FR3037053A1 - PRODUCTION OF DIHYDROGEN WITH PHOTOCATALYST SUPPORTED ON NANODIAMANTS - Google Patents

Abstract

The invention relates to a process for the preparation of dihydrogen by photodissociation of water by irradiation using UV, visible or near-IR radiation, comprising the use of a photocatalytic composite comprising at least one semiconductor compound with forbidden band from 2 to 5 eV; ▪ diamond nanoparticles. The invention also relates to such a photocatalytic composite and methods for its preparation.

Description

The invention relates to a process for the preparation of dihydrogen by photodissociation of water by irradiation using UV, visible or near IR radiation, comprising the use of a photocatalytic composite. comprising at least one bandgap semiconductor compound ranging from 2 to 5 eV; ^ diamond nanoparticles or nanodiamonds.

The invention also relates to this photocatalytic composite and methods for its preparation. For several years, alternative energy sources to fossil fuels have become increasingly important. Thus, dihydrogen is an energy source that is increasingly used, in particular because it makes it possible to avoid releasing CO2 during its combustion. By preparing dihydrogen by photodissociation of water by irradiation, in particular by irradiation from solar radiation, it is therefore possible to transform light energy, in particular solar energy, into chemical energy in the form of dihydrogen which can then be stored. This chemical energy in the form of stored dihydrogen can then be transported or used later. However, at present, the amounts of available hydrogen or dihydrogen production technologies are still limited, particularly for economic reasons. One of the sources of dihydrogen production is the water from which dihydrogen can be produced by photodissociation. Photodissociation of water under solar irradiation is a promising way to generate clean energy quantities from an abundant and renewable source without the use of fossil resources. Indeed, solar energy is available in abundance and very widely. In general, the production of dihydrogen by photodissociation of water uses a photocatalyst. Most often, it is a noble metal, especially platinum 3037053. In addition to the high costs of using noble metals, the available quantities of these metals are limited and can therefore make them difficult to access. This is a major obstacle to the development of dihydrogen production by photodissociation of water, especially from solar energy, and using a photocatalyst of noble metal. In addition, the performance of these noble metal catalysts is a further obstacle to their use for the production of dihydrogen by photodissociation of water on a scale economically or industrially viable.

Thus, the technologies currently available do not allow to produce hydrogen in satisfactory quantities, while obtaining acceptable production costs. It is therefore necessary to have means for producing dihydrogen by photodissociation of water which employs reduced amounts of noble metals or which avoids the use of noble metals, while improving the production yield of dihydrogen. at acceptable cost levels. The invention provides a process for the preparation of dihydrogen by photodissociation of water employing a particular photocatalytic composite. The process for the preparation of dihydrogen according to the invention provides solutions to all or part of the problems of the processes of the state of the art and in particular to the problems of processes requiring the use of large quantities of noble metals for the preparation of dihydrogen by photodissociation of water.

Thus, the invention provides a process for the preparation of dihydrogen by photodissociation of water by irradiation using at least one UV (wavelength ranging from 200 to 400 nm), visible (wavelength ranging from 400 to 800 nm) or near IR (wavelength 800 to 1200 nm), comprising the use of a photocatalytic composite comprising at least one bandgap semiconductor compound of from 2 to 5 eV; ^ diamond nanoparticles. The process for the preparation of dihydrogen according to the invention can therefore be carried out at different wavelengths. The radiation used may be UV radiation (wavelength ranging from 200 to 400 nm), visible radiation (wavelength ranging from 400 to 800 nm) or near IR radiation (wavelength ranging from 800 to 1200 nm) or combinations thereof.

The photocatalytic composite used for the process for the preparation of dihydrogen according to the invention therefore has the essential property of catalyzing the photodissociation reaction of water. Advantageously, the photocatalytic composite may comprise 1, 2 or 3 semi-conductor bandgap compounds ranging from 2 to 5 eV. In a preferred manner for the photocatalytic composite according to the invention, the forbidden band semiconductor compound ranging from 2 to 5 eV is chosen from transition metals, transition metal derivatives, metal carbides, metal nitrides, metal oxides, metal sulfides, carbon nitride (C3N4). As semiconductor compounds having a forbidden band ranging from 2 to 5 eV preferred, mention may be made of transition metal oxides, transition metal sulfides, in particular TiO 2, TiO 2 -B (in the form of titanate sheet), ZnO , WO 3, Fe 2 O 3, preferably TiO 2.

In a particularly advantageous manner, the photodissociation process of the water according to the invention can be carried out in the absence of platinum or in the absence of a platinum derivative or in the absence of another photocatalyst. Also advantageously, the band gap semiconductor compound of from 2 to 5 eV is in the form of a one-dimensional material. It can be selected from a tube, a fiber, a stick, a needle. It can also be in the form of a spherical material or a cubic material. Also advantageously, the bandgap semiconductor compound of from 2 to 5 eV is in the form of dispersed particles or in the form of aggregated particles. It can also be in crystalline form. Particles of semiconductor compound with a forbidden band ranging from 2 to 5 eV can be of variable average size, for example is particles of size ranging from 3 to 100, 140, 200 or 1000 nm or of size ranging from 5 to 20, 50, 100, 140 or 200 nm. Examples of average particle size of the forbidden band semiconductor compound ranging from 2 to 5 eV include particles ranging in size from 3 to 1000 nm or 3037053 from 3 to 200 nm or from 3 to 140 nm. nm or 3 to 100 nm or 5 to 200 nm or 5 to 140 nm or 5 to 100 nm or 5 to 50 nm or 5 to 20 nm. Preferably, the average particle size of the semiconductor band gap compound is from 5 to 20 nm.

