Preparation method, product and application of a composite photocatalyst

Abstract

The application provides a preparation method, product and application of a composite photocatalyst. In the preparation method, titanium dioxide nanorods are prepared by a hydrothermal method, and graphite-phase carbon nitride is prepared by a mixed calcination method, and then the two are ultrasonically mixed to obtain the composite photocatalyst, which has excellent visible light absorption capacity and high utilization rate of sunlight in a natural environment, and has outstanding photocatalytic efficiency and good photocatalytic self-cleaning capacity. After the composite photocatalyst is hydrophobically modified and applied to PVDF paint, the composite photocatalyst can be uniformly dispersed in the matrix to ensure the uniformity of the coating, can make the coating efficiently degrade organic pollutants and be antibacterial (Staphylococcus aureus and Escherichia coli) under sunlight, and has good acid, alkali, salt and ultraviolet resistance, and further improves the hydrophobicity of the coating. In addition, the prepared PVDF coating has high photocatalytic efficiency and self-cleaning performance, and has good durability in a long-term use process.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic self-cleaning technology, specifically relating to a method for preparing a composite photocatalyst, its product, and its application. Background Technology

[0002] Photocatalytic materials, as a type of semiconductor structural material, are widely used in air purification, water purification, self-purification, sterilization and deodorization, anti-fog and anti-fogging fields due to their advantages such as non-toxicity, environmental friendliness and high efficiency self-cleaning.

[0003] TiO2 photocatalytic coatings, as a functional material, offer advantages in terms of economy and versatility. TiO2's excellent photocatalytic properties enable highly efficient self-cleaning of the coating, thus giving it a large market potential in the field of photocatalytic chemical self-cleaning. However, some problems have gradually emerged during the use of TiO2 photocatalytic coatings: (i) During photocatalytic degradation, degradation products and environmental pollutants easily adhere to the coating surface, leading to photocatalytic deactivation. (ii) Due to the large band gap of TiO2, it has difficulty absorbing visible light, resulting in low utilization of sunlight in natural environments. (iii) During photocatalysis, the coating substrate is susceptible to photo-oxidation, leading to coating failure. Therefore, it is necessary to incorporate self-cleaning properties and visible light response characteristics into the photocatalytic coating and to use durable resins to ensure the coating's durability.

[0004] Traditional self-cleaning coatings are generally classified into superhydrophobic coatings and superhydrophilic coatings. Among them, superhydrophobic coatings with a lotus leaf-like structure have been widely used and can achieve physical self-cleaning properties. However, in practical applications, contaminants such as organic matter and bacteria easily adhere to the coating surface and are not easily removed by water. More importantly, the hydrophobic components of the coating may also be damaged, reducing its hydrophobic properties and ultimately causing it to lose its superhydrophobic self-cleaning ability. Therefore, developing a coating that combines superhydrophobicity and photocatalytic self-cleaning properties has significant inventive and application value. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a method for preparing a composite photocatalyst. The composite photocatalyst prepared by this method has a low band gap and a high electron-hole separation efficiency, and its application in coatings or membrane products can achieve highly efficient photocatalytic self-cleaning performance.

[0006] The present invention also provides a superhydrophobic photocatalytic self-cleaning PVDF coating prepared from the above-mentioned composite photocatalyst. The photocatalytic self-cleaning and superhydrophobic properties of the coating work synergistically to give the coating better stability and sustainability, while also having excellent mechanical stability and durability, ensuring the durability of the coating in practical applications.

[0007] A method for preparing a composite photocatalyst includes the following steps:

[0008] (1) Titanium dioxide nanoparticles undergo a hydrothermal reaction in an alkaline solution to prepare titanium dioxide nanorods;

[0009] (2) After urea and melamine are mixed evenly, they are calcined to obtain graphite phase carbon nitride;

[0010] (3) The above titanium dioxide nanorods are ultrasonically mixed with graphitic carbon nitride to obtain the composite photocatalyst.

