A type of N-doped TiO 2 -BiVO 4 Heterojunction photocatalytic coatings, their preparation methods and applications

Abstract

This invention provides an N-doped TiO₂ 2 -BiVO 4 This invention relates to heterojunction photocatalytic coatings, their preparation methods, and applications, belonging to the field of photocatalytic materials technology. The invention achieves nitrogen doping through nitrogen source pyrolysis, forming a N-doped Bi-Ti heterojunction. Furthermore, by optimizing the Bi:Ti molar ratio, a tight heterojunction interface can be formed, redshifting the light absorption edge to 600 nm and improving carrier separation efficiency. N doping introduces intermediate energy levels, resulting in BiVO₄… 4 By broadening the light response range, the two work together to achieve a net formaldehyde degradation rate of 78% in 24 hours, while also solving the problems of low visible light utilization and poor adhesion of existing photocatalytic coatings.

Description

A photocatalytic coating of N-doped TiO2-BiVO4 heterojunction, its preparation method and application Technical Field

[0001] This invention relates to the field of photocatalytic materials technology, and in particular to an N-doped TiO2-BiVO4 heterojunction photocatalytic coating, its preparation method, and its application. Background Technology

[0002] With the use of various plywood, paints, adhesives, and other materials in interior decoration, large amounts of toluene and formaldehyde are continuously released into newly renovated homes. Depending on the different decoration materials and processes, formaldehyde and toluene will continue to be released for 3 to 15 years. The release of formaldehyde and toluene due to interior decoration has attracted widespread social attention. Indoor formaldehyde concentrations exceeding 0.08 ppm can cause eye and nose irritation, and skin contact can easily cause symptoms such as dermatitis and urticaria. Short-term exposure to high concentrations of formaldehyde can lead to dizziness, headaches, and even difficulty breathing, while long-term exposure to formaldehyde concentrations above 1 ppm increases the risk of nasopharyngeal carcinoma and leukemia. Toluene exposure at 50 ppm can cause neurotoxicity, severely inhibiting the central nervous system and causing dizziness and headaches. Short-term exposure to large amounts may lead to coma or even respiratory failure.

[0003] Currently, among the commonly used methods for formaldehyde treatment, traditional physical adsorption carries the risk of secondary release after saturation, requires frequent replacement, and cannot decompose pollutants; chemical oxidation, on the other hand, produces byproducts (such as O3, NO). x It is harmful to the human respiratory system and cannot operate for a long time; while the activity of biodegradable microorganisms is limited by temperature and humidity, resulting in low processing efficiency (<30%) and long cycle.

[0004] The technological advantage of photocatalysis in the treatment of volatile organic compounds (VOCs) lies in the fact that photocatalytic materials generate photo-generated holes (h) + The hydroxyl radical (·OH) can break the benzene ring structure of toluene (C6H5-CH3) and the C=O bond of formaldehyde, ultimately converting them into CO2 and H2O. This avoids the accumulation of intermediate by-products (such as phenol and formic acid), and is suitable for home environments. It does not require high-temperature / high-pressure equipment, and its energy consumption cost is lower than that of thermal catalysis.

[0005] Traditional photocatalytic materials (such as TiO2) are highly dependent on ultraviolet light, absorbing almost only ultraviolet light (<387 nm), making them difficult to excite with indoor fluorescent lamps. Furthermore, the photogenerated electron-hole pairs in traditional photocatalytic materials are prone to recombination, resulting in low degradation efficiency. Therefore, special treatment is required for traditional photocatalytic materials.

