UiO-67-so2@anf fiber aerogel and preparation method and application thereof

Abstract

The application discloses a kind of UiO-67-SO2@ANF fiber aerogel and its preparation method and application, UiO-67-SO2@ANF fiber aerogel includes MOF precursor and aramid nanofiber ANF, the MOF precursor includes zirconium salt and dibenzo [b, d] thiophene-3, 7-dicarboxylic acid-5, 5-diketone H2DTDAO;The mass ratio of zirconium salt, H2DTDAO and ANF is (0.8-1.2):(1.8-2.2):(0.8-1.2);The specific surface area of UiO-67-SO2@ANF fiber aerogel is 670.29 m 2 / g, pore volume is 0.501 cm 3 / g, average pore size is 0.472nm.The application can be uniformly and large amount of MOF loaded on the surface of ANF fiber, and the UiO-66-SO2@ANF fiber aerogel of the application has excellent compression resilience, three-dimensional hierarchical pore structure, which can effectively improve the CO2 adsorption capacity.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of fiber aerogels, and particularly relates to a UiO-67-SO2@ANF fiber aerogel and a preparation method and application thereof. BACKGROUND

[0002] In the face of the continuous growth of global greenhouse gas emissions and the intensification of climate warming, CO2 capture technology has been extensively researched at home and abroad. Metal-organic frameworks (MOFs) have been widely reported and applied in CO2 capture due to their excellent structural characteristics such as high specific surface area, high porosity, adjustable pore size, and easy surface functionalization. However, there are still problems to be solved in order to make MOFs truly approach or meet the use requirements of high-performance CO2 adsorbents in the industrial field:

[0003] (1) How to accelerate the gas mass transfer performance of MOFs, expand their pore structure and compressive elasticity, in order to realize the efficient flowability and mass transfer efficiency of CO2 gas molecules in their interior; (2) How to regulate the physical and chemical microenvironment of MOFs to improve their affinity for CO2, so as to realize high CO2 adsorption capacity and high CO2 adsorption selectivity.

[0004] Therefore, there is an urgent need to develop a new MOF material to solve the defects of the existing MOF material, such as uneven mesopore distribution, poor mechanical properties, and low CO2 adsorption capacity. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a UiO-67-SO2@ANF fiber aerogel and a preparation method and application thereof. The present application can uniformly and massively load MOFs on the surface of ANF fibers. The UiO-66-SO2@ANF fiber aerogel of the present application has excellent compressive resilience and three-dimensional hierarchical pore structure, which can effectively improve the CO2 adsorption capacity.

[0006] To this end, the present application provides a UiO-67-SO2@ANF fiber aerogel, which comprises a MOF precursor and aramid nanofiber ANF. The MOF precursor comprises zirconium salt and dibenzo[b,d]thiophene-3,7-dicarboxylic acid-5,5-diketone H2DTDAO. The mass ratio of zirconium salt, H2DTDAO and ANF is (0.8-1.2):(1.8-2.2):(0.8-1.2).

[0007] The specific surface area of the UIO-67-SO2@ANF fiber aerogel is 500-700 m 2 / g, the pore volume is 0.5-0.8 cm 3 / g, and the average pore size is 0.4-1 nm.

[0008] The application further provides a preparation method of the UiO-67-SO2@ANF fiber aerogel, comprising the following steps:

[0009] (1) preparing aramid nanofiber

[0010] (1.1) alkali treatment: taking aramid fibril, adding into an alkali solution, refluxing under a constant temperature water bath, after the solution is cooled, the solution is filtered and washed to neutral with distilled water, and aramid fibril solution is obtained;

[0011] (1.2) high-pressure homogenization treatment: the aramid fibril solution is treated by using a high-pressure homogenizer, and aramid nanofiber solution is obtained; the aramid nanofiber solution is filtered and water is removed, and aramid nanofiber is obtained;

[0012] (2) preparing ANF water dispersion

[0013] phosphoric acid PA treatment: the aramid nanofiber is added into a PA solution and stirred under water bath conditions; then the above solution is washed to neutral with distilled water and configured into ANF water dispersion;

[0014] (3) preparing UiO-67-SO2@ANF fiber aerogel

[0015] (3.1) the ANF water dispersion is placed in N, N-dimethylformamide DMF and configured into ANF / DMF dispersion;

[0016] (3.2) zirconium salt is added into the ANF / DMF dispersion and stirred until it is completely dissolved; then H2DTDAO and trifluoroacetic acid TFA are added, and stirring is continued, and a mixed solution is obtained;

[0017] (3.3) the mixed solution is transferred into a reaction kettle for reaction, after the reaction is completed and cooled to room temperature, UiO-67-SO2@ANF fiber is obtained by filtration;

[0018] (3.4) the UiO-67-SO2@ANF fiber is washed with DMF and methanol respectively for three times, and unreacted impurities are removed; then the solvent is replaced with distilled water, and the UiO-67-SO2@ANF fiber is configured into UiO-67-SO2@ANF fiber dispersion;

[0019] (3.5) the UiO-67-SO2@ANF fiber dispersion is taken, an aqueous silane solution and tert-butyl alcohol are added, stirring is carried out, and after freeze-drying and heat curing processes, the UiO-67-SO2@ANF fiber aerogel is obtained.

[0020] Preferably, in the step (1.1), the alkali solution is a strong sodium hydroxide solution with a concentration of 10-20 wt%; the ratio of the mass of the aramid fibrils to the volume of the alkali solution is (1-3) g:(300-800) ml; and the refluxing is performed at 70-90℃ for 3-5h.

[0021] Preferably, in the step (1.2), the concentration of the aramid nanofiber solution is 0.3-0.6 wt%; the process of treating the aramid fibril solution by using a high-pressure homogenizer includes: first using a ball valve to increase the pressure to 700-900 MPa for 15-25 min; and then using a flat valve to increase the pressure to 900-1100 MPa for 20-40 min.

