A highly efficient heat-insulating, lightweight, transparent silica aerogel material and its preparation method

Abstract

The present invention relates to a highly efficient heat-insulating, lightweight, transparent silica aerogel material and a preparation method thereof. The method comprises the following steps: covering the upper surface of an amino acid aqueous solution with an incompatible organic solvent, then adding an organosilicon ester from above the covered organic solvent and performing an interfacial reaction; adding a catalyst solution above the obtained silica nanoparticle aqueous solution whose surface is covered with an organic solvent and performing a gel reaction; removing the organic solvent covered by the obtained silica hydrogel whose surface is covered with an organic solvent, then adding an amino acid aging mother liquor for aging; sequentially performing solvent replacement and supercritical drying on the obtained aged and enhanced silica hydrogel to obtain a highly efficient heat-insulating, lightweight, transparent silica aerogel material. The highly efficient heat-insulating, lightweight, transparent silica aerogel material prepared by the present invention has very low thermal conductivity at room temperature and relatively high temperature, achieving highly efficient heat insulation over a wide temperature range.

Description

Technical Field

[0001] The present invention belongs to the technical field of nanoporous materials, and in particular relates to a highly efficient heat-insulating, lightweight, transparent silica aerogel material and a preparation method thereof. Background Art

[0002] Silica aerogel is the most prominent representative of the aerogel family and currently the most mature and widely used type of oxide aerogel. First prepared in 1931 by Kistler in the United States using the sol-gel method and supercritical drying technology, it has shown promising applications in a wide range of fields, including space exploration, thermal insulation, energy storage, environmental protection, sensing, chemical catalysis, and high-energy physics. It has been hailed as one of the ten wonder materials that will change the world. Silica aerogel is composed of nano-colloidal silica particles stacked in three dimensions, exhibiting a rich porous network structure, making it a typical ultra-lightweight solid material. Silica aerogel possesses numerous unique properties, including ultra-low density, ultra-large specific surface area, ultra-high porosity, ultra-low dielectric constant, ultra-high optical transparency, and ultra-low thermal conductivity, with its thermal insulation performance undoubtedly being the most noteworthy. Due to its porous properties and nanoscale pore size, silica aerogel is a highly insulating material. At ambient temperature and atmospheric pressure, its thermal conductivity can be as low as 0.012 W / (m·K), which is lower than that of still air (0.025 W / (m·K)). In a vacuum, its thermal conductivity is only 0.006 W / (m·K).

[0003] Compared with general thermal insulation materials, silica aerogel has high-efficiency and highly reliable thermal insulation performance in multiple environments, including different temperature ranges, different air pressures, and different atmospheres. Aerogel materials are not only suitable for thermal insulation in the normal pressure environment of the Earth's surface, but also for thermal insulation in high vacuum environments such as the moon, low-Earth orbit, and the near-space stratosphere. They are also suitable for thermal insulation in low vacuum environments such as Mars, Saturn, and the near-space mesosphere. For aerogel thermal insulation materials, thermal insulation performance directly affects the thickness and weight of the insulation layer. Reducing the thermal conductivity of aerogel is of essential significance for reducing the weight and increasing the efficiency of the system. In particular, it is a decisive factor in determining whether the material can be used for high-efficiency thermal insulation in application scenarios such as confined space of aircraft, future deep space / ultra-deep space exploration, and high-payload manned exploration.

[0004] However, for low density (<0.1g / cm 3) for silica aerogel materials, improving thermal insulation performance is particularly difficult. This is because in the sol-gel preparation process of low-density aerogels, in order to obtain the ultimate low-density properties of the material, the silicon source content used is relatively small, and the controllable regulation of the sol-gel reaction is even more difficult. Ultimately, the size and uniformity of the silica nanoparticles and pore structure are difficult to adjust, resulting in large differences in the size of the silica nanoparticles, which directly or indirectly easily induce the production of complex cross-scale pore structures. The presence of larger pores (>100nm) reduces the structural uniformity of the aerogel. The pore size is significantly larger than the mean free path of gas molecules (70nm), resulting in an increase in gas-phase thermal conductivity, ultimately increasing the apparent thermal conductivity of the aerogel, which greatly affects the thermal insulation, light transmittance, and mechanical properties of the low-density aerogel.

[0005] Chinese patent application CN105271263A reports a low-density transparent silica aerogel and its preparation method. The silica gel is prepared by mixing water, alcohol, and hexamethyldisiloxane, adding the mixture to a reactor, heating the reaction, and further catalyzing it with hydrofluoric acid. The aerogel obtained after supercritical drying has a relative density of 15 to 100 mg / cm 3 , the thermal conductivity (25 ℃) is as low as 0.012W / (m·K), and the transparency is good; Chinese patent application CN109019611A reports a bulk transparent silica aerogel and its rapid preparation method and application. Silicone is used as a silicon source precursor, and a two-step acid-base method is used to prepare silica gel. A non-proton polar solvent is added during the gel stage, and a bulk transparent aerogel is prepared by supercritical drying with a density of 0.11g / cm 3 The thermal conductivity is about 0.013W / (m·K); Chinese patent application CN109179428A reports an enhanced transparent silica aerogel and its preparation method. The method uses organic silicon as raw material and generates uniformly dispersed silica nanoparticles as the dispersed phase in situ through an acid-base two-step method. After drying, the enhanced aerogel is obtained with a density of 0.11g / cm 3 The thermal conductivity is about 0.012W / (m·K), and the visible light transmittance is about 90%.

