Super-hydrophobic high-weather-resistance bismuth vanadate pigment and preparation method thereof

Abstract

The invention relates to the field of pigment preparation, and discloses a super-hydrophobic high-weather-resistance bismuth vanadate pigment and a preparation method thereof. The method comprises the following steps: synthesizing a bismuth vanadate precursor through liquid phase coprecipitation; the preparation method comprises the following steps: preparing a dispersion liquid from a bismuth vanadate precursor, adding an aluminum source compound, forming an aluminum oxide coating layer outside the bismuth vanadate precursor at a set pH value and temperature, adding a silicon source compound, forming a silicon dioxide coating layer outside the aluminum oxide coating layer at a set pH value and temperature, and obtaining a gradient-coated bismuth vanadate precursor; and modifying the gradient coated bismuth vanadate precursor with fluorosilane, and carrying out high-temperature calcination to obtain the super-hydrophobic high-weather-resistance bismuth vanadate pigment. In the super-hydrophobic high-weather-resistance bismuth vanadate pigment, through deep synergy of gradient coating, high-temperature calcination and fluorosilane modification, the comprehensive efficiency of super-hydrophobicity and high weather resistance is achieved, and the bottleneck of simple process superposition is broken through.

Description

Technical Field

[0001] This invention relates to the field of pigment preparation, specifically to a superhydrophobic, highly weather-resistant bismuth vanadate pigment and its preparation method. Background Technology

[0002] Bismuth vanadate pigment (BiVO4), a bright yellow inorganic environmentally friendly pigment, is an ideal alternative to toxic pigments such as lead chromate yellow because it does not contain heavy metals such as lead and cadmium, meeting international environmental standards. It is widely used in automotive paints, architectural exterior coatings, plastics, and high-end ceramic coloring. However, traditional bismuth vanadate pigments exhibit significant shortcomings in practical applications due to various scenarios: In outdoor environments, affected by factors such as sunlight, rain, and drastic temperature changes, traditional bismuth vanadate pigments are prone to fading and chalking, leading to a significant reduction in their decorative and protective properties. This necessitates frequent renovation and maintenance of products such as architectural exteriors and automotive paints using traditional bismuth vanadate pigments, increasing labor and material costs and affecting product lifespan and appearance stability. Furthermore, traditional bismuth vanadate pigments have poor hydrophobic properties, allowing rainwater and seawater to easily penetrate the coating, accelerating pigment performance degradation, especially in high-humidity and highly corrosive environments such as the ocean, where protective efficacy is severely weakened.

[0003] In recent years, research has been conducted both domestically and internationally on improving the performance of bismuth vanadate pigments. Regarding weather resistance enhancement, research has largely focused on single-material coatings, such as surface treatments using oxides and silicates like zirconium silicate. However, a single coating layer cannot simultaneously resist light, oxidation, and chemical corrosion, resulting in limited improvement in weather resistance. For example, patent CN116925571A discloses a zirconium silicate-coated bismuth vanadate yellow pigment and its preparation method. This method, under liquid-phase conditions, first coats bismuth vanadate pigment particles with a layer of zirconium hydroxide, then coats the zirconium hydroxide with a layer of silicic acid, and finally converts the two coatings into zirconium silicate through high-temperature calcination, thereby obtaining a zirconium silicate-coated bismuth vanadate yellow pigment with improved temperature resistance. However, this patent only addresses weather resistance improvement, does not address superhydrophobic properties, and uses a single coating layer, resulting in limited improvement in weather resistance.

[0004] Overall, current research on bismuth vanadate pigment modification has not yet yielded an effective solution that simultaneously achieves high weather resistance and superhydrophobicity. Therefore, there is an urgent need to develop superhydrophobic, high-weather-resistant bismuth vanadate pigments and their preparation methods. Summary of the Invention

[0005] In view of the above-mentioned problems in the prior art, the main objective of the present invention is to provide a superhydrophobic and highly weather-resistant bismuth vanadate pigment and its preparation method.

[0006] According to one aspect of the present invention, a method for preparing a superhydrophobic and highly weather-resistant bismuth vanadate pigment is provided, the method comprising the following steps: Bismuth vanadate precursor was synthesized via liquid-phase coprecipitation. A dispersion of bismuth vanadate precursor was prepared, an aluminum source compound was added, and the pH and temperature of the solution were adjusted to form an alumina coating layer on the bismuth vanadate precursor. A silicon source compound is added to the solution, and the pH and temperature of the solution are adjusted to form a silicon dioxide coating layer on the outside of the alumina coating layer, thus obtaining a gradient-coated bismuth vanadate precursor. The gradient-coated bismuth vanadate precursor was dispersed in an organic solvent, fluorosilane was added, the system temperature was adjusted and the reaction was carried out to obtain a fluorosilane-modified bismuth vanadate precursor. The fluorosilane-modified bismuth vanadate precursor was calcined at high temperature to obtain the superhydrophobic and highly weather-resistant bismuth vanadate pigment.

[0007] According to one embodiment of the present invention, the synthesis of bismuth vanadate precursor by liquid-phase coprecipitation includes the following steps: Bismuth salts are dissolved in acidic solutions to form bismuth salt solutions, and vanadium salts are dissolved in alkaline solutions to form vanadium salt solutions. While stirring, the vanadium salt solution is added dropwise to the bismuth salt solution. After the addition is complete, stirring is continued for a certain period of time to obtain a mixed solution. Add a precipitant to the mixed solution, adjust the pH value of the solution, and continue stirring until the bismuth vanadate precursor precipitates out; The precipitate was collected, washed, and dried to obtain the bismuth vanadate precursor.

[0008] According to one embodiment of the present invention, the bismuth salt is selected from one or more of bismuth nitrate, bismuth chloride, bismuth acetate, and bismuth oxide; the vanadium salt is selected from one or more of ammonium metavanadate, sodium vanadate, and vanadium pentoxide; the acid solution is selected from nitric acid solution or hydrochloric acid solution; the alkaline solution is selected from sodium hydroxide solution and has the same concentration as the acid solution; the bismuth ion concentration in the bismuth salt solution is 0.1~2.0 mol / L; the vanadium ion concentration in the vanadium salt solution is equal to the bismuth ion concentration; and the molar ratio of bismuth ions to vanadium ions in the mixed solution is 1:1.

