A room temperature curing self-cleaning photocatalytic film based on multi-level interface synergistic enhancement and a preparation method thereof

Abstract

This invention discloses a room-temperature curing self-cleaning photocatalytic film based on multi-level interface synergistic enhancement and its preparation method. The method includes: (1) preparing monodisperse TiO2 nanocrystals with controllable lattice strain using a non-equilibrium growth method; (2) constructing a TiO2 / UiO-66-NH2 / rGO ternary Z-type heterojunction photocatalytic material; (3) preparing a two-component room-temperature curing all-inorganic binder system composed of acid-catalyzed silica sol (ACSS) and fluorosilane-modified polysilazane; (4) compounding the heterojunction photocatalytic material with the binder system and adding nano-silica dispersion, and forming a coating liquid by ultrasonic-shear synergistic dispersion; (5) depositing it on a glass substrate using a gradient ultrasonic spraying process, and curing it into a film by room temperature-medium temperature stepwise curing. This invention achieves, for the first time, a fully inorganic self-cleaning film with both ultra-high photocatalytic activity and ultra-long weather resistance under room temperature curing conditions through multi-level interface synergy of ternary heterojunction synergistic photocatalytic enhancement, room temperature curing of two-component inorganic binder, and gradient film-forming structure design. It solves the technical problem of the difficulty in unifying photocatalytic activity, film-forming process, optical performance and service life in the prior art.

Description

Technical Field

[0001] This invention relates to the field of functional thin film preparation technology, specifically to an all-inorganic nanocomposite thin film with superhydrophilic, anti-fogging, self-cleaning and anti-reflective functions that can be applied to the surface of transparent substrates such as photovoltaic glass, building curtain walls, and car sunroofs. Background Technology

[0002] With the development of the photovoltaic industry, green building, and intelligent transportation, self-cleaning and anti-reflective technologies for glass surfaces have attracted much attention. Existing self-cleaning thin-film technologies mainly suffer from the following bottlenecks: 1. The contradiction between insufficient photocatalytic activity and dispersibility; Traditional thin films often use commercially available P25 titanium dioxide, which has weak absorption in the visible light band, and the nanoparticles tend to agglomerate in the coating, leading to the masking of active sites and reduced transparency. Although there are methods to modify the nanoparticles through doping or morphology control, it is often difficult to achieve both monodispersity and high crystallinity, thus limiting their application in transparent thin films.

[0003] 2. The challenge of film stability in MOF materials; Metal-organic frameworks (MOFs) have become a research hotspot due to their high porosity and excellent visible light response. However, MOF powders are difficult to form films on smooth substrates such as glass alone. When combined with traditional organic resins, the strong photo-oxidative properties of MOFs catalyze the degradation of the organic resins, leading to pulverization and failure of the film during long-term use.

[0004] 3. Trade-off between preparation process and performance; High-performance inorganic thin films typically require high-temperature sintering at 400-500℃ to achieve crystallization and curing, which limits their application on tempered glass or heat-sensitive substrates and consumes a lot of energy. Some existing room-temperature curing solutions often result in low film hardness and poor weather resistance due to the incompatibility between the binder system (such as organic resin) and the highly active photocatalyst.

[0005] To address the above problems, those skilled in the art have attempted various improvement schemes, but the following shortcomings still exist: (1) Zhejiang University Patent CN119263343B, "A Method for Preparing Monodisperse Doped Titanium Dioxide with In-situ Lattice Strain", discloses a method for preparing lattice-strained TiO2 by secondary injection of a titanium source and rapid heating solvothermal reaction. Its core technical feature is that lattice strain is introduced into TiO2 nanocrystals through non-equilibrium growth, thereby improving its photocatalytic activity.

[0006] However, this patented solution only focuses on the preparation of TiO2 monomers and does not involve its combination with MOF materials or other semiconductor materials, resulting in room for improvement in its photogenerated carrier separation efficiency; this patented technology does not involve the application of lattice-strained TiO2 in the field of room temperature curing films, nor does it solve the problems of photocatalyst dispersion and film stability in coatings; this patented technology does not consider the interfacial compatibility between TiO2 and the binder system, and if it is combined with organic binders in the presence of highly active photocatalysts, it still faces the risk of pulverization during long-term service.

[0007] (2) Zhao Zhenxia's team research (Appl. Catal. B, 2021) "TiOx@UiO-66-NH2 core-shell heterojunction photocatalyst", which discloses a TiOx@UiO-66-NH2 core-shell heterojunction photocatalyst that promotes charge separation by using the lattice mismatch between Zr and Ti clusters through the interfacial metal interpenetration strategy.

[0008] However, this study only focuses on laboratory powder catalysts and does not involve preparing them into practically applicable transparent films; the study uses TiOx as the core, whose lattice strain is uncontrollable, and does not introduce an electron transport medium (such as graphene) to further accelerate interfacial charge transfer; the study does not solve the problems of MOF materials being prone to agglomeration in coatings and having poor compatibility with the film-forming matrix; the study does not consider the comprehensive performance requirements of films in practical applications, such as mechanical hardness, light transmittance, and adhesion.

[0009] (3) Fudan University patent CN02150721.X "Preparation method of nano-titanium dioxide self-cleaning glass", which discloses a method for preparing nano-titanium dioxide self-cleaning glass by drying and curing at room temperature or treating at less than 300°C. This technology uses unmodified TiO2 nanoparticles, which have poor visible light response and insufficient photocatalytic activity; this technology uses an organic solvent system, and organic components remain after film formation, which are prone to aging and failure under long-term photocatalytic action.

