Modified g-c3n4 visible light response type interior wall photocatalytic coating, preparation method and application thereof

Abstract

The application discloses a modified g-C3N4 visible light response type interior wall photocatalytic coating and a preparation method and application thereof. The photocatalytic coating comprises water-based emulsion, titanium white, heavy calcium, talcum powder, doped modified g-C3N4 nanosheet, dispersing agent, defoaming agent, film-forming aid, thickening agent and water; the doped modified g-C3N4 nanosheet is a silane coupling agent doped modified g-C3N4 nanosheet, and the titanium white is an anatase type composite rutile type. The g-C3N4 after doping is prepared by compounding raw materials and then low-temperature calcination, and the g-C3N4 after doping is modified by a silane coupling agent; the g-C3N4 nanosheet after doping and modification has good compatibility with a coating system and does not affect the coating performance. The prepared coating can efficiently degrade volatile organic compounds such as formaldehyde and benzene series under indoor visible light conditions, has stable photocatalytic activity, and can be widely applied to the fields of indoor wall de-aldehyde and air purification.

Description

Technical Field

[0001] This invention belongs to the field of functional coatings technology, specifically relating to a modified g-C3N4 visible light responsive interior wall photocatalytic coating, its preparation method, and its application. Background Technology

[0002] As people's living standards improve, the quality of various interior decoration materials sold on the market varies greatly. Newly renovated homes often experience severe indoor air pollution due to the large release of formaldehyde from these materials, significantly impacting people's health. Therefore, photocatalytic coatings with formaldehyde removal and purification functions have attracted widespread attention. Currently, most photocatalytic coatings on the market use TiO2 as the photocatalytic component. However, TiO2 has a band gap of approximately 3.2 eV, meaning it can only respond to ultraviolet light, which accounts for less than 5% of sunlight. The lack of ultraviolet light in indoor environments leads to a significant reduction in photocatalytic efficiency.

[0003] To address the limitation of TiO2's responsiveness only to ultraviolet light, researchers have developed various visible-light-responsive photocatalytic materials. Among them, g-C3N4, a metal-free semiconductor material with a band gap of approximately 2.7 eV, can directly respond to visible light. Adding it to photocatalytic coatings can significantly improve the formaldehyde degradation efficiency of indoor photocatalytic coatings. Moreover, its raw materials are inexpensive and readily available, and its preparation process is simple, showing promising application prospects. However, g-C3N4 suffers from problems such as small specific surface area, easy aggregation in coatings, and poor compatibility with resins, which hinders its photocatalytic activity and affects the coating's application performance and appearance. Furthermore, existing modified g-C3N4 preparation processes are often complex and costly, making large-scale industrial production difficult. Therefore, developing a photocatalytic coating with inexpensive and readily available raw materials, a simple process, good dispersibility, and high visible-light response efficiency has become a pressing technical problem to be solved in the field of indoor formaldehyde removal coatings. Summary of the Invention

[0004] The main objective of this invention is to provide a modified g-C3N4 visible light responsive interior wall photocatalytic coating and its preparation method, thereby overcoming the shortcomings of the prior art.

[0005] Another object of the present invention is to provide the application of the modified g-C3N4 visible light responsive interior wall photocatalytic coating.

[0006] To achieve the aforementioned objectives, the technical solution adopted by this invention includes: The first aspect of this invention provides a modified g-C3N4 visible light responsive photocatalytic coating for interior walls, comprising: an aqueous emulsion, titanium dioxide, heavy calcium carbonate, talc, doped and modified g-C3N4 nanosheets, a dispersant, a defoamer, a film-forming aid, a thickener, and water; wherein the doped and modified g-C3N4 nanosheets include g-C3N4 nanosheets doped and modified with a silane coupling agent, and the titanium dioxide is anatase composite rutile.

[0007] A second aspect of this invention provides a method for preparing the modified g-C3N4 visible light responsive interior wall photocatalytic coating, comprising: (1) Mix water, dispersant, and defoamer, and perform a first low-speed dispersion; (2) Add doped and modified g-C3N4 nanosheets to the mixture obtained in step (1) and perform a first medium-high speed dispersion; (3) Add titanium dioxide, heavy calcium carbonate and talc to the mixture obtained in step (2) in sequence, and perform a second medium-high speed dispersion until the fineness of the slurry is 30~50μm; (4) Add aqueous emulsion and film-forming aid to the slurry obtained in step (3) and perform a second low-speed dispersion; (5) Add a thickener to the mixture obtained in step (4), and after filtration, obtain the modified g-C3N4 visible light responsive interior wall photocatalytic coating.

[0008] A third aspect of the present invention provides the application of the modified g-C3N4 visible light responsive interior wall photocatalytic coating in the field of formaldehyde removal or air purification on interior walls.

[0009] Compared with the prior art, the present invention has at least the following beneficial effects: 1) This invention uses raw materials containing different elements to prepare g-C3N4 through compounding, achieving sulfur, phosphorus, or boron co-doping, thereby reducing the band gap and broadening the visible light response. Compared to g-C3N4 prepared from a single raw material, it exhibits a wider visible light response range. Sulfur, phosphorus, or boron co-doping can produce a synergistic effect, forming defect energy levels, thereby suppressing photogenerated carrier recombination, and simultaneously optimizing surface active sites, resulting in a higher visible light response range than single-doped or pure g-C3N4. The photocatalytic activity of C3N4 was significantly enhanced. Simultaneously, the calcination of the precursor resulted in slight pore-forming etching, forming more mesoporous structures, thereby increasing the specific surface area and generating more adsorption and reaction sites. 2) This invention uses a silane coupling agent to modify the surface of the doped g-C3N4 nanosheets, which significantly improves their dispersion stability in aqueous emulsions, avoids agglomeration, and ensures the full exposure of photocatalytic active sites. 3) Because pure anatase is too active, it can easily cause resin degradation, pulverization, and even yellowing. This invention uses anatase-rutile composite titanium dioxide, which retains the high photocatalytic activity and high specific surface area of ​​anatase to improve the adsorption rate of formaldehyde and thus efficiently degrade formaldehyde, while introducing the high stability and optical properties of rutile. This solves the problems of easy aging, pulverization, and yellowing of single anatase and insufficient activity of single rutile, making the photocatalytic system stable and efficient. 4) This invention prepares ultrathin nanosheets from bulk g-C3N4 by ultrasonic exfoliation, which significantly increases the specific surface area and improves the light absorption efficiency and carrier separation efficiency. At the same time, the doped and modified g-C3N4 nanosheets have good visible light response performance and can efficiently degrade volatile organic compounds such as formaldehyde under indoor natural light. They also have the functions of formaldehyde removal, odor removal and antibacterial properties, without secondary pollution. Detailed Implementation

