Zinc oxide-based microparticle composite material grafted onto diatomaceous earth, method for preparing the same, and its use as an anti-UV active agent

Abstract

The present invention relates to a method for preparing a composite material containing zinc oxide crystals grafted on the surface of diatomaceous earth particles, the method including a grinding step in the presence of an agent for stabilizing the electron charge generated during grinding, further to a composite material containing zinc oxide crystals grafted on the surface of diatomaceous earth particles, and to its use as an active agent for protection against UV irradiation.

Description

Technical Field

[0001] The present invention relates to the field of microparticle composite materials, particularly microparticle composite materials based on zinc oxide.

Background Art

[0002] It is well known that ultraviolet (UV) irradiation, which is naturally emitted by the sun or emitted by an artificial light source, is beneficial to the human body in small amounts, is essential for fixing calcium in bones, and is essential for the synthesis of vitamin D that prevents osteoporosis. However, excessive exposure to UV irradiation causes damage to the skin (accelerated aging, cancer, etc.), eyes, and immune system.

[0003] A sunscreen cream is a cream or lotion used to reduce exposure of the skin to ultraviolet rays from the sun. Therefore, it constitutes a means of passive external light protection that functions as an ultraviolet screening agent. Such an anti-sun product contains an ultraviolet screening agent in a base that can be an oil or, more frequently, an emulsion (cream or lotion). Effective protection must block both UVA and UVB rays. UVB (and to a lesser extent UVA) can cause sunburn with inflammation, UVA causes premature skin aging, and UVA, especially UVB, causes skin cancer.

[0004] An ultraviolet screening agent, i.e., a UV screening agent, is a compound that blocks or absorbs UV irradiation. All anti-sun products contain an ultraviolet screening agent, which is divided into two molecular families (chemical (or organic) screening agents and mineral (or inorganic) sun blockers).

[0005] Organic screening agents are easier to use, but they contaminate water, are difficult to remove even in sewage treatment plants, may cause allergies, and have been found to be toxic to humans and the environment, particularly to aquatic biotopes.

[0006] An alternative to organic screening agents is the use of mineral sunblocks. In cosmetics, only two mineral sunblocks (titanium dioxide and zinc oxide) are permitted. These two sunblock agents provide immediate UV protection, unlike chemical screening agents which take up to 25 minutes to ensure the protection defined in the claims of this application.

[0007] The mineral sunblocks used in "environmentally friendly organic" creams are hypoallergenic and photo-stable (thereby making the cream a recommended anti-sun product for allergy sufferers and children). However, for a long time, they have been less appreciated by consumers because they are more difficult to spread and give users an unappealing whitish tint. To solve this problem and improve the aesthetic aspect, laboratories have formulated anti-sun creams by reducing these mineral sunblocks in the form of nanoparticles. Nevertheless, numerous studies have been conducted on nanoparticles, showing that they have harmful effects on the environment, particularly on phytoplankton, and that these particles can penetrate the skin and thus potentially affect health. In particular, TiO2 nanoparticles have become the main oxidizing agent entering coastal waters, giving direct ecological results to the ecosystem. Titanium dioxide nanoparticles disperse in water and enter the cells of filter-feeding organisms (especially oysters and mussels) and other marine animals.

[0008] Therefore, zinc oxide continues to be a preferred option as it has many properties as an efficient, photo-stable and non-allergenic agent for screening UVB and UVA radiation. However, in its original nanoparticle form (particles smaller than 100 nm), it poses a risk to the environment and potentially to human health due to its size and its oxidation characteristics under the action of UV radiation.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

SUMMARY OF THE INVENTION

PROBLEM TO BE SOLVED BY THE INVENTION

[0010] In view of these findings regarding the limitations and risks of using organic screening agents in anti - sun creams, and considering the risks of using nanoparticle mineral blocks, it is necessary to find an alternative that can be effective for humans and harmless to the environment and that enables compliance with protection.

MEANS FOR SOLVING THE PROBLEM

[0011] The applicant has solved this problem by developing a method that enables the production of a composite material containing zinc oxide nanoparticles grafted onto natural mineral microparticles of diatomaceous earth, the composite material having a particle size in the range of 30 to 200 nm.