[0006] To achieve this goal, existing improved solutions (such as BiVO4 / TiO2 heterojunctions), such as the patent application "A Preparation Method of a Photocatalyst for the Photodegradation of Organic Pollutants" (application number 201611166581.1), disclose a method for preparing a BiVO4-TiO2-graphene photocatalyst. However, this method not only results in extremely low graphene yield, making it unsuitable for large-scale production, but also incurs excessively high costs. Furthermore, the drilling process on the ceramic substrate damages the ceramic substrate, making it unsuitable for traditional building materials. Additionally, the hydrolysis of Bi(NO3)3 in ethanol releases H2O. + Nitric acid causes rapid hydrolysis of tetrabutyl titanate, potentially leading to premature gelation of the sol and affecting impregnation uniformity. During calcination at 350℃, the temperature is too low to allow TiO2 to transform into the anatase form, and it falls outside the optimal formation temperature range of 400-500℃ for BiVO4. Furthermore, the high-temperature, oxygen-rich environment during calcination causes graphene to oxidize and decompose. For example, the patent application "A Method for Preparing a BiVO4-Supported Mixed-Phase TiO2 Visible Light Composite Photocatalyst" (application number 201710829743.3) discloses a method for preparing a BiVO4-supported TiO2 mesoporous microsphere structure photocatalyst, but it first calcines the TiO2, failing to form a heterojunction structure with BiVO4 in solution, resulting in low photocatalytic performance. However, while the above technical solutions expand the visible light response range, they still have the following shortcomings: the heterojunction interface is not tightly bonded, resulting in insufficient carrier transport efficiency; the visible light absorption enhancement is limited; and the coating has poor adhesion to the substrate, making it prone to peeling. Summary of the Invention

[0007] The purpose of this invention is to provide an N-doped TiO2-BiVO4 heterojunction photocatalytic coating, its preparation method, and its application. This photocatalytic coating exhibits tight bonding at the heterojunction interface, high carrier transport efficiency, a wide light response range, strong adhesion between the coating and the substrate, and high efficiency in degrading toluene and formaldehyde under visible light irradiation. The preparation process is simple and feasible, and it has broad prospects in the fields of ceramic tiles, walls, and glass.

[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0009] This invention provides a method for preparing an N-doped TiO2-BiVO4 heterojunction photocatalytic coating, comprising the following steps:

[0010] The chelating agent, titanium source, and organic solvent are mixed to obtain a mixture;

[0011] The mixture was then mixed with an aqueous alcohol solution and a nitrogen source to obtain an N-TiO2 precursor solution;

[0012] Bismuth source, vanadium source and acid solution are mixed to obtain BiVO4 precursor solution;

[0013] The N-TiO2 precursor solution and the BiVO4 precursor solution are mixed, and the resulting N-TiO2-BiVO4 slurry is mixed with a binder to obtain a mixed slurry.

[0014] The mixed slurry was screen-printed onto the substrate surface, and then pre-dried and annealed sequentially to obtain an N-doped TiO2-BiVO4 heterojunction photocatalytic coating.

[0015] The screen printing is performed by scraping in a single direction.

[0016] Preferably, the chelating agent includes acetylacetone, ethylene glycol, citric acid, or oxalic acid; the titanium source includes tetrabutyl titanate, tetraisopropyl titanate, or titanium acetylacetone; and the nitrogen source includes urea, melamine, or ethylenediamine.

[0017] The volume ratio of the chelating agent to the titanium source is 1~5:3~15;

[0018] The ratio of titanium source to nitrogen source is 3~15 mL:0.1~5 g;

[0019] The mixture is mixed with the alcohol-water solution and the nitrogen source at room temperature for 20-100 minutes.

[0020] Preferably, the bismuth source includes bismuth oxide or bismuth nitrate; the vanadium source includes ammonium metavanadate or vanadium pentoxide.

[0021] The mass ratio of the bismuth source to the vanadium source is 1.5~2:0.5~1.2.

[0022] Preferably, the acid solution comprises an aqueous solution of nitric acid; the concentration of the acid solution is 4~6 mol / L.

[0023] Preferably, the molar ratio of bismuth in the bismuth source to titanium in the titanium source is 1.5:1 to 1:3; and the volume ratio of the N-TiO2 precursor solution to the BiVO4 precursor solution is 1.2 to 3:2 to 5.

[0024] Preferably, the binder comprises terpineol and methylcellulose; the ratio of terpineol to methylcellulose is 10~40mL:0.5~3g.