[0022] Preferably, in the step (2), the concentration of the PA solution is 15-25 wt.%; the ratio of the mass of the aramid nanofiber to the volume of the PA solution is (0.5-1.5) g:(200-400) ml; and the stirring is performed at 40℃ for 2h.

[0023] The concentration of the ANF aqueous dispersion is 0.2-0.5 wt%.

[0024] Preferably, in the step (3.1), the concentration of the ANF / DMF dispersion is 0.2-0.5 wt%.

[0025] Preferably, in the step (3.2), the mass ratio of trifluoroacetic acid to zirconium salt is (0.8-1.2):(4-6).

[0026] Preferably, in the step (3.3), the reaction temperature in the reaction kettle is 110-130℃, and the reaction time is 10-14h; and in the step (3.4), the concentration of the UiO-67-SO2@ANF fiber dispersion is 0.2-0.5 wt%.

[0027] Preferably, in the step (3.5), the volume of the UiO-67-SO2@ANF fiber dispersion, the mass of the aqueous silane solution, and the volume of the tert-butyl alcohol are in the ratio of (8-12) mL:(0.01-0.05) g:(0.5-1.5) ml; the freeze-drying temperature is -60--40℃, and the time is 30-40 h; and the heat curing temperature is 160-200 ℃, and the time is 3-8 min.

[0028] The application also provides the use of the UiO-67-SO2@ANF fiber aerogel in the preparation of carbon dioxide separation and / or adsorption materials.

[0029] Compared with the prior art, the application has the following advantages and positive effects:

[0030] (1) Compared with the traditional method of using potassium hydroxide (KOH) and 2-methyl sulfoxide (DMSO) to deprotonate aramid primary fibers first and then using water as a proton donor for reduction to obtain ANF, the application adopts a high-pressure homogenization process, which can convert micron-sized aramid fibers into aramid nanofibers ANF, realize batch production of ANF, does not need to use organic solvents, and has high ANF production efficiency, safety, environmental protection and no pollution.

[0031] (2) The phosphoric acid treatment of ANF can expose a large number of active groups (amino and carboxyl) on the surface of ANF, so that the carboxyl group can form a strong interfacial hydrogen bond with the metal Zr 4+ , and finally realize the uniform and large loading of UiO-67-SO2 on the surface of ANF, which can better promote the in-situ growth of UiO-67-SO2 on the surface of ANF.

[0032] (3) Through the fiber freeze-drying technology, by freezing the water dispersion liquid of UiO-67-SO2@ANF fiber, a solid material with a block-shaped three-dimensional structure (with ice crystals) can be obtained, which is beneficial to promote the formation of ice crystal structure with good morphology of UiO-67-SO2@ANF fiber dispersion liquid in the freezing process; and then after the drying process, the ice crystals will sublimate, and the places where the ice crystals exist will form the pores of the UiO-67-SO2@ANF fiber aerogel, so that the aerogel forms a three-dimensional porous structure, which endows the aerogel with excellent mechanical properties, such as compression-rebound characteristics; the UiO-67-SO2@ANF fiber aerogel can still maintain the integrity of the aerogel structure after 800 times of compression-rebound experiment test.

[0033] (4) The UiO-67-SO2@ANF fiber aerogel of the application has a three-dimensional multi-level pore structure integrating macropores, mesopores and micropores, wherein the macropores and mesopores formed by the interconnection of the three-dimensional fiber network can be used as continuous long-range gas transmission channels, effectively improving the efficient diffusion of gas molecules inside; and the UiO-67-SO2 distributed in the three-dimensional nanofiber network channel retains an open micropore structure, which can provide more contact area, active site and transmission channel for CO2, thereby improving its adsorption capacity for CO2; at the same time, the hydrophobic micropores can also limit the H2O molecules, and can promote the adsorption of CO2 molecules to the inside of the UiO-67-SO2 fiber aerogel.

[0034] (5) The MOF precursor of the present application comprises zirconium chloride (ZrCl4) and dibenzo[b,d]thiophene-3,7-dicarboxylic acid-5,5-dione (H2DTDAO). H2DTDAO carries a sulfone functional group (O=S=O functional group), which is beneficial to promote the adsorption of CO2 by the UiO-67-SO2@ANF fibrous aerogel. There are three adsorption sites for CO2 molecules in the UiO-67-SO2 structural unit, including Zr 4+ clusters, O=S=O groups and benzene rings. Through molecular dynamics calculation, it is found that for the UiO-67-SO2 structural unit, the static adsorption energy at O=S=O is 0.268 eV, which is significantly higher than that of Zr4+clusters (0.226 eV) and benzene rings (0.183 eV), indicating that the introduction of O=S=O functional groups can promote the affinity of UiO-67-SO2@ANF aerogel for CO2, which is beneficial to promote the adsorption of CO2 by the UiO-67-SO2@ANF fibrous aerogel.

[0035] Other features and advantages of the present application will become more apparent from the detailed description of the application in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 SEM image of the UiO-67-SO2@ANF fibrous aerogel of Example 1;

[0037] Figure 2 Stress-strain curve of the UiO-67-SO2@ANF fibrous aerogel of Example 1 under the test condition of a deformation of 50% and a cycle of 800 times of compression-rebound test;

[0038] Figure 3 Pore size distribution test graph of the UiO-67-SO2@ANF fibrous aerogel of Example 1;

[0039] Figure 4 SEM image of the ANF fibrous aerogel of Comparative Example 1;

[0040] Figure 5 CO2 adsorption capacity test graph of the UiO-67-SO2@ANF fibrous aerogel of Example 1 and the ANF fibrous aerogel of Comparative Example 1 at 25°C;

[0041] Figure 6 XRD test graph of the UiO-67-SO2@ANF fibrous aerogel of Example 1, the ANF fibrous aerogel of Comparative Example 1 and UiO-67-SO2 crystal. DETAILED DESCRIPTION

[0042] The application will be further described in connection with the following specific examples. These examples are only used to illustrate the application and not used to limit the scope of the application. Meanwhile, after reading the content of the application, those skilled in the art can make various modifications or changes to the application, and these equivalent forms also fall within the scope defined by the appended claims.

