Preparation method of aluminum oxide aerogel with super-hydrophobicity

Abstract

The invention belongs to the field of chemical research service, and particularly relates to a preparation method of aluminum oxide aerogel with super-hydrophobicity. Comprising the following steps: mixing aluminum salt, deionized water and aluminum powder, and heating and stirring for reaction to form stable aluminum sol; adding a spinning aid into the aluminum sol, uniformly stirring, and standing to obtain an aerogel precursor solution; uniformly mixing and stirring aluminum sol, acid, alcohol, a water repellent agent and a spinning aid to obtain prepolymer sol; spinning the prepolymer sol into an aerogel precursor through electrostatic spinning; and drying the gel precursor to obtain the aluminum oxide hydrophobic aerogel. The aluminum oxide aerogel material prepared by the method has high specific surface area, excellent heat insulation performance and stable super-hydrophobic performance.

Description

Technical Field

[0001] This invention belongs to the field of chemical research services, specifically a method for preparing superhydrophobic alumina aerogel. Background Technology

[0002] Aerogels are lightweight solid materials with a three-dimensional nano-network structure, high porosity (90%), low density, and low thermal conductivity, and have broad application prospects in fields such as high-efficiency thermal insulation, adsorption, and catalysis. Alumina aerogels, due to their high specific surface area, excellent thermal stability, and chemical stability, are considered ideal materials for high-temperature thermal insulation.

[0003] However, the surface of traditional alumina aerogel framework is rich in hydroxyl groups (-OH), exhibiting strong hydrophilicity and readily adsorbing moisture from the environment. The capillary forces of moisture cause its fragile nanostructure to collapse during drying, while moisture absorption during use significantly reduces its thermal insulation performance and damages its structural integrity, severely limiting its practical application in humid environments.

[0004] Although researchers have attempted to impart hydrophobicity to alumina aerogels through surface modification, they often face specific challenges, the root of which lies in the mismatch between the modification strategy and the properties of alumina materials.

[0005] 1. The reactivity of the modifier and the alumina surface is mismatched. Differences in surface functional groups: The surface of alumina is mainly rich in hydroxyl groups, but its chemical properties are significantly different from those of the silanol groups on the surface of silica. When mature silica aerogel modifiers (such as trimethylchlorosilane TMCS) are directly applied, their reaction efficiency with the alumina surface is low, and complete monolayer coverage cannot be achieved.

[0006] 2. The "Incompatibility" of Aqueous Phase Modification Strategies Precursor hydrolysis disrupts structure: Many effective hydrophobic modification reactions (such as silanization) require organic solvents. If the aqueous phase modification strategy of silica is directly adopted, and the modifier is added to an aqueous solution containing an alumina precursor (such as aluminum salt or aluminum alkoxide), the presence of the modifier and water will drastically accelerate the hydrolysis-condensation reaction of the precursor, leading to uncontrolled gelation, the formation of a heterogeneous gel with a disrupted structure, and even phase separation.

[0007] 3. The modified layer is unstable. Insufficient bond strength and uneven coverage: Even if grafting is successful, if the chemical bonds formed between the modifier and the alumina surface (such as Al-O-Si bonds, when using silanes) are not stable enough, they may hydrolyze and break during subsequent processing, storage, or use, leading to the failure of hydrophobic properties. Due to mismatched reactivity, the modifier may form island-like distributions on the surface rather than a uniform and dense monolayer. These uncovered "defects" become weak points for water molecule attack, compromising the overall hydrophobicity.

[0008] 4. The process is complex and has poor compatibility with atmospheric pressure drying. Multi-step process involving solvent exchange: A typical modification process usually involves: gel formation → aging → solvent exchange (replacing the water in the pores with water or alcohol, then replacing the alcohol with an organic solvent) → modification reaction → drying at atmospheric pressure. This process is cumbersome, time-consuming, and uses a large amount of organic solvents.

[0009] Therefore, developing a simple, low-cost preparation method that can impart stable and durable superhydrophobic properties to alumina aerogel is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0010] In order to overcome the shortcomings of the prior art, at least one technical problem raised in the background art is solved.

[0011] The technical solution adopted by this invention to solve its technical problem is: a method for preparing superhydrophobic alumina aerogel according to this invention, comprising the following steps: S1. Sol preparation: Mix aluminum salt, deionized water and aluminum powder, and stir at 80-100℃ for 1-6 hours to form a stable aluminum sol; S2. Preparation of precursor solution: Add spinning aid to the aluminum sol obtained in step S1, stir evenly and let stand to obtain aerogel precursor solution; S3. Preparation of prepolymer sol: Aluminum sol, acid, alcohol, hydrophobic agent and spinning aid are mixed and hydrolyzed to obtain prepolymer sol; S4. Preparation of aerogel precursor: The prepolymer sol is spun into an aerogel precursor by electrospinning; S5. Drying under normal pressure: Place the prepolymer sol in a desiccator and heat it to 400℃ for 3 minutes to obtain alumina aerogel blocks with superhydrophobicity.