[0010] (4) Patent CN201910155427.1 from the Institute of Earth Environment, Chinese Academy of Sciences, entitled "Preparation of Superhydrophilic Self-Cleaning Photocatalytic Thin Films of Titanium Dioxide by Modified PTA Method". This patent discloses a technique for obtaining superhydrophilic self-cleaning thin films by compounding SiO2 additives with TiO2 sol and drying at room temperature. However, this technique uses ordinary TiO2 sol and does not perform lattice strain regulation or heterostructure construction on TiO2, resulting in limited photocatalytic activity; the SiO2 additives in this technique only play a dispersing role and do not form an inorganic network structure with high cross-linking density, resulting in insufficient film hardness; this technique does not involve room temperature ceramicizing reinforcing agents such as polysilazane, and the mechanical strength and weather resistance of the film are difficult to meet the requirements for long-term outdoor service.

[0011] In summary, developing a self-cleaning film preparation technology that can simultaneously achieve high visible light activity, excellent dispersibility, room temperature curability, high hardness, high light transmittance, and long-term weather resistance is a problem that urgently needs to be solved in this field. Summary of the Invention

[0012] This invention aims to provide a room-temperature curing self-cleaning photocatalytic thin film based on multi-level interface synergistic enhancement and its preparation method. Through multi-level synergy of "ternary heterojunction synergistic photocatalytic enhancement," "two-component inorganic binder room-temperature curing system," and "gradient film-forming structure design," the photocatalytic activity, film-forming process, optical performance, and service life are synergistically improved, thereby effectively solving the aforementioned technical problems existing in the prior art.

[0013] To achieve the objectives of this invention, the following technical solution is adopted: Option 1: A room-temperature curing self-cleaning photocatalytic film based on multi-level interface synergistic enhancement, comprising a solid component and a solvent, wherein the solid component includes the following components by weight: Lattice strain TiO2 nanocrystals 10%–25%, UiO-66-NH2 3%~20%, Reduced graphene oxide (rGO) 0.1%–2.5%, Acid-catalyzed silica sol (ACSS) 30%–60%, Fluorosilane-modified polysilazane 5%–20%, Nano-silica dispersion 2%–12%; The mass ratio of the solid component to the solvent is 1:5 to 1:20.

[0014] In this room temperature curing self-cleaning photocatalytic film, the lattice strain of the TiO2 nanocrystals is 0.5% to 3%, and the oxygen vacancy concentration is 5% to 15%.

[0015] In this room temperature curing self-cleaning photocatalytic film, the mass ratio of TiO2, UiO-66-NH2 to rGO is 100:30~80:1~10.

[0016] In this room temperature curing self-cleaning photocatalytic film, the acid-catalyzed silica sol (ACSS) is obtained by hydrolysis and condensation of tetraethyl orthosilicate under conditions of pH=1-3 and water-to-silica ratio of 2-6, and is rich in active silanol groups.

[0017] In this room temperature curing self-cleaning photocatalytic film, the fluorosilane-modified polysilazane is prepared by grafting polysilazane with perfluorodecyltrimethoxysilane under anhydrous conditions, and the amount of fluorosilane modification is 1-10 wt%.

[0018] In this room temperature curing self-cleaning photocatalytic film, the particle size of the nano-silica dispersion is 10-50 nm, and the solid content is 20-30%.

[0019] Option 2: The method for preparing a room-temperature curing self-cleaning photocatalytic thin film provided by the present invention includes the following steps: S1. Preparation of lattice-strained TiO2 nanocrystals: Monodisperse TiO2 nanocrystals with controllable lattice strain were prepared by using a non-equilibrium growth method, through secondary injection of titanium source and control of reaction kinetics. S2. Construction of TiO2 / UiO-66-NH2 / rGO ternary heterostructure: The TiO2 nanocrystals prepared in step S1 and graphene oxide (GO) were ultrasonically dispersed in DMF, ZrCl4 and 2-aminoterephthalic acid were added, and UiO-66-NH2 was grown in situ on the TiO2 / rGO surface through a solvothermal reaction, while GO was reduced to rGO; S3. Preparation of two-component inorganic binders: Acid-catalyzed silica sol (ACSS) and fluorosilane-modified polysilazane were prepared respectively; S4. Preparation of composite coating solution: The ternary heterojunction material prepared in step S2 is mixed with the ACSS, fluorosilane-modified polysilazane and nano silica dispersion prepared in step S3 in a solvent, and a uniform and stable coating solution is obtained by ultrasonic-shear synergistic dispersion. S5. Gradient ultrasonic spraying deposition: The gradient ultrasonic spraying process is used to deposit the coating liquid onto the surface of the glass substrate in stages, forming a gradient structure of a bottom dense transition layer, a middle functional host layer and a surface fluorine-rich functional layer. S6. Step-by-step curing: Step-by-step curing is carried out in stages within the range of room temperature to 80°C, so that the silanol condenses and crosslinks, and the polysilazane is moisture-cured to form the SiO2 ceramic phase, while the fluorine-containing side groups migrate and accumulate to the surface of the film.

[0020] Further, in step S1 of this preparation method, the non-equilibrium growth method for preparing lattice-strained TiO2 nanocrystals includes: mixing a first titanium source precursor with a surfactant in a solvent and heating to 120-180°C to form a primary crystal nucleus; after heating to 180-260°C, rapidly adding a second titanium source precursor solution with an injection time of 1-30 seconds to form an instantaneous supersaturated environment, so that the newly generated shell layer is epitaxially deposited on the surface of the crystal nucleus, and constructing a stretched lattice strain by utilizing the interfacial lattice mismatch.

[0021] Furthermore, in step S4 of this preparation method, the ultrasonic-shear synergistic dispersion is performed by first performing ultrasonic dispersion at 100-500W for 10-30 minutes, followed by high-shear dispersion at 5000-20000rpm for 10-30 minutes.

[0022] Further, in step S5 of this preparation method, the gradient ultrasonic spraying deposition includes: First spraying: The liquid solid content of the coating film is 1-3%, the spraying thickness is 20-50nm, and it is dried immediately at 60-80℃ for 2-5 minutes after spraying to form a dense transition layer; Second coating: The liquid solid content of the coating film is 5-10%, the coating thickness is 80-120nm, and after spraying, it is left to stand at room temperature for 10-30 minutes to form the main layer; Third coating: The liquid-solid content of the coating is 2-4%, and the coating thickness is 5-10nm, forming a fluorine-rich surface layer.

