Graphene separation membrane and preparation method and application thereof

Abstract

The application discloses a graphene separation membrane, which comprises a support layer and a separation layer, and the separation layer is a double-layer graphene film with nano-pores. The application adopts a double-layer CVD graphene film as a separation layer material of a composite membrane, which better improves the problems of easy breakage, high requirement for raw materials and high cost of a single-layer CVD graphene film applied in a separation membrane field, and obviously improves the performance, and is suitable for a separation membrane of a thin film conductance method TOC analyzer. A preparation method of the graphene separation membrane is also disclosed, which prepares a double-layer graphene separation membrane by using a laminated transfer graphene film technology, avoids technical difficulties and material limitations of preparation of a large-area continuous double-layer and multi-layer CVD graphene film material, introduces high-density ordered nano-pores into the double-layer graphene film prepared by using a plasma etching method for the laminated transfer method, and guarantees the selectivity and permeability of the graphene separation membrane.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of material preparation, and particularly relates to a graphene separation membrane and a preparation method and application thereof. BACKGROUND

[0002] Production quality control and safety management are related to people's life and property safety. The manufacturing and processing of electronic components, semiconductor chips, biological and pharmaceutical products, fine chemicals, and the purity detection and monitoring of drinking water and process water for future space exploration manned spacecraft and space stations all require accurate measurement and strict control of organic pollutant content. Taking drug production as an example, organic pollutant detection in the cleaning verification process is critical, which can effectively prevent safety hazards caused by pollution and cross contamination and ensure the safety and effectiveness of products. Compared with traditional organic pollutant detection methods, TOC (total organic carbon) detection method is a non-specific detection method, which has more advantages in analyzing the organic composition of samples and can determine all organic matters. It is simple, fast and sensitive to operate. Therefore, TOC detection technology is concerned in many high-end application fields.

[0003] Compared with the existing combustion method and wet oxidation method for TOC detection in the market, the thin film conductivity method has the advantages of small sample requirement, high detection precision, fast detection speed, no need for carrier gas, stable performance, high reliability, few interference factors and minimum interference degree, low maintenance requirement, and is suitable for TOC analysis and detection in various application scenarios, especially in cleaning verification and electronic grade water detection. At present, the TOC analysis equipment based on the thin film conductivity method depends on foreign imports, the main reason is that the preparation technology of the core component separation membrane in the equipment is monopolized and blocked by foreign countries. At present, the domestic polymer membranes developed for the application of thin film conductivity TOC analyzer cannot meet the performance requirements, and there are problems such as poor repeatability, poor linear correlation, poor long-term stability, poor mechanical properties, and great influence of temperature in the application of instruments, which seriously limits the application of domestic TOC analyzers in high-tech fields.

[0004] Graphene film material has atomic level ultra-thin thickness, and can introduce uniform high density nanopores, and can realize high selectivity and high permeability, and has stable physical and chemical properties, and is considered as a preferred material for preparing separation membranes. Using the advantages of graphene material, CVD (chemical vapor deposition) graphene film material is used for preparing separation membranes of TOC analyzers to solve the technical problems of existing separation membranes of TOC analyzers, which is a new method to break through the bottleneck of the existing technology, and there are few researches and reports. However, high-quality perfect large-area single-layer graphene film is difficult to prepare, is easy to break, and has poor practicability, and at present, large-size multi-layer continuous CVD graphene film cannot be prepared in a practical area size. Therefore, a multi-layer graphene separation membrane capable of exerting the advantages of graphene film and forming a practical area size is needed to be developed, so as to adapt to the mass-produced high-performance separation membrane products and preparation process of the thin film conductance method TOC analysis equipment, solve the performance problems and industrial development problems of the TOC analyzer caused by the separation membrane, and break through and surpass the foreign market monopoly and technical blockade. SUMMARY

[0005] In order to overcome the above problems, the present application provides a graphene separation membrane and a preparation method thereof and a TOC analyzer comprising the graphene separation membrane.

[0006] The present application provides a graphene separation membrane, comprising a support layer and a separation layer, wherein the separation layer is a double-layer graphene film with nanopores.

[0007] According to an embodiment of the present application, the surface pore size of the support layer is distributed in the range of 0.1-5 μm, the through-hole pore size is distributed in the range of 0.1-1 μm, and the porosity is 70%-90%; the pore density of the separation layer is 1×10 11 -1×10 12 cm -1 .

[0008] The present application also provides a preparation method of the above graphene separation membrane, comprising the following steps: S1, forming a support layer on the surface of a single-layer graphene grown on a substrate; S2, adhering an auxiliary transfer medium to the support layer to obtain an auxiliary transfer medium / support layer / single-layer graphene / substrate composite layer, then removing the substrate and releasing the auxiliary transfer medium to obtain a support layer / single-layer graphene composite layer; S3, adhering the support layer / single-layer graphene composite layer to the surface of a single-layer graphene grown on a substrate to form a support layer / double-layer graphene / substrate composite layer, then adhering an auxiliary transfer medium to the support layer of the support layer / double-layer graphene / substrate composite layer, and then removing the substrate and releasing the auxiliary transfer medium to obtain a support layer / double-layer graphene composite membrane; and S4, forming pores in the support layer / double-layer graphene composite membrane to form nanopores on the double-layer graphene.

[0009] According to an embodiment of the present application, in the S1 step, a polymer is dissolved in an organic solvent to form a casting solution, and the support layer is formed by using the casting solution; wherein the content of the polymer is 10wt%-30wt% and the content of the organic solvent is 70wt%-90wt%, based on the total weight of the casting solution.

[0010] According to another embodiment of the present application, the casting solution is coated on the single-layer graphene surface after being degassed, and then is placed in a constant temperature and humidity atmosphere or immersed in a coagulation bath for solidification, or is first gelled in a constant temperature and humidity atmosphere and then is immersed in a coagulation bath for solidification, to obtain the support layer.

[0011] According to another embodiment of the present application, the support layer has a film thickness of 15-150μm, preferably 25-75μm; the gelation process is controlled at a temperature of 25-95℃, preferably 40-70℃; the gelation process is controlled at a humidity of 25-95%, preferably 40-70%; the gelation time is controlled at 0.5-90min, preferably 2-60min; the coagulation bath temperature is controlled at 15-90℃, preferably 25-45℃; and the coagulation bath time is controlled at 20min-480min, preferably 120-240min.

[0012] According to another embodiment of the present application, the polymer is selected from one or more of polyvinylidene fluoride, polyether sulfone resin, polystyrene, polyimide, polyacrylonitrile, polydimethylsiloxane, polysulfone, cellulose acetate, polycarbonate, polyvinyl acetate, polyether ether ketone, polyvinyl imine, and polyphenyl ether; and the organic solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl pyrrolidone, dimethyl sulfoxide, tetrahydrofuran, toluene, acetone, cyclohexane, ethanol, acetic acid, and ethyl acetate.

