Active mediated bimetal MOFs interface assembled gas purification nano-fiber membrane as well as preparation method and application of active mediated bimetal MOFs interface assembled gas purification nano-fiber membrane

Abstract

The invention provides an active mediated bimetal MOFs interface assembled gas purification nano-fiber membrane as well as a preparation method and application thereof. The method comprises the following steps: step S1, preparing a nano-fiber membrane with a three-dimensional network structure from polylactic acid through a spinning technology; s2, dipping the nano-fiber membrane obtained in the step S1 in a mixed solution of a buffer solution and dopamine hydrochloride to prepare a polydopamine modified nano-fiber membrane; step S3, putting the polydopamine modified nano-fiber membrane obtained in the step S2 into a zinc-cobalt source co-precursor solution to prepare a zinc-cobalt co-loaded nano-fiber membrane; and step S4, dipping the zinc-cobalt co-loaded nanofiber membrane obtained in the step S3 in a ligand solution, and inducing MOFs nanocrystals rich in micropores to grow in situ on the surface of nanofibers through a coordination reaction, so as to prepare the gas purification nanofiber membrane. The prepared nano-fiber membrane has the remarkable advantages of double-metal adsorption sites, a graded porous structure, a three-dimensional network channel, efficient gas adsorption, separation and screening capacity and the like, and is a nano-fiber membrane material for deep purification of gas.

Description

Technical Field

[0001] The present invention relates to the technical field of gas adsorption separation and deep purification of nanofiber membrane materials, and particularly relates to an active-mediated bimetallic MOF interfacial assembly gas purification nanofiber membrane, a preparation method thereof, and an application thereof. Background Art

[0002] The effective separation of methane (CH4) and nitrogen (N2) is a core problem in the energy and chemical industry, which is directly related to the economic development value of unconventional natural gas resources. Methane (also known as gas), as the main component of coalbed methane, has become a valuable clean energy source due to its high calorific value and low environmental pollution effect compared with other fossil fuels. However, the effective utilization of coalbed methane is limited by the low methane content (accounting for 30% - 50%) and the obstruction of nitrogen as the main impurity. CH4 and N2 are both non-polar molecules and have highly similar physical and chemical properties (CH4 is 3.82×3.94×4.10 N2 is 2.99×3.05×4.05 ), which poses a great challenge to the traditional low-temperature rectification technology based on the boiling point difference (CH4: 111.7K, N2: 77.4K). This process has bottlenecks such as low separation efficiency and high energy consumption intensity (>2.5 kWh / m 3 ) under the condition of low-concentration methane (<50%), seriously restricting the economic purification and cascade utilization of coalbed methane.

[0003] The adsorption separation technology based on porous materials has become a research hotspot in the field of gas separation due to its low energy consumption characteristics. Metal-organic framework materials (MOFs), as crystalline porous materials formed by the self-assembly of metal nodes and organic ligands, have shown significant advantages in the field of gas screening due to their ultra-high specific surface area, adjustable pore size, and structural functionalization. In recent years, researchers have developed bimetallic MOFs through the metal ion doping strategy. By utilizing the synergistic effect of bimetallic sites and reconstructing the electron transfer between heterogeneous metals, gradient adsorption sites can be formed and the surface polarity of the pores can be regulated, breaking through the performance bottleneck of the single-metal system. However, the existing synthesis technology of bimetallic MOFs still faces the problem of comprehensive performance optimization of thermodynamics-kinetics. In addition, problems such as high synthesis cost, poor hydrothermal stability, and difficulty in forming and processing powder materials commonly exist in bimetallic MOFs, resulting in engineering challenges such as large pressure drop and mass transfer limitation in industrial adsorption separation applications, restricting the engineering implementation of large-scale separation devices.

[0004] To alleviate the current situation of difficult forming and film-making of MOFs nanocrystals, inducing the in-situ growth of MOFs nanocrystals on the surface of electrospun nanofibers through coordination reactions has become a practical solution. The electrospun nanofiber membrane itself has high permeability, flexibility, and mechanical strength. The in-situ growth of MOFs nanocrystals on the fiber surface not only achieves the internal trade-off between selective adsorption separation and low gas permeation resistance but also exhibits good durability and environmental adaptability. However, to further improve its performance in practical applications, the current research focus is on optimizing the loading uniformity of MOFs nanocrystals, enhancing the stability of the membrane material, and developing multifunctional integrated systems to meet the requirements of efficient encapsulation and selective separation and purification of nanoscale gases for industrial applications.

[0005] The surface modification technology of polydopamine (PDA) based on biomimetic interface engineering has become an important means to improve the composite stability and effectiveness of materials. PDA forms a uniform adhesion layer on the substrate surface through an oxidative self-polymerization reaction. Its molecular structure is rich in catechol, amino, and quinone groups, endowing the material with unique interfacial interaction capabilities: on the one hand, the catechol hydroxyl group and amino group can achieve strong interfacial adhesion through hydrogen bonding and cation-π interactions; on the other hand, the π-π stacking effect formed by the aromatic ring system provides a growth template for the directional assembly of functional materials. By combining the PDA modification layer with the electrospun nanofiber substrate and utilizing the metal chelating properties of PDA, the heterogeneous nucleation density of MOFs nanocrystals on the fiber surface is significantly increased. Therefore, the PDA-mediated interface engineering strategy provides a new idea for constructing high-stability MOFs / polymer composite membrane materials, especially suitable for gas adsorption and separation systems that require precise control of the distribution and density of active sites. Summary of the Invention

[0006] The purpose of the present invention is to prepare an active-mediated bimetallic MOFs interfacial assembly gas purification nanofiber membrane to meet the requirements of selective adsorption screening of natural gas impurities and deep purification of gas.

