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

Abstract

The application discloses a self-repairing photocatalytic degradation super-hydrophobic coating and a preparation method and application thereof. The application selects halloysite nanotubes as wall materials, perfuses low-surface-energy substances, and then composites the halloysite nanotubes with TiO2 with photocatalytic performance under acidic conditions with a pH value of 5-6, realizes construction of a multi-level structure of a coating and improvement of photocatalytic performance through mutual attraction by regulation of coulomb electrostatic attraction, and then mixes the halloysite nanotubes with polydimethylsiloxane to obtain the self-repairing photocatalytic degradation super-hydrophobic coating. The super-hydrophobic coating formed after curing of the super-hydrophobic coating can realize self-repairing of the coating through a self-similar structure method, can decompose surface organic pollutants to realize self-cleaning, and has 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, a preparation method thereof, and applications thereof. Background Art

[0002] Inorganic pollutants mostly adhere to the coating surface in the form of particles, 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 mostly adhere to the coating surface and are difficult to achieve self-cleaning through the carrying effect of water droplets, thereby destroying the rough structure and causing the surface to gradually lose its self-cleaning properties.

[0003] In order to solve the problem of significantly reduced superhydrophobicity and durability of coatings after being contaminated by organic attachments, some researchers have proposed adding photocatalytic materials to superhydrophobic coatings to construct photocatalytic superhydrophobic self-cleaning coatings with multiple functions and better durability. Currently, there are three main methods for constructing photocatalytic superhydrophobic composite coatings: (1) surface construction method, but the photocatalytic superhydrophobic coating constructed solely by the surface construction method is too weak, resulting in generally poor mechanical wear resistance of the coating and inability to maintain high-efficiency photocatalytic performance and superhydrophobicity for a long time; (2) blending method, the coating performance 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 superhydrophobic self-cleaning coatings, and improving the mechanical wear resistance and self-healing properties of photocatalytic superhydrophobic 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:

[0007] performing pore enlargement treatment on the halloysite nanotubes, and then infusing low surface energy substances to obtain halloysite nanotubes infused with low surface energy substances;

[0008] Halloysite nanotubes infused with low surface energy substances and anatase-phase nano-titanium dioxide are dispersed in a first organic solvent, the pH is adjusted to 5-6, and then an electrostatic adsorption reaction is carried out. Finally, the TiO2 / HNTs composite material is obtained by washing and drying.

[0009] The TiO2 / HNTs composite material and polydimethylsiloxane are dispersed in a second organic solvent to obtain a self-repairing photocatalytic degradation super-hydrophobic coating.

[0010] In a second aspect, the present invention provides a self-repairing photocatalytically degradable super-hydrophobic coating, which is obtained by the preparation method of the self-repairing photocatalytically degradable super-hydrophobic coating provided by the first aspect of the present invention.

[0011] 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.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] 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, and realizes coating multi-level structure construction and photocatalytic performance improvement by mutual attraction of regulating and controlling Coulomb electrostatic attraction, and then obtains tool self-repairing photocatalytic degradation super-hydrophobic coating by mixing 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 possessing good wear resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a SEM image of the TiO2 / HNTs composite material obtained in Example 1 of the present invention;

[0015] Figure 2 This is a SEM image of the coating obtained in Example 1 of the present invention;

[0016] 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 contamination and light exposure times;

[0017] Figure 4 Graphs showing the wear resistance of the coating obtained in Example 1 of the present invention; (a) is a diagram showing the wear resistance test process in Example 1, and (b) is a photograph showing the static water contact angle of the coating after 20 wear resistance cycles. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to 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.

[0019] In a first aspect, the present invention provides a method for preparing a self-repairing photocatalytic degradation super-hydrophobic coating, comprising the following steps:

[0020] S1, performing pore expansion treatment on halloysite nanotubes (HNTs), and then infusing low surface energy materials to obtain halloysite nanotubes infused with low surface energy materials;

[0021] 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;

[0022] S3. Dispersing the TiO2 / HNTs composite material and polydimethylsiloxane (PDMS) in a second organic solvent to obtain a self-repairing photocatalytic degradation superhydrophobic coating.