[0013] According to another embodiment of the present application, in the S3 step, after the support layer / double-layer graphene / substrate composite layer is formed, it is clamped between two hot-pressing plates for hot-pressing, at a hot-pressing temperature of 60-150℃ and a hot-pressing time of 6-12h.

[0014] According to another embodiment of the present application, in the S4 step, the hole making is plasma etching, the etching gas source is one or more of argon or oxygen, the etching pressure is 0.1-250Pa, preferably 5-50Pa, the power is 1-100w, preferably 30-60w, and the processing time is 1-300s, preferably 10-100s.

[0015] The present application further provides a TOC analyzer comprising the graphene separation membrane.

[0016] The application adopts double-layer CVD graphene film as the separation layer material of the composite layer, which better improves the problems of easy breakage, high requirement for raw materials and high cost of single-layer CVD graphene film applied in the separation membrane field, and the performance is obviously improved, and the double-layer graphene separation membrane is suitable for the separation membrane of the TOC analyzer. Meanwhile, the double-layer graphene separation membrane is prepared by using the laminated transfer graphene film technology, the preparation technical problems and material limitations of large-area continuous double-layer or multi-layer CVD graphene film material are avoided; the high-density ordered nanometer holes are introduced into the double-layer graphene film prepared by the laminated transfer method by using the plasma etching method, so that the selectivity and permeability of the graphene separation membrane are ensured. The graphene separation membrane product is suitable for the industrialized preparation. The preparation difficulty of the separation membrane of the thin film conductivity method TOC analyzer core component is effectively solved. BRIEF DESCRIPTION OF DRAWINGS

[0017] The following drawings are used to provide further understanding of the application and constitute a part of the specification, and together with the following specific embodiments, are used to explain the application, but do not constitute a limitation on the application.

[0018] Figure 1 It is a preparation method flow chart of the graphene separation membrane of one embodiment of the application.

[0019] Figure 2 It is a scanning electron microscope graph of the cross-sectional structure of the composite layer prepared in step 10 of example 1.

[0020] Figure 3 It is a scanning electron microscope graph of the surface of the support layer on the side without graphene of the composite layer prepared in step 10 of example 1.

[0021] Figure 4 It is a scanning electron microscope graph of the surface of the graphene side of the composite layer prepared in step 10 of example 1.

[0022] Figure 5 It is a pore size distribution graph of the support layer of the composite layer of example 1.

[0023] Figure 6 It is a porosity test result graph of the support layer of the composite layer of example 1.

[0024] Figure 7 They are respectively the composite layer prepared in step 10 of example 1 and the graphene separation membrane prepared in step of example 1.

[0025] Figure 8 It is a transmission electron microscope graph of the graphene separation membrane prepared in step of example 1.

[0026] Figure 9 It is a scanning electron microscope graph of the cross-sectional structure of the composite layer prepared in step 4 of example 2.

[0027] Figure 10 is a scanning electron microscope image of the support layer surface on the side of the composite layer prepared in Step IV of Example 2 to which graphene did not adhere.

[0028] Figure 11 is a scanning electron microscope image of the surface of the side of the composite layer prepared in Step IV of Example 2 to which graphene adhered.

[0029] Figure 12 is a scanning electron microscope image of the cross-sectional structure of the composite layer prepared in Step IV of Example 3.

[0030] Figure 13 is a scanning electron microscope image of the support layer surface on the side of the composite layer prepared in Step IV of Example 3 to which graphene did not adhere.

[0031] Figure 14 is a scanning electron microscope image of the surface of the side of the composite layer prepared in Step IV of Example 3 to which graphene adhered.

[0032] Figure 15 is a scanning electron microscope image of the cross-sectional structure of the composite layer prepared in Step IV of Example 4.

[0033] Figure 16 is a scanning electron microscope image of the support layer surface on the side of the composite layer prepared in Step IV of Example 4 to which graphene did not adhere.

[0034] Figure 17 is a scanning electron microscope image of the surface of the side of the composite layer prepared in Step IV of Example 4 to which graphene adhered.

[0035] Figure 18 is a pore size distribution graph of the support layer of the composite layer of Example 4.

[0036] Figure 19 is a graph of the results of a porosity test of the support layer of the composite layer of Example 4.

[0037] Figure 20 is a scanning electron microscope image of the cross-sectional structure of the composite layer prepared in Step IV of Example 5.

[0038] Figure 21 is a scanning electron microscope image of the support layer surface on the side of the composite layer prepared in Step IV of Example 5 to which graphene did not adhere.

[0039] Figure 22 is a scanning electron microscope image of the surface of the side of the composite layer prepared in Step IV of Example 5 to which graphene adhered.

[0040] Figure 23 is a scanning electron microscope image of the surface of the side of the "PVDF / single layer graphene" composite layer prepared in Example 6 to which graphene adhered.

[0041] Figure 24is a scanning electron microscope image of the surface of the graphene layer of the "PVDF / single layer graphene" composite film prepared in Example 6.

[0042] Figure 25 is a scanning electron microscope image of the surface of the graphene layer of the "PVDF / single layer graphene" composite film prepared in Example 6.

[0043] Figure 26 are Raman spectra of the surface of the graphene layer of the "PVDF / single layer graphene" composite film after different time of Ar plasma treatment in Example 6, respectively.

[0044] Figure 27 are Raman spectra of the surface of the graphene layer of the "PVDF / double layer graphene" composite film after different time of Ar plasma treatment in Example 6, respectively.

[0045] Figure 28 are Raman spectra of the surface of the graphene layer of the composite film prepared in Example 7 after different parameters of Ar plasma treatment, respectively.

[0046] Figure 29 is a graph showing the relationship between the pore density and the pore spacing of the graphene layer of the graphene composite film of the present application and the time of plasma treatment in Example 7 under the preferred conditions.

[0047] Figure 30 is a graph showing the comparison of the salt rejection test results of the graphene layer in the "PVDF / single layer graphene" composite film and the "PVDF / double layer graphene" composite film in Test Example 1.

[0048] Figure 31 is a graph showing the salt rejection test results of the graphene separation membrane in Test Example 2.

[0049] Figure 32 is a graph showing the comparison of the TOC reproducibility of the graphene separation membrane and the commercial membrane in Test Example 3.

[0050] Figure 33 is a graph showing the comparison of the TOC linear correlation of the graphene separation membrane and the commercial membrane in Test Example 3.

[0051] Figure 34 is a graph showing the stability data of the commercial membrane provided by the enterprise in the TOC analyzer.

