Self-repairing photocatalytic degradation super-hydrophobic coating as well as preparation method and application thereof

Abstract

The invention discloses a self-repairing photocatalytic degradation super-hydrophobic coating as well as a preparation method and application thereof. Halloysite nanotubes are selected as wall materials, low-surface-energy substances are poured, then the halloysite nanotubes are compounded with TiO2 with photocatalytic performance under the acidic condition that the pH is 5-6, and multistage structure construction and photocatalytic performance improvement of the coating are achieved by regulating coulomb electrostatic attraction. And then mixing with polydimethylsiloxane to obtain the self-repairing photocatalytic degradation super-hydrophobic coating. A super-hydrophobic coating formed after the super-hydrophobic coating is cured not only can realize self-repairing of the coating through a self-similar structure method, but also can decompose organic pollutants on the surface to realize self-cleaning, and meanwhile, the super-hydrophobic coating has relatively good wear resistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of super-hydrophobic materials, and in particular relates to a self-repairing photocatalytic degradation super-hydrophobic coating, and a preparation method and application thereof. Background Art

[0002] With the development of modern industrialization, coating pollution has become more and more serious. Inorganic pollutants are mostly attached to the coating surface in the form of particles, which generally do not cause permanent damage to the coating surface performance and can usually be carried away and rolled off by the adhesion of water droplets; while organic pollutants are mostly attached to the coating surface, which is difficult to achieve self-cleaning through the carrying effect of water droplets, thus destroying the rough structure and causing the surface to gradually lose its self-cleaning performance.

[0003] In order to solve the problem that the super-hydrophobicity and durability of the coating are greatly reduced after being contaminated by organic attachments, some researchers have proposed adding photocatalytic materials to the super-hydrophobic coating to construct a photocatalytic super-hydrophobic self-cleaning coating with multiple functions and better durability. At present, there are three main methods for constructing photocatalytic super-hydrophobic composite coatings: (1) Surface construction method, but the photocatalytic super-hydrophobic coating constructed by the surface construction method alone is too weak, making the mechanical wear resistance of the coating generally poor, and it is impossible to maintain high-efficiency photocatalytic performance and super-hydrophobic performance for a long time; (2) Blending method, the performance of the coating prepared by this method is too dependent on the performance of the material itself, and the organic or inorganic components in the hybrid material are prone to aggregation, and the phase separation phenomenon is relatively serious, resulting in generally poor durability of the coating; (3) Coating method, but the preparation of coatings by this method has too many influencing factors in industry and the preparation process is slightly cumbersome, and it does not have the conditions for large-scale preparation.

[0004] At present, there are many problems in preparing durable photocatalytic super-hydrophobic self-cleaning coatings, and improving the mechanical wear resistance and self-healing properties of photocatalytic super-hydrophobic self-cleaning coatings faces huge challenges. Summary of the invention

[0005] The purpose of the present invention is to overcome the above-mentioned technical deficiencies, propose a self-repairing photocatalytic degradation super-hydrophobic coating and its preparation method and application, and solve the technical problems of insufficient mechanical wear resistance and self-repairing properties of photocatalytic super-hydrophobic self-cleaning coatings in the prior art.

[0006] In a first aspect, the present invention provides a method for preparing a self-repairing photocatalytic degradation super-hydrophobic coating, comprising the following steps: Performing pore expansion treatment on the halloysite nanotubes, and then infusing low surface energy substances to obtain halloysite nanotubes infusing low surface energy substances; The halloysite nanotubes and anatase phase nano-titanium dioxide infused with low surface energy substances are dispersed in a first organic solvent, the pH is adjusted to 5-6 and then an electrostatic adsorption reaction is performed, and finally a TiO2 / HNTs composite material is obtained by washing and drying. The TiO2 / HNTs composite material and polydimethylsiloxane are dispersed in a second organic solvent to obtain a self-repairing photocatalytic degradation super-hydrophobic coating.

[0007] In a second aspect, the present invention provides a self-repairing photocatalytically degradable super-hydrophobic coating, and the self-repairing photocatalytically degradable super-hydrophobic coating is obtained by the preparation method of the self-repairing photocatalytically degradable super-hydrophobic coating provided by the first aspect of the present invention.

[0008] In a third aspect, the present invention provides a self-repairing photocatalytically degradable super-hydrophobic coating, which is formed by applying the above-mentioned self-repairing photocatalytically degradable super-hydrophobic coating to the surface of a substrate and curing it.

