Preparation method and application of reversible super-hydrophilic-super-hydrophobic silica aerogel

Abstract

The application discloses a preparation method and application of reversible super-hydrophilic-super-hydrophobic silica aerogel. The preparation method comprises the following steps: performing sol-gel reaction on an organosiloxane precursor solution containing organosiloxane monomers and a solvent in the presence of an acidic catalyst and an alkaline catalyst, and through acid hydrolysis and alkaline condensation, to obtain a wet gel; performing high-temperature solvent replacement on the wet gel by using a modified solvent, or performing drying treatment on the wet gel, and then performing gas-phase modification on the obtained aerogel by using a gas-phase modified solvent, to obtain the reversible super-hydrophilic-super-hydrophobic silica aerogel. The method provided by the application can realize the whole-process hydrophilic-hydrophobic modification of the preparation of the silica aerogel, and for specific silica precursors, the application can realize the preparation of the hydrophilic aerogel and the hydrophobic aerogel respectively through high-temperature solvent replacement or gas-phase modification treatment, and can realize the reversible hydrophilic-hydrophobic modification.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for regulating the surface properties of silica aerogels, and in particular to a reversible superhydrophilic-superhydrophobic silica aerogel preparation method, a method for reversibly regulating the hydrophilic and hydrophobic properties of silica aerogels based on solvents, and applications thereof, belonging to the technical field of nanoporous materials. BACKGROUND

[0002] In 1931, Kistler of Stanford University first applied the concept of replacing liquid phase with gas phase to the preparation of silica aerogels. However, due to the limitations of this preparation method, the development of silica aerogels almost stagnated. In 1966, the method of preparing silica aerogels through sol-gel transition rapidly promoted the research progress in the field of aerogels. Since then, silica aerogels have been systematically studied and rapidly commercialized. Silica aerogels have high porosity, large specific surface area, ultra-low thermal conductivity, adjustable reflectivity and scattering rate, and these unique properties make them widely used in environmental remediation, thermal insulation, optics and acoustics, etc. Commercial silica aerogel products mainly include: blocks, microspheres, powders, aerogel mats and aerogel coatings, which are widely used in aerospace, manufacturing and construction fields (Energy Storage Materials, 2021, 40: 329-336; Renewable and Sustainable Energy Reviews, 2014, 34: 273-299).

[0003] The traditional synthesis route of silica aerogels mainly includes: (1) sol-gel. This is the core process, by controlling the amount of catalyst to adjust the hydrolysis and condensation rate of the precursor, so as to regulate the size of the micro-structural unit; (2) solvent replacement. Through solvent replacement, impurities in the gel are removed, and at the same time, the solvent in the gel is replaced with a solvent with smaller surface tension, so as to facilitate the subsequent drying process; (3) drying. Mainly includes: supercritical drying, freeze drying or atmospheric drying, replacing the liquid phase in the gel with a gas phase while maintaining the gel skeleton structure.

[0004] Currently, the traditional silica sol-gel transition method is mainly divided into one-step method (CN111039295A) and two-step method (CN105439154A). The one-step method is to directly condense the precursor solution under acidic or basic catalyst, and to control the size of the building unit by adjusting the amount of catalyst. However, this method is very limited in controlling the size and uniformity of the building unit, which limits the performance of the silica aerogel. The two-step method can well solve the above problems. The two-step method is to first hydrolyze the precursor solution under acidic catalyst, and then condense under basic catalyst. The two-step method can highly control the size and uniformity of the building unit of the silica aerogel and the pore structure, which is the best technical means for preparing the silica aerogel. However, regardless of the method used, most researches focus on finding suitable reaction materials (such as silica precursor, catalyst, etc.) in the sol-gel process to adjust the aerogel structure, including the size of the building unit, the pore structure and the three-dimensional network, to meet the requirements of specific application scenarios. In addition, as the reaction medium and drying medium of the silica aerogel, the solvent plays a crucial role in sample preparation. For example, in the process of preparing the silica aerogel, various solvent treatments including solvent exchange are required. Sequential treatment with water and alcohol is usually used to effectively remove inorganic salts and other impurities. These processes involve changes in the solvent environment, which can potentially change the properties of the final aerogel. However, despite nearly a century of history, the influence of solvents on the performance of silica aerogels has been ignored, leading to inaccurate and ambiguous performance evaluation.

[0005] Although some prior art applications have been proposed by those skilled in the art, such as CN106829972A, CN108017062A, CN109052415A, etc. However, the above traditional silica aerogel preparation process ignores the influence of solvent replacement process on the surface properties of the silica aerogel, can only perform one-way hydrophobic surface chemical modification, and cannot perform hydrophilic modification. In addition, traditional hydrophobic modification usually involves adding a hydrophobic modification reagent to the reaction system, thus requiring subsequent complex processes to remove excess reagents. At the same time, traditional surface modification reagents have problems such as high cost and environmental pollution. SUMMARY

[0006] The main purpose of the present application is to provide a reversible superhydrophilic-superhydrophobic silica aerogel preparation method and application to overcome the deficiencies in the prior art.

[0007] Another purpose of the present application is to provide a method for reversibly controlling the hydrophilic and hydrophobic properties of silica aerogels based on solvents.

[0008] To achieve the above-mentioned purposes of the application, the following technical solutions are adopted:

[0009] Embodiments of the present application provide a preparation method of reversible super-hydrophilic-super-hydrophobic silica aerogel, which comprises:

[0010] Providing an organosiloxane precursor solution comprising organosiloxane monomers and a solvent, wherein the organosiloxane monomers comprise a combination of siloxanes with one methyl and siloxanes without methyl;

[0011] Performing a sol-gel reaction on the organosiloxane precursor solution by acid hydrolysis and alkaline condensation in the presence of an acidic catalyst and an alkaline catalyst to obtain a wet gel;

[0012] Performing high-temperature solvent replacement on the wet gel with a modified solvent to obtain reversible super-hydrophilic-super-hydrophobic silica aerogel;

[0013] Alternatively, after drying treatment on the wet gel, performing gas-phase modification on the obtained aerogel with a gas-phase modified solvent to obtain reversible super-hydrophilic-super-hydrophobic silica aerogel.

[0014] In some embodiments, the modified solvent comprises any one or a combination of two or more of methanol, ethanol, tert-butanol, n-decanol, n-hexane, n-heptane, and water.

[0015] In some embodiments, the molar ratio of the siloxanes with one methyl to the siloxanes without methyl is 7:3 to 3:7.

[0016] In some embodiments, the temperature of the high-temperature solvent replacement is 40°C to 100°C.

[0017] In some embodiments, the temperature of the gas-phase modification is 100°C to 150°C.

[0018] Embodiments of the present application also provide a method for reversibly regulating the surface properties of silica aerogel based on a solvent, which comprises:

[0019] Providing an organosiloxane precursor solution comprising organosiloxane monomers and a solvent, wherein the organosiloxane monomers comprise a combination of siloxanes with one methyl and siloxanes without methyl:

[0020] Performing a sol-gel reaction on the organosiloxane precursor solution by acid hydrolysis and alkaline condensation in the presence of an acidic catalyst and an alkaline catalyst to obtain a wet gel;

[0021] The wet gel is subjected to high-temperature solvent replacement with a modified solvent, or after the wet gel is subjected to a drying treatment, the obtained aerogel is subjected to gas-phase modification with a modified solvent in a gas phase, to obtain a reversible super-hydrophilic-super-hydrophobic silica aerogel, and to realize reversible regulation of the hydrophilicity and hydrophobicity of the silica aerogel.

