes. It is understood that the particles according to the invention can be used in the form of a mixture. In particular, the particles according to the invention can be used in a mixture in any proportion of platelets and/or of rods and/or of tubes. According to a preferred embodiment, the particles used according to the invention are predominantly or exclusively in the form of platelets. A particle in “platelet” form has a length greater than the width thereof, and a width greater than the thickness thereof. In particular, when in platelet form, the bismuth oxycarbonate particles, and the solvates thereof, such as the hydrates thereof, have: - a mean length L ranging from 15 to 300 nm, in particular ranging from 30 to 250 nm, preferably ranging from 50 to 200 nm, more preferentially ranging from 70 to 150 nm; - a mean width l ranging from 10 to 250 nm, in particular ranging from 20 to 200 nm, preferably ranging from 30 to 150 nm, more preferentially ranging from 50 to 120 nm; - a mean thickness e ranging from 2 to 120 nm, in particular ranging from 5 to 100 nm, preferably ranging from 10 to 80 nm, more preferentially ranging from 20 to 50 nm; and - with e < l < L. According to a preferred embodiment, the bismuth oxycarbonate particles, and the solvates thereof, such as the hydrates thereof, are predominantly or exclusively in the form of rods. A particle in “rod” form has a solid cylindrical form and the length thereof L is greater than the diameter thereof d, or has a prism form, the base of which is solid and polygonal, preferably triangular or hexagonal, and the diameter d of the circle within which this polygonal base is circumscribed is less than the length L of the prism. In particular, when they are in the form of rods, whether cylindrical or in the form of prisms, the bismuth oxycarbonate particles, and the solvates thereof, such as the hydrates thereof, have: - a mean length L ranging from 30 to 300 nm, in particular ranging from 50 to 250 nm, preferably ranging from 70 to 230 nm, more preferentially ranging from 70 to 140 nm; - a mean diameter d ranging from 15 to 150 nm, in particular ranging from 20 to 130 nm, preferably ranging from 25 to 120 nm, more preferentially ranging from 25 to 100 nm, and even more preferentially ranging from 25 to 60 nm, and - with L > d. According to a preferred embodiment, the bismuth oxycarbonate particles, and the solvates thereof, such as the hydrates thereof, are predominantly or exclusively in the form of tubes. A particle in “tube” form has a hollow cylindrical form and the length thereof L is greater than the diameter thereof d. In particular, when in tube form, the bismuth oxycarbonate particles, and the solvates thereof, such as the hydrates thereof, have: - a mean length L ranging from 10 to 300 nm, in particular ranging from 20 to 250 nm, preferably ranging from 40 to 200 nm, more preferentially ranging from 60 to 200 nm; - a mean diameter d ranging from 2 to 30 nm, in particular ranging from 3 to 20 nm, and preferably ranging from 5 to 15 nm; and - with L > d. For the purposes of the present invention, the term “predominantly in the form of platelets/rods/tubes” is intended to denote that at least 50% by number, in particular at least 70% by number, or even at least 90% by number of the particles are in the form of platelets/rods/tubes, respectively. Doping of the particles a) According to a particular embodiment, the bismuth oxycarbonate particles, and the solvates thereof, such as the hydrates thereof, may be doped. In particular, the bismuth oxycarbonate particles, and the solvates thereof, such as the hydrates thereof, can be doped with one or more chemical elements which are capable of being inserted into the structure, or of partially replacing elements that are already present. The particles can be doped via substitutions of all or some of the cations and/or of all or part of the anions. According to a particular embodiment, doping relates in part to inserted cations or cations as substitution for the bismuth, to the limit of 20% of the composition in terms of bismuth. According to this variant, the degree of doping ranges in particular from 0.005% to 15%, preferably from 0.05% to 12%, more preferentially from 0.1% to 10%, and even more preferentially from 0.5% to 6%. In particular, the bismuth oxycarbonate particles, and the solvates thereof, such as the hydrates thereof, may be doped with cations derived from elements chosen from aluminum (Al), silicon (Si), scandium (Sc), titanium (Ti), vanadium (V), manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), gallium (Ga), germanium (Ge), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), silver (Ag), indium (In), lanthanum (La), cerium (Ce), tantalum (Ta), tungsten (W) and/or gold (Au). Preferably, the bismuth oxycarbonate particles may be doped with cations derived from elements chosen from titanium, vanadium, manganese, iron, copper, zinc, lanthanum and/or cerium, more preferentially from manganese, iron and/or cerium, and even more preferentially from manganese or iron. According to one embodiment variant, the bismuth oxycarbonate particles are doped with cations derived from manganese, and the degree of doping ranges in particular from 0.5% to 2%. According to another embodiment variant, the bismuth oxycarbonate particles are doped with cations derived from iron, and the degree of doping ranges in particular from 0.5% to 2%. According to another particular embodiment, the doping relates in part or entirely to inserted anions or anions as substitution for the carbonate group, to the limit of 20% of the composition in terms of carbonate. According to this variant, the degree of doping ranges in particular from 0.001% to 1%, preferably from 0.002% to 0.5%, more preferentially from 0.003% to 0.2%, and even more preferentially from 0.005% to 0.1%. In particular, the bismuth oxycarbonate particles may be doped with anions derived from elements chosen from fluorine (F), sulfur (S), chlorine (Cl), bromine (Br), iodine (I), and/or with polyatomic anions, in particular chosen from the sulfate ion (SO4^2-), the sulfonate ion (S(=O)2-O-), the sulfite ion (SO3^2-), the phosphate ion (PO4^3-) and/or the iodate ion (IO3-). Preferably, the bismuth oxycarbonate particles may be doped with S^2-, SO₃ ^2-, SO₄ ^2-, Cl- and/or I-, more preferentially with SO₃ ^2-, SO₄ ^2- and/or Cl-, and more preferentially with Cl- or SO4^2-. According to one embodiment variant, the bismuth oxycarbonate particles are doped with anions derived from chlorine, and the degree of doping ranges in particular from 0.01% to 0.1%. According to another embodiment variant, the bismuth oxycarbonate particles are doped with anions derived from iodine, and the degree of doping ranges in particular from 0.003% to 0.01%. According to another embodiment variant, the bismuth oxycarbonate particles are doped with the sulfate ion, and the degree of doping ranges in particular from 0.005% to 0.1%. According to another embodiment variant, the bismuth oxycarbonate particles are doped with cations, preferably derived from elements chosen from titanium, vanadium, manganese, iron, copper, zinc, lanthanum and/or cerium, more preferentially chosen from manganese, iron and/or cerium, and even more preferentially chosen from manganese or iron, and with anions, preferably derived from elements chosen from fluorine (F), sulfur (S), chlorine (Cl), bromine (Br), iodine (I), and/or with polyatomic anions, in particular chosen from the sulfate ion (SO₄ ^2-), the sulfonate ion (S(=O)₂-O-), the sulfite ion (SO₃ ^2-), the phosphate ion (PO₄ ^3-) and/or the iodate ion (IO3-), more preferentially with S^2-, SO3^2-, SO4^2-, Cl- and/or I-, even more preferentially with SO₃ ^2-, SO₄ ^2- and/or Cl-, and particularly preferably with Cl-, I- or SO4^2-. According to a preferred embodiment, the bismuth oxycarbonate particles, and the solvates thereof, such as the hydrates thereof, required according to the invention are non-doped. According to another preferred embodiment, the bismuth oxycarbonate particles, and the solvates thereof, such as the hydrates thereof, required according to the invention are doped. According to another preferred embodiment, the bismuth oxycarbonate particles, and the solvates thereof, such as the hydrates thereof, required according to the invention are a mixture of doped particles and of non-doped particles. Protocol for preparing the bismuth oxycarbonate particles a) The bismuth oxycarbonate particles a), and the solvates thereof, such as the hydrates thereof, may be obtained via any preparation process known to those skilled in art. For example, the synthesis of the bismuth oxycarbonate particles is described in the article by Ni et al. (Fabrication, modification and application of (BiO)₂CO₃-based photocatalysts: A review, Applied Surface Science, 365, 2016, 314–335). In particular, the bismuth oxycarbonate particles, and the solvates thereof, such as the hydrates thereof, may be prepared via the solvothermal route, via the electrochemical route, by co-precipitation, or else at reflux, and preferably via the solvothermal route or at reflux. According to a first embodiment variant, the bismuth oxycarbonate particles, and the solvates thereof, such as the hydrates thereof, are obtained via the solvothermal route, in particular from bismuth nitrate and various carbonating agents such as sodium carbonate, ammonium carbonate or urea, in a polar protic solvent in the presence of polyols. Such a synthesis makes it possible to obtain bismuth oxycarbonate particles in the form of platelets and/or rods, the largest dimension of which ranges from 50 to 300 nm. The solvothermal synthesis of particles is notably described in the articles by Cheng, G. et al. (Shape-controlled solvothermal synthesis of bismuth subcarbonate nanomaterials, J. Solid State Chem. 183, 1878–1883 (2010)); Ruan, M.M. et al. (Facile Green Synthesis of Highly Monodisperse Bismuth Subcarbonate Micropompons Self-assembled by Nanosheets: Improved Photocatalytic Performance, Acta Physico-Chimica Sinica, 33, 2017, 1033-1042); Quin et al. (Template‐Free Fabrication of Bi₂O₃ and (BiO)₂CO₃ Nanotubes and Their Application in Water Treatment, Chem. Eur. J., 18, 2012, 16491–16497); Cheng, G. et al. (Shape-controlled solvothermal synthesis of bismuth subcarbonate nanomaterials, J. Solid State Chem., 183, 2010, 1878–1883); Liu, Y.Y. et al. (Preparation, electronic structure, and photocatalytic properties of Bi2O2CO3 nanosheet, Appl. Surf. Sci., 257, 2010, 172–175); Zheng et al. (Synthetic Bi₂O₂CO₃ nanostructures: Novel photocatalyst with controlled special surface exposed, Journal of Molecular Catalysis A: Chemical, 2010, 317 (1-2), 34- 40); Liu, S.Q. et al. (The effects of citrate ion on morphology and photocatalytic activity of flower-like Bi₂O₂CO₃, Ceram. Int., 40, 2014, 2343–2348); or Chen, R. et al. (Bismuth subcarbonate nanoparticles fabricated by water-in-oil microemulsion-assisted hydrothermal process exhibit anti-Helicobacter pylori properties, Mater. Res. Bull., 45, 2010, 654–658). The electrochemical synthesis of particles is notably described in the article by Hu, Y. et al. (Simple hydrolysis route to synthesize Bi₂O₂CO₃ nanoplate from Bi nanopowder and its photocatalytic application, Materials Letters, 170, 2016, 72–75). The synthesis of particles by co-precipitation is notably described in the article by Chen, X.Y. et al. (Controlled synthesis of bismuth oxo nanoscale crystals (BiOCl, Bi₁₂O₁₇Cl₂, α- Bi₂O₃, and (BiO)₂CO₃) by solution-phase methods, J. Solid State Chem., 180, 2007, 2510– 2516). The synthesis of particles by reflux is notably described in the article by Chen et al. (Fabrication of bismuth subcarbonate nanotube arrays from bismuth citrate, Chem. Commun., 2006, 2265–2267). According to a preferred embodiment, the bismuth oxycarbonate particles, and the solvates thereof, such as the hydrates thereof, required according to the invention are obtained via the solvothermal route, for example according to the process described by Cheng et al., or at reflux, for example according to the process described by Chen et al.. According to a preferred embodiment, the bismuth oxycarbonate particles, and the solvates thereof, such as the hydrates thereof, required according to the invention are obtained via a preparation process using one or more bismuth(III) complexes, one or more carbonating agents, one or more polyols and optionally one or more polar solvents other than polyols. When the particles used according to the invention are doped, one or more additional reagents including the doping elements may be added. In particular, the bismuth(III) complex(es) are chosen from bismuth nitrate and the hydrated forms thereof, bismuth citrate and the hydrated forms thereof, bismuth sulfate and the hydrated forms thereof, and bismuth chloride and the hydrated forms thereof. The bismuth(III) complex(es) may also be obtained from bismuth minerals, such as elemental bismuth and/or bismuth oxide and/or bismuth sulfide. Preferably, the bismuth(III) complex(es) are bismuth(III) nitrate and the hydrated forms thereof of formula Bi(NO₃)₃·xH₂O, and is preferably bismuth nitrate pentahydrate of formula Bi(NO₃)₃·5H₂O. In particular, the carbonating agent(s) are chosen from Li2CO3, Na2CO3, K2CO3, Rb2CO3, Cs₂CO₃, (NH₄)₂CO₃, LiHCO₃, NaHCO₃, KHCO₃, RbHCO₃, CsHCO₃, (NH₄)HCO₃, urea (NH₂)₂CO and urea derivatives, CO₂, preferably from Na₂CO₃, K₂CO₃, (NH₂)₂CO, (NH4)2CO3, and more preferentially from (NH2)2CO and/or (NH4)2CO3. Polyols are compounds having a plurality of hydroxyl functions. They may in particular be chosen from glycols, in particular ethylene glycol, propylene glycol, butylene glycol, pentylene glycol, hexylene glycol; short- or long-chain glycol polymers, for example polyethylene glycol, polypropylene glycol, polybutylene glycol; glycerol and derivatives thereof, or for example sugars, in particular glucose, fructose, sucrose, xylitol, mannitol, such as D-mannitol, sorbitol or maltitol. According to one embodiment, the bismuth oxycarbonate particles, and the solvates thereof, such as the hydrates thereof, required according to the invention are obtained via a preparation process using a polyol or a mixture of polyols. According to a first embodiment variant, the polyol(s) may also be used as solvent. The bismuth oxycarbonate particles, and the solvates thereof, such as the hydrates thereof, can then be obtained, for example, according to the process described below. A solution A is formed from the dissolution of the bismuth(III) complex, preferably at a concentration of 0.001 to 0.5 M, in the polyol or mixture of polyols. A solution B is formed by the partial or full dissolution of the carbonating agent, preferably from 1 to 100 equivalents relative to the bismuth, in the polyol or mixture of polyols or in a polyol or mixture of polyols other than that (those) used in solution A. In the case of doping with a cation, the dopant is preferably integrated into solution A. In the case of doping with an anion, the dopant is preferably integrated into solution B. In the case of doping with one or more cations and/or with one or more anions, the cationic dopant(s) are preferably integrated into solution A and the anionic dopant(s) are preferably integrated into solution B. Solution A is then added to solution B at room temperature. If the polyol or mixture of polyols is not liquid at room temperature, all the solids are mixed. The mixture obtained is then heated at between 90 and 250 °C for a reaction time of between 10 minutes and 48 hours. If the desired reaction temperature is greater than or equal to the boiling point of the solvent, solvothermal synthesis is performed using an autoclave. Preferably, the reaction temperature is between 95 °C and 200 °C and the reaction time is between 1 and 24 hours, and more preferentially the reaction temperature is between 100 °C and 180 °C and the reaction time is between 2 and 16 hours. The particles obtained are isolated from the reaction medium by centrifugation and washed by successive cycles of dispersion and centrifugation. After drying under vacuum at a temperature of between 40 °C and 60 °C, a white powder is obtained. In the case in which the polyol(s) are used as solvents, the bismuth oxycarbonate particles, and the solvates thereof, such as the hydrates thereof, obtained are in the form of platelets, preferably with a mean thickness e of between 2 and 15 nm, and/or in the form of tubes. According to another embodiment variant, the polyol(s) are used solely as additives and not as solvent. The bismuth oxycarbonate particles, and the solvates thereof, such as the hydrates thereof, can then be obtained, for example, according to the process described below. A solution A is formed from the dissolution of the bismuth complex, and the solvates thereof, such as the hydrates thereof, preferably at a concentration from 0.001 to 0.5 M, and of the polyol(s), preferably at a total concentration of polyols preferably from 0.01 to 5 M, in a solvent, preferably a polar