EP4440316A1

EP4440316A1 - Transparent composite material having antimicrobial properties

Info

Publication number: EP4440316A1
Application number: EP22830305.3A
Authority: EP
Inventors: Fabio Di Fonzo; Federica ARENA; Antonio Alfano; Mirko PRATO; Stefano Perugini; Simone MUTTI
Original assignee: Kenosistec Srl; Fondazione Istituto Italiano di Tecnologia; Politecnico di Milano
Current assignee: Kenosistec Srl; Fondazione Istituto Italiano di Tecnologia; Politecnico di Milano
Priority date: 2021-11-29
Filing date: 2022-11-29
Publication date: 2024-10-09
Also published as: WO2023095102A1

Abstract

Object of the present invention is a transparent composite material having antimicrobial properties in particular antibacterial, antiviral, anti-fungal and anti-protozoal activities, a method for its preparation and use in articles, surfaces and coatings for outdoor, indoor environments, human and animal devices.

Description

“Transparent composite material having antimicrobial properties”

FIELD OF THE INVENTION

Object of the present invention is a transparent composite material having antimicrobial properties in particular antibacterial, antiviral, anti-fungal and antiprotozoal activities, a method for its preparation and use in articles, surfaces and coatings for outdoor, indoor environments, human and animal devices.

KNOWN PRIOR ART

It is well known that the development of health care products that may prevent microorganism-related infections is a first line in preserving human health. The severity of the hazard depends on several factors such as specific exposure, crosscontamination and many others, which are often difficult to control. While a rough classification of the risk level may be related to the environment (home, transportation, hospital, public places, etc.), it is difficult to ensure that risk reduction procedures are effective in uncontrolled environments. In this regard, surface disinfection is currently the most feasible means of meeting safety regulations. In addition to this, high-risk environments are often equipped with antibacterial/antiviral devices ranging from personal protective equipment to UV/chemical treatments. The latter are within routine procedures whose effectiveness fades away over time. Within this picture, the commonly used surfaces represent a passive element where microorganisms that may lead to the spread of infections proliferate. Therefore, the use of antibacterial/antiviral coatings may enable a pattern change, in which surfaces of various materials (metals, plastics, ceramics, etc.) may become an active first element in reducing the risk of infection.

Various methods, aimed at exploiting the properties of materials with known antibacterial properties such as silver, copper and zinc as well as their oxides, have already been devised.

There are solutions in which a method configured to provide antibacterial properties to a substrate and a coated substrate is provided. In these solutions, the method enables to obtain a coating suitable for any substrate, endowed with mechanical and thermal resistance to wear and aging, while at the same time achieving antibacterial properties that are active for a prolonged period. Using a radio frequency (rf) co-sputtering technique that employs a silica-based glass and a metal with antibacterial properties as a target, it is possible to provide deposition of silica-based thin films containing high concentrations of metals and metal ions with antibacterial properties. This technique allows to obtain a coating with mechanical and thermal resistance properties and, thanks to the stability of the silica films, the release of antibacterial ions also has stable behavior over time. Furthermore, by adjusting the parameters during the deposition process, it is possible to control the concentration of the antibacterial metal ions in order to impart adequate antibacterial properties and, therefore, also adequate efficacy in terms of durability over time.

Still according to the known art, an antibacterial composition that comprises an antibacterial agent constituted by silver nanoparticles (Ag NP) that show a nearly spherical structure and are bound to the surface of a dispersing agent that prevents their agglomeration, is known. In particular, the silver nanoparticles Ag NP do not form agglomerates, that is, these are dispersed and homogeneously distributed on the surface of the dispersing agent.

The aforementioned composite materials of the known art, despite aiming to provide an antibacterial action and/or antimicrobial composition as well as an antibacterial and/or antimicrobial surface and/or material, still fail to disclose an adequate size and concentration of the active material nanoparticles in a composite material, which is crucial, in combination with the size and arrangement of said active material in the composite material, in light of an exchange between antibacterial activity - transparency - adequate mechanical properties.

Thus, there is still a need to provide composite materials with antimicrobial, preferably antibacterial and/or antiviral properties, that are capable of showing one or more, preferably two or more, of the following properties: i) keeping high mechanical and antibacterial/antimicrobial properties for a long period of time; ii) ensuring that the aesthetic appearance of the component/surface to which the composite material is to be applied is not altered by the composite material itself; iii) minimizing the amount of heavy metals or non-biocompatible substances of active materials used while retaining excellent antibacterial, antiviral, anti-fungal and anti -protozoal activity, preferably antibacterial and/or antiviral; iv) enabling the composite material itself to be electrically conductive, if required by the specific application.

Documents W02019/053037 in the name of Hecosol GmbH, W02019/082001 in the name of Torino Politecnico, and WO2022/101428 in the name of ZEISS Carl Vision Int. are known.

However, such documents do not describe transparent materials that offer the possibility of obtaining the benefits sought above.

OBJECTS OF THE INVENTION

Therefore, an object of the present invention is to provide a composite and antimicrobial material that overcomes the drawbacks of the prior art.

Another object of the invention is to provide a transparent composite and antimicrobial material.

Another object of the invention is to provide a process for the preparation of said composite material.

A further object of the invention is to provide the use of said composite material for making articles, surfaces, coatings and devices with antimicrobial properties and a method for making such articles, surfaces, coatings and devices.

SUMMARY OF THE INVENTION

Object of the present invention is to provide a preferably transparent antimicrobial composite material comprising a preferably transparent matrix, an antimicrobial active material, characterized in that said active material is present at least inside said composite material in the form of a plurality of clusters arranged in at least one portion of layer inside said composite material, wherein each cluster is separated from the adjacent cluster by a specific distance. Advantageously, said matrix material allows the contact of the active material inside the composite material with the external environment. It should be emphasized that by "active material present inside the composite material” is meant that the active material is completely included in the matrix. An embodiment in which the active material is only inside the composite material is within the scope of protection of the present invention. In particular, said plurality of clusters has at least one dimension of less than 10 nm, preferably less than 5 nm, wherein each cluster is separated from the adjacent cluster by a distance ranging from 3 nm to 1 pm, preferably less than 100 nm, even more preferably less than 50 nm.

The clusters of active material of the invention have a size that enables the quantum confinement effect in at least one direction. The active material is present in the composite material at the concentration (C) of 0.01% < C < 10%.

