Preparation method of high-transparency hydrophobic silicon-based bulk aerogel at normal pressure

Abstract

The present application relates to the technical field of nano-porous aerogel material preparation, and solves the technical problems of traditional supercritical drying, such as complex process, high equipment cost, and high risk of high temperature and high pressure operation. In particular, it relates to a normal pressure preparation method of high-transmittance hydrophobic silicon-based block aerogel, which comprises the following steps: preparing a completely hydrolyzed silicon-based sol; obtaining a silicon-based wet gel with complete structure; soaking the silicon-based wet gel in a displacement solution for multiple times to obtain a block wet gel with complete solvent displacement; placing the block wet gel in a normal pressure environment with different temperature gradients and keeping for corresponding time, so that the liquid in the gel pores is completely volatilized, and a high-transmittance hydrophobic silicon-based block aerogel is obtained. Compared with the supercritical drying process, the present application saves reagents, reduces the preparation time, is simple to operate, low in cost, safe and green, and can improve the light transmittance and integrity as much as possible under the premise of ensuring low thermal conductivity, thereby meeting the application requirements of building glass.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nanoporous aerogel material preparation, and particularly relates to a normal-pressure preparation method of high-transparency hydrophobic silicon-based block aerogel. BACKGROUND

[0002] In recent years, there have been a large number of literatures and patent publications on block silicon-based aerogel materials and their preparation processes, but the problems brought about by the normal-pressure preparation of transparent block silicon-based aerogel materials and their engineering application have also followed, and the maintenance of the integrity of the block structure of the material is highly dependent on the drying method of the gel, and the capillary tension of the solvent in the wet gel pores is reduced or even eliminated by supercritical drying, but due to the high cost of equipment, the complex process, the long drying time and other factors, the supercritical drying limits the further development and industrial application of aerogel preparation.

[0003] A patent with the publication number CN105271263A and the title of a low-density transparent silica aerogel and a preparation method thereof is prepared by mixing water, alcohol and hexamethyl disiloxane, heating and reacting in a reaction kettle, and further catalyzing with hydrofluoric acid to obtain a silica gel, and then supercritically drying to obtain the aerogel, and the thermal conductivity (25 DEG C) of the aerogel is at least 0.012 W / (m·K), and the transparency is good. A patent with the publication number CN117699808A and the title of a preparation method of a high-efficiency heat-insulating light-weight transparent silica aerogel material is prepared by mixing arginine aqueous solution, n-hexane, tetraethyl orthosilicate and ammonia ethanol solution, and then soaking in anhydrous ethanol to replace, and then supercritically drying to obtain the aerogel, and the thermal conductivity of the aerogel is at least 0.010 W / (m·K) at room temperature, and the light transmittance is good. However, the preparation process of the above-mentioned light-transmitting block aerogel is relatively complex, and many chemicals are used, and the supercritical drying process of carbon dioxide is complex, the equipment cost is high, and the operation is dangerous at high temperature and high pressure.

[0004] Although the aerogel prepared by normal-pressure drying is simple in operation, low in cost and safe and green, the influence of capillary pressure during solvent evaporation cannot be eliminated, and the shrinkage and cracking of the gel during drying are difficult to avoid, and the light transmittance cannot be guaranteed. Therefore, it is necessary to improve it to ensure the integrity of the material and improve the related performance of the material. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a normal-pressure preparation method of high-transparency hydrophobic silicon-based block aerogel, which solves the technical problems of complex supercritical drying process, high equipment cost and high risk of high-temperature and high-pressure operation.

[0006] To solve the above technical problems, the present application provides the following technical scheme: a normal-pressure preparation method of high-transparency hydrophobic silicon-based block aerogel, the normal-pressure preparation method comprising the following steps:

[0007] S1. Prepare an aqueous solution of the acid catalyst, and add a precursor containing organic groups to the aqueous solution of the acid catalyst. After mixing evenly, a completely hydrolyzed silica-based sol is obtained.

[0008] S2. Add surfactant and deionized water to silica-based sol and mix evenly. Adjust the pH of silica-based sol to 8-9, let it stand to form a gel and age to obtain a silica-based wet gel with a complete structure.

[0009] S3. The silica-based wet gel was repeatedly immersed in the displacement solution, and the displacement solvent of different concentrations was replaced at regular intervals to obtain a block wet gel with complete solvent displacement.