solvent. A solution B is formed from the partial or full dissolution of the carbonating agent, preferably from 1 to 100 equivalents relative to the bismuth complex, in the polar solvent (miscible with the solvent from A) which is identical to or different from, preferably identical to, that of solution A. In the case of doping with a cation, the dopant is preferably integrated into solution A. In the case of doping with an anion, the dopant is preferably integrated into solution B. In the case of doping with one or more cation(s) and/or with one or more anion(s), the cationic dopant(s) are preferably integrated into solution A and the anionic dopant(s) are preferably integrated into solution B. Solution A is then added to solution B at room temperature. The mixture obtained is then heated at between 90 °C and 250 °C for 10 minutes to 48 hours. If the desired reaction temperature is greater than or equal to the boiling point of the solvent, solvothermal synthesis is performed using an autoclave. Preferably, the reaction temperature is between 90 °C and 150 °C and the reaction time is between 4 and 16 hours. The particles obtained are isolated from the reaction medium by centrifugation and washed by successive cycles of dispersion and centrifugation. After drying under vacuum at a temperature of between 40 °C and 60 °C, a white powder is obtained. When the polyol(s) are used solely as additives, they may in particular be chosen from ethylene glycol, propylene glycol, glycerol and/or a sugar, preferably a sugar, more preferentially D-mannitol. According to this variant, the synthetics process also uses a solvent other than the polyols, or a mixture of solvents other than the polyols. In particular, the solvent or mixture of solvents is chosen from polar solvents, preferably from polar and protic solvents, such as water, C1-C6 alcohols such as ethanol or isopropanol, and mixtures thereof, and the solvent is even more preferentially water. In particular, when the polyol(s) are chosen solely as additives and the water as solvent, the bismuth oxycarbonate particles, and the solvates thereof, such as the hydrates thereof, are preferably obtained in the form of platelets and/or in the form of rods. Organosilicon compound b) As mentioned previously, the composite material according to the invention comprises b) at least one organosilicon compound. The organosilicon compound(s) used in the composite materials according to the invention are chosen from silanes and the polymerized forms thereof, and siloxanes and the polymerized forms thereof (silicones). Preferably, the organosilicon compound(s) are chosen from silanes including at least one hydrolysable function. In particular, the organosilicon compound(s) are chosen from alkoxysilanes, notably monoalkoxysilanes, dialkoxysilanes, trialkoxysilanes, oligomers thereof and polymerized forms thereof. The term "alkoxysilane" is used in the context of the present invention to mean a compound comprising at least one silicon atom bearing at least one alkoxyl group, preferably two, three or four alkoxyl groups, even more preferentially 3 alkoxyl groups. The term "polymerized forms of alkoxysilanes" means their forms which have been partially or totally hydrolyzed by at least one compound bearing hydroxyl groups, including water. According to a preferred embodiment, the organosilicon compounds are chosen from the alkoxysilanes of formula (I) below, oligomers thereof, polymerized forms thereof and/or mixtures thereof: R¹xSi(OR²)(4-x) (I) in which: - R¹ independently represents an alkoxy group containing from 1 to 10 carbon atoms; an NH2 amino group; a C1 to C50, notably C1 to C30, linear or branched, saturated or unsaturated, cyclic or acyclic hydrocarbon-based radical, optionally interrupted with one or more atoms chosen from O, NH, NR₃, S or with a carbonyl diradical (CO) or combinations thereof, and/or said hydrocarbon-based radical being optionally substituted with at least one group chosen from a hydroxyl group (OH) or a thiol group (SH); an aryl group containing from 6 to 30 carbon atoms; a (di)alkylamino group NR³R⁴ in which R³ and R⁴ independently denote a hydrogen atom, an alkyl group containing from 1 to 20 carbon atoms, an aminoalkyl group containing from 1 to 20 carbon atoms, an aryl group containing from 6 to 12 carbon atoms or a linear or branched (cyclo)alkyl radical containing from 1 to 20 carbon atoms, notably from 1 to 10 carbon atoms; - R² represents a hydrogen atom or an alkyl group containing from 1 to 20 carbon atoms, preferably from 1 to 6 carbon atoms; - x denotes an integer ranging from 1 to 3; it being understood that if all the radicals R² represent a hydrogen atom, then R¹ represents an alkoxy group containing from 1 to 10 carbon atoms. R¹ and R² may be identical or different. The term “oligomer” means compound(s) including at least two silicon atoms, obtained by oligomerization or polymerization of the compounds of formula (I). Preferably, R¹ represents a C₁ to C₅₀, notably C₁ to C₃₀, linear or branched, saturated or unsaturated, cyclic or acyclic hydrocarbon-based radical, optionally interrupted with one or more atoms chosen from O, NH, NR3, S or a carbonyl diradical (CO) or combinations thereof, and/or said hydrocarbon-based radical being optionally substituted with at least one group chosen from a hydroxyl group (OH) or a thiol group (SH) or an aryl radical containing from 6 to 30 carbon atoms, such as phenyl. Preferably, R² represents an alkyl group containing from 1 to 10 carbon atoms, preferably from 1 to 6 carbon atoms and more preferentially from 1 to 2 carbon atoms such as methyl or ethyl. The alkoxysilane(s) of formula (I), the oligomers thereof and/or mixtures thereof may be chosen from: - the compounds of formula (Ia) and/or (Ib) and/or (Ic) below, oligomers thereof, alone or as a mixture: [Chem 1] or or R^1'ySi(OR^2')(4-y) (Ic) in which: - Ra and Rb, which may be identical or different, represent a hydrogen atom; an alkyl group containing from 1 to 20 carbon atoms, preferably from 1 to 10 carbon atoms and notably from 1 to 4 carbon atoms; a cycloalkyl group containing from 3 to 20 carbon atoms; an aryl group containing from 6 to 12 carbon atoms; an aminoalkyl group containing from 1 to 20 carbon atoms; - Rc independently represents an alkyl group containing from 1 to 40 carbon atoms, preferably from 1 to 30 carbon atoms, more preferentially from 1 to 10 carbon atoms and in particular from 1 to 4 carbon atoms such as a methyl, said alkyl group being optionally substituted with an aryl group; or an alkoxy group containing from 1 to 10 carbon atoms, preferably from 1 to 4 carbon atoms and in particular from 1 to 2 carbon atoms such as methoxy or ethoxy; an aryl group containing from 6 to 12 carbon atoms such as phenyl; - Rd and Re, which may be identical or different, represent an alkyl group containing from 1 to 10 carbon atoms, preferably from 1 to 4 carbon atoms, in particular from 1 to 2 carbon atoms, such as methyl or ethyl; - k denotes an integer ranging from 0 to 5, preferably ranging from 0 to 3; - Rf represents a hydrogen atom; an alkyl group containing from 1 to 10 carbon atoms and notably from 1 to 4 carbon atoms; or a group of formula (II) below: [Chem 3] in which Rn represents a hydroxyl group (OH); an alkyl group containing from 1 to 10 carbon atoms, preferably a methyl; R’¹ represents a C₁ to C₅₀, notably C₁ to C₃₀, linear or branched, saturated or unsaturated, cyclic or acyclic hydrocarbon-based radical, optionally interrupted with one or more oxygen atoms and/or said hydrocarbon-based radical being optionally substituted with at least one group chosen from hydroxyl (OH) or aryl containing from 6 to 12 carbon atoms, such as phenyl, R’² represents an alkyl group containing from 1 to 4 carbon atoms and preferably from 1 to 2 carbon atoms, such as methyl or ethyl, y denotes an integer from 1 to 3 and preferably y = 1. Among the alkoxysilanes of formula (Ia), the oligomers thereof and/or mixtures thereof, mention may notably be made of 3-aminopropyltriethoxysilane (APTES), 3- aminopropylmethyldiethoxysilane (APMDES) and N- cyclohexylaminomethyltriethoxysilane. APTES may be purchased, for example, from the company Dow Corning under the name Xiameter OFS-6011 Silane or from the company Momentive Performance Materials under the name Silsoft A-1100 or from the company Shin-Etsu under the name KBE-903. The compounds of formula (Ia) may also denote Dynasylan SIVO 210 or Dynasylan 1505 sold by the company Evonik. N-Cycloheylaminomethyltriethoxysilane may be purchased, for example, from the company Wacker under the name Geniosil XL 926. Among the alkoxysilanes of formula (Ib), the oligomers thereof and/or mixtures thereof, mention may notably be made of tetraethoxysilane (TEOS), methyltriethoxysilane (MTES), dimethyldiethoxysilane (DMDES), diethyldiethoxysilane, dipropyldiethoxysilane, propyltriethoxysilane, isobutyltriethoxysilane, phenyltriethoxysilane, phenylmethyldiethoxysilane, diphenyldiethoxysilane, benzyltriethoxysilane, benzylmethyldiethoxysilane, dibenzyldiethoxysilane, acetoxymethyltriethoxysilane and mixtures thereof. According to a preferred embodiment, the organosilicon compounds b) are chosen from the alkoxysilanes of formula (Ic), oligomers thereof, polymerized forms thereof and/or mixtures thereof. According to one embodiment, R'¹ represents a linear or branched, saturated, acyclic C₁ to C₃₀, notably C₂ to C₂₀, hydrocarbon-based radical such as an octyl, decyl, dodecyl, tetradecyl, preferably octyl or dodecyl radical. According to one embodiment, R'¹ represents a C1 to C50, notably C1 to C30, linear or branched, saturated or unsaturated, acyclic hydrocarbon-based radical interrupted with one or more oxygen atoms, said hydrocarbon-based radical being optionally substituted with at least one hydroxyl (OH) group; in particular, R'¹ represents a 2- [methoxy(polyethyleneoxy)propyl (n = 1) radical or a [hydroxy(polyethyleneoxy)propyl (n = 8 - 12) radical. According to one embodiment, R'¹ represents a linear or branched, saturated, C1 to C20, notably C₁ to C₁₀, hydrocarbon-based radical substituted with at least one hydroxyl group (OH) and/or with at least one aryl radical containing from 6 to 12 carbon atoms, such as phenyl, preferably with at least one aryl radical containing from 6 to 12 carbon atoms, such as phenyl; in particular, R'¹ represents a benzyl radical. According to a preferred embodiment, y = 3. According to one embodiment, R’² represents a methyl or ethyl group. According to one embodiment, the organosilicon compound(s) b) are chosen from octyltriethoxysilane, dodecyltriethoxysilane, 2- [methoxy(polyethyleneoxy)propyl]trimethoxysilane (n = 1) or [hydroxy(polyethyleneoxy)propyl]triethoxysilane (n = 8 - 12), benzyltriethoxysilane, triethoxy(2,4,4-trimethylpently)silane, oligomers and/or polymerized forms thereof and mixtures thereof. According to one embodiment, the alkoxysilane(s) chosen from the compounds of formula (I), the oligomers thereof and/or mixtures thereof are chosen from 3- aminopropyltriethoxysilane (APTES), 3-aminopropylmethyldiethoxysilane (APMDES), N- cyclohexylaminomethyltriethoxysilane, tetraethoxysilane (TEOS), methyltriethoxysilane (MTES), dimethyldiethoxysilane (DMDES), diethyldiethoxysilane, dipropyldiethoxysilane, propyltriethoxysilane, isobutyltriethoxysilane, phenyltriethoxysilane, phenylmethyldiethoxysilane, diphenyldiethoxysilane, benzyltriethoxysilane, benzylmethyldiethoxysilane, dibenzyldiethoxysilane, acetoxymethyltriethoxysilane and mixtures thereof, more preferentially 3-aminopropyltriethoxysilane (APTES), tetraethoxysilane (TEOS) and mixtures thereof. According to one embodiment, the organosilicon compound(s) are chosen from the compounds of formula (III) below: [Chem 4] in which: - R1 independently represents a hydroxyl group or an alkoxy group containing from 1 to 2 carbon atoms; - R2 independently represents a hydrogen atom; a hydroxyl group; an alkoxy group containing from 1 to 10 carbon atoms; or an alkyl group containing from 1 to 20 carbon atoms, optionally substituted with at least one group chosen from a hydroxyl group (OH) or a thiol-based group (SH), said alkyl group preferably being optionally substituted with at least one hydroxyl group (OH); - A independently represents an alkylene group containing from 2 to 3 carbon atoms, - m denotes an integer ranging from 1 to 3, n denotes an integer ranging from 0 to 2 and m+n = 3; - Y independently represents an oxygen atom or an -NH-CO- group, or a -CO-NH- group or an -NH-CO-NH- group; - p is equal to 0 or 1, - q is equal to 0 or 1, - r is equal to 0 or 1, - x denotes an integer ranging from 0 to 500, with the following conditions: - if Y represents an -NH-CO- group or a -CO-NH- group then p = 1 and q = 0, and x > 0, - if Y represents an -NH-CO-NH- group, then q = 1 and p = 1, and x > 0, - if r = 0, then p = 1 and q = 0, - if x = 0 then q = r = 0 and p = 1. According to one embodiment, the compounds of formula (III) are such that: - R1 independently represents a hydroxyl group or an alkoxy group containing from 1 to 2 carbon atoms; - R2 independently represents a hydrogen atom; a hydroxyl group; an alkyl group containing from 1 to 10 carbon atoms, preferably methyl; or an alkoxy group containing from 1 to 10 carbon atoms; - A represents an alkylene group containing from 2 to 3 carbon atoms; - m denotes an integer ranging from 1 to 3, n denotes an integer ranging from 0 to 2 and m+n = 3; - Y represents an -NH-CO- group, a -CO-NH- group or an -NH-CO-NH- group; - p is equal to 0 or 1, - q is equal to 0 or 1, - r is equal to 1, - x denotes an integer ranging from 1 to 500; The compound(s) of formula (III) that may be used in the context of the invention may be chosen from: the compounds of formula (IIIa) below: [Chem 5] in which: - R’2 and R’’2 independently represent a hydrogen atom; a hydroxyl group; an alkyl group containing from 1 to 10 carbon atoms, preferably methyl; or an alkoxy group containing from 1 to 10 carbon atoms, preferably an alkoxy group; - A independently represents an alkylene group containing from 2 to 3 carbon atoms; - x denotes an integer ranging from 1 to 500; the compounds of formula (IIIb) below: [Chem 6] in which: - R1 represents a hydroxyl group or an alkoxy group containing from 1 to 2 carbon atoms, preferably an alkoxy group; - R’2 and R’’2 independently represent an alkyl group containing 1 or 2 carbon atoms; - A independently represents an alkylene group containing from 2 to 3 carbon atoms; - x denotes an integer ranging from 1 to 500; the compounds of formula (IIIc) below: [Chem 7] in which: - R1 represents a hydrogen atom, a hydroxyl group, an alkyl group containing from 1 to 10 carbon atoms, preferably methyl, or an alkoxy group containing from 1 to 2 carbon atoms; preferably an alkoxy group containing from 1 to 2 carbon atoms; - R’2 and R’’2 independently represent a hydrogen atom, an alkyl group containing 1 or 2 carbon atoms; - A independently represents an alkylene group containing from 2 to 3 carbon atoms; - x denotes an integer ranging from 1 to 500; the compounds of formula (IIId) below: [Chem 8] in which: - R1 represents a hydrogen atom, a hydroxyl group, an alkyl group containing from 1 to 10 carbon atoms, preferably methyl, or an alkoxy group containing from 1 to 2 carbon atoms; preferably an alkoxy group containing from 1 to 2 carbon atoms; - R’2 and R’’2 independently represent a hydrogen atom, an alkyl group containing 1 or 2 carbon atoms; - A independently represents an alkylene group containing from 2 to 3 carbon atoms; - x denotes an integer ranging from 1 to 500; Among the polyoxyalkylenes of formula (IIIa), mention may be made of the following compounds: [Table 1] Among the compounds of formula (IIIb), mention may be made of PEO compounds: - bearing triethoxysilane end functions, such as the compounds sold by the company Specific Polymers under the name SP-1P-2-006 (CAS Number: 666829-33-0), SP-1P-2-007 (PEO 18 Bis Triethoxysilane, CAS Number: 623933-43-7), SP-1P-2-015 (PEO 9 Triethoxysilane, CAS Number: 97969-60-3), SP-1P-2-016 (PEO 21 Triethoxysilane, CAS Number: 97969- 60-3), SP-1P-2-017 (PEO 44 Triethoxysilane, CAS Number: 97969-60-3), SP-1P-2-018 (PEO 11 Bis Triethoxysilane, (PEO 11 Bis Triethoxysilane, CAS Number: 97969-60-3), SP- 1P-2-019 (PEO 25 Bis Triethoxysilane, CAS Number: 666829-33-0), SP-1P-2-020 (PEO 6 Bis Triethoxysilane, CAS Number: 666829-33-0), SP-1P-2-035 (PEO 5 Bis Triethoxysilane, CAS Number: 328239-08-3), or those sold by the company Gelest SIB1824.84 (Bis(3- triethoxysilylpropyl)polyethylene oxide (25-30 EO), CAS Number: 666829-33-0), - bearing trimethoxysilane end functions, such as those sold by the company Specific Polymers under the reference SP-1P-2-013, (CAS Number: 70776-52-2). Among the polyoxyalkylenes of formula (IIIb), mention may be made of PPO compounds: - bearing triethoxysilane end functions, such as the compounds sold by the company Specific Polymers under the name SP-1P-2-026 (PPO 19 Bis Triethoxysilane, CAS Number: 1017971-44-6), SP-1P-2-036 (PPO Bis Triethoxysilane, CAS Number: 1017971-44-6). Among the compounds of formula (IIIc), mention may be made of compounds bearing triethoxysilane end functions, such as the following compounds sold by the company Gelest: SIB1824.81 (Bis[(3-triethoxysilylpropyl)aminocarbonyl]polyethylene oxide (7-10 EO), CAS Number: 178884-91-8), SIB1824.82 (N,N'-Bis-[(3- triethoxysilylpropyl)aminocarbonyl]polyethylene oxide (10-15 EO, CAS Number: 178884- 91-8). Among the compounds of formula (IIId), mention may be made of compounds bearing triethoxysilane end functions, such as the compounds sold by the company Creative PEGWorks under the names PSB-3380, PSB-3381, PSB-3382 and PSB-3383. According to a particular embodiment, the organosilicon compound(s) of the composite materials according to the invention are chosen from siloxanes. Among the siloxanes, mention may be made in particular of dimethylsiloxanes, such as hexamethyldisiloxane, or else decamethylcyclopentasiloxane, octamethylcyclotetrasiloxane, dodecamethylcyclohexasiloxane, decamethyltetrasiloxane or polydimethylsiloxanes. Preferably, the organosilicon compound(s) of the composite materials according to the invention are chosen from alkoxysilanes, oligomers thereof and/or polymerized forms thereof. Preferably, the organosilicon compound(s) of the composite materials according to the invention are chosen from octyltriethoxysilane, dodecyltriethoxysilane, triethoxy(2,4,4- trimethylpentyl)silane, benzyltriethoxysilane, 2- [methoxy(polyethyleneoxy)propyl]trimethoxysilane (n = 1) and [hydroxy(polyethyleneoxy)propyl]triethoxysilane (n = 8 - 12). Preferably, the organosilicon compound(s) of the composite materials according to the invention are chosen from octyltriethoxysilane and dodecyltriethoxysilane. According to a particular embodiment, the molar ratio between the organosilicon compound(s) b) and the bismuth oxycarbonate particle(s) a), and solvates thereof, such as hydrates thereof, according to the invention ranges from 0.0001 to 20, in particular from 0.001 to 5, preferably from 0.01 to 2, and more preferentially from 0.05 to 1. Inorganic compound c) According to a particular embodiment, the composite materials according to the invention may also comprise at least one inorganic compound c) different from said bismuth oxycarbonate particles a), and solvates thereof, such as hydrates thereof. The inorganic compound(s) c) may be amorphous or crystalline, hydrated or non-hydrated forms of oxides or hydroxides or oxy-hydroxides of alkali metals or alkaline-earth metals, notably sodium, potassium, magnesium and calcium, or transition metals, notably titanium, aluminum, manganese, iron, copper, niobium and tantalum, or lanthanides, notably cerium, or poor metals, notably zinc, indium and bismuth. The inorganic oxides may also denote amorphous or crystalline, hydrated or non-hydrated forms of metalloid oxides or hydroxides or oxy-hydroxides. In particular, the inorganic compounds c) may be amorphous or crystalline, hydrated or non- hydrated forms, including clays, of silicon oxides or hydroxides or oxy-hydroxides such as silica SiO2, lithium and/or sodium and/or potassium and/or ammonium and/or calcium and/or magnesium and/or aluminum and/or titanium and/or iron and/or zinc and/or bismuth silicates, aluminum and/or calcium and/or magnesium and/or sodium and/or titanium and/or iron and/or zinc and/or bismuth borosilicates. In particular, the inorganic compounds c) may be amorphous or crystalline, hydrated or non- hydrated forms of inorganic carbides or sulfides or nitrides, such as silicon carbides, iron, copper and zinc sulfides or such as boron and silicon nitrides. As metal oxides, mention may be made of the hydrated or non-hydrated forms of Al2O3, Al(OH)₃, SiO₂, TiO₂, MnO, MnO₂, FeO(OH), Fe₃O₄, Fe₂O₃, Cu(OH)₂, Cu₂O, CuO, Zn(OH)₂, ZnO, Nb₂O₅, In(OH)₃, In₂O₃, Ce₂O₃, CeO₂, Ta₂O₅, WO₃, Bi₂O₃, and mixtures thereof. Preferably, hydrated or non-hydrated forms of Al₂O₃ such as Al(OH)₃, hydrated or non- hydrated forms of SiO2, TiO2, ZnO, and mixtures thereof, are used, more preferentially hydrated or non-hydrated forms of Al2O3 such as Al(OH)3, or the hydrated or non-hydrated forms of SiO₂, TiO₂, ZnO and mixtures thereof, and even more preferentially the hydrated or non-hydrated forms of Al₂O₃ such as Al(OH)₃, or SiO₂, and mixtures thereof. According to a preferred embodiment, the composite materials according to the invention do not comprise any inorganic compound c) different from said bismuth oxycarbonate particles a), and solvates thereof, such as hydrates thereof. According to another preferred embodiment, the composite materials according to the invention comprise only one inorganic compound c) different from said bismuth oxycarbonate particles a), and solvates thereof, such as hydrates thereof, preferably chosen from inorganic oxides, and more preferentially from silica, alumina, titanium dioxide and zinc oxide, and better still from silica. According to another preferred embodiment, the composite materials according to the invention comprise only one inorganic compound c) different from said bismuth oxycarbonate particles a), preferably chosen from inorganic hydroxides or inorganic oxy- hydroxides, more preferentially from inorganic hydroxides, more preferentially from Al(OH)₃, Zn(OH)₂, In(OH)₃ or mixtures thereof, even more preferentially from Al(OH)₃, Zn(OH)2, and better still Al(OH)3. Preferably, the composite material according to the invention comprises one or more inorganic compounds c) different from said bismuth oxycarbonate particles a), preferably chosen from inorganic oxides, and more preferentially from zinc, titanium, silicon and/or aluminum oxides, preferably from silicon and/or aluminum oxides, which are optionally hydrated. Preferably, the composite material according to the invention comprises one or more inorganic compounds c) different from said bismuth oxycarbonate particles a), preferably chosen from an inorganic oxide, more preferentially chosen from Al(OH)₃, SiO₂, TiO₂ and ZnO, and even more preferentially chosen from Al(OH)₃ or SiO₂. According to a particular embodiment, when one or more inorganic compounds c) are present, the mean size of the largest dimension of the composite material particle is less than 10 µm, in particular less than 2.5 µm, preferably less than 1 µm, and more preferentially less than 500 nm. PROCESS FOR PREPARING THE COMPOSITE MATERIAL The composite materials according to the invention may notably be obtained via the preparation processes described below. In particular, the composite materials according to the invention may be obtained by chemical grafting or physical adsorption of the organosilicon compound(s) b), directly onto the surface of the bismuth oxycarbonate particle(s) a), and solvates thereof, such as hydrates thereof, as defined previously, or onto the surface of particles comprising bismuth oxycarbonate particles a), and solvates thereof, such as hydrates thereof, and an inorganic compound c) as defined previously. In particular, the composite materials according to the invention may be obtained by reaction, on the inorganic part of the material under consideration, of one or more alkoxysilanes, which are preferably amphiphilic, more preferentially octyltriethoxysilane or dodecyltriethoxysilane, notably via a variant of the process described by Zhang et al. (Preparation Method of Silicone Rubber Radiation Protection Nano Composite Material. CN109608890B, 2018) with functionalized alkoxysilanes. The particles comprising at least one bismuth oxycarbonate particle, and solvates thereof, such as hydrates thereof, and one or more inorganic compounds c) as defined previously may be prepared in one or more steps. In particular, the composite materials according to the invention as defined previously may be obtained in one or more steps. In particular, the process for preparing the composite materials according to the invention uses: - at least one particle a) of bismuth oxycarbonate of empirical formula (BiO)_2-x(CO₃), and solvates thereof, such as hydrates thereof, in which -0.4 < x < 0.6, the largest mean dimension of said particles being less than 400 nm; - optionally one or more precursors intended to form the inorganic compound(s) c) different from said bismuth oxycarbonate particles, and solvates thereof, such as hydrates thereof; - one or more organosilicon compound(s) b) as defined previously, in particular the alkoxysilanes as defined previously; - optionally one or more additives; and - optionally one or more solvents. According to a particular embodiment, the process for preparing the composite materials according to the invention may comprise one or more separation steps, for example by filtration and/or centrifugation. According to a particular embodiment, the process for preparing the composite materials according to the invention may comprise one or more heat treatment steps, performed with or without solvent, under an inert or non-inert atmosphere, for example at temperatures ranging from 50 °C to 1200 °C, in particular to remove solvents and/or other volatile residual molecules from the materials and/or to induce a transformation, such as dehydration or crystallization. In particular, the precursor(s) intended to form the inorganic compound(s) c) different from said bismuth oxycarbonate particles a) are chosen from organic or inorganic compounds which afford particles of bismuth oxycarbonate a) and of inorganic compound c) by chemical reaction or physical adsorption. In particular, said precursor(s) may be chosen from: - the inorganic compounds c) as described previously, - inorganic metal precursors of chemical elements and hydrates thereof, in particular dissolved metal oxides, notably sodium silicates or aluminates, halides and hydrates thereof, nitrates and hydrates thereof, carbonates and hydrates thereof, sulfonates and hydrates thereof, sulfates and hydrates thereof, or phosphates and hydrates thereof, - organic metal precursors and hydrates thereof, in particular alkoxides and hydrates thereof, carboxylates and hydrates thereof, lactates and hydrates thereof, or citrates and hydrates thereof, and - mixtures thereof. Said precursor(s) intended to form the ancillary inorganic compound(s) c) may also be chosen from oxidizing precursors, in particular air, hydrogen peroxide, peroxides and hydrates thereof, and/or sulfiding agents, in particular hydrogen sulfide, alkali metal sulfides and hydrates thereof, and/or nitriding agents. According to a preferred embodiment, the process for preparing the composite materials according to the invention does not use precursors to form the inorganic compound(s) c) different from said bismuth oxycarbonate particles a). According to a preferred embodiment, the process for preparing the composite materials according to the invention uses at least one precursor intended to form the inorganic compound(s) c) different from said bismuth oxycarbonate particles a), and preferably chosen from sodium silicate and sodium aluminate. According to a particular embodiment, the process for preparing the composite materials according to the invention uses at least one solvent. The choice of solvent(s) may in particular depend on the precursor(s) and additives used in the process. In particular, the solvent(s) may be chosen from polar or apolar, protic or aprotic solvents. Preferably, the solvent used is a polar protic solvent, in particular chosen from water, alcohols, polyols and mixtures thereof. According to a particular embodiment, the process for preparing the composite materials according to the invention uses at least one additive. In particular, the additive(s) may be chosen from acids, in particular mineral acids such as hydrochloric acid or sulfuric acid, and bases, preferably mineral bases such as sodium hydroxide or potassium hydroxide. They may also be chosen from oxidizing agents, reducing agents and/or any reagent required for the precipitation of the species and/or for their adhesion. The organosilicon compound(s) b) as defined previously may be used pure or as a mixture. The organosilicon compound(s) b) as defined previously may be used dissolved in a solvent or without a solvent. According to a particular embodiment, the present invention is directed towards a process for preparing the composite materials as defined previously, comprising the steps of: (i) providing a dispersion of bismuth oxycarbonate a) of empirical formula (I) (BiO)2-x(CO3), and solvates thereof, such as hydrates thereof, in which -0.4 < x < 0.6, the largest mean dimension of said particles being less than 400 nm, in at least one solvent, in particular in an amount ranging from 0.05 g/L to 500 g/L; (ii) providing a solution of at least one organosilicon compound b), optionally as a mixture with at least one solvent; (iii) placing said dispersion (i) and said solution (ii) in contact to form the composite material; (iv) isolating said composite material. In particular, the solvent(s) of steps (i) and (ii) may be identical or different. In particular, the solvent(s) of step (i) are chosen from polar protic solvents, more preferentially from water, alcohols, polyols and mixtures thereof, and even more preferentially the solvent is water. In particular, the solvent(s) of step (ii) are chosen from polar protic solvents, more preferentially from alcohols, and even more preferentially the solvent is an alcohol corresponding to the alkoxide radical of the organosilicon compound b). According to a particular embodiment, the dispersion medium (i) may be heated to reflux, preferably to a temperature of less than or equal to 80 °C. According to a particular embodiment, solution (ii) may be heated to reflux, preferably to a temperature of 80 °C, prior to mixing in step (iii). According to a particular embodiment, the molar ratio in step (iii) of organosilicon compound(s) b)/bismuth oxycarbonate a) ranges from 0.0001 to 20, preferably ranges from 0.005 to 10, better still from 0.01 to 5, and even more preferentially from 0.05 to 3. According to a particular embodiment, the pH in step (iii) is adjusted to between 1.5 and 5, preferably between 2 and 4. According to a particular embodiment, the pH in step (iii) is adjusted to between 8 and 12, preferably between 9 and 11. According to a particular embodiment, step (iii) is performed with stirring. According to a preferred embodiment, step (iii) is performed with heating of the reaction medium, preferably to a temperature ranging from 70 °C to 80 °C. According to a particular embodiment, step (iii) is performed for a time ranging from 15 minutes to 48 hours, preferably from 1 hour to 24 hours, and more preferentially from 2 hours to 8 hours. According to a particular embodiment, a cooling step may be performed between steps (iii) and (iv). According to a particular embodiment, step (iv) may be performed by centrifugation. According to a particular embodiment, step (iv) is followed by a washing step, notably in successive cycles, and optionally by a drying step such as oven drying, for example at a temperature ranging from 40 °C to 100 °C and optionally under vacuum (pressure below 100 mbar). According to a particular embodiment, the present invention is directed towards a process for preparing the composite materials as defined previously, comprising the steps of: (a) providing a dispersion of particles a) of bismuth oxycarbonate of empirical formula (I) (BiO)_2-x(CO₃), and solvates thereof, such as hydrates thereof, in which -0.4 < x < 0.6, the largest mean dimension of said particles being less than 400 nm, in at least one solvent, in particular in an amount ranging from 0.05 g/L to 500 g/L; (b) providing an aqueous sodium silicate solution; (c) placing said dispersion (a) and said solution (b) in contact to form particles of bismuth oxycarbonate and of silica; (d) isolating said particles of bismuth oxycarbonate and of silica; (e) dispersing said particles of bismuth oxycarbonate and of silica (d) in at least one solvent, in particular in an amount ranging from 0.05 g/L to 500 g/L; (f) providing a solution of at least one organosilicon compound (b), optionally as a mixture with at least one solvent; (g) placing said dispersion (e) and said solution (f) in contact to form the composite material; (h) isolating said composite material. According to a particular embodiment, the preparation process comprises a calcination step (d') prior to step (e). According to a particular embodiment, the calcination step (d') is performed at a temperature ranging from 200 °C to 400 °C, preferably from 250 °C to 300 °C, in particular for a period ranging from 15 minutes to 2 hours. In particular, the solvent(s) of steps (a), (e) and (f) may be identical or different, and are preferably chosen from polar protic solvents, more preferentially from water, alcohols, polyols and mixtures thereof. According to a particular embodiment, the dispersion medium (a) may be heated to reflux, preferably to a temperature of less than or equal to 100 °C. According to a particular embodiment, the