Hydrophobic silicon oxide aerogel and preparation method thereof

Abstract

The invention relates to the technical field of chemical material preparation, in particular to hydrophobic silicon oxide aerogel and a preparation method thereof. The preparation method comprises the following steps: preparing a silicate aqueous solution, and carrying out ion exchange on the silicate aqueous solution through ion exchange resin until the pH value of the solution is 6.0-7.5 to obtain silica sol; mixing the silica sol with tert-butyl alcohol to obtain mixed sol, and aging to obtain gel; mixing a tert-butyl alcohol aqueous solution with a modifier to obtain a modified solution; mixing the gel with the modified liquid, and carrying out a modification reaction to obtain modified gel; the modified gel is subjected to freeze drying, and the hydrophobic silicon oxide aerogel is obtained. According to the preparation method, cheap silicate is used as a raw material, the hydrophobic silicon oxide aerogel is prepared through a freeze-drying method, the gel is directly modified under the aqueous condition, solvent replacement is not needed, and the freeze-drying time is remarkably shortened and the drying efficiency is improved while the mesoporous structure of the gel is maintained.

Description

Technical Field

[0001] The invention relates to the technical field of chemical material preparation, and in particular to a hydrophobic silicon oxide aerogel and a preparation method thereof. Background Art

[0002] Silica aerogel is a highly porous mesoporous material with ultra-low density, high porosity, high specific surface area and low thermal conductivity. Due to these excellent properties, silica aerogel has great application potential in various fields such as thermal insulation, catalysis and adsorption. At present, the industrial production of silica aerogel is usually prepared by supercritical drying using organic silicon such as tetraethyl orthosilicate (TEOS) and tetramethyl orthosilicate (TMOS) as raw materials. The high raw material cost, huge equipment investment and dangerous and complicated manufacturing process limit its wide industrial application.

[0003] In order to reduce costs, a preparation method using cheap sodium silicate as a precursor has been developed in recent years. However, in order to promote its hydrolysis gel process, a catalyst is often introduced. The addition of additional impurities and the sodium ions themselves will affect the performance of the product. Another way to reduce production costs is to change the drying method, such as atmospheric pressure drying, freeze drying, etc. Atmospheric pressure drying has attracted widespread attention in recent years due to its simple operation and low cost. However, in order to maintain the mesoporous skeleton structure of the gel, a large amount of solvent replacement and surface methylation modification of the gel is required to reduce the shrinkage effect of capillary forces during the drying process. This process still requires the use of a large amount of organic solvents.

[0004] At present, hydrophobic silica aerogels with inorganic silicon sources as raw materials are mostly modified by silane coupling agents and then dried at normal pressure or supercritically, or hydrophilic silica is prepared by supercritical drying and then modified by chemical vapor phase to make it hydrophobic. In the article published in Journal of Non-Crystalline Solids, 481 (2018) 267-275, Zhi Li et al. used sodium silicate as a precursor, synthesized alcohol gel by two-step acid-base catalysis and sol-gel process, and then prepared hydrophobic silica aerogel by aging, solvent exchange, surface modification and normal pressure drying. The patent with publication number CN111484021A discloses a preparation method of hydrophilic silica aerogel prepared by supercritical drying of carbon dioxide with sodium silicate as raw material, and then modified by silane modifier to obtain a hydrophobic product. Both methods have the disadvantages of solvent replacement, long cycle, and use of a large amount of organic solvent. In contrast, the freeze-drying process is simple and can be carried out under aqueous conditions. The principle is to convert the porous liquid in the gel into a solid, and then remove the solid by sublimation, avoiding the destruction of the pore structure by surface tension during the gas-liquid phase change. However, due to the high expansion coefficient of pure water in the nanoscale space, ice will grow and expand during the freezing stage, destroying the skeleton structure inside the gel and causing the mesoporous structure of the gel to collapse. Only silica xerogel with a microporous structure can be obtained by freeze-drying. Summary of the invention

[0005] The present invention aims to solve at least one of the technical problems in the related art to a certain extent. To this end, the present invention provides a hydrophobic silica aerogel and a preparation method thereof. The preparation method uses cheap silicate as a raw material, and prepares a silica aerogel with excellent hydrophobic properties by freeze-drying. The preparation method directly modifies the gel under aqueous conditions without solvent replacement, and while maintaining the mesoporous structure of the gel, significantly shortens the freeze-drying time and improves the drying efficiency. The preparation method has low raw material cost, simple and environmentally friendly process, short preparation cycle, and is conducive to industrial-scale production.