The combination of antimicrobial activity and hardness and, depending on need, transparency, ensures that this composite material is potentially applied both on transparent surfaces per se, such as electronic device screens, eye wear, goggles, masks and face masks, breathing and filtration systems with integral face protection, gowns, panes and plexiglass for separation or protection, transparent components for biomedical field, etc., but also on all those metal and non-metal non-transparent objects for which the antimicrobial function is required and whose aesthetics are not to be altered, such as handles, buttons, banknotes and surfaces in general subject to being touched by more than one person. Further applications may be found in all of those fields in which the combination of antimicrobial activity and hardness is required, such as surfaces of biomedical instruments and equipment: scalpels, operating room tables and various tools, prosthetics, etc.

DESCRIPTION OF THE FIGURES

These and other aspects of the present invention will be made clearer by the following detailed description of a preferred embodiment provided herein for illustrative and non-limiting purposes only, with reference to the attached Figures, in which:

Figures 1 to 4 show schematic representations of the composite material of the invention according to different embodiments;

Figure 5 shows the band gap calculated by the Tauc plot method of AgO nanoparticles deposited on glass;

Figure 6 shows an atomic-force microscope image of a composite material containing pure AZO (on the left) and a composite material containing AgO_x:AZO (on the right); Figure 7 shows the antibacterial activity of different M and M:AM coating formulations on the pathogen E. coll ATTC 8739 (on the left) and the pathogen S. aureus 6538P (on the right) according to the ISO method 22196, as a function of time by calculation of the percent reduction of the colony forming unit (CFU/mL);

Figure 8 shows a summary of the biocidal properties of a composite material comprising a) AZO and b) AgO-AZO against A. coll, S. aureus and SARS-CoV-19, in which it may be seen that the AgO clusters significantly increase the antibacterial activity and confer antiviral activity;

Figure 9 shows a sample of transparent composite material of the invention;

Figures 10 and 11 show two SEM images of the composite material of the invention.

DESCRIPTION OF THE INVENTION

According to one of its aspects, object of the present invention is an antimicrobial composite material comprising a matrix material and an antimicrobial active material, characterized in that said active material is present at least inside the composite material in the form of a plurality of clusters having at least one dimension of less than 10 nm, preferably less than 5 nm, which are arranged in at least one portion of layer inside said composite material, each cluster being separated from the adjacent cluster by a distance (d) ranging from 3 nm to 1 pm, preferably less than 100 nm, even more preferably less than 50 nm, said matrix material allowing contact of the active material present inside the composite material with the external environment.

According to an embodiment, said active material is present only inside said composite material.

According to an alternative embodiment, in addition to inside said composite material, said active material is also present on the surface of said composite material.

The matrix material allows the contact of the active material inside the composite material with the external environment by one or more of the following options: a. the matrix material is porous; and/or b. the matrix material may be deteriorated, for example, it is water- soluble. Option a. allows the active material to contact the external environment and thus exert its antimicrobial, preferably antibacterial and/or antiviral action through the pores of the said matrix material, as for example schematically shown in Figure 4 and Figures 10 and 11, which show two SEM images of a composite material representative of the invention from which it may be seen that said composite material has an open structure to the outside.

On the other hand, option b. allows contact between the active material and the external environment through the deterioration, as for example the dissolution of the matrix material itself. In this case, when droplets of moisture containing microbes, for example, viruses and/or bacteria, contact the composite material, the matrix material which is at least partially water-soluble dissolves, thus allowing contact between the active material and said droplets of moisture.

The possible selection between the two options will be primarily sprung from the end use for which the composite material of the invention is intended. In particular, option a. is to be preferred when is intended to maximize the antimicrobial activity, whereas option b. is to be preferred when is intended to maximize the mechanical stability of the composite material.

According to a preferred embodiment, the matrix is porous according to option a. Even more preferably, the matrix comprises a plurality of communicating mesopores and/or nanopores.

According to embodiment b., the matrix is entirely occluded but configured to provide at least partial dissolution over time, that is, it provides at least partial deterioration of its structure over time, for example by dissolution in water.

Advantageously, in both embodiments, the active material that is included in the matrix results or ends up being partially exposed to the external environment and, when the composite of the invention is in an operational condition, may provide an antimicrobial action toward any pathogenic agents/organisms present in the external environment with which the composite of the invention is in contact.

Preferably, the matrix may also provide at least minimal antimicrobial activity. According to the present invention, the term "antimicrobial" denotes antibacterial, antiviral, anti-fungal and anti-protozoal activity, preferably antibacterial and/or antiviral.

According to the present invention, the term "cluster" denotes at least a single particle of active material, preferably a pool including two or more particles of active material, said cluster having at least one size of less than 10 nm.

According to the present invention, the term "particle" denotes an atomic and/or molecular aggregate having an equivalent diameter greater than 0.5 nm, preferably between 0.5 nm and 10 nm, even more preferably between 0.5 nm and 5 nm.

It should be noted that from here on, by layer it will be meant a region constituting the composite material having its own thickness and extending along a prevailing direction. In particular, one layer occupies the entire length of such composite material. A portion of layer, on the other hand, is a region of composite material having its own thickness that extends along a prevailing direction but not capable of extending along the entire length of the composite material, but only along part of its length.

According to an embodiment, said cluster has a substantially spherical structure and an equivalent diameter of less than 10 nm, preferably less than 5 nm, said equivalent diameter being at least greater than 0.5 nm.

According to another embodiment, said cluster has a "disk" structure, that is, it has a two-dimensional structure with a first dimension of less than 10 nm, preferably in the range of 0.5 nm to 5 nm, and a second dimension of less than 100 nm, preferably in the range of 10 nm to 100 nm.

The clusters of active material of the invention have a size that is configured to provide the quantum confinement effect in at least one direction. Particularly, the quantum confinement effect takes place along the smallest dimension of the cluster.

By the term "quantum confinement," without wishing to be bound by any theory, it is meant in this patent application all of those electronic effects that increase the effective forbidden band in a semiconductor, relative to the value of related perfect and infinite crystal.

The term "transparent" or "transparency" herein denotes the physical property of the composite material to enable the visible light to pass through without appreciable dispersion or absorption. In particular, "transparent" herein is defined as any material with an average total transmittance T greater than 50% and a diffuse transmittance of less than 10% over the visible range of the light spectrum, i.e., 380- 700 nm.

According to a preferred embodiment said composite material and said matrix material are transparent.

When transparency is not a necessary requirement, said composite material and said matrix material may be less transparent than as stated above or not transparent at all.