[0023] Further, in step S6 of this preparation method, the step-curing includes: First stage curing: 15-30℃, relative humidity 40-60%, curing time 2-4 hours; Second stage curing: 50-80℃, relative humidity 60-80%, curing time 2-4 hours; Third stage of curing: Let stand at room temperature for 12-24 hours.

[0024] Option 3: A glass product with self-cleaning function, comprising a glass substrate and a functional film attached to the surface of the glass substrate, wherein the functional film is the above-mentioned room temperature curing self-cleaning photocatalytic film.

[0025] Furthermore, in this glass product, the total thickness of the functional thin film is 100-180 nm, the refractive index is 1.25-1.35, and it has a multi-level pore structure composed of UiO-66-NH2 micropores, solvent evaporation mesopores and rGO sheet voids, with a porosity of 30%-50%. Attached Figure Description

[0026] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0027] Figure 1 This is a transmission electron microscope (TEM) image of the photocatalytic material in the coating solution prepared in Example 1 of the present invention; Figure 2 This is a scanning electron microscope (SEM) image of the surface morphology of the composite film prepared in Example 1 of the present invention.

[0028] Figure 3 The X-ray diffraction (XRD) pattern of the lattice-strained TiO2 nanoparticles prepared in Example 1 of this invention. Detailed Implementation

[0029] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific illustrations.

[0030] <Ternary Z-type heterojunction photocatalytic system> The photocatalytic material of the present invention is composed of three parts: lattice strained TiO2, UiO-66-NH2 and reduced graphene oxide (rGO), thereby constructing a ternary heterojunction structure with Z-shaped band arrangement.

[0031] Lattice-strained TiO2, through a non-equilibrium growth method, introduces controllable tensile lattice strain (0.5%-3%) into TiO2, causing lattice distortion and introducing defect energy levels in the band gap, resulting in a redshift of its absorption edge to the visible light region (>450nm). Simultaneously, the lattice strain generates a large number of oxygen vacancies, which serve as surface active sites, significantly enhancing surface reactivity.

[0032] UiO-66-NH2, as a MOF material with visible light response, has a narrow bandgap (approximately 2.7 eV) that enables efficient absorption of visible light, generating photogenerated electron-hole pairs. Its porous structure (pore size approximately 0.8-1.2 nm) not only increases the specific surface area of ​​the film but also has a "moisture trapping" effect, endowing the film with excellent initial hydrophilicity and anti-fogging properties.

[0033] rGO, as a two-dimensional electron transport medium, exhibits excellent conductivity (conductivity up to 10⁻⁶). 3 The large surface area (S / m) and high specific surface area provide a fast migration channel for photogenerated electrons. The introduction of rGO constructs a Z-type heterojunction transport path: photogenerated electrons on the conduction band of UiO-66-NH2 are rapidly transferred to the valence band of TiO2 via rGO, recombine with holes, while electrons on the conduction band of TiO2 and holes on the valence band of UiO-66-NH2 are retained, achieving efficient spatial separation of electron-hole pairs.

[0034] <Two-component all-inorganic room temperature curing adhesive system> The binder system of the present invention consists of acid-catalyzed silica sol (ACSS) and fluorosilane-modified polysilazane, which synergistically crosslink at room temperature to form a high-density inorganic network structure.

[0035] Acid-catalyzed silica sol (ACSS) can hydrolyze and condense under acidic conditions (pH=1-3), mainly forming linear and low-crosslinked silica-oxygen segments rich in active silanol groups (Si-OH). These active groups not only undergo condensation reactions with the silanol groups on the substrate glass surface to form chemical bonds (Si-O-Si), ensuring the adhesion of the film, but also form hydrogen bonds and electrostatic interactions with the amino groups (-NH2) on the UiO-66-NH2 surface, achieving stable dispersion of the photocatalytic material in the binder.

[0036] Fluorosilane-modified polysilazane, where (-SiH-NH-)n is a compound that can crosslink and solidify under room temperature and humidity conditions, transforming into a SiO2 ceramic phase, is further modified by introducing fluorosilanes (such as perfluorodecyltrimethoxysilane) to introduce fluorinated side groups onto the polysilazane molecular chain. During room temperature curing, the modified polysilazane not only forms a highly crosslinked Si-O-Si three-dimensional network structure through hydrolysis and condensation, but also the fluorinated side groups spontaneously migrate to the film surface, forming a fluorine-rich layer with low surface energy, endowing the film with superhydrophilicity (water contact angle ≤5°) and antifouling properties.

[0037] <Gradient film formation structure> The film of the present invention is not a homogeneous structure, but a multilayer structure with gradient composition and gradient porosity formed by gradient ultrasonic spraying process and room temperature-medium temperature stepped curing.

[0038] Underlying Layer (Dense Transition Layer): A dense silicon-oxygen transition layer (20-50 nm thick) is formed on the glass surface by initially spraying a low-solids content coating liquid and rapidly curing it. This layer acts as an "anchor layer," firmly bonding to the glass substrate through chemical bonding, while providing a smooth deposition substrate for the upper layers.

[0039] Middle layer (functional host layer): A host layer (80-120 nm thick) rich in photocatalytic materials and porous structure is formed by secondary spraying of a high-solids content coating liquid and controlling the curing speed. The porous structure (porosity 30%-50%) of this layer originates from the micropores of UiO-66-NH2, the voids between rGO sheets, and the mesopores formed by solvent evaporation. The porous structure effectively reduces the refractive index of the film (1.25-1.35), achieving an anti-reflection effect.