According to the invention, the bandgap semiconductor compound of from 2 to 5 eV can also be modified or doped. In particular, it may be doped with at least one cation or doped with at least one anion. Examples of anions include carbide or nitride. Examples of cations include transition metal cations such as tantalum, tungsten or niobium cations.

According to the invention, the photocatalytic composite comprises diamond nanoparticles. Preferably, the diamond nanoparticles have a size ranging from 1 to 50, 100, 200 or 500 nm or a size ranging from 2 to 50, 100, 200 or 500 nm. Examples of the average size of diamond nanoparticles are particles having a size ranging from 1 to 500 nm or from 2 to 500 nm or from 1 to 200 nm or from 2 to 200 nm or from 1 to 100 nm or from 2 to 200 nm or 1 to 50 nm or 2 to 50 nm. Preferably, the average particle size of the nanodiamonds ranges from 2 to 50 nm. Advantageously, the diamond nanoparticles are in the form of a one-dimensional material or are in steric or platelet form. Also advantageously, the diamond nanoparticles may be doped, in particular nitrogen-doped or boron doped. The diamond nanoparticles can also be modified, especially surface-modified. They can be hydrogenated on the surface. According to the invention, the photocatalytic composite may comprise relatively variable relative proportions of semiconductor compound with a band gap ranging from 2 to 5 eV and diamond nanoparticles. Preferably, the photocatalytic composite may comprise from 0.5 to 30, 50 or 80% by weight or from 1 to 30, 50 or 80% by weight of diamond nanoparticles relative to the amount of semiconductor band-gap compound ranging from 2 to 5 eV. Examples of photocatalytic composite include from 0.5 to 80% by weight of diamond nanoparticles relative to the amount of a bandgap semiconductor compound of from 2 to 5 eV; or 3037053 5 1 to 80% by weight of diamond nanoparticles relative to the amount of semiconductor compound with bandgap ranging from 2 to 5 eV; or from 0.5 to 50 mass% of diamond nanoparticles relative to the amount of banded semiconductor compound ranging from 2 to 5 eV; or 5% from 1 to 50% by weight of diamond nanoparticles relative to the amount of banded semiconductor compound ranging from 2 to 5 eV; or 0.5 to 30% by weight of diamond nanoparticles relative to the amount of banded semiconductor compound ranging from 2 to 5 eV; or 1 to 30% by weight of diamond nanoparticles relative to the amount of a bandgap semiconductor compound ranging from 2 to 5 eV. Preferably, the photocatalytic composite according to the invention comprises from 1 to 30% by mass of diamond nanoparticles relative to the amount of semiconductor compound with a band gap ranging from 2 to 5 eV.

According to the invention, the photocatalytic composite comprises diamond nanoparticles and at least one semiconductor compound with a band gap ranging from 2 to 5 eV. The photocatalytic composite may also comprise at least one other bandgap semiconductor compound ranging from 2 to 5 eV. It may in particular comprise one or two other semiconductor compounds with bandgap ranging from 2 to 5 eV.

The other forbidden semiconductor compound ranging from 2 to 5 eV can also be chosen from transition metals, transition metal derivatives, metal carbides, metal nitrides, metal oxides, metal sulphides, carbon nitride (C3N4), in particular transition metal oxides, transition metal sulfides, especially in particular TiO2, TiO2-B (in the form of titanate sheet), ZnO, WO3, Fe2O3. The other semiconductor compound with a band gap ranging from 2 to 5 eV can also be chosen from noble metals; noble metal carbides; nitrides of noble metals; noble metal oxides; sulphides of noble metals; transition metal carbides; transition metal nitrides; transition metal oxides; transition metal sulphides; plasmon-effect compounds or carbon nitride. Advantageously, the photocatalytic composite may comprise from 0.1 to 1, 2 or 5 wt% or from 0.3 to 1, 2 or 5 wt% of another non-wavelength semiconductor compound ranging from 2 to 5 wt. eV with respect to the amount of first bandgap semiconductor compound ranging from 2 to 5 eV. It may also comprise from 0.1 to 5% by weight of the other forbidden band semiconductor compound ranging from 2 to 5 eV with respect to the amount of first band-gap semiconductor compound ranging from 2 to 5 eV. 5 eV; or from 0.3 to 5% by weight of the other forbidden band semiconductor compound ranging from 2 to 5 eV with respect to the amount of first banded semiconductor compound ranging from 2 to 5 eV; or from 0.1 to 2% by weight of the other forbidden band semiconductor compound ranging from 2 to 5 eV with respect to the amount of first banded semiconductor compound ranging from 2 to 5 eV; or 10% from 0.3 to 2% by weight of the other forbidden band semiconductor compound ranging from 2 to 5 eV with respect to the amount of first banded semiconductor compound ranging from 2 to 5 eV; or from 0.1 to 1% by weight of the other bandgap semiconductor compound of from 2 to 5 eV relative to the amount of the first bandgap semiconductor compound of from 2 to 5 eV. Preferably, the photocatalytic composite according to the invention comprises from 1 to 5% by mass of another semiconductor compound with a forbidden band ranging from 2 to 5 eV with respect to the quantity of first semiconductor band-gap compound from 2 to 5 eV.

