Photocatalytic composite slurry, photocatalytic air purification exterior wall coating and preparation method of photocatalytic air purification exterior wall coating

Abstract

The invention discloses photocatalytic composite slurry, a photocatalytic air purification exterior wall coating and a preparation method thereof, and belongs to the technical field of photocatalytic coating preparation. According to the invention, a specific photocatalytic composite material is compounded with silica powder and an anti-ultraviolet assistant to prepare the photocatalytic composite slurry. By adding the silica powder, the agglomeration of the nano titanium dioxide can be effectively inhibited, the sedimentation can be prevented, and the storage stability and the photocatalytic efficiency of the slurry can be obviously improved; by adding the anti-ultraviolet assistant, part of ultraviolet radiation is shielded, and the light corrosion degradation of the photocatalyst is slowed down. After the photocatalytic composite slurry is introduced into the exterior wall coating, the exterior wall coating has high-efficiency air purification rate, the artificial weathering aging resistance of the exterior wall coating can be remarkably prolonged, and the long-term outdoor use requirement is met.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic coating preparation technology, specifically relating to a photocatalytic composite slurry, a photocatalytic air-purifying exterior wall coating, and their preparation methods. Background Technology

[0002] Photocatalysis technology has moved from the laboratory to engineering, becoming one of the core methods for environmental governance and clean energy production. Introducing it into exterior wall coatings can degrade outdoor pollutants such as formaldehyde and nitrogen oxides in the air, and endow walls with self-cleaning functions, possessing irreplaceable strategic value in the field of energy conservation and environmental protection. However, while traditional photocatalysts absorb light energy to excite electron-hole pairs and drive redox reactions to decompose pollutants, they also continuously degrade themselves, leading to reduced catalytic efficiency and ultimately losing their ability to purify the air.

[0003] Patent application CN119281353A, concerning photocatalytic composite materials, their preparation methods, and their application in coatings, describes a method for preparing a photocatalytic composite material. After application in coatings, this photocatalytic composite material exhibits 250 hours of artificial weathering resistance, but this only meets the requirements for qualified exterior wall paints in GB / T 9755-2014. The new version of GB / T 9755-2024 requires qualified exterior wall paints to withstand 300 hours, and superior products to withstand 800 hours, indicating that the existing technology is still insufficient.

[0004] Traditional photocatalytic materials continuously induce micronization on the paint film surface under light irradiation, thereby maintaining its air purification function; however, this process simultaneously weakens the aging resistance of the paint film, leading to defects such as chalking and fading. To date, no publicly available technology has been found that can simultaneously inhibit the degradation of photocatalytic materials and coatings, significantly improve the artificial weathering resistance of exterior wall coatings, and extend their service life. Summary of the Invention

[0005] The purpose of this invention is to provide a photocatalytic composite slurry, a photocatalytic air-purifying exterior wall coating, and a method for preparing the same. This invention combines a specific photocatalytic composite material with silica powder and an anti-UV additive to prepare the photocatalytic composite slurry. The addition of silica powder effectively inhibits the agglomeration of nano-titanium dioxide and prevents sedimentation, significantly improving the slurry's storage stability and photocatalytic efficiency. The addition of the anti-UV additive shields part of the UV radiation, slowing down the photo-corrosion degradation of the photocatalyst. Introducing the photocatalytic composite slurry of this invention into an exterior wall coating not only results in a high air purification rate but also significantly extends its resistance to artificial weathering, meeting the requirements for long-term outdoor use.

[0006] To solve the above problems, the present invention is achieved through the following technical solution:

[0007] The first objective of this invention is:

[0008] A photocatalytic composite slurry is provided, comprising the following raw material components in parts by weight:

[0009] The composition consists of 10-20 parts photocatalytic composite material, 40-60 parts silica powder, 1.5-5 parts UV-resistant additive, 0.1-0.3 parts anti-settling agent, 0.2-0.4 parts wetting agent, 0.5-3 parts dispersant A, 0.2-0.5 parts defoamer A, and the balance being water, with a total mass of 100 parts.

