Metal-organic coordination complex induced assembled ZIF-8 composite membrane as well as preparation method and application of metal-organic coordination complex induced assembled ZIF-8 composite membrane

Abstract

The invention belongs to the technical field of membrane separation, and particularly relates to a metal-organic coordination complex induced assembled ZIF-8 composite membrane as well as a preparation method and application thereof. The ZIF-8 composite film is formed by tightly adhering ZIF-8 nano-particles of a core-shell structure, the shell of the ZIF-8 nano-particles of the core-shell structure is a metal-organic coordination complex, and the core is a ZIF-8 nano-particle; wherein the average particle size of each ZIF-8 nanoparticle with the core-shell composite structure is about 20 to 100 nm. The preparation of the composite membrane is simple and controllable, and the prepared compact and defect-free self-supporting ZIF-8 composite membrane has excellent H2 / CO2 separation performance. Under the conditions of room temperature and air inlet pressure of 1 atm, the H2 permeation rate of the ZIF-8 composite membrane reaches 1984.8 GPU, and the H2 / CO2 separation selectivity is 176.0. The composite membrane has a good application prospect in the fields of carbon capture before combustion and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of membrane separation, and specifically relates to a metal-organic coordination complex-induced assembled ZIF-8 composite membrane, a preparation method thereof, and an application thereof Background Art

[0002] With the rapid economic development, the problems of energy and environment have become increasingly severe. The total annual global carbon dioxide (CO 2 ) emissions are about 40 billion tons, of which about 46% remains in the atmosphere, resulting in an increase in the concentration of CO 2 in the atmosphere, exacerbating the greenhouse effect and seriously threatening the global ecological environment

[0003] CO 2 separation technology has great application prospects in the fields of environment, energy, and chemical industry. For example, H 2 / CO 2 and CO 2 / N 2 separation are one of the important ways to achieve pre-combustion and post-combustion carbon capture. Traditional CO 2 separation technologies have disadvantages such as high energy consumption and environmental unfriendliness, while membrane separation technology can overcome the above disadvantages and has advantages such as simple operating equipment and small floor area. Therefore, it has become a research hotspot in CO 2 separation technology. ZIF-8 is composed of tetrahedrally coordinated zinc ions and 2-methylimidazole ligands, and has high stability, a large specific surface area, and high porosity. Therefore, the preparation and application of ZIF-8 composite membranes have received extensive attention. First, since the theoretical window pore size of ZIF-8 crystals is 0.34 nm, which is larger than the kinetic diameters of H 2 and CO 2 gas molecules (H 2 - 0.29 nm, CO 2 - 0.33 nm), it leads to relatively low gas separation selectivity. Second, problems such as easy generation of interfacial defects and relatively low gas separation selectivity still generally exist in the preparation process of ZIF-8 membranes. Therefore, the present invention proposes a metal-organic coordination complex-induced assembled ZIF-8 composite membrane, which uses a metal-organic ligand complex interfacial layer to enhance gas separation selectivity and simultaneously repair the defects between ZIF-8 nanoparticles Summary of the Invention

[0004] The purpose of the present invention is to provide a metal-organic coordination complex-induced assembled ZIF-8 composite membrane, a preparation method thereof, and an application thereof

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows

[0006] A ZIF-8 composite membrane induced by metal-organic coordination complex assembly, the ZIF-8 composite membrane is composed of "core-shell" structure ZIF-8 nanoparticles tightly adhered together, and in the "core-shell" structure ZIF-8 nanoparticles, the shell is a metal-organic coordination complex and the core is a ZIF-8 nanoparticle; wherein, the average particle size of each "core-shell" structure ZIF-8 nanoparticle is about 20-100 nm.

[0007] The composite membrane is synthesized by in-situ reaction of a metal-organic coordination complex, which is coated on the surface of ZIF-8 nanoparticles, and then self-assembled by solvent evaporation to form a membrane composed of tightly adhered "core-shell" structure ZIF-8 nanoparticles;

[0008] The preparation of a composite membrane as described above is to synthesize a metal-organic coordination complex in-situ on the surface of ZIF-8 nanoparticles to coat it to form a "core-shell" structure ZIF-8 nanoparticle sol; then centrifuge to remove the solvent, and then self-assemble by solvent evaporation to obtain a composite membrane formed by tightly adhered "core-shell" structure ZIF-8 nanoparticles.