[0040] Surface layer (fluorine-rich functional layer): During the later stages of curing, by controlling humidity and temperature, the fluorine-containing side groups in the fluorosilane-modified polysilazane migrate and accumulate to the film surface, forming a fluorine-rich layer with a thickness of approximately 5-10 nm. This layer imparts superhydrophilicity and antifouling properties to the film, while not hindering the contact between photocatalytic active sites and pollutants.

[0041] <Room-temperature curing self-cleaning photocatalytic film> Based on the above mechanism, this invention provides a formulation for a room-temperature curing self-cleaning photocatalytic thin film: This room-temperature curing self-cleaning photocatalytic film is composed of solid components and a solvent, wherein the solid components include the following components by weight:

[0042] Based on this, the mass ratio of the solids of the above components to the solvent (ethanol / water mixed solvent) is 1:5 to 1:20.

[0043] As a further preferred option, in the TiO2 / UiO-66-NH2 / rGO ternary heterojunction formed by this formulation, the mass ratio of TiO2, UiO-66-NH2 to rGO is 100:30~80:1~10.

[0044] <Lattice-Strained TiO2 Nanocrystals> In this formulation, the lattice-strained TiO2 nanocrystals serve as the core component of the heterojunction, providing the main ultraviolet light response and the lattice strain-induced visible light response; the oxygen vacancies on their surface act as active sites, participating in photocatalytic reactions; and their nanoscale size ensures the light transmittance of the film.

[0045] The lattice-strained TiO2 nanocrystals are specifically composed of anatase TiO2 with a particle size of 10-20 nm, a lattice strain of 0.5%-3%, and an oxygen vacancy concentration of 5%-15% (based on the XPS O1s peak area).

[0046] Regarding the weight content of lattice-strained TiO2 nanocrystals in this formulation, when the weight content of lattice-strained TiO2 is less than 10%, the photocatalytic activity is insufficient and the methylene blue degradation rate is less than 90%; when it is higher than 25%, the nanoparticles are prone to agglomeration in the coating solution, resulting in a decrease in light transmittance (<90%), and the interfacial bonding with the binder deteriorates, leading to a decrease in film hardness.

[0047] < UiO-66-NH2> The UiO-66-NH2 in this formulation provides a visible light response, and its narrow bandgap (approximately 2.7 eV) enables efficient absorption of visible light; its porous structure imparts anti-reflective properties and moisture-trapping capabilities to the film, enhancing its anti-fogging performance; the amino groups (-NH2) on the surface form hydrogen bonds with the silanol groups of ACSS, achieving uniform dispersion.

[0048] The specific composition of this UiO-66-NH2 is Zr6O4(OH)4(BDC-NH2)6, with a particle size of 50-200 nm, a pore size of 0.8-1.2 nm, and a specific surface area of ​​800-1200 m². 2 / g.

[0049] Regarding the content of UiO-66-NH2 in this formulation, when the weight content of UiO-66-NH2 is less than 3%, the visible light response is insufficient, the photocatalytic activity is only slightly improved, and the anti-fogging performance is poor. When it is higher than 20%, the TiO2 surface is over-coated, which hinders the migration of photogenerated electrons to TiO2. In addition, the photostability of UiO-66-NH2 itself is insufficient, and structural collapse may occur during long-term use, resulting in a decrease in weather resistance.

[0050] <Reduced graphene oxide (rGO)> The reduced graphene oxide (rGO) in this formulation acts as an electron transport medium, accelerating the migration of photogenerated electrons from UiO-66-NH2 to TiO2; its two-dimensional sheet structure can induce the directional growth and uniform dispersion of TiO2 and UiO-66-NH2; and its high specific surface area provides more active sites for photocatalytic reactions.

[0051] The reduced graphene oxide (rGO) is preferably a single-layer or few-layer (≤5-layer) rGO with a sheet diameter of 100-500 nm, a C / O atomic ratio of ≥10, and an electrical conductivity of ≥1000 S / m.

[0052] Regarding the content of reduced graphene oxide (rGO) in this formulation: when the weight content of rGO is less than 0.1%, the electron transport channels are insufficient, the carrier separation efficiency is not significantly improved, and the photocatalytic activity is limited; when it is higher than 2.5%, the black color of rGO itself will cause a significant decrease in the transmittance of the film (>5%), and excessive rGO will mask the active sites of TiO2 and UiO-66-NH2, thus reducing the photocatalytic activity.

[0053] <Acid-catalyzed silica sol (ACSS)> In this formulation, acid-catalyzed silica sol (ACSS) serves as the main film-forming substance, forming chemical bonds with the glass substrate and interfacial coupling with the photocatalytic material to provide mechanical strength to the film; its abundant silanol groups (Si-OH) are key to achieving room temperature crosslinking and curing.

[0054] The acid-catalyzed silica sol (ACSS) is specifically obtained by hydrolysis and condensation of tetraethyl orthosilicate (TEOS) under conditions of pH=1-3 and water-to-silica ratio of 2-6. It has a solid content of 5%-20%, a particle size of 5-20nm, and is rich in Si-OH groups.

[0055] Regarding the content of acid-catalyzed silica sol (ACSS) in this formulation, when the weight content of ACSS is less than 30%, the film-forming matrix is ​​insufficient, the film cannot form a continuous network, the hardness decreases (<4H), and the adhesion deteriorates; when it is higher than 60%, the relative content of photocatalytic material decreases, the photocatalytic activity of the film decreases, and an excessively thick matrix layer will hinder the contact between the photocatalytic material and pollutants.

[0056] <Fluorosilane-modified polysilazane> In this formulation, fluorosilane-modified polysilazane acts as an inorganic crosslinking enhancer. It forms a SiO2 ceramic phase with high crosslinking density through moisture curing at room temperature, which significantly improves the hardness of the film. Fluorosilane modification introduces fluorine-containing side groups, which migrate to the surface during the curing process, giving the film surface superhydrophilicity and antifouling properties.

