UiO-66-nh2-f4@anf fiber aerogel, and preparation method and application thereof

Abstract

The application discloses a kind of UiO-66-NH2-F4@ANF fiber aerogel and its preparation method and application, UiO-66-NH2-F4@ANF fiber aerogel includes: MOF precursor and aramid nanofiber ANF, the MOF precursor includes zirconium salt, 2-amino terephthalic acid H2BDC-NH2 and 2,3,5,6-tetrafluoroterephthalic acid H2BDC-F4;Zirconium salt, H2BDC-NH2, H2BDC-F4 and ANF mass ratio is (0.8-1.2):(1-1.5):(1-1.5):(0.8-1.2);UiO-66-NH2-F4@ANF fiber aerogel specific surface area 728.52 m 2 / g, pore volume is 0.628cm 3 / g, average pore size is 0.519nm.The application can be uniformly and large amount of MOF loaded on the surface of ANF fiber, the application of UiO-66-NH2-F4@ANF fiber aerogel has excellent compression resilience, three-dimensional multistage pore structure, excellent wet stability, can effectively improve CO2 adsorption capacity.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of fiber aerogels, and particularly relates to a UiO-66-NH2-F4@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 technologies have 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 properties such as high specific surface area, high porosity, adjustable pore size, and easy surface functionalization. However, there are still some 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 inside them; (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; (3) How to improve the chemical stability of MOFs to expand their application possibilities in high humidity environments.

[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, poor moisture resistance, and low CO2 adsorption capacity. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a UiO-66-NH2-F4@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-NH2-F4@ANF fiber aerogel of the present application has excellent compressive resilience, three-dimensional hierarchical pore structure, and excellent moisture stability, which can effectively improve the CO2 adsorption capacity.

[0006] To this end, the present application provides a UiO-66-NH2-F4@ANF fiber aerogel, which comprises a MOF precursor and aramid nanofiber ANF. The MOF precursor comprises a zirconium salt, 2-amino terephthalic acid H2BDC-NH2, and 2,3,5,6-tetrafluoroterephthalic acid H2BDC-F4. The mass ratio of the zirconium salt, H2BDC-NH2, H2BDC-F4, and ANF is (0.8-1.2):(1-1.5):(1-1.5):(0.8-1.2). The specific surface area of the UiO-66-NH2-F4@ANF fiber aerogel is 600-750 m 2 / g, the pore volume is 0.5-0.8 cm 3 / g, the average pore size is 0.3-1 nm.

[0007] The application also provides a preparation method of the UiO-66-NH2-F4@ANF fiber aerogel, comprising:

[0008] (1) preparing aramid nanofiber

[0009] (1.1) alkali treatment: taking aramid fibril, adding to 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, to obtain an aramid fibril solution;

[0010] (1.2) high-pressure homogenization 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 nanofiber;

[0011] (2) preparing an ANF water dispersion

[0012] phosphoric acid PA treatment: adding the aramid nanofiber to a PA solution, and stirring under water bath conditions; then washing the ANF to neutral with distilled water and configuring into an ANF water dispersion;

[0013] (3) preparing UiO-66-NH2-F4 fiber aerogel

[0014] (3.1) placing the ANF water dispersion into N, N-dimethylformamide DMF, to configure into an ANF / DMF dispersion;

[0015] (3.2) weighing zirconium salt and adding into the ANF / DMF dispersion, stirring until it is completely dissolved; then adding H2BDC-NH2, H2BDC-F4 and glacial acetic acid HOAc, continuing to stir, to obtain a mixed solution;

[0016] (3.3) transferring the mixed solution into a reaction kettle to react, after the reaction is completed and cooled to room temperature, the UiO-66-NH2-F4@ANF fiber is obtained by filtration;

[0017] (3.4) washing the UiO-66-NH2-F4@ANF fiber with DMF and methanol respectively three times, to remove unreacted impurities; then replacing the solvent with distilled water, to configure the UiO-66-NH2-F4@ANF fiber into a UIO-66-NH2-F4@ANF fiber dispersion;

[0018] (3.5) Taking the UiO-66-NH2-F4@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-66-NH2-F4@ANF fiber aerogel.

[0019] Preferably, in the step (1.1), the alkali solution is a sodium hydroxide solution with a concentration of 10-20 wt%; the mass of the aramid fibrils to the volume of the alkali solution is (1-3) g:(300-800) ml.