[0023] The present invention is by selecting mechanical strength high, chemical stability is good and with the halloysite nanotube of hollow tubular structure as wall material, perfusion low surface energy material, make material surface and inside have identical hydrophobic component and structure, when surface structure or composition are by mechanical friction and other environmental destruction, the rough structure inside halloysite nanotube is exposed, and the low surface energy material stored in inside is by migrating to the surface so that material recovers its original super-hydrophobicity, realizes the self-repairing performance of super-hydrophobic coating. Under the acidic conditions of pH being 5~6, TiO2 surface is positively charged, halloysite surface is negatively charged, utilizes electrostatic adsorption reaction, by nano-TiO2 particles are composited on the halloysite surface of tubular structure, build multi-level rough structure on material surface, realize the compound of super-hydrophobic-photocatalytic performance, obtain the TiO2 / HNTs composite material with photocatalytic activity, multi-scale structure. The cleaning mechanism brought by the super-hydrophobic surface can effectively remove Class I pollutants such as dust, water stains, mud and water from the material surface; the cleaning mechanism brought by the photocatalytic performance can remove Class II pollutants such as oil stains, grease stains, and organic molecules such as microorganisms from the material surface. The two cleaning mechanisms complement and protect each other on the surface, realizing the dual self-cleaning function of RD on the material surface. At the same time, the addition of halloysite nanotubes gives the coating 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.

[0024] In this embodiment, halloysite (HNTs) is a silicate mineral with a molecular formula of Al2SiO2(OH)4·nH2O. The inner and outer surfaces are composited with Al-OH and Si-OH groups. It has a tubular shape with an outer diameter in the range of 40-60 nm and a length in the range of 700-1500 nm.

[0025] In this embodiment, in step S1 , the hole enlarging process is performed by acid etching.

[0026] Preferably, the acid etching and pore enlargement process comprises: subjecting the halloysite nanotubes to an 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.

[0027] During the acid etching and pore enlargement process, the acid solution is dilute sulfuric acid or dilute hydrochloric acid with a concentration of 1 to 3 mol / L; the solid-liquid ratio is 1: (10 to 30); the temperature of the acid etching and pore enlargement process is 60 to 90° C., and the time of the acid etching and pore enlargement process is 2 to 4 hours; the acid etching and pore enlargement process is carried out under stirring conditions.

[0028] In this embodiment, in step S1 , the low surface energy substance is fluorosilane.

[0029] Preferably, the fluorosilane is at least one of 1H,1H,2H,2H-perfluorooctyltrichlorosilane and 1H,1H,2H,2H-perfluorodecyltriethoxysilane.

[0030] 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 allowing the solution to stand at atmospheric pressure to obtain the halloysite nanotubes infused with the low-surface-energy substance. The vacuum extraction and atmospheric pressure allowing the solution to stand ensure that the halloysite is fully loaded with the low-surface-energy substance.

[0031] 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%.

[0032] Preferably, the third organic solvent is anhydrous ethanol.

[0033] 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).

[0034] Preferably, the vacuum extraction temperature is 70-90° C., the vacuum extraction time is 1-2 hours, and the vacuum pressure is 0.1-133 Pa.

[0035] 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.

[0036] In this embodiment, in step S2, the particle size of the anatase phase nano-titanium dioxide is 5-10 nm.

[0037] 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. This process can transform amorphous nano-TiO2 into anatase nano-TiO2 with photocatalytic activity under high temperature conditions.

[0038] In this embodiment, in step S2, the mass ratio of the halloysite nanotubes infused with the low-surface-energy material to anatase-phase nano-titanium dioxide is (5-8):1. If the TiO2 ratio is too low, the surface roughness of the halloysite nanotubes is low, and the photocatalytic efficiency is low. If the TiO2 ratio is too high, there are insufficient halloysite nanotubes to provide a skeletal support, resulting in a high amount of free TiO2. While photocatalytic performance may be improved, the lack of a multi-level roughness structure may actually reduce hydrophobicity.

[0039] In this embodiment, in step S2, the first organic solvent is anhydrous ethanol.

[0040] 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).