[0043] The UiO-67-SO2@ANF fiber aerogel of the application comprises a MOF precursor and aramid nanofiber, wherein the MOF precursor comprises a zirconium salt and dibenzo[b,d]thiophene-3,7-dicarboxylic acid-5,5-dione H2DTDAO.

[0044] The mass ratio of the zirconium salt, H2DTDAO and ANF is (0.8-1.2):(1.8-2.2):(0.8-1.2), which can obtain the UiO-67-SO2 particles with appropriate particle size, effectively avoid the accumulation distribution of the UiO-67-SO2 particles on the surface of the ANF, make the UiO-67-SO2 particles uniformly loaded on the surface of the ANF, effectively improve the specific surface area of the UiO-67-SO2@ANF fiber aerogel, and be beneficial to the CO2 gas transmission, so as to improve the adsorption capacity of the UiO-67-SO2@ANF fiber aerogel to CO2.

[0045] The UiO-67-SO2@ANF fiber aerogel of the application has excellent thermal insulation performance, and the thermal conductivity coefficient at 25℃ can be as low as 28 mW / mk.

[0046] The specific surface area of the UiO-67-SO2@ANF fiber aerogel of the application is 500-700 m 2 / g, the pore volume is 0.5-0.8 cm 3 / g, and the average pore size is 0.4-1nm.

[0047] Preferably, the specific surface area of the UiO-67-SO2@ANF fiber aerogel of the application is 600-680 m 2 / g, the pore volume is 0.5-0.7 cm 3 / g, and the average pore size is 0.4-0.6nm.

[0048] The UiO-67-SO2@ANF fiber aerogel of the application has high specific surface area and porous structure, high porosity, can provide more active sites and transmission channels for CO2, and thus can improve the adsorption capacity of the UiO-67-SO2@ANF fiber aerogel to CO2.

[0049] The UiO-67-SO2@ANF fiber aerogel of the present invention has excellent compressive elasticity, with a maximum compressive stress of 14.24 kPa. After 800 compression cycle tests, the plastic deformation is only 5.26%, the maximum compressive stress loss is 4.13%, the Young's modulus loss is only 4.29%, and the energy loss factor loss is only 16.46%.

[0050] The preparation method of the UiO-67-SO2@ANF fiber aerogel of the present invention comprises the following steps:

[0051] (1) Preparation of aramid nanofibers

[0052] (1.1) Alkali treatment: chop aramid fibrils, add them to an alkaline solution, and reflux them in a constant temperature water bath at 70-90°C for 3-5 hours. After the solution cools, filter and wash it with distilled water until it is neutral to obtain an aramid fibril solution.

[0053] The aramid fibrils selected in the present invention may be para-aramid PPTA fibers. Para-aramid PPTA fibers have a distinct skin-core structure and can be easily broken down into nanofibers.

[0054] The aramid fibrils may also be other aramid fibers commonly used in the technical field, and are not specifically limited here.

[0055] The alkaline solution selected in the present invention can be a sodium hydroxide solution, which is not specifically limited here.

[0056] The purpose of the present invention of subjecting aramid fibrils to alkali treatment is that aramid fibers have a distinct skin-core structure, i.e., the fiber core has a higher molecular chain orientation and a higher degree of crystallinity, while the fiber cortex has a lower degree of crystallinity. After alkali treatment, the amide bonds on the surface of the aramid fibers are hydrolyzed, thereby causing the surface of the aramid fibers to acquire electronegativity, i.e., the charges on the surface of the aramid fibers repel each other, which is beneficial for fiber splitting; at the same time, the alkaline solution can damage the cortex of the aramid fibers to a certain extent. In other words, after being treated with an alkaline solution, the aramid fibrils are more easily broken down, thereby being more conducive to their conversion into nanofibers. During the subsequent high-pressure homogenization process, the cortex of the aramid fibers will be further broken down and broken down, making it easier for them to break down into nanofibers.

[0057] If the concentration of the alkaline solution is too high, the high-concentration alkaline solution will cause serious corrosion damage to the aramid fibrils; if the concentration of the alkaline solution is too low, the low-concentration alkaline solution cannot make the aramid fiber surface obtain effective electronegativity. After the subsequent high-pressure homogenization treatment, the aramid fiber cannot be effectively broken down into nanofibers, and the obtained aramid fiber diameter distribution is uneven, and the aramid fiber shape is irregular.

[0058] The concentration of the alkali solution selected by the application is 10-20 wt%, in this concentration range, the aramid fibrils will not be corroded and damaged, and the surface of the aramid fiber can obtain effective electronegativity, after subsequent high-pressure homogenization treatment, the aramid fiber can be effectively cracked into nanofibers, the obtained aramid fiber has uniform diameter distribution, and the morphology of the aramid fiber is regular.

[0059] Preferably, the concentration of the alkali solution selected by the application is 15 wt%, the aramid fibrils will not be corroded and damaged, and the surface of the aramid fiber can obtain effective electronegativity, after subsequent high-pressure homogenization treatment, the aramid fiber can be effectively cracked into nanofibers, the obtained aramid fiber has uniform diameter distribution, and the morphology of the aramid fiber is regular.

[0060] The mass ratio of aramid fibrils to the volume of alkali solution is (1-3) g:(300-800) ml, preferably, the mass ratio of aramid fibrils to the volume of alkali solution is 2 g:500 ml; on the basis of not causing corrosion and damage to the aramid fibrils, the amide bond on the surface of the aramid fiber can be fully hydrolyzed, the surface of the aramid fiber can obtain effective electronegativity, the aramid fiber is more easily cracked in the subsequent high-pressure homogenization process, and the obtained aramid fiber has uniform diameter distribution and regular fiber morphology.