[0006] It can be seen that it has become very difficult to further reduce the room temperature thermal conductivity of transparent low-density aerogels, and related research has entered a bottleneck period. In addition, what is more serious is that as the ambient temperature of the transparent silica aerogels reported in the above patent applications increases, the molecular mean free path inside the transparent aerogel pores rapidly decreases, and the large pores inside the aerogel cannot effectively restrain the conduction of gas molecules, resulting in a rapid increase in thermal insulation performance. Therefore, there is an urgent need to develop transparent low-density aerogels that exhibit ultra-low thermal conductivity over a wide temperature range (25-100°C). Summary of the Invention

[0007] To address one or more technical problems in the prior art, the present invention provides a highly efficient, thermally insulating, lightweight, transparent silica aerogel material and a method for preparing the same. The present invention develops a two-phase sol-gel method based on temporal and spatial separation and assisted by amino acids, effectively separating the generation of the sol and the formation of the gel in time and space. Furthermore, the amino acids are utilized to stabilize and induce the alignment of the nanoparticles, thereby achieving a sufficiently small and uniform silica nanoparticle skeleton and pore structure in the hydrogel. The highly efficient, thermally insulating, lightweight, transparent silica aerogel material prepared by the present invention exhibits very low thermal conductivity at both room temperature and relatively high temperatures, achieving highly efficient thermal insulation over a wide temperature range.

[0008] In a first aspect, the present invention provides a method for preparing a highly efficient heat-insulating, lightweight, transparent silica aerogel material, the method comprising the following steps:

[0009] (1) covering the upper surface of the amino acid aqueous solution with an incompatible organic solvent, then adding an organosilicone ester from above the covered organic solvent and performing an interfacial reaction to obtain an aqueous solution of silica nanoparticles with the surface covered with the organic solvent;

[0010] (2) adding a catalyst solution onto the aqueous solution of silica nanoparticles whose surfaces are covered with an organic solvent and performing a gel reaction to obtain a silica hydrogel whose surface is covered with an organic solvent;

[0011] (3) removing the organic solvent covering the surface of the silica hydrogel covered with the organic solvent, and then adding an amino acid aging mother solution for aging to obtain an aging-enhanced silica hydrogel;

[0012] (4) The aged and enhanced silica hydrogel is subjected to solvent replacement and supercritical drying in sequence to produce a lightweight and transparent silica aerogel material with high efficiency and thermal insulation.

[0013] Preferably, in step (1), the amino acids contained in the amino acid aqueous solution are one or more of lysine, arginine and histidine; the concentration of the amino acid aqueous solution is 0.005-0.05 mol / L, preferably 0.01 mol / L; the organic solvent is one or more of n-hexane, cyclohexane, n-pentane, n-heptane and n-octane; and / or the organic silicone ester is one or more of ethyl orthosilicate, methyl orthosilicate, methyltrimethoxysilane, ethyltriethoxysilane and hexamethyldisiloxane.

[0014] Preferably, in step (1): the molar ratio of the organosilicon ester to the amino acid contained in the amino acid aqueous solution is 1:(0.0005-0.05), preferably 1:0.01; and / or the molar ratio of the organosilicon ester to the organic solvent is 1:(2-20), preferably 1:8.

[0015] Preferably, the temperature of the interfacial reaction is 40-80° C., preferably 60° C.; and / or the time of the interfacial reaction is 8-48 h, preferably 24 h.

[0016] Preferably, the catalyst solution is one or more of an ethanol solution of ammonia, a 1,4-dioxane solution of ammonia, an isopropanol solution of ammonia and a tetrahydrofuran solution of ammonia; and / or the molar ratio of ammonia to the organosilicon ester in the catalyst solution is (0.01-0.1):1, preferably 0.04:1.

[0017] Preferably, the temperature of the gel reaction is 20-70° C., preferably 50° C.; and / or the time of the gel reaction is 0.5-16 h, preferably 2 h.

[0018] Preferably, the amino acid aging mother liquor contains amino acids and water, and the amino acids contained in the amino acid aging mother liquor are one or more of lysine, arginine and histidine; the concentration of the amino acid aging mother liquor is 0.02-0.2 mol / L, preferably 0.05 mol / L; and / or the volume usage of the amino acid aging mother liquor is 0.05-0.8 times, preferably 0.2 times, the volume of the amino acid aqueous solution in step (1).

[0019] Preferably, the aging temperature is 30-70° C., preferably 50° C.; and / or the aging time is 24-120 h, preferably 72 h.

[0020] Preferably, in step (4), the aged enhanced silica hydrogel is first subjected to solvent replacement in ethanol to obtain an alcohol gel, and then the alcohol gel is subjected to supercritical carbon dioxide drying. During the supercritical carbon dioxide drying of the alcohol gel, the pressure in the drying kettle is maintained at 8 to 20 MPa, the temperature in the drying kettle is controlled at 10 to 20°C, and the solvent replacement is carried out using circulating liquid carbon dioxide for 24 to 120 hours. Then, the temperature is raised to 60°C at a rate of 5 to 10°C / h to reach a supercritical state, and the circulating supercritical carbon dioxide is continued to be replaced for 12 to 48 hours to remove the ethanol waste liquid, and then the pressure is released to atmospheric pressure at a rate of 0.3 to 1 MPa / h.