[0006] To this end, the first aspect of the present invention provides a method for preparing a hydrophobic silica aerogel, comprising the following steps:

[0007] A silicate aqueous solution is prepared, and ion exchange is performed on the silicate aqueous solution through an ion exchange resin until the pH value of the solution is 6.0 to 7.5 to obtain a silica sol;

[0008] The silica sol is mixed with tert-butyl alcohol to obtain a mixed sol, and the mixed sol is aged to obtain a gel;

[0009] The tert-butyl alcohol aqueous solution and the modifier are mixed to obtain a modified liquid;

[0010] The gel and the modified liquid are mixed to perform a modification reaction to obtain a modified gel;

[0011] The modified gel is freeze-dried to obtain the hydrophobic silica aerogel.

[0012] The preparation method provided by the present invention uses cheap silicate as a raw material, and obtains a silicon oxide aerogel with excellent hydrophobic properties by a freeze-drying method. The preparation method directly modifies the gel under aqueous conditions without the need for solvent replacement, and while maintaining the mesoporous structure of the gel, significantly shortens the freeze-drying time and improves the drying efficiency.

[0013] According to an embodiment of the present invention, the content of silicate in the silicate aqueous solution is 0.45 mol / L to 0.66 mol / L.

[0014] According to an embodiment of the present invention, the silicate in the silicate aqueous solution includes at least one of sodium silicate, potassium silicate and hydrates thereof.

[0015] According to an embodiment of the present invention, the ion exchange resin includes at least one of a strongly acidic cation exchange resin and a weakly acidic cation exchange resin.

[0016] According to an embodiment of the present invention, the content of tert-butyl alcohol in the mixed sol is 10 wt % to 20 wt %.

[0017] According to an embodiment of the present invention, the aging time is 24 hours to 72 hours.

[0018] According to an embodiment of the present invention, the preparation method further comprises: allowing the mixed sol to stand and age to obtain the gel.

[0019] According to an embodiment of the present invention, the standing time is 2 hours to 4 hours.

[0020] According to an embodiment of the present invention, the content of tert-butanol in the tert-butanol aqueous solution is the same as the content of tert-butanol in the mixed sol.

[0021] According to an embodiment of the present invention, the volume ratio of the modifier to the tert-butyl alcohol aqueous solution is (1.5-4.0):100.

[0022] According to an embodiment of the present invention, the modifier is hexamethyldisilazane.

[0023] According to an embodiment of the present invention, the gel and the modified liquid are mixed in a volume ratio of 1:1.

[0024] According to an embodiment of the present invention, the temperature of the modification reaction is 40°C to 60°C.

[0025] According to an embodiment of the present invention, the modification reaction time is 2h to 8h.

[0026] According to an embodiment of the present invention, the freezing temperature and / or the drying temperature in the freeze-drying is -60°C to -20°C.

[0027] According to an embodiment of the present invention, the freezing time in the freeze-drying is 2 hours to 6 hours.

[0028] According to an embodiment of the present invention, the drying time in the freeze-drying is 20 hours to 40 hours.

[0029] According to an embodiment of the present invention, the drying process in the freeze-drying is carried out under vacuum conditions, and the vacuum degree is <5Pa.

[0030] The second aspect of the present invention provides a hydrophobic silica aerogel obtained according to the preparation method described in the first aspect.

[0031] The hydrophobic silicon oxide aerogel can be prepared by the preparation method provided by the present invention, and has the advantages of high hydrophobicity, low apparent density, high porosity, high specific surface area, high pore volume and the like.

[0032] According to an embodiment of the present invention, the contact angle between the hydrophobic silica aerogel and water is greater than 140°.

[0033] According to an embodiment of the present invention, the apparent density of the hydrophobic silica aerogel is 0.04 g / cm 3 ~0.05g / cm 3 .

[0034] According to an embodiment of the present invention, the porosity of the hydrophobic silica aerogel is 97% to 98%.

[0035] According to an embodiment of the present invention, the specific surface area of ​​the hydrophobic silica aerogel is 600 m 2 / g~900m 2 / g.

[0036] According to an embodiment of the present invention, the pore volume of the hydrophobic silica aerogel is 2.5 cm 3 / g~5.5cm 3 / g.

[0037] According to an embodiment of the present invention, the average pore size of the hydrophobic silica aerogel is 10 nm to 25 nm.

[0038] According to an embodiment of the present invention, the pore size distribution range of the hydrophobic silica aerogel is 1 nm to 70 nm.