[0009] According to one embodiment of the present invention, the precipitant is selected from one or more of ammonia, sodium hydroxide, and sodium carbonate. The pH value of the solution is adjusted to 6-9 by adding the precipitant and stirring for 30-120 minutes.

[0010] According to one embodiment of the present invention, the aluminum source compound is selected from one or more of aluminum nitrate, aluminum chloride, and aluminum sulfate. The amount of the aluminum source compound is 3% to 8% of the mass of the bismuth vanadate precursor. When forming the alumina coating layer, the pH value of the solution is adjusted to 7 to 10, the temperature is controlled at 25 to 80°C, and the reaction time is 1 to 2 hours.

[0011] According to one embodiment of the present invention, the silicon source compound is selected from one or more of tetraethyl orthosilicate, sodium silicate, and silica sol. The amount of the silicon source compound is 4% to 10% of the mass of the bismuth vanadate precursor. When forming the silica coating layer, the pH value of the solution is adjusted to 6 to 8, the temperature is controlled at 25 to 90°C, and the reaction time is 1 to 2 hours.

[0012] According to one embodiment of the present invention, the organic solvent is selected from one or more of toluene, xylene, and chloroform.

[0013] According to one embodiment of the present invention, the fluorosilane is selected from one or more of KH-550 silane coupling agent, perfluorooctyltriethoxysilane, tridecafluorooctyltrimethoxysilane, and heptadecafluorodecyltrimethoxysilane. The amount of the fluorosilane is 2% to 8% of the mass of the gradient-coated bismuth vanadate precursor. After adding the fluorosilane, the system temperature is adjusted to 40 to 70°C, and the reaction is carried out for 1 to 3 hours.

[0014] According to one embodiment of the present invention, the high-temperature calcination includes calcination at 350~650°C for 1~3 hours in an air atmosphere.

[0015] According to another aspect of the present invention, a superhydrophobic and highly weather-resistant bismuth vanadate pigment is provided, the bismuth vanadate pigment being prepared by the method described in any of the above embodiments.

[0016] The superhydrophobic and weather-resistant bismuth vanadate pigment and its preparation method of the present invention, compared with the limitations of existing technologies that cannot achieve multiple properties by "single coating (such as only Al2O3 or only SiO2) or single modification (such as only hydrophobic treatment)", achieve a comprehensive effect of 1+1+1>3 through the deep synergy of gradient coating, high-temperature calcination and fluorosilane modification, breaking through the bottleneck of simple process superposition, and has at least one of the following beneficial effects: (1) The gradient coating of Al2O3 / SiO2 and high-temperature calcination form a “protection-reinforcement” synergy: the inner layer of Al2O3 is resistant to chemical corrosion and the outer layer of SiO2 is dense and resistant to light, and the two complement each other. High-temperature calcination not only optimizes the crystal structure of bismuth vanadate to enhance stability, but also strengthens the bonding force between the coating layer and the pigment core, and avoids the coating layer from cracking and falling off. This synergistic effect makes the pigment’s resistance to harsh environments increase exponentially, and its weather resistance is significantly better than the single process of “gradient coating only” or “high-temperature calcination only”. (2) Fluorosilane hydrophobic modification and gradient coating layer form a “substrate-function” synergy: Fluorosilane hydrophobic modification forms a stable hydrophobic layer on the surface of the coating layer. Fluorosilane does not act in isolation, but relies on the hydroxyl groups on the outer surface of SiO2 to form a stable chemical bond, making the hydrophobic layer stronger and more uniform. Compared with hydrophobic modification of bismuth vanadate alone, this design allows the hydrophobic layer to effectively repel rainwater and seawater, and can block liquid penetration with the protection of Al2O3 / SiO2 substrate layer. The superhydrophobic performance is more durable and solves the problem that “single hydrophobic modification is prone to failure due to lack of substrate protection”. (3) The entire process is coordinated to achieve a balance between “functional enhancement and performance retention”: gradient coating with nanoscale thickness avoids obscuring the color, fluorosilane modification only modifies the surface without destroying the lattice, high-temperature calcination optimizes the structure without damaging the hiding power, and each step is adapted to each other rather than simply superimposed. In the end, while greatly improving weather resistance and superhydrophobicity, the original bright yellow color and high hiding power of bismuth vanadate are fully preserved. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A flowchart illustrating a method for preparing a superhydrophobic, highly weather-resistant bismuth vanadate pigment according to an embodiment of the present invention is shown; Figure 2 X-ray diffraction patterns of Embodiments 1 and 4, and blank example and comparative example 3 according to the present invention are shown. Figure 3 Transmission electron microscope (TEM) images of bismuth vanadate particles, a blank example (without surface treatment) of the present invention, are shown. Figure 4 Scanning electron microscope (SEM) images of the superhydrophobic and highly weather-resistant bismuth vanadate pigment prepared according to Example 1 of the present invention are shown. Figure 5 Transmission electron microscopy (TEM) images of the superhydrophobic and highly weather-resistant bismuth vanadate pigment prepared according to Example 1 of the present invention are shown. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0020] Furthermore, the reference to "embodiment" herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0021] It should be understood that the embodiments of the invention shown in the exemplary embodiments are merely illustrative. Although only a few embodiments have been described in detail in this invention, those skilled in the art will readily recognize that various modifications are possible without substantially departing from the teachings of the invention. Accordingly, all such modifications should be included within the scope of the invention. Other substitutions, modifications, variations, and deletions can be made to the design, operating conditions, and parameters of the following exemplary embodiments without departing from the spirit of the invention.