[0011] In the above technical solutions, titanium dioxide nanorods prepared by the hydrothermal method have higher roughness, specific surface area, and active hydroxyl functional groups than titanium dioxide nanoparticles. On the one hand, under light irradiation, the larger specific surface area allows for the formation of more active sites, thereby generating more electron-hole pairs. These react with water and oxygen in the air to generate oxidizing groups, which can better degrade organic pollutants. On the other hand, the use of titanium dioxide nanorods also provides a rough structure and modified sites for their application in coatings or membrane products. Among these, a large number of modified sites (active hydroxyl functional groups) can react with various groups, improving the success rate of chemical grafting reactions.

[0012] Under ultrasound assistance, titanium dioxide nanorods induce charge transfer through intermolecular forces and mix with graphitic carbon nitride to form a heterojunction structure, extending the charge transfer path and thus promoting a redshift in the light absorption range. Furthermore, the heterojunction structure accelerates electron-hole pair separation and increases carrier concentration, thereby generating more oxidizing groups and improving the photocatalytic efficiency of sunlight under natural conditions.

[0013] The above steps (1) and (2) can be performed simultaneously, and there is no requirement for their order.

[0014] In the above preparation method, in step (1):

[0015] Preferably, the hydrothermal reaction is carried out at a temperature of 80–200°C for 4–24 hours. More preferably, the reaction temperature is 120–160°C for 12–18 hours.

[0016] Preferably, the alkaline solution is one or more selected from potassium hydroxide solution, sodium hydroxide solution, sodium carbonate solution, and sodium bicarbonate solution. More preferably, the alkaline solution is one of potassium hydroxide solution and sodium hydroxide solution.

[0017] Preferably, the concentration of the alkaline solution is 2–20 mol / L. More preferably, it is 8–12 mol / L.

[0018] Preferably, after the hydrothermal reaction is completed, the reaction product is washed, filtered, and dried to obtain titanium dioxide nanorods.

[0019] Preferably, the titanium dioxide nanoparticles have an average particle size of 20–30 nm. More preferably, they have an average particle size of 25 nm (P25).

[0020] In the above preparation method, in step (2):

[0021] Preferably, the mass ratio of urea to melamine is 1:(1-32). More preferably, it is 1:(1-15). Even more preferably, it is 1:(4-8).

[0022] Preferably, the calcination temperature is 300℃~800℃ and the calcination time is 1h~5h. More preferably, the calcination temperature is 500℃~600℃ and the calcination time is 1.5h~3h.

[0023] Preferably, the heating rate is 2–30 °C / min. More preferably, it is 5–15 °C / min.

[0024] In the above preparation method, in step (3):

[0025] Preferably, the mass ratio of titanium dioxide nanorods to graphitic carbon nitride is 1:(1-15). More preferably, it is 1:(1-7).

[0026] A composite photocatalyst is prepared by any one of the methods described above. This composite photocatalyst not only possesses excellent visible light absorption capacity and high utilization rate of sunlight under natural conditions, but also exhibits excellent photocatalytic efficiency, enabling coatings or films to possess good photocatalytic self-cleaning properties.

[0027] A method for preparing a superhydrophobic photocatalytic self-cleaning PVDF coating includes the following steps:

[0028] 1) The above composite photocatalyst was hydrophobically modified to obtain a modified composite photocatalyst;

[0029] 2) After the modified composite photocatalyst and fluororesin are mixed evenly, they are dispersed in an ethyl acetate solution to obtain the superhydrophobic photocatalytic self-cleaning PVDF coating.

[0030] In the preparation method of this technical solution, hydrophobic modification of the composite photocatalyst not only enables the composite photocatalyst to be more efficiently and uniformly dispersed in ethyl acetate solvent, making it less prone to agglomeration and improving its dispersion performance in the matrix, but also further improves the hydrophobicity of the PVDF coating.

[0031] In the above preparation method, in step 1),

[0032] Preferably, the modifier used for hydrophobic modification is one or more of 1H-1H-2H-2H perfluorodecyltriethoxysilane, dodecyltriethoxysilane, and hexadecyltriethoxysilane. More preferably, it is 1H-1H-2H-2H perfluorodecyltriethoxysilane.