[0007] To achieve the above purpose, the present invention provides an active-mediated bimetallic MOFs interfacial assembly gas purification nanofiber membrane and its preparation method and application. The present invention prepares a polylactic acid nanofiber membrane with a three-dimensional network structure by electrospinning polylactic acid, and undergoes a dopamine self-polymerization reaction in a mixed solution composed of a buffer solution and hydrochloric acid dopamine to prepare a polydopamine-modified nanofiber membrane; subsequently, the polydopamine-modified nanofiber membrane is impregnated in a zinc-cobalt source co-precursor solution to prepare a zinc-cobalt co-loaded nanofiber membrane; finally, the zinc-cobalt co-loaded nanofiber membrane is transferred to a ligand solution, and a coordination reaction induces the in-situ growth of MOFs nanocrystals rich in micropores on the nanofiber surface to prepare a gas purification nanofiber membrane.

[0008] According to the first aspect of the present invention, a preparation method of an active-mediated bimetallic MOFs interfacially assembled gas purification nanofiber membrane is provided, including the following steps: Step S1, preparing a poly(lactic acid) nanofiber membrane with a three-dimensional network structure by a spinning technique using poly(lactic acid); Step S2, mixing a buffer solution with dopamine hydrochloride to obtain a mixed solution, and immersing the poly(lactic acid) nanofiber membrane obtained in Step S1 in the mixed solution to induce the self-polymerization reaction of dopamine to prepare a polydopamine-modified nanofiber membrane; Step S3, mixing a zinc source and a cobalt source to prepare a zinc-cobalt source co-precursor solution, and immersing the polydopamine-modified nanofiber membrane obtained in S2 in the zinc-cobalt source co-precursor solution to prepare a zinc-cobalt co-loaded nanofiber membrane; Step S4, dissolving a ligand in a solvent to prepare a ligand solution, transferring the zinc-cobalt co-loaded nanofiber membrane obtained in S3 to the ligand solution, and inducing the in-situ growth of microporous MOFs nanocrystals on the nanofiber surface through a coordination reaction to prepare an active-mediated bimetallic MOFs interfacially assembled gas purification nanofiber membrane.

[0009] Preferably, the poly(lactic acid) in Step S1 is one or more of poly(L-lactic acid), poly(D-lactic acid), poly(DL-lactic acid), stereocomplex poly(lactic acid), and highly oriented poly(lactic acid); the spinning technique in Step S1 is one or more of high-voltage electrospinning, wet solution spinning, dry solution spinning, high-temperature melt spinning, rotary centrifugal spinning, high-speed air jet spinning, microfluidic spinning, emulsion spinning, reaction spinning, gel spinning, and liquid crystal spinning techniques.

[0010] Preferably, the spinning technique in Step S1 is high-voltage electrospinning technique, and the spinning parameters are set as follows: the working voltage is 5 - 30 kV, the injection flow rate is 0.5 - 5 mL / h, the receiving distance is 10 - 20 cm, the temperature is 0 - 40 °C, the humidity is 20% - 60% RH, and the reciprocating speed is 1 - 20 cm / min.

[0011] Preferably, the spinning technique in Step S1 is high-temperature melt spinning technique, and the spinning parameters are set as follows: the spinning temperature is 170 - 220 °C, the extrusion pressure is 5 - 20 MPa, the melt flow rate is 0.1 - 5 g / min, the winding speed is 1000 - 8000 m / min, and the spinneret hole diameter is 0.1 - 0.5 mm.

[0012] Preferably, the spinning technique in Step S1 is wet solution spinning technique, and the spinning parameters are set as follows: the spinneret hole diameter is 0.1 - 0.5 mm, the spinneret pressure is 0.1 - 1 MPa, the injection speed is 1 - 10 mL / min, and the receiving distance is 10 - 30 cm.

[0013] Preferably, in step S1, the spinning technology is high-speed air flow spinning technology, and the spinning parameters are set as follows: the air flow speed is 50 - 300 m / s, the air flow temperature is 30 - 150 °C, the injection pressure is 0.2 - 10 MPa, the aperture of the spinneret is 0.05 - 0.3 mm, and the receiving distance is 10 - 50 cm.

[0014] Preferably, in step S2, the buffer solution is one or more of tris(hydroxymethyl)aminomethane hydrochloride buffer solution, borate buffer solution, and phosphate buffer solution, and the concentration of the buffer solution in the mixed solution is 0.05 - 0.5 mol / L; the pH of the buffer solution is 7.5 - 9.5.

[0015] Preferably, in step S2, the pH value of the buffer solution is adjusted by adding a pH regulator, and the pH regulator is one or more of hydrochloric acid, acetic acid, sulfuric acid, and citric acid.

[0016] Preferably, in step S2, the concentration of dopamine hydrochloride in the mixed solution is 0.1 - 5 g / L, and the dipping conditions in step S2 are that the temperature is 0 - 50 °C and the time is 0.5 - 48 h.

[0017] Preferably, in step S2, the thickness of the obtained polydopamine modification layer is 10 - 200 nm, and the surface roughness of the nanofiber membrane is 0.5 - 1.4.

[0018] Preferably, in step S3, the zinc source is one or more of zinc acetate dihydrate, zinc nitrate hexahydrate, zinc sulfate heptahydrate, zinc chloride, zinc fluoride, zinc bromide, zinc formate, and zinc citrate; the cobalt source is one or more of cobalt acetate tetrahydrate, cobalt nitrate hexahydrate, cobalt chloride hexahydrate, cobalt sulfate heptahydrate, cobalt perchlorate hexahydrate, cobalt thiocyanate, cobalt acetylacetonate, and cobalt citrate.

[0019] Preferably, in step S3, the molar ratio of the zinc source to the cobalt source is 10:1 - 1:10, the total concentration of the zinc source and the cobalt source in the zinc-cobalt source co-precursor solution is 0.05 - 2.0 mol / L, and the dipping condition is that the dipping time in step S3 is 0.5 - 48 h.

[0020] Preferably, in step S4, the solvent used to dissolve the ligand is a solvent, and the solvent is one or more of N,N-dimethylformamide, dimethyl sulfoxide, methanol, ethanol, and water. In step S4, the types of ligands are one or more of 2-methylimidazole, 2-ethylimidazole, 2-aminoimidazole, benzimidazole, terephthalic acid, trimesic acid, and 2,5-dihydroxyterephthalic acid, and the solution concentration of the ligand in the ligand solution is 0.05 - 4.0 mol / L.

