Preparation method of aluminum-based MOF nanofiber aerogel

Abstract

The application relates to the technical field of functional nanomaterial preparation, in particular to a preparation method of aluminum-based MOF nanofiber aerogel. The specific technical scheme is as follows: S1: calcining prepared precursor nanofiber membranes with different diameters to obtain amorphous silicon aluminum oxide precursor nanofiber membranes, placing the membranes into reaction solution A for synthesis to obtain aluminum-based MOF nanofiber membranes X, Y and Z with different diameters; S2: placing the aluminum-based MOF nanofiber membranes with different diameters into reaction solution B respectively after being broken, carrying out ultrasonic homogenization dispersion after reaction to obtain homogeneous dispersions X1, Y1 and Z1; S3: filling the homogeneous dispersions X1, Y1 and Z1 into a mold after being frozen and broken to obtain solidified blocks, then carrying out drying treatment, placing the solidified blocks into reaction solution C for activation treatment to obtain aluminum-based MOF nanofiber aerogel, so that the aluminum-based MOF nanofiber aerogel can be effectively used in the fields of chemical protection and toxic and harmful gas treatment.

Description

Technical Field

[0001] This invention relates to the field of functionalized nanomaterial preparation technology, specifically to an aluminum-based MOF nanofiber aerogel and its preparation method, and more particularly to an aluminum-based MOF nanofiber aerogel with a spatial gradient cellular cavity structure and its preparation method. Background Technology

[0002] Metal-organic frameworks (MOFs) possess high specific surface area, tunable pore structure, and abundant active sites, showing great promise in adsorption, catalysis, and separation. Among them, aluminum-based MOFs have become a research hotspot in chemical protection and gas treatment due to their low toxicity and good stability. Compared to two-dimensional porous fiber materials, fibrous aerogels are ideal carriers for MOF materials due to their high porosity, rich pore structure, and tunable radial dimensions. However, the preparation and application of aluminum-based MOF nanofiber aerogels still have many shortcomings in current technologies.

[0003] Existing methods for preparing aluminum-based MOF nanofiber aerogels mostly involve mixing MOF powder with a fiber substrate or post-loading the mixture. The MOF powder and nanofibers are only bound by weak molecular forces, resulting in poor interfacial bonding and easy detachment. At the same time, the aerogels obtained by existing preparation processes have a simple cell structure and no gradient in pore size distribution, leading to low gas mass transfer efficiency and poor adsorption-decomposition synergy, which makes it difficult to meet the requirements for rapid adsorption and efficient decomposition of toxic and harmful gases in chemical protection.

[0004] Therefore, this invention proposes an aluminum-based MOF nanofiber aerogel that does not require the addition of an additional metal source, has a gradient pore structure, and exhibits excellent adsorption-decomposition performance, so as to realize its special application in fields such as chemical protection and treatment of toxic and harmful gases. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing aluminum-based MOF nanofiber aerogels with a spatially gradient cellular structure. The resulting product can efficiently adsorb and degrade harmful substances such as toxic small molecules, thereby achieving its special utilization in fields such as chemical protection and treatment of toxic and harmful gases.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention discloses a method for preparing aluminum-based MOF nanofiber aerogels, comprising the following steps:

[0008] S1: The prepared precursor nanofiber membranes of different diameters are calcined to obtain amorphous silica-alumina precursor nanofiber membranes. The amorphous silica-alumina precursor nanofiber membranes are placed in reaction solution A to obtain aluminum-based MOF nanofiber membranes X, Y, and Z of different diameters. The reaction solution A includes organic carboxylic acid ligands and solvents.

[0009] S2: After breaking the aluminum-based MOF nanofiber membranes of different diameters prepared in step S1, they were placed into reaction solution B, which was prepared by mixing thickener, crosslinking agent, catalyst and solvent, respectively, for reaction. After the reaction was completed, they were ultrasonically homogenized and dispersed to obtain homogenized dispersions X1, Y1 and Z1.

[0010] S3: After freezing and crushing the homogeneous dispersions X1, Y1, and Z1, they are stacked on a template in descending order of fiber diameter and from bottom to top. After leveling, they are frozen again to obtain a solidified block. Subsequently, a low-pressure vacuum drying process is performed to prepare an aerogel with a spatial gradient cavity structure. This aerogel is then placed in a reaction solution C for activation treatment to obtain an aluminum-based MOF nanofiber aerogel with adsorption-dissipation function. The reaction solution C is one or more of sodium hypochlorite solution, calcium hypochlorite solution, sodium hypobromite solution, and potassium bromate solution.

