Zwitterionic cross-linked graphene oxide nanofiltration membrane and preparation method thereof

Abstract

The invention discloses a zwitter-ion cross-linked graphene oxide nanofiltration membrane and a preparation method thereof. The nanofiltration membrane is prepared by synthesizing a zwitter-ion cross-linking agent, mixing the zwitter-ion cross-linking agent and a graphene oxide nanosheet dispersion liquid, and carrying out ultrasonic treatment, suction filtration and thermal cross-linking. The invention also discloses a preparation method and application of the nanofiltration membrane. The preparation method comprises the following steps: taking a macroporous polymer membrane as a supporting layer, loading a zwitterionic cross-linking agent and graphene oxide on the supporting layer in a vacuum suction filtration manner, and carrying out thermal cross-linking to obtain the zwitterionic cross-linked graphene oxide nanofiltration membrane. The method is simple to operate and ingenious in design, and the obtained membrane has excellent separation performance. Through crosslinking of the zwitterionic cross-linking agent and the graphene oxide nanosheets, the interlayer spacing of the nanofiltration membrane is stabilized, and quaternary amine groups are introduced between the layers, so that the selectivity to monovalent / divalent anions is improved. Due to the hydrophilicity of zwitterions, the permeability of the cross-linked graphene oxide nanofiltration membrane is improved.

Description

Technical Field

[0001] The invention relates to a zwitterionic cross-linked graphene oxide nanofiltration membrane and a preparation method thereof, belonging to the technical field of cross-linked graphene oxide nanofiltration membrane materials and preparation thereof. Background Art

[0002] Industries such as petroleum, pharmaceutical and paper mills often produce large amounts of high-salinity wastewater containing sulfate and chloride. - and SO4 2- The separation of water is crucial. Among many water treatment technologies, membrane separation technology has attracted much attention due to its high efficiency, low energy consumption and wide application range. Two-dimensional materials, such as graphene oxide, have tunable nanochannels and are becoming ideal materials for the development of selective separation membranes. However, due to the swelling and expansion of the interlayer spacing of graphene oxide membranes in aqueous solutions, the screening size is not accurate, and because of Cl - and SO4 2- The similar ion sizes and properties further increase the challenge of precise selective separation.

[0003] In order to achieve high selectivity of graphene-based membranes for monovalent / divalent anions, many studies in recent years have focused on adjusting the interlayer spacing or increasing electrostatic repulsion, but this method has not achieved the expected effect in improving the selectivity of graphene oxide membranes for anions. Therefore, it is of great significance to develop a graphene-based membrane material that has both structural stability and high anion transmission rate and separation efficiency. Summary of the invention

[0004] To solve the above problems, the present invention aims to provide a zwitterionic cross-linked graphene oxide nanofiltration membrane to solve the problems of easy swelling of existing graphene oxide-based membrane materials and low selectivity of nanofiltration membranes for monovalent / divalent anions.

[0005] In view of the above purpose, the present invention first provides a method for preparing a zwitterionic cross-linked graphene oxide nanofiltration membrane, namely, firstly using 2,6-diaminopyridine and 3-bromopropionic acid as raw materials to synthesize a zwitterionic cross-linking agent, then mixing the zwitterionic cross-linking agent with a dispersion of graphene oxide nanosheets, and preparing a zwitterionic cross-linked graphene oxide nanofiltration membrane after ultrasonication, filtration and thermal cross-linking.

[0006] In one embodiment of the present invention, the method for preparing the zwitterionic cross-linked graphene oxide nanofiltration membrane comprises the following steps:

[0007] (1) Preparation of graphene oxide nanosheet dispersion: flake graphite, concentrated sulfuric acid and concentrated phosphoric acid were mixed and stirred, potassium permanganate was slowly added, and 0.8-3L of deionized water was added after reacting in a water bath at 50°C for 24 hours, and then 10-30mL of 30% hydrogen peroxide was added dropwise until the solution turned golden yellow. After standing overnight, the solution was centrifuged at 3000-3500 r / min for 15-30 minutes, and the total number of centrifugations was 15-20 times. The centrifuged product was washed with 1-5% dilute hydrochloric acid and deionized water to a pH of 5-6, and then dialyzed and dispersed with ultrapure water to obtain a graphene oxide nanosheet dispersion;

[0008] (2) Preparation of zwitterionic crosslinker dispersion: respectively mixing a solution of 2,6-diaminopyridine (BPA) and a solution of 3-bromopropionic acid (DAP), and continuously stirring the mixture in a constant temperature water bath to obtain a zwitterionic crosslinker dispersion;

[0009] (3) Preparation of zwitterionic cross-linked graphene oxide nanofiltration membrane: The graphene oxide nanosheet dispersion obtained in step (1) and the zwitterionic cross-linking agent dispersion obtained in step (2) are mixed and diluted, stirred and ultrasonically treated, and loaded on the surface of a macroporous polymer support membrane by vacuum filtration. After thermal cross-linking, a zwitterionic cross-linked graphene oxide nanofiltration membrane is obtained.

[0010] In one embodiment of the present invention, in step (1), the size of the flake graphite used is 100-400 mesh, the concentrations of concentrated sulfuric acid and concentrated phosphoric acid are 98% and 85% respectively, and the volume ratio of the two is 9:1.

[0011] In one embodiment of the present invention, in step (1), the mass volume ratio of the flake graphite to concentrated sulfuric acid is 1 g: (100-120) mL.