In general, said composite material is transparent when a transparent matrix material is used but, as it is evident to the skilled in the art, the passage of light is a function of the thickness of said material and the related absorption coefficient a. In particular, the matrix material and the active material of the composite material may be selected such that the absorption coefficient a of the composite material, as a function of the thickness to be made and the number and type of clusters present per unit volume, should be such that the absorptivity A is always less than 50%.

The absorption coefficient a is an intrinsic characteristic of a material and expresses the ability of that material to absorb the energy associated with the electromagnetic radiation propagating inside a given body.

The absorptivity A is, on the other hand, the intensity of the electromagnetic radiation that is absorbed by a body. In spectroscopy it is also defined as the opposite of the logarithm of the transmittance.

According to formulas known and well understood by the technician in the field, the absorptivity A of a material may be expressed as follows:

A= l- e' ^a* ^x where a is precisely the absorption coefficient and x is the thickness of the body subjected to electromagnetic radiation.

From the aforementioned formula, it follows that, for the same thickness, the greater the absorption coefficient a the greater the absorptivity A of that given material.

According to a preferred embodiment of the invention, the composite material may be selected with an absorption coefficient a having a value between 100 cm'¹ and 700000 cm'¹.

Clearly, in the case of composite material having absorption coefficient a that is maximum in the range mentioned above, the maximum thickness that may be achieved to obtain an absorptivity A that is, at most, 50% is 10 nm. With values close to 100 cm'¹, the thickness for which there is still less than 50% absorptivity, assuming a value of about 70 pm, increases significantly.

In case it is necessary to make a transparent composite material having greater thickness, materials whose absorption coefficient is still less than the maximum absorption coefficient of 700000 cm'¹ mentioned above should be selected.

For example, in case a product is to be made from a composite material according to the invention having thickness of 100 nm, the maximum absorption coefficient of the material may be 70,000 cm'¹, whereas for thicknesses close to 1,000 nm, the maximum absorption coefficient of the material selected to make a composite material may be at most 7000 cm'¹. Thus, in this case, an absorptivity A that is at most 50% will be ensured.

However, the minimum value of the absorption coefficient may be maintained at 100 cm'¹.

It should, finally, be noted that absorptivity A may be directly correlated with transmittance T and reflectance R, therefore if the absorptivity is less than 50%, the transmittance will be greater than 50%, thus falling within the above definition of transparency.

According to a preferred embodiment, the active material may have one or more crystalline domains, alternatively it may be entirely amorphous, still alternatively it may include a mixture of amorphous and crystalline fraction. Preferably, the active material is in the matrix in amorphous phase.

The composite material must be transparent and must have mechanical properties which ensure its use in real-world environments, such as high adhesion, resistance to rubbing and hardness comparable to or greater than that of the coated surface.

According to an embodiment, the matrix comprises a preferably transparent, suitable material preferably selected from SiCh, AI2O3, TiCh, ZnO, SnO, CeCh, ZrCh, I112O3, Fe_xOy, WO3, SiN, Y2O3, MgO, rare earth oxides, Li2O, ZrCh, AIN, SiC and mixtures thereof; transparent conducting oxides (TCOs) preferably selected from Al:ZnO (otherwise defined “AZO”, "Aluminum doped Zinc Oxide”), F:SnO, Ta:TiO2 e Sn:In2O3. It has to be understood that any mixture of non-conductive oxides and TCO is within the scope of the present patent.

According to a preferred embodiment, the matrix comprises or alternatively consists of AZO.

According to the invention, said active material is a compound of a cation and an anion and has the electronic characteristics of a semiconductor (and not a metal), capable of producing bioactive ions (Ag, Cu, Zn, others) and/or oxidizing radical species such as ROS, oxysulfides and oxynitrides in contact with water, said compound being in particle form as defined.

According to an embodiment, said active material is selected from oxides, chalcogenides, sulfates, sulfites, chlorides, chlorates, bromides, bromates, iodides and iodates of metals and mixtures thereof, said metals being preferably selected from Ag, Cu, Zn, Sn, Fe, Ni, Al and mixtures thereof.

According to a preferred embodiment, said active material may be described by the average stoichiometry AgOx/2 with 0 < x <3 and CuOx/2 with 0 < x <2.

According to an embodiment, said composite material comprises only one layer of active material.

According to an embodiment, said composite material comprises two or more layers of active material or portions of two or more layers. According to this embodiment, in the composite material said two or more layers, or portions of two or more layers, are each separated by a layer of matrix material having thickness (s), said thickness being preferably between 3 nm and 1 pm, more preferably between 5 nm and 100 nm, even more preferably between 10 and 50 nm.

The term "distance d" may refer to two distances: dl and d2.

According to an embodiment, in the composite material of the invention said two or more layers are arranged along different planes and/or axes inside the composite material. According to a first embodiment, the term "distance d" refers to a first distance dl between two adjacent clusters along the same axis and/or plane in the composite material.

According to a second embodiment, the term "distance d" refers to a second distance d2 between adjacent clusters arranged in layers along different axes and/or planes in the composite material.

Therefore, according to an embodiment, in the composite material of the invention said distance (d) comprises a first distance (dl) measured between at least two clusters adjacent to each other in the same layer inside the material of the composite material and a second distance (d2) measured between at least two adjacent clusters placed in different layers inside the composite material.

These characteristics will be better depicted in the attached Figures.

According to an embodiment, in the composite material of the invention said first distance (dl) and said second distance (d2) are equal or different.

According to an embodiment, in the composite material of the invention said distance (d) is selected so that the total concentration (C) of the active material in the composite material is greater than 0.01% by weight with respect to the total weight of the composite material, preferably so that said concentration is 0.01% < C < 50%, and even more preferably such concentration (C) is 0.1% < C < 20%.

According to an embodiment, in the composite material of the invention said concentration (C) of the active material is less than 10%.

As mentioned, the active material is present inside the matrix in the form of a plurality of clusters, each cluster having at least one size of less than 10 nm. According to a still preferred embodiment, said at least one dimension is less than 5 nm. According to a still preferred embodiment, said dimension is designed to provide the quantum confinement effect for the plurality of clusters of active material in at least one direction, depending on the type of active material employed. Such at least one optimized cluster size of active material does not affect the transparency of the matrix and composite material. Each cluster of active material is separated from the adjacent cluster by a distance d.

Such distance d separates two adjacent clusters and is between 3 nm and 1 pm, preferably between 5 nm and 100 nm, even more preferably between 10 nm and 50 nm.