[0011] Preferably, in step S1, precursor nanofiber membranes of different diameters are prepared by electrospinning. The electrospinning parameters are: solution injection rate of 0.5-2 mL / h, voltage of 15-20 kV, spinning distance of 15-20 cm, relative humidity of 30%-40%, and ambient temperature of 20-25 °C. The average diameter ranges of the prepared nanofiber membranes X, Y, and Z are 400 nm-600 nm, 600 nm-1 μm, and 1-1.5 μm, respectively.

[0012] Preferably, in step S1, the calcination temperature is 400-600℃, the heating rate is 5-10℃ / min, and the duration is 2-6h. At this time, the precursor nanofiber membrane is mainly composed of amorphous silicon-aluminum-oxygen precursor.

[0013] Preferably, in step S1, the organic carboxylic acid ligand is one or more of 2-aminoterephthalic acid, 1H-pyrazole-3,5-dicarboxylic acid, and (E)-5-(2-carboxyvinyl)-1H-pyrazole-3-carboxylic acid; the solvent is one or more of N,N-dimethylformamide, dimethyl sulfoxide, methanol, ethanol, and deionized water; the mass fraction of the organic carboxylic acid ligand in the solvent is 0.01%-0.2%; and the mass ratio of the amorphous silica-alumina precursor nanofiber membrane to the organic carboxylic acid ligand is 1:5-1:12. The metal source is provided by hydrolysis of the precursor nanofiber membrane obtained in step S1, without the need for additional metal sources such as metal salts, metal oxides, or metal particles.

[0014] Preferably, in step S1, the reaction temperature is 100-200℃ and the time is 18-48h. After the reaction is completed and cooled, a first filtration is performed. The nanofiber membrane obtained after the first filtration is washed with one or more of N,N-dimethylformamide, dimethyl sulfoxide, methanol, and ethanol on a shaker for 12-24h. Then, a second filtration is performed, and the membrane obtained after the second filtration is washed with deionized water on a shaker for 12-24h. Then, a third filtration is performed, and the membrane obtained after the third filtration is dried at a temperature of 50-200℃ for 4-24h.

[0015] Preferably, in step S2, the thickener is one or more of polyacrylamide, polyvinyl alcohol, chitosan, methylcellulose, and poly(N-isopropylacrylamide); the crosslinking agent is one or more of methyltriethoxysilane, trimethylmethoxysilane, and dimethyldimethoxysilane; the catalyst is one or more of hydrochloric acid, acetic acid, anhydrous oxalic acid, and ammonium chloride; and the solvent is deionized water.

[0016] Preferably, in step S2, the mass ratio of the thickener to the solvent is 1:100-1:500, the mass ratio of the aluminum-based MOF nanofiber membrane to the crosslinking agent is 1:1-1:4, the mass ratio of the crosslinking agent to the catalyst is 1:50-1:400, and the mass ratio of the crosslinking agent to the solvent is 1:100-1:300.

[0017] Preferably, in step S2, the reaction time of the aluminum-based MOF nanofiber membrane in reaction solution B is 0.5-2 h; the frequency band of the ultrasonic homogenization is 15-30 kHz, and the power is 30-80%.

[0018] Preferably, in step S3, the ice fragments obtained by freezing and crushing have a particle size of 10-500 μm, and the ice fragments obtained by homogeneous dispersions Z1, Y1, and X1 are stacked in the template in order of fiber diameter from large to small and from bottom to top to obtain solidified blocks; the volume ratio of homogeneous dispersions X1, Y1, and Z1 is 1:1:1-1:2:4.

[0019] The low-pressure vacuum drying process takes 24-72 hours, the drying temperature is -45-25°C, the pH of the reaction solution C is 3-7, the activation temperature is 15-40°C, and the activation time is 1-10 hours.

[0020] Accordingly, an aluminum-based MOF nanofiber aerogel prepared by the preparation method described above has a spatially gradient cellular structure.

[0021] The present invention has the following beneficial effects:

[0022] 1. The material of this invention features structural stability and a balance between mechanical and breathable properties. This invention uses a silicon-aluminum-oxygen amorphous precursor film with excellent mechanical properties and stability as a substrate, and transforms it onto an aluminum-based MOF through an in-situ conversion method, forming a stable interfacial bond and effectively solving the problem of easy detachment of traditional materials. This meets the requirements for protective clothing.