[0012] European Patent No. 2 375 575 describes a cosmetic composition containing a composite material mainly composed of diatomaceous earth and zinc. This composite material is prepared mainly from unmodified diatomaceous earth and thus has an average size of 10 microns, resulting in insufficient dispersion of the material in the cosmetic composition. Furthermore, the applicant has found that under the zinc chloride concentration conditions described in the patent, the proposed zinc oxide concentration results in very partial coating of the diatomaceous earth particles by zinc crystals, and the zinc oxide concentration in the final product is one - tenth of the indicated concentration. Currently, the proposed preparation method cannot lead to the production of a material that can claim to have the reported UV - stabilizing properties.

[0013] On the one hand, in the composite material according to the present invention, the modification of diatomaceous earth into the form of microparticles enables a very significant increase in the specific surface area of the material and results in a very significant increase in the crystallization surface area of zinc oxide. This makes it possible to increase the surface properties for the same amount of material, in particular the surface area exposed to light including UV rays, as well as the possibility of diffraction and refraction of these light rays. This approach allows for the expression of large surface area zinc nanocrystals while very strongly limiting the diffusion of the material into the environment at the same time, since the zinc oxide nanoparticles are fixed to this non-nanometer support and thus cannot passively diffuse into living cells or organisms.

[0014] Accordingly, a first subject of the present invention is a method for preparing a composite material comprising zinc oxide crystals grafted onto the surface of diatomaceous earth particles, comprising: 1) a step of preparing diatomaceous earth microparticles by grinding diatomaceous earth; 2) a step of grafting zinc salt crystals onto the surface of the diatomaceous earth microparticles; 3) a step of converting the zinc salt crystals grafted onto the surface of the diatomaceous earth microparticles into zinc oxide crystals grafted onto the surface of the diatomaceous earth microparticles; 4) a step of grinding the microparticles obtained in step 3) to an individual particle size in the range of 10 - 300 nm, this grinding step being carried out in the presence of an agent for stabilizing the electronic charges generated during grinding. The method comprises the steps.

[0015] A second subject of the present invention is a composite material comprising zinc oxide crystals grafted onto the surface of diatomaceous earth particles, wherein the grafted diatomaceous earth particles have an individual particle size in the range of 10 - 300 nm. This composite material is advantageously prepared by the method according to the present invention. The present invention also relates to the use of the composite material according to the present invention or the composite material prepared by the method according to the present invention as an active agent for protecting against UV irradiation, in particular in cosmetic compositions.

[0016] Another subject of the present invention is a cosmetic composition comprising the composite material according to the present invention or the composite material prepared by the method according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0017] A first subject of the present invention is a method for preparing a composite material comprising zinc oxide crystals grafted on the surface of diatomaceous earth particles, comprising: 1) preparing diatomaceous earth microparticles by grinding diatomaceous earth in an aqueous medium; 2) grafting zinc salt crystals onto the surface of the diatomaceous earth microparticles; 3) converting the zinc salt crystals grafted on the surface of the diatomaceous earth microparticles into zinc oxide crystals grafted on the surface of the diatomaceous earth microparticles; 4) a step of grinding the microparticles obtained in step 3) to an individual particle size in the range of 10 to 300 nm in an aqueous medium, the grinding step being carried out in the presence of an agent for stabilizing the electronic charge generated during grinding. The method comprises the steps.

[0018] Diatomaceous earth (sometimes called kieselguhr or diatomite) is a microscopic unicellular fossilized alga found in large geological deposits in ancient marine sedimentary basins. This sedimentary rock has a silica-based protective envelope called a frustule, which is mostly composed of silica and thus has various shapes and sizes depending on the age and origin of the deposit. The frustule is composed of a large network of macroscopic channels that can occupy more than 80% of the total volume of the structure, and thus has a remarkable structure.

[0019] In step 1) of the method according to the invention, the diatomaceous earth is advantageously ground to individual particle sizes in the range of 50 nm to 2 μm, preferably 100 nm to 1 μm, and even more preferably 150 nm to 500 nm. The term "individual particle size" means that each particle of the material has a particle size falling within the indicated range of values. The particle size is determined by scanning electron microscopy (SEM).

[0020] Advantageously, the grinding in the first step is carried out so as to preserve the silanol groups on the surface of the diatomaceous earth. Specifically, the applicant has noticed that an increase in the temperature of the material leads to an excessive amorphization of the silica structure and results in the loss of surface silanol groups as a result of the dehydroxylation of these groups.

[0021] The preservation of the maximum number of surface silanol groups can be achieved by a technique involving grinding in an aqueous and sequential medium that enables the temperature rise during grinding to be maintained below a threshold of 200 °C.