[0033] Preferably, the composite photocatalyst is hydrophobically modified in the following manner:

[0034] The composite photocatalyst and the modifier were mixed in ethanol and heated in a water bath to react. After the reaction was completed, the reaction product was washed, filtered, and dried to obtain the modified composite photocatalyst.

[0035] As a further preferred option, the reaction temperature for water bath heating is 20–80℃, and the reaction time is 4–24 h. Even more preferred is a reaction temperature of 60–80℃ and a reaction time of 8–12 h. Since reaction time and temperature significantly affect the dispersibility and hydrophobicity of the modified powder, it is necessary to adjust the temperature and time to achieve optimal experimental conditions.

[0036] In the above preparation method, in step 2),

[0037] Preferably, the fluororesin is a mixture of polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), wherein the mass ratio of PTFE to PVDF is 1:(1-15). More preferably, it is 1:(1-4).

[0038] In this technical solution, polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) are used in combination. On the one hand, PTFE's low surface energy, high electronegativity, and low coefficient of friction provide the composite coating with low surface energy and excellent wear resistance. On the other hand, due to the different glass transition temperatures of PVDF and PTFE, PTFE can be embedded in the PVDF coating in particle form, thereby increasing the roughness of the composite coating and further reducing its surface energy. Simultaneously, the increased roughness allows ultraviolet light to enter the air through refraction / reflection, thus improving the coating's UV resistance.

[0039] Preferably, the mass ratio of the modified composite photocatalyst to the fluororesin is 1:(1-30). More preferably, it is 1:(4-19).

[0040] Preferably, the mass ratio of the modified composite photocatalyst and the fluororesin to the ethyl acetate solution is 1:(1-40). More preferably, it is 1:(4-24).

[0041] A superhydrophobic photocatalytic self-cleaning PVDF coating is prepared by any of the preparation methods described above.

[0042] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0043] The composite photocatalyst of this invention is prepared by a hydrothermal method to prepare titanium dioxide nanorods and a mixed calcination method to prepare graphitic carbon nitride. The resulting composite photocatalyst, prepared by ultrasonic mixing of the two, exhibits excellent visible light absorption capacity and high utilization rate of sunlight under natural conditions. It also demonstrates outstanding photocatalytic efficiency and good photocatalytic self-cleaning ability. When this composite photocatalyst is hydrophobically modified and applied to PVDF coatings, it not only disperses uniformly in the matrix, ensuring coating uniformity, but also enables the coating to efficiently degrade organic pollutants and exhibit antibacterial properties (Staphylococcus aureus and Escherichia coli) under sunlight, while possessing good resistance to acids, alkalis, salts, and ultraviolet radiation; simultaneously, it further improves the hydrophobicity of the coating. Furthermore, the resulting superhydrophobic photocatalytic self-cleaning PVDF coating exhibits high visible light catalytic efficiency and self-cleaning performance, and demonstrates good durability during long-term use. Attached Figure Description

[0044] Figure 1 Electron micrographs of graphitic carbon nitride prepared by different ratios of urea and melamine in Example 1;

[0045] Figure 2 Electron micrographs of composite photocatalysts prepared by titanium dioxide nanorods and graphitic carbon nitride in different proportions in Example 2.

[0046] Figure 3 This is a SEM image of the No. 3 coating obtained in Example 2;

[0047] Figure 4 The images show a comparison of the superhydrophobic self-cleaning properties of coating #3 in Example 2 and the pure PVDF coating prepared in Comparative Example 1. Detailed Implementation

[0048] The present invention will be further described below with reference to specific embodiments.

[0049] Example 1: Selection of the mass ratio of urea to melamine

[0050] 1.0 g of titanium dioxide nanoparticles (P25) was mixed with 70 mL of 10 mol / L sodium hydroxide solution and transferred to a high-pressure reactor for hydrothermal reaction (200 °C for 12 h). After the reaction was completed, the reaction product was washed, filtered and dried to obtain titanium dioxide nanorods.

