Silicon dioxide aerogel as well as preparation method and application thereof

Abstract

The invention discloses silicon dioxide aerogel as well as a preparation method and application thereof. The preparation method of the silicon dioxide aerogel comprises the following steps: 1) preparing silicon dioxide sol; 2) preparing silicon dioxide wet gel; (3) preparing aged silicon dioxide wet gel; 4) soaking the aged silicon dioxide wet gel in a modifier solution prepared from hexamethyldisiloxane, ethanol and hydrochloric acid, and heating and soaking to obtain modified silicon dioxide wet gel; and 5) drying the modified silicon dioxide wet gel to obtain the silicon dioxide aerogel. The silicon dioxide aerogel has the advantages of extremely low density, strong hydrophobicity, excellent heat insulation performance and the like, and can be used in the fields of fire prevention, heat insulation, heat preservation, adsorbents, catalyst carriers, sound insulation and the like, and the preparation method is simple to operate, safe, environment-friendly, low in production cost and suitable for large-scale industrial production and application.

Description

Technical Field

[0001] The present invention relates to the technical field of aerogel materials, and particularly relates to a silica aerogel and its preparation method and application. Background Art

[0002] An aerogel is a nano-porous amorphous solid material, which has a nano-porous network structure formed by the aggregation of nano-scale colloidal particles or polymer molecules, and there are a large number of gaseous dispersion media in the network pores. Silica aerogel has the characteristics of low density, large specific surface area, high porosity, low thermal conductivity, etc., and is widely used in the fields of fire prevention and heat insulation, thermal insulation, adsorbent, catalyst carrier, sound insulation, etc., and has extremely high application value.

[0003] The preparation of silica aerogel usually consists of two processes: a sol-gel process and a drying process. The drying process refers to the process of discharging the remaining solvents (such as alcohols, water), so that the medium between the space network structures is transformed into gas and the gel skeleton structure is maintained as much as possible. However, the drying method under normal pressure conditions essentially cannot avoid the appearance of the gas-liquid interface, and capillary force will be generated during the drying process, causing the unstrengthened aerogel skeleton to shrink and the pore structure to collapse, ultimately resulting in a decline in the performance of the aerogel. In addition, the existing preparation methods of silica aerogel also have problems such as easy corrosion of equipment, large solvent consumption, and high raw material costs, and it is difficult to fully meet the actual application requirements.

[0004] Therefore, it is of great significance to develop a preparation method of silica aerogel that is simple to operate, safe and environmentally friendly, and has low production cost, and to prepare a silica aerogel with more excellent performance. Summary of the Invention

[0005] The purpose of the present invention is to provide a silica aerogel and its preparation method and application.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A preparation method of a silica aerogel includes the following steps:

[0008] 1) Mix a silicon source, ethanol and water evenly, then add an acid solution to adjust the pH value to 2-5 and react to obtain a silica sol;

[0009] 2) Use ammonia water to adjust the pH value of the silica sol to 5.5-8, stand still to obtain a silica wet gel;

[0010] 3) Immerse the silica wet gel in ethanol for soaking to obtain an aged silica wet gel;

[0011] 4) Immerse the aged silica wet gel in a modifier solution made of hexamethyldisiloxane, ethanol, and hydrochloric acid, and heat and soak it to obtain a modified silica wet gel;

[0012] 5) Dry the modified silica wet gel to obtain silica aerogel.

[0013] Preferably, the molar ratio of the silicon source, cetyltrimethylammonium bromide, ethanol, and water in step 1) is 1:0.0003 - 0.05:4 - 27:5 - 29.

[0014] More preferably, the molar ratio of the silicon source, cetyltrimethylammonium bromide, ethanol, and water in step 1) is 1:0.005 - 0.03:8 - 15:10 - 15.

[0015] Preferably, the silicon source in step 1) is one of tetraethyl orthosilicate and tetraethyl orthosilicate-methyltriethoxysilane complex.

[0016] Preferably, the acid solution in step 1) is at least one of oxalic acid solution, hydrochloric acid solution, phosphoric acid solution, sulfuric acid solution, and nitric acid solution.

