Ultrathin swelling-resistant GO (graphene oxide) cross-linked membrane as well as preparation method and application thereof

Abstract

The invention provides an ultrathin swelling-resistant GO cross-linked membrane as well as a preparation method and application thereof, and belongs to the technical field of nanofiltration separation membrane technology separation. The composite membrane comprises a cross-linked GO separation layer and a supporting layer, a m-xylylenediamine MXDA cross-linked GO layer is used as the separation layer, and a hydrolyzed polyacrylonitrile hPAN polymer membrane is used as the supporting layer; wherein the GO layer and the hPAN polymer film are covalently bonded through MXDA to form a cross-linked network. The preparation method comprises the following steps: firstly, respectively preparing graphene oxide GO; secondly, hydrolyzing a polyacrylonitrile (hPAN) matrix membrane; and finally, constructing a dual cross-linked network system through heat treatment, so that covalent cross-linked bonds are formed between GO nanosheet layers and between GO-hPAN base membranes, and the GO cross-linked membrane is prepared. The density of carboxylic acid groups on the surface of the hPAN membrane can be dynamically optimized by regulating and controlling the type of the basic catalyst, the concentration of the solution, the hydrolysis temperature and the hydrolysis time, a high-efficiency mass transfer channel is created for the composite membrane through a two-dimensional covalent cross-linked structure, and the composite membrane is endowed with excellent dye selective separation performance and anti-swelling stability.

Description

Technical Field

[0001] The invention belongs to the technical field of nanofiltration separation membrane separation, and relates to an ultra-thin swelling-resistant GO cross-linked membrane, a preparation method and application thereof. The obtained GO cross-linked membrane can be used for, but is not limited to, a nanofiltration separation system. Background Art

[0002] With the rapid development of the modern industrial system, the textile printing and dyeing industry, as one of the pillar industries of the national economy, has become a key factor threatening the safety of the water environment due to the organic pollutants produced in its production process. Especially in the use of dye auxiliaries, about 10-15% of chemical substances eventually enter the water environment, forming a complex pollutant system with biological toxicity. It is urgent to develop a deep treatment technology that is both economical and ecologically safe. Membrane separation technology, with its unique selective permeability mechanism (molecular weight cutoff 500-5000Da) and modular design advantages, shows significant technical and economic characteristics. The key issue in achieving efficient nanofiltration separation through membrane separation is to prepare membrane materials with both high water flux and high selectivity.

[0003] Graphene oxide (GO) membranes have excellent hydrophilicity and molecular size screening capabilities due to their unique layered nanochannels and abundant oxygen-containing functional groups, and have broad application prospects in the field of nanofiltration separation. GO nanosheets are easily dispersed evenly in the aqueous phase. By assembling into a dense layered structure, their two-dimensional nanochannels can achieve the synergy of high water flux and high retention rate through size screening effect, which provides an ideal choice for the efficient separation of small molecule pollutants such as dyes and ions. However, the structural stability of GO membranes in aqueous environments seriously restricts their practical application. The strong hydrogen bonding between oxygen-containing groups and water molecules leads to interlayer swelling, destroying the uniformity of nanochannels and reducing separation. In addition, the interaction between the GO layer and the organic support membrane (such as polysulfone, polyacrylonitrile, etc.) is weak, and long-term immersion in water is prone to membrane peeling or dissolution, resulting in failure of the composite membrane. Although existing studies have attempted to enhance the stability of GO membranes through cross-linking agents, traditional cross-linking strategies focus on the covalent connection between GO sheets, while ignoring the enhancement of the interfacial bonding between GO and the supporting membrane. In addition, the cross-linking process may block nanochannels or sacrifice membrane flux, making it difficult to strike a balance between stability and separation performance. Therefore, it is still a challenge to prepare swelling-resistant GO cross-linked membranes to achieve a breakthrough in high-performance nanofiltration separation. Summary of the invention

[0004] The present invention aims to provide an ultra-thin swelling-resistant GO cross-linked membrane material to solve the problem that it is difficult to prepare a high-performance swelling-resistant GO composite structure in the prior art. At the same time, an ultra-thin swelling-resistant GO cross-linked membrane, a preparation method and its application are provided. The preparation process is simple to operate, and a GO nanofiltration cross-linked composite membrane with high swelling resistance and nanofiltration separation performance can be obtained.