[0057] The fluorosilane-modified polysilazane is specifically obtained by grafting perfluorodecyltrimethoxysilane onto a polysilazane (such as Durazane 1800) under anhydrous conditions. The amount of fluorosilane modification is 1 to 10 wt%.

[0058] Regarding the content of fluorosilane-modified polysilazane in this formulation, when the weight content of fluorosilane-modified polysilazane is less than 5%, the crosslinking density is insufficient, the film hardness is <4H, the surface fluorine content is low, and the water contact angle is >10°; when it is higher than 20%, the excessive polysilazane will generate too much shrinkage stress during the curing process, leading to film cracking and a decrease in light transmittance.

[0059] <Nano Silica Dispersion> The nano-silica dispersion in this formulation acts as a rheology modifier and porosity regulator, adjusting the viscosity and rheological behavior of the coating solution to prevent sagging; at the same time, it participates in film formation, increasing the porosity of the film, reducing the refractive index, and achieving an anti-reflection effect.

[0060] This nano-silica dispersion is specifically formed by dispersing nano-SiO2 particles with a particle size of 10-50 nm and a solid content of 20-30% in an ethanol / water mixed solvent.

[0061] Regarding the content of the nano-silica dispersion in this formulation, when the weight content of nano-silica is less than 2%, the rheological regulation effect is insufficient, the coating liquid is prone to sagging, and the porosity of the film is low, resulting in an insignificant anti-reflection effect; when it is higher than 12%, the internal stress of the film increases, microcracks are easily generated, and the relative content of photocatalytic material decreases.

[0062] <Improved Formula> The formulation of the above-mentioned room temperature curing self-cleaning photocatalytic film may, as needed, include one or more of the following: colorant, leveling agent, defoamer, and antioxidant.

[0063] <Preparation process of room temperature curing self-cleaning photocatalytic thin films> This invention provides a corresponding preparation process for the room-temperature curing self-cleaning photocatalytic thin film, which mainly includes the following steps: Step S1: Prepare lattice-strained TiO2 nanocrystals.

[0064] (1) Dissolve the first titanium source precursor (selected from one or more of tetraisopropyl titanate and tetrabutyl titanate, 2-5 mmol) and the surfactant (selected from oleylamine, oleic acid or a combination thereof, 10-20 mL) in a non-polar high-boiling solvent (selected from octadecane, octadecane or a combination thereof, 20-50 mL); (2) Under an inert atmosphere (argon or nitrogen), heat to 120-180℃ for a pre-reaction of 20-60 minutes to form primary crystal nuclei; (3) After heating to a reaction temperature of 180-260℃, add the second titanium source precursor solution (concentration of 0.1-1.0 mol / L, injection time controlled within 1-30 seconds) by continuous injection or rapid injection to form an instantaneous supersaturated environment; (4) Maintain the reaction temperature for 5 to 60 minutes to allow the newly generated amorphous or low-crystallinity shell to be epitaxially deposited on the surface of the original crystal nucleus, and use the interface lattice mismatch to construct a tensile lattice strain. (5) Centrifugation and washing yielded monodisperse TiO2 nanocrystals with a particle size of 10-20 nm and a lattice strain of 0.5%-3%.

[0065] In this step, a "nucleus-shell" structure is constructed in TiO2 nanocrystals through "secondary injection-induced non-equilibrium growth". Controllable stretching lattice strain is introduced by using interfacial lattice mismatch. Rapid injection forms an instantaneous supersaturated environment, which promotes the epitaxial deposition of the shell on the surface of the nucleus, rather than self-nucleation, thus ensuring the monodispersity of the product. The lattice strain is accompanied by the generation of oxygen vacancies, which serve as photocatalytic active sites.

[0066] Step S2: Construct a TiO2 / UiO-66-NH2 / rGO ternary heterojunction.

[0067] (1) Disperse the lattice-strained TiO2 nanocrystals (100 mg) prepared in step S1 in DMF (30 mL); (2) Add graphene oxide (GO, 2-10 mg) and ultrasonically disperse for 30 minutes to make GO uniformly coat the TiO2 surface; (3) Add ZrCl4 (0.3-0.8 mmol) and 2-aminoterephthalic acid (0.3-0.8 mmol), and add glacial acetic acid (1-3 mL) as a regulator; (4) Transfer the mixture to a reaction vessel and react at 100-150°C for 12-24 hours; (5) During the reaction, GO is partially reduced to rGO, and UiO-66-NH2 grows in situ on the TiO2 / rGO surface; (6) Centrifuge washing, vacuum drying at 60℃ to obtain TiO2 / UiO-66-NH2 / rGO ternary heterojunction composite material.

[0068] In this step, rGO is introduced as an electron transport medium to construct a Z-shaped heterojunction transport path; during the solvothermal reaction, GO is simultaneously reduced to rGO, eliminating the need for an additional reduction step; glacial acetic acid is used as a regulator to control the nucleation rate and crystal size of UiO-66-NH2, ensuring its uniform growth on the TiO2 / rGO surface.

[0069] Step S3: Prepare a two-component inorganic binder.

[0070] (1) Preparation of acid-catalyzed silica sol (ACSS): Tetraethyl orthosilicate (TEOS), ethanol and water are mixed in a molar ratio of 1:20-40:2-6, the pH is adjusted to 1-3 with hydrochloric acid, and the mixture is stirred at 20-60°C for 6-48 hours to obtain ACSS; (2) Preparation of fluorosilane-modified polysilazane: Dissolve polysilazane (such as Durazane 1800) in anhydrous toluene, add perfluorodecyltrimethoxysilane (1-10 wt%), react at 60-80°C for 2-6 hours under an inert atmosphere, remove the solvent by vacuum distillation to obtain fluorosilane-modified polysilazane.