[0061] (1.2) High-pressure homogenization method treatment: using a high-pressure homogenizer to treat the aramid fibril solution to obtain an aramid nanofiber solution; the aramid nanofiber solution is filtered and water is removed to obtain aramid nanofibers;

[0062] The process of using a high-pressure homogenizer to treat the aramid fibril solution includes: first using a ball valve to treat, gradually increasing the pressure to 700-900 MPa, treating for 15-25 min; then using a flat valve to treat, gradually increasing the pressure to 900-1100 MPa, treating for 20-40 min.

[0063] Using a ball valve can coarsely process the aramid fibrils, shearing the aramid fibrils to reduce the diameter and length of the aramid fibrils.

[0064] Using a flat valve can finely process the aramid fibrils, shearing the aramid fibrils to further reduce the diameter and length of the aramid fibrils.

[0065] The fiber diameter after flat valve treatment is smaller than that after ball valve treatment, and the diameter distribution of the fiber is more uniform, which is beneficial to obtain aramid nanofibers.

[0066] The application treats aramid fibrils by a high-pressure homogenization method, so that the aramid fibrils are cracked into nanofibers, which is beneficial to realize batch production of aramid nanofibers, and does not need to use organic solvents, which is safe, environmentally friendly and pollution-free.

[0067] The concentration of the aramid nanofiber solution is 0.3-0.6wt%, preferably, the concentration of the aramid nanofiber solution is 0.4wt%, which can facilitate the solution to be filtered to remove water, thereby facilitating the obtaining of pure aramid nanofibers.

[0068] (2) Preparation of ANF water dispersion

[0069] Phosphoric acid PA treatment: the aramid nanofiber is added to the PA solution and stirred for 2h under the condition of 40℃ water bath; then the ANF is washed to neutral with distilled water and configured into an ANF water dispersion;

[0070] After the phosphoric acid treatment, the affinity substitution reaction and / or hydrolysis reaction can occur between the phosphoric acid and the aramid nanofiber ANF, which can promote the exposure of a large number of active groups (amino and carboxyl) on the surface of the ANF. The active groups (amino and carboxyl) on the surface of the ANF can form a strong interfacial hydrogen bond with the metal Zr 4+ between them in the subsequent step (3.2), and finally realize the uniform and large loading of the UiO-66-NH2-F4 particles on the surface of the ANF.

[0071] The concentration of the PA solution is 15-25wt%, preferably, the concentration of the PA solution is 20wt%; which can promote the ANF surface to fully expose a large number of active groups (amino and carboxyl), which is conducive to the uniform and large loading of the UiO-66-NH2-F4 particles on the surface of the ANF, and will not cause corrosion damage to the ANF fiber.

[0072] The ratio of the mass of the aramid nanofiber to the volume of the PA solution is (0.5-1.5)g:(200-400)ml; which can promote the ANF to be fully hydrolyzed, so that the ANF surface fully exposes a large number of active groups (amino and carboxyl), which is conducive to the uniform and large loading of the UiO-66-NH2-F4 particles on the surface of the ANF, and will not cause corrosion damage to the ANF fiber.

[0073] The concentration of the ANF water dispersion is 0.2-0.5wt%, preferably, the concentration of the ANF water dispersion is 0.3-0.4wt%, which is conducive to improving the specific surface area, porosity and mechanical properties of the fiber aerogel. Specifically, the fiber aerogel prepared by the ANF dispersion with the concentration after the later freeze-drying and heat curing treatment can simultaneously have the characteristics of light weight and excellent mechanical properties. If the concentration is further increased, the density of the fiber aerogel prepared by the same volume of water dispersion will be large, and the structure will be more dense, resulting in the decrease of the porosity and specific surface area of the fiber aerogel; at the same time, the high MOF content will cause the increase of the brittleness of the aerogel, and finally lead to the decrease of the mechanical properties of the fiber aerogel.

[0074] (3) Preparation of UiO-67-SO2@ANF fiber aerogel

[0075] (3.1) The ANF aqueous dispersion is placed in N, N-dimethylformamide DMF to configure an ANF / DMF dispersion;

[0076] The concentration of the ANF / DMF dispersion is 0.2-0.5wt%, preferably, the concentration of the ANF / DMF dispersion is 0.3-0.4wt%, which is beneficial to improve the specific surface area, porosity and mechanical properties of the fiber aerogel. Specifically, the fiber aerogel prepared by the ANF dispersion with the concentration after the later freeze-drying and heat curing treatment can have the characteristics of light weight and excellent mechanical properties at the same time. If the concentration of the ANF / DMF dispersion is too large, the density of the fiber aerogel prepared by the same volume of the aqueous dispersion will be large, and the structure will be more dense, resulting in the decrease of the porosity and specific surface area of the fiber aerogel. At the same time, if the concentration of the ANF / DMF dispersion is too large, the MOF content is high, which will cause the increase of the brittleness of the aerogel, and finally lead to the decrease of the mechanical properties of the fiber aerogel.

[0077] (3.2) Zirconium salt ZrCl4 is weighed and added to the ANF / DMF dispersion, and stirred until it is completely dissolved; then H2DTDAO and trifluoroacetic acid TFA are added, and the stirring is continued to obtain a mixed solution;

[0078] The role of adding zirconium salt first: after the PA treatment of ANF, a large number of carboxyl functional groups will be generated on the surface of the fiber ANF, and the metal zirconium ions will produce metal complexation with the carboxyl groups, so as to induce the adsorption of the metal zirconium ions to the surface of the ANF. With the addition of the ligand H2DTDAO later, the H2DTDAO will spontaneously combine with the metal zirconium ions, so as to assemble UiO-67-SO2 in situ on the surface of the ANF, which is beneficial to the uniform and large loading of UiO-67-SO2 on the surface of the ANF.