[0005] To achieve the above-mentioned invention objectives, the technical solution of the present invention is as follows:

[0006] A preparation method of an ultra-thin swelling-resistant GO cross-linked membrane material, comprising the following steps:

[0007] The first step: Prepare graphene oxide GO;

[0008] Step 1.1) Slowly add flaky graphite and sodium nitrate into concentrated sulfuric acid, continuously stir in an ice bath environment for 0.5 - 3 h, then dropwise inject potassium permanganate and maintain stirring for 0.5 - 3 h. Heat up to the constant temperature reaction in the range of 35 - 70 °C for 0.5 - 2 h. In this stage, the super strong acid penetrates into the graphite interlayer structure to form a graphite - super strong acid intercalation complex, promoting a significant expansion of the layer spacing. Under the acidic catalytic action, the strong oxidant gradually advances the oxidation process from the edge to the core of the sheet, and oxygen-containing functional groups such as hydroxyl, carboxyl, epoxy, and carbonyl are successfully grafted on the surface and inside of the graphite.

[0009] Step 1.2) First inject deionized water into the reaction system, and adjust the temperature to maintain the reaction in the range of 85 - 98 °C for 0.5 - 1.5 h. During this process, OH - and HSO4 - have an ion exchange effect, and part of HSO4 - is replaced and combines with carbon atoms while further expanding the sheet gap. Subsequently, add deionized water for the second time and continue the reaction for 0.5 - 3 h, and then let the solution stand and cool to room temperature.

[0010] Step 1.3) Introduce hydrogen peroxide solution into the system to eliminate the residual oxidant, and wash and centrifuge several times until the supernatant is neutral. After ultrasonic uniform dispersion and vacuum drying treatment, graphene oxide GO is finally obtained.

[0011] In the said step 1.1), for every 30 mL of concentrated sulfuric acid, add: 1.0 - 3.0 g of flaky graphite, 0.5 - 1.5 g of sodium nitrate, 3.0 - 6.0 g of potassium permanganate.

[0012] In the said step 1.2), for every 30 mL of concentrated sulfuric acid, correspond to: add 50 - 100 mL of water for the first time and 50 - 100 mL of supplementary water for the second time.

[0013] In the said step 1.3), for every 30 mL of concentrated sulfuric acid, add 10 - 50 mL of hydrogen peroxide solution, and the mass concentration of the hydrogen peroxide solution is 30%.

[0014] The second step: Preparation of the hPAN support layer;

[0015] Step 2.1) Mix N,N-dimethylacetamide, polyacrylonitrile (PAN) powder, and lithium chloride, and stir at room temperature for 48 h to form a uniform casting solution;

[0016] Step 2.2) After the casting solution is left standing overnight for degassing treatment, a PAN wet film is prepared by the phase inversion method. The obtained wet film is immersed in deionized water for 24 h to obtain a PAN polymer film.

[0017] Step 2.3) The PAN wet film is placed in an aqueous solution of an alkaline catalyst with a concentration of 0.1 - 5.0 mol / L and left in a constant temperature environment of 25 - 85 °C for 0.5 - 24 h for hydrolysis reaction. After the reaction ends, it is thoroughly washed with deionized water until neutral, and the obtained hPAN film is stored in deionized water for use.

[0018] In the said step 2.1), 0 g of N,N-dimethylacetamide and 9 g of polyacrylonitrile (PAN) powder are added corresponding to 1 g of lithium chloride.

[0019] In the said step 2.2), the thickness of the PAN film is 50 - 500 μm.

[0020] In the said step 2.3), the alkaline catalyst is NaOH, KOH, or Na3PO4.

[0021] The reaction mechanism of this step is as follows: During the treatment with the aqueous solution of the alkaline catalyst, the cyano functional groups on the surface of the PAN film undergo a nucleophilic substitution-hydrolysis mechanism. The hydroxide ions in the alkaline medium act as strong nucleophiles to selectively attack the α-carbon atom of the cyano group, and the first-stage nucleophilic substitution reaction is completed through the SN2 mechanism to generate an intermediate product containing an amide group. Under continuous heating and catalysis by OH - The amide group is further hydrolyzed, the C-N bond is broken and a hydroxyl group is introduced, and finally a carboxylic acid group is generated by oxidation. This process forms a gradient distribution of carboxylic acid functional groups on the surface of the PAN film. The negative charges generated by their ionization not only enhance the hydrophilicity of the film but also provide covalent cross-linking sites for the amino groups of subsequent MXDA, and the chemical bonding between the GO layer and the hPAN substrate is achieved through an amidation condensation reaction to construct a stable heterogeneous interface.