[0051] Urea and melamine (the mass ratios of urea to melamine were 1:2, 1:4, 1:6, and 1:8, respectively) were mixed evenly and placed in a muffle furnace and calcined at 550°C for 3 hours to obtain graphitic carbon nitride.

[0052] Titanium dioxide nanorods and graphitic carbon nitride were ultrasonically stirred for 1 hour at a mass ratio of 1:5 to obtain four composite photocatalysts.

[0053] Electron micrographs of the four composite photocatalysts prepared above are shown below. Figure 1 As shown, by Figure 1 It can be seen that when the ratio is 1:2, 1:4, and 1:8, the resulting graphitic carbon nitride exhibits a layered structure, while when the ratio is 1:6, the resulting graphitic carbon nitride exhibits a coiled, porous, multi-layered sheet-like structure. Compared to the sheet-like structure, this structure has a larger specific surface area. When exposed to sunlight, it can generate more active sites, increasing the concentration of electron-hole pairs, thereby producing more active groups and improving photocatalytic efficiency.

[0054] Testing of the photocatalytic performance of composite photocatalysts:

[0055] The chemical self-cleaning properties of the prepared composite photocatalyst were characterized by degrading an MB solution (20.0 mg / L) under visible light using methylene blue (MB) to simulate organic oil contaminants. The light source used had a power density of 45 mW / cm². 2 A 300W xenon lamp was used, and the absorbance of the MB solution was measured every 30 minutes using a UV-Vis spectrophotometer. The specific procedure is as follows:

[0056] Add 0.1g of composite photocatalyst to 50ml of MB solution, carry out a dark reaction for 30min, and then irradiate under visible light. Take 15ml of the reaction solution at 1h and 2h respectively, centrifuge, and perform UV-Vis test to calculate the degradation efficiency.

[0057] The degradation efficiency is calculated by the following formula:

[0058]

[0059] In the formula, η is the degradation efficiency of MB, C0 is the initial concentration of MB, C is the concentration of MB at the sampling time, and K is the reaction rate constant (min). -1 ).

[0060] Table 1. Test results of catalytic performance of composite photocatalyst

[0061]

[0062] As shown in Table 1, the degradation rates of the four composite photocatalysts prepared in this embodiment all reached approximately 35% after 1 hour of degradation and approximately 80% after 2 hours of degradation. Furthermore, the composite photocatalyst exhibited the best photocatalytic degradation rate when the mass ratio of urea to melamine was 1:6. Figure 1The electron micrographs show that a mass ratio of urea to melamine of 1:6 is the optimal ratio.

[0063] Example 2: Selection of the mass ratio of titanium dioxide nanorods to graphitic carbon nitride

[0064] 1.0 g of titanium dioxide nanoparticles (P25) was mixed with 70 mL of 10 mol / L sodium hydroxide solution and transferred to a high-pressure reactor for hydrothermal reaction (200 °C for 12 h). After the reaction was completed, the reaction product was washed, filtered and dried to obtain titanium dioxide nanorods.

[0065] Urea and melamine (mass ratio of urea to melamine is 1:6) were mixed evenly and placed in a muffle furnace and calcined at 550°C for 3 hours to obtain graphitic carbon nitride.

[0066] The prepared titanium dioxide nanorods were mixed with graphitic carbon nitride (the mass ratio of titanium dioxide nanorods to graphitic carbon nitride was 1:1, 1:3, 1:5, and 1:7, respectively) by ultrasonic stirring for 1 h to obtain four composite photocatalysts, which were labeled as composite photocatalysts 1#, 2#, 3#, and 4#, respectively.

[0067] The four composite photocatalysts were dispersed in anhydrous ethanol solution with 1g of 1H-1H-2H-2H perfluorodecyltriethoxysilane, and the reaction was carried out in a water bath at 80°C for 10h. The reaction products were washed, filtered and dried to obtain the four corresponding modified composite photocatalysts.