[0052] Figure 35 is a graph showing the TOC stability data of the graphene separation membrane in Test Example 3. DETAILED DESCRIPTION

[0053] The present application will be described in detail below with reference to specific embodiments.

[0054] The graphene separation membrane of the present application comprises a support layer and a separation layer, and the separation layer is a double-layer graphene film with nanopores. The support layer plays a supporting and protective role for the separation layer, and the main function of the separation layer is to realize the gas-liquid separation function of the membrane.

[0055] In optional embodiments, the surface pore size of the support layer ranges from 0.1 to 5 μm, the through-hole pore size ranges from 0.1 to 1 μm, the porosity is more than 70% to 90%, and the pore density of the separation layer is 1×10 11 -1×10 12 cm -1 When the surface pore size, through-hole pore size, porosity of the support layer, and the pore density of the separation layer are within the above ranges, the permeability and membrane flux of the separation membrane can be ensured. Specifically, the surface pore size of the support layer can be, but is not limited to, 0.1 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, etc.; the through-hole pore size can be, but is not limited to, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, etc.; the porosity can be, but is not limited to, 70%, 75%, 80%, 85%, 90%, etc.; and the pore density of the separation layer can be 1×10 11 cm -1 , 1×10 12 cm -1 , etc.

[0056] In optional embodiments, the thickness of the graphene separation membrane is 15 μm to 150 μm. If the thickness of the separation membrane is too thin, the mechanical performance is poor, the film formation is uneven, leading to poor membrane performance and limited application; if the thickness is too thick, the mass transfer resistance during film formation is too high, affecting the permeability of the membrane, and a too thick support layer will make it difficult to combine the interface between the separation layer and the support layer during the preparation of the membrane. The thickness of the separation membrane can be any value within the above range, such as, but not limited to, 15 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, etc.

[0057] For example, the graphene separation membrane of the present application can be used for the separation of gas mixtures, such as air, oxygen, nitrogen, hydrogen, carbon dioxide, methane, etc. Figure 1As shown, the preparation method of the graphene separation membrane can include: S1, forming a support layer on a single-layer graphene surface grown on a substrate; S2, laminating an auxiliary transfer medium on the support layer to obtain an auxiliary transfer medium / support layer / single-layer graphene / substrate composite layer, then removing the substrate and releasing the auxiliary transfer medium to obtain a support layer / single-layer graphene composite layer; S3, laminating the support layer / single-layer graphene composite layer to a single-layer graphene surface grown on a substrate to form a support layer / two-layer graphene / substrate composite layer, then laminating an auxiliary transfer medium on the support layer of the support layer / two-layer graphene / substrate composite layer, and then removing the substrate and releasing the auxiliary transfer medium to obtain a support layer / two-layer graphene composite membrane; and S4, forming nanopores on the two-layer graphene by making holes in the support layer / two-layer graphene composite membrane. In this patent, S1, S2, S3 and S4 are only used to distinguish different steps, and the steps are not limited to occur continuously. Auxiliary steps such as but not limited to cleaning, drying and the like can be performed between the steps.

[0058] In the S1 step, the polymer can be dissolved in an organic solvent to form a casting solution, and the casting solution can be used to form the support layer. The content of the polymer is 10wt%-30wt% and the content of the organic solvent is 70wt%-90wt% based on the total weight of the casting solution. If the content of the polymer in the casting solution is less than 10wt%, the viscosity of the casting solution is too low, the film formation is discontinuous, and the film formation selectivity and mechanical properties are poor. If the content of the polymer is more than 30wt%, it is difficult to be completely dissolved in the actual operation process, the viscosity is too high, the film formation is uneven, and the film formation is easy to fall off from the graphene layer and is difficult to be combined with the graphene layer.

[0059] The polymer can be selected from one or more of polyvinylidene fluoride (PVDF), polyether sulfone resin (PES), polystyrene (PS), polyimide (PI), polyacrylonitrile (PAN), polydimethylsiloxane (PDMS), polysulfone (PSF), cellulose acetate (CA), polycarbonate (PC), polyvinyl acetate (PVAC), polyether ether ketone (PEEK), polyethyleneimine (PEI), and polyphenylene oxide (PPO). The organic solvent can be selected from one or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), toluene (TL), acetone (AC), cyclohexane (CYH), ethanol (EA), acetic acid (HAc), and ethyl acetate (EAC).

[0060] The casting solution is coated on the surface of the single-layer graphene after degassing to form a support layer. The degassing of the casting solution can be static or using a vacuum degassing device, and the degassed casting solution is poured onto the surface of the single-layer graphene grown on the substrate to allow the casting solution to fully contact the graphene. The casting solution on the graphene surface supported on the substrate is coated to a certain thickness, and then the casting solution is solidified to form a support layer. The solidification can be carried out in a constant temperature and humidity atmosphere or immersed in a coagulation bath, or first gel in a constant temperature and humidity atmosphere and then solidified in a coagulation bath to obtain a support layer structure. The thickness of the support layer is controlled to be 15-150 μm, preferably 25-75 μm. The gel process temperature is controlled at 25-95℃, preferably 40-70℃; the gel process humidity is controlled at 25-95%, preferably 40-70%; the gel time is controlled at 0.5-90 min, preferably 2-60 min; the coagulation bath temperature is controlled at 15-90℃, preferably 25-45℃; the coagulation bath time is controlled at 20 min-480 min, preferably 120-240 min.

[0061] After the preparation of the support layer, the "support layer / single-layer graphene / substrate" composite layer is dried, and then the auxiliary transfer medium is attached to the support layer side in the S2 step. Then the substrate of the "auxiliary transfer medium / support layer / single-layer graphene / substrate" composite layer is removed. The auxiliary transfer medium can be any suitable component, such as but not limited to adhesive tape and the like. The substrate can be removed by etching, and copper foil is used as the substrate to illustrate the removal process of the substrate, but those skilled in the art can understand that the removal of the substrate is not limited to etching, but can be any suitable method. The "auxiliary transfer medium / support layer / single-layer graphene / copper foil" composite layer can be first treated with etching solution, the copper foil side is close to the solution, and is floated on the surface of the solution for 10-30 min, and then is thoroughly washed with deionized water after pretreatment; finally, the copper foil in the "medium / support layer / single-layer graphene / copper foil" composite layer after back etching is completely etched with etching solution, and is thoroughly washed with deionized water after etching to obtain the "auxiliary transfer medium / support layer / single-layer graphene" composite layer. The etchant is selected from one or more of sodium persulfate, ammonium persulfate, ferric chloride, and iron sulfate, and the concentration is controlled at 0.1-15 wt%, preferably 1-10 wt%.