[0012] As a further technical solution of the present invention: in S1, the aluminum salt can be aluminum chloride, aluminum isopropoxide, aluminum sec-butoxide or aluminum nitrate.

[0013] As a further technical solution of the present invention: in S1, the molar ratio of aluminum salt, deionized water and aluminum powder is 1:8-40:2.

[0014] As a further technical solution of the present invention: in S2, the spinning aid is polyethylene oxide, and the molar ratio of the spinning aid to the aluminum salt is 1:80-400.

[0015] As a further technical solution of the present invention: in S3, the acid includes sulfuric acid or hydrochloric acid; the alcohol is ethanol; and the spinning aid is polyethylene oxide.

[0016] As a further technical solution of the present invention: In S3, the hydrophobic agent includes at least one of hexamethyldisiloxane, trimethylethoxysilane, trimethylmethoxysilane, trimethylchlorosilane and hexamethyldisilazane.

[0017] As a further technical solution of the present invention: the aerogel has a three-dimensional nano-network structure, with a water contact angle greater than 150°, a roll-off angle less than 10°, a specific surface area greater than 300 m² / g, a porosity greater than 95%, a density of 0.05-0.15 g / cm³, and a thermal conductivity less than 0.03 W / (m·K) at 25℃.

[0018] As a further technical solution of the present invention: aerogel is applied in extreme environment heat insulation, oil-water separation or chemical catalytic carrier in the fields of building energy conservation, aerospace, and petrochemicals.

[0019] The beneficial effects of this invention are as follows: This invention provides a method for preparing superhydrophobic alumina aerogels by combining surface property modification with atmospheric pressure drying. This method effectively solves the problems of alumina aerogels being hydrophilic, prone to cracking during drying, and limited by environmental constraints.

[0020] Another object of the present invention is to provide an alumina aerogel prepared by the above method, which not only has the characteristics of low density, high porosity, high specific surface area and low thermal conductivity of traditional aerogels, but also has stable and long-lasting superhydrophobicity.

[0021] Specifically, a stable aluminum sol is first prepared by high-temperature stirring reaction, and then the surface is modified using silicon-based products by grafting low surface energy methyl (-CH3) groups, thereby achieving a fundamental change in surface properties. Finally, the superhydrophobic product can be obtained by mild atmospheric pressure drying.

[0022] The alumina aerogel prepared by the method of this invention exhibits excellent superhydrophobic properties, with a water contact angle greater than 150° and a roll-off angle less than 10°. Simultaneously, it has a specific surface area greater than 300 m² / g, a porosity higher than 95%, a density between 0.05 and 0.15 g / cm³, and a room temperature thermal conductivity less than 0.03 W / (m·K). Detailed Implementation

[0023] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0024] Example 1 The method for preparing superhydrophobic alumina aerogel according to an embodiment of the present invention includes the following steps: S1. Sol preparation: Aluminum salt, deionized water and aluminum powder are mixed and stirred at 80°C for 3 hours to form a stable aluminum sol; The aluminum source is aluminum chloride; the molar ratio of aluminum salt, deionized water and aluminum powder is 1:20:2.

[0025] S2. Preparation of precursor solution: Add spinning aid to the aluminum sol obtained in step S1, stir evenly for 10 hours and let stand to obtain aerogel precursor solution; The spinning aid is polyethylene oxide, and the molar ratio of the spinning aid to the aluminum salt is 1:160. S3. Preparation of prepolymer sol: Mix the precursor solution, acid, alcohol and hydrophobic agent, and stir for 3 hours to obtain the prepolymer sol; S4. Preparation of aerogel precursor: The prepolymer sol is spun into an aerogel precursor by electrospinning; S5. Drying under normal pressure: Place the prepolymer gel in a desiccator and heat it to 400℃ for 3 minutes to obtain alumina aerogel blocks with superhydrophobicity; The specific steps of S5 are as follows: The modified gel was taken out and placed in a ventilated oven, heated to 400℃ and dried for 3 minutes to obtain superhydrophobic alumina aerogel blocks.