[0009] Compared with the prior art, the beneficial effects of the present invention include: The present invention selects halloysite nanotubes as wall material, perfuses low surface energy substances, and then compounds them with TiO2 with photocatalytic performance under acidic conditions of pH 5 to 6, realizes coating multi-level structure construction and photocatalytic performance improvement by regulating and controlling Coulomb electrostatic attraction to attract each other, and then obtains self-repairing photocatalytic degradation super-hydrophobic coating with polydimethylsiloxane. The super-hydrophobic coating formed after the super-hydrophobic coating is cured can not only realize the self-repair of coating by self-similar structure method, but also can decompose surface organic pollutants to realize self-cleaning, while having good wear resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a SEM image of the TiO2 / HNTs composite material obtained in Example 1 of the present invention; Figure 2 This is a SEM image of the coating obtained in Example 1 of the present invention; Figure 3 This is a graph showing the change in water contact angle of the coating obtained in Example 1 of the present invention under different oleic acid pollution-light exposure times; Figure 4 The wear resistance test diagram of the coating obtained in Example 1 of the present invention; wherein (a) is a diagram of the wear resistance test process in Example 1, and (b) is a photo of the static water contact angle of the coating after 20 wear resistance cycles. DETAILED DESCRIPTION

[0011] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0012] In a first aspect, the present invention provides a method for preparing a self-repairing photocatalytic degradation super-hydrophobic coating, comprising the following steps: S1, performing pore expansion treatment on halloysite nanotubes (HNTs), and then infusing low surface energy substances to obtain halloysite nanotubes infused with low surface energy substances; S2, dispersing the halloysite nanotubes and anatase phase nano-titanium dioxide infused with low surface energy substances into a first organic solvent, adjusting the pH to 5-6 and then performing an electrostatic adsorption reaction, and finally washing and drying to obtain a TiO2 / HNTs composite material; S3. Dispersing the TiO2 / HNTs composite material and polydimethylsiloxane (PDMS) in a second organic solvent to obtain a self-repairing photocatalytic degradation super-hydrophobic coating.

[0013] The present invention uses the halloysite nanotubes with high mechanical strength, good chemical stability and hollow tubular structure as wall materials, perfuse low surface energy substances, make the material surface and interior have the same hydrophobic components and structures, when the surface structure or composition is damaged by mechanical friction and other environmental conditions, the rough structure inside the halloysite nanotubes is exposed, and the low surface energy substances stored inside migrate to the surface so that the material restores its original super-hydrophobicity, and realizes the self-repairing performance of super-hydrophobic coating. Under acidic conditions of pH 5 to 6, the TiO2 surface is positively charged and the halloysite surface is negatively charged. Electrostatic adsorption reaction is used to composite nano-TiO2 particles on the halloysite surface of the tubular structure, and multi-level rough structures are constructed on the material surface to realize the composite of super-hydrophobic-photocatalytic performance, and obtain TiO2 / HNTs composite materials with photocatalytic activity and multi-scale structure. The cleaning mechanism brought by the super-hydrophobic surface can effectively clean Class I pollutants on the surface of the material, such as dust, water stains, muddy water, etc.; the cleaning mechanism brought by the photocatalytic performance can remove Class II pollutants on the surface of the material, such as oil stains, oil stains and organic molecules such as microorganisms. The two cleaning mechanisms complement and protect each other on the surface, realizing the RD dual self-cleaning function of the material surface. At the same time, the addition of halloysite nanotubes makes the coating have better mechanical properties, making the super-hydrophobic coating more wear-resistant. The coating of the present invention can be widely used in a variety of complex environments.

[0014] In this embodiment, halloysite (HNTs) is a silicate mineral with a molecular formula of Al2SiO2(OH)4·nH2O, with Al-OH and Si-OH groups on the inner and outer surfaces, and has a tubular shape with an outer diameter in the range of 40 to 60 nm and a length in the range of 700 to 1500 nm.

[0015] In this embodiment, in step S1, the hole enlarging treatment is performed by acid etching.

[0016] Preferably, the process of acid etching and pore enlargement includes: subjecting the halloysite nanotubes to acid etching and pore enlargement treatment using an acid solution, followed by filtering, washing and drying to obtain the acid-etched and pore-enlarged halloysite nanotubes.

[0017] Among them, during the acid etching and pore enlargement process, the acid solution is dilute sulfuric acid or dilute hydrochloric acid with a concentration of 1~3 mol / L; the solid-liquid ratio is 1:(10~30); the temperature of the acid etching and pore enlargement treatment is 60~90℃, and the time of the acid etching and pore enlargement treatment is 2~4h; the acid etching and pore enlargement treatment is carried out under stirring conditions.

[0018] In this embodiment, in step S1, the low surface energy substance is fluorosilane.

[0019] Preferably, the fluorosilane is at least one of 1H,1H,2H,2H-perfluorooctyltrichlorosilane and 1H,1H,2H,2H-perfluorodecyltriethoxysilane.