[0020] 70-90℃ constant temperature water bath under reflux 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 using a high-pressure homogenizer to treat the aramid fibril solution includes: first using a ball valve to process, the pressure is raised to 700-900 MPa, and the treatment time is 15-25 min; then using a flat valve, the pressure is raised to 900-1100 MPa, and the treatment time is 20-40 min.

[0022] Preferably, in the step (2), the concentration of the PA solution is 15-25 wt.%; the mass of the aramid nanofiber to the volume of the PA solution is (0.5-1.5) g:(200-400) ml; stirring under the condition of 40 ℃ water bath for 2 h; the concentration of the ANF water dispersion solution is 0.2-0.5 wt%.

[0023] Preferably, in the step (3.1), the concentration of the ANF / DMF dispersion solution is 0.2-0.5 wt%.

[0024] Preferably, in the step (3.2), the mass ratio of the glacial acetic acid to the zirconium salt is (0.8-1.2):(3-6).

[0025] Preferably, in the step (3.3), the reaction temperature in the reaction kettle is 110-130℃, and the reaction time is 10-14h; in the step (3.4), the concentration of the UiO-66-NH2-F4@ANF fiber dispersion solution is 0.2-0.5 wt%.

[0026] Preferably, in the step (3.5), the volume of the UiO-66-NH2-F4@ANF fiber dispersion solution, 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; the heat curing temperature is 160-200 ℃, and the time is 3-8 min.

[0027] The application further provides application of the UiO-66-NH2-F4@ANF fiber aerogel in preparation of a carbon dioxide separation and / or adsorption material.

[0028] Compared with the prior art, the application has the advantages and positive effects that include:

[0029] (1) Compared with the traditional method of using potassium hydroxide (KOH) and 2-methyl sulfoxide (DMSO) to deprotonate aramid primary fibers and then using water as a proton donor for reduction to obtain ANF, the application adopts a high-pressure homogenization process, can convert micron-level aramid fibers into aramid nanofiber ANF, can realize batch production of ANF, does not need to use organic solvents, has high ANF production efficiency, and is safe, environmentally friendly and pollution-free.

[0030] (2) Phosphoric acid treatment of ANF can expose a large number of active groups (such as amino and carboxyl groups) on the surface of ANF, so that the ANF can form a strong interfacial hydrogen bond with metal Zr 4+ , and ultimately realize uniform and large loading of UiO-66-NH2-F4 on the surface of ANF, which can better promote in-situ growth of UiO-66-NH2-F4 on the surface of ANF.

[0031] (3) Through the fiber freeze-drying technology, the MOF fiber aerogel can be three-dimensionally reconstructed. By adding aqueous silane to the UiO-66-NH2-F4 fiber water dispersion, blocky UiO-66-NH2-F4 fiber aerogel is obtained after freeze-drying, and then high-temperature heat curing treatment is performed, and finally the UiO-66-NH2-F4 fiber aerogel with enhanced mechanical properties is obtained, which exhibits very excellent compression and rebound characteristics. After 800 compression-rebound experiment tests, it can still maintain the integrity of the aerogel structure.

[0032] (4) The UiO-66-NH2-F4 fiber aerogel of the application has a three-dimensional multi-level pore structure integrating macropores, mesopores and micropores. The macropores and mesopores formed by the three-dimensional interpenetrating fiber network can serve as continuous long-range gas transmission channels, effectively improving the efficient diffusion of gas molecules inside; the UiO-66-NH2-F4 distributed in the three-dimensional nanofiber network channels retains an open micropore 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 limit H2O molecules and promote CO2 molecules to be adsorbed into the UiO-66-NH2-F4 fiber aerogel.

[0033] (5) The MOF precursor of the present application comprises zirconium chloride (ZrCl4) and two organic ligands 2-amino terephthalic acid (H2BDC-NH2), 2,3,5,6-tetrafluoroterephthalic acid (H2BDC-F4). The use of ligand H2BDC-F4 containing fluorine and other non-polar functional groups for fluorination modification design can greatly improve the moisture stability of the MOF chemical microenvironment, can expand its application possibility in high humidity environment, can make the MOF change from hydrophilic to hydrophobic, and construct a microporous environment that is CO2 molecule and H2O molecule. When using ligands with polar functional groups (such as amino and carboxyl), the microporous environment of the MOF can have strong affinity for CO2 molecules.