[0023] 2. The aerogel prepared by this invention has a unique spatial gradient cavity structure. Aluminum-based MOF nanofibers of different diameters are stacked in a gradient from large to small diameter, so that the cavity pore size of the aerogel is distributed in a gradient, which effectively improves the gas mass transfer efficiency and realizes rapid adsorption and efficient decomposition of toxic and harmful gases. The adsorption-decomposition synergistic performance is significantly better than that of traditional single-structure aerogels.

[0024] 3. This invention employs a customized template process. The template can be designed as needed and combined with a layered nested freezing process, enabling the flexible preparation of aerogel products of different sizes and shapes. These can be made into small granular or cylindrical fillers for use in the internal filling of equipment for industrial waste gas treatment and indoor air purification; they can also be made into large-area sheet or block materials for wearable protective products such as protective clothing and face shields. Furthermore, the product size and gradient structure ratio can be adjusted according to the specific application scenario, making it suitable for applications in multiple fields such as chemical protection, toxic and harmful gas treatment, and environmental pollutant degradation, demonstrating extremely high adaptability.

[0025] 4. The materials of this invention exhibit excellent synergistic performance, enabling integrated adsorption and degradation functions. Compared to traditional two-dimensional porous fiber materials, the three-dimensional aerogel of this invention features high porosity, rich pore structure, and adjustable radial dimensions. Furthermore, the aluminum-based MOF material, converted in situ on the surface, can be modified with chlorine bleach to introduce active chlorine groups, thereby achieving pollutant degradation. This solves the problems of easy saturation and secondary pollution associated with traditional materials, achieving synergistic functional enhancement. Attached Figure Description

[0026] Figure 1 An optical photograph of the aluminum-based MOF nanofiber aerogel prepared in Example 1;

[0027] Figure 2 The image shows the XRD pattern of the aluminum-based MOF nanofiber aerogel prepared in Example 1.

[0028] Figure 3 The images show cross-sectional SEM images (a) and magnified SEM images (b) of the aluminum-based MOF nanofiber aerogel prepared in Example 1.

[0029] Figure 4 The nitrogen adsorption-desorption isotherm and BET specific surface area of ​​the aluminum-based MOF nanofiber aerogel prepared in Example 1 are shown.

[0030] Figure 5The image shows the pore size distribution of the aluminum-based MOF nanofibers prepared in Example 1.

[0031] Figure 6 This is a schematic diagram of the gradient cavity structure aerogel prepared in Example 2. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0033] Unless otherwise specified, the technical means used in the implementation examples are conventional means well known to those skilled in the art.

[0034] This invention provides a method for preparing aluminum-based MOF nanofiber aerogels with a spatially gradient cellular cavity structure based on in-situ transformation, comprising the following steps:

[0035] S1: Precursor nanofiber membranes of different diameters were prepared by combining the sol-gel method with electrospinning technology. They were then calcined to obtain amorphous silica-alumina precursor nanofiber membranes. The membranes were placed in reaction solution A to react and obtain aluminum-based MOF nanofiber membranes X, Y, and Z of different diameters.

[0036] The relevant parameters for electrospinning are as follows: solution injection rate of 0.5-2 mL / h, voltage of 15-20 kV, spinning distance of 15-20 cm, relative humidity of 30%-40%, and ambient temperature of 20-25℃. The average diameters of the prepared nanofiber membranes X, Y, and Z range from 400 nm to 600 nm, 600 nm to 1 μm, and 1-1.5 μm, respectively. The calcination temperature is 400-600℃, the heating rate is 5-10℃ / min, and the duration is 2-6 h. At this time, the main component of the precursor nanofiber membrane is an amorphous silicon-aluminum-oxygen precursor.

[0037] The reaction solution A comprises an organic carboxylic acid ligand and a solvent. The organic carboxylic acid ligand is one or more of 2-aminoterephthalic acid, 1H-pyrazole-3,5-dicarboxylic acid, and (E)-5-(2-carboxyvinyl)-1H-pyrazole-3-carboxylic acid. The solvent is one or more of N,N-dimethylformamide, dimethyl sulfoxide, methanol, ethanol, and deionized water. The mass fraction of the organic carboxylic acid ligand in the solvent is 0.01%-0.2%, and the mass ratio of the amorphous silica-alumina precursor nanofiber membrane to the organic carboxylic acid ligand is 1:5-1:12. The metal source is provided by hydrolysis of the precursor nanofiber membrane obtained in step S1, without the need for additional metal sources such as metal salts, metal oxides, or metal particles.

