A method for preparing bulk zirconia aerogel using acetic acid as a low-cost zirconium source

Abstract

The present invention provides a method for preparing bulk zirconia aerogel using acetic acid as a ligand as a low-cost zirconium source. A zirconium source is first prepared by reacting acetic acid and basic zirconium carbonate, which is then dissolved in an alcohol-water mixed solvent to prepare a zirconium sol. Without or with the addition of a gelling agent, gelation occurs at 40 to 60°C. Subsequently, the zirconium sol is subjected to aging, solvent replacement, and ethanol supercritical drying to obtain a bulk zirconia aerogel. The zirconium source used in the present invention is not only cheap and readily available, but also has a controllable sol-gel rate and can be gelled using a variety of gel initiators. The resulting aerogel has good bulking properties and a uniform and controllable pore structure, with a density of 0.14 g / cm 3 After heat treatment at 1000℃ for 2h, the shrinkage rate is only 35%, and it can maintain the mesoporous structure within 20nm and the complete block shape, which can meet the diverse needs of applications such as thermal insulation, adsorption and catalysis, and can also be used to promote the industrial application of zirconia aerogel.

Description

Technical Field

[0001] The invention provides a method for preparing bulk zirconia aerogel by using acetic acid as a low-cost zirconium source, belonging to the technical field of new materials. Background Art

[0002] Metal oxide aerogels are porous materials formed by stacking nanoparticles in a beaded structure. They possess properties such as extremely low density, high specific surface area, high porosity, and low thermal conductivity, and have garnered increasing attention over the past few decades. Zirconia aerogels are widely used not only as catalyst supports, adsorption media, and electrodes in solid oxide fuel cells, but also as important thermal management materials due to their extremely low thermal conductivity and high porosity, particularly for high-temperature insulation in aerospace systems. Compared to silica aerogels, which exhibit sintering and mesoporous structure collapse at 800°C, zirconia's high melting point (2715°C) and low thermal conductivity make its aerogel form more attractive.

[0003] Zirconia aerogels are typically prepared from two types of zirconium sources: inorganic zirconium sources, such as zirconium oxychloride and zirconium oxynitrate, and organic zirconium salts, such as zirconium alkoxides. Inorganic zirconium salts use a variety of gelling agents to control the gelation rate and promote the formation of a rigid gel network. These include the common propylene oxide, citric acid, and amino acids (RSC Adv., 2018, 8, 8011). However, inorganic zirconium sources are prone to the following drawbacks: First, the presence of anions and organic matter in the aerogel skeleton hinders the high-temperature stability of the aerogel. Second, due to the rapid sol-gel rate, aerogels derived from inorganic salts often have an uneven pore structure and low strength when dried, making it difficult to fully utilize the thermal insulation benefits of zirconium aerogels in practical applications. Organic zirconium salts can be used to easily produce zirconia aerogels with high purity, intact skeletons, and high strength. For example, Chinese patent document CN103011280B discloses a method for preparing zirconia aerogel using zirconium alkoxide as a zirconium source and propylene oxide as a gelation initiator. Chinese patent document CN108483493B discloses a method for preparing high-strength zirconia aerogel using zirconium polyacetylacetonate and multiple gelation initiators. When propylene oxide is used as a gelling agent, a translucent aerogel with uniform pore structure on the micrometer scale can be obtained. However, the existing organic zirconium salt synthesis steps are cumbersome, expensive, and difficult to obtain, which restricts the industrial application of aerogel materials.