[0039] The beneficial effects of the present invention compared to the prior art are as follows:

[0040] (1) Tert-butyl alcohol acts as an antisolvent in the mixed sol to promote sol gelation without the need for additional catalyst;

[0041] (2) By controlling the proportion of tert-butyl alcohol in the mixed sol, the mesopore size distribution of the aerogel can be adjusted, without the need to perform a large amount of solvent replacement on the gel in order to maintain the mesoporous skeleton structure of the gel as in the prior art, thereby saving a large amount of organic solvent, reducing costs, and simplifying the preparation process;

[0042] (3) In the prior art, the modification of silica gel is usually carried out under non-polar solvent conditions, for example, the gel is modified after the modifier is mixed with n-hexane, and then the subsequent drying steps are carried out. However, there are few reports on direct modification in aqueous solution. Non-polar solvent systems such as n-hexane require that the liquid in the gel pores be replaced with a non-polar solvent before modification, which takes a long replacement time and a large amount of solvent. Moreover, non-polar solvents such as n-hexane require a very low freezing temperature as freeze-drying media, resulting in high energy consumption for freeze-drying. In order to improve the freeze-drying effect, the n-hexane needs to be replaced with a polar solvent after modification, which consumes time and solvent. The preparation method provided by the present invention directly mixes the aged gel with the modifying liquid under aqueous solvent conditions, and can complete the hydrophobic modification without changing the concentration of the freezing solvent in the subsequent freeze-drying process, without the need for solvent replacement. In addition, the present invention controls the volume content of the modifier in the modifying liquid so that the modification reaction does not destroy the mesoporous structure of the gel, and the modification process significantly improves the drying efficiency of freeze-drying and shortens the drying cycle.

[0043] (4) The hydrophobic silica aerogel provided by the present invention has excellent performance, high hydrophobicity, low apparent density, high porosity, high specific surface area, high pore volume, and uniform pore size distribution;

[0044] (5) The preparation method provided by the present invention has a simple production process, a short cycle, is easy to operate, consumes less organic solvent in the production process, generates less waste liquid, and is suitable for industrial production and application.

[0045] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0047] Figure 1 A physical picture of the hydrophobic silicon oxide aerogel prepared in Example 1 of the present invention is shown;

[0048] Figure 2The transmission electron microscope image of the hydrophobic silicon oxide aerogel prepared in Example 1 of the present invention is shown;

[0049] Figure 3 The hydrophobic angle test diagram of the hydrophobic silicon oxide aerogel prepared in Example 1 of the present invention is shown. DETAILED DESCRIPTION

[0050] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be understood as limiting the present invention.

[0051] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. Further, in the description of the present invention, unless otherwise specified, the meaning of "plurality" is two or more.

[0052] The endpoints and any values ​​of the ranges disclosed in this article 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 endpoint values ​​of each range, the endpoint values ​​of each range and the 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 as specifically disclosed in this article.

[0053] In order to make the present invention more easily understood, certain technical and scientific terms are specifically defined below. Unless otherwise clearly defined elsewhere in this document, all other technical and scientific terms used herein have the meanings commonly understood by those skilled in the art to which the present invention belongs.

[0054] In this document, the terms “include” or “comprising” are open expressions, that is, including the contents specified in the present invention but not excluding other contents.

[0055] As used herein, the terms "optionally", "optional" or "optionally" generally mean that the subsequently described event or circumstance may but need not occur, and that the description includes instances where the event or circumstance occurs and instances where it does not.

[0056] According to an embodiment of the present invention, a first aspect of the present invention provides a method for preparing a hydrophobic silica aerogel, comprising the following steps:

[0057] (1) A silicate aqueous solution is prepared, and ion exchange is performed on the silicate aqueous solution by using an ion exchange resin until the pH value of the solution is 6.0 to 7.5 to obtain a silica sol.

[0058] Specifically, the silica sol does not contain cations (such as sodium ions) in the silicate, as all cations have been removed by ion exchange resin.

[0059] According to a specific embodiment of the present invention, the content of silicate in the silicate aqueous solution is 0.45 mol / L to 0.66 mol / L. As some specific examples, the content of silicate in the silicate aqueous solution may be 0.45 mol / L, 0.5 mol / L, 0.55 mol / L, 0.6 mol / L, 0.66 mol / L, etc.

[0060] According to a specific embodiment of the present invention, the type of silicate in the silicate aqueous solution is not particularly limited. As some specific examples, the silicate in the silicate aqueous solution includes at least one of sodium silicate, potassium silicate and their hydrates. Specifically, the type of the hydrate is not particularly limited, for example, it can be sodium silicate nonahydrate. The silicate aqueous solution can also be a solution obtained by leaching rice husk ash with sodium hydroxide or potassium hydroxide solution to achieve resource utilization.