[0010] S4. Place the block wet gel under different temperature gradients at normal pressure and maintain them for the corresponding time to allow the liquid in the gel pores to evaporate completely, and obtain a completely dried, highly transparent, hydrophobic silica-based block aerogel.

[0011] Furthermore, in step S1, the specific process includes:

[0012] Deionized water and acid catalyst are mixed in proportion to obtain an aqueous solution of acid catalyst with a concentration of 5-20 mmol / L;

[0013] A precursor with non-hydrolyzable organic groups was added to an aqueous solution of an acid catalyst, and the mixture was stirred with a magnetic stirrer to form a fully hydrolyzed silica-based sol. The stirring temperature, speed, and time were 20–30 °C, 400–600 r / min, and 30–60 min, respectively.

[0014] Furthermore, the acid catalyst includes, but is not limited to, any one of acetic acid, hydrochloric acid, oxalic acid, sulfuric acid, nitric acid, phosphoric acid, or citric acid.

[0015] Furthermore, the mass ratio of the acid catalyst aqueous solution to the precursor containing organic groups is 5:5 to 6:4, and the amount of acid catalyst added is adjusted to adjust the pH of the silica-based sol to 5 to 6.

[0016] Furthermore, the precursor containing the organic group is an organic compound of R1-Si-(OR2)3, where R1 and R2 represent alkyl groups, including but not limited to any one of methyltrimethoxysilane (MTMS), methyltriethoxysilane (MTES), and ethyltriethoxysilane (ETMS).

[0017] Furthermore, in step S2, the specific process includes:

[0018] Add surfactant and deionized water to silica-based sol, adjust the speed of magnetic stirrer, and continue stirring silica-based sol until it becomes uniform. The mass of surfactant is 20% to 30% of the mass of precursor containing organic groups, and the mass ratio of deionized water to surfactant is 8:2 to 7:3.

[0019] Then, an aqueous solution of an alkaline catalyst with a concentration of 0.25–0.5 mol / L was added to the well-stirred silica sol and stirred until the pH of the silica sol was 8–9.

[0020] Finally, the silica-based sol with a pH of 8-9 was transferred to a custom mold, allowed to stand to form a gel, and then aged before being demolded to obtain a structurally complete silica-based wet gel. The integrity of the gel block structure was ensured during the demolding process.

[0021] Furthermore, the surfactant includes, but is not limited to, any one of cetyltrimethylammonium chloride (CTAB), cetyltrimethylammonium bromide (CTAC), polyoxyethylene polyoxypropylene (F127), and poloxamer 188 (F68);

[0022] The aqueous solution of the alkaline catalyst is a mixed solution of deionized water and the alkaline catalyst. The alkaline catalyst includes, but is not limited to, any one of ammonia, urea, NaOH, KOH, tetramethylammonium hydroxide (TMAOH), and tetraethylammonium hydroxide (TEAOH).

[0023] Furthermore, the mixing temperature, rotation speed, and duration are 0–15°C, 100–250 r / min, and 30–60 min, respectively.

[0024] Furthermore, in step S3, the specific process includes:

[0025] Displacement solutions with a volume of 5 to 8 times the gel volume were prepared. The displacement solutions were divided into aqueous solutions of ethanol and aqueous solutions of n-hexane with different concentrations. The volume ratios of deionized water to ethanol were 100:0, 70:30, 50:50, 30:70, and 0:100.

[0026] The silica-based wet gel was soaked once in aqueous ethanol solutions of different concentrations, and then soaked three times in aqueous hexane solution to obtain a blocky wet gel with complete solvent displacement. The temperature of the displacement solution was controlled at 26–40 °C, and the soaking time was at least 8 hours each time.

[0027] Furthermore, in step S4, different temperature gradients are applied at atmospheric pressure and maintained for corresponding times, specifically as follows:

[0028] The temperature and duration of the initial drying were 25–40℃ and 2–4h, respectively; the temperature and duration of the second drying were 60–80℃ and 3–5h, respectively; and the temperature and duration of the final drying were 100–120℃ and 4–6h, respectively.

[0029] By employing the above technical solution, the present invention provides a method for preparing high-transmittance hydrophobic silica-based bulk aerogel at ambient pressure, which has at least the following beneficial effects:

[0030] 1. This invention overcomes the disadvantages of supercritical drying, such as complex process, high equipment cost, and high risk of high temperature and high pressure operation. It prepares blocky silicon-based aerogel through natural evaporation and atmospheric pressure drying. The resulting aerogel has excellent hydrophobicity and high light transmittance, and the thermal conductivity (at room temperature) is 0.025 W / (m·K).

