Dual-mode synergistic composite photocatalyst, method of preparation and use thereof in a phenylpropylene emulsion paint composition

Abstract

This invention discloses a dual-mode synergistic composite photocatalyst, its preparation method, and its application in styrene-acrylic emulsion coating compositions, belonging to the field of architectural coating technology. The dual-mode synergistic composite photocatalyst possesses a TiO2@dense SiO2@mesoporous SiO2-MnO2-GQDs three-layer core-shell structure. The styrene-acrylic emulsion coating provided by this invention utilizes the aforementioned dual-mode synergistic composite photocatalyst, and innovatively employs a yellowing-resistant composition composed of hollow titanium dioxide-supported phenyltriazole particles, a sulfonic acid-grafted hindered amine light stabilizer, and nano-zinc oxide. This composition synergistically inhibits yellowing of the paint film through enhanced UV absorption and improved interfacial compatibility. The styrene-acrylic emulsion coating provided by this invention successfully solves the two major problems of traditional photocatalytic coatings: "purification depends on light" and "self-catalysis leads to yellowing of the paint film." It can efficiently degrade formaldehyde under both light and dark conditions and exhibits excellent yellowing resistance.

Description

Technical Field

[0001] This invention belongs to the field of architectural coatings technology, specifically relating to a dual-mode synergistic composite photocatalyst, its preparation method, and its application in styrene-acrylic emulsion coating compositions. Background Technology

[0002] Indoor formaldehyde pollution mainly originates from decorative and finishing materials such as engineered wood products, adhesives, and paints. Long-term exposure can cause serious harm to human health. As one of the mainstream products for interior wall decoration, styrene-acrylic emulsion paints have become a hot research topic in the industry, with the ability to actively degrade formaldehyde becoming a key focus.

[0003] Currently, photocatalysis (especially nano-titanium dioxide, TiO2) is the main pathway for formaldehyde degradation. However, existing technologies have the following drawbacks: Firstly, limited lighting conditions lead to discontinuous purification. Traditional TiO2-based photocatalysts can only work effectively under lighting conditions. Indoor environments have many areas without light (such as rooms on the shaded side, inside wardrobes, and backlit surfaces) and periods without light (nighttime). In such scenarios, photocatalysts cannot generate active oxygen species, resulting in extremely low formaldehyde purification efficiency or even complete ineffectiveness.

[0004] Secondly, the non-selective nature of oxide species leads to yellowing of the paint film. During the photocatalytic process of TiO2, highly oxidizing hydroxyl radicals (·OH) are generated. While degrading formaldehyde, these radicals indiscriminately attack organic resins, additives, and other components in the paint film, causing polymer chain breakage and oxidative discoloration, which manifests as yellowing and chalking of the paint film, severely shortening the service life of the coating.

[0005] Third, existing anti-yellowing systems lack innovation. Current anti-yellowing technologies generally employ a simple compound of ultraviolet absorbers, hindered amine light stabilizers, and layered clay. This can only passively counteract the free radicals generated by photocatalysts and cannot fundamentally block the attack of strong oxidizing holes on the paint film. Furthermore, small molecule additives are prone to migration and volatilization, and hindered amines are easily deactivated, leading to a rapid decline in anti-yellowing effects during long-term use.

[0006] To address the aforementioned issues, there is an urgent need to develop an innovative styrene-acrylic emulsion coating that can continuously degrade formaldehyde under different lighting conditions, selectively protect the paint film, and has a yellowing-resistant system. Summary of the Invention

