CN115010140B - A kind of preparation method of superhydrophobic silica aerogel - Google Patents

Abstract

The invention discloses a preparation method of super-hydrophobic silica aerogel. The preparation method comprises the following steps: 1) Slowly dripping an alcohol compound into chlorosilane at a selected temperature to generate an organosilicon monomer and hydrogen chloride, adding water, and removing the hydrogen chloride to obtain a silicon oxide aerogel precursor; adding water and a base catalyst into the solution containing the silica aerogel precursor obtained in the step 1), and performing polycondensation reaction to obtain silica gel; and (3) performing solvent replacement and drying treatment on the silica gel obtained in the step (2) to obtain the super-hydrophobic silica aerogel. The hydrophobic angle of the super-hydrophobic silica aerogel is 150-160 degrees. The preparation method of the super-hydrophobic silica aerogel provided by the invention has the advantages of low cost, simple process and low cost, and is favorable for large-scale industrial production.

Description

A kind of preparation method of superhydrophobic silica aerogel

Technical field

The invention relates to a preparation method of superhydrophobic silica aerogel and belongs to the technical field of nanomaterials.

Background technique

Airgel materials are materials that use gas to replace liquid components in a gel while keeping the gel network from collapsing. As the first discovered and commercialized silica aerogel, it has broad application prospects in the fields of thermal insulation, adsorption, catalysis, and optics. After decades of development, a variety of preparation methods for silica aerogels have been invented. For example, patent CN106430219A discloses a low-cost method for preparing silica aerogels. It uses cheap industrial water glass as the precursor, water as the reaction solvent, and oxalic acid as the acidic catalyst. The silica aerogel is prepared through a normal pressure drying process. The airgel sample prepared by this method has low density, high specific surface area and good temperature resistance. Patent CN107572538A discloses a hydrophilic silica aerogel material and its preparation method. The silicon source is mixed and stirred with water, acidic catalyst, and alkaline catalyst to form a gel, and is aged and freeze-dried to obtain hydrophilicity. Silica airgel material has high porosity (82~99.6%) and high specific surface area (300~ ^1300m2 /g). Chen Xingming et al. (Fast preparation of SiO ₂ aerogels by HCl-NH ₃ two-component catalytic ethyl orthosilicate [J]. Modern Chemicals, 2003.) Using tetraethyl orthosilicate (TEOS) as raw material, water and ethanol as solvents Using hydrochloric acid and ammonia as catalysts, SiO ₂ aerogel was prepared using the sol-gel method. The SiO ₂ aerogel prepared had a nanoporous structure, with skeleton particles of 15 to 20 nm and pore sizes of 10 to 30 nm.

Although silica aerogels can be quickly synthesized using water glass, methyl orthosilicate or ethyl orthosilicate as the silicon source, silica itself is hydrophilic, and pure silica aerogels are The pore structure of the aerogel will produce huge capillary force on water molecules. When placed in the air, it will gradually absorb water and cause the three-dimensional nano-skeleton to collapse. The porosity, specific surface area and pore volume of the aerogel will decrease sharply. Excellent adsorption, catalysis and heat insulation Performance is no longer there. In order to increase the environmental resistance of silica aerogels, it is necessary to prepare hydrophobic or even superhydrophobic silica aerogels. There are three common methods for preparing hydrophobic silica aerogels:

1. Use hydrophobic reagents to chemically modify hydrophilic silica wet gel. For example, patent CN109850909A discloses a normal pressure preparation method of superhydrophobic silica aerogel. Mix ethyl orthosilicate, absolute ethanol and water to obtain a mixed solution, adjust the pH value to 2 to 3, and then add DMF And adjust the pH value of the reaction solution to 5-6, let it stand to form a gel, soak it in a mixed solution of hexamethylenetetramine, DMF and ethanol for modification, and finally dry it under normal pressure to obtain superhydrophobic SiO ₂ Aerogel. Patent CN101844771A discloses a method for preparing superhydrophobic silica aerogels under normal pressure by adding a first surface modifier, a second surface modifier, a non-polar organic solvent and an inorganic acid to a water glass solution And react to prepare hydrophobic silica wet gel, and wash and dry the hydrophobic silica wet gel to obtain superhydrophobic silica aerogel. Superhydrophobic silica gel can be obtained by modifying it with hydrophobic reagents without affecting the structure of silica aerogel. However, this method has a complicated process, requires multiple solvent replacements, has a long cycle and is high in cost, which limits the use of silica aerosol. Large-scale application of gels.