[0021] In a second aspect, the present invention provides a highly efficient heat-insulating, lightweight, transparent silica aerogel material prepared by the preparation method described in the first aspect of the present invention; preferably, the highly efficient heat-insulating, lightweight, transparent silica aerogel material has one or more of the following properties: the density of the highly efficient heat-insulating, lightweight, transparent silica aerogel material is 0.012 to 0.095 g / cm 3The light transmittance of the highly efficient thermal insulating lightweight transparent silica aerogel material with a thickness of 10 mm at 550 nm is 93.8%; the thermal conductivity of the highly efficient thermal insulating lightweight transparent silica aerogel material is as low as 0.010 W / (m·K) at room temperature; the thermal conductivity of the highly efficient thermal insulating lightweight transparent silica aerogel material is as low as 0.014 W / (m·K) at 100°C; the thermal conductivity of the highly efficient thermal insulating lightweight transparent silica aerogel material increases slightly over a wide temperature range from room temperature to 100°C.

[0022] Compared with the prior art, the present invention has at least the following beneficial effects:

[0023] (1) The present invention provides a novel method based on interface and amino acid catalytic reaction to prepare ultrasmall monodisperse silica nanoparticles. The interface diffusion reaction contributes to the formation of monodisperse nanoparticles, and the surface adsorption of basic amino acids contributes to the stable existence of ultrasmall nanoparticles, especially at higher concentrations.

[0024] (2) The present invention develops a two-phase sol-gel method based on time-space separation and assisted by amino acids. The present invention effectively separates the generation of sol and the formation of gel in time and space, and realizes the precise regulation of the complex reaction process of sol and gel, thereby realizing the effective control of the fine structure of aerogel. The obtained silica aerogel nanoskeleton is slender and uniform, and the aerogel nanopore structure is small and uniform.

[0025] (3) The thermal conductivity of the aerogel prepared by the present invention is very small at room temperature and relatively high temperature, achieving efficient thermal insulation in a wide temperature range. On the one hand, since the nanoparticle skeleton constituting the aerogel can be as small as 6nm and has excellent monodispersity, the neck contact between the particles is small, so the solid-phase heat conduction is small; on the other hand, due to the stabilization and induction arrangement of the nanoparticles by the alkaline amino acids on the surface of silica, the nanopores of the aerogel are small and uniform, so the gas-phase heat conduction is also very small, especially the smaller pore size. Even if the mean free path of the gas molecules decreases rapidly as the ambient temperature rises, the conduction of the gas molecules can still be effectively restrained, so that the thermal insulation performance changes less with the increase in temperature, which is significantly different from the currently prepared transparent low-thermal conductivity aerogel (the thermal conductivity increases faster with the increase in temperature). BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the preparation of monodisperse ultra-small silica nanoparticles obtained in Example 1 of the present invention;

[0027] Figure 2 This is a transmission electron microscope image of the monodisperse ultra-small size silicon dioxide nanoparticles prepared in Example 1 of the present invention;

[0028] Figure 3 This is an appearance picture of the highly efficient heat-insulating, lightweight, transparent silica aerogel material prepared in Example 1 of the present invention placed on a piece of paper with the word "Aerogel" written all over it;

[0029] Figure 4 This is a scanning electron microscope image of the highly efficient heat-insulating, lightweight, transparent silica aerogel material prepared in Example 1 of the present invention;

[0030] Figure 5 This is a transmission electron microscope image of the highly efficient heat-insulating, lightweight, transparent silica aerogel material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0031] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the embodiments described are part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0032] In a first aspect, the present invention provides a method for preparing a highly efficient heat-insulating, lightweight, transparent silica aerogel material, the method comprising the following steps:

[0033] (1) An incompatible organic solvent (oil phase solvent) is covered on the upper surface of an amino acid aqueous solution, and then an organic silicone ester is added from above the covered organic solvent and an interfacial reaction (two-phase interface diffusion reaction) is carried out to obtain an aqueous solution of silica nanoparticles with the surface covered with an organic solvent (i.e., an aqueous solution containing silica nanoparticles with the surface covered with an organic solvent); in the present invention, the amino acid aqueous solution is composed of amino acids and water, i.e., a mixture of amino acids and water; in the present invention, the silica nanoparticles contained in the obtained aqueous solution of silica nanoparticles are monodisperse ultra-small particle size silica nanoparticles; in the present invention, the aqueous solution of silica nanoparticles with the surface covered with an organic solvent is an oil-water mixed solution with the lower layer being the aqueous solution of silica nanoparticles and the upper layer being the organic solvent;

[0034] (2) adding a catalyst solution onto the aqueous solution of silica nanoparticles whose surfaces are covered with an organic solvent and performing a gel reaction to obtain a silica hydrogel whose surface is covered with an organic solvent;

[0035] (3) removing the organic solvent covering the surface of the silica hydrogel covered with the organic solvent, and then adding an amino acid aging mother liquor for aging to obtain an aging-enhanced silica hydrogel; the present invention uses an amino acid aging mother liquor in the aging stage, because the supplemented amino acid will be partially adsorbed on the surface of the silica nanoparticles, which can effectively slow down the coarsening of the particles. If other aging mother liquors are used, the skeleton particles of the aerogel will easily grow in the aging stage, and the particles will become coarsened. The coarsening of the particles will affect the thermal conductivity and other properties of the aerogel;

[0036] (4) The aged and enhanced silica hydrogel is subjected to solvent replacement and supercritical drying in sequence to produce a lightweight and transparent silica aerogel material with high efficiency and thermal insulation.

[0037] The method of the present invention first prepares monodisperse ultra-small silica nanoparticles through a two-phase interface reaction, then prepares a fine-structured silica hydrogel through time-space separation, and then performs aging of the fine-structured silica hydrogel and aging-enhanced silica hydrogel drying.