[0007] This invention aims to overcome the technical challenges of existing photocatalytic coatings failing to purify under light-free conditions and exhibiting yellowing of the paint film. It provides a dual-mode synergistic composite photocatalyst, its preparation method, and its application in styrene-acrylic emulsion coating compositions. The dual-mode synergistic composite photocatalyst is a composite photocatalyst with "spatial separation-dual-mode synergy" function. This catalyst has a three-layer core-shell structure of TiO2@dense SiO2@mesoporous SiO2-MnO2-GQDs. The dense SiO2 layer physically blocks the outward migration of holes, achieving selective oxidation of formaldehyde. The nano-MnO2 embedded in the mesoporous layer enables thermocatalytic degradation under light-free conditions, thus enabling continuous and efficient formaldehyde purification in both light- and light-free environments. The styrene-acrylic emulsion coating composition of this invention is a styrene-acrylic emulsion coating that combines formaldehyde purification in all scenarios with excellent resistance to yellowing. Its core lies in the use of the aforementioned dual-mode synergistic composite photocatalyst. Furthermore, this invention innovatively employs a yellowing-resistant composition composed of hollow titanium dioxide-supported phenyltriazole particles, a sulfonic acid-grafted hindered amine light stabilizer, and nano-zinc oxide. This composition synergistically inhibits yellowing of the paint film through enhanced UV absorption and improved interfacial compatibility. The styrene-acrylic emulsion coating provided by this invention successfully solves the two major problems of traditional photocatalytic coatings: "purification depends on light" and "self-catalysis leads to yellowing of the paint film." It can efficiently degrade formaldehyde under both light and dark conditions and exhibits excellent resistance to yellowing.

[0008] To solve the above problems, the present invention is achieved through the following technical solution: The first objective of this invention is: A dual-mode synergistic composite photocatalyst is provided, which has a three-layer core-shell structure, consisting of, from the inside out: Photocatalytic core: Its material is anatase nano-titanium dioxide; Electron-selective permeable layer: a dense silicon dioxide layer coating the surface of the photocatalytic core; Dual-mode functional outer shell layer: a mesoporous silica-nano manganese oxide composite layer covering the outer surface of the electron selectively permeable layer; The outer surface and inner wall of the pores of the mesoporous silica-nano manganese oxide composite layer are chemically grafted with graphene quantum dots.

[0009] The dual-mode synergistic composite photocatalyst described in this invention is further optimized as follows: a. The particle size of the anatase nano-titanium dioxide is 20–50 nm; b. The dense silica layer has a non-porous continuous coating structure with a thickness of 2–5 nm and a porosity of less than 5%; c. In the mesoporous silica-nano manganese oxide composite layer, the pore size of the mesoporous silica is 3-10 nm and the porosity is 40-70%.

[0010] The dual-mode synergistic composite photocatalyst described in this invention is further optimized as follows: The nano-manganese oxide in the mesoporous silica-nano-manganese oxide composite layer is uniformly dispersed in the pores of the mesoporous silica and the matrix, with a particle size of 2–5 nm; and / or, The weight ratio of the nano-manganese oxide to the anatase nano-titanium dioxide is 1:5 to 20.

[0011] The dual-mode synergistic composite photocatalyst described in this invention is further optimized as follows: The graphene quantum dots have a particle size of 2–5 nm and a surface oxygen-containing functional group content of 10–30 at.

[0012] The dual-mode synergistic composite photocatalyst described in this invention is further optimized as follows: The graphene quantum dots are chemically grafted onto the mesoporous silica-nano manganese oxide composite layer via a silane coupling agent.