[0022] Compared with the prior art, the application has the following beneficial technical effects:

[0023] 1) The method provided by the application can realize hydrophilic and hydrophobic modification of the whole process of silica aerogel preparation. For a specific silica precursor, the application can realize the preparation of hydrophilic aerogel and hydrophobic aerogel respectively through high-temperature solvent replacement or gas-phase modification treatment, can realize reversible hydrophilic and hydrophobic modification, and solves the problem of irreversible change of the surface properties of the existing silica aerogel.

[0024] 2) The method provided by the application does not add a hydrophobic modifier during the modification process, and is a more green and economical preparation method. However, the prior art usually involves adding a hydrophobic modification reagent with significant physiological toxicity into the reaction system, which complicates and makes subsequent sample processing steps cumbersome. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only some embodiments described in the application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0026] Figure 1 is a preparation flowchart of the reversible super-hydrophilic-super-hydrophobic silica aerogel based on solvent regulation in a typical embodiment of the application;

[0027] Figure 2 is a sample diagram of the super-hydrophobic silica aerogel obtained in Example 1 of the application;

[0028] Figure 3 is a scanning electron microscope diagram of the super-hydrophobic silica aerogel obtained in Example 1 of the application;

[0029] Figure 4 is a contact angle diagram of the super-hydrophobic silica aerogel obtained in Example 1 of the application;

[0030] Figure 5 is a nitrogen adsorption curve diagram of the super-hydrophobic silica aerogel obtained in Example 1 of the application;

[0031] Figure 6 is a pore size distribution curve diagram of the super-hydrophobic silica aerogel obtained in Example 1 of the application;

[0032] Figure 7 Sample graph of superhydrophilic silica aerogel obtained in Example 3 of the present application;

[0033] Figure 8 Scanning electron microscope graph of superhydrophilic silica aerogel obtained in Example 3 of the present application;

[0034] Figure 9 Contact angle graph of superhydrophilic silica aerogel obtained in Example 3 of the present application;

[0035] Figure 10 Nitrogen adsorption curve graph of superhydrophilic silica aerogel obtained in Example 3 of the present application;

[0036] Figure 11 Pore size distribution curve graph of superhydrophilic silica aerogel obtained in Example 3 of the present application;

[0037] Figure 12 Contact angle change graph of superhydrophobic silica aerogel obtained in Example 2 and 3 of the present application converted into superhydrophilic silica aerogel;

[0038] Figure 13 Contact angle change graph of superhydrophilic silica aerogel obtained in Example 1 and 4 of the present application converted into superhydrophobic silica aerogel;

[0039] Figure 14 Infrared spectrum graph of reversible superhydrophobic-superhydrophilic silica aerogel obtained in Comparative Example 1 and Example 1 of the present application;

[0040] Figure 15a and Figure 15b Reversibility graph of superhydrophobic-superhydrophilic silica aerogel based on gas phase modification obtained in Example 5 and 6 of the present application;

[0041] Figures 16a-16d Contact angle graph of hydrophobic silica aerogel obtained in Comparative Example 3 of the present application prepared using only siloxane precursor having one methyl group;

[0042] Figures 17a-17d Contact angle graph of hydrophilic silica aerogel obtained in Comparative Example 4 of the present application prepared using only siloxane precursor having no methyl group;

[0043] Figure 18a and Figure 18b Graph of hydrophilic silica aerogel obtained in Comparative Example 5 of the present application using other high temperature displacement organic solvents (benzene, carbon tetrachloride, glycerol, styrene, etc.);

[0044] Figure 19The contact angle of the silica aerogel prepared from other molar ratio precursors obtained in Invention Comparative Example 6 is shown in the figure. DETAILED DESCRIPTION

[0045] In view of the defects of the prior art, the present inventors have long studied and practiced and have finally proposed the technical solution of the present invention, i.e. a more convenient and simplified method for regulating the surface properties of silica aerogel, i.e. the reversible change of the hydrophilic and hydrophobic properties of silica aerogel can be realized by directly heating the solvent, the main scheme is to obtain silica aerogel with reversible superhydrophobic-superhydrophilic transition by subjecting a precursor solution with a certain molar ratio to sol-gel transition and specific solvent replacement process under the condition of acidic catalyst and alkaline catalyst, so as to realize the reversible change of the surface properties of silica aerogel in an environmentally friendly manner at low cost.

[0046] The technical solution, its implementation process and principles will be further explained as follows. However, it should be understood that within the scope of the present invention, the above-mentioned technical features of the present invention and the technical features specifically described in the following (Examples) can be combined with each other to form new or preferred technical solutions. Due to the limited space, they will not be listed one by one here.

[0047] As one aspect of the technical solution of the present invention, a method for preparing reversible superhydrophilic-superhydrophobic silica aerogel comprises:

[0048] providing an organosiloxane precursor solution comprising organosiloxane monomers and a solvent, wherein the organosiloxane monomers comprise a combination of siloxanes with one methyl group and siloxanes without methyl group;

[0049] subjecting the organosiloxane precursor solution to acid hydrolysis and alkaline condensation in the presence of an acidic catalyst and an alkaline catalyst to perform a sol-gel reaction and obtain a wet gel;

[0050] subjecting the wet gel to high-temperature solvent replacement with a modified solvent to obtain reversible superhydrophilic-superhydrophobic silica aerogel;

[0051] or, after drying treatment of the wet gel, subjecting the obtained aerogel to gas-phase modification with a gaseous modified solvent to obtain reversible superhydrophilic-superhydrophobic silica aerogel.

[0052] In another aspect, the present invention can also provide a method for reversibly regulating the surface properties of silica aerogel based on solvent, which comprises:

[0053] providing an organosiloxane precursor solution comprising organosiloxane monomers and a solvent, wherein the organosiloxane monomers comprise a combination of siloxanes with one methyl group and siloxanes without methyl group;

[0054] The organic siloxane precursor solution is subjected to acid hydrolysis and alkaline condensation in the presence of an acid catalyst or an alkaline catalyst to perform a sol-gel reaction, thereby obtaining a wet gel;

[0055] The wet gel is subjected to high-temperature solvent replacement with a modified solvent, or the wet gel is dried and then subjected to gas-phase modification with a gas-phase modified solvent, thereby obtaining a reversible superhydrophilic-superhydrophobic silica aerogel, and realizing reversible regulation of the hydrophilic and hydrophobic properties of the silica aerogel.

[0056] The above technical solution provided by the present application includes: after a precursor silicon source with a certain molar ratio is subjected to sol-gel conversion under the action of an acid catalyst or an alkaline catalyst in a reaction solvent and at a reaction temperature, the superhydrophobic-superhydrophilic property of the surface of the silica aerogel can be reversibly regulated at high temperature by using a modified solvent. In addition, the superhydrophobic-superhydrophilic property of the surface of the silica aerogel can also be reversibly regulated under the action of a high-temperature gas-phase solvent. However, the prior art can only perform one-way hydrophobic modification and is irreversible.

