A transparent aerogel and its preparation method and application

Abstract

The present invention relates to the technical field of aerogel preparation, and discloses a transparent aerogel, its preparation method, and application. The method comprises: contacting a silica sol with a silicon source in the presence of a solvent and a catalyst I to undergo a first reaction to obtain a mixture I; then, in the presence of a solvent and a catalyst II, reacting the mixture I with a modifier to obtain a wet gel; and sequentially subjecting the wet gel to solvent replacement and atmospheric pressure drying to obtain a transparent aerogel. The transparent aerogel prepared using the method of the present invention has a slender skeleton and uniformly distributed pores.

Description

Technical Field

[0001] The present invention relates to the technical field of aerogel preparation, and in particular to a transparent aerogel and a preparation method and application thereof. Background Art

[0002] Silica (SiO2) aerogel is a lightweight, nanoporous, amorphous solid material with a spatial network structure composed of cross-linked colloidal particles or polymer molecules. Its pore and skeleton sizes range from 1-100nm and 1-50nm, respectively. Silica aerogel possesses many unique properties, such as high specific surface area, high porosity, high thermal insulation, and low density. These exceptional properties offer broad and promising applications in optics, thermal insulation, acoustics, catalyst supports, microelectronics, chemistry, chemical engineering, aerospace, and other fields.

[0003] Currently, the preparation of silica aerogels generally involves two steps: preparing a wet gel using the sol-gel method and drying the wet gel to obtain the aerogel. However, the existing acid-base two-step method is difficult to control the nucleation and growth rates. The resulting aerogel skeleton has large particle and pore sizes and is poorly distributed, resulting in a blue or milky white color after drying. This limits its application in optical applications.

[0004] CN105110340A, CN113247912A and CN115180629A use a supercritical drying process to prepare transparent aerogels, but the equipment cost investment is high, resulting in a low input-output ratio and a low production capacity ceiling; and although CN106629750A uses a normal pressure drying process to prepare transparent aerogels, its preparation process is cumbersome and has poor repeatability.

[0005] Therefore, there is an urgent need to provide a low-cost, reproducible method for preparing high-transparency aerogels. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for preparing aerogel with high transparency, fine skeleton and uniform pore distribution.

[0007] In order to achieve the above object, the first aspect of the present invention provides a method for preparing a transparent aerogel, the method comprising:

[0008] (1) contacting a silica sol with a silicon source in the presence of a solvent and a catalyst I to carry out a first reaction to obtain a mixture I; the silica sol does not contain a hydrophobic group, and the linear average particle size of the solid matter in the silica sol is 6-10 nm; the weight ratio of the silica sol to the silicon source is 1:0.3-1.3;

[0009] The conditions of the first reaction include: carrying out under stirring conditions, with a stirring speed of 50-300 rpm, a temperature of 5-35° C., and a time of 0.5-4 h;

[0010] (2) contacting the mixture I with a modifier in the presence of a solvent and a catalyst II to perform a second reaction to obtain a wet gel; the weight ratio of the mixture I to the catalyst II is 100:0.1-1;

[0011] (3) The wet gel is subjected to solvent replacement and normal pressure drying in sequence to obtain the transparent aerogel.

[0012] The second aspect of the present invention provides a transparent aerogel prepared by the method described in the first aspect.

[0013] The third aspect of the present invention provides a use of the transparent aerogel described in the second aspect in optical materials and thermal insulation materials.

[0014] The present invention uses a silica sol without hydrophobic groups and with a solid particle size within a specific range to react with a silicon source, and controls the reaction conditions to control the nucleation and nucleus growth rates to obtain a target sol. Then, in the presence of a catalyst and a modifier, the target sol undergoes cluster surface hydrophobization while continuing the nucleus growth reaction to form a wet gel. After solvent replacement, the wet gel is dried at normal pressure to remove the solvent, forming a transparent aerogel with a slender skeleton and uniformly distributed pores. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a macroscopic image of the transparent aerogel J1 prepared in Example 1 of the present invention;