[0013] The second objective of this invention is: A method for preparing the aforementioned dual-mode synergistic composite photocatalyst is provided, comprising the following steps (by weight): S1. Disperse 0.5-3.5 parts of anatase nano-titanium dioxide in 150-200 parts of a mixed solvent of ethanol and water with an ethanol concentration of 65-85%, add 1-5 parts of tetraethyl orthosilicate and 3-8 parts of ammonia water with an ammonia mass content of 10%, and react at 20-40℃ for 2-6 hours to form a dense silica layer on the surface of anatase nano-titanium dioxide. After centrifugation, washing with ethanol, and drying at 50-70℃, TiO2@dense SiO2 core-shell particles are obtained. S2. Disperse 0.5-5 parts of the TiO2@dense SiO2 core-shell particles in a deionized water reaction solution containing 0.8-6.5 parts of template agent, 3-4 parts of tetraethyl orthosilicate, and 0.1-1 parts of manganese source. Adjust the pH to 9-11 with ammonia water containing 10% ammonia by mass. React at 50-70°C for 4-8 hours. Form a mesoporous silica-manganese precursor composite layer on the surface by sol-gel method. After centrifugation, washing, and drying, calcine at 400-600°C for 2-4 hours (to remove the template agent and convert it into a mesoporous structure, while the manganese precursor is oxidized to nano-MnO2) to obtain TiO2@dense SiO2@mesoporous SiO2-MnO2 composite particles. The template agent is hexadecyltrimethylammonium bromide or polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer; The manganese source is at least one of manganese acetate, manganese nitrate, or manganese chloride. S3. Disperse 0.3-1.7 parts of the TiO2@dense SiO2@mesoporous SiO2-MnO2 composite particles in a solution containing 0.05-0.5 parts of silane coupling agent for surface activation treatment, and then react with graphene quantum dot dispersion at 40-80℃ for 4-12 hours. Through amidation reaction, the graphene quantum dots are chemically grafted onto the surface and pore walls of the mesoporous silica-nano manganese oxide composite layer to obtain the dual-mode synergistic composite photocatalyst. The silane coupling agent is at least one of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; The amidation reaction was carried out in the presence of the coupling agents N-hydroxysuccinimide and 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride.

[0014] The third objective of this invention is: A styrene-acrylic emulsion coating composition is provided, comprising the following components in parts by weight: 30-50 parts of styrene-acrylic emulsion, 1-8 parts of the aforementioned dual-mode synergistic composite photocatalyst, 0.5-4 parts of the yellowing-resistant composition, 20-35 parts of pigments and fillers, 2-8 parts of additives, and 15-25 parts of deionized water; The anti-yellowing composition comprises: hollow titanium dioxide supported benzotriazole particles, sulfonic acid-grafted hindered amine light stabilizer, and nano zinc oxide; The pigments and fillers include at least one of titanium dioxide, heavy calcium carbonate, and calcined kaolin. The additives include at least two of the following: dispersants, wetting agents, defoamers, leveling agents, thickeners, and film-forming aids.

[0015] The styrene-acrylic emulsion coating composition described above in this invention is further optimized as follows: The anti-yellowing composition comprises the following components in parts by weight: The composition includes 0.3–1.5 parts of hollow titanium dioxide-supported benzotriazole particles, 0.2–1.2 parts of sulfonic acid-grafted hindered amine light stabilizer, and 0.2–1 parts of nano zinc oxide.

[0016] The styrene-acrylic emulsion coating composition described above in this invention is further optimized as follows: The hollow titanium dioxide-supported benzotriazole particles have a particle size of 100–200 nm, and the loading of benzotriazole is 5–15 wt%. The sulfonic acid-grafted hindered amine light stabilizer is a piperidine derivative hindered amine light stabilizer grafted with sulfonic acid groups, with a grafting rate of 2-8%. The particle size of the nano zinc oxide is 50–150 nm.

[0017] The fourth objective of this invention is: A method for preparing the aforementioned styrene-acrylic emulsion coating composition is provided, comprising the following preparation steps: A. Pre-dispersion a: The dual-mode synergistic composite photocatalyst, hollow titanium dioxide-supported benzotriazole particles and nano zinc oxide in the yellowing-resistant composition are mixed with some deionized water and some additives, and dispersed at high speed at 1300-1500 rpm for 20 minutes to obtain the first slurry; B. Pre-dispersion b: After mixing the first slurry with the pigments and fillers, high-speed dispersion is carried out at a speed of 1400-1500 rpm until the fineness is ≤20μm to obtain the second slurry; C. Paint mixing: Under stirring, the styrene-acrylic emulsion, the sulfonic acid-based grafted hindered amine light stabilizer in the anti-yellowing composition, and the remaining additives are added to the second slurry in sequence and mixed evenly; D. Adjustment and filtration: Add the remaining deionized water to adjust the viscosity and filter to obtain the styrene-acrylic emulsion coating composition.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention introduces room-temperature thermocatalytically active nano-MnO2 by constructing a three-layer core-shell structure of TiO2@dense SiO2@mesoporous SiO2-MnO2-GQDs. Under illumination, TiO2 photocatalysis dominates degradation, while photogenerated electrons reduce and regenerate the active sites on the MnO2 surface. Under no illumination, MnO2 continuously catalyzes the oxidation of formaldehyde using surface lattice oxygen via the Mars-van Krevelen mechanism. This achieves highly efficient formaldehyde purification in all scenarios, including day and night, and under no-light conditions, solving the technical challenge of discontinuous purification.