[0020] In this embodiment, in step S1, the process of infusing the low surface energy substance includes: preparing a third organic solvent solution of the low surface energy substance, mixing the acid-etched and expanded halloysite nanotubes with the third organic solvent solution of the low surface energy substance, and then performing vacuum extraction and standing at normal pressure to obtain the halloysite nanotubes infused with the low surface energy substance. The present invention ensures that the halloysite is fully loaded with the low surface energy substance by performing vacuum extraction and standing at normal pressure.

[0021] Preferably, in the third organic solvent solution of the low surface energy substance, the mass fraction of the low surface energy substance is 1% to 2%.

[0022] Preferably, the third organic solvent is anhydrous ethanol.

[0023] Preferably, the mass ratio of the halloysite nanotubes after acid etching and pore expansion to the third organic solvent solution of the low surface energy substance is 1:(5-20).

[0024] Preferably, the vacuum extraction temperature is 70-90° C., the vacuum extraction time is 1-2 h, and the vacuum pressure is 0.1-133 Pa.

[0025] Preferably, the temperature for standing at normal pressure is 20-30° C., and the time for standing at normal pressure is 0.5-1 h.

[0026] In this embodiment, in step S2, the particle size of the anatase phase nano-titanium dioxide is 5-10 nm.

[0027] In this embodiment, in step S2, anatase nano-titanium dioxide is obtained by calcining amorphous nano-titanium dioxide at 550° C. to 650° C. for 2 to 4 hours. Through this process, amorphous nano-TiO2 can be transformed into anatase nano-TiO2 with photocatalytic activity under high temperature conditions.

[0028] In this embodiment, in step S2, the mass ratio of the halloysite nanotubes infused with low surface energy substances to the anatase phase nano-titanium dioxide is (5-8): 1. If the ratio of TiO2 is too low, the surface roughness of the halloysite nanotubes is low, and the photocatalytic efficiency is low; if the ratio of TiO2 is too high, there are not enough halloysite nanotubes as a skeleton support, and more free TiO2 appears. Although the photocatalytic performance will be improved, the hydrophobic performance will be reduced due to the lack of a multi-level rough structure.

[0029] In this embodiment, in step S2, the first organic solvent is anhydrous ethanol.

[0030] In this embodiment, in step S2, the mass ratio of the halloysite nanotubes infused with the low surface energy substance to the first organic solvent is 1:(10-30).

[0031] In this embodiment, in step S2, the pH is adjusted to 5-6 by dropwise adding hydrochloric acid or glacial acetic acid.

[0032] In this embodiment, in step S2, the temperature of the electrostatic adsorption reaction is 20-30° C., the time of the electrostatic adsorption reaction is 1-3 hours, and the electrostatic adsorption reaction is performed under stirring.

[0033] In this embodiment, in step S3, the mass ratio of TiO2 / HNTs composite material to polydimethylsiloxane is 1:(1-3). In the present invention, PDMS can not only be used as a low surface energy material, but also as a binder between multi-scale structured micro-nanoparticles and substrates. Under the combined effect of rough structure and low surface energy, the super-hydrophobic property of the composite surface is achieved. At the same time, the exposure degree of TiO2 will determine the photocatalytic property of the composite coating. If the amount of PDMS is too small, the multi-scale structure can be exposed to a greater extent, improving the hydrophobic effect, but the particles cannot be connected and fixed, which is not conducive to the stability of the coating; if the amount of PDMS is too much, the fine structure on the surface of the particles will be coated, and the super-hydrophobic property cannot be achieved.

[0034] In this embodiment, in step S3, the polydimethylsiloxane includes a prepolymer (ie, component A) and a cross-linking agent (ie, component B), and the mass ratio of component A to component B is (8-10):1.

[0035] In this embodiment, in step S3, the second organic solvent is hexane.

[0036] In this embodiment, in step S3, the mass ratio of polydimethylsiloxane to the second organic solvent is 1:(3-8).

[0037] In this embodiment, in step S3, ultrasonic dispersion is adopted.

[0038] Preferably, the ultrasonic dispersion time is 20 to 40 minutes.

[0039] In a second aspect, the present invention provides a self-repairing photocatalytically degradable super-hydrophobic coating, and the self-repairing photocatalytically degradable super-hydrophobic coating is obtained by the preparation method of the self-repairing photocatalytically degradable super-hydrophobic coating provided by the first aspect of the present invention.

[0040] In a third aspect, the present invention provides a self-repairing photocatalytically degradable super-hydrophobic coating, which is formed by applying the above-mentioned self-repairing photocatalytically degradable super-hydrophobic coating to the surface of a substrate and curing it.

[0041] The present invention does not limit the coating method, and those skilled in the art can choose according to actual conditions. In some specific embodiments of the present invention, a spray coating method is adopted. More specifically, the spray gun is 15 to 20 cm away from the substrate, the spraying amount is 8 to 10 mL / min, and the coating thickness is 3 to 5 μm.