[0004] Our research team previously prepared a spinnable zirconium sol suitable for fiber production using acetic acid and basic zirconium carbonate. This system achieved large-scale production of high-strength, extremely lightweight, and low-thermal-conductivity zirconium oxide fibers (Chinese Patents CN110511020A and CN106929947A), initially demonstrating the potential of this system in the preparation of zirconium oxide materials. However, this spinnable zirconium sol is only suitable for fiber production, as excess solvents (acetic acid and water) hinder control of the sol-gel rate. Therefore, if this system is to be used in aerogel applications, the development of a compatible sol-gel process is urgently needed. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention provides a method for preparing bulk zirconia aerogel using acetic acid as a low-cost zirconium source. Using this readily available and inexpensive zirconium source, the method employs a flexible sol-gel process, followed by aging, solvent replacement, and supercritical drying to successfully produce bulk zirconia aerogel.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for preparing bulk zirconia aerogel using acetic acid as a low-cost zirconium source as a ligand comprises the following steps:

[0008] (1) Dissolving a zirconium source in a mixed solvent of a low-carbon alcohol and water at room temperature to prepare a zirconium sol, and then reacting with or without a gel initiator at 40-60°C to obtain a wet gel;

[0009] (2) soaking and aging the wet gel obtained in step (1) and performing solvent replacement three times each at 40-60° C. to obtain an anhydrous wet gel;

[0010] (3) supercritical drying the anhydrous wet gel obtained in step (2) to finally obtain a zirconia aerogel with a uniform mesoporous structure.

[0011] According to the present invention, preferably, in step (1), the zirconium source is prepared as follows:

[0012] Acetic acid and basic zirconium carbonate are mixed in a mass ratio of 0.5 to 1:1, reacted at room temperature for 18 to 24 hours, and then concentrated under reduced pressure at 40 to 60° C. to obtain a powdered zirconium source.

[0013] According to the present invention, preferably, the low-carbon alcohol in step (1) is one or a combination of two or more of methanol, ethanol, isopropanol, and n-propanol.

[0014] More preferably, the low-carbon alcohol in step (1) is ethanol.

[0015] Preferably, according to the present invention, in step (1), the volume percentage of the lower alcohol in the mixed solvent of lower alcohol and water is 70 to 90 vol%.

[0016] According to a preferred embodiment of the present invention, in step (1), the amount of zirconium source added is such that the concentration of zirconium ions in the zirconium sol is 0.25 to 0.5M.

[0017] According to the present invention, preferably, in step (1), when a gel initiator is added, the gel initiator is epoxide, amide, amine or ammonia.

[0018] According to the present invention, preferably, in step (1), the epoxide is propylene oxide, 2,3-butylene oxide, 1,2-propylene oxide or 1,4-butylene oxide.

[0019] According to the present invention, preferably, in step (1), the amide is formamide, acetamide, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylformamide or N-methylacetamide.

[0020] According to the present invention, preferably, in step (1), the amine is methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine or n-propylamine.

[0021] According to the present invention, preferably, in step (1), the ammonia is aqueous ammonia or ammonia gas.

[0022] Preferably, according to the present invention, in step (1), the molar ratio of the amount of the gel initiator added to the amount of zirconium ions in the zirconium sol is 6 to 12:1.

[0023] According to the present invention, preferably, in step (2), the aging liquid of the wet gel is a mixture of fatty alkyl orthosilicate and low-carbon alcohol, the volume ratio of fatty alkyl orthosilicate to low-carbon alcohol is 1:1, the fatty alkyl orthosilicate is one or a combination of two or more of tetramethyl orthosilicate, tetraethyl orthosilicate, tetrapropyl orthosilicate, tetraisopropyl orthosilicate, and tetrabutyl orthosilicate, and the low-carbon alcohol is one or a combination of two or more of methanol, ethanol, isopropanol, and n-propanol.

[0024] According to the preferred embodiment of the present invention, in step (2), the replacement solvent used is one or a combination of two or more of acetone, ethanol, isopropanol, and n-propanol.

[0025] Preferably, according to the present invention, in step (3), supercritical drying is performed by heating the temperature to 250-280°C at a heating rate of 1-4°C / min, controlling the pressure at 8-20 MPa, keeping the temperature for 0.5-2h, and then discharging ethanol at a rate of 1-5 MPa / min.

[0026] The technical features and advantages of the present invention are as follows:

[0027] 1. The present invention uses a zirconium source prepared with acetic acid as a ligand as a raw material. It is not only cheap and easily available, but also easy to control the sol-gel rate, making the gelation method flexible. The resulting aerogel has high macroscopic strength, good blockiness and thermal stability. At the same time, the pore structure of the aerogel can also change from a mesoporous to a microporous distribution according to different gelation conditions to meet different application scenarios.