Si/Bi molar ratio in step (c) ranges from 0.001 to 10, preferably from 0.01 to 2, and more preferentially from 0.1 to 1. According to a particular embodiment, the pH in step (c) is adjusted to a pH ranging from 3 to 11, in particular from 5 to 8, preferably from 6 to 7. According to a particular embodiment, step (c) is performed with stirring. According to a particular embodiment, step (c) is performed for a time ranging from 15 minutes to 48 hours, preferably from 1 hour to 24 hours and more preferentially from 2 hours to 8 hours. According to a preferred embodiment, step (c) is performed at a temperature below 100 °C. According to a particular embodiment, step (d) may be performed by centrifugation. According to a particular embodiment, step (d) is followed by a washing step, notably in successive cycles, and optionally by a drying step such as oven drying, for example at a temperature ranging from 40 °C to 100 °C and optionally under vacuum (pressure below 100 mbar). According to a particular embodiment, the dispersion medium (e) may be heated to reflux, preferably to a temperature of less than or equal to 80 °C. According to a particular embodiment, the solution (f) may be heated to reflux, preferably to a temperature of 80 °C, prior to mixing in step (g). According to a particular embodiment, the molar ratio in step (g) of organosilicon compound(s) b)/particles of bismuth oxycarbonate and of silica ranges from 0.0001 to 20, preferably from 0.005 to 10, better still from 0.01 to 5, and even more preferentially from 0.05 to 3. According to a particular embodiment, the pH in step (g) is adjusted to between 1.5 and 5, preferably between 2 and 4. According to a particular embodiment, the pH in step (g) is adjusted to between 8 and 12, preferably between 9 and 11. According to a particular embodiment, step (g) is performed with stirring. According to a preferred embodiment, step (g) is performed at a temperature ranging from 70 °C to 80 °C. According to a particular embodiment, step (g) is performed for a time ranging from 15 minutes to 48 hours, preferably from 1 hour to 24 hours, and more preferentially from 2 hours to 8 hours. According to a particular embodiment, a cooling step may be performed between steps (g) and (h). According to a particular embodiment, step (h) may be performed by centrifugation. According to a particular embodiment, step (h) is followed by a washing step, notably in successive cycles, and optionally by oven drying, for example at a temperature ranging from 40 °C to 100 °C and optionally under vacuum (pressure below 100 mbar). According to a particular embodiment, the present invention is directed towards a process for preparing the composite materials as defined previously, comprising the steps of: (1) providing a dispersion of particles a) of bismuth oxycarbonate of formula (I) (BiO)_2- _x(CO₃), and solvates thereof, such as hydrates thereof, in which -0.4 < x < 0.6, the largest mean dimension of said particles being less than 400 nm, in at least one solvent, in particular in an amount ranging from 0.05 g/L to 500 g/L; (2) providing a solution of a soluble and/or hydrated form of alumina, such as a solution of aluminum salts, in at least one solvent; (3) placing said dispersion (1) and said solution (2) in contact; (3') optionally, isolating said mixture obtained from step (3); (3'') optionally, subjecting said isolated mixture from step (3') to a calcination step to obtain particles of bismuth oxycarbonate and of alumina; (3''') optionally, dispersing said particles of bismuth oxycarbonate and of alumina (3''), in at least one solvent, in particular in an amount ranging from 0.05 g/L to 500 g/L; (4) providing a solution of at least one organosilicon compound b), optionally as a mixture with at least one solvent; (5) placing the mixture obtained on conclusion of step (3) or the dispersion (3''') in contact with said solution (4) to form the composite material; (6) isolating said composite material. According to a particular embodiment, the calcination step is performed at a temperature ranging from 200 °C to 400 °C, preferably from 250 °C to 300 °C, in particular for a time ranging from 15 minutes to 12 hours. In particular, the solvent(s) of steps (1), (2) and (4) may be identical or different, and are preferably chosen from polar protic solvents, more preferentially from water, alcohols, polyols and mixtures thereof. According to a particular embodiment, said bismuth oxycarbonate particles, and solvates thereof, such as hydrates thereof, are present in the dispersion (1) in a concentration ranging from 0.05 g/L to 500 g/L, preferably from 10 g/L to 250 g/L, and more preferentially from 50 g/L to 150 g/L. According to a particular embodiment, the dispersion medium (1) may be heated to a temperature ranging from 40 °C to 200 °C, preferably ranging from 50 °C to 100 °C, in particular for a period ranging from 1 minute to 24 hours, preferably ranging from 20 minutes to 2 hours. According to a particular embodiment, when the solvent or solvent mixture of step (1) contains water, the pH can be adjusted to between 5 and 10, preferably between 6 and 8, for example by adding at least one base, preferably a mineral base such as alkali metal or alkaline-earth metal hydroxides; in particular, the pH can be adjusted with sodium hydroxide. According to a preferred embodiment, the aluminum salts in step (2) are sodium aluminate. According to a particular embodiment, the Al/Bi molar ratio in step (3) ranges from 0.0001 to 20, preferably from 0.005 to 10, better still from 0.01 to 5, and even more preferentially from 0.05 to 3. According to a particular embodiment, the pH in step (3) is adjusted to pH 6.5, for example by adding at least one acid, preferably a mineral acid such as sulfuric acid. According to a particular embodiment, step (3) is performed with stirring. According to a particular embodiment, step (3) is performed for a time ranging from 1 minute to 24 hours, preferably from 20 minutes to 8 hours. According to a preferred embodiment, step (3) is performed at a temperature ranging from 60 °C to 70 °C. According to a particular embodiment, step (4) is preceded by a washing step, notably in successive cycles, and optionally by oven drying, for example at a temperature of 50 °C and optionally under vacuum (pressure below 100 mbar). According to a particular embodiment, the solution (4) may be heated to reflux, preferably at a temperature of 80 °C, prior to mixing in step (5). According to a particular embodiment, the dispersion medium (5) may be heated to reflux, preferably to a temperature of less than or equal to 80 °C. According to a particular embodiment, the molar ratio in step (5) of organosilicon compound(s) b)/bismuth oxycarbonate particles ranges from 0.0001 to 20, preferably from 0.005 to 10, better still from 0.01 to 5, and even more preferentially from 0.05 to 3. According to a particular embodiment, the pH in step (5) is adjusted to between 1.5 and 5, preferably between 2 and 4. According to a particular embodiment, the pH in step (5) is adjusted to between 8 and 12, preferably between 9 and 11. According to a particular embodiment, step (5) is performed with stirring. According to a preferred embodiment, step (5) is performed at a temperature ranging from 70 °C to 80 °C. According to a particular embodiment, step (5) is performed for a time ranging from 15 minutes to 48 hours, preferably from 1 hour to 24 hours, and more preferentially from 2 hours to 8 hours. According to a particular embodiment, a cooling step may be performed between steps (5) and (6). According to a particular embodiment, step (6) may be performed by centrifugation. According to a particular embodiment, step (6) is followed by a washing step, notably in successive cycles, and optionally by oven drying, for example at a temperature ranging from 40 °C to 100 °C and optionally under vacuum (pressure below 100 mbar). COSMETIC COMPOSITION The composite materials according to the invention may in particular be used in a composition, notably in a cosmetic composition. Thus, the present invention also relates to a composition, notably a cosmetic composition, comprising at least one composite material as defined previously. According to a preferred embodiment, the present invention also relates to a composition, notably a cosmetic composition, comprising: i) at least one composite material as defined previously; ii) at least one aqueous phase and/or at least one fatty phase; and iii) at least one compound chosen from: 1) UV-screening agents different from the composite materials i); 2) colorants; 3) cosmetic active agents for caring for keratin materials; 4) surfactants; 5) thickeners; and mixtures thereof. Said composite materials may be present in the composition, preferably a cosmetic composition, in a content ranging from 0.5% to 70% by weight, preferably from 1% to 50% by weight, better still from 2% to 40% by weight relative to the total weight of the composition. Aqueous phase A composition, notably a cosmetic composition, according to the invention may comprise at least one aqueous phase. The aqueous phase may comprise water and optionally a water-soluble solvent. In the present invention, the term “water-soluble solvent” denotes a compound that is liquid at room temperature and water-miscible (miscibility with water of greater than 50% by weight at 25 °C and atmospheric pressure). The water-soluble solvents that may be used in a composition according to the invention may also be volatile. Among the water-soluble solvents that may be used in a composition in accordance with the invention, mention may be made notably of lower monoalcohols containing from 1 to 5 carbon atoms, such as ethanol and isopropanol, C₂-C₃₂ polyols, C₃ and C₄ ketones and C₂- C4 aldehydes. Among the water-soluble solvents that may be used in a composition in accordance with the invention, mention may notably be made of polyols. For the purposes of the present invention, the term “polyol” means any organic molecule including at least two free hydroxyl groups. A polyol that is suitable for use in the invention may be a compound of linear, branched or cyclic, saturated or unsaturated alkyl type, bearing on the alkyl chain at least two -OH functions and in particular at least three -OH functions. The polyols that are advantageously suitable for formulating a composition according to the present invention are those notably containing from 2 to 32 carbon atoms and preferably 3 to 16 carbon atoms. Advantageously, the polyol may be chosen, for example, from pentaerythritol, trimethylolpropane, caprylyl glycol, glycerol, polyglycerols, such as glycerol oligomers, for instance diglycerol, polyethylene glycols, polypropylene glycols, and mixtures thereof. Fatty phase A composition, notably a cosmetic composition, according to the invention may also comprise at least one fatty phase, in particular an oily phase. For the purposes of the invention, the term "fatty phase" means a phase comprising at least one fatty substance and all the liposoluble and lipophilic ingredients used for formulating the compositions of the invention. Preferably, the fatty phase comprises at least one oil, notably a cosmetic oil. The term “oil” means a water-immiscible non-aqueous compound that is liquid at room temperature (25 °C) and atmospheric pressure (760 mmHg). The fatty phase may comprise at least one volatile or non-volatile hydrocarbon-based oil and/or a fatty substance. As non-volatile hydrocarbon-based oils, mention may notably be made of hydrocarbon- based oils of plant origin, synthetic ethers containing from 10 to 40 carbon atoms, linear or branched hydrocarbons of mineral or synthetic origin, synthetic esters, fatty alcohols that are liquid at room temperature and bearing a branched and/or unsaturated carbon chain containing from 12 to 26 carbon atoms, C₁₂-C₂₂ higher fatty acids, carbonates, and mixtures thereof. As volatile hydrocarbon-based oils, mention may notably be made of hydrocarbon-based oils containing from 8 to 16 carbon atoms. The non-volatile silicone oils may notably be chosen from non-volatile polydimethylsiloxanes (PDMSs) and phenyl silicones. As volatile silicone oils, mention may be made, for example, of volatile linear or cyclic silicone oils. Use may also be made of volatile fluoro oils, such as nonafluoromethoxybutane, nonafluoromethoxybutane, decafluoropentane, tetradecafluorohexane, dodecafluoropentane, and mixtures thereof. The oily phase may also comprise other fatty substances, mixed with or dissolved in the oil. Another fatty substance that may be present in the oily phase may be, for example, a fatty acid, a wax, a gum, a pasty compound, or mixtures thereof. 1) Additional UV-screening agents According to a particular embodiment, a composition according to the invention comprises a) at least one additional UV-screening agent other than the composite materials required according to the invention and defined above. For the purposes of the present invention, the term “UV-screening agent other than the composite materials” is intended to denote any UV-screening agent, the chemical nature of which differs from that of the composite materials required according to the invention and defined above. The composite materials according to the invention may thus be used alone or in combination with 1) other UV-screening agents, in particular chosen from organic and/or inorganic UV-screening agents. Thus, the cosmetic composition may also contain one or more additional UV-screening agents chosen from hydrophilic, lipophilic or insoluble organic UV-screening agents and/or mineral UV-screening agents different from the composite materials according to the invention. The term “hydrophilic UV-screening agent” means any cosmetic or dermatological organic or inorganic compound for filtering UV radiation, which may be fully dissolved in molecular form in a liquid aqueous phase or else which may be in a colloidal suspension (for example in micellar form) in a liquid aqueous phase. The term “lipophilic UV-screening agent” means any cosmetic or dermatological organic or inorganic compound for filtering UV radiation, which may be fully dissolved in molecular form in a liquid fatty phase or else which may be in a colloidal suspension (for example in micellar form) in a liquid fatty phase. The term “insoluble UV-screening agent” means any cosmetic or dermatological organic or inorganic compound for filtering UV radiation which has a solubility in water of less than 0.5% by weight and a solubility of less than 0.5% by weight in the majority of organic solvents such as liquid paraffin, fatty alcohol benzoates and fatty acid triglycerides, for example Miglyol 812^®. This solubility, determined at 70 °C, is defined as the amount of product in solution in the solvent at equilibrium with an excess of solid in suspension after returning to room temperature. It can be easily evaluated in the laboratory. The additional organic UV-screening agents are notably chosen from: - cinnamic compounds, in particular Ethylhexyl Methoxycinnamate, - anthranilate compounds, in particular Menthyl anthranilate, - salicylic compounds, in particular Homosalate and Ethylhexyl Salicylate, - dibenzoylmethane compounds, in particular Butyl Methoxydibenzoylmethane, - benzylidenecamphor compounds, in particular 3-Benzylidene camphor, 4- Methylbenzylidene camphor, Benzylidene Camphor Sulfonic Acid and Terephthalylidene Dicamphor Sulfonic Acid, - benzophenone compounds, in particular oxybenzone and n-hexyl 2-(4-diethylamino-2- hydroxybenzoyl)benzoate, - β,β-diphenylacrylate compounds, in particular octocrylene, - triazine compounds, in particular Phenylene Bis-Diphenyl triazine, Bis- Ethylhexyloxyphenol Methoxyphenyl Triazine, Ethylhexyl Triazone and Diethylhexyl Butamido Triazone, - benzotriazole compounds, in particular Drometrizole Trisiloxane, - benzalmalonate compounds, notably those mentioned in patent US 5624663, in particular Polysilicone-15, - benzimidazole derivatives, in particular Phenylbenzimidazole Sulfonic Acid, - imidazoline compounds, in particular Ethylhexyl Dimethoxybenzylidene Dioxoimidazoline Propionate, - bis-benzazolyl compounds, such as those described in patents EP 0669323 and US 2463264, in particular Disodium Phenyl Dibenzimidazole Tetra-sulfonate, - para-aminobenzoic compounds, in particular PABA, Ethylhexyl Dimethyl PABA and PEG-25 PABA, - methylenebis(hydroxyphenylbenzotriazole) compounds, such as those described in patent applications US 5237071, US 5166355, GB 2303549, DE 19726184 and EP 0893119, in particular Methylenebis-Benzotriazolyl Tetramethylbutylphenol, - benzoxazole compounds, such as those described in patent applications EP 0832642, EP 1027883, EP 1300137 and DE 10162844, in particular 2,4-bis-[5- 1(dimethylpropyl)benzoxazol-2-yl-(4-phenyl)imino]-6-(2-ethylhexyl)imino-1,3,5-triazine, - polymeric screening agents and silicone screening agents, such as those notably described in patent application WO 93/04665, - α-alkylstyrene-based dimers, such