Such minimum separation advantageously avoids cross talk and collective cluster behaviors, which would compromise the transparency of the composite material proposed herein. Preferably, said distance d provides a total concentration C of the active material in the composite material greater than 0.01%, such concentration being preferably in the range of 0.01% < C < 50%. Preferably, this concentration C may vary in the range of 0.1% < C < 20%.

According to a more preferred embodiment, such concentration C of the active material may be set to be less than 10%.

All values are selected to achieve optimal antimicrobial activity while maintaining the transparency of the composite material. Therefore, said distance d and consequently said concentration values of the active material, in combination with the optimized cluster diameter, were selected according to the present invention with the aim of not affecting the transparency of the composite material.

Thus, as mentioned, in the composite material of the invention, the active material provides strong antimicrobial activity, for example, antibacterial/antiviral activity while providing transparency thanks to the small cluster size that enables the quantum confinement effect to be achieved.

According to an embodiment, the space that lies between two adjacent clusters, the length of which is d, is occupied by the matrix. Consequently, each cluster is surrounded, in at least one direction, by the matrix for a distance d. Depending on the axis and/or plane along which the clusters of active material are located in the composite material, it is possible to identify at least one layer of active material in the composite material, as will be better shown in the attached figures. Said figures represent the embodiment in which the clusters are substantially spherical in shape, and the size refers to the equivalent diameter.

Figure 1 shows a schematic representation of an embodiment of the composite material proposed herein.

Figure 1 shows a composite material 1 comprising a matrix 2 and active material in the form of a plurality of clusters 3, wherein each cluster 3 has an equivalent diameter of less than 10 nm and is separated from an adjacent cluster by a distance d. The composite material 1 provides a linear multilayer architecture, as the clusters 3 are arranged along two different axes and/or planes in the composite material in a linear fashion, as further depicted in Figure 2. Such distance d may be the same both in the case of two adjacent clusters along the same axis and/or plane in the composite material and between two adjacent clusters arranged along different axes and/or planes in the composite material. According to Figure 1, said first distance dl is equal to said second distance d2. According to an embodiment, the clusters 3 may be arranged along the composite material in a more random way, as best depicted in Figure 3. As previously described, according to the axis and/or plane along which the clusters of active materials are present in the composite material, it is possible to identify at least one active material layer in the composite material, as shown in Figure 2.

When two or more layers of active material are present, such layers may be separated by at least one distance s.

By the term "layer," referring to at least one layer of active material, is meant a non-homogeneous layer. In fact, the active material is present in said at least one layer in the form of a plurality of clusters, in which each cluster is separated from the adjacent cluster by a space of length d and such space is occupied by the matrix.

Therefore, by the term "active material layer" is meant a plurality of clusters arranged along the same axis and/or plane in the composite material, wherein each cluster is separated from the adjacent one by matrix material.

Two or more layers of active materials may be separated by a distance s. Such distance s may be equal to, less than, or greater than the distance d between two adjacent clusters of active material. Such space separating two or more layers by a distance s will correspond to a layer of matrix material, as best depicted in Figure 2 and Figure 3.

Such at least one layer of (homogeneous) matrix material correspondingly shows a thickness equal to the distance between said two layers of active material; such at least one layer of matrix material in fact has a thickness s.

Figure 2 depicts a composite material 1 comprising a matrix 2 and an active material in the form of a plurality of clusters 3, in which each cluster 3 has a diameter of less than 10 nm and is separated from an adjacent cluster by a distance d.

In Figure 2 is shown a schematic representation of an embodiment of the composite material according to the invention with a view of the layers 30, 31 of active material.

Referring to Figure 2, the composite material 1 provides a linear multilayer architecture as the clusters 3 are arranged in two layers 30, 31 of active materials along two different axes and/or planes in the composite material in a linear fashion. Said distance d may be the same both in the case of two adjacent clusters along the same axis and/or plane in the composite material and between two adjacent clusters arranged along different axes and/or planes in the composite material. According to Figure 2, the first distance dl is equal to the second distance d2. The layers 30, 31 of active material are separated from each other by a layer 20 of matrix material. Such layer 20 of matrix has a thickness s.

Such thickness s may be set so as to provide a total concentration C of the active material in the composite material greater than 0.01%, such concentration being preferably of 0.01% < C < 50%.

Preferably, this concentration C is 0.1% < C < 20%. According to a still preferred embodiment, such concentration C of the active material may be set to be less than 10%.

Accordingly, said thickness s may preferably be in the range of 3 nm to 1 pm, more preferably 5 nm to 100 nm, even more preferably 10 nm to 50 nm.

The compound 1 in Figure 2 provides a distance d between the clusters 3 that is equal in the case of adjacent clusters belonging to the same layer 30 or 31 of active material, as well as in the case of adjacent clusters belonging to different layers 30, 31.

Figure 3 depicts another embodiment of the composite material 1, in which the clusters 3 are arranged in two layers 30, 31 of active materials but not in a linear fashion. Each cluster 3 in the two layers 30, 31 of active material is separated from the adjacent cluster along the same layer by a first distance dl.

In this example embodiment, each cluster 3 of the layer 30 is separated from the adjacent cluster 3 of the layer 31 by a second distance d2, such distance d2 being variable but greater than dl. The two layers 30, 31 of active material are separated from each other by a layer 20 of matrix. Such a layer 20 of matrix has a thickness s, s being greater than the distance dl but less than d2.

Such thickness s may be set so to provide a total concentration C of the active material in the composite material greater than 0.01%, such concentration being preferably of 0.01% < C < 50%.

Preferably, this concentration C is 0.1% < C < 20%. According to a still preferred embodiment, such concentration C of the active material may be set to be less than 10%. Accordingly, said thickness s may preferably be in the range of 3 nm to 1 pm, more preferably 5 nm to 100 nm, even more preferably 10 nm to 50 nm.

Figure 3 shows a schematic representation of an embodiment of a composite material with a view related to the layers 30, 31 of active material.

According to a further possible embodiment depicted in the following Figure 4, the composite material 1 may comprise a matrix 2 and a plurality of clusters 3 of active material, in which the clusters 3 of active material are arranged, inside the composite material 1, according to different portions 10, 11 of layer.

Figure 4 shows a schematic representation of an embodiment of the composite material according to the invention, comprising a plurality of pores connected through the body of the composite material.

