Water-based biomass coating with self-cleaning function and preparation method thereof

Abstract

The invention belongs to the technical field of coating preparation, and provides a water-based biomass coating with a self-cleaning function and a preparation method of the water-based biomass coating. After lignin is subjected to alkali dissolution purification, acrylic anhydride modification and dopamine grafting, the lignin and soybean protein subjected to enzymolysis treatment are subjected to dopamine modification and glutaraldehyde cross-linking compounding to form modified lignin protein, the modified lignin protein is introduced into an acrylic monomer emulsion polymerization system to be copolymerized with ethyl acrylate and methyl methacrylate, and the modified lignin protein is obtained. The preparation method comprises the following steps: preparing a water-based acrylic copolymer emulsion, preparing a PDA-metal network and low-surface-energy particles at the same time, enabling the low-surface-energy particles to form a super-hydrophobic structure through an electrolyte layer and surface modification, compounding the water-based acrylic emulsion with chitosan-citrate, the PDA-metal network and the low-surface-energy particles, and adding a flatting agent and a defoaming agent to adjust the performance of the coating. The water-based biomass coating with the self-cleaning function is prepared.

Description

Technical Field

[0001] The present invention belongs to the technical field of coating preparation, and relates to an aqueous biomass coating with self-cleaning function and a preparation method thereof. Background Art

[0002] Self-cleaning coatings have become one of the hotspots in the research field of functional coatings in recent years. They can achieve automatic removal of dirt through special physicochemical properties on the surface. Based on the bionic design concept in nature, such as the superhydrophobicity of lotus leaf surfaces and the superhydrophilicity of photocatalytic surfaces, the self-cleaning function is applied to various fields, including building facades, photovoltaic modules, and medical devices, etc. However, the preparation of traditional self-cleaning coatings usually relies heavily on chemical substances such as fluorine-containing compounds or siloxanes. Their preparation processes may cause environmental pollution and pose certain challenges to ecological friendliness. With the enhancement of environmental awareness, the development of green coatings based on renewable resources has become an important direction in the research of materials science and environmental chemistry. As renewable resources, biomass materials have become an important choice in the research of green coatings due to their rich chemical structures, diverse functional groups, and environmental friendliness. Biomass materials not only have a wide range of sources, but also possess excellent film-forming properties, mechanical properties, and potential for chemical modification. Using these biomass materials as the matrix of coatings can not only reduce the dependence on petrochemical resources, but also endow the coatings with various functional properties, such as stain resistance, antibacterial property, and water resistance, through reasonable chemical or physical modification.

[0003] Aqueous biomass coatings avoid the harm of traditional solvent-based coatings to the environment and human health. Compared with solvent-based coatings, the emissions of volatile organic compounds (VOCs) during their production and application are significantly reduced, which helps to improve air quality and meets the requirements of green chemistry and sustainable development. Such coatings have wide application values in fields such as building facades, industrial painting, home decoration, and surface protection of medical devices. Especially on the surfaces of building facades and photovoltaic modules, the self-cleaning function can effectively prevent the attachment of dust, dirt, and water stains, reduce the cleaning frequency, and thus lower the maintenance cost. The development of biomass coatings is not limited to environmental friendliness. It also reflects the innovation of material multifunctionality and structural design. By utilizing the degradability and biocompatibility of biomass materials, such coatings can be naturally degraded after application, avoiding the environmental burden caused by the difficulty of recycling traditional coatings. Therefore, it is of great significance to develop an aqueous biomass coating with self-cleaning function. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide an aqueous biomass coating with self-cleaning function and its preparation method. First, lignin is treated by alkali dissolution purification, acrylic anhydride modification and dopamine grafting to prepare functionalized dopamine-grafted lignin. At the same time, soy protein is enzymatically hydrolyzed, and through dopamine modification and glutaraldehyde cross-linking, it is compounded with lignin to form a modified lignin-protein material. The modified lignin-protein is introduced into the acrylic emulsion polymerization system and copolymerized with acrylic monomers to prepare an aqueous acrylic copolymer emulsion based on biomass. In order to further enhance the functionality of the coating, PDA-metal network and low surface energy particles are prepared. The low surface energy particles are constructed with a superhydrophobic surface structure through electrolyte layer and hydrophobic modification. Finally, the aqueous acrylic copolymer emulsion is mixed with chitosan-citrate, PDA-metal network, low surface energy particles and leveling agent and defoaming agent are added to prepare an aqueous biomass coating with self-cleaning function, so as to meet the needs of actual production.

[0005] To achieve this purpose, the present invention adopts the following technical solutions:

[0006] In the first aspect, the present invention provides a preparation method of an aqueous biomass coating with self-cleaning function, and the preparation method includes:

[0007] S1, disperse lignin in NaOH solution, stir to dissolve and then adjust the pH to 6, filter and wash to obtain purified lignin. Disperse the purified lignin, pyridine and acrylic anhydride in anhydrous dichloromethane, stir and react at room temperature, centrifuge, wash and vacuum dry to obtain modified lignin. Then disperse the modified lignin, 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide in deionized water, adjust the pH to 6, stir at room temperature and then add hydrochloric acid dopamine to continue the reaction. After centrifuging and washing, dopamine-grafted lignin is obtained;

[0008] S2, disperse soy protein in NaOH solution, add trypsin, adjust the pH to 8 and react in a water bath at 37 °C. After the reaction, heat to inactivate, separate the supernatant to obtain a partially hydrolyzed protein solution. Mix the partially hydrolyzed protein solution with hydrochloric acid dopamine solution, adjust the pH to 8, stir and react at room temperature, and freeze-dry to obtain modified protein. Disperse dopamine-grafted lignin and modified protein in deionized water, add glutaraldehyde solution, adjust the pH to 8 and react at room temperature, filter, wash and dry to obtain modified lignin-protein. Then disperse sodium dodecyl sulfate and modified lignin-protein in deionized water, stir evenly and then add ethyl acrylate, methyl methacrylate and acrylic acid to obtain an emulsion. Adjust the temperature to the first temperature under a nitrogen atmosphere, add ammonium persulfate and sodium bisulfite to react to obtain an aqueous acrylic copolymer emulsion;

[0009] S3. Add dopamine hydrochloride, metal salt solution and CQDs dispersion into Tris-HCl buffer solution with a pH of 8.5. After stirring and reacting, freeze-dry to obtain PDA-metal network;

[0010] S4. Disperse tetraethyl orthosilicate in absolute ethanol. Add hydrochloric acid solution under ice-water bath condition and stir to form a transparent sol. Adjust the pH of the mixed solution of titanium tetrachloride and zinc nitrate hexahydrate to 9 to form a hydroxide sol. Then mix and stir the transparent sol and the hydroxide sol to obtain a composite sol. Mix the composite sol with chitosan solution and adjust the pH to 8 to obtain a precursor solution. Then add the precursor solution to Span 80@liquid paraffin, stir evenly, add sodium hydroxide solution, and centrifuge and wash to obtain core particles;

[0011] S5. Disperse the core particles in PDA-PEI solution, stir well, centrifuge and wash, then transfer to PAA solution, stir well and centrifuge and wash, and immerse in glutaraldehyde solution to obtain electrolyte layer particles. Then disperse the electrolyte layer particles in 1H,1H,2H,2H-perfluorooctyltriethoxysilane ethanol solution to obtain low surface energy particles;

[0012] S6. Mix the aqueous acrylic copolymer emulsion and chitosan-citrate mixture evenly and adjust the pH to 6. Then add PDA-metal network, low surface energy particles, leveling agent and defoaming agent, and mix evenly to obtain a water-based biomass coating with self-cleaning function.

