Titanium dioxide photocatalytic solution and preparation method thereof

Abstract

The invention discloses a titanium dioxide photocatalytic solution and a preparation method thereof, and belongs to the technical field of photovoltaic materials and nano functional materials. The solution is a water-based dispersion liquid, and is a composite system comprising a peroxy titanic acid aqueous solution (component A) and an anatase type nano titanium dioxide aqueous dispersion liquid (component B). The preparation method comprises the following steps: by taking titanium tetrachloride as a raw material, hydrolyzing, carrying out alkali precipitation, washing, complexing with hydrogen peroxide, and aging to obtain a component A; carrying out thermal conversion on the component A at 80-120 DEG C to obtain a component B; and finally mixing A and B in proportion. The solution can be used for preparing a self-cleaning film on the surface of a base material such as glass. The process is simple and environment-friendly, high-activity anatase nano TiO2 can be obtained in a low-temperature water phase, the formed film is transparent, super-hydrophilic (the contact angle can be as low as about 11.2 degrees), high in photocatalytic activity and good in hardness and adhesive force, the problem of dust accumulation on the surfaces of photovoltaic panels and outer walls can be effectively solved, the power generation efficiency is improved, and the maintenance cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic materials and nanomaterials technology, and in particular to a titanium dioxide photocatalytic solution and its preparation method. Specifically, it relates to a photocatalytic solution based on the sol-gel method, which prepares a nano-TiO2 aqueous dispersion with high dispersibility, small particle size, and anatase crystal form and its precursor peroxytitanic acid solution through a specific process, and combines the two to form a uniform, stable photocatalytic solution suitable for spray coating. Background Technology

[0002] As the global energy structure transitions towards green and low-carbon practices, photovoltaic (PV) power generation, as a crucial component of clean energy, has seen its installed capacity grow rapidly. However, during long-term outdoor operation, PV modules inevitably accumulate pollutants such as dust, sand, bird droppings, and pollen on their surfaces. Dust accumulation significantly reduces the light transmittance of PV glass, leading to a decrease in module power generation efficiency. Furthermore, uneven dust accumulation can cause localized hot spots, accelerating module aging and even posing a fire hazard. In addition, certain pollutants (such as acidic or alkaline substances) can corrode the glass cover. Statistics show that severe dust accumulation can cause a loss of over 20% in the power generation efficiency of PV systems. Therefore, how to economically, efficiently, and persistently maintain the cleanliness of PV module surfaces has become one of the key issues in the operation and maintenance of PV power plants and the development of PV industry technology.

[0003] Currently, common methods for cleaning photovoltaic modules include manual wiping, mechanical cleaning (such as cleaning robots), and electrostatic discharge (ESD) based on the principle of electrostatic repulsion. These methods all have limitations: manual cleaning is inefficient, costly, and poses safety risks; mechanical cleaning may scratch the glass surface and has requirements regarding the installation environment (such as roof slope); ESD requires continuous power supply, making the system complex and resulting in high initial investment and maintenance costs. Therefore, developing a coating technology that endows photovoltaic glass surfaces with "self-cleaning" capabilities, reducing dust adhesion or allowing it to be easily washed away by rainwater, thereby lowering maintenance frequency and costs, has significant practical application value.

[0004] Self-cleaning coating technology mainly revolves around two paths: superhydrophobicity and superhydrophilicity (photocatalysis). Superhydrophobic coatings rely on low surface energy materials and micro / nano composite rough structures to prevent water droplets from spreading and instead cause them to roll off in spherical shapes, thus carrying away contaminants. However, when used in the photovoltaic field, superhydrophobic coatings face many challenges: First, their micro / nano structures often affect the transmittance of visible light, increasing light scattering and reducing the photoelectric conversion efficiency of photovoltaic modules; second, the complex surface structure preparation process is cumbersome and costly; third, low surface energy materials in the coating (such as fluorine-containing and silicon-containing compounds) may degrade under long-term ultraviolet irradiation, releasing harmful substances or causing performance degradation; most importantly, fine dust particles in the air may gradually embed and fill the micro / nano rough structure, leading to permanent loss of hydrophobicity, the so-called "structural failure". For example, the recently published patent CN118994980A provides a transparent self-cleaning coating based on hydrophobic modified silica sol and composite resin. Its technical route clearly points to superhydrophobicity. It pursues high weather resistance and environmental friendliness by introducing fluorine-free modifiers and resins. However, its core still relies on building a hydrophobic surface and has not solved the potential structural blockage and long-term stability problems.

[0005] In contrast, superhydrophilic photocatalytic coatings based on titanium dioxide (TiO2) exhibit greater application potential. Anatase TiO2 is a wide-bandgap semiconductor photocatalytic material. Under ultraviolet light irradiation, its valence band electrons are excited and jump to the conduction band, generating electron-hole pairs. After these charge carriers migrate to the surface, the holes can oxidize adsorbed water molecules or hydroxyl groups to produce highly oxidizing hydroxyl radicals (·OH), while the electrons can reduce oxygen to produce superoxide radical anions (O2··OH). - The TiO2 coating contains reactive oxygen species such as grease and biological debris. These reactive species can non-selectively decompose organic pollutants (such as grease and biological residues) attached to the coating surface, ultimately mineralizing them into CO2 and H2O—this is photocatalytic degradation. Simultaneously, during photocatalysis, oxygen vacancy defects are generated on the TiO2 surface. These defect sites have a strong adsorption effect on water molecules, allowing water to spread completely on the coating surface, forming a uniform water film—this is the photoinduced superhydrophilic effect. Under rainy or lightly sprayed conditions, this water film can effectively wet and encapsulate dust particles, which can then be easily washed away by the water flow, thus achieving a self-cleaning function. Furthermore, the TiO2 coating itself is transparent and colorless, having minimal impact on the light transmittance of photovoltaic modules, and is chemically stable, non-toxic, and relatively inexpensive.

[0006] To form an effective TiO2 photocatalytic self-cleaning film on the surface of photovoltaic glass, the key lies in preparing a high-performance coating solution. This solution needs to meet the following requirements: the TiO2 particles in the solution should be anatase, the crystal form with the highest photocatalytic activity; the TiO2 nanoparticles should be sufficiently small (typically below tens of nanometers) and have a uniform particle size distribution to ensure high transparency after film formation; the particles should have good dispersion stability in the solution to prevent agglomeration and sedimentation, thus ensuring coating uniformity; the solution system should be environmentally friendly (e.g., water-based) and have suitable viscosity to facilitate large-scale application (e.g., spraying, spin coating, dip coating, etc.); and the film after formation should possess high hardness, adhesion, and weather resistance.

[0007] Currently, the mainstream methods for preparing TiO2 thin film solutions for photovoltaic self-cleaning and their limitations are as follows: Traditional sol-gel method: This method typically uses titanium alkoxides (such as tetrabutyl titanate) as precursors, which are hydrolyzed and polycondensed in organic solvents. This method easily introduces organic matter, and post-processing requires high-temperature calcination (>400℃) to obtain the anatase phase. This directly conflicts with the low-temperature tolerance (typically <150℃) of photovoltaic module encapsulation materials, limiting its application in encapsulated modules.

[0008] Peroxytitanic acid (PTC) method: As a promising low-temperature aqueous preparation route, it utilizes hydrogen peroxide to form a peroxytitanic acid complex with a titanium source, followed by heat treatment and crystallization. Existing technologies, such as the Anhui University of Technology patent (CN103771511B), disclose a method for controlled hydrolysis to prepare anatase TiO2 sol in an acidic ethanol-acetic acid system, but the system still contains organic solvents. The Chongqing University patent (CN102219255B) discloses a method for preparing a highly stable mixed-crystal TiO2 suspension using TiCl4 as a raw material. This method involves the addition of an inorganic alkali for precipitation and may involve high-temperature hydrothermal or calcination steps, resulting in different process control points. Furthermore, it does not mention the use of peroxytitanic acid complexation or composite sol systems.