[0019] 2. This invention utilizes a dense silicon dioxide layer to photoexcite TiO2 to generate strong oxidizing holes (h). + Physically confined to the core, preventing it from contacting the organic resins and additives in the paint film; only electrons (electrons) are allowed. - It conducts outward through tunneling, reacting with oxygen to generate superoxide anions (·O2), which have relatively mild oxidizing properties. - The active oxygen species (NOS) and hydrogen peroxide (H2O2) are used. These NOS molecules preferentially oxidize formaldehyde molecules, while their attack on polymer resins is significantly weaker than that of hydroxyl radicals. This structure solves the problem of yellowing caused by photocatalysts attacking the paint film from the source, thus significantly inhibiting yellowing and chalking of the paint film while effectively degrading formaldehyde.

[0020] 3. This invention employs a yellowing-resistant composition formulated with hollow titanium dioxide-supported benzotriazole particles, a sulfonic acid-based grafted hindered amine light stabilizer, and nano-zinc oxide. The hollow titanium dioxide-supported benzotriazole particles effectively inhibit the migration, volatilization, and photolysis of small-molecule UV absorbers by encapsulating the UV absorber within a hollow carrier, achieving long-term stable UV absorption. The sulfonic acid-based grafted hindered amine light stabilizer, through chemical modification, significantly improves the dispersion uniformity in water-based coating systems and its interfacial compatibility with styrene-acrylic emulsions, preventing agglomeration failure and enhancing resistance to acid and alkali corrosion, ensuring the continuous effectiveness of free radical scavenging. Nano-zinc oxide, as an inorganic UV absorber component, forms an organic-inorganic hybrid synergy with the aforementioned two components, synergistically inhibiting yellowing of the paint film from multiple dimensions, including UV shielding, free radical scavenging, and photocatalytic source isolation. This overcomes the inherent defects of existing yellowing-resistant additives, such as easy migration, easy deactivation, single function, and antagonism with photocatalysts.

[0021] 4. This invention solves the agglomeration problem of nanomaterials (TiO2) in styrene-acrylic emulsion coatings by using a dense SiO2 layer and surface-grafted GQDs, which have a stable core-shell structure. Its preparation method and coating preparation process are highly compatible with existing industrial equipment and are easy to scale up for production. Detailed Implementation

[0022] To make the application, technical solution, and advantages of this invention clearer, the invention is described in detail with reference to specific embodiments. It should be understood that the embodiments are for illustrative purposes only and are not intended to limit the scope of protection of this invention. Any simple improvements to the preparation method of this invention based on the inventive concept fall within the scope of protection of this invention. The operational details used in the embodiments are all derived from the foregoing technical description. Example 1