[0061] According to a specific embodiment of the present invention, the type of the ion exchange resin is not particularly limited. As some specific examples, the ion exchange resin includes at least one of a strongly acidic cation exchange resin and a weakly acidic cation exchange resin.

[0062] (2) The silica sol is mixed with tert-butyl alcohol to obtain a mixed sol, and the mixed sol is aged to obtain a gel.

[0063] Tert-butyl alcohol as an antisolvent can promote the gelation process of the mixed sol without the need for additional catalyst.

[0064] Specifically, the method for determining the gel in the present invention is: if the gel does not flow when tilted at 45 degrees, it is a gel.

[0065] According to a specific embodiment of the present invention, the content of tert-butanol in the mixed sol is 10wt% to 20wt%. As some specific examples, the content of tert-butanol in the mixed sol may be 10wt%, 15wt%, 20wt% and the like.

[0066] By controlling the proportion of tert-butanol in the mixed sol, the mesopore size distribution of the aerogel can be adjusted without the need for a large amount of solvent replacement of the gel in order to maintain the mesoporous skeleton structure of the gel as in the prior art, thereby saving a large amount of organic solvent, reducing costs and simplifying the preparation process.

[0067] According to a specific embodiment of the present invention, the aging time is 24 hours to 72 hours. As some specific examples, the aging time may be 24 hours, 48 ​​hours, 72 hours, etc.

[0068] According to a specific embodiment of the present invention, the preparation method further comprises: allowing the mixed sol to stand and age to obtain the gel.

[0069] According to a specific embodiment of the present invention, the standing time is 2 hours to 4 hours. As some specific examples, the standing time may be 2 hours, 3 hours, 4 hours, etc.

[0070] (3) The tert-butyl alcohol aqueous solution and the modifier are mixed to obtain a modified solution.

[0071] According to a specific embodiment of the present invention, the content of tert-butanol in the tert-butanol aqueous solution is the same as the content of tert-butanol in the mixed sol. Controlling the content of tert-butanol in both to be the same can keep the content of tert-butanol in the gel unchanged, and no subsequent solvent replacement is required.

[0072] According to a specific embodiment of the present invention, the volume ratio of the modifier to the tert-butanol aqueous solution is (1.5-4.0):100. As some specific examples, the volume ratio of the modifier to the tert-butanol aqueous solution may be 1.5:100, 2.0:100, 2.5:100, 3.0:100, 3.5:100, 4.0:100, etc.

[0073] According to a specific embodiment of the present invention, the type of the modifier is not particularly limited. As some specific examples, the modifier is hexamethyldisilazane.

[0074] (4) The gel and the modifying liquid are mixed to carry out a modification reaction to obtain a modified gel.

[0075] The preparation method provided by the present invention directly mixes the aged gel with the modifying liquid under aqueous conditions for reaction, and can complete the hydrophobic modification without changing the concentration of the freezing solvent in the subsequent freeze-drying process, and there is no need for solvent replacement; in addition, the present invention controls the volume content of the modifier in the modifying liquid so that the modification reaction does not destroy the mesoporous structure of the gel, and the modification process significantly improves the drying efficiency of freeze-drying and shortens the drying cycle.

[0076] According to a specific embodiment of the present invention, the gel and the modified liquid are mixed in a volume ratio of 1:1.

[0077] According to a specific embodiment of the present invention, the temperature of the modification reaction is 40°C to 60°C. As some specific examples, the temperature of the modification reaction may be 40°C, 50°C, 60°C, etc.

[0078] According to a specific embodiment of the present invention, the modification reaction time is 2 hours to 8 hours. As some specific examples, the modification reaction time can be 2 hours, 4 hours, 6 hours, 8 hours, etc.

[0079] (5) freeze-drying the modified gel to obtain the hydrophobic silica aerogel.

[0080] According to a specific embodiment of the present invention, the freezing temperature and / or drying temperature in the freeze-drying is -60°C to -20°C. As some specific examples, the freezing temperature and / or drying temperature in the freeze-drying may be -60°C, -50°C, -40°C, -30°C, -20°C, etc.

[0081] According to a specific embodiment of the present invention, the freezing time in the freeze-drying process is 2 hours to 6 hours. As some specific examples, the freezing time in the freeze-drying process may be 2 hours, 4 hours, 6 hours, etc.