[0038] The reaction temperature is 100-200℃, and the time is 18-48h. After the reaction is completed and cooled, the first filtration is performed. The nanofiber membrane obtained after the first filtration is washed with one or more of N,N-dimethylformamide, dimethyl sulfoxide, methanol, and ethanol on a shaker for 12-24h. Then, the second filtration is performed, and the membrane obtained after the second filtration is washed with deionized water on a shaker for 12-24h. Then, the third filtration is performed, and the membrane obtained after the third filtration is dried at a temperature of 50-200℃ for 4-24h.

[0039] S2: The aluminum-based MOF nanofiber membranes of different diameters prepared in step S1 were crushed and then placed into reaction solution B, which was prepared by mixing thickener, crosslinking agent, catalyst and solvent, respectively. After the reaction was completed, they were ultrasonically homogenized and dispersed to obtain homogenized dispersions X1, Y1 and Z1.

[0040] The thickener is one or more of polyacrylamide, polyvinyl alcohol, chitosan, methylcellulose, and poly(N-isopropylacrylamide); the crosslinking agent is one or more of methyltriethoxysilane, trimethylmethoxysilane, and dimethyldimethoxysilane; the catalyst is one or more of hydrochloric acid, acetic acid, anhydrous oxalic acid, and ammonium chloride; and the solvent is deionized water.

[0041] The mass ratio of the thickener to the solvent is 1:100-1:500, the mass ratio of the aluminum-based MOF nanofiber membrane to the crosslinking agent is 1:1-1:4, the mass ratio of the crosslinking agent to the catalyst is 1:50-1:400, and the mass ratio of the crosslinking agent to the solvent is 1:100-1:300.

[0042] The reaction time of the aluminum-based MOF nanofiber membrane in reaction solution B is 0.5-2 h; the ultrasonic homogenization frequency band is 15-30 kHz, the power is 30-80%, and the ultrasonic time is 10-30 min.

[0043] S3: Homogeneous dispersions X1, Y1, and Z1 are placed in a low-temperature drum for freeze-crushing and then filled into a template. After leveling, they are frozen again to obtain a solidified block. Subsequently, aerogels with spatial gradient cellular structures are prepared by low-pressure vacuum drying. After being placed in reaction solution C for activation treatment, aluminum-based MOF nanofiber aerogels with adsorption-dissipation functions are obtained.

[0044] The ice fragments obtained by freezing and crushing have a particle size of 10-500μm. The ice fragments obtained by homogeneous dispersions Z1, Y1, and X1 are stacked in a template in order of fiber diameter from large to small and from bottom to top to obtain solidified blocks. The volume ratio of homogeneous dispersions X1, Y1, and Z1 is 1:1:1-1:2:4.

[0045] The low-pressure vacuum drying time is 24-72h, the drying temperature is -45℃ to 25℃, the vacuum degree is 1-10Pa, the pH value of the reaction solution C is 3-7, the activation temperature is 15-40℃, and the activation time is 1-10h.

[0046] This invention provides an aluminum-based MOF nanofiber aerogel with a spatially gradient cellular cavity structure prepared by the above-described preparation method.

[0047] The present invention will be further described below with reference to specific embodiments.

[0048] Example 1

[0049] A method for preparing aluminum-based MOF nanofiber aerogels with a spatially gradient cellular cavity structure includes the following steps:

[0050] S1: Alumina silica sol was prepared using the sol-gel method, and then injected into an electrospinning apparatus for electrospinning. The electrospinning process parameters were: solution injection rate 1 mL / h, spinning voltage 18 kV, spinning distance 18 cm, relative humidity 35%, and ambient temperature 22 °C. Through this step, precursor fiber membranes with average diameters of 500 nm (X), 800 nm (Y), and 1.2 μm (Z) were prepared. The obtained fiber membranes were then calcined in a muffle furnace. The calcination process parameters were set as follows: calcination temperature 500 °C, heating rate 8 °C / min, and calcination duration 4 h, yielding amorphous alumina silica precursor nanofiber membranes X, Y, and Z.