[0022] Therefore, the grinding step 1) of the method according to the invention is advantageously carried out in an aqueous medium using a planetary mill.

[0023] This type of mill operates on the following principle. The grinding bowl is eccentrically arranged on the sun gear of the planetary ball mill. The sun gear rotates in a direction opposite to that of the grinding bowl. The grinding balls (balls) in the bowl are deflected by superimposing rotational movements, which results in the Coriolis force. The Coriolis force is the force that deflects the trajectory of an object moving on the surface of a rotating body. It particularly applies to moving masses of air and water. The speed difference between the balls (balls) and the grinding bowl results in the interaction of the impact force and the frictional force, releasing significant dynamic energy. The combination of these forces is reflected in the high grinding efficiency of the planetary ball mill.

[0024] This grinding step can be carried out by changing one or more of the following parameters. - The volume of the grinding raw material, i.e., the volume occupied by the grinding balls with respect to the volume of the grinding bowl. - The particle size of the pulverized raw material (the size of the pulverized body determines the fineness of the output particle size: the smaller the pulverizing balls (spheres), the finer the final particle size can be), - The product raw material to be pulverized and the corresponding water raw material, - The rotational speed of the mill, - The number of pulverization cycles, - The temperature of the mixture during pulverization.

[0025] One skilled in the art can adjust those parameters to obtain the desired particle size. Generally, one skilled in the art uses a pulverized raw material with a volume of about 15% - 25%. The pulverizing balls are preferably smaller than 1 mm, preferably 0.5 mm. The number of pulverization cycles is generally 1 - 20, preferably 5 - 15, and even more preferably 8 - 12. As shown above, the temperature during pulverization is preferably maintained below 200°C, preferably below 150°C. Regarding the rotational speed of the mill, this is advantageously about 300 - 800 rpm, for example 550 rpm.

[0026] Step 2) of the method according to the present invention is a) A step of introducing the diatomaceous earth particles obtained in step 1 together with calcium carbonate into an aqueous suspension, b) A step of bringing the mixture obtained at the end of step a) into contact with an aqueous suspension of zinc chloride, c) A step of stirring the mixture obtained at the end of step b) at a temperature in the range of 5°C - 40°C, preferably 15°C - 25°C, for a period in the range of 24 - 72 hours, preferably 48 hours, d) A step of recovering the composite material obtained at the end of step c), particularly by sedimentation or centrifugation, e) A step of drying the composite material at a temperature in the range of 50°C - 90°C, preferably 70°C, for a period in the range of 12 - 48 hours, preferably 24 hours can be included.

[0027] This second process step enables the zinc salt to react with the silanol groups on the surface of the diatomaceous earth particles. In particular, this step enables the calcium carbonate present in the diatomaceous earth to dissolve, releasing hydroxyl and carbonate species into the medium and resulting in the crystallization of the basic zinc carbonate hydrate phase of the chemical formula Zn4(CO3)(OH)6·H2O on the surface of the diatomaceous earth particles on the surface silanol groups.

[0028] In particular, the diatomaceous earth particles obtained in step 1 can be suspended in water at a ratio of 0.1 to 100 grams of powder per liter of water, preferably 10 grams of powder per liter of water.

[0029] Similarly, calcium carbonate can be suspended in water at a ratio of 0.1 to 100 grams of calcium carbonate per liter of water, preferably 10 grams of calcium carbonate per liter of water.

[0030] The aqueous zinc chloride suspension used in step b) is 5×10 -3 ~5 mol·L -1 Preferably 2~3 mol·L -1 In particular, about 1 mol·L -1 Has a concentration of.

[0031] Advantageously, the suspension obtained at the end of step a) and the zinc chloride suspension may be hydrated separately for 15 to 60 minutes, preferably 30 minutes, before the two suspensions are introduced together in step b).

[0032] The step c) of stirring the mixture may be carried out using a paddle mixer at a rotational speed of about 100 rpm.

[0033] The step e) of drying the composite material may be carried out in a furnace (oven) or a kiln.

[0034] Step 3) of the method according to the invention may be carried out by heat treatment at a temperature in the range of 500 °C to 900 °C, preferably 700 °C, for a time in the range of 1 hour to 4 hours, preferably 2 hours.