2. Hydrophobic materials are combined with hydrophilic silica aerogel to obtain hydrophobic silica aerogel. For example, patent CN112079618A discloses a method for preparing a modified silica airgel heat insulation sheet. Orthosilicate is used as the silicon source, and after being combined with a fiber matrix, a silica airgel heat insulation sheet is obtained, and then the silicon oxide airgel heat insulation sheet is obtained by roller coating. , prepare a hydrophobic encapsulating coating on the surface of the silica airgel heat insulation sheet by brushing or spraying, and then solidify the coating to obtain a modified silica airgel heat insulation sheet. Patent CN108504006A discloses a silica aerogel/organofluoropolymer composite film. Its preparation method and application include fully mixing silica aerogel powder and organofluoropolymer cross-linking agent, and calendering to obtain silica aerosol. Gel/organofluoropolymer composite film. The silicon oxide aerogel/organofluoropolymer composite film of the invention is hydrophobic and can be used in the air for a long time. However, hydrophobic material composite modified hydrophilic silica aerogel will inevitably reduce the content of silica aerogel, the density of the composite will increase, and the thermal insulation and adsorption properties will decrease, limiting the application scope of silica aerogel. .

3. Use methyl-containing siloxane to prepare superhydrophobic silica aerogels. For example, patent CN109052415A discloses a silica aerogel based on MTMS and its preparation method. Deionized water and cetyltrimethylammonium bromide are mixed, then methyltrimethoxysilane is added, and after stirring at a constant temperature Add ammonia hydrogel, wash the wet gel and dry it to obtain superhydrophobic silica aerogel. Patent CN105731470A discloses a method for preparing silica airgel composite materials. Surfactant, methanol and acetic acid solutions are mixed and stirred to dissolve the surfactant, then DMF, MTMS and DMDMS are added, and placed in a constant temperature magnetic stirrer. Hydrolyze, then add alkali solution to adjust the pH value so that the solution forms a gel. After aging, solvent replacement, and drying under normal pressure, an elastic superhydrophobic aerogel is prepared. Superhydrophobic silica aerogels can be prepared in a short time using methylsiloxane and can reduce process steps. However, the added surfactant is difficult to remove, and the raw materials containing methylsiloxane are expensive, making the price of silica aerogels high.

Silica itself is hydrophilic, so pure silica aerogel has a huge capillary force on water molecules due to its nanoscale pore structure. In the air, it will gradually absorb water molecules, causing the three-dimensional nano-skeleton to collapse and gradually Invalid. Superhydrophobic silica aerogels are usually obtained by hydrolysis and polycondensation of organosilicon precursors and then hydrophobic modification. This not only increases the process and cost, but also increases the use of organic solvents in the solvent replacement step. Therefore, it is of great significance to synthesize superhydrophobic silica aerogels quickly and at low cost using cheap raw materials.

Contents of the invention

The main purpose of the present invention is to provide a method for preparing superhydrophobic silica aerogels, and to solve the technical problems in the prior art of high preparation costs, complicated processes, and large consumption of organic solvents for superhydrophobic silica aerogels.

In order to achieve the foregoing invention objectives, the technical solutions adopted by the present invention include:

The embodiment of the present invention provides a method for preparing superhydrophobic silica aerogel, which includes:

1) Slowly drop alcohol compounds into chlorosilane at a selected temperature to generate silicone monomer and hydrogen chloride, add water, and remove hydrogen chloride to obtain a silicon oxide aerogel precursor;

2) Add water and an alkali catalyst to the solution containing the silica airgel precursor obtained in step 1), and obtain silica gel through a polycondensation reaction;

3) Perform solvent replacement and drying on the silica gel obtained in step 2) to obtain superhydrophobic silica aerogel.

The embodiments of the present invention also provide superhydrophobic silica aerogel prepared by the above preparation.