[0057] In some embodiments, the organic siloxane precursor solution includes an organic siloxane monomer and a solvent.

[0058] In some embodiments, the organic siloxane monomer includes a combination of a siloxane having one methyl group and a siloxane having no methyl group in a specific molar ratio.

[0059] In some preferred embodiments, the molar ratio of the siloxane having one methyl group to the siloxane having no methyl group is 7:3 to 3:7, and the optimal molar ratio is 7:3 to 4:6.

[0060] In some preferred embodiments, the siloxane having one methyl group can include any one or a combination of two or more of methyltrimethoxysilane, methyltriethoxysilane, sodium methylsiliconate, propyltrimethoxysilane, butyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, allyltriethoxysilane, allyltrimethoxysilane, ethyltrimethoxysilane, hexyltriethoxysilane, n-butyltrimethoxysilane, n-butyltrimethoxysilane, etc., but is not limited thereto.

[0061] In some preferred embodiments, the siloxane having no methyl group can include any one or a combination of two or more of tetramethoxysilane (i.e., tetramethyl orthosilicate), tetraethoxysilane, sodium silicate, tetrapropoxysilane, chlorotriethoxysilane, triethoxysilane, etc., but is not limited thereto.

[0062] In some preferred embodiments, the solvent used in the organosiloxane precursor solution of the present application can include any one of, but not limited to, methanol, ethanol, n-hexane, n-heptane, dimethyl sulfoxide, acetone, dimethylformamide, water, and the like. Among them, when the solvent is selected from methanol, ethanol, n-hexane, n-heptane, dimethyl sulfoxide, acetone, dimethylformamide, and the like, the prepared aerogel is hydrophobic, and when the solvent is selected from water, the prepared aerogel is hydrophilic.

[0063] In some preferred embodiments, the molar content of silicon in the organosiloxane precursor solution used in the present application is 1 mol / L to 5 mol / L.

[0064] In some embodiments, the acidic catalyst includes an acidic substance and a catalyst solvent, wherein the acidic substance includes any one of, but not limited to, hydrochloric acid, sulfuric acid, acetic acid, and the like, or a combination of two or more thereof.

[0065] In some preferred embodiments, the concentration of the acidic substance in the acidic catalyst is 0.001 mol / L to 0.1 mol / L.

[0066] In some embodiments, the basic catalyst includes a basic substance and a catalyst solvent, wherein the basic substance includes any one of, but not limited to, aqueous ammonia, sodium hydroxide, triethylamine acid, and the like, or a combination of two or more thereof.

[0067] Further, the solvent used in the acidic catalyst or the basic catalyst includes any one of, but not limited to, methanol, ethanol, water, and the like, or a combination of two or more thereof.

[0068] In some preferred embodiments, the concentration of the basic substance in the acidic catalyst is 0.1 mol / L to 10 mol / L.

[0069] In some preferred embodiments, the organosiloxane precursor solution used in the present application is added to the solution at a molar concentration of 1 mol / L to 5 mol / L, the acidic catalyst is added at a concentration of 0.001 mol / L to 0.1 mol / L, and the basic catalyst is added at a concentration of 0.1 mol / L to 10 mol / L.

[0070] In some embodiments, the preparation method includes: mixing the organosiloxane precursor solution with the acidic catalyst, stirring at room temperature for 60 to 240 min, performing acid hydrolysis, then adding the basic catalyst to perform basic condensation, and heating to perform a sol-gel reaction to obtain a wet gel.

[0071] In some embodiments, the temperature of the sol-gel reaction is 40°C to 100°C, and the preferred temperature is 50 to 90°C, and the time is 6 to 48 h.

[0072] In some embodiments, the temperature for the high-temperature solvent replacement is 40-100°C, preferably 50-90°C, and the time is 6-48h, and the number of replacements is 3-6. The method of the present application for hydrophilic-hydrophobic modification by solvent treatment can achieve reversible transformation between superhydrophilic and superhydrophobic of silica aerogels by using different reaction solvents and replacement solvents at high temperature during the synthesis and solvent replacement of the sample.

[0073] In some preferred embodiments, the replacement solvent (also referred to as "modification solvent") used in the high-temperature solvent replacement is selected from any one or a combination of two or more of methanol, ethanol, tert-butanol, n-decanol, n-hexane, n-heptane, water, etc., but is not limited thereto.

[0074] In some embodiments, the present application can directly perform reversible hydrophilic-hydrophobic modification of silica aerogels by using vapors of different solvents at high temperature. The temperature for the gas-phase modification is 100-150°C, the time is 6-48h, and the number of replacements is 3-6.

[0075] In some preferred embodiments, the gas-phase modification solvent used in the gas-phase modification includes any one or a combination of two or more of methanol, ethanol, tert-butanol, n-decanol, n-hexane, n-heptane, water, etc., but is not limited thereto.

[0076] Further, the modification solvent or gas-phase modification solvent used in the present application can be classified into hydrophobic modification solvents, hydrophilic modification solvents, etc. If hydrophobic modification is needed, a hydrophobic modification solvent is used, such as any one or a combination of two or more of methanol, ethanol, tert-butanol, n-decanol, n-hexane, n-heptane, etc. If hydrophilic modification is needed, a hydrophilic modification solvent is used, such as water.

[0077] In some embodiments, the preparation method can further include the following step which is selectively performed or not performed: before or after the high-temperature solvent replacement of the wet gel with the modification solvent, the wet gel is subjected to a normal-temperature solvent replacement.

[0078] In some embodiments, the preparation method can further include the following step which is selectively performed or not performed: after the normal-temperature solvent replacement or the high-temperature solvent replacement of the wet gel, the wet gel is subjected to a drying treatment.

[0079] In some embodiments, the preparation method can further include the following step which is selectively performed or not performed: after the normal-temperature solvent replacement or the high-temperature solvent replacement of the wet gel, the wet gel is subjected to a drying treatment.

[0080] Further, if the drying treatment is performed after the solvent replacement of the wet gel at room temperature, the gas phase modification treatment also needs to be continued, and the reversible superhydrophilic-superhydrophobic silica aerogel is obtained.

[0081] Further, the present application can also be that the drying treatment is performed after the solvent replacement of the wet gel at high temperature.

[0082] In some more specific embodiments, the method for reversibly regulating the surface properties of silica aerogel based on solvent includes the following steps:

[0083] (1) The sol-gel transition is performed on the specific molar ratio of organosiloxane precursor in the specific reaction solvent at the specific reaction temperature through acid hydrolysis and alkaline condensation.

[0084] (2) The obtained wet gel is subjected to the specific replacement solvent replacement process at high temperature to reversibly change the superhydrophilic-superhydrophobic surface of silica, i.e., to change the surface properties of silica.

[0085] (3) The obtained aerogel is subjected to gas phase modification in the gas phase solvent at high temperature to reversibly change the superhydrophilic-superhydrophobic surface of silica aerogel.