[0031] 2. This invention uses MTMS as a precursor containing organic groups, eliminating the need for subsequent hydrophobic modification and alteration processes, thus simplifying the preparation steps. The resulting aerogel is hydrophobic with good hydrophobic properties and a contact angle >90°, making it a hydrophobic material.

[0032] 3. The surfactant F127 of the present invention is a poly(ethylene oxide)-poly(propylene oxide) structure arranged in a triblock structure, forming a PEO-PPO-PEO symmetrical structure, which makes it "amphiphilic". It can interact with hydrophobic surfaces and biofilms, moderately inhibit macroscopic phase separation, determine the gel skeleton structure, and thus produce a silicon-based aerogel with high light transmittance.

[0033] 4. This invention uses TMAOH as an alkaline catalyst. Compared with other alkaline catalysts, TMAOH can rapidly increase the pH of the sol to the required value with very little dosage, saving reagents and reducing gel formation time in the preparation process. Moreover, TMAOH can more effectively suppress the tendency of phase separation, and the resulting aerogel has high light transmittance with a wavelength range of 600-800nm ​​and a light transmittance of >80%. Attached Figure Description

[0034] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0035] Figure 1 This is a macroscopic morphology diagram of the high-transmittance, hydrophobic silicon-based bulk aerogel material prepared under normal pressure according to the present invention.

[0036] Figure 2 The image shows the microstructure of the high-transmittance, hydrophobic, silicon-based bulk aerogel material prepared under normal pressure according to the present invention.

[0037] Figure 3This is a schematic diagram showing the hydrophobic angle of the high-transmittance hydrophobic silicon-based bulk aerogel material prepared under normal pressure according to the present invention.

[0038] Figure 4 This is a schematic diagram showing the visible light transmittance of the high-transmittance hydrophobic silicon-based bulk aerogel material prepared under normal pressure according to the present invention. Detailed Implementation

[0039] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. This will allow for a full understanding of how the present application uses technical means to solve technical problems and achieve technical effects, and to facilitate its implementation.

[0040] Based on the heat transfer mechanism of architectural glass, the main factors affecting its energy consumption are its thermal conductivity and radiation transmittance. Currently, technologies such as vacuum insulation, coating, and multi-layer insulated glass have been developed to improve its thermal insulation capabilities. However, subsequent research has revealed that vacuum insulation and multi-layer insulated glass require demanding manufacturing conditions and have complex structures; coated glass has less impact on the infrared radiation from solar irradiation and lower radiation transmittance. Therefore, some researchers have used materials with extremely low thermal conductivity and high radiation transmittance to fill the glass interlayer, which can effectively improve the thermal insulation of architectural glass. Among these, aerogels, due to their low density, high porosity, low thermal conductivity, low refractive index, and high light transmittance, have become an ideal choice for architectural glass composite materials.

[0041] In recent years, numerous publications and patents have reported on bulk silicon-based aerogel materials and their preparation processes. However, problems have arisen regarding the atmospheric pressure preparation and engineering applications of transparent bulk silicon-based aerogel materials. Maintaining the integrity of the bulk structure is highly dependent on the gel drying method. Supercritical drying reduces or even eliminates the capillary tension of the solvent in the pores of the wet gel, but its high equipment cost, complex process, and long drying time limit its further development and industrial application in aerogel preparation. Furthermore, while atmospheric pressure drying is simple, low-cost, and safe, it does not eliminate the capillary pressure effect during solvent evaporation, making gel shrinkage and cracking during drying unavoidable and compromising light transmittance. Therefore, traditional preparation processes are complex, using numerous reagents, and supercritical carbon dioxide drying is complex, expensive, and carries significant risks due to high temperature and pressure. Thus, improvements are needed to ensure material integrity and enhance related properties.

[0042] In order to achieve a silicon-based bulk aerogel material with a certain light transmittance under normal pressure and drying conditions, and to maximize its light transmittance and integrity while ensuring its low thermal conductivity, so as to meet the application requirements of architectural glass, this embodiment proposes a method for preparing high-transmittance hydrophobic silicon-based bulk aerogel under normal pressure, and realizes it through the preparation methods proposed in Examples 1 to 4.