[0038] The present invention develops a two-phase sol-gel method based on time-space separation and assisted by amino acids, which effectively separates the generation of sol and the formation of gel in time and space, and utilizes the stabilization and induction arrangement of amino acids on nanoparticles, thereby achieving a sufficiently small and uniform skeleton and pore structure of silica nanoparticles in the hydrogel; in the present invention, the preparation process of the highly efficient heat-insulating lightweight transparent silica aerogel material is specifically as follows: an immiscible oil phase reagent is covered on the amino acid aqueous solution, and then an organic silicone ester is added to the oil phase reagent, and the organic silicone ester is diffused in the oil phase. At the oil-water interface, the organic silicone ester undergoes precise hydrolysis and condensation reactions with water under the catalysis of amino acids to form monodisperse ultrasmall silica nanoparticles with alkaline amino acids adsorbed on the surface (see the schematic diagram of the preparation of monodisperse ultrasmall silica nanoparticles for details). Figure 1Due to the precise characteristics of the interfacial reaction and the charge repulsion stabilizing effect of the amino acids, ultra-small monodisperse silica nanoparticles are able to stably exist in the aqueous solution; a catalyst is then added to the oil phase to promote the gelation of the ultra-small monodisperse silica nanoparticles below the oil phase, thereby obtaining a silica hydrogel; after aging, solvent replacement, and supercritical drying, the silica hydrogel is subjected to a highly efficient, heat-insulating, lightweight, transparent silica aerogel material. Because the nanoparticle skeletons that make up the highly efficient, heat-insulating, lightweight, transparent silica aerogel described in the present invention are as low as 6nm and have excellent monodispersity, the neck contact between the particles is small, resulting in low solid-phase heat conduction; and due to the induced arrangement of the basic amino acids on the silica surface, the nanopores of the aerogel are small and uniform, resulting in low gas-phase heat conduction. In summary, the room temperature thermal conductivity of the high-efficiency heat-insulating, lightweight, transparent silica aerogel prepared by the present invention is as low as 0.010 W / (m·K). When the temperature rises to 100°C, the room temperature thermal conductivity of the aerogel increases slightly, only to 0.014 W / (m·K).

[0039] According to some specific embodiments, the preparation of the highly efficient heat-insulating lightweight transparent silica aerogel material comprises the following steps:

[0040] ① Preparation of monodisperse ultra-small silica nanoparticles by two-phase interfacial reaction: Cover the surface of the amino acid aqueous solution with a certain thickness of incompatible organic solvent, carefully add (slowly add) organic silicone ester, and after raising it to a certain temperature, an interfacial diffusion reaction occurs at this temperature. After a period of time, the organic silicone ester reacts completely to obtain a monodisperse ultra-small silica nanoparticle aqueous solution.

[0041] ② Prepare fine-structured silica hydrogel by time-space separation: Carefully (slowly) add the catalyst solution on top of the aqueous solution of silica nanoparticles covered with an organic solvent, then adjust the reaction temperature. After the catalyst diffuses into the aqueous phase, it promotes gelation and forms a fine-structured silica hydrogel.

[0042] ③ Aging of fine-structured silica hydrogel: The organic solvent covering the surface of the fine-structured silica hydrogel is removed, and then a certain volume of amino acid aging mother solution is added and aged at a certain temperature to obtain an aging-enhanced silica hydrogel.

[0043] ④ Drying of aging-enhanced silica hydrogel: After solvent replacement of the aging-enhanced silica hydrogel, supercritical drying is used to obtain a lightweight transparent silica aerogel material with high efficiency and thermal insulation.

[0044] According to some preferred embodiments, in step (1): the amino acid contained in the amino acid aqueous solution is one or more of lysine, arginine and histidine, preferably arginine; the concentration of the amino acid aqueous solution (concentration containing amino acids) is 0.005-0.05 mol / L (for example, 0.005, 0.008, 0.01, 0.02, 0.03, 0.04 or 0.05 mol / L), preferably 0.008-0.02 mol / L, more preferably 0.01 mol / L; in the present invention, the concentration of the amino acid aqueous solution refers to the initial concentration; the organic solvent is one or more of n-hexane, cyclohexane, n-pentane, n-heptane and n-octane, preferably n-hexane; and / or the organic silicone ester is one or more of tetraethyl orthosilicate, methyl orthosilicate, methyltrimethoxysilane, ethyltriethoxysilane and hexamethyldisiloxane, preferably tetraethyl orthosilicate.

[0045] According to some preferred embodiments, in step (1), the molar ratio of the organosilicon ester to the amino acid contained in the amino acid aqueous solution is 1:(0.0005-0.05) (e.g., 1:0.0005, 1:0.0008, 1:0.001, 1:0.005, 1:0.008, 1:0.01, 1:0.02, 1:0.03, 1:0.04 or 1:0.05), preferably 1:(0.008-0. 02), more preferably 1:0.01; and / or the molar ratio of the organosilicone ester to the organic solvent is 1:(2-20) (for example, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19 or 1:20), preferably 1:(5-12), more preferably 1:8.