[0010] The photocatalytic composite material includes a bismuth oxychloride / titanium dioxide composition having a semiconductor-semiconductor interleaved heterojunction; the specific composition and preparation method of the photocatalytic composite material are detailed in patent application publication CN119281353A Photocatalytic Composite Material, Preparation Method and Its Application in Coatings;

[0011] The silicon micropowder is a quasi-spherical crystalline silicon dioxide powder with a silicon dioxide content >99% and D. 50 <10μm;

[0012] The aforementioned UV-resistant additive is one or a combination of benzotriazole or triazine UV absorbers.

[0013] The photocatalytic composite slurry of the present invention is further optimized as follows:

[0014] It includes one or more of the following features:

[0015] The anti-settling agent is attapulgite.

[0016] The wetting agent is an alkylphenol polyoxyethylene ether nonionic surfactant;

[0017] The dispersant A is a hydrophobically modified copolymer ammonium salt additive;

[0018] The defoamer A is a polymer-composite mineral oil defoamer.

[0019] The photocatalytic composite slurry of the present invention is further optimized as follows:

[0020] It includes one or more of the following features:

[0021] The silicon micro powder mentioned is LE-CA1500 ultrafine silicon micro powder from Renxin Industrial Development (Xinyang) Co., Ltd.

[0022] The UV-resistant additive mentioned is BASF Tinuvin 9945-DW light stabilizer.

[0023] The photocatalytic composite slurry of the present invention is further optimized as follows:

[0024] It includes one or more of the following features:

[0025] The anti-settling agent is BASF Attagel 40 water-based rheology modifier;

[0026] The wetting agent mentioned is Emulsogen LCN070 from Clariant (Chemicals) Ltd.

[0027] The dispersant A is Sanopco SN-DISPERSANT 5027;

[0028] The defoamer A mentioned is BASF FOAMSTAR ST 2410AG.

[0029] The second objective of this invention is:

[0030] A method for preparing the aforementioned photocatalytic composite slurry is provided, comprising the following preparation steps:

[0031] S1. Add an appropriate amount of initial water to the container, start the stirrer and set the speed to 800 rpm; add the anti-settling agent, wetting agent, dispersant A and defoamer A in proportion, wait 2 minutes after each addition before adding the next one, and continue stirring for 2 minutes after all the additions are completed;

[0032] S2. Reduce the speed to 500 rpm, slowly add the silica powder, and rinse the container walls, dispersion plate and stirring shaft with an appropriate amount of water after adding. Increase the speed to 1500 rpm and stir at high speed for 15 minutes.

[0033] S3. Adjust the rotation speed to 800 rpm, add the photocatalytic composite material, and stir for 2 minutes; finally, add the anti-ultraviolet light additive and the remaining water, and continue stirring for 10 minutes to obtain the photocatalytic composite slurry.

[0034] The third objective of this invention is:

[0035] A photocatalytic air-purifying exterior wall coating is provided, comprising the following raw material components in parts by weight:

[0036] The composition comprises 30-40 parts acrylic emulsion, 10-20 parts titanium dioxide, 5-10 parts calcined kaolin, 30-40 parts of the aforementioned photocatalytic composite slurry, 0.1-0.4 parts thickener, 0.5-1.5 parts antifreeze-thaw agent, 1-4 parts film-forming agent, 0.1-0.6 parts dispersant B, 0.1-0.2 parts pH adjuster, 0.1-0.3 parts bactericide and preservative, 0.1-0.6 parts mildew inhibitor, 0.1-0.5 parts defoamer B, and the balance being water, for a total mass of 100 parts.

[0037] The photocatalytic air-purifying exterior wall coating of the present invention is further optimized as follows:

[0038] It includes one or more of the following features:

[0039] The acrylic emulsion is one or a combination of pure acrylic emulsion and silicone acrylic emulsion;

[0040] The titanium dioxide mentioned is rutile titanium dioxide powder;

[0041] The calcined kaolin is anhydrous aluminum silicate powder;

[0042] The dispersant B is a sodium polycarboxylate salt additive;

[0043] The thickener is one or a combination of hydroxyethyl cellulose and nonionic water-soluble polymer; the pH adjuster is 2-amino-2-methyl-1-propanol.

[0044] The defoamer B is a mineral oil-based foam control agent;

[0045] The bactericidal and preservative agent is one or a combination of two of formaldehyde and isothiazolone compounds;

[0046] The antifungal agent is a benzimidazole adjuvant;

[0047] The aforementioned antifreeze-thaw aid is ethylene glycol;

[0048] The film-forming aid is a dodecyl alcohol ester.