[0022] The third step: Preparation of the GO cross-linked film;

[0023] Step 3.1) The GO obtained in the first step is added to deionized water, and a uniform GO dispersion is obtained through stirring and ultrasonic treatment, and a dispersion with a concentration of 0.0005 - 2.0 g / L is prepared; MXDA is added to deionized water, and a uniform MXDA dispersion is obtained through stirring and ultrasonic treatment, and a dispersion with a concentration of 0.0005 - 0.02 g / L is prepared; 50 mL of the GO dispersion and 50 mL of the MXDA dispersion are mixed uniformly to form a GO-MXDA mixed dispersion.

[0024] Step 3.2) The obtained GO-MXDA mixed dispersion is subjected to pressure filtration to uniformly stack GO on the surface of the hPAN matrix membrane at a pressure of 1-10 bar for 0.5-2 h to obtain a wet GO composite membrane; the wet GO composite membrane is placed in an electrothermal constant temperature drying oven at a temperature of 25-85 °C for 0.5-10 h to obtain a GO crosslinked membrane.

[0025] In the said step 3.1), the concentration ratio of GO to MXDA is 1:1-1:100.

[0026] In the said step 3.2), the deposition amount of GO is 10-1000 mg / m 2 , and the interlayer spacing of GO sheets is 0.3-2 nm.

[0027] The reaction mechanism of this step is as follows: when the GO suspension is deposited on the surface of the substrate membrane under the action of pressure driving, the solvent aqueous phase permeates through the substrate membrane while the MXDA and GO components in the separation layer are intercepted. By increasing the temperature of the oxidation reaction and prolonging the treatment time, the oxidation degree of GO sheets can be improved, and the content of oxygen-containing groups such as carboxyl groups on its surface increases significantly. The resulting electrostatic repulsion effect will expand the distance between nanosheets. In addition, applying a greater forming pressure and prolonging the pressurization duration can promote the formation of a denser stacking structure between GO sheets, thereby reducing the interlayer voids. Therefore, by adjusting the oxidation conditions for GO preparation and the pressurization parameters in the membrane preparation process, precise control of its interlayer spacing can be achieved.

[0028] Under a thermal environment, the amino group of MXDA undergoes ring-opening reaction or condensation reaction with oxygen-containing functional groups such as epoxy groups, carboxyl groups, and hydroxyl groups on the surface of GO, thereby forming covalent cross-linking bonds between GO sheets. At the same time, as a bifunctional cross-linking agent, the amino groups of MXDA are respectively condensed with the oxygen-containing groups of GO and the carboxylic acid groups of hPAN to construct a stable heterogeneous interface between the GO layer and the substrate. In addition, at the interface between the GO layer and hPAN, the two amino groups of MXDA respectively undergo condensation reactions with the oxygen-containing functional groups of GO sheets and the carboxylic acid groups on the surface of the hPAN membrane, forming covalent cross-linking bonds between the two. Therefore, a dual cross-linking network system is constructed between GO sheets and between GO and the hPAN matrix membrane.

[0029] An ultrathin swelling-resistant GO crosslinked membrane, comprising a crosslinked GO separation layer and a support layer, with the m-xylylenediamine (MXDA) crosslinked GO layer as the separation layer and the hydrolyzed polyacrylonitrile (hPAN) polymer membrane as the support layer; the GO layer is deposited on the substrate membrane, and a crosslinked network is formed by covalent bonding of MXDA between the GO layer and the hPAN membrane. In the ultrathin swelling-resistant GO crosslinked membrane, an adjacent GO sheet and GO-hPAN crosslinked network structure are formed through MXDA, and the interlayer gap of GO serves as a two-dimensional dye retention channel, with stable membrane performance and high nanofiltration separation performance.

[0030] An ultrathin swelling-resistant GO cross-linked membrane material, used in but not limited to nanofiltration separation systems.

[0031] Advantages of the present invention:

[0032] (1) MXDA molecules bridge adjacent GO sheets through covalent bonds, inhibit the interlayer swelling caused by the intrusion of water molecules, and maintain the size sieving stability of nanochannels.

