A method for synthesizing silica-based aerogel materials by a soft template method

Abstract

The present invention relates to a method for synthesizing silica-based aerogel materials by a soft template method, belonging to the technical field of the preparation of aerogel materials. Specifically: tetraethyl orthosilicate is used as the silicon source, ethanol and deionized water are used as the solvent system, based on the microemulsion micelle soft template formed by surfactants, under the action of acid-base catalysts, the silicon source undergoes hydrolysis and polycondensation reactions on the surface of the soft template, and a silica / soft template composite is formed through the sol-gel process. Then, through the methods of solvent replacement and atmospheric drying, water and ethanol in the gel are removed. Then, the soft template agent is removed by calcination in a muffle furnace to obtain a hierarchical pore silica-based aerogel material. This method has simple equipment, a simple and environmentally friendly preparation process, the prepared silicon-based aerogel has a stable structure and a uniform internal structure, and can effectively solve the problems of difficult control of the synthesis conditions, poor structural stability, and poor mechanical properties of silicon-based aerogels.

Description

Technical Field

[0001] The present invention relates to a novel aerogel material, in particular to a method for synthesizing silica-based aerogel materials by a soft template method, and belongs to the technical field of aerogel material preparation. Background Art

[0002] With the rapid development of science and technology, the research and application of high-performance materials have become the key to promoting social progress. Silica-based aerogel materials have a wide range of applications in the fields of thermal insulation, adsorption, catalysis, etc. due to their unique pore structure, high specific surface area and good thermal stability. However, traditional synthesis methods have problems such as complex preparation processes, high costs, and insufficient structural stability (for example, KR20090008084A discloses a method for manufacturing silica aerogel and the silica aerogel manufactured thereby, which includes an atmospheric pressure drying step of drying a surface-modified wet gel at atmospheric pressure; CN109790037A discloses a method for manufacturing a plate-shaped metal-silica composite aerogel and the plate-shaped metal-silica composite aerogel manufactured thereby. In this method, first, the metal salt concentration and the alkaline catalyst concentration are adjusted to form a plate-shaped intermediate, and then an appropriate amount of sodium silicate solution is added, so that a plate-shaped metal-silica composite aerogel can be manufactured in a short time under the conditions of low temperature and atmospheric pressure; CN114180581A discloses a method for synthesizing silica aerogel, which uses 1,2-bis(trialkoxysilyl)ethane and tetrafunctional silane as silicon sources, methyltrialkoxysilane or methyl silicate oligomer as a copolymerization precursor, and a basic functional silane as a catalyst, and performs one-step hydrolysis and condensation in the presence of water and alcohol to prepare a silica wet gel). Especially during the drying process, when using low-cost atmospheric pressure drying technology, problems such as large gel brittleness and easy collapse and deformation of the structure will occur. Therefore, developing a simple, efficient and environmentally friendly synthesis method is of great significance for the further development of silica-based aerogel materials. Summary of the Invention

[0003] In view of the above-mentioned defects existing in the prior art, the present invention proposes a method for synthesizing silica-based aerogel materials by a soft template method. This method uses a soft template as a structure-directing agent to prepare silica-based aerogel materials with stable structure and excellent performance through a sol-gel process. It can effectively solve the problems of difficult control of the synthesis conditions of silicon-based aerogels, structural stability and poor mechanical properties.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0005] A method for synthesizing silica-based aerogel materials by a soft template method, and the preparation method is carried out according to the following steps:

[0006] Step 1: Dissolve the soft template agent in deionized water to form a transparent solution;

[0007] Step 2: Sequentially add tetraethyl orthosilicate, ethanol, and water to the solution obtained in Step 1, and magnetically stir for 30 min to 60 min to obtain a precursor system coated with micelles;

[0008] Step 3: Place the precursor system obtained in Step 2 in a water bath at 50 °C, and dropwise add hydrochloric acid solution under stirring to adjust the pH value of the mixed solution;

[0009] Step 4: Continue to place the solution obtained in Step 3 in a water bath at 50 °C and magnetically stir to fully hydrolyze tetraethyl orthosilicate;

[0010] Step 5: Dropwise add ammonia water solution to the solution obtained in Step 4 to adjust the pH value of the solution. After stirring evenly, place it in a 50 °C water bath and wait for it to gel to form a wet gel;

[0011] Step 6: Age the wet gel obtained in Step 5;

[0012] Step 7: Remove water and ethanol in the gel from the wet gel obtained in Step 6 by means of solvent replacement and atmospheric pressure fractional drying; then calcine in a muffle furnace to remove the soft template agent to obtain a hierarchical porous silica-based aerogel material.

[0013] Further, in Step 1, the soft template agent is a surfactant, and the surfactant is sodium carboxymethyl cellulose or emulsifier OP-10, and its mass fraction is 0.02% to 0.04%.