[0042] The present invention does not limit the type of substrate, and those skilled in the art can select according to actual conditions. In some specific embodiments of the present invention, the substrate is wood, a plastic substrate of PVC or PC material, a glass substrate or an aluminum substrate and its alloy substrate.

[0043] Preferably, the substrate needs to be pretreated before coating, and the pretreatment method includes: washing and drying the substrate.

[0044] In this embodiment, the curing temperature is 80-100° C., and the curing time is 0.5-2 hours.

[0045] Example 1 (1) 6 g of halloysite nanotubes were placed in 100 g of 2 mol / L H2SO4 solution, stirred by magnetic force, and acid-etched in a water bath at 80°C for 2 h, then filtered, washed, and dried to obtain the acid-etched HNTs powder. The acid-etched HNTs powder was added to a 50 g 1 wt% 1H,1H,2H,2H-perfluorodecyltriethoxysilane / anhydrous ethanol mixed solution, placed in a vacuum drying oven at 80°C and 8 Pa for 1 h, and then allowed to stand at room temperature and pressure for 0.5 h to obtain the halloysite nanotubes infused with fluorosilane.

[0046] (2) Take 1 g of amorphous nano-TiO2 powder and calcine it at 600℃ for 3 h to prepare anatase phase TiO2 powder with photocatalytic properties.

[0047] (3) 6 g of fluorosilane-infused halloysite nanotubes and 1 g of anatase phase TiO2 powder with photocatalytic properties were dispersed in 100 g of anhydrous ethanol. Under magnetic stirring, hydrochloric acid was added dropwise to adjust the pH of the suspension to 6. The suspension was then stirred at room temperature for 2 h. The TiO2 particles were adsorbed on the surface of the halloysite nanotubes by electrostatic adsorption. After the reaction was completed, the product was washed three times by centrifugation with ethanol and dried at 80 °C to obtain a TiO2 / HNTs composite material with photocatalytic properties.

[0048] (4) 10 g of PDMS component A and 1 g of component B (purchased from Shanghai Deji Trading Co., Ltd.) were dissolved in 50 g of hexane, and 7 g of TiO2 / HNTs composite material with photocatalytic properties was added. Ultrasonic treatment was performed for 30 min to uniformly disperse the powder in the solution to obtain a self-repairing photocatalytic degradation super-hydrophobic coating.

[0049] (5) The glass substrate was cleaned and dried at 60°C. The self-repairing photocatalytic degradation super hydrophobic coating was evenly sprayed on the surface of the pretreated substrate by spraying. The spray gun was 15 cm away from the substrate, the spraying volume was 8 mL / min, the coating thickness was 4 μm, and then it was placed in an oven at 100°C for curing for 1 h to obtain a self-repairing photocatalytic degradation super hydrophobic coating.

[0050] Example 2 (1) 80g of halloysite nanotubes were placed in 1000g of 2mol / L H2SO4 solution, stirred by magnetic force, and acid-etched in a water bath at 80℃ for 2h, then filtered, washed, and dried to obtain the acid-etched HNTs powder. The acid-etched HNTs powder was added to 1000g of a 1wt% 1H,1H,2H,2H-perfluorooctyltrichlorosilane / anhydrous ethanol mixed solution, placed in a vacuum drying oven at 75℃ and 20Pa for 2h, and then allowed to stand at room temperature and pressure for 1h to obtain the halloysite nanotubes infused with fluorosilane.

[0051] (2) Take 10g of amorphous nano-TiO2 powder and calcine it at 650℃ for 3h to prepare anatase phase TiO2 powder with photocatalytic properties.

[0052] (3) 80 g of fluorosilane-infused halloysite nanotubes and 10 g of anatase phase TiO2 powder with photocatalytic properties were dispersed in 1000 g of anhydrous ethanol. Under magnetic stirring, glacial acetic acid was added dropwise to adjust the pH of the suspension to 6. The suspension was then stirred at room temperature for 2 h. The TiO2 particles were adsorbed on the surface of the halloysite nanotubes by electrostatic adsorption. After the reaction was completed, the product was washed twice by centrifugation with ethanol and dried at 100 °C to obtain a TiO2 / HNTs composite material with photocatalytic properties.

[0053] (4) 100 g of component A and 10 g of component B of PDMS (purchased from Shanghai Deji Trading Co., Ltd.) were dissolved in 500 g of hexane, and then 90 g of TiO2 / HNTs composite material with photocatalytic properties was added. Ultrasonic treatment was performed for 30 min to uniformly disperse the powder in the solution to obtain a self-repairing photocatalytic degradation super-hydrophobic coating.

[0054] (5) The wood substrate was cleaned and dried at 60°C. The self-repairing photocatalytic degradation super hydrophobic coating was evenly sprayed on the pretreated substrate surface by spraying. The spray gun was 20 cm away from the substrate, the spraying volume was 10 mL / min, the coating thickness was 5 μm, and then it was placed in an oven at 80°C for curing for 2 h to obtain a self-repairing photocatalytic degradation super hydrophobic coating.

