Green preparation method of halloysite nano sol with high transparency and high solution stability and application of halloysite nano sol as photovoltaic glass coating filler

Abstract

The invention discloses a green preparation method of halloysite nano sol with high transparency and high solution stability and application of the halloysite nano sol as a photovoltaic glass coating filler. The method comprises the following steps: carrying out surface modification on halloysite through an amination-carboxylation two-step modification strategy: firstly, carrying out surface amination on the halloysite by adopting a silane coupling agent method, a polymer grafting method or a click chemistry method, and then reacting with anhydride or active ester molecules containing electrophilic groups to prepare carboxylation modified halloysite nano sol; finally, mixing with tetraethyl orthosilicate, resin and a surfactant to prepare a photovoltaic glass spraying solution; the surface charge of halloysite is regulated and controlled through amination-carboxylation, so that the absolute value of the Zeta potential of the modified solution is increased, and the stability of the solution is greatly improved; the visible light transmittance is greater than 90%, and the material can significantly improve the power generation efficiency of a photovoltaic module as a photovoltaic glass coating filler, and has a good industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of self-cleaning photovoltaic glass coating technology, specifically to a green preparation method of halloysite nanosol with high transparency and high solution stability and its application as a filler in photovoltaic glass coatings. Background Technology

[0002] As a crucial component of solar cell modules, photovoltaic glass relies heavily on self-cleaning coatings to enhance solar energy absorption and conversion efficiency. Halloysite (HNTs) and surfactants work synergistically to achieve long-lasting self-cleaning properties in coatings: Halloysite, a natural nano-hollow tubular material, possesses a unique hollow cavity structure with excellent loading capacity, efficiently loading functional substances (such as low surface energy molecules). In coating applications, it slowly releases the loaded material within the cavity, creating a long-lasting functional release effect. This prevents the rapid loss of functional components due to environmental factors such as rainwater erosion and UV radiation, ensuring the coating's sustained performance. Simultaneously, the surfactants in the system, through molecular adsorption, construct a stable hydrophilic layer on the HNTs surface and the overall coating interface. This allows rainwater to form a continuous water film on the coating surface, quickly washing away dust, stains, and other contaminants, reducing contaminant adhesion.

[0003] Based on the above synergistic properties, halloysite and surfactants are ideal choices for fillers in photovoltaic glass coatings. However, unmodified halloysite nanosols have several problems: on the one hand, halloysite solutions have insufficient light transmittance, and its nanoparticles aggregate randomly in the solution to form scattering centers, resulting in an average transmittance of less than 80% in the visible light region, far below the performance requirements of photovoltaic glass for high-transmittance coatings (transmittance ≥90%); on the other hand, the dispersion defects of halloysite in solution are more prominent. Affected by the hydrogen bonding initiated by its surface hydroxyl groups, the particles are prone to agglomeration, making it difficult to form a stable electrostatic repulsion system. This agglomeration phenomenon not only leads to poor storage stability of the coating solution, with obvious stratification after standing for 24 hours and cotton-like precipitates appearing in the lower liquid, but also causes uneven thickness during film formation, further aggravating the light scattering effect, significantly reducing the transparency of the coating, and ultimately increasing the optical loss of the photovoltaic glass.