[0012] In one embodiment of the present invention, in step (1), the mass ratio of potassium permanganate to flake graphite is 6:1.

[0013] In one embodiment of the present invention, in step (1), the concentration of graphene oxide nanosheets in the graphene oxide nanosheet dispersion is 1 to 5 mg / mL.

[0014] In one embodiment of the present invention, in step (2), the concentration of the 2,6-diaminopyridine solution is 0.5-2 mmol / L, the concentration of the 3-bromopropionic acid solution is 0.5-2 mmol / L, and the molar ratio of 2,6-diaminopyridine to 3-bromopropionic acid is 1:1.

[0015] In one embodiment of the present invention, in step (2), the temperature of the constant temperature water bath is 30-50° C., the stirring rate is 300-500 r / min, and the time is 12-24 h.

[0016] In one embodiment of the present invention, in step (2), the concentration of the zwitterionic crosslinking agent in the zwitterionic crosslinking agent dispersion is 0.5 to 2 mmol / L.

[0017] In one embodiment of the present invention, the mass ratio of the solutes when the graphene oxide nanosheet dispersion and the zwitterionic crosslinker dispersion are mixed in step (3) is 1:0.05 to 1:2, preferably 1:0.05 to 1:1, and more preferably 1:0.05 to 1:0.8.

[0018] In one embodiment of the present invention, in step (3), the volume of the diluted mixed solution is 100-200 mL, the stirring rate is 300-500 r / min, the stirring time is 0.5-12 h; the ultrasonic power is 60-180 W, and the ultrasonic time is 0.2-0.5 h.

[0019] In one embodiment of the present invention, the polymer support membrane in step (3) includes any one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyethersulfone (PES), and mixed cellulose (MCEM) microporous filter membrane.

[0020] In one embodiment of the present invention, the polymer support membrane has a pore size of 0.22 to 0.44 μm and a diameter of 25 to 50 cm.

[0021] In one embodiment of the present invention, the heat cross-linking time in step (3) is 12 to 24 hours, and the heat cross-linking temperature is 45 to 80°C.

[0022] The invention also discloses a zwitterionic cross-linked graphene oxide nanofiltration membrane prepared according to the preparation method.

[0023] The present invention also provides a separation device comprising the zwitterionic cross-linked graphene oxide nanofiltration membrane.

[0024] The present invention also provides application of the zwitterionic cross-linked graphene oxide nanofiltration membrane in the field of water treatment.

[0025] Beneficial effects:

[0026] (1) The present invention cross-links graphene oxide nanosheets by a zwitterionic cross-linking agent, thereby stabilizing the interlayer spacing of the nanofiltration membrane and introducing quaternary amine groups between the layers, thereby improving the selectivity for monovalent / divalent anions.

[0027] (2) A zwitterionic crosslinker is prepared by first reacting 2,6-diaminopyridine with 3-bromopropionic acid, and then the zwitterionic crosslinker is used to crosslink graphene oxide nanosheets. The crosslinker with zwitterions improves the permeability of the crosslinked graphene oxide nanofiltration membrane due to the hydrophilicity of the zwitterions.

[0028] (3) The nanofiltration membrane prepared by the method of the present invention has excellent membrane permeability and its pure water flux can be as high as 2.5 L·m -2 ·h -1 bar -1 , for Cl - With SO4 2- The selectivity coefficient is as high as 5.4. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is the carbon NMR spectrum of the zwitterion in Example 1 ( 13 C NMR) and H NMR spectra ( 1 H NMR), where (a) is the carbon nuclear magnetic resonance spectrum and (b) is the hydrogen nuclear magnetic resonance spectrum.

[0030] Figure 2 It is a detailed spectrum of the N element of the X-ray photoelectron spectrum of 2,6-diaminopyridine and zwitterion in Example 1, wherein (a) corresponds to 2,6-diaminopyridine and (b) corresponds to the zwitterion.

[0031] Figure 3 This is the infrared spectrum of 2,6-diaminopyridine, 3-bromopropionic acid and zwitterion in Example 1.

[0032] Figure 4 This is a diagram showing the separation performance of the zwitterionic cross-linked graphene oxide nanofiltration membrane prepared in Examples 1 to 6. DETAILED DESCRIPTION

[0033] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0034] To Cl - With SO4 2- The test method of the selection coefficient:

[0035] The water flux (PWP, L·h) was calculated according to formulas 1 and 2. -1 ·m -2 bar -1 ) and retention rate (R, %):

[0036] PWP=V / (A·Δt·P) (1)

[0037] R=(1-C P / C F )*100% (2)

[0038] Where V(L) is the volume of water permeating through the membrane, A(m 2 ) is the effective membrane area, Δt(h) is the operation time, P(bar) is the test pressure, C F and C P (g / L) are the concentrations of the feed and permeate solutions, respectively. The concentrations of the feed and permeate solutions were measured by a conductivity meter (S230-K, Mettler Toledo).

[0039] The mixed ion selectivity coefficient was calculated according to Formula 3

[0040]

[0041] Where R Cl - and Represents Cl - and SO4 2- Retention rate in mixed brine solution, Cl in feed and permeate - and SO4 2- The concentration was determined by ion chromatograph (D150, Shenghan Chromatography Technology Co., Ltd.).