[0035] This third step enables the change of the zinc salt crystals formed in step 2) into zinc oxide crystals to spread over the entire surface of the diatomaceous earth particles. The zinc oxide preferably covalently bonds to the surface of the diatomaceous earth particles.

[0036] The heat treatment performed in step 3) is carried out in a furnace (oven), specifically by raising the temperature to 700 °C at 190 °C / hour, then performing a steady-state stage at 700 °C for 2 hours, and then turning off the furnace to return to room temperature. A more gradual temperature increase and a longer steady-state stage can also be used without compromising the results.

[0037] The grinding step 4) of the microparticles obtained in step 3) to an individual particle size in the range of 10 to 300 nm is carried out in an aqueous medium in the presence of an agent for stabilizing the electronic charges generated during grinding. Specifically, the inventors have found that when these microparticles are ground in an aqueous medium without any addition, re-aggregation or recrystallization of the microparticles obtained during and at the end of grinding occurs, and thus the desired particle size is not achieved. The inventors have surprisingly found, after extensive research, that grinding in the presence of an agent for stabilizing the electronic charges generated during grinding, such as an aqueous alkali metal silicate solution (aqueous alkali metal silicate), prevents or at least limits this phenomenon of re-aggregation or recrystallization, thereby resulting in an individual particle size in the range of 10 to 300 nm. Without wishing to be bound by any theory, the inventors believe that when the zinc crystals are ground, an imbalance of electronic charges is created, and the phenomenon of re-aggregation or recrystallization is due to the attraction of opposite charges generated during grinding. According to the inventors' findings, the use of an agent for stabilizing the electronic charges generated during grinding, such as an aqueous alkali metal silicate solution, enables the stabilization of the new electronic environment generated during grinding by compensating for the charges that appear. Specifically, in the case of an alkali metal silicate, the alkali metal cation will compensate for the negative charge, and the anions generated by the dissolution of the alkali metal silicate will compensate for the positive charge.

[0038] The alkali metal silicate (alkali metal silicate) can be selected from sodium silicate, lithium silicate, and potassium silicate. Preferably, the alkali metal silicate is sodium silicate.

[0039] The alkali metal silicate (alkali metal silicate) is used in the form of an aqueous solution. The alkali metal silicate is used in an amount suitable for stabilizing the electron charge imbalance during grinding. In the case of sodium silicate, conveniently, it is used in an amount of 3% to 20%, preferably 5% to 15%, particularly 10% to 15%, and the percentage is expressed by mass with respect to the mass of the microparticles obtained in step 3) of the method according to the present invention.

[0040] The grinding in step 4) may be carried out in the same manner as the grinding in step 1), and in particular, it can be carried out using the same type of apparatus, and more particularly a planetary ball mill. Those skilled in the art know how to adapt the grinding conditions to obtain the desired particle size.

[0041] The microparticles obtained in step 3) are ground to an individual particle size in the range of 10 to 300 nm in step 4). Preferably, they are ground to an individual particle size in the range of 15 nm to 250 nm. As far as the inventors know, until now, it has not been possible to reach such a particle size for zinc oxide particles grafted onto the surface of diatomaceous earth particles.

[0042] Therefore, the second subject of the present invention is a composite material containing zinc oxide particles grafted onto the surface of diatomaceous earth particles, wherein the grafted diatomaceous earth particles have an individual particle size in the range of 10 to 300 nm, preferably 15 to 250 μm. As shown above, the term "individual particle size" means that each particle of the material has a particle size within the indicated value range. The particle size is determined by scanning electron microscopy (SEM).

[0043] Advantageously, the composite material according to the present invention contains zinc oxide present on the surface of diatomaceous earth particles at a concentration of 50% to 90% by mass, preferably 50% to 80% by mass, more preferably 65% to 75% by mass, and even more preferably about 70% by mass, based on the mass of the composite material.

[0044] The present invention also relates to the use of the composite material according to the present invention or the composite material prepared by the method according to the present invention as an active agent for protecting against UV radiation, particularly in cosmetic compositions.

[0045] Regarding cosmetic compositions, the composite material according to the present invention has both high UV stabilization effectiveness and numerous advantages due to its particle size. This material has a much stronger restricted diffusion into the environment compared to zinc oxide nanoparticles alone, and at the same time, it diffuses very homogeneously into the additive, and the visible light reflection effect is restricted by the particles. These reduce the main drawback of a whitish surface effect on the skin compared to materials with a larger particle size (size) such as unground diatomaceous earth.