[0021] Preferably, in step S4, the molar ratio of the ligand to the total of the zinc source and the cobalt source in the zinc-cobalt co-loaded nanofiber membrane obtained in step S3 is 8:1 to 1:8. The conditions for the coordination reaction in step S4 are as follows: the reaction temperature is 0 to 40°C, the reaction time is 0.5 to 24 h, and the stirring speed is 100 to 800 rpm.

[0022] To achieve the above object, according to the second aspect of the present invention, the present invention also provides a bimetallic MOFs interfacially assembled gas purification nanofiber membrane obtained by the foregoing preparation method.

[0023] Preferably, the specific surface area of the obtained bimetallic MOFs interfacially assembled gas purification nanofiber membrane is 457 m 2 / g to 611 m 2 / g, the pore size is 0.72 nm to 1.36 nm, and the metal atom content is 7.9 to 10.4 wt%.

[0024] To achieve the above object, according to the third aspect of the present invention, the present invention also provides the application of the foregoing gas purification nanofiber membrane in the deep purification of gas and unconventional natural gas, the upgrading of biogas and the synergistic removal of hydrogen sulfide, the recovery of low-concentration methane in coal mine ventilation gas, and the enrichment of syngas and rare gas resources.

[0025] Preferably, the gas adsorption capacity of the bimetallic MOFs interfacially assembled gas purification nanofiber membrane is 1.7 to 2.0 mmol / g, and the CH4 / N2 separation selectivity is 6.5 to 7.1.

[0026] The beneficial effects of the present invention are as follows: (1) Utilize the self-polymerization reaction of dopamine to in-situ load a polydopamine functional layer on the surface of nanofibers. Its special structural functional groups can achieve strong interfacial adhesion through hydrogen bonding and cation-π interactions, and the π-π stacking effect formed by its aromatic ring system provides a growth template for the directional assembly of MOFs nanocrystals. (2) Combining the polydopamine coating with nanofibers can utilize the metal chelating ability of polydopamine to mediate the interfacial assembly of MOFs nanocrystals on the nanofiber interface, thereby forming a highly stable and multifunctional nanofiber composite membrane. (3) Bimetallic MOFs nanocrystals with two different metal adsorption sites can regulate the electron transfer process, generating more active centers and adsorption sites. (4) Through the optimization of the synthesis process for the interfacial assembly of active-mediated bimetallic MOFs on nanofibers, the prepared nanofiber membrane has significant advantages such as bimetallic adsorption sites, hierarchical porous structure, three-dimensional network channels, high-efficiency gas adsorption, separation, and purification capabilities. The preparation process is simple and the conditions are mild, and it is a nanofiber membrane material for deep gas purification and purification.

[0027] The active-mediated bimetallic MOFs interfacial assembled gas purification nanofiber membrane proposed by the present invention has bimetallic adsorption sites, hierarchical porous structures, three-dimensional network channels, high specific surface areas, small pore sizes, rich metal atom contents, high methane adsorption capacities, and excellent CH4 / N2 separation selectivities. The design of this material aims to meet the requirements of selective adsorption screening of natural gas impurities and deep purification of gas, and has broad application potential and market prospects. Description of the Drawings

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0029] Figure 1 It is a schematic flow chart of the method of the present invention.

[0030] Figure 2 It is a scanning electron microscope image of the bimetallic MOFs interfacial assembled gas purification nanofiber membrane in Example 1.

[0031] Figure 3 It is a transmission electron microscope image of the bimetallic MOFs interfacial assembled gas purification nanofiber membrane in Example 1.

[0032] Figure 4 It is an elemental mapping image of the bimetallic MOFs interfacial assembled gas purification nanofiber membrane in Example 1.

[0033] Figure 5 It is a Fourier transform infrared spectroscopy diagram of the bimetallic MOFs interfacial assembled gas purification nanofiber membrane in Example 1.

[0034] Figure 6 It is an X-ray diffraction spectroscopy diagram of the bimetallic MOFs interfacial assembled gas purification nanofiber membrane in Example 1.

[0035] Figure 7 It is a nitrogen adsorption-desorption isotherm curve diagram of the bimetallic MOFs interfacial assembled gas purification nanofiber membrane in Example 1.

[0036] Figure 8 It is a pore size distribution curve diagram of the bimetallic MOFs interfacial assembled gas purification nanofiber membrane in Example 1.

[0037] Figure 9 It is a scanning electron microscope image of the bimetallic MOFs interfacial assembled gas purification nanofiber membrane in Example 2.

[0038] Figure 10It is a scanning electron microscope image of the bimetallic MOFs interfacial assembled gas purification nanofiber membrane in Example 3.

[0039] Figure 11 It is a scanning electron microscope image of the bimetallic MOFs interfacial assembled gas purification nanofiber membrane in Example 4. Detailed implementation manners

[0040] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be described in detail below. Apparently, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. All other implementation manners obtained by those of ordinary skill in the art based on the embodiments of the present invention without any creative efforts fall within the scope of protection of the present invention. The present invention will be described in detail below in conjunction with the embodiments.