[0042] Example 1

[0043] A method for preparing a zwitterionic cross-linked graphene oxide nanofiltration membrane comprises the following steps:

[0044] (1) Preparation of graphene oxide nanosheet dispersion: 4 g of 325 mesh flake graphite, 480 mL of concentrated sulfuric acid and 54 mL of concentrated phosphoric acid were mixed and stirred, 24 g of potassium permanganate was slowly added, and 800 mL of deionized water was added after reacting in a water bath at 50°C for 24 h, and then 15 mL of 30% hydrogen peroxide solution was added dropwise until the solution turned golden yellow, and the solution was allowed to stand overnight and then centrifuged. The centrifuged product was washed with 1.8% dilute hydrochloric acid and deionized water to pH = 5-6, and after dialysis, it was dispersed with ultrapure water to obtain a graphene oxide nanosheet dispersion with a concentration of 1 mg / mL.

[0045] (2) Preparation of zwitterionic crosslinker dispersion: Dissolve 0.1 mmol 2,6-diaminopyridine (10.9 mg) and 0.1 mmol 3-bromopropionic acid (15.3 mg) in 100 mL ultrapure water, respectively, and then mix the two at a speed of 400 r / min and react at 30°C for 24 h to obtain a zwitterionic crosslinker (BPA-DAP) dispersion with a concentration of 1 mmol / L.

[0046] (3) Preparation of zwitterionic cross-linked graphene oxide nanofiltration membrane The graphene oxide nanosheet dispersion (0.5 mL) obtained in step (1) and the zwitterionic cross-linking agent dispersion obtained in step (2) were mixed at a solute volume ratio of 1:2.778, that is, a solute mass ratio of 1:0.5, and diluted to 200 mL of solution. The dispersion was stirred at 400 r / min for 30 min to mix evenly. After ultrasonication at 180 W for 0.5 h, the mixed dispersion was filtered onto a PES microporous filter membrane with a pore size of 0.22 μm and a diameter of 50 mm by vacuum assisted filtration. The cross-linking reaction was carried out at 45°C for 24 h to obtain a charge-compensated cross-linked graphene oxide nanofiltration membrane. The separation performance of the membrane was tested using a cross-flow filtration device, and its pure water flux was 2.5 L·m -2 ·h -1 bar -1 , for Cl - With SO4 2- The selectivity coefficient is as high as 5.4.

[0047] The zwitterionic crosslinker prepared in step (2) was characterized by nuclear magnetic resonance spectroscopy. Figure 1 It can be seen that the zwitterions were successfully synthesized.

[0048] Figure 2 The detailed spectra of the N element in the X-ray photoelectron spectrum of 2,6-diaminopyridine and zwitterions are shown. As can be seen from Figure 2, the synthesized zwitterions have added characteristic peaks of quaternary amines compared to the detailed spectrum of the N element in the X-ray photoelectron spectrum of 2,6-diaminopyridine.

[0049] Figure 3 The infrared spectra of 2,6-diaminopyridine, 3-bromopropionic acid and zwitter ion are shown. Figure 3 It can be seen that 3-bromopropionic acid has a peak at 1710 cm -1 The infrared characteristic peak of -COOH appears at 1610 cm -1 Appearance-COO - The characteristic peak of 2,6-diaminopyridine at -1450cm -1The stretching vibration peak of the -CH bond in the pyridine ring appears at -1450cm. However, in the zwitterion, the pyridine ring changes due to the reaction, so there is no -1450cm -1 In summary, it can be proved that the synthesis of zwitterionic BPA-DAP is successful.

[0050] Figure 4 The separation performance of the prepared zwitterionic cross-linked graphene oxide nanofiltration membrane is given. As can be seen from Figure 4, the zwitterionic cross-linked graphene oxide nanofiltration membrane has a good separation performance for Cl - With SO4 2- Has excellent separation performance.

[0051] Example 2

[0052] The difference between Example 2 and Example 1 is that the mixing ratio of the graphene oxide nanosheet dispersion and the zwitterionic crosslinking agent dispersion in step (3) is different.

[0053] A method for preparing a zwitterionic cross-linked graphene oxide nanofiltration membrane comprises the following steps:

[0054] (1) Preparation of graphene oxide nanosheet dispersion: 4 g of 325 mesh flake graphite, 480 mL of concentrated sulfuric acid and 54 mL of concentrated phosphoric acid were mixed and stirred, 24 g of potassium permanganate was slowly added, and 800 mL of deionized water was added after reacting in a water bath at 50°C for 24 h, and then hydrogen peroxide was added dropwise until the solution turned golden yellow, and centrifuged after standing overnight. The centrifuged product was washed with dilute hydrochloric acid and deionized water to pH = 5-6, and then dialyzed and dispersed with ultrapure water to obtain a graphene oxide nanosheet dispersion with a concentration of 1 mg / mL.

[0055] (2) Preparation of zwitterionic crosslinker dispersion: Dissolve 0.1 mmol 2,6-diaminopyridine (10.9 mg) and 0.1 mmol 3-bromopropionic acid (15.3 mg) in 100 mL ultrapure water, respectively, and then mix the two at a rotation speed of 400 r / min, react at 30°C for 24 h, and obtain a zwitterionic crosslinker dispersion with a concentration of 1 mmol / L.