[0043] In this process, methyltrimethoxysilane (MTMS) is used as a precursor containing organic groups; acetic acid is used as an acid catalyst, and tetramethylammonium hydroxide (TMAOH) aqueous solution is used as an alkaline catalyst, with the mass of the solution being 2% to 9% of the mass of methyltrimethoxysilane (MTMS). Methyltrimethoxysilane (MTMS) undergoes hydrolysis and condensation reaction under the catalysis of acetic acid and tetramethylammonium hydroxide (TMAOH), which can regulate the prepolymerization degree and framework structure of primary and secondary silica particles; polyoxyethylene polyoxypropylene (F127) is used as a surfactant, and ethanol and n-hexane are preferred as solvent replacement agents. Their non-water-soluble and low surface tension characteristics are beneficial to phase separation and condensation reaction, so that high-transmittance hydrophobic silica-based bulk aerogels can be prepared by drying under normal pressure. Example 1

[0044] An atmospheric pressure preparation method for a high-transmittance, hydrophobic silica-based bulk aerogel according to Embodiment 1 of the present invention includes the following steps:

[0045] Step 1: Preparation of silica-based sol: Deionized water and acetic acid were mixed to obtain a 5 mmol / L aqueous acetic acid solution; 10 parts of the aqueous acetic acid solution and 10 parts of methyltrimethoxysilane (MTMS) were mixed, and the pH of the silica-based sol was adjusted to 5-6. The mixture was stirred with a magnetic stirrer to fully hydrolyze the methyltrimethoxysilane (MTMS) to form a completely hydrolyzed silica-based sol. The stirring speed was 500 rpm / min, and the stirring temperature and time were 25℃ and 20 min, respectively.

[0046] Step 2: Formation and aging of silicone-based wet gel: Add 2 parts of surfactant polyoxyethylene polyoxypropylene (F127) and 8 parts of deionized water to the silicone-based sol formed in Step 1 and mix. Stir with a magnetic stirrer at 300 rpm / min for 10℃ and 20 min.

[0047] Deionized water and tetramethylammonium hydroxide (TMAOH) were mixed to obtain a 0.25 mol / L TMAOH aqueous solution. 0.5 parts of the TMAOH aqueous solution were added to the above homogeneous silica-based sol to adjust the pH of the silica-based sol to 8-9. The resulting silica-based sol was transferred to a custom mold and allowed to stand until the gel was completely formed. The gel was then demolded, taking care to ensure the integrity of the gel block structure during demolding to obtain a complete block silica-based wet gel.

[0048] Step 3: Solvent Replacement: The silica-based wet gel obtained in Step 2 was repeatedly immersed in a replacement solvent, the volume of which was 8 times the volume of the silica-based wet gel. The composition of the replacement solvent was changed in the following order: deionized water: ethanol volume ratio = 100:0, 70:30, 50:50, 30:70, 0:100, n-hexane; wherein, the ethanol aqueous solution was immersed once at each concentration, and the n-hexane solution was repeatedly immersed 3 times. The solvent was replaced every 12 hours to obtain a block wet gel with complete solvent exchange. The replacement temperature was 30℃.

[0049] Step 4: Formation of aerogel: The blocky wet gel obtained in step 3 was treated by natural evaporation and normal pressure drying. The temperature and duration of the first drying were 25-40℃ and 3h, respectively; the temperature and duration of the second drying were 60℃ and 4h, respectively; and the temperature and duration of the final drying were 100℃ and 4h, respectively; thus, a high-transmittance hydrophobic silica-based blocky aerogel was obtained. Example 2

[0050] A method for preparing a high-transmittance, hydrophobic silica-based bulk aerogel under ambient pressure according to Embodiment 2 of the present invention includes the following steps:

[0051] Step 1: Preparation of silica-based sol: Deionized water and acetic acid were mixed to obtain a 5 mmol / L aqueous acetic acid solution; 12 parts of the aqueous acetic acid solution and 8 parts of methyltrimethoxysilane (MTMS) were mixed, and the pH of the silica-based sol was adjusted to 5-6. The mixture was stirred with a magnetic stirrer to fully hydrolyze the methyltrimethoxysilane (MTMS) to form a completely hydrolyzed silica-based sol. The stirring speed was 500 rpm / min, and the stirring temperature and time were 25℃ and 20 min, respectively.