[0009] Furthermore, polyethyleneimine, 2-methylimidazole and zinc salt are respectively dissolved in a solvent. At room temperature, the 2-methylimidazole solution and the zinc salt solution are poured into the ZIF-8 nanoparticle sol, and polyethyleneimine is added to the above mixture. Under the action of polyethyleneimine, an imidazole-Zn-Zn salt anion-polyethyleneimine coordination complex is synthesized in-situ on the surface of ZIF-8 nanoparticles, so that the ZIF-8 nanoparticles are coated therein to form a "core-shell" structure; wherein, when forming the imidazole-Zn-Zn salt anion-polyethyleneimine coordination complex, the molar ratio of 2-methylimidazole to zinc salt is 1:1-5:1, and the molar ratio of polyethyleneimine to zinc salt is 0-0.001:1.

[0010] Still further, polyethyleneimine, 2-methylimidazole and zinc salt are respectively dissolved in a solvent to obtain three solutions with final concentrations of 0-10 mg / mL, 10-1000 mg / mL and 10-100 mg / mL in sequence; after mixing the 2-methylimidazole solution and the zinc salt solution, it is poured into the ZIF-8 nanoparticle sol, and polyethyleneimine is added to the above mixture to obtain a "core-shell" structure ZIF-8 nanoparticle sol.

[0011] After adding polyethyleneimine to the above mixture, it is stirred and reacted at room temperature for 1-24 h, and then centrifuged to obtain "core-shell" structure white gel ZIF-8 nanoparticles coated with a metal-organic coordination complex; the solvents for dissolving polyethyleneimine, 2-methylimidazole and zinc salt can be the same or different and are selected from one or more of methanol, ethanol or N,N-dimethylformamide.

[0012] The zinc salts in the metal-organic coordination complex and the ZIF-8 nanoparticle sol are different and are selected from one or more of zinc acetate dihydrate, zinc nitrate hexahydrate, zinc chloride, zinc oxide, and zinc phosphate; among them, the zinc salts in the metal-organic coordination complex and the zinc salts in the ZIF-8 nanoparticle sol are selected from the above different zinc salts.

[0013] Preparation of the ZIF-8 nanoparticle sol: Dissolve 2-methylimidazole and zinc salt in a solvent respectively. At room temperature, add the zinc salt solution to the 2-methylimidazole solution to obtain a mixture, stir and react, centrifuge to obtain a white sediment, add a solvent to the above white sediment to obtain a nanoparticle dispersion, and centrifuge to collect the upper-layer dispersed ZIF-8 nanoparticle sol (concentration is 1 mg / mL - 5 mg / mL).

[0014] When the solutions are mixed at room temperature, stir and mix at room temperature for 0.1 - 10 h; the centrifugation speed for collecting the upper-layer ZIF-8 nanoparticle sol is 1000 - 10000 rpm; the white sediment is added to the solvent and ultrasonicated for 0 - 60 min; the solvents for dissolving 2-methylimidazole and zinc acetate dihydrate and the solvent added to the white sediment can be the same or different and are selected from one or more of methanol, ethanol, or N,N-dimethylformamide.

[0015] The time for the solvent evaporation process of the composite membrane is 0.5 - 5 d; the temperature for the solvent evaporation process is 0 - 50 °C.

[0016] The molecular weight (Mw) of the polyethyleneimine is one or more of 300, 600, 1800, 10000, or 70000.

[0017] The specific preferred process is as follows:

[0018] (a) Preparation of the ZIF-8 nanoparticle sol: Dissolve 2-methylimidazole and zinc salt in a solvent respectively. At room temperature, add the zinc salt solution to the 2-methylimidazole solution to obtain a mixture, stir and react, centrifuge to obtain a white sediment, add a solvent to the above white sediment to obtain a nanoparticle dispersion, and centrifuge to collect the upper-layer dispersed ZIF-8 nanoparticle sol with a concentration of 1 mg / mL - 5 mg / mL.

[0019] (b) Preparation of the "core-shell" ZIF-8 nanoparticle sol coated with a metal-organic coordination complex: Dissolve polyethyleneimine, 2-methylimidazole, and zinc salt in a solvent respectively. At room temperature, pour the 2-methylimidazole solution and the zinc salt solution into the ZIF-8 nanoparticle sol formed in the above step (a), add polyethyleneimine to the above mixture, and continue to stir and react to obtain a "core-shell" structure ZIF-8 nanoparticle sol liquid.