[0004] While some progress has been made in the modification of halloysite, such as surface grafting and coating, or improving its properties by adding dispersants, existing technologies still have significant limitations. For example, the surface grafting or coating of halloysite relies on organic solvents such as toluene and DMF, and residual solvents can form micropores during the curing stage, affecting the consistency of the optical performance of photovoltaic glass. Increasing the dispersant concentration can alleviate agglomeration, but it introduces impurities that affect the coating quality, reducing the optical uniformity and light transmittance of the photovoltaic glass. Notably, no research reports have yet been found on how to improve the transparency of self-cleaning halloysite solutions. Therefore, developing a method for preparing halloysite coatings that can synergistically improve transparency and solution stability is particularly important. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a green preparation method for halloysite nanosols with high transparency and high solution stability, as well as their application as a filler in photovoltaic glass coatings. This method uses an ethanol / water green solvent system and modifies the surface of halloysite through a two-step modification strategy of "amylation-carboxylation": First, halloysite surface amylation is achieved using a silane coupling agent method, polymer grafting method, or click chemistry method. Then, it reacts with anhydrides or active esters containing electrophilic groups to obtain carboxylated modified halloysite nanosols. Finally, it is mixed with tetraethyl orthosilicate, resin, and surfactant to obtain a photovoltaic glass coating solution. This invention regulates the surface charge of halloysite through "amylation-carboxylation," increasing the absolute value of the Zeta potential of the modified solution and significantly improving solution stability. The visible light transmittance is >90%, optimizing the halloysite system, which is prone to stratification due to density differences and has poor stability. This not only improves the stability of the halloysite solution but also enhances its film-forming transparency. As a filler in photovoltaic glass coatings, it can significantly improve the power generation efficiency of photovoltaic modules and has good prospects for industrial application.

[0006] To achieve the above technical effects, the following technical solution is adopted: A green preparation method for halloysite nanosols with high transparency and high solution stability includes: Step S1: Take a certain amount of halloysite and disperse it in an ethanol / water mixed solvent. After the halloysite is dispersed to form a homogeneous suspension, perform surface amination treatment on the halloysite. Step S2: After the surface amination reaction in step S1 is completed, the mixture is centrifuged, washed alternately with deionized water and anhydrous ethanol, and dried under vacuum to obtain ammoniated halloysite. Step S3: Take the aminated halloysite obtained in step S2, disperse it in an ethanol solution, and after it is evenly dispersed, add an acid anhydride compound or active ester molecule containing an electrophilic group and stir to react with the aminated halloysite. Step S4: After the reaction in step S3 is completed, centrifuge and wash the product to obtain carboxylated modified halloysite; Step S5: Disperse the carboxylated modified halloysite obtained in step S4 in water, add tetraethyl orthosilicate and ammonia in sequence, stir once, then add surfactant, acrylic resin and amino resin, and stir and mix twice under vacuum to obtain photovoltaic glass spraying solution, which is the halloysite nanosol with high transparency and high solution stability.

[0007] Furthermore, in step S1, the dispersion method of halloysite in the ethanol / water mixed solvent is ultrasonic dispersion, and the volume ratio of ethanol to water in the ethanol / water mixed solvent is 7:3.

[0008] Furthermore, in step S1, the method for surface amination treatment of halloysite is silane coupling agent method, polymer grafting method, or click chemistry method.

[0009] Furthermore, the silane coupling agent method introduces amino groups by reacting a silane coupling agent with the hydroxyl groups on the halloysite surface; the polymer grafting method introduces amino groups by adding a silane coupling agent containing double bonds, grafting double bonds, and then polymerizing with an amino-containing monomer; the click chemistry method first grafts alkynyl groups, and then reacts with an amino reagent containing azide groups under copper catalysis to undergo a 1,3-dipolar cycloaddition reaction, thus introducing amino groups.

[0010] Furthermore, in step S3, the method of dispersing in the ethanol solution is ultrasonic dispersion; the anhydride compounds containing electrophilic groups include, but are not limited to, maleic anhydride, acetic anhydride, succinic anhydride, phthalic anhydride, hexanoic anhydride, and indigo anhydride; the active ester molecules include, but are not limited to, succinimide monosuccinate and 6-carboxyhexanoic acid succinimide.

[0011] Furthermore, in step S3, the stirring reaction temperature is 25-60℃, and the stirring time is 3-8 hours.

[0012] Furthermore, in step S5, the first stirring temperature is 50℃ and the stirring time is 0.5 h; the vacuum condition is 0.01 MPa; the second stirring temperature is 80℃ and the time is 2 hours; the viscosity of the photovoltaic glass spraying solution is 15-20 mPa·s; the solid content is 10-15 wt%; the transmittance in the visible light range is >90%; and it is stable and does not separate after standing for 1 day.