[0033] (2) Chemically cross-linked anchor points are formed between the carboxyl-functionalized PAN substrate and the GO layer, enhancing the interfacial bonding strength and avoiding the peeling of the GO selective layer during long-term operation. At the same time, the negative charges generated by the ionization of carboxylic acid groups on the hPAN membrane not only improve the membrane hydrophilicity but also provide reaction sites for subsequent covalent cross-linking with GO.

[0034] (3) By regulating the hydrolysis conditions, the carboxyl density is precisely adjusted, and the matching of the cross-linking network density and the water transport path of nanochannels is optimized, maintaining a high permeation flux while enhancing the swelling resistance. Description of the Drawings

[0035] Figure 1 It is the scanning electron microscope image of Example 2 and Comparative Example 1.

[0036] Figure 2 It is the nanofiltration separation performance diagram of the examples and comparative examples. Detailed Embodiments

[0037] Example 1: The method of the present invention includes the following steps:

[0038] The first step: Preparation of graphene oxide GO

[0039] 1.1) Slowly add flaky graphite and sodium nitrate to concentrated sulfuric acid, continuously stir in an ice bath environment for 0.5 h, then dropwise inject potassium permanganate and maintain stirring for 0.5 h. Heat up to the 35 °C range and carry out a constant temperature reaction for 0.5 h.

[0040] 1.2) First inject deionized water into the reaction system, adjust the temperature to the 85 °C range and maintain the reaction for 0.5 h. Then add deionized water for the second time and continue the reaction for 0.5 h, and then let the solution stand and cool to room temperature.

[0041] 1.3) Introduce 30% hydrogen peroxide solution into the system to eliminate the residual oxidant, and carry out multiple washings and centrifugal separations until the upper layer liquid is neutral. After ultrasonic uniform dispersion and vacuum drying treatment, finally obtain GO solid.

[0042] In the step 1.1), for every 30 mL of concentrated sulfuric acid, the following are added: 3.0 g of flaky graphite, 0.5 g of sodium nitrate, and 3.0 g of potassium permanganate.

[0043] In step 1.2), for every 30 mL of concentrated sulfuric acid, the first water addition is 50 mL and the second water replenishment is 50 mL.

[0044] In step 1.3), for every 30 mL of concentrated sulfuric acid, 10 mL of hydrogen peroxide solution is added.

[0045] Second step: Preparation of hPAN support layer

[0046] 2.1) Add 40 g of N,N-dimethylacetamide, 9 g of PAN powder and 1 g of lithium chloride into a 100 mL sample bottle in sequence, and stir at room temperature for 48 h to form a uniform casting solution.

[0047] 2.2) After standing the casting solution overnight for degassing treatment, prepare a PAN wet film by the phase inversion method. The obtained wet film is soaked in deionized water for 24 h to obtain a PAN polymer film.

[0048] 2.3) Place the PAN wet film in an aqueous solution of alkaline catalyst with a concentration of 0.1 mol / L, and place it in a constant temperature environment of 25 °C for 0.5 h for hydrolysis reaction. After the reaction, wash it thoroughly with deionized water until neutral, and store the obtained hPAN film in deionized water for use.

[0049] In step 2.2), the thickness of the PAN film is 50 μm.

[0050] In step 2.3), the alkaline catalyst is NaOH.

[0051] Third step: Preparation of GO crosslinked film

[0052] 3.1) Add the GO obtained in the first step into deionized water, and obtain a uniform GO dispersion through stirring and ultrasonic treatment, and configure it into a dispersion with a concentration of 0.0005 g / L; add MXDA into deionized water, and obtain a uniform MXDA dispersion through stirring and ultrasonic treatment, and configure it into a dispersion with a concentration of 0.0005 g / L; mix 50 mL of GO dispersion and 50 mL of MXDA dispersion evenly to form a GO-MXDA mixed dispersion.

[0053] 3.2) Make the obtained GO-MXDA mixed dispersion stack uniformly on the surface of the hPAN substrate film by pressure filtration, with a pressure of 1 bar and keep it for 0.5 h to obtain a wet GO composite film; place the wet GO composite film in an electrothermal constant temperature drying oven at a temperature of 25 °C for 0.5 h to obtain a GO crosslinked film.

[0054] In step 3.1), the concentration ratio of GO to MXDA is 1:1.

[0055] In step 3.2), the deposition amount of GO is 10 mg / m2 The interlayer spacing of the GO sheets is 2 nm.