as those described in patent application DE 19855649, - 4,4-diarylbutadiene compounds, such as those described in patent applications EP 0967200, DE 19746654, DE 19755649, EP 1008586, EP 1133980 and EP 0133981, in particular 1,1-dicarboxy(2,2’-dimethylpropyl)-4,4-diphenylbutadiene, and - mixtures thereof. The additional inorganic UV-screening agents are generally mineral UV-screening agents, in particular chosen from metal oxides. The metal oxides may notably be chosen from titanium oxide, zinc oxide, iron oxide, zirconium oxide and cerium oxide, and mixtures thereof. The metal oxide particles may be coated or uncoated. The coated particles are more particularly titanium oxides coated with silica, with silica and iron oxide, with silica and alumina, with alumina, with alumina and aluminum stearate, with silica, alumina and alginic acid, with alumina and aluminum laurate, with iron oxide and iron stearate, with zinc oxide and zinc stearate, with silica and alumina and treated with a silicone, with silica, alumina and aluminum stearate and treated with a silicone, with silica and treated with a silicone, with alumina and treated with a silicone, with triethanolamine, with stearic acid, with sodium hexametaphosphate, or else TiO2 treated with octyltrimethylsilane, TiO2 treated with a polydimethylsiloxane, anatase/rutile TiO2 treated with a polydimethylhydrogenosiloxane, TiO₂ coated with triethylhexanoin, with aluminum stearate and with alumina, TiO₂ coated with aluminum stearate, with alumina and with silicone, TiO2 coated with lauroyl lysine, or TiO2 coated with C9-15 fluoro alcohol phosphate and aluminum hydroxide. The metal oxides may optionally be doped. In this regard, mention may be made of TiO2 particles doped with at least one transition metal, such as iron, zinc or manganese and more particularly manganese. The doped particles may be in the form of a dispersion, preferably an oily dispersion. The oil present in the oily dispersion is preferably chosen from triglycerides including those of capric/caprylic acids. The oily dispersion of titanium oxide particles may additionally include one or more dispersants, for example a sorbitan ester or a polyoxyalkylenated glycerol fatty acid ester. Mention may be made more particularly of the oily dispersion of TiO2 particles doped with manganese in capric/caprylic acid triglyceride in the presence of tri-PPG-3 myristyl ether citrate and polyglyceryl-3 polyricinoleate and sorbitan isostearate. Mention may also be made of mixtures of metal oxides, notably of titanium dioxide and of cerium dioxide, including the equal-weight mixture of titanium dioxide and cerium dioxide coated with silica, and the mixture of titanium dioxide and zinc dioxide coated with alumina, silica and silicone, or coated with alumina, silica and glycerol. 2) Colorants According to a particular embodiment, a composition according to the invention comprises 2) at least one colorant. In general, the term “colorant” is understood to denote any compound that is capable of coloring a composition, that is to say which absorbs in the visible spectrum, in particular so as to appear to the human eye to have a color such as yellow, orange, red, purple, blue or green. Preferably, a composition according to the invention comprises at least one pigment. The term “pigments” should be understood as meaning white or colored, mineral or organic particles that are insoluble in liquid lipophilic and hydrophilic phases, and which are intended to color and/or opacify the composition containing them, and which are different from the composite materials according to the invention. More particularly, the pigments have little or no solubility in aqueous-alcoholic media. The pigments that may be used are notably chosen from the organic and/or mineral pigments known in the art, notably those described in Kirk-Othmer’s Encyclopedia of Chemical Technology and in Ullmann’s Encyclopedia of Industrial Chemistry (Ullmann's Encyclopedia of Industrial Chemistry “Pigment organics”, 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 10.1002/14356007.a20 371 and ibid, “Pigments, Inorganic, 1. General” 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim10.1002/14356007.a20_243.pub3. These pigments may be in pigment powder or paste form. They may be coated or uncoated. The pigments may be chosen, for example, from mineral pigments, organic pigments, lakes, pigments with special effects such as nacres or glitter flakes, and mixtures thereof. The pigment may be a mineral pigment. The term “mineral pigment” refers to any pigment that satisfies the definition in Ullmann’s encyclopedia in the chapter on inorganic pigments. Among the mineral pigments that are useful in the present invention, mention may be made of iron oxides, chromium oxides, manganese violet, ultramarine blue, chromium hydrate, ferric blue and titanium oxide. The pigment may be an organic pigment. The term “organic pigment” refers to any pigment that satisfies the definition in Ullmann’s encyclopedia in the chapter on organic pigments. The organic pigment may notably be chosen from nitroso, nitro, azo, xanthene, quinoline, anthraquinone, phthalocyanine, metal-complex type, isoindolinone, isoindoline, quinacridone, perinone, perylene, diketopyrrolopyrrole, thioindigo, dioxazine, triphenylmethane or quinophthalone compounds. Preferably, the pigment(s) that are suitable for use in the invention are chosen from carbon black, iron oxides, notably red, brown or black iron oxides, and micas coated with iron oxide, triarylmethane pigments, notably blue and purple triarylmethane pigments, such as Blue 1 Lake, azo pigments, notably red azo pigments, such as D&C Red 7, alkali metal salts of lithol red, such as the calcium salt of lithol red B; more preferentially, the pigment(s) used are chosen from red iron oxides and azo pigments, notably red azo pigments such as D&C Red 7. The colorant(s) may be present in a composition according to the invention in a content ranging from 0.001% to 10% by weight and preferably from 0.005% to 5% by weight relative to the total weight of the composition. According to a particular embodiment of the invention, the amount of pigments ranges from 0.5% to 40% and preferably from 1% to 20% relative to the weight of the composition of the invention comprising them. 3) Cosmetic active agent According to a particular embodiment, a composition according to the invention comprises 3) at least one cosmetic active agent for caring for keratin materials, preferably for skincare. In particular, the cosmetic active agent may be at least one hydrophilic active agent and/or one lipophilic active agent. The term “hydrophilic active agent” means a water-soluble or water-dispersible active agent which is capable of forming hydrogen bonds. As cosmetic active agents, mention may be made, for example, of moisturizers, depigmenting agents, desquamating agents, humectants, anti-ageing agents, mattifying agents, cicatrizing agents, antibacterial agents, vitamins and derivatives or precursors thereof, antioxidants, free-radical scavengers, anti-pollutants, self-tanning agents, anti- glycation agents, calmatives, deodorant agents, essential oils, NO-synthase inhibitors, agents for stimulating the synthesis of dermal or epidermal macromolecules and/or for preventing degradation thereof, agents for stimulating fibroblast proliferation, agents for stimulating keratinocyte proliferation, muscle relaxants, refreshing agents, tensioning agents, depigmenting agents, propigmenting agents, keratolytic agents, slimming agents, agents which act on cell energy metabolism, insect repellents, substance P antagonists or CRGP antagonists, agents for preventing hair loss, and mixtures thereof. The active agent(s) may notably be chosen from: - vitamins and derivatives thereof, notably esters thereof, such as niacinamide (3- pyridinecarboxamide), nicotinamide (vitamin B3), tocopherol (vitamin E) and esters thereof (for instance tocopheryl acetate), ascorbic acid and derivatives thereof (vitamin C), retinol (vitamin A), - humectants or moisturizers such as urea, hydroxyureas, glycerol, polyglycerols, glyceryl glucoside, diglyceryl glucoside, polyglyceryl glucosides, xylityl glucoside and plant extracts (notably of tea, mint, orchid, soybean, aloe vera, honey), and in particular glycerol; - C-glycoside compounds, and preferably hydroxypropyl tetrahydropyrantriol (INCI name) (or proxylane); - antioxidant compounds; - anti-ageing active agents, such as hyaluronic acid compounds, and notably sodium hyaluronate, salicylic acid compounds and in particular 5-n-octanoylsalicylic acid (capryloylsalicylic acid), adenosine, and the sodium salt of (3-hydroxy-2- pentylcyclopentyl)acetic acid; - keratolytic agents such as lactic acid or glycolic acid; and - mixtures thereof. Such active agents may be present in a composition according to the invention in a content ranging from 0.05% to 10% by weight and preferably from 1.0% to 8.0% by weight relative to the total weight of the composition. 4) Surfactant According to a particular embodiment, a composition according to the invention comprises 4) at least one surfactant. The surfactants may be chosen from nonionic, anionic, cationic and amphoteric surfactants, and mixtures thereof. Reference may be made to the Kirk-Othmer Encyclopedia of Chemical Technology, volume 22, pages 333-432, 3rd Edition, 1979, Wiley, for the definition of the emulsifying properties and functions of surfactants, in particular pages 347-377 of this reference, for anionic, amphoteric and nonionic surfactants. Examples of amphoteric surfactants that are suitable for use in the invention are notably chosen form betaines, preferably chosen from alkyl betaines, in particular lauryl betaine, N- alkylamido betaines and derivatives thereof, in particular cocamidopropyl betaine, lauramidopropy betaine and N-disodium N-carboxyethoxyethyl N-cocoylamidoethyl aminoacetate; sultaines, in particular cocoyl amidopropylhydroxy sultaine; and mixtures thereof. The nonionic surfactants may notably be chosen from alkyl and polyalkyl esters of poly(ethylene oxide), oxyalkylenated alcohols, alkyl and polyalkyl ethers of poly(ethylene oxide), optionally polyoxyethylenated alkyl and polyalkyl esters of sorbitan, optionally polyoxyethylenated alkyl and polyalkyl ethers of sorbitan, in particular alkyl and polyalkyl esters of sucrose, optionally polyoxyethylenated alkyl and polyalkyl esters of glycerol, and optionally polyoxyethylenated alkyl and polyalkyl ethers of glycerol, gemini surfactants, cetyl alcohol, stearyl alcohol, and mixtures thereof. The anionic surfactants may be chosen from alkyl ether sulfates, carboxylates, amino acid derivatives, sulfonates, isethionates, taurates, sulfosuccinates, alkylsulfoacetates, phosphates and alkyl phosphates, polypeptides, metal salts of C₁₀-C₃₀ and notably C₁₆-C₂₅ fatty acids, in particular metal stearates and behenates, and mixtures thereof. The cationic surfactants may be chosen from alkylimidazolidiniums, such as isostearyl ethylimidonium ethosulfate, ammonium salts such as (C_12-30-alkyl)-tri(C_1-4-alkyl)ammonium halides such as N,N,N-trimethyl-1-docosanaminium chloride (or behentrimonium chloride). The silicone surfactants may be chosen from dimethicone copolyols or silicone elastomers. A composition according to the invention may comprise between 0.01% and 2.0% by weight of surfactant, preferably between 0.05% and 1.5% by weight, more preferentially between 0.1% and 1.0% by weight, relative to the total weight of the composition. 5) Thickener According to a particular embodiment, a composition according to the invention comprises 5) at least one thickener, also sometimes referred to as gelling agent or viscosity modifier. The thickeners may be synthetic, natural or of natural origin, preferably natural or of natural origin. Such thickeners may more particularly be chosen from natural polymers or polymers of natural origin, in particular of plant origin. These thickeners are preferably hydrophilic, i.e. soluble or dispersible in water. Advantageously, the thickener(s) are chosen from modified or native polysaccharides, in particular modified or unmodified starches, fructans, gellans, glucans, amylose, amylopectin, glycogen, pullulan, dextrans, celluloses and derivatives thereof, in particular methylcelluloses, hydroxyalkylcelluloses, ethylhydroxyethylcelluloses and carboxymethylcelluloses, mannans, xylans, lignins, arabans, galactans, galacturonans, alginate-based compounds, chitin, chitosans, glucuronoxylans, arabinoxylans, xyloglucans, glucomannans, pectic acids and pectins, arabinogalactans, carrageenans, agars, glycosaminoglucans, gum Arabic, sclerotium gum, tragacanth gums, ghatti gums, karaya gums, locust bean gums, konjac gums, galactomannans such as guar gums and nonionic derivatives thereof, in particular hydroxypropyl guar, and ionic derivatives thereof, biopolysaccharide gums of microbial origin, in particular scleroglucan or xanthan gums, mucopolysaccharides, carboxyvinyl polymers, polyacrylamides, polymers and copolymers of 2-acrylamido 2-methylpropane sulfonic acid, optionally crosslinked and/or neutralized, water-soluble or water-dispersible silicone derivatives, such as acrylic silicones, polyether silicones and cationic silicones, and mixtures thereof. The thickener(s) may be present in a composition according to the invention in a content ranging from 0.05% to 5.0% by weight, in particular from 0.3% to 4.0% by weight, more particularly from 0.4% to 2.5% by weight, relative to the total weight of the composition. Adjuvants A composition according to the invention may also include at last one adjuvant that is common in the cosmetic field, chosen from fragrances, film-forming polymers, pH adjusters (acid or base), for example citric acid, tartaric acid or oxalic acid, chelating agents, preserving agents, softeners, sweeteners, antifoaming agents, fillers, trace elements, propellants, and mixtures thereof. It is understood that a person skilled in the art will take care to select this or these optional additional compound(s), and/or the amount thereof, such that the advantageous properties of a composition according to the invention are not, or are not substantially, adversely affected by the envisioned addition. It is understood that a person skilled in the art will take care to select this or these optional additional compound(s), and/or the amount thereof, such that the advantageous properties of the particles according to the invention are not, or are not substantially, adversely affected by the envisaged addition. As stated previously, a composition according to the invention may be cosmetic, and preferably is cosmetic. A composition according to the invention is generally suitable for topical application to the skin and thus generally comprises a physiologically acceptable medium, i.e. a medium that is compatible with the skin. It is preferably a cosmetically acceptable medium, i.e. a medium which has a pleasant color, odor and feel and which does not cause any unacceptable discomfort, i.e. stinging or tautness, liable to discourage the user from applying this composition. Presentation forms of the compositions The compositions, notably cosmetic compositions, containing the particles according to the invention, may be prepared according to techniques that are well known to those skilled in the art. They may be in any conventional presentation form depending on the targeted applications and are suitable for topical application, i.e. application to the surface of the keratin materials under consideration. The cosmetic compositions may be in the form of an aqueous or aqueous-alcoholic gel. They may be in the form of a simple or complex (O/W, W/O, O/W/O or W/O/W) emulsion, such as a cream, a milk or a gel-cream. They may also be in anhydrous form, for example in the form of an oil. The term “anhydrous composition” means a composition containing less than 5% by weight of water, or even less than 2% of water, better still less than 1% of water and notably being free of water, the water not being added during the preparation of the composition but corresponding to the residual water provided by the mixed ingredients. The cosmetic compositions may for example be used as a makeup product. The cosmetic compositions may be used, for example, as care and/or sun protection products for the face and/or body, of liquid to semi-liquid consistency, and may have the appearance of a more or less unctuous white or colored cream, an ointment, a milk, a cream-gel, a lotion, a serum, a paste or a foam. It may optionally be applied to the skin in aerosol form. It may also be in solid form, for example in the form of a stick. The cosmetic compositions may be in the form of products for caring for the skin or semi- mucous membranes, such as a protective or cosmetic care composition for the face, for the lips, for the hands, for the feet, for the anatomical folds or for the body (for example, day creams, night cream, day serum, night serum, makeup-removing cream, makeup