[0062] After the release of the auxiliary transfer medium, the "auxiliary transfer medium / support layer / single-layer graphene" composite layer is infiltrated with the infiltration solution, and the medium is released after complete infiltration to obtain the "support layer / single-layer graphene" composite layer. The infiltration solution can be selected from one or more of ethanol, methanol, and isopropanol. Of course, the release method of the auxiliary transfer medium is not limited to the above, but can be any suitable release method

[0063] In S3, the "support layer / single layer graphene" composite layer is attached to the surface of the single layer graphene grown on the substrate to form a "support layer / double layer graphene / substrate" composite layer. The specific method can be to heat press the "support layer / double layer graphene / substrate" composite layer between two pieces of hot press plate, the hot press temperature is 60-150℃, and the hot press time is 6-12h. The hot press process can make the first layer of graphene and the second layer of graphene attach perfectly. Compared with the lamination transfer process at room temperature and normal pressure, the lamination transfer by hot pressing utilizes the capillary force generated by the volatilization of volatile small molecules under high temperature and certain pressure, so that the combination between the two layers of graphene is more compact and complete.

[0064] Then, the "support layer / double layer graphene / substrate" composite layer after hot pressing is attached to the side of the support layer of the "support layer / double layer graphene / substrate" composite layer to form a "auxiliary transfer medium / support layer / double layer graphene / substrate" composite layer.

[0065] Then, the "auxiliary transfer medium / support layer / double layer graphene / substrate" composite layer is subjected to the substrate removal and release medium step to form a "support layer / double layer graphene" composite film. The method of removing the substrate and releasing the medium can be the same as that in S2.

[0066] Finally, in S4, the "support layer / double layer graphene" composite film is subjected to hole making. The hole making can be made by plasma etching. Specifically, the "support layer / double layer graphene" composite film is placed in a plasma device, an etching gas source is introduced, the pressure of the plasma device is adjusted to 0.1-250Pa, preferably 5-50Pa, the power is 1-100W, preferably 30-60W, the processing time is 1-300s, preferably 10-100s, and the selected etching gas source is one or more of argon or oxygen. After plasma treatment, the double layer graphene film can be introduced into sub-nanopores to complete the preparation of the nanopore double layer graphene separation film.

[0067] The method of the present application can prepare a double layer or multi-layer graphene separation film containing a large area (for example, 10cmx15cm), which is suitable for TOC analyzer. The separation film of the present application effectively solves the problems of poor repeatability, poor linear correlation and poor long-term stability in the application of thin film conductivity method TOC analyzer caused by the performance of the separation film. It lays a foundation for the industrial application of large area single layer CVD graphene film in the field of separation film, and has good development prospect and practical application value.

[0068] The present application will be further described by specific examples. However, these examples are only exemplary and do not constitute any limitation on the scope of protection of the present application. In the following examples and comparative examples, the reagents, materials and instruments used are commercially available unless otherwise specified.

[0069] Example 1

[0070] ①The PVDF with weight average molecular weight of 26.1W was dried at 105℃ to constant weight, and 16g of the dried PVDF was dissolved in 64g of DMAc solvent at 75℃ constant temperature oil bath to form a uniform casting solution.

[0071] ②The casting solution was deaerated for 12h, and then poured onto the surface of the 5cm×5cm single-layer CVD graphene film grown on a copper foil to allow the casting solution to fully contact with the graphene film for 12h.

[0072] ③The casting solution on the graphene surface of the copper foil was spin-coated to a certain thickness by using a spin coater (the spin coater parameters were set as low rotation speed 200r, time 10s, high rotation speed 2000r, time 60s), and the "casting solution / single-layer graphene / copper foil" structure coated with the casting solution was immersed in a 500ml room temperature deionized water coagulation bath for solidification for 2h. After solidification, it was taken out of the coagulation bath and dried for 0.5h to obtain a "PVDF / single-layer graphene / copper foil" composite layer, and the support layer preparation was completed.

[0073] ④The "PVDF / single-layer graphene / copper foil" composite layer was pressed on the side of the support layer (PVDF) with adhesive tape to assist the graphene transfer.

[0074] ⑤The obtained "adhesive tape / PVDF / single-layer graphene / copper foil" composite layer was subjected to copper foil etching treatment. First, the "adhesive tape / PVDF / single-layer graphene / copper foil" composite layer was subjected to back etching treatment with 10% sodium persulfate etching solution for 30min, a small amount of isopropyl alcohol was added to the etching solution, and then the sample was washed with deionized water after back etching treatment. Then, the copper foil part of the "adhesive tape / PVDF / single-layer graphene / copper foil" composite layer after washing was completely etched with 2% sodium persulfate etching solution, a small amount of isopropyl alcohol was added to the etching solution, and then the sample was thoroughly washed with deionized water after etching to obtain a "adhesive tape / PVDF / single-layer graphene" composite layer.

[0075] ⑥The auxiliary transfer adhesive tape was released, and the first layer of graphene film was transferred. Specifically, the "adhesive tape / PVDF / single-layer graphene" composite layer was immersed in anhydrous ethanol, and after complete immersion, the adhesive tape was released to obtain a "PVDF / single-layer graphene" composite layer.

[0076] ⑦The "PVDF / single-layer graphene" composite layer was taken out of the immersion liquid and quickly attached to the surface of a 5cm×5cm single-layer CVD graphene film (the same as the graphene material used before) grown on a copper foil, and the obtained "PVDF / double-layer graphene / copper foil" composite layer was clamped between two glass plates for hot pressing, with a hot pressing temperature of 110℃ and a hot pressing time of 10h.

[0077] ⑧ Press adhesive tape onto the support layer (PVDF) side of the hot-pressed “PVDF / double-layer graphene / copper foil” composite layer to assist in the transfer of the second layer of graphene.

[0078] ⑨ The obtained "tape / PVDF / bilayer graphene / copper foil" composite layer was subjected to copper foil etching. The method was as follows: the "tape / PVDF / bilayer graphene / copper foil" composite layer was first back-etched with 10% sodium persulfate etching solution for 30 minutes, with a small amount of isopropanol added to the etching solution. After back-etching, it was cleaned with deionized water. The copper foil portion of the cleaned "tape / PVDF / bilayer graphene / copper foil" composite layer was completely etched with 2% sodium persulfate etching solution, with a small amount of isopropanol added to the etching solution. After etching, it was thoroughly cleaned with deionized water to obtain the "tape / PVDF / bilayer graphene" composite layer.

[0079] ⑩ Release the auxiliary transfer tape to complete the transfer of the second graphene film. The specific operation process is to soak the "tape / PVDF / bilayer graphene" composite layer with anhydrous ethanol. After complete soaking, release the tape and let the resulting "PVDF / bilayer graphene" composite layer air dry naturally to complete the transfer of the bilayer graphene film and obtain the "PVDF / bilayer graphene" composite film.