[0010] Given the limitations of existing photocatalytic coatings, which mostly respond only to ultraviolet light and have low visible light utilization, as well as the drawbacks of poor dispersibility and high cost of functional powders, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention. The main method involves using inexpensive and readily available traditional raw materials, compounding them, and then preparing doped g-C3N4 through low-temperature calcination. The doped g-C3N4 nanosheets are then modified with a silane coupling agent to improve their dispersibility in the coating. The doped and modified g-C3N4 nanosheets exhibit good compatibility with the coating system and do not affect the coating performance. Furthermore, the prepared interior wall coating can efficiently degrade formaldehyde, benzene compounds, and other volatile organic compounds under indoor visible light conditions, effectively reducing the total amount of indoor VOCs, and exhibits stable photocatalytic activity.

[0011] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0012] Specifically, as one aspect of the technical solution of this invention, a modified g-C3N4 visible light responsive interior wall photocatalytic coating includes: an aqueous emulsion, titanium dioxide, heavy calcium carbonate, talc, doped and modified g-C3N4 nanosheets, a dispersant, a defoamer, a film-forming aid, a thickener, and water; wherein the doped and modified g-C3N4 nanosheets include g-C3N4 nanosheets doped and modified with a silane coupling agent, and the titanium dioxide is anatase composite rutile.

[0013] The above-mentioned scheme, by introducing silane coupling agent-modified g-C3N4 nanosheets, significantly improves the dispersibility and compatibility of photocatalytic materials in aqueous coating systems. Combined with titanium dioxide of a specific crystal form, it achieves efficient degradation of formaldehyde under visible light while ensuring the physicochemical properties of the coating. The doped and modified g-C3N4 nanosheets of this invention employ sulfur, phosphorus, or boron co-doped g-C3N4 nanosheets and graft silane coupling agents onto their surfaces. On the one hand, the defect energy levels generated by doping reduce the band gap width, significantly broadening the visible light response range of the material and improving the separation efficiency of photogenerated carriers. On the other hand, the modification with silane coupling agents effectively improves the dispersion stability of the nanosheets in aqueous systems, prevents aggregation, and fully exposes the photocatalytic active sites.

[0014] In some embodiments, the modified g-C3N4 visible light responsive photocatalytic coating for interior walls comprises the following components by weight: 35-45 parts aqueous emulsion, 15-20 parts titanium dioxide, 20-25 parts heavy calcium carbonate, 10-15 parts talc, 1-2 parts doped and modified g-C3N4 nanosheets, 0.3-0.5 parts dispersant, 0.1-0.2 parts defoamer, 1-2 parts film-forming aid, 0.2-0.4 parts thickener, and 8-12 parts water. This invention, by optimizing the proportions of each component, maximizes the efficiency of the photocatalytic components while ensuring the basic physical properties of the coating, thus ensuring that the coating has good application performance and formaldehyde removal effect.

[0015] Furthermore, the doped and modified g-C3N4 nanosheets are the core photocatalytic component of this invention. They broaden the visible light response range through co-doping with sulfur, phosphorus, or boron, and improve dispersion stability in the coating through surface modification with a silane coupling agent. The content of the doped and modified g-C3N4 nanosheets is 1-2 parts, specifically 1 part, 1.5 parts, or 2 parts. This addition amount ensures that the coating has sufficient visible light-responsive active sites for efficient formaldehyde degradation, while avoiding problems such as system thickening, dispersion difficulties, and rough coating surface caused by excessive nanomaterial addition.

[0016] In some embodiments, the doped and modified g-C3N4 nanosheets have a sheet thickness of 5-20 nm and a sheet diameter of 200-800 nm.

[0017] In some embodiments, the present invention also provides a method for preparing the doped and modified g-C3N4 nanosheets, specifically involving first mixing the precursor raw materials in a certain proportion, calcining, then ultrasonically exfoliating, and then modifying with a silane coupling agent to finally obtain the doped and modified g-C3N4 nanosheets. The present invention obtains an ultrathin nanosheet structure through ultrasonic exfoliation, significantly increasing the specific surface area and improving the light absorption efficiency and carrier separation efficiency. Further surface modification with a silane coupling agent effectively solves the problem of nanosheet agglomeration in coatings.

[0018] In some preferred embodiments, the specific steps of the preparation method of the doped and modified g-C3N4 nanosheets are as follows: After the precursor raw materials are mixed, they are heated to 500-600℃ at a heating rate of 3-5℃ / min and calcined for 3-5h. After cooling, they are ground to obtain doped g-C3N4 powder. Mix the doped g-C3N4 powder, dispersant and solvent, stir for 20-40 min, and then sonicate for 3-6 h to obtain the doped g-C3N4 nano-dispersion. A silane coupling agent was added to the doped g-C3N4 nanodispersion and stirred at room temperature for 1.5 to 2.5 h to obtain doped and modified g-C3N4 nanosheets.

[0019] Furthermore, the solvent includes ethanol, preferably anhydrous ethanol.