Further, the superhydrophobic silica aerogel includes a three-dimensional porous network structure formed by interconnected silica nanoparticles. The three-dimensional porous network structure includes micropores with a pore diameter of less than 2 nm and mesopores with a pore diameter of 2 to 50 nm. and macropores with a pore diameter of 50 nm to 50 μm, the hydrophobic angle of the superhydrophobic silica aerogel is 150 to 160°, and the chemical composition of the silica nanoparticles includes silica and polymethylsiloxane. Any one or a combination of both.

Embodiments of the present invention also provide the application of the aforementioned superhydrophobic silica aerogel, which has great application prospects in the fields of thermal insulation, adsorption, composite materials, environmental protection, catalysis, etc.

Compared with the prior art, the advantages of the present invention are at least:

1) The superhydrophobic silica aerogel provided by the present invention is directly prepared from chlorosilane monomer, with cheap raw materials, simple process and low cost, which is conducive to large-scale industrial production;

2) The superhydrophobic silica aerogel provided by the present invention does not require a hydrophobic modification process and has superhydrophobicity, with a hydrophobic angle of 150 to 160°.

Description of the drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are only These are some embodiments recorded in the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without exerting creative efforts.

Figure 1 is a schematic diagram of the preparation process of a superhydrophobic silica aerogel in a typical embodiment of the present invention;

Figure 2 is a nitrogen adsorption and desorption curve of the superhydrophobic silica aerogel obtained in Example 1 of the present invention;

Figure 3 is a pore size distribution diagram of the superhydrophobic silica aerogel obtained in Example 1 of the present invention;

Figure 4 is a scanning electron microscope photograph of the superhydrophobic silica aerogel obtained in Example 1 of the present invention;

Figure 5 is a transmission electron microscope photograph of the superhydrophobic silica aerogel obtained in Example 1 of the present invention;

Figure 6 is a schematic diagram of the contact angle of the superhydrophobic silica aerogel obtained in Example 1 of the present invention;

Figure 7 is a scanning electron microscope photograph of the superhydrophobic silica aerogel obtained in Example 2 of the present invention;

Figure 8 is a transmission electron microscope photograph of the superhydrophobic silica aerogel obtained in Example 2 of the present invention;

Figure 9 is a TG curve of the superhydrophobic silica aerogel obtained in Example 2 of the present invention;

Figure 10 is a schematic diagram of the contact angle of the superhydrophobic silica aerogel obtained in Example 2 of the present invention;

Figure 11 is an optical photograph of the superhydrophobic silica aerogel obtained in Example 2 of the present invention.

Detailed ways

In view of the deficiencies in the prior art, the inventor of this case was able to propose the technical solution of the present invention after long-term research and extensive practice, which mainly involves obtaining silica gel through esterification and polycondensation reaction of chlorosilane, followed by solvent replacement and drying steps. A superhydrophobic silica aerogel is obtained, as well as a series of applications of the superhydrophobic silica aerogel. The technical solution, its implementation process and principles will be further explained below.

The embodiment of the present invention provides a method for preparing superhydrophobic silica aerogel, which includes:

1) Slowly drop alcohol compounds into chlorosilane at a selected temperature to generate silicone monomer and hydrogen chloride, add water, and remove hydrogen chloride to obtain a silicon oxide aerogel precursor;

2) Add water and an alkali catalyst to the solution containing the silica airgel precursor obtained in step 1), and obtain silica gel through a polycondensation reaction;

3) Perform solvent replacement and drying on the silica gel obtained in step 2) to obtain superhydrophobic silica aerogel.

In some more specific implementation cases, as shown in Figure 1, the preparation method may include the following steps:

1) Slowly drop excess alcohol compounds into a certain proportion of chlorosilane under constant temperature conditions in a water bath to generate silicone monomer and hydrogen chloride. After adding a certain proportion of water, remove the hydrogen chloride by refluxing, and cool to room temperature to obtain silicon oxide gas condensation. glue precursor;

2) Add water and an alkali catalyst to the silica airgel precursor solution obtained in step 1), and obtain silica gel through a polycondensation reaction;

3) Solvent replacement and drying of the silica gel obtained in step 2) to obtain superhydrophobic silica aerogel.

In some embodiments, in step 1), the selected temperature of the constant temperature of the water bath is 5-30°C, preferably 15-25°C.