[0049] The photocatalytic air-purifying exterior wall coating of the present invention is further optimized as follows:

[0050] The acrylic emulsion mentioned is Badifu RS-727 emulsion;

[0051] The titanium dioxide mentioned is Longmang Titanium Industry's titanium dioxide R-996;

[0052] The calcined kaolin mentioned is Inner Mongolia Chao brand calcined kaolin DG-80;

[0053] The dispersant B is Sanopco SN-DISPERSANT-5040;

[0054] The thickener is Ashland cellulose 250HBR;

[0055] The pH adjuster mentioned is AMP-95;

[0056] The defoamer B mentioned is Blackburn. CF 246;

[0057] The bactericidal preservative mentioned is Dow BT NV2 preservative;

[0058] The aforementioned antifungal agent is from Lanxess Chemical. BCM anti-mold agent.

[0059] The fourth objective of this invention is:

[0060] A method for preparing the aforementioned photocatalytic air-purifying exterior wall coating is provided, comprising the following preparation steps:

[0061] s1. Add an appropriate amount of initial water to the container, start the stirrer and set the speed to 800 rpm; add thickener, pH adjuster, dispersant B and defoamer B in proportion, wait 2 minutes after each addition before adding the next one, and continue stirring for 2 minutes after all additions are completed;

[0062] s2. Reduce the speed to 500 rpm, slowly add titanium dioxide and calcined kaolin, and rinse the container wall, dispersion plate and stirring shaft with an appropriate amount of water after adding. Increase the speed to 1500 rpm and stir at high speed for 15 minutes.

[0063] s3. Adjust the speed to 800 rpm, and add acrylic emulsion, antifreeze-thaw aid, film-forming aid, bactericide, preservative and mildew inhibitor respectively. After adding each one, wait 2 minutes before adding the next one. After all the ingredients are added, continue stirring for 2 minutes. Finally, add the photocatalytic composite slurry mentioned above and the remaining water, and continue stirring for 10 minutes to obtain the photocatalytic air-purifying exterior wall coating.

[0064] The core of this invention lies in: through a "photocatalytic compounding-synergistic protection" strategy, silicon micropowder and UV-resistant additives are simultaneously introduced into a nano-titanium dioxide system under mild dispersion conditions to construct a highly stable photocatalytic composite slurry. This technical solution solves two major problems at once:

[0065] 1. Storage and Dispersion Stability

[0066] Nano-TiO2 particles are prone to aggregation due to their small size and large specific surface area. Once aggregated, not only does the photocatalytic activity drop sharply, but it also forms precipitates, leading to system instability.

[0067] Silica powder, as a physical isolation framework, can significantly inhibit the aggregation and sedimentation of nano-TiO2, maintaining the long-term homogeneity of the system; at the same time, it increases the effective specific surface area, thereby improving the photocatalytic efficiency compared to the unmodified system.

[0068] 2. Weather resistance and paint film protection

[0069] The UV-resistant additive forms a "sacrifice-buffer" layer on the TiO2 surface, preferentially absorbing and dissipating UV energy, blocking the continuous attack of photogenerated charge carriers on the exterior wall coating; it avoids the self-degradation of the photocatalyst and prevents the paint film from chalking and fading, thus giving the water-based exterior wall coating ≥800h of artificial weathering resistance (GB / T9755-2024 superior grade). Detailed Implementation

[0070] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention. Any simple improvements to the preparation method of this invention based on the inventive concept are within the scope of protection of this invention.

[0071] Example 1

[0072] A photocatalytic air-purifying exterior wall coating, comprising the following raw material components in parts by weight:

[0073] The ingredients are: 35 parts acrylic emulsion, 15 parts titanium dioxide, 8 parts calcined kaolin, 30 parts of the aforementioned photocatalytic composite slurry, 0.3 parts thickener, 0.9 parts antifreeze-thaw agent, 2 parts film-forming agent, 0.2 parts dispersant B, 0.15 parts pH adjuster, 0.2 parts bactericide and preservative, 0.5 parts mildew inhibitor, 0.3 parts defoamer B, and 7.45 parts water.

[0074] The acrylic emulsion is a pure acrylic emulsion, specifically a Badifu RS-727 emulsion.