[0041] In this embodiment, in step S2, the pH is adjusted to 5-6 by dropwise addition of hydrochloric acid or glacial acetic acid.

[0042] 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.

[0043] In this embodiment, in step S3, the mass ratio of the TiO2 / HNTs composite material to polydimethylsiloxane is 1:(1-3). In the present invention, PDMS not only serves as a low-surface-energy material but also as a binder between the multi-scale micro-nanoparticles and the substrate. The combined effects of the rough structure and low surface energy achieve super-hydrophobic properties on the composite surface. Furthermore, the degree of TiO2 exposure determines the photocatalytic properties of the composite coating. Too little PDMS can significantly expose the multi-scale structure, enhancing the hydrophobic effect, but it fails to connect and secure the particles, compromising coating stability. Too much PDMS can coat the fine surface structure of the particles, preventing super-hydrophobic properties.

[0044] 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.

[0045] In this embodiment, in step S3, the second organic solvent is hexane.

[0046] In this embodiment, in step S3, the mass ratio of polydimethylsiloxane to the second organic solvent is 1:(3-8).

[0047] In this embodiment, in step S3, ultrasonic dispersion is adopted.

[0048] Preferably, the ultrasonic dispersion time is 20 to 40 minutes.

[0049] In a second aspect, the present invention provides a self-repairing photocatalytically degradable super-hydrophobic coating, which is obtained by the preparation method of the self-repairing photocatalytically degradable super-hydrophobic coating provided by the first aspect of the present invention.

[0050] 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.

[0051] The present invention does not limit the coating method, and those skilled in the art may select a coating method based on actual circumstances. In some embodiments of the present invention, spray coating is employed. More specifically, the spray gun is positioned 15 to 20 cm from the substrate, the spray rate is 8 to 10 mL / min, and the coating thickness is 3 to 5 μm.

[0052] 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 or alloy substrate.

[0053] Preferably, the substrate needs to be pretreated before coating, and the pretreatment method includes: washing and drying the substrate.

[0054] In this embodiment, the curing temperature is 80-100° C., and the curing time is 0.5-2 hours.

[0055] Example 1

[0056] (1) Take 6 g of halloysite nanotubes and put them into 100 g of H2SO4 solution with a concentration of 2 mol / L. Stir magnetically, and acid-etch at a water bath temperature of 80 °C for 2 h. Then filter, wash, and dry to obtain the HNTs powder after acid-etching and hole expansion. Add the HNTs powder after acid-etching and hole expansion to 50 g of a mixed solution of 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane and anhydrous ethanol with a concentration of 1 wt%, and place it in a vacuum drying oven with a temperature of 80 °C and a vacuum pressure of 8 Pa for vacuum extraction for 1 h. Then stand at room temperature and normal pressure for 0.5 h to obtain halloysite nanotubes filled with fluorosilane.

[0057] (2) Take 1 g of amorphous nano-TiO2 powder and calcine it at 600 °C for 3 h to prepare anatase TiO2 powder with photocatalytic properties.

[0058] (3) Disperse 6 g of halloysite nanotubes filled with fluorosilane and 1 g of anatase TiO2 powder with photocatalytic properties in 100 g of anhydrous ethanol. Under magnetic stirring, add hydrochloric acid dropwise to adjust the pH of the suspension to 6, and then stir at room temperature for 2 h. Through electrostatic adsorption, TiO2 particles are adsorbed on the surface of the halloysite nanotubes. After the reaction is completed, the obtained product is washed by centrifugation with ethanol for 3 times, and dried at 80 °C to obtain a TiO2 / HNTs composite material with photocatalytic properties.

[0059] (4) Dissolve 10 g of the A component and 1 g of the B component of PDMS (purchased from Shanghai Deji Commerce and Trade Co., Ltd.) in 50 g of hexane, and then add 7 g of the TiO2 / HNTs composite material with photocatalytic properties. Ultrasonic for 30 min to uniformly disperse the powder in the solution, and obtain a self-repairing photocatalytic degradation super-hydrophobic coating.