In some embodiments, the alcohol compound includes any one or a combination of two or more of methanol, ethanol, propanol, butanol, and is not limited thereto.

In some embodiments, the chlorosilane includes any one or a combination of two or more of trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane, silicon tetrachloride, etc., and is not limited to this.

Further, the molar percentage of trimethylchlorosilane in the chlorosilane is 0-20%, the molar percentage of dimethyldichlorosilane is 0-50%, and the molar percentage of silicon tetrachloride is no more than 80%, The remainder consists of methyltrichlorosilane and silicon tetrachloride.

In some embodiments, in step 1), the molar ratio of the alcohol compound to chlorosilane is 5-20:1, preferably 5-10:1.

Further, the dripping rate of the alcohol compound is 20 to 2000 mL/min, preferably 100 to 500 mL/min.

Further, a certain proportion of water is added in step 1), and the molar ratio of water to chlorosilane is 1 to 4:1, preferably 1.5 to 3:1.

Further, the reflux temperature is 60-130°C, preferably 70-100°C; the reflux time is 1-12 hours, preferably 3-6 hours.

In some embodiments, in step 2), the molar ratio of water to chlorosilane added is 0 to 3:1, preferably 1 to 1.5:1.

Further, the alkali catalyst includes any one or a combination of two or more of sodium hydroxide, triethylamine, ammonia, sodium carbonate, sodium bicarbonate, tetramethylammonium hydroxide, etc., and is not limited thereto.

Further, the molar ratio of the alkali catalyst to chlorosilane is 110 ^-4 :1, preferably 10 ^-1 to 10 ^-3 :1.

In some embodiments, in step 2), the time of the polycondensation reaction is 1 to 96 hours, preferably 48 to 72 hours, and the temperature of the polycondensation reaction is 20 to 90°C, preferably 60 to 80°C.

In some embodiments, in step 3), the replacement solvent used in the solvent replacement includes any one or a combination of two or more of water, ethanol, acetone, n-hexane, benzene, tetrahydrofuran, dimethyl sulfoxide, etc. , and not limited to this.

Further, the number of solvent substitutions is 3 to 10 times.

Further, the drying treatment includes any one or a combination of two or more of normal pressure drying, vacuum drying, supercritical drying, etc.

Further, the normal pressure drying temperature ranges from 20 to 120°C, preferably from 30 to 60°C, and the drying time ranges from 6 to 48 hours.

Further, the vacuum drying technology includes freeze vacuum drying, room temperature vacuum drying, etc. The cold trap temperature of the freeze vacuum drying is -45~-80°C, the vacuum degree is less than 0.1kPa, and the drying time is 6~48 hours. The temperature of the normal temperature vacuum drying is room temperature, and the vacuum degree is less than 0.1kPa.

Further, the supercritical drying includes any one of supercritical CO ₂ , supercritical ethanol, etc., wherein the supercritical drying may specifically include: using a supercritical fluid to replace a specific supercritical fluid in a supercritical environment. The liquid component inside the gel material is dried for 12 to 48 hours to obtain the airgel material.

In summary, the present invention obtains silica gel through esterification and polycondensation of cheap raw material chlorosilane, and then obtains superhydrophobic silica aerogel through solvent replacement and drying steps. This method does not require the use of expensive materials containing Using methylsiloxane as a raw material, superhydrophobic silica aerogel can be obtained without multiple solvent substitutions and modification with hydrophobic reagents. This method not only reduces the preparation cost of superhydrophobic silica aerogels, but also shortens the preparation cycle, laying the foundation for the large-scale application of silica aerogels.

Another aspect of the embodiments of the present invention also provides a superhydrophobic silica aerogel prepared by the aforementioned preparation method.

Further, the superhydrophobic silica aerogel is composed of a three-dimensional porous network structure formed by interconnections. The three-dimensional porous network structure includes micropores with a pore diameter below 2 nm, mesopores with a pore diameter of 2 to 50 nm, and pores with a pore diameter of 50 nm. ~50 μm macropores; the composition of the superhydrophobic silica aerogel includes any one or a combination of two of silica and polymethylsiloxane, but is not limited thereto.

Furthermore, the superhydrophobic silica aerogel has superhydrophobicity, and its hydrophobic angle is 150-160°.