[0022] According to one aspect of the present invention, a method for preparing a superhydrophobic, highly weather-resistant bismuth vanadate pigment is provided. For example... Figure 1 As shown, the method mainly includes the following steps: Step S1: Synthesize bismuth vanadate precursor by liquid-phase coprecipitation; Step S2: Prepare a dispersion of bismuth vanadate precursor, add an aluminum source compound, adjust the pH and temperature of the solution, and form an alumina coating layer on the bismuth vanadate precursor. Step S3: Continue to add silicon source compound to the solution, adjust the pH and temperature of the solution, and form a silica coating layer outside the alumina coating layer to obtain a gradient-coated bismuth vanadate precursor. Step S4: Disperse the gradient-coated bismuth vanadate precursor in an organic solvent, add fluorosilane, adjust the system temperature and react to obtain the fluorosilane-modified bismuth vanadate precursor. Step S5: The fluorosilane-modified bismuth vanadate precursor is calcined at high temperature to obtain a superhydrophobic and highly weather-resistant bismuth vanadate pigment.

[0023] In the superhydrophobic and weather-resistant bismuth vanadate pigment of this invention, the gradient coating (Al first, then Si) process design is an important improvement. The principle is that the porous structure formed first in the Al2O3 inner layer can provide uniform adhesion sites for the silicon source, ensuring that the SiO2 outer layer can be controlled to hydrolyze and condense to form a high-density layer, avoiding the protection failure caused by single coating or reversing the order, highlighting the necessity of this coating order and process. Among them, the Al2O3 inner layer resists acid, alkali and oxygen penetration with its excellent chemical corrosion resistance, and the SiO2 outer layer weakens photoaging with its high density. The two complement each other to build dual protection. The subsequent high-temperature calcination further strengthens the bonding force between the coating layer and the core and optimizes the crystal structure to improve environmental resistance. Meanwhile, the hydroxyl groups abundant on the outer surface of SiO2 can chemically bond with fluorosilane molecules, ensuring a uniform and firm adhesion of the hydrophobic layer and effectively repelling liquid penetration. This ultimately forms a three-in-one protective system: porous Al2O3 facilitates the formation of dense SiO2 → Al2O3 / SiO2 synergistic corrosion resistance → high-temperature calcination provides strong stability → dense SiO2 promotes hydrophobicity of fluorosilanes. Each step is interconnected and synergistically enhances the effect, achieving a 1+1+1>3 result. The absence of any step or alteration of the order would prevent the dual breakthroughs in weather resistance and superhydrophobicity, fully demonstrating the scientific nature and necessity of the process design. If the order is reversed, first coating with dense SiO2, the lack of adsorption sites on the surface will prevent the formation of a gradient structure.

[0024] In some embodiments of the present invention, in step S1, a bismuth vanadate precursor is synthesized by liquid-phase co-precipitation. This process may specifically include the following steps: Bismuth salts are dissolved in acidic solutions to form bismuth salt solutions, and vanadium salts are dissolved in alkaline solutions to form vanadium salt solutions. While stirring, the vanadium salt solution is slowly added dropwise to the bismuth salt solution. After the addition is complete, stirring is continued for a certain period of time to obtain a mixed solution. Add a precipitant to the mixed solution, adjust the pH value of the solution, and continue stirring until the bismuth vanadate precursor precipitates out; The precipitate was collected, washed, and dried to obtain the bismuth vanadate precursor.

[0025] The bismuth vanadate precursor synthesized by liquid-phase coprecipitation method has more uniform size and more controllable morphology.

[0026] In some embodiments of the present invention, the bismuth salt is selected from one or more of bismuth nitrate, bismuth chloride, bismuth acetate, and bismuth oxide, and the concentration of bismuth ions in the bismuth salt solution is 0.1~2.0 mol / L.

[0027] In some embodiments of the present invention, the vanadium salt is selected from one or more of ammonium metavanadate, sodium vanadate, and vanadium pentoxide, and the concentration of vanadium ions in the vanadium salt solution is equal to the concentration of bismuth ions.

[0028] In some embodiments of the present invention, the acid solution is selected from nitric acid solution or hydrochloric acid solution, and the concentration of HNO3 or HCl in the solution is 3~5 mol / L.

[0029] In some embodiments of the present invention, the alkaline solution is selected from sodium hydroxide solution and has the same concentration as the acid solution.

[0030] In some embodiments of the present invention, the molar ratio of bismuth ions to vanadium ions in the mixed solution is 1:1.

[0031] In some embodiments of the present invention, the precipitant is selected from one or more of ammonia, sodium hydroxide, and sodium carbonate. The pH value of the solution is adjusted to 6-9 by adding the precipitant and stirring for 30-120 minutes.

[0032] In some embodiments of the present invention, in step S2, the bismuth vanadate precursor is prepared into a dispersion, an aluminum source compound is added, and the pH and temperature of the solution are adjusted to form an alumina coating layer on the bismuth vanadate precursor. This process may specifically include the following steps: dispersing the bismuth vanadate precursor prepared in step S1 in deionized water to form a uniform dispersion; first adding an aluminum source compound, adjusting the pH of the solution, and stirring the reaction at a certain temperature for a period of time to form an Al2O3 coating layer on the bismuth vanadate precursor.

[0033] In some embodiments of the present invention, the aluminum source compound is selected from one or more of aluminum nitrate, aluminum chloride, and aluminum sulfate. The amount of the aluminum source compound is 3% to 8% of the mass of the bismuth vanadate precursor. When forming the alumina coating layer, the pH value of the solution is adjusted to 7 to 10, the temperature is controlled at 25 to 80°C, and the reaction time is 1 to 2 hours. In this embodiment, the pH value for forming the alumina coating layer is controlled at 7 to 10 and the temperature is controlled at 25 to 80°C. Under these pH and temperature conditions, Al forms porous and loose gibbsite. Its rich pores and high adsorption provide a uniform substrate for subsequent Si sources (such as tetraethyl orthosilicate). The Al2O3 layer converted from calcined gibbsite can act as a "first barrier" to resist acid, alkali, and oxygen erosion. Its porous structure also ensures that the outer layer of SiO2 is dense and firm through physical anchoring, avoiding cracking. Furthermore, its own porous structure breaks the tendency of bismuth vanadate particles to agglomerate, improves pigment dispersion, and enhances the uniformity of subsequent fluorosilane modification. Furthermore, in some embodiments, when forming the alumina coating layer, the pH value of the solution is adjusted to 8-10 and the temperature is controlled at 45-70°C. Using this temperature can control the hydrolysis rate and ensure that the gibbsite forms a uniform morphology with a reasonable pore distribution, rather than an irregular agglomerate, thus providing a uniform substrate for subsequent silica coating.