[0080] The PVDF / bilayer graphene composite membrane was placed in a plasma device, Ar gas was introduced, the pressure of the plasma device was adjusted to 10 Pa, the power was 50 W, and the processing time was 40 s. After plasma treatment, the graphene separation membrane of the present invention was obtained.

[0081] Figures 2-4 The images show the cross-sectional and surface structure SEM images of the "PVDF / bilayer graphene" composite film obtained in step ⑩, which visually reflect the overall microstructure of the composite layer. The graphene layer is intact and without obvious defects, and the composite layer as a whole consists of a support layer and a graphene layer. Figure 2 As shown, the composite layer is 30 μm thick. The support layer, from top to bottom, consists of a 2 μm thick mesh-like upper surface layer, a 23 μm thick middle layer with micron-sized finger-like pores, and a 5 μm thick lower surface layer with continuous sponge pores. Figure 3 As shown, the pore size distribution on the support layer surface of the side of the composite layer without graphene attachment ranges from 50 nm to 300 nm. Figure 4 As shown, the pore size of the support layer on one side of the composite graphene layer ranges from 100 nm to 1000 nm.

[0082] According to GB / T 32361-201 standard for composite layer pore size testing, Figure 5The pore size distribution of the support layer of the composite layer is shown in the figure, and the pore size range of the through hole of the support layer is 200-400 nm, and the average pore size is 210.4 nm. According to the porosity test standard GB / T23561.2-2009, Figure 6 The porosity test result of the support layer of the composite layer is shown in the figure, and the through hole porosity of the composite layer is 75.09%.

[0083] Figure 7 The pore size distribution of the support layer of the composite layer is shown in the figure, and the pore size range of the through hole of the support layer is 200-400 nm, and the average pore size is 210.4 nm. According to the porosity test standard GB / T23561.2-2009, The Raman spectrum of the prepared "PVDF / double-layer graphene" composite membrane and the prepared graphene separation membrane is shown in the figure. The graphene characteristic peak in the spectrum of the "PVDF / double-layer graphene" composite membrane is obvious (G peak and 2D peak), and there is no obvious defect peak (D peak), which indicates that the graphene layer of the composite layer is complete and has no obvious micro defects. Compared with Figure 7 The obvious change of the defect peak in the Raman spectrum before and after the plasma treatment, combined with Figure 8 TEM characterization results show that after the step After the plasma treatment, the graphene layer in the "PVDF / double-layer graphene" composite membrane prepared in step 10 successfully introduces uniform high-density nanopores.

[0084] Example 2

[0085] ①The PES with a weight average molecular weight of 30W was dried at 105℃ to a constant weight, and 16g of the dried PES was dissolved in 64g of DMAc solvent at 75℃ constant temperature oil bath to form a uniform casting solution.

[0086] ②The casting solution was deaerated for 12h, and then poured onto the surface of the 5cm×5cm single-layer CVD graphene film grown on the copper foil to make the casting solution and the graphene film fully contact for 12h.

[0087] ③The casting solution on the graphene surface of the copper foil was spin-coated to a certain thickness by using a spin coater (the spin coater parameter was set to low rotation speed 200r, time 60s), and the "casting solution / single-layer graphene / copper foil" structure coated with the casting solution was immersed in a 500ml room temperature deionized water coagulation bath for 2h. After coagulation, it was taken out from the coagulation bath and dried for 0.5h to obtain a "PES / single-layer graphene / copper foil" composite layer, and the support layer preparation was completed.

[0088] ④ Copper foil etching treatment of the "PES / single layer graphene / copper foil" composite layer. First, the "PES / single layer graphene / copper foil" composite layer is back etched with 10% sodium persulfate etching solution for 10 min, a small amount of isopropyl alcohol is added to the etching solution, and after back etching, the composite layer is washed with deionized water; the copper foil part of the washed "PES / single layer graphene / copper foil" composite layer is completely etched with 10% sodium persulfate etching solution, a small amount of isopropyl alcohol is added to the etching solution, and after etching, the composite layer is thoroughly washed with deionized water to obtain a "PES / single layer graphene" composite layer, and the support layer preparation is completed.

[0089] Figures 9-11 The SEM image of the cross-section and surface structure of the "PES / single layer graphene" composite layer prepared in step ④ directly reflects the overall microstructure of the composite layer, and the composite layer is composed of a support layer and a graphene layer. As shown in FIG. 4, the thickness of the prepared composite layer is 39 μm, and the support layer is composed of a 5-10 μm thick reticular upper surface layer, a 24-31 μm thick middle layer with micron-sized finger-shaped pores, and a 3-5 μm thick lower surface layer with continuous sponge pores from top to bottom. As shown in FIG. 5, the pore size of the support layer surface on the side without graphene of the composite layer ranges from 20 nm to 200 nm. As shown in FIG. 6, the pore size of the support layer surface on the side with graphene of the composite layer ranges from 500 nm to 1000 nm. Figure 9 Figure 10 Figure 11

[0090] Example 3

[0091] ① 16 g of PS with a weight average molecular weight of 28W was dried at 105°C until the weight was constant, and then dissolved in 64 g of DMAc solvent at 75°C in a constant temperature oil bath to form a uniform casting solution.

[0092] ② The casting solution was deaerated for 12 h, and then poured onto the surface of a 5 cm x 5 cm single layer CVD graphene film grown on a copper foil to allow the casting solution to fully contact the graphene film for 12 h.

[0093] ③ The casting solution on the graphene surface was spin-coated to a certain thickness using a spin coater (the spin coater parameters were set to low speed 200 r, time 60 s), and the "casting solution / single layer graphene / copper foil" structure coated with the casting solution was immersed in a 500 ml room temperature deionized water coagulation bath for 2 h, then taken out of the coagulation bath, and dried for 0.5 h to obtain a "PS / single layer graphene / copper foil" composite layer, and the support layer preparation was completed.

[0094] ​​​④ Copper foil etching treatment of the "PS / single layer graphene / copper foil" composite layer. First, the "PS / single layer graphene / copper foil" composite layer is back etched for 10 min using a 10% sodium persulfate etching solution, with a small amount of isopropyl alcohol added to the etching solution. After back etching, the composite layer is washed with deionized water. The copper foil portion of the washed "PS / single layer graphene / copper foil" composite layer is completely etched using a 10% sodium persulfate etching solution, with a small amount of isopropyl alcohol added to the etching solution. After etching, the composite layer is thoroughly washed with deionized water to obtain a "PS / single layer graphene" composite layer, completing the preparation of the support layer.

