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CN-116371213-B - Ultrathin defect-free ZIFs@GO composite membrane, preparation method and application thereof

CN116371213BCN 116371213 BCN116371213 BCN 116371213BCN-116371213-B

Abstract

An ultrathin flawless ZIFs@GO composite membrane, a preparation method and application thereof are disclosed, wherein 1) a modified Hummers method is adopted to prepare GO, 2) GO is deposited on a polymer base membrane to prepare the GO composite membrane, and 3) the ZIFs coordination polymer is grown by an interface back diffusion method through the GO composite membrane and the ZIFs precursor solution to prepare the composite membrane. The invention improves the separation performance of the ZIFs membrane by optimizing the synthesis conditions of the ZIFs and reducing non-selective defects. In the back diffusion process, GO is used as a barrier to diffuse the precursor along the interlayer space of the sheet and greatly slow down the diffusion rate, and the ZIFs crystallization rate can be precisely matched by optimizing the driving force of diffusion in the solution, so that the growth content of the ZIFs is effectively reduced, and the generation of inter-crystal defects is reduced. The GO sheet layer is rich in oxygen functional groups to provide sites for heterogeneous nucleation of ZIFs, particularly at the edges and defects of the GO sheet layer, so that nonselective defects in the GO film are effectively reduced, and meanwhile, the limitation of nano scale enables the heteroepitaxial growth of the ZIFs to be carried out along a two-dimensional channel instead of a vertical direction, thereby being beneficial to the formation of ultrathin crystal structures and realizing the preparation of ultrathin defect-free composite films.

Inventors

  • ZHANG NING
  • LI ZHIYING
  • CHEN CONG
  • BAO JUNJIANG
  • HE GAOHONG

Assignees

  • 大连理工大学

Dates

Publication Date
20260512
Application Date
20230331

Claims (10)