[0023] A method for preparing a dual-mode synergistic composite photocatalyst, comprising the following steps (by weight): S1. 1.0 part of anatase nano-titanium dioxide with a particle size of 25 nm was dispersed in 175 parts of a mixed solvent of ethanol and water with a concentration of 75% ethanol, 2.0 parts of tetraethyl orthosilicate and 5.0 parts of ammonia water with a mass content of 10% were added, and the mixture was reacted at 30 °C for 4 hours; after the reaction, the mixture was centrifuged, washed with ethanol, and dried at 60 °C to obtain TiO2@dense SiO2 core-shell particles; S2. Disperse 0.5 parts of the particles obtained in step S1 in 150 parts of deionized water, add 0.8 parts of the template agent hexadecyltrimethylammonium bromide, stir to dissolve, add 3.5 parts of tetraethyl orthosilicate and 0.15 parts of manganese nitrate hexahydrate (manganese source) in sequence, adjust the pH to 10.5 with ammonia water with an ammonia content of 10%, react at 50℃ for 6 hours, centrifuge, wash, dry after reaction, calcine at 550℃ for 3 hours to obtain TiO2@dense SiO2@mesoporous SiO2-MnO2 composite particles; S3. Disperse 0.5 parts of the particles obtained in step S2 in 50 parts of anhydrous ethanol, add 0.1 parts of silane coupling agent γ-aminopropyltriethoxysilane (KH550), reflux at 60℃ for 4 hours for surface activation, centrifuge, wash, disperse the particles in 40 parts of phosphate buffer at pH=7.4, add 0.05 parts of N-hydroxysuccinimide (NHS) and 0.1 parts of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC·HCl), activate at room temperature for 15 minutes, add 20 parts of an aqueous dispersion containing 0.05 parts of carboxylated graphene quantum dots (GQDs), react at 60℃ for 8 hours, centrifuge, wash with water, and dry to obtain the dual-mode synergistic composite photocatalyst; a. The particle size of the anatase nano-titanium dioxide is 25 nm; b. The dense silica layer has a non-porous continuous coating structure, a thickness of 3 nm, and a porosity of less than 5%; c. In the mesoporous silica-nano manganese oxide composite layer, the pore size of the mesoporous silica is 6 nm and the porosity is 53%.

[0024] The nano-manganese oxide in the mesoporous silica-nano-manganese oxide composite layer is uniformly dispersed in the pores and matrix of the mesoporous silica, and its particle size is 3nm. The weight ratio of the nano-manganese oxide to the anatase nano-titanium dioxide is 1:7.

[0025] The graphene quantum dots have a particle size of 3 nm and a surface oxygen-containing functional group content of 20 at. Example 2

[0026] Preparation and performance testing of a styrene-acrylic emulsion coating composition The styrene-acrylic emulsion coating composition comprises the following components in parts by weight: The composition includes 40 parts of styrene-acrylic emulsion, 5 parts of the aforementioned dual-mode synergistic composite photocatalyst, 2 parts of the yellowing-resistant composition, 30 parts of pigments and fillers (16 parts of titanium dioxide, 7 parts of heavy calcium carbonate, and 7 parts of calcined kaolin), 3.5 parts of additives (1 part of dispersant, 0.5 parts of wetting agent, 0.5 parts of defoamer, 0.5 parts of leveling agent, 0.5 parts of thickener, and 0.5 parts of film-forming aid), and 23 parts of deionized water. The anti-yellowing composition comprises the following components in parts by weight: One part of hollow titanium dioxide supported benzotriazole particles, 0.6 parts of sulfonic acid-grafted hindered amine light stabilizer, and 0.4 parts of nano zinc oxide.

[0027] The hollow titanium dioxide-supported benzotriazole particles have a particle size of 100–200 nm, and the loading of benzotriazole is 5–15 wt%. The sulfonic acid-grafted hindered amine light stabilizer is a piperidine derivative hindered amine light stabilizer grafted with sulfonic acid groups, with a grafting rate of 2-8%. The particle size of the nano zinc oxide is 50–150 nm.

[0028] The preparation method of the styrene-acrylic emulsion coating composition includes the following preparation steps: A. Pre-dispersion a: The dual-mode synergistic composite photocatalyst, hollow titanium dioxide-supported benzotriazole particles and nano zinc oxide in the yellowing-resistant composition are mixed with some deionized water and some additives, and dispersed at high speed at 1300 rpm for 20 minutes to obtain the first slurry; B. Pre-dispersion b: After mixing the first slurry with the pigments and fillers, high-speed dispersion is carried out at 1500 rpm until the fineness is ≤20μm to obtain the second slurry; C. Paint mixing: Under stirring, the styrene-acrylic emulsion, the sulfonic acid-based grafted hindered amine light stabilizer in the anti-yellowing composition, and the remaining additives are added to the second slurry in sequence and mixed evenly; D. Adjustment and filtration: Add the remaining deionized water to adjust the viscosity and filter to obtain the styrene-acrylic emulsion coating composition. Example 3