[0013] Lignin is a complex three-dimensional high molecular polymer, which is cross-linked by phenylpropane units through ether bonds and carbon-carbon single bonds. The molecule contains abundant functional groups such as phenolic hydroxyl groups, primary hydroxyl groups, secondary hydroxyl groups and methoxy groups. These functional groups endow lignin with high chemical reactivity. First, lignin is dispersed in NaOH solution for treatment. As a strong base, NaOH can break the hydrogen bonds between lignin molecules and the ester bonds within the molecules. The breaking of these bonds not only dissociates lignin from the complex matrix of the plant cell wall, but also promotes its dissolution in the solution. Specifically, NaOH forms soluble phenolates and carboxylates by undergoing acid-base reactions with phenolic hydroxyl groups and carboxyl groups in lignin, thereby reducing the aggregation of lignin and increasing its solubility. In addition, the alkaline environment of NaOH can also partially hydrolyze the ester bonds in lignin, releasing more free phenolic hydroxyl groups and carboxyl groups. These reactive functional groups provide important active sites for subsequent chemical modification. After the dissolution is completed, by adjusting the pH of the solution to 6, lignin can be precipitated, while some impurities (such as low molecular weight sugars, small molecule organic acids and other soluble impurities) remain in the solution. The precipitation of lignin is due to its low water solubility under neutral conditions, thus achieving effective separation and purification by adjusting the acidity and alkalinity of the solution. At this time, the lignin treated with NaOH not only removes most of the impurities, but also due to the cleavage of ester bonds and the destruction of intermolecular hydrogen bonds, the degree of intramolecular cross-linking is reduced, the structure is more loose, and more phenolic hydroxyl groups and carboxyl groups are exposed. Then, the purified lignin is dispersed in anhydrous dichloromethane, and pyridine and acrylic anhydride are added for chemical modification. Acrylic anhydride is a commonly used acylating reagent, and its molecule contains two acylating groups, which can undergo acylation reactions with hydroxyl groups in lignin. In this reaction, on the one hand, pyridine acts as a solvent to effectively dissolve acrylic anhydride and lignin, increasing the contact area between the reactants; on the other hand, pyridine acts as a basic catalyst, and its nitrogen atom can have a weak interaction with the carbonyl oxygen of acrylic anhydride, enhancing the electropositivity of acrylic anhydride, thereby increasing its reactivity towards nucleophiles. In this system, the phenolic hydroxyl groups in the lignin molecule act as nucleophiles, attacking the carbonyl carbon atom of acrylic anhydride, undergoing nucleophilic substitution reactions, forming ester bonds, and releasing by-product acetic acid. Through this reaction, the surface of the lignin molecule is modified by acrylic anhydride, introducing unsaturated structures such as propenyl groups. These propenyl groups endow lignin with higher chemical reactivity, providing active sites for subsequent radical polymerization reactions or other chemical functionalization reactions. In addition, the surface unsaturation and hydrophilicity of lignin are also significantly enhanced, laying a foundation for its use as a composite matrix.

[0014] Subsequently, the modified lignin, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, N-hydroxysuccinimide, and dopamine hydrochloride were co-dispersed in water for grafting reaction. 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide, as a classic amide bond coupling system, play a core role in activating the carboxyl groups on the surface of lignin molecules, enabling them to undergo amidation reactions with the amino groups in dopamine molecules to form stable amide bonds. Specifically, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride first reacts with the carboxyl groups on the surface of lignin to generate a reactive intermediate, which then reacts with N-hydroxysuccinimide to form a more stable N-hydroxysuccinimide ester. The carboxyl carbon atom of this N-hydroxysuccinimide ester intermediate has high electrophilicity and can be attacked by the amino group in dopamine molecules, ultimately forming a stable amide bond. Dopamine molecules contain two types of functional groups, phenolic hydroxyl groups and amino groups. After grafting onto lignin, they significantly enhance the chemical functionality of lignin. First, the phenolic hydroxyl group structure of dopamine molecules introduces polyphenol functionality to lignin, which not only enhances the antioxidant capacity of the material but also improves its free radical scavenging performance, making it more stable in certain special environments. Second, the benzene ring structure of dopamine and the aromatic ring of lignin can further enhance the intermolecular synergistic effect through π-π stacking, improving the mechanical properties of the material. In addition, the amino group of dopamine provides more active sites for subsequent chemical modification and cross-linking reactions, thus laying the foundation for the multifunctional application of lignin.

[0015] Soybean protein is a polymer of complex polypeptide chains of natural origin, mainly formed by the connection of various amino acids through amide bonds (peptide bonds). Soybean protein contains a large number of functional groups, including carboxyl groups, amino groups and amide bonds, and these functional groups endow it with unique chemical reactivity and structural characteristics. However, due to the high molecular weight and tertiary structure of proteins, their solubility in solution is poor, and intermolecular hydrogen bonds and hydrophobic interactions further stabilize their structure, making it difficult to be directly used for chemical modification or the preparation of composite materials. In the present invention, soybean protein is first dispersed in an alkaline solution and partially hydrolyzed using trypsin. The alkaline environment can dissociate the carboxyl groups and amino groups in the soybean protein molecules to form carboxylates and free amino groups. The dissociation of these functional groups on the surface of the protein molecules reduces the intermolecular hydrogen bonds and hydrophobic interactions, thereby destroying the higher-order structure of the protein and significantly improving the solubility of the protein. In addition, the alkaline environment also makes the protein molecular structure more loose, providing a more open substrate structure for the enzymatic hydrolysis of trypsin. Trypsin is a protein hydrolase with high specificity. It can recognize the carboxyl-terminal peptide bonds of lysine and arginine in the polypeptide chain and selectively hydrolyze the peptide bonds at these positions. Its mechanism of action is that the serine in the active center makes a nucleophilic attack on the carbonyl group of the peptide bond to form an enzyme-substrate complex, and then combines with water molecules to break the peptide bond, finally releasing short peptides and free amino acids. Through this controlled hydrolysis process, the long-chain polypeptides in soybean protein are degraded into short peptides and amino acids with low molecular weight. This partial hydrolysis not only significantly reduces the molecular weight of the protein and improves its solubility, but also exposes more carboxyl groups and amino groups, and these functional groups provide active sites for subsequent chemical modification and cross-linking reactions. In addition, due to the reduction of the molecular weight, the diffusibility and reactivity of the partially hydrolyzed soybean protein in solution are enhanced, thus laying a good foundation for dopamine modification and material composite. After the partial hydrolysis of the protein is completed, trypsin is inactivated by heating to terminate the enzymatic reaction, avoiding the over-hydrolysis or degradation of the protein and ensuring the functionality and chemical modification activity of the protein.

[0016] Next, the partially hydrolyzed soy protein was chemically modified with hydrochloric acid dopamine under alkaline conditions. Dopamine is a small molecule nitrogen-containing compound with two functional groups, phenolic hydroxyl and amino groups, in its molecule, and has high chemical reactivity. Under alkaline conditions, dopamine will be oxidized to form dopamine quinone. This oxidation process usually occurs under the catalysis of oxygen or metal ions, accompanied by the deprotonation and structural transformation of dopamine molecules. Dopamine quinone is a highly reactive intermediate, and the quinone group in its molecule has strong electrophilicity and can react chemically with amino or thiol groups in soy protein molecules. The amino group attacks the carbonyl group of the quinone group as a nucleophile to form an imine bond, and the carboxyl group or other nucleophilic groups attack the double bond of the quinone group to form a covalent connection. In addition, the phenolic hydroxyl group in dopamine molecules can also have non-covalent interactions with protein molecules through hydrogen bonding or π-π stacking. These non-covalent interactions not only enhance the binding stability between dopamine and the protein, but also endow the material with more excellent physical and chemical properties. Through dopamine modification, a large number of phenolic hydroxyl groups were introduced onto the surface of soy protein, and this polyphenol structure significantly improved the antioxidant capacity and free radical scavenging performance of the protein, while increasing the chemical activity of the protein. After the dopamine modification was completed, the dopamine-grafted lignin and the modified protein were cross-linked by glutaraldehyde. Glutaraldehyde is a commonly used bifunctional cross-linking agent with active aldehyde groups at both ends of its molecule. Under alkaline conditions, the aldehyde groups of glutaraldehyde can react chemically with amino groups in dopamine-grafted lignin and modified protein molecules to form imine bonds. In addition, the aldehyde groups of glutaraldehyde can also combine with hydroxyl or phenolic hydroxyl groups through acetalization reactions to further enhance the degree of cross-linking. During the cross-linking process, the phenolic hydroxyl and propenyl groups of dopamine-grafted lignin and the amino and carboxyl groups in protein molecules formed a three-dimensional network structure through the bridging action of glutaraldehyde. This chemical cross-linking not only significantly enhanced the mechanical strength of the composite material, but also improved the chemical stability, water resistance and thermal stability of the material. In addition, dopamine molecules played a synergistic role between lignin and protein, and their phenolic hydroxyl and aromatic ring structures further enhanced the interfacial binding force and intermolecular interactions through hydrogen bonding or π-π stacking. This process combined lignin and protein into one, forming a composite structure with high strength and functionality.