[0016] Figure 2 is a SEM image of the transparent aerogel J1 prepared in Example 1 of the present invention;

[0017] Figure 3 is a particle size distribution diagram of the transparent aerogel J1 prepared in Example 1 of the present invention;

[0018] Figure 4 is a pore size distribution diagram of the transparent aerogel J1 prepared in Example 1 of the present invention;

[0019] Figure 5 This is a macroscopic image of the transparent aerogel DJ1 prepared in Comparative Example 1 of the present invention;

[0020] Figure 6 is a SEM image of the transparent aerogel DJ1 prepared in Comparative Example 1 of the present invention;

[0021] Figure 71 is a particle size distribution diagram of the transparent aerogel DJ1 prepared in Comparative Example 1 of the present invention;

[0022] Figure 8 This is a pore size distribution diagram of the transparent aerogel DJ1 prepared in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0023] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0024] In the present invention, the linear average particle size of the solid matter in the silica sol is measured by transmission electron microscopy (TEM).

[0025] As mentioned above, the first aspect of the present invention provides a method for preparing a transparent aerogel, the method comprising:

[0026] (1) contacting a silica sol with a silicon source in the presence of a solvent and a catalyst I to carry out a first reaction to obtain a mixture I; the silica sol does not contain a hydrophobic group, and the linear average particle size of the solid matter in the silica sol is 6-10 nm; the weight ratio of the silica sol to the silicon source is 1:0.3-1.3;

[0027] The conditions of the first reaction include: carrying out under stirring conditions, with a stirring speed of 50-300 rpm, a temperature of 5-35° C., and a time of 0.5-4 h;

[0028] (2) contacting the mixture I with a modifier in the presence of a solvent and a catalyst II to perform a second reaction to obtain a wet gel; the weight ratio of the mixture I to the catalyst II is 100:0.1-1;

[0029] (3) The wet gel is subjected to solvent replacement and normal pressure drying in sequence to obtain the transparent aerogel.

[0030] The present inventors discovered that if a silica sol containing hydrophobic groups is continuously contacted with a silicon source for a sol reaction, the pore size distribution of the gel increases significantly, significantly reducing visible light transmittance. The present inventors also discovered that if the linear average particle size of the solids in the silica sol is greater than 10 nm, the visible light transmittance decreases, resulting in a macroscopically blue aerogel appearance. If the linear average particle size of the solids in the silica sol is less than 6 nm, the mechanical properties of the aerogel skeleton are significantly reduced, and the gel skeleton is prone to collapse during atmospheric pressure drying.

[0031] It should be noted that the hydrophobic groups in the present invention are hydrophobic groups known to those skilled in the art.

[0032] It should be noted that the present invention has no particular limitation on the source of the silica sol. Commercially available silica sol can be used, or a silicon source precursor can be used for preparation; as long as it does not contain hydrophobic groups and the linear average particle size of the solid matter therein is within the aforementioned range.

[0033] According to a preferred embodiment, in step (1), the method for preparing the silica sol comprises: subjecting a silicon source precursor to a hydrolysis reaction in the presence of a solvent and a catalyst III.

[0034] Preferably, in step (1), the hydrolysis reaction is carried out under stirring conditions at a speed of 50-300 rpm, a temperature of 5-45° C., and a time of 0.5-4 h.

[0035] Preferably, in step (1), the silicon source precursor is selected from at least one of methyl orthosilicate, ethyl orthosilicate, butyl orthosilicate, isopropyl orthosilicate, sodium silicate, and potassium silicate.

[0036] Preferably, in step (1), the weight ratio of the silicon source precursor to the catalyst III is 100:0.1-1.

[0037] Preferably, in step (1), the catalyst I and the catalyst III are each independently selected from at least one of hydrochloric acid, sulfuric acid, nitric acid, oxalic acid, acetic acid, phosphoric acid, boric acid, formic acid, and citric acid.

[0038] Preferably, in step (1), the weight ratio of the silicon source to the catalyst I is 100:0.1-2.