[0020] (c) Remove the reaction solvent from the obtained solution by centrifugation at a rotational speed of 1000 - 10000 rpm for 5 - 30 min.

[0021] (d) After the above centrifugation, the solvent is volatilized at 0 - 50 °C for 0.5 - 5 d, and the solvent is volatilized to self-assemble under the driving force of the assembly of the metal-organic coordination complex, thereby obtaining a composite membrane formed by the close adhesion of "core-shell" structure ZIF-8 nanoparticles.

[0022] Application of a composite membrane as described above, the composite membrane is used in H 2 / CO 2 separation.

[0023] The present invention has the following advantages:

[0024] The present invention utilizes the abundant amino functional groups of dendritic polyethyleneimine to coordinate with Zn ions at the interface of ZIF-8 nanoparticles, which can effectively improve the interfacial compatibility between ZIF-8 nanoparticles, enhance the driving force for interfacial assembly of ZIF-8 nanoparticles, improve the gas separation performance of the membrane, and thereby obtain a dense and defect-free ZIF-8 composite membrane induced by the assembly of metal-organic coordination complexes.

[0025] The preparation process of the present invention is simple, controllable, and the conditions are mild; the modification with polyethyleneimine further improves the driving force for the assembly of metal-organic coordination complexes, and at the same time, as a stabilizer and bridging agent, makes the interfacial structure tighter, and thus the ZIF-8 composite membrane induced by the assembly of metal-organic coordination complexes prepared has good H 2 / CO 2 gas separation performance. At room temperature and an inlet pressure of 1 atm, the H 2 permeation rate of the ZIF-8 composite membrane reaches 1985 GPU, and the H 2 / CO 2 separation selectivity is 176, and this composite membrane has good application prospects in fields such as pre-combustion carbon capture. Description of the Drawings

[0026] Figure 1 is the TEM image of the ZIF-8 nanoparticles prepared in Example 1 of the present invention.

[0027] Figure 2 is the XRD spectra of the ZIF-8 nanoparticles and single crystal simulated ZIF-8 prepared in Example 1 of the present invention.

[0028] Figure 3 is the TEM image and corresponding elemental distribution map of the sol of "core-shell" ZIF-8 nanoparticles coated with metal-organic coordination complexes prepared in Example 1 of the present invention.

[0029] Figure 4 Digital photograph of the self - supported ZIF - 8 composite membrane induced by the metal - organic coordination complex prepared in Example 1 of the present invention.

[0030] Figure 5 Surface SEM image of the self - supported ZIF - 8 composite membrane induced by the metal - organic coordination complex prepared in Example 1 of the present invention.

[0031] Figure 6 Surface SEM image of the self - supported ZIF - 8 composite membrane induced by the metal - organic coordination complex prepared in Example 3 of the present invention.

[0032] Figure 7 Cross - section SEM image of the self - supported ZIF - 8 composite membrane induced by the metal - organic coordination complex prepared in Example 3 of the present invention.

[0033] Figure 8 H 2 / CO 2 gas separation performance of different composite membranes in Application Example 1.

[0034] Figure 9 H 2 / CO 2 gas separation operation stability of the composite membrane prepared in Example 3 in Application Example 3. Detailed implementation manners

[0035] The following further illustrates the detailed implementation manners of the present invention in combination with examples. It should be noted that the detailed implementation manners described here are only for explaining and interpreting the present invention and are not limited to the present invention.

[0036] In the following examples, the molecular weight (Mw) of polyethyleneimine is 600.

[0037] Example 1

[0038] (a) Preparation of ZIF - 8 nanoparticle sol: 2 - methylimidazole and zinc nitrate hexahydrate were respectively dissolved in methanol, and the final dissolved concentrations were 34.1 mg / mL and 14.8 mg / mL respectively. The zinc nitrate hexahydrate solution was added to the 2 - methylimidazole solution, and the mixture was stirred at room temperature for 1 h. The reaction mixture was centrifuged to obtain a white sediment (ZIF - 8 nanoparticles). Methanol was added to disperse the above - mentioned white sediment, and ZIF - 8 nanoparticle sol with a concentration of 1.5 mg / mL was collected by centrifugation (see Figure 1 and Figure 2 ).