[0046] In the present invention, preferably, the molar ratio of the organosilicon ester to the organic solvent is 1:(2-20). The present invention controls the organosilicon ester to the organic solvent to have a suitable molar ratio, which can control the diffusion time of the organosilicon ester in the organic solvent layer, thereby ensuring that the lightweight transparent silica aerogel with excellent performance and ultra-low thermal conductivity in a wide temperature range (25-100°C) is obtained; the present invention finds that if there is too little organic solvent and the thickness of the organic solvent layer is too thin, the organosilicon ester will diffuse quickly to the interface. If there is too much organic solvent and the thickness of the organic solvent layer is too thick, the reaction will be too rapid and the particle size control will be poor; if there is too much organic solvent and the thickness of the organic solvent layer is too thick, the organosilicon ester will diffuse very slowly to the interface. If there is too little organic solvent at the interface, the reaction will be too slow, the particle preparation efficiency will be very slow, and due to the lack of organosilicon ester, the particle size control will also be difficult.

[0047] According to some preferred embodiments, the temperature of the interfacial reaction is 40-80°C (e.g., 40°C, 50°C, 60°C, 70°C or 80°C), preferably 60°C; and / or the time of the interfacial reaction is 8-48h (e.g., 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46 or 48h), preferably 24h.

[0048] According to some preferred embodiments, the catalyst solution is one or more of an ethanol solution of ammonia, a 1,4-dioxane solution of ammonia, an isopropanol solution of ammonia and a tetrahydrofuran solution of ammonia, preferably an ethanol solution of ammonia, the ethanol solution of ammonia being composed of ammonia and ethanol, that is, a mixture of ammonia and ethanol, and the concentration of ammonia in the ethanol solution of ammonia is 0.05 to 1.5 mol / L; and / or the molar ratio of ammonia to the organosilicon ester in the catalyst solution is (0.01 to 0.1): 1 (for example, 0.01:1, 0.02:1, 0.03:1, 0.04:1, 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1 or 0.1:1), preferably 0.04:1.

[0049] According to some preferred embodiments, the temperature of the gel reaction is 20-70°C (e.g., 20°C, 30°C, 40°C, 50°C, 60°C or 70°C), preferably 50°C; and / or the time of the gel reaction is 0.5-16h (e.g., 0.5, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 or 16h), preferably 1-4h, more preferably 2h.

[0050] According to some preferred embodiments, the amino acid aging mother solution contains amino acids and water, and the amino acids contained in the amino acid aging mother solution are one or more of lysine, arginine and histidine; preferably, the amino acid aging mother solution is composed of amino acids and water, that is, it is a mixture of amino acids and water. Preferably, the amino acids in the amino acid aging mother solution are the same as the amino acids in the amino acid aqueous solution in step (1), that is, they are kept consistent; the concentration of the amino acid aging mother solution (the concentration of amino acids) is 0.0 2 to 0.2 mol / L (e.g., 0.02, 0.05, 0.08, 0.1, 0.15 or 0.2 mol / L), preferably 0.05 mol / L; and / or the volume of the amino acid aging mother solution is 0.05 to 0.8 times (e.g., 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 or 0.8 times) the volume of the amino acid aqueous solution in step (1), preferably 0.2 times.

[0051] According to some preferred embodiments, the aging temperature is 30-70°C (e.g., 30°C, 40°C, 50°C, 60°C or 70°C), preferably 50°C; and / or the aging time is 24-120h (e.g., 24, 28, 32, 36, 40, 44, 48, 52, 56, 60, 64, 68, 72, 76, 80, 84, 88, 92, 96, 100, 104, 108, 112, 116 or 120h), preferably 72h.

[0052] According to some preferred embodiments, in step (4), the aged enhanced silica hydrogel is first subjected to solvent replacement in ethanol to obtain an alcohol gel, and then the alcohol gel is subjected to supercritical carbon dioxide drying. During the supercritical carbon dioxide drying of the alcohol gel, the pressure in the drying kettle is maintained at 8 to 20 MPa (e.g., 8, 10, 12, 14, 16, 18 or 20 MPa), the temperature in the drying kettle is controlled to be 10 to 20° C. (e.g., 10° C., 15° C. or 20° C.), and the solvent replacement is performed using circulating liquid carbon dioxide for 24 to 12 0h (for example, 24, 36, 48, 60, 72, 84, 96, 108 or 120h), then raise the temperature to 60°C at a rate of 5-10°C / h (for example, 5, 6, 7, 8, 9 or 10°C / h) to reach a supercritical state, continue to replace with circulating supercritical carbon dioxide for 12-48h (for example, 12, 24, 36 or 48h) to take out the ethanol waste liquid, and then release the pressure to atmospheric pressure at a rate of 0.3-1MPa / h (for example, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1MPa / h).

[0053] According to some preferred embodiments, in step (4), optionally, a hydrophobic treatment step may be performed between solvent replacement and supercritical drying. The present invention has no particular limitation on the step of performing the hydrophobic treatment, and conventional techniques in the art may be employed.

[0054] In a second aspect, the present invention provides a highly efficient heat-insulating, lightweight, transparent silica aerogel material prepared by the preparation method described in the first aspect of the present invention.

[0055] According to some preferred embodiments, the highly efficient heat-insulating, lightweight, transparent silica aerogel material has one or more of the following properties:

[0056] The density of the highly efficient heat-insulating, lightweight, transparent silica aerogel material is 0.012 to 0.095 g / cm 3 ;

[0057] The light transmittance of the highly efficient heat-insulating, lightweight, transparent silica aerogel material with a thickness of 10 mm at 550 nm is 93.8%;

[0058] The thermal conductivity of the highly efficient heat-insulating, lightweight, transparent silica aerogel material at room temperature is as low as 0.010 W / (m·K);

[0059] The highly efficient heat-insulating, lightweight, transparent silica aerogel material has a minimum thermal conductivity of 0.014 W / (m·K) at 100°C;

[0060] The highly efficient heat-insulating, lightweight, transparent silica aerogel material has a small increase in thermal conductivity within a wide temperature range from room temperature to 100°C.

