Hydrophobic SiO2-Al2O3-MgO composite aerogel and preparation method thereof

Abstract

The invention discloses hydrophobic SiO2-Al2O3-MgO composite aerogel and a preparation method thereof. The preparation method comprises the following steps: respectively preparing a silicon solution, an aluminum solution and a magnesium solution, mixing the silicon solution and the aluminum solution, then adding epoxypropane and the magnesium solution, and carrying out standing gel, aging, hydrophobic modification, solvent replacement and drying to obtain the hydrophobic SiO2-Al2O3-MgO composite aerogel. According to the preparation method disclosed by the invention, excellent properties of SiO2 and MgO are combined, the composite aerogel with a high specific surface area and a microporous structure is prepared by optimizing types and proportions of raw materials and reaction conditions, and compared with a supercritical drying process, the adopted normal-pressure drying and vacuum freeze-drying processes have the outstanding advantages of low cost, high efficiency, high safety and environmental friendliness.

Description

Technical Field

[0001] The invention belongs to the technical field of aerogel preparation, and specifically relates to a hydrophobic SiO2-Al2O3-MgO composite aerogel and a preparation method thereof. Background Art

[0002] Aerogel, as a nano-scale porous material with a three-dimensional network structure, has won wide attention and praise in the scientific and industrial communities for its low density, high porosity, excellent specific surface area, outstanding adsorption performance and extremely low thermal conductivity. The gas filled in its nano-scale pore skeleton gives aerogel an extremely light quality, and its density can even be as low as one-sixth of the density of air, making it the solid substance with the lowest density known so far. The pore size of aerogel is mainly distributed between 1 and 100 nanometers, and different types of aerogels show unique differences in pore size distribution. For example, as a top-level insulating nanomaterial, silica aerogel has a pore size mostly at the micropore and mesopore scale, so it has an extremely low thermal conductivity. Alumina aerogel, with its low density, large specific surface area, high porosity and excellent structural strength, shows a wide range of application prospects in the fields of high-temperature environment insulation materials and catalyst carriers. In addition, magnesium oxide aerogel also has unique physical and chemical properties, including non-toxic, antibacterial, catalytic and other properties. It plays an important role in organic catalytic reactions such as catalyzing the dehydrogenation of methanol and formic acid, catalyzing the formation of methoxy radicals and denitrification of methane, and can also be used as a buffer material for ferroelectric materials, a secondary emission material for plasma display panels, and a humidity sensor.

[0003] Due to the diverse physical and chemical properties of different types of aerogels, they have been widely used in aerospace, building energy conservation, catalysis, energy storage and other fields. In addition, pure Al2O3 aerogel will collapse its internal skeleton and destroy its structure when it comes into contact with water. Summary of the invention

[0004] The purpose of this section is to summarize some aspects of embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the specification abstract and the invention title of this application to avoid blurring the purpose of this section, the specification abstract and the invention title, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0005] In view of the above problems and / or the problems existing in the prior art, the present invention is proposed.

[0006] Therefore, the purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for preparing a hydrophobic SiO2-Al2O3-MgO composite aerogel.

[0007] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0008] The silicon source, deionized water and alcohol solvent are stirred evenly to obtain a silicon solution;

[0009] Aluminum salt, deionized water and alcohol solvent are stirred evenly to obtain an aluminum solution;

[0010] The magnesium alkoxide, alcohol solvent and glycerol are stirred uniformly to obtain a magnesium solution;

[0011] After the silicon solution and the aluminum solution are mixed, propylene oxide and the magnesium solution are added, stirred evenly and allowed to stand to gel to obtain a silicon-aluminum-magnesium gel;

[0012] Add ethanol to the silica-aluminum-magnesium gel and let it stand for aging to obtain an aged silica-aluminum-magnesium gel;

[0013] Trimethylsilyl chloride, n-hexane and alcohol solvent are stirred evenly to obtain a hydrophobic modified liquid;

[0014] After removing ethanol from the aged magnesium-silicon-aluminum-gel, a hydrophobic modification liquid is added, and the hydrophobic magnesium-silicon-aluminum-gel is obtained by standing for modification;

[0015] After removing the modifying liquid from the hydrophobic silica-aluminum-magnesium gel, n-hexane is added for solvent replacement, and finally dried to obtain the hydrophobic SiO2-Al2O3-MgO composite aerogel;

[0016] The amount of propylene oxide added to the mixed solution of silicon solution and aluminum solution is 12.5-25 vol%, and the volume ratio of the silicon solution, aluminum solution and magnesium solution is 20-25:10-20:10-35.