[0013] Furthermore, in step S5, the mass-to-volume ratio of carboxylated modified halloysite, water, tetraethyl orthosilicate, ammonia, surfactant, acrylic resin, and amino resin is: 0.1–0.5 g carboxylated modified halloysite: 85–95 mL water: 1–4 g tetraethyl orthosilicate: 1–3 mL ammonia: 1–6 g surfactant: 0.8–3 g acrylic resin, 0.2–1 g amino resin; the surfactant includes, but is not limited to, sodium dodecylbenzenesulfonate, sodium hexadecyl sulfate, sodium dodecyl sulfate, and sodium α-alkenyl sulfonate.

[0014] In anhydrous ethanol, the reaction of acid anhydrides with aminated halloysite (HNTs-NH2) mainly involves the ring-opening reaction of the anhydride with the aminated halloysite. Essentially, this involves the nucleophilic attack of the amino group (-NH2) on the anhydride ring, leading to ring breakage and the formation of an amide bond (-CONH-). Simultaneously, a carboxyl group (-COOH) is introduced at the end of the modified chain, and this carboxyl group is covalently linked to the HNTs surface via a carbon chain. Taking succinic anhydride as an example, the reaction formula is as follows: HNTs-NH2+(CH2CO)2O→HNTs-NH-CO-CH2-CH2-COOH; In anhydrous ethanol, the active ester molecule and aminated halloysite primarily undergo an amine uncoupling reaction. The ester group of the active ester molecule is connected to a strongly electron-withdrawing group, which significantly enhances the positive charge of the ester group carbon atom and greatly improves the nucleophilic reactivity. When in contact with aminated halloysite, the lone pair electrons in the amino group attack the electron-deficient carbon atom of the active ester group, initiating the breakage of the carbon-oxygen single bond of the ester group and forming a stable amide bond. Simultaneously, a carboxyl group is introduced at the end of the modified chain, and the carboxyl group is covalently connected to the HNTs surface through the carbon chain. Taking succinic acid monosuccinimide ester as an example, the reaction formula is as follows: HNTs-NH2 + HOOC-CH2-CH2-CO-O-NHS → HNTs-NH-CO-CH2-CH2-COOH + NHS-H The introduction of carboxyl groups significantly increases the absolute value of the Zeta potential on the halloysite surface, enhances the electrostatic repulsion between particles, effectively suppresses the aggregation phenomenon caused by hydroxyl hydrogen bonds, and makes the nanosol less prone to stratification during storage, thus greatly improving its stability. At the same time, the uniformly dispersed single particles or small aggregates reduce the scattering and absorption of light, significantly improving the visible light transmittance of the solution and the film, thereby achieving a synergistic improvement in transparency and stability.

[0015] A halloysite nanosol with high transparency and high solution stability is prepared by any of the above preparation methods.

[0016] The application of halloysite nanosol in the field of self-cleaning photovoltaic glass coating.

[0017] The beneficial effects of this invention are as follows: 1. A simple modification strategy of "amylation-carboxylation" of halloysite is adopted to simultaneously achieve solution stability and high transparency of film coating; 2. Breaking through the limitations of traditional halloysite modification which relies on organic solvents such as toluene and DMF, this method uses ethanol and water as solvents throughout the process, making it green, environmentally friendly, and safe. 3. By utilizing the double bond structure of acid anhydride molecules and reactive ester molecules, reactive sites are retained while introducing carboxyl groups, providing anchor points for subsequent functionalization. 4. The preparation process of carboxylation to regulate the surface charge of halloysite and improve the dispersion stability and high transparency of the film coating is simple and easy to operate, does not require expensive and complex equipment, has low process cost, and has significant effects. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the preparation process of the carboxylated halloysite-based photovoltaic glass spraying solution with self-cleaning properties in an embodiment of the present invention; Figure 2 Transmission electron microscopy (TEM) images of unmodified halloysite and carboxyl-modified halloysite in the embodiments of the present invention; Figure 3 The infrared spectra of unmodified halloysite and modified halloysite in the embodiments of the present invention are shown. Figure 4 These are the Zeta potential distribution curves of the unmodified halloysite coating solution and the carboxyl-modified halloysite coating solution in the embodiments of the present invention; Figure 5 This is a photograph of the sedimentation state of halloysite in the amino-modified halloysite solution after it has been left to stand for 12 hours in an embodiment of the present invention. Figure 6 The images show the sedimentation state of halloysite in the solutions of the unmodified halloysite solution and the carboxyl-modified halloysite coating solution after standing for 24 hours in an embodiment of the present invention. Figure 7 The transmittance-wavelength curves of the unmodified halloysite coating solution and the carboxyl-modified halloysite solution in the embodiments of the present invention are shown. Figure 8 The transmittance-wavelength curves of photovoltaic glasses with unmodified halloysite coating and carboxyl-modified halloysite coating in embodiments of the present invention are shown. Figure 9The photoelectric conversion efficiency curves of photovoltaic glasses with unmodified halloysite coating and carboxyl-modified halloysite coating in embodiments of the present invention are shown. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0021] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0022] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, and / or combinations thereof.