[0020] Furthermore, the dispersant accounts for 1% to 3% of the volume of the solvent, and the solid-liquid ratio of the doped g-C3N4 powder to the solvent is 1 to 3 g: 150 mL.

[0021] In some more specific embodiments, the preparation method of the doped and modified g-C3N4 nanosheets includes the following steps: (1) The precursor raw materials are first mixed evenly and then placed in a crucible, covered, and placed in a muffle furnace. The temperature is raised to 500-600℃ at a heating rate of 3-5℃ / min and calcined for 3-5 hours. After natural cooling, the powder is ground to obtain the doped and modified g-C3N4 powder. The heating rate can be 3℃ / min, 4℃ / min, or 5℃ / min; the calcination temperature can be 500℃, 550℃, or 600℃; and the holding time can be 3 hours, 4 hours, or 5 hours. Precise control of the heating rate and calcination temperature is crucial here. If the heating rate is too fast (exceeding 5℃ / min), the precursor reaction is violent, which can easily lead to incomplete polycondensation or structural collapse of the product; if the rate is too slow, the production efficiency is low. The calcination temperature is controlled in the range of 500-600℃, which can ensure the full formation of the g-C3N4 framework and avoid material decomposition or reduction of specific surface area caused by excessive temperature.

[0022] The precursor raw materials are a combination of three raw materials: a first raw material, a second raw material, and a third raw material. The first raw material includes, but is not limited to, any one or more combinations of melamine, urea, cyanuric acid, and melamine cyanurate. The second raw material includes, but is not limited to, sulfur powder, thiourea, thioacetamide, trithiocyanate, and dibenzothiophene. The third raw material includes, but is not limited to, any one or more combinations of ammonium dihydrogen phosphate, phosphoric acid, hydrogen peroxide, and boric acid. The first raw material primarily provides the basic carbon and nitrogen source for the g-C3N4 framework; the second raw material introduces sulfur as a sulfur source; and the third raw material introduces phosphorus or boron as a phosphorus or boron source. Through co-doping with sulfur, phosphorus, or boron, defect energy levels can be introduced into the g-C3N4 lattice. Specifically, the large radius of sulfur atoms, when replacing nitrogen or carbon atoms, causes lattice distortion, forming defect sites; while the introduction of phosphorus or boron atoms can adjust the valence band position. This synergistic effect effectively reduces the band gap of the material, enabling it to absorb longer wavelengths of visible light, thereby significantly broadening the photoresponse range and suppressing the recombination of photogenerated carriers. Simultaneously, the dopant elements can also act as traps for photogenerated electrons, suppressing electron-hole pair recombination and improving quantum efficiency. Furthermore, the precursor undergoes slight pore-forming etching during calcination, forming more mesoporous structures, thereby increasing the specific surface area and generating more adsorption and reaction sites. The mass ratio of the first, second, and third raw materials is (95~97):(1~3):2.

[0023] (2) First, add a certain amount of dispersant to anhydrous ethanol and stir to mix evenly. Then, add the doped and modified g-C3N4 powder. Stir at low speed for 20-40 minutes, then sonicate for 3-6 hours. Then, centrifuge to remove large particles and take the supernatant to obtain the doped and modified g-C3N4 nano-dispersion. The low-speed stirring time can be 20 minutes, 30 minutes, or 40 minutes; the sonication time can be 3 hours, 4 hours, 5 hours, or 6 hours. The amount of dispersant added is 1%-3% of the volume of anhydrous ethanol, specifically, it can be 1%, 2%, or 3%; and the solid-liquid ratio of the silane coupling agent doped and modified g-C3N4 powder to anhydrous ethanol is 1-3 g:150 mL, specifically, it can be 1 g:150 mL, 2 g:150 mL, or 3 g:150 mL. The principle of ultrasonic exfoliation is to utilize the cavitation effect generated by ultrasound in a liquid. The resulting high-temperature, high-pressure microbubbles collapse instantaneously, generating strong shock waves and microjets that peel away the bulk g-C3N4 layer by layer to prepare ultrathin nanosheets. The stirring step is to pre-wet the powder and prevent splashing or uneven dispersion caused by direct ultrasound. The exfoliated nanosheets have a larger specific surface area, exposing more photocatalytic active sites, thereby significantly improving the adsorption and degradation capacity for pollutants such as formaldehyde.

[0024] (3) Add a silane coupling agent to the doped and modified g-C3N4 nano-dispersion, stir at room temperature for 1.5 to 2.5 hours, and dry by rotary evaporation to obtain silane coupling agent-modified doped g-C3N4 nanosheets. The room temperature stirring time can be 1.5 hours, 2 hours, or 2.5 hours. The silane coupling agent includes, but is not limited to, one or a mixture of two of KH550, KH560, or KH570. The amount of silane coupling agent added during modification is 0.5% to 1% of the mass of the doped and modified g-C3N4 nanosheets, specifically, it can be 0.5%, 0.8%, or 1%. This modification step is the core of solving the problem of dispersing nanomaterials in coatings. The silane coupling agent molecule has a unique amphiphilic structure: the alkoxy group at one end can undergo a condensation reaction with the amino or hydroxyl groups on the surface of the g-C3N4 nanosheets after hydrolysis to form a strong chemical bond; the organic functional group at the other end has good compatibility with the organic resin in the coating. Through this "molecular bridging" effect, the originally hydrophilic and highly surface-energy g-C3N4 nanosheets are encapsulated by organic segments, reducing their surface energy. This allows them to be uniformly and stably dispersed in the coating system, avoiding the problems of decreased photocatalytic activity and rough coating surface caused by agglomeration. The stirring time of 1.5 to 2.5 hours at room temperature is set to ensure that the coupling reaction proceeds fully and completely, while avoiding the introduction of impurities or excessive solvent evaporation caused by prolonged stirring.