According to the invention, the photocatalytic composite may also comprise at least one organic compound chosen from organic compounds capable of supplying or transferring light energy during a light irradiation or during the photodissociation reaction. the water ; compounds improving the absorption and transfer properties of the light energy of the photocatalytic composite; the compounds selected from organic dyes. Advantageously, the photocatalytic composite may comprise from 0.1 to 1, 2 or 5 wt% or from 0.3 to 1, 2 or 5 wt% of organic compound relative to the amount of first semiconductor compound to forbidden band from 2 to 5 eV. It may also comprise from 0.3 to 1% by weight of organic compound relative to the amount of first banded semiconductor compound ranging from 2 to 5 eV; or 35% from 0.1 to 5% by weight of organic compound based on the amount of the first banded semiconductor compound ranging from 2 to 5 eV; or from 0.3 to 5% by weight of organic compound relative to the amount of first banded semiconductor compound ranging from 2 to 5 eV; or from 0.1 to 2% by weight of organic compound based on the amount of first banded semiconductor compound ranging from 2 to 5 eV; or from 0.3 to 2% by weight of organic compound relative to the amount of first banded semiconductor compound ranging from 2 to 5 eV; or from 0.1 to 1% by weight of organic compound relative to the amount of first bandgap semiconductor compound ranging from 2 to 5 eV; or 10 ^ 0.3 to 1% by weight organic compound based on the amount of first banded semiconductor compound ranging from 2 to 5 eV. Preferably, the photocatalytic composite according to the invention comprises from 1 to 5% by weight of organic compound relative to the amount of first band-gap semiconductor compound ranging from 2 to 5 eV.

Thus, during the photodissociation reaction of water to prepare dihydrogen, such compounds may make it possible to improve the absorption and transfer properties of the light energy of the photocatalytic composite. The yield of the photodissociation reaction of the water can then be improved.

Preferably, the photodissociation process of the water according to the invention can be carried out by irradiation by means of natural radiation or solar radiation. Particularly advantageously, the photodissociation process of the water according to the invention can be carried out in the absence of an energy input other than UV radiation (wavelength ranging from 200 to 400 nm), visible (wavelength ranging from 400 to 800 nm) or near IR (wavelength ranging from 800 to 1200 nm). In a preferred manner, the process for preparing dihydrogen by photodissociation of the water according to the invention is carried out at normal temperature and pressure.

The pressure may be atmospheric pressure. Generally, the photodissociation process of the water according to the invention may be carried out at a temperature ranging from 1 to 90 ° C., in particular from 15 to 55 ° or 60 ° C., and preferably from 25 to 30 ° C. or 50 ° C. As temperature ranges for carrying out the water photodissociation process according to the invention, mention may be made of temperatures ranging from 1 to 90 ° C or from 15 to 60 ° C or from 15 to 55 ° C or from 25 to 50 ° C or 30 to 50 ° C or 40 to 50 ° C. Thus, in general, the temperature can be between 1 and 90 ° C and preferably, it is between 40 and 50 ° C. Advantageously, when it is used for photodissociation of water in the process according to the invention, the photocatalytic composite can be suspended in the reaction water. Also advantageously, the photodissociation process of the water according to the invention comprises stirring the reaction medium.

Preferably, the photodissociation process of the water according to the invention may be carried out in the presence of an inert gas, for example in the presence of a gas chosen from nitrogen, argon or helium. The photodissociation process of the water according to the invention can also be carried out in the presence of a reducing gas.

Advantageously, the process for the preparation of dihydrogen according to the invention can be carried out in the presence of a compound which improves the yield of the production of dihydrogen. As a compound improving the yield of dihydrogen production, a sacrificial agent may be used.

In the photodissociation reaction of water, the irradiation of the photocatalytic composite causes an energy transition within the band gap semiconductor compound of from 2 to 5 eV. By electron displacement, this energy transition from the valence band to the conduction band generates positive charges, or holes, within the valence band.

The sacrificial agent used can react with these holes or positive charges. The electrons generated can not fill the holes that remain free. The use of a sacrificial agent therefore makes it possible to increase the number of electrons available to react with the surrounding species of the photocatalytic composite, in particular the chemical species allowing the dissociation of water.

The photodissociation yield of the water by photocatalyzed irradiation using a photocatalytic composite according to the invention is then improved. During photodissociation of the water, the formed oxygen can also react with the sacrificial agent. In this case, the formed oxygen will not be able to react with the dihydrogen formed to reform water. By reaction with the oxygen formed, the sacrificial agent therefore increases the photodissociation yield of water to produce a larger amount of hydrogen. Advantageously, the sacrificial agent used according to the invention is a compound which must be able to react with photogenerated holes in the photocatalytic composite according to the invention or which must be capable of being oxidized by the dioxygen formed during the photodissociation of water. Thus, the process for preparing dihydrogen according to the invention is advantageously carried out in the presence of a compound improving the yield of the production of dihydrogen and capable of being oxidized by the oxygen formed during the photodissociation reaction of the water. . Also advantageously, the process for the preparation of dihydrogen according to the invention is carried out in the presence of a compound which improves the yield of the production of dihydrogen and is capable of reacting with the photogenerated positive electric charge holes during the energy transition of the electrons of the bandgap semiconductor compound ranging from 2 to 5 eV, from its valence band to its conduction band. This process is then carried out in the presence of a compound improving the yield of hydrogen production and capable of reacting with photogenerated holes or of reacting with oxygen.