[0017] Preferably, the reaction in step 1) is carried out at a temperature of 30°C - 50°C for a reaction time of 0.5 h - 5 h.

[0018] Preferably, the volume ratio of the silica wet gel to ethanol in step 3) is 1:0.5 - 5.

[0019] Preferably, the soaking in step 3) is carried out at a temperature of 45°C - 60°C for a soaking time of 12 h - 72 h, and the ethanol is replaced every 12 h - 24 h.

[0020] Preferably, the volume ratio of hexamethyldisiloxane, ethanol, and hydrochloric acid in step 4) is 1:0.03 - 0.2:0.001 - 0.015.

[0021] Preferably, the volume ratio of the aged silica wet gel to the modifier solution in step 4) is 1:2 - 5.

[0022] Preferably, the heating and soaking in step 4) is carried out at a temperature of 55°C - 65°C for a soaking time of 12 h - 48 h.

[0023] Preferably, the drying in step 5) includes the following operations: first place it at room temperature for 12 h - 48 h, then place it in an oven and bake it at 55°C - 65°C for 3 h - 5 h, then at 75°C - 85°C for 1 h - 3 h, and then at 90°C - 110°C for 1 h - 3 h.

[0024] A silica aerogel prepared by the above preparation method.

[0025] Use of a silica aerogel as described above in the preparation of a fireproof and heat-insulating material, a sound-insulating material, an adsorbent or a catalyst.

[0026] The beneficial effects of the present invention are as follows: The silica aerogel of the present invention has the advantages of extremely low density, strong hydrophobicity, excellent heat-insulating performance, etc., and can be used in the fields of fireproof and heat-insulating, heat preservation, adsorbent, catalyst carrier, sound insulation, etc. Moreover, the preparation method thereof is simple to operate, safe, environmentally friendly, and has low production cost, and is suitable for large-scale industrial production and application.

[0027] Specifically:

[0028] 1) In the present invention, hexamethyldisiloxane is used as a modifier to modify the silica wet gel, and the modification efficiency of hexamethyldisiloxane is improved by means of hydrochloric acid catalysis and heating, achieving an excellent modification effect. Moreover, since the amount of hydrochloric acid in the reaction system is extremely low and controllable, it is beneficial to reduce the equipment corrosion problem during the preparation process. In addition, the surface tension of hexamethyldisiloxane is relatively low, and it can be used as the pore liquid for atmospheric pressure drying of the wet gel, enabling solvent replacement and surface modification to be carried out simultaneously, reducing the time required for the entire process. Additionally, the modifier hexamethyldisiloxane is easy to recover, greatly improving the utilization rate of the modifier;

[0029] 2) The silica aerogel of the present invention has the advantages of extremely low density (the lowest density can reach 0.08273 g / cm 3 ), strong hydrophobicity (the maximum water contact angle can reach 154.403°), excellent heat-insulating performance (the lowest thermal conductivity at room temperature can reach 0.0278 W / (m·K)), etc., and can be used in the fields of fireproof and heat-insulating, heat preservation, adsorbent, catalyst carrier, sound insulation, etc., and has a very broad application prospect;

[0030] 3) The preparation method of the silica aerogel of the present invention is simple to operate, safe, environmentally friendly, and has low production cost, and is suitable for large-scale industrial production and application. Description of the Drawings

[0031] Figure 1 Is the nitrogen adsorption-desorption isotherm of the silica aerogel in Example 1.

[0032] Figure 2 Is the pore size distribution diagram of the silica aerogel in Example 2.

[0033] Figure 3 Is the infrared spectrum diagram of the silica aerogel in Example 2.

[0034] Figure 4 Is the SEM diagram of the silica aerogel in Example 2.

[0035] Figure 5 It is the test result diagram of the water contact angle of the silica aerogel in Example 4. Specific embodiments

[0036] The present invention will be further explained and described below in conjunction with specific embodiments.