[0060] (5) Clean the glass substrate and dry it at 60 °C. Use the spraying method to uniformly spray the self-repairing photocatalytic degradation super-hydrophobic coating on the surface of the pretreated substrate. The distance between the spray gun and the substrate is 15 cm, the spraying amount is 8 mL / min, and the coating thickness is 4 μm. Then place it in an oven at 100 °C for 1 h to cure, and obtain a self-repairing photocatalytic degradation super-hydrophobic coating.

[0061] Example 2

[0062] (1) 80 g of halloysite nanotubes were placed in 1000 g of a 2 mol / L H2SO4 solution, magnetically stirred, and acid-etched in an 80°C water bath for 2 h. The solution was then filtered, washed, and dried to obtain acid-etched HNT powder. The acid-etched HNT powder was then added to 1000 g of a 1 wt% 1H,1H,2H,2H-perfluorooctyltrichlorosilane / anhydrous ethanol mixed solution. The solution was then placed in a vacuum drying oven at 75°C and a vacuum pressure of 20 Pa for 2 h. The solution was then allowed to stand at room temperature and pressure for 1 h to obtain halloysite nanotubes impregnated with fluorosilane.

[0063] (2) Take 10g of amorphous nano-TiO2 powder and calcine it at 650℃ for 3h to prepare anatase phase TiO2 powder with photocatalytic properties.

[0064] (3) 80 g of fluorosilane-infused halloysite nanotubes and 10 g of anatase 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 obtained product was centrifuged and washed twice with ethanol and dried at 100 °C to obtain a TiO2 / HNTs composite material with photocatalytic properties.

[0065] (4) 100 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 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 superhydrophobic coating.

[0066] (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, and the coating thickness was 5 μm. Then, the substrate was placed in an oven at 80°C for 2 h to cure, thereby obtaining a self-repairing photocatalytic degradation super-hydrophobic coating.

[0067] Example 3

[0068] (1) 25 g of halloysite nanotubes were placed in 500 g of a 2 mol / L H2SO4 solution, magnetically stirred, and acid-etched in an 80°C water bath for 2 h. The solution was then filtered, washed, and dried to obtain acid-etched HNT powder. The acid-etched HNT powder was then added to 300 g of a 2 wt% 1H,1H,2H,2H-perfluorooctyltrichlorosilane / anhydrous ethanol mixed solution. The solution was then placed in a vacuum drying oven at 85°C and a vacuum pressure of 15 Pa for 2 h. The solution was then allowed to stand at room temperature and pressure for 1 h to obtain halloysite nanotubes impregnated with fluorosilane.

[0069] (2) 5 g of amorphous nano-TiO2 powder was calcined at 650 °C for 3 h to prepare anatase phase TiO2 powder with photocatalytic properties.

[0070] (3) 25 g of fluorosilane-infused halloysite nanotubes and 5 g of anatase 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. Then, the suspension was 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 obtained product was centrifuged and washed twice with ethanol and dried at 100 °C to obtain a TiO2 / HNTs composite material with photocatalytic properties.

[0071] (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 superhydrophobic coating.

[0072] (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, and the coating thickness was 5 μm. Then, the substrate was placed in an oven at 80°C for curing for 2 h to obtain a self-repairing photocatalytic degradation super-hydrophobic coating.

[0073] Comparative Example 1

[0074] The only difference from Example 1 is that: step (2) is omitted, 6 g of fluorosilane-infused halloysite nanotubes and 1 g of amorphous nano-TiO2 powder are directly dispersed in 100 g of anhydrous ethanol, and hydrochloric acid is added dropwise under magnetic stirring to adjust the pH of the suspension to 6. Then, the suspension is stirred at room temperature for 2 h, and the TiO2 particles are adsorbed on the surface of the halloysite nanotubes by electrostatic adsorption. After the reaction is completed, the obtained product is centrifuged and washed three times with ethanol, and dried at 80°C to obtain a TiO2 / HNTs composite material.

[0075] The remaining steps are consistent with Example 1.

[0076] Comparative Example 2

[0077] The difference from Example 1 is only that in step (1), 6 g of halloysite nanotube powder is directly added to a mixed solution of 50 g of 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane / anhydrous ethanol with a concentration of 1 wt%, and after stirring for 30 minutes, drying at 80°C to obtain fluorosilane-loaded halloysite nanotubes.