The process for preparing dihydrogen according to the invention is then advantageously carried out in the presence of a compound chosen from amines, alcohols, preferably methanol. Moreover, the compound used as sacrificial agent can also act directly on the formation of dihydrogen by photoreforming. It may be a compound chosen from amines and alcohols. Advantageously, it is then preferred to use an alcohol and, preferably, use methanol. The process for the preparation of dihydrogen according to the invention can therefore be carried out in the presence of a compound which improves the yield of the production of dihydrogen by photoreforming by the action of the photocatalyst, in particular a compound chosen from amines and alcohols. preferably methanol. In addition to a process for the preparation of dihydrogen by photodissociation of water, the invention also relates to the preparation of a photocatalytic composite useful for this reaction. The photocatalytic composite according to the invention comprises at least one semiconductor compound with a band gap ranging from 2 to 5 eV and diamond nanoparticles. Preferably, the photocatalytic composite according to the invention is prepared according to a process (A) comprising the preparation of at least one semiconductor compound with a band gap ranging from 2 to 5 eV; the preparation of diamond nanoparticles; the preparation of at least one suspension of the forbidden band semiconductor compound ranging from 2 to 5 eV or diamond nanoparticles; the mixture of the 2 to 5 eV bandgap semiconductor compound with the diamond nanoparticle suspension or the mixture of the diamond nanoparticles with the semiconductor compound suspension with a band gap of 2 to 5 eV or the mixture of the two suspensions; Separation of the photocatalytic composite and the solvent. Thus, the process (A) may comprise the preparation of a suspension of the bandgap semiconductor compound ranging from 2 to 5 eV and the mixing of the diamond nanoparticles with this suspension.

Process (A) may also comprise preparing a suspension of diamond nanoparticles and mixing the semiconductor compound with a band gap of from 2 to 5 eV with this suspension. Process (A) may also include preparing a suspension of diamond nanoparticles, preparing a suspension of the bandgap semiconductor compound of from 2 to 5 eV and mixing these two suspensions. Also preferably, the photocatalytic composite according to the invention is prepared according to a process (B) comprising the preparation of diamond nanoparticles; then the sol-gel or hydrothermal process preparation of the bandgap semiconductor compound ranging from 2 to 5 eV in the presence of the diamond nanoparticles; then separation of the photocatalytic composite.

Also preferably, the photocatalytic composite according to the invention is prepared according to a process (C) comprising: preparing the bandgap semiconductor compound of from 2 to 5 eV; then detonation or chemical vapor phase deposition of diamond nanoparticles in the presence of the bandgap semiconductor compound of from 2 to 5 eV; then separation of the photocatalytic composite. Also preferably, the photocatalytic composite according to the invention is prepared according to a process (D) comprising the sol-gel or hydrothermal process preparation of the semiconductor compound with a band gap of from 2 to 5 eV, and simultaneous preparation by detonation or chemical vapor deposition of diamond nanoparticles; then the separation of the photocatalytic composite. Advantageously, during the sol-gel process preparation of the semiconductor compound with a forbidden band ranging from 2 to 5 eV, the precursor compounds of the semiconductor compound with a forbidden band ranging from 2 to 5 eV and the diamond nanoparticles 20 are placed simultaneously. Precursor compounds of the semiconductor compound with a band gap of from 2 to 5 eV are known per se for sol-gel processes. As a precursor compound of the semiconductor compound with a band gap of from 2 to 5 eV, it is possible to use titanium hydroxide (TiOH).

The precursor compounds of the 2 to 5 eV bandgap semi-conductor compound for the sol-gel processes must be soluble or they must be suspendable. In preparing the photocatalytic composite according to the invention, the preparation of the bandgap semiconductor compound of from 2 to 5 eV can comprise the preparation of particles of this semiconductor compound with a band gap ranging from 2 to 5 eV . In the preparation of the photocatalytic composite according to the invention, the diamond nanoparticles may be prepared by a method comprising a detonation step or by a method comprising a chemical vapor deposition (CVD) step. . According to the invention, the diamond nanoparticles of the photocatalytic composite are not prepared according to an atomic layer deposition (ALD) method or atomic thin film deposition method. The diamond nanoparticles can be prepared by detonation of a nanostructured explosive charge in which a charge of explosive is placed in a pocket filled with water suspended in the center of a steel detonation tank. The soot resulting from the detonation is collected, filtered and then purified with an acid solution. A final purification step is to perform a selective oxidation treatment to remove unwanted carbon phases and retain only the diamond nanoparticles (see Example 2 of the patent application WO 2013-127967). The process for preparing the photocatalytic composite can be carried out under an inert atmosphere, in particular under a nitrogen, argon or helium atmosphere. The process for preparing the photocatalytic composite can also be carried out in the presence of a reducing gas of the semiconductor compound with a forbidden band ranging from 2 to 5 eV, for example in the presence of hydrogen. It can also be carried out in the presence of an oxidizing gas of the semiconductor compound with a bandgap ranging from 2 to 5 eV, for example in the presence of air or in the presence of oxygen. The process for preparing the photocatalytic composite according to the invention may also comprise the drying of the photocatalytic composite or the thermal treatment of the photocatalytic composite. The photocatalytic composite can be processed by irradiation, heating or p-wave radiation. The heat treatment can be carried out at a temperature of from 5 to 600 ° C or from 15 to 600 ° C or from room temperature to 600 ° C. The heat treatment may also be carried out at a temperature of from 5 to 500 ° C or from 15 to 500 ° C or from room temperature to 500 ° C. The heat treatment may also be carried out at a temperature of from 5 to 400 ° C or from 15 to 400 ° C or from room temperature to 400 ° C. The heat treatment can also be carried out at a temperature ranging from 5 to 300 ° C or from 15 to 300 ° C or from the temperature at 300 ° C. The heat treatment may also be carried out at a temperature of from 5 to 150 ° C or from 15 to 150 ° C or from room temperature to 150 ° C. The heat treatment can be from 10 s to 30 h or from 10 s to 20 h or from 10 s to 10 h. The heat treatment can also be of duration ranging from 1 min to 30 h or from 1 min to 20 h or from 1 min to 10 h. The heat treatment may also be from 10 minutes to 30 hours or 10 minutes to 20 hours or 10 minutes to 10 hours. Preferably, this duration can range from 3 to 5 hours, in particular 4 hours. During the preparation of the photocatalytic composite according to the invention, at least one of the preparation steps can be carried out in the presence of at least one compound selected from another forbidden band semiconductor compound ranging from 2 to 5 eV; or a precursor compound of a bandgap semiconductor compound of from 2 to 5 eV. At least one of the preparation steps may also be carried out in the presence of at least one organic compound chosen from organic compounds capable of supplying or transferring light energy during a light irradiation or during a period of time. photodissociation reaction of water; organic compounds improving the absorption and light energy transfer properties of the photocatalytic composite; The compounds selected from organic dyes. Similarly, at least one of the preparation steps can be carried out in the presence of at least one precursor compound of an organic compound chosen from organic compounds capable of supplying or transferring light energy during a light irradiation or during a photodissociation reaction of water; organic compounds improving the absorption and light energy transfer properties of the photocatalytic composite; the compounds selected from organic dyes.