[0009] Physical compounding method: Commercially available TiO2 nanoparticles are redispersed in a solvent using methods such as ultrasound and the addition of dispersants to prepare coatings. For example, patent CN107043567A discloses a method of organically modifying mixed-phase nano-TiO2 using titanate coupling agents and then formulating a coating. This method is difficult to guarantee the long-term stable dispersion of nanoparticles in an aqueous phase, and the modifier may affect the photocatalytic activity of the TiO2 surface. Patent EP4299176A2 discloses a zinc-doped TiO2 nanoparticle photocatalytic composition for agricultural and surface antibacterial applications. Its focus is on doping modification and specific applications, rather than a composite sol system with a specific microstructure for photovoltaic self-cleaning.

[0010] Composite functional coatings: Some recent research focuses on developing multifunctional coatings, such as coatings that combine self-cleaning and anti-reflection functions, or coatings combined with materials such as carbon nitride to improve visible light response. However, these methods often complicate the system, increasing processing costs and uncontrollability.

[0011] In summary, existing technologies suffer from the following common shortcomings: poor process and substrate compatibility: the high-temperature processing steps contradict the high-temperature intolerant nature of photovoltaic modules; poor environmental protection and safety: extensive use of organic solvents or organic modifiers; difficulty in achieving comprehensive performance: either high crystallinity but demanding processing, or easy preparation but poor dispersibility, stability, or thin film mechanical properties; lack of innovative design for the solution system itself: most methods focus on single-component sols or simple physical mixing, failing to synergistically improve film formation, photocatalytic activity, and thin film mechanical properties through clever design of solution components.

[0012] Therefore, there is an urgent need in the field for an improved method for preparing titanium dioxide photocatalytic solutions. This method should utilize inexpensive and readily available inorganic titanium sources and employ a green process with a fully aqueous phase and controlled low temperature to prepare highly dispersed, small-particle-size, and highly anatase-crystalline nano-TiO2 solution. More importantly, this solution system should, through innovative composite design, not only be suitable for direct coating to form thin films at low temperatures, but also possess excellent light transmittance, superhydrophilicity, high photocatalytic activity, and good mechanical strength and adhesion. This would provide a practical, high-performance, and easily industrialized technical solution for improving efficiency and reducing costs in photovoltaic power plants. The present invention is proposed precisely to overcome the shortcomings of the aforementioned prior art. Summary of the Invention

[0013] To address the aforementioned problems in the prior art, the primary objective of this invention is to provide a titanium dioxide photocatalytic solution. This solution uses water as the dispersion medium and contains nano-anatase titanium dioxide particles of a specific morphology and proportion, along with its precursor, peroxytitanic acid. It exhibits high dispersion stability and suitable rheological properties, and can be directly used to prepare transparent, superhydrophilic, and highly photocatalytically active self-cleaning films on substrates (such as photovoltaic glass).

[0014] The process of this invention is simple and environmentally friendly. Highly active anatase nano-TiO2 can be obtained in a low-temperature aqueous phase. The resulting film is transparent, superhydrophilic (contact angle can be as low as about 11.2°), has high photocatalytic activity, good hardness and adhesion, and can effectively solve the problem of dust accumulation on photovoltaic panels and exterior wall surfaces, improve power generation efficiency and reduce maintenance costs.

[0015] The above-mentioned objective of this invention is achieved through the following technical solutions: This invention provides a titanium dioxide photocatalytic solution, which is an aqueous dispersion comprising a mixture of component A and component B: Component A is an aqueous solution of peroxytitanic acid, which is a clear, transparent liquid ranging from orange-yellow to orange in color. Component B is an anatase nano-titanium dioxide aqueous dispersion, which is a white, semi-transparent to milky white liquid. Component A and component B are mixed in a volume ratio of (1:9) to (9:1).

[0016] According to one embodiment of the present invention, the average particle size D50 of the anatase nano-titanium dioxide particles in component B is 10 nm to 50 nm.

[0017] According to one embodiment of the present invention, the average particle size D50 of the anatase nano-titanium dioxide particles in component B is 20 nm to 40 nm.

[0018] According to one embodiment of the present invention, the titanium dioxide in component B is in the form of pure anatase phase, or the content of anatase phase accounts for more than 90% of all titanium dioxide crystal phases.

[0019] According to one embodiment of the present invention, the solid content of the titanium dioxide photocatalytic solution is 0.1 wt% to 5.0 wt% based on TiO2.

[0020] The present invention also provides a method for preparing the titanium dioxide photocatalytic solution of the above embodiments, comprising the following steps: Step S1: Prepare an aqueous solution of peroxytitanic acid (component A): Step S11: Add titanium tetrachloride to deionized water for hydrolysis to obtain hydrolysate; Step S12: Add alkaline solution to the hydrolysate to adjust the pH to 6-8, generate a precipitate, and wash to remove impurity ions to obtain a titanium hydroxide suspension; Step S13: Add hydrogen peroxide to the suspension, react and allow it to stand for aging to obtain a clear and transparent orange-yellow aqueous solution of peroxytitanic acid, i.e. component A; Step S2: Preparation of anatase nano-titanium dioxide aqueous dispersion (component B): The component A obtained in step S1 is heated at a constant temperature of 80℃ to 120℃ to obtain a white, translucent or milky white anatase nano-titanium dioxide aqueous dispersion, i.e., component B. Step S3, Solution Combination: Component A obtained in step S1 and component B obtained in step S2 are mixed at a volume ratio of (1:9) to (9:1) to obtain the titanium dioxide photocatalytic solution.

[0021] According to one embodiment of the present invention, in step S12, the alkaline solution is diluted ammonia water; the washing is performed by multiple precipitation-decantation or centrifugal washing with deionized water until the NH4+ in the suspension is reduced. + and Cl -The ion concentration decreased significantly.

[0022] According to one embodiment of the present invention, in step S13, the ratio of the amount of hydrogen peroxide added to the molar amount of titanium tetrachloride in step S11 is (2:1) to (10:1); the aging time is 2 to 5 days.

[0023] According to one embodiment of the present invention, in step S2, the temperature of the isothermal heating treatment is 90°C to 110°C, and the time is 1 to 10 hours.

[0024] The present invention also provides a method for preparing a self-cleaning film, comprising: coating a titanium dioxide photocatalytic solution of the above embodiment onto the surface of a substrate, and then drying and curing it at a temperature of 25°C to 80°C (preferably 40°C to 50°C) to form a titanium dioxide photocatalytic self-cleaning film; wherein the coating method is spraying, spin coating, dip-coating or scraping, the present invention also provides; wherein the substrate is a glass substrate or the like.

[0025] In summary, compared with the prior art, the present invention includes at least one of the following beneficial technical effects: The environmentally friendly process is "green" throughout: the entire preparation process uses water as the sole solvent and titanium tetrachloride, ammonia, and hydrogen peroxide as basic raw materials. The main byproducts are ammonium chloride, water, and oxygen, with no toxic or harmful organic substances produced or remaining. This stands in stark contrast to other methods that use titanates, large amounts of organic solvents, or organic modifiers, truly achieving clean production.

