Aerogel material with high specific surface area and method for its production

Abstract

This invention discloses an aerogel material with a large specific surface area and its preparation method, relating to the field of nanoporous materials technology. The aerogel material is a silica-based aerogel with a specific surface area of ​​800–1500 m². 2 / g, density is 0.05~0.20 g / cm³ 3 The pore size distribution is 2–50 nm, and the porosity is 90%–98%. This invention optimizes the size and network structure of silica nanoparticles by precisely controlling the pH conditions, hydrolysis temperature, and time of acid and base catalysis during the sol-gel process, laying the foundation for obtaining aerogels with large specific surface area.

Description

Technical Field

[0001] This invention relates to the field of nanoporous materials technology, specifically to an aerogel material with a large specific surface area and its preparation method. Background Technology

[0002] Aerogel is a lightweight nanoporous solid material composed of nanoscale particles aggregated together or nanoscale polymer chains cross-linked to form a nanoporous network structure, with gaseous dispersion medium filling the pores. It has excellent properties such as large specific surface area, high porosity, low density, and low thermal conductivity, and has broad application prospects in fields such as thermal insulation, catalyst carrier, adsorption separation, aerospace, and building energy conservation.

[0003] Currently, SiO2 aerogel is the most widely used and industrialized aerogel, with a specific surface area as high as 1000 m². 2 / g. However, the preparation of traditional SiO2 aerogels usually adopts supercritical drying technology. Although this technology can better maintain the pore structure of aerogels, it involves large equipment investment, complex operation, long production cycle, high cost, and certain safety risks, which seriously limits the large-scale production and widespread application of aerogel materials.

[0004] To address the aforementioned issues, researchers have attempted to prepare aerogels using atmospheric pressure drying techniques. For example, Chinese patent CN101348255A discloses a method for preparing hydrophobic silica aerogels from rice husk ash-based hydrogels, which, after solvent replacement and surface modification, yields a specific surface area of ​​500–1000 m² after atmospheric pressure drying. 2 / g silica aerogel. Chinese patent CN102584010A discloses a method for preparing a multi-component aerogel, which adds compounds such as phosphorus, tin, and zinc to silica aerogel to form a specific surface area exceeding 1000 m². 2 / g porous composite material. Another study reported the preparation of silica aerogels via a two-step acid-base sol-gel method using tetraethyl orthosilicate as a precursor and glycerol as a drying control chemical additive.

[0005] However, existing atmospheric pressure drying technology still has the following shortcomings: (1) The solvent replacement and surface modification steps in the preparation process are cumbersome, time-consuming, and inefficient; (2) During atmospheric pressure drying, the pore structure is prone to collapse due to capillary force, making it difficult to obtain aerogels with ultra-high specific surface area; (3) Some methods rely on expensive organosilicon sources or complex process conditions, which are not conducive to industrial promotion. Therefore, developing a simple, low-cost preparation method that is suitable for large-scale production and can obtain aerogels with large specific surface area is of great practical significance. Summary of the Invention

[0006] The purpose of this invention is to provide an aerogel material with a large specific surface area and a method for preparing the same, so as to solve the technical problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: an aerogel material with a large specific surface area, wherein the aerogel material is a silica-based aerogel with a specific surface area of ​​800–1500 m². 2 / g, density is 0.05~0.20 g / cm³ 3 The pore size distribution is 2–50 nm, and the porosity is 90%–98%.

[0008] Preferably, the specific surface area of ​​the aerogel material is 1000–1500 m². 2 / g.

[0009] Preferably, the aerogel material is a hydrophobic aerogel with a water contact angle of 130° to 160°.

[0010] Preferably, it includes the following steps: S1: Mix tetraethyl orthosilicate, anhydrous ethanol and deionized water in a volume ratio of 1:(2-5):(2-6), stir for 10-30 min, add an acidic catalyst to adjust the pH to 2-4, and hydrolyze at 30-60℃ for 1-4 h to obtain silica sol. S2: Add an alkaline catalyst to the silica sol obtained in step S1 to adjust the pH to 6-8, stir for 1-5 min and let the gel stand, then age at 20-40℃ for 12-48 h to obtain a wet gel. S3: The wet gel obtained in step S2 is placed in a low surface tension solvent for solvent replacement. The replacement time is 12 to 48 h and the number of replacements is 2 to 5 times to obtain the solvent-replaced wet gel. S4: The solvent-displaced wet gel obtained in step S3 is placed in a surface modifier solution for surface hydrophobic modification. The modification temperature is 40-80℃ and the modification time is 2-24 h to obtain the modified wet gel. S5: The modified wet gel obtained in step S4 is subjected to graded drying under normal pressure. First, it is dried at 40-60℃ for 4-12 h, then at 80-120℃ for 4-12 h, and finally at 150-200℃ for 2-6 h to obtain the aerogel material with a large specific surface area.