[0051] The amorphous silica-alumina precursor nanofiber membranes X, Y, and Z were placed in reaction solution A and synthesized at 120°C for 24 hours. The reaction solution A was a DMF / deionized water mixture of 2-aminoterephthalic acid (volume ratio 3:1), wherein the mass fraction of 2-aminoterephthalic acid was 0.1%, and the mass ratio of the precursor nanofiber membrane to 2-aminoterephthalic acid was 1:8.

[0052] After the synthesis reaction was completed, the reaction system was cooled to room temperature and subjected to three separate filtration and washing processes: after the first filtration, DMF was used as the washing solution and the membrane was washed in a shaker for 18 hours; after the second filtration, deionized water was used as the washing solution and the membrane was washed in a shaker for 18 hours; after the third filtration, the resulting membrane was placed in an oven and dried at 120°C for 12 hours to obtain aluminum-based MOF nanofiber membranes X, Y, and Z.

[0053] S2: The aluminum-based MOF nanofiber membranes X, Y, and Z are crushed to a particle size of less than 100 μm and added to reaction solution B respectively. The reaction solution B is reacted at room temperature for 1 hour. The components of reaction solution B are: thickener polyvinyl alcohol, crosslinking agent methyltriethoxysilane, catalyst acetic acid, and solvent deionized water. The proportions of each component are as follows: the mass ratio of polyvinyl alcohol to deionized water is 1:200, the mass ratio of aluminum-based MOF nanofiber membrane to methyltriethoxysilane is 1:2, the mass ratio of methyltriethoxysilane to acetic acid is 1:200, and the mass ratio of methyltriethoxysilane to deionized water is 1:200.

[0054] After the reaction was completed, the reaction mixture was placed in an ultrasonic homogenizer and ultrasonically homogenized for 20 min at 20 kHz frequency and 50% power to obtain homogenized dispersions X1, Y1 and Z1.

[0055] S3: The homogeneous dispersions X1, Y1, and Z1 are placed in a low-temperature drum at -30°C for 20 minutes to undergo freeze-crushing treatment, resulting in fiber ice fragments with an average particle size of 200 μm. The fiber ice fragments are then filled into a cylindrical template in a volume ratio of 1:1:1, in descending order of fiber diameter (Z1→Y1→X1), and frozen at -25°C to form a solidified block.

[0056] The solidified block was placed in a low-pressure vacuum drying oven and dried for 48 hours under a vacuum of 5 Pa and a temperature of 20 °C to obtain an aerogel with a spatial gradient cellular structure.

[0057] The aerogel was placed in reaction solution C and activated at 25°C for 5 hours; the reaction solution C was a sodium hypochlorite solution with a pH of 5; finally, an aluminum-based MOF nanofiber aerogel with adsorption-decomposition function was prepared.

[0058] The resulting aluminum-based MOF nanofiber aerogel with a spatially gradient cellular structure has a bulk density of 6 mg / cm³. 3 Specific surface area is 320m² 2 / g, with an available chlorine content of 4225ppm.

[0059] A 20 mg sample of aluminum-based MOF nanofiber aerogel was weighed and placed in a 20 mL sealed adsorption chamber. A 1 mL open vial containing 20 μL of 2-chloroethyl ethyl sulfide (CEES), a mustard gas mimic, was placed next to the sample. After standing at 25 °C for two days, the sample was removed and weighed. The adsorption capacity for CEES was calculated to be 210 mg / g. After the reaction was complete, the degradation products were qualitatively analyzed using NMR. A linear regression analysis showed a reaction half-life of 3.1 min. Furthermore, after 10 adsorption-degradation cycles, the material's adsorption capacity remained above 85% of its initial value, and the structure showed no significant damage, demonstrating its good stability.

[0060] from Figure 1 It can be seen that aluminum-based MOF nanofiber aerogels of different sizes can be prepared according to different needs.

[0061] from Figure 2 XRD analysis of the material shows that the synthesized aluminum-based MOF nanofiber aerogel possesses the characteristic peaks of MOF materials, and is composed of... Figure 3 The SEM images of the material show that a large number of MOFs were transformed in situ on the material surface.

[0062] from Figure 4 Nitrogen adsorption-desorption isotherms and Figure 5 The pore size distribution diagram shows that the material has a high specific surface area and the pore size is concentrated in the micropore size, indicating that the material has good adsorption capacity.