[0034] Other characteristics and advantages of the present application will become more apparent after reading the specific embodiments of the present application in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 SEM image of the UiO-66-NH2-F4@ANF fiber aerogel of Example 1;

[0036] Figure 2 Stress-strain curve of the UiO-66-NH2-F4@ANF fiber aerogel of Example 1 under a deformation of 50% and a test condition of 800 cycles of compression-rebound test;

[0037] Figure 3 Pore size distribution test chart of the UiO-66-NH2-F4@ANF fiber aerogel of Example 1;

[0038] Figure 4 SEM image of the ANF fiber aerogel of Comparative Example 1;

[0039] Figure 5 CO2 adsorption capacity test chart of the UiO-66-NH2-F4@ANF fiber aerogel of Example 1 and the ANF fiber aerogel of Comparative Example 1 under a condition of 25°C;

[0040] Figure 6 H2O (gaseous) adsorption capacity test chart of the UiO-66-NH2-F4@ANF fiber aerogel of Example 1 and the ANF fiber aerogel of Comparative Example 1 under a condition of 25°C;

[0041] Figure 7 XRD test chart of the UiO-66-NH2-F4@ANF fiber aerogel of Example 1, the ANF fiber aerogel of Comparative Example 1 and the UiO-66-NH2-F4 crystal. DETAILED DESCRIPTION

[0042] The application will be further described in conjunction with specific examples. These examples are only used to illustrate the application and not 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-66-NH2-F4@ANF fiber aerogel of the application comprises a MOF precursor and aramid nanofiber ANF, the MOF precursor comprising a zirconium salt, 2-amino terephthalic acid H2BDC-NH2 and 2,3,5,6-tetrafluoroterephthalic acid H2BDC-F4.

[0044] The mass ratio of the zirconium salt, H2BDC-NH2, H2BDC-F4 and ANF is (0.8-1.2):(1-1.5):(1-1.5):(0.8-1.2), and within the above mass ratio range, the UiO-66-NH2-F4 particles (i.e. MOF precursor) with suitable particle size can be obtained, which effectively avoids the accumulation distribution of the UiO-66-NH2-F4 particles on the surface of the ANF, so that the UiO-66-NH2-F4 particles can be uniformly loaded on the surface of the ANF, effectively improving the specific surface area of the UiO-66-NH2-F4@ANF fiber aerogel, which is conducive to obtaining the aerogel with three-dimensional porous structure and conducive to the CO2 gas transmission, so as to improve the adsorption capacity of the aerogel for CO2.

[0045] The UiO-66-NH2-F4@ANF fiber aerogel of the application has excellent thermal insulation performance, and the thermal conductivity at 25℃ can be as low as 27 mW / mk.

[0046] The specific surface area of the UiO-66-NH2-F4@ANF fiber aerogel of the application is 600-750 m 2 / g, the pore volume is 0.5-0.8 cm 3 / g, and the average pore size is 0.3-1 nm.

[0047] Preferably, the specific surface area of the UiO-66-NH2-F4@ANF fiber aerogel of the application is 690-740 m 2 / g, the pore volume is 0.5-0.7 cm 3 / g, and the average pore size is 0.4-0.7 nm.

[0048] The UiO-66-NH2-F4@ANF fiber aerogel of the application has high specific surface area and porous structure, high porosity, and can provide more active sites and transmission channels for CO2, so as to improve the adsorption capacity of the aerogel for CO2.

[0049] The UiO-66-NH2-F4@ANF fiber aerogel has excellent compression elasticity, the maximum compression stress is 15.47 kPa, the plastic deformation is only 7.26% after 800 compression cycle tests, the maximum compression stress loss is 4.72%, the Young's modulus loss is only 5.25%, and the energy loss factor loss is only 24.39%.

[0050] The preparation method of the UiO-66-NH2-F4@ANF fiber aerogel comprises the following steps:

[0051] (1) Preparation of aramid nanofiber

[0052] (1.1) Alkali treatment: the aramid fibril is cut into pieces and added into an alkali solution, and is refluxed at 70-90 DEG C constant temperature water bath for 3-5 h, and after the solution is cooled, the solution is filtered and washed to neutral with distilled water to obtain an aramid fibril solution;

[0053] The aramid fibril selected in the application can be para-aramid PPTA fiber, and the para-aramid PPTA fiber has a clear skin-core structure, which can facilitate the splitting into nanofiber.

[0054] The aramid fibril can also be other aramid fibers commonly used in the technical field, which is not specifically limited here.