[0075] The titanium dioxide mentioned is rutile titanium dioxide powder, specifically Longmang Titanium Industry's titanium dioxide R-996;

[0076] The calcined kaolin is anhydrous aluminum silicate powder, specifically Inner Mongolia Chao brand calcined kaolin DG-80.

[0077] The dispersant B is a sodium polycarboxylate salt additive, namely Sanopco SN-DISPERSANT-5040;

[0078] The thickener is hydroxyethyl cellulose, specifically Ashland cellulose 250HBR;

[0079] The pH adjuster is 2-amino-2-methyl-1-propanol, AMP-95;

[0080] The defoamer B mentioned above is a mineral oil-based foam control agent, specifically Blackburn. CF 246;

[0081] The bactericidal preservative mentioned is an isothiazolone, specifically Dow BT NV2 preservative;

[0082] The aforementioned antifungal agent is a benzimidazole adjuvant, manufactured by Lanxess Chemical. BCM anti-mold agent;

[0083] The aforementioned antifreeze-thaw aid is ethylene glycol;

[0084] The film-forming aid is a dodecyl alcohol ester.

[0085] The photocatalytic air-purifying exterior wall coating comprises the following preparation steps:

[0086] s1. Add 5 parts water to the container, start the stirrer and set the speed to 800 rpm; add thickener, pH adjuster, dispersant B and defoamer B in proportion, wait 2 minutes after each addition before adding the next one, and continue stirring for 2 minutes after all additions are completed;

[0087] s2. Reduce the speed to 500 rpm, slowly add titanium dioxide and calcined kaolin, and after adding, rinse the container walls, dispersion plate and stirring shaft with 1 part water; increase the speed to 1500 rpm and stir at high speed for 15 minutes;

[0088] s3. Adjust the speed to 800 rpm, and add acrylic emulsion, antifreeze-thaw aid, film-forming aid, bactericide, preservative and mildew inhibitor respectively. After adding each one, wait 2 minutes before adding the next one. After all the ingredients are added, continue stirring for 2 minutes. Finally, add the photocatalytic composite slurry mentioned above and the remaining water, and continue stirring for 10 minutes to obtain the photocatalytic air-purifying exterior wall coating.

[0089] in:

[0090] The photocatalytic composite slurry comprises the following raw material components in parts by weight:

[0091] The composition consists of 15 parts photocatalytic composite material, 50 parts silica powder, 2 parts anti-UV light additive, 0.2 parts anti-settling agent, 0.3 parts wetting agent, 2 parts dispersant A, 0.5 parts defoamer A, and 30 parts water.

[0092] The photocatalytic composite material includes a bismuth oxychloride / titanium dioxide composition having a semiconductor-semiconductor interleaved heterojunction; the specific composition and preparation method of the photocatalytic composite material are detailed in patent application publication CN119281353A Photocatalytic Composite Material, Preparation Method and Its Application in Coatings;

[0093] The silicon micropowder is a quasi-spherical crystalline silicon dioxide powder with a silicon dioxide content >99% and D. 50 <10μm, is LE-CA1500 ultrafine silica powder from Renxin Industrial Development (Xinyang) Co., Ltd.;

[0094] The aforementioned UV-resistant additive is a benzotriazole UV absorber, specifically BASF's Tinuvin 9945-DW light stabilizer;

[0095] The anti-settling agent is BASF Attagel 40 water-based rheology modifier;

[0096] The wetting agent mentioned is Emulsogen LCN070 from Clariant (Chemicals) Ltd.

[0097] The dispersant A is Sanopco SN-DISPERSANT 5027;

[0098] The defoamer A mentioned is BASF FOAMSTAR ST 2410AG.

[0099] The photocatalytic composite slurry comprises the following preparation steps:

[0100] S1. Add 15 parts water to the container, start the stirrer and set the speed to 800 rpm; add the anti-settling agent, wetting agent, dispersant A and defoamer A in proportion, wait 2 minutes after each addition before adding the next one, and continue stirring for 2 minutes after all the additions are completed;

[0101] S2. Reduce the speed to 500 rpm, slowly add the silica powder, and after adding, rinse the container walls, dispersion plate and stirring shaft with 1 part water; increase the speed to 1500 rpm and stir at high speed for 15 minutes;

[0102] S3. Adjust the rotation speed to 800 rpm, add the photocatalytic composite material, and stir for 2 minutes; finally, add the anti-ultraviolet light additive and the remaining water, and continue stirring for 10 minutes to obtain the photocatalytic composite slurry.