  1. 1. The preparation method of the ultrathin defect-free ZIFs@GO composite membrane material is characterized by comprising the following steps of: First step, GO is prepared by modified Hummers method 1.1 Slowly injecting the scaly graphite and sodium nitrate into concentrated sulfuric acid, stirring in ice-water bath for 0.5-3h hours, slowly adding potassium permanganate, continuously stirring for 0.5-3 hours, and continuously reacting for 0.5-2 hours at the temperature of 35-70 ℃; 1.2 Adding deionized water into the reaction system for the first time, continuously reacting for 0.5-1.5h at the temperature of 85-98 ℃, adding deionized water for the second time, continuously reacting for 0.5-3h, standing and cooling to room temperature; 1.3 Adding hydrogen peroxide into the reaction system to remove excessive potassium permanganate, repeatedly cleaning with deionized water, centrifuging until the obtained supernatant is neutral; Second step, preparing GO composite film 2.1 Adding the GO obtained in the first step into the solvent A at room temperature, stirring and performing ultrasonic treatment to obtain uniform GO dispersion liquid, and preparing the dispersion liquid into 0.0005-2.0g/L dispersion liquid; 2.2 Uniformly stacking GO on the surface of a polymer base film through a filter pressing mode by the aid of the obtained GO dispersion liquid, wherein the pressure is 1-10 bar, and the GO is kept at 0.5-2 h to obtain a wet-state GO composite film, the GO deposition amount on the surface of the polymer base film is 0.5-10 g/m 2 , and the interlayer spacing of a GO stacking structure is 0.5-1.3 nm; 2.3 Placing the wet-state GO composite membrane in an electric heating constant temperature drying oven for standing to obtain a GO composite membrane; Third step, preparing ZIFs@GO composite film 3.1 Adding metal salt into the solvent B at room temperature, stirring and dispersing to form uniform metal salt solution, and preparing a dispersion liquid of 0.1-1.5 g/L; adding an organic ligand into the solvent C, stirring and dispersing to form a uniform organic ligand solution, and preparing a dispersion liquid of 0.1-18 g/L; 3.2 Taking the GO composite membrane obtained in the second step as an interface, wherein the GO layer side of the GO composite membrane is an organic ligand solution, the base membrane side is a metal salt solution, ZIFs are grown in surface pore channels of the GO layer by adopting a back diffusion method, and the ZIFs@GO material composite membrane in a wet state is obtained by placing 6-24 h at the temperature of 25-50 ℃, wherein the mass ratio of the metal salt to the organic ligand is 1:1-1:12; 3.3 Placing the ZIFs@GO composite film in an electric heating constant temperature drying oven for standing to obtain the ZIFs@GO composite film.
  2. 2. The preparation method of the ultrathin defect-free ZIFs@GO composite membrane material according to claim 1 is characterized in that 1.0-3.0 g flaky graphite, 0.5-1.5 g sodium nitrate and 3.0-6.0 g potassium permanganate are added in every 30 mL concentrated sulfuric acid in the step 1.1), 50-100 mL deionized water is added in every 30 mL step 1.1), 50-100 mL deionized water is added in every 30 mL step 1.1), and 10-50 mL mass percent of 30% hydrogen peroxide is added in every 30 mL step 1.1).
  3. 3. The preparation method of the ultrathin defect-free ZIFs@GO composite membrane material is characterized in that in the step 2.1), the solvent A is one or more of deionized water, methanol and ethanol, and in the step 2.2), the polymer base membrane is one of polysulfone, polyethersulfone and polyacrylonitrile.
  4. 4. The preparation method of the ultrathin defect-free ZIFs@GO composite membrane material according to claim 1 is characterized in that in the step 2.3), the temperature of a constant-temperature drying oven is 25-40 ℃ and the time is 15-30 h, and in the step 3.3), the temperature of the constant-temperature drying oven is 25-50 ℃ and the time is 15-30 h.
  5. 5. The preparation method of the ultrathin defect-free ZIFs@GO composite membrane material according to claim 1 is characterized in that in the step 3.1), the metal salt is selected from one of zinc nitrate hexahydrate and cobalt nitrate hexahydrate, the organic ligand is one of dimethyl imidazole and benzimidazole, and in the step 3.2), the ZIFs are one of ZIF-7, ZIF-8 and ZIF-67.
  6. 6. The method for preparing the ultrathin defect-free ZIFs@GO composite membrane material according to claim 1, wherein in the step 3.1), the solvent B is one or more of deionized water, methanol and ethanol, and the solvent C is one or more of deionized water, methanol and ethanol.
  7. 7. The ultrathin defect-free ZIFs@GO composite membrane is obtained by adopting the preparation method of any one of claims 1-6, and comprises a ZIFs@GO separation layer and a support layer, and is characterized in that the support layer is a polymer membrane serving as a base membrane, the separation layer is a ZIFs embedded GO layer, and the ZIFs embedded GO layer is formed by depositing a GO layer on the base membrane and compounding the ZIFs thin layer embedded GO inner pore channels.
  8. 8. The ultra-thin defect-free ZIFs@GO composite membrane according to claim 7, wherein regular pore channels in ZIFs and lamellar interlayer gaps of GO in the membrane material are used as two-dimensional gas transmission channels, and the two pore channels and the lamellar interlayer gaps cooperate with each other to form a defect-free structure.
  9. 9. The ultrathin defect-free ZIFs@GO composite film according to claim 7, wherein the thickness of the ZIFs@GO composite film material is 20-100nm.
  10. 10. Use of an ultra-thin defect-free zifs@go composite membrane material according to any one of claims 7-9 for a gas separation system.