[0034] In some embodiments of the present invention, in step S3, a silicon source compound is added to the solution, the pH value and temperature of the solution are adjusted, and a silicon dioxide coating layer is formed outside the alumina coating layer to obtain a gradient-coated bismuth vanadate precursor. This process may specifically include the following steps: adding a silicon source compound to the solution after the reaction in step S2, adjusting the pH value of the solution, stirring the reaction at a specific temperature for a period of time to form a SiO2 coating layer, and then filtering, washing, and drying to obtain the gradient-coated bismuth vanadate precursor.

[0035] In some embodiments of the present invention, the silicon source compound is selected from one or more of tetraethyl orthosilicate, sodium silicate, and silica sol. The amount of silicon source compound used is 4% to 10% of the mass of the bismuth vanadate precursor. When forming the silica coating layer, the pH value of the solution is adjusted to 6 to 8, the temperature is controlled at 25 to 90°C, and the reaction time is 1 to 2 hours. In this embodiment, the pH value for forming the silica coating layer is controlled at 6 to 8. At a pH of 6 to 8 (weakly acidic to neutral), the silicon source (such as tetraethyl orthosilicate) can achieve controlled hydrolysis and condensation, avoiding the problems of excessively rapid hydrolysis leading to layer agglomeration when too acidic and loose layer when too alkaline, thus forming a uniform and dense SiO2 coating layer. Under these conditions, the coating layer is firmly bonded without cracks and does not affect the pigment color, further improving the pigment's resistance to environmental corrosion. The external silica coating can construct a highly dense protective layer, blocking external light and moisture penetration, synergistically enhancing weather resistance with the inner Al2O3 layer, and also providing a smooth substrate for fluorosilane modification. The dense silica coating layer has the following effects on subsequent fluorosilane modification: It provides stable reaction sites: The silica surface is rich in hydroxyl groups (-OH), which can undergo hydrolysis and condensation reactions with siloxane groups (such as -Si-OR) in fluorosilane molecules to form strong chemical bonds, making the fluorosilane-modified layer less prone to detachment and improving the stability of the hydrophobic layer; it ensures uniform modification: The dense and flat silica layer can fill in minor defects on the pigment surface, allowing the fluorosilane to spread and adhere evenly, avoiding local voids or accumulation in the hydrophobic layer caused by uneven substrate, and ensuring excellent overall hydrophobic properties of the pigment. Furthermore, in some embodiments, the pH of the solution is adjusted to 6.5~7.5 when forming the silica coating layer.

[0036] In some embodiments of the present invention, in step S4, the gradient-coated bismuth vanadate precursor is dispersed in an organic solvent, fluorosilane is added, the system temperature is adjusted and the reaction is carried out to obtain a fluorosilane-modified bismuth vanadate precursor.

[0037] In some embodiments of the present invention, the organic solvent is selected from one or more of toluene, xylene, and chloroform. The fluorosilane is selected from one or more of KH-550 silane coupling agent, perfluorooctyltriethoxysilane, tridecafluorooctyltrimethoxysilane, and heptadecafluorodecyltrimethoxysilane. The fluorocarbon groups in the above materials have extremely low surface energy, making it difficult for water and oil to wet their surface, thus improving the hydrophobicity of bismuth vanadate pigments.

[0038] In some embodiments of the present invention, the amount of fluorosilane used is 2% to 8% of the mass of the gradient-coated bismuth vanadate precursor. If the amount of fluorosilane is too low, it will not be enough to completely cover the outer surface of the pigment, resulting in poor improvement of hydrophobicity; if the amount of fluorosilane is too high, it will affect the gloss and color saturation of the pigment.

[0039] In some embodiments of the present invention, after adding fluorosilane, the reaction is carried out at 40~70°C for 1~3 hours.

[0040] In some embodiments of the present invention, in step S5, the fluorosilane-modified bismuth vanadate precursor is subjected to high-temperature calcination to obtain a superhydrophobic, highly weather-resistant bismuth vanadate pigment. Specifically, this process may include placing the hydrophobically modified bismuth vanadate in a muffle furnace, pusher kiln, or rotary kiln, and calcining it at 350-650°C for 1-3 hours in air. High-temperature calcination can make the coating layer and the hydrophobic modification layer more stable, while optimizing the crystal structure of the bismuth vanadate pigment, further improving its weather resistance and superhydrophobic properties.

[0041] According to another aspect of the present invention, a superhydrophobic and highly weather-resistant bismuth vanadate pigment is provided, which is prepared by the method described in any of the above embodiments. In the superhydrophobic and highly weather-resistant bismuth vanadate pigment according to the present invention, the Al2O3 / SiO2 gradient coating layer blocks the penetration of ultraviolet rays, oxygen and moisture through the physical barrier effect. The Al2O3 layer has strong chemical corrosion resistance and the SiO2 layer has high density, and the double protection reduces the damage to the pigment crystal structure. Combined with high-temperature calcination, the bonding force between the coating layer and the core is further strengthened and the crystal structure is optimized, so that the weather resistance is greatly improved compared with the single coating. The fluorosilane forms a low surface energy hydrophobic layer on the surface of the coating layer through chemical bonding, forming a "protection + hydrophobicity" synergistic system with the gradient coating layer, achieving a comprehensive effect of 1+1+1>3, which not only solves the problem of insufficient hydrophobicity of the single coating, but also makes up for the defect of poor weather resistance of the single modification. The superhydrophobic and highly weather-resistant bismuth vanadate pigment prepared by this invention exhibits excellent performance in fields such as construction, automobiles, and marine applications where weather resistance and waterproofing are highly demanding. It has broad application prospects, can meet the needs of different fields, and improve the quality and performance of related products.

[0042] The method of the present invention will be further described and illustrated below with reference to embodiments.