[0079] H2DTDAO has a sulfonyl functional group (O=S=O functional group), which is beneficial to promote the adsorption of CO2 by the UiO-67-SO2@ANF fiber aerogel. There are three adsorption sites for CO2 molecules in the UiO-67-SO2 structural unit, including: Zr 4+ clusters, O=S=O groups and benzene rings. Through molecular dynamics calculation, it is known that for the UiO-67-SO2 structural unit, the static adsorption energy at O=S=O is 0.268 eV, which is significantly higher than that of Zr 4+The static adsorption energy of the cluster (0.226 eV) and benzene ring (0.183 eV) indicates that the introduction of the O=S=O functional group can promote the affinity of the UiO-67-SO2@ANF fiber aerogel for CO2, and is conducive to promoting the adsorption of CO2 by the UiO-67-SO2@ANF fiber aerogel and improving the adsorption capacity of CO2.

[0080] The role of trifluoroacetic acid is to promote the better crystallization of UiO-67-SO2, which is conducive to the better crystal structure of UiO-67-SO2.

[0081] The mass ratio of trifluoroacetic acid to zirconium salt is (0.8-1.2):(3-6), preferably, the mass ratio of trifluoroacetic acid to zirconium salt is 1:5, which can promote the better crystallization of UiO-67-SO2, which is conducive to the better crystal structure and crystal morphology.

[0082] (3.3) The mixed solution is transferred to a reaction kettle for reaction, and after the reaction is completed and cooled to room temperature, UiO-67-SO2@ANF fiber is obtained by suction filtration;

[0083] In the reaction kettle, the reaction temperature is 110-130℃, and the reaction time is 10-14h.

[0084] (3.4) The UiO-67-SO2@ANF fiber is washed with DMF and methanol three times respectively to remove unreacted impurities; then the solvent is replaced with distilled water, and the UiO-67-SO2@ANF fiber is configured into a UiO-67-SO2@ANF fiber dispersion;

[0085] The concentration of the UiO-67-SO2@ANF fiber dispersion is 0.2-0.5wt%, preferably, the concentration of the UiO-67-SO2@ANF fiber dispersion is 0.3-0.4wt%, which is conducive to improving the specific surface area, porosity and mechanical properties of the fiber aerogel. Specifically, the ANF dispersion with this concentration can simultaneously have the characteristics of light weight and excellent mechanical properties after the later freeze-drying and heat curing treatment. If the concentration of the UiO-67-SO2@ANF fiber dispersion is too large, the density of the fiber aerogel prepared by the same volume of water dispersion will be large, and the structure will be more dense, resulting in a decrease in the porosity and specific surface area of the fiber aerogel. At the same time, if the concentration of the UiO-67-SO2@ANF fiber dispersion is too large, the MOF content is high, which will cause the brittleness of the aerogel to increase, and finally lead to a decrease in the mechanical properties of the fiber aerogel.

[0086] (3.5) Taking the UiO-67-SO2@ANF fiber dispersion solution, adding an aqueous silane solution and tert-butyl alcohol, stirring, and subjecting to a freeze-drying and heat-curing process to obtain a UiO-67-SO2@ANF fiber aerogel.

[0087] The volume of the UiO-67-SO2@ANF fiber dispersion solution, the mass of the aqueous silane solution, and the volume ratio of the tert-butyl alcohol are (8-12) mL:(0.01-0.05) g:(0.5-1.5) ml; on the one hand, the tert-butyl alcohol can maximize the formation of good ice crystal structure and ice crystal morphology of the UiO-67-SO2@ANF fiber dispersion solution in the freezing process; on the other hand, it can ensure that the aqueous silane is completely heat-cured, which effectively promotes the adhesion between the fibers, and ensures that the UiO-67-SO2@ANF fiber aerogel has excellent compression-rebound properties.

[0088] The freeze-drying temperature is -60--40℃, and the time is 30-40 h; the heat-curing temperature is 160-200 ℃, and the time is 3-8 min.

[0089] The role of tert-butyl alcohol: by adding tert-butyl alcohol to the UiO-67-SO2@ANF fiber dispersion solution, it is beneficial to promote the formation of good ice crystal structure and ice crystal morphology of the UiO-67-SO2@ANF fiber dispersion solution in the freezing process; after the drying process, the ice crystals will sublimate, and the places where the ice crystals exist will form pores of the UiO-67-SO2@ANF fiber aerogel, finally obtaining a block-shaped three-dimensional structure of the UiO-67-SO2@ANF fiber aerogel, which has a three-dimensional hierarchical pore structure and excellent mechanical properties, such as compression-rebound properties. If tert-butyl alcohol is not added, the size of the ice crystals will be abnormal and chaotic after the water dispersion solution of the UiO-67-SO2@ANF fiber is directly frozen, resulting in a very chaotic pore structure of the UiO-67-SO2@ANF fiber aerogel, which cannot give it excellent mechanical properties.

[0090] The purpose of freeze-drying: by freezing the water dispersion solution of the UiO-67-SO2@ANF fiber, a block-shaped three-dimensional solid material (with ice crystals) can be obtained, which is beneficial to promote the formation of good ice crystal structure of the UiO-67-SO2@ANF fiber dispersion solution in the freezing process; and then after the drying process, the ice crystals will sublimate, and the places where the ice crystals exist will form pores of the UiO-67-SO2@ANF fiber aerogel, so that the aerogel forms a three-dimensional porous structure and has excellent mechanical properties, such as compression-rebound properties.

[0091] The role of the aqueous silane: By high-temperature heat treatment of the UiO-67-SO2@ANF fiber aerogel after freeze-drying, the silane therein will be heat-cured, thereby facilitating the adhesion between the fibers, and finally endowing the UiO-67-SO2@ANF fiber aerogel with excellent mechanical properties, such as compression-rebound characteristics. If no silane is added, the UiO-67-SO2@ANF fiber aerogel will not have elasticity after compression.

[0092] The purpose of heat curing: By high-temperature heat treatment of the UiO-67-SO2@ANF fiber aerogel after freeze-drying, the silane therein will be heat-cured, thereby facilitating the adhesion between the fibers, and finally endowing the UiO-67-SO2@ANF fiber aerogel with excellent mechanical properties (compression-rebound characteristics).