[0071] In this step, ACSS undergoes hydrolysis and condensation under acidic conditions, mainly forming a linear and low-crosslinking structure rich in active Si-OH, which facilitates chemical bonding with photocatalytic materials and glass substrates. Fluorosilane-modified polysilazane introduces fluorine-containing side groups, which migrate to the surface during subsequent curing, endowing the film with superhydrophilicity and antifouling properties.

[0072] Step S4: Prepare the composite coating solution.

[0073] (1) Disperse the ternary heterojunction material (100 parts) prepared in step S2 in an ethanol / water mixed solvent (500-2000 parts) and pre-disperse it by ultrasound for 10-30 minutes; (2) Add ACSS (150-400 parts) and nano silica dispersion (10-50 parts), and stir until homogeneous; (3) Add fluorosilane-modified polysilazane (20-100 parts); (4) Use ultrasonic-shear synergistic dispersion: first ultrasonic dispersion (100-500W, 10-30 minutes), then high shear dispersion (5000-20000rpm, 10-30 minutes). (5) Let stand to defoam and obtain a uniform and stable composite coating liquid.

[0074] In this step, ultrasonic-shear synergistic dispersion ensures the monodisperse state of nanomaterials in the coating solution, avoiding aggregation; an ethanol / water mixed solvent is used, which is environmentally friendly and allows for easy control of the evaporation rate; and the components are added in sequence to ensure the orderly establishment of interfacial interactions.

[0075] Step S5: Gradient ultrasonic spraying deposition.

[0076] (1) First spraying (undercoat): Using ultrasonic spraying equipment, the coating liquid is diluted to a solid content of 1-3% and sprayed onto a clean glass substrate with a thickness of 20-50 nm. After spraying, it is dried at 60-80℃ for 2-5 minutes to form a dense transition layer. (2) Second spraying (main layer): Use the original concentration of coating liquid with a solid content of 5-10% and continue spraying on the bottom layer. Control the total dry film thickness to 100-150nm. After spraying, let it stand at room temperature for 10-30 minutes to allow the solvent to evaporate slowly. (3) Third spraying (surface layer): Use diluted coating liquid (solid content 2-4%), spray thickness 5-10nm to form surface enrichment.

[0077] In this step, gradient spraying is used to achieve a gradient distribution of film composition and porosity; the bottom layer is rapidly cured to form an anchoring layer to ensure adhesion; the main layer is slowly cured to form a porous structure to achieve enhanced transparency; and the surface thin coating promotes the migration and enrichment of fluorine-containing side groups to the surface.

[0078] Step S6: Step curing.

[0079] (1) First stage curing: room temperature (15-30℃), relative humidity 40-60%, curing for 2-4 hours, mainly the condensation reaction of silanol groups and the initial crosslinking of polysilazane; (2) Second stage curing: heat to 50-80℃, relative humidity 60-80%, cure for 2-4 hours to promote deep cross-linking of polysilazane and formation of SiO2 ceramic phase; (3) Third stage curing: Let stand at room temperature for 12 to 24 hours to allow the film to fully cure and the fluorine-containing side groups to migrate fully to the surface.

[0080] In this step, the crosslinking rate is controlled by step curing to avoid internal stress and microcracks caused by excessive curing; the second stage of moisture curing promotes the ceramic transformation of polysilazane; and the room temperature standing stage promotes the migration and enrichment of fluorine-containing side groups.

[0081] Based on the above formulation and process, the room-temperature curing self-cleaning photocatalytic film formed by the present invention has the following structural and performance characteristics: (1) Gradient multilayer structure: It consists of a bottom dense transition layer (20-50nm), a middle functional host layer (80-120nm) and a surface fluorine-rich functional layer (5-10nm), with a total thickness of 100-180nm.

[0082] (2) Multilevel pore structure: The micropores (0.8-1.2nm) of UiO-66-NH2, the mesopores (2-50nm) formed by solvent evaporation, and the gaps between rGO sheets together constitute a multilevel pore network with a porosity of 30-50%.

[0083] (3) Z-type heterojunction interface: TiO2 and UiO-66-NH2 form a Z-type heterojunction through rGO. There is a strain field induced by lattice mismatch at the interface, which promotes the separation of photogenerated carriers.

[0084] See further Figure 1The image shown is a transmission electron microscope (TEM) image of the photocatalytic material in the coating solution prepared in Example 1 of this invention. The image clearly shows that the TiO2 nanocrystals (approximately 15 nm) are uniformly coated with a UiO-66-NH2 layer (approximately 5-10 nm thick), and the rGO sheets act as an electron transport medium, closely contacting both, forming a typical ternary heterojunction structure. The particles are monodisperse, with no obvious agglomeration observed.

[0085] See Figure 2 The image shown is a scanning electron microscope (SEM) image of the surface morphology of the composite film prepared in Example 1 of this invention. The film surface is smooth and dense, without cracks, and a uniformly distributed porous structure is visible, with pore sizes in the range of 10-50 nm.

[0086] See Figure 3 The figure shows the X-ray diffraction (XRD) pattern of the lattice-strained TiO2 nanoparticles prepared in Example 1 of this invention. The figure shows that the diffraction peak of the anatase phase (101) is significantly broadened, and the grain size is calculated to be about 13 nm according to the Scherrer formula. At the same time, the position of the (101) peak is shifted by about 0.2° compared with the standard anatase (2θ=25.3°), which confirms the existence of lattice strain.

[0087] <Application Products> The room-temperature curing, self-cleaning photocatalytic thin film prepared by this invention can be applied to the following products: 1. Self-cleaning photovoltaic glass The thin film of this invention is coated onto the surface of the cover glass of a photovoltaic module to form a self-cleaning anti-reflective functional layer. This product has the following characteristics: a 3-5% increase in light transmittance, improving the power generation efficiency of the photovoltaic module; a super-hydrophilic surface, allowing rainwater to carry away dust and dirt, reducing the frequency of manual cleaning; photocatalytic degradation of organic pollutants, keeping the glass surface clean; and an entirely inorganic composition, exhibiting excellent weather resistance, matching the 25-year lifespan of the photovoltaic module.