[0025] The doped and modified g-C3N4 nanosheets prepared through the above steps not only have excellent visible light response capabilities, but also solve the industry pain point of inorganic nanomaterials being difficult to disperse and easy to agglomerate in organic coating systems, laying a material foundation for the preparation of high-performance interior wall photocatalytic coatings.

[0026] In some embodiments, the aqueous emulsion includes, but is not limited to, one or more combinations of pure acrylic emulsion, styrene-acrylic emulsion, vinyl acetate-acrylic emulsion, and silicone-acrylic emulsion. As the film-forming substance of the coating, the aqueous emulsion directly affects the coating's water resistance, weather resistance, adhesion, and application performance. Pure acrylic emulsion possesses excellent weather resistance, gloss and color retention, and water resistance, making it suitable for indoor environments with high requirements for decoration and durability. Styrene-acrylic emulsion offers good cost-effectiveness, scrub resistance, and adhesion, and has a wide range of applications. Vinyl acetate-acrylic emulsion has a lower film-forming temperature and good application properties. Silicone-acrylic emulsion, by introducing organosilicon segments, further enhances the coating's hydrophobicity, stain resistance, and weather resistance. In practical applications, the aqueous emulsion can be flexibly selected or compounded according to the specific construction environment, performance requirements, and cost budget. The content of the aqueous emulsion can be adjusted within a certain range; specifically, the content can be 35 parts, 38 parts, 40 parts, 42 parts, or 45 parts. If the content of the aqueous emulsion is too low (less than 35 parts), there will be insufficient film-forming material, which will lead to poor coating continuity and reduced scrub resistance; if the content is too high (more than 45 parts), it will lead to reduced coating hardness and increased cost.

[0027] In some embodiments, the mass ratio of anatase to rutile in the titanium dioxide is 1:3 to 1:5, the anatase particle size is 5 to 20 nm, and the rutile particle size is 250 to 350 nm.

[0028] This invention abandons the traditional approach of using only anatase or rutile titanium dioxide in photocatalytic coatings, instead employing a composite of both crystal forms. While anatase titanium dioxide possesses extremely high photocatalytic activity, its crystal structure is relatively unstable, making it prone to crystal transformation or leading to powdering and yellowing of the coating under prolonged light exposure and complex environments, thus affecting its durability. Rutile titanium dioxide, on the other hand, while exhibiting excellent stability, has relatively weaker photocatalytic activity. This invention, by combining anatase and rutile titanium dioxide, utilizes the high activity of anatase to provide the primary adsorption and degradation sites, while leveraging the high stability of rutile as a supporting framework. This synergistic effect ensures efficient degradation of pollutants such as formaldehyde under indoor visible light, while significantly improving the coating's weather resistance, scrub resistance, and service life, thus overcoming the performance shortcomings of single-crystal titanium dioxide in applications. The preferred composite ratio of anatase to rutile is 1:3, 1:4, or 1:5. The preferred particle size for anatase titanium dioxide is 5 nm, 10 nm, 15 nm, or 20 nm, while the preferred particle size for rutile titanium dioxide is 250 nm, 300 nm, or 350 nm. Nanoscale anatase titanium dioxide has a large specific surface area, providing abundant surface hydroxyl groups and active sites, enhancing its adsorption and degradation capacity for formaldehyde molecules. Meanwhile, micron-sized rutile titanium dioxide can fill the coating framework, acting as a physical shield and support, effectively inhibiting the aggregation and photocorrosion of nanoscale anatase.

[0029] Furthermore, the calcium carbonate and talc are used as fillers to adjust the volume solids content, application viscosity, and cost of the coating. The calcium carbonate content is 20-25 parts, specifically 20, 22, 23, or 25 parts. The talc content is 10-15 parts, specifically 10, 12, 13, or 15 parts. Within the above-mentioned ratio range, the calcium carbonate and talc can effectively adjust the volume solids content and application viscosity of the coating, while also imparting good sanding and filling properties to the coating.

[0030] In some embodiments, the dispersant includes, but is not limited to, one or a combination of two of polyacrylate dispersants, polyacid copolymer dispersants, etc. These polymeric dispersants can effectively encapsulate doped and modified g-C3N4 nanosheets and titanium dioxide particles through steric hindrance and electrostatic repulsion, preventing flocculation and sedimentation in aqueous media and ensuring the stability of the coating during storage.

[0031] Furthermore, the dispersant is the same type used in the preparation method of the doped and modified g-C3N4 nanosheets.

[0032] Furthermore, the polyacrylate dispersants (ammonium salts and sodium salts) specifically include, but are not limited to, one or more combinations of BYK-191, TEGO Dispers 715W, Efka PX 4570, etc.

[0033] Furthermore, the polyacid copolymer dispersant specifically includes, but is not limited to, one or more combinations of BYK-183 / 185, Disperse-AYD EF 6080, BYK-110, TEGO Dispers 670, etc.

[0034] In some implementations, the defoamer includes, but is not limited to, one or more combinations of BYK-024, TEGO Airex 922, FoamStar SI 2210, and Wacker SE-47. The defoamer is used to eliminate bubbles generated during the preparation and application of the coating, ensuring a smooth coating free of pinholes.

[0035] In some embodiments, the film-forming aid includes, but is not limited to, one or more combinations of Optifilm 400, Texanol, and PPH (propylene glycol phenyl ether). The film-forming aid is used to lower the minimum film-forming temperature of the latex particles, ensuring that the coating forms a continuous and dense film at low temperatures.

[0036] In some preferred embodiments, the film-forming aid is a combination of Texanol and Optifilm 400, wherein the mass ratio of Texanol to Optifilm 400 is 3 to 5:2.

[0037] In another preferred embodiment, the film-forming aid is a combination of Texanol and PPH (propylene glycol phenyl ether), wherein the mass ratio of Texanol to PPH is 3~5:2.