In some embodiments, the density of the superhydrophobic silica aerogel is 30-300 mg/cm ³ , preferably 50-200 mg/cm ³ .

Further, the specific surface area of the superhydrophobic silica aerogel is 100-1200 m ² /g, preferably 400-800 m ² /g.

Further, the pore volume of the superhydrophobic silica airgel is 0.5-5cm ³ /g, preferably 1-3cm ³ /g.

Furthermore, the porosity of the superhydrophobic silica airgel is 70-99%, preferably 75-99%, and particularly preferably 85-95%.

Furthermore, the use temperature of the superhydrophobic silica aerogel is -196~250°C, preferably -50~200°C.

Furthermore, the thermal conductivity of the superhydrophobic silica aerogel is 0.015-0.04W/(m·K), preferably 0.018-0.03W/(m·K).

In summary, the preparation method of superhydrophobic silica aerogel provided by the present invention has a simple process, cheap raw materials, and low cost, and is conducive to large-scale industrial production.

The technical solution of the present invention will be further described in detail below with reference to several preferred embodiments and the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without any creative work fall within the scope of protection of the present invention. Experimental methods without specifying specific conditions in the following examples usually follow conventional conditions or conditions recommended by the manufacturer.

Example 1

(1) Slowly add methanol dropwise to trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane and silicon tetrachloride in a water bath at a constant temperature (5°C) to generate silicone monomer and hydrogen chloride. Then add water, remove hydrogen chloride by refluxing (temperature: 130°C, time: 1 h), and cool to room temperature to obtain a silicon oxide airgel precursor. Among them, the dropping rate of methanol is 50 mL/min. The molar ratio of water, methanol, trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane and silicon tetrachloride is 1:5:0.1:0.2:0.3:0.4.

(2) Add water and ammonia to the silica airgel precursor solution obtained in step 1), and obtain silica gel through a polycondensation reaction; wherein the molar ratio of water:ammonia:chlorosilane monomer is 1.5:10 ^-4 ∶1, the polycondensation reaction time is 48h, and the temperature is 60℃.

(3) The silica gel obtained in step 2) was replaced with ethanol solvent 6 times and then dried with supercritical ethanol. The drying time was 48 hours to obtain superhydrophobic silica aerogel.

The nitrogen adsorption and desorption curve of the superhydrophobic silica aerogel obtained in this example is shown in Figure 2, the pore size distribution is shown in Figure 3, the SEM structure is shown in Figure 4, the TEM picture is shown in Figure 5, and the contact angle is shown in Figure 6. Please refer to Table 1 for the physical parameters such as specific surface area, hydrophobic angle, pore volume and density of the superhydrophobic silica aerogel obtained in this example.

Example 2

(1) Slowly add methanol dropwise to trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane and silicon tetrachloride in a water bath at a constant temperature (30°C) to generate silicone monomer and hydrogen chloride. Then add water, remove hydrogen chloride by refluxing (temperature: 60°C, time: 12 hours), and cool to room temperature to obtain a silicon oxide airgel precursor. Among them, the dripping rate of methanol is 2000mL/min. The molar ratio of water, methanol, trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane and silicon tetrachloride is 3:10:0:0:0.5:0.5.

(2) Add water and sodium carbonate to the silica airgel precursor solution obtained in step 1), and obtain silica gel through a polycondensation reaction; wherein the molar ratio of water:sodium carbonate:chlorosilane monomer is 1:10 ^-1 :1, the polycondensation reaction time is 48h, and the temperature is 60℃.

(3) The silica gel obtained in step 2) is replaced with ethanol solvent 6 times and then dried with supercritical carbon dioxide. The drying time is 12 hours to obtain superhydrophobic silica aerogel.

The SEM structure of the superhydrophobic silica gel obtained in this example is shown in Figure 7, the TEM picture is shown in Figure 8, the thermogravimetric analysis picture is shown in Figure 9, the contact angle is shown in Figure 10, and the hydrophobic optical photo is shown in Figure 11. Please refer to Table 1 for the physical parameters such as specific surface area, hydrophobic angle, pore volume and density of the superhydrophobic silica gel obtained in this example.