[0028] 2. The present invention mixes acetic acid and basic zirconium carbonate in a mass ratio of 0.5 to 1:1, reacts at room temperature for 18 to 24 hours, and then concentrates under reduced pressure at 40 to 60° C. to obtain a zirconium source. Basic zirconium carbonate is low in price and its cost is much lower than zirconyl nitrate, which greatly reduces the cost.

[0029] 3. The zirconium source prepared by using acetic acid as a ligand in the present invention has low acetic acid and water content, so that the obtained zirconium source can participate in the sol-gel reaction with low activity, making it possible to prepare low-cost bulk aerogels.

[0030] 4. The preparation method of the present invention is flexible, allowing for flexible selection of gelation methods based on pore structure requirements. It produces transparent monolithic zirconia aerogels with high macroscopic strength, which resist pulverization after heat treatment and maintain a well-maintained morphology. When alcohol-water or epoxides are used as gelation initiators, the aerogels exhibit a uniform mesoporous structure. When amides or ammonia are used as gelation initiators, the aerogels exhibit a predominantly microporous structure and are opaque. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 These are the optical photograph (a) and SEM photograph (b) of the zirconia aerogel obtained by drying in Example 1.

[0032] Figure 2 These are the optical photograph (a) and SEM photograph (b) of the zirconia aerogel obtained by drying in Example 2.

[0033] Figure 3 These are the optical photograph (a) and SEM photograph (b) of the zirconia aerogel obtained by drying in Example 5.

[0034] Figure 4 These are optical photographs of the zirconia aerogels obtained by drying in Examples 1, 2, and 5, with Examples 1, 2, and 5 from left to right.

[0035] Figure 5 These are the optical photographs of the aerogel before and after heat treatment in Experimental Example 1 and the N2 adsorption-desorption curves before and after heat treatment, a is the optical photograph of the aerogel before heat treatment, b is the optical photograph of the aerogel after heat treatment, c is the N2 adsorption-desorption curve before heat treatment, and d is the N2 adsorption-desorption curve after heat treatment. DETAILED DESCRIPTION

[0036] The technical solutions and effects of the present invention are further illustrated below with reference to specific examples and accompanying drawings. It should be understood that these examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. It should also be noted that a person skilled in the art may make several improvements and modifications without departing from the scope of the present invention, and such improvements and modifications are also within the scope of protection of the present invention. The raw materials used in the examples are all conventional commercially available products or prepared according to existing technologies.

[0037] Example 1:

[0038] A method for preparing bulk zirconia aerogel using acetic acid as a low-cost zirconium source as a ligand, comprising the following steps:

[0039] (1) Acetic acid and basic zirconium carbonate were mixed in a mass ratio of 1:1, reacted at room temperature for 24 hours, and then concentrated under reduced pressure at 50°C to obtain a zirconium source, which was then dissolved in a mixed solvent of ethanol and water at room temperature to prepare a zirconium sol; the amount of zirconium source added was such that the concentration of zirconium ions in the zirconium sol was 0.3M, and the volume fraction of ethanol in the mixed solvent of ethanol and water was 80 vol%; then, a gelation reaction occurred at 60°C, and the gelation time was 18 minutes to obtain a wet gel;

[0040] (2) aging and solvent replacement of the wet gel obtained in step (1) at 50° C. for three times, each with an interval of 24 hours to obtain an alcohol gel; the aging solution used is a mixture of ethyl orthosilicate and ethanol in a volume ratio of 1:1; the replacement solvent is ethanol;

[0041] (3) Immerse the alcohol gel from step (2) in a drying kettle, wherein the drying medium occupies 50% of the volume of the drying kettle; fill the drying kettle with 3 MPa of nitrogen, and then raise the pressure from room temperature to 260°C at a rate of 2°C / min, while maintaining the pressure at 10 MPa; after maintaining the pressure for 1 hour, discharge the ethanol at a rate of 2 MPa / h, and finally purge with nitrogen; when the drying kettle is cooled to room temperature, a bulk zirconia aerogel with good optical transparency is obtained, as shown in the optical and SEM photographs. Figure 1 shown.