[0023] In the following examples, unless otherwise specified, all reagents and consumables were purchased from conventional reagent manufacturers in the art; unless otherwise specified, the experimental methods and techniques used are conventional methods and techniques in the art.

[0024] Example 1: Figure 1 This is a schematic diagram illustrating the preparation process of the carboxylated halloysite-based photovoltaic glass spraying solution with self-cleaning properties in an embodiment of the present invention: 1. Disperse 5g halloysite (HNTs) in 100 mL of ethanol / water mixed solvent (7:3 v / v), sonicate for 2 hours at 300W power (water temperature ≤30℃, avoid solvent evaporation); 2. Add 5 mL of triethylamine (TEA) and 1 mL of 3-aminopropyltriethoxysilane (APTES), and react with continuous mechanical stirring in a 60°C water bath under nitrogen protection. 3. After the reaction is complete, the mixture is centrifuged, washed alternately with deionized water and anhydrous ethanol, and then dried under vacuum to obtain aminated halloysite (HNTs-NH2). 4. Take 2.5 g of aminated halloysite (HNTs-NH2), disperse it in anhydrous ethanol solution, and sonicate to achieve uniform dispersion. Add 1 g of maleic anhydride (MA), and stir the reaction at 40℃. 5. After the reaction is complete, the product is collected by centrifugation and washing to obtain carboxylated modified halloysite (HNTs-COOH). 6. Disperse 0.2 g of carboxylated halloysite in water to form a uniform suspension. Then, add 2 mL of tetraethyl orthosilicate and 1 mL of ammonia water in sequence, and stir at 50°C for 0.5 h. Subsequently, add 4 g of sodium α-alkenyl sulfonate, 1.4 g of acrylic resin and 0.6 g of amino resin in sequence to the solution. Stir at 80°C for 2 h under vacuum (0.01 MPa) until the mixture is homogeneous to obtain a carboxylated halloysite-based photovoltaic glass spraying solution with self-cleaning properties, i.e., modified halloysite-based photovoltaic glass spraying solution.

[0025] In contrast, an unmodified halloysite-based photovoltaic glass coating solution was prepared, specifically as follows: 0.2 g of unmodified halloysite was dispersed in water to form a uniform suspension. Then, 2 mL of tetraethyl orthosilicate and 1 mL of ammonia were added sequentially, and the mixture was stirred at 50 °C for 0.5 h. Subsequently, 4 g of sodium α-alkenyl sulfonate, 1.4 g of acrylic resin and 0.6 g of amino resin were added sequentially to the solution, and the mixture was stirred at 80 °C for 2 h under vacuum (0.01 MPa) until homogeneous, thus obtaining an unmodified halloysite-based photovoltaic glass coating solution.

[0026] Figure 2 To observe unmodified halloysite and carboxyl-modified halloysite using TEM, the results showed that the modified halloysite still maintained the nanotube structure and had a relatively smoother surface without obvious agglomeration. This indicates that the modification process did not destroy the basic structure of halloysite, but improved its surface properties, which is beneficial to improving the uniformity and stability of the coating.