[0017] As a preferred embodiment of the method for preparing the hydrophobic SiO2-Al2O3-MgO composite aerogel of the present invention, the volume ratio of the silicon source, deionized water and alcohol solvent is 6-10:1-5:9-14.

[0018] As a preferred scheme of the preparation method of the hydrophobic SiO2-Al2O3-MgO composite aerogel described in the present invention, the silicon source includes one or more of tetraethyl orthosilicate, methyl orthosilicate, methyltriethoxysilane, and water glass, and the alcohol solvent includes one or more of methanol and ethanol.

[0019] As a preferred embodiment of the method for preparing the hydrophobic SiO2-Al2O3-MgO composite aerogel of the present invention, the mass ratio of the aluminum salt, deionized water and alcohol solvent is 4-8:5-9:0.8-4.

[0020] As a preferred embodiment of the method for preparing the hydrophobic SiO2-Al2O3-MgO composite aerogel of the present invention, the aluminum salt comprises one or more of aluminum chloride hexahydrate, aluminum nitrate, and aluminum trichloride.

[0021] As a preferred embodiment of the method for preparing the hydrophobic SiO2-Al2O3-MgO composite aerogel of the present invention, the volume ratio of the magnesium alkoxide, the alcohol solvent and the glycerol is 1-5:16-24:1-3.

[0022] As a preferred embodiment of the method for preparing the hydrophobic SiO2-Al2O3-MgO composite aerogel of the present invention, the magnesium alkoxide includes one or more of magnesium methoxide, magnesium ethoxide and magnesium propoxide.

[0023] As a preferred scheme of the preparation method of the hydrophobic SiO2-Al2O3-MgO composite aerogel described in the present invention, the volume ratio of trimethylsilyl chloride, n-hexane and alcohol solvent is 1-5:2-8:1-5, and the drying method includes one of vacuum freeze drying and normal pressure drying.

[0024] As a preferred scheme of the preparation method of the hydrophobic SiO2-Al2O3-MgO composite aerogel described in the present invention, the gelling time is 10 to 15 minutes, the aging time is 4 to 5 hours, the modification time is 4 to 5 hours, and the solvent replacement time is 4 to 5 hours.

[0025] Another object of the present invention is to overcome the deficiencies in the prior art and provide a method for preparing a hydrophobic SiO2-Al2O3-MgO composite aerogel and a composite aerogel prepared therefrom.

[0026] Beneficial effects of the present invention:

[0027] The present invention combines the excellent properties of SiO2 and MgO aerogels to prepare a hydrophobic SiO2-Al2O3-MgO composite aerogel with excellent performance. The composite aerogel has good integrity, good hydrophobicity, higher specific surface area, and microporous structure. Compared with the supercritical drying process, the drying technology of the present invention has outstanding advantages such as low cost, high efficiency, high safety, and environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative labor. Among them:

[0029] Figure 1 This is a diameter diagram of the aerogel sample prepared in Example 1 of the present invention.

[0030] Figure 2 This is a thickness diagram of the aerogel sample prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0031] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification.

[0032] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0033] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0034] The raw materials used in the present invention are commercially available unless otherwise specified.

[0035] Example 1

[0036] This embodiment provides a method for preparing a hydrophobic SiO2-Al2O3-MgO composite aerogel, specifically:

[0037] (1) 9 mL of ethyl orthosilicate, 3 mL of deionized water, and 12 mL of ethanol were mixed evenly, and hydrochloric acid was added to adjust the pH value to 2 to obtain a silicon solution;

[0038] (2) 6 g of aluminum chloride hexahydrate, 6 g of deionized water, and 3.16 g of ethanol were mixed and uniformly stirred to obtain an aluminum solution;

[0039] (3) Take 5 mL of magnesium methoxide, 5 mL of methanol, and 1 mL of glycerol and stir evenly to obtain a magnesium solution;

[0040] (4) 12 mL of the silicon solution prepared in step (1) and 8 mL of the aluminum solution prepared in step (2) were mixed evenly, 9 mL of propylene oxide and 5 mL of the magnesium solution prepared in step (3) were added, stirred evenly and allowed to stand for 10 minutes to obtain a silicon-aluminum-magnesium gel;