[0093] The beneficial technical effects of the present application include:

[0094] (1) Compared with the traditional method of using potassium hydroxide (KOH) and 2-methyl sulfoxide (DMSO) to first deprotonate aramid primary fibers and then use water as a proton donor for reduction to obtain ANF, the present application uses a high-pressure homogenization process to convert micron-sized aramid fibers into aramid nanofibers ANF, which can realize batch production of ANF, does not require the use of organic solvents, has high ANF production efficiency, and is safe, environmentally friendly and pollution-free.

[0095] (2) Phosphoric acid treatment of ANF can expose a large number of active groups (amino and carboxyl groups) on the surface of ANF, thereby enabling the carboxyl groups to form strong interfacial hydrogen bonds with the metal Zr 4+ , and finally realizing uniform and large loading of UiO-67-SO2 on the surface of ANF, which can better promote the in-situ growth of UiO-67-SO2 on the surface of ANF.

[0096] (3) By fiber freeze-drying technology, the water dispersion of UiO-67-SO2@ANF fibers is frozen to obtain a solid material (with ice crystals) in the form of a block-shaped three-dimensional structure, which is conducive to the formation of ice crystal structures with good morphology in the freezing process of the UiO-67-SO2@ANF fiber dispersion; and then after the drying process, the ice crystals sublimate, and the places where the ice crystals exist form pores in the UiO-67-SO2@ANF fiber aerogel, resulting in a three-dimensional porous structure of the aerogel and endowing the aerogel with excellent mechanical properties, such as compression-rebound characteristics; the UiO-67-SO2@ANF fiber aerogel can still maintain the integrity of the aerogel structure after 800 compression-rebound test experiments.

[0097] (4) The UiO-67-SO2@ANF fiber aerogel of the present invention has a three-dimensional multi-level pore structure integrating macropores, mesopores and micropores. The macropores and mesopores formed by the three-dimensional interconnected fiber network can serve as continuous long-range gas transmission channels, effectively improving the efficient diffusion of gas molecules inside them; and the UiO-67-SO2 distributed in the three-dimensional nanofiber network channels retains an open microporous structure, which can provide more contact area, active sites and transmission channels for CO2, thereby improving its adsorption capacity for CO2; at the same time, the hydrophobic micropores can also limit H2O molecules and promote the adsorption of CO2 molecules into the interior of the UiO-67-SO2 fiber aerogel.

[0098] (5) The MOF precursors of this application include zirconium chloride (ZrCl4) and dibenzo[b,d]thiophene-3,7-dicarboxylic acid-5,5-dione (H2DTDAO). H2DTDAO has a sulfone functional group (O=S=O functional group), which is beneficial to promote the adsorption of CO2 by UiO-67-SO2@ANF fiber aerogel. CO2 molecules have three adsorption sites in the UiO-67-SO2 structural unit, including Zr 4+ Molecular dynamics calculations show that for the UiO-67-SO2 structural unit, the static adsorption energy at the O=S=O position is 0.268 eV, which is significantly higher than that of the Zr4+ cluster (0.226 eV) and the benzene ring (0.183 eV). This indicates that the introduction of the O=S=O functional group can promote the affinity of the UiO-67-SO2@ANF fiber aerogel for CO2 and is conducive to promoting the adsorption of CO2 by the UiO-67-SO2@ANF fiber aerogel.

[0099] Therefore, the UiO-67-SO2@ANF fiber aerogel of the present application has a strong affinity for CO2 molecules and can improve the CO2 adsorption efficiency and adsorption performance.

[0100] The UiO-67-SO2@ANF fiber aerogel of the present invention can be used to prepare carbon dioxide separation and / or adsorption materials. Example

[0101] The preparation method of the UiO-67-SO2@ANF fiber aerogel of this embodiment includes the following steps:

[0102] (1) Preparation of aramid nanofibers

[0103] (1.1) Alkali treatment: Weigh 2 g of aramid fibrils and chop them into small pieces. Add them to 500 mL of a 15 wt% sodium hydroxide (NaOH) alkaline solution. Reflux the solution in a constant temperature water bath at 80 °C for 4 h. After the solution cools, filter it with distilled water and wash it until neutral to obtain an aramid fibril solution.

[0104] (1.2) High-pressure homogenization method treatment: using a high-pressure homogenizer to treat the aramid fibril solution, and obtaining an aramid nanofiber solution with a concentration of 0.4 wt%; the aramid nanofiber solution is filtered and the water is removed to obtain aramid nanofibers;

[0105] The process of using a high-pressure homogenizer to treat the aramid fibril solution includes: first using a ball valve treatment, gradually increasing the pressure to 800 MPa, and treating for 20 min; then using a flat valve treatment, gradually increasing the pressure to 1000 MPa, and treating for 30 min.

[0106] (2) Preparation of ANF water dispersion

[0107] Phosphoric acid PA treatment: 0.1 g of ANF is added to 30 mL of a 20 wt% PA solution, and stirred at 40°C water bath for 2 h; then the ANF is washed to neutral with distilled water and configured into a 0.3 wt% ANF water dispersion.

[0108] (3) Preparation of UiO-67-SO2@ANF fiber aerogel

[0109] (3.1) 30 mL of ANF water dispersion with a concentration of 0.3 wt% is placed in N, N-dimethylformamide DMF to configure an ANF / DMF dispersion with a concentration of 0.3 wt%;

[0110] (3.2) 0.09 g of zirconium salt ZrCl4 is weighed and added to the ANF / DMF dispersion, and stirred for 15 min until it is completely dissolved; then 0.18 g of H2DTDAO and 0.018 g of trifluoroacetic acid TFA are added, and continue to stir for 15 min to obtain a mixed solution;

[0111] (3.3) The mixed solution is transferred to a reaction kettle and reacted at 120°C for 12 h; after the reaction is completed and cooled to room temperature, UiO-67-SO2@ANF fibers are obtained by filtration;

[0112] (3.4) The UiO-67-SO2@ANF fibers are washed with DMF and methanol three times to remove unreacted impurities; then the solvent is replaced with distilled water, and the UiO-67-SO2@ANF fibers are configured into a 0.3 wt% UiO-67-SO2@ANF fiber dispersion;

[0113] (3.5) Take 10 ml of the above UiO-67-SO2@ANF fiber dispersion, add 0.03 g of aqueous silane solution and 1 mL of tert-butyl alcohol, stir for 15 min, and go through the freeze-drying and heat-curing processes to obtain UiO-67-SO2@ ANF fiber aerogel. The freeze-drying temperature is -50℃, and the time is 36 h; the thermal curing temperature is 180℃, and the time is 5 min.