[0043] Example 1 Synthesis of bismuth vanadate precursor: (1) Dissolve Bi(NO3)3·5H2O in 3.5mol / L nitric acid, stir evenly, cool to room temperature, and prepare 50mL of bismuth salt solution with a concentration of 1.2mol / L; dissolve NH4VO3 in 3.5mol / L NaOH, stir evenly, cool to room temperature, and prepare 50mL of vanadium salt solution with a concentration of 1.2mol / L; (2) Under stirring, slowly add 50mL of vanadium salt solution to 50mL of bismuth salt solution at a rate of 20mL / min. After the addition is completed, continue stirring for 30min to obtain a mixed solution; (3) Add sodium hydroxide to the mixed solution to adjust the pH value of the solution to 8, and then continue stirring for 1h to precipitate the bismuth vanadate precursor. Filter, wash and dry the precipitate to obtain the bismuth vanadate precursor.

[0044] Gradient coating (Al2O3 / SiO2): (1) 5g of bismuth vanadate precursor was dispersed in 100mL of deionized water and ultrasonically dispersed for 30min to form a uniform dispersion. Then 0.2g of aluminum nitrate was added and stirred evenly. The pH of the solution was adjusted to 8 with ammonia and stirred at 55℃ for 1h to form an Al2O3 coating layer. (2) After the reaction was completed, 0.3g of tetraethyl orthosilicate was added to the solution and stirred evenly. The pH of the solution was adjusted to 7 with nitric acid and stirred at 50℃ for 1h to form a SiO2 coating layer. The solution was filtered, washed and dried to obtain the gradient-coated bismuth vanadate precursor.

[0045] Fluorosilane hydrophobic modification: 5g of gradient-coated bismuth vanadate precursor was dispersed in 50mL of toluene and ultrasonically dispersed for 20min to form a uniform dispersion; 0.2g of tridecafluorooctyltrimethoxysilane was added and stirred at 50℃ for 2h; after the reaction was completed, the mixture was filtered, washed with toluene / deionized water, and dried to obtain hydrophobically modified bismuth vanadate.

[0046] High-temperature calcination: The hydrophobically modified bismuth vanadate was placed in a muffle furnace and calcined at 450°C for 2 hours in air atmosphere. It was then cooled to room temperature with the furnace to obtain a superhydrophobic and highly weather-resistant bismuth vanadate pigment.

[0047] Example 2 Synthesis of bismuth vanadate precursor: (1) Dissolve bismuth chloride in nitric acid with a concentration of 3 mol / L, stir evenly, cool to room temperature, and prepare 50 mL of bismuth salt solution with a concentration of 1.2 mol / L; dissolve sodium vanadate in NaOH with a concentration of 3 mol / L, stir evenly, cool to room temperature, and prepare 50 mL of vanadium salt solution with a concentration of 1.2 mol / L; (2) Under stirring, slowly add 50 mL of vanadium salt solution to 50 mL of bismuth salt solution at a rate of 25 mL / min. After the addition is completed, continue stirring for 40 min to obtain a mixed solution; (3) Add sodium hydroxide to the mixed solution to adjust the pH value of the solution to 8, and then continue stirring for 80 min to precipitate the bismuth vanadate precursor. Filter, wash and dry the precipitate to obtain the bismuth vanadate precursor.

[0048] Gradient coating (Al2O3 / SiO2): (1) 5g of bismuth vanadate precursor was dispersed in 100mL of deionized water and ultrasonically dispersed for 30min to form a uniform dispersion. Then, 0.3g of aluminum nitrate was added and stirred evenly. The pH of the solution was adjusted to 8 with ammonia and stirred at 55℃ for 1h to form an Al2O3 coating layer. (2) After the reaction was completed, 0.3g of tetraethyl orthosilicate was added to the solution and stirred evenly. The pH of the solution was adjusted to 7 with nitric acid and stirred at 50℃ for 1h to form a SiO2 coating layer. The solution was filtered, washed and dried to obtain the gradient-coated bismuth vanadate precursor.

[0049] Fluorosilane hydrophobic modification: 5g of gradient-coated bismuth vanadate precursor was dispersed in 50mL of toluene and ultrasonically dispersed for 20min to form a uniform dispersion; 0.3g of KH-550 silane coupling agent was added and the mixture was stirred at 50℃ for 2h; after the reaction was completed, the mixture was filtered, washed with toluene / deionized water, and dried to obtain hydrophobically modified bismuth vanadate.

[0050] High-temperature calcination: The hydrophobically modified bismuth vanadate was placed in a muffle furnace and calcined at 450°C for 2 hours in air atmosphere. It was then cooled to room temperature with the furnace to obtain a superhydrophobic and highly weather-resistant bismuth vanadate pigment.

[0051] Example 3 Synthesis of bismuth vanadate precursor: (1) Dissolve bismuth acetate in 4.5 mol / L hydrochloric acid, stir evenly, cool to room temperature, and prepare 50 mL of bismuth salt solution with a concentration of 0.1 mol / L; dissolve sodium vanadate in 4.5 mol / L NaOH, stir evenly, cool to room temperature, and prepare 50 mL of vanadium salt solution with a concentration of 0.1 mol / L; (2) Under stirring, slowly add 50 mL of vanadium salt solution to 50 mL of bismuth salt solution at a rate of 15 mL / min. After the addition is completed, continue stirring for 40 min to obtain a mixed solution; (3) Add ammonia water to the mixed solution to adjust the pH value of the solution to 6, and then continue stirring for 1.5 h to precipitate the bismuth vanadate precursor. Filter, wash and dry the precipitate to obtain the bismuth vanadate precursor.

[0052] Gradient coating (Al2O3 / SiO2): (1) 5g of bismuth vanadate precursor was dispersed in 100mL of deionized water and ultrasonically dispersed for 30min to form a uniform dispersion. Then, 0.15g of aluminum chloride was added and stirred evenly. The pH of the solution was adjusted to 7 with ammonia and stirred at 25℃ for 2h to form an Al2O3 coating layer. (2) After the reaction was completed, 0.2g of sodium silicate was added to the solution and stirred evenly. The pH of the solution was adjusted to 6 with nitric acid and stirred at 25℃ for 2h to form a SiO2 coating layer. The solution was filtered, washed and dried to obtain the gradient-coated bismuth vanadate precursor.