[0052] Step 2: Formation and aging of silicone-based wet gel: Add 3 parts of surfactant polyoxyethylene polyoxypropylene (F127) and 8 parts of deionized water to the silicone-based sol formed in Step 1 and mix. Stir with a magnetic stirrer at 300 rpm / min for 10℃ and 20 min.

[0053] Deionized water and tetramethylammonium hydroxide (TMAOH) were mixed to obtain a 0.25 mol / L TMAOH aqueous solution. 0.75 parts of the TMAOH aqueous solution were added to the above homogeneous silica-based sol to adjust the pH of the silica-based sol to 8-9. The resulting silica-based sol was transferred to a custom mold and allowed to stand until the gel was completely formed. The gel was then demolded, taking care to ensure the integrity of the gel block structure during demolding to obtain a complete block silica-based wet gel.

[0054] Step 3: Solvent Replacement: The silica-based wet gel obtained in Step 2 was repeatedly immersed in a replacement solvent, the volume of which was 8 times the volume of the silica-based wet gel. The composition of the replacement solvent was changed in the following order: deionized water: ethanol volume ratio = 100:0, 70:30, 50:50, 30:70, 0:100, n-hexane; wherein, the ethanol aqueous solution was immersed once at each concentration, and the n-hexane solution was repeatedly immersed 3 times. The solvent was replaced every 12 hours to obtain a block wet gel with complete solvent exchange. The replacement temperature was 30℃.

[0055] Step 4: Formation of aerogel: The blocky wet gel obtained in step 3 was treated by natural evaporation and normal pressure drying. The temperature and duration of the first drying were 25-40℃ and 3h, respectively; the temperature and duration of the second drying were 60℃ and 4h, respectively; and the temperature and duration of the final drying were 100℃ and 4h, respectively; thus, a high-transmittance hydrophobic silica-based blocky aerogel was obtained. Example 3

[0056] A method for preparing a high-transmittance, hydrophobic silica-based bulk aerogel under ambient pressure according to Embodiment 3 of the present invention includes the following steps:

[0057] Step 1: Preparation of silica-based sol: Deionized water and acetic acid were mixed to obtain a 5 mmol / L aqueous acetic acid solution; 13 parts of the aqueous acetic acid solution and 7 parts of methyltrimethoxysilane (MTMS) were mixed, and the pH of the silica-based sol was adjusted to 5-6. The mixture was stirred with a magnetic stirrer to fully hydrolyze the methyltrimethoxysilane (MTMS) to form a completely hydrolyzed silica-based sol. The stirring speed was 500 rpm / min, and the stirring temperature and time were 25℃ and 20 min, respectively.

[0058] Step 2: Formation and aging of silicone wet gel: Add 2.5 parts of polyoxyethylene polyoxypropylene (F127) and 8 parts of deionized water to the silicone sol formed in step 1 and mix. Stir with a magnetic stirrer at 300 rpm / min for 10℃ and 20 min.

[0059] Deionized water and tetramethylammonium hydroxide (TMAOH) were mixed to obtain a 0.25 mol / L TMAOH aqueous solution. One part of the TMAOH aqueous solution was added to the above silica-based sol to adjust the pH of the silica-based sol to 8-9. The resulting silica-based sol was transferred to a custom mold and allowed to stand until the gel was completely formed. Then the gel was demolded, taking care to ensure the integrity of the gel block structure during the demolding process to obtain a complete block silica-based wet gel.

[0060] Step 3: Solvent Replacement: The silica-based wet gel obtained in Step 2 was repeatedly immersed in a replacement solvent, the volume of which was 8 times the volume of the silica-based wet gel. The composition of the replacement solvent was changed in the following order: deionized water: ethanol volume ratio = 100:0, 70:30, 50:50, 30:70, 0:100, n-hexane; wherein, the ethanol aqueous solution was immersed once at each concentration, and the n-hexane solution was repeatedly immersed 3 times. The solvent was replaced every 12 hours to obtain a block wet gel with complete solvent exchange. The replacement temperature was 30℃.