[0026] A technological breakthrough in achieving high crystallinity through "low temperature": Pure anatase nano-TiO2 with a crystallinity exceeding 95% was successfully prepared under mild conditions of ≤120℃ via a synergistic pathway of "peroxy complexation-low-temperature hydrothermal conversion." This completely eliminates the reliance on high-temperature calcination at ≥400℃, enabling the technology to be safely applied to temperature-sensitive photovoltaic modules (especially encapsulated modules) and other heat-sensitive substrates such as plastics and coatings, greatly expanding its application scope.

[0027] Synergistic effects of the "composite sol" system: The A / B two-component composite sol system created in this invention is the core for obtaining high-performance thin films. Its synergistic effects are manifested in: Film-forming properties and mechanical properties: Component B (crystallized sol) provides a hard framework, while component A (precursor sol) acts as a "molecular binder," promoting chemical bonding between particles during the drying and curing process. This results in a film hardness of up to 9H and an adhesion grade of 0, far exceeding the performance of films formed using either component alone (see comparative example).

[0028] Functionality and Durability: The composite film possesses both the immediate high photocatalytic activity of component B and the continuous film formation and repair potential of component A. During long-term outdoor use, the surface TiO2 may be slightly depleted due to wear or contamination, but the underlying peroxytitanic acid precursor can be slowly converted into new active TiO2 under light irradiation, achieving a certain degree of "self-repair" and extending the coating life.

[0029] Process tolerance: By adjusting the A / B ratio, the viscosity, solid content, film formation rate, and initial performance of the hydrophilic / photocatalytic properties of the film can be flexibly adjusted to adapt to different construction conditions and usage environment requirements.

[0030] Comprehensive performance advantages for photovoltaic applications: Superior light transmittance: Based on uniform nanoparticles of ~32 nm and an ultra-thin, dense film layer of 0.1-0.2 µm, the average transmittance loss in the visible light region is less than 2%, maximizing the retention of incident light flux in photovoltaic glass. Highly efficient superhydrophilic self-cleaning: The film's water contact angle is as low as approximately 11.2°, exhibiting excellent photo-induced superhydrophilicity. A small amount of rainwater can completely spread to form a water film, efficiently removing dust. Simulated dust accumulation and erosion experiments show that its transmittance recovery rate (>96%) is significantly higher than that of ordinary glass (approximately 88%) and single-component films. Strong environmental resistance: The film not only has high hardness and strong adhesion, but also resists wind and sand abrasion and rain erosion. After preliminary UV aging tests (168 hours), the contact angle change is minimal, demonstrating good weather resistance potential. Convenient and economical construction: The solution has good stability, allowing for spray application. The drying temperature is low (40℃ to 50℃), requiring no complex equipment. The raw material costs are low, and the overall solution has a high cost-performance ratio and industrialization potential.

[0031] Extensive application potential: The core of this invention is a general-purpose, high-performance TiO2 photocatalytic solution platform technology. Besides photovoltaic self-cleaning, with slight adjustments (such as doping, composite with other semiconductors, or changes in coating processes), it can be applied to multiple functional material fields such as air purification (photocatalytic degradation of VOCs), water treatment, antibacterial coatings, and anti-fog glass, demonstrating broad technological expansion potential.

[0032] In summary, this invention, through its unique "deep washing-peroxide complexation-low-temperature conversion-two-component composite" technical route, successfully solves the challenge of preparing highly crystalline anatase TiO2 and its high-performance coatings under low-temperature, aqueous conditions. The provided titanium dioxide photocatalytic solution and its preparation method achieve multiple breakthroughs in environmental friendliness, process compatibility, overall film performance, and cost control. In particular, it offers an efficient, long-lasting, and on-site-implementable solution to the dust accumulation problem in photovoltaic power plants. Attached Figure Description

[0033] Figure 1This is a particle size distribution diagram of TiO2 particles in the titanium dioxide photocatalytic solution prepared in Example 1 of the present invention.

[0034] Figure 2 This is a schematic diagram of a transmission electron microscope (TEM) image of the titanium dioxide self-cleaning film prepared in Example 1 of the present invention.

[0035] Figure 3 This is a schematic diagram of a contact angle test photograph of a water droplet on a normal glass surface.

[0036] Figure 4 This is a schematic diagram of a contact angle test photograph of water droplets on a glass surface coated with the self-cleaning film prepared in Example 1 of the present invention. Detailed Implementation

[0037] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0038] The primary objective of this invention is to provide a titanium dioxide photocatalytic solution. This solution uses water as the dispersion medium and contains nano-anatase titanium dioxide particles of a specific morphology and proportion, along with its precursor, peroxytitanic acid. It exhibits high dispersion stability and suitable rheological properties, and can be directly used to prepare transparent, superhydrophilic, and highly photocatalytically active self-cleaning films on substrates (such as photovoltaic glass).

[0039] Another objective of this invention is to provide a method for preparing the aforementioned titanium dioxide photocatalytic solution. This method uses titanium tetrachloride as raw material and, through controlled hydrolysis, precipitation and washing, hydrogen peroxide complexation, low-temperature thermal conversion, and solution recombination, achieves the controllable preparation of highly crystalline anatase nano-TiO2 under mild aqueous phase conditions. The process is simple, environmentally friendly, and low-cost, making it suitable for large-scale production.

[0040] Another object of the present invention is to provide the application of the above-mentioned titanium dioxide photocatalytic solution, particularly the application of forming a self-cleaning functional film on the glass surface of photovoltaic modules, in order to solve the problem of reduced power generation efficiency caused by dust accumulation on photovoltaic panels.

[0041] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a titanium dioxide photocatalytic solution.

[0042] The titanium dioxide photocatalytic solution is an aqueous dispersion containing component A and component B: Component A: Peroxytitanic acid aqueous solution, which is a clear, orange-yellow to orange transparent liquid, wherein titanium exists in the form of a peroxytitanic acid complex; Component B: Anatase-type nano-titanium dioxide aqueous dispersion, which is a white, translucent to milky white liquid containing well-crystallized anatase phase titanium dioxide nanoparticles; In this mixture, component A and component B are mixed in a volume ratio to form a uniform and stable composite dispersion.

[0043] Preferably, the average particle size (D50) of the anatase-type nano-titanium dioxide particles in component B is 10 nm to 50 nm, more preferably 20 nm to 40 nm, and even more preferably about 32 nm. The particle size distribution exhibits a unimodal normal distribution, and the polydispersity index (PDI) is less than 0.25, preferably less than 0.20. Such narrowly distributed small-sized particles are a primary condition for ensuring high light transmittance of the film.

[0044] Preferably, the titanium dioxide in component B has a pure anatase phase crystal form, or the anatase phase content accounts for more than 90% of all titanium dioxide crystal phases, preferably more than 98%. X-ray diffraction (XRD) pattern analysis shows that its strongest diffraction peak (101 crystal plane) has a small full width at half maximum (FWHM), indicating good crystallinity.

[0045] Preferably, the overall solid content of the titanium dioxide photocatalytic solution, calculated as TiO2, is 0.1 wt% to 5.0 wt%, more preferably 0.5 wt% to 2.0 wt%. Within this solid content range, the solution has a suitable viscosity (approximately 1-10 mPa·s at room temperature), which facilitates construction operations such as spraying and ensures the formation of a film with sufficient thickness and functionality.

[0046] Preferably, the titanium dioxide photocatalytic solution is sprayed onto a clean glass substrate, and the resulting film, after drying, has a static contact angle with water of less than 20°, preferably less than 15°, and more preferably about 11.2°. The thickness of the film is 0.05 μm to 0.5 μm, preferably 0.1 μm to 0.2 μm. The film surface has a pencil hardness of 9H or higher, and an adhesion (cross-cut test) grade of 0.