Advantageously, the process for preparing the photocatalytic composite according to the invention may also comprise the deposition on the photocatalytic composite formed of at least one other bandgap semiconductor compound ranging from 2 to 5 eV. Similarly, the process for the preparation of the photocatalytic composite according to the invention may also comprise the deposition on the photocatalytic composite formed of at least one organic compound chosen from 3037053 organic compounds capable of supplying or transferring light energy during a light irradiation or during a photodissociation reaction; organic compounds improving the absorption and light energy transfer properties of the photocatalytic composite; the compounds selected from organic dyes. Preferably, the process for preparing the photocatalytic composite according to the invention may also comprise the addition to the photocatalytic composite formed of at least one other semiconductor compound with a band gap ranging from 2 to 5 eV. Also preferably, the process for preparing the photocatalytic composite according to the invention may also comprise adding to the photocatalytic composite formed of at least one organic compound selected from organic compounds capable of supplying or transferring light energy during a light irradiation or during a photodissociation reaction; organic compounds improving the absorption and light energy transfer properties of the photocatalytic composite; the compounds selected from organic dyes.

In addition to a process for preparing dihydrogen by water photodissociation and a process for preparing a photocatalytic composite useful for this reaction, the invention also relates to a photocatalytic composite comprising at least one semiconductor compound with a band gap ranging from 2 to 5 eV and diamond nanoparticles which is prepared according to the preparation method according to the invention.

Preferably, the photocatalytic composite according to the invention is prepared according to one of the preparation processes (A), (B), (C) or (D). The photocatalytic composite according to the invention is also defined by all of its characteristics that are useful for its implementation in the process for the preparation of dihydrogen by photodissociation of the water according to the invention. These feature combinations also define preferred photocatalytic composites, advantageous or particular according to the invention.

The various aspects of the invention can be illustrated by the following examples.

EXAMPLE 1 Preparation of Photocatalytic Composite Materials According to the Invention The composite materials according to the invention were prepared from nanostructured TiO 2 prepared by a sol-gel synthesis process under mild pressure conditions and at room temperature. The reagents employed for this synthesis are titanium tetraisopropoxide Ti (OC 3 H 7) 4 (Aldrich, 97%), ethanol (Aldrich> 99.8%) and acetic acid (Aldrich> 99.8%). 1.1. Preparation of TiO2Nanostructured Titanium tetraisopropoxide Ti (OC3H7) 4 (20.4 mL) was dissolved in ethanol (70.8 mL). After 30 min under strong magnetic stirring and at room temperature, a mixture of distilled water (1 mL), ethanol (2 mL) and acetic acid (74 mL) is added dropwise to the previous solution, still with magnetic stirring. Then, the precursor solution is stirred for one hour. It is then protected from light and left standing for 24 hours. A uniform, white, opaque gel of Ti (OH) 4 is obtained. It is dried in an oven overnight at 110 ° C by evaporation of the solvent. The material obtained is then ground with a mortar to recover a powder of Ti (OH) 4. This powder is then calcined under a stream of air (50 cm3 / min) at 400 ° C. for 3 h. The temperature ramp used for this heat treatment is 5 ° C / min. The nanostructured TiO 2 thus obtained, called C400, is then stored protected from light. 1.2. Preparation of diamond nanoparticles The nanodiamonds are prepared by detonation using an explosive charge containing a mixture of TNT / RDX (trinitrotoluene / cyclotrimethylenetrinitramine) in a proportion of 70/30 respectively placed in a detonation tank. The explosive charge is placed in a polyethylene bag filled with water that prevents the oxidation of carbon during the detonation. Once fired, the walls of the detonation tank are rinsed with deionized water. The recovered soot is then filtered and purified with aqua regia (HCl + 3HNO3) to remove the plastic from the cartridge and the metal oxides from the detonation tank. Then, this soot is purified and sieved wet by means of a sieve with a pore size of 80 μm. The solution thus recovered is dried at 100 ° C. and a black, dry powder is then obtained. This powder is purified to remove metal impurities, amorphous carbon and graphite. The metal impurities are removed by chemical treatment with aqua regia. The removal of unwanted carbon is achieved by a heat treatment at 420 ° C in the presence of air to oxidize the graphite carbon. Purified nanodiamonds are thus obtained whose size is of the order of 5 nm.

The nanodiamonds prepared have a unit cell of parameter a = 0.3567 nm. At the vertices of the cube inscribed in this mesh and in the center of each face, four of the eight tetrahedral sites are occupied, which finally gives eight carbon atoms per mesh. The volume of a mesh is 4.537 nm3 (45.37 Å3).