[0063] Example 2

[0064] A method for preparing aluminum-based MOF nanofiber aerogels with a spatially gradient cellular cavity structure specifically includes the following steps:

[0065] S1: Alumina silica sol was prepared using the sol-gel method, and then injected into an electrospinning apparatus for electrospinning. The electrospinning process parameters were set as follows: solution injection rate 0.5 mL / h, spinning voltage 15 kV, spinning distance 15 cm, relative humidity 30%, and ambient temperature 20 °C. Precursor fiber membranes with average diameters of 400 nm (X), 600 nm (Y), and 1 μm (Z) were prepared through this step. The obtained fiber membranes were then calcined in a muffle furnace. The calcination process parameters were set as follows: calcination temperature 400 °C, heating rate 5 °C / min, and calcination duration 6 h, yielding amorphous alumina silica precursor nanofiber membranes X, Y, and Z.

[0066] The amorphous silica-alumina precursor nanofiber membranes X, Y, and Z were placed in reaction solution A and synthesized at 100°C for 48 hours. The reaction solution A was a mixture of ethanol and deionized water (volume ratio 2:1) of 2-aminoterephthalic acid, wherein the mass fraction of 2-aminoterephthalic acid was 0.01%, and the mass ratio of the precursor nanofiber membrane to 2-aminoterephthalic acid was 1:5.

[0067] After the synthesis reaction was completed, the membranes were subjected to three separate filtration and washing processes: after the first filtration, ethanol was used as the washing solution and the membranes were washed in a shaker for 24 hours; after the second filtration, deionized water was used as the washing solution and the membranes were washed in a shaker for 24 hours; after the third filtration, the membranes were placed in an oven and dried at 50°C for 24 hours to obtain aluminum-based MOF nanofiber membranes X, Y, and Z.

[0068] S2: The aluminum-based MOF nanofiber membrane is broken down to below 80 μm and added to reaction solution B, and reacted at room temperature for 0.5 h; the components of reaction solution B are: thickener polyacrylamide, crosslinking agent trimethylmethoxysilane, catalyst hydrochloric acid, and solvent deionized water; the proportions of each component are as follows: the mass ratio of polyacrylamide to deionized water is 1:100, the mass ratio of aluminum-based MOF nanofiber membrane to crosslinking agent is 1:1, the mass ratio of crosslinking agent to hydrochloric acid is 1:50, and the mass ratio of crosslinking agent to deionized water is 1:100;

[0069] After the reaction was completed, the reaction mixture was subjected to ultrasonic homogenization. The ultrasonic parameters were set as follows: 15KHz frequency band, 30% power, and ultrasonic duration of 30min, to obtain homogeneous dispersions X1, Y1, and Z1.

[0070] S3: The homogeneous dispersions X1, Y1, and Z1 are placed in a low-temperature drum at -40℃ for freeze-crushing treatment for 15 minutes to obtain fiber ice fragments with an average particle size of 250μm; the crushed ice fragments are filled into a cube template in the order of Z1→Y1→X1 according to a volume ratio of 1:2:4, and frozen at -25℃ to obtain a solid block; the solid block is subjected to low-pressure vacuum drying treatment, and the drying parameters are set as follows: vacuum degree 10Pa, temperature 10℃, and drying time 72h;

[0071] The dried aerogel was placed in a calcium hypochlorite solution with pH=3 and activated at 15℃ for 10h to finally prepare aluminum-based MOF nanofiber aerogel.

[0072] Performance testing showed that the bulk density of the aluminum-based MOF nanofiber aerogel with a spatially gradient cellular structure obtained in this embodiment was 5 mg / cm³. 3 Specific surface area is 280m² 2 / g, available chlorine content 4400ppm, its structural diagram is as follows Figure 6 As shown. The adsorption experiment was the same as in Example 1. The adsorption capacity was measured to be 195 mg / g, and the degradation half-life was 5 min.

[0073] Example 3

[0074] A method for preparing aluminum-based MOF nanofiber aerogels with a spatially gradient cellular cavity structure specifically includes the following steps:

[0075] S1: Alumina silica sol was prepared using the sol-gel method, and then injected into an electrospinning apparatus for electrospinning. The electrospinning process parameters were set as follows: solution injection rate 2 mL / h, spinning voltage 20 kV, spinning distance 20 cm, relative humidity 40%, and ambient temperature 25 °C. Through this step, precursor fiber membranes with average diameters of 600 nm (X), 1 μm (Y), and 1.5 μm (Z) were prepared. The obtained fiber membranes were then calcined in a muffle furnace. The calcination process parameters were set as follows: calcination temperature 600 °C, heating rate 10 °C / min, and calcination duration 2 h, yielding amorphous alumina silica precursor nanofiber membranes X, Y, and Z.