[0086] And, steps (4) and (5) can be optionally performed, including:

[0087] (4) The wet gel obtained in step (1) is subjected to solvent replacement to remove the acid and base catalysts and by-products in the wet gel.

[0088] (5) The wet gel obtained in step (1) is subjected to a special drying method to obtain silica aerogel.

[0089] In some preferred embodiments, the special drying method includes at least any one of normal pressure drying, supercritical drying, freeze drying, etc., preferably at least any one of supercritical drying and normal pressure drying.

[0090] Further, the principle of the normal pressure drying is to evaporate the solvent with low surface tension in the gel skeleton at normal pressure and a specific temperature (25-200°C) to form the aerogel material.

[0091] Further, the principle of the supercritical drying is based on the replacement of the high surface tension liquid inside the pore skeleton of the wet gel with supercritical fluid at a specific pressure (8-10 MPa) and temperature (35-45°C), and then the supercritical fluid is evaporated to obtain the aerogel material. The supercritical fluid used includes but is not limited to any one of supercritical CO2, supercritical methanol, supercritical ethanol, etc.

[0092] Further, the freeze-drying technique includes vacuum freeze-drying and reduced pressure drying, etc., which is based on the principle of sublimating solvent from liquid to solid in the frozen gel at a cold trap temperature of -45°C to -80°C under a vacuum degree of less than 0.1 kPa to form an aerogel material.

[0093] Further, the preparation method includes: hydrolyzing a certain molar ratio of siloxane having one methyl group and siloxane precursor without methyl group in a specific reaction solvent and acidic catalyst, and undergoing sol-gel transition under an alkaline catalyst and a specific temperature; after removing impurities, placing the gel in a certain displacement solvent at a certain temperature for a certain time; and obtaining the reversible superhydrophobic-superhydrophilic silica aerogel material after drying. In addition, the obtained aerogel can also realize the reversible modification of the superhydrophobic-superhydrophilic surface of the silica aerogel under a specific temperature and gas-phase solvent.

[0094] In some embodiments, the density of the reversible superhydrophilic-superhydrophobic silica aerogel is 0.08 g / cm 3 ~0.12 g / cm 3 .

[0095] In some preferred embodiments, the specific surface area of the hydrophobic silica aerogel prepared by the preparation method is between 720 m 2 / g and 1007 m 2 / g.

[0096] In some preferred embodiments, the specific surface area of the hydrophilic silica aerogel prepared by the preparation method is between 500 m 2 / g and 600 m 2 / g.

[0097] Referring to Figure 1 Fig. 1 shows a preparation flowchart of the reversible superhydrophilic-superhydrophobic silica aerogel based on solvent regulation in a typical embodiment of the present application. The present application first develops a method for reversibly changing the surface properties of silica aerogel based on solvent regulation, which includes: reacting silane precursor, acidic catalyst, alkaline catalyst and reaction solvent at a certain temperature, and obtaining the reversible superhydrophobic-superhydrophilic silica aerogel material after drying. The obtained aerogel can also realize the reversible modification of the superhydrophobic-superhydrophilic surface of the silica aerogel under a specific temperature and gas-phase solvent.

[0098] The "solvent 1" in the formula is the solvent of the aforementioned organosiloxane precursor solution, and the "solvent 2" is a modified solvent used for high-temperature solvent replacement. If the modified solvent used for the solvent of the organosiloxane precursor solution is an organic solvent, an organic gel is obtained, and after drying, a superhydrophobic silica aerogel is prepared. If the solvent of the organosiloxane precursor solution is water, a hydrogel is obtained, and after drying, a superhydrophilic silica aerogel is prepared. Among them, the organic gel and the hydrogel can be replaced by a liquid-phase modified solvent at high temperature to realize the reversible modification of the superhydrophobic-superhydrophilic surface of the silica aerogel. Further, the superhydrophobic silica aerogel and the superhydrophilic silica aerogel can also be modified by a gas-phase modified solvent in the gas phase to realize the reversible modification of the superhydrophobic-superhydrophilic surface of the silica aerogel.

[0099] The above scheme of the present application can realize the whole-process hydrophilic-hydrophobic modification of the preparation of the silica aerogel. For a specific silica precursor, the present application can realize the preparation of hydrophilic and hydrophobic aerogels respectively at the sol-gel stage, the solvent replacement stage, and the post-processing stage by selecting solvents / steam (such as water / organic solvent). However, the prior art can only realize one-way hydrophobic modification at the solvent replacement stage.

[0100] The method of the present application only uses solvent heating, and no additional hydrophobic modifier is added during the modification process, and the solvent used is water / organic solvent. However, the prior art usually involves adding a hydrophobic modification reagent with significant physiological toxicity to the reaction system, which makes the subsequent sample processing steps complex and cumbersome. The present application provides a more green and economical preparation method.

[0101] In summary, the method for reversibly controlling the surface properties of the silica aerogel provided by the present application can realize the conversion of the silica aerogel from a superhydrophobic surface to a superhydrophilic surface, and vice versa. At the same time, the above surface modification can also be carried out under gas-phase modification conditions, which can solve the problem of irreversible change of the surface properties of the existing silica aerogel.

[0102] The technical solutions of the present application will be described in more detail below in combination with the corresponding drawings and detailed inventive examples, and the purpose, detailed implementation technology and significant advantages of the present application will be more clearly and specifically demonstrated. The examples listed below are only a small part of the inventive examples, and the relevant personnel in the field can adjust them flexibly according to the actual situation. In the following examples, the specific experimental steps not mentioned are all carried out by conventional experimental operations. In addition, if the relevant personnel in the field make related examples based on the examples in the present application without making creative efforts, they all belong to the scope of protection of the present application.

[0103] The implementation conditions used in the following examples can be further adjusted according to actual needs, and the implementation conditions not marked are usually the conditions in conventional experiments.

[0104] Comparative Example 1

[0105] Take 342 μL of methyl triethoxysilane and 236 μL of tetraethoxysilane to form an organosiloxane precursor solution in 1 mL of water, the content of silicon in the organosiloxane is 4 mol / L; take a certain amount of hydrochloric acid and add it to water to stir to form an acidic catalyst, the concentration of the hydrochloric acid in water is 0.1 mol / L. Take a certain amount of ammonia water and add it to water to stir to form an alkaline catalyst, the concentration of the ammonia water in water is 4 mol / L.

[0106] (1) Mix the precursor solution with 130 μL of the acidic catalyst, stir at room temperature for 30 min, then add 87 μL of the alkaline catalyst, and place in a 100°C oven for sol-gel transition.

[0107] (2) Use ethanol to perform room temperature solvent replacement on the gel prepared in step (1) to wash away excess catalyst and by-products.

[0108] (3) Perform supercritical drying on the gel prepared in step (2), the drying pressure is 10 MPa and the temperature is 40°C, to obtain super-hydrophilic silica aerogel.