[0014] Further, in Step 2, the molar ratio of tetraethyl orthosilicate, ethanol, and water is 1:7:3 to 6.

[0015] Further, in Step 3, the concentration of the hydrochloric acid solution is 0.05 to 0.1 mol / L, and the pH value of the mixed solution is 2 to 4.

[0016] Further, in Step 4, the hydrolysis time is 2 to 4 h.

[0017] Further, in Step 5, the concentration of ammonia water is 0.05 to 0.1 mol / L, and the pH value of the adjusted solution is 6 to 7.

[0018] Further, in Step 6, the aging temperature of the wet gel aging is 50 °C, and the aging time is 24 h.

[0019] Further, in Step 7, the solvent replacement is carried out with n-hexane for 2 to 3 times, and the replacement time is 12 h each time.

[0020] Further, in the step 7, the temperatures for atmospheric pressure fractional drying are 50°C, 70°C, 90°C, 110°C, and 130°C respectively, and drying is carried out for 2 hours at each temperature.

[0021] Further, in the step 7, the calcination temperature is 300°C and the calcination time is 2 hours.

[0022] Compared with the prior art, the present invention can achieve the following remarkable effects:

[0023] (1) The present invention uses the microemulsion micelle soft template method based on surfactants to prepare a silica-based aerogel with a three-dimensional network structure, which has a stable structure and a uniform internal structure.

[0024] (2) In the present invention, by changing parameters such as the type and dosage of the template agent, the concentration of the acid-base catalyst, and the pH, the regulation of the microscopic structure of the gel skeleton can be realized.

[0025] (3) The experimental steps and conditions in the synthesis method of the present invention are simple, the cost is low, and it is suitable for large-scale industrial production. Description of the Drawings

[0026] Figure 1 is the sample diagram of the silica-based aerogel of the present invention;

[0027] Figure 2 is the SEM diagram of the silica-based aerogel of the present invention;

[0028] Figure 3 is the SEM diagram of the silica-based aerogel without adding a soft template agent. Detailed Embodiments

[0029] The following combines the attached Figures 1 - 3 drawings and specific embodiments to further elaborate on the present invention in detail, which is convenient for clearly understanding the present invention, but they do not constitute a limitation to the present invention.

[0030] Example 1

[0031] (1) Dissolve 0.0512 g of sodium carboxymethyl cellulose (mass fraction is 0.04%) in 128 g of deionized water, and stir to form a transparent solution.

[0032] (2) Add 42 g of tetraethyl orthosilicate, 64 g of ethanol, and 22 g of deionized water to the above solution. The molar ratio of tetraethyl orthosilicate, ethanol, and water is 1:7:6. Stir magnetically for 40 minutes to obtain a precursor system solution coated with micelles.

[0033] (3) Place the obtained precursor system in a water bath at 50°C, and dropwise add 0.1 mol / L hydrochloric acid solution under stirring to adjust the pH of the solution to 3.

[0034] (4) Continue stirring for 2 h to fully hydrolyze tetraethyl orthosilicate.

[0035] (5) Dropwise add 0.1 mol / L ammonia water solution into the solution obtained above, adjust the pH value of the solution to 7, stir evenly and place it in a 50 °C water bath to wait for it to gel.

[0036] (6) Age the wet gel obtained above at 50 °C for 24 h;

[0037] (7) Immerse the wet gel obtained above in n-hexane for solvent replacement 3 times, each time lasting for 12 h.

[0038] (8) Place the replaced wet gel in an oven and dry it at 50 °C for 2 h, 70 °C for 2 h, 90 °C for 2 h, 110 °C for 2 h, and finally dry it at 130 °C for two hours.

[0039] (9) Calcinate the aerogel obtained above in a muffle furnace at 300 °C for 2 h to remove sodium carboxymethyl cellulose, and obtain the final silica-based aerogel. As Figures 1 - 2 shown.

[0040] After testing, the comparison results of the thermal conductivity of adding sodium carboxymethyl cellulose and not adding sodium carboxymethyl cellulose (see Figure 3 ) are shown in Table 1 below. Obviously, the thermal conductivity of adding sodium carboxymethyl cellulose is lower and the test results are better.

[0041] Table 1 Test comparison results of Example 1

[0042] Test item Test result Unit Soft template agent Thermal conductivity (at room temperature) 0.0254 W / (m·K) Without adding sodium carboxymethyl cellulose Thermal conductivity (after calcination at 300°C for 2 h) 0.0234 W / (m·K) Adding sodium carboxymethyl cellulose

[0043] Example 2

[0044] (1) Dissolve 0.0256 g of emulsifier OP-10 (mass fraction is 0.02%) in 128 g of deionized water, stir to form a transparent solution.

[0045] (2) Add 42 g of tetraethyl orthosilicate, 64 g of ethanol, and 22 g of deionized water to the above solution. The molar ratio of tetraethyl orthosilicate, ethanol, and water is 1:7:6. Stir magnetically for 40 min to obtain a micelle-coated precursor system solution.