[0047] Furthermore, component A (aqueous peroxytitanic acid solution) exhibits excellent stability, remaining stable for over 30 days at room temperature in the dark without precipitation or gelation. Component B (anatase TiO2 aqueous dispersion) shows no significant hard precipitate after 7 days of standing and can be easily redispersed with gentle shaking. The photocatalytic solution composed of A and B can be stably stored at room temperature for at least 14 days without significant performance changes, providing a convenient window for its actual production and application.

[0048] Secondly, the present invention provides a method for preparing the above-mentioned titanium dioxide photocatalytic solution, comprising the following steps: Step S1: Prepare TiO2 precursor solution (i.e., component A, aqueous solution of peroxytitanic acid): Step S11, Controlled Hydrolysis: Titanium tetrachloride (TiCl4) is slowly added to deionized water cooled in an ice-water bath while stirring vigorously to ensure complete and stable hydrolysis, yielding a Ti-containing product. 4+ A clear, acidic hydrolysate containing ions. The volume ratio of TiCl4 to deionized water is controlled between 1:5 and 1:20, preferably between 1:8 and 1:12. An ice-water bath and slow dropwise addition are crucial to avoid rapid localized hydrolysis caused by intense exothermic reactions, which can lead to the formation of coarse particles.

[0049] Step S12, Precision Precipitation and Deep Washing: Slowly add diluted ammonia (concentration 1-10 wt%) to the hydrolysate. Under continuous stirring and pH monitoring, precisely adjust and stabilize the pH of the system at 6-8 (preferably 7.0±0.2) to promote Ti precipitation. 4+ The precipitate completely forms a flocculent precipitate of titanium hydroxide (Ti(OH)4·xH2O). After settling, carefully discard the supernatant. Add deionized water to the precipitate, stir to disperse, set aside to settle again, and discard the supernatant. Repeat this washing process at least 3 times, preferably 5-7 times, until the conductivity of the wash solution is close to the background value of deionized water, and Cl cannot be detected with 0.1 mol / L AgNO3 solution. - Ions (no white precipitate). This deep washing step is crucial to maximize the removal of NH4. + and Cl - Impurities, if these impurity ions remain, will seriously affect the stability of the subsequent peroxide complex and the final purity and dispersibility of TiO2. Washing finally yields a relatively pure titanium hydroxide suspension, the concentration of which (based on Ti) should be less than 0.2 mol / L.

[0050] Step S13, Efficient Complexation and Static Aging: Under continuous stirring, hydrogen peroxide (H2O2, concentration 30-35%) is rapidly added dropwise or directly to the suspension obtained in step S12 at a relatively fast rate (e.g., within 1-3 minutes). The ratio of the amount of hydrogen peroxide added to the molar amount of titanium tetrachloride in step S11 is (2:1) to (10:1), preferably (4:1) to (6:1). During the dropwise addition, the suspension can be observed to rapidly change color and generate bubbles (oxygen). After the dropwise addition is complete, the mixture is transferred to a sealed container and aged at room temperature (15-30℃) in the dark for 2 to 5 days (preferably 2-3 days). During aging, the appearance of the solution undergoes a typical change process from milky white → golden yellow → orange → orange transparent, finally yielding an orange-yellow, clear, transparent aqueous solution of peroxytitanic acid with characteristic color, which is component A. The aging process is the process of peroxytitanic acid complexing (e.g., [Ti(O2)]). 2+Insufficient time is a critical stage for the formation and stabilization of complexes (or more complex polynuclear complexes). Incomplete complexation and unstable solutions can result from insufficient time.

[0051] Step S2: Preparation of TiO2 aqueous dispersion (i.e., component B, anatase-type nano-titanium dioxide aqueous dispersion): The aged peroxytitanic acid aqueous solution (component A) obtained in step S1 is placed in a sealed pressure-resistant container (such as a stainless steel reactor lined with polytetrafluoroethylene) and subjected to isothermal heating at 80°C to 120°C for 1 to 10 hours. Preferred process conditions are heating at 90°C to 110°C for 2 to 6 hours. As the heat treatment proceeds, the orange-yellow peroxytitanic acid solution gradually transforms into a white, translucent, or milky-white solution, indicating that the peroxytitanic acid complex has undergone thermal decomposition and in-situ crystallization to generate anatase-type titanium dioxide nanoparticles. This low-temperature hydrothermal conversion process is key to obtaining a highly crystalline anatase phase, avoiding the high-temperature calcination required by traditional methods. After the reaction, the solution is naturally cooled to room temperature to obtain component B. The TiO2 particles in this dispersion are rich in hydroxyl groups on their surface, maintaining good dispersion in the aqueous phase through electrostatic repulsion.

[0052] Step S3, Innovative Solution Combination: Component A (peroxytitanic acid aqueous solution) obtained in step S1 and component B (anatase-type nano-titanium dioxide aqueous dispersion) obtained in step S2 are mixed in a certain volume ratio, and stirred or gently sonicated at room temperature to achieve uniform mixing, ultimately obtaining the titanium dioxide photocatalytic solution. The volume mixing ratio of component A to component B is (1:9) to (9:1), preferably (1:4) to (4:1), and more preferably (1:2) to (2:1). A proven and effective optimal ratio is 1:1 (volume ratio).

[0053] One of the core innovations of this invention lies in this composite step. Its technical effect is not simply a physical mixing: component B provides readily available, highly active anatase TiO2 nanocrystal nuclei, serving as the "skeleton" and photocatalytic center of the film; component A acts as an active precursor binder. During subsequent film drying and outdoor light exposure, the peroxytitanic acid in component A can further decompose or transform slowly, not only generating new TiO2 itself, but also acting as a "bridge" and "stitch" between TiO2 particles and between the particles and the glass substrate, thereby significantly enhancing the film's density, cohesion, and adhesion to the substrate, without affecting its superhydrophilicity and photocatalytic performance. This design cleverly solves the problems of weak adhesion in films formed by pure TiO2 dispersions and poor mechanical properties in films formed by pure peroxytitanic acid solutions.

[0054] Thirdly, this invention provides the application of the aforementioned titanium dioxide photocatalytic solution in the preparation of self-cleaning films. It is particularly suitable for transparent substrate surfaces requiring high light transmittance and durable self-cleaning functions, such as photovoltaic module cover glass, architectural glass curtain walls, automotive glass, and lamp covers.

[0055] Fourthly, the present invention provides a method for preparing a self-cleaning film, comprising: coating the above-mentioned titanium dioxide photocatalytic solution onto a clean substrate surface by spraying, spin coating, dip-coating or scraping, and then drying and curing at a low temperature of 25°C to 80°C to form a TiO2 photocatalytic self-cleaning film.

[0056] Preferably, the substrate is the cover glass of a photovoltaic module, which needs to be thoroughly cleaned (e.g., ultrasonically cleaned with acetone, ethanol, or deionized water) to remove oil stains before coating.

[0057] Preferably, when using the spraying method, a spray gun with a nozzle diameter of less than 0.5 mm is used, the air pressure is adjusted to 0.2-0.4 MPa, the spraying distance is 25-40 cm, and the amount of solution sprayed is 10 g / m² to 50 g / m², preferably 10 g / m² to 20 g / m².

[0058] Preferably, the drying and curing temperature is 40°C to 50°C, and the time is 1-3 hours. This low-temperature curing condition is fully compatible with the temperature tolerance of photovoltaic module encapsulation materials, enabling this technology to be applied to the on-site maintenance and repair of encapsulated modules, and has significant practical application value. Example 1: Preparation of Titanium Dioxide Photocatalytic Solution and Characterization of Thin Film Properties

[0059] 1. Experimental materials and equipment: The main chemical reagents and raw materials are shown in Table 1, and the main instruments and equipment are shown in Table 2.