[0114] The SEM test results of the UiO-67-SO2@ANF fiber aerogel of Example 1 are shown in Figure 1 From Figure 1 it can be seen that after the UiO-67-SO2 is assembled in situ on the surface of the ANF, the surface of the UiO-67-SO2@ANF fiber aerogel is uniformly distributed with particles of UiO-67-SO2 (i.e., MOF).

[0115] The stress-strain curve of the UiO-67-SO2@ANF fiber aerogel of the present example under the test condition of a deformation of 50% and a cycle of 800 times of compression-rebound experiment is shown in Figure 2 From Figure 2 it can be seen that the UiO-67-SO2@ANF fiber aerogel of the present example can still maintain the complete aerogel morphological structure after the cycle of 800 times of compression-rebound experiment, which indicates that the UiO-67-SO2@ANF fiber aerogel of Example 1 has excellent compression-rebound performance.

[0116] The MOF loading of the UiO-67-SO2@ANF fiber aerogel of the present example is calculated, and the MOF loading on the surface of the UiO-67-SO2@ANF fiber aerogel is calculated to be 58.23% by the way of balance weighing.

[0117] The pore size distribution of the UiO-67-SO2@ANF fiber aerogel of the present example is tested, and according to Figure 3 (a) the pore size distribution curve calculated by the mercury injection method, it can be seen that the macropore diameter of the UiO-67-SO2@ANF fiber aerogel is distributed between 10-110μm; according to Figure 3 (b) the pore size distribution curve calculated by the BJH model, it can be seen that the micropore and mesopore of the UiO-67-SO2@ANF fiber aerogel are concentratedly distributed between 0.3-4nm. From this it can be seen that the UiO-67-SO2@ANF fiber aerogel has obvious three-dimensional hierarchical pore structure, in which the macropore and mesopore are conducive to promoting the transmission and diffusion of CO2 gas molecules, and the micropore can effectively improve the adsorption of CO2 gas molecules by the UiO-67-SO2@ANF fiber aerogel.

[0118] The specific surface area, pore volume and average pore diameter can be obtained by the full-automatic specific surface area and porosity analyzer. The specific surface area of the UiO-67-SO2@ANF fiber aerogel of Example 1 is 670.36 m 2 / g, and the pore volume was 0.521 cm3 / g 3 The specific surface area of the UiO-67-SO2@ANF fiber aerogel of Example 1 was high, and the UiO-67-SO2@ANF fiber aerogel had a porous structure and high porosity, which could provide more active sites and transmission channels for CO2, thereby improving the adsorption capacity of the UiO-67-SO2@ANF fiber aerogel for CO2.

[0119] Comparative Example 1

[0120] The preparation method of the ANF fiber aerogel of the present comparative example includes the following preparation process:

[0121] (1) Preparation of aramid nanofiber

[0122] (1.1) Alkali treatment: 2 g of aramid fibrils were weighed and cut into pieces, and were added to a 500 mL sodium hydroxide (NaOH) alkali solution with a mass fraction of 15 wt. %, and were refluxed at a constant temperature water bath of 80 ℃ for 4 h. After the solution was cooled, it was filtered and washed with distilled water until it was neutral, to obtain an aramid fibril solution;

[0123] (1.2) High-pressure homogenization treatment: the aramid fibril solution was treated by using a high-pressure homogenizer to obtain an aramid nanofiber solution with a concentration of 0.4 wt. %. The aramid nanofiber solution was filtered and the water was removed to obtain aramid nanofibers;

[0124] The process of treating the aramid fibril solution by using a high-pressure homogenizer includes: first using a ball valve to gradually increase the pressure to 800 MPa for 20 min, and then using a flat valve to gradually increase the pressure to 1000 MPa for 30 min.

[0125] (2) Preparation of ANF fiber aerogel

[0126] 10 ml of the above ANF fiber dispersion liquid was taken, 0.03 g of aqueous silane solution and 1 mL of tert-butyl alcohol were added, and stirring was performed for 15 min. After the freezing drying and heat curing processes, the ANF fiber aerogel was obtained. The freezing drying temperature was -50 ℃, and the time was 36 h; the heat curing temperature was 180 ℃, and the time was 5 min.

[0127] Figure 4 The SEM image of the ANF fiber aerogel prepared for Comparative Example 1 is shown in FIG. 2. Figure 4 It can be seen that the surface of the ANF fiber aerogel of Comparative Example 1 is smooth and flat, and does not load other substances. The diameters of the ANF fibers are concentrated in the range of 30-180 nm.

[0128] The CO2 adsorption capacity of the UiO-67-SO2@ANF fiber aerogel of Example 1 and the ANF fiber aerogel of Comparative Example 1 at 25 ℃ was tested, and the results are shown in FIG. 3.Figure 5 As shown in FIG. 6, the UiO-67-SO2@ANF fiber aerogel of Example 1 has a much higher CO2 adsorption capacity than the ANF fiber aerogel of Comparative Example 1. Figure 5 As shown in FIG. 6, the UiO-67-SO2@ANF fiber aerogel of Example 1 has a much higher CO2 adsorption capacity than the ANF fiber aerogel of Comparative Example 1.