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

[0056] The purpose of alkali treatment of the aramid fibril is that the aramid fiber has a clear skin-core structure, that is, the fiber core layer has a higher molecular chain orientation and a higher crystallinity, and the fiber skin layer has a lower crystallinity. After alkali treatment, the amide bond on the surface of the aramid fiber will hydrolyze, so that the aramid fiber surface obtains electronegativity, that is, the charges on the surface of the aramid fiber repel each other, which is beneficial to the splitting of the fiber; at the same time, the alkali solution can damage the skin layer of the aramid fiber to a certain extent. That is, the aramid fibril is more easily split after being treated by the alkali solution, so as to be more conducive to being converted into nanofiber. In the subsequent high-pressure homogenization process, the skin layer of the aramid fiber will be further damaged and split, so as to be more easily split into nanofiber.

[0057] If the concentration of the alkali solution is too high, the high-concentration alkali solution will cause serious corrosion damage to the aramid fibril; if the concentration of the alkali solution is too low, the low-concentration alkali solution cannot make the surface of the aramid fiber obtain effective electronegativity, and after the subsequent high-pressure homogenization, the aramid fiber cannot be effectively split into nanofiber, the diameter distribution of the obtained aramid fiber is uneven, and the morphology of the aramid fiber 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 aramid fiber surface 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 aramid fiber surface 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 the 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 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 aqueous dispersion

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

[0070] After the phosphoric acid treatment, the affinity substitution reaction and / or the hydrolysis reaction between the phosphoric acid and the aramid nanofiber ANF can cause a large number of active groups (amino and carboxyl) to be exposed on the surface of the ANF. The active groups (amino and carboxyl) on the surface of the ANF can form strong interfacial hydrogen bonding with the metal Zr 4+ 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 facilitate the ANF surface to fully expose a large number of active groups (amino and carboxyl), and 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 fibers.

[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 facilitate the hydrolysis of the ANF, so that a large number of active groups (amino and carboxyl) are fully exposed on the surface of the ANF, and 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 fibers.

[0073] The concentration of the ANF aqueous dispersion is 0.2-0.5wt%, preferably, the concentration of the ANF aqueous 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 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, 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-66-NH2-F4 fiber aerogel

[0075] (3.1) Put the ANF aqueous dispersion into 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 brittleness of the aerogel to increase, and finally lead to the decrease of the mechanical properties of the fiber aerogel.

[0077] The high MOF content will cause the brittleness of the aerogel to increase, and finally lead to the decrease of the mechanical properties of the fiber aerogel.

[0078] (3.2) Weigh the zirconium salt ZrCl4 and add it to the ANF / DMF dispersion, stir until it is completely dissolved; then add H2BDC-NH2, H2BDC-F4 and glacial acetic acid HOAc, continue to stir to obtain a mixed solution;

[0079] The role of adding zirconium salt first: after the PA treatment of the ANF fiber, a large number of carboxyl functional groups will be generated on the surface of the ANF fiber, and the metal Zr 4+ will form a metal complex with the carboxyl group, so as to induce the metal Zr 4+ adsorption to the surface of the ANF fiber. With the addition of the ligands H2BDC-NH2 and H2BDC-F4 later, H2BDC-NH2 and H2BDC-F4 will spontaneously combine with the metal Zr 4+ loaded on the surface of the ANF, so as to assemble UiO-66-NH2-F4 in situ on the surface of the ANF, which is beneficial to the uniform and large loading of UiO-66-NH2-F4 on the surface of the ANF.

[0080] 2-amino terephthalic acid H2BDC-NH2 contains polar functional groups of amino and carboxyl, which can make the microporous environment of the fiber aerogel have strong affinity to CO2 molecules.

[0081] 2,3,5,6-tetrafluoroterephthalic acid H2BDC-F4 contains non-polar functional groups such as fluorine, and can be designed for fluorination modification, which greatly improves the moisture stability of the chemical microenvironment of the fiber aerogel, and makes the fiber aerogel change from hydrophilic to hydrophobic, and constructs a microporous environment that is CO2 molecule-philic and H2O molecule-phobic.

[0082] The role of glacial acetic acid is to promote the better crystallization of UiO-66-NH2-F4, which is conducive to making it show better UiO-66-NH2-F4 crystal structure.

[0083] The mass ratio of glacial acetic acid to zirconium salt is (0.8-1.2):(3-6), preferably, the mass ratio of glacial acetic acid to zirconium salt is 1:5, which can promote the better crystallization of UiO-66-NH2-F4, which is conducive to promoting it to show good crystal structure and crystal morphology.

[0084] (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-66-NH2-F4@ANF fiber is obtained by suction filtration;

[0085] In the reaction kettle, the reaction temperature is 110-130℃, and the reaction time is 10-14h.