[0039] (b) Preparation of "core-shell" structured ZIF-8 nanoparticle sol coated with metal-organic coordination complex: Polyethyleneimine, 2-methylimidazole, and zinc acetate dihydrate were separately dissolved in methanol solvent, and the obtained dissolution concentrations were 0.8 mg / mL, 164 mg / mL, and 36.5 mg / mL, respectively. At room temperature, the above-obtained 2-methylimidazole solution and zinc acetate dihydrate solution were poured into 5 mL of ZIF-8 nanoparticle sol. After reacting for 12 h, a particle sol with a metal-organic coordination complex coated on the surface of the ZIF-8 nanoparticle sol was obtained (see Figure 3 ).

[0040] (c) The reaction solvent of the ZIF-8 nanoparticle sol coated with the metal-organic coordination complex was removed by centrifugation at a centrifugal speed of 6000 rpm for 10 min.

[0041] (d) The residual solvent of the above "core-shell" ZIF-8 nanoparticle gel was volatilized at room temperature to obtain a composite membrane formed by self-supporting core-shell structured ZIF-8 induced by metal-organic coordination complex assembly (see Figure 4 and Figure 5 ).

[0042] It is shown by Figure 1 that the ZIF-8 nanoparticle sol is uniformly dispersed, and the particle size of the nanoparticles is 20 - 50 nm.

[0043] Figure 2 It is shown that the ZIF-8 nanoparticle sol maintains the integrity of the crystal structure of the ZIF-8 nanoparticles.

[0044] Figure 3 It is shown that by in-situ reaction, a metal-organic coordination complex is coated on the surface of the ZIF-8 nanoparticles to obtain "core-shell" structured and mutually adhered ZIF-8 nanoparticles.

[0045] Figure 4 It is shown that the ZIF-8 composite membrane induced by metal-organic coordination complex assembly has a transparent and self-supporting structural property.

[0046] Figure 5 It is shown that the surface nanoparticles of the ZIF-8 composite membrane induced by metal-organic coordination complex assembly are closely packed, presenting a dense and defect-free structure.

[0047] Example 2

[0048] (a) Preparation of ZIF-8 nanoparticle sol: 2-methylimidazole and zinc nitrate hexahydrate were dissolved in methanol respectively, and the final dissolved concentrations were 34.1 mg / mL and 14.8 mg / mL respectively. The zinc nitrate hexahydrate solution was added to the 2-methylimidazole solution, and the mixture was stirred at room temperature for 1 h. The reaction mixture was centrifuged to obtain a white sediment (ZIF-8 nanoparticles). Methanol was added to the above white sediment for dispersion, and ZIF-8 nanoparticle sol with a concentration of 1.5 mg / mL was collected by centrifugation.

[0049] (b) Preparation of metal-organic coordination complex-coated "core-shell" ZIF-8 nanoparticle sol: Polyethyleneimine, 2-methylimidazole and zinc acetate dihydrate were dissolved in methanol solvent respectively, and the dissolved concentrations were 0.8 mg / mL, 164 mg / mL and 36.5 mg / mL respectively. At room temperature, the 2-methylimidazole solution and zinc acetate dihydrate were poured into 5 mL of ZIF-8 nanoparticle sol. After reacting for 11 h, 50 μL of polyethyleneimine was added to the above mixed solution, and the reaction was continued with stirring for 1 h to obtain metal-organic coordination complex-coated "core-shell" ZIF-8 nanoparticle sol.

[0050] (c) The metal-organic coordination complex-coated ZIF-8 nanoparticle sol was centrifuged to remove the reaction solvent, with a centrifugation speed of 6000 rpm and a centrifugation time of 10 min.

[0051] (d) The above "core-shell" ZIF-8 nanoparticle gel was volatilized to remove the residual solvent at room temperature to obtain a self-supporting ZIF-8 composite membrane induced by metal-organic coordination complex assembly.