[0068] Four parts of fluoropolymer resin were mixed evenly (the mass ratio of polyvinylidene fluoride to polytetrafluoroethylene was 3:1). A modified composite photocatalyst was added to each part of fluoropolymer resin (the mass ratio of the modified composite photocatalyst to the fluoropolymer resin was 1:10), and the mixture was stirred evenly. The mixed modified composite photocatalyst and fluoropolymer resin were dispersed in ethyl acetate solvent (the mass ratio of the total amount of modified composite photocatalyst and fluoropolymer resin to ethyl acetate solvent was 1:9), and stirred evenly to obtain four kinds of superhydrophobic photocatalytic self-cleaning PVDF coatings.

[0069] Superhydrophobic photocatalytic self-cleaning PVDF coatings were sprayed onto the substrate surface using an air spray gun. After drying, four types of superhydrophobic photocatalytic self-cleaning PVDF coatings were obtained, which were labeled as coatings 1#, 2#, 3#, and 4#, respectively.

[0070] Electron micrographs of the above-mentioned composite photocatalysts #1, #2, #3, and #4 are shown below. Figure 2 As shown, by Figure 2It can be seen that from #1 to #4, the proportion of titanium dioxide nanorods gradually decreases while the proportion of graphitic carbon nitride gradually increases. Within a certain region of the electron microscope, the heterojunction hybridization ratio and position between titanium dioxide nanorods and graphitic carbon nitride continuously change, reaching an optimal ratio at #3. At this ratio, the two semiconductor materials can form an effective heterojunction structure, fully leveraging the promoting effect of the heterojunction structure in the photocatalytic process. From the perspective of electron transfer, this heterojunction structure prolongs the electron transfer path, slows down the recombination of electron-hole pairs, and allows the carrier concentration to increase steadily over a certain period of time, thereby increasing the photocatalytic efficiency.

[0071] The SEM image of the PVDF coating (coating #3) prepared by titanium dioxide nanorods and graphitic carbon nitride at a mass ratio of 1:5 is shown below. Figure 3 As shown, by Figure 3 It can be seen that the surface of coating #3 contains a large number of cross-linked network papillae and pore structures. The modified composite photocatalyst, PTFE and PVDF are superimposed and interwoven on the coating surface, forming a high roughness, which gives the coating superhydrophobic properties.

[0072] Comparative Example 1

[0073] PVDF resin is dispersed in ethyl acetate solvent, and the mixed solution is sprayed onto the substrate surface using an air spray gun to obtain a pure PVDF coating.

[0074] Performance testing

[0075] Physical self-cleaning performance test:

[0076] Methylene blue (MB), rhodamine (RhB), and micron-sized carbon black (CK) were used to simulate contaminants. Different coating samples were placed at an angle and sprinkled with simulated contaminants. The removal of simulated contaminants from the surface of the coating samples was observed by rinsing with water, which was used to characterize the physical self-cleaning performance of the coating.

[0077] The physical self-cleaning properties of coating #3 in Example 2 and the pure PVDF coating in Comparative Example 1 were tested using the above method, and the results are as follows: Figure 4 As shown. By Figure 4 It can be seen that the simulated contaminants on the surface of coating #3 in Example 2 were easily removed, while the simulated contaminants on the surface of the pure PVDF coating in Comparative Example 1 still had a lot of residue. The coating #3 prepared in Example 2 has good physical self-cleaning properties. This is because the coating #3 has a superhydrophobic surface due to the dual synergistic effect of the rough structure formed by organic-inorganic hybridization and the low surface energy interface formed after modification. This results in superhydrophobic physical self-cleaning properties.

[0078] Coating photocatalytic self-cleaning performance test:

[0079] Methylene blue (MB) was used to simulate organic oil and fat contaminants. The chemical self-cleaning properties of the coated samples were characterized by the degradation of an MB solution (20.0 mg / L) under visible light. The light source used had a power density of 45 mW / cm². 2 A 300W xenon lamp was used, and the absorbance of the MB solution was measured every 30 minutes using a UV-Vis spectrophotometer. The specific procedure is as follows:

[0080] Add a 10*10cm coating sample to 50ml of MB solution, perform a dark reaction for 30min, and then irradiate under visible light. Take 15ml of the reaction solution at 1h, 2h, and 3h, centrifuge, and perform UV-Vis testing to calculate the degradation efficiency.