[0041] Such as Figure 1As shown in the method flow, Embodiment 1 of the present invention provides a preparation method of an active-mediated bimetallic MOFs interfacial assembled gas purification nanofiber membrane, including the following steps: Step S11, preparing a polylactic acid nanofiber membrane: preparing a polylactic acid nanofiber membrane with a three-dimensional network structure by using the high-voltage electrospinning technique (working voltage is 20 kV, injection flow rate is 1.5 mL / h, receiving distance is 15 cm, temperature is 20 °C, humidity is 30% RH, reciprocating speed is 5 cm / min) for polyl-lactic acid; Step S12, preparing a polydopamine-modified nanofiber membrane: immersing the polylactic acid nanofiber membrane obtained in Step S11 in a mixed solution of tris(hydroxymethyl)aminomethane hydrochloride buffer solution and dopamine hydrochloride (the concentration of the buffer solution in the mixed solution is 0.1 mol / L, adjusting the pH of the buffer solution to 8.5 with hydrochloric acid, and the concentration of dopamine hydrochloride in the mixed solution is 1 g / L), and preparing a polydopamine-modified nanofiber membrane through the self-polymerization reaction of dopamine (temperature is 25 °C, time is 12 h), with the thickness of the obtained polydopamine modification layer being 100 nm and the surface roughness of the nanofiber membrane being 0.9; Step S13, preparing a zinc-cobalt co-loaded nanofiber membrane: mixing a zinc source and a cobalt source to prepare a zinc-cobalt source co-precursor solution, and immersing the polydopamine-modified nanofiber membrane obtained in Step S12 in a solution of zinc acetate dihydrate and cobalt acetate tetrahydrate (the molar ratio of the zinc source to the cobalt source is 1:1, and the total concentration of the zinc-cobalt source in the zinc-cobalt source co-precursor solution is 0.2 mol / L) for 2 h to prepare a zinc-cobalt co-loaded nanofiber membrane; Step S14, preparing a bimetallic MOFs interfacial assembled gas purification nanofiber membrane: transferring the zinc-cobalt co-loaded nanofiber membrane obtained in Step S13 to an aqueous solution of 2-methylimidazole (the molar ratio of the zinc-cobalt source to the ligand is 1:1), and inducing the in-situ growth of MOFs nanocrystals rich in micropores on the surface of the nanofiber through a coordination reaction (reaction temperature is 25 °C, reaction time is 12 h, stirring speed is 400 rpm) to prepare a bimetallic MOFs interfacial assembled gas purification nanofiber membrane. The specific surface area of the obtained nanofiber membrane is 611 m 2 / g, and the average pore diameter is 0.72 nm.

[0042] As Figure 2 shown, the scanning electron microscope image of the bimetallic MOFs interfacial assembled gas purification nanofiber membrane obtained in Embodiment 1 of the present invention shows that the active-mediated bimetallic MOFs are anchored on the surface of polylactic acid nanofibers through interfacial assembly, forming a unique "core-shell-shell" structure.

[0043] As Figure 3 shown, the transmission electron microscope image of the bimetallic MOFs interfacial assembled gas purification nanofiber membrane obtained in Embodiment 1 of the present invention shows that the core is polylactic acid nanofibers, and the shell layers are respectively the polydopamine layer and the bimetallic MOFs nanocrystal layer.

[0044] As Figure 4As shown, the elemental mapping image of the bimetallic MOFs interfacially assembled gas purification nanofiber membrane obtained in Example 1 of the present invention shows the uniform distribution of carbon, nitrogen, oxygen, zinc, and cobalt elements, confirming the in-situ growth of bimetallic MOFs nanocrystals at the interface of polylactic acid nanofibers.

[0045] As Figure 5 shown, the Fourier transform infrared spectroscopy diagram of the bimetallic MOFs interfacially assembled gas purification nanofiber membrane obtained in Example 1 of the present invention shows the stretching vibration signal peaks of –OH, –NH2, C≡N, and C=N bonds in the structure of the material.

[0046] As Figure 6 shown, the powder X-ray diffraction pattern of the bimetallic MOFs interfacially assembled gas purification nanofiber membrane obtained in Example 1 of the present invention observes the characteristic diffraction signal peaks originating from the (011), (002), (112), and (222) crystal planes.

[0047] As Figure 7 shown, the nitrogen adsorption-desorption isotherm curve of the bimetallic MOFs interfacially assembled gas purification nanofiber membrane obtained in Example 1 of the present invention performs nitrogen adsorption at low, medium, and high pressures, indicating that the nanofiber membrane has a hierarchical porous structure.

[0048] As Figure 8 shown, the pore size distribution curve of the bimetallic MOFs interfacially assembled gas purification nanofiber membrane obtained in Example 1 of the present invention shows that the average pore size of the material is concentrated in the micropore and mesopore regions.

[0049] Example 2 of the present invention provides a method for preparing an active-mediated bimetallic MOFs interfacial assembled gas purification nanofiber membrane, including the following steps: Step S21, preparing a polylactic acid nanofiber membrane: dissolving poly-D-lactic acid and preparing a polylactic acid nanofiber membrane with a three-dimensional network structure through a high-temperature melt spinning technique (spinning temperature is 180 °C, extrusion pressure is 10 MPa, melt flow rate is 1 g / min, winding speed is 3000 m / min, spinneret hole diameter is 0.2 mm); Step S22, preparing a polydopamine-modified nanofiber membrane: immersing the polylactic acid nanofiber membrane obtained in Step S21 in a mixed solution of borate buffer and dopamine hydrochloride (the concentration of the buffer in the mixed solution is 0.05 mol / L, adjusting the pH of the buffer to 8.0 with acetic acid, the concentration of dopamine hydrochloride in the mixed solution is 0.5 g / L), through the self-polymerization reaction of dopamine (temperature is 0 °C, time is 6 h), the thickness of the obtained polydopamine modification layer is 50 nm, and the surface roughness of the nanofiber membrane is 0.7, to prepare a polydopamine-modified nanofiber membrane; Step S23, preparing a zinc-cobalt co-loaded nanofiber membrane: mixing a zinc source and a cobalt source to prepare a zinc-cobalt source co-precursor solution, immersing the polydopamine-modified nanofiber membrane obtained in Step S22 in a solution of zinc nitrate hexahydrate and cobalt nitrate hexahydrate (the molar ratio of the zinc source to the cobalt source is 3:1, the total concentration of the zinc-cobalt source in the zinc-cobalt source co-precursor solution is 0.1 mol / L) for 0.5 h, to prepare a zinc-cobalt co-loaded nanofiber membrane; Step S24, preparing a bimetallic MOFs interfacial assembled gas purification nanofiber membrane: transferring the zinc-cobalt co-loaded nanofiber membrane obtained in Step S23 to a 2-ethylimidazole methanol solution (the molar ratio of the zinc-cobalt source to the ligand is 3:1), inducing the in-situ growth of microporous-rich MOFs nanocrystals on the nanofiber surface through a coordination reaction (reaction temperature is 0 °C, reaction time is 6 h, stirring speed is 100 rpm), to prepare a bimetallic MOFs interfacial assembled gas purification nanofiber membrane. The specific surface area of the obtained nanofiber membrane is 576 m 2 / g, and the average pore diameter is 0.89 nm.