[0060] Table 1 Main Chemical Reagents and Raw Materials

[0061] Table 2 Main Instruments and Equipment

[0062] 2. Preparation of titanium dioxide photocatalytic solution: Step S1: Prepare an aqueous solution of peroxytitanic acid (component A): a. Measure 50 ml of deionized water into a 250 ml beaker and stir at medium speed on a magnetic stirrer. In a fume hood, use a pipette to measure 5 ml of titanium tetrachloride (TiCl4) and slowly add it dropwise to the deionized water in the beaker. During the addition, white fumes are observed accompanied by exothermic reactions, indicating vigorous hydrolysis of TiCl4. After the addition is complete, continue stirring for 30 minutes to obtain a milky white, turbid hydrolysate.

[0063] b. Dilute concentrated ammonia (25-28%) 10 times with deionized water to prepare a dilute ammonia solution of approximately 2.5%. While continuously stirring, slowly add this dilute ammonia solution dropwise to the above hydrolysate using a dropper. With the addition of ammonia, a large amount of white flocculent precipitate gradually forms in the solution. Simultaneously, monitor the pH value of the solution in real time using a pH meter. When the pH value rises to approximately 7.0, stop adding ammonia and continue stirring for 30 minutes to ensure the precipitation reaction is complete. At this point, Ti... 4+ It has been largely converted into titanium hydroxide precipitate.

[0064] c. Stop stirring and let the beaker stand for 4 hours to allow the precipitate to settle completely. Carefully remove the supernatant using a siphon. Then add about 100 ml of deionized water to the precipitate and stir vigorously with a glass rod or stirrer to redisperse the precipitate evenly. Let it stand for another 4 hours to settle, and remove the supernatant. Repeat this washing process a total of 5 times. Take the supernatant from the last wash and measure its conductivity using a conductivity meter; the conductivity is < 10 µS / cm, close to the background value of the deionized water used. Take a small amount of the supernatant and add 0.1 mol / L AgNO3 solution; no white turbidity or precipitate is formed, indicating that Cl... - The removal was almost complete. Approximately 30 ml of concentrated white suspension of titanium hydroxide was obtained, with an estimated Ti concentration of about 0.15 mol / L.

[0065] d. Transfer the washed suspension to a 100 ml Erlenmeyer flask and place it on a magnetic stirrer with medium speed. Measure 15 ml of 35% hydrogen peroxide (H2O2) using a graduated cylinder and inject it rapidly into the suspension within 1 minute using a syringe. Immediately observe that the suspension begins to turn pale yellow, with small bubbles (oxygen) continuously being generated. After the addition is complete, seal the flask with sealing film and place it in a dark cabinet at room temperature (25±2℃) for aging. Observe and record the color change of the solution during aging: initially milky white (0 hours), turning distinctly golden yellow after 6 hours, turning stable orange-red after 24 hours, and by the 3rd day (72 hours), the solution has completely transformed into a clear, transparent, uniformly colored orange-yellow liquid with no sediment or suspended matter at the bottom of the flask. This is a qualified peroxytitanic acid aqueous solution, labeled as component A. Take a portion of the sample and place it in a transparent sample bottle, storing it at room temperature in the dark for subsequent testing and compounding.

[0066] Step S2: Preparation of anatase-type nano-titanium dioxide aqueous dispersion (component B): Take 20 ml of component A (peroxytitanic acid aqueous solution) obtained in step S1 and aged for 3 days, and inject it into a 50 ml high-pressure reactor lined with polytetrafluoroethylene. Tighten the reactor lid to ensure a seal. Place the reactor in a preheated forced-air drying oven, set the temperature to 100℃, and begin constant-temperature heating treatment. Start timing from when the temperature reaches 100℃ and treat for 4 hours. After treatment, turn off the oven power and allow the reactor to cool naturally to room temperature (approximately 6-8 hours). Note: Do not forcibly open the reactor at high temperature to prevent the liquid from boiling violently. After cooling, open the reactor and observe that the internal liquid has completely changed from an orange-yellow transparent liquid to a homogeneous, slightly bluish, milky white translucent liquid, resembling diluted milk, and shows no sedimentation or stratification upon standing. This is the anatase-type nano-titanium dioxide aqueous dispersion, labeled as component B.

[0067] Step S3, Solution Combination: Accurately measure 10.0 ml of component A and 10.0 ml of component B using a pipette and place them in a 50 ml capped glass sample bottle. Place the bottle on a magnetic stirrer with a magnetic stir bar and stir at 200 rpm for 30 minutes at room temperature. During the mixing process, the solution will gradually change from a mixture of orange-yellow and milky white to a homogeneous, pale milky white, translucent solution. The solution will be uniform and stable, with no particles adhering to the bottle walls. Stop stirring. This yields the titanium dioxide photocatalytic solution of the present invention, denoted as sample solution S1 (A:B = 1:1).

[0068] 3. Preparation of self-cleaning films: A standard glass slide with dimensions of 75 mm × 25 mm × 1 mm was selected as the substrate. The slide was ultrasonically cleaned for 15 minutes each with acetone, anhydrous ethanol, and deionized water, then dried with high-purity nitrogen gas and placed in a clean petri dish for later use, ensuring that the surface was hydrophilic and free of marks.

[0069] Pour sample solution S1 into the storage tank of the spray gun. Use an Iwata spray gun with a nozzle diameter of 0.4 mm, connect an air compressor, and adjust the outlet air pressure to 0.3 MPa. Fix a clean glass slide on a platform approximately 20 cm from the spray gun nozzle. Move the spray gun back and forth at a uniform speed to uniformly spray one side of the glass slide, ensuring the coating covers the entire surface without runs or orange peel. Control the wet film spraying amount to approximately 30 g / m² using a pre-experimental weighing method. Place the sprayed glass slide horizontally in a 50°C forced-air drying oven and dry for 2 hours. After removal, allow it to cool naturally to room temperature. A uniform, transparent TiO2 self-cleaning film without obvious interference colors is obtained on the glass surface, denoted as film F1.

[0070] 4. Thin film performance characterization: 4.1 Particle Size Distribution and Zeta Potential Test: A small amount of sample solution S1 was placed in a petri dish and dried at 80℃ to obtain a light yellow powder. 5 mg of powder was accurately weighed and dispersed in 10 ml of anhydrous ethanol. The mixture was sonicated for 15 minutes to obtain a well-dispersed suspension. Dynamic light scattering (DLS) was performed using a Malvern Zetasizer Nano ZS particle size analyzer to determine the particle size distribution and Zeta potential of TiO2 particles in ethanol. The results are as follows: Figure 1 As shown in the figure. Tests indicate that the Z-Average particle size is approximately 35 nm, the polydispersity index (PDI) is 0.15, and the volume average particle size (D50) is 32 nm, exhibiting a single-peaked and narrow distribution. The Zeta potential value is +35.2 mV (measured in ethanol; it is typically positive in aqueous phases). This high absolute value indicates strong electrostatic repulsion between particles, which is beneficial for dispersion stability.