[0095] Figures 12-14 The SEM images of the cross-section and surface structure of the "PS / single layer graphene" composite layer prepared in step ④ directly reflect the overall microstructure of the composite layer, which is composed of a support layer and a graphene layer. As shown in FIG. 4, the thickness of the prepared composite layer is 52 μm. The support layer is composed of a 3-5 μm thick reticular upper surface layer, a 42-46 μm thick middle layer with micron-sized finger-shaped pores, and a 3-5 μm thick lower surface layer with continuous sponge pores. Figure 12 As shown in FIG. 5, the pore size of the support layer surface on the side without graphene attachment of the composite layer ranges from 10 nm to 100 nm. Figure 13 As shown in FIG. 6, the pore size of the support layer surface on the side with graphene of the composite layer ranges from 500 nm to 1000 nm. Figure 14

[0096] Example 4

[0097] ① PVDF with a weight average molecular weight of 26.1 W is dried at 105°C until the weight is constant. 16 g of the dried PVDF is dissolved in 64 g of DMF solvent at 60°C in a constant temperature oil bath to obtain a uniform casting solution.

[0098] ② The casting solution is deaerated for 12 h, and then poured onto the surface of a 5 cm x 5 cm single layer CVD graphene film grown on a copper foil to allow the casting solution to fully contact the graphene film for 12 h.

[0099] ③ The casting solution on the graphene surface of the copper foil is spin-coated to a certain thickness using a spin coater (the spin coater parameters are set as low speed 200 r, time 10 s, high speed 2000 r, time 60 s). The "casting solution / single layer graphene / copper foil" structure coated with the casting solution is placed in a constant temperature and humidity (humidity 60%, temperature 60°C) atmosphere for 30 min to obtain a support layer composite layer.

[0100] ​④ The "PVDF / single-layer graphene / copper foil" composite layer is subjected to copper foil etching. The method is as follows: First, the "PVDF / single-layer graphene / copper foil" composite layer is back-etched for 10 minutes with a 10% sodium persulfate etching solution. A small amount of isopropanol is added to the etching solution. After the back-etching treatment, it is cleaned with deionized water. The copper foil portion of the cleaned "PVDF / single-layer graphene / copper foil" composite layer is completely etched with a 2% sodium persulfate etching solution. A small amount of isopropanol is added to the etching solution. After etching, it is thoroughly cleaned with deionized water to obtain the "PVDF / single-layer graphene" composite layer, thus completing the preparation of the support layer.

[0101] Figures 15-17 The SEM images of the cross-section and surface structure of the "PVDF / monolayer graphene" composite layer obtained in step ④ visually reflect the overall microstructure of the composite layer, which consists of a support layer and a graphene layer. Figure 15 As shown, the composite layer has a thickness of 16 μm and contains continuous sponge pores of 3-5 μm in size. Figure 16 As shown, the pore size distribution on the support layer surface of the side of the composite layer without graphene attachment ranges from 3 to 5 μm. Figure 17 As shown, the pore size distribution on the surface of the support layer on one side of the composite graphene layer ranges from 1 to 3 micrometers. According to the GB / T 32361-201 standard for composite layer pore size testing, Figure 18 This is a pore size distribution diagram of the composite layer support layer. The pore size ranges from 600-900 nm, with an average pore size of 830.8 nm. According to the GB / T23561.2-2009 porosity testing standard... Figure 19 The diagram shows the test results of the porosity of the support layer of the composite layer. The porosity of the through-hole layer of the composite layer is 70.86%.

[0102] The characterization and test results of Examples 1-4 demonstrate that different types of polymers and solvents, different support layer preparation methods, and different condition parameters as claimed in this invention can all form a structure suitable for the support layer of a TOC separation membrane.

[0103] Example 5

[0104] ① The PVDF with a weight average molecular weight of 53.4W was dried at 105℃ to constant weight. 30g of the dried PVDF was dissolved in 170g of DMAc solvent in a constant temperature oil bath at 60℃ and stirred to form a homogeneous casting solution.

[0105] ② The casting solution was allowed to stand for 12 hours to remove bubbles. The degassed casting solution was then poured onto the surface of a 10cm×15cm monolayer CVD graphene film grown on copper foil, allowing the casting solution and the graphene film to be in full contact for 12 hours.

[0106] ③Using a coater, the casting solution on the surface of graphene supported on a copper foil is coated to a certain thickness (the doctor blade is controlled at a height of 100 pm), and the "casting solution / single layer graphene / copper foil" structure coated with the casting solution is placed in a constant temperature and humidity (humidity 65%, temperature 65°C) atmosphere for curing for 60 minutes to obtain a support layer composite layer.

[0107] ④The "PVDF / single layer graphene / copper foil" composite layer is subjected to copper foil etching treatment. The method is that the "PVDF / single layer graphene / copper foil" composite layer is first subjected to back etching treatment with 10% sodium persulfate etching solution for 30 min, a small amount of isopropyl alcohol is added to the etching solution, and after back etching treatment, the sample is washed with deionized water; the copper foil part of the washed "PVDF / single layer graphene / copper foil" composite layer is completely etched with 2% sodium persulfate etching solution, a small amount of isopropyl alcohol is added to the etching solution, and after etching, the sample is thoroughly washed with deionized water to obtain a "PVDF / single layer graphene" composite layer, and the preparation of a large-size support layer is completed.

[0108] Figures 20-22 The SEM images of the cross section and surface structure of the "PVDF / single layer graphene" composite layer prepared in step ④ intuitively reflect the overall microstructure of the composite layer, and the composite layer is composed of a support layer and a graphene layer. As shown in Figure 20 , the thickness of the prepared composite layer is 42 pm, and there are continuous sponge pores with a size of 3-5 pm. As shown in Figure 21 , the pore size range of the support layer surface on the side of the composite layer without graphene is distributed in the range of 3-5 pm. As shown in Figure 22 , the pore size range of the support layer surface on the side of the graphene of the composite layer is distributed in the range of 1-3 pm.

[0109] The characterization results of Example 5 can prove that the large-size support layer preparation method claimed in the present application can form a structure suitable for the support layer of a TOC separation membrane.

[0110] Example 6

[0111] The "PVDF / single layer graphene" composite layer prepared in step ⑥ of Example 1 and the "PVDF / double layer graphene" composite membrane prepared in step ⑩ are subjected to plasma pore making. The specific operation process is that argon gas is first introduced, and then the pressure of the plasma equipment is adjusted to 201 Pa and the power is 20 W. The "PVDF / single layer graphene" composite layer sample is treated for 10 s, 30 s and 60 s, and the four "PVDF / double layer graphene" composite membrane samples are treated for 30 s, 60 s, 2 min and 4 min.

