A zwitterionic crosslinked graphene oxide nanofiltration membrane and its preparation method

Abstract

This invention discloses a zwitterionic crosslinked graphene oxide nanofiltration membrane and its preparation method. The nanofiltration membrane is prepared by first synthesizing a zwitterionic crosslinking agent, then mixing the zwitterionic crosslinking agent with a dispersion of graphene oxide nanosheets, followed by ultrasonication, vacuum filtration, and thermal crosslinking. This invention also discloses the preparation method and application of the above-mentioned nanofiltration membrane. This invention uses a macroporous polymer membrane as a support layer. The zwitterionic crosslinking agent and graphene oxide are loaded onto the support layer through vacuum filtration, followed by thermal crosslinking to obtain the zwitterionic crosslinked graphene oxide nanofiltration membrane. This method is simple to operate, ingeniously designed, and yields a membrane with excellent separation performance. By crosslinking the zwitterionic crosslinking agent with graphene oxide nanosheets, quaternary ammonium groups are introduced into the interlayer space of the nanofiltration membrane while stabilizing the interlayer spacing, thereby improving the selectivity for monovalent / divalent anions. Due to the hydrophilicity of zwitterions, the permeability of the crosslinked graphene oxide nanofiltration membrane is improved.

Description

Technical Field

[0001] This invention relates to a zwitterionic crosslinked graphene oxide nanofiltration membrane and its preparation method, belonging to the technical field of crosslinked graphene oxide nanofiltration membrane materials and their preparation. Background Technology

[0002] Industries such as petroleum, pharmaceutical, and paper mills frequently generate large quantities of high-salinity wastewater containing sulfates and chlorides. Therefore, Cl... - and SO4 2- Separation is crucial. Among numerous water treatment technologies, membrane separation technology has attracted much attention due to its high efficiency, low energy consumption, and wide applicability. Two-dimensional materials, such as graphene oxide, possess tunable nanochannels and are becoming ideal materials for developing selective separation membranes. However, the swelling and expansion of the interlayer spacing of graphene oxide membranes in aqueous solutions leads to inaccurate sieving sizes, and because of Cl... - and SO4 2- Having similar ion size and ion properties further increases the challenge of precise selective separation.

[0003] To achieve high selectivity of graphene-based membranes for monovalent / divalent anions, many studies in recent years have focused on adjusting interlayer spacing or increasing electrostatic repulsion. However, these methods have not achieved the expected results in improving the selectivity of graphene oxide membranes for anions. Therefore, developing a graphene-based membrane material that simultaneously possesses structural stability and high anion transport rate and separation efficiency is of great significance. Summary of the Invention

[0004] To address the aforementioned problems, this invention aims to provide a zwitterionic crosslinked graphene oxide nanofiltration membrane, thereby solving the issues of easy swelling of existing graphene oxide-based membrane materials and low selectivity of nanofiltration membranes for monovalent / divalent anions.

[0005] To achieve the above objectives, the present invention first provides a method for preparing a zwitterionic crosslinked graphene oxide nanofiltration membrane. Specifically, a zwitterionic crosslinking agent is first synthesized using 2,6-diaminopyridine and 3-bromopropionic acid as raw materials. Then, the zwitterionic crosslinking agent is mixed with a dispersion of graphene oxide nanosheets, and the mixture is ultrasonicated, filtered, and thermally crosslinked to obtain a zwitterionic crosslinked graphene oxide nanofiltration membrane.

[0006] In one embodiment of the present invention, the method for preparing the zwitterionic crosslinked graphene oxide nanofiltration membrane includes 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 the mixture was reacted in a water bath at 50°C for 24 hours. Then 0.8-3L of deionized water was added, followed by 10-30mL of 30% hydrogen peroxide dropwise until the solution turned golden yellow. After standing overnight, the mixture was centrifuged at 3000-3500r / min for 15-30min, for a total of 15-20 centrifugations. The centrifuged product was washed with 1-5% dilute hydrochloric acid and deionized water until pH=5-6. After dialyzing, the product was dispersed in ultrapure water to obtain graphene oxide nanosheet dispersion.

[0008] (2) Preparation of zwitterionic crosslinking agent dispersion: The solution of 2,6-diaminopyridine (BPA) and the solution of 3-bromopropionic acid (DAP) were mixed and stirred continuously in a constant temperature water bath to obtain zwitterionic crosslinking agent dispersion.