[0038] Texanol has high film-forming efficiency, while Optifilm 400 or propylene glycol phenyl ether has lower odor and better hydrolytic stability. By compounding the two in a specific ratio, the above solutions can not only effectively reduce the minimum film-forming temperature of latex particles and ensure that the coating forms a continuous and dense film at low temperatures, but also balance the drying speed and the open time of application, reducing problems such as coating blooming or micro-cracks caused by poor film formation.

[0039] In some embodiments, the thickener includes, but is not limited to, one or more combinations of hydroxyethyl cellulose HEC 250HBR, Rohm & Haas TT-935, and BYK-425. The thickener is used to adjust the rheological behavior of the coating system, giving it good thixotropic and anti-sagging properties, facilitating application.

[0040] As another aspect of the technical solution of the present invention, it also relates to a method for preparing the aforementioned modified g-C3N4 visible light responsive interior wall photocatalytic coating, which includes: (1) Mix water, dispersant, and defoamer, and perform a first low-speed dispersion; (2) Add doped and modified g-C3N4 nanosheets to the mixture obtained in step (1) and perform a first medium-high speed dispersion; (3) Add titanium dioxide, heavy calcium carbonate and talc to the mixture obtained in step (2) in sequence, and perform a second medium-high speed dispersion until the fineness of the slurry is 30~50μm; (4) Add aqueous emulsion and film-forming aid to the slurry obtained in step (3) and perform a second low-speed dispersion; (5) Add a thickener to the mixture obtained in step (4), and after filtration, obtain the modified g-C3N4 visible light responsive interior wall photocatalytic coating.

[0041] The above-mentioned solution of the present invention effectively avoids excessive agglomeration of nanomaterials through stepwise feeding and variable speed dispersion, ensuring uniform dispersion of each component of the coating. The preparation process is simple and suitable for industrial production.

[0042] In one implementation, in step (1), the rotation speed of the first low-speed dispersion is 600~800 r / min, and the time is 4~6 min.

[0043] In one implementation method, in step (2), the rotation speed of the first high-speed dispersion is 1500~2500 r / min, and the time is 15~25 min.

[0044] In one implementation method, in step (3), the rotation speed of the second high-speed dispersion is 1500~2500 r / min, and the time is 20~40 min.

[0045] In one implementation, in step (4), the rotation speed of the second low-speed dispersion is 600~800 r / min, and the time is 10~20 min.

[0046] In one implementation method, in step (5), a thickener is added to adjust the viscosity to 90~110KU, and then filtered.

[0047] The above-mentioned solution of the present invention, by precisely controlling the dispersion speed and time at each stage, ensures the dispersion effect while avoiding emulsion demulsification and coating performance degradation.

[0048] In some more specific embodiments, the preparation method of the modified g-C3N4 visible light responsive interior wall photocatalytic coating includes the following steps: (1) Mix deionized water, dispersant, and defoamer, and disperse at low speed for 4-6 minutes; the low-speed dispersion speed is 600-800 r / min, specifically, it can be 600 r / min, 700 r / min, or 800 r / min; the dispersion time can be 4 minutes, 5 minutes, or 6 minutes. The purpose of this step is to premix the liquid phase components evenly, creating a good dispersion environment for the subsequent addition of powder; (2) Add the doped and modified g-C3N4 nanosheets and disperse them at medium to high speed for 15 to 25 minutes; the speed of the medium to high speed dispersion is 1500 to 2500 r / min, specifically, it can be 1500 r / min, 2000 r / min or 2500 r / min; the dispersion time can be 15 minutes, 20 minutes or 25 minutes. The purpose of this step is to fully disperse the doped and modified g-C3N4 nanosheets in the aqueous medium and avoid agglomeration; (3) Add titanium dioxide, heavy calcium carbonate, and talc in sequence, and disperse at medium to high speed for 20 to 40 minutes until the slurry fineness is 30 to 50 μm; the speed of medium to high speed dispersion is 1500 to 2500 r / min, specifically, it can be 1500 r / min, 2000 r / min or 2500 r / min; the dispersion time can be 20 minutes, 30 minutes or 40 minutes; the slurry fineness can be 30 μm, 40 μm or 50 μm. The purpose of this step is to fully disperse the pigments and fillers and achieve the required fineness to ensure a smooth and even coating. (4) Add the aqueous emulsion and film-forming aid, and disperse at a low speed for 10-20 minutes; the low-speed dispersion speed is 600-800 r / min, specifically, it can be 600 r / min, 700 r / min or 800 r / min; the dispersion time can be 10 minutes, 15 minutes or 20 minutes. The purpose of this step is to uniformly disperse the film-forming substance in the slurry, while avoiding high-speed shearing that damages the emulsion particles; (5) Add a thickener to adjust the viscosity to 90~110KU, and filter to obtain the modified g-C3N4 visible light responsive interior wall photocatalytic coating. The viscosity can be 90KU, 100KU or 110KU. The purpose of this step is to adjust the rheological properties of the coating to meet the construction requirements.

[0049] As another aspect of the technical solution of this invention, it also relates to the application of the aforementioned modified g-C3N4 visible light responsive photocatalytic coating for interior walls. Specifically, it includes applications in the field of formaldehyde removal or air purification on indoor walls, and can also be applied to visible light responsive photocatalytic systems.

[0050] The g-C3N4 nanosheets modified by this invention exhibit excellent visible light response performance, efficiently degrading volatile organic compounds such as formaldehyde under natural indoor light. They also possess formaldehyde removal, odor neutralization, and antibacterial functions without secondary pollution. The raw materials used in the coating preparation of this invention are inexpensive and readily available, and the process is simple, making it widely applicable to interior wall coatings in residences, offices, and other spaces.

[0051] The above solution expands the application scenarios of the photocatalytic coating and provides an environmentally friendly and efficient means of indoor air purification.