[0056] (3) Preparation of zwitterionic cross-linked graphene oxide nanofiltration membrane: 0.5 mL of the graphene oxide nanosheet dispersion obtained in step (1) and the zwitterionic cross-linker dispersion obtained in step (2) were mixed at a solution volume ratio of 1:0.2778, that is, the solute mass ratio was 1:0.05, and diluted to 200 mL of solution. The dispersion was stirred at 400 r / min for 30 min to mix evenly, and after ultrasonication at 180 W for 0.5 h, the mixed dispersion was filtered onto a PES microporous filter membrane with a pore size of 0.22 μm and a diameter of 50 mm by vacuum assisted filtration. The cross-linking reaction was carried out at 45°C for 24 h to obtain a charge-compensated cross-linked graphene oxide nanofiltration membrane. The separation performance of the membrane was tested using a cross-flow filtration device, and its pure water flux was 5.0 L·m -2 ·h -1 bar -1 , for Cl - With SO4 2- The selectivity coefficient is 3.6.

[0057] Example 3

[0058] The difference between Example 3 and Example 1 is that the mixing ratio of the graphene oxide nanosheet dispersion and the zwitterionic crosslinking agent dispersion in step (3) is different.

[0059] A method for preparing a zwitterionic cross-linked graphene oxide nanofiltration membrane comprises the following steps:

[0060] (1) Preparation of graphene oxide nanosheet dispersion: 4 g of 325 mesh flake graphite, 480 mL of concentrated sulfuric acid and 54 mL of concentrated phosphoric acid were mixed and stirred, 24 g of potassium permanganate was slowly added, and 800 mL of deionized water was added after reacting in a water bath at 50°C for 24 h, and then hydrogen peroxide was added dropwise until the solution turned golden yellow, and centrifuged after standing overnight. The centrifuged product was washed with dilute hydrochloric acid and deionized water to pH = 5-6, and then dialyzed and dispersed with ultrapure water to obtain a graphene oxide nanosheet dispersion with a concentration of 1 mg / mL.

[0061] (2) Preparation of zwitterionic crosslinker dispersion: Dissolve 0.1 mmol 2,6-diaminopyridine (10.9 mg) and 0.1 mmol 3-bromopropionic acid (15.3 mg) in 100 mL ultrapure water, respectively, and then mix the two at a rotation speed of 400 r / min, react at 30°C for 24 h, and obtain a zwitterionic crosslinker dispersion with a concentration of 1 mmol / L.

[0062] (3) Preparation of zwitterionic cross-linked graphene oxide nanofiltration membrane: 0.5 mL of the graphene oxide nanosheet dispersion obtained in step (1) and the zwitterionic cross-linker dispersion obtained in step (2) were mixed at a solution volume ratio of 1:0.5556, that is, the solute mass ratio was 1:0.1, and diluted to 200 mL of solution. The dispersion was stirred at 400 r / min for 30 min to mix evenly. After ultrasonication at 180 W for 0.5 h, the mixed dispersion was filtered onto a PES microporous filter membrane with a pore size of 0.22 μm and a diameter of 50 mm by vacuum assisted filtration. The cross-linking reaction was carried out at 45°C for 24 h to obtain a charge-compensated cross-linked graphene oxide nanofiltration membrane. The separation performance of the membrane was tested using a cross-flow filtration device, and its pure water flux was 4.3 L·m -2 ·h -1 bar -1 , for Cl - With SO4 2- The selectivity coefficient is 4.0.

[0063] Example 4

[0064] The difference between Example 4 and Example 1 is that the mixing ratio of the graphene oxide nanosheet dispersion and the zwitterionic crosslinking agent dispersion in step (3) is different.

[0065] A method for preparing a zwitterionic cross-linked graphene oxide nanofiltration membrane comprises the following steps:

[0066] (1) Preparation of graphene oxide nanosheet dispersion: 4 g of 325 mesh flake graphite, 480 mL of concentrated sulfuric acid and 54 mL of concentrated phosphoric acid were mixed and stirred, 24 g of potassium permanganate was slowly added, and 800 mL of deionized water was added after reacting in a water bath at 50°C for 24 h, and then hydrogen peroxide was added dropwise until the solution turned golden yellow, and centrifuged after standing overnight. The centrifuged product was washed with dilute hydrochloric acid and deionized water to pH = 5-6, and then dialyzed and dispersed with ultrapure water to obtain a graphene oxide nanosheet dispersion with a concentration of 1 mg / mL.

[0067] (2) Preparation of zwitterionic crosslinker dispersion: Dissolve 0.1 mmol 2,6-diaminopyridine (10.9 mg) and 0.1 mmol 3-bromopropionic acid (15.3 mg) in 100 mL ultrapure water, respectively, and then mix the two at a rotation speed of 400 r / min, react at 30°C for 24 h, and obtain a zwitterionic crosslinker dispersion with a concentration of 1 mmol / L.

[0068] (3) Preparation of zwitterionic cross-linked graphene oxide nanofiltration membrane: 0.5 mL of the graphene oxide nanosheet dispersion obtained in step (1) and the zwitterionic cross-linker dispersion obtained in step (2) were mixed at a solution volume ratio of 1:1.1112, that is, the solute mass ratio was 1:0.2, and diluted to 200 mL of solution. The dispersion was stirred at 400 r / min for 30 min to mix evenly, and after ultrasonication at 180 W for 0.5 h, the mixed dispersion was filtered onto a PES microporous filter membrane with a pore size of 0.22 μm and a diameter of 50 mm by vacuum assisted filtration. The cross-linking reaction was carried out at 45°C for 24 h to obtain a charge-compensated cross-linked graphene oxide nanofiltration membrane. The separation performance of the membrane was tested using a cross-flow filtration device, and its pure water flux was 3.6 L·m -2 ·h -1 bar -1 , for Cl - With SO4 2- The selectivity coefficient is 5.1.