[0088] 2. Self-cleaning building curtain wall glass The film of this invention is coated onto the surface of building curtain wall glass to form an outer layer with self-cleaning, anti-fogging, and anti-reflective functions. This product has the following characteristics: a super-hydrophilic surface to prevent raindrop residue from forming water stains; visible light responsive photocatalysis to maintain self-cleaning effects even on rainy days; high hardness (6H) and high adhesion to resist wind and sand erosion; and a room temperature curing process, making it applicable to the renovation of existing building glass.

[0089] 3. Car sunroof glass The film of this invention is coated onto the inner or outer surface of an automotive sunroof glass to form an anti-fog, self-cleaning functional layer. This product has the following characteristics: super hydrophilicity, quickly eliminating fog caused by temperature differences and ensuring driving safety; high light transmittance, not affecting lighting; and excellent weather resistance, enduring the automotive service environment.

[0090] <Examples and Comparative Examples> The present invention will be further illustrated below with reference to specific embodiments. It should be understood that the following examples are only for providing best practice models of the invention and should not be construed as limiting the scope of the invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed according to conventional operating methods and conditions, or according to the conditions recommended by the manufacturer. Unless otherwise stated, percentages and parts are by weight.

[0091] In the following examples, the components used to formulate the surface treatment agent are as follows: Lattice-strained TiO2 (Al): self-made according to step S1, with a particle size of 15 nm, lattice strain of 1.2%, and oxygen vacancy concentration of 8.5%; Lattice-strained TiO2 (A2): self-made according to step S1, with a particle size of 12 nm, lattice strain of 1.5%, and oxygen vacancy concentration of 10.2%; UiO-66-NH2(B1): Prepared according to step S2, with a particle size of 80nm; UiO-66-NH2(B2): Prepared according to step S2, with a particle size of 120nm; Reduced graphene oxide (C1): prepared according to step S2, with a sheet diameter of 200 nm, a C / O ratio of 12, and an electrical conductivity of 1500 S / m; Reduced graphene oxide (C2): prepared according to step S2, with a sheet diameter of 150 nm, a C / O ratio of 10, and an electrical conductivity of 1100 S / m; Acid-catalyzed silica sol (D1): prepared according to step S3, with a solid content of 10% and a particle size of 10 nm; Acid-catalyzed silica sol (D2): prepared according to step S3, with a solid content of 15% and a particle size of 15nm; Fluorosilane-modified polysilazane (E1): Prepared according to step S3, with a modification amount of 5 wt%; Fluorosilane-modified polysilazane (E2): prepared according to step S3, with a modification amount of 8 wt%; Nano silica dispersion (F1): Particle size 20nm, solid content 25%; Nano silica dispersion (F2): Particle size 15nm, solid content 25%.

[0092] According to the solid component ratios listed in Table 1, the above components and solvents were mixed uniformly at room temperature and then dispersed by ultrasonic-shear synergistic dispersion to obtain the composite coating liquid. Gradient ultrasonic spraying was used to deposit the coating liquid onto the surface of photovoltaic glass, followed by step curing to obtain samples 1–16.

[0093] Table 1. Solid composition and content of room temperature curing self-cleaning photocatalytic films

[0094] For performance test preparation and testing methods, please refer to Table 2.

[0095] Table 2

[0096] For samples 1 to 16 obtained in Table 1, the corresponding performance indicators were tested based on the test methods in Table 2, and the sample performance test results listed in Table 3 were obtained.

[0097] Table 3 Results of sample performance tests

[0098] Analysis of the results listed in Table 3: 1. Synergistic enhancement effect of ternary heterojunctions; The comparison between Example 1 and Comparative Examples 1 (without rGO), 2 (without UiO-66-NH2), and 3 (without lattice strain) shows that the TiO2 / UiO-66-NH2 / rGO ternary heterojunction of the present invention has a significant synergistic enhancement effect on photocatalytic activity. The degradation rate of Comparative Example 1 (without rGO) was 92.5%, that of Comparative Example 2 (without UiO-66-NH2) was 89.0%, and that of Comparative Example 3 (without lattice strain) was 84.5%, while the degradation rate of Example 1 (intact ternary system) reached 99.2%. This indicates that the electron transport effect of rGO, the visible light response of UiO-66-NH2, and the active sites of lattice strained TiO2 together constitute a highly efficient Z-shaped heterojunction.

[0099] 2. Advantages of two-component inorganic binder systems; A comparison of Example 1 with Comparative Example 4 (fluorine-free silane modification) and Comparative Example 5 (organic binder) shows that the ACSS + fluorosilane modified polysilazane system of the present invention has significant advantages in hardness, hydrophilicity, and weather resistance. Comparative Example 5 (organic binder) pulverized after 200 hours of UV aging, while Example 1 maintained 92% of its performance after 500 hours of aging, demonstrating the weather resistance advantage of the all-inorganic system. Fluorosilane modification reduced the water contact angle from 18° (Comparative Example 4) to 4° (Example 1), proving the surface enrichment effect of fluorine-containing side groups.

[0100] 3. Criticality of component ratios; Examples 1 and 6-10 demonstrate the performance of each component within its preferred range: Example 7 (TiO2=10%, UiO-66-NH2=5%): The hardness dropped to 4H and the aging retention rate dropped to 88%, indicating that the crosslinking density was insufficient when the content of active components was too low. In Example 6 (TiO2=20%, UiO-66-NH2=12%), the transmittance decreased to 92.5%, indicating that excessively high levels of active components caused increased scattering. Example 9 (modified polysilazane = 5%) had a water contact angle of 8° and a hardness that decreased to 4H, indicating that both hydrophilicity and hardness decreased when the reinforcing agent was insufficient. Example 10 (modified polysilazane = 15%) had a water contact angle of 3° and a hardness of 6H, demonstrating that appropriately increasing the reinforcing agent can further optimize the hydrophilicity.