[0078] The remaining steps are consistent with Example 1.

[0079] Comparative Example 3

[0080] The difference from Example 1 is only that there is no step (3), and 10 g of the A component of PDMS, 1 g of the B component, 1 g of anatase TiO2 powder with photocatalytic properties, and 6 g of fluorosilane-filled halloysite nanotubes are dissolved in 50 g of hexane, and ultrasonic dispersion is performed for 30 min to obtain a self-repairing photocatalytic degradation superhydrophobic coating.

[0081] The remaining steps are consistent with Example 1.

[0082] Comparative Example 4

[0083] The difference from Example 1 is only that in step (3), ammonia water is added to adjust the pH of the suspension to 9.

[0084] The remaining steps are consistent with Example 1.

[0085] Comparative Example 5

[0086] The difference from Example 1 is only that in step (3), hydrochloric acid is added to adjust the pH of the suspension to 3.5.

[0087] The remaining steps are consistent with Example 1.

[0088] Comparative Example 6

[0089] The difference from Example 1 is only that there is no step (1) and (3), and 10 g of the A component of PDMS, 1 g of the B component, and 7 g of anatase TiO2 powder with photocatalytic properties are dissolved in 50 g of hexane, and ultrasonic dispersion is performed for 30 min to obtain a photocatalytic degradation superhydrophobic coating.

[0090] The remaining steps are consistent with Example 1.

[0091] Performance Test

[0092] Contact Angle and Sliding Angle Measurements: Static WCA and sliding angle measurements were performed at room temperature using a contact angle goniometer (DCA 35, Dataphysics, Germany) equipped with a digital camera. The WCA was measured using the droplet method using 2 μL of deionized water at five randomly selected points on each sample surface. The average of these points was used as the representative WCA value for the sample.

[0093] Oleic acid degradation resistance test: The sample surface was contaminated with oleic acid. The coated coating was immersed in a 7% oleic acid-ethanol solution for 1 minute and then removed from the sample. The sample was then oven-dried at 60°C for 10 minutes before removal and contact angle measurement. After 24 hours of exposure to simulated sunlight using a xenon lamp, the contact angle change was measured. Three cycles of this operation were repeated to examine the change in contact angle before and after oleic acid contamination and exposure.

[0094] Testing the abrasion resistance of superhydrophobic coatings: A 600-grit sandpaper loaded with a 150g weight was placed on the coating and pushed at a constant speed in one direction. This friction test examined the effect of wear on the coating's hydrophobic properties. The paper was then pulled back in the opposite direction at the same speed, resulting in one abrasion cycle. After 20 cycles, the coating's wettability was tested.

[0095] Table 1 Test results of coating wettability, oil resistance and wear resistance in different examples and comparative examples

[0096]

[0097] 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 3As can be seen from Table 1, the initial water contact angle of the coating surface in Example 1 was 159°. After oleic acid contamination, the contact angle of the coating dropped below 150°; after 24 hours of sunlight exposure, the contact angle rebounded to 157°. The reason for the recovery of the wettability of the coating surface is that, under the action of light, the electrons in the valence band of the anatase phase TiO2 exposed on the coating surface are excited and transferred to the conduction band, leaving relatively stable holes in the valence band. The defects and dangling bonds in the nanomaterials capture electrons or holes, causing them to diffuse 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, breaking down the oleic acid into smaller inorganic substances, water, and carbon dioxide. After three oil pollution cycles, 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, the hydrophobic angle of the coating surface of Example 1 is still 151° after 20 wear cycles. 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 on the inside and outside of 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, allowing the material to restore its original superhydrophobic properties.

[0098] 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°. 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.

[0099] 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.

[0100] Refer to Table 1. As can be seen, the initial water contact angle and sliding angle of the coating in Comparative Example 1 were 158° and 4.1°, respectively, comparable to those in Example 1, demonstrating excellent superhydrophobicity. However, after three oil stain tests, the contact angle was only 130°. This is because the amorphous nano-TiO2 powder was not calcined during the coating preparation process in Comparative Example 1. As a result, the amorphous TiO2 lacks photocatalytic properties and cannot decompose oil stains, thus failing to achieve self-cleaning properties.