[0055] Example 3 (1) 25g of halloysite nanotubes were placed in 500g of 2mol / L H2SO4 solution, stirred by magnetic force, and acid-etched in a water bath at 80℃ for 2h, then filtered, washed, and dried to obtain the acid-etched HNTs powder. The acid-etched HNTs powder was added to 300g of a 2wt% 1H,1H,2H,2H-perfluorooctyltrichlorosilane / anhydrous ethanol mixed solution, placed in a vacuum drying oven at 85℃ and 15Pa for 2h, and then allowed to stand at room temperature and pressure for 1h to obtain the halloysite nanotubes infused with fluorosilane.

[0056] (2) Take 5 g of amorphous nano-TiO2 powder and calcine it at 650℃ for 3 h to prepare anatase phase TiO2 powder with photocatalytic properties.

[0057] (3) 25 g of fluorosilane-infused halloysite nanotubes and 5 g of anatase phase TiO2 powder with photocatalytic properties were dispersed in 500 g of anhydrous ethanol. Under magnetic stirring, hydrochloric acid was added dropwise to adjust the pH of the suspension to 5. The suspension was then stirred at room temperature for 2 h. The TiO2 particles were adsorbed on the surface of the halloysite nanotubes by electrostatic adsorption. After the reaction was completed, the product was washed twice by centrifugation with ethanol and dried at 100 °C to obtain a TiO2 / HNTs composite material with photocatalytic properties.

[0058] (4) 80 g of PDMS component A and 10 g of component B (purchased from Shanghai Deji Trading Co., Ltd.) were dissolved in 500 g of hexane, and 30 g of TiO2 / HNTs composite material with photocatalytic properties was added. Ultrasonic treatment was performed for 30 min to uniformly disperse the powder in the solution to obtain a self-repairing photocatalytic degradation super-hydrophobic coating.

[0059] (5) The aluminum alloy substrate was cleaned and dried at 60°C. The self-repairing photocatalytic degradation super hydrophobic coating was evenly sprayed on the pretreated substrate surface by spraying. The spray gun was 20 cm away from the substrate, the spraying volume was 10 mL / min, the coating thickness was 5 μm, and then it was placed in an oven at 80°C for curing for 2 h to obtain a self-repairing photocatalytic degradation super hydrophobic coating.

[0060] Comparative Example 1 The only difference from Example 1 is that: there is no step (2), and 6 g of halloysite nanotubes infused with fluorosilane and 1 g of amorphous nano-TiO2 powder are directly dispersed in 100 g of anhydrous ethanol. Under magnetic stirring conditions, hydrochloric acid is added dropwise to adjust the pH of the suspension to 6, followed by stirring at room temperature for 2 h. The TiO2 particles are adsorbed on the surface of the halloysite nanotubes by electrostatic adsorption. After the reaction is completed, the obtained product is washed three times by centrifugation with ethanol and dried at 80°C to obtain a TiO2 / HNTs composite material.

[0061] The remaining steps are consistent with those in Example 1.

[0062] Comparative Example 2 The only difference from Example 1 is that in step (1), 6 g of halloysite nanotube powder is directly added to 50 g of a 1 wt % mixed solution of 1H,1H,2H,2H-perfluorodecyltriethoxysilane / anhydrous ethanol, stirred for reaction for 30 minutes, and then dried at 80° C. to obtain fluorosilane-loaded halloysite nanotubes.

[0063] The remaining steps are consistent with those in Example 1.

[0064] Comparative Example 3 The only difference from Example 1 is that there is no step (3), and 10 g of component A and 1 g of component B of PDMS are directly dissolved in 50 g of hexane, and then 1 g of anatase phase TiO2 powder with photocatalytic properties and 6 g of halloysite nanotubes infused with fluorosilane are added, and ultrasonic treatment is performed for 30 min to uniformly disperse the powder in the solution to obtain a self-repairing photocatalytic degradation super hydrophobic coating.

[0065] The remaining steps are consistent with those in Example 1.

[0066] Comparative Example 4 The only difference from Example 1 is that in step (3), aqueous ammonia is added dropwise to adjust the pH of the suspension to 9.

[0067] The remaining steps are consistent with those in Example 1.

[0068] Comparative Example 5 The only difference from Example 1 is that in step (3), hydrochloric acid is added dropwise to adjust the pH of the suspension to 3.5.

[0069] The remaining steps are consistent with those in Example 1.

[0070] Comparative Example 6 The only difference from Example 1 is that steps (1) and (3) are omitted. 10 g of component A and 1 g of component B of PDMS are dissolved in 50 g of hexane, and 7 g of anatase phase TiO2 powder with photocatalytic properties is added. The solution is ultrasonicated for 30 min to uniformly disperse the powder in the solution to obtain a photocatalytically degradable super-hydrophobic coating.