[0056] Example 2: The method of the present invention comprises the following steps:

[0057] First step: Preparation of graphene oxide GO

[0058] 1.1) Flaky graphite and sodium nitrate were slowly added to concentrated sulfuric acid, and continuously stirred in an ice bath environment for 1 h. Subsequently, potassium permanganate was dropwise injected and stirring was maintained for 1 h. The temperature was raised to 50 °C and the reaction was carried out at a constant temperature for 1 h.

[0059] 1.2) Deionized water was first injected into the reaction system, and the temperature was adjusted to the range of 92 °C and maintained for 1 h of reaction. Subsequently, deionized water was added for the second time and the reaction continued for 1 h. Then the solution was allowed to stand and cool to room temperature.

[0060] 1.3) 30% hydrogen peroxide solution was introduced into the system to eliminate the residual oxidant. After multiple washings and centrifugal separations until the supernatant was neutral. After ultrasonic dispersion and vacuum drying, GO solid was finally obtained.

[0061] In the step 1.1), for every 30 mL of concentrated sulfuric acid, the following were added: 2.0 g of flaky graphite, 1 g of sodium nitrate, and 4.5 g of potassium permanganate.

[0062] In the step 1.2), for every 30 mL of concentrated sulfuric acid, the following were added: 75 mL of water was added for the first time, and 75 mL of water was added for the second time.

[0063] In the step 1.3), for every 30 mL of concentrated sulfuric acid, 30 mL of hydrogen peroxide solution was added.

[0064] Second step: Preparation of the hPAN support layer

[0065] 2.1) 40 g of N,N-dimethylacetamide, 9 g of PAN powder and 1 g of lithium chloride were successively added to a 100 mL sample bottle, and stirred at room temperature for 48 h to form a uniform casting solution;

[0066] 2.2) After the casting solution was allowed to stand overnight for degassing treatment, a PAN wet film was prepared by the phase inversion method. The obtained wet film was soaked in deionized water for 24 h to obtain a PAN polymer film;

[0067] 2.3) The PAN wet film was placed in an aqueous solution of an alkaline catalyst with a concentration of 1 mol / L, and placed in a constant temperature environment of 55 °C for 10 h for hydrolysis reaction. After the reaction, it was washed thoroughly with deionized water until neutral, and the obtained hPAN film was stored in deionized water for later use.

[0068] In the step 2.2), the thickness of the PAN film was 250 μm.

[0069] In step 2.3), the alkaline catalyst is KOH.

[0070] Step 3: Preparation of GO crosslinked membrane

[0071] 3.1) Add the GO obtained in the first step to deionized water, and obtain a uniform GO dispersion through stirring and ultrasonic treatment, and prepare a dispersion with a concentration of 0.1 g / L; add MXDA to deionized water, and obtain a uniform MXDA dispersion through stirring and ultrasonic treatment, and prepare a dispersion with a concentration of 0.01 g / L; mix 50 mL of the GO dispersion and 50 mL of the MXDA dispersion evenly to form a GO-MXDA mixed dispersion.

[0072] 3.2) Make the obtained GO-MXDA mixed dispersion stack uniformly on the surface of the hPAN matrix membrane by pressure filtration, with a pressure of 5 bar and keep it for 1 h to obtain a wet GO composite membrane; place the wet GO composite membrane in an electrothermal constant temperature drying oven at a temperature of 55 °C for 5 h to obtain the GO crosslinked membrane.

[0073] In step 3.1), the concentration ratio of GO to MXDA is 1:10.

[0074] In step 3.2), the deposition amount of GO is 50 mg / m 2 , and the layer spacing of GO sheets is 1 nm.

[0075] Example 3: The method of the present invention includes the following steps:

[0076] Step 1: Preparation of graphene oxide GO

[0077] 1.1) Slowly add flaky graphite and sodium nitrate to concentrated sulfuric acid, continuously stir in an ice bath environment for 3 h, then dropwise inject potassium permanganate and maintain stirring for 3 h. Raise the temperature to 70 °C and keep the reaction at a constant temperature for 2 h.

[0078] 1.2) First inject deionized water into the reaction system, adjust the temperature to the range of 98 °C and maintain the reaction for 1.5 h. Then add deionized water for the second time and continue the reaction for 3 h, and then let the solution stand and cool to room temperature.

[0079] 1.3) Introduce 30% hydrogen peroxide solution into the system to eliminate the residual oxidant, and wash and centrifuge several times until the upper layer liquid is neutral. After ultrasonic uniform dispersion and vacuum drying treatment, finally obtain GO solid.