[0071] 4.2 Transmission Electron Microscopy (TEM) and X-ray Diffraction (XRD) Analysis: The ethanol dispersion used for particle size testing was pipetted onto an ultrathin carbon film copper grid and allowed to evaporate naturally before air drying. Observation was performed using a JEM-2100 transmission electron microscope at an accelerating voltage of 200 kV. The results are as follows: Figure 2 As shown in the TEM images, the TiO2 particles exhibit a regular, flat, rhomboid (or spindle-shaped) morphology, with particle sizes ranging from 20 to 40 nm, consistent with the DLS results. High-resolution images (not shown separately) reveal clear lattice fringes, and the measured interplanar spacing is approximately 0.35 nm, consistent with the (101) plane of anatase TiO2, indicating good particle crystallization.

[0072] Another dried powder was subjected to XRD (Cu Kα rays, scanning range 10-80°). The spectrum showed obvious diffraction peaks at 25.3°, 37.8°, 48.0°, 53.9°, and 55.1°, corresponding to the (101), (004), (200), (105), and (211) crystal planes of anatase TiO2, respectively. No obvious diffraction peaks of rutile phase (characteristic peak ~27.4°) or brookite phase were detected. The half-width at half-maximum (FWHM) of the (101) crystal plane diffraction peak was calculated using the Scherrer formula, and the average grain size was estimated to be about 30 nm, which is consistent with the results of TEM and DLS.

[0073] 4.3 Contact Angle Test: Using an OSA60 contact angle meter, the static contact angles of clean, untreated glass slides and glass slides coated with film F1 to deionized water were measured at room temperature (25℃). Approximately 5 μL of water droplets were added to different locations on the sample surface using a microsyringe. After the droplets stabilized (approximately 5 seconds), the contact angle was automatically analyzed and calculated using the instrument's software. Five different locations were tested for each sample, and the average value was taken.

[0074] Test results are as follows Figure 3 and Figure 4 As shown. Figure 3 The original slide showed a water contact angle of 43.7° ± 1.5°. Figure 4 The results show that the water contact angle of the glass slide coated with film F1 is 11.2° ± 0.8°. This indicates that the self-cleaning film prepared in this invention has excellent superhydrophilicity, and water spreads almost completely on its surface.

[0075] 4.4 Film Thickness, Hardness, and Adhesion Tests: A step tester (Dektak XT) was used to create a step at the edge of film F1 to measure the film thickness. Measurements were taken five times at different locations on the sample, with an average thickness of approximately 0.15 µm.

[0076] According to the national standard GB / T 6739-2006 "Determination of Hardness of Paints and Varnishes by Pencil Method", the hardness of the film F1 was tested using a pencil hardness tester. The test started with the hardest pencil, 9H, and continued until the film surface was scratched. The test result showed that the 9H pencil could not scratch the film surface, indicating that the film has a very high surface hardness.

[0077] According to the national standard GB / T 9286-2021 "Cross-cut test for paints and varnishes", a 6×6 grid was drawn on the film surface using a cross-cutting tool (1mm blade spacing). The grid was then tightly adhered with 3M 600 tape and quickly peeled off. Under magnification, the grid edges were completely smooth, with no squares detached, indicating the highest adhesion level of 0.

[0078] 4.5 Transmittance Test: Using a UV-Vis spectrophotometer (UV-3600 Plus) and air as a reference, the transmittance curves of the original glass slide and the coated glass slide (thin film F1) in the visible light range of 380 nm to 780 nm were tested. The transmittance curve of the original glass slide was used as the baseline (set as 100% relative transmittance) to calculate the relative transmittance of the coated glass. The results show that the average relative transmittance of the coated glass in the entire visible light region is only about 1.5%-2.0% lower than that of the original glass, indicating that the thin film has minimal impact on the transmittance of the glass, meeting the requirements for photovoltaic applications. Example 2: Investigating the effect of different A:B composite ratios on thin film properties

[0079] Following steps S1 and S2 in Example 1, sufficient quantities of stable components A and B were prepared.

[0080] Nine different volume mixing ratios (A:B) were set up to prepare a series of composite solutions: 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2, and 9:1. Each solution was coated onto a clean glass slide under the same spraying and drying conditions as in Example 1 (spraying amount 30 g / m², drying at 50°C for 2 h) to obtain a series of thin films.

[0081] The static water contact angle, pencil hardness, and cross-cut adhesion of each film were tested. Key results are summarized in Table 3.

[0082] Table 3. Effect of different A:B volume ratios on film contact angle

[0083] Conclusion: When the volume ratio of component A to component B is within the range of 3:7 to 6:4, the films exhibit excellent overall performance (contact angle <15°, hardness ≥8H, adhesion grade 0). Among them, the 1:1 (5:5) ratio achieves the best balance of performance, with the strongest hydrophilicity and the highest mechanical properties. When the proportion of component B is too high (>8:2), the initial hydrophilicity and mechanical properties of the film are acceptable, but the long-term performance or "self-healing" potential may be affected due to insufficient active precursor (A). When the proportion of component A is too high (>2:8), although the initial hydrophilicity is acceptable, the hardness and adhesion of the film decrease significantly, which is consistent with the phenomenon in Comparative Example 1. This proves that the composite ratio has a significant impact on the final film performance, and there is an optimal range. The optimal ratio is 1:1, but high-performance films can be obtained in the range of 3:7 to 6:4, providing a flexible process window for actual production. Example 3: Investigating the effects of thermal conversion temperature and time on component B and the final film properties

[0084] Prepare a sufficient amount of component A according to step S1 in Example 1.

[0085] Multiple equal portions (20 ml each) of aged component A were placed in several 50 ml high-pressure reactors and subjected to isothermal heating at different temperatures to prepare different components B. The temperatures were set at 80℃, 90℃, 100℃, 110℃, and 120℃. At each temperature, three time points were set: 2 hours, 4 hours, and 6 hours. After heating, the samples were allowed to cool naturally to obtain a series of component B samples.

[0086] The appearance (color, transparency, and presence of precipitation) of component B obtained under various conditions was observed. Component B was then compounded with an equal amount of component A in a 1:1 ratio to prepare a photocatalytic solution, which was then deposited into films using a standard process. The static water contact angle of each film was measured, and a simple photocatalytic degradation test of methylene blue was performed (the film was immersed in a 10 µmol / L methylene blue solution, irradiated under a UV lamp for 1 hour, and the change in absorbance was measured to calculate the degradation rate) to evaluate the photocatalytic activity. Key results are summarized in Table 4.

[0087] Table 4. Effects of thermal conversion temperature and time on component B and film properties

[0088] Conclusion: Thermal conversion temperature and time jointly affect the crystallization process and particle size. Component B with good performance can be obtained at 90℃ to 110℃ for 2-6 hours. Among these, treatment at 100℃ for 4 hours is the optimal condition, yielding TiO2 with high crystallinity, moderate particle size, and good dispersibility, resulting in the best overall film performance. Too low a temperature (80℃) or too short a time leads to incomplete conversion, potentially leaving undecomposed peroxide complexes or amorphous components in the product, resulting in insufficient hydrophilicity and photocatalytic activity of the film. Too high a temperature (120℃) or too long a time may cause Ostwald ripening of nanoparticles, leading to growth or aggregation and precipitation, affecting the stability of the dispersion and the transparency and performance of the final film. Example 4: Comprehensive Test of Simulated Dust Accumulation and Self-Cleaning Effect of Photovoltaic Modules

[0089] 4.1 Sample Preparation: Take four identical pieces of commercially available tempered photovoltaic glass (size 100mm×100mm×3.2mm, light transmittance >91.5%). Divide them into four groups: Group 1 (Self-cleaning glass - the present invention): Coating film F1 according to the method of Example 1.

[0090] Group 2 (Comparative glass - single component B): Component B prepared in Example 1 was used only and sprayed into a film using the same process.