[0017] The crosslinked lignin-protein complex is subjected to emulsion polymerization reaction with acrylic monomers. Sodium dodecyl sulfate is used as an emulsifier. Its molecules have a hydrophilic head and a lipophilic tail, which can stabilize the interface between the aqueous phase and the oil phase to form a uniform emulsion. In the emulsion system, the lignin-protein complex further enhances the stability of the emulsion through interfacial adsorption. Subsequently, ammonium persulfate and sodium bisulfite are added as initiators to initiate a free radical polymerization reaction under heating conditions. Ammonium persulfate decomposes to generate sulfate radicals, which attack the double bonds of ethyl acrylate, methyl methacrylate and acrylic acid to form polymer chains. The progress of the free radical polymerization reaction polymerizes the monomers step by step into acrylic copolymers, which combine with the lignin-protein complex to generate a copolymer emulsion with high structural stability. Through partial hydrolysis of soy protein, dopamine modification and crosslinking with lignin, a composite substrate with high chemical activity and mechanical properties is successfully constructed. This composite material exposes more reactive groups (such as amino and carboxyl groups) through protein hydrolysis, dopamine modification significantly improves the antioxidant performance, and glutaraldehyde crosslinking further enhances the structural stability of the material. The final emulsion polymerization system provides a stable and high-performance functional emulsion for the preparation of subsequent coatings.

[0018] Polydopamine is a highly functional material formed by the oxidation and self-polymerization of dopamine molecules under alkaline conditions. Its molecular structure is rich in various key functional groups such as phenolic hydroxyl groups and quinone groups. The phenolic hydroxyl groups and quinone groups play important roles in the redox properties and self-cleaning characteristics of polydopamine. The phenolic hydroxyl groups have strong free radical scavenging ability, which can effectively neutralize reactive oxygen species in the environment such as hydroxyl radicals and superoxide radicals, thereby reducing the damage of the external environment to the coating or material. There are also abundant amino groups and aromatic rings in the molecular structure of polydopamine. These structural characteristics enable it to strongly adsorb on the surfaces of various substrates through hydrogen bonding, electrostatic interaction, and π-π stacking interactions. This strong adhesion of polydopamine enables it to form a uniform and stable coating, providing a solid substrate for the construction of functional materials. In addition, the antioxidant property of polydopamine further enhances its durability and functionality. Polydopamine can effectively capture reactive oxygen species in the environment, especially in photocatalytic reactions or oxidative environments. This property can prevent the degradation and pollution accumulation on the material surface. By reducing the influence of oxidative pollutants in the external environment, polydopamine provides guarantee for the long-term stable use of materials. After introducing metal ions into the polydopamine network, the formed polydopamine-metal complex structure significantly improves the self-cleaning performance and functional diversity of the material. The phenolic hydroxyl groups and quinone groups in the polydopamine molecules can coordinate with metal ions to generate stable metal complexes. This complex structure not only enhances the three-dimensional crosslinking degree and mechanical properties of the polydopamine network, but also endows the material with unique photocatalytic and antibacterial properties by introducing metal ions. For example, the introduction of zinc ions provides the material with strong antibacterial ability on the basis of improving the stability of the complex network. Zinc ions can inhibit the proliferation of microorganisms through various mechanisms. This antibacterial property enables the material to effectively inhibit bacterial growth in humid or polluted environments, thereby further improving the self-cleaning performance of the coating.

[0019] To further enhance the photocatalytic performance and light response range of the polydopamine-metal complex network, doping carbon quantum dots into the complex network is a highly promising modification strategy. Carbon quantum dots are nanoscale carbon-based materials with unique optical properties and surface chemical activity. The doping of carbon quantum dots brings about the following several significant functional enhancements to the complex network: First, carbon quantum dots can absorb ultraviolet and visible light and convert light energy into long-lived electron-hole pairs, thereby expanding the light absorption range of the material and improving the photocatalytic efficiency. In traditional photocatalytic materials, usually ultraviolet light with higher energy is required to excite the photocatalytic reaction, while the introduction of carbon quantum dots enables the utilization of low-energy visible light, greatly improving the practical applicability of the photocatalytic process. Second, the π-conjugated system of carbon quantum dots can promote the rapid transfer of electrons and reduce the recombination probability of electrons and holes during the photocatalytic process. This acceleration of electron transfer ensures that more reactive oxygen species can be generated, thereby enhancing the degradation efficiency of pollutants. At the same time, the hydroxyl and carboxyl groups on the surface of carbon quantum dots can bind to polydopamine molecules and metal complexes through hydrogen bonds or covalent bonds, further improving the structural stability and interfacial binding force of the complex network. This binding method not only enhances the mechanical properties of the material but also enables it to maintain excellent durability under complex environmental conditions. The high specific surface area and nanoscale size of carbon quantum dots further enhance the adsorption capacity of the complex network for pollutants, providing a higher reaction efficiency for photocatalytic degradation.

[0020] Under acidic conditions, tetraethyl orthosilicate serves as the silicon source and generates silanol intermediates through hydrolysis reactions. The ethoxy functional groups in the tetraethyl orthosilicate molecules are gradually replaced by hydroxyl groups under acid catalysis to form silanol molecules. The silanol molecules further form silicon-oxygen bonds through polycondensation reactions, resulting in a silicon-oxygen sol with a three-dimensional network structure. Such a silicon-oxygen network has excellent chemical stability and mechanical strength and can provide durability and wear resistance as the core component of the particles. During this process, uncondensed silanol groups are usually retained on the surface of the silicon-oxygen network. These silanol groups not only provide active sites for subsequent chemical modification. In addition, the high mechanical strength and stability of the silicon-oxygen network enable it to maintain the structural integrity of the particles during subsequent functionalization processes, providing long-term functional support for the particles. To further enhance the functionality of the core particles, titanium tetrachloride and zinc nitrate hexahydrate are introduced into the system, and titanium oxide and zinc oxide sols are generated through hydrolysis reactions under alkaline conditions. Titanium tetrachloride and zinc nitrate hexahydrate generate titanium hydroxide and zinc hydroxide respectively under alkaline conditions. These intermediates are stably dispersed in the solution to form a uniform sol. The introduction of titanium oxide and zinc oxide into the core particles greatly enriches the functionality of the material. Titanium oxide is a classic photocatalytic material that can excite electron transitions under ultraviolet or visible light irradiation, thereby generating reactive oxygen species such as superoxide radicals and hydroxyl radicals. These reactive oxygen species have extremely strong oxidation capabilities and can rapidly degrade organic pollutants attached to the particle surface, such as oils, dye molecules, or microbial metabolites. Through photocatalysis, the particle surface can always remain clean. In addition, the introduction of zinc oxide not only enhances the photocatalytic performance but also endows the particles with antibacterial functions. Zinc ions disrupt the cell membranes and enzyme activities of bacteria through multiple mechanisms, inhibiting their growth and reproduction, thereby reducing biological contamination on the particle surface. This antibacterial property is particularly important in humid environments because humid conditions usually promote the growth of microorganisms. Mix the silicon-oxygen sol with the titanium and zinc sols and stir evenly to form a composite sol. During this process, the silicon-oxygen sol and the metal oxide sol are combined together through hydrogen bonding or electrostatic interactions to form a uniformly dispersed composite system. On the other hand, titanium oxide and zinc oxide endow the sol with photocatalytic and antibacterial functions. The synergistic effect of the two significantly improves the self-cleaning ability of the core particles, enabling them to effectively remove pollutants and microorganisms in complex application environments.