[0009] (3) Preparation of zwitterionic crosslinked graphene oxide nanofiltration membrane: The graphene oxide nanosheet dispersion obtained in step (1) and the zwitterionic crosslinking agent dispersion obtained in step (2) are mixed and diluted, stirred and ultrasonically treated, and loaded onto the surface of a macroporous polymer support membrane by vacuum filtration. After thermal crosslinking, zwitterionic crosslinked 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, and the concentrations of concentrated sulfuric acid and concentrated phosphoric acid are 98% and 85%, respectively, with a volume ratio of 9:1.

[0011] In one embodiment of the present invention, in step (1), the mass-to-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 solution of 2,6-diaminopyridine is 0.5-2 mmol / L, the concentration of the solution of 3-bromopropionic acid 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 constant temperature water bath temperature 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, when the graphene oxide nanosheet dispersion and the zwitterionic crosslinking agent dispersion are mixed in step (3), the mass ratio of the solute 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 mixture 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 thermal crosslinking time in step (3) is 12 to 24 hours and the thermal crosslinking temperature is 45 to 80°C.

[0022] The present invention also discloses a zwitterionic crosslinked graphene oxide nanofiltration membrane prepared according to the above preparation method.

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

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

[0025] Beneficial effects:

[0026] (1) In this invention, a zwitterionic crosslinking agent is used to crosslink graphene oxide nanosheets, thereby stabilizing the interlayer spacing of the nanofiltration membrane and introducing quaternary ammonium groups into the interlayer, which improves the selectivity for monovalent / divalent anions.

[0027] (2) A zwitterionic crosslinking agent was prepared by first mixing 2,6-diaminopyridine with 3-bromopropionic acid, and then crosslinked with graphene oxide nanosheets using the zwitterionic crosslinking agent. Due to the hydrophilicity of zwitterions, the crosslinking agent with zwitterions improved the permeability of the crosslinked graphene oxide nanofiltration membrane.

[0028] (3) The nanofiltration membrane prepared by the method of the present invention has excellent membrane permeability, and its pure water flux can reach up to 2.5 L·m -2 ·h -1 ·bar -1 , for Cl - With SO4 2- The selection coefficient is as high as 5.4. Attached Figure Description

[0029] Figure 1 The carbon NMR spectrum of the zwitterion in Example 1 ( 13 C10 NMR spectrum and proton NMR spectrum 1 (H NMR), where (a) is the carbon NMR spectrum and (b) is the hydrogen NMR spectrum.

[0030] Figure 2 The fine N-element X-ray photoelectron spectra of 2,6-diaminopyridine and zwitterion in Example 1 are shown, where (a) corresponds to 2,6-diaminopyridine and (b) corresponds to zwitterion.

[0031] Figure 3 The infrared spectra of 2,6-diaminopyridine, 3-bromopropionic acid, and zwitterions in Example 1 are shown.

[0032] Figure 4 The diagram shows the separation performance of the zwitterionic crosslinked graphene oxide nanofiltration membranes prepared in Examples 1-6. Detailed Implementation

[0033] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0034] For Cl - With SO4 2- The test method for the selection coefficient:

[0035] Calculate the water flux (PWP, L·h) using 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 that permeates through the membrane, and A(m 2 ) is the effective membrane area, Δt(h) is the operating time, P(bar) is the test pressure, and C F and C P (g / L) represent the concentrations of the feed and permeate solution, respectively. The concentrations of the feed and permeate solution were determined using a conductivity meter (S230-K, Mettler Toledo).

[0039] Calculate the mixed ion selectivity coefficient according to Formula 3.

[0040]

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

[0042] Example 1

[0043] A method for preparing a zwitterionic crosslinked graphene oxide nanofiltration membrane includes the following steps:

[0044] (1) Preparation of graphene oxide nanosheet dispersion: 4g of 325-mesh graphite flakes, 480mL of concentrated sulfuric acid and 54mL of concentrated phosphoric acid were mixed and stirred. 24g of potassium permanganate was slowly added, and the mixture was reacted in a water bath at 50℃ for 24h. Then, 800mL of deionized water was added, followed by dropwise addition of 15mL of 30% hydrogen peroxide solution until the solution turned golden yellow. After standing overnight, the mixture was centrifuged. The centrifuged product was washed with 1.8% dilute hydrochloric acid and deionized water until pH=5-6. After dialyzing, the product was dispersed in ultrapure water to obtain a graphene oxide nanosheet dispersion with a concentration of 1mg / mL.