[0050] As Figure 9 shown, the scanning electron microscope image of the bimetallic MOFs interfacial assembled gas purification nanofiber membrane obtained in Example 2 of the present invention shows that the active-mediated bimetallic MOFs are anchored on the surface of polylactic acid nanofibers through interfacial assembly, forming a unique "core-shell-shell" structure.

[0051] Example 3 of the present invention provides a preparation method of an active-mediated bimetallic MOFs interfacial assembly gas purification nanofiber membrane, including the following steps: Step S31, preparing a polylactic acid nanofiber membrane: preparing a polylactic acid nanofiber membrane with a three-dimensional network structure by wet solution spinning technology (the pore diameter of the spinneret is 0.3 mm, the spinneret pressure is 0.5 MPa, the injection speed is 2 mL / min, and the receiving distance is 25 cm) for poly-rac-lactic acid; Step S32, preparing a polydopamine-modified nanofiber membrane: impregnating the polylactic acid nanofiber membrane obtained in Step S31 in a mixed solution of phosphate buffer and dopamine hydrochloride (the concentration of the buffer in the mixed solution is 0.15 mol / L, the pH of the buffer is adjusted to 9.0 with sulfuric acid, and the concentration of dopamine hydrochloride in the mixed solution is 1.5 g / L), and preparing a polydopamine-modified nanofiber membrane through the self-polymerization reaction of dopamine (the temperature is 30 °C and the time is 24 h), with the thickness of the obtained polydopamine modification layer being 140 nm and the surface roughness of the nanofiber membrane being 1.1; Step S33, preparing a zinc-cobalt co-loaded nanofiber membrane: mixing a zinc source and a cobalt source to prepare a zinc-cobalt source co-precursor solution, and impregnating the polydopamine-modified nanofiber membrane obtained in Step S32 in a solution of zinc sulfate heptahydrate and cobalt sulfate heptahydrate (the molar ratio of the zinc source to the cobalt source is 1:2, and the total concentration of the zinc-cobalt source in the zinc-cobalt source co-precursor solution is 0.3 mol / L) for 6 h to prepare a zinc-cobalt co-loaded nanofiber membrane; Step S34, preparing a bimetallic MOFs interfacial assembly gas purification nanofiber membrane: transferring the zinc-cobalt co-loaded nanofiber membrane obtained in Step S33 to a 2-aminoimidazole ethanol solution (the molar ratio of the zinc-cobalt source to the ligand is 1:2), and inducing the in-situ growth of MOFs nanocrystals rich in micropores on the nanofiber surface through a coordination reaction (the reaction temperature is 30 °C, the reaction time is 18 h, and the stirring speed is 600 rpm) to prepare a bimetallic MOFs interfacial assembly gas purification nanofiber membrane. The specific surface area of the obtained nanofiber membrane is 514 m 2 / g, and the average pore diameter is 1.05 nm.

[0052] As Figure 10 shown, the scanning electron microscope image of the bimetallic MOFs interfacial assembly gas purification nanofiber membrane obtained in Example 3 of the present invention shows that the active-mediated bimetallic MOFs are anchored on the surface of polylactic acid nanofibers through interfacial assembly, forming a unique "core-shell-shell" structure.

[0053] Example 4 of the present invention provides a method for preparing an active-mediated bimetallic MOFs interfacial assembled gas purification nanofiber membrane, including the following steps: Step S41, preparing a polylactic acid nanofiber membrane: preparing a polylactic acid nanofiber membrane with a three-dimensional network structure by using high-speed air flow spinning technology (air flow speed is 200 m / s, air flow temperature is 100 °C, injection pressure is 5 MPa, spinneret hole diameter is 0.15 mm, receiving distance is 20 cm) for stereocomplex polylactic acid; Step S42, preparing a polydopamine-modified nanofiber membrane: impregnating the polylactic acid nanofiber membrane obtained in Step S41 in a mixed solution of tris(hydroxymethyl)aminomethane hydrochloride buffer solution and dopamine hydrochloride (the concentration of the buffer solution in the mixed solution is 0.2 mol / L, adjusting the pH of the buffer solution to 9.5 with sulfuric acid, the concentration of dopamine hydrochloride in the mixed solution is 2.0 g / L), and preparing a polydopamine-modified nanofiber membrane through the self-polymerization reaction of dopamine (temperature is 40 °C, time is 48 h), with the thickness of the obtained polydopamine modification layer being 180 nm and the surface roughness of the nanofiber membrane being 1.3; Step S43, preparing a zinc-cobalt co-loaded nanofiber membrane: mixing a zinc source and a cobalt source to prepare a zinc-cobalt source co-precursor solution, and impregnating the polydopamine-modified nanofiber membrane obtained in Step S42 in a solution of zinc chloride and cobalt chloride hexahydrate (the molar ratio of the zinc source to the cobalt source is 1:3, and the total concentration of the zinc-cobalt source in the zinc-cobalt source co-precursor solution is 0.5 mol / L) for 12 h to prepare a zinc-cobalt co-loaded nanofiber membrane; Step S44, preparing a bimetallic MOFs interfacial assembled gas purification nanofiber membrane: transferring the zinc-cobalt co-loaded nanofiber membrane obtained in Step S43 to an N,N-dimethylformamide solution of benzimidazole (the molar ratio of the zinc-cobalt source to the ligand is 1:5), and inducing the in-situ growth of MOFs nanocrystals rich in micropores on the surface of the nanofiber through a coordination reaction (reaction temperature is 40 °C, reaction time is 24 h, stirring speed is 800 rpm) to prepare a bimetallic MOFs interfacial assembled gas purification nanofiber membrane. The specific surface area of the obtained nanofiber membrane is 457 m 2 / g, and the average pore diameter is 1.36 nm.