[0021] To further optimize the morphology and properties of the particles, after mixing the composite sol with the chitosan solution, the pH was adjusted to 8. Chitosan is a natural polysaccharide with excellent biocompatibility and chemical activity. Under alkaline conditions, chitosan molecules can dissolve and physically adsorb or chemically bond with the silanol groups or metal hydroxides in the sol. This bonding not only stabilizes the morphology of the sol but also provides preliminary functional modification to the particle surface. The introduction of chitosan can also improve the antibacterial performance of the core particles because chitosan itself has certain antibacterial properties and can inhibit the proliferation of bacteria by inhibiting cell wall synthesis or interfering with the metabolic processes of bacteria. Subsequently, the precursor solution was added to the oil phase containing Span 80 and liquid paraffin, and further control of the particles was achieved through emulsification. Span 80, as an emulsifier, can form a stable emulsion at the water-oil interface and disperse the composite sol in the aqueous phase into tiny droplets. The size of these droplets can be precisely regulated by the stirring speed and emulsifier concentration, thereby affecting the particle size and morphology of the final particles. Liquid paraffin provides a uniform oil-phase environment to ensure the stable existence of the sol droplets. To solidify the sol droplets into a particulate structure, sodium hydroxide solution was gradually added to the system. Under alkaline conditions, further condensation reactions or precipitation reactions occur between the silicon-oxygen network and metal hydroxides to form solid particles. The condensation reaction further cross-links the three-dimensional structure of the silicon-oxygen network, enhancing the mechanical strength and durability of the particles. At the same time, the metal hydroxides are gradually transformed into stable oxide forms, endowing the particles with photocatalytic and antibacterial functions. These particles combine the mechanical properties of the silicon-oxygen network and the functionality of metal oxides, exhibiting multiple self-cleaning characteristics. In addition, the photocatalytic performance of the particles can effectively degrade organic pollutants on the surface under light illumination, while the antibacterial function can inhibit the growth of bacteria. This multifunctionality enables the core particles to adapt to a variety of complex environments, being able to achieve pollutant degradation under light illumination and effectively prevent microbial contamination in humid environments.

[0022] The nuclear particles are dispersed in a poly(dopamine)-polyethylenimine (PDA-PEI) solution and fully coated. The silanol groups exposed on the surface of the nuclear particles and the hydroxyl groups on the metal oxides provide chemical active sites for coating. These groups can be firmly bound to the coating material through hydrogen bonding, electrostatic interaction, etc., providing a basis for the formation of a stable coating. Poly(dopamine) is generated by the self-polymerization reaction of dopamine molecules under alkaline conditions. The molecule is rich in various active functional groups, including phenolic hydroxyl groups, amino groups, and quinone groups. These functional groups endow poly(dopamine) with good adhesion and can be firmly attached to the surface of the nuclear particles through various chemical or physical interactions. The phenolic hydroxyl groups and amino groups can form hydrogen bonds with the hydroxyl groups or silanol groups on the surface of the nuclear particles, while the quinone groups can further stabilize the binding interface through electrostatic interaction. In addition, the aromatic ring structure of poly(dopamine) can also interact with the aromatic groups that may exist on the surface of the nuclear particles through π-π stacking, thereby further enhancing the adhesion strength. Polyethylenimine (PEI) is a cationic polymer with a high density of amino groups. Its abundant amino groups enable it to bind to poly(dopamine) through hydrogen bonding, electrostatic interaction, etc., forming a stable composite coating. The introduction of polyethylenimine significantly increases the positive charge density on the particle surface, laying an important chemical foundation for the subsequent multi-layer electrolyte coating. On the one hand, the interaction between the amino groups and the quinone groups or phenolic hydroxyl groups in poly(dopamine) further strengthens the stability of the coating; on the other hand, the positively charged property of the particle surface provides the necessary charge driving force for coating with negatively charged polymers through electrostatic self-assembly technology. After the initial poly(dopamine)-polyethylenimine coating is completed, the particles are transferred to a poly(acrylic acid) (PAA) solution to further construct a multi-layer electrolyte structure. Poly(acrylic acid) is a polymer with carboxyl groups. The carboxyl groups in its molecule are partially dissociated into carboxylate salts under the condition that the pH is close to neutral to weakly alkaline. The dissociated carboxylate salts carry negative charges and can form a stable bond with the positively charged polyethylenimine on the particle surface through electrostatic adsorption. This electrostatic adsorption is the core principle of the layer-by-layer self-assembly process, and its driving force comes from the Coulomb attraction between positive and negative charges.

[0023] After the electrolyte coating is completed, the particles are immersed in a glutaraldehyde solution for cross-linking treatment. Glutaraldehyde is a compound containing two aldehyde groups. The symmetrically distributed aldehyde groups in its molecular structure can chemically react with the amino groups in the polydopamine, polyethyleneimine, and polyacrylic acid molecules in the multi-layer electrolyte coating. The essence of this cross-linking process is that the aldehyde groups and amino groups form imine bonds through Schiff base reaction, thereby achieving intermolecular cross-linking. The cross-linking reaction makes the molecular structure inside the multi-layer coating more compact, significantly enhancing the mechanical strength and chemical resistance of the coating. Another important role of glutaraldehyde cross-linking is to enhance the anti-hydrolysis performance of the coating. The uncross-linked coating may dissolve or peel off in water or other polar solvents, while the cross-linked coating has higher stability due to the chemical bond connection between molecules and can resist the erosion of moisture. In addition, cross-linking also reduces the risk of peeling of the coating under mechanical stress, improving the durability and service life of the particles in the coating system. After the glutaraldehyde cross-linking is completed, the electrolyte layer particles are further dispersed in a trifluoropropyltriethoxysilane ethanol solution for surface modification. Trifluoropropyltriethoxysilane is a fluorinated silane compound. The siloxane groups in its molecular structure can undergo a condensation reaction with the silanol groups or hydroxyl groups on the particle surface to form stable silicon-oxygen-silicon bonds. This reaction firmly binds the trifluoropropyltriethoxysilane molecules to the particle surface through the formation of covalent bonds. The trifluoropropyltriethoxysilane molecule contains long-chain fluorinated groups, and these groups have extremely low surface energy, excellent hydrophobicity, and lipophobicity. During the surface modification process, the fluorinated groups of the trifluoropropyltriethoxysilane molecules are exposed on the particle surface through molecular arrangement, forming an outer layer structure rich in fluorocarbon chains. This outer layer structure of fluorinated groups has extremely strong hydrophobicity and lipophobicity, and the interaction with water molecules or pollutant molecules is extremely weak, thereby significantly reducing the surface energy of the particles. The multi-layer structure of the electrolyte layer and the surface fluorination modification of trifluoropropyltriethoxysilane form a synergistic effect. The electrolyte coating provides the micro-nano scale roughness of the particle surface, while the fluorinated groups of trifluoropropyltriethoxysilane further reduce the surface energy of the particles. The combination of the two makes the particles exhibit hydrophobicity, which can effectively prevent the attachment of moisture on the particle surface and improve the anti-adhesion performance of the particles to oil stains and dust.

[0024] As a preferred technical solution of the present invention, in step S1, the mass-volume ratio of the lignin to the NaOH solution is 1 g: 10 mL.

[0025] In some alternative embodiments, the mass fraction of the NaOH solution is 10 wt.%.

[0026] In some alternative embodiments, the mass-volume ratio of the purified lignin, pyridine, and acrylic anhydride is 1 g: 1 mL: 1 mL.

[0027] In some alternative embodiments, the mass-to-volume ratio of the purified lignin to anhydrous dichloromethane is 1 g: 10 mL.

[0028] In some alternative embodiments, the time for stirring at room temperature is 4 - 5 h. For example, it can be 4.0 h, 4.1 h, 4.2 h, 4.3 h, 4.4 h, 4.5 h, 4.6 h, 4.7 h, 4.8 h, 4.9 h, or 5.0 h. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0029] In some alternative embodiments, the mass ratio of the modified lignin, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, N-hydroxysuccinimide, and dopamine hydrochloride is 30:5:3:20.

[0030] As a preferred technical solution of the present invention, in step S2, the mass-to-volume ratio of the soy protein, NaOH solution, and trypsin is 10 g: 100 mL: 0.01 g.

[0031] In some alternative embodiments, the concentration of the NaOH solution is 0.1 M.

[0032] In some alternative embodiments, the time for the water bath reaction is 2 - 3 h. For example, it can be 2.0 h, 2.1 h, 2.2 h, 2.3 h, 2.4 h, 2.5 h, 2.6 h, 2.7 h, 2.8 h, 2.9 h, or 3.0 h. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0033] In some alternative embodiments, the volume ratio of the partially hydrolyzed protein solution to the dopamine hydrochloride solution is 2:1.

[0034] In some alternative embodiments, the mass fraction of the dopamine hydrochloride solution is 10 wt.%.