[0053] Fluorosilane hydrophobic modification: 5g of gradient-coated bismuth vanadate precursor was dispersed in 50mL of xylene and ultrasonically dispersed for 30min to form a uniform dispersion; 0.1g of perfluorooctyltriethoxysilane was added and stirred at 40℃ for 3h; after the reaction was completed, the mixture was filtered, washed with toluene / deionized water, and dried to obtain hydrophobically modified bismuth vanadate.

[0054] High-temperature calcination: The hydrophobically modified bismuth vanadate was placed in a muffle furnace and calcined at 350°C for 3 hours in air atmosphere. The furnace was then cooled to room temperature to obtain a superhydrophobic and highly weather-resistant bismuth vanadate pigment.

[0055] Example 4 Synthesis of bismuth vanadate precursor: (1) Dissolve Bi(NO3)3·5H2O in 5mol / L nitric acid, stir evenly, cool to room temperature, and prepare 50mL of bismuth salt solution with a concentration of 2mol / L; dissolve NH4VO3 in 5mol / L NaOH, stir evenly, cool to room temperature, and prepare 50mL of vanadium salt solution with a concentration of 2mol / L; (2) Under stirring, slowly add 50mL of vanadium salt solution to 50mL of bismuth salt solution at a rate of 20mL / min. After the addition is completed, continue stirring for 80min to obtain a mixed solution; (3) Add sodium hydroxide to the mixed solution to adjust the pH value of the solution to 9, and then continue stirring for 120min to precipitate the bismuth vanadate precursor. Filter, wash and dry the precipitate to obtain the bismuth vanadate precursor.

[0056] Gradient coating (Al2O3 / SiO2): (1) 5g of bismuth vanadate precursor was dispersed in 100mL of deionized water and ultrasonically dispersed for 30min to form a uniform dispersion. Then, 0.4g of aluminum nitrate was added and stirred evenly. The pH of the solution was adjusted to 10 with ammonia and stirred at 80℃ for 1h to form an Al2O3 coating layer. (2) After the reaction was completed, 0.5g of tetraethyl orthosilicate was added to the solution and stirred evenly. The pH of the solution was adjusted to 8 with nitric acid and stirred at 90℃ for 1h to form a SiO2 coating layer. The solution was filtered, washed and dried to obtain the gradient-coated bismuth vanadate precursor.

[0057] Fluorosilane hydrophobic modification: 5g of gradient-coated bismuth vanadate precursor was dispersed in 50mL of toluene and ultrasonically dispersed for 20min to form a uniform dispersion; 0.4g of heptadecafluorodecyltrimethoxysilane was added and the mixture was stirred at 70℃ for 1h; after the reaction was completed, the mixture was filtered, washed with toluene / deionized water, and dried to obtain hydrophobically modified bismuth vanadate.

[0058] High-temperature calcination: The hydrophobically modified bismuth vanadate was placed in a muffle furnace and calcined at 650°C for 1 hour in air atmosphere. The furnace was then cooled to room temperature to obtain a superhydrophobic and highly weather-resistant bismuth vanadate pigment.

[0059] Blank example 1 Synthesis of bismuth vanadate precursor: (1) Dissolve Bi(NO3)3·5H2O in 3.5mol / L nitric acid, stir evenly, cool to room temperature, and prepare 50mL of bismuth salt solution with a concentration of 1.2mol / L; dissolve NH4VO3 in 3.5mol / L NaOH, stir evenly, cool to room temperature, and prepare 50mL of vanadium salt solution with a concentration of 1.2mol / L; (2) Under stirring, slowly add 50mL of vanadium salt solution to 50mL of bismuth salt solution at a rate of 20mL / min. After the addition is completed, continue stirring for 30min to obtain a mixed solution; (3) Add sodium hydroxide to the mixed solution to adjust the pH value of the solution to 8, and then continue stirring for 1h to precipitate the bismuth vanadate precursor. Filter, wash and dry the precipitate to obtain the bismuth vanadate precursor.

[0060] High-temperature calcination: The bismuth vanadate precursor was placed in a muffle furnace and calcined at 450°C for 2 hours in air atmosphere. The furnace was then cooled to room temperature to obtain untreated bismuth vanadate pigment.

[0061] Comparative Example 1 Synthesis of bismuth vanadate precursor: (1) Dissolve Bi(NO3)3·5H2O in 3.5mol / L nitric acid, stir evenly, cool to room temperature, and prepare 50mL of bismuth salt solution with a concentration of 1.2mol / L; dissolve NH4VO3 in 3.5mol / L NaOH, stir evenly, cool to room temperature, and prepare 50mL of vanadium salt solution with a concentration of 1.2mol / L; (2) Under stirring, slowly add 50mL of vanadium salt solution to 50mL of bismuth salt solution at a rate of 20mL / min. After the addition is completed, continue stirring for 30min to obtain a mixed solution; (3) Add sodium hydroxide to the mixed solution to adjust the pH value of the solution to 8, and then continue stirring for 1h to precipitate the bismuth vanadate precursor. Filter, wash and dry the precipitate to obtain the bismuth vanadate precursor.

[0062] Gradient coating (Al2O3 / SiO2): (1) 5g of bismuth vanadate precursor was dispersed in 100mL of deionized water and ultrasonically dispersed for 30min to form a uniform dispersion. Then 0.2g of aluminum nitrate was added and stirred evenly. The pH of the solution was adjusted to 8 with ammonia and stirred at 55℃ for 1h to form an Al2O3 coating layer. (2) After the reaction was completed, 0.3g of tetraethyl orthosilicate was added to the solution and stirred evenly. The pH of the solution was adjusted to 7 with nitric acid and stirred at 50℃ for 1h to form a SiO2 coating layer. The solution was filtered, washed and dried to obtain the gradient-coated bismuth vanadate precursor.

[0063] High-temperature calcination: The gradient-coated bismuth vanadate precursor was placed in a muffle furnace and calcined at 450°C for 2 hours in air atmosphere. It was then cooled to room temperature with the furnace to obtain a superhydrophobic and highly weather-resistant bismuth vanadate pigment.