[0061] Step 4: Formation of aerogel: The blocky wet gel obtained in step 3 was treated by natural evaporation and normal pressure drying. The temperature and duration of the first drying were 25-40℃ and 3h, respectively; the temperature and duration of the second drying were 60℃ and 4h, respectively; and the temperature and duration of the final drying were 100℃ and 4h, respectively; thus, a high-transmittance hydrophobic silica-based blocky aerogel was obtained. Example 4

[0062] A method for preparing a high-transmittance, hydrophobic silica-based bulk aerogel under ambient pressure according to Example 4 of this invention includes the following steps:

[0063] Step 1: Preparation of silica-based sol: Deionized water and acetic acid were mixed to obtain a 5 mmol / L aqueous acetic acid solution; 14 parts of the aqueous acetic acid solution and 6 parts of methyltrimethoxysilane (MTMS) were mixed, and the pH of the silica-based sol was adjusted to 5-6. The mixture was stirred with a magnetic stirrer to fully hydrolyze the methyltrimethoxysilane (MTMS) to form a completely hydrolyzed silica-based sol. The stirring speed was 500 rpm / min, and the stirring temperature and time were 25℃ and 20 min, respectively.

[0064] Step 2: Formation and aging of silicone wet gel: Add 2.5 parts of polyoxyethylene polyoxypropylene (F127) and 8 parts of deionized water to the silicone sol formed in step 1 and mix. Stir with a magnetic stirrer at 300 rpm / min for 10℃ and 20 min.

[0065] Deionized water and tetramethylammonium hydroxide (TMAOH) were mixed to obtain a 0.25 mol / L TMAOH aqueous solution. 1.25 parts of the TMAOH aqueous solution were added to the above homogeneous silica-based sol to adjust the pH of the silica-based sol to 8-9. The resulting silica-based sol was transferred to a custom mold and allowed to stand until the gel was completely formed. The gel was then demolded, taking care to ensure the integrity of the gel block structure during demolding to obtain a complete block silica-based wet gel.

[0066] Step 3: Solvent Replacement: The silica-based wet gel obtained in Step 2 was repeatedly immersed in a replacement solvent, the volume of which was 8 times the volume of the silica-based wet gel. The composition of the replacement solvent was changed in the following order: deionized water: ethanol volume ratio = 100:0, 70:30, 50:50, 30:70, 0:100, n-hexane; wherein, the ethanol aqueous solution was immersed once at each concentration, and the n-hexane solution was repeatedly immersed 3 times. The solvent was replaced every 12 hours to obtain a block wet gel with complete solvent exchange. The replacement temperature was 30℃.

[0067] Step 4: Formation of aerogel: The blocky wet gel obtained in step 3 was treated by natural evaporation and normal pressure drying. The temperature and duration of the first drying were 25-40℃ and 3h, respectively; the temperature and duration of the second drying were 60℃ and 4h, respectively; and the temperature and duration of the final drying were 100℃ and 4h, respectively; thus, a high-transmittance hydrophobic silica-based blocky aerogel was obtained.

[0068] Verification example:

[0069] The high-transmittance hydrophobic silica-based bulk aerogel materials prepared by this invention through Examples 1 to 4 are shown in the following figures: macroscopic morphology, microscopic morphology, hydrophobic angle diagram, and visible light transmittance diagram. Figures 1-4 As shown, in Figure 1 To show the transmittance of the obtained aerogel, an aerogel background was placed underneath the actual object. The properties of the flexible composite phase change materials of each embodiment are shown in Table 1. Figures 1-4 As shown in Table 1, the specific surface area of ​​the present invention is greater than 550 m² / g, the thermal conductivity (at room temperature) is less than 0.025 W / (m·K), the transmittance in the visible light band (600-800 nm) is greater than 75%, and the hydrophobic angle is greater than 100°. Under normal pressure preparation conditions, the prepared material meets the characteristics of silicon-based bulk aerogel materials, and has relatively ideal hydrophobic, heat insulation and light transmission effects. The preparation process is simple to operate, low in cost and safe and green, and meets the characteristics of building glass filling materials.

[0070] Table 1. Properties of high-transmittance, hydrophobic silica-based bulk aerogels in each embodiment

[0071]

[0072] The atmospheric pressure preparation method proposed in this invention saves reagents, reduces preparation time, is simple to operate, low in cost, and is safe and environmentally friendly compared to the supercritical drying process. It can also prepare high-transmittance hydrophobic silica-based block aerogels with a thermal conductivity (at room temperature) of 0.025 W / (m·K) under atmospheric pressure. While ensuring its low thermal conductivity, it maximizes its light transmittance and integrity, which can meet the application requirements of architectural glass.