[0029] Preparation and performance testing of a styrene-acrylic emulsion coating composition The difference from Example 2 is as follows: The styrene-acrylic emulsion coating composition comprises the following components in parts by weight: The composition includes 30 parts of styrene-acrylic emulsion, 1 part of the aforementioned dual-mode synergistic composite photocatalyst, 0.5 parts of the yellowing-resistant composition, 20 parts of pigments and fillers (15 parts of titanium dioxide, 5 parts of heavy calcium carbonate, and 5 parts of calcined kaolin), 3.5 parts of additives (1 part of dispersant, 0.5 parts of wetting agent, 0.5 parts of defoamer, 0.5 parts of leveling agent, 0.5 parts of thickener, and 0.5 parts of film-forming aid), and 25 parts of deionized water. The anti-yellowing composition comprises the following components in parts by weight: The mixture consists of 0.3 parts of hollow titanium dioxide-supported benzotriazole particles, 0.2 parts of sulfonic acid-grafted hindered amine light stabilizer, and 0.2 parts of nano zinc oxide.

[0030] Everything else is the same as in Example 2. Example 4

[0031] Preparation and performance testing of a styrene-acrylic emulsion coating composition The difference from Example 2 is as follows: The styrene-acrylic emulsion coating composition comprises the following components in parts by weight: The composition includes 50 parts of styrene-acrylic emulsion, 8 parts of the aforementioned dual-mode synergistic composite photocatalyst, 4 parts of the yellowing-resistant composition, 35 parts of pigments and fillers (17 parts of titanium dioxide, 9 parts of heavy calcium carbonate, and 9 parts of calcined kaolin), 3.5 parts of additives (1 part of dispersant, 0.5 parts of wetting agent, 0.5 parts of defoamer, 0.5 parts of leveling agent, 0.5 parts of thickener, and 0.5 parts of film-forming aid), and 15 parts of deionized water. The anti-yellowing composition comprises the following components in parts by weight: 1.5 parts of hollow titanium dioxide supported benzotriazole particles, 1.2 parts of sulfonic acid-grafted hindered amine light stabilizer, and 1.0 part of nano zinc oxide.

[0032] Everything else is the same as in Example 2.

[0033] Comparative Example 1 (without dense SiO2 layer) Preparation and performance testing of a styrene-acrylic emulsion coating composition It is basically the same as Example 2, with the main difference being: Comparative Example 1 did not use the dual-mode synergistic composite photocatalyst in Example 1, but instead used a composite photocatalyst without a dense SiO2 layer, i.e., directly with a TiO2@mesoporous SiO2-MnO2-GQDs structure.

[0034] Comparative Example 2 (without MnO2 thermocatalytic component) Preparation and performance testing of a styrene-acrylic emulsion coating composition It is basically the same as Example 2, with the main difference being: Comparative Example 2 did not use the dual-mode synergistic composite photocatalyst of Example 1, but instead used a composite photocatalyst with a TiO2@dense SiO2@mesoporous SiO2-GQDs structure.

[0035] Comparative Example 3 (Composition without yellowing resistance) Preparation and performance testing of a styrene-acrylic emulsion coating composition It is basically the same as Example 2, with the main difference being: No anti-yellowing composition was added to the styrene-acrylic emulsion coating composition of Comparative Example 3.

[0036] Comparative Example 4 (Traditional TiO2 photocatalyst + ordinary UV absorber) It is basically the same as Example 2, with the main difference being: Ordinary anatase nano-TiO2 (uncoated, without MnO2, and without GQDs) is used, and the yellowing resistance system is ordinary benzotriazole + unmodified hindered amine light stabilizer.

[0037] Performance Tests and Results: The coatings prepared in Examples 2-4 and Comparative Examples 1-4 were used to prepare paint films according to GB / T 9755-2024 standard, and the following tests were conducted. The test results are shown in Table 1.

[0038] Table 1

[0039] Results analysis: Examples 2-4 showed excellent formaldehyde degradation rates under both light and dark conditions, especially maintaining over 85% under dark conditions, demonstrating the effectiveness of the dual-mode synergistic photocatalyst.