[0086] (3.4) The UiO-66-NH2-F4@ANF fiber is washed with DMF and methanol respectively for three times to remove unreacted impurities; then the solvent is replaced with distilled water, and the UiO-66-NH2-F4@ANF fiber is configured into a UiO-66-NH2-F4@ANF fiber dispersion;

[0087] The concentration of the UiO-66-NH2-F4@ANF fiber dispersion is 0.2-0.5wt%, preferably, the concentration of the UiO-66-NH2-F4@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-66-NH2-F4@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 the decrease of the porosity and specific surface area of the fiber aerogel; at the same time, if the concentration of the UiO-66-NH2-F4@ANF fiber 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.

[0088] (3.5) Taking the UiO-66-NH2-F4@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-66-NH2-F4@ANF fiber aerogel.

[0089] The volume of the UiO-66-NH2-F4@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 ice crystal structures and ice crystal morphologies in the UiO-66-NH2-F4@ANF fiber dispersion solution during the freezing process; on the other hand, the aqueous silane can be completely heat-cured to effectively promote the adhesion between the fibers, ensuring that the UiO-66-NH2-F4@ANF fiber aerogel has excellent compression-rebound properties.

[0090] The freeze-drying temperature is -60--40℃; the time is 30-40 h. The heat-curing temperature is 160-200 ℃, and the time is 3-8 min.

[0091] The role of tert-butyl alcohol: by adding tert-butyl alcohol to the UiO-66-NH2-F4@ANF fiber dispersion solution, it is beneficial to promote the formation of ice crystal structures and ice crystal morphologies in the UiO-66-NH2-F4@ANF fiber dispersion solution during the freezing process; after the drying process, the ice crystals sublimate, and the places where the ice crystals exist form the pores of the UiO-66-NH2-F4@ANF fiber aerogel, ultimately obtaining a block-shaped three-dimensional structure of the UiO-66-NH2-F4@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 unusually chaotic when the aqueous dispersion solution of the UiO-66-NH2-F4@ANF fiber is directly frozen, resulting in very chaotic pores in the UiO-66-NH2-F4@ANF fiber aerogel obtained ultimately, which cannot endow it with excellent mechanical properties.

[0092] The purpose of freeze-drying: by freezing the aqueous dispersion solution of the UiO-66-NH2-F4@ANF fiber, a block-shaped three-dimensional solid material (with ice crystals) can be obtained, which is beneficial to promote the formation of ice crystal structures in the UiO-66-NH2-F4@ANF fiber dispersion solution during the freezing process; and then after the drying process, the ice crystals sublimate, and the places where the ice crystals exist form the pores of the UiO-66-NH2-F4@ANF fiber aerogel, which forms a three-dimensional porous structure and endows the aerogel with excellent mechanical properties, such as compression-rebound properties.

[0093] The role of the aqueous silane: by high-temperature heat treatment of the freeze-dried UiO-66-NH2-F4@ANF fiber aerogel, the silane therein will be thermally cured, thereby promoting the adhesion between the fibers, ultimately endowing the UiO-66-NH2-F4@ANF fiber aerogel with excellent mechanical properties, such as compression-rebound characteristics. If no silane is added, the UiO-66-NH2-F4@ANF fiber aerogel will not have elasticity after compression.

[0094] The purpose of thermal curing: by high-temperature heat treatment of the freeze-dried UiO-66-NH2-F4@ANF fiber aerogel, the silane therein will be thermally cured, thereby promoting the adhesion between the fibers, ultimately endowing the UiO-66-NH2-F4@ANF fiber aerogel with excellent mechanical properties (compression-rebound characteristics).

[0095] The beneficial technical effects of the present application include:

[0096] (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.

[0097] (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+ , ultimately realizing uniform and large-scale loading of UiO-66-NH2-F4 on the surface of ANF and better promoting in-situ growth of UiO-66-NH2-F4 on the surface of ANF.

[0098] (3) By fiber freeze-drying technology, by freezing the aqueous dispersion of UiO-66-NH2-F4@ANF fibers, a solid material with a block-shaped three-dimensional structure (with ice crystals) can be obtained, which is conducive to the formation of good ice crystal structure of UiO-66-NH2-F4@ANF fiber dispersion during 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-66-NH2-F4@ANF fiber aerogel, so that the aerogel forms a three-dimensional porous structure, endowing the aerogel with excellent mechanical properties, such as compression-rebound characteristics; the UiO-66-NH2-F4@ANF fiber aerogel can still maintain the integrity of the aerogel structure after 800 compression-rebound experimental tests.