[0039] According to another preferred embodiment, in step (1), the silicon source is selected from at least one of methyl orthosilicate, ethyl orthosilicate, butyl orthosilicate, isopropyl orthosilicate, sodium silicate, potassium silicate, methyltrimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, dimethyldimethoxysilane, vinyltriethoxysilane, propyltrimethoxysilane, propyltriethoxysilane, sodium methylsilicate, and potassium methylsilicate.

[0040] The present invention has found that when a silicon source containing a hydrophobic group is reacted with silica sol, the amount of modifier used can be significantly reduced while shortening the reaction time of the second reaction, and the hydrophobicity and high-temperature stability of the obtained aerogel are greatly improved.

[0041] Further preferably, in step (1), the silicon source is selected from at least one of methyl orthosilicate and ethyl orthosilicate.

[0042] Preferably, in step (2), before the mixture I is contacted with the modifier, the mixture I is contacted with a nano-functional agent. The present invention has found that the aerogel obtained in this preferred embodiment has a higher infrared blocking rate.

[0043] Further preferably, in step (2), the weight ratio of the mixture I to the nano-functional agent is 100:0.5-3.

[0044] More preferably, in step (2), the nanofunctional agent is selected from at least one of indium tin compounds (ITO), rare earth compounds, cesium tungsten oxide (CTO), antimony-doped tin oxide (ATO), vanadium dioxide, and nanosilver.

[0045] Preferably, in step (2), the rare earth compound is selected from at least one of cerium oxide and praseodymium oxide.

[0046] Particularly preferably, in step (2), the linear average particle size of the nano-functional agent is 10-100 nm.

[0047] Preferably, in step (2), the catalyst II is selected from at least one of aqueous ammonia, sodium hydroxide, potassium hydroxide, ammonium fluoride, ethanolamine, diethanolamine, triethanolamine, methylamine, dimethylamine, ethylamine, diethylamine, propylamine, dipropylamine, isopropanolamine, aniline, o-phenylenediamine, m-phenylenediamine, and p-phenylenediamine.

[0048] According to a preferred embodiment, in step (2), the conditions of the second reaction include: carrying out under stirring conditions, with a stirring speed of 50-300 rpm, a temperature of 5-35° C., and a time of 0.5-4 h.

[0049] Preferably, in step (2), the modifier is selected from at least one of trimethylchlorosilane, dimethyldichlorosilane, hexamethyldisilazane, and hexamethyldisiloxane. More preferably, the modifier is selected from at least one of hexamethyldisilazane and hexamethyldisiloxane. In this preferred embodiment, the obtained transparent aerogel has better visible light transmittance.

[0050] Preferably, in step (2), the weight ratio of the mixture I to the modifier is 100:3-7.

[0051] Preferably, in step (2), the weight ratio of the mixture I to the catalyst II is 100:0.1-1.

[0052] Preferably, in step (3), the solvent replacement conditions include: using an organic solvent, the number of replacements is 2-4, the interval time is 3-5 hours, and the temperature is 40-60° C. More preferably, in step (3), the organic solvent is anhydrous ethanol.

[0053] According to another preferred embodiment, in step (3), the conditions for drying at normal pressure include: a temperature of 70-90°C.

[0054] It should be noted that when the wet gel of the present invention is dried at normal pressure, there is no particular requirement for the method of providing the above temperature, as long as the drying temperature can reach 70-90° C. For example, air blast heating, infrared heating, or microwave heating can be used.

[0055] According to another particularly preferred embodiment, the solvent is deionized water.

[0056] As mentioned above, the second aspect of the present invention provides a transparent aerogel prepared by the method described in the first aspect.

[0057] Preferably, the transparent aerogel has a skeleton size of 13 nm to 23 nm and a pore size of 16 nm to 32 nm.

[0058] As mentioned above, the third aspect of the present invention provides a use of the transparent aerogel described in the second aspect in optical materials and thermal insulation materials.

[0059] The transparent aerogel in the present invention can be made into lighting glass, aerogel coating, or aerogel film as an optical material or heat insulation material.

[0060] The present invention will be described in detail below through examples.