[0035] In some alternative embodiments, the time for the stirring reaction at room temperature is 4 - 5 h. For example, it can be 4.0 h, 4.1 h, 4.2 h, 4.3 h, 4.4 h, 4.5 h, 4.6 h, 4.7 h, 4.8 h, 4.9 h, or 5.0 h. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0036] In some alternative embodiments, the mass-to-volume ratio of the dopamine-grafted lignin, modified protein, and glutaraldehyde solution is 5 g: 5 g: 2 mL.

[0037] In some alternative embodiments, the mass fraction of the glutaraldehyde solution is 10 wt.%.

[0038] In some alternative embodiments, the room temperature reaction time is 2 - 3 h, for example, it can be 2.0 h, 2.1 h, 2.2 h, 2.3 h, 2.4 h, 2.5 h, 2.6 h, 2.7 h, 2.8 h, 2.9 h or 3.0 h, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0039] In some alternative embodiments, the mass ratio of sodium dodecyl sulfate, modified lignin protein, ethyl acrylate, methyl methacrylate, acrylic acid, ammonium persulfate and sodium bisulfite is 5:0.5:10:5:5:0.5:0.25.

[0040] In some alternative embodiments, the first temperature is 70 - 80 °C, for example, it can be 70 °C, 71 °C, 72 °C, 73 °C, 74 °C, 75 °C, 76 °C, 77 °C, 78 °C, 79 °C or 80 °C, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0041] As a preferred technical solution of the present invention, in step S3, the mass - to - volume ratio of dopamine hydrochloride, metal salt solution, CQDs dispersion and Tris - HCl buffer is 0.2 g:4 mL:10 mL:20 mL.

[0042] In some alternative embodiments, the concentration of the metal salt solution is 0.1 M, the solutes are FeCl3·6H2O and ZnCl2, and the molar ratio is 1:1.

[0043] In some alternative embodiments, the concentration of the CQDs dispersion is 10 mg / mL.

[0044] In some alternative embodiments, the stirring reaction time is 10 - 12 h, for example, it can be 10.0 h, 10.2 h, 10.4 h, 10.6 h, 10.8 h, 11.0 h, 11.2 h, 11.4 h, 11.6 h, 11.8 h or 12.0 h, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0045] As a preferred technical solution of the present invention, in step S4, the volume ratio of tetraethyl orthosilicate, absolute ethanol and hydrochloric acid solution is 2:10:1.

[0046] In some alternative embodiments, the concentration of the hydrochloric acid solution is 0.1 M.

[0047] In some alternative embodiments, the mass ratio of titanium tetrachloride and zinc nitrate hexahydrate is 1:1.

[0048] In some alternative embodiments, the mass ratio of the transparent sol to the hydroxide sol is 2:1.

[0049] In some alternative embodiments, the volume ratio of the composite sol to the chitosan solution is 5:2.

[0050] In some alternative embodiments, the mass fraction of the chitosan solution is 2 wt.%, and the solvent is a 1 wt.% acetic acid solution.

[0051] In some alternative embodiments, the volume ratio of the precursor solution, Span 80@liquid paraffin, and sodium hydroxide solution is 5:10:1.

[0052] In some alternative embodiments, the mass fraction of Span 80@liquid paraffin is 3 wt.%, and the solvent is liquid paraffin.

[0053] In some alternative embodiments, the concentration of the sodium hydroxide solution is 1 M.

[0054] As a preferred technical solution of the present invention, in step S5, the mass-volume ratio of the core particles, PDA-PEI solution, and PAA solution is 1 g:100 mL:100 mL.

[0055] In some alternative embodiments, the mass fraction of the glutaraldehyde solution is 0.5 wt.%.

[0056] In some alternative embodiments, the mass fraction of the trifluoropropyltriethoxysilane ethanol solution is 0.5 wt.%.

[0057] As a preferred technical solution of the present invention, in step S6, the mass-volume ratio of the aqueous acrylic copolymer emulsion, chitosan-citrate mixture, PDA-metal network, low surface energy particles, leveling agent, and defoaming agent is 100 mL:5 mL:10 g:15 g:1 g:1 g.

[0058] In the chitosan-citrate mixture, the mass fraction of chitosan is 0.5 wt.%, and the mass fraction of sodium citrate is 1 wt.%.

[0059] In a second aspect, the present invention provides an aqueous biomass coating with self-cleaning function prepared by the preparation method described in the first aspect.

[0060] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Natural biomass materials such as lignin and protein are used. These materials are renewable, low-cost, and environmentally friendly. Compared with the petroleum-based chemicals widely used in the prior art, the present invention is more sustainable in terms of raw material selection. Lignin and protein are given multiple active sites through chemical modification, forming a strong chemical bond with the coating matrix and other components, which not only increases the added value of the biomass materials but also reduces the dependence on non-renewable resources; (2) Through multi-layer electrolyte coating and glutaraldehyde cross-linking treatment, the mechanical strength and chemical stability of the particles and the coating are enhanced. The introduction of the cross-linking technology also significantly improves the hydrolysis resistance of the coating, enabling it to maintain its function in humid or high-humidity environments. The introduction of fluorine-containing low surface energy particles endows the coating with excellent hydrophobicity. Description of the Drawings

[0061] Figure 1 SEM image of the water-based biomass coating with self-cleaning function provided in Example 1 of the present invention;

[0062] Figure 2 Contact angle diagram of the water-based biomass coating with self-cleaning function provided in Example 1 of the present invention and water. Detailed Embodiments

[0063] The technical solutions of the present invention will be described in detail below in conjunction with specific embodiments and their accompanying drawings. The embodiments recorded herein are specific specific embodiments of the present invention for explaining the concept of the present invention; these explanations are all explanatory and exemplary, and should not be construed as limiting the embodiments of the present invention and the protection scope of the present invention. Except for the embodiments recorded herein, those skilled in the art can also adopt other obvious technical solutions based on the content disclosed in the claims and the specification of this application. These technical solutions include technical solutions that make any obvious substitutions and modifications to the embodiments recorded herein.

[0064] The chemical reagents used in the embodiments and comparative examples of the present invention are all commercially available products and have not been further purified.

[0065] Example 1

[0066] This example provides a preparation method of a water-based biomass coating with self-cleaning function. The preparation method specifically includes the following steps:

[0067] S1. Disperse 10 g of lignin in 100 mL of 10 wt.% NaOH solution. After stirring and dissolving, adjust the pH to 6, filter and wash to obtain purified lignin. Disperse 10 g of purified lignin, 10 mL of pyridine and 10 mL of acrylic anhydride in 100 mL of anhydrous dichloromethane, stir and react at room temperature for 4.2 h, centrifuge, wash and dry under vacuum to obtain modified lignin. Then disperse 6 g of modified lignin, 1 g of 1-ethyl-3-(dimethylaminopropyl)carbodiimide hydrochloride and 0.6 g of N-hydroxysuccinimide in 100 mL of deionized water, adjust the pH to 6, stir at room temperature, add 4 g of dopamine hydrochloride and continue the reaction. After centrifuging and washing, dopamine-grafted lignin is obtained.

[0068] S2. Disperse 10 g of soy protein in 100 mL of 0.1 M NaOH solution, add 1 mL of 10 mg / mL trypsin, adjust the pH to 8 and react in a water bath at 37 °C for 2.3 h. After the reaction, heat to inactivate, separate the supernatant to obtain a partially hydrolyzed protein solution. Mix 10 mL of the partially hydrolyzed protein solution with 5 mL of 10 wt.% dopamine hydrochloride solution, adjust the pH to 8, stir and react at room temperature for 4.1 h, and freeze-dry to obtain modified protein. Disperse 5 g of dopamine-grafted lignin and 5 g of modified protein in 50 mL of deionized water, add 2 mL of 10 wt.% glutaraldehyde solution, adjust the pH to 8 and react at room temperature for 2.2 h. Filter, wash and dry to obtain modified lignin protein. Then disperse 10 g of sodium dodecyl sulfate and 1 g of modified lignin protein in 100 mL of deionized water, stir evenly, add 20 g of ethyl acrylate, 10 g of methyl methacrylate and 10 g of acrylic acid to obtain an emulsion. Under a nitrogen atmosphere, adjust the temperature to 73 °C, add 1 g of ammonium persulfate and 0.5 g of sodium bisulfite and react for 4.8 h to obtain an aqueous acrylic copolymer emulsion.