[0054] As Figure 11 shown, the scanning electron microscope image of the bimetallic MOFs interfacial assembled gas purification nanofiber membrane obtained in Example 4 of the present invention shows that the active-mediated bimetallic MOFs interface assembly is anchored on the surface of polylactic acid nanofibers, forming a unique "core-shell-shell" structure.

[0055] Comparative Example 1 of the present invention provides a method for preparing an active-mediated bimetallic MOFs interfacial assembled gas purification nanofiber membrane, which basically uses the method of Example 1 to prepare the bimetallic MOFs interfacial assembled gas purification nanofiber membrane. The difference is that in this example, polydopamine is not used to coat the nanofibers and mediate the interfacial assembly of bimetallic MOFs nanocrystals on the nanofiber interface. Specifically, poly-L-lactic acid was prepared into a poly(lactic acid) nanofiber membrane with a three-dimensional network structure by high-voltage electrospinning technology (working voltage: 20 kV, injection flow rate: 1.5 mL / h, receiving distance: 15 cm, temperature: 20 °C, humidity: 30% RH, reciprocating speed: 5 cm / min); the obtained poly(lactic acid) nanofiber membrane was impregnated in a solution of zinc acetate dihydrate and cobalt acetate tetrahydrate (the molar ratio of zinc source to cobalt source is 1:1, and the total concentration of zinc-cobalt source in the zinc-cobalt source co-precursor solution is 0.2 mol / L) for 2 h to prepare a zinc-cobalt co-loaded nanofiber membrane; the obtained zinc-cobalt co-loaded nanofiber membrane was transferred to an aqueous 2-methylimidazole solution (the molar ratio of zinc-cobalt source to ligand is 1:1), and the in-situ growth of microporous-rich MOFs nanocrystals on the nanofiber surface was induced by a coordination reaction (reaction temperature: 25 °C, reaction time: 12 h, stirring speed: 400 rpm) to prepare the bimetallic MOFs interfacial assembled gas purification nanofiber membrane. The specific surface area of the obtained nanofiber membrane is 137 m 2 / g, and the average pore size is 1.91 nm.

[0056] Comparative Example 2 of the present invention provides a preparation method of an activity-mediated bimetallic MOFs interfacial assembled gas purification nanofiber membrane, and basically adopts the method of Example 2 to prepare the MOFs interfacial assembled gas purification nanofiber membrane. The difference is that in this example, only the zinc source is used to react with the ligand solution to form single-metal MOFs nanocrystals for interfacial assembly on the nanofibers. Specifically, poly-D-lactic acid is prepared into a poly(lactic acid) nanofiber membrane with a three-dimensional network structure by high-temperature melt spinning technology (spinning temperature is 180 °C, extrusion pressure is 10 MPa, melt flow rate is 1 g / min, winding speed is 3000 m / min, and spinneret hole diameter is 0.2 mm); the obtained poly(lactic acid) nanofiber membrane is immersed in a mixed solution of borate buffer and dopamine hydrochloride (the concentration of the buffer in the mixed solution is 0.05 mol / L, the pH of the buffer is adjusted to 8.0 with acetic acid, and the concentration of dopamine hydrochloride in the mixed solution is 0.5 g / L), and through the self-polymerization reaction of dopamine (temperature is 0 °C, time is 6 h), the thickness of the obtained polydopamine modification layer is 50 nm, and the surface roughness of the nanofiber membrane is 0.7, to prepare a polydopamine-modified nanofiber membrane; the obtained polydopamine-modified nanofiber membrane is immersed in a solution of zinc nitrate hexahydrate (the concentration of the zinc source in the ligand solution is 0.1 mol / L) for 0.5 h to prepare a zinc-loaded nanofiber membrane; the obtained zinc-loaded nanofiber membrane is transferred to a 2-ethylimidazole methanol solution (the molar ratio of the zinc source to the ligand is 3:1), and through a coordination reaction, MOFs nanocrystals rich in micropores are induced to grow in-situ on the surface of the nanofibers (reaction temperature is 0 °C, reaction time is 6 h, stirring speed is 100 rpm) to prepare the MOFs interfacial assembled gas purification nanofiber membrane. The specific surface area of the obtained nanofiber membrane is 215 m 2 / g, and the average pore diameter is 2.17 nm.

[0057] Comparative Example 3 of the present invention provides a method for preparing a gas purification nanofiber membrane by active-mediated interfacial assembly of bimetallic MOFs, and basically adopts the method of Example 3 to prepare the gas purification nanofiber membrane. The difference is that in this example, only the cobalt source reacts with the ligand solution to form single-metal MOFs nanocrystals for interfacial assembly on the nanofibers. Specifically, poly(rac-lactic acid) is prepared into a poly(lactic acid) nanofiber membrane with a three-dimensional network structure by wet solution spinning technology (the spinneret pore diameter is 0.3 mm, the spinneret pressure is 0.5 MPa, the injection speed is 2 mL / min, and the receiving distance is 25 cm); the obtained poly(lactic acid) nanofiber membrane is impregnated in a mixed solution of phosphate buffer and dopamine hydrochloride (the concentration of the buffer in the mixed solution is 0.15 mol / L, the pH of the buffer is adjusted to 9.0 with sulfuric acid, and the concentration of dopamine hydrochloride in the mixed solution is 1.5 g / L), and through the self-polymerization reaction of dopamine (the temperature is 30 °C and the time is 24 h), the obtained polydopamine modification layer has a thickness of 140 nm and the surface roughness of the nanofiber membrane is 1.1, to prepare a polydopamine-modified nanofiber membrane; the obtained polydopamine-modified nanofiber membrane is impregnated in a solution of cobalt sulfate heptahydrate (the concentration of the cobalt source in the ligand solution is 0.3 mol / L) for 6 h to prepare a cobalt-loaded nanofiber membrane; the obtained cobalt-loaded nanofiber membrane is transferred to a 2-aminoimidazole ethanol solution (the molar ratio of the cobalt source to the ligand is 1:2), and the in-situ growth of microporous-rich MOFs nanocrystals on the nanofiber surface is induced through a coordination reaction (the reaction temperature is 30 °C, the reaction time is 18 h, and the stirring speed is 600 rpm) to prepare a MOFs interfacial assembly gas purification nanofiber membrane. The specific surface area of the obtained nanofiber membrane is 232 m 2 / g, and the average pore diameter is 1.05 nm.