[0040] Comparative Example 1 showed no dense SiO2 layer, and the paint film exhibited severe yellowing and chalking, indicating that hole isolation is crucial for protecting the paint film.

[0041] Comparative Example 2, without MnO2, showed a sharp decrease in degradation rate to 12.4% under light-free conditions, proving that MnO2 is the key component for achieving light-free purification.

[0042] Comparative Example 3 showed that the yellowing resistance composition had a yellowing index as high as 12.4, indicating that the yellowing resistance system is indispensable.

[0043] Comparative Example 4 uses a traditional photocatalyst and a common yellowing-resistant additive. It almost loses its light-free purification ability and suffers from severe yellowing. Its overall performance is far inferior to that of the embodiments of the present invention.

[0044] This invention achieves two goals that are usually difficult to achieve simultaneously: "high-efficiency purification in all scenarios" and "excellent resistance to yellowing" through a specific catalyst structure design and an innovative yellowing-resistant system, resulting in unexpected technical effects.

[0045] In summary, the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any changes, modifications, and evolutions made by those skilled in the art without departing from the scope of the present invention based on the disclosed technical content shall be considered equivalent embodiments of the present invention. Furthermore, any changes, modifications, and evolutions made to the above embodiments based on the essential technology of the present invention shall still fall within the protection scope of the present invention.

[0046] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0047] Experimental methods not specified in this invention are generally performed under conventional conditions or as recommended by the manufacturer.

[0048] Unless otherwise stated, the various optimized technical solutions in this invention can be combined with each other.

[0049] Unless otherwise stated, percentages and parts are weight percentages and weight parts.

[0050] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as are familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be used in the methods of this invention.

Claims

1. A dual-mode synergistic composite photocatalyst, characterized in that: It has a three-layered core-shell structure, from the inside out as follows: Photocatalytic core: Its material is anatase nano-titanium dioxide; Electron-selective permeable layer: a dense silicon dioxide layer coating the surface of the photocatalytic core; Dual-mode functional outer shell layer: a mesoporous silica-nano manganese oxide composite layer covering the outer surface of the electron selectively permeable layer; The outer surface and inner wall of the pores of the mesoporous silica-nano manganese oxide composite layer are chemically grafted with graphene quantum dots.

2. The dual-mode synergistic composite photocatalyst according to claim 1, characterized in that: a. The particle size of the anatase nano-titanium dioxide is 20–50 nm; b. The dense silica layer has a non-porous continuous coating structure with a thickness of 2–5 nm and a porosity of less than 5%; c. In the mesoporous silica-nano manganese oxide composite layer, the pore size of the mesoporous silica is 3-10 nm and the porosity is 40-70%.

3. The dual-mode synergistic composite photocatalyst according to claim 1, characterized in that: The nano-manganese oxide in the mesoporous silica-nano-manganese oxide composite layer is uniformly dispersed in the pores of the mesoporous silica and the matrix, with a particle size of 2–5 nm; and / or, The weight ratio of the nano-manganese oxide to the anatase nano-titanium dioxide is 1:5 to 20.

4. The dual-mode synergistic composite photocatalyst according to claim 1, characterized in that: The graphene quantum dots have a particle size of 2–5 nm and a surface oxygen-containing functional group content of 10–30 at.

5. The dual-mode synergistic composite photocatalyst according to claim 1, characterized in that: The graphene quantum dots are chemically grafted onto the mesoporous silica-nano manganese oxide composite layer via a silane coupling agent.