[0046] Another subject of the present invention is a cosmetic composition containing the composite material according to the present invention or the composite material prepared by the method according to the present invention. The cosmetic composition according to the present invention includes, but is not limited to, formulations for topical application, such as creams, oils, milks, suspensions, sprays, lotions, perfumes, and serums.

[0047] The present invention is better understood with the aid of the following drawings and examples.

Brief Description of the Drawings

[0048]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Examples

[0049] Example 1: Zinc oxide crystals grafted onto the surface of diatomaceous earth microparticles Preparation of composite material containing (Steps 1) to 3) of the method according to the present invention) 40 grams of diatomaceous earth was ground in a planetary mill (PM100 from Retsch) equipped with a 50 mL bowl with the following parameters. - Grinding raw material volume: 60% of the capacity of the grinding bowl; - Grinding raw material particle size: grinding balls with a diameter of 0.5 mm; - Product raw material: 16% of the bowl volume; - Water supply raw material: 24% of the bowl volume; - Rotation speed: 550 rpm; - Number of grinding cycles: 8 cycles in 10 minutes, with a 10-minute break during each grinding period.

[0050] Several batches of 40 grams of diatomaceous earth were ground by this method to recover 1000 grams of diatomaceous earth powder. According to scanning electron microscope analysis, this powder shows a fairly homogeneous grinding of diatomaceous earth particles less than 500 nm (see Figure 1). The recovered powder was suspended in tap water at a mass concentration of 10 g of powder per liter of water, and then 1000 grams of calcium carbonate was added at a mass concentration of 10 g per liter of water.

[0051] In parallel, 13600 grams of ZnCl2 was dissolved in tap water to prepare a solution with a concentration of 1 mol / liter.

[0052] The hydration of the two suspensions was carried out separately for 30 minutes before mixing the two. Subsequently, the two aqueous phases thus obtained were mixed in a suitable container. The stirring of the aqueous mixture thus obtained was carried out by a paddle mixer at a rotational speed of about 100 rpm and a temperature of 15 °C to 25 °C for 48 hours.

[0053] Subsequently, the composite obtained as a result of the mixing of the two aqueous phases was recovered by a first step of gravity discharge into the collection tank of the mixing container equipped with a plastic bag. Several decantation steps were carried out to remove the surface water, and the material thus recovered in the form of a cream was then placed in a tray and then placed in a furnace (oven) and dried at 90 °C for 24 hours.

[0054] Subsequently, the powder obtained by this drying process was transferred into a sagger and finally placed in a furnace, calcined at a programmed temperature rise to 700 °C at 190 °C / h, and then at a steady state at 700 °C for 2 hours, and then returned to room temperature by switching off the furnace. At the end of this process, about 10 kg of the composite material according to the present invention was recovered.

[0055] Example 2: Grinding of the composite material obtained in Example 1 in the presence of sodium silicate In a planetary mill equipped with a 50 ml bowl and 0.5 mm grinding balls in an amount of 1 / 10 of the usable amount, i.e., about 100 g, 10 g of the composite material obtained according to Example 1 was ground in the presence of tap water and an aqueous sodium silicate solution (40% sodium silicate from Arcane Industries, CAS No. 1344-09-8). The grinding parameters were as follows. - Total cycle time: 8 hours - Parameter: 32 cycles of 10-minute grinding separated by 5-minute pauses (i.e., effective grinding for 5 hours and 20 minutes) - Rotational speed: 500 rpm - Wait for the bowl to cool after the above cycle ends - Rinse with water using an unused 250 μm Retsch sieve, brush, and recover the balls. Weigh the added water. - Recovery and storage of the various creams obtained: Approximately 10 g of dry equivalent was recovered per test.

[0056] Two tests were conducted at different sodium hydroxide silicate concentrations. - Test 2-1: 5% by mass of sodium silicate based on the mass of the composite material, i.e., 1250 mg of 40% sodium silicate solution per 10 g of the composite material used. - Test 2-2: 10% by mass of sodium silicate based on the mass of the composite material, i.e., 2500 mg of 40% sodium silicate solution per 10 g of the composite material used.

[0057] In both tests, the individual particle sizes are in the range of 10 - 300 nm as shown in Figures 1 and 2.