[0052] To clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the technical solutions of the present invention will be further described and illustrated below through specific embodiments. It should be understood that the specific embodiments described herein are only for helping to understand the present invention and are not intended to limit the present invention. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commonly used in the art, and the methods used in the embodiments are all conventional methods in the art. Parts not mentioned in the present invention can be implemented by adopting or referencing existing technologies.

[0053] Example 1 1. Preparation of doped and modified g-C3N4 nanosheets: (1) Melamine, thiourea and ammonium dihydrogen phosphate are mixed and compounded in a ratio of 95:3:2. After thorough mixing, the mixture is placed in a crucible, covered, and placed in a muffle furnace. The temperature is raised to 500°C at a rate of 3°C / min and kept at that temperature for 5 hours. After natural cooling, the mixture is ground to obtain doped and modified g-C3N4 powder. (2) First, add 1% dispersant (BYK-191) to anhydrous ethanol and stir to mix. Then, add the doped and modified g-C3N4 powder at a solid-liquid ratio of 1g:150mL, stir at 600r / min for 40 minutes, then sonicate for 3 hours, then centrifuge to remove large particles, and take the supernatant to obtain the doped and modified g-C3N4 nano dispersion. (3) Add 0.5% KH550 silane coupling agent to the doped and modified g-C3N4 nano-dispersion, stir at room temperature for 1.5 hours, and dry by rotary evaporation to obtain silane coupling agent modified doped g-C3N4 nanosheets.

[0054] 2. The preparation steps of the modified g-C3N4 visible light responsive interior wall photocatalytic coating are as follows: (1) Mix 12 parts of deionized water, 0.3 parts of BYK-191 dispersant, and 0.1 parts of BYK-024 defoamer, and disperse at a low speed of 600 r / min for 6 minutes; (2) Add 2 parts of doped and modified g-C3N4 nanosheets and disperse at a medium-high speed of 1500 r / min for 25 minutes; (3) Add 15 parts of anatase-rutile titanium dioxide with a composite ratio of 1:3, wherein the anatase particle size is 5 nm, the rutile particle size is 250 nm, 25 parts of heavy calcium carbonate, and 10 parts of talc powder, and disperse at medium-high speed of 2500 r / min for 20 minutes until the fineness of the slurry is 30 μm. (4) Add 35 parts of pure acrylic aqueous emulsion and 1 part of film-forming aid with a combination ratio of Texanol:Optifilm 400 of 3:2, and disperse at a low speed of 600r / min for 20 minutes; (5) Add 0.2 parts of hydroxyethyl cellulose HEC 250HBR thickener to adjust the viscosity to 90KU, and filter to obtain photocatalytic coating.

[0055] Performance testing: The formaldehyde degradation rate of this photocatalytic coating under indoor natural light is 0.15 mg. m - ² h - ¹, No delamination after 6 months of storage, coating whiteness of 88, and 3500 washes resistance.

[0056] Example 2 1. Preparation of doped and modified g-C3N4 nanosheets: (1) After mixing cyanuric acid, thioacetamide and phosphoric acid in a ratio of 97:1:2, the mixture is placed in a crucible, covered, and placed in a muffle furnace. The temperature is raised to 600°C at a rate of 5°C / min and held for 3 hours. After natural cooling, the mixture is ground to obtain doped and modified g-C3N4 powder. (2) First, add 3% dispersant (TEGO Dispers 715W) to anhydrous ethanol and stir to mix. Then, add the doped and modified g-C3N4 powder at a solid-liquid ratio of 3g:150mL, stir at 800r / min for 20 minutes, then sonicate for 6 hours, then centrifuge to remove large particles, and take the supernatant to obtain the doped and modified g-C3N4 nano-dispersion. (3) Add 1% KH570 silane coupling agent to the doped and modified g-C3N4 nano-dispersion, stir at room temperature for 2.5 hours, and dry by rotary evaporation to obtain silane coupling agent modified doped g-C3N4 nanosheets.

[0057] 2. The preparation steps of the modified g-C3N4 visible light responsive interior wall photocatalytic coating are as follows: (1) Mix 8 parts of deionized water, 0.5 parts of TEGO Dispers 715W dispersant, and 0.2 parts of TEGO Airex 922 defoamer, and disperse at a low speed of 800r / min for 4 minutes; (2) Add 1 part of doped modified g-C3N4 nanosheets and disperse at medium-high speed of 2500 r / min for 15 minutes; (3) Add 20 parts of anatase-rutile titanium dioxide with a composite ratio of 1:5, wherein the anatase particle size is 20 nm, the rutile particle size is 350 nm, 20 parts of heavy calcium carbonate and 15 parts of talc, and disperse at 1500 r / min at medium-high speed for 40 minutes until the slurry fineness is 50 μm. (4) Add 45 parts of styrene-acrylic aqueous emulsion and 2 parts of film-forming aid with a combination ratio of Texanol:PPH of 5:2, and disperse at a low speed of 800 r / min for 10 minutes. (5) Add 0.4 parts of Rohm & Haas TT-935 thickener to adjust the viscosity to 110 KU, and filter to obtain photocatalytic coating.

[0058] Performance testing: The formaldehyde degradation rate of this photocatalytic coating under indoor natural light is 0.12 mg. m - ² h - ¹, No delamination after 6 months of storage, coating whiteness of 86, and resistance to 3200 scrub cycles.

[0059] Example 3 1. Preparation of doped and modified g-C3N4 nanosheets: (1) Mix melamine cyanurate, dibenzothiophene and boric acid in a ratio of 96:2:2 and mix thoroughly. Place the mixture in a crucible, cover it, and place it in a muffle furnace. Heat the mixture to 550°C at a heating rate of 4°C / min and keep it at that temperature for 4 hours. After natural cooling, grind the mixture to obtain doped and modified g-C3N4 powder. (2) First, add 2% dispersant (Disperse-AYD EF 6080) to anhydrous ethanol and stir to mix. Then, add the doped and modified g-C3N4 powder at a solid-liquid ratio of 2g:150mL, stir at a low speed of 700r / min for 30 minutes, then sonicate for 4 hours, then centrifuge to remove large particles, and take the supernatant to obtain the doped and modified g-C3N4 nano dispersion. (3) Add 0.8% KH560 silane coupling agent to the doped and modified g-C3N4 nano-dispersion, stir at room temperature for 2 hours, and dry by rotary evaporation to obtain silane coupling agent modified doped g-C3N4 nanosheets.