6. A method for preparing the dual-mode synergistic composite photocatalyst according to claim 1, characterized in that: Includes the following steps: S1. Disperse 0.5-3.5 parts of anatase nano-titanium dioxide in 150-200 parts of a mixed solvent of ethanol and water with an ethanol concentration of 65-85%, add 1-5 parts of tetraethyl orthosilicate and 3-8 parts of ammonia water with an ammonia mass content of 10%, and react at 20-40℃ for 2-6 hours to form a dense silica layer on the surface of anatase nano-titanium dioxide. After centrifugation, washing with ethanol, and drying at 50-70℃, TiO2@dense SiO2 core-shell particles are obtained. S2. Disperse 0.5-5 parts of the TiO2@dense SiO2 core-shell particles in a deionized water reaction solution containing 0.8-6.5 parts of template agent, 3-4 parts of tetraethyl orthosilicate and 0.1-1 parts of manganese source. Adjust the pH to 9-11 with ammonia water containing 10% ammonia by mass. React at 50-70°C for 4-8 hours. Form a mesoporous silica-manganese precursor composite layer on the surface by sol-gel method. After centrifugation, washing and drying, calcine at 400-600°C for 2-4 hours to obtain TiO2@dense SiO2@mesoporous SiO2-MnO2 composite particles. The template agent is hexadecyltrimethylammonium bromide or polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer; The manganese source is at least one of manganese acetate, manganese nitrate, or manganese chloride. S3. Disperse 0.3-1.7 parts of the TiO2@dense SiO2@mesoporous SiO2-MnO2 composite particles in a solution containing 0.05-0.5 parts of silane coupling agent for surface activation treatment, and then react with graphene quantum dot dispersion at 40-80℃ for 4-12 hours. Through amidation reaction, the graphene quantum dots are chemically grafted onto the surface and pore walls of the mesoporous silica-nano manganese oxide composite layer to obtain the dual-mode synergistic composite photocatalyst. The silane coupling agent is at least one of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; The amidation reaction was carried out in the presence of the coupling agents N-hydroxysuccinimide and 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride.

7. A styrene-acrylic emulsion coating composition, characterized in that: Includes the following components by weight: The composition comprises 30-50 parts of styrene-acrylic emulsion, 1-8 parts of the dual-mode synergistic composite photocatalyst as described in claim 1, 0.5-4 parts of the yellowing-resistant composition, 20-35 parts of pigments and fillers, 2-8 parts of additives, and 15-25 parts of deionized water. The anti-yellowing composition comprises: hollow titanium dioxide supported benzotriazole particles, sulfonic acid-grafted hindered amine light stabilizer, and nano zinc oxide; The pigments and fillers include at least one of titanium dioxide, heavy calcium carbonate, and calcined kaolin. The additives include at least two of the following: dispersants, wetting agents, defoamers, leveling agents, thickeners, and film-forming aids.

8. The styrene-acrylic emulsion coating composition according to claim 7, characterized in that: The anti-yellowing composition comprises the following components in parts by weight: Hollow titanium dioxide supported on benzotriazole particles: 0.3–1.5 parts; sulfonic acid-grafted hindered amine light stabilizer: 0.2–1.2 parts; nano zinc oxide: 0.2–1 parts.

9. The styrene-acrylic emulsion coating composition according to claim 7, characterized in that: The hollow titanium dioxide-supported benzotriazole particles have a particle size of 100–200 nm, and the loading of benzotriazole is 5–15 wt%. The sulfonic acid-grafted hindered amine light stabilizer is a piperidine derivative hindered amine light stabilizer grafted with sulfonic acid groups, with a grafting rate of 2-8%. The particle size of the nano zinc oxide is 50–150 nm.

10. A method for preparing the styrene-acrylic emulsion coating composition according to claim 7, characterized in that: The preparation steps include the following: A. Pre-dispersion a: The dual-mode synergistic composite photocatalyst, hollow titanium dioxide-supported benzotriazole particles and nano zinc oxide in the yellowing-resistant composition are mixed with some deionized water and some additives, and dispersed at high speed at 1300-1500 rpm for 20 minutes to obtain the first slurry; B. Pre-dispersion b: After mixing the first slurry with the pigments and fillers, high-speed dispersion is carried out at a speed of 1400-1500 rpm until the fineness is ≤20μm to obtain the second slurry; C. Paint mixing: Under stirring, the styrene-acrylic emulsion, the sulfonic acid-based grafted hindered amine light stabilizer in the anti-yellowing composition, and the remaining additives are added to the second slurry in sequence and mixed evenly; D. Adjustment and filtration: Add the remaining deionized water to adjust the viscosity and filter to obtain the styrene-acrylic emulsion coating composition.

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