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

[0046] (3) Preparation of zwitterionic crosslinked graphene oxide nanofiltration membrane: The graphene oxide nanosheet dispersion (0.5 mL) obtained in step (1) and the zwitterionic crosslinking agent dispersion obtained in step (2) were mixed at a solute-to-volume ratio of 1:2.778, i.e., a solute-to-mass ratio of 1:0.5, and diluted to 200 mL. The dispersion was stirred at 400 r / min for 30 min to ensure uniform mixing. After ultrasonication at 180 W for 0.5 h, the uniformly mixed dispersion was filtered onto a PES microporous membrane with a pore size of 0.22 μm and a diameter of 50 mm using vacuum-assisted filtration. The crosslinking reaction was carried out at 45 °C for 24 h to obtain a charge-compensated 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 2.5 L·m -2 ·h -1 ·bar -1 , for Cl - With SO4 2- The selection coefficient is as high as 5.4.

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

[0048] Figure 2 The fine N-element spectra of X-ray photoelectron spectroscopy of 2,6-diaminopyridine and zwitterion are shown. As can be seen from Figure 2, the synthesized zwitterion has added a quaternary amine characteristic peak compared with the fine N-element spectra of X-ray photoelectron spectroscopy of 2,6-diaminopyridine.

[0049] Figure 3 The infrared spectra of 2,6-diaminopyridine, 3-bromopropionic acid, and zwitterions are shown. Figure 3 It can be seen from this that 3-bromopropionic acid is at 1710 cm⁻¹ -1 The characteristic infrared peak of -COOH appears at 1610 cm⁻¹, while that of zwitterions is at 1610 cm⁻¹. -1 -COO appears at the location - The characteristic peak at -1450 cm⁻¹ confirms the presence of negative ions. Simultaneously, 2,6-diaminopyridine exhibits a characteristic peak at -1450 cm⁻¹, indicating the presence of negative ions. -1The stretching vibration peak of the -CH bond in the pyridine ring appears at -1450 cm⁻¹, but this is altered in zwitterions due to the reaction of the pyridine ring, so there is no peak at -1450 cm⁻¹. -1 The peak at that location demonstrates the successful synthesis of the zwitterionic BPA-DAP.

[0050] Figure 4 The separation performance of the prepared zwitterionic crosslinked graphene oxide nanofiltration membrane is presented. As shown in Figure 4, the zwitterionic crosslinked graphene oxide nanofiltration membrane exhibits good separation performance for Cl... - With SO4 2- It has excellent separation performance.

[0051] Example 2

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

[0053] A method for preparing a zwitterionic crosslinked graphene oxide nanofiltration membrane includes the following steps:

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

[0055] (2) Preparation of zwitterionic crosslinking agent dispersion: 0.1 mmol of 2,6-diaminopyridine (10.9 mg) and 0.1 mmol of 3-bromopropionic acid (15.3 mg) were dissolved in 100 mL of ultrapure water, and then the two were mixed evenly at a speed of 400 r / min and reacted at 30 °C for 24 h to obtain a zwitterionic crosslinking agent dispersion with a concentration of 1 mmol / L.

[0056] (3) Preparation of zwitterionic crosslinked graphene oxide nanofiltration membrane: 0.5 mL of the graphene oxide nanosheet dispersion obtained in step (1) and the zwitterionic crosslinking agent dispersion obtained in step (2) were mixed at a volume ratio of 1:0.2778, i.e., a solute mass ratio of 1:0.05, and diluted to 200 mL. The dispersion was stirred at 400 r / min for 30 min to ensure uniform mixing. After ultrasonication at 180 W for 0.5 h, the uniformly mixed dispersion was filtered onto a PES microporous membrane with a pore size of 0.22 μm and a diameter of 50 mm using vacuum-assisted filtration. The crosslinking reaction was carried out at 45 °C for 24 h to obtain a charge-compensated 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 5.0 L·m -2 ·h -1 ·bar -1 , for Cl - With SO4 2- The selection factor 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 crosslinked graphene oxide nanofiltration membrane includes the following steps:

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

[0061] (2) Preparation of zwitterionic crosslinking agent dispersion: 0.1 mmol of 2,6-diaminopyridine (10.9 mg) and 0.1 mmol of 3-bromopropionic acid (15.3 mg) were dissolved in 100 mL of ultrapure water, and then the two were mixed evenly at a speed of 400 r / min and reacted at 30 °C for 24 h to obtain a zwitterionic crosslinking agent dispersion with a concentration of 1 mmol / L.