[0011] Preferably, the acidic catalyst in step S1 is at least one of hydrochloric acid, nitric acid, or oxalic acid, and the concentration of the acidic catalyst is 0.01 to 1 mol / L.

[0012] Preferably, the alkaline catalyst in step S2 is at least one of ammonia water, sodium hydroxide solution or ammonium bicarbonate solution, and the concentration of the alkaline catalyst is 0.1 to 2 mol / L.

[0013] Preferably, the low surface tension solvent in step S3 is at least one of n-hexane, cyclohexane, n-heptane, or acetone.

[0014] Preferably, the surface modifier in step S4 is at least one of hexamethyldisilazane, trimethylchlorosilane, or methyltrimethoxysilane, and the concentration of the surface modifier solution is 5-20 wt%.

[0015] Preferably, the heating rate of the graded drying in step S5 is 0.5 to 2 °C / min.

[0016] Preferably, the volume ratio of tetraethyl orthosilicate, anhydrous ethanol and deionized water in step S1 is 1:(3-4):(3-5).

[0017] Compared with the prior art, the beneficial effects of the present invention are: (1) By precisely controlling the pH conditions, hydrolysis temperature and time of acid catalysis and alkali catalysis in the sol-gel process, this invention optimizes the size and network structure of silica nanoparticles, laying the foundation for obtaining aerogels with a large specific surface area.

[0018] (2) The present invention uses low surface tension solvents (such as n-hexane, cyclohexane, etc.) to replace high surface tension solvents (water and ethanol) in wet gel, which effectively reduces the destructive effect of capillary force on the pore structure during subsequent drying.

[0019] (3) By modifying the surface hydrophobicity, the present invention introduces hydrophobic groups (such as -Si(CH3)3) on the surface of the gel skeleton, which not only endows the aerogel with good hydrophobic properties (the water contact angle can reach 130°~160°), but also further reduces the influence of moisture on the pore structure during the drying process.

[0020] (4) This invention employs a staged atmospheric pressure drying process, controlling the solvent evaporation rate by gradually increasing the temperature, thus avoiding the severe shrinkage and collapse of the pore structure caused by rapid drying. This achieves a specific surface area as high as 800–1500 m² without the need for supercritical drying equipment. 2 / g aerogel material significantly reduces production costs and equipment investment.

[0021] (5) The preparation process of this invention is simple, easy to operate, has a wide range of raw material sources, and is inexpensive. It is suitable for large-scale production and industrial application, and has good economic and social benefits. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1 This embodiment provides an aerogel material with a large specific surface area and its preparation method, including the following steps: S1: Tetraethyl orthosilicate, anhydrous ethanol, and deionized water were mixed in a volume ratio of 1:4:4 and stirred at room temperature for 20 min. The pH was adjusted to 3 by adding 0.1 mol / L hydrochloric acid solution, and hydrolyzed at 50℃ for 2 h to obtain silica sol. S2: 1 mol / L ammonia solution was added to the silica sol obtained in step S1 to adjust the pH to 7. After stirring for 3 min, the mixture was allowed to stand and aged at 30℃ for 24 h to obtain a wet gel. S3: The wet gel obtained in step S2 was subjected to solvent replacement in n-hexane for 24 h, repeated 3 times, to obtain a solvent-replaced wet gel. S4: The solvent-replaced wet gel obtained in step S3 was subjected to surface hydrophobic modification in a 10 wt% hexamethyldisilazane / n-hexane solution at 60℃ for 12 h, to obtain a modified wet gel. S5: The modified wet gel obtained in step S4 was subjected to fractional drying under normal pressure. The aerogel material with a large specific surface area was obtained by drying at a heating rate of ℃ / min, first at 50℃ for 8 h, then at 100℃ for 8 h, and finally at 180℃ for 4 h. The performance of the aerogel material obtained in this embodiment was tested: the specific surface area was determined to be 1250 m² using the nitrogen adsorption method (BET). 2 / g; the density determined by the density method is 0.08 g / cm³. 3 The average pore size was determined to be 12 nm using the Barrett-Joyner-Halenda (BJH) method; the porosity was determined to be 96% using the mercury porosimetry method; and the water contact angle was determined to be 152° using a contact angle meter.