[0082] According to a specific embodiment of the present invention, the drying time in the freeze-drying process is 20 hours to 40 hours. As some specific examples, the drying time in the freeze-drying process may be 20 hours, 30 hours, 40 hours, etc.

[0083] According to a specific embodiment of the present invention, the drying process in the freeze-drying is carried out under vacuum conditions, and the vacuum degree is <5Pa.

[0084] According to a specific embodiment of the present invention, the preparation method further comprises: filtering, washing, and freeze-drying the modified gel to obtain the hydrophobic silica aerogel.

[0085] According to a specific embodiment of the present invention, the washing detergent is an aqueous solution of tert-butanol, and its concentration is the same as the concentration of tert-butanol in the mixed sol.

[0086] According to an embodiment of the present invention, a second aspect of the present invention provides a hydrophobic silica aerogel obtained according to the preparation method described in the first aspect.

[0087] The hydrophobic silicon oxide aerogel can be prepared by the preparation method provided by the present invention, and has the advantages of high hydrophobicity, low apparent density, high porosity, high specific surface area, high pore volume and the like.

[0088] According to a specific embodiment of the present invention, the contact angle between the hydrophobic silica aerogel and water is greater than 140°. As some specific examples, the contact angle between the hydrophobic silica aerogel and water may be 141°, 142°, 143°, 144°, etc.

[0089] According to a specific embodiment of the present invention, the apparent density of the hydrophobic silica aerogel is 0.04 g / cm 3 ~0.05g / cm 3 As some specific examples, the apparent density of the hydrophobic silica aerogel may be 0.04 g / cm 3, 0.045g / cm 3 , 0.05g / cm 3 wait.

[0090] According to a specific embodiment of the present invention, the porosity of the hydrophobic silica aerogel is 97% to 98%. As some specific examples, the porosity of the hydrophobic silica aerogel may be 97%, 97.5%, 98%, etc.

[0091] According to a specific embodiment of the present invention, the specific surface area of ​​the hydrophobic silica aerogel is 600 m 2 / g~900m 2 / g, as some specific examples, the specific surface area of ​​the hydrophobic silica aerogel may be 600m 2 / g、700m 2 / g、800m 2 / g、900m 2 / g, etc.

[0092] According to a specific embodiment of the present invention, the pore volume of the hydrophobic silica aerogel is 2.5 cm 3 / g~5.5cm 3 / g, as some specific examples, the pore volume of the hydrophobic silica aerogel may be 2.5cm 3 / g, 3.5cm 3 / g, 4.5cm 3 / g, 5.5cm 3 / g, etc.

[0093] According to a specific embodiment of the present invention, the average pore size of the hydrophobic silica aerogel is 10 nm to 25 nm. As some specific examples, the average pore size of the hydrophobic silica aerogel may be 10 nm, 15 nm, 20 nm, 25 nm, etc.

[0094] According to a specific embodiment of the present invention, the pore size distribution range of the hydrophobic silica aerogel is 1nm to 70nm. As some specific examples, the pore size distribution range of the hydrophobic silica aerogel may be 1nm, 5nm, 10nm, 20nm, 50nm, 70nm, etc.

[0095] The scheme of the present invention will be explained below in conjunction with the embodiments. It will be appreciated by those skilled in the art that the following embodiments are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. Where specific techniques or conditions are not indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used are not indicated by the manufacturer and are all conventional products that can be obtained commercially.

[0096] Example 1

[0097] This embodiment provides a hydrophobic silicon oxide aerogel and a preparation method thereof, wherein the preparation method comprises the following steps:

[0098] Weigh Na 2 SiO 3 9H 2 O was added into deionized water, and a magnetic stirrer was added to prepare a 0.64 mol / L sodium silicate solution;

[0099] Add H-type weakly acidic cation exchange resin intermittently to the sodium silicate solution while stirring, use a pH meter to detect the pH change of the solution, adjust the pH of the solution to about 7, and use a Buchner funnel to vacuum filter and separate to obtain the silica sol after ion exchange;

[0100] Take 100 mL of silica sol in a beaker, add tert-butanol, and make the content of tert-butanol be 18 wt %, stir evenly, seal, let stand at room temperature for 2 hours, then continue to seal and age at room temperature for 24 hours to obtain a gel;

[0101] A tert-butanol aqueous solution with a mass fraction of 18 wt % was prepared, hexamethyldisilazane (HMDS) was added, and the volume ratio of HMDS to the tert-butanol aqueous solution was 1.5:100, and the mixture was mixed uniformly to obtain a modified solution;

[0102] 100 mL of the modified liquid and 100 mL of the gel were mixed, sealed and subjected to modification reaction at 50° C. for 6 h to obtain a modified gel, which was washed three times with an 18 wt % tert-butyl alcohol aqueous solution to remove residual modified liquid;

[0103] The modified gel was frozen in a freeze dryer (cold trap temperature -60°C to -20°C) for 2 hours, and vacuum dried at -40°C (vacuum degree <5 Pa) for 20 hours to obtain a light blue hydrophobic silica aerogel. Figure 1 As shown in the transmission electron microscope (TEM) image Figure 2 shown.