[0042] Example 2:

[0043] The method for preparing bulk zirconia aerogel using acetic acid as a low-cost zirconium source as described in Example 1 is different in that acetone is used instead of ethanol as the alcohol-water mixed solvent in step (1).

[0044] Example 3:

[0045] The method for preparing bulk zirconia aerogel using acetic acid as a low-cost zirconium source as described in Example 1 is different in that the alcohol-water mixed solvent used in step (1) is isopropanol instead of ethanol.

[0046] Example 4:

[0047] The method for preparing bulk zirconia aerogel using acetic acid as a low-cost zirconium source as described in Example 1 is different in that methanol is used as the alcohol-water mixed solvent instead of ethanol in step (1).

[0048] Example 5:

[0049] The method for preparing bulk zirconia aerogel using acetic acid as a low-cost zirconium source as described in Example 1 is different in that: in step (1), after obtaining the zirconium sol, propylene oxide is added, and the molar ratio of zirconium ions to propylene oxide in the zirconium sol is 1:8; gelation is carried out at 50°C for 5 minutes; and a translucent bulk zirconia aerogel is obtained. The rest of the process is carried out as in Example 1.

[0050] The optical and SEM images of the obtained bulk zirconia aerogel are shown in Figure 2. Figure 2 shown.

[0051] Example 6:

[0052] The method for preparing bulk zirconia aerogel using acetic acid as a low-cost zirconium source as described in Example 1 is different in that: in step (1), after obtaining the zirconium sol, formamide and propylene oxide are added as gel initiators, and the molar ratio of zirconium ions, formamide, and propylene oxide in the zirconium sol is 1:0.1:6; gelation is carried out at 50°C for 3 minutes.

[0053] Example 7:

[0054] The method for preparing bulk zirconia aerogel using acetic acid as a low-cost zirconium source as described in Example 1 is different in that: in step (1), after obtaining the zirconium sol, ethylenediamine is added as a gel initiator, and the molar ratio of zirconium ions to ethylenediamine in the zirconium sol is 1:0.1; gelation is carried out at 50°C for 3 minutes.

[0055] Example 8:

[0056] The method for preparing bulk zirconia aerogel using acetic acid as a low-cost zirconium source as described in Example 1 is different in that: in step (1), after obtaining the zirconium sol, ammonia water is added as a gel initiator, and the molar ratio of zirconium ions to ammonia water in the zirconium sol is 1:0.1; the gelation time is 50°C and the gelation time is 3 minutes. The optical and SEM photos of the finally obtained white aerogel are shown in Figure 2. Figure 3 shown.

[0057] Comparative Example 1:

[0058] The method for preparing bulk zirconia aerogel using acetic acid as a low-cost zirconium source is the same as that described in Example 1, except that:

[0059] Acetic acid and basic zirconium carbonate were mixed in a mass ratio of 1:1, reacted at room temperature for 24 hours without vacuum concentration, and used as a zirconium source. A mixed solvent of ethanol and water was added, and the rest was carried out as in Example 1.

[0060] The results showed that after gelation, a white wet gel was obtained, and after supercritical fluidization, white hard particles with severe shrinkage were obtained, and no aerogel was obtained.

[0061] Comparative Example 2:

[0062] The method for preparing bulk zirconia aerogel using acetic acid as a low-cost zirconium source as described in Example 1 is different in that: if the alcohol-water mixed solvent used in step (1) contains 100 vol% ethanol, zirconium sol cannot be formed.

[0063] Comparative Example 3:

[0064] The method for preparing bulk zirconia aerogel using acetic acid as a low-cost zirconium source as described in Example 1 is different in that: the volume percentage of ethanol in the alcohol-water mixed solvent used in step (1) is 60 vol%, so no complete bulk wet gel is obtained after gelation, and the subsequent supercritical fluidization obtains a white powder, which cannot achieve the preparation of bulk aerogel.