Example 3

(1) Slowly add ethanol dropwise to trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane and silicon tetrachloride in a water bath at a constant temperature (20°C) to generate silicone monomer and hydrogen chloride. Then add water, remove hydrogen chloride by refluxing (temperature: 80°C, time: 6 hours), and cool to room temperature to obtain a silicon oxide airgel precursor. Among them, the dripping rate of ethanol is 20 mL/min. The molar ratio of water, ethanol, trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane and silicon tetrachloride is 3:8:0.2:0.3:0.4:0.1.

(2) Add water and triethylamine to the silica airgel precursor solution obtained in step 1), and obtain silica gel through polycondensation reaction; wherein the molar ratio of water:triethylamine:chlorosilane monomer is 1.5 ∶10 ^-3 ∶1, the polycondensation reaction time is 48h, and the temperature is 20℃.

(3) The silica gel obtained in step 2) was replaced with ethanol and n-hexane solvents 6 times and then dried under normal pressure (temperature: 30°C) for 48 hours to obtain superhydrophobic silica aerogel.

Please refer to Table 1 for the physical parameters such as specific surface area, hydrophobic angle, pore volume and density of the superhydrophobic silica gel obtained in this example.

Example 4

(1) Slowly add propanol dropwise to trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane and silicon tetrachloride in a water bath at a constant temperature (20°C) to generate silicone monomer and hydrogen chloride , then add water, remove the hydrogen chloride by refluxing (temperature: 80°C, time: 6h), and cool to room temperature to obtain a silicon oxide airgel precursor. Among them, the dripping rate of propanol is 50 mL/min. The molar ratio of water, propanol, trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane and silicon tetrachloride is 3:10:0.1:0.1:0.4:0.4.

(2) Add water and sodium hydroxide to the silica airgel precursor solution obtained in step 1), and obtain silica gel through a polycondensation reaction; wherein the molar ratio of water:sodium hydroxide:chlorosilane monomer is 1.5 ∶10 ^-3 ∶1, the polycondensation reaction time is 1 hour, and the temperature is 90°C.

(3) The silica gel obtained in step 2) is replaced with ethanol solvent 6 times and then dried under normal pressure (temperature is 60°C) to obtain superhydrophobic silica aerogel.

Please refer to Table 1 for the physical parameters such as specific surface area, hydrophobic angle, pore volume and density of the superhydrophobic silica gel obtained in this example.

Example 5

(1) Slowly add butanol dropwise to trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane and silicon tetrachloride in a water bath at constant temperature (20°C) to generate silicone monomer and hydrogen chloride , then add water, remove the hydrogen chloride by refluxing (temperature: 80°C, time: 6h), and cool to room temperature to obtain a silicon oxide airgel precursor. Among them, the dripping rate of butanol is 50 mL/min. The molar ratio of water, propanol, trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane and silicon tetrachloride is 3:10:0.1:0.1:0.3:0.5.

(2) Add water and sodium bicarbonate to the silica airgel precursor solution obtained in step 1), and obtain silica gel through a polycondensation reaction; wherein the molar ratio of water:sodium bicarbonate:chlorosilane monomer is 1.5 ∶10 ^-3 ∶1, the polycondensation reaction time is 48h, and the temperature is 60℃.

(3) The silica gel obtained in step 2) was replaced with dimethyl sulfoxide solvent 10 times and then dried under normal pressure (temperature: 120°C) for 6 hours to obtain superhydrophobic silica aerogel.

Please refer to Table 1 for the physical parameters such as specific surface area, hydrophobic angle, pore volume and density of the superhydrophobic silica gel obtained in this example.

Example 6

(1) Slowly add butanol dropwise to trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane and silicon tetrachloride in a water bath at constant temperature (20°C) to generate silicone monomer and hydrogen chloride , then add water, remove the hydrogen chloride by refluxing (temperature: 75°C, time: 6h), and cool to room temperature to obtain a silicon oxide airgel precursor. Among them, the butanol dripping acceleration rate is 50mL/min. The molar ratio of water, butanol, trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane and silicon tetrachloride is 3:9:0.05:0.15:0.6:0.2.