Description

Ultrathin defect-free ZIFs@GO composite membrane, preparation method and application thereof Technical Field The invention belongs to the technical field of gas separation membrane separation, and relates to an ultrathin defect-free ZIFs@GO composite membrane and a preparation method thereof. Background Global warming and climate change problems have attracted considerable attention due to emissions of greenhouse gases (carbon dioxide (CO 2), methane, nitrous oxide, ozone, chlorofluorocarbons, and the like). Simulation studies show that when the concentration of CO 2 reaches 450 mu L/L, critical points of climate and environment mutation appear, so that the control of the concentration of CO 2 in the atmosphere is an important strategy for coping with climate crisis. The membrane separation technology is increasingly applied to efficient capture of CO 2 due to the advantages of environmental friendliness, low energy and capital costs, small equipment floor space and the like. A key problem in achieving efficient CO 2 capture by membrane separation is the preparation of membrane materials with both high permeability and high selectivity. The conventional organic polymer membrane is widely used because of its low cost and easy processing, and the novel separation membrane represented by microporous material has been attracting attention because of its advantages such as easy membrane formation and nanoscale transmission channel. Metal Organic Frameworks (MOFs) materials are microporous crystals formed from rigid organic units by metal-organic ligand coordination or hydrogen bonding, with regular and sized pore sizes. Because MOFs have various structures and functions, unsaturated metal sites on the surface can coordinate with gas molecules to achieve the functions of adsorption and separation, and meanwhile, the MOFs have the advantages of good thermal stability, discrete and ordered structure, ultralow density, large internal surface area (more than 6000m 2/g), easiness in synthesis and the like. In addition, the shape, size, and chemical functionality of the pores within MOFs materials can be tuned by selecting appropriate linker-metal pairs. Among them, zeolitic Imidazolate Frameworks (ZIFs) are increasingly being used in the field of gas separation membranes. According to the report of Kwon et al in article "Heteroepitaxially Grown Zeolitic Imidazolate Framework Membranes with Unprecedented Propylene/Propane Separation Performances", ZIF-67 is very susceptible to uniform nucleation in solution and is difficult to heterogeneous nucleate on the substrate surface, thus making the preparation of ultra-thin (< 100 nm) ZIF films very challenging. Thus, the preparation of ultra-thin ZIF membranes with defect-free structures is a critical technique to achieve high performance gas separations. Disclosure of Invention The invention aims to provide an ultrathin defect-free ZIFs@GO composite membrane material, which solves the problem that an ultrathin defect-free ZIF selective layer is difficult to prepare in the prior art. Meanwhile, the preparation method of the defect-free ultrathin ZIFs@GO composite membrane is simple in operation in the preparation process, and the MOFs gas separation composite membrane with stable performance and high gas selectivity can be obtained. In order to achieve the above object, the present invention has the following technical scheme: An ultrathin defect-free ZIFs@GO composite membrane material comprises a ZIFs@GO separating layer and a supporting layer. The supporting layer is a polymer film and is used as a base film. The separation layer is a ZIFs embedded Graphene Oxide (GO) layer, and is formed by depositing the graphene oxide layer on a base film and compounding the ZIFs thin layer embedded in an inner pore channel of the graphene oxide. Regular pore channels in ZIFs and lamellar interlayer gaps of GO in the membrane material are used as two-dimensional gas transmission channels, and the regular pore channels and the lamellar interlayer gaps cooperate with each other to form a defect-free structure, so that the membrane material has stable membrane performance and higher gas selectivity. The thickness of the ZIFs@GO composite film material is 20-100nm. A preparation method of an ultrathin defect-free ZIFs@GO composite membrane material comprises the following steps: First step, preparing graphene oxide GO 1.1 Slowly injecting the scaly graphite and sodium nitrate into concentrated sulfuric acid, stirring for 0.5-3h in an ice-water bath, slowly adding potassium permanganate, continuously stirring for 0.5-3h, continuously reacting for 0.5-2h at the temperature of 35-70 ℃, and penetrating the graphite interlayer by the super-strong acid in the reaction process to form a graphite-super-strong acid first-order intercalation compound, so that the interlayer spacing of the graphite is enlarged. Strong acid is used as a catalyst, a strong oxidant starts to oxidize gradually from the pe