[0109] Comparative Example 2

[0110] Take 143 μL of methyl trimethoxysilane and 148 μL of tetramethyl orthosilicate to form an organosiloxane precursor solution in 1 mL of ethanol, the content of silicon in the organosiloxane is 2 mol / L; take a certain amount of hydrochloric acid and add it to water to stir to form an acidic catalyst, the concentration of the hydrochloric acid in water is 0.01 mol / L. Take a certain amount of ammonia water and add it to water to stir to form an alkaline catalyst, the concentration of the ammonia water in water is 1 mol / L.

[0111] (1) Mix the precursor solution with 130 μL of the acidic catalyst, stir at room temperature for 30 min, then add 87 μL of the alkaline catalyst, and place in an 80°C oven for sol-gel transition.

[0112] (2) Use ethanol to perform room temperature solvent replacement on the gel prepared in step (1) to wash away excess catalyst and by-products.

[0113] (3) Perform supercritical drying on the gel prepared in step (2), the drying pressure is 10 MPa and the temperature is 40°C, to obtain super-hydrophobic silica aerogel.

[0114] Example 1

[0115] Take 286 μL of allyl triethoxysilane and 296 μL of triethoxysilane to form an organosiloxane precursor solution in 1 mL of water, the content of silicon in the organosiloxane is 4 mol / L; take a certain amount of hydrochloric acid into water to stir to form an acidic catalyst, the concentration of the hydrochloric acid in water is 0.04 mol / L. Take a certain amount of ammonia into water to stir to form an alkaline catalyst, the concentration of the ammonia in water is 5 mol / L.

[0116] (1) After mixing the precursor solution with 130 μL of the acidic catalyst, stir at room temperature for 120 min, then add 87 μL of the alkaline catalyst, and place in a 50°C oven to perform sol-gel transition for 36 h.

[0117] (2) Use ethanol to perform room-temperature solvent replacement on the gel prepared in step (1) to wash away the excess catalyst and by-products.

[0118] (3) Soak the gel prepared in step (2) in n-decane at 60°C to perform high-temperature solvent replacement for 3 h, 6 h, 9 h, and 12 h.

[0119] (4) Perform supercritical drying on the gel prepared in step (3) at a drying pressure of 10 MPa and a temperature of 40°C to obtain silica aerogels with different wettabilities, the contact angle of the obtained samples gradually increases with different high-temperature solvent treatment times, and finally a hydrophobic silica is formed.

[0120] Example 2

[0121] Take 57 μL of hexyl triethoxysilane and 89 μL of chloro triethoxysilane to form an organosiloxane precursor solution in 1 mL of water, the content of silicon in the organosiloxane is 1 mol / L; take a certain amount of hydrochloric acid into water to stir to form an acidic catalyst, the concentration of the hydrochloric acid in water is 0.05 mol / L. Take a certain amount of ammonia into water to stir to form an alkaline catalyst, the concentration of the ammonia in water is 2.5 mol / L.

[0122] (1) After mixing the precursor solution with 130 μL of the acidic catalyst, stir at room temperature for 240 min, then add 87 μL of the alkaline catalyst, and place in a 100°C oven to perform sol-gel transition for 6 h.

[0123] (2) Use ethanol to perform room-temperature solvent replacement on the gel prepared in step (1) to wash away the excess catalyst and by-products.

[0124] (3) Soak the gel prepared in step (2) in n-hexane at 60°C to perform high-temperature solvent replacement for 12 h.

[0125] (4) Soak the gel prepared in step (3) in water at 100°C to perform high-temperature solvent replacement for 3 h, 6 h, 9 h, and 12 h.

[0126] (5) The gel prepared in step (4) is subjected to solvent exchange with ethanol at room temperature.

[0127] (6) The gel prepared in step (5) is subjected to supercritical drying at a drying pressure of 10 MPa and a temperature of 40°C to obtain silica aerogels with different wettabilities, indicating that the contact angle of the final silica aerogel with water decreases with increasing water solvent treatment time.

[0128] Example 3

[0129] An organosiloxane precursor solution is formed by taking 570 μL of methyltrimethoxysilane and 150 μL of tetraethoxysilane in 1 mL of acetone, the content of silicon in the organosiloxane being 5 mol / L; a certain amount of hydrochloric acid is added to water to form an acidic catalyst, the concentration of the hydrochloric acid in water being 0.02 mol / L. A certain amount of ammonia water is added to water to form an alkaline catalyst, the concentration of the ammonia water in water being 1 mol / L.

[0130] (1) The precursor solution is mixed with 130 μL of the acidic catalyst and stirred at room temperature for 60 min, then 87 μL of the alkaline catalyst is added, and the mixture is placed in a 60°C oven to undergo sol-gel transition for 24 h.

[0131] (2) The gel prepared in step (1) is subjected to room temperature solvent exchange with ethanol to wash away excess catalyst and by-products.

[0132] (3) The gel prepared in step (2) is soaked in 80°C water for high-temperature solvent exchange for 3 h, 6 h, 9 h, and 12 h, respectively.

[0133] (4) The gel prepared in step (3) is subjected to solvent exchange at room temperature.

[0134] (5) The gel prepared in step (4) is subjected to supercritical drying at a drying pressure of 10 MPa and a temperature of 40°C to obtain silica aerogels with different wettabilities.

[0135] Example 4

[0136] An organosiloxane precursor solution is formed by taking 30 μL of vinyltrimethoxysilane and 119 μL of tetrapropoxysilane in 1 mL of n-hexane, the content of silicon in the organosiloxane being 1 mol / L; a certain amount of hydrochloric acid is added to water to form an acidic catalyst, the concentration of the hydrochloric acid in water being 0.03 mol / L. A certain amount of ammonia water is added to water to form an alkaline catalyst, the concentration of the ammonia water in water being 3 mol / L.

[0137] (1) The precursor solution was mixed with 130 μL of acidic catalyst and stirred at room temperature for 90 min, then 87 μL of basic catalyst was added, and the sol-gel transition was carried out in a 40°C oven for 48 h.

[0138] (2) The gel prepared in step (1) was subjected to room temperature solvent replacement with ethanol to wash away the excess catalyst and by-products.

[0139] (3) The gel prepared in step (2) was soaked in 40°C water for high-temperature solvent replacement for 48 h.

[0140] (4) The gel prepared in step (3) was subjected to high-temperature methanol solvent replacement at 80°C for 6 h, 12 h, 18 h, and 24 h.

[0141] (5) The gel prepared in step (4) was subjected to supercritical drying at a drying pressure of 10 MPa and a temperature of 40°C to obtain silica aerogels with different wettabilities, and the contact angle change process of the samples after different solvent treatment times was exhibited.

[0142] Example 5

[0143] An organosiloxane precursor solution was formed by taking 258 μL of n-butyl trimethoxysilane and 177 μL of tetrapropoxysilane in 1 mL of dimethyl sulfoxide, and the silicon content in the organosiloxane was 3 mol / L; a certain amount of hydrochloric acid was taken and stirred in water to form an acidic catalyst, and the concentration of the hydrochloric acid in water was 0.08 mol / L. A certain amount of ammonia water was taken and stirred in water to form a basic catalyst, and the concentration of the ammonia water in water was 8 mol / L.

[0144] (1) The precursor solution was mixed with 130 μL of acidic catalyst and stirred at room temperature for 180 min, then 87 μL of basic catalyst was added, and the sol-gel transition was carried out in a 50°C oven for 18 h.