The portions 10 and 11 of layer, as also described in the previous Figures, relate to multilayer architectures in which the clusters 3 of active material are arranged in a plurality of layers 30, 31 of active material along different axes and/or planes in the composite material 1, in which each layer 30 is separated from the adjacent layer 31 by a layer 20 of matrix. The portions 10, 11 of layer are substantially surrounded by the matrix 2 and each occupies only part of the length of the composite material.

Inside the portions 10, 11 of layer, each cluster 3 is separated from the adjacent clusters and each cluster 3 is surrounded, in at least one direction, by the matrix 2. The portions 10, 11 of layer extend along the composite material 1 from the basal face of the composite material 1 in contact with a substrate z toward the opposite face of the composite material directly exposed to the ambient air. According to such embodiment, the composite material 1 may comprise a plurality of pores. Each pore 4 is preferably in communication with an adjacent pore 4, thus constituting at least one channel that, starting from the top face of the composite material 1 exposed to the ambient air, branches inside the composite material 1. In more detail, the channel which is constituted by a plurality of connected holes 4 may branch into the space between the portions 10, 11 of layer, and the channel may branch at least partially through the portions 10, 11 of layer as shown in Figure 4.

Such configuration may provide the following advantages:

- increase of the kinetics related to the release of active species thanks to a greater available surface;

- the activity of the composite material is ensured even in case of contamination and/or mechanical abrasion of the surface;

- physical bactericidal effect due to the topography;

- increased transparency due to a) lower absorption and b) reduced reflection, thanks to a lower refractive index of the composite material.

The composite material of the invention may have varying thickness. According to an embodiment, such thickness may range from 100 nm to 100 pm. The lower limit mentioned above is related to the durability of the composite material over time; in case the composite material proposed herein is to be used as a disposable product, such lower limit may also be less than 100 nm, since for disposables even thinner thicknesses may provide the desired properties.

The upper limit mentioned above is closely related to a trade-off in terms of feasibility by a sputtering production process (actual production technique employed) and a final cost of the resulting product.

Depending on the manufacturing technique employed to produce the composite material, an upper limit of different and even greater thickness is possible. Preferably, the composite material as described has a thickness of about 200 nm.

As mentioned above, the composite material of the invention may comprise a single layer of active material inside the matrix or two or more layers of active material, or two or more portions of layer: such layers or portions of layer of active material are separated from each other by a layer of matrix material.

As mentioned, according to an embodiment, said composite material may also have clusters in addition to the internal clusters on at least one matrix surface directly exposed to the external environment. In other words, the composite material of the invention may comprise clusters of active material only inside it, or clusters of active material inside it and also on at least one surface of the matrix.

According to an embodiment, the composite material proposed herein may also include further nanoparticles and/or layers of other materials, with the aim of providing additional properties. For example, when selecting the matrix from TCO, the composite material proposed herein may also include clusters and/or homogeneous layers of iron oxide and/or tungsten oxide; said oxides may impart a specific color to the composite material, without altering the transparency of the composite material as defined. Such additional nanoparticles may also be added to the composite material with the aim of maximizing the efficiency against specific types of bacteria or viruses. The composite material described herein may be used alone or, alternatively, in combination with a substrate, such as for example a transparent substrate. Suitable substrates may include glass, silicone, polypropylene non-woven fabric, steel, aluminum, plastics and metals in general, and others.

According to another of its aspects, object of the invention is a method for the preparation of the composite material as described herein, preferably by a deposition process.

Said deposition process may comprise at least one source of matrix material, one source of active material and one substrate.

According to an embodiment, said deposition process on a substrate may be carried out through the cathodic sputtering technique.

The deposition process according to the aforementioned examples may involve the steps of: a) setting a first distance between the source of the matrix material and the substrate; b) setting a second distance between the source of active material and the substrate; c) setting a first power density for the source of matrix material; d) setting a second power density for the source of active material; e) activating the two sources; and f) exposing the substrate to the source of matrix material and the source of active material.

Preferably, in step f), the substrate is exposed to the source of matrix material and the source of active material in such a way that said active material is present inside the composite material in the form of a plurality of clusters having a diameter of less than 10 nanometers, preferably less than 5 nanometers, which are arranged in at least one layer inside said composite material, and in which each cluster is separated from the adjacent cluster by a distance d) which is at least greater than 5 nanometers. Advantageously, said matrix material allows the contact of the active material inside the composite material with the external environment.

Preferably, said first distance between the source of matrix material and the substrate is set shorter than said second distance between the source of active material and the substrate.

Preferably, said first power density for the source of matrix material is set greater than said second power density for the source of active material.

Advantageously, in the case of the source of matrix material said first lower distance as well as said first higher power density will provide a densification effect that will be responsible for the desired mechanical and optical properties of the composite material. In the case of the source of active material, said second greater distance and said second density with lower power will provide nanoparticles having less energy to reorganize and form clusters having large size on the substrate, thus, remaining finely dispersed in the form of clusters having a diameter of less than 10 nm, preferably less than 5 nm, such nanoparticles do not interact with each other.

The activation of the source of matrix material and the source of active material may be performed simultaneously and alternately; when the two sources are activated simultaneously, the deposition may additionally comprise at least one separator screen so that the substrate is exposed to only one source at a time. The exposure of the substrate to the sources may be achieved, according to a first embodiment, by moving the substrate under the two sources while keeping them in a single, fixed position. Otherwise, according to an alternative embodiment, the exposure of the substrate to the sources may take place by moving the two sources and taking the substrate fixed in one position.

The deposition process preferably takes place in an oxidizing atmosphere; thereby, the nanoparticles of active material are completely oxidized once they reach the substrate. Preferably, the atmosphere may comprise an inert gas mixture. For example, such an atmosphere may comprise argon and oxygen.

Preferably, argon and oxygen are present in a volume ratio of 60:40. The deposition process proposed herein may last for a variable time interval; preferably, said deposition process may last 4 minutes. In such time frame, the deposition process proposed herein may provide an antimicrobial/antiviral composite material having a thickness of 150 nm, with optical transparency averaging more than 50% over the entire visible range (380-700 nm).

Alternatively, it is possible to provide a single source with a mixed target of matrix (M) and active material (AM).