[0062] (3) Preparation of zwitterionic crosslinked graphene oxide nanofiltration membrane: 0.5 mL of the graphene oxide nanosheet dispersion obtained in step (1) and the zwitterionic crosslinking agent dispersion obtained in step (2) were mixed at a volume ratio of 1:0.5556, i.e., a solute mass ratio of 1:0.1, and diluted to 200 mL. The dispersion was stirred at 400 r / min for 30 min to ensure uniform mixing. After ultrasonication at 180 W for 0.5 h, the uniformly mixed dispersion was filtered onto a PES microporous membrane with a pore size of 0.22 μm and a diameter of 50 mm using vacuum-assisted filtration. The crosslinking reaction was carried out at 45 °C for 24 h to obtain a charge-compensated 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 4.3 L·m -2 ·h -1 ·bar -1 , for Cl - With SO4 2- The selection factor 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 crosslinked graphene oxide nanofiltration membrane includes the following steps:

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

[0067] (2) Preparation of zwitterionic crosslinking agent dispersion: 0.1 mmol of 2,6-diaminopyridine (10.9 mg) and 0.1 mmol of 3-bromopropionic acid (15.3 mg) were dissolved in 100 mL of ultrapure water, and then the two were mixed evenly at a speed of 400 r / min and reacted at 30 °C for 24 h to obtain a zwitterionic crosslinking agent dispersion with a concentration of 1 mmol / L.

[0068] (3) Preparation of zwitterionic crosslinked graphene oxide nanofiltration membrane: 0.5 mL of the graphene oxide nanosheet dispersion obtained in step (1) and the zwitterionic crosslinking agent dispersion obtained in step (2) were mixed at a volume ratio of 1:1.1112, i.e., a solute mass ratio of 1:0.2, and diluted to 200 mL. The dispersion was stirred at 400 r / min for 30 min to ensure uniform mixing. After ultrasonication at 180 W for 0.5 h, the uniformly mixed dispersion was filtered onto a PES microporous membrane with a pore size of 0.22 μm and a diameter of 50 mm using vacuum-assisted filtration. The crosslinking reaction was carried out at 45 °C for 24 h to obtain a charge-compensated 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 3.6 L·m -2 ·h -1 ·bar -1 , for Cl - With SO4 2- The selection factor 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 crosslinked graphene oxide nanofiltration membrane includes the following steps:

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

[0073] (2) Preparation of zwitterionic crosslinking agent dispersion: 0.1 mmol of 2,6-diaminopyridine (10.9 mg) and 0.1 mmol of 3-bromopropionic acid (15.3 mg) were dissolved in 100 mL of ultrapure water, and then the two were mixed evenly at a speed of 400 r / min and reacted at 30 °C for 24 h to obtain a zwitterionic crosslinking agent dispersion with a concentration of 1 mmol / mL.

[0074] (3) Preparation of zwitterionic crosslinked graphene oxide nanofiltration membrane: 0.5 mL of the graphene oxide nanosheet dispersion obtained in step (1) and the zwitterionic crosslinking agent dispersion obtained in step (2) were mixed at a volume ratio of 1:5.556, i.e., a solute mass ratio of 1:1, and diluted to 200 mL. The dispersion was stirred at 400 r / min for 30 min to ensure uniform mixing. After ultrasonication at 180 W for 0.5 h, the uniformly mixed dispersion was filtered onto a PES microporous membrane with a pore size of 0.22 μm and a diameter of 50 mm using vacuum-assisted filtration. The crosslinking reaction was carried out at 45 °C for 24 h to obtain a charge-compensated 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 0.7 L·m -2 ·h -1 ·bar -1 , for Cl - With SO4 2- The selection factor 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 crosslinked graphene oxide nanofiltration membrane includes the following steps:

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

[0079] (2) Preparation of zwitterionic crosslinking agent dispersion: 0.1 mmol of 2,6-diaminopyridine (10.9 mg) and 0.1 mmol of 3-bromopropionic acid (15.3 mg) were dissolved in 100 mL of ultrapure water, and then the two were mixed evenly at a speed of 400 r / min and reacted at 30 °C for 24 h to obtain a zwitterionic crosslinking agent dispersion with a concentration of 1 mmol / L.