[0145] (2) The gel prepared in step (1) was subjected to room temperature solvent replacement with ethanol to wash away the excess catalyst and by-products.

[0146] (3) The gel prepared in step (2) was subjected to supercritical drying at a drying pressure of 10 MPa and a temperature of 40°C to obtain superhydrophobic silica aerogels.

[0147] (4) The superhydrophobic silica aerogel prepared in step (3) was placed in 100°C water vapor for 48 h, and the number of times was 3, to obtain a silica aerogel with a surface that could be infiltrated in water.

[0148] Example 6

[0149] Take 500 μL methyl sodium silicate and 220 μL sodium silicate to form organosiloxane precursor solution in 1 mL water, the content of silicon in the organosiloxane is 5 mol / L; take a certain amount of hydrochloric acid into water to stir to form an acidic catalyst, the concentration of the hydrochloric acid in water is 0.1 mol / L. Take a certain amount of ammonia into water to stir to form an alkaline catalyst, the concentration of the ammonia in water is 10 mol / L.

[0150] (1) Mix the precursor solution with 130 μL acidic catalyst, stir at room temperature for 90 min, then add 87 μL alkaline catalyst, and place in a 100°C oven for sol-gel transition for 12 h.

[0151] (2) The gel prepared in step (1) is subjected to room temperature solvent replacement with ethanol to wash away excess catalyst and byproducts.

[0152] (3) The gel prepared in step (2) is subjected to supercritical drying, with a drying pressure of 10 MPa and a temperature of 40°C, to obtain super-hydrophilic silica aerogel.

[0153] (4) The super-hydrophilic silica aerogel prepared in step (3) is placed in 150°C n-heptane vapor for 6 h, for 6 times, to obtain hydrophobic silica aerogel.

[0154] Example 7

[0155] Take 700 μL allyl trimethoxysilane and 300 μL tetraethoxysilane to form organosiloxane precursor solution in 1 mL methanol, the content of silicon in the organosiloxane is 5 mol / L; take a certain amount of sulfuric acid into water to stir to form an acidic catalyst, the concentration of the sulfuric acid in water is 0.001 mol / L. Take a certain amount of sodium hydroxide into water to stir to form an alkaline catalyst, the concentration of the sodium hydroxide in water is 0.1 mol / L.

[0156] (1) Mix the precursor solution with 130 μL acidic catalyst, stir at room temperature for 60 min, then add 87 μL alkaline catalyst, and place in a 100°C oven for sol-gel transition for 10 h.

[0157] (2) The gel prepared in step (1) is subjected to room temperature solvent replacement with ethanol to wash away excess catalyst and byproducts.

[0158] (3) The gel prepared in step (2) is subjected to supercritical drying, with a drying pressure of 10 MPa and a temperature of 40°C, to obtain super-hydrophilic silica aerogel.

[0159] (4) The super-hydrophilic silica aerogel prepared in step (3) was placed in n-hexane vapor at 120℃ for 48h, for 3 times, to obtain a hydrophobic silica aerogel.

[0160] Example 8

[0161] An organic siloxane precursor solution was prepared by mixing 300μL of butyl triethoxysilane and 700μL of tetramethoxysilane in 1mL of water, the concentration of silicon in the organic siloxane was 2mol / L; an acid catalyst was prepared by mixing a certain amount of acetic acid in water, the concentration of the acetic acid in water was 0.5mol / L; and a basic catalyst was prepared by mixing a certain amount of triethylamine acid in water, the concentration of the triethylamine acid in water was 5mol / L.

[0162] (1) The precursor solution was mixed with 130μL of the acid catalyst and stirred at room temperature for 80min, then 87μL of the basic catalyst was added, and the mixture was placed in an oven at 80℃ for 12h to undergo sol-gel transition.

[0163] (2) The gel prepared in step (1) was subjected to room temperature solvent replacement with ethanol to remove excess catalyst and by-products.

[0164] (3) The gel prepared in step (2) was immersed in t-butyl alcohol at 40℃ for 48h to undergo high-temperature solvent replacement.

[0165] (4) The gel prepared in step (3) was immersed in water at 100℃ for 6h, 9h, 12h and 24h to undergo high-temperature solvent replacement.

[0166] (5) The gel prepared in step (4) was subjected to ethanol solvent replacement at room temperature.

[0167] (6) The gel prepared in step (5) was subjected to supercritical drying at a pressure of 10MPa and a temperature of 40℃ to obtain silica aerogels with different wettability.

[0168] The inventors also tested the product aerogel obtained in the above preferred embodiment, and the results are as follows:

[0169] Figure 2 Figure 1 is a sample image of the super-hydrophobic silica aerogel obtained in Example 1. Figure 3 Figure 2 is a scanning electron microscope image of the super-hydrophobic silica aerogel obtained in Example 1. Figure 4 Figure 3 is a contact angle image of the super-hydrophobic silica aerogel obtained in Example 1. Figure 5 Figure 4 is a nitrogen adsorption curve of the super-hydrophobic silica aerogel obtained in Example 1. Figure 6 Figure 5 is a pore size distribution curve of the super-hydrophobic silica aerogel obtained in Example 1. The pore size distribution curve was obtained by using the BJH method. Figures 2-6It can be found that the superhydrophobic silica aerogel has a three-dimensional porous network structure, a high contact angle and a specific surface area.

[0170] Figure 7 A sample graph of the superhydrophilic silica aerogel obtained in Example 3. Figure 8 A scanning electron microscope graph of the superhydrophilic silica aerogel obtained in Example 3. Figure 9 A contact angle graph of the superhydrophilic silica aerogel obtained in Example 3. Figure 10 A nitrogen adsorption curve graph of the superhydrophilic silica aerogel obtained in Example 3. Figure 11 A pore size distribution curve graph of the superhydrophilic silica aerogel obtained in Example 3. By Figures 7-11 It can be found that the superhydrophilic silica aerogel also has a three-dimensional porous network structure, an ultra-low contact angle and a high specific surface area.

[0171] Figure 12 A contact angle change graph of the superhydrophobic silica aerogel obtained in Examples 2 and 3 being converted into a superhydrophilic silica aerogel. Figure 13 A contact angle change graph of the superhydrophilic silica aerogel obtained in Examples 1 and 4 being converted into a superhydrophobic silica aerogel. By Figures 12-13 It can be found that the superhydrophobic-superhydrophilic silica aerogel based on solvent modification is reversible.

[0172] Figure 14 An infrared spectrum graph of the reversible superhydrophobic-superhydrophilic silica aerogel obtained in Comparative Example 1 and Example 1. By Figure 14 It can be found that the chemical structure of the silica aerogel is changed based on solvent modification, thereby causing the sample to present a superhydrophilic or hydrophobic structure.

[0173] Figure 15a and Figure 15b A reversible schematic diagram of the superhydrophobic-superhydrophilic silica aerogel based on gas phase modification obtained in Examples 5 and 6. By Figure 15a and Figure 15b It can be found that the superhydrophobic-superhydrophilic silica aerogel based on gas phase modification is reversible.