[0052] Example 3

[0053] (a) Preparation of ZIF-8 nanoparticle sol: 2-methylimidazole and zinc nitrate hexahydrate were dissolved in methanol respectively, and the final dissolved concentrations were 34.1 mg / mL and 14.8 mg / mL respectively. The zinc nitrate hexahydrate solution was added to the 2-methylimidazole solution, and the mixture was stirred at room temperature for 1 h. The reaction mixture was centrifuged to obtain a white sediment (ZIF-8 nanoparticles). Methanol was added to the above white sediment for dispersion, and ZIF-8 nanoparticle sol with a concentration of 1.5 mg / mL was collected by centrifugation.

[0054] (b) Preparation of "core-shell" ZIF-8 nanoparticle sol coated with metal-organic coordination complex: Polyethyleneimine, 2-methylimidazole, and zinc acetate dihydrate were respectively dissolved in methanol solvent, and the obtained dissolution concentrations were 0.8 mg / mL, 164 mg / mL, and 36.5 mg / mL, respectively. At room temperature, after mixing the 2-methylimidazole solution with the zinc acetate dihydrate solution, it was poured into 5 mL of ZIF-8 nanoparticle sol. After reacting for 11 h, 100 μL of polyethyleneimine was added to the above mixed solution, and after continuously stirring and reacting for 1 h, "core-shell" ZIF-8 nanoparticle sol coated with metal-organic coordination complex was obtained.

[0055] (c) The reaction solvent of the "core-shell" ZIF-8 nanoparticle sol coated with metal-organic coordination complex was removed by centrifugation at a centrifugal speed of 6000 rpm for 10 min.

[0056] (d) The above "core-shell" ZIF-8 nanoparticle gel was volatilized of the residual solvent at room temperature to obtain a self-supporting ZIF-8 composite membrane induced by metal-organic coordination complex assembly (see Figure 6 and Figure 7 ).

[0057] As Figure 6 can be seen, the surface of the composite membrane is dense and defect-free, the nanoparticles are tightly adhered, and the particle size distribution is between 20 - 100 nm. At the same time Figure 7 it shows that the thickness of the self-supporting ZIF-8 composite membrane is about 90 μm.

[0058] Example 4

[0059] (a) Preparation of ZIF-8 nanoparticle sol: 2-Methylimidazole and zinc nitrate hexahydrate were respectively dissolved in methanol, and the final obtained dissolution concentrations were 34.1 mg / mL and 14.8 mg / mL, respectively. The zinc nitrate hexahydrate solution was added to the 2-methylimidazole solution, and the reaction was stirred at room temperature for 1 h. The reaction mixture was centrifuged to obtain a white sediment (ZIF-8 nanoparticles). Methanol was added to disperse the above white sediment, and ZIF-8 nanoparticle sol with a concentration of 1.5 mg / mL was collected by centrifugation.

[0060] (b) Preparation of "core-shell" ZIF-8 nanoparticle sol coated with metal-organic coordination complex: Polyethyleneimine, 2-methylimidazole, and zinc acetate dihydrate were respectively dissolved in methanol solvent, and the obtained dissolution concentrations were 0.8 mg / mL, 164 mg / mL, and 36.5 mg / mL, respectively. At room temperature, the 2-methylimidazole solution and the zinc acetate dihydrate solution were poured into 5 mL of ZIF-8 nanoparticle sol. After reacting for 11 h, 400 μL of polyethyleneimine was added to the above mixed solution, and after continuously stirring and reacting for 1 h, the "core-shell" ZIF-8 nanoparticle sol coated with metal-organic coordination complex was obtained.

[0061] (c) The reaction solvent of the ZIF-8 nanoparticle sol coated with metal-organic coordination complex was removed by centrifugation at a centrifugal speed of 6000 rpm for 10 min.

[0062] (d) The above "core-shell" ZIF-8 nanoparticle gel was volatilized of the residual solvent at room temperature to obtain a self-supporting ZIF-8 composite membrane induced by metal-organic coordination complex assembly.

[0063] Example 5

[0064] (a) Preparation of ZIF-8 nanoparticle sol: 2-Methylimidazole and zinc nitrate hexahydrate were respectively dissolved in methanol, and the obtained final dissolution concentrations were 34.1 mg / mL and 14.8 mg / mL, respectively. The zinc nitrate hexahydrate solution was added to the 2-methylimidazole solution, and the reaction was stirred at room temperature for 1 h. The reaction mixture was centrifuged to obtain a white deposit (ZIF-8 nanoparticles). Methanol was added to disperse the above white deposit, and ZIF-8 nanoparticle sol with a concentration of 1.5 mg / mL was collected by centrifugation.