[0080] (3) Preparation of zwitterionic crosslinked graphene oxide nanofiltration membrane: 0.5 mL of the graphene oxide nanosheet dispersion obtained in step (1) and the zwitterionic crosslinking agent dispersion obtained in step (2) were mixed at a volume ratio of 1:11.112, i.e., a solute mass ratio of 1:2, and diluted to 200 mL. The dispersion was stirred at 400 r / min for 30 min to ensure uniform mixing. After ultrasonication at 180 W for 0.5 h, the uniformly mixed dispersion was filtered onto a PES microporous membrane with a pore size of 0.22 μm and a diameter of 50 mm using vacuum-assisted filtration. The crosslinking reaction was carried out at 45 °C for 24 h to obtain a charge-compensated 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 0.5 L·m -2 ·h -1 ·bar -1 , for Cl - With SO4 2- The selection factor is 7.4.

[0081] Comparative Example 1:

[0082] 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 in Example 1. 0.5 mL of the graphene oxide nanosheet dispersion was diluted to 200 mL. After sonication at 180 W for 0.5 h, the uniformly mixed dispersion was filtered through a PES microporous membrane with a pore size of 0.22 μm and a diameter of 50 mm using vacuum-assisted filtration. The membrane was 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·m³. -2 ·h -1 ·bar -1 , for Cl - With SO4 2- The selection factor is 3.3.

[0083] Comparative Example 2:

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

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

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

[0087] (2) Preparation of 2,6-diaminopyridine dispersion: 0.1 mmol of 2,6-diaminopyridine (10.9 mg) was dissolved in 100 mL of ultrapure water and 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 crosslinked graphene oxide nanofiltration membrane: 0.5 mL of the graphene oxide nanosheet dispersion obtained in step (1) and the 2,6-diaminopyridine dispersion obtained in step (2) were mixed at a volume ratio of 1:2.778 and diluted to 200 mL. The dispersion was stirred at 400 r / min for 30 min to ensure uniform mixing. After ultrasonication at 180 W for 0.5 h, the uniformly mixed dispersion was filtered onto a PES microporous membrane with a pore size of 0.22 μm and a diameter of 50 mm using vacuum-assisted filtration. The crosslinking reaction was carried out at 45 °C for 24 h to obtain the 2,6-diaminopyridine 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 1.3 L·m -2 ·h -1 ·bar -1 , for Cl - With SO4 2- The selection factor is 4.2.

[0089] Comparative Example 3

[0090] The difference between Comparative Example 3 and Example 1 is that the zwitterionic crosslinking agent was replaced with 3-bromopropionic acid.

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

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

[0093] (2) Preparation of 3-bromopropionic acid dispersion: 0.1 mmol of 3-bromopropionic acid (15.3 mg) was dissolved in 100 mL of 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: 0.5 mL of the graphene oxide nanosheet dispersion obtained in step (1) and 0.5 mL of the 3-bromopropionic acid dispersion obtained in step (2) were mixed at a volume ratio of 1:2.778 and diluted to 200 mL. The dispersion was stirred at 400 r / min for 30 min to ensure uniform mixing. After ultrasonication at 180 W for 0.5 h, the uniformly mixed dispersion was filtered onto a PES microporous membrane with a pore size of 0.22 μm and a diameter of 50 mm using vacuum-assisted filtration. The membrane was dried at 45 °C for 24 h to obtain the 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 selection factor is 3.2.

[0095] Comparative Example 4

[0096] The difference between Comparative Example 4 and Example 1 is that the zwitterionic crosslinking agent was replaced with a common commercially available zwitterion: N,N-dimethylglycine.

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

[0098] (1) Preparation of graphene oxide nanosheet dispersion: 4g of 325-mesh graphite flakes, 480mL of concentrated sulfuric acid and 54mL of concentrated phosphoric acid were mixed and stirred. 24g of potassium permanganate was slowly added, and the mixture was reacted in a water bath at 50℃ for 24h. Then, 800mL of deionized water was added, followed by dropwise addition of hydrogen peroxide until the solution turned golden yellow. After standing overnight, the mixture was centrifuged. The centrifuged product was washed with dilute hydrochloric acid and deionized water until the pH was 5-6. After dialyzing, the product was dispersed in ultrapure water to obtain a graphene oxide nanosheet dispersion with a concentration of 1mg / 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 stirred at 400 r / min and 30 °C for 24 h to obtain an N,N-dimethylglycine dispersion with a concentration of 1 mmol / L.