[0069] Example 5

[0070] The difference between Example 5 and Example 1 is that the mixing ratio of the graphene oxide nanosheet dispersion and the zwitterionic crosslinking agent dispersion in step (3) is different.

[0071] A method for preparing a zwitterionic cross-linked graphene oxide nanofiltration membrane comprises the following steps:

[0072] (1) Preparation of graphene oxide nanosheet dispersion: 4 g of 325 mesh flake graphite, 480 mL of concentrated sulfuric acid and 54 mL of concentrated phosphoric acid were mixed and stirred, 24 g of potassium permanganate was slowly added, and 800 mL of deionized water was added after reacting in a water bath at 50°C for 24 h, and then hydrogen peroxide was added dropwise until the solution turned golden yellow, and centrifuged after standing overnight. The centrifuged product was washed with dilute hydrochloric acid and deionized water to pH = 5-6, and then dialyzed and dispersed with ultrapure water to obtain a graphene oxide nanosheet dispersion with a concentration of 1 mg / mL.

[0073] (2) Preparation of zwitterionic crosslinker dispersion: Dissolve 0.1 mmol 2,6-diaminopyridine (10.9 mg) and 0.1 mmol 3-bromopropionic acid (15.3 mg) in 100 mL ultrapure water, respectively, and then mix the two at a rotation speed of 400 r / min, react at 30°C for 24 h, and obtain a zwitterionic crosslinker dispersion with a concentration of 1 mmol / mL.

[0074] (3) Preparation of zwitterionic cross-linked graphene oxide nanofiltration membrane: 0.5 mL of the graphene oxide nanosheet dispersion obtained in step (1) and the zwitterionic cross-linker dispersion obtained in step (2) were mixed at a solution volume ratio of 1:5.556, that is, the solute mass ratio was 1:1, and diluted to 200 mL of solution. The dispersion was stirred at 400 r / min for 30 min to mix evenly. After ultrasonication at 180 W for 0.5 h, the mixed dispersion was filtered onto a PES microporous filter membrane with a pore size of 0.22 μm and a diameter of 50 mm by vacuum assisted filtration. The cross-linking reaction was carried out at 45°C for 24 h to obtain a charge-compensated cross-linked graphene oxide nanofiltration membrane. The separation performance of the membrane was tested using a cross-flow filtration device, and its pure water flux was 0.7 L·m -2 ·h -1 bar -1 , for Cl - With SO4 2- The selectivity coefficient is 6.9.

[0075] Example 6

[0076] The difference between Example 6 and Example 1 is that the mixing ratio of the graphene oxide nanosheet dispersion and the zwitterionic crosslinking agent dispersion in step (3) is different.

[0077] A method for preparing a zwitterionic cross-linked graphene oxide nanofiltration membrane comprises the following steps:

[0078] (1) Preparation of graphene oxide nanosheet dispersion: 4 g of 325 mesh flake graphite, 480 mL of concentrated sulfuric acid and 54 mL of concentrated phosphoric acid were mixed and stirred, 24 g of potassium permanganate was slowly added, and 800 mL of deionized water was added after reacting in a water bath at 50°C for 24 h, and then hydrogen peroxide was added dropwise until the solution turned golden yellow, and centrifuged after standing overnight. The centrifuged product was washed with dilute hydrochloric acid and deionized water to pH = 5-6, and then dialyzed and dispersed with ultrapure water to obtain a graphene oxide nanosheet dispersion with a concentration of 1 mg / mL.

[0079] (2) Preparation of zwitterionic crosslinker dispersion: Dissolve 0.1 mmol 2,6-diaminopyridine (10.9 mg) and 0.1 mmol 3-bromopropionic acid (15.3 mg) in 100 mL ultrapure water, respectively, and then mix the two at a rotation speed of 400 r / min, react at 30°C for 24 h, and obtain a zwitterionic crosslinker dispersion with a concentration of 1 mmol / L.

[0080] (3) Preparation of zwitterionic cross-linked graphene oxide nanofiltration membrane: 0.5 mL of the graphene oxide nanosheet dispersion obtained in step (1) and the zwitterionic cross-linker dispersion obtained in step (2) were mixed at a solution volume ratio of 1:11.112, that is, the solute mass ratio was 1:2, and diluted to 200 mL of solution. The dispersion was stirred at 400 r / min for 30 min to mix evenly. After ultrasonication at 180 W for 0.5 h, the mixed dispersion was filtered onto a PES microporous filter membrane with a pore size of 0.22 μm and a diameter of 50 mm by vacuum assisted filtration. The cross-linking reaction was carried out at 45°C for 24 h to obtain a charge-compensated cross-linked graphene oxide nanofiltration membrane. The separation performance of the membrane was tested using a cross-flow filtration device, and its pure water flux was 0.5 L·m -2 ·h -1 bar -1 , for Cl - With SO4 2- The selectivity coefficient is 7.4.