[0027] Figure 3 To compare the infrared spectra of unmodified halloysite and carboxyl-modified halloysite, it was found that unmodified halloysite has a certain number of hydroxyl groups on its surface, as seen at 3689 cm⁻¹. -1 and 3627 cm -1 The stretching vibration peak of the free hydroxyl group appears at the position. Carboxyl-modified halloysite may still contain unreacted amino groups or formed amide bonds, in which case the peak appears at 3350-3450 cm⁻¹. -1 The characteristic peak of the amino group may not completely disappear, but the peak intensity may change. At 3689 cm⁻¹... -1 and 3627 cm -1 The position of the peaks differs from that of the previously free hydroxyl groups due to potential association within the newly introduced carboxyl groups. Even if peaks appear, their shape and intensity will differ from those before modification. Furthermore, the associated hydroxyl groups within the carboxyl groups will also be present at 3400-3500 cm⁻¹. -1The appearance of a broad peak may be due to the superposition of factors such as amino peaks and incompletely disappeared free hydroxyl peaks. The OH group of the carboxyl group (3400-3500 cm⁻¹) may also be affected. -1 (broad peak), C=O (1700-1725 cm) -1 The strong peak will cover / interfere with the residual hydroxyl peak, making the 3689 / 3627cm peak appear smaller. -1 The peak weakened further, resulting in a value of 3689 cm. -1 Peak intensity below 3627 cm -1 This fully demonstrates that the carboxyl groups were successfully grafted onto the halloysite surface.

[0028] Figure 4 To analyze the unmodified halloysite coating solution and the carboxyl-modified halloysite coating solution using the Zeta potential test, it was found that the absolute value of the Zeta potential of the modified halloysite coating solution was significantly increased. This means that there is a stronger electrostatic repulsion between the particles in the solution, which effectively inhibits particle aggregation. As a result, the self-cleaning modified halloysite coating solution can maintain a good dispersion state during long-term storage and use, and is not prone to precipitation and stratification, thus significantly improving stability.

[0029] Figure 5 This is a photograph showing the sedimentation state of halloysite in an amino-modified halloysite solution (HNTs-NH2) after standing for 12 hours. The amino groups on the surface of the amino-modified halloysite can bind protons in aqueous solution, giving the halloysite particles a positive charge. Ammonia is alkaline, and its addition increases the number of hydroxide ions in the system. These hydroxide ions interact with the proton-bound groups on the halloysite surface, neutralizing some of the positive charge and weakening the electrostatic repulsion between halloysite particles caused by the same positive charge. Originally, the halloysite particles were stably dispersed by electrostatic repulsion, but due to the weakened electrostatic repulsion, the particles aggregated more easily, thus reducing the system's stability. Ultimately, after standing in water for 12 hours, stratification occurred, and all the halloysite settled to the lower layer.

[0030] Figure 6 This comparison shows the dispersion behavior of unmodified and carboxyl-modified halloysite in water after 24 hours of standing. HNTs (Hydrogen-Nutrient Toluenes) have surfaces rich in hydrophilic groups such as hydroxyl groups. In water or polar media, water molecules readily adsorb onto the particle surface, and particles interact through hydrogen bonds and van der Waals forces. After 24 hours of standing, the intermolecular forces of unmodified halloysite continue to drive particle aggregation, with small aggregates gradually merging into large flocs, further reducing light transmittance and resulting in macroscopically visible agglomerations. With carboxyl-modified halloysite, on the one hand, the repulsive forces between particles in the medium (electrostatic repulsion and steric hindrance repulsion) dominate, inhibiting aggregation; on the other hand, the more uniformly dispersed single particles / small aggregates have weaker light scattering and relatively higher light transmittance. During prolonged standing, the stable dispersion state prevents the formation of macroscopic flocs, indicating that modification improves the dispersion stability of the solution.