[0174] The above shows that the silica aerogel with different surface properties induced by solvents has a high specific surface area, pore volume and similar three-dimensional porous microstructure, but its contact angle can be changed from 0° to 150°, further confirming the feasibility of the solvent modified silica aerogel.

[0175] Comparative Example 3

[0176] Take 286 μL methyl trimethoxysilane to form organosiloxane precursor solution in 1 mL ethanol, the content of silicon in the organosiloxane is 2 mol / L; take a certain amount of hydrochloric acid to form acidic catalyst by stirring in water, the concentration of the hydrochloric acid in water is 0.01 mol / L. Take a certain amount of ammonia water to form alkaline catalyst by stirring in water, the concentration of the ammonia water in water is 2 mol / L.

[0177] (1) Mix the precursor solution with 130 μL acidic catalyst, then stir at room temperature for 60 min, and then add 87 μL alkaline catalyst, and place in an 80°C oven for sol-gel transition.

[0178] (2) Use ethanol to perform room temperature solvent replacement on the gel prepared in step (1) to wash away excess catalyst and by-products.

[0179] (3) Soak the gel prepared in step (2) in 80°C water to perform high-temperature solvent replacement for 5 days, 10 days, 15 days, and 20 days, respectively.

[0180] (4) Perform solvent replacement on the gel prepared in step (3) at room temperature.

[0181] (5) Perform supercritical drying on the gel prepared in step (4) at a drying pressure of 10 MPa and a temperature of 40°C to obtain hydrophobic silica aerogel.

[0182] The comparative example differs from example 3 in that the organosiloxane precursor solution only contains siloxane with one methyl group, and therefore only hydrophobic silica aerogel can be obtained. Figure 16a 、 Figure 16b 、 Figure 16c 、 Figure 16d The hydrophobic silica aerogel prepared from the precursor containing only siloxane with one methyl group obtained in comparative example 3 cannot realize the reversible hydrophilic-hydrophobic transition of the silica aerogel through high-temperature solvent replacement.

[0183] Comparative example 4

[0184] Take 296 μL tetramethyl orthosilicate to form organosiloxane precursor solution in 1 mL ethanol, the content of silicon in the organosiloxane is 2 mol / L; take a certain amount of hydrochloric acid to form acidic catalyst by stirring in water, the concentration of the hydrochloric acid in water is 0.01 mol / L. Take a certain amount of ammonia water to form alkaline catalyst by stirring in water, the concentration of the ammonia water in water is 2 mol / L.

[0185] (1) Mix the precursor solution with 130 μL acidic catalyst, then stir at room temperature for 60 min, and then add 87 μL alkaline catalyst, and place in an 80°C oven for sol-gel transition.

[0186] (2) The gel prepared in step (1) is subjected to room temperature solvent exchange using ethanol to wash away the excess catalyst and by-products.

[0187] (3) The gel prepared in step (2) is soaked in 80°C methanol for high temperature solvent exchange for 5 days, 10 days, 15 days and 20 days, respectively.

[0188] (4) The gel prepared in step (3) is subjected to room temperature solvent exchange.

[0189] (5) The gel prepared in step (4) is subjected to supercritical drying at a pressure of 10 MPa and a temperature of 40°C to obtain a hydrophilic silica aerogel.

[0190] The comparative example differs from example 1 in that the organosiloxane precursor solution only contains siloxanes without methyl groups, and thus only a hydrophilic silica aerogel can be obtained. Figure 17a 、 Figure 17b 、 Figure 17c 、 Figure 17d The hydrophilic silica aerogel prepared from the precursor containing only siloxanes without methyl groups in comparative example 4 cannot be modified to be hydrophobic and reversibly switch between hydrophilic and hydrophobic by high temperature solvent exchange.

[0191] Comparative example 5

[0192] 286 μL of methyltrimethoxysilane and 296 μL of tetramethyl orthosilicate are taken to form an organosiloxane precursor solution in 1 mL of water, and the content of silicon in the organosiloxane is 4 mol / L; a certain amount of hydrochloric acid is taken and stirred in water to form an acidic catalyst, and the concentration of the hydrochloric acid in water is 0.01 mol / L. A certain amount of ammonia water is taken and stirred in water to form an alkaline catalyst, and the concentration of the ammonia water in water is 2 mol / L.

[0193] (1) The precursor solution is mixed with 130 μL of the acidic catalyst and stirred at room temperature for 60 min, then 87 μL of the alkaline catalyst is added, and the sol-gel transition is carried out in an 80°C oven.

[0194] (2) The gel prepared in step (1) is subjected to room temperature solvent exchange using ethanol to wash away the excess catalyst and by-products.

[0195] (3) The gel prepared in step (2) is soaked in 80°C benzene or carbon tetrachloride or glycerol or styrene solvent for high temperature solvent exchange for 48 h, respectively.

[0196] (4) The gel prepared in step (3) is subjected to room temperature solvent exchange.

[0197] (5) The gel prepared in step (4) is subjected to supercritical drying at a drying pressure of 10 MPa and a temperature of 40°C to obtain a hydrophilic silica aerogel.

[0198] The comparative example differs from example 1 in that the organic solvent used in the high-temperature solvent replacement in step (3) is a solvent other than methanol, ethanol, tert-butanol, n-decanol, n-hexane, n-heptane, such as benzene or carbon tetrachloride or glycerol or styrene, Figure 18a and Figure 18b It is shown that the obtained silica aerogel still retains its original hydrophilic property, and other solvents cannot convert the hydrophilic silica aerogel into a hydrophobic silica aerogel, nor can they achieve the reversible hydrophilic-hydrophobic conversion of the silica aerogel. Because benzene or carbon tetrachloride or glycerol or styrene cannot undergo esterification with the silicon hydroxyl groups on the surface of the silica, while methanol, ethanol, tert-butanol, n-decanol, n-hexane, n-heptane, etc. can undergo esterification with the silicon hydroxyl groups on the surface of the silica to obtain a hydrophobic silica aerogel.

[0199] Comparative example 6

[0200] Take 515 μL of methyltrimethoxysilane and 60 μL of tetramethyl orthosilicate to form an organosiloxane precursor solution in 1 mL of ethanol, and the silicon content in the above organosiloxane is 4 mol / L; take a certain amount of hydrochloric acid and add it to water to stir to form an acidic catalyst, and the concentration of the hydrochloric acid in water is 0.01 mol / L. Take a certain amount of ammonia water and add it to water to stir to form an alkaline catalyst, and the concentration of the ammonia water in water is 2 mol / L.

[0201] (1) The precursor solution is mixed with 130 μL of the acidic catalyst and stirred at room temperature for 60 min, then 87 μL of the alkaline catalyst is added, and the sol-gel transition is carried out in an 80°C oven.

[0202] (2) The gel prepared in step (1) is subjected to room-temperature solvent replacement with ethanol to wash away excess catalyst and by-products.

[0203] (3) The gel prepared in step (2) is soaked in 80°C water for high-temperature solvent replacement for 48 h.

[0204] (4) The gel prepared in step (3) is subjected to solvent replacement at room temperature.