[0065] (b) Preparation of "core-shell" ZIF-8 nanoparticle sol coated with metal-organic coordination complex: Polyethyleneimine, 2-methylimidazole, and zinc acetate dihydrate were respectively dissolved in methanol solvent, and the obtained dissolution concentrations were 0.8 mg / mL, 164 mg / mL, and 36.5 mg / mL, respectively. At room temperature, the 2-methylimidazole solution and the zinc acetate dihydrate solution were poured into 5 mL of ZIF-8 nanoparticle sol. After reacting for 11 h, 1000 μL of polyethyleneimine was added to the above mixed solution, and after continuously stirring and reacting for 1 h, the "core-shell" ZIF-8 nanoparticle sol coated with metal-organic coordination complex was obtained.

[0066] (c) The reaction solvent of the ZIF-8 nanoparticle sol coated with metal-organic coordination complex was removed by centrifugation at a centrifugal speed of 6000 rpm for 10 min.

[0067] (d) The above-mentioned "core-shell" ZIF-8 nanoparticle gel was volatilized to remove the residual solvent at room temperature to obtain a self-supporting ZIF-8 composite membrane induced by metal-organic coordination complex assembly.

[0068] Example 6

[0069] (a) Preparation of ZIF-8 nanoparticle sol: 2-Methylimidazole and zinc nitrate hexahydrate were respectively dissolved in methanol, and the final dissolved concentrations were 34.1 mg / mL and 14.8 mg / mL respectively. The zinc nitrate hexahydrate solution was added to the 2-methylimidazole solution, and the mixture was stirred at room temperature for 1 h. The reaction mixture was centrifuged to obtain a white deposit (ZIF-8 nanoparticles). Methanol was added to the above white deposit for dispersion, and ZIF-8 nanoparticle sol with a concentration of 1.5 mg / mL was collected by centrifugation.

[0070] (b) Preparation of "core-shell" ZIF-8 nanoparticles sol coated with metal-organic coordination complex: Polyethyleneimine, 2-methylimidazole and zinc acetate dihydrate were respectively dissolved in methanol solvent, and the dissolved concentrations were 0.8 mg / mL, 164 mg / mL and 36.5 mg / mL respectively. At room temperature, after mixing the 2-methylimidazole solution and the zinc acetate dihydrate solution, the mixture was poured into 5 mL of ZIF-8 nanoparticle sol. After reacting for 11 h, 4000 μL of polyethyleneimine was added to the above mixed solution, and the reaction was continued with stirring for 1 h to obtain "core-shell" ZIF-8 nanoparticles sol coated with metal-organic coordination complex.

[0071] (c) The reaction solvent of the "core-shell" ZIF-8 nanoparticles sol coated with metal-organic coordination complex was removed by centrifugation at a centrifugal speed of 6000 rpm for 10 min.

[0072] (d) The above-mentioned "core-shell" ZIF-8 nanoparticle gel was volatilized to remove the residual solvent at room temperature to obtain a self-supporting ZIF-8 composite membrane induced by metal-organic coordination complex assembly.

[0073] Example 7

[0074] (a) Preparation of ZIF-8 nanoparticle sol: 2-Methylimidazole and zinc nitrate hexahydrate were respectively dissolved in methanol, and the final dissolved concentrations were 34.1 mg / mL and 14.8 mg / mL respectively. The zinc nitrate hexahydrate solution was added to the 2-methylimidazole solution, and the mixture was stirred at room temperature for 1 h. The reaction mixture was centrifuged to obtain a white deposit (ZIF-8 nanoparticles). Methanol was added to the above white deposit for dispersion, and ZIF-8 nanoparticle sol with a concentration of 2.0 mg / mL was collected by centrifugation.

[0075] (b) Preparation of "core-shell" ZIF-8 nanoparticle sol coated with metal-organic coordination complex: Polyethyleneimine, 2-methylimidazole, and zinc acetate dihydrate were respectively dissolved in methanol solvent, and the resulting dissolution concentrations were 0.8 mg / mL, 164 mg / mL, and 36.5 mg / mL, respectively. At room temperature, the 2-methylimidazole solution and zinc acetate dihydrate solution were poured into 5 mL of ZIF-8 nanoparticle sol. After reacting for 11 h, 100 μL of polyethyleneimine was added to the above mixed solution, and after continuing to stir and react for 1 h, "core-shell" ZIF-8 nanoparticle sol coated with metal-organic coordination complex was obtained.