These nanodiamonds can be heat-treated under hydrogen flow (1 bar) at a temperature of 600, 700 or 800 ° C to obtain hydrogenated nanodiamonds. This heat treatment makes it possible to modify the surface functions of the nanodiamonds by reducing the oxygenated alcohol and acid groups. These modifications are analyzed by infrared spectroscopy to identify oxygenated surface groups (carboxylic acids, hydroxyls, lactones, etc.) and hydrogenated and thus to deduce the reduction reaction of oxygenated surface groups with hydrogen. The infrared spectra are obtained thanks to a Tensor 27 (Brüker) apparatus equipped with a PIKE MIRacle ATR cell (Attenuated Total Reflectance) making it possible to analyze pulverulent samples. A reference spectrum (without sample) is subtracted from the spectrum of the sample analyzed. Starting from nanodiamonds or hydrogenated nanodiamonds, the TiO 2 -nano-diamond composites (TiO 2 -ND) are prepared according to two processes, by sol-gel process or by impregnation. 1.3. Preparation of composite materials by sol-gel process During the preparation of the nanostructured TiO 2 by sol-gel process according to Example 1.1, the nanodiamonds are added to the solution of titanium tetraisopropoxide (TIP) and ethanol. Then complexing acetic acid is then added. The nanodiamonds are dispersed in the gel during its formation. The gel formed is then put in an oven overnight at 110 ° C and then calcined at 400 ° C for 3 h. The relative amounts of nanodiamonds within the different materials are measured by thermo-gravimetric analysis (TGA). A Seiko Instruments Exstar 6000 (TG / DTA 6200) SII device is used. Alumina crucibles serve as a container for 3037053 samples. The thermal program used is generally a heating ramp ranging from 20 ° C to 1000 ° C with a heating rate of 5 ° C per minute. The experiment is carried out under air flow in order to oxidize the nanodiamonds. The loss of mass corresponding to nanodiamonds can be measured from the curves obtained. 5 1.4. Preparation of composite materials by impregnation A suspension is prepared in nanostructured TiO 2 water prepared according to Example 1.1 and nanodiamonds. The suspension is stirred for 2 h under an inert gas (N 2) and then filtered and oven dried (100 ° C) to recover the photocatalytic composite material. Similarly, composite materials according to the invention are prepared by impregnation from a known TiO2 photocatalyst (product Evonik Aeroxide TiO2 P25). 1.5 1.5. Platinization of composite materials A deposit of Pt nanoparticles can be produced by impregnation, with magnetic stirring, with platinum salt H 2 PtCl 4 in water. The Pt salt is then chemically reduced at room temperature using NaBH4 (in excess). After some 20 minutes of reduction, the platinum composite material is washed and filtered. 1.6. Composite Materials Prepared According to the process of preparation used, optionally including the hydrogenation of the nanodiamonds, composite materials according to the invention are prepared according to the conditions and characteristics presented in Table 1. Example of a catalyst hydrogenation method of content ND material TiO2 ND preparation (% by weight) composite 1 C400 non sol-gel 0.5 2 C400 non sol-gel 0.7 3 C400 non sol-gel 2.6 4 C400 non sol-gel 5.2 5 C400 non-sol-gel 8.6 C400 non-sol-gel 20.1 3037053 18 7 C400 non-sol-gel 24.1 8 C400 non sol-gel 34.6 9 C400 non-impregnated 0.5 10 C400 non-impregnation 1, 1 11 C400 non-impregnation 2.9 12 C400 non-impregnation 8.5 13 C400 non-impregnation 10.5 14 C400 non-impregnation 26.5 15 C400 non-impregnation 31.5 16 C400 non-impregnation 42.5 17 C400 yes impregnation 4.2 18 C400 yes impregnation 9.2 19 C400 yes impregnation 18 20 C400 yes impregnation 28.3 21 C400 yes impregnation 37, 6 22 C400 yes impregnation 47.1 23 P25 non impregnation 4.6 24 P25 non impregnation 8.7 25 P25 non impregnation 17.1 26 P25 non impregnation 27.6 27 P25 non impregnation 37.8 28 P25 yes impregnation 4.7 29 P25 yes impregnation 9.7 30 P25 yes impregnation 20.5 31 P25 yes impregnation 28.9 Table 1 1.7. Preparation of reference materials by sol-gel process or by impregnation Similarly, reference materials are prepared in order to compare them with the composite materials according to the invention. According to the process of preparation used, including optionally hydrogenation of the nanodiamonds, reference materials are prepared according to the conditions and characteristics presented in Table 2.

3037053 19 Example of hydrogenation catalyst method of ND content TiO2 material of ND preparation (`) / 0 by weight) reference C400 non-sol-gel 0 c2 C400 non-impregnation 0 c3 C400 yes impregnation 0 c4 P25 non-impregnation 0 Table 2 Example 2 Evaluation of the Properties of Photocatalytic Composite Materials According to the Invention and Reference Materials 2.1. Hydrogen was produced by catalytic dissociation of water in the presence of composite material according to the invention and in the presence of methanol (1 mL). The reaction is carried out under a continuous flow of an inert carrier gas (N2) at atmospheric temperature and pressure under artificial solar irradiation using a mercury vapor lamp (150 W). Reference materials have also been used to compare their activity under the same conditions. Hydrogen production was measured as a function of the time and amount of catalyst used. The results obtained are shown in Table 3. Production H2 (umol / h / g catalyst) composite material according to the invention 5 6 12 8 23 6 24 8 25 10 26 8 27 9.5 28 6 29 9.5 30 The composite material according to the invention makes it possible to produce hydrogen by photodissociation of water. Of the reference materials, only the P25 catalyst comprising platinum has catalytic activity. However, the amount of hydrogen produced is much less than the amount produced using composite materials according to the invention which do not include platinum. 2.2. The value of the band gap of the composite materials according to the invention was measured by UV-visible absorption spectroscopy as a function of the amount of nanodiamonds present within each material. The UV-visible absorption spectra were obtained using a Varian CARY 100 SCAN spectrophotometer equipped with a Labsphere DRA-CA-301 diffuse reflectance (integrating sphere) integrator cell (internal walls covered with PTFE, 70mm diameter) . The first step is to perform a zero using a reference (BaSO4) that does not absorb in the energy zone to be analyzed. The samples, in pulverulent form, to be analyzed are then deposited in a specific sample holder and then analyzed at wavelengths between 800 and 200 nm. The results obtained are shown in Table 4.