[0031] Figure 7 The transmittance of unmodified halloysite coating solutions and carboxyl-modified halloysite coating solutions was tested using a UV-Vis spectrophotometer. In the visible light range (400-800 nm), the transmittance of the carboxyl-modified halloysite coating solution was significantly higher than that of the unmodified halloysite solution. This is because the modified halloysite is more uniformly dispersed in the solution, reducing light scattering and absorption, thereby improving the transparency of the solution.

[0032] Figure 8 Carboxyl-modified halloysite coating solution and unmodified halloysite coating solution were sprayed onto the surface of photovoltaic glass to form coatings of uniform thickness. The transmittance-wavelength curves of the coatings were then tested. The photovoltaic glass with carboxyl-modified halloysite coating showed significantly higher transmittance in the visible light region than the unmodified halloysite coating. This high transparency allows more sunlight to pass through and reach the photovoltaic material layer beneath the photovoltaic glass, providing more light energy for photoelectric conversion and improving the power generation efficiency of the photovoltaic module.

[0033] Figure 9 Outdoor power generation performance tests were conducted on photovoltaic glass modules coated with carboxylated halloysite and those coated with unmodified halloysite. The results showed that, under the same illumination conditions, the power generation efficiency of the photovoltaic glass module coated with carboxylated halloysite was 10%-15% higher than that of the module coated with unmodified halloysite. This demonstrates the significant advantages of carboxylated halloysite sol, which has high transparency and solution stability, in improving the light transmittance and power generation performance of photovoltaic glass.

[0034] Example 2 1. Disperse 5g halloysite (HNTs) in 100mL of ethanol / water mixed solvent (7:3 v / v), sonicate for 2 hours at 300W power (water temperature ≤30℃, avoid solvent evaporation); 2. Add 5 mL of triethylamine (TEA) and 0.2 g of propargyltrimethoxysilane, and react with continuous mechanical stirring for 6 hours in a water bath at 60°C under nitrogen protection. 3. After the reaction is complete, the product is centrifuged, washed alternately with deionized water and anhydrous ethanol, and then dried under vacuum to obtain acetylated halloysite.

[0035] 4. Take 2.5 g of alkynylated halloysite and disperse it in 80 mL of ethanol / water mixed solvent (7:3 v / v). Add 1 mL of an amino reagent containing an azide group (e.g., 3-azidopropylamine), 0.05 g of copper sulfate, and 0.1 g of sodium ascorbate. Stir and react for 12 hours at room temperature in the dark under nitrogen protection. Amino groups are efficiently grafted onto the halloysite surface via a 1,3-dipolar cycloaddition reaction between alkynyl and azide groups. After the reaction is complete, remove residual copper ions with 0.05 M EDTA solution and centrifuge to obtain aminated halloysite solid. 5. The above-mentioned aminated halloysite was redispersed in anhydrous ethanol solution and ultrasonically treated to achieve uniform dispersion. 1 g of maleic anhydride was added, and the mixture was stirred at 40°C. 6. After the reaction is complete, the product is collected by centrifugation and washing to obtain carboxylated modified halloysite (HNTs-COOH).

[0036] 7. Disperse 0.2 g of carboxylated halloysite in water to form a uniform suspension. Then, add 2 mL of tetraethyl orthosilicate and 1 mL of ammonia water sequentially, and stir at 50°C for 0.5 h. Subsequently, add 4 g of sodium α-alkenyl sulfonate, 1.4 g of acrylic resin, and 0.6 g of amino resin sequentially to the solution. Stir at 80°C for 2 h under vacuum (0.01 MPa) until homogeneous, and obtain a carboxylated halloysite sol with high transparency and solution stability, which is a self-cleaning carboxylated halloysite-based photovoltaic glass spraying solution.