Main technical characteristics of the composite material of the invention:

• transparent and antimicrobial composite material comprised of a transparent matrix and an antimicrobial active material;

• concentration C of the active material in the matrix of 0.01% < C < 50%;

• active material in the form of a plurality of clusters in the quantum confinement regimen;

• each cluster is separated from the adjacent cluster by a distance d greater than 3 nm and less than 1 pm, preferably less than 100 nm, even more preferably less than 50 nm;

• d refers to the distance between two adjacent clusters along the same axis and/or plane in the composite material and between two adjacent clusters arranged along different axes and/or planes in the composite material;

• each layer, or portion of layer, of active material is separated from another by a matrix layer having thickness s;

• s may be equal to, less than or greater than the distance d, and is preferably 3 nm to 1 pm, more preferably 5 nm to 100 nm, even more preferably 10 nm to 50 nm.

Therefore, object of the invention is a transparent, mechanically robust, antimicrobial coating, for example, antibacterial and/or antiviral coating, which allows overcoming the inherent limitations of the existing solutions.

The invention has several distinctive characteristics enabling it to be used in applications ranging from the household to the portable electronics and the health care sector. This product allows imparting antibacterial/antiviral properties to the surfaces and objects without altering their aesthetic appearance, thanks to its high optical transparency (>50% on average in the visible range).

The superior adhesion and mechanical properties also ensure that the efficiency of the coating is preserved if exposed to high wear conditions or environmental agents.

Although the composite coatings already exist, they fail to ensure transparency, good mechanical properties and sufficient antibacterial/antiviral activity at the same time. The reason is that high transparency requires a small amount of active material, which is often not enough to preserve the antimicrobial effect. The proposed invention overcomes this problem by exploiting the quantum confinement effects. It is known from the literature that the nano-scale behavior of materials is markedly different from its counterpart in bulk form. This is especially true when referring to the optical properties. There are several examples of band gap adjustment, which show a shift towards blue of the absorption edge for the semiconductors whose size is reduced from 3D to 0D (in the range of 10 to 2 nm). This shift is due to the quantum confinement effect.

This effect occurs when the Bohr radius of the charge carriers exceeds the size of the nanoparticles, thus leading to the formation of discrete (quantized) energy levels responsible for the electronic transitions of the material. Thus, by employing an active semiconductor material whose particle size may be adjusted to the nano-scale allows precise control of the absorption property. In order to achieve maximum transparency, as mentioned, the active material comprises oxides, chalcogenides, chlorides, bromides and iodides of metals such as Ag, Cu, Zn, Sn, Fe, Ni, Al with at least one size of less than 10 nm, preferably less than 5 nm. In fact, the smaller the crystal size of a semiconductor, the wider its band gap becomes, possibly shifting its absorption limit into the UV. The extreme case is that of an amorphous semiconductor or cluster of molecular size. In addition to transparency, the advantage of the composite semiconductors over their base metals is their higher activity due to a combination of ionic availability, redox reactions and the formation of reactive oxygen species or other active anionic species. Thus, it is possible to reduce the amount of metal.

As mentioned, the composite material of the invention has antimicrobial, preferably antibacterial and antiviral properties.

As will be shown in detail below, the antibacterial activity was evaluated by the standardized ISO 22196 method. Herein below by the term "minimal antibacterial activity" is meant at least a 90% reduction in the maximum number of viable bacteria present on the transparent material after 24 hours.

The Applicant has made a first generation of coatings having transmittance above 90% in the visible range and with antibacterial and antiviral activity above 90% within the 24-hour test period.

Thus, the invention solved the problem posed by providing a transparent coating with antimicrobial activity and high mechanical strength, i.e., providing a useful technical solution to solve the disadvantages and fill the gaps in the prior art.

It was surprisingly observed that quantum-confined active nanoparticles (QCANs) must be separated from each other in the matrix by at least one diameter in order to avoid cross talk and collective behaviors, which would compromise the transparency. A multilayer architecture is the easiest to implement for the control. From the studies performed, an AgO concentration of 1% in Al:ZnO is sufficient to achieve antibacterial activity (ISO 22196) and antiviral activity against SARS-CoV2 and other viruses with less than 10% absorption in the range of 400 to 700 nm.

The manufacturing of the composite material may be carried out by pulsed DC Magnetron Sputtering. Two sources are employed so that the deposition parameters of the matrix (M) and active material (AM) may be adjusted independently. The matrix material employed belongs to the family of the transparent conductive oxides (TCOs). Their good electrical conductivity allows pDC-MS to be used instead of rf-MS, thus achieving a high deposition rate. The material of choice is Aluminum-doped Zinc Oxide (AZO). However, the selection of this material is mainly made on the basis of its high optical transparency in the visible range (Eg ~ 3.4 eV).

According to the present invention: i) the active material must induce a significant increase in the antimicrobial, for example, antibacterial and/or antiviral efficacy compared to the bare matrix; ii) the species of active material must exhibit quantum confinement effects; iii) the active material must not induce significant changes to the aesthetic appearance of the coating; iv) the loading of active material must be sufficient to ensure adequate coating durability without significant loss of performance. In order to meet the above requirements, quantum-confined semiconductor nanoparticles (particle diameter < 10 nm) of metal oxides such as Ag_xO and CuxO were considered to be exploited, and the composite obtained material of the invention unexpectedly provided very satisfactory results, solving the problem posed.

In the following example, we present the calculated band gap (by using the Tauc graph method) of AgO nanoparticles deposited directly on glass with nominal sizes between 10 and 5 nm. The band gap (forbidden band) increases from 2.85 eV to 3.27 eV (corresponding to a wavelength of 379 nm, outside the visible spectrum) as the particle size decreases.

In Figure 5 is shown the band gap calculated by the Tauc plot method of AgO nanoparticles deposited on glass.

An example of the approach to manufacture the M:AM coating is described herein.

The deposition equipment may employ two pDC-MS sources and a supporting structure of the mobile substrate. Screens may be used in such a way as to ensure that the substrates are exposed to only one source at a time.

In such a configuration, several parameters need to be adjusted to achieve the desired result. The source-substrate distance (StS) plays a key role in obtaining the desired M:AM structure. In particular, a short M-StS distance in the range of 30 mm to 200 mm is preferred, so that the densification effect is achieved during the deposition of the matrix material to provide the desired mechanical and optical properties. The AM-StS distance, in the range of 50 mm to 300 mm, is selected to be > than the M-StS distance, so that the nanoparticles have less energy to reorganize and form large clusters on the substrate, thus remaining finely dispersed but not interacting with each other. Such process may be carried out in an oxidizing atmosphere; so that the metallized nanoparticles of AM are completely oxidized once they reach the substrate. An indicative process atmosphere might comprise a mixture of an inert gas (e.g., Argon) and oxygen in a volume ratio of 60:40, with a pressure in the range of 0.5 Pa to 5 Pa.