[0025] Preferably, the volume ratio of the N-TiO2-BiVO4 slurry to the binder is 5~20:1; the area ratio of the mixed slurry on the substrate surface is 10~25%.

[0026] Preferably, the substrate is impregnated with anhydrous ethanol before use; the annealing treatment is performed at a temperature of 500~550℃ for 2~3 hours.

[0027] The present invention provides an N-doped TiO2-BiVO4 heterojunction photocatalytic coating prepared by the preparation method described above.

[0028] This invention provides the application of the N-doped TiO2-BiVO4 heterojunction photocatalytic coating described above in ceramic tiles, walls, or glass.

[0029] This invention provides a method for preparing an N-doped TiO2-BiVO4 heterojunction photocatalytic coating. The invention achieves nitrogen doping through nitrogen source pyrolysis, forming an N-doped Bi-Ti heterojunction. By optimizing the Bi:Ti molar ratio, nitrogen doping aligns the energy bands of TiO2 and BiVO4, reducing the interfacial barrier and passivating interfacial defects, thereby reducing charge trapping. N doping also increases carrier concentration and induces a built-in electric field at the interface. Furthermore, N doping significantly reduces surface cracks, forming a tight interface with a heterojunction, redshifting the light absorption edge to 600 nm, and improving carrier separation efficiency. N doping introduces intermediate energy levels, while BiVO4 broadens the photoresponse range. The synergistic effect of both increases the 24-hour formaldehyde degradation rate (78%) by 5 times compared to undoped titanium dioxide (15.3%).

[0030] This invention improves the screen printing process by applying the coating ≥50 times in a single direction (from the coated area to the uncoated area) while the substrate is impregnated with anhydrous ethanol and combined with gradient drying (pre-drying at 60℃ + annealing at 500℃). The addition of anhydrous ethanol improves the problem of uneven printing caused by the liquid tension of aqueous solutions in traditional screen printing methods. The multiple coatings in a single direction ensure the uniformity of the coating, solve the problem of coating cracking, and reduce the surface roughness to <50 nm. The annealing treatment enables the coating to form a chemical bond with the surface of building materials, and the adhesion reaches the GB / T 9266-2009 standard 5B level. After 4 cycles of use, the degradation efficiency still remains at 70%, making it suitable for a wide range of ceramic products.

[0031] This invention optimizes the sol-gel method by using a chelating agent to control the hydrolysis rate of the titanium source, thereby preventing premature gelation of the sol under acidic conditions of the Ti source and ensuring coating uniformity.

[0032] This invention solves the problems of low visible light utilization and poor adhesion of existing photocatalytic coatings by optimizing material composition (nitrogen doping + heterojunction), innovating process (directional coating + annealing) and focusing on application scenarios (ceramic substrate). At the same time, the film preparation cost is low and the process is simple, which has significant technological progress and market application value. Attached Figure Description

[0033] Figure 1 shows SEM images of the N-TiO2 thin film on the ceramic surface after annealing at 500℃ for 2 hours in Example 1; where (a) is 10 μm and (b) is 5 μm.

[0034] Figure 2 shows SEM images of the TiO2 film on the ceramic surface after annealing at 500℃ for 2h in Comparative Example 1, where (a) is 10μm and (b) is 5μm.

[0035] Figure 3 is a comparison of the formaldehyde degradation efficiency of the TiO2 film on the ceramic surface in Comparative Example 1 and the N-TiO2 film on the ceramic surface in Example 1.

[0036] Figure 4 is a comparison of the formaldehyde degradation of mixed slurries with different Bi:Ti ratios in Example 1 and Comparative Examples 2-3;

[0037] Figure 5 shows the degradation effect of Rhodamine B on the N-TiO2 film after annealing at 450℃ in Comparative Example 4, where (a) is Rhodamine B before degradation and (b) is Rhodamine B after degradation.

[0038] Figure 6 shows the degradation effect of Rhodamine B on the N-TiO2 film after annealing at 500℃ in Example 1; where (a) is Rhodamine B before degradation and (b) is Rhodamine B after degradation.