[0064] Comparative Example 2 Synthesis of bismuth vanadate precursor: (1) Dissolve Bi(NO3)3·5H2O in 3.5mol / L nitric acid, stir evenly, cool to room temperature, and prepare 50mL of bismuth salt solution with a concentration of 1.2mol / L; dissolve NH4VO3 in 3.5mol / L NaOH, stir evenly, cool to room temperature, and prepare 50mL of vanadium salt solution with a concentration of 1.2mol / L; (2) Under stirring, slowly add 50mL of vanadium salt solution to 50mL of bismuth salt solution at a rate of 20mL / min. After the addition is completed, continue stirring for 30min to obtain a mixed solution; (3) Add sodium hydroxide to the mixed solution to adjust the pH value of the solution to 8, and then continue stirring for 1h to precipitate the bismuth vanadate precursor. Filter, wash and dry the precipitate to obtain the bismuth vanadate precursor.

[0065] Fluorosilane hydrophobic modification: 5g of bismuth vanadate precursor was dispersed in 50mL of toluene and ultrasonically dispersed for 20min to form a uniform dispersion; 0.2g of tridecafluorooctyltrimethoxysilane was added and stirred at 50℃ for 2h; after the reaction was completed, the mixture was filtered, washed with toluene / deionized water, and dried to obtain hydrophobically modified bismuth vanadate.

[0066] High-temperature calcination: The hydrophobically modified bismuth vanadate was placed in a muffle furnace and calcined at 450°C for 2 hours in air atmosphere. It was then cooled to room temperature with the furnace to obtain a superhydrophobic and highly weather-resistant bismuth vanadate pigment.

[0067] Comparative Example 3 Foreign paint manufacturers use bismuth vanadate pigments.

[0068] Bismuth vanadate structure and morphology analysis: Figure 2 The X-ray diffraction patterns of Embodiments 1 and 4, and the blank example and comparative example 3 according to the present invention are shown. Figure 2 It can be seen that the diffraction peak positions of Examples 1 and 4 correspond to those of the blank example and Comparative Example 3, and are all characteristic peaks of monoclinic bismuth vanadate. This indicates that the method of the present invention successfully prepared monoclinic bismuth vanadate, and its crystal phase did not change during the modification treatment. The diffraction peaks of Examples 1 and 4 are sharper and have higher intensity because the gradient coating and high-temperature calcination optimize the crystal structure, reduce defects, and improve crystallinity, which is beneficial to enhancing weather resistance. In addition, no diffraction peaks of Al2O3 / SiO2 were found in the XRD patterns of Examples 1 and 4, because its content is low or it is in an amorphous structure.

[0069] Figure 3 Transmission electron microscopy (TEM) images of bismuth vanadate particles, a blank example (without surface treatment) of the present invention, are shown. From... Figure 3 It can be seen that the untreated bismuth vanadate particles are 100-200 nm in size and have an irregular shape. Due to the lack of coating or other protection, the particles are prone to aggregation due to van der Waals forces. The absence of a protective layer makes the particles susceptible to corrosion from light and moisture, which can damage the crystal structure and explain the large color change of the blank examples in the weathering resistance test below.

[0070] Figure 4 Scanning electron microscope (SEM) images of the superhydrophobic and highly weather-resistant bismuth vanadate pigment prepared according to Example 1 of the present invention are shown. The images show that the particles are nearly spherical with a relatively uniform particle size distribution, and the particles are stacked together to form a certain porous structure. The gradient coating (Al₂O₃ / SiO₂) and fluorosilane modification processes make the particle surface more regular, the pores help to build superhydrophobic properties, and the dense structure helps to block external erosion, synergistically improving weather resistance and superhydrophobicity while retaining the original advantages of bismuth vanadate.

[0071] Figure 5 Transmission electron microscopy (TEM) images of the superhydrophobic and highly weather-resistant bismuth vanadate pigment prepared according to Example 1 of the present invention are shown. The images show that after gradient coating (Al₂O₃ / SiO₂) and fluorosilane modification, the bismuth vanadate particles have clear outlines and a uniform coating layer on the surface (which can be inferred to be an Al₂O₃ / SiO₂ layer due to the gradient coating process). This coating layer effectively isolates the particles, reduces agglomeration, and enhances resistance to erosion from light and rain. Combined with fluorosilane modification and high-temperature calcination, the crystal structure is optimized, providing microscopic support for high weather resistance and superhydrophobic properties.

[0072] Bismuth vanadate performance testing: Example 1 4. The main performance indicators of the bismuth vanadate products in the blank examples and comparative examples 1-3 are as follows: (1) Color performance test: The CIELAB color space parameters of the pigment were measured using a colorimeter; (2) Weather resistance test: The pigment was subjected to accelerated aging test using a QUV aging test chamber for 500 hours, and the color difference ΔE before and after aging was measured; (3) Contact angle test: The water contact angle of the pigment surface was measured using a contact angle measuring instrument. The test results are shown in Table 1 below.

[0073] Table 1. Test results of main performance indicators of bismuth vanadate

[0074] As shown in Table 1: First, Examples 1-4, which simultaneously employed gradient coating and fluorosilane modification, exhibited a color difference ΔE of only 1.9-2.3 before and after aging, with a contact angle exceeding 150°. This is significantly superior to Comparative Example 1 (gradient coating only, ΔE=3.8, contact angle 52.6°) and Comparative Example 2 (fluorosilane modification only, ΔE=9.3, contact angle 144.8°) using a single process. This demonstrates that gradient coating and fluorosilane modification synergistically enhance overall performance. Examples 1-4, by coating with a silica layer before fluorosilane modification, possess a dense and smooth surface that can fill minor defects on the pigment surface, allowing the fluorosilane to spread and adhere evenly. This avoids local voids or accumulations in the hydrophobic layer caused by uneven substrate, ensuring excellent overall hydrophobic performance of the pigment. Comparative Example 2, which directly modified the bismuth vanadate surface with fluorosilane, failed to achieve uniform spreading and adhesion of the fluorosilane, resulting in relatively poor hydrophobicity.

[0075] Secondly, the performance of the product of this invention comprehensively surpasses that of the blank sample and imported similar products. The blank sample, without any treatment, has a ΔE of 12.5 and a contact angle of only 47.8°. Due to the lack of a protective layer, the pigment particles are directly exposed to the aging environment, resulting in strong surface hydrophilicity and lattice susceptibility to damage from light and moisture. Comparative Example 3, with a ΔE of 4.5 and a contact angle of 105.9°, while superior to the blank sample, is significantly inferior to the performance of the pigments prepared in Examples 1-4 of this invention.