[0091] Group 3 (Comparative glass - single component A): Component A prepared in Example 1 was used only and sprayed into a film using the same process (the film was slightly soft after drying).

[0092] Group 4 (Control Glass): Keep as is, only clean.

[0093] All samples were rinsed with deionized water and dried with nitrogen. The initial transmittance (T0) was then measured and recorded.

[0094] 4.2 Artificial Dust Accumulation and Transmittance Attenuation Test: Simulating the composition of sand and dust in the arid Northwest region, the mixture was prepared by mass ratio: 70% quartz sand (200 mesh), 20% clay, 5% calcium carbonate, and 5% carbon black (simulating organic matter and light-absorbing components). The mixed dust was passed through a 150-mesh sieve to obtain the standard dust for the test.

[0095] Four sets of glass samples were fixed in the environmental chamber at a 15° tilt angle (simulating the common installation tilt angle of photovoltaic panels). Standard dust was uniformly deposited onto the glass surface at a constant rate using a dust spraying device. By controlling the time, the dust density was made to reach approximately 5 g / m². After dust accumulation, the samples were carefully removed, and the transmittance (T_d) after dust accumulation was measured.

[0096] Calculate the transmittance attenuation rate: Attenuation rate = [(T0 - T_d) / T0] × 100%. The results are shown in Table 5.

[0097] Table 5. Light transmittance reduction after dust accumulation

[0098] Conclusion: Under the same dust accumulation conditions, the film of the present invention (Group 1) exhibited the lowest transmittance attenuation (5.4%), significantly superior to the two comparative examples and the blank control. This indicates that the surface properties of the film of the present invention (superhydrophilicity and low surface energy) can effectively reduce the initial adhesion and amount of dust.

[0099] 4.3 Simulated Rainwater Washing Self-Cleaning Effect Test: The four sets of samples that had completed the dust accumulation test were fixed at a 15° angle under the spray test frame. A spray device was used to simulate natural rainfall, with the spray intensity set to 20 mm / h (medium rain intensity), and spraying continued for 5 minutes. After spraying, the samples were kept at the angle and left to stand for 10 minutes to allow the surface water to drain completely, and then placed in a 50°C oven to dry for 1 hour.

[0100] The transmittance (T_c) of each group of samples was measured after drying.

[0101] Calculate the light transmittance recovery rate: Recovery rate = [(T_c - T_d) / (T0 - T_d)] × 100%. The closer this value is to 100%, the more thoroughly the dust is removed and the better the self-cleaning effect. The results are shown in Table 6.

[0102] Table 6. Light transmittance recovery after rainwater washing

[0103] Conclusion: After simulated rain washing, the light transmittance of the film (Group 1) of this invention almost completely recovered to its initial state (recovery rate 98.2%), and its self-cleaning effect was significantly better than that of single-component B (78.9%) and single-component A (62.5%) films, and far superior to that of ordinary glass (61.5%). This fully demonstrates the synergistic advantages of the A / B composite system in achieving efficient self-cleaning using rainwater: superhydrophilicity (contributed by both A and B) allows the water film to spread completely and wet the dust; the dense and rigid film layer (B provides the framework, A enhances adhesion) makes it difficult for dust to embed and easy to be washed away by the water flow.

[0104] 4.4 Preliminary accelerated tests for abrasion resistance and weather resistance: Abrasion resistance test: The abrasion resistance of the film in Group 1 (the present invention) was tested using a standard drop tester (compliant with ASTM D968) and standard quartz sand. The results showed that after abrasion by each liter of sand, the haze of the film increased by less than 1%, and the contact angle remained below 15°, indicating that the film has good abrasion resistance.

[0105] UV aging test: The film sample of Group 1 (this invention) was placed in a UV aging test chamber using a UVA-340 lamp with an irradiation intensity of 1.0 W / m² @ 340nm for 500 hours (equivalent to several months of strong outdoor sunlight). After the aging test, its water contact angle was measured to be 12.5°, which was very small compared to before aging (11.2°); a simulated dust accumulation and rinsing test was performed again, and the transmittance recovery rate remained above 95%. This indicates that the film's superhydrophilicity and self-cleaning function have good UV aging stability.

[0106] Comparative Example 1: Film formation from a single peroxytitanic acid solution (component A) Using only component A (aqueous solution of peroxytitanic acid) prepared in Example 1, a film was formed on glass under the same spraying dosage (30 g / m²) and drying conditions (50°C, 2 h). Tests revealed that the film initially exhibited some hydrophilicity (contact angle approximately 25°), but its hardness was very poor (pencil hardness <2H), easily scratched or even partially peeling off with a light wiping with a damp cloth. After being placed outdoors in a natural environment for one week, the hydrophilicity significantly decreased (contact angle increased to over 35°), and the film layer showed slight powdering. This indicates that the film formed from a single component A is mainly composed of incompletely converted precursors and amorphous components, resulting in severely insufficient mechanical properties and long-term stability, failing to meet the requirements for outdoor use.

[0107] Comparative Example 2: Film Formation of a Single TiO2 Dispersion (Component B) Using only component B (anatase TiO2 aqueous dispersion) prepared in Example 1, a film was formed on glass under the same spraying and drying conditions. This film exhibited high hardness (approximately 6H) and acceptable initial hydrophilicity (contact angle approximately 18°), but its cross-cut adhesion test result was only level 2 (partial detachment at the cross-cut points), inferior to the composite film of Example 1 (level 0). In simulated rainwater washing and dust accumulation tests, its transmittance recovery rate (78.9%) was significantly lower than that of the composite film of Example 1 (98.2%). Analysis suggests that the film formed from single component B primarily relies on physical stacking and van der Waals forces between particles, lacking strong chemical "bonding." This results in relatively weak adhesion between the film and the substrate, as well as relatively weak cohesion between particles. Therefore, its long-term reliability under repeated rainwater washing or thermal stress is questionable.

[0108] Comparative Example 3: Compared with the traditional sol-gel method The traditional sol-gel method is employed: using tetrabutyl titanate as a precursor, anhydrous ethanol as a solvent, and a small amount of acetylacetone as an inhibitor, deionized water is slowly added under stirring to hydrolyze the solution, yielding a TiO2 sol. This sol is sprayed onto glass, first requiring drying at 100°C, and then calcined at 450°C for 1 hour to obtain a crystalline anatase film. The performance of this film (contact angle ~12°, hardness 8H) is close to that of the F1 film of this invention. However, the key differences are: 1) Process: The process uses a large amount of organic solvent and requires high-temperature treatment at 450°C, making it completely unsuitable for encapsulated photovoltaic modules; 2) Solution stability: Traditional sols have a short gelation time (a few days to a week), resulting in a tight storage and application window; while the composite solution of this invention can be stably stored for several weeks; 3) Environmental friendliness: This invention is entirely aqueous, with no volatile organic compounds (VOCs).

[0109] Through a thorough comparison of the above examples and comparative examples, the originality and superiority of the "titanium dioxide photocatalytic solution composite system" provided by this invention in the preparation of high-performance self-cleaning films are convincingly demonstrated. The composite of A and B produces a synergistic effect of "1+1>2", which not only ensures the high hardness, strong adhesion and excellent light transmittance of the film, but also endows it with significant and lasting superhydrophilicity and efficient self-cleaning function. At the same time, the entire preparation process is green, low-temperature and has good compatibility. Example 5: Different titanium sources and process variations

[0110] This embodiment aims to illustrate that the core concept of the present invention is not limited to a specific reagent specification or absolute parameter. Adaptive adjustments can be made while ensuring the consistency of the process principle. Any equivalent substitutions or adaptive adjustments made within the core concept of the present invention—namely, "preparing a stable peroxytitanic acid precursor solution (A) through hydrolysis of titanium tetrachloride, deep washing, and hydrogen peroxide complexation, followed by low-temperature hydrothermal conversion to obtain a highly crystalline anatase TiO2 dispersion (B), and finally combining A and B to obtain a photocatalytic coating solution with excellent comprehensive performance"—should be considered to fall within the protection scope of the present invention.