[0061] In the following examples, unless otherwise specified, all raw materials used were commercially available.

[0062] Preparation Example 1: Preparation of Silica Sol I

[0063] In the presence of deionized water (solvent) and phosphoric acid (catalyst III), tetraethyl orthosilicate (silicon source precursor) is hydrolyzed; the weight ratio of the silicon source precursor to the catalyst III is 100:0.15;

[0064] The hydrolysis reaction conditions include: stirring at a speed of 50 rpm, a temperature of 45° C., and a time of 4 h;

[0065] Silica sol I was prepared, wherein the linear average particle size of the solid matter in the silica sol I was 6 nm.

[0066] Silica sol II: HDK® H15 hydrophobic silica sol, with a linear average particle size of 12 nm, purchased from Wacker, Germany.

[0067] Example 1

[0068] (1) In the presence of deionized water (solvent) and phosphoric acid (catalyst I), silica sol I is contacted with methyl orthosilicate (silicon source) to perform a first reaction to obtain a mixture I; the weight ratio of silica sol to silicon source is 1:0.3; and the weight ratio of silicon source to catalyst I is 100:0.1;

[0069] The first reaction was carried out under stirring conditions at a speed of 300 rpm, a temperature of 35° C., and a time of 0.5 h.

[0070] (2) in the presence of deionized water (solvent) and ammonia (catalyst II), the mixture I is reacted with hexamethyldisilazane (modifier) ​​to obtain a wet gel; the weight ratio of the mixture I, modifier, and catalyst II is 100:3:0.5;

[0071] The second reaction was carried out under stirring conditions at a speed of 50 rpm, a temperature of 35° C., and a time of 4 h.

[0072] (3) The wet gel was subjected to solvent replacement and atmospheric pressure drying in sequence. The solvent replacement conditions were as follows: using anhydrous ethanol, the number of replacements was 2, the interval time was 4 hours, and the temperature was 50°C;

[0073] The conditions for atmospheric drying are: temperature 80°C;

[0074] Transparent aerogel J1 was prepared.

[0075] Example 2

[0076] (1) In the presence of deionized water (solvent) and oxalic acid (catalyst I), silica sol I is contacted with ethyl orthosilicate (silicon source) to perform a first reaction to obtain a mixture I; the weight ratio of silica sol to silicon source is 1:1.3; and the weight ratio of silicon source to catalyst I is 100:2;

[0077] The first reaction was carried out under stirring conditions at a speed of 50 rpm, a temperature of 5° C., and a time of 4 h.

[0078] (2) in the presence of deionized water (solvent) and sodium hydroxide (catalyst II), the mixture I is reacted with hexamethyldisiloxane (modifier) ​​to obtain a wet gel; the weight ratio of the mixture I, modifier, and catalyst II is 100:7:0.5;

[0079] The second reaction was carried out under stirring conditions at a speed of 300 rpm, a temperature of 5° C., and a time of 0.5 h.

[0080] (3) The wet gel was subjected to solvent replacement and atmospheric pressure drying in sequence. The solvent replacement conditions were as follows: using anhydrous ethanol, the number of replacements was 2, the interval time was 4 h, and the temperature was 60°C;

[0081] Drying conditions are: temperature 80°C;

[0082] Transparent aerogel J2 was prepared.

[0083] Example 3

[0084] This example is carried out in a similar manner to Example 1, except that:

[0085] In step (2), the modifier was adjusted to an equal weight of dimethyldichlorosilane, and the amount of ammonia water was adjusted so that the weight ratio of the mixture I to the catalyst II was 100:1. The other conditions were the same as those in Example 1, and a transparent aerogel J3 was prepared.

[0086] Example 4

[0087] This embodiment is carried out in a similar manner to that of embodiment 1, except that:

[0088] In step (2), before the mixture I is contacted with the modifier, the mixture I is contacted with an indium tin compound (nanofunctional agent), and the weight ratio of the mixture I to the nanofunctional agent is 100:0.5. The other conditions are the same as those in Example 1, and a transparent aerogel J4 is prepared.