[0039] Figure 7 shows the formaldehyde degradation effect of the photocatalytic coating in Example 1 within 24 hours;

[0040] Figure 8 shows the formaldehyde cyclic degradation effect of the photocatalytic coating in Example 1 at different times. Detailed Implementation

[0041] In this invention, unless otherwise specified, the raw materials or reagents required for preparation are all commercially available products well known to those skilled in the art.

[0042] This invention provides a method for preparing an N-doped TiO2-BiVO4 heterojunction photocatalytic coating, comprising the following steps:

[0043] The chelating agent, titanium source, and organic solvent are mixed to obtain a mixture;

[0044] The mixture was then mixed with an aqueous alcohol solution and a nitrogen source to obtain an N-TiO2 precursor solution;

[0045] Bismuth source, vanadium source and acid solution are mixed to obtain BiVO4 precursor solution;

[0046] The N-TiO2 precursor solution and the BiVO4 precursor solution are mixed, and the resulting N-TiO2-BiVO4 slurry is mixed with a binder to obtain a mixed slurry.

[0047] The mixed slurry was screen-printed onto the substrate surface, and then pre-dried and annealed sequentially to obtain an N-doped TiO2-BiVO4 heterojunction photocatalytic coating.

[0048] The screen printing is performed by scraping in a single direction.

[0049] In this invention, the chelating agent preferably includes acetylacetone, ethylene glycol, citric acid or oxalic acid; the titanium source preferably includes tetrabutyl titanate, tetraisopropyl titanate or titanium acetylacetone; the volume ratio of the chelating agent to the titanium source is preferably 1~5:3~15, more preferably 2~3:5~10, and even more preferably 2.5:8.55.

[0050] In this invention, the organic solvent preferably includes anhydrous ethanol; the volume ratio of the organic solvent to the chelating agent is preferably 15~50:1~5, more preferably 20~35:2~3, and even more preferably 30:2.5.

[0051] In this invention, the chelating agent is preferably added to an organic solvent, and after magnetic stirring for 10-40 min (more preferably 10-20 min), a titanium source is added, and magnetic stirring is continued for 10-60 min, more preferably 30 min, to obtain a mixture.

[0052] In this invention, the nitrogen source preferably includes urea, melamine or ethylenediamine; the ratio of the titanium source to the nitrogen source is preferably 3~15 mL:0.1~5g, more preferably 5~10 mL:0.5~3g, and even more preferably 8.55mL:0.753g.

[0053] In this invention, the alcohol used in the alcohol-water solution is preferably anhydrous ethanol; preferably, 20-30 mL (more preferably 25 mL) of alcohol is added to deionized water to 20-60 mL (more preferably 30 mL) to obtain the alcohol-water solution.

[0054] In this invention, an aqueous alcohol solution is preferably added to a mixture, followed by a nitrogen source, and the mixture is stirred to obtain an N-TiO2 precursor solution. The mixture is then mixed with the aqueous alcohol solution and the nitrogen source at room temperature, and the mixing time is preferably 20-100 min, more preferably 30-60 min. This invention does not impose any specific limitations on the amount of the aqueous alcohol solution; it can be adjusted according to requirements.

[0055] In this invention, the concentration of Ti element in the N-TiO2 precursor solution is preferably 0.1~1 mol / L, more preferably 0.2~0.8 mol / L, and even more preferably 0.35~0.5 mol / L.

[0056] In this invention, the bismuth source preferably includes bismuth oxide or bismuth nitrate; the vanadium source preferably includes ammonium metavanadate or vanadium pentoxide; the mass ratio of the bismuth source to the vanadium source is preferably 1.5~2:0.5~1.2; more preferably 1.6~1.9:0.6~1.0; and even more preferably 1.86:0.936.

[0057] In this invention, the acid solution preferably comprises an aqueous solution of nitric acid, and the concentration of the acid solution is preferably 4-6 mol / L, more preferably 4.5-5.5 mol / L, and even more preferably 5.0-5.2 mol / L. This invention does not impose any particular limitation on the amount of acid solution used, as long as sufficient quantities are used to completely mix and react completely with the bismuth source and vanadium source.