base, protective or care body milk, after sun milk, skincare or scalp-care lotion, gel or foam, serum, mask, or aftershave composition). The composition may be applied by hand or using an applicator. In particular, the cosmetic compositions have an SPF of greater than 5 and preferably greater than 10. For the purposes of the invention, the term “SPF” means the sun protection factor, which measures the level of protection from UV rays. The SPF value corresponds to the ratio between the minimum time required to obtain an (erythematogenic) sunburn with a sun protection composition and the minimum time without a sun protection composition to obtain said sunburn. More specifically, the term “SPF” is defined in the article “A new substrate to measure sunscreen protection factors across the ultraviolet spectrum”, J. Soc. Cosmet. Chem., 40, 127-133 (May/June 1989). The SPF (Sun Protection Factor) may be evaluated in vitro using a Labsphere® spectrophotometer. The sheet is the material onto which the sun protection composition is applied. Poly(methyl methacrylate) (PMMA) sheets have proven to be ideal for this protocol. The Sun Protection Factor (SPF) of the compositions may also be evaluated in vivo in accordance with the ISO 24444 protocol “Cosmetics - Sun protection test methods - in vivo determination of the Sun Protection Factor (SPF) (2010)”. The term “UVAPF” means the index characterizing protection from UV-A radiation. In particular, this index was able to be measured in vivo using the PPD (Persistent Pigment Darkening) method: “PPD” measures the color of the skin observed 2 to 4 hours after exposure to UV-A rays. This method has been adopted since 1996 by the Japan Cosmetic Industry Association (JCIA) as the official test procedure for UV-A labelling of products, and is frequently used by test laboratories in Europe and the United States (Japan Cosmetic Industry Association Technical Bulletin. Measurement standards for the efficacy of UVA protection issued on 21 November 1995 and in force since 1 January 1996). The UV-A protection can also be evaluated in vitro using the Labsphere® spectrophotometer. The sheet is the material onto which the sun protection composition is applied. For this protocol, polymethyl methacrylate (PMMA) sheets have proven to be ideal. The ISO 24443 protocol describes such an in vitro method. C^{OSMETIC USES AND PROCESSES} The present invention also relates to the non-therapeutic cosmetic use of the composite materials according to the invention for filtering UV radiation, preferably UV-B, comprising at least the application to keratin materials of a composition comprising at least one composite material as defined previously. The present invention also relates to a non-therapeutic cosmetic process for filtering UV radiation, in particular UV-B, comprising at least the application to keratin materials of a composition comprising at least one composite material as defined previously. According to yet another aspect thereof, the present invention also relates to the non- therapeutic cosmetic use of a cosmetic composition comprising at least one composite material defined previously, for preventing the appearance on the skin, in particular on the face, the neckline, the arms, the hands and/or the shoulders, of darker and/or more colored marks which give the skin a non-uniform color. The present invention is also directed towards a non-therapeutic cosmetic process for limiting the darkening of the skin and/or improving the color and/or uniformity of the complexion, comprising the application, to the surface of the keratin material, of at least one cosmetic composition comprising at least one composite material defined previously. The present invention is also directed towards the non-therapeutic cosmetic use of a cosmetic composition comprising at least one composite material defined previously, for preventing premature ageing of the skin, notably of the skin of the face, the neckline, the arms, the hands and/or the shoulders. The invention also relates to a non-therapeutic cosmetic process for preventing and/or treating the signs of ageing of a keratin material, comprising the application, to the surface of the keratin material, of at least one cosmetic composition comprising at least one composite material defined previously. According to one of its aspects, the present invention relates to the composite materials as defined previously, for use as agents for filtering UV radiation, in particular UV-B radiation. For the purposes of the present invention, the term “preventing” or “prevention” means reducing, at least in part, the risk of occurrence of a given phenomenon, for example the signs of ageing of a keratin material or the appearance on the skin of darker and/or more colored marks which give the skin a non-uniform color, and/or premature ageing of the skin. In the description and the examples, the percentages are weight or molar percentages. The ingredients are mixed in the order and under the conditions that are readily determined by a person skilled in the art. The invention will now be described by means of the following examples, which are of course given as non-limiting illustrations of the invention. Example Example 1: Preparation of the bismuth oxycarbonate particles according to the invention The bismuth oxycarbonate particles 1 are synthesized according to the preparation method described below. A solution of bismuth nitrate pentahydrate Bi(NO₃)₃·5H₂O (0.40 M) and of D-mannitol (0.87 M) is prepared in 800 mL of water and stirred until the reagents have completely dissolved.160 mL of ammonium carbonate solution (2.1 equivalents relative to the bismuth) are then added. A white solid precipitates. This mixture is then transferred into a Teflon autoclave reactor and heated for 7.5 hours at 125 °C. Product 1 is isolated by centrifugation and washed three times with water before being oven-dried at 60 °C. The morphology of the bismuth oxycarbonate particles was determined by direct observation by transmission electron microscopy. 1 to 5 milligrams of dry particles are dispersed in 10 mL of absolute ethanol and treated in an ultrasound bath for two minutes.5 µL of dispersion are then placed on an observation grid (copper with surface layer of carbon) and dried in ambient air. The observation is performed using a Hitachi HT 7700 transmission electron microscope at an acceleration voltage of 100 kV. The mean dimensions are obtained by measurement of the dimensions of the particles by image analysis using the ImageJ software (C.A. Schneider, W.S. Rasband, K.W. Eliceiri, NIH Image to ImageJ: 25 years of image analysis, Nat. Methods. 9 (2012) 671–675). The bismuth oxycarbonate particles 1 are platelets having the following mean dimensions: Mean length L: 86 nm Mean width l: 53 nm Mean thickness e: 28 nm Example 2: Synthesis of the composite materials according to the invention Example 2.A: Synthesis of the bismuth oxycarbonate - octyltriethoxysilane composite materials A The bismuth oxycarbonate particles according to Example 1 (253 mg) are stirred in 5 mL of distilled water at room temperature. The temperature of the medium is then brought to 50 °C, with stirring. A solution of octyltriethoxysilane (99 mg) in ethanol (5 mL) is added dropwise. The pH is adjusted to 2 by addition of dilute sulfuric acid H2SO4 (0.2 M). The mixture is stirred for 3 h at 50 °C. After cooling to room temperature, composite material A is isolated by centrifugation, washed three times with water and then once with ethanol, then oven-dried at 80 °C under vacuum (below 100 mbar). Composite material A is obtained in the form of a white powder and is characterized by UV/Vis spectrophotometry. Example 2.B: Synthesis of the bismuth oxycarbonate - dodecyltriethoxysilane composite materials B The bismuth oxycarbonate particles according to Example 1 (253 mg) are stirred in 5 mL of distilled water at room temperature. The temperature of the medium is then brought to 50 °C, with stirring. A solution of dodecyltriethoxysilane (119 mg) in ethanol (5 mL) is added dropwise. The pH is adjusted to 2 by addition of dilute sulfuric acid H₂SO₄ (0.2 M). The mixture is stirred for 3 h at 50 °C. After cooling to room temperature, composite material B is isolated by centrifugation, washed three times with water and then once with ethanol, then oven-dried at 80 °C under vacuum (below 100 mbar). Composite material B is obtained in the form of a white powder and is characterized by UV/Vis spectrophotometry. Example 2.C: Synthesis of the bismuth oxycarbonate - triethoxy(2,4,4- trimethylpentyl)silane composite materials C The bismuth oxycarbonate particles according to Example 1 (253 mg) are stirred in 5 mL of distilled water at room temperature. The temperature of the medium is then brought to 50 °C, with stirring. A solution of triethoxy(2,4,4-trimethylpentyl)silane (99 mg) in ethanol (5 mL) is added dropwise. The pH is adjusted to 2 by addition of dilute sulfuric acid H₂SO₄ (0.2 M). The mixture is stirred for 3 h at 50 °C. After cooling to room temperature, composite material C is isolated by centrifugation, washed three times with water and then once with ethanol, then oven-dried at 80 °C under vacuum (below 100 mbar). Composite material C is obtained in the form of a white powder and is characterized by UV/Vis spectrophotometry. Example 2.D: Synthesis of the bismuth oxycarbonate - benzyltriethoxysilane composite materials D The bismuth oxycarbonate particles according to Example 1 (253 mg) are stirred in 5 mL of distilled water at room temperature. The temperature of the medium is then brought to 50 °C, with stirring. A solution of benzyltriethoxysilane (91 mg) in ethanol (5 mL) is added dropwise. The pH is adjusted to 2 by addition of dilute sulfuric acid H₂SO₄ (0.2 M). The mixture is stirred for 3 h at 50 °C. After cooling to room temperature, composite material D is isolated by centrifugation, washed three times with water and then once with ethanol, then oven-dried at 80 °C under vacuum (below 100 mbar). Composite material D is obtained in the form of a white powder and is characterized by UV/Vis spectrophotometry. Example 2.E: Synthesis of the bismuth oxycarbonate - 2- [methoxy(polyethyleneoxy)propyl]trimethoxysilane (n = 1) composite materials E The bismuth oxycarbonate particles according to Example 1 (253 mg) are stirred in 5 mL of distilled water at room temperature. The temperature of the medium is then brought to 50 °C, with stirring. A solution of 2-[methoxy(polyethyleneoxy)propyl]trimethoxysilane (n = 1) (85 mg) in ethanol (5 mL) is added dropwise. The pH is adjusted to 2 by addition of dilute sulfuric acid H₂SO₄ (0.2 M). The mixture is stirred for 3 h at 50 °C. After cooling to room temperature, composite material E is isolated by centrifugation, washed three times with water and then once with ethanol, then oven-dried at 80 °C under vacuum (below 100 mbar). Composite material E is obtained in the form of a white powder and is characterized by UV/Vis spectrophotometry. Example 2.F: Synthesis of the bismuth oxycarbonate - [hydroxy(polyethyleneoxy)propyl]triethoxysilane (n = 8 - 12) composite materials F The bismuth oxycarbonate particles according to Example 1 (253 mg) are stirred in 5 mL of distilled water at room temperature. The temperature of the medium is then brought to 50 °C, with stirring. A solution of [hydroxy(polyethyleneoxy)propyl]triethoxysilane (n = 8 - 12) (85 mg) at 50% by mass in ethanol (4 mL) is added dropwise. The pH is adjusted to 2 by addition of dilute sulfuric acid H2SO4 (0.2 M). The mixture is stirred for 3 h at 50 °C. After cooling to room temperature, composite material F is isolated by centrifugation, washed three times with water and then once with ethanol, then oven-dried at 80 °C under vacuum (below 100 mbar). Composite material F is obtained in the form of a white powder and is characterized by UV/Vis spectrophotometry. Example 2.G: Synthesis of the bismuth oxycarbonate - silica - octyltriethoxysilane composite materials G The bismuth oxycarbonate particles according to Example 1 (2 g) are stirred in 40 mL of distilled water at room temperature. The temperature of the medium is then brought to 80 °C, with stirring. At this temperature, 26.6 mL of an aqueous sodium silicate solution prepared from a 26.9% by mass solution and diluted by a factor of 10 are added dropwise. During the addition, the pH is maintained at 6.5 with dilute sulfuric acid H2SO4 (0.2 M). Stirring and heating are maintained for 5 h, and the reaction medium is then allowed to cool to room temperature. The intermediate material, bismuth oxycarbonate and silica, is isolated by centrifugation and washed twice with water, before being oven-dried at 60 °C under vacuum (below 100 mbar). The bismuth oxycarbonate-silica intermediate material (253 mg) is then stirred in 5 mL of distilled water at room temperature. The temperature of the medium is then brought to 50 °C, with stirring. A solution of octyltriethoxysilane (99 mg) in ethanol (5 mL) is added dropwise. The pH is adjusted to 2 by addition of dilute sulfuric acid H₂SO₄ (0.2 M). The mixture is stirred for 3 h at 50 °C. After cooling to room temperature, composite material G is isolated by centrifugation, washed three times with water and then once with ethanol, then oven-dried at 80 °C under vacuum (below 100 mbar). Composite material G is obtained in the form of a white powder and is characterized by UV/Vis spectrophotometry. Example 2.H: Synthesis of the bismuth oxycarbonate - silica - dodecyltriethoxysilane composite materials H The bismuth oxycarbonate particles according to Example 1 (2 g) are stirred in 40 mL of distilled water at room temperature. The temperature of the medium is then brought to 80 °C, with stirring. At this temperature, 26.6 mL of an aqueous sodium silicate solution prepared from a 26.9% by mass solution and diluted by a factor of 10 are added dropwise. During the addition, the pH is maintained at 6.5 with dilute sulfuric acid H2SO4 (0.2 M). Stirring and heating are maintained for 5 h, and the reaction medium is then allowed to cool to room temperature. The intermediate material, bismuth oxycarbonate and silica, is isolated by centrifugation and washed twice with water, before being oven-dried at 60 °C under vacuum (below 100 mbar). The bismuth oxycarbonate-silica intermediate material (253 mg) is then stirred in 5 mL of distilled water at room temperature. The temperature of the medium is then brought to 50 °C, with stirring. A solution of dodecyltriethoxysilane (119 mg) in ethanol (5 mL) is added dropwise. The pH is adjusted to 2 by addition of dilute sulfuric acid H₂SO₄ (0.2 M). The mixture is stirred for 3 h at 50 °C. After cooling to room temperature, composite material H is isolated by centrifugation, washed three times with water and then once with ethanol, then oven-dried at 80 °C under vacuum (below 100 mbar). Composite material H is obtained in the form of a white powder and is characterized by UV/Vis spectrophotometry. Example 2.I: Synthesis of the bismuth oxycarbonate - aluminum hydroxide - octyltriethoxysilane composite materials I The bismuth oxycarbonate particles according to Example 1 (2 g) are stirred in 40 mL of distilled water at a concentration of 100 g/L at room temperature. The temperature of the medium is then maintained at 70 °C for 30 minutes. The pH is adjusted to 8 with sodium hydroxide. A sodium aluminate solution at 100 g/L in water is added dropwise in an amount such that the sodium aluminate/bismuth oxycarbonate molar ratio is equal to 0.027. Once the addition is complete, the reaction medium is stirred for 1 h at 70 °C. The pH is adjusted to 6.5 by addition of sulfuric acid. The bismuth oxycarbonate - aluminum hydroxide intermediate material is isolated by centrifugation and washed with water, before being oven-dried at 50 °C under vacuum (pressure 10 mmHg). The bismuth oxycarbonate-aluminum hydroxide intermediate material (253 mg) is then stirred in 5 mL of distilled water at room temperature. The temperature of the medium is then brought to 50 °C, with stirring. A solution of octyltriethoxysilane (99 mg) in ethanol (5 mL) is added dropwise. The pH is adjusted to 2 by addition of dilute sulfuric acid H₂SO₄ (0.2 M). The mixture is stirred for 3 h at 50 °C. After cooling to room temperature, composite material I is isolated by centrifugation, washed three times with water and then once with ethanol, then oven-dried at 80 °C under vacuum (below 100 mbar). Composite material I is obtained in the form of a white powder and is characterized by UV/Vis spectrophotometry. Example 2.J: Synthesis of the bismuth oxycarbonate – titanium dioxide - octyltriethoxysilane composite materials J The bismuth oxycarbonate particles according to Example 1 (2 g) are dispersed in 190 mL of 2-propanol. 2.5 mL of an aqueous sodium hydroxide solution (5 × 10^-4 M) is added dropwise under stirring. A solution composed of 116 µL of titanium isopropoxide (0.05 equivalent vs. Bi) in 10 mL of 2-propanol is then added dropwise under stirring. The resulting medium is then stirred for 1 hour. The intermediate material bismuth oxycarbonate – titanium dioxide is isolated by centrifugation, washed twice with ethanol and dried at 60 °C under vacuum (P < 100 mbar). 