[0112] Figures 23-25 The SEM characterization results of the "PVDF / single layer graphene" composite layer without introducing nanopores are compared with Figure 4The SEM characterization results of the "PVDF / double-layer graphene" composite film of Example 1 can find that the graphene layer of the "PVDF / single-layer graphene" composite layer has obvious macroscopic defects, and the quality and integrity of the graphene layer of the "PVDF / double-layer graphene" composite film are higher.

[0113] Comparison Figure 26 and Figure 27 It can be found that after the same plasma intensity and the same etching time of plasma treatment, the Raman spectrum of the "PVDF / single-layer graphene" composite layer appears obvious defect peak (D peak), while the Raman spectrum of the "PVDF / double-layer graphene" composite film has no obvious change, and the Raman spectrum of the "PVDF / double-layer graphene" composite film still has no obvious change when the plasma treatment time is extended to 4 min under the same intensity, which indicates that the stability of the "PVDF / double-layer graphene" composite film is higher than that of the "PVDF / double-layer graphene" composite film.

[0114] The characterization results of Example 6 can prove that the performance and stability of the double-layer graphene separation film claimed in the application are better than those of the single-layer graphene separation film, and the double-layer graphene separation film is suitable for the structure and performance requirements of the TOC separation film.

[0115] Example 7

[0116] The "PVDF / double-layer graphene" composite film prepared in step ⑩ of Example 1 was subjected to plasma pore forming. The specific experimental process is that the above sample is subjected to Ar plasma treatment, and the "pressure-power-time" parameter combination of the plasma equipment is selected as "50W-10Pa-80s", "50W-10Pa-60s", "50W-10Pa-40s", "50W-10Pa-20s", "20W-120Pa-1min", "20W-150Pa-1min", "20W-150Pa-1min", "20W-180Pa-1min", "20W-201Pa-3min", "20W-201Pa-4min". The treated sample is subjected to Raman spectrum characterization, and the influence of plasma treatment on the film structure is analyzed by the peak shape change in the characterization results.

[0117] As Figure 28As shown, by comparing the Raman spectra of samples treated with different parameters, it can be found that the Raman spectra change obviously with the change of treatment parameters, the D peak (defect peak) appears from nothing to something, the D' peak appears, the 2D peak changes from strong to weak and even disappears, and the peak width gradually widens, indicating that the pore structure of the graphene layer changes from nothing to something, the pore size changes from small to large, the number changes from few to many, the graphene structure changes from intrinsic continuous film to porous film, and finally becomes amorphous carbon structure, losing the intrinsic properties. Through the above change process, according to the intensity ratio of D peak and G peak, the pore density of graphene layer can be calculated and optimized, and the high pore density data and the corresponding plasma treatment parameters are as follows Figure 29 As shown, the plasma treatment parameters and the preferred range of double-layer graphene are determined, and the pore density introduced by the separation membrane under the preferred parameters can reach 1.2 x 10 12 cm -1 .

[0118] The composite layer prepared in steps ⑥, ⑩ and of Example 1 was tested, and the test types and processes are as follows:

[0119] In order to evaluate the performance of the membrane and the performance of the membrane in the TOC analyzer, the diffusion cell and the TOC analyzer were used to test the membrane respectively, the quality of the graphene selection layer was fed back according to the diffusion cell liquid potassium chloride permeation experiment, and the application of the nanopore graphene separation membrane in the equipment was judged according to the performance of the TOC analyzer, and the specific test indexes and operation steps are as follows:

[0120] (1) Performance test of separation membrane

[0121] The salt resistance of the graphene composite layer and the graphene transfer quality were mainly evaluated by the liquid KCl permeation experiment method, and the test instrument was a multi-parameter tester connected with conductivity electrodes (Mettler Toledo). The device used was a diffusion cell, and the effective test membrane area of the diffusion cell was a circular area with a diameter of 5 mm. The specific test steps are as follows:

[0122] ① Anhydrous ethanol and deionized water were respectively heated and stirred at 140℃ and 310℃ for 1h for degassing treatment, and then cooled to room temperature for standby.

[0123] ② The composite layer to be tested was installed in the middle part of the diffusion cell, and the effective diameter of the composite layer was 5mm.

[0124] ③ After degassing, anhydrous ethanol was added to both sides of the diffusion cell, and then stirred by magnetic force for 3min and discharged.

[0125] ④ Prepare 50% ethanol aqueous solution and add to both sides of the diffusion cell, and then stir by magnetic force for 3min and discharge.

[0126] ⑤Finally, deionized water after degassing was injected into both sides, and the magnetic stirring was performed for 3 min before discharging.

[0127] ⑥The KCl salt solution with a concentration of 0.5 mol / L was prepared (Note: The deionized water used for preparing the solution has been degassed).

[0128] ⑦The prepared KCl solution was injected into one side of the diffusion cell, and the same volume of deionized water was injected into the other side, and magnetic stirring was performed at the same time.

[0129] ⑧The conductivity electrode was used to test the conductivity change of the deionized water side to represent the salt resistance of the composite layer and the quality of the graphene transfer.

[0130] (2) TOC performance test

[0131] The application performance of the separation membrane in the TOC analyzer was tested by using the HTY-MC20 type total organic carbon analyzer produced by Zhejiang Tailin Biotechnology Co., Ltd. In order to ignore the experimental error caused by other parts of the equipment as much as possible, and better reflect the real situation of the influence of the membrane product on the performance of the instrument, all the analysis data are the original signal values detected by the conductivity sensor of the TOC analyzer.

[0132] ① Inorganic carbon detection repeatability

[0133] Within the calibrated range of the instrument, the inorganic carbon standard solution (0%, 10%, 20%, 50%, 80%, and 100% inorganic carbon standard solution with full scale concentration) was used as the sample, and the detection was repeated 6 times, and the relative standard deviation (RSD) was calculated, and the calculation formula was as follows:

[0134]

[0135] Among them, X Ii represents the measured value of the inorganic carbon measurement of the instrument; is the average value of the measured value of the inorganic carbon measurement of the instrument; n is the number of measurements.

[0136] ② Linear correlation

[0137] Within the calibrated range of the instrument, the inorganic carbon standard solution with full scale concentration of 0%, 10%, 20%, 50%, 80%, and 100% was selected for testing. Each concentration was tested 6 times, and the arithmetic mean of the 6 measurement results was calculated, and the arithmetic mean of the measurement values of different concentrations of standard solution was linearly fitted.

[0138] ③ Long-term stability

[0139] In the range of the instrument has been calibrated, the inorganic carbon standard solution (50% of the full scale concentration) was used for the sample, and the arithmetic mean of 6 measurement results selected randomly in 14 days was calculated. The RSD was calculated using the 14 arithmetic means, and the calculation formula is shown in 1-1 and 1-2.