[0069] S3. Add 1 g of dopamine hydrochloride, 20 mL of metal salt solution and 50 mL of CQDs dispersion to 100 mL of Tris-HCl buffer solution with a pH of 8.5, stir and react for 10.5 h, and then freeze-dry to obtain a PDA-metal network; the concentration of the metal salt solution is 0.1 M, the solute is FeCl3·6H2O and ZnCl2, and the molar ratio is 1:1; the concentration of the CQDs dispersion is 10 mg / mL.

[0070] S4. Disperse 4 mL of tetraethyl orthosilicate in 20 mL of absolute ethanol. Under ice-water bath conditions, add 2 mL of 0.1 M hydrochloric acid solution and stir to form a transparent sol. Adjust the pH of the mixed solution of titanium tetrachloride and zinc nitrate hexahydrate to 9 to form a hydroxide sol. Then mix 20 g of the transparent sol and 10 g of the hydroxide sol and stir to obtain a composite sol. Mix 20 mL of the composite sol with 8 mL of 2 wt.% chitosan solution and adjust the pH to 8 to obtain a precursor solution. Then add 50 mL of the precursor solution to 100 mL of 3 wt.% Span 80@liquid paraffin, stir evenly, add 10 mL of 1 M sodium hydroxide solution, and centrifuge and wash to obtain core particles;

[0071] S5. Disperse 1 g of core particles in 100 mL of PDA-PEI solution, stir well, centrifuge and wash, then transfer to 100 mL of PAA solution, stir well, centrifuge and wash, and immerse in 0.5 wt.% glutaraldehyde solution to obtain electrolyte layer particles. Then disperse the electrolyte layer particles in 0.5 wt.% ethanol solution of 3-trifluoropropyltriethoxysilane to obtain low surface energy particles;

[0072] S6. Mix 100 mL of aqueous acrylic copolymer emulsion with 5 mL of chitosan-citrate mixture evenly and adjust the pH to 6. Then add 10 g of PDA-metal network, 15 g of low surface energy particles, 1 g of leveling agent and 1 g of defoaming agent, and mix evenly to obtain a waterborne biomass coating with self-cleaning function; in the chitosan-citrate mixture, the mass fraction of chitosan is 0.5 wt.%, and the mass fraction of sodium citrate is 1 wt.%.

[0073] Figure 1 SEM image of the waterborne biomass coating with self-cleaning function prepared in this example; Figure 2 Contact angle of the waterborne biomass coating with self-cleaning function prepared in this example and water. The contact angle is 162.4°, indicating that the coating has good hydrophobicity.

[0074] Example 2

[0075] This example provides a preparation method of a waterborne biomass coating with self-cleaning function. The preparation method specifically includes the following steps:

[0076] S1. Disperse 10 g of lignin in 100 mL of 10 wt.% NaOH solution. After stirring and dissolving, adjust the pH to 6, filter and wash to obtain purified lignin. Disperse 10 g of purified lignin, 10 mL of pyridine and 10 mL of acrylic anhydride in 100 mL of anhydrous dichloromethane, stir and react at room temperature for 4.9 h, centrifuge, wash and dry in vacuum to obtain modified lignin. Then disperse 6 g of modified lignin, 1 g of 1-ethyl-3-(dimethylaminopropyl)carbodiimide hydrochloride and 0.6 g of N-hydroxysuccinimide in 100 mL of deionized water, adjust the pH to 6, stir at room temperature, add 4 g of dopamine hydrochloride and continue to react. After centrifuging and washing, dopamine-grafted lignin is obtained.

[0077] S2. Disperse 10 g of soy protein in 100 mL of 0.1 M NaOH solution, add 1 mL of 10 mg / mL trypsin, adjust the pH to 8 and react in a water bath at 37 °C for 2.8 h. After the reaction, heat to inactivate, separate the supernatant to obtain a partially hydrolyzed protein solution. Mix 10 mL of the partially hydrolyzed protein solution with 5 mL of 10 wt.% dopamine hydrochloride solution, adjust the pH to 8, stir and react at room temperature for 4.7 h, and freeze-dry to obtain modified protein. Disperse 5 g of dopamine-grafted lignin and 5 g of modified protein in 50 mL of deionized water, add 2 mL of 10 wt.% glutaraldehyde solution, adjust the pH to 8 and react at room temperature for 2.7 h, filter, wash and dry to obtain modified lignin protein. Then disperse 10 g of sodium dodecyl sulfate and 1 g of modified lignin protein in 100 mL of deionized water, stir evenly, add 20 g of ethyl acrylate, 10 g of methyl methacrylate and 10 g of acrylic acid to obtain an emulsion. Under a nitrogen atmosphere, adjust the temperature to 77 °C, add 1 g of ammonium persulfate and 0.5 g of sodium bisulfite and react for 4.6 h to obtain an aqueous acrylic copolymer emulsion.

[0078] S3. Add 1 g of dopamine hydrochloride, 20 mL of metal salt solution and 50 mL of CQDs dispersion to 100 mL of Tris-HCl buffer solution with a pH of 8.5, stir and react for 10.9 h, and then freeze-dry to obtain a PDA-metal network; the concentration of the metal salt solution is 0.1 M, the solute is FeCl3·6H2O and ZnCl2, and the molar ratio is 1:1; the concentration of the CQDs dispersion is 10 mg / mL.

[0079] S4. Disperse 4 mL of tetraethyl orthosilicate in 20 mL of absolute ethanol. Under ice-water bath conditions, add 2 mL of 0.1 M hydrochloric acid solution and stir to form a transparent sol. Adjust the pH of the mixed solution of titanium tetrachloride and zinc nitrate hexahydrate to 9 to form a hydroxide sol. Then mix 20 g of the transparent sol with 10 g of the hydroxide sol and stir to obtain a composite sol. Mix 20 mL of the composite sol with 8 mL of 2 wt.% chitosan solution, adjust the pH to 8 to obtain a precursor solution. Then add 50 mL of the precursor solution to 100 mL of 3 wt.% Span 80@liquid paraffin, stir evenly, add 10 mL of 1 M sodium hydroxide solution, and centrifuge and wash to obtain core particles;

[0080] S5. Disperse 1 g of core particles in 100 mL of PDA-PEI solution, stir well, centrifuge and wash, then transfer to 100 mL of PAA solution, stir well and centrifuge and wash, and immerse in 0.5 wt.% glutaraldehyde solution to obtain electrolyte layer particles. Then disperse the electrolyte layer particles in 0.5 wt.% trifluoropropyltriethoxysilane ethanol solution to obtain low surface energy particles;

[0081] S6. Mix 100 mL of aqueous acrylic copolymer emulsion with 5 mL of chitosan-citrate mixture evenly and adjust the pH to 6. Then add 10 g of PDA-metal network, 15 g of low surface energy particles, 1 g of leveling agent and 1 g of defoaming agent, and mix evenly to obtain a water-based biomass coating with self-cleaning function; in the chitosan-citrate mixture, the mass fraction of chitosan is 0.5 wt.%, and the mass fraction of sodium citrate is 1 wt.%.