[0041] (5) adding ethanol to the silica-aluminum-magnesium gel and aging the gel for 4 hours to obtain an aged silica-aluminum-magnesium gel, wherein the volume ratio of the silica-aluminum-magnesium gel to the ethanol is 1:2;

[0042] (6) Take 1 mL of trimethylsilyl chloride, 8 mL of n-hexane and 1 mL of ethanol and stir evenly to obtain a hydrophobic modified solution;

[0043] (7) removing ethanol from the aged silica-aluminum-magnesium gel prepared in step (5), adding the hydrophobic modification liquid prepared in step (6), and standing for modification for 4 hours to obtain a hydrophobic silica-aluminum-magnesium gel, wherein the volume ratio of the aged silica-aluminum-magnesium gel after removing ethanol to the hydrophobic modification liquid is 1:2;

[0044] (8) After removing the modifying liquid from the hydrophobic silica-aluminum-magnesium gel obtained in step (7), n-hexane is added for solvent replacement for 4 hours, wherein the volume ratio of the hydrophobic silica-aluminum-magnesium gel after removing the modifying liquid to n-hexane is 1:2, and finally drying is carried out at normal pressure, successively drying at 60°C for 4 hours, drying at 80°C for 4 hours, drying at 100°C for 4 hours, and drying at 120°C for 4 hours, to finally obtain a hydrophobic SiO2-Al2O3-MgO composite aerogel.

[0045] The sample prepared in Example 1 was tested for morphology, and the results were as follows: Figures 1-2 As shown. Figure 1 is the diameter diagram of the aerogel sample, Figure 2 is the thickness diagram of the aerogel sample.

[0046] Example 2

[0047] This embodiment provides a method for preparing a hydrophobic SiO2-Al2O3-MgO composite aerogel, specifically:

[0048] (1) 8 mL of methyl orthosilicate, 4 mL of deionized water, and 10 mL of methanol were mixed evenly, and hydrochloric acid was added to adjust the pH value to 2 to obtain a silicon solution;

[0049] (2) 5 g of aluminum nitrate, 7 g of deionized water, and 1.58 g of ethanol were mixed and uniformly obtained to obtain an aluminum solution;

[0050] (3) Take 2 mL of magnesium ethoxide, 18 mL of methanol, and 1 mL of glycerol and stir evenly to obtain a magnesium solution;

[0051] (4) 12 mL of the silicon solution prepared in step (1) and 8 mL of the aluminum solution prepared in step (2) were mixed evenly, 9 mL of propylene oxide and 5 mL of the magnesium solution prepared in step (3) were added, stirred evenly and allowed to stand for 10 minutes to obtain a silicon-aluminum-magnesium gel;

[0052] (5) adding ethanol to the silica-aluminum-magnesium gel and aging the gel for 4 hours to obtain an aged silica-aluminum-magnesium gel, wherein the volume ratio of the silica-aluminum-magnesium gel to the ethanol is 1:2;

[0053] (6) Take 2 mL of trimethylsilyl chloride, 7 mL of n-hexane and 1 mL of ethanol and stir evenly to obtain a hydrophobic modified solution;

[0054] (7) removing ethanol from the aged silica-aluminum-magnesium gel prepared in step (5), adding the hydrophobic modification liquid prepared in step (6), and standing for modification for 4 hours to obtain a hydrophobic silica-aluminum-magnesium gel, wherein the volume ratio of the aged silica-aluminum-magnesium gel after removing ethanol to the hydrophobic modification liquid is 1:2;

[0055] (8) After removing the modifying liquid from the hydrophobic silica-aluminum-magnesium gel obtained in step (7), n-hexane is added for solvent replacement for 4 hours, wherein the volume ratio of the hydrophobic silica-aluminum-magnesium gel after removing the modifying liquid to n-hexane is 1:2, and finally vacuum freeze-drying is performed, the vacuum degree is maintained at 90 Pa, and vacuum drying is performed at -60°C for 12 hours. The total freeze-drying time is 72 hours to obtain a hydrophobic SiO2-Al2O3-MgO composite aerogel.