500 mg of the intermediate material bismuth oxycarbonate – titanium dioxide are then dispersed in 10 mL of water. The dispersion is heated at 50 °C. A solution of octyltriethoxysilane (180 mg) in 10 mL of ethanol is then added dropwise under stirring. The pH is then adjusted to 2 using H₂SO₄ (0.25 M). The dispersion is then stirred and heated at 50 °C for 3 hours. The composite material J is isolated by centrifugation, washed twice with water and once with ethanol and dried at 60 °C under vacuum (P < 100 mbar). Composite material J is obtained as a white powder and characterized by UV/Vis spectrophotometry. Example 2.K: Synthesis of bismuth oxycarbonate – zinc oxide - octyltriethoxysilane composite materials K The bismuth oxycarbonate particles according to Example 1 (1 g) are dispersed in 90 mL of water. The dispersion pH is adjusted to 5 using H₂SO₄ (0.1 M). Then, a solution of zinc nitrate hexahydrate (58.3 mg, 0.05 equivalent vs. Bi) in 10 mL of water is added. The pH is then adjusted to 10 by adding dropwise NaOH (0.5 M). The resulting medium is then heated under stirring at 70 °C for five minutes and then stirred for 1 hour. A white solid is isolated by centrifugation, washed twice with water and once with ethanol, then dried under vacuum at 50 °C for one hour. Then, 500 mg of the dried solid are placed in an alumina crucible and heated in a muffle furnace up to 200 °C (temperature ramp of 10 °C/min) for one hour. After cooling down to room temperature, the intermediate material bismuth oxycarbonate – zinc oxide is obtained as a whitish powder. 300 mg of the intermediate material bismuth oxycarbonate – zinc oxide are then dispersed in 10 mL of water. The dispersion is heated at 50 °C. A solution of octyltriethoxysilane (108 mg) in 10 mL of ethanol is then added dropwise under stirring. The pH is then adjusted to 10 using NaOH (0.5 M). The dispersion is then stirred and heated at 50 °C for 3 h. The composite material K is isolated by centrifugation, washed three times with ethanol and dried at 60 °C under vacuum (P < 100 mbar). Composite material K is obtained as a whitish powder and characterized by UV/Vis spectrophotometry. Comparative Example 2.L: Synthesis of bismuth oxycarbonate - octyltriethoxysilane composite materials Z not in accordance with the invention Bismuth oxycarbonate particles not in accordance with the invention (Alfa Aesar, platelet particles about 500 nm in diameter by 50 nm thick, 253 mg) are stirred in 5 mL of distilled water at room temperature. The temperature of the medium is then brought to 50 °C, with stirring. A solution of octyltriethoxysilane (99 mg) in ethanol (5 mL) is added dropwise. The pH is adjusted to 2 by addition of dilute sulfuric acid H₂SO₄ (0.2 M). The mixture is stirred for 3 h at 50 °C. After cooling to room temperature, composite material Z is isolated by centrifugation, washed three times with water and then once with ethanol, then oven-dried at 80 °C under vacuum (below 100 mbar). Composite material Z is obtained in the form of a white powder and is characterized by UV/Vis spectrophotometry. Example 2.M: Summary of the conditions for synthesizing materials A to K and Z Table 2 below summarizes all the composite materials prepared in Examples 2.A to 2.L. [Table 2] Intermediate M_aterial ^Bismuth inorganic Organosilicon derivative oxycarbonate compound A Compliant / Octyltriethoxysilane B Compliant / Dodecyltriethoxysilane C Compliant / Triethoxy(2,4,4-trimethylpentyl)silane D Compliant / Benzyltriethoxysilane E_{Compliant /} ^{2-[Methoxy(polyethyleneoxy)propyl]trimethoxysilane} (_{n = 1)} _{F Compliant /} ^{[Hydroxy(polyethyleneoxy)propyl]triethoxysilane (n =} 8_{- 12)} G Compliant Silica Octyltriethoxysilane H Compliant Silica Dodecyltriethoxysilane I Compliant ^Aluminum h_ydroxide Octyltriethoxysilane J Compliant ^Titanium d_ioxide Octyltriethoxysilane K Compliant Zinc oxide Octyltriethoxysilane Z Non-compliant / Octyltriethoxysilane Example 3: Absorbance spectra of bismuth oxycarbonate composite materials UV-visible spectrophotometric absorbance spectra of the composite materials prepared according to Example 2 were produced. They were obtained by UV-visible spectrophotometry on dispersions at 0.005% by mass of composite material in isododecane for composite materials A, B, G, H, I, J, K, and Z and in a water/propylene glycol/polysorbate 20 (Tween 20, sold by the company Acros Organics) mixture of respective mass fractions 49.85/49.85/0.30 for composite materials C, D, E and F. The quartz cell used for the absorbance measurements has a side length of 1 cm. The spectrophotometer used is the Genesys 10S machine from Thermo Fischer Scientific. Preparation of dispersions of products A, B, G, H, I and Z The dispersion of composite materials of bismuth oxycarbonate and of organosilicon derivatives, at 0.05% by mass in isododecane, is ultrasonicated for 1 minute and then stirred with a magnetic stirrer for 10 minutes. It is then ultrasonicated again for 1 minute, then diluted to 0.005% by mass of bismuth oxycarbonate, ultrasonicated again for 1 minute and stirred again with magnetic stirring for 5 hours. The sample is ultrasonicated for 1 minute just before performing the absorbance measurement. Preparation of the dispersions of products C, D, E and F The dispersion of composite materials of bismuth oxycarbonate and of organosilicon derivatives, at 0.10% by mass in a mixture of water/propylene glycol/polysorbate 20 with respective mass fractions of 49.85/49.85/0.30, is ultrasonicated for 15 minutes and then stirred with a magnetic stirrer for 2 hours. It is then diluted to 0.005% by mass of bismuth oxycarbonate in the same solvent mixture and stirred again for 10 minutes. The absorbance measurement is then performed. The spectra of the materials in accordance with the invention (A to I) are compared with bismuth oxycarbonate - octyltriethoxysilane particles not in accordance with the invention (material Z) prepared from a commercial reference of bismuth oxycarbonate (BiO)2CO3 obtained from Alfa Aesar (platelet particles about 500 nm in diameter by 50 nm thick). Beyond a predetermined threshold UV absorbance measurement value, the filtering of the UV radiation is considered to be effective. In particular, composite materials with a UV absorbance threshold, in the dispersion medium comprising said composite materials, at a mass fraction of 0.005%, of greater than 0.25 are considered as effective for filtering UV radiation. The absorbance spectra are presented in figures 1 to 12. The results are collated in Table 3 below. [Table 3] A_bsorbance ^Composite Composite Composite Composite Composite A B C D _E ^{Composite F} Absorbance a_{t 220 nm} ^{0.36 0.40 0.80 0.80 0.80 0.76} Absorbance a_{t 300 nm} ^{0.44 0.50 1 0.96 0.96 0.92} Absorbance a_{t 400 nm} ^{0.20 0.38 0.44 0.44 0.42 0.40} Absorbance a_{t 620 nm} ^{0.06 0.08 0.12 0.12 0.12 0.12} A_bsorbance ^Composite Composite Composite Composite Composite Composite Z G H I J K Comparative Absorbance a_{t 220 nm} ^{0.66 0.44 0.30 0.34 0.21 0.1} Absorbance a_{t 300 nm} ^{0.72 0.50 0.24 0.43 0.27 0.14} Absorbance a_{t 400 nm} ^{0.32 0.20 0.14 0.24 0.15 0.12} Absorbance a_{t 620 nm} ^{0.10 0.06 0.06 0.08 0.05 0.08} The composite materials in accordance with the invention show good absorbance of UV rays and consequently efficient screening of UV rays, notably the UV-B range. In contrast, the comparative composite material Z shows low absorbance, and does not afford sufficient screening of the entire UV range. The absorbance spectra also show that the composite materials in accordance with the invention have high transparency in the visible range between 400 and 780 nm. Example 4: Absorbance spectra of composite material A according to Example 2.A The UV-Visible absorbance spectra of composite material A according to Example 2.A are measured in various solvents i). The measurements are performed on dispersions of composite material A in a solvent i) at a concentration of 0.005 % by weight. Preparation of the dispersions of composite material A The composite material A, synthesized according to Example 2.A, is added at the concentration of 0.1 % by weight into solvent i). The mixture is homogenized by magnetic stirring at 600 rpm for 5 min, then sonicated in an ultrasonic bath (Prolabo TP 680/DH) at 100% power in continuous mode for 15 min. The mixture is finally placed under magnetic stirring at 600 rpm for 16 h. The dispersions obtained are referred to as An in Table 4 below. [Table 4] D_ispersion ^{Composite material} a_{ccording to the invention} ^{Solvent i)} A1 A (Example 2.A) Caprylic capric triglyceride A2 A (Example 2.A) Propylene carbonate Each of the dispersions A1 and A2 prepared according to the protocol described above is diluted by addition of solvent i) to reach the final concentration in composite material A of 0.005% by weight, then placed under magnetic stirring at 600 rpm for 20 min before running the absorbance measurement. The quartz cell used for absorbance measurements is 1 cm thick. The absorbance spectrum is acquired using a UV-2600 UV-Vis Spectrophotometer (Shimadzu). The baseline determination is previously performed on a quartz cell filled with solvent i). Above a predetermined threshold value of the measured UV absorbance, filtration of UV rays is considered to be efficient. Particularly, the composite material A according to Example 2.A, when dispersed in solvent i) at a concentration of 0.005% by weight, is considered to efficiently filter UV rays if the maximum of absorbance measured in the UV range is higher than 0.25. The absorbance spectrum of dispersions A1 and A2 according to Example 4 are presented in Figures 13 and 14. The resulting absorbance values are reported in Table 5. [Table 5] Absorbance Dispersion A1 Dispersion A2 Absorbance at 220 nm 0.42 0.46 Absorbance at 280 nm 0.51 1.21 Absorbance at 300 nm 0.54 1.19 Absorbance at 320 nm 0.56 1.10 Absorbance at 400 nm 0.43 0.52 Absorbance at 620 nm 0.16 0.15 Absorbance at 780 nm 0.10 0.08 Example 5: Preparation of compositions A3, A4, A5 and A6 according to the invention A solution of surfactant ii) is prepared at a concentration of 1% by weight in a solvent i) by stirring until complete solubilization. It is then diluted in solvent i) to reach the concentration of 0.1% by weight. During the preparation step of the surfactant solution for compositions A4, A5 and A6, the mixture of surfactant ii) and solvent i) was heated at 50 °C until complete solubilization, then left cool down to room temperature before the addition step of the composite material A described hereafter. The composite material A, synthesized according to Example 2.A, is added at the concentration of 0.1 % by weight to the diluted solution of surfactant ii) in solvent i). The mixture is homogenized by magnetic stirring at 600 rpm for 5 min, then sonicated in an ultrasonic bath (Prolabo TP 680/DH) at 100% power in continuous mode for 15 min. It is finally placed under magnetic stirring at 600 rpm for 16 h. The compositions obtained as dispersions are referred to as An in Table 6 below. [Table 6] Composition Composite according to material according Solvent i) Surfactant ii) the invention to the invention Polyglyceryl-6- Caprylic capric polyricinoleate (SY Glyster A^{3 A} (_{Example 2.A)} triglyceride CRS-75 MB, commercialized by Sakamoto Yakuhin) PEG-150 distearate A (Dapracare P6000 DS NV, A⁴ _{(Example 2.A)} ^Propanediol commercialized by Italmatch Chemicals) PEG-100 stearate (SP MYRJ A^{5 A} (_{Example 2.A)} ^Propanediol S100, commercialized by Croda) PEG-100 stearate (SP MYRJ A^{6 A} Propylene (_{Example 2.A)} S100, commercialized by carbonate Croda) Example 6: Absorbance spectra of compositions A3 to A6 according to the invention Each of the compositions A3 to A6 according to Example 5 is diluted by addition of solvent i) to reach the final concentration in composite material A of 0.005 % by weight, then placed under magnetic stirring at 600 rpm for 20 min before running the absorbance measurement. The quartz cell used for absorbance measurements is 1 cm thick. The absorbance spectrum is acquired using a UV-2600 UV-Vis Spectrophotometer (Shimadzu). The baseline determination is previously performed on a quartz cell filled with solvent i). Above a predetermined threshold value of the measured UV absorbance, filtration of UV rays is considered to be efficient. Particularly, the compositions containing 0.005% by weight of composite material A according to Example 2.A are considered to efficiently filter UV rays if their maximum of absorbance in the UV range is higher than 0.25. The resulting absorbance values for compositions A3, A4, A5 and A6 according to the invention are reported in Table 7 below. [Table 7] Absorbance Composition A3 Composition A4 Composition A5 Composition A6 Absorbance at 220 nm 0.36 0.66 0.66 0.45 Absorbance at 280 nm 0.80 0.70 0.72 1.23 Absorbance at 300 nm 0.77 0.70 0.72 1.21 Absorbance at 320 nm 0.67 0.68 0.71 1.11 Absorbance at 400 nm 0.28 0.44 0.47 0.51 Absorbance at 620 nm 0.08 0.17 0.19 0.14 Absorbance at 780 nm 0.05 0.11 0.12 0.08 Compositions A3, A4, A5 and A6 according to the invention show good absorbance of UV rays and consequently efficient filtration of UV rays, particularly in the UV-B range. The absorbance values also show that compositions A3, A4, A5 and A6 according to the invention have a high transparency in the visible range between 400 and 780 nm. Example 7: Preparation of aqueous compositions A7 and A8 according to the invention A solution of surfactant ii) is prepared at a concentration of 1% by weight in water by stirring until complete solubilization. It is then diluted in water to reach the concentration 0.1% by weight. During the preparation step of the surfactant solution for composition A7, the lauryl glucoside (Plantacare 1200 UP, aqueous solution commercialized by BASF) was heated at 50 °C until a homogeneous solution was obtained prior to its introduction at the concentration of 1% by weight in water. During the preparation step of the surfactant solution for composition A8, the mixture of PEG-150 distearate and water was heated at 50 °C until complete solubilization, then left to cool down to room temperature before the addition step of the composite material A described hereafter. The composite material A, synthesized according to Example 2.A, is added at the concentration of 0.1% by weight to the diluted solution of surfactant ii) in water. The mixture is homogenized by magnetic stirring at 600 rpm for 5 min, then sonicated in an ultrasonic bath (Prolabo TP 680/DH) at 100% power in continuous mode for 15 min. The mixture is finally placed under magnetic stirring at 600 rpm for 16 hours. The compositions obtained as dispersions are referred to as An in Table 8 below. [Table 8] Composition Composite according to material according Solvent i) Surfactant ii) the invention to the invention Lauryl glucoside (Plantacare A^{7 A} (_{Example 2.A)} ^Water 1200 UP, aqueous solution commercialized by BASF) PEG-150 distearate (Dapracare A^{8 A} (_{Example 2.A)} ^Water P6000 DS NV, commercialized by Italmatch Chemicals) Example 8: Absorbance spectra of aqueous compositions A7 and A8 according to the invention Each of compositions A7 and A8 according to Example 7 is diluted by addition of deionized water to reach the final concentration in composite material A of 0.005% by weight, then placed under magnetic stirring at 600 rpm for 20 min before performing the absorbance measurement. The quartz cell used for absorbance measurements is 1 cm thick. The absorbance spectrum is acquired using a UV-2600 UV-Vis Spectrophotometer (Shimadzu). The baseline determination is previously performed on a quartz cell filled with water. Above a predetermined threshold value of the measured UV absorbance, filtration of UV rays is considered to be efficient. Particularly, the compositions containing 0.005% by weight of composite material A according to Example 2.A are considered to efficiently filter UV rays if their maximum of absorbance in the UV range is higher than 0.25. The absorbance spectra of aqueous compositions A7 and A8 according to the invention are presented in Figures 15 and 16. The resulting absorbance values are reported in Table 9 below. [Table 9] Absorbance Composition A7 Composition A8 Absorbance at 220 nm 0.46 0.82 Absorbance at 280 nm 0.50 0.96 Absorbance at 300 nm 0.49 0.95 Absorbance at 320 nm 0.47 0.90 Absorbance at 400 nm 0.33 0.48 Absorbance at 620 nm 0.17 0.15 Absorbance at 780 nm 0.12 0.09 Aqueous compositions A7 and A8 according to the invention show good absorbance of UV rays and consequently efficient filtration of UV rays, particularly in the UV-B range. The absorbance spectra also show that compositions A7 and A8 according to the invention have a high transparency in the visible range between 400 and 780 nm.