[0103] Example 2

[0104] The raw material composition and preparation method of Example 2 and Example 1 are basically the same, the main difference is:

[0105] The amounts of raw material components in the aforementioned photocatalytic composite slurry vary.

[0106] The photocatalytic composite slurry comprises the following raw material components in parts by weight:

[0107] The composition consists of 20 parts photocatalytic composite material, 45 parts silica powder, 2 parts anti-UV light additive, 0.2 parts anti-settling agent, 0.3 parts wetting agent, 2 parts dispersant A, 0.5 parts defoamer A, and 30 parts water.

[0108] Example 3

[0109] The raw material composition and preparation method of Example 3 and Example 1 are basically the same, the main difference is:

[0110] The raw material components of the aforementioned photocatalytic air-purifying exterior wall coating and photocatalytic composite slurry are used in different amounts.

[0111] The aforementioned photocatalytic air-purifying exterior wall coating comprises the following raw material components in parts by weight:

[0112] The ingredients are: 33 parts acrylic emulsion, 15 parts titanium dioxide, 8 parts calcined kaolin, 32 parts of the aforementioned photocatalytic composite slurry, 0.3 parts thickener, 0.9 parts antifreeze-thaw agent, 2 parts film-forming agent, 0.2 parts dispersant B, 0.15 parts pH adjuster, 0.2 parts bactericide and preservative, 0.5 parts mildew inhibitor, 0.3 parts defoamer B, and 7.45 parts water.

[0113] The photocatalytic composite slurry comprises the following raw material components in parts by weight:

[0114] The composition consists of 15 parts photocatalytic composite material, 50 parts silica powder, 4 parts anti-UV light additive, 0.2 parts anti-settling agent, 0.3 parts wetting agent, 2 parts dispersant A, 0.5 parts defoamer A, and 28 parts water.

[0115] Comparative Example 1

[0116] The raw material composition and preparation method of Comparative Example 1 and Example 1 are basically the same, the main difference being:

[0117] The raw material components of the photocatalytic composite slurry do not contain anti-ultraviolet light additives, and are supplemented with water.

[0118] The photocatalytic composite slurry comprises the following raw material components in parts by weight:

[0119] The composition consists of 15 parts photocatalytic composite material, 50 parts silica powder, 0.2 parts anti-settling agent, 0.3 parts wetting agent, 2 parts dispersant A, 0.5 parts defoamer A, and 32 parts water.

[0120] Comparative Example 2

[0121] The raw material composition and preparation method of Comparative Example 2 and Example 1 are basically the same, the main difference being:

[0122] In Comparative Example 2, the photocatalytic composite slurry did not use the silicon micropowder from Example 1, but instead used an equal amount of conventional powder.

[0123] Comparative Example 3

[0124] A photocatalytic air-purifying exterior wall coating, comprising the following raw material components in parts by weight:

[0125] 35 parts acrylic emulsion, 15 parts titanium dioxide, 15 parts silica powder, 8 parts calcined kaolin, 4.5 parts photocatalytic composite material, 0.3 parts thickener, 0.9 parts antifreeze-thaw aid, 2 parts film-forming aid, 1 part dispersant B, 0.15 parts pH adjuster, 0.2 parts bactericide and preservative, 0.5 parts mildew inhibitor, 0.5 parts defoamer B, 0.2 parts anti-settling agent, 0.6 parts UV protection agent, and 16.15 parts water;

[0126] The photocatalytic air-purifying exterior wall coating comprises the following preparation steps:

[0127] s1. Add 14 parts water to the container, start the stirrer and set the speed to 800 rpm; add thickener, anti-settling agent, pH adjuster, dispersant B and defoamer B in proportion, wait 2 minutes after each addition before adding the next one, and continue stirring for 2 minutes after all additions are completed;

[0128] s2. Reduce the speed to 500 rpm, slowly add titanium dioxide, silica powder, and calcined kaolin. After adding, rinse the container walls, dispersion plate, and stirring shaft with 1 part water. Increase the speed to 1500 rpm and stir at high speed for 15 minutes.