[0056] Example 3

[0057] This embodiment provides a method for preparing a hydrophobic SiO2-Al2O3-MgO composite aerogel, specifically:

[0058] (1) 9 mL of methyltriethoxysilane, 3 mL of deionized water, and 9 mL of ethanol were mixed and uniformly stirred, and hydrochloric acid was added to adjust the pH value to 2 to obtain a silicon solution;

[0059] (2) 5 g of aluminum chloride hexahydrate, 9 g of deionized water, and 3.95 g of ethanol were mixed and uniformly stirred to obtain an aluminum solution;

[0060] (3) Take 5 mL of magnesium methoxide, 23 mL of ethanol, and 2.5 mL of glycerol and stir evenly to obtain a magnesium solution;

[0061] (4) 12 mL of the silicon solution prepared in step (1) and 8 mL of the aluminum solution prepared in step (2) were mixed evenly, 10 mL of propylene oxide and 5 mL of the magnesium solution prepared in step (3) were added, stirred evenly and allowed to stand for 10 minutes to obtain a silicon-aluminum-magnesium gel;

[0062] (5) adding ethanol to the silica-aluminum-magnesium gel and aging the gel for 4 hours to obtain an aged silica-aluminum-magnesium gel, wherein the volume ratio of the silica-aluminum-magnesium gel to the ethanol is 1:2;

[0063] (6) Take 4 mL of trimethylsilyl chloride, 7 mL of n-hexane and 5 mL of ethanol and stir evenly to obtain a hydrophobic modified solution;

[0064] (7) removing ethanol from the aged silica-aluminum-magnesium gel prepared in step (5), adding the hydrophobic modification liquid prepared in step (6), and standing for modification for 4 hours to obtain a hydrophobic silica-aluminum-magnesium gel, wherein the volume ratio of the aged silica-aluminum-magnesium gel after removing ethanol to the hydrophobic modification liquid is 1:2;

[0065] (8) After removing the modifying liquid from the hydrophobic silica-aluminum-magnesium gel obtained in step (7), n-hexane is added for solvent replacement for 4 hours, wherein the volume ratio of the hydrophobic silica-aluminum-magnesium gel after removing the modifying liquid to n-hexane is 1:2, and finally vacuum freeze-drying is performed, the vacuum degree is maintained at 90 Pa, and vacuum drying is performed at -60°C for 12 hours. The total freeze-drying time is 72 hours to obtain a hydrophobic SiO2-Al2O3-MgO composite aerogel.

[0066] Comparative Example 1

[0067] The difference between this comparative example and Example 1 is that the magnesium solution is removed, and the rest of the preparation process is the same as that of Example 1 to prepare the SiO2-Al2O3 composite aerogel of this comparative example.

[0068] Comparative Example 2

[0069] The difference between this comparative example and Example 2 is that the vacuum freeze-drying is adjusted to normal pressure drying, that is, drying at 60°C for 4 h, drying at 80°C for 4 h, drying at 100°C for 4 h, and drying at 120°C for 4 h, respectively, and the rest of the preparation process is the same as that in Example 2 to prepare the SiO2-Al2O3-MgO composite aerogel of this comparative example.

[0070] The composite aerogels prepared in Examples 1 to 3 and Comparative Examples 1 to 2 were tested for structure and performance. The results are shown in Table 1.

[0071] Table 1 Structure and properties of hydrophobic SiO2-Al2O3-MgO composite aerogel

[0072]

[0073] It can be seen from Table 1 that the hydrophobic SiO2-Al2O3-MgO composite aerogels prepared in Examples 1 to 3 of the present invention have higher specific surface area, lower density and good hydrophobicity than those in Comparative Examples 1 to 2, and Examples 1 to 3 are all in block form, while Comparative Examples 1 to 2 are powders.

[0074] Comparative Example 3

[0075] This comparative example provides a method for preparing a hydrophobic SiO2-Al2O3-MgO composite aerogel, specifically:

[0076] (1) 4 mL of ethyl orthosilicate, 8 mL of deionized water, and 16 mL of ethanol were mixed and uniformly stirred, and hydrochloric acid was added to adjust the pH value to 2 to obtain a silicon solution;

[0077] (2) 2 g of aluminum chloride hexahydrate, 10 g of deionized water, and 8 g of ethanol were mixed and uniformly stirred to obtain an aluminum solution;

[0078] (3) Take 6 mL of magnesium methoxide, 40 mL of methanol, and 5 mL of glycerol and stir evenly to obtain a magnesium solution;

[0079] (4) Take 20 mL of the silicon solution prepared in step (1) and 10 mL of the aluminum solution prepared in step (2), mix them evenly, add 20 mL of propylene oxide and 10 mL of the magnesium solution prepared in step (3), stir evenly and let stand, and it is found that no gel can be obtained.