[0046] (3) Place the precursor system obtained above in a 50 °C water bath and dropwise add 0.1 mol / L hydrochloric acid solution under stirring to adjust the pH of the solution to 2.

[0047] (4) Continue stirring for 2 h to fully hydrolyze tetraethyl orthosilicate.

[0048] (5) Dropwise add 0.1 mol / L ammonia water solution into the solution obtained above, adjust the pH value of the solution to 6, stir evenly and place it in a 50 °C water bath to wait for it to gel.

[0049] (6) Age the wet gel obtained above at 50 °C for 24 h;

[0050] (7) Immerse the wet gel obtained above in n-hexane for solvent replacement 3 times, each time lasting for 12 h.

[0051] (8) Place the replaced wet gel in an oven, dry it at 50 °C for 2 h, at 70 °C for 2 h, at 90 °C for 2 h, at 110 °C for 2 h, and finally dry it at 130 °C for two hours.

[0052] (9) Bake the aerogel obtained above in a muffle furnace at 300 °C for 2 h to remove the emulsifier OP-10 to obtain the final silica-based aerogel.

[0053] After testing, the comparison results of the thermal conductivity with and without the emulsifier OP-10 are shown in Table 2 below. Obviously, the thermal conductivity of the sample with the emulsifier OP-10 is lower and the test results are better.

[0054] Table 2 Test comparison results of Example 2

[0055] Test item Test result Unit Soft template agent Thermal conductivity (at room temperature) 0.0289 W / (m·K) Without adding emulsifier OP - 10 Thermal conductivity (after calcination at 300°C for 2 h) 0.0255 W / (m·K) Adding emulsifier OP - 10

[0056] The above are only the preferred embodiments of the present invention, and do not impose any form of restriction on the structure of the present invention. The arrangement type and the usage quantity of the present invention are not limited to this example either, and can be optimized according to the actual engineering situation. Any modification, equivalent change and decoration made to the above embodiments based on the technical principle of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for synthesizing silica-based aerogel materials by a soft template method, characterized in that: The preparation method is carried out according to the following steps: Step 1: Dissolve the soft template agent in deionized water to form a transparent solution; in Step 1, the soft template agent is a surfactant, and the surfactant is sodium carboxymethyl cellulose or emulsifier OP-10, and its mass fraction is 0.02% - 0.04%; Step 2: Sequentially add tetraethyl orthosilicate, ethanol, and water to the solution obtained in Step 1, and magnetically stir for 30 min - 60 min to obtain a precursor system coated with micelles; in Step 2, the molar ratio of tetraethyl orthosilicate, ethanol, and water is 1:7:3 - 6; Step 3: Place the precursor system obtained in Step 2 in a water bath at 50 °C, and dropwise add hydrochloric acid solution under stirring to adjust the pH value of the mixed solution; In Step 3, the concentration of the hydrochloric acid solution is 0.05 - 0.1 mol / L, and the pH value of the mixed solution is 2 - 4; Step 4: Continue to place the solution obtained in Step 3 in a water bath at 50 °C and magnetically stir to fully hydrolyze tetraethyl orthosilicate; Step 5: Dropwise add ammonia water solution to the solution obtained in Step 4 to adjust the pH value of the solution. After stirring evenly, place it in a water bath at 50 °C and wait for it to gel to form a wet gel; In Step 5, the concentration of ammonia water is 0.05 - 0.1 mol / L, and the pH value of the adjusted solution is 6 - 7; Step 6: Age the wet gel obtained in Step 5; Step 7: Remove water and ethanol in the gel from the wet gel obtained in Step 6 by solvent replacement and atmospheric pressure gradient drying methods; then calcine in a muffle furnace to remove the soft template agent to obtain a hierarchical porous silica-based aerogel material.

2. The method for synthesizing a silica-based aerogel material by a soft template method according to claim 1, wherein: In Step 4, the hydrolysis time is 2 - 4 h.

3. The method for synthesizing a silica-based aerogel material by a soft template method according to claim 2, characterized in that: In Step 6, the aging temperature of the wet gel aging is 50 °C, and the aging time is 24 h.

4. The method for synthesizing a silica-based aerogel material by a soft template method according to claim 3, wherein: In Step 7, the solvent replacement is carried out with n-hexane for 2 - 3 times, and the replacement time is 12 h each time.

5. The method for synthesizing a silica-based aerogel material by a soft template method according to claim 4, characterized in that: In Step 7, the temperatures of atmospheric pressure gradient drying are 50 °C, 70 °C, 90 °C, 110 °C, and 130 °C respectively, and drying is carried out for 2 h at each temperature.

6. The method for synthesizing a silica-based aerogel material by a soft template method according to claim 5, characterized in that: In Step 7, the calcination temperature is 300 °C, and the calcination time is 2 h.

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