[0058] In this invention, bismuth and vanadium sources are preferably added to an acid solution and magnetically stirred for 30 minutes to obtain a BiVO4 precursor solution.

[0059] In this invention, the concentration of Bi element in the BiVO4 precursor solution is preferably 0.1~1 mol / L, more preferably 0.1~0.8 mol / L, and even more preferably 0.2~mol / L.

[0060] In this invention, the molar ratio of bismuth in the bismuth source to titanium in the titanium source is preferably 1.5:1 to 1:3, and more preferably 1:1.

[0061] In this invention, the volume ratio of the N-TiO2 precursor solution to the BiVO4 precursor solution is 1.2~3:2~5, more preferably 1.5~2.5:3~4, and even more preferably 2:3.6.

[0062] In this invention, the binder preferably comprises terpineol and methylcellulose; the ratio of terpineol to methylcellulose is 10-40 mL:0.5-3 g, more preferably 15-30 mL:0.8-2 g, and even more preferably 25 mL:1 g. Preferably, the binder is obtained by magnetically stirring the terpineol and methylcellulose in the specified mass ratio for 12-72 h, more preferably 36 h.

[0063] In this invention, the volume ratio of the N-TiO2-BiVO4 slurry to the binder is preferably 5~20:1, more preferably 10~15:1. Preferably, the binder and N-TiO2-BiVO4 slurry are mixed according to the volume ratio and then magnetically stirred for 20~30 minutes to obtain the mixed slurry.

[0064] In this invention, the substrate preferably comprises ceramic or glass. Before use, the substrate is preferably placed in an ultrasonic cleaner and cleaned at a water temperature of 20~60℃ (more preferably 30~50℃) for 10~60 minutes (more preferably 30~50 minutes), then removed and dried, and then treated with anhydrous ethanol.

[0065] In this invention, the area ratio of the mixed slurry on the substrate surface is preferably 10-25%, more preferably 15-20%; this invention does not have a special limitation on the area of ​​the substrate, which can be adjusted according to needs; in the embodiment of this invention, it is specifically a 5cm×5cm ceramic tile.

[0066] In this invention, the screen is preferably placed on a dried substrate. Anhydrous ethanol is dropped onto the substrate surface and then completely covered by screen printing. Excess anhydrous ethanol is scraped off, and a mixed slurry is then coated on the substrate surface. The slurry is scraped until the surface is uniform, dried, and then the screen is separated from the substrate. The substrate is then placed in a drying oven for pre-drying and then placed in a muffle furnace for annealing. The substrate is then allowed to cool naturally in the furnace to obtain a photocatalytic coating.

[0067] Excessive ethanol will reduce the concentration of the mixed slurry. In this invention, after a small amount of ethanol is dropped onto the substrate, the excess ethanol needs to be scraped off using screen printing.

[0068] The present invention wets the surface of the substrate with anhydrous ethanol after drying, and adds a mixed slurry while the substrate is wetted, which can significantly reduce the surface tension of the liquid, so that the uniformity of the photocatalytic reagent is not affected when the screen is separated from the substrate surface.

[0069] The present invention does not have a special limitation on the amount of anhydrous ethanol used, as long as it fully wets the substrate.

[0070] In this invention, the coating thickness is preferably 5~50μm, more preferably 15~30μm.

[0071] In this invention, the screen printing is performed by scraping in a single direction, preferably ≥50 times, more preferably 50-60 times.

[0072] In this invention, the pre-drying temperature is preferably 60°C, and the time is preferably 20-40 min, more preferably 30 min.

[0073] In this invention, the annealing temperature is preferably 500~550℃, more preferably 500~520℃, and the time is preferably 2~3 h, more preferably 2 h; the heating rate to the annealing temperature is preferably 3~5℃ / min, more preferably 4℃ / min.

[0074] The present invention provides an N-doped TiO2-BiVO4 heterojunction photocatalytic coating prepared by the preparation method described above.