[0037] Example 1:

[0038] A silica aerogel, and its preparation method is as follows:

[0039] 1) Mix 0.04 mol of tetraethyl orthosilicate, 0.01 mol of methyltriethoxysilane, 0.0011 mol of cetyltrimethylammonium bromide, 0.5 mol of ethanol and 0.65 mol of water, stir for 2 h, then dropwise add 3 mL of oxalic acid solution with a concentration of 0.1 mol / L to adjust the pH value to 3-4, and then place it in a water bath at 45 °C and stir for 1 h to obtain a silica sol;

[0040] 2) Dropwise add 2 mL of ammonia water with a concentration of 0.5 mol / L into the stirring silica sol to adjust the pH value to 6.5, stir vigorously for 1 min, and let it stand until the sol no longer flows to obtain a silica wet gel;

[0041] 3) Immerse the silica wet gel in 200 mL of absolute ethanol, and the volume ratio of the silica wet gel to ethanol is 1:4. Soak it at 60 °C for 48 h, and replace the absolute ethanol every 24 h to obtain an aged silica wet gel;

[0042] 4) Stir 300 mL of hexamethyldisiloxane, 11.2 mL of absolute ethanol and 1.98 mL of hydrochloric acid with a mass fraction of 37% evenly to prepare a modifier solution, and then immerse the aged silica wet gel in the modifier solution and soak it at 65 °C for 24 h. The volume ratio of the aged silica wet gel to the modifier solution is 1:3 to obtain a modified silica wet gel;

[0043] 5) Place the modified silica wet gel at room temperature for 24 h, then place it in an oven and bake it at 60 °C for 4 h, then at 80 °C for 2 h, and then at 100 °C for 2 h to obtain the silica aerogel.

[0044] The nitrogen adsorption-desorption isotherm of the silica aerogel in this example is as Figure 1 shown.

[0045] From Figure 1It can be seen that the adsorption isotherm rises slowly in the relative pressure range of 0 - 0.8, and rises rapidly in the relative pressure range of 0.8 - 1, which is a typical type IV isotherm with an obvious H1-type hysteresis loop, indicating that the silica aerogel has a relatively uniform mesoporous structure.

[0046] After testing, the density of the silica aerogel in this example is 0.09415 g / cm 3 , the thermal conductivity at room temperature is 0.0278 W / (m·K), the pore volume is 4.7539 mL / g, the specific surface area is 913.1065 m 2 / g, the average pore diameter is 10.8048 nm, and the water contact angle is 146.31°.

[0047] Example 2:

[0048] A silica aerogel, and its preparation method is as follows:

[0049] 1) Mix 0.045 mol of tetraethyl orthosilicate, 0.005 mol of methyltriethoxysilane, 0.0011 mol of cetyltrimethylammonium bromide, 0.6 mol of ethanol and 0.65 mol of water, stir for 2 h, then dropwise add 3 mL of oxalic acid solution with a concentration of 0.1 mol / L to adjust the pH value to 3 - 4, and then place it in a water bath at 45 °C and stir for 1 h to obtain a silica sol;

[0050] 2) Dropwise add 2 mL of ammonia water with a concentration of 0.5 mol / L into the stirring silica sol to adjust the pH value to 6.5, stir vigorously for 1 min, and let it stand until the sol no longer flows to obtain a silica wet gel;

[0051] 3) Immerse the silica wet gel in 200 mL of absolute ethanol, and the volume ratio of the silica wet gel to ethanol is 1:4. Soak it at 60 °C for 48 h, and change the absolute ethanol every 24 h to obtain an aged silica wet gel;

[0052] 4) Stir 300 mL of hexamethyldisiloxane, 11.2 mL of absolute ethanol and 1.98 mL of hydrochloric acid with a mass fraction of 37% evenly to prepare a modification solution, and then immerse the aged silica wet gel in the modifier solution and soak it at 65 °C for 24 h. The volume ratio of the aged silica wet gel to the modifier solution is 1:3 to obtain a modified silica wet gel;

[0053] 5) Place the modified silica wet gel at room temperature for 24 h, then put it in an oven and bake it at 60 °C for 4 h, then at 80 °C for 2 h, and then at 100 °C for 2 h to obtain the silica aerogel.