[0026] Example 2 The method for preparing superhydrophobic alumina aerogel according to an embodiment of the present invention includes the following steps: S1. Sol preparation: Aluminum salt, deionized water and aluminum powder are mixed and stirred at 80°C for 3 hours to form a stable aluminum sol; The aluminum source is aluminum chloride; the molar ratio of aluminum salt, deionized water and aluminum powder is 1:20:2.

[0027] S2. Preparation of prepolymer sol: Aluminum sol, acid, alcohol, spinning aid and hydrophobic agent are mixed and stirred for 2 hours to obtain prepolymer sol; wherein, the spinning aid is polyethylene oxide, and the molar ratio of spinning aid to aluminum salt is 1:10; S3. Preparation of aerogel precursor: The prepolymer sol is spun into an aerogel precursor by electrospinning; S4. Drying under normal pressure: The prepolymer gel is placed in a desiccator and dried under normal pressure at 80°C to obtain alumina aerogel blocks with superhydrophobicity; The specific steps of S4 are as follows: The modified gel was taken out and placed in a ventilated oven, heated to 400℃ and dried for 3 minutes to obtain superhydrophobic alumina aerogel blocks.

[0028] Example 3 The alumina aerogel prepared by the methods in Examples 1-2 above has a chemical composition including γ-AlOOH and / or γ-Al2O3.

[0029] This superhydrophobic alumina aerogel can be used in extreme environment insulation, oil-water separation, or chemical catalyst carriers in building energy conservation, aerospace, and petrochemical fields.

[0030] Performance testing The performance of the superhydrophobic alumina aerogels prepared in Examples 1-2 above was tested, and the test results are as follows: As can be seen from the table above, the aerogel has a three-dimensional nano-network structure, with a water contact angle greater than 150°, a roll-off angle less than 10°, a specific surface area greater than 300 m² / g, a porosity greater than 95%, a density of 0.05-0.15 g / cm³, and a thermal conductivity less than 0.03 W / (m·K) at 25℃.

[0031] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing alumina aerogel with superhydrophobic properties, characterized in that: Includes the following steps: S1. Sol preparation: Mix aluminum salt, deionized water and aluminum powder, and stir at 80-100℃ for 1-6 hours to form a stable aluminum sol; S2. Preparation of precursor solution: Add spinning aid to the aluminum sol obtained in S1, stir evenly and let stand to obtain aerogel precursor solution; S3. Preparation of prepolymer sol: Aluminum sol, acid, alcohol, hydrophobic agent and spinning aid are mixed and hydrolyzed to obtain prepolymer sol; S4. Preparation of aerogel precursor: The prepolymer sol is spun into an aerogel precursor by electrospinning; S5. Drying under normal pressure: Place the prepolymer sol in a desiccator and dry it under normal pressure at 100-500℃ to obtain alumina aerogel blocks with superhydrophobicity.

2. The method for preparing alumina aerogel with superhydrophobicity according to claim 1, characterized in that: In S1, the aluminum salt may be aluminum chloride, aluminum isopropoxide, aluminum sec-butoxide, or aluminum nitrate.

3. The method for preparing alumina aerogel with superhydrophobicity according to claim 1, characterized in that: In S1, the molar ratio of aluminum salt, deionized water and aluminum powder is 1:8-40:

2.

4. The method for preparing alumina aerogel with superhydrophobicity according to claim 1, characterized in that: In S2, the spinning aid is polyethylene oxide, and the molar ratio of the spinning aid to the aluminum salt is 1:80-400.

5. The method for preparing alumina aerogel with superhydrophobicity according to claim 1, characterized in that: In S3, the acid includes sulfuric acid or hydrochloric acid; the alcohol is ethanol; and the spinning aid is polyethylene oxide.

6. The method for preparing alumina aerogel with superhydrophobicity according to claim 1, characterized in that: In S3, the hydrophobic agent includes at least one of hexamethyldisiloxane, trimethylethoxysilane, trimethylmethoxysilane, trimethylchlorosilane, and hexamethyldisilazane.

7. The method for preparing alumina aerogel with superhydrophobicity according to claim 1, characterized in that: Aerogels have a three-dimensional nano-network structure with a water contact angle greater than 150°, a roll-off angle less than 10°, a specific surface area greater than 300 m² / g, a porosity greater than 95%, a density of 0.05-0.15 g / cm³, and a thermal conductivity less than 0.03 W / (m·K) at 25℃.

8. The method for preparing alumina aerogel with superhydrophobicity according to claim 1, characterized in that: Aerogels are used in building energy conservation, aerospace, petrochemical and extreme environment insulation, oil-water separation or chemical catalyst carriers.

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