[0075] This invention provides the application of the N-doped TiO2-BiVO4 heterojunction photocatalytic coating described above in ceramic tiles, walls, or glass. This invention does not impose any particular limitation on the method of application; any method well-known in the art can be used.

[0076] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0077] Unless otherwise specified, the experimental methods described in the various embodiments of this invention are conventional methods; unless otherwise specified, the reagents and raw materials described below are all commercially available.

[0078] Example 1

[0079] Measure 2.5 mL of acetylacetone and 30 mL of anhydrous ethanol, mix them thoroughly, and then stir on a magnetic stirrer for 10 min. After stirring thoroughly, add 8.55 mL of tetrabutyl titanate and stir on a magnetic stirrer for 30 min to obtain a mixture.

[0080] Measure 25 mL of anhydrous ethanol, add deionized water to make 30 mL of ethanol solution, add the ethanol solution to the above mixture, then add 0.753 g of urea, stir on a magnetic stirrer for 30 min to obtain N-TiO2 precursor solution with Ti element concentration of 0.35 mol / L;

[0081] Weigh out 1.860 g (4 mmol) of bismuth oxide and 0.936 g (8 mmol) of ammonium metavanadate, respectively. Titrate 13.2 mL of pure nitric acid with deionized water to 40 mL. Add bismuth oxide and ammonium metavanadate to the resulting nitric acid solution (concentration of 5.2 mol / L) and stir on a magnetic stirrer for 30 min to obtain a BiVO4 precursor solution with a Bi element concentration of 0.2 mol / L.

[0082] Measure 25 mL of terpineol and weigh 1.0 g of methylcellulose. Mix the terpineol and methylcellulose together and stir on a magnetic stirrer for 36 h to obtain the binder.

[0083] Take 2 mL of N-TiO2 precursor solution and 3.6 mL of BiVO4 precursor solution, mix them, and then add 0.56 mL of binder to the resulting N-TiO2-BiVO4 slurry. Stir on a magnetic stirrer for 30 min to obtain a mixed slurry (molar ratio Bi:Ti=1:1).

[0084] Prepare a 5cm x 5cm tile. Place the tile in an ultrasonic cleaner and clean it at 30℃ for 30 minutes. Remove the tile and let it dry. After drying, drop anhydrous ethanol onto the surface of the tile and use screen printing to completely cover the substrate. Scrape off any excess anhydrous ethanol. Then, apply a mixed slurry to the surface of the tile, covering 15% of the area. Screen print the slurry 50 times in one direction. Scrape the slurry with a brush until the surface is uniform. The coating thickness should be 15μm. Dry the surface with a dryer. Separate the screen from the tile. Place the coated tile in a drying oven at 60℃ for 30 minutes. Place the dried tile in a heating device and heat it to 500℃ at a rate of 4℃ / min. Hold the temperature for 2 hours and allow it to cool naturally in the oven. This yields a tile with a photocatalytic coating on the surface.

[0085] Comparative Example 1

[0086] The only difference from Example 1 is that urea is not added, and TiO2 sol is used to coat the ceramic tile; otherwise, it is the same as Example 1.

[0087] The preparation of TiO2 sol:

[0088] Measure 2.5 mL of acetylacetone and 30 mL of anhydrous ethanol, mix them, and stir on a magnetic stirrer for 10 min. After stirring evenly, add 8.55 mL of tetrabutyl titanate and stir on a magnetic stirrer for 30 min to obtain a mixture.

[0089] Measure 25 mL of anhydrous ethanol, add deionized water to make 30 mL of ethanol solution, add the ethanol solution to the above mixture, stir well to obtain TiO2 sol.

[0090] Comparative Example 2

[0091] The only difference from Example 1 is that different Bi:Ti molar ratios were used to prepare the mixed slurry; otherwise, they are the same as in Example 1.

[0092] Take 0.725 mL of BiVO4 precursor solution and 2 mL of N-TiO2 precursor solution from Example 1, add them to a 25 mL beaker, and then measure 0.28 mL of binder from Example 1 into the beaker. After stirring for 30 min, a mixed slurry of N-TiO2 and BiVO4 with a molar ratio of Bi:Ti = 1:5 is obtained.