[0054] The pore size distribution diagram of the silica aerogel in this example is asFigure 2 As shown, the infrared spectrum is as Figure 3 shown, and the scanning electron microscope (SEM) image is as Figure 4 shown.

[0055] From Figure 2 it can be seen that the average pore size of the silica aerogel is 11.5961 nm, the pore size distribution is relatively uniform, and it is mainly distributed within the pore size range of 20 nm.

[0056] From Figure 3 it can be seen that the O-H absorption peak of the silica aerogel is extremely small, and the C-H absorption peak is small, indicating that there are very few hydroxyl groups on the surface of the skeleton after gelation. After gelation, more hydroxyl groups condense into Si-O-Si. After modification, almost all the surface O-H is replaced by hydrophobic groups, which can effectively prevent irreversible shrinkage during drying, thus facilitating the obtaining of a less dense aerogel.

[0057] From Figure 4 it can be seen that the skeleton of the silica aerogel is relatively thick and presents a standard three-dimensional nano-network structure.

[0058] After testing, the density of the silica aerogel in this example is 0.08273 g / cm 3 , the thermal conductivity at room temperature is 0.02914 W / (m·K), the pore volume is 4.8195 mL / g, the specific surface area is 869.5044 m 2 / g, the average pore size is 11.5961 nm, and the water contact angle is 147.583°.

[0059] Example 3:

[0060] A silica aerogel, and its preparation method is as follows:

[0061] 1) Mix 0.045 mol of tetraethyl orthosilicate, 0.005 mol of methyltriethoxysilane, 0.0005 mol of cetyltrimethylammonium bromide, 0.6 mol of ethanol and 0.65 mol of water, stir for 2 h, then gradually add 3 mL of oxalic acid solution with a concentration of 0.1 mol / L to adjust the pH value to 3 - 4, and then place it in a water bath at 45 °C and stir for 1 h to obtain a silica sol;

[0062] 2) Gradually add 2 mL of ammonia water with a concentration of 0.5 mol / L to the stirring silica sol to adjust the pH value to 6.5, stir vigorously for 1 min, and let it stand until the sol no longer flows to obtain a silica wet gel;

[0063] 3) Immerse the silica wet gel in 200 mL of absolute ethanol. The volume ratio of the silica wet gel to ethanol is 1:4. Soak it at 60 °C for 48 h, and replace the absolute ethanol every 24 h to obtain the aged silica wet gel;

[0064] 4) Stir 300 mL of hexamethyldisiloxane, 11.2 mL of absolute ethanol, and 1.98 mL of 37% hydrochloric acid thoroughly to make a modifier solution. Then immerse the aged silica wet gel in the modifier solution and soak it at 65 °C for 24 h. The volume ratio of the aged silica wet gel to the modifier solution is 1:3 to obtain the modified silica wet gel;

[0065] 5) Place the modified silica wet gel at room temperature for 24 h, then put it in an oven and bake it at 60 °C for 4 h, then at 80 °C for 2 h, and then at 100 °C for 2 h to obtain the silica aerogel.

[0066] After testing, the density of the silica aerogel in this example is 0.08858 g / cm 3 , the thermal conductivity at room temperature is 0.02853 W / (m·K), the pore volume is 4.465 mL / g, the specific surface area is 866.5743 m 2 / g, the average pore diameter is 11.049 nm, and the water contact angle is 145.462°.

[0067] Example 4:

[0068] A silica aerogel, and its preparation method is as follows:

[0069] 1) Mix 0.05 mol of tetraethyl orthosilicate, 0.0011 mol of cetyltrimethylammonium bromide, 0.5 mol of ethanol, and 0.65 mol of water, stir for 2 h, then gradually add 3 mL of 0.1 mol / L oxalic acid solution to adjust the pH value to 3 - 4, and then place it in a water bath and stir at 45 °C for 1 h to obtain a silica sol;

[0070] 2) Gradually add 2 mL of 0.5 mol / L ammonia water to the stirring silica sol to adjust the pH value to 6.5, stir vigorously for 1 min, and let it stand until the sol no longer flows to obtain a silica wet gel;