[0099] (4) The UiO-66-NH2-F4 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 three-dimensional interpenetrating fiber network can serve as continuous long-range gas transmission channels, effectively improving the efficient diffusivity of gas molecules in the interior thereof; and the UiO-66-NH2-F4 distributed in the three-dimensional nanofiber network channels retains an open micropore structure, which can provide more contact area, active sites and transmission channels for CO2, thereby improving the adsorption capacity of CO2; at the same time, the hydrophobic micropores can also limit H2O molecules and promote the adsorption of CO2 molecules to the interior of the UiO-66-NH2-F4 fiber aerogel.

[0100] (5) The MOF precursor of the application comprises zirconium chloride (ZrCl4) and two organic ligands 2-amino terephthalic acid (H2BDC-NH2) and 2,3,5,6-tetrafluoro terephthalic acid (H2BDC-F4). 2-amino terephthalic acid H2BDC-NH2 contains polar functional groups amino and carboxyl, which can make the microporous environment of the fiber aerogel have strong affinity for CO2 molecules. 2,3,5,6-tetrafluoro terephthalic acid H2BDC-F4 contains nonpolar functional groups such as fluorine, which can be designed for fluorination modification, greatly improving the moisture stability of the chemical microenvironment of the fiber aerogel, making the fiber aerogel change from hydrophilic to hydrophobic, and constructing a microporous environment that is CO2 molecule-loving and H2O molecule-hating.

[0101] Therefore, the UiO-66-NH2-F4 fiber aerogel of the application has strong affinity for CO2 molecules, which can improve the CO2 adsorption efficiency and performance. The UiO-66-NH2-F4@ANF fiber aerogel of the application can be used to prepare carbon dioxide separation and / or adsorption materials. Embodiment

[0102] The preparation method of the UiO-66-NH2-F4@ANF fiber aerogel of the embodiment comprises the following steps:

[0103] (1) Preparation of aramid nanofiber

[0104] (1.1) Alkali treatment: 2 g of aramid fibrils are weighed and cut into pieces, added to a 500 mL 15 wt% sodium hydroxide solution, and refluxed at a constant temperature water bath of 80 ℃ for 4 h. After the solution is cooled, it is filtered and washed with distilled water until it is neutral, to obtain an aramid fibril solution;

[0105] (1.2) High-pressure homogenization treatment: the aramid fibril solution is treated by using a high-pressure homogenizer to obtain 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;

[0106] The process of treating the aramid fibril solution by using a high-pressure homogenizer 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.

[0107] (2) Preparation of ANF aqueous dispersion

[0108] Phosphoric acid PA treatment: 0.1 g of ANF was added to 30 mL of a 20 wt% PA solution, and stirred for 2 h under the condition of a 40 ℃ water bath; then the ANF was washed to neutral with distilled water and configured into an ANF aqueous dispersion with a mass fraction of 0.3 wt%.

[0109] (3) Preparation of UiO-66-NH2-F4@ANF fiber aerogel

[0110] (3.1) 30 mL of ANF aqueous dispersion with a concentration of 0.3 wt% was placed in N, N-dimethylformamide DMF to configure an ANF / DMF dispersion with a concentration of 0.3 wt%;

[0111] (3.2) 0.09 g of zirconium salt ZrCl4 was weighed and added to the ANF / DMF dispersion, and stirred for 15 min until it was completely dissolved; then 0.108 g of H2BDC-NH2, 0.108 g of H2BDC-F4 and 0.108 g of glacial acetic acid HOAc were added, and stirring was continued for 15 min to obtain a mixed solution;

[0112] (3.3) The mixed solution was transferred to a reaction kettle and reacted at 120 ℃ for 12 h; after the reaction was completed and cooled to room temperature, UiO-66-NH2-F4@ANF fibers were obtained by suction filtration;

[0113] (3.4) The UiO-66-NH2-F4@ANF fibers were washed with DMF and methanol three times respectively to remove unreacted impurities; then the solvent was replaced with distilled water, and the UiO-66-NH2-F4@ANF fibers were configured into a UiO-66-NH2-F4@ANF fiber dispersion with a concentration of 0.3 wt%;

[0114] (3.5) 10 ml of the above UiO-66-NH2-F4@ANF fiber dispersion was taken, 0.03 g of aqueous silane solution and 1 mL of tert-butyl alcohol were added, and stirred for 15 min, and then subjected to a freeze-drying process and a heat curing process to obtain UiO-66-NH2-F4@ANF fiber aerogel. The freeze-drying temperature was -50 ℃, and the time was 36 h; the heat curing temperature was 180 ℃, and the time was 5 min.