[0061] According to some preferred embodiments, the density of the highly efficient heat-insulating, lightweight, transparent silica aerogel material is 0.012 to 0.095 g / cm 3 , the thermal conductivity is less than 0.013W / (m·K) at room temperature and less than 0.016W / (m·K) at 100℃.

[0062] The present invention will be further described below by way of examples, but the protection scope of the present invention is not limited to these examples.

[0063] Example 1

[0064] ① Add 1L of arginine aqueous solution (concentration of 0.01mol / L, arginine 0.01mol) to a 5000mL circular flat mold, then slowly add 689.4g of n-hexane (8mol) to the upper surface of the arginine aqueous solution to cover it, and then slowly add 208.3g of ethyl orthosilicate (1mol) from above the n-hexane, raise the temperature to 60℃, react at the interface for 24h, and cool to room temperature to obtain an aqueous solution of silica nanoparticles with the surface covered with an organic solvent (n-hexane).

[0065] ② Slowly add 40 mL of ethanolic ammonia solution (the concentration of ammonia is 1 mol / L, and the amount of ammonia is 0.04 mol) above the aqueous solution of silica nanoparticles whose surface is covered with an organic solvent (n-hexane), raise the temperature to 50°C, and perform a gelation reaction for 2 hours. Cool to room temperature to obtain a silica hydrogel whose surface is covered with an organic solvent (n-hexane).

[0066] ③ Remove the n-hexane covering the upper surface of the silica hydrogel covered with an organic solvent (n-hexane), then add 200 mL of arginine aging mother solution (arginine concentration 0.05 mol / L) on the hydrogel, raise the temperature to 50°C, carry out aging reaction, the reaction time is 72 hours, and cool to room temperature to obtain aging-enhanced silica hydrogel; the arginine aging mother solution consists of arginine and water.

[0067] ④ Using a porous aluminum plate, the aged and enhanced silica hydrogel was placed in 10 times the volume of anhydrous ethanol and soaked for 2 days. The solution was replaced twice to obtain an alcohol gel, which was then dried with supercritical carbon dioxide. Using a porous aluminum plate, the alcohol gel was carefully placed in a drying kettle, anhydrous ethanol was added to cover the alcohol gel, and liquid carbon dioxide was injected into the drying kettle. The pressure in the kettle was maintained at 16 MPa, and the temperature in the drying kettle was controlled at 10°C. The solvent was replaced with circulating liquid carbon dioxide for 72 hours. The temperature was then raised to 60°C at a rate of 5°C / h to reach a supercritical state. At this temperature, the solvent was replaced with circulating supercritical carbon dioxide for 24 hours to ensure that the ethanol waste liquid was completely removed. The temperature in the drying kettle was maintained at 60°C, and the pressure was released to atmospheric pressure at a rate of 0.3 MPa / h. After the temperature in the kettle dropped to room temperature, the silica aerogel was taken out to obtain a highly efficient thermally insulating, lightweight, transparent silica aerogel material.

[0068] Example 2

[0069] Example 2 is basically the same as Example 1, except that:

[0070] ① Add 1L of arginine aqueous solution (concentration of 0.01mol / L, arginine 0.01mol) to a 5000mL circular flat mold, then slowly add 86.175g of n-hexane (1mol) to the upper surface of the arginine aqueous solution to cover it, and then slowly add 208.3g of ethyl orthosilicate (1mol) from above the n-hexane, raise the temperature to 60℃, react at the interface for 24h, and cool to room temperature to obtain an aqueous solution of silica nanoparticles with the surface covered with an organic solvent (n-hexane).

[0071] Example 3

[0072] Example 3 is basically the same as Example 1, except that:

[0073] ① Add 1L of arginine aqueous solution (concentration of 0.01mol / L, arginine 0.01mol) to a 5000mL circular flat mold, then slowly add 2068.2g of n-hexane (24mol) to the upper surface of the arginine aqueous solution to cover it, and then slowly add 208.3g of ethyl orthosilicate (1mol) from above the n-hexane, raise the temperature to 60℃, react at the interface for 24h, and cool to room temperature to obtain an aqueous solution of silica nanoparticles with the surface covered with an organic solvent (n-hexane).

[0074] Comparative Example 1

[0075] Comparative Example 1 is substantially the same as Example 1, except that:

[0076] ③ Remove the n-hexane covering the upper surface of the silica hydrogel covered with an organic solvent (n-hexane), then add 200 mL of ethanol on the hydrogel, raise the temperature to 50°C, carry out aging reaction, the reaction time is 72 hours, and cool to room temperature to obtain aging-enhanced silica hydrogel.

[0077] Comparative Example 2

[0078] ① Add 1 L of arginine aqueous solution (concentration of 0.01 mol / L, arginine 0.01 mol) and 208.3 g of ethyl orthosilicate (1 mol) to a 5000 mL circular flat mold and mix well. Raise the temperature to 60°C, allow the interface to react for 24 h, and cool to room temperature to obtain an aqueous solution containing silica particles.

[0079] ② Add 40 mL of ethanolic ammonia solution (1 mol / L ammonia concentration, 0.04 mol ammonia) to the aqueous solution containing silica particles and mix well. Raise the temperature to 50°C for gelation reaction for 2 h. Cool to room temperature to obtain silica hydrogel.