[0104] The contact angle of the hydrophobic silica aerogel with water is 143° (hydrophobic angle test diagram as shown in FIG. Figure 3 The apparent density is 0.045 g / cm 3 The porosity is 97.9% and the specific surface area is 873m 2 / g, pore volume is 5.3cm 3 / g, the average pore size is 18.0nm, and the pore size distribution range is 1nm to 70nm.

[0105] Example 2

[0106] This embodiment provides a hydrophobic silicon oxide aerogel and a preparation method thereof, wherein the preparation method comprises the following steps:

[0107] Weigh Na 2 SiO 3 9H 2 O was added into deionized water, and a magnetic stirrer was added to prepare a 0.45 mol / L sodium silicate solution;

[0108] Add H-type weakly acidic cation exchange resin intermittently to the sodium silicate solution while stirring, use a pH meter to detect the pH change of the solution, adjust the pH of the solution to about 6, and use a Buchner funnel to vacuum filter and separate to obtain the silica sol after ion exchange;

[0109] Take 100 mL of silica sol in a beaker, add tert-butanol, and make the content of tert-butanol be 10 wt %, stir evenly, seal, and let stand at room temperature for 2 hours, then continue to seal and age at room temperature for 24 hours to obtain a gel;

[0110] A 10 wt % tert-butanol aqueous solution was prepared, hexamethyldisilazane (HMDS) was added, and the volume ratio of HMDS to the tert-butanol aqueous solution was 3:100, and the mixture was mixed uniformly to obtain a modified solution;

[0111] 100 mL of the modified liquid and 100 mL of the gel were mixed, sealed and subjected to modification reaction at 40° C. for 8 h to obtain a modified gel, which was washed three times with a 10 wt % tert-butyl alcohol aqueous solution to remove residual modified liquid;

[0112] The modified gel was frozen in a freeze dryer (cold trap temperature -60°C to -20°C) for 2 hours, and vacuum dried at -40°C (vacuum degree <5 Pa) for 20 hours to obtain a hydrophobic silica aerogel.

[0113] The contact angle of the hydrophobic silica aerogel with water is 141°, and the apparent density is 0.042 g / cm 3 , porosity is 98.0%, specific surface area is 624m 2 / g, pore volume is 2.53cm 3 / g, the average pore size is 11.4nm, and the pore size distribution range is 1nm to 70nm.

[0114] Example 3

[0115] This embodiment provides a hydrophobic silicon oxide aerogel and a preparation method thereof, wherein the preparation method comprises the following steps:

[0116] Weigh Na 2 SiO 3 9H 2O was added into deionized water, and a magnetic stirrer was added to prepare a 0.66 mol / L sodium silicate solution;

[0117] Add H-type weakly acidic cation exchange resin intermittently to the sodium silicate solution while stirring, use a pH meter to detect the pH change of the solution, adjust the pH of the solution to about 7.5, and use a Buchner funnel to vacuum filter and separate to obtain the silica sol after ion exchange;

[0118] Take 100 mL of silica sol in a beaker, add tert-butanol, and make the content of tert-butanol be 20wt%, stir evenly, seal, and let stand at room temperature for 2 hours, then continue to seal and age at room temperature for 24 hours to obtain a gel;

[0119] A 20 wt % tert-butanol aqueous solution was prepared, hexamethyldisilazane (HMDS) was added, and the volume ratio of HMDS to the tert-butanol aqueous solution was 4:100, and the mixture was mixed uniformly to obtain a modified solution;

[0120] 100 mL of the modified liquid and 100 mL of the gel were mixed, sealed and subjected to modification reaction at 60° C. for 2 h to obtain a modified gel, which was washed three times with a 20 wt % tert-butyl alcohol aqueous solution to remove residual modified liquid;

[0121] The modified gel was frozen in a freeze dryer (cold trap temperature -60°C to -20°C) for 2 hours, and vacuum dried at -40°C (vacuum degree <5 Pa) for 20 hours to obtain a hydrophobic silica aerogel.