[0081] Comparative Example 1:

[0082] The graphene oxide nanosheets were dispersed in deionized water to obtain a graphene oxide nanosheet dispersion with a concentration of 1 mg / mL. The preparation method of the graphene oxide nanosheets was the same as that in Example 1. 0.5 mL of the graphene oxide nanosheet dispersion was diluted to 200 mL of solution. After ultrasonication at 180 W for 0.5 h, the uniformly mixed dispersion was filtered on a PES microporous filter membrane with a pore size of 0.22 μm and a diameter of 50 mm by vacuum assisted filtration, and dried at 45 ° C for 24 h to obtain a pure graphene oxide nanofiltration membrane. The separation performance of the membrane was tested using a cross-flow filtration device, and its pure water flux was 5.6 L·m -2 ·h -1 bar -1 , for Cl - With SO4 2- The selectivity coefficient is 3.3.

[0083] Comparative Example 2:

[0084] The difference between Comparative Example 2 and Example 1 is that the zwitterionic crosslinking agent is replaced by 2,6-diaminopyridine.

[0085] A method for preparing a graphene oxide nanofiltration membrane comprises the following steps:

[0086] (1) Preparation of graphene oxide nanosheet dispersion: 4 g of 325 mesh flake graphite, 480 mL of concentrated sulfuric acid and 54 mL of concentrated phosphoric acid were mixed and stirred, 24 g of potassium permanganate was slowly added, and 800 mL of deionized water was added after reacting in a water bath at 50°C for 24 h, and then hydrogen peroxide was added dropwise until the solution turned golden yellow, and centrifuged after standing overnight. The centrifuged product was washed with dilute hydrochloric acid and deionized water to pH = 5-6, and then dialyzed and dispersed with ultrapure water to obtain a graphene oxide nanosheet dispersion with a concentration of 1 mg / mL.

[0087] (2) Preparation of 2,6-diaminopyridine dispersion: 0.1 mmol 2,6-diaminopyridine (10.9 mg) was dissolved in 100 mL ultrapure water, and the mixture was stirred at 400 r / min and 30° C. for 24 h to obtain a 2,6-diaminopyridine dispersion with a concentration of 1 mmol / L.

[0088] (3) Preparation of 2,6-diaminopyridine cross-linked graphene oxide nanofiltration membrane: Take 0.5 mL of the graphene oxide nanosheet dispersion obtained in step (1) and the 2,6-diaminopyridine dispersion obtained in step (2) and mix them at a solution volume ratio of 1:2.778, and dilute them into 200 mL of solution. Stir at 400 r / min for 30 min to mix the dispersion evenly. After ultrasonication at 180 W for 0.5 h, the mixed dispersion is filtered on a PES microporous filter membrane with a pore size of 0.22 μm and a diameter of 50 mm by vacuum assisted filtration. Cross-linking reaction is carried out at 45 ° C for 24 h to obtain 2,6-diaminopyridine cross-linked graphene oxide nanofiltration membrane. The separation performance of the membrane was tested using a cross-flow filtration device, and its pure water flux was 1.3 L·m -2 ·h -1 bar -1 , for Cl - With SO4 2- The selectivity coefficient is 4.2.

[0089] Comparative Example 3

[0090] The difference between Comparative Example 3 and Example 1 is that the zwitterionic cross-linking agent is replaced by 3-bromopropionic acid.

[0091] A method for preparing a graphene oxide nanofiltration membrane comprises the following steps:

[0092] (1) Preparation of graphene oxide nanosheet dispersion: 4 g of 325 mesh flake graphite, 480 mL of concentrated sulfuric acid and 54 mL of concentrated phosphoric acid were mixed and stirred, 24 g of potassium permanganate was slowly added, and 800 mL of deionized water was added after reacting in a water bath at 50°C for 24 h, and then hydrogen peroxide was added dropwise until the solution turned golden yellow, and centrifuged after standing overnight. The centrifuged product was washed with dilute hydrochloric acid and deionized water to pH = 5-6, and then dialyzed and dispersed with ultrapure water to obtain a graphene oxide nanosheet dispersion with a concentration of 1 mg / mL.

[0093] (2) Preparation of 3-bromopropionic acid dispersion: 0.1 mmol 3-bromopropionic acid (15.3 mg) was dissolved in 100 mL ultrapure water, and stirred at 400 r / min and 30° C. for 24 h to obtain a 3-bromopropionic acid dispersion with a concentration of 1 mmol / L.

[0094] (3) Preparation of 3-bromopropionic acid doped graphene oxide nanofiltration membrane: Take 0.5 mL of the graphene oxide nanosheet dispersion obtained in step (1) and the 3-bromopropionic acid dispersion obtained in step (2) at a solution volume ratio of 1:2.778, and dilute to 200 mL of solution. Stir at 400 r / min for 30 min to mix the dispersion evenly, ultrasonicate at 180 W for 0.5 h, and then filter the evenly mixed dispersion onto a PES microporous filter membrane with a pore size of 0.22 μm and a diameter of 50 mm by vacuum assisted filtration, and dry at 45 ° C for 24 h to obtain a 3-bromopropionic acid doped graphene oxide nanofiltration membrane. The separation performance of the membrane was tested using a cross-flow filtration device, and its pure water flux was 6.0 L·m -2 ·h -1 bar -1 , for Cl - With SO4 2- The selectivity coefficient is 3.2.

[0095] Comparative Example 4

[0096] The difference between Comparative Example 4 and Example 1 is that the zwitterionic crosslinking agent is replaced by a common commercial zwitterionic agent: N,N-dimethylglycine.