Example of catalyst TiO2 hydrogenation method of content of material ND material ND preparation (% prohibited composite weight) (eV) C400 non sol-gel 0 3 1 C400 non sol-gel 0.5 3.05 2 C400 non sol -gel 0.7 3.02 3 C400 non-sol-gel 2.6 3.05 4 C400 non-sol-gel 5.2 3.1 5 C400 non-sol-gel 8.6 3.01 6 C400 non-sol-gel 20,1 3,05 7 C400 non-sol-gel 24,1 3 3037053 21 8 C400 non-sol-gel 34,6 3 c2 C400 non-impregnating 0 3 9 C400 non-impregnating 0,5 3,01 10 C400 non-impregnating 1, 1 3 11 C400 non-impregnation 2.9 2.7 12 C400 non-impregnation 8.5 2.97 13 C400 non-impregnation 10.5 3.3 14 C400 non-impregnation 26.5 3.02 15 C400 non-impregnation 31.5 3 16 C400 non-impregnation 42.5 3 c3 C400 yes impregnation 0 3 17 C400 yes impregnation 4.2 2.99 18 C400 yes impregnation 9.2 3 19 C400 yes impregnation 18 2.97 20 C400 yes impregnation 28.3 3 21 C400 yes impregnation 37,6 2,75 22 C400 yes impregnation 47,1 2,55 Table 4 The band gap values for materials Composites according to the invention for which the nanodiamonds are not hydrogenated vary little according to the amount of nanodiamonds within the material. These values are close to 3 eV.

For the materials according to the invention of which the nanodiamonds have been hydrogenated, it can be seen that the values of the forbidden band change as a function of the quantity of nanodiamonds present in the material. When this quantity increases, the band gap has a value of less than 3 eV and is between 2.5 and 2.7 eV. Thus, for these composite materials according to the invention, the nanodiamonds of which have been hydrogenated, the production of hydrogen by photodissociation of water can be carried out for values of wavelength in the visible. For composite materials according to the invention, the nanodiamonds of which are not hydrogenated, the photodissociation of the water must be carried out by irradiation in the UV. The hydrogenation of the nanodiamonds present in the composite material according to the invention therefore makes it possible to reduce the band gap.

Claims (13)