[0058] Example 3: Grinding of the composite material obtained in Example 1 without adding sodium silicate (comparative example) 10 g of the composite material obtained according to Example 1 was milled in a planetary mill equipped with a 50 mL bowl and 0.5 mm milling balls in an amount of 1 / 10 of the usable amount, i.e., approximately 100 g, in the presence of 20 g of tap water. The milling parameters were as follows. - Total cycle time: 8 hours - Parameters: 32 cycles of 10 - minute milling separated by 5 - minute pauses (i.e., effective milling time of 5 hours and 20 minutes) - Rotation speed: 500 rpm - Wait for the bowl to cool after the above cycle ends. - Rinse with water, brush, and recover the balls using an unused 250 - μm Retsch sieve. Weigh the water addition. - Recover and store the cream obtained: Approximately 10 g of dry equivalent was recovered.

[0059] Example 4: Evaluation of the in vivo UV stabilization effect of the material of Example 2 prepared using 10% sodium silicate The material of Example 2 prepared using 10% sodium silicate was tested to evaluate its ability to protect human skin against UV radiation (UV stabilization effect). The test was conducted on healthy human volunteers with type I skin, i.e., skin that always turns red but never sunburns, without any photosensitivity problems.

[0060] Using 10% sodium silicate, approximately 1 g of the cream recovered from Example 2 was applied in a V shape to the volunteer's torso and then exposed to sunlight from 1 pm to 3 pm at the end of May in Brittany, France.

[0061] After exposure, the unprotected skin became quite red, while the V-shaped area protected with the material according to the invention remained unchanged. As can be seen in Figure 4, after 24 hours, the unprotected skin was still very red and the protected area remained unchanged.

Claims

1. A method for producing a composite material containing zinc oxide crystals grafted on the surface of diatomaceous earth particles, comprising: 1) A step of preparing diatomaceous earth microparticles by pulverizing diatomaceous earth in an aqueous medium; 2) A step of grafting zinc salt crystals onto the surface of the diatomaceous earth microparticles; 3) A step of converting the zinc salt crystals grafted on the surface of the diatomaceous earth microparticles into zinc oxide crystals grafted on the surface of the diatomaceous earth microparticles; 4) A step of pulverizing the microparticles obtained in step 3) to an individual particle size in the range of 10 to 300 nm in an aqueous medium, wherein this pulverization step is carried out in the presence of an agent for stabilizing the electronic charges generated during pulverization. A method comprising the above steps.

2. The method according to claim 1, wherein the pulverization step 1 is carried out using a planetary mill.

3. Step 2 comprises the following steps: a) A step of introducing the diatomaceous earth particles obtained in step 1) together with calcium carbonate into an aqueous suspension; b) A step of bringing the mixture obtained at the end of step a) into contact with an aqueous suspension of zinc chloride; c) A step of stirring the mixture obtained at the end of step b) at a temperature in the range of 5°C to 40°C, preferably 15°C to 25°C, for a period in the range of 24 to 72 hours, preferably 48 hours; d) A step of recovering the composite material obtained at the end of step c), particularly by sedimentation or centrifugation; e) A step of drying the composite material at a temperature in the range of 50°C to 90°C, preferably 70°C, for a period in the range of 12 to 48 hours, preferably 24 hours. A method comprising the above steps.

4. The method according to any one of claims 1 to 3, wherein step 3 is carried out by heat treatment at a temperature in the range of 500°C to 900°C, preferably 700°C, for a time in the range of 1 to 4 hours, preferably 2 hours.

5. The method according to any one of claims 1 to 4, wherein the agent for stabilizing the electron charge generated during the pulverization is an aqueous alkali metal silicate solution.

6. The method according to claim 5, wherein the alkali metal silicate solution is a sodium silicate solution.

7. A composite material containing zinc oxide crystals grafted on the surface of diatomaceous earth particles, wherein the grafted diatomaceous earth particles have an individual particle size in the range of 10 to 300 nm.

8. The composite material according to claim 7, wherein zinc oxide is present on the surface of the diatomaceous earth particles at a concentration of 50% to 80% by mass, preferably 65% to 75% by mass, and even more preferably about 70% by mass based on the mass of the composite material.

9. Use of the composite material according to claim 7 or 8 or the composite material prepared as described in any one of claims 1 to 6 as an active agent for protecting against UV radiation, particularly in cosmetic compositions.

10. A cosmetic composition comprising the composite material according to claim 7 or 8 or the composite material prepared as described in any one of claims 1 to 6.

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