[0100] (3) Preparation of N,N-dimethylglycine-doped graphene oxide nanofiltration membrane: 0.5 mL of the graphene oxide nanosheet dispersion obtained in step (1) and 0.5 mL of the N,N-dimethylglycine dispersion obtained in step (2) were mixed at a volume ratio of 1:2.778 and diluted to 200 mL. The dispersion was stirred at 400 r / min for 30 min to ensure uniform mixing. After ultrasonication at 180 W for 0.5 h, the uniformly mixed dispersion was filtered onto a PES microporous membrane with a pore size of 0.22 μm and a diameter of 50 mm using vacuum-assisted filtration. The membrane was dried at 45 °C for 24 h to obtain the 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 selection factor 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 was changed.

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

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

[0105] (2) Preparation of zwitterionic crosslinking agent dispersion: 0.1 mmol of 2,6-diaminopyridine (10.9 mg) and 0.11 mmol of 3-bromopropionic acid (16.8 mg) were dissolved in 100 mL of ultrapure water, and then the two were mixed evenly at a speed of 400 r / min and reacted at 30 °C for 24 h to obtain zwitterionic crosslinking agent dispersion.

[0106] (3) Preparation of zwitterionic crosslinking agent-doped graphene oxide nanofiltration membrane: Take 0.5 mL of the graphene oxide nanosheet dispersion obtained in step (1) and 0.5 mL of the zwitterionic crosslinking agent dispersion obtained in step (2) and mix them at a volume ratio of 1:2.778, then dilute to 200 mL. Stir at 400 r / min for 30 min to make the dispersion uniformly mixed. After sonication at 180 W for 0.5 h, use vacuum-assisted filtration to filter the uniformly mixed dispersion onto a PES microporous filter membrane with a pore size of 0.22 μm and a diameter of 50 mm. Dry at 45 °C for 24 h to obtain 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 selection factor 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 was changed.

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

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

[0111] (2) Preparation of zwitterionic crosslinking agent dispersion: 0.11 mmol of 2,6-diaminopyridine (12.0 mg) and 0.1 mmol of 3-bromopropionic acid (15.3 mg) were dissolved in 100 mL of ultrapure water, and then the two were mixed evenly at a speed of 400 r / min and reacted at 30 °C for 24 h to obtain zwitterionic crosslinking agent 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 0.5 mL of the zwitterionic crosslinker dispersion obtained in step (2) and mix them at a volume ratio of 1:2.778, then dilute to 200 mL. Stir at 400 r / min for 30 min to make the dispersion uniform, and sonicate at 180 W for 0.5 h. Then, use vacuum-assisted filtration to filter the uniformly mixed dispersion onto a PES microporous filter membrane with a pore size of 0.22 μm and a diameter of 50 mm. Dry at 45 °C for 24 h to obtain 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 selection factor is 4.5.

[0113] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for preparing a zwitterionic crosslinked graphene oxide nanofiltration membrane, characterized in that, Includes the following steps: (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 the mixture was reacted in a water bath at 50°C for 24 hours. Then 0.8-3L of deionized water was added, followed by 10-30mL of 30% hydrogen peroxide dropwise until the solution turned golden yellow. After standing overnight, the mixture was centrifuged at 3000-3500r / min for 15-30min, for a total of 15-20 centrifugations. The centrifuged product was washed with 1-5% dilute hydrochloric acid and deionized water until pH=5-6. After dialyzing, the product was dispersed in ultrapure water to obtain graphene oxide nanosheet dispersion. (2) Preparation of zwitterionic crosslinking agent dispersion: The solution of 2,6-diaminopyridine and the solution of 3-bromopropionic acid were mixed and stirred continuously in a constant temperature water bath to obtain zwitterionic crosslinking agent dispersion. (3) Preparation of zwitterionic crosslinked graphene oxide nanofiltration membrane: The graphene oxide nanosheet dispersion obtained in step (1) and the zwitterionic crosslinking agent dispersion obtained in step (2) are mixed and diluted, stirred and ultrasonically treated, and loaded onto the surface of a macroporous polymer support membrane by vacuum filtration. After thermal crosslinking, zwitterionic crosslinked 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 mesh, 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 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 solution of 2,6-diaminopyridine is 0.5-2 mmol / L, the concentration of the solution of 3-bromopropionic acid 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℃, the stirring rate is 300-500r / min, the time is 12-24h, and the concentration of the zwitterionic crosslinking agent in the zwitterionic crosslinking agent dispersion is 0.5-2mmol / 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 solute 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 mixture 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 mentioned 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 thermal crosslinking time in step (3) is 12-24 hours, and the thermal crosslinking temperature is 45-80°C.

9. The zwitterionic crosslinked graphene oxide nanofiltration membrane prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the zwitterionic crosslinked graphene oxide nanofiltration membrane of claim 9 in the field of water treatment.

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