[0076] (c) The reaction solvent of the "core-shell" ZIF-8 nanoparticle sol coated with metal-organic coordination complex was removed by centrifugation at a rotation speed of 6000 rpm for 10 min.

[0077] (d) The residual solvent of the above "core-shell" ZIF-8 nanoparticle gel was volatilized at room temperature to obtain a self-supporting ZIF-8 composite membrane induced by metal-organic coordination complex assembly.

[0078] Example 8

[0079] (a) Preparation of ZIF-8 nanoparticle sol: 2-Methylimidazole and zinc nitrate hexahydrate were respectively dissolved in methanol, and the resulting final dissolution concentrations were 34.1 mg / mL and 14.8 mg / mL, respectively. The zinc nitrate hexahydrate solution was added to the 2-methylimidazole solution, and the mixture was stirred and reacted at room temperature for 1 h. The reaction mixture was centrifuged to obtain a white deposit (ZIF-8 nanoparticles). Methanol was added to disperse the above white deposit, and ZIF-8 nanoparticle sol with a concentration of 2.0 mg / mL was collected by centrifugation.

[0080] (b) Preparation of "core-shell" ZIF-8 nanoparticle sol coated with metal-organic coordination complex: Polyethyleneimine, 2-methylimidazole, and zinc acetate dihydrate were respectively dissolved in N,N-dimethylformamide solvent, and the resulting dissolution concentrations were 0.8 mg / mL, 164 mg / mL, and 36.5 mg / mL, respectively. At room temperature, the 2-methylimidazole solution and zinc acetate dihydrate solution were poured into 5 mL of ZIF-8 nanoparticle sol. After reacting for 11 h, 100 μL of polyethyleneimine was added to the above mixed solution, and after continuing to stir and react for 1 h, "core-shell" ZIF-8 nanoparticle sol coated with metal-organic coordination complex was obtained.

[0081] (c) The reaction solvent of the "core-shell" ZIF-8 nanoparticle sol coated with metal-organic coordination complex was removed by centrifugation at a rotation speed of 6000 rpm for 10 min.

[0082] (d) The above "core-shell" ZIF-8 nanoparticle gel was volatilized to remove the residual solvent at 50 °C to obtain a self-supporting ZIF-8 composite membrane induced by metal-organic coordination complex assembly.

[0083] Application Example 1

[0084] Using the membranes prepared in the above Examples 1-6 to conduct H 2 / CO 2 separation performance tests. Test conditions: H 2 / CO 2 (50 / 50, vol%) 25 °C, 1 bar (see Figure 8 ).

[0085] Figure 8 It was shown that the H 2 permeation rate of the ZIF-8 composite membrane induced by the metal coordination complex prepared in Example 1 was 938.3 GPU (1 GPU = 10 -6 cm 3 (STP) cm -2 s -1 cmHg -1 ), and the H 2 / CO 2 selectivity was 100.9; the H 2 permeation rate of the ZIF-8 composite membrane induced by the metal-organic coordination complex prepared in Example 2 was 1439.3 GPU, and the H 2 / CO 2 selectivity was 163.4; the H 2 permeation rate of the ZIF-8 composite membrane induced by the metal-organic coordination complex prepared in Example 3 was 1984.8 GPU, and the H 2 / CO 2 selectivity was 176.0; the H 2 permeation rate of the ZIF-8 composite membrane induced by the metal-organic coordination complex prepared in Example 4 was 1258.0 GPU, and the H 2 / CO 2 selectivity was 170.0; the H 2 permeation rate of the ZIF-8 composite membrane induced by the metal-organic coordination complex prepared in Example 5 was 1018.4 GPU, and the H 2 / CO 2 selectivity was 91.6; the H 2 permeation rate of the ZIF-8 composite membrane induced by the metal-organic coordination complex prepared in Example 6 was 833.5 GPU, and the H 2 / CO 2 selectivity was.

[0086] Application Example 2

[0087] The membrane prepared by using the above Example 3 was used for the H 2 / CO 2 separation performance stability test. Test conditions: H 2 / CO 2 (50 / 50, vol%) 25 °C, 1 bar (see Figure 9 ).