[0058] The structure characterization and performance testing are as follows.

[0059] Scanning electron microscope observation: The microstructure of the bimetallic MOFs interfacial assembly gas purification nanofiber membrane was observed by a field emission scanning electron microscope (model JSM-7900F, JEOL, Japan) ( Figure 2 、 Figure 9 、 Figure 10 、 Figure 11 ).

[0060] Transmission electron microscope observation: The microstructure of the bimetallic MOFs interfacial assembly gas purification nanofiber membrane was observed by a transmission electron microscope (model TECNI G2 TF20, FEI) ( Figure 3 ).

[0061] Surface element distribution test: The surface element distribution of the bimetallic MOFs interfacial assembly gas purification nanofiber membrane was recorded by an energy dispersive X-ray spectrometer (model Vario EL, JEOL, Japan) ( Figure 4 ).

[0062] Functional group structure test: An infrared spectrometer (model VERTEX 70, Bruker, USA) was used to record the functional groups of the bimetallic MOFs interfacial assembled gas purification nanofiber membrane ( Figure 5 ).

[0063] Crystal structure test: An X-ray spectrometer (model D / Max-2400, Rigaku Corporation, Japan) was used to record the crystal structure of the layer-by-layer heteroepitaxial self-assembled gas purification nanofiber membrane ( Figure 6 ).

[0064] Specific surface area test: A gas sorption analyzer (ASAP 2060, Micromeritics, USA) was used to measure the nitrogen adsorption-desorption isotherm and pore size distribution curve of the bimetallic MOFs interfacial assembled gas purification nanofiber membrane at 77K ( Figure 7 、 Figure 8 ).

[0065] Gas adsorption performance test: A gas sorption analyzer (ASAP 2020, Micromeritics, USA) was used to test the CH4 and N2 adsorption performance of the bimetallic MOFs interfacial assembled gas purification nanofiber membrane. High-purity gases CH4 (99.999%) and N2 (99.999%) were used for adsorption measurement, while free space was measured with helium (99.999%). Isothermal adsorption was carried out at 273K (ice-water bath).

[0066] Experimental results: As shown in Figure 2 、 Figure 9 、 Figure 10 and Figure 11 , it can be observed that a layer of polydopamine is uniformly encapsulated on the surface of the polylactic acid spun fiber. Through the mediating effect of polydopamine, the in-situ growth of bimetallic MOFs nanocrystals at the nanofiber interface is promoted, realizing the orderly assembly of the bimetallic MOFs layer and the polydopamine layer at the polylactic acid nanofiber interface.

[0067] As shown in Figure 3 , it can be clearly observed that the fiber membrane has a unique "core-shell-shell" structure, with the polylactic acid nanofiber as the core and the bimetallic MOFs nanocrystals and polydopamine as the shell layers, achieving dense and uniform encapsulation through in-situ growth.

[0068] As shown in Figure 4 , it can be observed that carbon, nitrogen, oxygen, zinc, and cobalt elements are uniformly distributed on the material surface, and the metal element content is rich, indicating the in-situ growth of bimetallic MOFs nanocrystals on the surface of the polylactic acid nanofiber membrane.

[0069] As shown in Figure 4As shown, stretching vibration signal peaks of –OH, –NH2, C≡N, and C=N bonds can be observed in the structure of the fiber membrane material. The stretching vibration intensities of –OH and –NH2 near 3100 cm –1 and C≡N at 2240 cm –1 decrease, indicating the successful assembly of bimetallic MOFs at the interface of the polydopamine-coated nanofiber membrane.

[0070] As Figure 5 shown, unique diffraction patterns representing polylactic acid, metal zinc MOFs, and metal cobalt MOFs are simultaneously observed in the spectrum of the bimetallic MOFs interfacially assembled gas purification nanofiber membrane, indicating the successful growth of bimetallic MOFs nanocrystals on the surface of the polydopamine-modified nanofiber membrane.

[0071] As Figure 6 and Figure 7 shown, the nitrogen adsorption-desorption curve and pore size distribution curve of the bimetallic MOFs interfacially assembled gas purification nanofiber membrane show continuous distribution characteristics in the micropore, mesopore, and macropore ranges, indicating that the nanofiber membrane has a hierarchical porous structure, providing more space and adsorption sites for CH4 adsorption and separation.

[0072] Table 1 compares the specific surface area, average pore size, metal atom content, CH4 adsorption capacity, and CH4 / N2 separation selectivity results of the bimetallic MOFs interfacially assembled gas purification nanofiber membranes obtained in the examples and comparative examples.

[0073] Table 1

[0074]

[0075] Examples 1 to 4 have a relatively high specific surface area (457 m 2 / g to 611 m 2 / g) and a relatively small pore size (0.72 nm to 1.36 nm). This is because by introducing a polydopamine connection layer, the bimetallic MOFs nanocrystals are densely and uniformly mediated to the interface of the polylactic acid spinning fibers, resulting in a larger specific surface area and excellent pore properties of the membrane. The specific surface areas of Comparative Examples 1 to 3 are only 137 to 232 m 2 / g, and the average pore size is 1.91 to 2.29 nm, which is due to the ineffective regulation of the active mediation effect and the assembly method of bimetallic MOFs nanocrystals at the interface of the polylactic acid nanofibers.

[0076] The CH4 adsorption and separation selectivity of the bimetallic MOFs interfacial assembled gas purification nanofiber membrane are closely related to the specific surface area, pore size, and density of metal atom adsorption sites. The CH4 adsorption capacities of Examples 1-4 with a large specific surface area, small pore size, and high density of metal atom adsorption sites are all above 1.7 mmol / g, and the CH4 / N2 separation selectivities are all above 6.5, showing good CH4 adsorption and separation selectivity. Among them, Example 1 with the highest specific surface area, the smallest pore size, and the highest density of metal atom adsorption sites performs the best in gas adsorption separation tests, with a CH4 adsorption capacity of 2.0 mmol / g and a CH4 / N2 separation selectivity of 7.1, far higher than Comparative Examples 1-3 with a low specific surface area, large pore size, and low density of metal atom adsorption sites due to non-uniform assembly of MOF nanocrystals (CH4 adsorption capacity ≤ 0.6 mmol / g, CH4 / N2 separation selectivity ≤ 2.5).