[0080] ③ Add 200 mL of arginine aging mother solution (arginine concentration 0.05 mol / L) to the above-mentioned silica hydrogel, raise the temperature to 50°C, carry out aging reaction for 72 hours, and cool to room temperature to obtain aging-enhanced silica hydrogel; the arginine aging mother solution consists of arginine and water.

[0081] ④ Using a porous aluminum plate, the aged and enhanced silica hydrogel was placed in 10 times the volume of anhydrous ethanol and soaked for 2 days. The solution was replaced twice to obtain an alcohol gel, which was then dried with supercritical carbon dioxide. Using a porous aluminum plate, the alcohol gel was carefully placed in a drying kettle, anhydrous ethanol was added to cover the alcohol gel, and liquid carbon dioxide was injected into the drying kettle. The pressure in the kettle was maintained at 16 MPa, and the temperature in the drying kettle was controlled at 10°C. The solvent was replaced with circulating liquid carbon dioxide for 72 hours, and then the temperature was raised to 60°C at a rate of 5°C / h to reach a supercritical state. At this temperature, the solvent was replaced with circulating supercritical carbon dioxide for 24 hours to ensure that the ethanol waste liquid was completely removed. Then, while maintaining the temperature in the drying kettle at 60°C, the pressure was released to atmospheric pressure at a rate of 0.3 MPa / h. After the temperature in the kettle dropped to room temperature, the silica aerogel was taken out.

[0082] Comparative Example 3

[0083] ① Add 1L of arginine aqueous solution (concentration of 0.01mol / L, arginine 0.01mol) to a 5000mL circular flat mold, then slowly add 689.4g of n-hexane (8mol) to the upper surface of the arginine aqueous solution to cover it, and then slowly add 208.3g of ethyl orthosilicate (1mol) from above the n-hexane, raise the temperature to 60℃, react at the interface for 24h, and cool to room temperature to obtain an aqueous solution of silica nanoparticles with the surface covered with an organic solvent (n-hexane).

[0084] ② Remove the n-hexane covering the upper surface of the above-mentioned aqueous solution of silica nanoparticles covered with an organic solvent (n-hexane), then add 40 mL of ethanolic ammonia solution (with an ammonia concentration of 1 mol / L and an ammonia amount of 0.04 mol) and mix evenly, raise the temperature to 50°C, carry out a gelation reaction, and react for 2 hours. Cool to room temperature to obtain silica hydrogel.

[0085] ③ Add 200 mL of arginine aging mother solution (arginine concentration 0.05 mol / L) to the above-mentioned silica hydrogel, raise the temperature to 50°C, carry out aging reaction for 72 hours, and cool to room temperature to obtain aging-enhanced silica hydrogel; the arginine aging mother solution consists of arginine and water.

[0086] ④ Using a porous aluminum plate, the aged and enhanced silica hydrogel was placed in 10 times the volume of anhydrous ethanol and soaked for 2 days. The solution was replaced twice to obtain an alcohol gel, which was then dried with supercritical carbon dioxide. Using a porous aluminum plate, the alcohol gel was carefully placed in a drying kettle, anhydrous ethanol was added to cover the alcohol gel, and liquid carbon dioxide was injected into the drying kettle. The pressure in the kettle was maintained at 16 MPa, and the temperature in the drying kettle was controlled at 10°C. The solvent was replaced with circulating liquid carbon dioxide for 72 hours. The temperature was then raised to 60°C at a rate of 5°C / h to reach a supercritical state. At this temperature, the solvent was replaced with circulating supercritical carbon dioxide for 24 hours to ensure that the ethanol waste liquid was completely removed. The temperature in the drying kettle was maintained at 60°C, and the pressure was released to atmospheric pressure at a rate of 0.3 MPa / h. After the temperature in the kettle dropped to room temperature, the silica aerogel was taken out to obtain a highly efficient thermally insulating, lightweight, transparent silica aerogel material.

[0087] Comparative Example 4

[0088] A low-density transparent silica aerogel was synthesized with reference to Example 1 of Chinese patent application CN 105271263 A.

[0089] Comparative Example 5

[0090] A bulk transparent aerogel was synthesized with reference to Example 2 of Chinese patent application CN 109019611 A.

[0091] Comparative Example 6

[0092] A reinforced bulk transparent aerogel was synthesized with reference to Example 3 of Chinese patent application CN109179428A.

[0093] The present invention conducted performance tests on the highly efficient heat-insulating, lightweight, transparent silica aerogel materials prepared in each embodiment and the aerogel materials finally prepared in each comparative example. The results are shown in Table 1.

[0094] Table 1

[0095]

[0096]

[0097] In Table 1, the symbol " / " indicates that the performance indicator was not tested. The light transmittance described in this invention refers to the light transmittance of a 10 mm thick silica aerogel sample at 550 nm. The light transmittance at 550 nm is used as the indicator because the human eye is most sensitive to visible light at a wavelength of 550 nm.