[0071] 3) Immerse the silica wet gel in 200 mL of absolute ethanol. The volume ratio of the silica wet gel to ethanol is 1:4. Soak it at 60 °C for 48 h, and replace the absolute ethanol every 24 h to obtain the aged silica wet gel;

[0072] 4) 300 mL of hexamethyldisiloxane, 11.2 mL of absolute ethanol, and 1.98 mL of 37% hydrochloric acid were thoroughly stirred to make a modification solution. Then, the aged silica wet gel was immersed in the modifier solution and soaked at 65 °C for 24 h. The volume ratio of the aged silica wet gel to the modifier solution was 1:3 to obtain a modified silica wet gel.

[0073] 5) The modified silica wet gel was placed at room temperature for 24 h, then put into an oven and dried at 60 °C for 4 h, then at 80 °C for 2 h, and then at 100 °C for 2 h to obtain silica aerogel.

[0074] After testing, the density of the silica aerogel in this example was 0.1013 g / cm 3 , the thermal conductivity at room temperature was 0.02903 W / (m·K), the pore volume was 4.4392 mL / g, the specific surface area was 712.8848 m 2 / g, the average pore diameter was 13.7832 nm, and the water contact angle was 154.403° (the test result diagram of the water contact angle is as Figure 5 shown).

[0075] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A preparation method of silica aerogel, characterized in that, It includes the following steps: 1) Mix the silicon source, cetyltrimethylammonium bromide, ethanol and water evenly, then add an acid solution to adjust the pH value to 2 - 5 and carry out a reaction to obtain a silica sol; 2) Use ammonia water to adjust the pH value of the silica sol to 5.5 - 8, and let it stand to obtain a silica wet gel; 3) Immerse the silica wet gel in ethanol for soaking to obtain an aged silica wet gel; 4) Immerse the aged silica wet gel in a modifier solution made of hexamethyldisiloxane, ethanol and hydrochloric acid for heating and soaking to obtain a modified silica wet gel; 5) Dry the modified silica wet gel to obtain a silica aerogel.

2. The preparation method according to claim 1, characterized in that: In step 1), the molar ratio of the silicon source, cetyltrimethylammonium bromide, ethanol and water is 1:0.0003 - 0.05:4 - 27:5 - 29; the silicon source in step 1) is one of tetraethyl orthosilicate and tetraethyl orthosilicate-methyltriethoxysilane complex.

3. The preparation method according to claim 1 or 2, characterized in that: The reaction in step 1) is carried out under the condition of a temperature of 30°C - 50°C, and the reaction time is 0.5h - 5h.

4. The preparation method according to claim 1, characterized in that: In step 3), the volume ratio of the silica wet gel to ethanol is 1:0.5 - 5.

5. The preparation method according to claim 1 or 4, characterized in that: The soaking in step 3) is carried out under the condition of a temperature of 45°C - 60°C, the soaking time is 12h - 72h, and the ethanol is replaced every 12h - 24h.

6. The preparation method according to claim 1, wherein: In step 4), the volume ratio of hexamethyldisiloxane, ethanol and hydrochloric acid is 1:0.03 - 0.2:0.001 - 0.015; the volume ratio of the aged silica wet gel to the modifier solution in step 4) is 1:2 - 5.

7. The preparation method according to claim 1 or 6, characterized in that: The heating and soaking in step 4) is carried out under the condition of a temperature of 55°C - 65°C, and the soaking time is 12h - 48h.

8. The preparation method according to claim 1, characterized in that: The drying in step 5) includes the following operations: first place it at room temperature for 12h - 48h, then place it in an oven and bake at 55°C - 65°C for 3h - 5h, then bake at 75°C - 85°C for 1h - 3h, and then bake at 90°C - 110°C for 1h - 3h.

9. A silica aerogel, characterized in that, It is made by the preparation method described in any one of claims 1 - 8.

10. Use of a silica aerogel as described in claim 9 in the preparation of a fireproof and heat-insulating material, a sound-insulating material, an adsorbent or a catalyst.

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