[0089] Comparative Example 1

[0090] Tetraethyl orthosilicate, water, ethanol, and hydrochloric acid are mixed in proportion to generate a sol reaction, thereby obtaining a sol; wherein the weight ratio of tetraethyl orthosilicate, water, ethanol, and hydrochloric acid is 100:40:90:0.8;

[0091] The sol reaction conditions are as follows: under stirring conditions, with a stirring speed of 50 rpm, a temperature of 30°C, and a time of 3 h;

[0092] Then, ammonia water is added to the above reaction system to cause a gelation reaction to obtain a wet gel; wherein the weight ratio of ethyl orthosilicate to ammonia water is 100:0.16;

[0093] The gelation reaction was carried out under stirring conditions with a stirring speed of 50 rpm and a temperature of 30°C;

[0094] The wet gel was hydrophobically modified with hexamethyldisilazane and then solvent replaced with anhydrous ethanol and dried at normal pressure. The replacement times were 2, the interval time was 4 h, and the temperature was 60°C. The normal pressure drying temperature was 80°C to prepare a transparent aerogel DJ1.

[0095] Comparative Example 2

[0096] This comparative example was carried out in a similar manner to Example 1, except that:

[0097] In step (1), silica sol I was replaced by silica sol II of equal weight, and the other conditions were the same as those in Example 1 to obtain transparent aerogel DJ2.

[0098] Comparative Example 3

[0099] This comparative example was carried out in a similar manner to Example 1, except that:

[0100] In step (1), the amount of silicon source was adjusted so that the weight ratio of silica sol to silicon source was 1:2. The other conditions were the same as those in Example 1, and a transparent aerogel DJ3 was obtained.

[0101] Test Case

[0102] The transparent aerogels prepared in the examples and comparative examples were tested according to the following methods, specifically as follows. The test results are shown in Table 1:

[0103] Skeleton size and pore size: The crystal microstructure of the aerogel sample was photographed using a scanning electron microscope and the data was analyzed using Nano Measure software.

[0104] Table 1

[0105] Skeleton size (nm) Pore ​​size (nm) Example 1 18.31 26.57 Example 2 20.08 30.17 Example 3 17.69 21.97 Example 4 17.94 24.43 Comparative Example 1 25.05 32.81 Comparative Example 2 29.75 37.02 Comparative Example 3 31.31 36.29

[0106] It can be seen from the results in Table 1 that the transparent aerogel prepared by the method provided by the present invention has a slender skeleton and basically consistent pore sizes.

[0107] The macroscopic images, SEM images, particle size distribution images, and pore size distribution images of the transparent aerogels prepared in the remaining examples of the present invention are similar to those of the transparent aerogel JI prepared in Example 1. The macroscopic images of the transparent aerogel JI are exemplarily provided in the present invention ( Figure 1 )、SEM images( Figure 2 )、Particle size distribution diagram( Figure 3 )、pore size distribution diagram( Figure 4 ).

[0108] like Figure 1As shown, the transparent aerogel J1 prepared by the method provided by the present invention has high transparency, while the aerogel DJ1 prepared by the method in Comparative Example 1 has obvious blue light (as shown in FIG. Figure 5 As shown in Figure 3, the light transmittance of the visible aerogel DJ1 is significantly lower than that of the transparent aerogel J1.

[0109] from Figure 2 、 Figure 3 and Figure 4 It can be seen from the figure that the transparent aerogel J1 prepared by the method provided by the present invention has uniform and small particle size and basically consistent pore size. Figure 6 、 Figure 7 and Figure 8 It can be seen that the particle size of the aerogel DJ1 prepared by the method in Comparative Example 1 is not as uniform and fine as that of the transparent aerogel J1, and the pore size consistency is also poor.