[0080] In step 1.1), for every 30 mL of concentrated sulfuric acid, add: 1.0 g of flaky graphite, 1.5 g of sodium nitrate, 6.0 g of potassium permanganate.

[0081] In step 1.2), for every 30 mL of concentrated sulfuric acid, the first addition of water is 100 mL and the second supplementary water addition is 100 mL.

[0082] In step 1.3), for every 30 mL of concentrated sulfuric acid, 50 mL of hydrogen peroxide solution is added.

[0083] Second step: Preparation of the hPAN support layer

[0084] 2.1) Add 40 g of N,N-dimethylacetamide, 9 g of PAN powder, and 1 g of lithium chloride into a 100 mL sample bottle in sequence, and stir at room temperature for 48 h to form a uniform casting solution.

[0085] 2.2) After standing the casting solution overnight for degassing treatment, use the phase inversion method to prepare a PAN wet film. The obtained wet film is soaked in deionized water for 24 h to obtain a PAN polymer film.

[0086] 2.3) Place the PAN wet film in an aqueous solution of an alkaline catalyst with a concentration of 5.0 mol / L, and place it in a constant temperature environment of 85 °C for 24 h for hydrolysis reaction. After the reaction, wash it thoroughly with deionized water until neutral, and store the obtained hPAN film in deionized water for use.

[0087] In step 2.2), the thickness of the PAN film is 500 μm.

[0088] In step 2.3), the alkaline catalyst is Na3PO4.

[0089] Third step: Preparation of the GO crosslinked film

[0090] 3.1) Add the GO obtained in the first step into deionized water, and obtain a uniform GO dispersion through stirring and ultrasonic treatment, and configure it into a dispersion with a concentration of 2.0 g / L; add MXDA into deionized water, and obtain a uniform MXDA dispersion through stirring and ultrasonic treatment, and configure it into a dispersion with a concentration of 0.02 g / L; mix 50 mL of the GO dispersion and 50 mL of the MXDA dispersion evenly to form a GO-MXDA mixed dispersion.

[0091] 3.2) Make the obtained GO-MXDA mixed dispersion stack GO evenly on the surface of the hPAN matrix film through pressure filtration, with a pressure of 10 bar and keep it for 2 h to obtain a wet GO composite film; place the wet GO composite film in an electrothermal constant temperature drying oven at a temperature of 85 °C for 10 h to obtain the GO crosslinked film.

[0092] In step 3.1), the concentration ratio of GO to MXDA is 1:100.

[0093] In step 3.2), the deposition amount of GO is 1000 mg / m 2, the interlayer spacing of the GO sheets is 0.3 nm.

[0094] Comparative Example 1: The method of the present invention comprises the following steps:

[0095] First step: Preparation of GO

[0096] 1.1) Scaly graphite and sodium nitrate were slowly added to concentrated sulfuric acid, and continuously stirred in an ice bath environment for 3 h. Subsequently, potassium permanganate was injected dropwise and stirring was maintained for 3 h. The temperature was raised to 70 °C for constant temperature reaction for 2 h.

[0097] 1.2) Deionized water was first injected into the reaction system, and the temperature was adjusted to 98 °C for 1.5 h of reaction. Subsequently, deionized water was added for the second time and the reaction continued for 3 h. Then the solution was allowed to stand and cool to room temperature.

[0098] 1.3) 30% hydrogen peroxide solution was introduced into the system to eliminate the residual oxidant. After multiple washings and centrifugal separations until the upper layer liquid was neutral. After ultrasonic uniform dispersion and vacuum drying treatment, GO solid was finally obtained.

[0099] In the step 1.1), for every 30 mL of concentrated sulfuric acid, the following were added: 1.0 g of scaly graphite, 1.5 g of sodium nitrate, and 6.0 g of potassium permanganate.

[0100] In the step 1.2), for every 30 mL of concentrated sulfuric acid, the following corresponded: 100 mL of water was added for the first time, and 100 mL of water was added for the second time.

[0101] In the step 1.3), for every 30 mL of concentrated sulfuric acid, 50 mL of hydrogen peroxide solution was added.