According to a further embodiment, a single AZO target containing 1% molar Ag is sputtered by pDC-MS in an Ar:O2 atmosphere as in the previous case, at a targetsubstrate distance of 50 mm.

Any mixture of M and AM selected from the materials previously described may in principle be used as a target.

The parameters of the pDC source are those that, in this example, ensure that the desired result is achieved. For M and AM, an appropriate power density indication could be 1 - 10 W/cm², preferably 3 - 8 W/cm² for M and 0.1 - 1 W/cm², preferably 0.1 - 0.6 W/cm² for AM, respectively.

In case of a single mixed target, the typical power density used may be in the range of 1 to 10 W/cm², preferably 3 to 8 W/cm².

The interaction between all of these parameters ensures that the AM nanoparticles are: i) approx. 5 nm in diameter; ii) finely dispersed in the matrix. The processing time for such a configuration is about 4' for an M:AM thickness of 150 nm with average transparency optics of 95% over the entire visible range.

More generally, the processing time depends on the number of coated substrates and the power.

To obtain information on the morphological organization of M:AM thin film, AFM mapping was performed on pure material M and composite structure. The two conditions are shown in Figure 6. The most pronounced roughness profile of the M: AM topographic image was consistent with the expected growth dynamics. In fact, the sputtered AM nanoclusters (diameter < 10 nm) are finely dispersed on the material M, not forming a continuous film. As the substrate is subsequently exposed to the sputtering source of the material M, a homogeneous overlay layer is formed whose thickness is sufficient (> 2 nm) to incorporate the AM clusters. The surface roughness thus increases due to the presence of the underlying clusters. This effect adds up during the process, resulting in a final topography as the one shown on the right. Thus, the bulk structure of the coating is expected to comprise a fine dispersion of AM nanoclusters and nanoparticles (d < 10 nm) embedded in a compact matrix material. The AM clusters and nanoparticles must be separated by s > 5 nm in all directions inside the matrix. The maximum separation between the clusters is sprang from the need to maintain a total concentration C of AM > 0.1%, with an optimum at 0.5% < C < 10%.

Figure 6 shows an atomic-force microscope image of a pure AZO matrix and AgO_x:AZO compound.

The antibacterial activity of the M and M: AM coating was evaluated by using non-pathogenic E. coli ATTC 8739 and the pathogenic S. aureus 6538P according to ISO 22196 method. Both bacterial strains were grown in Luria Bertani (LB) medium at 37°C overnight and diluted to obtain a bacterial concentration between 10⁵ cells/mL and 10⁶ cells/mL. The M and M:AM coatings were incubated with bacterial suspensions at 35°C for different periods. At the end of each incubation time, the bacterial culture was recovered to quantify viable bacteria and to determine the percentage of biocidal activity. Figure 8 describes the antibacterial effect of different coatings on the growth of both microorganisms, confirming the ability to kill the bacteria within 24 h. After 2 h incubation, significant growth inhibition of E. coli and S. aureus close to 100% was detected when M:AM coatings were used. In contrast, the near- 100% antibacterial effect of the M coatings was demonstrated only after 6 h incubation with the surface. These results support the claim of this patent according to which the active material must induce a significant and rapid increase in the antibacterial efficacy compared to the bare matrix. Both 2.5% and 5% molar concentration of AgO in the AZO matrix showed extremely high antibacterial activity and achieve >6 log reduction for E. coli in less than 20 minutes and >6 log reduction for S. aureus in 2 hours. CuSO:AZO and CuO:AZO thin films also show a significant increase in the antibacterial activity compared with the base AZO matrix.

Figure 7 shows the antibacterial activity of various M and M:AM coating formulations on the pathogen E. coli ATTC 8739 (on the left) and the pathogen S. aureus 6538P (on the right) according to the ISO method 22196, as a function of time by calculation of percent reduction of the colony forming unit (CFU/mL).

A direct comparison of 5% AgO:AZO vs. pure AZO is presented in Figure 8. The reduction kinetics of the bacteria is greatly enhanced by the addition of AgO. In the case of SARS-CoV-2, the AZO matrix shows no activity, while 5% AgO:AZO achieves a 90% reduction compared to the glass control in 4 hours and complete inhibition in 24 hours.

Figure 8 shows a summary of the biocidal properties of a) AZO and b) AgO- AZO composite material against E. coh. S. aureus and SARS-CoVv-19. The AgO clusters significantly increase antibacterial activity and confer antiviral activity. The transparent composite material proposed herein is shown below in Figure 10.

Figure 9 shows an image of the new composite material of the invention.

From a mechanical point of view, all the coatings tested showed significantly higher hardness than pure Ag (about 0.25 GPa) or Cu (about 0.5 GPa) although lower than pure AZO as shown in the following Table. In any case, the coatings may be considered mechanically robust.

According to another of its aspects, object of the invention is the use of the composite material of the invention in surfaces and coatings for outdoor environments, indoor environments, human and animal devices.

According to another of its aspects, object of the invention is the use of the composite material of the invention for making articles, surfaces, coatings and devices with antimicrobial properties.

According to another of its aspects, object of the invention is a method for providing antimicrobial activity to articles, surfaces, coatings and devices that comprises including in such articles, surfaces, coatings and devices the composite material of the invention.

According to another of its aspects, object of the invention is a mixed target of matrix (M) and active material (AM), wherein said matrix is selected from SiCh, AI2O3, TiCh, ZnO, SnO, CeCh, ZrCh, ImCh, Fe_xO_y, WO3, SiN, Y2O3, MgO, rare earth oxides, Li2O, ZrCb, AIN, SiC and mixtures thereof, and transparent conducting oxides (TCOs) preferably selected from Al:ZnO (also known as AZO), F:SnO, Ta:TiO2 and SmlmCh, and said active material is selected from oxides, chalcogenides, chlorides, bromides, iodides of metals and mixtures thereof, said metals being preferably selected from Ag, Cu, Zn, Sn, Fe, Ni, Al and mixtures thereof.

According to another aspect of the invention, the use of the mixed target mentioned above in the preparation of the composite material according to the invention is also protected.

According to another of its aspects, object of the invention is a method for the preparation of the composite material of the invention that comprises the step of depositing a mixed target of matrix (M) and active material (AM) as defined above on a substrate.

Preferably, by exploiting a mixed target such a deposition process is carried out through the cathodic sputtering technique.

It should be noted that, in general, in the deposition processes, especially by using sputtering or cathodic sputtering techniques, the targets can also be distinct from each other.