[0088] Figure 9 It was shown that the metal-organic coordination complex-induced ZIF-8 composite membrane prepared in Example 3 was continuously operated for 160 h, and the H 2 permeation rate and the H 2 / CO 2 separation selectivity remained basically unchanged, indicating that the composite membrane had excellent operating stability under long-term continuous gas permeation.

Claims

1. A ZIF-8 composite membrane induced by metal-organic coordination complex self-assembly, characterized in that: The ZIF-8 composite membrane is composed of "core-shell" structured ZIF-8 nanoparticles tightly adhered together. In the "core-shell" structured ZIF-8 nanoparticles, the shell is a metal-organic coordination complex, and the core is a ZIF-8 nanoparticle; among them, the average particle size of each "core-shell" composite structure ZIF-8 nanoparticle is about 20-100 nm.

2. The composite membrane according to claim 1, characterized in that: The composite membrane is synthesized by in-situ reaction to form a metal-organic coordination complex, which is coated on the surface of ZIF-8 nanoparticles, and then self-assembled by solvent evaporation to form a composite membrane composed of tightly adhered "core-shell" structured ZIF-8 nanoparticles.

3. The preparation of a composite membrane according to claim 1, characterized in that: A metal-organic coordination complex is in-situ synthesized on the surface of ZIF-8 nanoparticles, and it is coated to form a "core-shell" structured ZIF-8 nanoparticle sol; then the solvent is removed by centrifugation, and the composite membrane formed by tightly adhering "core-shell" structured ZIF-8 nanoparticles is obtained by self-assembly through solvent evaporation.

4. The preparation of a composite membrane according to claim 3, characterized in that: Polyethyleneimine, 2-methylimidazole and zinc salt are respectively dissolved in a solvent. At room temperature, the 2-methylimidazole solution and the zinc salt solution are poured into the ZIF-8 nanoparticle sol, and polyethyleneimine is added to the above mixture. Under the action of polyethyleneimine, an in-situ synthesized metal-organic coordination complex of imidazole-Zn-Zn salt anion-polyethyleneimine is formed on the surface of the ZIF-8 nanoparticle sol, so that the ZIF-8 nanoparticles are coated therein to form a "core-shell" structure; among them, when forming the metal-organic coordination complex of imidazole-Zn-Zn salt anion-polyethyleneimine, the molar ratio of 2-methylimidazole to zinc salt is 1:1-5:1, and the molar ratio of polyethyleneimine to zinc salt is 0-0.001:

1.

5. The preparation of a composite membrane according to claim 3 or 4, characterized in that: After adding polyethyleneimine to the mixture, the mixture is stirred and reacted at room temperature for 1-24 h, and centrifuged to obtain a white gel of "core-shell" structured ZIF-8 nanoparticles coated with a metal-organic coordination complex; the solvents for dissolving polyethyleneimine, 2-methylimidazole and zinc salt can be the same or different and are selected from one or more of methanol, ethanol or N,N-dimethylformamide.

6. The preparation of a composite membrane according to claim 4, characterized in that: The zinc salts in the metal-organic coordination complex and the ZIF-8 nanoparticle core are different and are selected from one or more of zinc acetate dihydrate, zinc nitrate hexahydrate, zinc chloride, zinc oxide, zinc phosphate; among them, the zinc salts in the metal-organic coordination complex and the ZIF-8 nanoparticle core are selected from the above different zinc salts.

7. The preparation of a composite membrane according to claim 1 or 6, characterized in that: Preparation of the ZIF-8 nanoparticle sol: 2-methylimidazole and a zinc salt are respectively dissolved in a solvent. At room temperature, the zinc salt solution is added to the 2-methylimidazole solution to obtain a mixed solution, which is stirred and reacted, and then centrifuged to obtain a white deposit. A solvent is added to the above-mentioned white deposit to obtain a nanoparticle dispersion liquid, and the ZIF-8 nanoparticle sol dispersed in the upper layer is collected by centrifugation.

8. Preparation of the composite film according to claim 3, characterized in that: the time of the solvent evaporation process of the composite film is 0.5 - 5 d; the temperature of the solvent evaporation process is 0 - 50 °C.

9. Application of the composite film according to claim 1, characterized in that: The application of the composite membrane in H 2 / CO 2 separation.

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