[0037] Example 3 1. Disperse 5g halloysite in 100mL of ethanol / water mixed solvent (7:3 v / v), and sonicate at 300W power for 2 hours (water temperature ≤30℃) to form a uniform suspension; 2. Add 3 mL of γ-methacryloxypropyltrimethoxysilane and 2 mL of triethylamine (TEA), and react with mechanical stirring for 4 hours in a water bath at 60°C under nitrogen protection to graft polymerizable double bond groups onto the surface of halloysite. 3. After the reaction is complete, the mixture is separated by centrifugation, washed alternately with deionized water and anhydrous ethanol, and then dried under vacuum to obtain double bond functionalized halloysite (HNTs-C=C).

[0038] 4. Take 2 g of HNTs-C=C and disperse it in 100 mL of anhydrous ethanol. Add 0.8 g of N-vinylpyrrolidone, 0.2 g of 2-aminoethyl methacrylate and 0.01 g of azobisisobutyronitrile. After purging with nitrogen to remove oxygen for 30 minutes, stir the mixture in a water bath at 65 °C for 8 hours. 5. After the reaction is complete, the product is collected by centrifugation and washing to obtain aminated halloysite; 6. Redisperse the above product in 100 mL of ethanol solution, add 0.84 g NaHCO3, cool to 0-5℃ in an ice bath, stir at 300 rpm, and sonicate for 30 minutes. 7. Adjust the pH to 8.0 with 0.1M HCl, dissolve 0.5 mL of succinimide monosuccinate in 5 mL of pre-cooled anhydrous ethanol, and slowly add it dropwise (0.5 mL / min) in the dark.

[0039] 8. After the dripping is complete, remove the ice bath, raise the temperature to 35°C, and react under nitrogen protection for 3 hours in the dark. After the reaction is complete, collect the product by centrifugation and washing to obtain carboxylated halloysite.

[0040] 9. Disperse 0.2 g of carboxylated halloysite in water to form a uniform suspension. Then, add 2 mL of tetraethyl orthosilicate and 1 mL of ammonia water sequentially, and stir at 50°C for 0.5 h. Subsequently, add 4 g of sodium α-alkenyl sulfonate, 1.4 g of acrylic resin, and 0.6 g of amino resin sequentially to the solution. Stir at 80°C for 2 h under vacuum (0.01 MPa) until homogeneous, and obtain a carboxylated halloysite sol with high transparency and solution stability, which is a self-cleaning carboxylated halloysite-based photovoltaic glass spraying solution.

[0041] In summary, this invention discloses a green preparation method for halloysite nanosols with high transparency and high solution stability, and their application as a filler in photovoltaic glass coatings. The method uses an ethanol / water green solvent system and employs a two-step modification strategy of "amylation-carboxylation" to modify the surface of halloysite. First, halloysite surface amylation is achieved using a silane coupling agent method, polymer grafting method, or click chemistry method. Then, it reacts with anhydrides or active esters containing electrophilic groups to obtain carboxylated modified halloysite nanosols. Finally, it is mixed with tetraethyl orthosilicate, resin, and surfactant to prepare a photovoltaic glass coating solution. This invention regulates the surface charge of halloysite through "amylation-carboxylation," increasing the absolute value of the Zeta potential of the modified solution and significantly improving solution stability. With a visible light transmittance >90%, it can significantly improve the power generation efficiency of photovoltaic modules as a filler in photovoltaic glass coatings, showing promising prospects for industrial application.

[0042] Therefore, those skilled in the art will recognize that although embodiments of the present invention have been shown and described in detail herein, many other variations or modifications conforming to the principles of the present invention can be directly determined or derived from the disclosure of the present invention without departing from the spirit and scope of the invention. Therefore, the scope of the present invention should be understood and recognized as covering all such other variations or modifications.