[0080] It can be seen that if the ratio is beyond the range of the present invention, the composite aerogel cannot be prepared.

[0081] In summary, the present invention prepares silicon solution, aluminum solution and magnesium solution respectively, mixes silicon solution and aluminum solution, adds propylene oxide and magnesium solution, and obtains hydrophobic SiO2-Al2O3-MgO composite aerogel after standing gelation, aging, hydrophobic modification, solvent replacement and drying. The excellent properties of SiO2 and MgO aerogels are combined to prepare a composite aerogel with excellent performance. The composite aerogel has good integrity, higher specific surface area, lower density, good hydrophobicity and microporous structure.

[0082] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a hydrophobic SiO2-Al2O3-MgO composite aerogel, characterized in that: include, The silicon source, deionized water and alcohol solvent are stirred evenly to obtain a silicon solution; Aluminum salt, deionized water and alcohol solvent are stirred evenly to obtain an aluminum solution; The magnesium alkoxide, alcohol solvent and glycerol are stirred uniformly to obtain a magnesium solution; After the silicon solution and the aluminum solution are mixed, propylene oxide and the magnesium solution are added, stirred evenly and allowed to stand to gel to obtain a silicon-aluminum-magnesium gel; Add ethanol to the silica-aluminum-magnesium gel and let it stand for aging to obtain an aged silica-aluminum-magnesium gel; Trimethylsilyl chloride, n-hexane and alcohol solvent are stirred evenly to obtain a hydrophobic modified liquid; After removing ethanol from the aged magnesium-silicon-aluminum-gel, a hydrophobic modification liquid is added, and the hydrophobic magnesium-silicon-aluminum-gel is obtained by standing for modification; After removing the modifying liquid from the hydrophobic silica-aluminum-magnesium gel, n-hexane is added for solvent replacement, and finally dried to obtain the hydrophobic SiO2-Al2O3-MgO composite aerogel; The amount of propylene oxide added to the mixed solution of silicon solution and aluminum solution is 12.5-25 vol%, and the volume ratio of the silicon solution, aluminum solution and magnesium solution is 20-25:10-20:10-35.

2. The method for preparing the hydrophobic SiO2-Al2O3-MgO composite aerogel according to claim 1, characterized in that: The volume ratio of the silicon source, deionized water and alcohol solvent is 6-10:1-5:9-14.

3. The method for preparing the hydrophobic SiO2-Al2O3-MgO composite aerogel according to claim 2, characterized in that: The silicon source includes one or more of ethyl orthosilicate, methyl orthosilicate, methyltriethoxysilane, and water glass, and the alcohol solvent includes one or more of methanol and ethanol.

4. The method for preparing the hydrophobic SiO2-Al2O3-MgO composite aerogel according to claim 1, characterized in that: The mass ratio of the aluminum salt, deionized water and alcohol solvent is 4-8:5-9:0.8-4.

5. The method for preparing the hydrophobic SiO2-Al2O3-MgO composite aerogel according to claim 4, characterized in that: The aluminum salt includes one or more of aluminum chloride hexahydrate, aluminum nitrate, and aluminum trichloride.

6. The method for preparing the hydrophobic SiO2-Al2O3-MgO composite aerogel according to claim 1, characterized in that: The volume ratio of the magnesium alkoxide, the alcohol solvent and the glycerol is 1-5:16-24:1-3.

7. The method for preparing the hydrophobic SiO2-Al2O3-MgO composite aerogel according to claim 6, characterized in that: The magnesium alkoxide includes one or more of magnesium methoxide, magnesium ethoxide and magnesium propoxide.

8. The method for preparing the hydrophobic SiO2-Al2O3-MgO composite aerogel according to claim 1, characterized in that: The volume ratio of trimethylsilyl chloride, n-hexane and alcohol solvent is 1-5:2-8:1-5, and the drying method includes vacuum freeze drying and normal pressure drying.

9. The method for preparing the hydrophobic SiO2-Al2O3-MgO composite aerogel according to claim 1, characterized in that: The gelling time is 10 to 15 minutes, the aging time is 4 to 5 hours, the modification time is 4 to 5 hours, and the solvent replacement time is 4 to 5 hours.

10. A hydrophobic SiO2-Al2O3-MgO composite aerogel prepared by the preparation method according to any one of claims 1 to 9.

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