[0081] The degradation efficiency is calculated by the following formula:

[0082]

[0083] In the formula, η is the degradation efficiency of MB, C0 is the initial concentration of MB, C is the concentration of MB at the sampling time, and K is the reaction rate constant (min). -1 ).

[0084] The photocatalytic performance and water contact angle of coatings #1, #2, #3, and #4 were tested in accordance with the above method, and the results are shown in Table 2.

[0085] Table 2. Test results of photocatalytic performance of different coatings and water contact angle.

[0086]

[0087] As shown in Table 2, the photocatalytic degradation rates of the coatings prepared by the four different composite photocatalysts all reached over 90% after 3 hours, with a water contact angle of 145°, exhibiting excellent photocatalytic degradation performance and superhydrophobic properties. Among them, coating #3 showed the best photocatalytic performance. This is because a 1:5 ratio of titanium dioxide nanorods to graphitic carbon nitride allows for the formation of more effective heterojunction structures and active sites, generating more electron-hole pairs and increasing carrier concentration, thereby effectively improving photocatalytic performance. This ratio also provides higher roughness, resulting in a higher water contact angle and achieving superhydrophobicity.

[0088] Durability of the coating's photocatalytic performance:

[0089] To further investigate the durability of the coating's photocatalytic performance, a 10*10cm coating sample was placed in 50ml of 20.0mg / L MB solution and subjected to a 30min dark reaction. After irradiation under visible light, the degradation rate of MB was tested at 1h, 2h, and 3h, which constituted one cycle. The degradation was repeated 5 times, and the final degradation rate of each cycle was tested.

[0090] The photocatalytic performance durability of coating #3 in Example 1 was tested in accordance with the above method, and the test results are shown in Table 1.

[0091] Table 3. Results of photocatalytic performance durability test for coating #3

[0092]

[0093] As shown in Table 3, the MB dye was basically completely degraded within 3 hours in the first cycle. After 5 cycles of degradation, the No. 4 coating in Example 1 still showed excellent detergency. The degradation rate at 3 hours only decreased from 98.2% in the first cycle to 87.6%, a decrease of only 10.6%, demonstrating excellent photocatalytic durability.

[0094] Resistance to acids, alkalis, salts, and ultraviolet radiation:

[0095] The coated samples were immersed in 10% sulfuric acid solution, 10% sodium hydroxide solution, and 10% sodium chloride solution, respectively, and irradiated with 300W ultraviolet light. The water contact angle of the coating under different treatment conditions at 0h, 6h, 12h, 18h, and 24h was tested to characterize the acid, alkali, salt, and ultraviolet resistance of the coated samples.

[0096] The above-mentioned acid resistance, alkali resistance, and UV resistance tests were performed on the No. 3 coating sample in Example 2, and the results are shown in Table 4.

[0097] Table 4. Test results of the acid, alkali, salt, and UV resistance of coating #3.

[0098]

[0099] As shown in Table 4, the water contact angle of the coating samples remained basically unchanged after 24 hours of immersion in acid, alkali, or salt or irradiation with ultraviolet light, enabling the coating to be used for a long time and maintain excellent superhydrophobic self-cleaning properties.

[0100] Example 3: Selection of the mass ratio of polyvinylidene fluoride to polytetrafluoroethylene in fluoropolymers

[0101] 1.0 g of titanium dioxide nanoparticles (P25) was mixed with 70 mL of 10 mol / L sodium hydroxide solution and transferred to a high-pressure reactor for hydrothermal reaction (200 °C for 12 h). After the reaction was completed, the reaction product was washed, filtered and dried to obtain titanium dioxide nanorods.

[0102] Urea and melamine (mass ratio of urea to melamine is 1:6) were mixed evenly and placed in a muffle furnace and calcined at 550°C for 3 hours to obtain graphitic carbon nitride.

[0103] The prepared titanium dioxide nanorods were mixed with graphitic carbon nitride (the mass ratio of titanium dioxide nanorods to graphitic carbon nitride was 1:5) by ultrasonic stirring for 1 h to obtain a composite photocatalyst.