Claims

1. A green preparation method for halloysite nanosol with high transparency and high solution stability, characterized in that, The preparation method includes: Step S1: Take a certain amount of halloysite and disperse it in an ethanol / water mixed solvent. After the halloysite is dispersed to form a homogeneous suspension, perform surface amination treatment on the halloysite. Step S2: After the surface amination reaction in step S1 is completed, the mixture is centrifuged, washed alternately with deionized water and anhydrous ethanol, and dried under vacuum to obtain ammoniated halloysite. Step S3: Take the aminated halloysite obtained in step S2, disperse it in an ethanol solution, and after it is evenly dispersed, add an acid anhydride compound or active ester molecule containing an electrophilic group and stir to react with the aminated halloysite. Step S4: After the reaction in step S3 is completed, centrifuge and wash the product to obtain carboxylated modified halloysite; Step S5: Disperse the carboxylated modified halloysite obtained in step S4 in water, add tetraethyl orthosilicate and ammonia in sequence, stir once, then add surfactant, acrylic resin and amino resin, and stir and mix twice under vacuum to obtain photovoltaic glass spraying solution, which is the halloysite nanosol with high transparency and high solution stability.

2. The green preparation method of halloysite nanosol with high transparency and high solution stability as described in claim 1, characterized in that, In step S1, halloysite is dispersed in an ethanol / water mixed solvent by ultrasonic dispersion, wherein the volume ratio of ethanol to water in the ethanol / water mixed solvent is 7:

3.

3. The green preparation method of halloysite nanosol with high transparency and high solution stability as described in claim 1, characterized in that, In step S1, the method for surface amination of halloysite is silane coupling agent method, polymer grafting method or click chemistry method.

4. The green preparation method of halloysite nanosol with high transparency and high solution stability as described in claim 3, characterized in that, The silane coupling agent method introduces amino groups by reacting a silane coupling agent with the hydroxyl groups on the surface of halloysite; the polymer grafting method introduces amino groups by adding a silane coupling agent containing double bonds, grafting double bonds, and then polymerizing with a monomer containing amino groups; the click chemistry method first grafts alkynyl groups, and then reacts with an amino reagent containing azide groups under copper catalysis to undergo a 1,3-dipolar cycloaddition reaction, thus introducing amino groups.

5. The green preparation method of halloysite nanosol with high transparency and high solution stability as described in claim 1, characterized in that, In step S3, the method of dispersing in the ethanol solution is ultrasonic dispersion; the anhydride compounds containing electrophilic groups include, but are not limited to, maleic anhydride, acetic anhydride, succinic anhydride, phthalic anhydride, hexanoic anhydride and indigo anhydride; the active ester molecules include, but are not limited to, succinic anhydride monosuccinimide ester and 6-carboxyhexanoic anhydride succinimide ester.

6. The green preparation method of halloysite nanosol with high transparency and high solution stability as described in claim 1, characterized in that, In step S3, the stirring reaction temperature is 25-60℃, and the stirring time is 3-8 hours.

7. The green preparation method of halloysite nanosol with high transparency and high solution stability as described in claim 1, characterized in that, In step S5, the first stirring temperature is 50℃ and the stirring time is 0.5 h; the vacuum condition is 0.01 MPa; the second stirring temperature is 80℃ and the time is 2 hours; the viscosity of the photovoltaic glass spraying solution is 15-20 mPa・s; the solid content is 10-15 wt%; the transmittance in the visible light range is >90%; and it is stable and does not separate after standing for 1 day.

8. The green preparation method of halloysite nanosol with high transparency and high solution stability as described in claim 1, characterized in that, In step S5, the mass-volume ratio of carboxylated modified halloysite, water, tetraethyl orthosilicate, ammonia, surfactant, acrylic resin, and amino resin is as follows: 0.1–0.5 g carboxylated modified halloysite: 85–95 mL water: 1–4 g tetraethyl orthosilicate: 1–3 mL ammonia: 1–6 g surfactant: 0.8–3 g acrylic resin, 0.2–1 g amino resin; the surfactant includes, but is not limited to, sodium dodecylbenzenesulfonate, sodium hexadecyl sulfate, sodium dodecyl sulfate, and sodium α-olefin sulfonate.

9. A halloysite nanosol with high transparency and high solution stability, characterized in that, The halloysite nanosol is prepared by any one of the preparation methods in claims 1-8.

10. The application of halloysite nanosol with high transparency and high solution stability as described in claim 9, characterized in that, The application of halloysite nanosol in the field of self-cleaning photovoltaic glass coating.

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