[0102] Second step: Preparation of the PAN support layer

[0103] 2.1) 40 g of N,N-dimethylacetamide, 9 g of PAN powder and 1 g of lithium chloride were successively added to a 100 mL sample bottle, and stirred at room temperature for 48 h to form a uniform casting solution;

[0104] 2.2) After the casting solution was allowed to stand overnight for degassing treatment, a PAN wet film was prepared by the phase inversion method. The obtained wet film was soaked in deionized water for 24 h to obtain a PAN polymer film;

[0105] Third step: Preparation of the GO composite film

[0106] 3.1) The GO obtained in the first step was added to deionized water, and a uniform GO dispersion was obtained through stirring and ultrasonic treatment, and a dispersion of 2.0 g / L was prepared;

[0107] 3.2) The obtained GO dispersion is uniformly stacked on the surface of the PAN matrix membrane by pressure filtration at a pressure of 10 bar for 2 h to obtain a wet GO composite membrane; the wet GO composite membrane is placed in an electrothermal constant temperature drying oven at 85 °C for 10 h to obtain the GO composite membrane.

[0108] In the step 3.1) described above, the concentration ratio of GO to MXDA is 1:100.

[0109] In the step 3.2) described above, the deposition amount of GO is 1000 mg / m 2 , and the interlayer spacing of GO sheets is 0.3 nm.

[0110] After soaking the GO crosslinked membrane prepared in the above example in an environment with pH = 7 for 30 days, the nanofiltration separation performance test of methylene blue is carried out, and the results are shown in the following table:

[0111] Table 1. Nanofiltration separation performance of examples and comparative examples

[0112] Example <![CDATA[Water flux (Lh -1 m -2 bar -1 )]]> Retention / % Example 1 3.15 90.0 Example 2 1.24 94.6 Example 3 1.12 99.3 Comparative Example 1 10.13 58.1

[0113] It can be seen from the data that the GO crosslinked membrane obtained by this method exhibits good nanofiltration separation performance. Comparing Examples 1-3 with crosslinked structures and Comparative Example 1 without crosslinked structures, it can be seen that the water fluxes in Examples 1-3 are all at 1.1 Lh -1 m -2 bar -1 above, the retention of methylene blue is all above 90.0%, and the retention of methylene blue increases by nearly 55%-71% compared with Comparative Example 1. By constructing a dual crosslinked network system, the covalent crosslinking between GO nanosheets and the interfacial chemical bonding between GO-hPAN matrix membranes produce a synergistic effect, significantly improving the structural stability of the composite membrane. Using covalent crosslinking to precisely lock the interlayer spacing of GO, and at the same time enhancing the material binding strength through interfacial chemical bonding, the composite membrane exhibits excellent anti-swelling characteristics in the aqueous environment. The interlayer nanochannel size precisely regulated by the crosslinked network not only endows the material with high-precision nanofiltration separation performance, but also ensures its structural stability during long-term operation.

[0114] The above embodiments only represent the implementation manners of the present invention, but should not be construed as limiting the scope of the patent of the present invention. It should be noted that for those skilled in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A preparation method of an ultra-thin swelling-resistant GO cross-linked membrane, characterized in that, It includes the following steps: The first step: Prepare graphene oxide GO; Using flaky graphite, sodium nitrate, concentrated sulfuric acid, potassium permanganate, and deionized water as raw materials, prepare graphene oxide GO; The second step: Prepare the hPAN support layer; Step 2.1) Mix N,N-dimethylacetamide, polyacrylonitrile PAN powder, and lithium chloride, and stir at room temperature to form a uniform casting solution; Step 2.2) After standing the casting solution overnight for degassing treatment, use the phase inversion method to prepare a PAN wet film, and soak the obtained wet film in deionized water to obtain a PAN polymer film; Step 2.3) Place the PAN wet film in an aqueous solution of an alkaline catalyst, and place it in a constant temperature environment of 25-85 °C for 0.5-24 h for hydrolysis reaction. After the reaction, wash it thoroughly with deionized water until neutral to obtain an hPAN film; The third step: Prepare the GO cross-linked film; Step 3.1) Add the GO obtained in the first step to deionized water, stir and ultrasonicate to obtain a uniform GO dispersion, and prepare a dispersion with a concentration of 0.0005-2.0 g / L; Add MXDA to deionized water, stir and ultrasonicate to obtain a uniform MXDA dispersion, and prepare a dispersion with a concentration of 0.0005-0.02 g / L; Mix the dispersion and the MXDA dispersion evenly to form a GO-MXDA mixed dispersion; Step 3.2) Use the obtained GO-MXDA mixed dispersion to uniformly stack GO on the surface of the hPAN matrix film by pressure filtration, with a pressure of 1-10 bar and keep it for 0.5-2 h to obtain a wet GO composite film; Dry the wet GO composite film to obtain a GO cross-linked film.