[0065] Test Example 1:

[0066] The aerogel obtained in Example 1 was heat-treated at 1000°C for 2 h, and the apparent density before heat treatment was measured to be 0.14 g / cm 3 The linear shrinkage of the aerogel is only 35%, and its bulk morphology is completely preserved. Figure 5 (a) and (b); the specific surface area ranges from up to 595.1m 2 / g dropped to 171.9m 2 / g; the average pore size decreased from 17.3nm to 16.2nm, and the intact mesoporous structure was maintained before and after heat treatment, such as Figure 5 As shown in (c) and (d).

[0067] It can be seen that the present invention uses a zirconium source with acetic acid as a ligand, which is not only cheap and easily available, but also easy to control the sol-gel rate, making the gelation method flexible. The resulting aerogel has high macroscopic strength, good blockiness and thermal stability. At the same time, the pore structure of the aerogel can also change from a mesoporous to a microporous distribution according to different gelation conditions to meet different application scenarios.

Claims

1. A method for preparing bulk zirconia aerogel using acetic acid as a low-cost zirconium source ligand, comprising the following steps: (1) Acetic acid and basic zirconium carbonate were mixed in a mass ratio of 1:1, reacted at room temperature for 24 hours, and then concentrated under reduced pressure at 50°C to obtain a zirconium source, which was then dissolved in a mixed solvent of ethanol and water at room temperature to prepare a zirconium sol; the amount of zirconium source added was such that the concentration of zirconium ions in the zirconium sol was 0.3M, and the volume fraction of ethanol in the mixed solvent of ethanol and water was 80 vol%; then, a gelation reaction occurred at 60°C, and the gelation time was 18 minutes to obtain a wet gel; (2) aging and solvent replacement of the wet gel obtained in step (1) at 50° C. for three times, each with an interval of 24 hours to obtain an alcohol gel; the aging solution used is a mixture of ethyl orthosilicate and ethanol in a volume ratio of 1:1; the replacement solvent is ethanol; (3) Immersing the alcohol gel from step (2) in a drying kettle, wherein the drying medium occupies 50% of the volume of the drying kettle; filling the drying kettle with 3 MPa of nitrogen, and then raising the temperature from room temperature to 260°C at a rate of 2°C / min, while maintaining the pressure at 10 MPa; after maintaining the pressure for 1 hour, discharging the ethanol at a rate of 2 MPa / h, and finally purging with nitrogen; and when the drying kettle is cooled to room temperature, a bulk zirconia aerogel with good optical transparency is obtained.

2. A method for preparing bulk zirconia aerogel using acetic acid as a low-cost zirconium source ligand, comprising the following steps: (1) Acetic acid and basic zirconium carbonate were mixed in a mass ratio of 1:1, reacted at room temperature for 24 hours, and then concentrated under reduced pressure at 50°C to obtain a zirconium source, which was then dissolved in a mixed solvent of isopropanol and water at room temperature to prepare a zirconium sol; the amount of zirconium source added was such that the concentration of zirconium ions in the zirconium sol was 0.3M, and the volume fraction of ethanol in the mixed solvent of ethanol and water was 80 vol%; then, a gelation reaction occurred at 60°C, and the gelation time was 18 minutes to obtain a wet gel; (2) aging and solvent replacement of the wet gel obtained in step (1) at 50° C. for three times, each with an interval of 24 hours to obtain an alcohol gel; the aging solution used is a mixture of ethyl orthosilicate and ethanol in a volume ratio of 1:1; the replacement solvent is ethanol; (3) Immersing the alcohol gel from step (2) in a drying kettle, wherein the drying medium occupies 50% of the volume of the drying kettle; filling the drying kettle with 3 MPa of nitrogen, and then raising the temperature from room temperature to 260°C at a rate of 2°C / min, while maintaining the pressure at 10 MPa; after maintaining the pressure for 1 hour, discharging the ethanol at a rate of 2 MPa / h, and finally purging with nitrogen; and when the drying kettle is cooled to room temperature, a bulk zirconia aerogel with good optical transparency is obtained.

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