[0104] The composite photocatalyst and 1g of 1H-1H-2H-2H perfluorodecyltriethoxysilane modifier were dispersed in anhydrous ethanol solution and reacted in a water bath at 80°C for 10h. The reaction product was washed, filtered and dried to obtain the modified composite photocatalyst.

[0105] Five parts of fluororesin were mixed evenly (the mass ratio of polyvinylidene fluoride to polytetrafluoroethylene was 1:1, 2:1, 3:1, 4:1, and 5:1). The modified composite photocatalyst (the mass ratio of the modified composite photocatalyst to the fluororesin was 1:10) was added to each part of fluororesin and mixed thoroughly. The mixed modified composite photocatalyst and fluororesin were dispersed in ethyl acetate solvent (the mass ratio of the total amount of modified composite photocatalyst and fluororesin to ethyl acetate solvent was 1:9), and stirred evenly to obtain five kinds of superhydrophobic photocatalytic self-cleaning PVDF coatings.

[0106] Superhydrophobic photocatalytic self-cleaning PVDF coating was sprayed onto the substrate surface using an air spray gun. After drying, a superhydrophobic photocatalytic self-cleaning PVDF coating was obtained. The water contact angle of each coating was tested, and the results are shown in Table 5.

[0107] Table 5. Water contact angles of coatings prepared with different mass ratios of polyvinylidene fluoride and polytetrafluoroethylene.

[0108]

[0109] As shown in Table 5, the coating has the highest water contact angle when the mass ratio of polyvinylidene fluoride (PVDF) to polytetrafluoroethylene (PTFE) is 3:1. This is because at this ratio, PVDF and PTFE can form an effective cross-linked network structure on the coating surface, thus providing a stable rough structure and laying the foundation for the formation of a superhydrophobic interface.

[0110] Example 4: Selection of the mass ratio of modified composite photocatalyst to fluororesin

[0111] 1.0 g of titanium dioxide nanoparticles (P25) was mixed with 70 mL of 10 mol / L sodium hydroxide solution and transferred to a high-pressure reactor for hydrothermal reaction (200 °C for 12 h). After the reaction was completed, the reaction product was washed, filtered and dried to obtain titanium dioxide nanorods.

[0112] Urea and melamine (mass ratio of urea to melamine is 1:6) were mixed evenly and placed in a muffle furnace and calcined at 550°C for 3 hours to obtain graphitic carbon nitride.

[0113] The prepared titanium dioxide nanorods were mixed with graphitic carbon nitride (the mass ratio of titanium dioxide nanorods to graphitic carbon nitride was 1:5) by ultrasonic stirring for 1 h to obtain a composite photocatalyst.

[0114] The composite photocatalyst and 1g of 1H-1H-2H-2H perfluorodecyltriethoxysilane modifier were dispersed in anhydrous ethanol solution and reacted in a water bath at 80°C for 10h. The reaction product was washed, filtered and dried to obtain the modified composite photocatalyst.

[0115] Fluoropolymer resin was mixed evenly (the mass ratio of polyvinylidene fluoride to polytetrafluoroethylene was 3:1), and modified composite photocatalyst was added (the mass ratio of modified composite photocatalyst to fluoropolymer resin was 1:5, 1:10, 1:15, and 1:20, respectively). The modified composite photocatalyst and fluoropolymer resin were dispersed in ethyl acetate solvent (the mass ratio of the total amount of modified composite photocatalyst and fluoropolymer resin to ethyl acetate solvent was 1:9), and stirred evenly to obtain four types of superhydrophobic photocatalytic self-cleaning PVDF coatings.

[0116] Four types of superhydrophobic photocatalytic self-cleaning PVDF coatings were obtained by spraying superhydrophobic photocatalytic self-cleaning PVDF coatings onto the substrate surface using an air spray gun.

[0117] The four superhydrophobic photocatalytic self-cleaning PVDF coatings prepared in this embodiment were tested according to the above-described method for testing the photocatalytic self-cleaning performance of the coatings. The water contact angle of each coating was also tested. The results are shown in Table 6.