[0024] Example 2 This embodiment provides a large specific surface area aerogel material and its preparation method, including the following steps: S1: Tetraethyl orthosilicate, anhydrous ethanol, and deionized water are mixed at a volume ratio of 1:3:5, stirred at room temperature for 15 min, and the pH is adjusted to 2.5 by adding 0.05 mol / L nitric acid solution. The mixture is then hydrolyzed at 40°C for 3 h to obtain silica sol; S2: 0.5 mol / L ammonium bicarbonate solution is added to the silica sol obtained in step S1 to adjust the pH to 7.5, stirred for 2 min, and allowed to stand. The mixture is then aged at 25°C for 36 h to obtain a wet gel; S3: The wet gel obtained in step S2 is placed in cyclohexane for solvent replacement for 36 h, and the replacement is performed 4 times to obtain a solvent-replaced wet gel; S4: The solvent-replaced wet gel obtained in step S3 is placed in a 15 wt% trimethylchlorosilane / cyclohexane solution for surface hydrophobic modification at a modification temperature of 50°C for 18 hours. h, to obtain the modified wet gel; S5: The modified wet gel obtained in step S4 is subjected to staged drying under normal pressure, with a heating rate of 0.8 ℃ / min, first dried at 45℃ for 10 h, then dried at 90℃ for 10 h, and finally dried at 160℃ for 5 h, to obtain the aerogel material with a large specific surface area. The performance of the aerogel material obtained in this embodiment was tested: the BET specific surface area is 1180 m². 2 / g, density is 0.10 g / cm³ 3 It has an average pore size of 15 nm, a porosity of 94%, and a water contact angle of 148°.

[0025] Example 3 This embodiment provides a large specific surface area aerogel material and its preparation method, including the following steps: S1: Tetraethyl orthosilicate, anhydrous ethanol, and deionized water are mixed at a volume ratio of 1:5:3, stirred at room temperature for 25 min, and 0.2 mol / L oxalic acid solution is added to adjust the pH to 3.5. The mixture is then hydrolyzed at 55°C for 1.5 h to obtain silica sol; S2: 2 mol / L sodium hydroxide solution is added to the silica sol obtained in step S1 to adjust the pH to 6.5, stirred for 4 min, and allowed to stand. The mixture is then aged at 35°C for 18 h to obtain a wet gel; S3: The wet gel obtained in step S2 is placed in n-heptane for solvent replacement for 18 h, and the replacement is performed 3 times to obtain a solvent-replaced wet gel; S4: The solvent-replaced wet gel obtained in step S3 is placed in an 8 wt% methyltrimethoxysilane / n-heptane solution for surface hydrophobic modification at a modification temperature of 70°C for 8 hours. h, to obtain the modified wet gel; S5: The modified wet gel obtained in step S4 is subjected to staged drying under normal pressure, with a heating rate of 1.5 ℃ / min, first dried at 55℃ for 6 h, then dried at 110℃ for 6 h, and finally dried at 190℃ for 3 h, to obtain the aerogel material with a large specific surface area. The performance of the aerogel material obtained in this embodiment was tested: the BET specific surface area is 1050 m². 2 / g, density is 0.12 g / cm³ 3 It has an average pore size of 18 nm, a porosity of 93%, and a water contact angle of 140°.