[0076] The amorphous silica-alumina precursor nanofiber membranes X, Y, and Z were placed in reaction solution A and synthesized at 150°C for 18 hours. The reaction solution A was a deionized water mixture of 1H-pyrazole-3,5-dicarboxylic acid, wherein the mass fraction of 1H-pyrazole-3,5-dicarboxylic acid was 0.2%, and the mass ratio of the precursor nanofiber membrane to 1H-pyrazole-3,5-dicarboxylic acid was 1:10.

[0077] After the synthesis reaction was completed, three filtration and washing processes were performed sequentially: after the first filtration, deionized water was used as the washing liquid and the membrane was washed in a shaker for 12 hours; after the second filtration, fresh deionized water was used as the washing liquid and the membrane was washed in a shaker for 12 hours; after the third filtration, the obtained membrane was placed in an oven and dried at 200°C for 4 hours to obtain aluminum-based MOF nanofiber membranes X, Y, and Z.

[0078] S2: The aluminum-based MOF nanofiber membrane is broken down to below 120 μm and added to reaction solution B, and reacted at room temperature for 2 hours; the components of reaction solution B are: thickener chitosan, crosslinking agent dimethyldimethoxysilane, catalyst anhydrous oxalic acid, and solvent deionized water; the proportions of each component are as follows: the mass ratio of chitosan to deionized water is 1:500, the mass ratio of aluminum-based MOF nanofiber membrane to crosslinking agent is 1:4, the mass ratio of crosslinking agent to anhydrous oxalic acid is 1:400, and the mass ratio of crosslinking agent to deionized water is 1:300;

[0079] After the reaction was completed, the reaction mixture was subjected to ultrasonic homogenization. The ultrasonic parameters were set as follows: 30KHz frequency band, 80% power, and ultrasonic duration of 10min, to obtain homogeneous dispersions X1, Y1, and Z1.

[0080] S3: The homogeneous dispersions X1, Y1, and Z1 are placed in a low-temperature drum at -20°C for freeze-crushing treatment for 30 minutes to obtain fiber ice fragments with an average particle size of 100 μm; the crushed ice fragments are filled into a template in the order of Z1→Y1→X1 at a volume ratio of 1:1:2, and frozen at -25°C to obtain a solid block; the solid block is subjected to low-pressure vacuum drying treatment, with the drying parameters set as follows: vacuum degree 1 Pa, temperature 25°C, and drying time 24 h;

[0081] The dried aerogel was placed in a sodium hypochlorite solution at pH 7 and activated at 30°C for 1 hour to finally prepare an aluminum-based MOF nanofiber aerogel with adsorption-decomposition function.

[0082] Performance testing showed that the bulk density of the aluminum-based MOF nanofiber aerogel with a spatially gradient cellular structure obtained in this embodiment was 8 mg / cm³. 3 Specific surface area is 350m² 2 / g. The adsorption experiment was the same as in Example 1. The adsorption capacity was measured to be 155 mg / g, and the degradation half-life was 6 min.

[0083] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing aluminum-based MOF nanofiber aerogel, characterized in that... Includes the following steps: S1: The prepared precursor nanofiber membranes of different diameters are calcined to obtain amorphous silica-alumina precursor nanofiber membranes. The amorphous silica-alumina precursor nanofiber membranes are placed in reaction solution A to obtain aluminum-based MOF nanofiber membranes X, Y, and Z of different diameters. The reaction solution A includes organic carboxylic acid ligands and solvents. S2: After breaking the aluminum-based MOF nanofiber membranes of different diameters prepared in step S1, they were placed into reaction solution B, which was prepared by mixing thickener, crosslinking agent, catalyst and solvent, respectively, for reaction. After the reaction was completed, they were ultrasonically homogenized and dispersed to obtain homogenized dispersions X1, Y1 and Z1. The thickener is one or more of polyacrylamide, polyvinyl alcohol, chitosan, methylcellulose, and poly(N-isopropylacrylamide); the crosslinking agent is one or more of methyltriethoxysilane, trimethylmethoxysilane, and dimethyldimethoxysilane; and the catalyst is one or more of hydrochloric acid, acetic acid, anhydrous oxalic acid, and ammonium chloride. S3: After freezing and crushing the homogeneous dispersions X1, Y1, and Z1, they are stacked in a template in descending order of fiber diameter and from bottom to top. After leveling, they are frozen again to obtain a solidified block. Subsequently, a low-pressure vacuum drying process is performed to prepare an aerogel with a spatial gradient cavity structure. This aerogel is then placed in a reaction solution C for activation treatment to obtain an aluminum-based MOF nanofiber aerogel with adsorption-dissipation function. The reaction solution C is one or more of sodium hypochlorite solution, calcium hypochlorite solution, sodium hypobromite solution, and potassium bromate solution.