[0093] Take 0.36 mL of BiVO4 precursor solution and 2 mL of N-TiO2 precursor solution from Example 1, add them to a 25 mL beaker, and then measure 0.24 mL of binder from Example 1 into the beaker. After stirring for 30 min, a mixed slurry of N-TiO2 and BiVO4 with a molar ratio of Bi:Ti = 1:10 is obtained.

[0094] Comparative Example 3

[0095] The only difference from Example 1 is that no N-TiO2 precursor solution is added, and only BiVO4 precursor solution is used. Otherwise, it is the same as Example 1, and the product obtained is denoted as BVO (Bi:Ti=1:0).

[0096] Comparative Example 4

[0097] The only difference from Example 1 is that the annealing temperature used is 450°C, otherwise it is the same as Example 1.

[0098] Characterization and performance testing

[0099] Figure 1 shows SEM images of the N-TiO2 film on the ceramic surface after annealing at 500℃ for 2 hours in Example 1; where (a) is 10 μm and (b) is 5 μm. Figure 2 shows SEM images of the TiO2 film on the ceramic surface after annealing at 500℃ for 2 hours in Comparative Example 1; where (a) is 10 μm and (b) is 5 μm. By comparing Figures 1 and 2, it can be found that the addition of N element to TiO2 greatly reduces surface cracks in the samples. Surface N doping inhibits phase transformation, and the samples exist in a mixed crystal form, which can improve the photocatalytic activity of the samples.

[0100] Figure 3 shows a comparison of the formaldehyde degradation efficiency of the TiO2 film on the ceramic surface in Comparative Example 1 and the N-TiO2 film on the ceramic surface in Example 1, and a comparison with the blank without film; it proves that N doping significantly improves the photocatalytic effect of TiO2 (according to the requirements of the document "Indoor Air Purification Performance of Coated Materials", the pollutant degradation device was constructed with indexes, a 30 W fluorescent lamp was used as the light source to provide the light required for photocatalytic degradation, a cylindrical sealed formaldehyde degradation container was used for the experiment, the container bottom radius was 7 cm and the height was 16 cm, the methanol used was an analytical grade solution with a concentration of 2.12 g / L, 3 μL was taken for each degradation experiment, and the ceramic sample used was 5 cm × 5 cm).

[0101] Figure 4 is a comparison of the formaldehyde degradation of mixed slurries with different Bi:Ti ratios in Example 1 and Comparative Examples 2-3. As can be seen from Figure 4, the closer the Bi:Ti ratio is, the higher the photocatalytic effect. At the same time, BiVO4 and TiO2 will form heterojunctions. Compared with single photocatalytic reagents, the reagents that form heterojunctions will significantly improve the photocatalytic efficiency. Moreover, Figure 4 can prove that the closer the Bi:Ti ratio is to 1:1, the more heterojunctions are formed, and the higher the photocatalytic efficiency is.

[0102] Figure 5 shows the degradation effect of Rhodamine B by the N-TiO2 film after annealing at 450℃ in Comparative Example 4, where (a) is Rhodamine B before degradation and (b) is Rhodamine B after degradation; Figure 6 shows the degradation effect of Rhodamine B by the N-TiO2 film after annealing at 500℃ in Example 1, where (a) is Rhodamine B before degradation and (b) is Rhodamine B after degradation; Comparing Figures 5 and 6, it can be seen that the degradation efficiency of Rhodamine B by the TiO2 film formed by annealing at 500℃ is much higher than that of the TiO2 film formed by annealing at 450℃.

[0103] The photocatalytic activity of the photocatalytic film formed in Example 1 was determined according to QB / T 2761-2006. Figure 7 shows the formaldehyde degradation effect of the photocatalytic coating in Example 1 within 24 hours. As shown in Figure 7, the formaldehyde degradation rate was 83% after 24 hours; the natural degradation rate was 5%; and the net formaldehyde degradation rate was 78% after 24 hours. Figure 8 shows the formaldehyde cyclic degradation effect of the photocatalytic coating in Example 1 at different times, proving that the photocatalytic coating still has a net degradation rate of 70% after four days of degradation.