[0115] The SEM test results of the UiO-66-NH2-F4@ANF fiber aerogel in Example 1 are as follows: Figure 1 As shown. Figure 1 It can be seen that after UiO-66-NH2-F4 is in situ assembled on the ANF surface, evenly distributed particles appear on the surface of the UiO-66-NH2-F4@ANF fiber aerogel, and the particles are UiO-66-NH2-F4 (i.e., MOF).

[0116] The UiO-66-NH2-F4@ANF fiber aerogel of Example 1 was subjected to 800 cycles of compression-rebound test under the test condition of 50% deformation. The stress-strain curve is shown in the figure below. Figure 2 As shown. Figure 2 It can be shown that the UiO-66-NH2-F4@ANF fiber aerogel of this embodiment can still maintain a complete aerogel morphology structure after 800 cycles of compression-rebound test, indicating that the UiO-66-NH2-F4@ANF fiber aerogel of Example 1 has excellent compression rebound properties.

[0117] The MOF loading amount of the UiO-66-NH2-F4@ANF fiber aerogel of Example 1 was calculated. By weighing on a balance, it was found that the MOF loading amount on the surface of the UiO-66-NH2-F4@ANF fiber aerogel was 79.26%.

[0118] The pore size distribution of the UiO-66-NH2-F4@ANF fiber aerogel of Example 1 was tested. Figure 3 (a) The pore size distribution curve calculated by mercury intrusion method shows that the macropore diameter of UiO-66-NH2-F4@ANF fiber aerogel is distributed between 1-100 μm; Figure 3 (b) The pore size distribution curve calculated by the BJH model shows that the pore sizes of the micropores and mesopores of the UiO-66-NH2-F4@ANF fiber aerogel are concentrated between 0.18 and 2 nm. This indicates that the UiO-66-NH2-F4@ANF fiber aerogel has a distinct three-dimensional multi-level pore structure, in which the macropores and mesopores are conducive to promoting the transmission and diffusion of CO2 gas molecules, while the micropores can effectively improve the adsorption of CO2 gas molecules by the UiO-66-NH2-F4@ANF fiber aerogel.

[0119] The specific surface area, pore volume and average pore size can be obtained by using a fully automatic specific surface area and porosity analyzer. The specific surface area of ​​the UiO-66-NH2-F4@ANF fiber aerogel in Example 1 is 728.52 m 2 / g, pore volume 0.628cm 3 / g, and the average pore size was 0.519 nm. The specific surface area of the UiO-66-NH2-F4@ANF fiber aerogel of Example 1 was high, and 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-66-NH2-F4@ANF fiber aerogel for CO2.

[0120] Comparative Example 1

[0121] The preparation method of the ANF fiber aerogel of the present comparative example comprises the following preparation process:

[0122] (1) Preparation of aramid nanofiber

[0123] (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 80 ℃ in a constant temperature water bath 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;

[0124] (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;

[0125] The process of treating the aramid fibril solution by using a high-pressure homogenizer comprises the following steps: 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.

[0126] (2) Preparation of ANF fiber aerogel

[0127] 10 ml of the above ANF fiber dispersion liquid was taken, 0.03 g of an aqueous silane solution and 1 mL of tert-butyl alcohol were added, and stirring was performed for 15 min. After a freezing drying process and a heat curing process, an 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.

[0128] 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 20-200 nm.

[0129] The CO2 adsorption capacity of the UiO-66-NH2-F4@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 It can be seen from FIG. 3 that the CO2 adsorption capacity of the UiO-66-NH2-F4@ANF fiber aerogel of Example 1 was higher than that of the ANF fiber aerogel of Comparative Example 1.Figure 5 It can be seen that the CO2 adsorption capacity of the UiO-66-NH2-F4@ANF fiber aerogel of Example 1 is much greater than that of the ANF fiber aerogel of Comparative Example 1.