[0129] s3. Adjust the speed to 800 rpm, and add acrylic emulsion, antifreeze-thaw aid, film-forming aid, bactericide and preservative and mildew inhibitor respectively. After adding each one, wait 2 minutes before adding the next one. After all the ingredients are added, continue stirring for 2 minutes. Finally, add photocatalytic composite material, anti-ultraviolet light aid and the remaining water, and continue stirring for 10 minutes to obtain the photocatalytic air-purifying exterior wall coating.

[0130] The performance test results of Examples 1-3 and Comparative Examples 1-3 are shown in Table 1.

[0131] Table 1. Performance test results of Examples 1-3 and Comparative Examples 1-3

[0132]

[0133] In Table 1, test items 1 to 7 are tested according to the relevant test methods for exterior wall paints in GB / T 9755-2024 Synthetic Resin Emulsion Wall Coatings; test item 8 is a coating stability test; test item 9 is tested according to Q / LBZS102-2024 Purification performance of photocatalytic air purification functional coating materials for building exterior surfaces.

[0134] The comparison results between Examples 1-3 and Comparative Examples 1-3 show that:

[0135] Example 1, by preparing a photocatalytic composite slurry from photocatalytic materials, showed improved storage stability, resistance to artificial weathering, and nitrogen oxide purification efficiency compared to directly using photocatalytic materials (Comparative Example 3 involved directly adding the photocatalytic composite material, silicon micropowder, and UV-resistant additives to the formulation for dispersion). Compared to conventional powders (Comparative Example 2), the use of silicon micropowder (Example 1) in Example 1, where the silicon micropowder structure provides more dispersion and anchoring active sites for the nano-titanium dioxide particles in the photocatalytic material, not only improved photocatalytic efficiency but also reduced particle aggregation and precipitation.

[0136] Compared with Comparative Examples 1 and 3, Example 1 shows that neither adding UV-resistant additives nor directly adding UV-resistant additives to the exterior wall coating formulation reduces the material's resistance to artificial weathering.

[0137] 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 using the disclosed technical content are 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 are within the protection scope of the present invention.

[0138] 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.

[0139] Experimental methods not specified in this invention are generally performed under conventional conditions or as recommended by the manufacturer.

[0140] Unless otherwise stated, the various optimized technical solutions in this invention can be combined with each other.

[0141] Unless otherwise stated, percentages and parts are percentages and parts by mass.

[0142] Experimental methods not specified in the instructions and examples are generally performed under standard conditions or as recommended by the manufacturer.

[0143] The various raw materials, reagents and components used in this invention are all commonly used raw materials in the field unless otherwise stated.

[0144] 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 photocatalytic composite slurry, characterized in that: It comprises the following raw material components by weight: The composition consists of 10-20 parts photocatalytic composite material, 40-60 parts silica powder, 1.5-5 parts UV-resistant additive, 0.1-0.3 parts anti-settling agent, 0.2-0.4 parts wetting agent, 0.5-3 parts dispersant A, 0.2-0.5 parts defoamer A, and the balance being water, with a total mass of 100 parts. The photocatalytic composite material includes a bismuth oxychloride / titanium dioxide composition having a semiconductor-semiconductor interleaved heterojunction; The silicon micropowder is a quasi-spherical crystalline silicon dioxide powder with a silicon dioxide content >99% and D. 50 <10μm; The aforementioned UV-resistant additive is one or a combination of benzotriazole or triazine UV absorbers.

2. The photocatalytic composite slurry according to claim 1, characterized in that: It includes one or more of the following features: The anti-settling agent is attapulgite. The wetting agent is an alkylphenol polyoxyethylene ether nonionic surfactant; The dispersant A is a hydrophobically modified copolymer ammonium salt additive; The defoamer A is a polymer-composite mineral oil defoamer.

3. The photocatalytic composite slurry according to claim 1, characterized in that: It includes one or more of the following features: The silicon micro powder mentioned is LE-CA1500 ultrafine silicon micro powder from Renxin Industrial Development (Xinyang) Co., Ltd. The UV-resistant additive mentioned is BASF Tinuvin 9945-DW light stabilizer.

4. The photocatalytic composite slurry according to claim 2, characterized in that: It includes one or more of the following features: The anti-settling agent is BASF Attagel 40 water-based rheology modifier; The wetting agent mentioned is Emulsogen LCN070 from Clariant (Chemicals) Ltd. The dispersant A is Sanopco SN-DISPERSANT 5027; The defoamer A mentioned is BASF FOAMSTAR ST 2410AG.