[0129] As shown in FIG. 6, the UiO-67-SO2@ANF fiber aerogel of Example 1 has a much higher CO2 adsorption capacity than the ANF fiber aerogel of Comparative Example 1. Figure 6 As shown in FIG. 6, the UiO-67-SO2@ANF fiber aerogel of Example 1 has a much higher CO2 adsorption capacity than the ANF fiber aerogel of Comparative Example 1. Figure 6 As shown in FIG. 6, the UiO-67-SO2@ANF fiber aerogel of Example 1 has a much higher CO2 adsorption capacity than the ANF fiber aerogel of Comparative Example 1.

[0130] The above examples are only used to illustrate the technical equivalents of the present application; these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions claimed by the present application, but limit the technical solutions; although the present application has been described in detail with reference to the foregoing examples, the ordinary skilled in the art can still modify the technical solutions recorded in the foregoing examples, or replace part of the technical features without departing from the spirit and scope of the present application.

Claims

1. A UiO-67-SO2@ANF fiber aerogel, characterized in that: include: A MOF precursor and aramid nanofibers ANF, wherein the MOF precursor comprises a zirconium salt and dibenzo[b,d]thiophene-3,7-dicarboxylic acid-5,5-dione H2DTDAO; The mass ratio of zirconium salt, H2DTDAO and ANF is (0.8-1.2): (1.8-2.2): (0.8-1.2); The specific surface area of ​​the UIO-67-SO2@ANF fiber aerogel is 500-700 m 2 / g, pore volume of 0.5-0.8 cm 3 / g, average pore size is 0.4-1nm; The preparation method of the UiO-67-SO2@ANF fiber aerogel includes: (1) Preparation of aramid nanofibers (1.1) Alkali treatment: chop aramid fibrils, add them to an alkaline solution, reflux in a constant temperature water bath, and after the solution cools, filter and wash the solution with distilled water until it is neutral to obtain an aramid fibril solution; (1.2) High-pressure homogenization treatment: treating the aramid fibril solution with a high-pressure homogenizer to obtain an aramid nanofiber solution; filtering the aramid nanofiber solution to remove water to obtain aramid nanofibers; (2) Preparation of ANF aqueous dispersion Phosphoric acid PA treatment: adding the aramid nanofibers to the PA solution and stirring under water bath conditions; then washing the solution with distilled water until it is neutral and preparing an ANF aqueous dispersion; (3) Preparation of UiO-67-SO2@ANF fiber aerogel (3.1) placing the ANF aqueous dispersion in N, N-dimethylformamide (DMF) to prepare an ANF / DMF dispersion; (3.2) Adding the zirconium salt to the ANF / DMF dispersion and stirring until it is completely dissolved; then adding H2DTDAO and trifluoroacetic acid (TFA) and continuing to stir to obtain a mixed solution; (3.3) The mixed solution was transferred to a reactor for reaction. After the reaction was completed and cooled to room temperature, UiO-67-SO2@ANF fibers were obtained by suction filtration. (3.4) Wash the UiO-67-SO2@ANF fibers three times with DMF and methanol, respectively, to remove unreacted impurities. Then, replace the solvent with distilled water to prepare a UiO-67-SO2@ANF fiber dispersion. (3.5) Adding aqueous silane solution and tert-butyl alcohol to the UiO-67-SO2@ANF fiber dispersion and stirring, and freeze-drying and thermal curing to obtain UiO-67-SO2@ANF fiber aerogel.

2. The method for preparing the UiO-67-SO2@ANF fiber aerogel according to claim 1, characterized in that: In the step (1.1), the alkaline solution is a strong sodium oxide solution with a concentration of 10-20 wt%; The ratio of the mass of the aramid fibrils to the volume of the alkaline solution is (1-3) g: (300-800) ml; Reflux in a constant temperature water bath at 70-90℃ for 3-5h.

3. The method for preparing the UiO-67-SO2@ANF fiber aerogel according to claim 1, characterized in that: In the step (1.2), the concentration of the aramid nanofiber solution is 0.3-0.6 wt %; The process of treating the aramid fibril solution with a high-pressure homogenizer includes: first using a ball valve to increase the pressure to 700-900 MPa and treating for 15-25 minutes; then using a flat valve to increase the pressure to 900-1100 MPa and treating for 20-40 minutes.

4. The method for preparing the UiO-67-SO2@ANF fiber aerogel according to claim 1, characterized in that: In the step (2), the concentration of the PA solution is 15-25wt.%; The ratio of the mass of the aramid nanofiber to the volume of the PA solution is (0.5-1.5) g: (200-400) ml; Stir in a 40 °C water bath for 2 h; The concentration of the ANF aqueous dispersion is 0.2-0.5 wt %.

5. The method for preparing UiO-67-SO2@ANF fiber aerogel according to claim 1, characterized in that: In the step (3.1), the concentration of the ANF / DMF dispersion is 0.2-0.5 wt %.

6. The method for preparing the UiO-67-SO2@ANF fiber aerogel according to claim 1, characterized in that: In the step (3.2), the mass ratio of trifluoroacetic acid to zirconium salt is (0.8-1.2):(4-6).

7. The method for preparing UiO-67-SO2@ANF fiber aerogel according to claim 1, characterized in that: In the step (3.3), the reaction temperature in the reactor is 110-130°C and the reaction time is 10-14h; In the step (3.4), the concentration of the UiO-67-SO2@ANF fiber dispersion is 0.2-0.5wt%.

8. The method for preparing UiO-67-SO2@ANF fiber aerogel according to claim 1, characterized in that: In step (3.5), the volume ratio of the UiO-67-SO2@ANF fiber dispersion, the mass of the aqueous silane solution, and the volume ratio of the tert-butyl alcohol is: (8-12) mL: (0.01-0.05) g: (0.5-1.5) ml; The freeze-drying temperature is -60--40℃ and the time is 30-40 h; The thermal curing temperature is 160-200 ℃ and the time is 3-8 minutes.

9. Use of the UiO-67-SO2@ANF fiber aerogel according to claim 1 in the preparation of carbon dioxide separation and / or adsorption materials.

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