[0026] Comparative Example 1 The only difference between this comparative example and Example 1 is that step S5 uses a one-step constant-temperature drying process (drying at 100°C for 20 h) instead of staged drying. The resulting aerogel material has a BET specific surface area of ​​620 m². 2 / g, far lower than 1250 m in Example 1 2 / g indicates that the fractional drying process plays a crucial role in obtaining a large specific surface area. Comparative Example 2 The only difference between this comparative example and Example 1 is that the surface modification treatment in step S4 is omitted. The resulting aerogel material experienced severe shrinkage and cracking during drying, with a BET specific surface area of ​​only 450 m². 2 / g indicates that surface hydrophobic modification is crucial for protecting the pore structure of aerogel and obtaining a large specific surface area.

[0027] The large specific surface area aerogel material and its preparation method provided by this invention can be widely used in fields such as thermal insulation materials, catalyst supports, adsorption and separation materials, gas sensors, aerospace materials, and building energy-saving materials. This invention uses an atmospheric pressure drying process instead of the traditional supercritical drying process, significantly reducing production equipment investment and operating costs, simplifying the process flow, and improving production efficiency, thus demonstrating good prospects for industrial application and promotional value.

[0028] 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 the spirit or essential characteristics of the invention. 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, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. An aerogel material with a large specific surface area, characterized in that: The aerogel material is a silica-based aerogel with a specific surface area of ​​800–1500 m². 2 / g, density is 0.05~0.20 g / cm³ 3 The pore size distribution is 2–50 nm, and the porosity is 90%–98%.

2. The aerogel material with a large specific surface area according to claim 1, characterized in that: The specific surface area of ​​the aerogel material is 1000–1500 m². 2 / g.

3. The aerogel material with a large specific surface area according to claim 1, characterized in that: The aerogel material is a hydrophobic aerogel with a water contact angle of 130° to 160°.

4. A method for preparing a large specific surface area aerogel material according to any one of claims 1-3, characterized in that: Includes the following steps: S1: Tetraethyl orthosilicate, anhydrous ethanol and deionized water are mixed in a volume ratio of 1:(2-5):(2-6), stirred for 10-30 min, acidic catalyst is added to adjust the pH to 2-4, and hydrolyzed at 30-60℃ for 1-4 h to obtain silica sol. S2: Add an alkaline catalyst to the silica sol obtained in step S1 to adjust the pH to 6-8, stir for 1-5 min and let the gel stand, then age at 20-40℃ for 12-48 h to obtain a wet gel. S3: The wet gel obtained in step S2 is placed in a low surface tension solvent for solvent replacement. The replacement time is 12 to 48 hours and the number of replacements is 2 to 5 times to obtain the solvent-replaced wet gel. S4: The solvent-displaced wet gel obtained in step S3 is placed in a surface modifier solution for surface hydrophobic modification. The modification temperature is 40-80℃ and the modification time is 2-24 h to obtain the modified wet gel. S5: The modified wet gel obtained in step S4 is subjected to graded drying under normal pressure. First, it is dried at 40-60℃ for 4-12 h, then at 80-120℃ for 4-12 h, and finally at 150-200℃ for 2-6 h to obtain the aerogel material with a large specific surface area.

5. The method for preparing a large specific surface area aerogel material according to claim 4, characterized in that: The acidic catalyst in step S1 is at least one of hydrochloric acid, nitric acid, or oxalic acid, and the concentration of the acidic catalyst is 0.01 to 1 mol / L.

6. The method for preparing a large specific surface area aerogel material according to claim 4, characterized in that: The alkaline catalyst in step S2 is at least one of ammonia water, sodium hydroxide solution or ammonium bicarbonate solution, and the concentration of the alkaline catalyst is 0.1 to 2 mol / L.

7. The method for preparing a large specific surface area aerogel material according to claim 4, characterized in that: The low surface tension solvent mentioned in step S3 is at least one of n-hexane, cyclohexane, n-heptane, or acetone.

8. The method for preparing a large specific surface area aerogel material according to claim 4, characterized in that: The surface modifier in step S4 is at least one of hexamethyldisilazane, trimethylchlorosilane or methyltrimethoxysilane, and the concentration of the surface modifier solution is 5 to 20 wt%.

9. The method for preparing a large specific surface area aerogel material according to claim 4, characterized in that: The heating rate for the graded drying in step S5 is 0.5–2 °C / min.

10. The method for preparing a large specific surface area aerogel material according to claim 4, characterized in that: The volume ratio of tetraethyl orthosilicate, anhydrous ethanol and deionized water in step S1 is 1:(3-4):(3-5).