[0205] (5) The gel prepared in step (4) is subjected to supercritical drying at a drying pressure of 10 MPa and a temperature of 40°C to obtain a hydrophilic silica aerogel

[0206] Comparative Example 2 is the same as Example 3 except that the molar ratio of methyltrimethoxysilane to tetramethylorthosilicate is 9:1, outside the range of 7:3 to 3:7. Even after the high temperature aqueous solvent exchange, the resulting silica aerogel retains its original hydrophobic properties. Figure 19 Comparative Example 6 is the same as Example 3 except that the molar ratio of methyltrimethoxysilane to tetramethylorthosilicate is 9:1, outside the range of 7:3 to 3:7. Even after the high temperature aqueous solvent exchange, the resulting silica aerogel retains its original hydrophobic properties.

[0207] In addition, the inventors have also tested other raw materials, process operations, and process conditions described in the specification, and have obtained relatively ideal results.

[0208] It should be understood that in the present application, where a composition is described as having, containing, or including other components, it can be possible that the description is not exhaustive or complete, and that other compositions within the scope of the present application are intended to be protected. That is, any alternative or equivalent or substitute or modification or improvement that falls within the logical and spiritual scope of the present application is intended to be within the scope of the present application.

[0209] It should be understood that the specific examples described above are merely preferred embodiments of the present application, and should not be construed as limiting the design concept of the present application. For those skilled in the relevant art, any other modifications and improvements made on the basis of the inventive concept of the present application are within the scope of protection of the present application.

Claims

1. A method for preparing reversible superhydrophilic-superhydrophobic silica aerogels, characterized by, The application relates to a method for preparing reversible super-hydrophilic-super-hydrophobic silica aerogel. Providing an organosiloxane precursor solution containing organosiloxane monomers and a solvent, wherein the organosiloxane monomers include a combination of siloxanes with one methyl and siloxanes without methyl, and the molar ratio of the siloxanes with one methyl to the siloxanes without methyl is 7:3 to 3:7; Performing a sol-gel reaction on the organosiloxane precursor solution by acid hydrolysis and alkaline condensation in the presence of an acidic catalyst and an alkaline catalyst to obtain a wet gel; Performing high-temperature solvent replacement on the wet gel with a modified solvent to obtain reversible super-hydrophilic-super-hydrophobic silica aerogel, wherein the modified solvent is any one of a hydrophobic modified solvent or a hydrophilic modified solvent, the hydrophobic modified solvent is any one of methanol, ethanol, t-butyl alcohol, n-decanol, n-hexane, n-heptane or a combination of two or more thereof, and the hydrophilic modified solvent is water; Or, after drying treatment on the wet gel, performing gas-phase modification on the obtained aerogel with a gas-phase modified solvent to obtain reversible super-hydrophilic-super-hydrophobic silica aerogel.

2. The production method according to claim 1, characterized by: The molar ratio of the siloxanes with one methyl to the siloxanes without methyl is 7:3 to 4:

6.

3. The method of claim 1, wherein: The siloxanes with one methyl include any one of methyltrimethoxysilane, methyltriethoxysilane, sodium methylsiliconate, propyltrimethoxysilane, butyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, allyltriethoxysilane, allyltrimethoxysilane, ethyltrimethoxysilane, hexyltriethoxysilane, n-butyltrimethoxysilane or a combination of two or more thereof.

4. The method of claim 1, wherein: The siloxanes without methyl include any one of tetramethoxysilane, tetraethoxysilane, sodium silicate, tetrapropoxysilane, chlorotriethoxysilane, triethoxysilane or a combination of two or more thereof.

5. The method of claim 1, wherein: The solvent includes any one of methanol, ethanol, n-hexane, n-heptane, dimethyl sulfoxide, acetone, dimethylformamide and water.

6. The method of claim 1, wherein: The molar content of silicon in the organosiloxane precursor solution is 1 mol / L to 5 mol / L.

7. The method of claim 1, wherein: The acidic catalyst includes an acidic substance and a catalyst solvent, wherein the acidic substance includes any one of hydrochloric acid, sulfuric acid and acetic acid or a combination of two or more thereof, and the catalyst solvent includes any one of methanol, ethanol and water or a combination of two or more thereof.

8. The method of claim 7, wherein: The concentration of the acidic substance in the acidic catalyst is 0.001 mol / L to 0.1 mol / L.

9. The method of claim 1, wherein: The alkaline catalyst includes an alkaline substance and a catalyst solvent, wherein the alkaline substance includes any one of ammonia, sodium hydroxide and triethylamine or a combination of two or more thereof, and the catalyst solvent includes any one of methanol, ethanol and water or a combination of two or more thereof.

10. The method of claim 9, wherein: The concentration of the alkaline substance in the alkaline catalyst is 0.1 mol / L to 10 mol / L.

11. The production method according to claim 1, characterized by, The application also discloses a method for preparing reversible super-hydrophilic-super-hydrophobic silica aerogel. First, the organosiloxane precursor solution is mixed with an acidic catalyst, then stirred at room temperature for 60 to 240 minutes to perform acid hydrolysis, and then an alkaline catalyst is added to perform a sol-gel reaction at high temperature to obtain a wet gel.

12. The method of claim 1, wherein: The temperature of the sol-gel reaction is 40-100°C, and the time is 6-48 hours.

13. The method of claim 12, wherein: The temperature of the sol-gel reaction is 50-90°C.

14. The method of claim 1, wherein: The temperature of the high-temperature solvent replacement is 40-100°C, the time is 6-48 hours, and the replacement times are 3-6 times.

15. The method of claim 14, wherein: The temperature of the high-temperature solvent replacement is 50-90°C.

16. The method of claim 1, wherein: The temperature of the gas-phase modification is 100-150°C, the time is 6-48 hours, and the times are 3-6 times.

17. The method of claim 1, wherein, Further comprising: Before or after the high-temperature solvent replacement of the wet gel with a modified solvent, the wet gel is subjected to a normal-temperature solvent replacement.

18. The method of claim 17, wherein: The replacement solvent used in the normal-temperature solvent replacement is selected from any one or a combination of two or more of methanol, ethanol, tert-butanol, and dimethyl sulfoxide.

19. The method of claim 1, wherein, Further comprising: After the normal-temperature solvent replacement or the high-temperature solvent replacement of the wet gel, a drying treatment is performed to obtain reversible superhydrophilic-superhydrophobic silica aerogel.

20. The method of claim 19, wherein: The drying treatment comprises at least any one of normal-pressure drying, supercritical drying, and freeze drying.

21. The method of claim 20, wherein: The drying treatment comprises at least any one of supercritical drying and normal-pressure drying.

22. The method of claim 1, wherein: The density of the reversible superhydrophilic-superhydrophobic silica aerogel is 0.08 g / cm 3 ~ 0.12 g / cm 3 .

23. The method of claim 1, wherein: The specific surface area of the hydrophobic silica aerogel obtained by the preparation method is 720 m 2 / g ~ 1007 m 2 / g.

24. The method of claim 1, wherein: The specific surface area of the hydrophilic silica aerogel prepared by the preparation method is 500 m 2 / g ~ 600 m 2 / g.

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