[0118] Table 6 shows the photocatalytic performance and water contact angle of coatings prepared with different mass ratios of modified composite photocatalyst and fluororesin.

[0119]

[0120] As shown in Table 6, the coating has the highest hydrophobic angle (water contact angle) when the ratio is 1:10. This is because the modified composite photocatalyst is most uniformly dispersed in the coating at this ratio, and the modified hydrophobic properties can be better exhibited. The photocatalytic effect is also best at 1:10 because the amount of modified composite photocatalyst added is less at ratios of 1:15 and 1:20, which leads to a decrease in photocatalytic effect. The photocatalytic effect is not optimal at a ratio of 1:5 because the amount of photocatalyst added is too large and it is not well dispersed in the resin, resulting in agglomeration, which in turn reduces the photocatalytic performance.

[0121] In summary, the experimental results show that the superhydrophobic photocatalytic self-cleaning PVDF coating prepared by the method of this invention not only possesses long-lasting durability and photocatalytic degradation of organic pollutants, but also provides superhydrophobic physical self-cleaning properties. Therefore, this photocatalytic PVDF superhydrophobic coating broadens the application range of traditional coatings and has good development prospects.

Claims

1. A method for preparing a composite photocatalyst, characterized in that, Includes the following steps: (1) Titanium dioxide nanoparticles undergo a hydrothermal reaction in an alkaline solution to prepare titanium dioxide nanorods; (2) After urea and melamine are mixed evenly, they are calcined to obtain graphite phase carbon nitride; (3) The above titanium dioxide nanorods are ultrasonically mixed with graphitic carbon nitride to obtain the composite photocatalyst; In step (1), the hydrothermal reaction temperature is 80~200℃ and the reaction time is 4~24h; In step (2), the mass ratio of urea to melamine is 1:6; In step (3), the mass ratio of titanium dioxide nanorods to graphite phase carbon nitride is 1:(3~7).

2. The method for preparing the composite photocatalyst according to claim 1, characterized in that, In step (1), the alkaline solution is one or more of potassium hydroxide solution, sodium hydroxide solution, sodium carbonate solution, and sodium bicarbonate solution.

3. The method for preparing the composite photocatalyst according to claim 1, characterized in that, In step (2), the calcination temperature is 300℃~800℃, and the calcination time is 1h~5h; The calcination heating rate is 2 ~ 30℃ / min.

4. A composite photocatalyst, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 3.

5. A method for preparing a superhydrophobic photocatalytic self-cleaning PVDF coating, characterized in that, Includes the following steps: 1) The composite photocatalyst described in claim 4 is hydrophobically modified to obtain a modified composite photocatalyst; 2) After the modified composite photocatalyst and fluororesin are mixed evenly, they are dispersed in an ethyl acetate solution to obtain the superhydrophobic photocatalytic self-cleaning PVDF coating.

6. The preparation method of the superhydrophobic photocatalytic self-cleaning PVDF coating according to claim 5, characterized in that, In step 1), the modifier used for hydrophobic modification is one or more of 1H-1H-2H-2H perfluorodecyltriethoxysilane, dodecyltriethoxysilane, and hexadecyltriethoxysilane.

7. The method for preparing the superhydrophobic photocatalytic self-cleaning PVDF coating according to claim 5, characterized in that, The fluororesin is a mixture of polytetrafluoroethylene and polyvinylidene fluoride; The mass ratio of polytetrafluoroethylene to polyvinylidene fluoride is 1:(1~15).

8. The method for preparing the superhydrophobic photocatalytic self-cleaning PVDF coating according to claim 5, characterized in that, The mass ratio of the modified composite photocatalyst to the fluororesin is 1:(1~30). The ratio of the total mass of the modified composite photocatalyst and fluororesin to the mass of the ethyl acetate solution is 1:(1~40).

9. A superhydrophobic photocatalytic self-cleaning PVDF coating, characterized in that, It is prepared by the preparation method according to any one of claims 5 to 8.

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