[0140] Test Example 1

[0141] The salt rejection performance and mass transfer of the graphene layer in the "PVDF / single-layer graphene" composite membrane prepared in step ⑥ of Example 1 and the graphene layer in the "PVDF / two-layer graphene" composite membrane prepared in step ⑩ of Example 1 were tested by using the aforementioned separation membrane performance test method.

[0142] As shown in Figure 30 , comparing the salt rejection data of the graphene layer in the "PVDF / single-layer graphene" composite membrane and the graphene layer in the "PVDF / two-layer graphene" composite membrane after immersion, it is shown that the salt rejection performance of the graphene layer in the "PVDF / two-layer graphene" composite membrane is much higher than that of the graphene layer in the "PVDF / single-layer graphene" composite membrane.

[0143] Test Example 2

[0144] The salt rejection performance of the graphene separation membrane prepared in step of Example 1 was tested by using the aforementioned separation membrane performance test method.

[0145] As shown in Figure 31 , the conductivity basically remains 0 over time, indicating that the nanopore two-layer graphene separation membrane is salt-tight and has good salt rejection performance during the test.

[0146] Test Example 3

[0147] The graphene separation membrane prepared in step of Example 1 was applied in the TOC analyzer to test its repeatability, linear correlation and stability. At the same time, commercial membrane 1 (manufacturer: Shanghai Minglie New Material Co., Ltd.) and commercial membrane 2 (manufacturer: BIOGENERAL, brand: Teflon) were applied in the TOC analyzer to test their repeatability, linear correlation and stability.

[0148] As shown in Figure 32 , the repeatability of the instrument during the experiment of the graphene separation membrane is better, and the RSD data is lower and more stable, meeting the requirement of the TOC analyzer industry that the RSD is less than 3%. As shown in Figure 33 , during the test in the TOC analyzer, compared with the commercial membranes, the linear correlation performance of the instrument during the experiment of the nanopore graphene separation membrane is better, and the degree of quadratic linear fitting is also higher, which can improve the detection accuracy and range of the instrument. As shown in Figure 35As shown, the RSD of the instrument continuous running for 14 days stability data is 1.88%, which is better than Figure 34 The RSD data of the commercial membrane (manufacturer: Shanghai Minglie New Material Co., Ltd.) in the application process of the enterprise (provided by Zhejiang Tailin Biotechnology Co., Ltd.) shows that the stability of the graphene separation membrane of the present application in the application of the TOC analyzer is better than that of the commercial membrane.

[0149] The above disclosed preferred embodiments of the present application are only used to help explain the present application. The preferred embodiments do not describe all the details and do not limit the present application to the specific embodiments described. Obviously, many modifications and changes can be made according to the content of the present application. The present application selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present application, so that those skilled in the art can well understand and utilize the present application. The present application is limited only by the claims and their full scope and equivalents.

Claims

1. A method for producing a graphene separation membrane, characterized by, Comprise: S1, forming a support layer on a monolayer graphene surface grown on a substrate; S2, laminating an auxiliary transfer medium on the support layer to obtain an auxiliary transfer medium / support layer / monolayer graphene / substrate composite layer, then removing the substrate and releasing the auxiliary transfer medium by immersing in an immersion liquid to obtain a support layer / monolayer graphene composite layer; S3, laminating the support layer / monolayer graphene composite layer to a monolayer graphene surface grown on a substrate to form a support layer / two-layer graphene / substrate composite layer, then clamping between two hot pressing plates for hot pressing, hot pressing temperature 60-150℃, hot pressing time 6-12h, then laminating an auxiliary transfer medium on the support layer of the support layer / two-layer graphene / substrate composite layer, then removing the substrate and releasing the auxiliary transfer medium to obtain a support layer / two-layer graphene composite film; And S4, forming nanopores on the two-layer graphene by punching the support layer / two-layer graphene composite film; Wherein the immersion liquid is selected from one or more of ethanol, methanol, isopropanol.

2. The production method according to claim 1, characterized by, In the S1 step, the polymer is dissolved in an organic solvent to form a casting solution, and the casting solution is used to form the support layer; Wherein, based on the total weight of the casting solution, the content of the polymer is 10wt%-30wt%, and the content of the organic solvent is 70wt%-90wt%.

3. The production method according to claim 2, characterized by, The casting solution is coated on the monolayer graphene surface after degassing, then placed in a constant temperature and humidity atmosphere or immersed in a coagulation bath for solidification, or first gelled in a constant temperature and humidity atmosphere and then immersed in a coagulation bath for solidification, to obtain the support layer.

4. The production method according to claim 3, characterized by, The film thickness of the support layer is 15-150μm; the gel process temperature is controlled at 25-95℃; the gel process humidity is controlled at 25-95%; the gel time is controlled at 0.5-90min; the coagulation bath temperature is controlled at 15-90℃; and the coagulation bath time is controlled at 20min-480min.

5. The preparation method according to claim 4, characterized in that, The film thickness of the support layer is 25-75μm; the gel process temperature is controlled at 40-70℃; the gel process humidity is controlled at 40-70%; the gel time is controlled at 2-60min; the coagulation bath temperature is controlled at 25-45℃; and the coagulation bath time is controlled at 120-240min.

6. The preparation method according to claim 2, characterized in that, The polymer is selected from one or more of polyvinylidene fluoride, polyether sulfone resin, polystyrene, polyimide, polyacrylonitrile, polydimethylsiloxane, polysulfone, cellulose acetate, polycarbonate, polyvinyl acetate, polyether ether ketone, polyethyleneimine, and polyphenyl ether; and the organic solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, tetrahydrofuran, toluene, acetone, cyclohexane, ethanol, acetic acid, and ethyl acetate.

7. The preparation method according to claim 1, characterized in that, In the S4 step, the punching is plasma etching, the etching gas source is one or more of argon or oxygen, the etching pressure is 0.1-250Pa, the power is 1-100w, and the processing time is 1-300s.

8. The production method according to claim 7, characterized by, In the S4 step, the etching pressure is 5-50 Pa, the power is 30-60 W, and the processing time is 10-100 s.

9. A graphene separation membrane, characterized by, Prepared by the preparation method of any one of claims 1-8; the graphene separation membrane comprises the support layer and a separation layer, and the separation layer is a double-layer graphene film with nanopores.

10. The graphene separation membrane of claim 9, wherein, The support layer has a surface aperture range distribution of 0.1-5 μm, a through-hole aperture range distribution of 0.1-1 μm, and a porosity of 70-90%; the separation layer has a pore density of 1×10 11 -1×10 12 cm -1 .

11. A TOC analyzer characterized by comprising: The graphene separation membrane of claim 9 or 10.

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