[0098] Parts of the present invention that are not described in detail are well known to those skilled in the art.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for preparing a lightweight transparent silica aerogel material with high efficiency and heat insulation, characterized in that: The method comprises the following steps: (1) Covering the upper surface of an amino acid aqueous solution with an incompatible organic solvent, then adding an organic silicone ester from above the covered organic solvent and performing an interfacial reaction to obtain an aqueous solution of silica nanoparticles whose surface is covered with the organic solvent; the amino acid contained in the amino acid aqueous solution is one or more of lysine, arginine and histidine; (2) adding a catalyst solution onto the aqueous solution of silica nanoparticles covered with an organic solvent and performing a gel reaction to obtain a silica hydrogel covered with an organic solvent; (3) removing the organic solvent covering the surface of the silica hydrogel covered with the organic solvent, and then adding an amino acid aging mother solution for aging to obtain an aging-enhanced silica hydrogel; the amino acid aging mother solution comprises amino acids and water, and the amino acids contained in the amino acid aging mother solution are one or more of lysine, arginine and histidine; (4) The aged and enhanced silica hydrogel was subjected to solvent replacement and supercritical drying in sequence to produce a lightweight and transparent silica aerogel material with high efficiency and thermal insulation.

2. The preparation method according to claim 1, characterized in that In step (1): The concentration of the amino acid aqueous solution is 0.005~0.05mol / L; The organic solvent is one or more of n-hexane, cyclohexane, n-pentane, n-heptane and n-octane; and / or The organic silicone ester is one or more of ethyl orthosilicate, methyl orthosilicate, methyltrimethoxysilane, ethyltriethoxysilane and hexamethyldisiloxane.

3. The preparation method according to claim 2, characterized in that In step (1): The concentration of the amino acid aqueous solution is 0.01 mol / L.

4. The preparation method according to claim 1, characterized in that In step (1): The molar ratio of the organosilicon ester to the amino acid contained in the amino acid aqueous solution is 1:(0.0005-0.05); and / or The molar ratio of the organic silicone ester to the organic solvent is 1:(2-20).

5. The preparation method according to claim 4, characterized in that In step (1): The molar ratio of the organosilicon ester to the amino acid contained in the amino acid aqueous solution is 1:0.

01.

6. The preparation method according to claim 4, characterized in that In step (1): The molar ratio of the organic silicone ester to the organic solvent is 1:

8.

7. The preparation method according to claim 1, wherein: The temperature of the interfacial reaction is 40-80°C; and / or The time of the interface reaction is 8 to 48 hours.

8. The preparation method according to claim 7, characterized in that: The temperature of the interface reaction is 60°C.

9. The preparation method according to claim 7, characterized in that: The interface reaction time is 24 hours.

10. The preparation method according to claim 1, characterized in that: The catalyst solution is one or more of an ethanol solution of ammonia, a 1,4-dioxane solution of ammonia, an isopropanol solution of ammonia, and a tetrahydrofuran solution of ammonia; and / or The molar ratio of ammonia to the organic silicon ester in the catalyst solution is (0.01-0.1):

1.

11. The preparation method according to claim 10, characterized in that: The molar ratio of ammonia to the organosilicone ester in the catalyst solution is 0.04:

1.

12. The preparation method according to claim 1, characterized in that: The temperature of the gel reaction is 20-70° C.; and / or The gel reaction time is 0.5 to 16 hours.

13. The preparation method according to claim 12, characterized in that: The temperature of the gel reaction is 50°C.

14. The preparation method according to claim 12, characterized in that: The gel reaction time is 2 hours.

15. The preparation method according to claim 1, characterized in that: The concentration of the amino acid aged mother solution is 0.02-0.2 mol / L; and / or The volume of the amino acid aged mother solution is 0.05 to 0.8 times the volume of the amino acid aqueous solution in step (1).

16. The preparation method according to claim 15, characterized in that: The concentration of the amino acid aged mother solution is 0.05 mol / L.

17. The preparation method according to claim 15, characterized in that: The volume of the amino acid aged mother solution is 0.2 times the volume of the amino acid aqueous solution in step (1).

18. The preparation method according to claim 1, characterized in that: The aging temperature is 30-70°C; and / or The aging time is 24 to 120 hours.

19. The preparation method according to claim 18, characterized in that: The aging temperature is 50°C.

20. The preparation method according to claim 18, characterized in that: The aging time is 72h.

21. The preparation method according to claim 1, characterized in that: In step (4), the aged enhanced silica hydrogel is first subjected to solvent replacement in ethanol to obtain an alcohol gel, and then the alcohol gel is dried with supercritical carbon dioxide. During the supercritical carbon dioxide drying of the alcohol gel, the pressure in the drying kettle is maintained at 8~20MPa, the temperature in the drying kettle is controlled at 10~20℃, and the solvent replacement is carried out for 24~120h using circulating liquid carbon dioxide. Then, the temperature is raised to 60℃ at a rate of 5~10℃ / h to reach a supercritical state. The circulating supercritical carbon dioxide is continued to replace for 12~48h to remove the ethanol waste liquid, and then the pressure is released to atmospheric pressure at a rate of 0.3~1MPa / h.

22. A highly efficient heat-insulating, lightweight, transparent silica aerogel material prepared by the preparation method according to any one of claims 1 to 21.

23. The highly efficient heat-insulating, lightweight, transparent silica aerogel material according to claim 22, characterized in that: The highly efficient heat-insulating, lightweight, transparent silica aerogel material has one or more of the following properties: The density of the highly efficient heat-insulating, lightweight, transparent silica aerogel material is 0.012-0.095 g / cm 3 ; The light transmittance of the highly efficient heat-insulating, lightweight, transparent silica aerogel material with a thickness of 10 mm at 550 nm is 93.8%; The thermal conductivity of the highly efficient heat-insulating, lightweight, transparent silica aerogel material at room temperature is as low as 0.010 W / (m·K); The highly efficient heat-insulating, lightweight, transparent silica aerogel material has a minimum thermal conductivity of 0.014 W / (m·K) at 100° C.

Images