[0071] The remaining steps are consistent with those in Example 1.

[0072] Performance Testing Contact angle and rolling angle test: The static WCA and rolling angle of the sample surface were measured at room temperature using a contact angle goniometer (DCA 35, Dataphysics, Germany) equipped with a digital camera. Five points were randomly selected on each sample surface, and 2uL of deionized water was used to measure the WCA on its surface using the droplet method. The average value of these points was taken as the representative value of the sample WCA.

[0073] Oleic acid decomposition resistance test: The sample surface was contaminated with oleic acid, and the coated coating was immersed in a 7w% oleic acid-ethanol solution for 1 minute, and then pulled out. Subsequently, it was placed in a 60°C oven for 10 minutes and then taken out to test its contact angle. Then, after 24 hours of irradiation with a xenon lamp to simulate sunlight, the change in contact angle was tested. The operation was performed continuously for three cycles to check the change in contact angle before and after oleic acid contamination and illumination.

[0074] Super hydrophobic coating wear resistance test: 600-grit sandpaper with a 150 g weight is placed on the coating and pushed at a constant speed in one direction to conduct a friction test to examine the effect of wear on the hydrophobicity of the coating. Pulling it back in the opposite direction at the same speed is recorded as one wear cycle, and the coating wetting performance is tested after 20 cycles.

[0075] Table 1 Test results of coating wettability, oil resistance and wear resistance in different embodiments and comparative examples

[0076] See also Figure 1 ,pass Figure 1 It can be seen that through Coulomb electrostatic adsorption, nano-TiO2 particles are tightly compounded on the surface of the tubular structure of halloysite, thus constructing a multi-level rough structure on the surface of the material. Figure 2 ,pass Figure 2 It can be seen that under the action of polydimethylsiloxane, the agglomerates of TiO2 / HNTs composite materials are more easily connected into large particles, forming larger surface protrusions, making the surface rougher, thereby achieving a higher contact angle. Figure 3 and Table 1, by Figure 3 It can be seen from Table 1 that the initial water contact angle of the coating surface of Example 1 is 159°. After oleic acid contamination, the contact angle of the coating drops below 150°; after 24 hours of sunlight exposure, the contact angle rises back to 157°. The reason why the wettability of the coating surface is restored is that the electrons in the valence band of the anatase phase TiO2 exposed on the surface of the coating are excited to transition to the conduction band under the action of light, leaving relatively stable holes in the valence band. The defects and dangling bonds in the nanomaterials will capture electrons or holes and diffuse them to the surface of the particles, forming active oxygen species (such as -OH and -O 2- ), these active oxygen species have strong oxidizing ability and can react with the chemical bonds in the oleic acid molecules to decompose oleic acid into smaller inorganic substances, water and carbon dioxide, etc. After three oil pollution cycle tests, the coating contact angle is still 155°, indicating that the coating has strong recovery ability and stability. Figure 4 and Table 1, by Figure 4 As can be seen from Table 1, after 20 wear cycles, the hydrophobic angle of the coating surface of Example 1 is still 151°. This is due to the fact that on the one hand, the coating introduces halloysite with strong mechanical properties, which improves the wear resistance of the coating. On the other hand, since fluorosilane is grafted both inside and outside the halloysite nanotubes, when the halloysite structure is destroyed, the rough structure inside the tube is exposed, and at the same time, the low surface energy substances stored inside migrate to restore the original super hydrophobic properties of the material.

[0077] Please refer to Table 1. It can be seen from Table 1 that the initial water contact angle and rolling angle of the coating of Example 2 are 156° and 5.4° respectively, the water contact angle after 3 oleic acid pollution tests is 152°, and the water contact angle after 20 wear resistance tests is 147°, indicating that it has excellent superhydrophobic properties, photocatalytic degradation effect and good wear resistance.

[0078] Please refer to Table 1. It can be seen from Table 1 that the initial water contact angle and rolling angle of the coating of Example 3 are 157° and 4.9° respectively, the contact angle after 3 oleic acid pollution tests is 153°, and the contact angle after 20 wear resistance tests is 150°, indicating that it has excellent superhydrophobic properties, photocatalytic degradation effect and good wear resistance.

[0079] Please refer to Table 1. It can be seen from Table 1 that the initial water contact angle and rolling angle of the coating of Comparative Example 1 are 158° and 4.1° respectively, which are equivalent to those of Example 1, and both have excellent superhydrophobic properties; but after three oil stain tests, the contact angle is only 130°. This is because during the preparation of the coating of Comparative Example 1, the amorphous nano-TiO2 powder was not calcined, and the amorphous TiO2 does not have photocatalytic properties and cannot decompose oil stains, thereby failing to achieve self-cleaning performance.