[0101] Refer to Table 1. The coating in Comparative Example 2 exhibits excellent superhydrophobic properties with initial water contact and sliding angles of 156° and 5.6°, respectively. However, after 20 abrasion tests, the contact angle is only 136°. This is because the halloysite nanotubes were not pore-enlarged and injected during the preparation of the coating in Comparative Example 2. Consequently, when the surface structure is damaged, there is no migration of low-surface-energy substances to replenish it, preventing self-repair.

[0102] 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. 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.

[0103] Refer to Table 1, which shows that the water contact angle and sliding angle of the coating in Comparative Example 4 are 145° and 14.8°, respectively, indicating significantly lower hydrophobicity compared to Example 1. The contact angle after three oleic acid resistance tests is 141°, and after 20 abrasion tests, the contact angle is 137°. This is because TiO2 exhibits a negative charge under alkaline conditions, while halloysite nanotubes also exhibit a negative charge. Like charges repel each other, making it difficult for TiO2 to grow and adhere to the halloysite nanotube surface, preventing the formation of a hierarchical roughness structure.

[0104] 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 resistance tests, the contact angle is 150°, indicating a slight decrease in hydrophobicity compared to Example 1. However, after 20 abrasion resistance tests, the contact angle is 140°, showing a significant decrease. 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 undergoes a hydrolysis reaction to form silanol (Si-OH), resulting in a decrease in the performance of the fluorosilane. After the abrasion resistance test, the low surface energy substances stored in the tubes cannot migrate to restore the material to its original superhydrophobic properties.

[0105] 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, indicating a significant decrease in hydrophobicity. 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 by depositing TiO2 on the surface of halloysite nanotubes, but also solves the problem of easy agglomeration of nano-TiO2. First, the composite of Ti and Si can, on the one hand, fix nano-TiO2 on the larger halloysite nanotubes to prevent their agglomeration; on the other hand, amorphous SiO2 can act as an adsorbent, causing organic molecules near the active sites of TiO2 to aggregate 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.

[0106] In summary, the present invention uses halloysite nanotubes as wall material, perfuses low surface energy substances, and then compounds them with TiO2 having photocatalytic properties under acidic conditions of pH 5 to 6. It is then mixed with polydimethylsiloxane, sprayed, and cured to prepare a super-hydrophobic coating. The prepared coating has a contact angle with water of 156 to 159°, and the rolling angle of water droplets on its surface is 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°.

[0107] The specific embodiments of the present invention described above do not limit the scope of protection 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 scope of protection 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 enlargement treatment on the halloysite nanotubes, and then infusing low surface energy substances to obtain halloysite nanotubes infused with low surface energy substances; The halloysite nanotubes and anatase 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 the 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; wherein, The low surface energy substance is fluorosilane.

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

3. The preparation method of the self-repairing photocatalytic degradation super-hydrophobic coating according to claim 1, wherein The process of the hole enlarging treatment 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 a self-repairing photocatalytic degradation super-hydrophobic coating according to claim 1, wherein The process of infusing the low surface energy material includes: 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 1-2 hours, and the vacuum pressure is 0.1-133 Pa; 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 preparation method of the self-repairing photocatalytic degradation super-hydrophobic coating according to claim 1, wherein The mass ratio of the halloysite nanotubes infused with low surface energy substances to anatase phase nano-titanium dioxide is (5-8):1; and / or, The mass ratio of the halloysite nanotubes infused with the low surface energy substance 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 a self-repairing photocatalytic degradation super-hydrophobic coating according to claim 1, wherein 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 a self-repairing photocatalytic degradation super-hydrophobic coating according to claim 1, wherein 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 photocatalytically degradable super-hydrophobic coating is formed by applying the self-repairing photocatalytically degradable 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 to 20 cm away from the substrate, the spraying amount is 8 to 10 mL / min; the coating thickness is 3 to 5 μm; and / or, The substrate is one of wood, a plastic substrate made 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.

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