[0077] The present invention provides an active-mediated bimetallic MOFs interfacial assembled gas purification nanofiber membrane and its preparation method and application. There are many methods and ways to specifically implement this technical solution. The above description is only the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention. Each component not clearly defined in this embodiment can be realized by existing technologies.

Claims

1. A preparation method of an activity-mediated bimetallic MOFs interfacial assembled gas purification nanofiber membrane, characterized in that, It includes the following steps: Step S1: Prepare a polylactic acid nanofiber membrane with a three-dimensional network structure from polylactic acid through a spinning technique; Step S2: Immerse the polylactic acid nanofiber membrane obtained in Step S1 in a mixed solution composed of a buffer solution and dopamine hydrochloride to prepare a polydopamine-modified nanofiber membrane; Step S3: Mix a zinc source and a cobalt source to prepare a zinc-cobalt source co-precursor solution, and immerse the polydopamine-modified nanofiber membrane obtained in Step S2 in the zinc-cobalt source co-precursor solution to prepare a zinc-cobalt co-loaded nanofiber membrane; Step S4: Dissolve a ligand in a solvent to prepare a ligand solution, immerse the zinc-cobalt co-loaded nanofiber membrane obtained in Step S3 in the ligand solution, and induce the in-situ growth of microporous MOFs nanocrystals on the nanofiber surface through a coordination reaction to prepare an active-mediated bimetallic MOFs interface-assembled gas purification nanofiber membrane.

2. The preparation method of an activity-mediated bimetallic MOFs interfacial assembled gas purification nanofiber membrane according to claim 1, characterized in that, In Step S1, the polylactic acid is one or more of poly-L-lactic acid, poly-D-lactic acid, poly-rac-lactic acid, stereocomplex polylactic acid, and highly oriented polylactic acid; in Step S1, the spinning technique is one or more of high-voltage electrospinning, wet solution spinning, dry solution spinning, melt spinning, rotary centrifugal spinning, high-speed air current spinning, microfluidic spinning, emulsion spinning, reaction spinning, gel spinning, and liquid crystal spinning techniques.

3. The preparation method of an activity-mediated bimetallic MOFs interfacial assembled gas purification nanofiber membrane according to claim 1, characterized in that, In Step S2, the buffer solution is one or more of tris(hydroxymethyl)aminomethane hydrochloride buffer solution, borate buffer solution, and phosphate buffer solution. The concentration of the buffer solution in the mixed solution is 0.05 - 0.5 mol / L, and the pH value of the buffer solution is 7.5 - 9.

5.

4. The preparation method of an activity-mediated bimetallic MOFs interfacial assembled gas purification nanofiber membrane according to claim 1, characterized in that In Step S2, the concentration of dopamine hydrochloride in the mixed solution is 0.1 - 5 g / L. The immersion conditions in Step S2 are a temperature of 0 - 50 °C and a time of 0.5 - 48 h.

5. The preparation method of an activity-mediated bimetallic MOFs interfacial assembled gas purification nanofiber membrane according to claim 1, characterized in that, In Step S3, the zinc source is one or more of zinc acetate dihydrate, zinc nitrate hexahydrate, zinc sulfate heptahydrate, zinc chloride, zinc fluoride, zinc bromide, zinc formate, and zinc citrate; the cobalt source is one or more of cobalt acetate tetrahydrate, cobalt nitrate hexahydrate, cobalt chloride hexahydrate, cobalt sulfate heptahydrate, cobalt perchlorate hexahydrate, cobalt thiocyanate, cobalt acetylacetonate, and cobalt citrate.

6. The preparation method of an activity-mediated bimetallic MOFs interfacial assembled gas purification nanofiber membrane according to claim 1, characterized in that, In Step S3, the molar ratio of the zinc source to the cobalt source is 10:1 - 1:10, and the total concentration of the zinc source and the cobalt source in the zinc-cobalt source co-precursor solution is 0.05 - 2.0 mol / L. The immersion conditions in Step S3 are an immersion time of 0.5 - 48 h.

7. The preparation method of an activity-mediated bimetallic MOFs interfacial assembled gas purification nanofiber membrane according to claim 1, characterized in that, In Step S4, the solvent is one or more of N,N-dimethylformamide, dimethyl sulfoxide, methanol, ethanol, and water. In Step S4, the ligand is one or more of 2-methylimidazole, 2-ethylimidazole, 2-aminoimidazole, benzimidazole, terephthalic acid, trimesic acid, and 2,5-dihydroxyterephthalic acid; The concentration of the ligand in the ligand solution is 0.05 - 4.0 mol / L.

8. The preparation method of an activity-mediated bimetallic MOFs interfacial assembled gas purification nanofiber membrane according to claim 1, characterized in that In the step S4, the molar ratio of the ligand to the total amount of the zinc source and the cobalt source in the zinc-cobalt co-loaded nanofiber membrane obtained in the step S3 is 8:1 to 1:

8. The conditions of the coordination reaction in the step S4 are as follows: the temperature is 0 to 40 °C, the time is 0.5 to 24 h, and the stirring speed is 100 to 800 rpm.

9. A bimetallic MOFs interfacially assembled gas purification nanofiber membrane prepared by the preparation method of an activity-mediated bimetallic MOFs interfacially assembled gas purification nanofiber membrane according to any one of claims 1 to 8.

10. Application of the bimetallic MOFs interfacially assembled gas purification nanofiber membrane according to claim 9 in the deep purification of gas and unconventional natural gas, the upgrading of biogas and the synergistic removal of hydrogen sulfide, the recovery of low-concentration methane in mine ventilation gas, and the enrichment of syngas and rare gas resources.

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