[0130] The H2O (gaseous) adsorption capacity of the UiO-66-NH2-F4@ANF fiber aerogel of Example 1 and the ANF fiber aerogel of Comparative Example 1 at 25°C was tested, and the results are shown in Figure 6 Figure 6 It can be seen that the H2O (gaseous) adsorption capacity of the UiO-66-NH2-F4@ANF fiber aerogel of Example 1 is much smaller than that of the ANF fiber aerogel of Comparative Example 1. This is because the surface of the UiO-66-NH2-F4@ANF fiber aerogel of Example 1 contains fluorine functional groups, and the use of fluorine-containing and other non-polar functional group ligands for fluorination modification design can greatly improve the moisture stability of the MOF chemical microenvironment, making the MOF change from hydrophilic to hydrophobic, and constructing a microporous environment that is CO2 molecule-friendly and H2O molecule-averse.

[0131] The XRD test results of the UiO-66-NH2-F4@ANF fiber aerogel of Example 1 and the ANF fiber aerogel of Comparative Example 1 and the UiO-66-NH2-F4 crystal are shown in Figure 7 Figure 7 It can be seen that the particulate matter on the surface of the fiber of the UiO-66-NH2-F4@ANF fiber aerogel is UiO-66-NH2-F4, indicating that the UiO-66-NH2-F4 is loaded on the surface of the ANF.

[0132] 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 them; 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 technical solutions.​​

Claims

1. A UiO-66-NH2-F4@ANF fiber aerogel, characterized in that: include: MOF precursor and aramid nanofiber ANF, wherein the MOF precursor includes zirconium salt, 2-aminoterephthalic acid H2BDC-NH2 and 2,3,5,6-tetrafluoroterephthalic acid H2BDC-F4; The mass ratio of zirconium salt, H2BDC-NH2, H2BDC-F4 and ANF is (0.8-1.2): (1-1.5): (1-1.5): (0.8-1.2); The specific surface area of ​​the UiO-66-NH2-F4@ANF fiber aerogel is 600-750 m 2 / g, pore volume of 0.5-0.8cm 3 / g, average pore size is 0.3-1nm; The preparation method of the UiO-66-NH2-F4@ANF fiber aerogel includes: (1) Preparation of aramid nanofibers (1.1) Alkali treatment: chop aramid fibrils, add them to an alkaline solution, reflux them in a constant temperature water bath, and after the solution cools, filter and wash it 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: the aramid nanofibers are added to the PA solution and stirred in a water bath; the ANF is then washed with distilled water until neutral and prepared into an ANF aqueous dispersion; (3) Preparation of UiO-66-NH2-F4@ANF fiber aerogel (3.1) Place the ANF aqueous dispersion in N, N-dimethylformamide (DMF) to prepare an ANF / DMF dispersion. (3.2) Weigh the zirconium salt and add it to the ANF / DMF dispersion, stirring until it is completely dissolved; then add H2BDC-NH2, H2BDC-F4, and glacial acetic acid (HOAc), and continue stirring 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-66-NH2-F4@ANF fibers were obtained by suction filtration. (3.4) Wash the UiO-66-NH2-F4@ANF fibers three times with DMF and methanol, respectively, to remove unreacted impurities. Then, replace the solvent with distilled water to prepare a UiO-66-NH2-F4@ANF fiber dispersion. (3.5) Adding aqueous silane solution and tert-butanol to the UiO-66-NH2-F4@ANF fiber dispersion, stirring, and freeze-drying and thermal curing to obtain UiO-66-NH2-F4@ANF fiber aerogel.

2. The method for preparing the UiO-66-NH2-F4@ANF fiber aerogel according to claim 1, characterized in that: In the step (1.1), the alkaline solution is a sodium hydroxide 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-66-NH2-F4@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 fiber solution with a high-pressure homogenizer includes: first using a ball valve to treat the solution, raising the pressure to 700-900 MPa, and treating the solution for 15-25 minutes; Then use a flat valve to increase the pressure to 900-1100 MPa and process for 20-40 minutes.

4. The method for preparing the UiO-66-NH2-F4@ANF fiber aerogel according to claim 1, characterized in that: In 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; 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 the UiO-66-NH2-F4@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-66-NH2-F4@ANF fiber aerogel according to claim 1, characterized in that: In the step (3.2), the mass ratio of the glacial acetic acid to the zirconium salt is (0.8-1.2):(3-6).

7. The method for preparing the UiO-66-NH2-F4@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-66-NH2-F4@ANF fiber dispersion is 0.2-0.5 wt%.

8. The method for preparing the UiO-66-NH2-F4@ANF fiber aerogel according to claim 1, characterized in that: In the step (3.5), the volume ratio of the UiO-66-NH2-F4@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-66-NH2-F4@ANF fiber aerogel according to claim 1 in preparing carbon dioxide separation and / or adsorption materials.

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