Claims

Claims 1. Composite material comprising: a) at least one particle of bismuth oxycarbonate of empirical formula (I) (BiO)2- x(CO₃), and solvates thereof, such as hydrates thereof, in which -0.4 < x < 0.6, the largest mean dimension of said particles being less than 400 nm; and b) at least one organosilicon compound.

2. Composite material according to Claim 1, characterized in that it has a mean size of the largest particle dimension of the composite material ranging from 0.005 µm to 10 µm, preferably from 0.01 µm to 1 µm.

3. Composite material according to any one of the preceding claims, comprising one or more inorganic compounds c) other than said bismuth oxycarbonate particles a), and solvates thereof, such as hydrates thereof, preferably chosen from inorganic oxides or hydrated forms thereof, more preferentially chosen from Al(OH)3, Al2O3, SiO2, TiO₂ and ZnO, and even more preferentially chosen from Al(OH)₃ and SiO₂. 4. Composite material according to any one of the preceding claims, comprising: - a core comprising at least a) at least one particle of bismuth oxycarbonate of empirical formula (BiO)_2-x(CO₃), and solvates thereof, such as hydrates thereof, in which -0.

4 < x < 0.6, the largest mean dimension of said particles being less than 400 nm; and - at least one layer continuously or discontinuously surrounding said core and comprising b) at least one organosilicon compound.

5. Composite material according to any one of the preceding claims, comprising: - a core comprising at least a) at least one particle of bismuth oxycarbonate of formula (I) (BiO)_2-x(CO₃), and solvates thereof, such as hydrates thereof, in which -0.4 < x < 0.6, the largest mean dimension of said particles being less than 400 nm; - an inner layer adjacent to said core, comprising at least one inorganic compound c) different from said bismuth oxycarbonate particles a), - an outer layer adjacent to said inner layer and comprising b) at least one organosilicon compound.

6. Composite material according to either one of Claims 4 and 5, the molar ratio between the number of moles of coating compound(s) and the number of moles of core compound(s) ranging from 0.0001 to 20, preferably from 0.005 to 10, better still from 0.01 to 5, and even more preferentially from 0.05 to 3.

7. Composite material according to any one of the preceding claims, said bismuth oxycarbonate particles being crystalline.

8. Composite material according to any one of the preceding claims, said bismuth oxycarbonate particles having the formula (BiO)2(CO3).

9. Composite material according to any one of the preceding claims, the largest mean dimension of said bismuth oxycarbonate particles being less than or equal to 300 nm.

10. Composite material according to any one of the preceding claims, said bismuth oxycarbonate particles being in the form of tubes, platelets and/or rods, preferably in the form of platelets and/or rods.

11. Composite material according to any one of the preceding claims, said organosilicon compound(s) being chosen from silanes, and polymerized forms thereof, and siloxanes, and polymerized forms thereof.

12. Composite material according to any one of the preceding claims, said organosilicon compound(s) being chosen from alkoxysilanes, in particular from octyltriethoxysilane, dodecyltriethoxysilane, triethoxy(2,4, 4-trimethylpentyl)silane, benzyltriethoxysilane, 2-[methoxy(polyethyleneoxy)propyl]trimethoxysilane (n = 1) and [hydroxy(polyethyleneoxy)propyl]triethoxysilane (n = 8 - 12), and preferably from octyltriethoxysilane and dodecyltriethoxysilane.

13. Process for preparing a composite material according to any one of Claims 1 to 12, comprising a step of chemical grafting or physical adsorption of said organosilicon compound(s) b), directly onto the surface of particles a) of bismuth oxycarbonate of empirical formula (BiO)_2-x(CO₃), and solvates thereof, such as hydrates thereof, in which -0.4 < x < 0.6, the largest mean dimension of said particles being less than 400 nm, or at the surface of particles comprising particles a) of bismuth oxycarbonate of empirical formula (BiO)_2-x(CO₃), and solvates thereof, such as hydrates thereof, in which -0.4 < x < 0.6, the largest mean dimension of said particles being less than 400 nm, and an inorganic compound c) different from said bismuth oxycarbonate particles a).

14. Preparation process according to Claim 13, comprising the steps of: (i) providing a dispersion of particles a) of bismuth oxycarbonate of empirical formula (I) (BiO)2-x(CO3), and solvates thereof, such as hydrates thereof, in which - 0.4 < x < 0.6, the largest mean dimension of said particles being less than 400 nm, in at least one solvent, in particular in an amount ranging from 0.05 g/L to 500 g/L; (ii) providing a solution of at least one organosilicon compound b), optionally as a mixture with at least one solvent; (iii) placing said dispersion (i) and said solution (ii) in contact to form the composite material; (iv) isolating said composite material.

15. Preparation process according to Claim 14, said solvent(s) of steps (i) and (ii) being identical or different; preferably, the solvent(s) of step (i) are chosen from polar protic solvents, more preferentially from water, alcohols, polyols and mixtures thereof, and even more preferentially is water, and the solvent(s) in step (ii) are chosen from polar protic solvents, more preferentially from alcohols, and even more preferentially is an alcohol corresponding to the alkoxide radical of the organosilicon compound b).

16. Composition, notably a cosmetic composition, comprising at least one composite material according to any one of Claims 1 to 12.

17. Composition according to the preceding claim, comprising: i) at least one composite material according to any one of Claims 1 to 12; ii) at least one aqueous phase and/or at least one fatty phase; and iii) at least one compound chosen from: 1) UV-screening agents different from the composite materials i); 2) colorants; 3) cosmetic active agents for caring for keratin materials; 4) surfactants; 5) thickeners; and mixtures thereof.

18. Composition according to either of Claims 16 and 17, said composite materials being present in a content ranging from 0.5% to 70% by weight, preferably from 1% to 50% by weight and better still from 2% to 40% by weight, relative to the total weight of the composition.

19. Non-therapeutic cosmetic use of a composite material according to any one of Claims 1 to 12, for filtering UV radiation, preferably UV-B radiation, comprising at least the application to keratin materials of a composition comprising a composite material according to any one of Claims 1 to 12.

20. Non-therapeutic cosmetic process for filtering UV radiation, preferably UV-B radiation, comprising at least the application to keratin materials of a composition comprising a composite material according to any one of Claims 1 to 12.