[0122] The contact angle of the hydrophobic silica aerogel with water is 154°, and the apparent density is 0.049 g / cm 3 The porosity is 97.7% and the specific surface area is 708m 2 / g, pore volume is 2.94cm 3 / g, the average pore size is 13.1nm, and the pore size distribution range is 1nm to 70nm.

[0123] Comparative Example 1

[0124] This comparative example provides a silicon oxide aerogel and a preparation method thereof, wherein the preparation method comprises the following steps:

[0125] Weigh Na 2 SiO 3 9H 2 O was added into deionized water, and a magnetic stirrer was added to prepare a 0.64 mol / L sodium silicate solution;

[0126] Add H-type weakly acidic cation exchange resin intermittently to the sodium silicate solution while stirring, use a pH meter to detect the pH change of the solution, adjust the pH of the solution to about 7, and use a Buchner funnel to vacuum filter and separate to obtain the silica sol after ion exchange;

[0127] Take 100 mL of silica sol in a beaker, add tert-butanol, and make the content of tert-butanol be 18 wt %, stir evenly, seal, let stand at room temperature for 2 hours, then continue to seal and age at room temperature for 24 hours to obtain a gel;

[0128] The gel was frozen in a freeze dryer (cold trap temperature -60°C to -20°C) for 2 hours, and vacuum dried at -40°C (vacuum degree <5 Pa) for 40 hours to obtain silica aerogel.

[0129] The contact angle of the silica aerogel with water is 8°, and the apparent density is 0.049 g / cm 3 The porosity is 97.7% and the specific surface area is 672m 2 / g, pore volume is 2.9cm 3 / g, the average pore size is 15.9nm, and the pore size distribution range is 1nm to 70nm. In this comparative example, since the gel surface is not methylated, the freeze-drying time required for this comparative example is 40h, which is twice the freeze-drying time of Example 1.

[0130] Comparative Example 2

[0131] This comparative example provides a silicon oxide aerogel and a preparation method thereof, wherein the preparation method comprises the following steps:

[0132] Weigh Na 2 SiO 3 9H 2 O was added into deionized water, and a magnetic stirrer was added to prepare a 0.64 mol / L sodium silicate solution;

[0133] Add H-type weakly acidic cation exchange resin intermittently to the sodium silicate solution while stirring, use a pH meter to detect the pH change of the solution, adjust the pH of the solution to about 7, and use a Buchner funnel to vacuum filter and separate to obtain the silica sol after ion exchange;

[0134] Take 100 mL of silica sol in a beaker, add tert-butanol, and make the content of tert-butanol be 18 wt %, stir evenly, seal, let stand at room temperature for 2 hours, then continue to seal and age at room temperature for 24 hours to obtain a gel;

[0135] 100 mL of the gel was subjected to solvent replacement with tert-butyl alcohol and n-hexane for one day respectively, so that the pore liquid in the gel was replaced with n-hexane;

[0136] Hexamethyldisilazane and n-hexane were mixed uniformly in a volume ratio of 2.5:100 to obtain a modified solution;

[0137] 100 mL of the modified liquid and 100 mL of the gel after solvent replacement were mixed, sealed and subjected to modification reaction at 50° C. for 6 hours to obtain a modified gel, the modified gel was subjected to solvent replacement with tert-butanol and 18 wt% tert-butanol aqueous solution for one day respectively, so that the pore liquid in the modified gel was replaced with 18 wt% tert-butanol aqueous solution, and then the modified gel was frozen in a freeze dryer (cold trap temperature -60° C. to -20° C.) for 2 hours, and vacuumed (vacuum degree <5 Pa) and dried at -40° C. for 20 hours to obtain silica aerogel.

[0138] The contact angle of the silica aerogel with water is 127°, and the apparent density is 0.048 g / cm 3 The porosity is 97.8% and the specific surface area is 685m 2 / g, pore volume is 6.9cm 3 / g, the average pore size is 22.2nm, and the pore size distribution range is 1nm to 70nm. In this comparative example, since the surface of the gel is methylated, the freeze-drying time required for this comparative example is still 20h, but the process requires a large amount of organic reagents for long-term solvent replacement.

[0139] Comparative Example 3

[0140] The only difference between this comparative example and Example 1 is that the volume ratio of HMDS to the aqueous solution of tert-butyl alcohol in the modifying liquid is 1:100.