[0104] Under the same experimental conditions as for formaldehyde degradation, the initial amount of toluene was 3 μL of saturated toluene aqueous solution at 25°C. In Example 1, the photocatalytic coating degraded toluene at an initial concentration of 3.386 ppm, decreasing to 2.458 ppm on the first day and 1.567 ppm on the second day, resulting in a degradation rate of 53.7%. Subtracting the natural degradation rate of 5%, the net degradation rate was 48%. In the toluene cyclic degradation, the photocatalytic coating, after four degradation cycles, had an initial toluene concentration of 1.75 ppm and a final concentration of 1.08 ppm, resulting in a cyclic degradation rate of 38.2% and a net degradation rate of 33%.

[0105] The above results demonstrate that the photocatalytic coating provided by this invention has excellent performance in degrading VOC gases such as formaldehyde and toluene.

[0106] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing an N-doped TiO2-BiVO4 heterojunction photocatalytic coating for use in ceramic tiles, walls, or glass, characterized in that, Includes the following steps: A chelating agent, a titanium source, and an organic solvent are mixed to obtain a mixture; the mixture is then mixed with an aqueous alcohol solution and a nitrogen source to obtain an N-TiO2 precursor solution; a bismuth source, a vanadium source, and an acid solution are mixed to obtain a BiVO4 precursor solution; the N-TiO2 precursor solution and the BiVO4 precursor solution are mixed, and the resulting N-TiO2-BiVO4 slurry is then mixed with a binder to obtain a mixed slurry; The mixed slurry is screen-printed onto the substrate surface, and then pre-dried and annealed sequentially to obtain an N-doped TiO2-BiVO4 heterojunction photocatalytic coating. The screen printing is performed in a single direction. The molar ratio of bismuth in the bismuth source to titanium in the titanium source is 1.5:1 to 1:

3. The nitrogen source includes urea, melamine, or ethylenediamine. Before use, the substrate is wetted with anhydrous ethanol. The annealing temperature is 500-550℃, and the time is 2-3 hours.

2. The preparation method according to claim 1, characterized in that, The chelating agent includes acetylacetone, ethylene glycol, citric acid, or oxalic acid; the titanium source includes tetrabutyl titanate, tetraisopropyl titanate, or titanium acetylacetone; the volume ratio of the chelating agent to the titanium source is 1~5:3~15; the amount ratio of the titanium source to the nitrogen source is 3~15 mL:0.1~5 g; the mixture is mixed with the alcohol-water solution and the nitrogen source at room temperature for 20~100 min.

3. The preparation method according to claim 1, characterized in that, The bismuth source includes bismuth oxide or bismuth nitrate; the vanadium source includes ammonium metavanadate or vanadium pentoxide; the mass ratio of the bismuth source to the vanadium source is 1.5~2:0.5~1.

2.

4. The preparation method according to claim 1 or 3, characterized in that, The acid solution includes an aqueous solution of nitric acid; the concentration of the acid solution is 4~6 mol / L.

5. The preparation method according to claim 1, characterized in that, The volume ratio of the N-TiO2 precursor solution to the BiVO4 precursor solution is 1.2~3:2~5.

6. The preparation method according to claim 1, characterized in that, The binder comprises terpineol and methylcellulose; the ratio of terpineol to methylcellulose is 10~40mL:0.5~3g.

7. The preparation method according to claim 1, characterized in that, The volume ratio of the N-TiO2-BiVO4 slurry to the binder is 5~20:1; the area ratio of the mixed slurry on the substrate surface is 10~25%.

8. The N-doped TiO2-BiVO4 heterojunction photocatalytic coating prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the N-doped TiO2-BiVO4 heterojunction photocatalytic coating of claim 8 in ceramic tiles, walls or glass.

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