[0110] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A method for preparing a transparent aerogel, characterized in that: The method includes: (1) contacting a silica sol with a silicon source in the presence of a solvent and a catalyst I to carry out a first reaction to obtain a mixture I; the silica sol does not contain a hydrophobic group, and the linear average particle size of the solid matter in the silica sol is 6-10 nm; the weight ratio of the silica sol to the silicon source is 1:0.3-1.3; The conditions of the first reaction include: carrying out under stirring conditions, with a stirring speed of 50-300 rpm, a temperature of 5-35° C., and a time of 0.5-4 h; (2) contacting the mixture I with a modifier in the presence of a solvent and a catalyst II to perform a second reaction to obtain a wet gel; the weight ratio of the mixture I to the catalyst II is 100:0.1-1; (3) The wet gel is subjected to solvent replacement and normal pressure drying in sequence to obtain the transparent aerogel.

2. The method according to claim 1, wherein In step (1), the preparation method of the silica sol includes: subjecting a silicon source precursor to a hydrolysis reaction in the presence of a solvent and a catalyst III.

3. The method according to claim 2, wherein: In step (1), the hydrolysis reaction conditions include: carrying out under stirring conditions, with a stirring speed of 50-300 rpm, a temperature of 5-45° C., and a time of 0.5-4 h; and / or, In step (1), the silicon source precursor is selected from at least one of methyl orthosilicate, ethyl orthosilicate, butyl orthosilicate, isopropyl orthosilicate, sodium silicate, and potassium silicate.

4. The method according to claim 2, wherein: In step (1), the catalyst I and the catalyst III are each independently selected from at least one of hydrochloric acid, sulfuric acid, nitric acid, oxalic acid, acetic acid, phosphoric acid, boric acid, formic acid, and citric acid; and / or, In step (1), the silicon source is selected from at least one of methyl orthosilicate, ethyl orthosilicate, butyl orthosilicate, isopropyl orthosilicate, sodium silicate, potassium silicate, methyltrimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, dimethyldimethoxysilane, vinyltriethoxysilane, propyltrimethoxysilane, propyltriethoxysilane, sodium methylsilicate, and potassium methylsilicate.

5. The method according to any one of claims 1 to 4, wherein: In step (2), before the mixture I is contacted with the modifier, the mixture I is contacted with a nano-functional agent.

6. The method according to claim 5, wherein: In step (2), the weight ratio of the mixture I to the nano-functional agent is 100:0.5-3; and / or, In step (2), the nano-functional agent is selected from at least one of indium tin compounds, rare earth compounds, cesium tungsten oxide, antimony-doped tin oxide, vanadium dioxide, and nano-silver; and / or, In step (2), the linear average particle size of the nano-functional agent is 10-100 nm.

7. The method according to any one of claims 1 to 4, wherein: In step (2), the catalyst II is selected from at least one of ammonia water, sodium hydroxide, potassium hydroxide, ammonium fluoride, ethanolamine, diethanolamine, triethanolamine, methylamine, dimethylamine, ethylamine, diethylamine, propylamine, dipropylamine, isopropanolamine, aniline, o-phenylenediamine, m-phenylenediamine, and p-phenylenediamine; and / or, In step (2), the conditions of the second reaction include: carrying out under stirring conditions, with a stirring speed of 50-300 rpm, a temperature of 5-35° C., and a time of 0.5-4 h.

8. The method according to any one of claims 1 to 4, wherein: In step (2), the modifier is selected from at least one of trimethylchlorosilane, dimethyldichlorosilane, hexamethyldisilazane, and hexamethyldisiloxane; and / or, In step (2), the weight ratio of the mixture I to the modifier is 100:3-7.

9. The method according to any one of claims 1 to 4, wherein: In step (3), the solvent replacement conditions include: using an organic solvent, the number of replacements is 2-4, the interval time is 3-5 hours, and the temperature is 40-60°C; and / or, In step (3), the conditions for normal pressure drying include: a temperature of 70-90°C.

10. A transparent aerogel prepared by the method according to any one of claims 1 to 9.

11. The transparent aerogel according to claim 10, wherein The transparent aerogel has a skeleton size of 13nm-23nm and a pore size of 16nm-32nm.

12. Use of the transparent aerogel according to claim 10 or 11 in optical materials and thermal insulation materials.

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