[0060] 2. The preparation steps of the modified g-C3N4 visible light responsive interior wall photocatalytic coating are as follows: (1) Mix 10 parts of deionized water, 0.4 parts of Disperse-AYD EF 6080 dispersant, and 0.15 parts of Wacker SE-47 defoamer, and disperse at a low speed of 700 r / min for 5 minutes; (2) Add 1.5 parts of doped and modified g-C3N4 nanosheets and disperse at a medium-high speed of 2000 r / min for 20 minutes; (3) Add 18 parts of anatase-rutile titanium dioxide with a composite ratio of 1:4, wherein the anatase particle size is 10 nm, the rutile particle size is 300 nm, 23 parts of heavy calcium carbonate, and 12 parts of talc, and disperse at 2000 r / min at medium-high speed for 30 minutes until the slurry fineness is 40 μm. (4) Add 40 parts of silicone-acrylic aqueous emulsion and 1.5 parts of film-forming aid with a combination ratio of Texanol:Optifilm 400 of 4:2, and disperse at a low speed of 700 r / min for 15 minutes; (5) Add 0.3 parts of BYK-425 thickener to adjust the viscosity to 100KU, and filter to obtain photocatalytic coating.

[0061] Performance testing: The formaldehyde degradation rate of this photocatalytic coating under indoor natural light is 0.16 mg. m - ² h - ¹, No delamination after 6 months of storage, coating whiteness of 89, and resistance to 3400 scrub cycles.

[0062] Comparative Example 1 The difference between this comparative example and Example 1 is that no doped and modified g-C3N4 nanosheets were added during the preparation of the coating. The remaining components and preparation process are the same as in Example 1.

[0063] Performance test: Formaldehyde degradation rate is only 0.02mg m - ² h - ¹, No actual formaldehyde removal effect.

[0064] Comparative Example 2 The difference between this comparative example and Example 1 is that, in preparing the coating, g-C3N4 nanosheets without silane coupling agent modification were used instead of the doped g-C3N4 nanosheets. The remaining components and preparation process are the same as in Example 1.

[0065] Performance testing: After one month of storage, the paint showed signs of stratification and sedimentation, with granular protrusions appearing on the coating surface. The formaldehyde degradation rate was 0.06 mg / L. m - ² h - ¹.

[0066] Comparative Example 3 The difference between this comparative example and Example 1 is that: when preparing the doped modified g-C3N4 nanosheets, ammonium dihydrogen phosphate was not added in step (1), that is, only sulfur doping was used.

[0067] Comparative Example 4 The difference between this comparative example and Example 1 is that thiourea was not added in step (1) when preparing the doped modified g-C3N4 nanosheets, i.e., only phosphorus was doped.

[0068] Tests showed that in Comparative Examples 3 and 4, the doping with sulfur or phosphorus atoms could only regulate the edge electronic structure, slightly narrow the band gap, and only have a small number of lattice vacancies. The carrier separation ability was limited, and electron-hole recombination was prone to occur. The visible light response range was narrow, and the activity improvement was weak.

[0069] In addition, the inventors of this case also conducted experiments with other raw materials, process operations, and process conditions described in this specification, referring to the aforementioned embodiments, and obtained relatively ideal results in all cases.

[0070] All aspects, embodiments, features, and examples of this invention are to be regarded as illustrative in all respects and are not intended to limit the invention, the scope of which is defined only by the claims. Other embodiments, modifications, and uses will become apparent to those skilled in the art without departing from the spirit and scope of the invention as claimed.

[0071] The use of headings and sections in this invention is not intended to limit the invention; each section can be applied to any aspect, embodiment or feature of the invention.

[0072] Throughout this invention, wherever a composition is described as having, containing, or including specific components, or wherever a process is described as having, containing, or including specific process steps, it is contemplated that the compositions taught in this invention are also substantially composed of or comprised of the described components, and that the processes taught in this invention are also substantially composed of or comprised of the described process steps.

[0073] Although the invention has been described with reference to illustrative embodiments, those skilled in the art will understand that various other changes, omissions, and / or additions can be made without departing from the spirit and scope of the invention, and that elements of the embodiments can be substituted with substantially equivalents. Furthermore, many modifications can be made without departing from the scope of the invention to adapt particular situations or materials to the teachings of the invention. Therefore, this invention is not intended to be limited to the specific embodiments disclosed for carrying out the invention, but rather is intended to encompass all embodiments falling within the scope of the appended claims. Moreover, unless specifically stated otherwise, any use of the terms first, second, etc., does not indicate any order or importance, but is used to distinguish one element from another.

Claims

1. A modified g-C3N4 visible light responsive photocatalytic coating for interior walls, characterized in that, include: The mixture comprises an aqueous emulsion, titanium dioxide, heavy calcium carbonate, talc, doped and modified g-C3N4 nanosheets, dispersant, defoamer, film-forming aid, thickener, and water; wherein the doped and modified g-C3N4 nanosheets include g-C3N4 nanosheets doped and modified with silane coupling agents, and the titanium dioxide is anatase composite rutile.

2. The modified g-C3N4 visible light responsive interior wall photocatalytic coating according to claim 1, characterized in that, It includes the following components by weight: 35-45 parts aqueous emulsion, 15-20 parts titanium dioxide, 20-25 parts heavy calcium carbonate, 10-15 parts talc, 1-2 parts doped and modified g-C3N4 nanosheets, 0.3-0.5 parts dispersant, 0.1-0.2 parts defoamer, 1-2 parts film-forming aid, 0.2-0.4 parts thickener, and 8-12 parts water.