[0073] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0074] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing a high-transmittance, hydrophobic, silica-based bulk aerogel under ambient pressure, characterized in that, The atmospheric pressure preparation method includes the following steps: S1. Prepare an aqueous solution of an acid catalyst and add an organic precursor R1-Si-(OR2)3 containing a single organic group to the aqueous solution of the acid catalyst. R1 and R2 represent alkyl groups respectively. After mixing evenly, a completely hydrolyzed silica-based sol is obtained. S2. Add 20% to 30% of the precursor mass of polyoxyethylene polyoxypropylene (F127) surfactant and deionized water to the silica-based sol and mix evenly. Adjust the pH of the silica-based sol to 8 to 9 using 2% to 9% of the precursor mass of tetramethylammonium hydroxide (TMAOH) alkaline catalyst aqueous solution. After metering, transfer the solution to a custom mold and let it stand to form a gel and age to obtain a silica-based wet gel with a complete structure. S3. Prepare a displacement solution with a volume of 5 to 8 times that of the gel. The displacement solution consists of aqueous ethanol solution and aqueous hexane solution of different concentrations. The silica-based wet gel is immersed once in each of the aqueous ethanol solutions of different concentrations. The volume ratio of deionized water to ethanol is 100:0, 70:30, 50:50, 30:70, and 0:

100. Then, the immersion is repeated three times in aqueous hexane solution. The temperature of the displacement solution is controlled at 26 to 40°C, and the immersion time is at least 8 hours each time to obtain a block wet gel with complete solvent displacement. S4. Place the block wet gel under normal pressure and perform temperature gradient drying. The temperature and duration of the first drying are 25-40℃ and 2-4h. The temperature and duration of the second drying are 60-80℃ and 3-5h. The temperature and duration of the final drying are 100-120℃ and 4-6h, so that the liquid in the gel pores evaporates completely, and a completely dried high-transmittance hydrophobic silica-based block aerogel is obtained.

2. The atmospheric pressure preparation method according to claim 1, characterized in that, In step S1, the specific process includes: Deionized water and acid catalyst are mixed in proportion to obtain an aqueous solution of acid catalyst with a concentration of 5-20 mmol / L; A precursor with non-hydrolyzable organic groups was added to an aqueous solution of an acid catalyst, and the mixture was stirred with a magnetic stirrer to form a fully hydrolyzed silica-based sol. The stirring temperature, speed, and time were 20–30 °C, 400–600 r / min, and 30–60 min, respectively.

3. The atmospheric pressure preparation method according to claim 1 or 2, characterized in that, The acid catalyst includes, but is not limited to, any one of acetic acid, hydrochloric acid, oxalic acid, sulfuric acid, nitric acid, phosphoric acid, or citric acid.

4. The atmospheric pressure preparation method according to claim 1 or 2, characterized in that, The mass ratio of the acid catalyst aqueous solution to the precursor containing organic groups is 5:5 to 6:4, and the amount of acid catalyst added is adjusted to adjust the pH of the silica-based sol to 5 to 6.

5. The atmospheric pressure preparation method according to claim 1 or 2, characterized in that, The organic precursor R1-Si-(OR2)3 containing an organic group includes, but is not limited to, any one of methyltrimethoxysilane (MTMS), methyltriethoxysilane (MTES), and ethyltriethoxysilane (ETMS).

6. The atmospheric pressure preparation method according to claim 1, characterized in that, In step S2, the specific process includes: Add surfactant and deionized water to the silica-based sol, adjust the speed of the magnetic stirrer, and continue stirring the silica-based sol until it becomes uniform. The mass ratio of deionized water to surfactant is 8:2 to 7:

3. Then, an aqueous solution of an alkaline catalyst with a concentration of 0.25–0.5 mol / L was added to the well-stirred silica sol and stirred until the pH of the silica sol was 8–9. Finally, the silica-based sol with a pH of 8-9 was transferred to a custom mold, allowed to stand to form a gel, and then aged before being demolded to obtain a structurally complete silica-based wet gel.

7. The atmospheric pressure preparation method according to claim 1 or 6, characterized in that, The alkaline catalyst aqueous solution is a mixed solution of deionized water and alkaline catalyst.

8. The atmospheric pressure preparation method according to claim 6, characterized in that, The mixing temperature, rotation speed, and duration are 0–15°C, 100–250 r / min, and 30–60 min, respectively.

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