[0076] Finally, the color properties of the pigments prepared using the method of this invention were effectively preserved during the modification process. The color properties of Examples 1-4 were minimally different from those of the blank examples and Comparative Examples 1-2, indicating that gradient coating and fluorosilane modification did not significantly affect the color properties of the bismuth vanadate pigments. This is because: the coating layer thickness was controlled at the nanometer level, which did not affect visible light transmittance; and the fluorosilane molecules only modified the surface and did not enter the pigment lattice, avoiding changes to the BiVO4 crystal structure. Thus, while improving functional performance, the original bright yellow color and color saturation of the pigment were maintained.

[0077] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the disclosed embodiments of the present invention is limited to these examples; within the framework of the embodiments of the present invention, the technical features of the above embodiments or different embodiments can also be combined, and there are many other variations of different aspects of the embodiments of the present invention as described above, which are not provided in detail for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the embodiments of the present invention should be included within the protection scope of the embodiments of the present invention.

Claims

1. A method for preparing a superhydrophobic, highly weather-resistant bismuth vanadate pigment, characterized in that, Includes the following steps: Bismuth vanadate precursor was synthesized via liquid-phase coprecipitation. A dispersion of bismuth vanadate precursor was prepared, an aluminum source compound was added, and the pH and temperature of the solution were adjusted to form an alumina coating layer on the bismuth vanadate precursor. A silicon source compound is added to the solution, and the pH and temperature of the solution are adjusted to form a silicon dioxide coating layer on the outside of the alumina coating layer, thus obtaining a gradient-coated bismuth vanadate precursor. The gradient-coated bismuth vanadate precursor was dispersed in an organic solvent, fluorosilane was added, the system temperature was adjusted and the reaction was carried out to obtain a fluorosilane-modified bismuth vanadate precursor. The fluorosilane-modified bismuth vanadate precursor was calcined at high temperature to obtain the superhydrophobic and highly weather-resistant bismuth vanadate pigment.

2. The preparation method of the superhydrophobic and highly weather-resistant bismuth vanadate pigment according to claim 1, characterized in that, The synthesis of bismuth vanadate precursors via liquid-phase coprecipitation includes the following steps: Bismuth salts are dissolved in acidic solutions to form bismuth salt solutions, and vanadium salts are dissolved in alkaline solutions to form vanadium salt solutions. While stirring, the vanadium salt solution is added dropwise to the bismuth salt solution. After the addition is complete, stirring is continued for a certain period of time to obtain a mixed solution. Add a precipitant to the mixed solution, adjust the pH value of the solution, and continue stirring until the bismuth vanadate precursor precipitates out; The precipitate was collected, washed, and dried to obtain the bismuth vanadate precursor.

3. The preparation method of the superhydrophobic and highly weather-resistant bismuth vanadate pigment according to claim 2, characterized in that, The bismuth salt is selected from one or more of bismuth nitrate, bismuth chloride, bismuth acetate, and bismuth oxide; the vanadium salt is selected from one or more of ammonium metavanadate, sodium vanadate, and vanadium pentoxide; the acid solution is selected from nitric acid solution or hydrochloric acid solution; the alkaline solution is selected from sodium hydroxide solution and has the same concentration as the acid solution; the bismuth ion concentration in the bismuth salt solution is 0.1~2.0 mol / L; the vanadium ion concentration in the vanadium salt solution is equal to the bismuth ion concentration; the molar ratio of bismuth ions to vanadium ions in the mixed solution is 1:

1.

4. The preparation method of the superhydrophobic and highly weather-resistant bismuth vanadate pigment according to claim 2, characterized in that, The precipitant is selected from one or more of ammonia, sodium hydroxide, and sodium carbonate. The pH of the solution is adjusted to 6-9 by adding the precipitant and then stirred for 30-120 minutes.

5. The method for preparing the superhydrophobic, highly weather-resistant bismuth vanadate pigment according to claim 1, characterized in that, The aluminum source compound is selected from one or more of aluminum nitrate, aluminum chloride, and aluminum sulfate. The amount of the aluminum source compound is 3% to 8% of the mass of the bismuth vanadate precursor. When forming the alumina coating layer, the pH value of the solution is adjusted to 7 to 10, the temperature is controlled at 25 to 80°C, and the reaction time is 1 to 2 hours.

6. The method for preparing the superhydrophobic, highly weather-resistant bismuth vanadate pigment according to claim 1, characterized in that, The silicon source compound is selected from one or more of tetraethyl orthosilicate, sodium silicate, and silica sol. The amount of the silicon source compound is 4% to 10% of the mass of the bismuth vanadate precursor. When forming the silica coating layer, the pH value of the solution is adjusted to 6 to 8, the temperature is controlled at 25 to 90°C, and the reaction time is 1 to 2 hours.

7. The method for preparing the superhydrophobic, highly weather-resistant bismuth vanadate pigment according to claim 6, characterized in that, The organic solvent is selected from one or more of toluene, xylene, and chloroform.

8. The method for preparing the superhydrophobic, highly weather-resistant bismuth vanadate pigment according to claim 7, characterized in that, The fluorosilane is selected from one or more of KH-550 silane coupling agent, perfluorooctyltriethoxysilane, tridecafluorooctyltrimethoxysilane, and heptadecafluorodecyltrimethoxysilane. The amount of fluorosilane used is 2% to 8% of the mass of the gradient-coated bismuth vanadate precursor. After adding the fluorosilane, the system temperature is adjusted to 40 to 70°C, and the reaction is carried out for 1 to 3 hours.

9. The method for preparing the superhydrophobic, highly weather-resistant bismuth vanadate pigment according to claim 1, characterized in that, The high-temperature calcination includes calcination at 350~650℃ for 1~3 hours in an air atmosphere.

10. A superhydrophobic, highly weather-resistant bismuth vanadate pigment, characterized in that, The bismuth vanadate pigment is prepared by the method according to any one of claims 1-9.

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