[0141] The contact angle of the silica aerogel prepared in this comparative example with water is 14.8°, and the apparent density is 0.045 g / cm 3 The porosity is 97.9% and the specific surface area is 807m 2 / g, pore volume is 5.35cm 3 / g, the average pore size is 24.9nm, and the pore size distribution range is 1nm to 70nm. Among them, the prepared sample still has the characteristics of aerogel. However, due to the low HMDS concentration, the modification is insufficient, the hydrophobic angle of the aerogel is less than 90°, and it still shows hydrophilicity. The freeze-drying time is 40h.

[0142] Comparative Example 4

[0143] The only difference between this comparative example and Example 1 is that the volume ratio of HMDS to the aqueous solution of tert-butyl alcohol in the modifying liquid is 5:100.

[0144] The contact angle of the silica aerogel prepared in this comparative example with water is 151°, and the apparent density is 0.163 g / cm 3 , porosity is 87.0%, specific surface area is 272m 2 / g, pore volume is 0.92cm 3 / g, the average pore size is 5.3nm, and the pore size distribution range is 1nm~10nm. Among them, although the hydrophobic angle of the modified aerogel is greater than 140°, it is hydrophobic and the freeze-drying time is 20h. However, the excess HMDS makes the apparent density of the aerogel after the reaction greater than 0.1g / cm 3 , specific surface area <300m 2 / g, pore volume <1cm 3 / g, the average pore size and porosity also decrease, which will significantly reduce the performance of the aerogel.

[0145] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0146] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a hydrophobic silicon oxide aerogel, characterized in that: The following steps are involved: A silicate aqueous solution is prepared, and ion exchange is performed on the silicate aqueous solution through an ion exchange resin until the pH value of the solution is 6.0 to 7.5 to obtain a silica sol; The silica sol is mixed with tert-butyl alcohol to obtain a mixed sol, and the mixed sol is aged to obtain a gel; The tert-butyl alcohol aqueous solution and the modifier are mixed to obtain a modified liquid; The gel and the modified liquid are mixed to perform a modification reaction to obtain a modified gel; The modified gel is freeze-dried to obtain the hydrophobic silica aerogel.

2. The preparation method according to claim 1, characterized in that: The silicate content in the silicate aqueous solution is 0.45 mol / L to 0.66 mol / L; Optionally, the silicate in the silicate aqueous solution includes at least one of sodium silicate, potassium silicate and hydrates thereof; Optionally, the ion exchange resin includes at least one of a strongly acidic cation exchange resin and a weakly acidic cation exchange resin.

3. The preparation method according to claim 1, characterized in that: The content of tert-butyl alcohol in the mixed sol is 10wt% to 20wt%.

4. The preparation method according to claim 1, characterized in that: The aging time is 24h to 72h; Optionally, the preparation method further comprises: allowing the mixed sol to stand and age to obtain the gel; Optionally, the standing time is 2 h to 4 h.

5. The preparation method according to claim 1, characterized in that: The content of tert-butanol in the tert-butanol aqueous solution is the same as the content of tert-butanol in the mixed sol; Optionally, the volume ratio of the modifier to the tert-butyl alcohol aqueous solution is (1.5-4.0):100; Optionally, the modifier is hexamethyldisilazane.

6. The preparation method according to claim 1, characterized in that: The gel and the modified liquid are mixed in a volume ratio of 1:1; Optionally, the temperature of the modification reaction is 40°C to 60°C; Optionally, the modification reaction time is 2 h to 8 h.

7. The preparation method according to claim 1, characterized in that: The freezing temperature and / or drying temperature in the freeze drying is -60°C to -20°C; Optionally, the freezing time in the freeze-drying is 2h to 6h; Optionally, the drying time in the freeze-drying is 20 h to 40 h; Optionally, the drying process in the freeze-drying is carried out under vacuum conditions, with a vacuum degree of <5Pa.

8. A hydrophobic silicon oxide aerogel obtained according to the preparation method according to any one of claims 1 to 7.

9. The hydrophobic silica aerogel according to claim 8, characterized in that: The contact angle between the hydrophobic silica aerogel and water is >140°; Optionally, the apparent density of the hydrophobic silica aerogel is 0.04 g / cm 3 ~0.05g / cm 3 ; Optionally, the porosity of the hydrophobic silica aerogel is 97% to 98%; Optionally, the specific surface area of ​​the hydrophobic silica aerogel is 600 m 2 / g~900m 2 / g.

10. The hydrophobic silica aerogel according to claim 8, characterized in that: The pore volume of the hydrophobic silica aerogel is 2.5 cm 3 / g~5.5cm 3 / g; Optionally, the average pore size of the hydrophobic silica aerogel is 10 nm to 25 nm; Optionally, the pore size distribution range of the hydrophobic silica aerogel is 1 nm to 70 nm.

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