REVENDICATIONS1. Process for the preparation of dihydrogen by photodissociation of water by irradiation using at least UV (wavelength from 200 to 400 nm), visible (wavelength from 400 to 800 nm) or IR radiation near (wavelength ranging from 800 to 1200 nm), comprising the use of a photocatalytic composite comprising at least one semiconductor compound with a band gap ranging from 2 to 5 eV; ^ diamond nanoparticles. 2. The method of claim 1 wherein the photocatalytic composite comprises 1, 2 or 3 semiconductor compounds with bandgap ranging from 2 to 5 eV. 3. Method according to one of claims 1 and 2 for which the semiconductor compound with a band gap ranging from 2 to 5 eV is selected from transition metals, transition metal derivatives, metal carbides, metal nitrides , metal oxides, metal sulfides, carbon nitride (C3N4). 4. Method according to one of claims 1 to 3 for which the semiconductor compound with a band gap ranging from 2 to 5 eV ^ is chosen from transition metal oxides, transition metal sulfides, in particular TiO2, TiO2-B, ZnO, WO3, Fe2O3, preferably TiO2; or ^ is a one-dimensional material (especially selected from tube, fiber, rod, needle), a spherical material, a cubic material or is in the form of dispersed particles or in the form of aggregated particles or in crystalline form; or is modified or doped with at least one cation or doped with at least one anion; or is in the form of particles ranging in size from 3 to 100, 140, 200 or 1000 nm or from 5 to 20, 50, 100, 140 or 200 nm in size. 5. Method according to one of claims 1 to 4 wherein the diamond nanoparticles have a size ranging from 1 to 50, 100, 200 or 500 nm or a size ranging from 2 to 50, 100, 200 or 500 nm; or are in the form of a one-dimensional material or are in steric form or in the form of platelets; or 3037053 23 ^ are doped, in particular nitrogen doped or doped with boron, or are modified, in particular surface-modified, or are surface-hydrogenated. 6. Method according to one of claims 1 to 5 for which the photocatalytic composite 5 comprises from 0.5 to 30, 50 or 80% by weight or from 1 to 30, 50 or 80% by mass of diamond nanoparticles relative to the amount of semiconductor compound with bandgap ranging from 2 to 5 eV. 7. Method according to one of claims 1 to 6 for which the photocatalytic composite 10 ^ also comprises at least one other semiconductor compound with bandgap ranging from 2 to 5 eV defined according to claims 1 to 6; or also comprises at least one organic compound selected from organic compounds capable of supplying or transferring light energy during light irradiation or during the photodissociation reaction of water; transfer of the compounds improving the absorption properties and light energy of the photocatalytic composite; o the compounds chosen from organic dyes. 20 8. Process according to one of claims 1 to 7 for which the photocatalytic composite also comprises at least one other semiconductor compound with a band gap ranging from 2 to 5 eV chosen from noble metals; noble metal carbides; nitrides of noble metals; noble metal oxides; sulphides of noble metals; O transition metals; transition metal carbides; transition metal nitrides; transition metal oxides; transition metal sulphides; o compounds with plasmonic effect; o carbon nitride; or 30 ^ comprises from 0.1 to 1, 2 or 5 wt% or from 0.3 to 1, 2 or 5 wt% of another semiconductor compound with a band gap of 2 to 5 eV with respect to quantity of first bandgap semiconductor compound ranging from 2 to 5 eV; or comprend comprises from 0.1 to 1, 2 or 5 wt% or from 0.3 to 1, 2 or 5 wt% of organic compound defined in claim 7, based on the amount of the first semiconductor compound bandgap ranging from 2 to 5 eV. 9. Method according to one of claims 1 to 8 ^ for which the radiation is natural or solar; or 5 which is carried out at a temperature of from 1 to 90 ° C, in particular from 15 to 55 or 60 ° C, and preferably from 25 to 30, 40 or 50 ° C; or in which the photocatalytic composite is suspended in the water of reaction; or comprising stirring the reaction medium; or 10 ^ which is carried out in the absence of a further energy supply than UV radiation (wavelength from 200 to 400 nm), visible (wavelength from 400 to 800 nm) or IR near (wavelength ranging from 800 to 1200 nm); or which is carried out in the presence of an inert gas or a reducing gas during the photodissociation reaction of the water; or which is carried out in the absence of platinum or in the absence of a platinum derivative or in the absence of another photocatalyst; or which is carried out in the presence of a compound which improves the yield of dihydrogen production by photoreforming by the action of the photocatalyst, in particular in the presence of a compound improving the yield of dihydrogen production by photoreforming chosen from amines, alcohols, preferably methanol; or which is carried out in the presence of a compound which improves the yield of dihydrogen production, in particular of a compound which improves the yield of hydrogen production and which is capable of reacting with photogenerated holes or of reacting with oxygen; or o being oxidized by the oxygen formed during the photodissociation reaction of the water; or by the photogenerated positive electric charge holes during the energy transition of electrons of the bandgap semiconductor compound ranging from 2 to 5 eV, from its valence band to its conduction band. 3037053 25 10. Process according to one of claims 1 to 9 for which the photocatalytic composite is prepared according to a process chosen from a process (A) comprising the preparation of at least one semiconductor compound with a band gap ranging from 2 at 5 eV; o the preparation of diamond nanoparticles; the preparation of at least one suspension of the semiconductor compound with a band gap ranging from 2 to 5 eV or diamond nanoparticles; o mixing the semiconductor compound with a forbidden band ranging from 2 to 10 eV with the suspension of diamond nanoparticles or the mixture of the diamond nanoparticles with the suspension of semiconductor compound with a band gap ranging from 2 to 5 eV or the mixture two suspensions; o the separation of the photocatalytic composite and the solvent; or a process (B) comprising: preparing diamond nanoparticles; then o the preparation by sol-gel process or hydrothermal process of the semiconductor compound with bandgap ranging from 2 to 5 eV in the presence of diamond nanoparticles; then the separation of the photocatalytic composite; or a process (C) comprising: preparing the bandgap semiconductor compound of from 2 to 5 eV; then the detonation or chemical vapor deposition preparation of diamond nanoparticles in the presence of the bandgap semiconductor compound ranging from 2 to 5 eV; then o the separation of the photocatalytic composite; or a process (D) comprising the sol-gel or hydrothermal process preparation of the bandgap semiconductor compound of from 2 to 5 eV, and the simultaneous detonation or chemical vapor deposition preparation diamond nanoparticles; then the separation of the photocatalytic composite. 3037053 26 11. Method according to one of claims 1 to 9 for which the photocatalytic composite is prepared according to a process defined by claim 10 for which the diamond nanoparticles are prepared according to a process comprising a detonation step or according to a process comprising a Step 5 Chemical Vapor Deposition (CVD); or which is carried out under an inert atmosphere, in particular under a nitrogen atmosphere, or in the presence of a reducing gas of the semiconductor compound with a forbidden band ranging from 2 to 5 eV or in the presence of an oxidizing gas of the semi compound -conductor bandgap ranging from 2 to 5 eV; or 10 ^ also comprising drying the photocatalytic composite or heat treatment of the photocatalytic composite, particularly by irradiation, heating or il-wave radiation; or for which at least one of the preparation steps is carried out in the presence of at least one compound selected from another semiconductor compound with a band gap of from 2 to 5 eV; or o a precursor compound of a semiconductor compound with a bandgap ranging from 2 to 5 eV; or an organic compound selected from organic compounds capable of providing or transferring light energy during light irradiation or in a photodissociation reaction of water; organic compounds improving the absorption and light energy transfer properties of the photocatalytic composite; the compounds selected from organic dyes; A precursor compound of an organic compound chosen from organic compounds capable of supplying or transferring light energy during a light irradiation or during a photodissociation reaction of water; organic compounds improving the absorption and light energy transfer properties of the photocatalytic composite; the compounds selected from organic dyes; or ^ comprising the deposition on the formed photocatalytic composite or the addition to the formed photocatalytic composite o of at least one other bandgap semiconductor compound ranging from 2 to 5 eV; or at least one organic compound chosen from organic compounds capable of supplying or transferring light energy during a light irradiation or during a photodissociation reaction; Organic compounds improving the absorption and light energy transfer properties of the photocatalytic composite; the compounds chosen from organic dyes. 12. Photocatalytic composite prepared according to the process defined according to one of Claims 10 and 11. 13. Use for the preparation of dihydrogen by photodissociation of water by irradiation by means of UV radiation (wavelength from 200 to 400 nm), visible (wavelength ranging from 400 to 800 nm) or near IR (wavelength ranging from 15 800 to 1200 nm), of at least one photocatalytic composite according to claim 12; or at least one photocatalytic composite defined by claims 1 to 11.