[0082] Example 3

[0083] This example provides a preparation method of a water-based biomass coating with self-cleaning function. The preparation method specifically includes the following steps:

[0084] S1. Disperse 10 g of lignin in 100 mL of 10 wt.% NaOH solution, stir to dissolve, adjust the pH to 6, filter and wash to obtain purified lignin. Disperse 10 g of purified lignin, 10 mL of pyridine and 10 mL of acrylic anhydride in 100 mL of absolute dichloromethane, stir and react at room temperature for 4.6 h, centrifuge and wash, and dry in vacuum to obtain modified lignin. Then disperse 6 g of modified lignin, 1 g of 1-ethyl-3-dimethylaminopropylcarbodiimide hydrochloride and 0.6 g of N-hydroxysuccinimide in 100 mL of deionized water, adjust the pH to 6, stir at room temperature, add 4 g of dopamine hydrochloride and continue to react, and centrifuge and wash to obtain dopamine-grafted lignin;

[0085] S2. Disperse 10 g of soy protein in 100 mL of 0.1 M NaOH solution, add 1 mL of 10 mg / mL trypsin, adjust the pH to 8 and react in a water bath at 37 °C for 2.1 h. After the reaction, inactivate by heating, separate the supernatant to obtain a partially hydrolyzed protein solution. Mix 10 mL of the partially hydrolyzed protein solution with 5 mL of 10 wt.% hydrochloric acid dopamine solution, adjust the pH to 8, stir and react at room temperature for 4.9 h, and freeze-dry to obtain a modified protein. Disperse 5 g of dopamine-grafted lignin and 5 g of the modified protein in 50 mL of deionized water, add 2 mL of 10 wt.% glutaraldehyde solution, adjust the pH to 8 and react at room temperature for 2.6 h, filter, wash and dry to obtain a modified lignin protein. Then disperse 10 g of sodium dodecyl sulfate and 1 g of the modified lignin protein in 100 mL of deionized water, stir evenly, add 20 g of ethyl acrylate, 10 g of methyl methacrylate and 10 g of acrylic acid to obtain an emulsion. Under a nitrogen atmosphere, adjust the temperature to 79 °C, add 1 g of ammonium persulfate and 0.5 g of sodium bisulfite and react for 4.1 h to obtain an aqueous acrylic copolymer emulsion;

[0086] S3. Add 1 g of hydrochloric acid dopamine, 20 mL of metal salt solution and 50 mL of CQDs dispersion to 100 mL of Tris-HCl buffer solution with a pH of 8.5, stir and react for 11.8 h and then freeze-dry to obtain a PDA-metal network; the concentration of the metal salt solution is 0.1 M, the solute is FeCl3·6H2O and ZnCl2, and the molar ratio is 1:1; the concentration of the CQDs dispersion is 10 mg / mL;

[0087] S4. Disperse 4 mL of tetraethyl orthosilicate in 20 mL of absolute ethanol, add 2 mL of 0.1 M hydrochloric acid solution under an ice-water bath condition, stir to form a transparent sol. Adjust the pH of the mixed solution of titanium tetrachloride and zinc nitrate hexahydrate to 9 to form a hydroxide sol. Then mix 20 g of the transparent sol and 10 g of the hydroxide sol and stir to obtain a composite sol. Mix 20 mL of the composite sol with 8 mL of 2 wt.% chitosan solution, adjust the pH to 8 to obtain a precursor solution. Then add 50 mL of the precursor solution to 100 mL of 3 wt.% Span 80@liquid paraffin, stir evenly, add 10 mL of 1 M sodium hydroxide solution, and centrifuge and wash to obtain core particles;

[0088] S5. Disperse 1 g of core particles in 100 mL of PDA-PEI solution, stir well, centrifuge and wash, then transfer to 100 mL of PAA solution, stir well and centrifuge and wash, and immerse in 0.5 wt.% glutaraldehyde solution to obtain electrolyte layer particles. Then disperse the electrolyte layer particles in 0.5 wt.% trifluoropropyltriethoxysilane ethanol solution to obtain low surface energy particles;

[0089] S6. Mix 100 mL of aqueous acrylic copolymer emulsion with 5 mL of chitosan-citrate mixture evenly and adjust the pH to 6. Then add 10 g of PDA-metal network, 15 g of low surface energy particles, 1 g of leveling agent and 1 g of defoaming agent, and mix evenly to obtain an aqueous biomass coating with self-cleaning function; in the chitosan-citrate mixture, the mass fraction of chitosan is 0.5 wt.% and the mass fraction of sodium citrate is 1 wt.%.

[0090] Example 4

[0091] This example provides a preparation method of an aqueous biomass coating with self-cleaning function. The preparation method specifically includes the following steps:

[0092] S1. Disperse 10 g of lignin in 100 mL of 10 wt.% NaOH solution, stir to dissolve and then adjust the pH to 6. Filter and wash to obtain purified lignin. Disperse 10 g of purified lignin, 10 mL of pyridine and 10 mL of acrylic anhydride in 100 mL of anhydrous dichloromethane, stir and react at room temperature for 4.3 h, centrifuge, wash and dry in vacuum to obtain modified lignin. Then disperse 6 g of modified lignin, 1 g of 1-ethyl-3-(dimethylaminopropyl)carbodiimide hydrochloride and 0.6 g of N-hydroxysuccinimide in 100 mL of deionized water, adjust the pH to 6, stir at room temperature and then add 4 g of dopamine hydrochloride to continue the reaction. After centrifuging and washing, dopamine-grafted lignin is obtained.

[0093] S2. Disperse 10 g of soy protein in 100 mL of 0.1 M NaOH solution, add 1 mL of 10 mg / mL trypsin, adjust the pH to 8 and react in a water bath at 37 °C for 2.5 h. After the reaction, heat to inactivate, separate the supernatant to obtain a partially hydrolyzed protein solution. Mix 10 mL of the partially hydrolyzed protein solution with 5 mL of 10 wt.% dopamine hydrochloride solution, adjust the pH to 8, stir and react at room temperature for 4.5 h, freeze-dry to obtain modified protein. Disperse 5 g of dopamine-grafted lignin and 5 g of modified protein in 50 mL of deionized water, add 2 mL of 10 wt.% glutaraldehyde solution, adjust the pH to 8 and react at room temperature for 2.1 h. Filter, wash and dry to obtain modified lignin protein. Then disperse 10 g of sodium dodecyl sulfate and 1 g of modified lignin protein in 100 mL of deionized water, stir evenly and then add 20 g of ethyl acrylate, 10 g of methyl methacrylate and 10 g of acrylic acid to obtain an emulsion. Adjust the temperature to 71 °C under a nitrogen atmosphere, add 1 g of ammonium persulfate and 0.5 g of sodium bisulfite and react for 4.3 h to obtain an aqueous acrylic copolymer emulsion.

[0094] S3. Add 1 g of dopamine hydrochloride, 20 mL of metal salt solution, and 50 mL of CQDs dispersion into 100 mL of Tris-HCl buffer solution with a pH of 8.5, stir and react for 11.4 h, and then freeze-dry to obtain PDA-metal network; the concentration of the metal salt solution is 0.1 M, the solute is FeCl3·6H2O and ZnCl2, and the molar ratio is 1:1; the concentration of the CQDs dispersion is 10 mg / mL;

[0095] S4. Disperse 4 mL of tetraethyl orthosilicate in 20 mL of absolute ethanol, add 2 mL of 0.1 M hydrochloric acid solution under an ice-water bath condition, stir to form a transparent sol, adjust the pH of the mixed solution of titanium tetrachloride and zinc nitrate hexahydrate to 9 to form a hydroxide sol, then mix 20 g of the transparent sol and 10 g of the hydroxide sol and stir to obtain a composite sol. Mix 20 mL of the composite sol with 8 mL of 2 wt.% chitosan solution, adjust the pH to 8 to obtain a precursor solution, and then add 50 mL of the precursor solution to 100 mL of 3 wt.% Span 80@liquid paraffin, stir evenly, add 10 mL of 1 M sodium hydroxide solution, and centrifuge and wash to obtain core particles;

[0096] S5. Disperse 1 g of core particles in 100 mL of PDA-PEI solution, stir well, centrifuge and wash, then transfer to 100 mL of PAA solution, stir well and centrifuge and wash, and immerse in 0.5 wt.% glutaraldehyde solution to obtain electrolyte layer particles. Then disperse the electrolyte layer particles in 0.5 wt.% ethanol solution of 3-trifluoropropyltriethoxysilane to obtain low surface energy particles;

[0097] S6. Mix 100 mL of aqueous acrylic copolymer emulsion with 5 mL of chitosan-citrate mixture evenly and adjust the pH to 6, then add 10 g of PDA-metal network, 15 g of low surface energy particles, 1 g of leveling agent, and 1 g of defoaming agent, and mix evenly to obtain a water-based biomass coating with self-cleaning function; in the chitosan-citrate mixture, the mass fraction of chitosan is 0.5 wt.%, and the mass fraction of sodium citrate is 1 wt.%.

[0098] Comparative Example 1

[0099] This comparative example provides a preparation method of a water-based biomass coating with self-cleaning function, which is different from Example 1 in that the mass of PDA-metal network in S6 is 20 g, which is 10 g more than that in Example 1, and other process parameters and operating conditions are exactly the same as those in Example 1.