[0097] A method for preparing a graphene oxide nanofiltration membrane comprises the following steps:

[0098] (1) Preparation of graphene oxide nanosheet dispersion: 4 g of 325 mesh flake graphite, 480 mL of concentrated sulfuric acid and 54 mL of concentrated phosphoric acid were mixed and stirred, 24 g of potassium permanganate was slowly added, and 800 mL of deionized water was added after reacting in a water bath at 50°C for 24 h, and then hydrogen peroxide was added dropwise until the solution turned golden yellow, and centrifuged after standing overnight. The centrifuged product was washed with dilute hydrochloric acid and deionized water to pH = 5-6, and then dialyzed and dispersed with ultrapure water to obtain a graphene oxide nanosheet dispersion with a concentration of 1 mg / mL.

[0099] (2) Preparation of N,N-dimethylglycine dispersion: 0.1 mmol N,N-dimethylglycine (10.3 mg) was dissolved in 100 mL of ultrapure water, and the mixture was stirred at 400 r / min and 30° C. for 24 h to obtain a 1 mmol / L N,N-dimethylglycine dispersion.

[0100] (3) Preparation of N,N-dimethylglycine doped graphene oxide nanofiltration membrane: Take 0.5 mL of the graphene oxide nanosheet dispersion obtained in step (1) and the N,N-dimethylglycine dispersion obtained in step (2) and mix them at a solution volume ratio of 1:2.778, and dilute them into 200 mL of solution. Stir at 400 r / min for 30 min to mix the dispersions evenly. After ultrasonication at 180 W for 0.5 h, the mixed dispersions are filtered on a PES microporous filter membrane with a pore size of 0.22 μm and a diameter of 50 mm by vacuum assisted filtration, and dried at 45 ° C for 24 h to obtain N,N-dimethylglycine doped graphene oxide nanofiltration membrane. The separation performance of the membrane was tested using a cross-flow filtration device, and its pure water flux was 5.1 L·m -2 ·h -1 bar -1 , for Cl - With SO4 2- The selectivity coefficient is 3.8.

[0101] Comparative Example 5

[0102] The difference between Comparative Example 5 and Example 1 is that the molar ratio of 2,6-diaminopyridine and 3-bromopropionic acid is changed.

[0103] A method for preparing a graphene oxide nanofiltration membrane comprises the following steps:

[0104] (1) Preparation of graphene oxide nanosheet dispersion: 4 g of 325 mesh flake graphite, 480 mL of concentrated sulfuric acid and 54 mL of concentrated phosphoric acid were mixed and stirred, 24 g of potassium permanganate was slowly added, and 800 mL of deionized water was added after reacting in a water bath at 50°C for 24 h, and then hydrogen peroxide was added dropwise until the solution turned golden yellow, and centrifuged after standing overnight. The centrifuged product was washed with dilute hydrochloric acid and deionized water to pH = 5-6, and then dialyzed and dispersed with ultrapure water to obtain a graphene oxide nanosheet dispersion with a concentration of 1 mg / mL.

[0105] (2) Preparation of zwitterionic crosslinker dispersion: Dissolve 0.1 mmol 2,6-diaminopyridine (10.9 mg) and 0.11 mmol 3-bromopropionic acid (16.8 mg) in 100 mL ultrapure water, respectively, and then mix the two at a rotation speed of 400 r / min, and react at 30° C. for 24 h to obtain a zwitterionic crosslinker dispersion.

[0106] (3) Preparation of zwitterionic crosslinker-doped graphene oxide nanofiltration membrane: Take 0.5 mL of the graphene oxide nanosheet dispersion obtained in step (1) and the zwitterionic crosslinker dispersion obtained in step (2) at a solution volume ratio of 1:2.778, and dilute to 200 mL of solution. Stir at 400 r / min for 30 min to mix the dispersion evenly. After ultrasonication at 180 W for 0.5 h, the mixed dispersion is filtered on a PES microporous filter membrane with a pore size of 0.22 μm and a diameter of 50 mm by vacuum assisted filtration, and dried at 45 ° C for 24 h to obtain a zwitterionic crosslinked graphene oxide nanofiltration membrane. The separation performance of the membrane was tested using a cross-flow filtration device, and its pure water flux was 2.9 L·m -2 ·h -1 bar -1 , for Cl - With SO4 2- The selectivity coefficient is 4.7.

[0107] Comparative Example 6

[0108] The difference between Comparative Example 6 and Example 1 is that the molar ratio of 2,6-diaminopyridine and 3-bromopropionic acid is changed.

[0109] A method for preparing a graphene oxide nanofiltration membrane comprises the following steps:

[0110] (1) Preparation of graphene oxide nanosheet dispersion: 4 g of 325 mesh flake graphite, 480 mL of concentrated sulfuric acid and 54 mL of concentrated phosphoric acid were mixed and stirred, 24 g of potassium permanganate was slowly added, and 800 mL of deionized water was added after reacting in a water bath at 50°C for 24 h, and then hydrogen peroxide was added dropwise until the solution turned golden yellow, and centrifuged after standing overnight. The centrifuged product was washed with dilute hydrochloric acid and deionized water to pH = 5-6, and then dialyzed and dispersed with ultrapure water to obtain a graphene oxide nanosheet dispersion with a concentration of 1 mg / mL.