In the case mentioned above, when a mixed target is referred to, it means a material obtained by preliminarily mixing the matrix material and the active material in the concentration ranges mentioned above. This allows for a very fine dispersion of the clusters of the active material.

Claims

1. A transparent antimicrobial composite material comprising a transparent matrix material and an antimicrobial active material, said active material being present at least inside the composite material in the form of a plurality of clusters arranged in at least one portion of layer inside said composite material, each cluster being separated from the adjacent cluster, said matrix material allowing contact of the active material present inside the composite material with the external environment, characterized in that said plurality of clusters has at least one dimension of less than 10 nm, wherein each cluster is separated from the adjacent cluster by a distance (d) ranging from 3 nm to 1 pm, and in that said active material is a compound of a cation and an anion with the electronic characteristics of a semiconductor, capable of producing bioactive ions and/or oxidizing radical species upon contact with the water, selected from metal oxides, chalcogenides, chlorides, bromides, iodides and mixtures thereof.

2. The composite material according to claim 1, characterized in that said plurality of clusters has at least one dimension of less than 5 nm, wherein each cluster is separated from the adjacent cluster by a distance (d) of less than 100 nm, even more preferably less than 50 nm.

3. The composite material according to claim 1 or 2, characterized in that said active material is present in the matrix as an amorphous or nanocrystalline phase, preferably amorphous.

4. The composite material according to one or more of claims 1 to 3, characterized in that said matrix comprises a material selected from SiCh, AI2O3, TiCh, ZnO, SnO, CeCh, ZrCh, ImCh, Fe_xO_y, WO3, SiN, Y2O3, MgO, rare earth oxides, Li2O, ZrCb, AIN, SiC and mixtures thereof; and transparent conducting oxides (TCOs) preferably selected from Al:ZnO (AZO), F:SnO, Ta:TiO2 and SnlmOs.

5. The composite material according to one or more of claims 1 to 4, characterized in that said metals of said active material are selected from Ag, Cu, Zn, Sn, Fe, Ni, Al and mixtures thereof.

6. The composite material according to one or more of claims 1 to 5, characterized in that said active material comprises AgOx/2 and/or CuOx/2.

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7. The composite material according to claim 6, characterized in that said active material is characterized by an average stoichiometry AgOx/2, with 0 < x <3 and/or CuOx/2 with 0 < x <2.

8. The composite material according to one or more of claims 1 to 7, characterized in that said cluster is selected from a cluster having a substantially spherical structure and an equivalent diameter of less than 10 nm, preferably less than 5 nm, said equivalent diameter being at least greater than 0.5 nm, and a cluster having a disc structure with a first dimension of less than 10 nm, preferably in the range 0.5 nm - 5 nm, and a second dimension of less than 100 nm, preferably in the range 10 nm - 100 nm.

9. The composite material according to one or more of claims 1 to 8, characterized in that it comprises two or more layers of said active material, or two or more portions of layer.

10. The composite material according to claim 9, characterized in that said two or more layers, or two or more portions of layer, are each separated by a layer of matrix material having thickness (5) of 3 nm - 1 pm, more preferably of 5 nm - 100 nm, even more preferably of 10 nm - 50 nm.

11. The composite material according to one or more of claims 1 to 10, characterized in that said distance (d) comprises a first distance (dl) measured between at least two clusters adjacent to each other in the same layer, or portion of layer, inside the material of the composite material and a second distance (d2) measured between at least two adjacent clusters placed in different layers, or different portions of layer, inside the material of the composite material.

12. The composite material according to claim 11, wherein said first distance (dl) and said second distance (d2) are equal or different.

13. The composite material according to one or more of claims 1 to 12, characterized in that said distance (d) is selected so that the total concentration (C) of the active material in the composite material is greater than 0.01% by weight with respect to the total weight of the composite material, preferably so that said concentration is 0.01% < C < 50%, and even more preferably such concentration (C) is 0.1% < C < 20%.

14. The composite material according to claim 13, characterized in that said concentration (C) of the active material is lower than 10%.

15. The composite material according to one or more of claims 8 to 14, characterized in that said two or more layers are arranged along different planes and/or axes inside the composite material.

16. The composite material according to one or more of claims 1 to 15, characterized in that said active material is further present on at least one surface of said composite material.

17. A method for preparing a composite material according to one or more of claims 1 to 16 by a deposition process on a substrate, wherein said deposition process comprises the following steps: a) setting a first distance between the source of the matrix material and the substrate; b) setting a second distance between the source of active material and the substrate; c) setting a first power density for the source of matrix material; d) setting a second power density for the source of active material; e) activating the two sources; and f) exposing the substrate to the source of matrix material and to the source of active material, so that said active material is present at least inside the composite material in the form of a plurality of clusters arranged in at least one portion of layer inside said composite material, each cluster being separated from the adjacent cluster, wherein said matrix material allows contact of the active material present inside the composite material with the external environment.

18. The method according to claim 17, characterized in that said deposition process is carried out by means of the cathodic sputtering technique.

19. Use of a composite material according to one or more of claims 1 to 16 in articles, surfaces and coatings for outdoor environments, indoor environments, human and animal devices.

20. The use of a composite material according to one or more of claims 1 to 16 for making articles, surfaces, coatings and devices with antimicrobial properties.

21. A method for providing antimicrobial activity to articles, surfaces, coatings and devices comprising including in said articles, surfaces, coatings and devices at least one composite material according to one or more of claims 1 to 16.

22. A mixed target of matrix (M) and active material (AM) wherein said matrix is selected from SiCh, AI2O3, TiCh, ZnO, SnO, CeCh, ZrCh, ImCh, Fe_xO_y, WO3,

SiN, Y2O3, MgO, rare earth oxides, Li2O, ZrCh, AIN, SiC and mixtures thereof, and transparent conducting oxides (TCOs) preferably selected from Al:ZnO (AZO), F:SnO, Ta:TiO2 and SmlmCh, and said active material is selected from oxides, chalcogenides, chlorides, bromides, iodides of metals and mixtures thereof, said metals being preferably selected from Ag, Cu, Zn, Sn, Fe, Ni, Al and mixtures thereof.

23. Use of the mixed target according to claim 22, in preparing the composite material of any one of claims 1 to 16.

24. A method for preparing a composite material according to one or more of claims 1 to 16, comprising at least the step of depositing on a substrate a mixed target of matrix (M) and active material (AM) according to at least claim 22.