[0100] Comparative Example 2

[0101] This comparative example provides a preparation method of an aqueous biomass coating with self-cleaning function. The difference from Example 1 is that the mass of the PDA-metal network in S6 is 1 g, which is 9 g less than that in Example 1. Other process parameters and operating conditions are exactly the same as those in Example 1.

[0102] Comparative Example 3

[0103] This comparative example provides a preparation method of an aqueous biomass coating with self-cleaning function. The difference from Example 1 is that the mass of the low surface energy particles in S6 is 30 g, which is 15 g more than that in Example 1. Other process parameters and operating conditions are exactly the same as those in Example 1.

[0104] Comparative Example 4

[0105] This comparative example provides a preparation method of an aqueous biomass coating with self-cleaning function. The difference from Example 1 is that the mass of the low surface energy particles in S6 is 2 g, which is 13 g less than that in Example 1. Other process parameters and operating conditions are exactly the same as those in Example 1.

[0106] The test standard for stain resistance is GB / T 9780-2013; the test standard for weather resistance is GB / T 14522-2008; the test standard for adhesion is GB / T 9286-2021. The test results are shown in Table 1.

[0107] Table 1 Test Results of an Aqueous Biomass Coating with Self-Cleaning Function for Examples 1-4 and Comparative Examples 1-4

[0108]

[0109] As can be seen from Table 1, compared with Example 1, the stain resistance, weather resistance, and adhesion of Comparative Example 1 all decreased; the stain resistance, weather resistance, and adhesion of Comparative Example 2 all decreased. This is because metal oxides in the PDA-metal network can generate reactive oxygen species under light conditions, which can degrade organic pollutants on the coating surface, thus endowing the coating with stain resistance. The multifunctional functional groups of PDA can form chemical bonds or intermolecular interactions with the acrylic matrix and other components, enhancing the adhesion of the coating. In Comparative Example 1, the PDA-metal network was excessive. Under the action of excessive reactive oxygen species, the coating matrix may be oxidized and degraded, resulting in a decrease in the strength of the coating, accelerating aging, and thus weakening the long-term self-cleaning performance of the coating. The excessive PDA-metal network may form a relatively thick inorganic layer, hindering the bonding between functional particles and the acrylic matrix, resulting in a decrease in the interfacial bonding force, and thus affecting the adhesion of the coating. In Comparative Example 2, the PDA-metal network was insufficient, the generation amount of reactive oxygen species was insufficient, the degradation ability of the coating to organic pollutants was weakened, and the ultraviolet shielding effect of metal oxides was insufficient, making the coating more vulnerable to damage by ultraviolet radiation in the outdoor environment, thus reducing the weather resistance. Too little PDA will lead to insufficient interfacial bonding force between it and the matrix and other components, weakening the overall adhesion performance of the coating.

[0110] As can be seen from Table 1, compared with Example 1, the stain resistance, weather resistance, and adhesion of Comparative Example 3 all decreased; the stain resistance, weather resistance, and adhesion of Comparative Example 4 all decreased. A large number of fluorinated groups are exposed on the surface of low surface energy particles, which have extremely low surface energy and can significantly reduce the adhesion force between the coating and pollutants. In Comparative Example 3, excessive low surface energy particles may accumulate on the coating surface, resulting in particle agglomeration, reducing the stain resistance, weakening the integrity of the coating matrix, reducing its mechanical strength and durability, and reducing the overall strength and adhesion of the coating. In Comparative Example 4, the low surface energy particles were insufficient, the stain resistance decreased, and the chemical corrosion resistance and ultraviolet resistance brought by fluorinated group modification would be significantly weakened, and the weather resistance of the coating decreased.

[0111] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A preparation method of an aqueous biomass coating with self-cleaning function, characterized in that, The preparation method includes: S1. Dispersing sodium dodecyl sulfate and modified lignin protein in deionized water, adding ethyl acrylate, methyl methacrylate and acrylic acid to obtain an emulsion, adding ammonium persulfate and sodium bisulfite to react to obtain an aqueous acrylic copolymer emulsion; S2. Adding hydrochloric acid dopamine, metal salt solution and CQDs dispersion into Tris-HCl buffer solution with a pH of 8.5, reacting to obtain a PDA-metal network; S3. Dispersing tetraethyl orthosilicate in absolute ethanol, adding hydrochloric acid solution to form a transparent sol, adjusting the pH of the mixed solution of titanium tetrachloride and zinc nitrate hexahydrate to 9 to form a hydroxide sol, then mixing the transparent sol and the hydroxide sol to obtain a composite sol, mixing the composite sol with chitosan solution, adjusting the pH to 8 to obtain a precursor solution, and then adding the precursor solution to Span 80@liquid paraffin, adding sodium hydroxide solution to obtain core particles; S4. Dispersing the core particles in PDA-PEI solution, then transferring them to PAA solution, and then immersing them in glutaraldehyde solution to obtain electrolyte layer particles, and then dispersing the electrolyte layer particles in trifluoropropyltriethoxysilane ethanol solution to obtain low surface energy particles; S5. Mixing the aqueous acrylic copolymer emulsion and chitosan-citrate mixed solution and adjusting the pH to 6, then adding PDA-metal network, low surface energy particles, leveling agent and defoaming agent to obtain an aqueous biomass coating with self-cleaning function; The mass volume ratio of the aqueous acrylic copolymer emulsion, chitosan-citrate mixed solution, PDA-metal network, low surface energy particles, leveling agent and defoaming agent is 100 mL: 5 mL: 10 g: 15 g: 1 g: 1 g.

2. The preparation method of an aqueous biomass coating with self-cleaning function according to claim 1, characterized in that, The preparation method of the modified lignin protein includes: Dispersing modified lignin, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide in deionized water, adjusting the pH to 6, adding hydrochloric acid dopamine to react to obtain dopamine-grafted lignin, dispersing soy protein in NaOH solution, adding trypsin, adjusting the pH to 8 and reacting in a water bath at 37°C to obtain a partially hydrolyzed protein solution, mixing the partially hydrolyzed protein solution with hydrochloric acid dopamine solution, adjusting the pH to 8 to obtain modified protein, dispersing dopamine-grafted lignin and modified protein in deionized water, adding glutaraldehyde solution, adjusting the pH to 8 to obtain modified lignin protein.

3. The preparation method of an aqueous biomass coating with self-cleaning function according to claim 2, characterized in that, The preparation method of the modified lignin includes: Dispersing lignin in NaOH solution, stirring and dissolving, then adjusting the pH to 6 to obtain purified lignin, dispersing the purified lignin, pyridine and acrylic anhydride in anhydrous dichloromethane to obtain modified lignin.

4. The preparation method of an aqueous biomass coating with self-cleaning function according to claim 1, characterized in that, In S1: The mass ratio of the sodium dodecyl sulfate, modified lignin protein, ethyl acrylate, methyl methacrylate, acrylic acid, ammonium persulfate and sodium bisulfite is 5: 0.5: 10: 5: 5: 0.5: 0.

25.

5. The preparation method of an aqueous biomass coating with self-cleaning function according to claim 1, characterized in that, In S2: The mass volume ratio of the hydrochloric acid dopamine, metal salt solution, CQDs dispersion and Tris-HCl buffer solution is 0.2 g: 4 mL: 10 mL: 20 mL.

6. The preparation method of an aqueous biomass coating with self-cleaning function according to claim 1, characterized in that, In S3: The mass ratio of the titanium tetrachloride to the zinc nitrate hexahydrate is 1:1; The mass ratio of the transparent sol to the hydroxide sol is 2:1; The volume ratio of the composite sol to the chitosan solution is 5:2; The volume ratio of the precursor solution, Span 80@liquid paraffin to the sodium hydroxide solution is 5:10:

1.

7. The preparation method of an aqueous biomass coating with self-cleaning function according to claim 1, characterized in that, In S4: The mass-volume ratio of the core particles, the PDA-PEI solution to the PAA solution is 1 g: 100 mL: 100 mL.

8. The preparation method of an aqueous biomass coating with a self-cleaning function according to claim 2, characterized in that The mass ratio of the modified lignin, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, N-hydroxysuccinimide to dopamine hydrochloride is 30:5:3:

20.

9. An aqueous biomass coating with a self-cleaning function obtained by the preparation method according to any one of claims 1-8.

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