[0111] (2) Preparation of zwitterionic crosslinker dispersion: Dissolve 0.11 mmol 2,6-diaminopyridine (12.0 mg) and 0.1 mmol 3-bromopropionic acid (15.3 mg) in 100 mL ultrapure water, respectively, and then mix the two at a rotation speed of 400 r / min, and react at 30° C. for 24 h to obtain a zwitterionic crosslinker dispersion.

[0112] (3) Preparation of zwitterionic crosslinker-doped graphene oxide nanofiltration membrane: Take 0.5 mL of the graphene oxide nanosheet dispersion obtained in step (1) and the zwitterionic crosslinker dispersion obtained in step (2) at a solution volume ratio of 1:2.778, and dilute to 200 mL of solution. Stir at 400 r / min for 30 min to mix the dispersion evenly, ultrasonicate at 180 W for 0.5 h, and then filter the evenly mixed dispersion onto a PES microporous filter membrane with a pore size of 0.22 μm and a diameter of 50 mm by vacuum assisted filtration, and dry at 45 ° C for 24 h to obtain a zwitterionic crosslinker-doped graphene oxide nanofiltration membrane. The separation performance of the membrane was tested using a cross-flow filtration device, and its pure water flux was 1.8 L·m -2 ·h -1 bar -1 , for Cl - With SO4 2- The selectivity coefficient is 4.5.

[0113] The embodiments provided above are not intended to limit the scope of the present invention, and the steps described are not intended to limit the execution order thereof. Those skilled in the art may make obvious improvements to the present invention in combination with existing common knowledge, which also fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing a zwitterionic cross-linked graphene oxide nanofiltration membrane, characterized in that: The following steps are involved: (1) Preparation of graphene oxide nanosheet dispersion: flake graphite, concentrated sulfuric acid and concentrated phosphoric acid were mixed and stirred, potassium permanganate was slowly added, and 0.8-3L of deionized water was added after reacting in a water bath at 50°C for 24 hours, and then 10-30mL of 30% hydrogen peroxide was added dropwise until the solution turned golden yellow. After standing overnight, the solution was centrifuged at 3000-3500 r / min for 15-30 minutes, and the total number of centrifugations was 15-20 times. The centrifuged product was washed with 1-5% dilute hydrochloric acid and deionized water to a pH of 5-6, and then dialyzed and dispersed with ultrapure water to obtain a graphene oxide nanosheet dispersion; (2) Preparation of zwitterionic crosslinking agent dispersion: respectively mixing a solution of 2,6-diaminopyridine and a solution of 3-bromopropionic acid, and continuously stirring in a constant temperature water bath to obtain a zwitterionic crosslinking agent dispersion; (3) Preparation of zwitterionic cross-linked graphene oxide nanofiltration membrane: The graphene oxide nanosheet dispersion obtained in step (1) and the zwitterionic cross-linking agent dispersion obtained in step (2) are mixed and diluted, stirred and ultrasonically treated, and loaded on the surface of a macroporous polymer support membrane by vacuum filtration. After thermal cross-linking, a zwitterionic cross-linked graphene oxide nanofiltration membrane is obtained.

2. The preparation method according to claim 1, characterized in that: In step (1), the size of the flake graphite used is 100-400 meshes, the concentrations of concentrated sulfuric acid and concentrated phosphoric acid are 98% and 85% respectively, the volume ratio of the two is 9:1, the mass volume ratio of the flake graphite to the concentrated sulfuric acid is 1g:(100-120)mL, the mass ratio of the potassium permanganate to the flake graphite is 6:1, and the concentration of the graphene oxide nanosheets in the graphene oxide nanosheet dispersion is 1-5mg / mL.

3. The preparation method according to claim 1, characterized in that: In step (2), the concentration of the 2,6-diaminopyridine solution is 0.5-2 mmol / L, the concentration of the 3-bromopropionic acid solution is 0.5-2 mmol / L, and the molar ratio of 2,6-diaminopyridine to 3-bromopropionic acid is 1:

1.

4. The preparation method according to claim 1, characterized in that: In step (2), the constant temperature water bath temperature is 30-50° C., the stirring rate is 300-500 r / min, the time is 12-24 h, and the concentration of the zwitterionic crosslinking agent in the zwitterionic crosslinking agent dispersion is 0.5-2 mmol / L.

5. The preparation method according to claim 1, characterized in that: When the graphene oxide nanosheet dispersion and the zwitterionic crosslinking agent dispersion are mixed in step (3), the mass ratio of the solutes is 1:0.05 to 1:

2.

6. The preparation method according to claim 1, characterized in that: In step (3), the volume of the diluted mixed solution is 100-200 mL, the stirring rate is 300-500 r / min, the stirring time is 0.5-12 h; the ultrasonic power is 60-180 W, and the ultrasonic time is 0.2-0.5 h.

7. The preparation method according to claim 1, characterized in that: The polymer support membrane in step (3) includes any one of polyvinylidene fluoride, polytetrafluoroethylene, polyethersulfone, and mixed cellulose microporous filter membrane. The pore size of the polymer support membrane is 0.22 to 0.44 μm and the diameter is 25 to 50 cm.

8. The preparation method according to claim 1, characterized in that: The heat cross-linking time in step (3) is 12 to 24 hours, and the heat cross-linking temperature is 45 to 80°C. 9 . The zwitterionic cross-linked graphene oxide nanofiltration membrane prepared according to the preparation method according to any one of claims 1 to 8 .

10. Use of the zwitterionic cross-linked graphene oxide nanofiltration membrane according to claim 9 in the field of water treatment.

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