2. The preparation method of an ultra-thin swelling-resistant GO crosslinked membrane according to claim 1, wherein The specific content of the first step is as follows: Step 1.1) Slowly add flaky graphite and sodium nitrate to concentrated sulfuric acid, continuously stir in an ice bath environment for 0.5-3 h, then dropwise inject potassium permanganate and maintain stirring for 0.5-3 h; Heat up to a constant temperature reaction in the range of 35-70 °C for 0.5-2 h. In this stage, the strong acid penetrates into the graphite interlayer structure to form a graphite-strong acid intercalation complex, which promotes a significant expansion of the layer spacing; Step 1.2) First inject deionized water into the reaction system, adjust the temperature to the range of 85-98 °C and maintain the reaction for 0.5-1.5 h; Then add deionized water for the second time and continue the reaction for 0.5-3 h, and let the solution stand and cool to room temperature; Step 1.3) Introduce hydrogen peroxide solution into the system to eliminate the residual oxidant, and wash and centrifuge several times until the upper layer liquid is neutral; After ultrasonic uniform dispersion and vacuum drying treatment, obtain graphene oxide GO.

3. The preparation method of an ultra-thin swelling-resistant GO crosslinked membrane according to claim 2, characterized in that, In the first step: In the step 1.1), for every 30 mL of concentrated sulfuric acid, add: 1.0-3.0 g of flaky graphite, 0.5-1.5 g of sodium nitrate, 3.0-6.0 g of potassium permanganate; In the step 1.2), for every 30 mL of concentrated sulfuric acid, add: 50-100 mL of water for the first time and 50-100 mL of water for the second time; In the step 1.3), for every 30 mL of concentrated sulfuric acid, add 10-50 mL of hydrogen peroxide solution, and the mass concentration of the hydrogen peroxide solution is 30%.

4. The preparation method of an ultra-thin swelling-resistant GO crosslinked membrane according to claim 1, characterized in that, In the step 2.1), 0 g of N,N-dimethylacetamide and 9 g of polyacrylonitrile (PAN) powder are added corresponding to 1 g of lithium chloride; the stirring time at room temperature is 48 h.

5. The preparation method of an ultra-thin swelling-resistant GO crosslinked membrane according to claim 1, characterized in that, In the step 2.1) and the step 2.2), the thickness of the PAN membrane is 50 - 500 μm; the immersion time of the wet membrane in deionized water is 24 h.

6. The preparation method of an ultra-thin swelling-resistant GO crosslinked membrane according to claim 1, characterized in that, In the step 2.1) and the step 2.3), the alkaline catalyst is NaOH, KOH, or Na3PO4; the concentration of the aqueous solution of the alkaline catalyst is 0.1 - 5.0 mol / L.

7. The preparation method of an ultra-thin swelling-resistant GO crosslinked membrane according to claim 1, characterized in that, In the step 2.1) and the step 3.1), in the GO-MXDA mixed dispersion liquid, the concentration ratio of GO to MXDA is 1:1 - 1:

100.

8. The preparation method of an ultra-thin swelling-resistant GO crosslinked membrane according to claim 1, characterized in that, In the described step 2.1) and step 3.2), the deposition amount of GO is 10 - 1000 mg / m 2 , the interlayer spacing of GO sheets is 0.3 - 2 nm; the drying temperature is 25 - 85 °C, and the time is 0.5 - 10 h.

9. An ultra-thin swelling-resistant GO crosslinked membrane, characterized in that, The ultra-thin swelling-resistant GO crosslinked membrane is prepared by using the preparation method according to any one of claims 1 - 8, and it includes a crosslinked GO separation layer and a support layer. The m-xylylenediamine MXDA crosslinked GO layer serves as the separation layer, and the hydrolyzed polyacrylonitrile hPAN polymer membrane serves as the support layer; wherein, a crosslinked network is formed by covalent bonding between the GO layer and the hPAN polymer membrane through MXDA.

10. Use of the ultra-thin swelling-resistant GO crosslinked membrane according to claim 9, characterized in that, The ultra-thin swelling-resistant GO crosslinked membrane is applied to the nanofiltration separation system.

Images