[0111] Titanium source: The core is to provide Ti 4+ In addition to analytical grade (AR) titanium tetrachloride, industrial grade titanium tetrachloride or titanium oxysulfate (TiOSO4) can also be used. However, it is necessary to increase the number of washing cycles, recrystallization, or other purification steps to ensure that the content of impurities such as Fe and Si in the raw materials does not affect the subsequent hydrolysis and complexation reactions.

[0112] Precipitation and washing: Besides ammonia, other precipitants can provide OH-. - Furthermore, weak bases or alkaline salts that do not introduce difficult-to-remove impurities can be considered, such as ammonium carbonate and urea (hydrolyzed by heating). In addition to static decantation, centrifugation or membrane filtration (such as ultrafiltration and dialysis) can significantly improve washing efficiency and effectiveness.

[0113] Complexation and Aging: The hydrogen peroxide concentration can be selected within the range of 20%-50%. The aging temperature and time can be fine-tuned; a higher temperature can shorten the aging time, but overheating should be avoided to prevent premature decomposition. The aging container should preferably be made of glass or polytetrafluoroethylene to prevent metal ions from catalyzing the decomposition of H2O2.

[0114] Thermal conversion: In addition to using a high-pressure reactor for closed hydrothermal conversion, it can also be carried out in an atmospheric pressure reflux device, but attention should be paid to replenishing the evaporated water and the reaction time may need to be extended.

[0115] Composites and Applications: In addition to stirring, mixing components A and B can also be aided by short-duration, gentle ultrasound to promote uniformity. Coating methods can be selected based on the substrate shape and production line requirements, such as slot coating, roller coating, or curtain coating. For flexible substrates, a lower drying temperature of 40-50℃ or infrared drying can be used.

[0116] This invention provides an innovative titanium dioxide photocatalytic solution and its low-temperature aqueous phase preparation method. This method successfully solves the challenge of preparing highly dispersed, small-particle-size, and highly anatase-crystalline nano-TiO2 from inexpensive inorganic titanium sources at low temperatures. Through a unique "precursor (A) and crystallized particles (B) composite" strategy, a high-performance coating solution is obtained. The self-cleaning film prepared from this solution integrates high light transmittance, superhydrophilicity, high photocatalytic activity, high hardness and strong adhesion, and good weather resistance. Furthermore, the process is green, requires low application temperature, and has controllable costs. It is particularly suitable for solving the dust accumulation problem of photovoltaic modules and can be extended to other transparent surfaces requiring self-cleaning functions, possessing significant industrialization potential and market value.

[0117] The implementation principle of this invention is as follows: This invention discloses a titanium dioxide photocatalytic solution, its preparation method, and its application, belonging to the technical field of photovoltaic materials and nanomaterials. The solution is an aqueous dispersion, comprising a composite system of peroxytitanic acid aqueous solution (component A) and anatase-type nano-titanium dioxide aqueous dispersion (component B). The preparation method includes: using titanium tetrachloride as raw material, after hydrolysis, alkali precipitation, washing, and complexation with hydrogen peroxide and aging to obtain component A; then thermally converting component A at 80-120℃ to obtain component B; finally, mixing A and B in a certain proportion. This solution can be used to prepare self-cleaning films on the surface of substrates such as glass. This invention features a simple and environmentally friendly process, obtaining highly active anatase nano-TiO2 in a low-temperature aqueous phase. The resulting film is transparent, superhydrophilic (contact angle can be as low as approximately 11.2°), has high photocatalytic activity, good hardness, and good adhesion, effectively solving the dust accumulation problem on photovoltaic panels and exterior wall surfaces, improving power generation efficiency, and reducing maintenance costs.

[0118] The embodiments described herein are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape, and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A titanium dioxide photocatalytic solution, characterized in that, This is an aqueous dispersion, comprising a mixture of component A and component B: Component A is an aqueous solution of peroxytitanic acid, which is a clear, transparent liquid ranging from orange-yellow to orange in color. Component B is an anatase nano-titanium dioxide aqueous dispersion, which is a white, semi-transparent to milky white liquid. Component A and component B are mixed in a volume ratio of (1:9) to (9:1).

2. The titanium dioxide photocatalytic solution according to claim 1, characterized in that, The average particle size D50 of the anatase nano-titanium dioxide particles in component B is 10 nm to 50 nm.

3. The titanium dioxide photocatalytic solution according to claim 2, characterized in that, The average particle size D50 of the anatase-type nano-titanium dioxide particles in component B is 20 nm to 40 nm.

4. A titanium dioxide photocatalytic solution according to any one of claims 1-3, characterized in that, The titanium dioxide in component B is in the form of pure anatase phase, or the anatase phase accounts for more than 90% of all titanium dioxide crystal phases.

5. The titanium dioxide photocatalytic solution according to claim 1, characterized in that, The solid content of the titanium dioxide photocatalytic solution is 0.1 wt% to 5.0 wt% based on TiO2.

6. A method for preparing a titanium dioxide photocatalytic solution according to any one of claims 1-5, characterized in that, Includes the following steps: Step S1: Prepare an aqueous solution of peroxytitanic acid. Step S11: Add titanium tetrachloride to deionized water for hydrolysis to obtain hydrolysate; Step S12: Add alkaline solution to the hydrolysate to adjust the pH to 6-8, generate a precipitate, and wash to remove impurity ions to obtain a titanium hydroxide suspension; Step S13: Add hydrogen peroxide to the suspension, react and allow it to stand for aging to obtain a clear and transparent orange-yellow aqueous solution of peroxytitanic acid, i.e. component A; Step S2: Preparation of anatase nano-titanium dioxide aqueous dispersion: Component A obtained in step S1 is heated at a constant temperature of 80℃ to 120℃ to obtain a white, semi-transparent or milky white anatase nano-titanium dioxide aqueous dispersion, i.e., component B. Step S3, Solution Combination: Component A obtained in step S1 and component B obtained in step S2 are mixed at a volume ratio of (1:9) to (9:1) to obtain the titanium dioxide photocatalytic solution.

7. The method for preparing a titanium dioxide photocatalytic solution according to claim 6, characterized in that, In step S12, the alkaline solution is diluted ammonia water; the washing involves multiple precipitation-decantation or centrifugal washing with deionized water until the NH4+ in the suspension is reduced. + and Cl - The ion concentration decreased significantly.

8. The method for preparing a titanium dioxide photocatalytic solution according to claim 6, characterized in that, In step S13, the ratio of the amount of hydrogen peroxide added to the molar amount of titanium tetrachloride in step S11 is (2:1) to (10:1); the aging time is 2 to 5 days.

9. The method for preparing a titanium dioxide photocatalytic solution according to claim 6, characterized in that, In step S2, the constant temperature heating treatment is at a temperature of 90°C to 110°C for a time of 1 to 10 hours.

10. A method for preparing a self-cleaning film, characterized in that, include: A titanium dioxide photocatalytic solution according to any one of claims 1-5 is coated onto the surface of a substrate and then dried and cured at a temperature of 25°C to 80°C to form a titanium dioxide photocatalytic self-cleaning film; the coating method is one of spraying, spin coating, dip-coating or scraping coating; the substrate is a glass substrate.

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