[0101] 4. Comparison with existing technologies Compared with Comparative Example 5 (organic binder), Example 1 of this invention shows significant advantages in hardness (6H vs 2H), light transmittance (94.2% vs 89.5%), and weather resistance (no powdering after 500 hours vs 200 hours of powdering). Compared with the comparative literature analyzed in the background art, this invention shows significant improvements in key indicators such as photocatalytic activity (99.2% vs 60-85% in the literature), light transmittance (94.2% vs 80-90% in the literature), hardness (6H vs 2-4H in the literature), and weather resistance (500 hours vs 200 hours in the literature), achieving unexpected technical effects.

[0102] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A room-temperature curing self-cleaning photocatalytic thin film based on multi-level interface synergistic enhancement, composed of solid components and solvent, characterized in that, The solids component comprises the following components by weight: Lattice strain TiO2 nanocrystals 10%–25%, UiO-66-NH2 3%~20%, Reduced graphene oxide (rGO) 0.1%–2.5%, Acid-catalyzed silica sol (ACSS) 30%–60%, Fluorosilane-modified polysilazane 5%–20%, Nano-silica dispersion 2%–12%; The mass ratio of the solid component to the solvent is 1:5 to 1:

20.

2. The room-temperature curing self-cleaning photocatalytic thin film according to claim 1, characterized in that, The lattice strain of the TiO2 nanocrystals is 0.5% to 3%, and the oxygen vacancy concentration is 5% to 15%.

3. The room-temperature curing self-cleaning photocatalytic thin film according to claim 1, characterized in that, The mass ratio of TiO2, UiO-66-NH2 to rGO is 100:30 to 80:1 to 10.

4. The room-temperature curing self-cleaning photocatalytic thin film according to claim 1, characterized in that, The acid-catalyzed silica sol (ACSS) is obtained by hydrolysis and condensation of tetraethyl orthosilicate under conditions of pH=1-3 and water-to-silica ratio of 2-6, and is rich in active silanol groups.

5. A method for preparing a room-temperature curing self-cleaning photocatalytic thin film according to any one of claims 1-4, characterized in that, The preparation method includes the following steps: S1. Preparation of lattice-strained TiO2 nanocrystals: Monodisperse TiO2 nanocrystals with controllable lattice strain were prepared by using a non-equilibrium growth method, through secondary injection of titanium source and control of reaction kinetics. S2. Construction of TiO2 / UiO-66-NH2 / rGO ternary heterostructure: The TiO2 nanocrystals prepared in step S1 and graphene oxide (GO) were ultrasonically dispersed in DMF, ZrCl4 and 2-aminoterephthalic acid were added, and UiO-66-NH2 was grown in situ on the TiO2 / rGO surface through a solvothermal reaction, while GO was reduced to rGO; S3. Preparation of two-component inorganic binders: Acid-catalyzed silica sol (ACSS) and fluorosilane-modified polysilazane were prepared respectively; S4. Preparation of composite coating solution: The ternary heterojunction material prepared in step S2 is mixed with the ACSS, fluorosilane-modified polysilazane and nano silica dispersion prepared in step S3 in a solvent, and a uniform and stable coating solution is obtained by ultrasonic-shear synergistic dispersion. S5. Gradient ultrasonic spraying deposition: The gradient ultrasonic spraying process is used to deposit the coating liquid onto the surface of the glass substrate in stages, forming a gradient structure of a bottom dense transition layer, a middle functional host layer and a surface fluorine-rich functional layer. S6. Step-by-step curing: Step-by-step curing is carried out in stages within the range of room temperature to 80°C, so that the silanol condenses and crosslinks, and the polysilazane is moisture-cured to form the SiO2 ceramic phase, while the fluorine-containing side groups migrate and accumulate to the surface of the film.

6. The preparation method according to claim 5, characterized in that, In step S1, the non-equilibrium growth method for preparing lattice-strained TiO2 nanocrystals includes: mixing a first titanium source precursor with a surfactant in a solvent and heating to 120-180°C to form a primary crystal nucleus; after heating to 180-260°C, rapidly adding a second titanium source precursor solution with an injection time of 1-30 seconds to form an instantaneous supersaturated environment, allowing the newly generated shell to be epitaxially deposited on the surface of the crystal nucleus, and constructing a stretched lattice strain by utilizing interfacial lattice mismatch.

7. The preparation method according to claim 5, characterized in that, In step S5, the gradient ultrasonic spraying deposition includes: First spraying: The liquid solid content of the coating film is 1-3%, the spraying thickness is 20-50nm, and it is dried immediately at 60-80℃ for 2-5 minutes after spraying to form a dense transition layer; Second coating: The liquid solid content of the coating film is 5-10%, the coating thickness is 80-120nm, and after spraying, it is left to stand at room temperature for 10-30 minutes to form the main layer; Third coating: The liquid-solid content of the coating is 2-4%, and the coating thickness is 5-10nm, forming a fluorine-rich surface layer.

8. The preparation method according to claim 5, characterized in that, In step S6, the stepped curing includes: First stage curing: 15-30℃, relative humidity 40-60%, curing time 2-4 hours; Second stage curing: 50-80℃, relative humidity 60-80%, curing time 2-4 hours; Third stage of curing: Let stand at room temperature for 12-24 hours.

9. A glass product with self-cleaning function, characterized in that, It includes a glass substrate and a functional film attached to the surface of the glass substrate, wherein the functional film is the room temperature curing self-cleaning photocatalytic film as described in any one of claims 1-4.

10. The glass article according to claim 9, characterized in that, The functional thin film has a total thickness of 100-180 nm, a refractive index of 1.25-1.35, and a multi-level porous structure consisting of UiO-66-NH2 micropores, solvent evaporation mesopores, and rGO sheet voids, with a porosity of 30%-50%.

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