(2) Add water and tetramethylammonium hydroxide to the silica airgel precursor solution obtained in step 1), and obtain silica gel through a polycondensation reaction; wherein water: tetramethylammonium hydroxide: chlorosilane mono The molar ratio of the polymers is 1.5:10 ^-3 :1, the polycondensation reaction time is 48h, and the temperature is 60°C.

(3) The silica gel obtained in step 2) was replaced with water five times and then freeze-vacuum dried. The drying time was 48 hours to obtain superhydrophobic silica aerogel.

Please refer to Table 1 for the physical parameters such as specific surface area, hydrophobic angle, pore volume and density of the superhydrophobic silica gel obtained in this example.

Example 7

(1) Slowly add ethanol dropwise to trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane and silicon tetrachloride in a water bath at a constant temperature (20°C) to generate silicone monomer and hydrogen chloride. Then add water, remove the hydrogen chloride by refluxing (temperature: 75°C, time: 6 hours), and cool to room temperature to obtain a silicon oxide airgel precursor. Among them, the dripping rate of ethanol is 50 mL/min. The molar ratio of water, ethanol, trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane and silicon tetrachloride is 3:10:0.1:0.2:0.5:0.2.

(2) Add water and ammonia to the silica airgel precursor solution obtained in step 1), and obtain silica gel through a polycondensation reaction; wherein the molar ratio of water:ammonia:chlorosilane monomer is 1.5:1:1 , the polycondensation reaction time is 48h, and the temperature is 80℃.

(3) Replace the silica gel obtained in step 2) with water five times and then vacuum-dry it at room temperature for 6 hours to obtain superhydrophobic silica aerogel.

Please refer to Table 1 for the physical parameters such as specific surface area, hydrophobic angle, pore volume and density of the superhydrophobic silica gel obtained in this example.

Example 8

(1) Slowly add ethanol dropwise to trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane and silicon tetrachloride in a water bath at a constant temperature (25°C) to generate silicone monomer and hydrogen chloride. Then add water, remove hydrogen chloride by refluxing (temperature: 70°C, time: 6 hours), and cool to room temperature to obtain a silicon oxide airgel precursor. Among them, the dripping rate of ethanol is 50 mL/min. The molar ratio of water, ethanol, trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane and silicon tetrachloride is 4:20:0.1:0.2:0.5:0.2.

(2) Add water and ammonia to the silica airgel precursor solution obtained in step 1), and obtain silica gel through a polycondensation reaction; wherein the molar ratio of water:ammonia:chlorosilane monomer is 1.5:10 ^-3 ∶1, the polycondensation reaction time is 48h, and the temperature is 80℃.

(3) The silica gel obtained in step 2) is replaced with acetone five times and then dried with supercritical ethanol to obtain superhydrophobic silica aerogel.

Please refer to Table 1 for the physical parameters such as specific surface area, hydrophobic angle, pore volume and density of the superhydrophobic silica gel obtained in this example.

Example 9

(1) Slowly add ethanol dropwise to trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane and silicon tetrachloride in a water bath at a constant temperature (15°C) to generate silicone monomer and hydrogen chloride. Then add water, remove hydrogen chloride by refluxing (temperature: 100°C, time: 6 hours), and cool to room temperature to obtain a silicon oxide airgel precursor. Among them, the dripping rate of ethanol is 50 mL/min. The molar ratio of water, ethanol, trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane and silicon tetrachloride is 3:10:0.1:0.2:0.5:0.2.

(2) Add water and ammonia water to the silica airgel precursor solution obtained in step 1), and obtain silica gel through a polycondensation reaction; wherein the molar ratio of water:ammonia water:chlorosilane monomer is 3:10 ^-3 ∶1, the polycondensation reaction time is 72h, and the temperature is 80℃.

(3) Replace the silica gel obtained in step 2) with benzene and ethanol five times and then dry it with supercritical ethanol to obtain superhydrophobic silica aerogel.

Please refer to Table 1 for the physical parameters such as specific surface area, hydrophobic angle, pore volume and density of the superhydrophobic silica gel obtained in this example.