5. A method for preparing the photocatalytic composite slurry according to claim 1, characterized in that: It includes the following preparation steps: S1. Add an appropriate amount of initial water to the container, start the stirrer and set the speed to 800 rpm; add the anti-settling agent, wetting agent, dispersant A and defoamer A in proportion, wait 2 minutes after each addition before adding the next one, and continue stirring for 2 minutes after all the additions are completed; S2. Reduce the speed to 500 rpm, slowly add the silica powder, and rinse the container walls, dispersion plate and stirring shaft with an appropriate amount of water after adding. Increase the speed to 1500 rpm and stir at high speed for 15 minutes. S3. Adjust the rotation speed to 800 rpm, add the photocatalytic composite material, and stir for 2 minutes; finally, add the anti-ultraviolet light additive and the remaining water, and continue stirring for 10 minutes to obtain the photocatalytic composite slurry.

6. A photocatalytic air-purifying exterior wall coating, characterized in that: It comprises the following raw material components by weight: The composition comprises 30-40 parts acrylic emulsion, 10-20 parts titanium dioxide, 5-10 parts calcined kaolin, 30-40 parts of the photocatalytic composite slurry as described in claim 1, 0.1-0.4 parts thickener, 0.5-1.5 parts antifreeze-thaw agent, 1-4 parts film-forming agent, 0.1-0.6 parts dispersant B, 0.1-0.2 parts pH adjuster, 0.1-0.3 parts bactericide and preservative, 0.1-0.6 parts mildew inhibitor, 0.1-0.5 parts defoamer B, and the balance being water, for a total mass of 100 parts.

7. The photocatalytic air-purifying exterior wall coating according to claim 6, characterized in that: It includes one or more of the following features: The acrylic emulsion is one or a combination of pure acrylic emulsion and silicone acrylic emulsion; The titanium dioxide mentioned is rutile titanium dioxide powder; The calcined kaolin is anhydrous aluminum silicate powder; The dispersant B is a sodium polycarboxylate salt additive; The thickener is one or a combination of hydroxyethyl cellulose and nonionic water-soluble polymers; The pH adjuster is 2-amino-2-methyl-1-propanol; The defoamer B is a mineral oil-based foam control agent; The bactericidal and preservative agent is one or a combination of two of formaldehyde and isothiazolone compounds; The antifungal agent is a benzimidazole adjuvant; The aforementioned antifreeze-thaw aid is ethylene glycol; The film-forming aid is a dodecyl alcohol ester.

8. The photocatalytic air-purifying exterior wall coating according to claim 6, characterized in that: The acrylic emulsion mentioned is Badifu RS-727 emulsion; The titanium dioxide mentioned is Longmang Titanium Industry's titanium dioxide R-996; The calcined kaolin mentioned is Inner Mongolia Chao brand calcined kaolin DG-80; The dispersant B is Sanopco SN-DISPERSANT-5040; The thickener is Ashland cellulose 250HBR; The pH adjuster mentioned is AMP-95; The defoamer B mentioned is Blackburn. CF 246; The bactericidal preservative mentioned is Dow BT NV2 preservative; The aforementioned antifungal agent is from Lanxess Chemical. BCM anti-mold agent.

9. A method for preparing the photocatalytic air-purifying exterior wall coating according to claim 6, characterized in that: It includes the following preparation steps: s1. Add an appropriate amount of initial water to the container, start the stirrer and set the speed to 800 rpm; add thickener, pH adjuster, dispersant B and defoamer B in proportion, wait 2 minutes after each addition before adding the next one, and continue stirring for 2 minutes after all additions are completed; s2. Reduce the speed to 500 rpm, slowly add titanium dioxide and calcined kaolin, and rinse the container wall, dispersion plate and stirring shaft with an appropriate amount of water after adding. Increase the speed to 1500 rpm and stir at high speed for 15 minutes. s3. Adjust the speed to 800 rpm, and add acrylic emulsion, antifreeze-thaw aid, film-forming aid, bactericide and preservative and mildew inhibitor respectively. After adding each one, wait 2 minutes before adding the next one. After all the ingredients are added, continue stirring for 2 minutes. Finally, add the photocatalytic composite slurry as described in claim 1 and the remaining water, and continue stirring for 10 minutes to obtain the photocatalytic air-purifying exterior wall coating.

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