[0080] Please refer to Table 1. It can be seen from Table 1 that the initial water contact angle and rolling angle of the coating of Comparative Example 2 are 156° and 5.6° respectively, which has good superhydrophobic performance. However, after 20 abrasion tests, the contact angle is only 136°. This is because during the preparation of the coating of Comparative Example 2, the halloysite nanotubes were not expanded and injected. When the surface structure was damaged, there was no low surface energy material migration to supplement, so self-repair could not be achieved.

[0081] Please refer to Table 1. It can be seen from Table 1 that the initial water contact angle and rolling angle of the coating of Comparative Example 3 are 150° and 9.8° respectively, and the hydrophobic performance is lower than that of Example 1. This is because in the preparation process of the coating of Comparative Example 3, the TiO2 particles are not adsorbed on the surface of the halloysite nanotubes through an electrostatic adsorption reaction in advance to construct a multi-level rough structure, which leads to a significant decrease in the hydrophobic performance.

[0082] Please refer to Table 1. It can be seen from Table 1 that the water contact angle and rolling angle of the coating of Comparative Example 4 are 145° and 14.8° respectively, and the hydrophobic performance is significantly lower than that of Example 1. The contact angle is 141° after 3 oleic acid resistance tests, and the contact angle is 137° after 20 wear resistance tests. This is because TiO2 is negatively charged under alkaline conditions, and halloysite nanotubes are also negatively charged. Like charges repel each other, and TiO2 is difficult to grow and adhere to the surface of halloysite nanotubes, and a multi-level rough structure cannot be constructed.

[0083] Please refer to Table 1. It can be seen from Table 1 that the water contact angle and rolling angle of the coating of Comparative Example 5 are 154° and 6.8° respectively. After three oleic acid tests, the contact angle is 150°, and the hydrophobicity is slightly lower than that of Example 1. However, after 20 wear tests, the contact angle is 140°, which is significantly lower. This is because although TiO2 is positively charged under strong acid conditions and can undergo strong electrostatic adsorption, under strong acid conditions, the fluorosilane infused into the halloysite nanotubes will undergo a hydrolysis reaction to generate silanol (Si-OH), resulting in a decrease in the performance of the fluorosilane. After the wear test, the low surface energy substances stored inside the tube cannot migrate to restore the original super-hydrophobic properties of the material.

[0084] Please refer to Table 1. It can be seen from Table 1 that the water contact angle and rolling angle of the coating of Comparative Example 6 are 157° and 4.8° respectively, and the hydrophobicity is slightly lower than that of Example 1. However, the contact angle is 137° after 3 oleic acid resistance tests, and the contact angle is 134° after 20 wear resistance tests, and the hydrophobicity is significantly reduced. This is because the specific surface area of ​​TiO2 nanoparticles is large, which makes it easy to agglomerate to form larger particles; since the photocatalytic reaction occurs on the surface of the material under light and pollutant adsorption, larger TiO2 particles will lead to a decrease in catalytic efficiency. The present invention not only solves the problem of the combination of the two properties, but also solves the problem of easy agglomeration of nano-TiO2 by depositing TiO2 on the surface of halloysite nanotubes. First, the composite of Ti and Si can fix nano-TiO2 on the larger halloysite nanotubes to prevent their agglomeration; on the other hand, amorphous SiO2 can act as an adsorbent to aggregate the organic molecules near the active sites of TiO2 on the particle surface; second, the hierarchical structure on the surface of the composite microspheres can further increase the local concentration of organic molecules near the TiO2 active layer, thereby improving the efficiency of the photocatalytic reaction; third, the hollow structure can improve the light collection efficiency by multiple reflections and scattering of light in the gaps inside the composite microspheres, which is beneficial to the progress of the photocatalytic reaction.

[0085] In summary, the present invention uses halloysite nanotubes as wall materials, perfuses low surface energy substances, and then compounds them with TiO2 having photocatalytic properties under acidic conditions of pH 5 to 6, and then sprays and cures them with polydimethylsiloxane to prepare a super-hydrophobic coating. The prepared coating has a contact angle with water of 156 to 159°, and a rolling angle of water droplets on its surface of 3.8° to 5.4°. After three oleic acid pollution decomposition tests, the hydrophobic angle was 152° to 155°; after 20 friction tests, the hydrophobic angle was 147° to 151°.

[0086] The specific implementation of the present invention described above does not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for preparing a self-repairing photocatalytic degradation super-hydrophobic coating, characterized in that: The following steps are involved: Performing pore expansion treatment on the halloysite nanotubes, and then infusing low surface energy substances to obtain halloysite nanotubes infusing low surface energy substances; The halloysite nanotubes and anatase phase nano-titanium dioxide infused with low surface energy substances are dispersed in a first organic solvent, the pH is adjusted to 5-6, and then an electrostatic adsorption reaction is performed, and finally a TiO2 / HNTs composite material is obtained by washing and drying; The TiO2 / HNTs composite material and polydimethylsiloxane are dispersed in a second organic solvent to obtain a self-repairing photocatalytic degradation super-hydrophobic coating.