Example 10

(1) Slowly add ethanol dropwise to trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane and silicon tetrachloride in a water bath at a constant temperature (20°C) to generate silicone monomer and hydrogen chloride. Then add water, remove the hydrogen chloride by refluxing (temperature: 75°C, time: 6 hours), and cool to room temperature to obtain a silicon oxide airgel precursor. Among them, the ethanol dripping acceleration rate is 50mL/min. The molar ratio of water, ethanol, trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane and silicon tetrachloride is 3:10:0.1:0.2:0.5:0.2.

(2) Add water and ammonia to the silica airgel precursor solution obtained in step 1), and obtain silica gel through a polycondensation reaction; wherein the molar ratio of water:ammonia:chlorosilane monomer is 1.5:10 ^-3 ∶1, the polycondensation reaction time is 96h, and the temperature is 80℃.

(3) The silica gel obtained in step 2) is replaced with tetrahydrofuran three times and then dried with supercritical ethanol to obtain superhydrophobic silica aerogel.

Please refer to Table 1 for the physical parameters such as specific surface area, hydrophobic angle, pore volume and density of the superhydrophobic silica gel obtained in this example.

Table 1. Structure and performance parameters of superhydrophobic silica aerogels obtained in Examples 1-10

Example hydrophobic angle Specific surface area (m ² /g) Pore volume (%) Density (mg/cm ³ ) 1 155.5° 120 0.6 117 2 157.3° 196 5 30 3 158.6° 977 1.3 54 4 151.0° 546 1.1 280 5 150.5° 351 4.3 105 6 160.0° 636 0.5 300 7 150.0° 587 4.7 251 8 159.9° 1200 2.5 146 9 154.4° 216 4.1 267 10 156.3° 867 2.3 222

In addition, the inventor of this case also used other raw materials and process conditions listed in this specification, and prepared a series of superhydrophobic silica aerogels with reference to Examples 1-10. After testing, it was found that these superhydrophobic silica aerogels also have various excellent properties described in this specification.

It should be understood that the above are only some embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, other modifications and improvements can be made without departing from the creative concept of the present invention. These all belong to the protection scope of the present invention.

Claims (7)

1. A method for preparing superhydrophobic silica aerogel, which is characterized by comprising: 1) Slowly add ethanol dropwise to trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane and silicon tetrachloride in a water bath at a constant temperature of 25°C to generate silicone monomer and hydrogen chloride, and then add water , remove hydrogen chloride at a reflux temperature of 70°C for 6 hours, and cool to room temperature to obtain a silicon oxide aerogel precursor, in which the dripping acceleration rate of ethanol is 50 mL/min, water, ethanol, trimethylchlorosilane, and dichlorosilane. The molar ratio of methyldichlorosilane, methyltrichlorosilane and silicon tetrachloride is 4:20:0.1:0.2:0.5:0.2; 2) Add water and ammonia to the silica airgel precursor solution obtained in step 1), and obtain silica gel through a polycondensation reaction; the molar ratio of water: ammonia: chlorosilane monomer is 1.5: 10 ^-3 : 1. The polycondensation reaction time is 48h and the temperature is 80℃; 3) Replace the silica gel obtained in step 2) with acetone five times and then dry it with supercritical ethanol to obtain superhydrophobic silica aerogel. 2. The preparation method according to claim 1, characterized in that in step 3), the supercritical ethanol drying time is 12 to 48 hours. 3. The preparation method according to claim 1, characterized in that: the superhydrophobic silica aerogel includes a three-dimensional porous network structure formed by interconnected silica nanoparticles, and the three-dimensional porous network structure includes a pore diameter of 2 Micropores below nm, mesopores with a pore diameter of 2 to 50 nm, and macropores with a pore diameter of 50 nm to 50 μm. The chemical composition of the silicon oxide nanoparticles includes any of silicon dioxide and polymethylsiloxane. One or a combination of both. 4. The preparation method according to claim 3, characterized in that: the porosity of the superhydrophobic silica aerogel is 70 to 99%. 5. The preparation method according to claim 4, characterized in that: the porosity of the superhydrophobic silica aerogel is 85 to 95%. 6. The preparation method according to claim 3, characterized in that: the thermal conductivity of the superhydrophobic silica aerogel is 0.015~0.04 W/(m·K). 7. The preparation method according to claim 6, characterized in that: the thermal conductivity of the superhydrophobic silica aerogel is 0.018~0.03 W/(m·K).