2. The preparation method according to claim 1, characterized in that... In step S1, precursor nanofiber membranes of different diameters are prepared by electrospinning. The electrospinning parameters are: solution injection rate of 0.5-2 mL / h, voltage of 15-20 kV, spinning distance of 15-20 cm, relative humidity of 30%-40%, and ambient temperature of 20-25℃. The average diameter ranges of the prepared nanofiber membranes X, Y, and Z are 400 nm-600 nm, 600 nm-1 μm, and 1-1.5 μm, respectively.

3. The preparation method according to claim 1 or 2, characterized in that... In step S1, the calcination temperature is 400-600℃, the heating rate is 5-10℃ / min, and the duration is 2-6h.

4. The preparation method according to claim 1, characterized in that... In step S1, the organic carboxylic acid ligand is one or more of 2-aminoterephthalic acid, 1H-pyrazole-3,5-dicarboxylic acid, and (E)-5-(2-carboxyvinyl)-1H-pyrazole-3-carboxylic acid; the solvent is one or more of N,N-dimethylformamide, dimethyl sulfoxide, methanol, ethanol, and deionized water; the mass fraction of the organic carboxylic acid ligand in the solvent is 0.01%-0.2%; and the mass ratio of the amorphous silica-alumina precursor nanofiber membrane to the organic carboxylic acid ligand is 1:5-1:

12.

5. The preparation method according to claim 1 or 4, characterized in that... In step S1, the reaction temperature is 100-200℃ and the time is 18-48h. After the reaction is completed and cooled, the first filtration is performed. The nanofiber membrane obtained after the first filtration is washed with one or more of N,N-dimethylformamide, dimethyl sulfoxide, methanol, and ethanol on a shaker for 12-24h. Then, the second filtration is performed, and the membrane obtained after the second filtration is washed with deionized water on a shaker for 12-24h. Then, the third filtration is performed, and the membrane obtained after the third filtration is dried at a temperature of 50-200℃ for 4-24h.

6. The preparation method according to claim 1, characterized in that... In step S2, the solvent is deionized water.

7. The preparation method according to claim 1 or 6, characterized in that... In step S2, the mass ratio of the thickener to the solvent is 1:100-1:500, the mass ratio of the aluminum-based MOF nanofiber membrane to the crosslinking agent is 1:1-1:4, the mass ratio of the crosslinking agent to the catalyst is 1:50-1:400, and the mass ratio of the crosslinking agent to the solvent is 1:100-1:

300.

8. The preparation method according to claim 1, characterized in that... In step S2, the reaction time of the aluminum-based MOF nanofiber membrane in reaction solution B is 0.5-2h; the frequency band of the ultrasonic homogenization is 15-30KHz, and the power is 30-80%.

9. The preparation method according to claim 1, characterized in that... In step S3, the ice fragments obtained by freezing and crushing have a particle size of 10-500μm. The ice fragments obtained by homogeneous dispersions Z1, Y1, and X1 are stacked in the template in order of fiber diameter from large to small and from bottom to top to obtain solidified blocks. The volume ratio of homogeneous dispersions X1, Y1, and Z1 is 1:1:1-1:2:

4. The low-pressure vacuum drying process takes 24-72 hours, the drying temperature is -45-25°C, the pH of the reaction solution C is 3-7, the activation temperature is 15-40°C, and the activation time is 1-10 hours.

10. An aluminum-based MOF nanofiber aerogel prepared by the preparation method according to any one of claims 1-9, characterized in that... The aluminum-based MOF nanofiber aerogel has a spatially gradient cellular structure.

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