2. The method for preparing the self-repairing photocatalytic degradation super-hydrophobic coating according to claim 1, characterized in that: The halloysite nanotubes are silicate minerals with an outer diameter of 40-60 nm and a length of 700-1500 nm; and / or, The low surface energy substance is fluorosilane; and / or, The particle size of the anatase phase nano titanium dioxide is 5-10 nm.

3. The method for preparing the self-repairing photocatalytic degradation super-hydrophobic coating according to claim 1, characterized in that: The process of hole enlargement includes: The halloysite nanotubes are subjected to acid etching and pore enlargement treatment using an acid solution, and then filtered, washed, and dried to obtain the acid-etched and pore-enlarged halloysite nanotubes; wherein, The acid solution is dilute sulfuric acid or dilute hydrochloric acid with a concentration of 1-3 mol / L and a solid-liquid ratio of 1:(10-30); and / or, The temperature of the acid etching pore expansion treatment is 60-90° C., the time of the acid etching pore expansion treatment is 2-4 hours, and the acid etching pore expansion treatment is performed under stirring conditions.

4. The method for preparing the self-repairing photocatalytic degradation super-hydrophobic coating according to claim 1, characterized in that: The process of infusing the low surface energy material comprises: A third organic solvent solution of a low surface energy substance is prepared, and the halloysite nanotubes after acid etching and pore expansion are mixed with the third organic solvent solution of the low surface energy substance, followed by vacuum extraction and standing at normal pressure to obtain halloysite nanotubes infused with the low surface energy substance; wherein, In the third organic solvent solution of the low surface energy substance, the mass fraction of the low surface energy substance is 1% to 2%; and / or, The third organic solvent is anhydrous ethanol; and / or, The mass ratio of the acid-etched and pore-expanded halloysite nanotubes to the third organic solvent solution of the low surface energy substance is 1:(5-20); and / or, The vacuum extraction temperature is 70-90°C, the vacuum extraction time is 1-2h, and the vacuum pressure is 0.1-133Pa; and / or, The temperature of the normal pressure standing is 20-30° C., and the time of the normal pressure standing is 0.5-1 h.

5. The method for preparing the self-repairing photocatalytic degradation super-hydrophobic coating according to claim 1, characterized in that: The mass ratio of the halloysite nanotubes infused with low surface energy substances to the anatase phase nano-titanium dioxide is (5-8):1; and / or, The mass ratio of the halloysite nanotubes infused with low surface energy substances to the first organic solvent is 1:(10-30); and / or, The first organic solvent is anhydrous ethanol; and / or, The temperature of the electrostatic adsorption reaction is 20-30° C., the time of the electrostatic adsorption reaction is 1-3 hours, and the electrostatic adsorption reaction is carried out under stirring.

6. The method for preparing the self-repairing photocatalytic degradation super-hydrophobic coating according to claim 1, characterized in that: The mass ratio of the TiO2 / HNTs composite material to polydimethylsiloxane is 1:(1-3); and / or, The mass ratio of the polydimethylsiloxane to the second organic solvent is 1:(3-8); and / or, The second organic solvent is hexane.

7. The method for preparing the self-repairing photocatalytic degradation super-hydrophobic coating according to claim 1, characterized in that: The polydimethylsiloxane includes a prepolymer and a cross-linking agent, and the mass ratio of the prepolymer to the cross-linking agent is (8-10):

1.

8. A self-repairing photocatalytic degradation super-hydrophobic coating, characterized in that: The self-repairing photocatalytically degradable super-hydrophobic coating is obtained by the preparation method of the self-repairing photocatalytically degradable super-hydrophobic coating according to any one of claims 1 to 7.

9. A self-repairing photocatalytic degradation super-hydrophobic coating, characterized in that: The self-repairing photocatalytic degradation super-hydrophobic coating is formed by applying the self-repairing photocatalytic degradation super-hydrophobic coating according to claim 8 to the surface of a substrate and curing it.

10. The self-repairing photocatalytic degradation super-hydrophobic coating according to claim 9, characterized in that: The coating method is spraying, and during the spraying process, the spray gun is 15-20 cm away from the substrate, the spraying amount is 8-10 mL / min; the coating thickness is 3-5 μm; and / or, The substrate is one of wood, a plastic substrate of PVC or PC, a glass substrate or an aluminum substrate or an alloy thereof; and / or, The curing temperature is 80-100° C., and the curing time is 0.5-2 hours.

Images