3. The modified g-C3N4 visible light responsive interior wall photocatalytic coating according to claim 1, characterized in that, The preparation method of the doped and modified g-C3N4 nanosheets includes: mixing the precursor raw materials and calcining them, then ultrasonically exfoliating them, and then modifying them with a silane coupling agent to obtain the doped and modified g-C3N4 nanosheets. And / or, the thickness of the doped and modified g-C3N4 nanosheets is 5~20 nm, and the sheet diameter is 200~800 nm.

4. The modified g-C3N4 visible light responsive interior wall photocatalytic coating according to claim 3, characterized in that, The preparation method of the doped and modified g-C3N4 nanosheets includes: After the precursor raw materials are mixed, they are heated to 500-600℃ at a heating rate of 3-5℃ / min and calcined for 3-5h. After cooling, they are ground to obtain doped g-C3N4 powder. Mix the doped g-C3N4 powder, dispersant and solvent, stir for 20-40 min, and then sonicate for 3-6 h to obtain the doped g-C3N4 nano-dispersion. A silane coupling agent was added to the doped g-C3N4 nanodispersion and stirred at room temperature for 1.5 to 2.5 h to obtain doped and modified g-C3N4 nanosheets.

5. The modified g-C3N4 visible light responsive interior wall photocatalytic coating according to claim 3 or 4, characterized in that: The precursor raw material includes a mixture of three compound raw materials: a first raw material, a second raw material, and a third raw material. The first raw material includes one or more of melamine, urea, cyanuric acid, and melamine cyanurate. The second raw material includes one or more of sulfur powder, thiourea, thioacetamide, melamine thiocyanate, and dibenzothiophene. The third raw material includes one or more of ammonium dihydrogen phosphate, phosphoric acid, hydrogen peroxide, and boric acid. Preferably, the mass ratio of the first raw material, the second raw material and the third raw material is (95~97):(1~3):

2.

6. The modified g-C3N4 visible light responsive interior wall photocatalytic coating according to claim 4, characterized in that: The solvent includes ethanol; and / or the dispersant accounts for 1% to 3% of the volume of the solvent, and the solid-liquid ratio of the doped g-C3N4 powder to the solvent is 1 to 3 g: 150 mL. And / or, the silane coupling agent includes one or more combinations of KH550, KH560, and KH570; And / or, the amount of the silane coupling agent added is 0.5% to 1% of the mass of the doped and modified g-C3N4 nanosheets.

7. The modified g-C3N4 visible light responsive interior wall photocatalytic coating according to claim 1 or 2, characterized in that: The aqueous emulsion includes one or more combinations of pure acrylic emulsion, styrene-acrylic emulsion, vinyl acetate-acrylic emulsion, and silicone-acrylic emulsion; And / or, the mass ratio of anatase to rutile in the titanium dioxide is 1:3 to 1:5, the anatase particle size is 5 to 20 nm, and the rutile particle size is 250 to 350 nm; And / or, the dispersant comprises one or a combination of two of polyacrylate dispersants and polyacid copolymer dispersants; preferably, the polyacrylate dispersant comprises one or a combination of BYK-191, TEGO Dispers 715W, and Efka PX 4570; preferably, the polyacid copolymer dispersant comprises one or a combination of BYK-183 / 185, Disperse-AYD EF 6080, BYK-110, and TEGO Dispers 670. And / or, the defoamer includes one or more combinations of BYK-024, TEGO Airex 922, FoamStar SI 2210, and Wacker SE-47; And / or, the film-forming aid comprises one or more combinations of Optifilm 400, Texanol, and propylene glycol phenyl ether; preferably, the film-forming aid comprises a combination of Texanol and Optifilm 400, wherein the mass ratio of Texanol to Optifilm 400 is 3~5:2; preferably, the film-forming aid comprises a combination of Texanol and propylene glycol phenyl ether, wherein the mass ratio of Texanol to propylene glycol phenyl ether is 3~5:2; And / or, the thickener comprises one or more combinations of hydroxyethyl cellulose HEC 250HBR, Rohm & Haas TT-935, and BYK-425.

8. The preparation method of the modified g-C3N4 visible light responsive interior wall photocatalytic coating as described in any one of claims 1 to 7, characterized in that, include: (1) Mix water, dispersant, and defoamer, and perform a first low-speed dispersion; (2) Add doped and modified g-C3N4 nanosheets to the mixture obtained in step (1) and perform a first medium-high speed dispersion; (3) Add titanium dioxide, heavy calcium carbonate and talc to the mixture obtained in step (2) in sequence, and perform a second medium-high speed dispersion until the fineness of the slurry is 30~50μm; (4) Add aqueous emulsion and film-forming aid to the slurry obtained in step (3) and perform a second low-speed dispersion; (5) Add a thickener to the mixture obtained in step (4), and after filtration, obtain the modified g-C3N4 visible light responsive interior wall photocatalytic coating.

9. The preparation method according to claim 8, characterized in that: In step (1), the rotation speed of the first low-speed dispersion is 600~800 r / min, and the time is 4~6 min; And / or, in step (2), the rotation speed of the first high-speed dispersion is 1500~2500 r / min and the time is 15~25 min; And / or, in step (3), the rotation speed of the second high-speed dispersion is 1500~2500 r / min, and the time is 20~40 min; And / or, in step (4), the rotation speed of the second low-speed dispersion is 600~800 r / min and the time is 10~20 min; And / or, in step (5), add a thickener to adjust the viscosity to 90~110KU, and then filter.

10. The application of the modified g-C3N4 visible light responsive interior wall photocatalytic coating according to any one of claims 1 to 7 in the field of formaldehyde removal or air purification on interior walls.