Preparation method of graphene oxide ceramic composite nanofiltration membrane

Abstract

The invention discloses a preparation method of a graphene oxide ceramic composite nanofiltration membrane, and belongs to the technical field of membrane separation, and the preparation method comprises the following steps: (1) preparing a graphene oxide aqueous solution; (2) soaking the porous ceramic membrane support body with a sodium hydroxide solution to obtain an activated ceramic membrane support body; (3) soaking the activated ceramic membrane support body in a 3-aminopropyldiethoxysilane ethanol solution, and reacting at room temperature to obtain a grafted ceramic membrane support body; (4) at room temperature, diluting a graphene oxide aqueous solution, and carrying out a cross-flow filtration reaction on the surface of the grafted ceramic membrane support body; and (5) carrying out heat treatment on the material obtained in the step (4) to obtain the graphene oxide ceramic composite nanofiltration membrane. The ordered graphene oxide functional layer is formed through silane modification and cross-flow filtration technologies, and the obtained nanofiltration membrane has excellent strong acid resistance, strong alkali resistance and organic solvent resistance and is suitable for the fields of seawater desalination, water purification and the like.

Description

Technical Field

[0001] The present invention belongs to the field of membrane separation technology, and in particular relates to a method for preparing a graphene oxide ceramic composite nanofiltration membrane. Background Art

[0002] With the acceleration of global industrialization and urbanization, water pollution is becoming increasingly serious. Industrial wastewater discharge, agricultural irrigation and drinking water demand pose a huge challenge to freshwater resources. Membrane separation technology has been widely used in seawater desalination, water purification, pharmaceuticals and petrochemicals due to its high efficiency, energy saving and environmental friendliness. Among them, nanofiltration membranes have unique advantages in intercepting divalent and multivalent ions, organic small molecules (such as dyes, drugs) and maintaining high flux with their nanoscale pore size (usually 1-2nm), making them one of the core technologies in the field of water treatment. However, traditional nanofiltration membranes still have many shortcomings in performance, durability and preparation process, which limit their application in complex environments.

[0003] Graphene and its derivatives (such as graphene oxide, GO) have become a research hotspot in the field of membrane separation in recent years due to their unique two-dimensional structure and chemical properties. Graphene oxide has a large interlayer distance (about 0.7-1nm), which can accommodate the passage of water molecules. At the same time, its original graphite area promotes rapid water penetration through almost frictionless fluid channels, making it have great potential in seawater desalination and water purification. In addition, the surface of GO is rich in functional groups such as hydroxyl and carboxyl groups, which can be chemically modified to enhance the binding force with the substrate, thereby improving the stability and durability of the membrane. However, the preparation methods of existing GO-based nanofiltration membranes have significant defects. For example, the preparation of porous GO membranes using electron beam or plasma etching requires harsh experimental conditions, complex equipment and high cost, making it difficult to achieve large-scale production. Although mixed matrix membranes (GO and polymer composites) are simple to prepare, their separation performance is limited by the polymer matrix, the flux is low, and the resistance to strong acids, strong bases and organic solvents is poor, making it difficult to meet the requirements of harsh environments in industrial wastewater treatment. In addition, the deposition of GO membranes on ceramic substrates usually adopts methods such as dip coating or spin coating. These techniques easily lead to disordered GO layer stacking and weak bonding force, affecting the retention rate and long-term stability of the membrane.

[0004] Ceramic membranes are often used as supports for nanofiltration membranes due to their excellent chemical stability, mechanical strength and high temperature resistance. In the prior art, some studies have enhanced the bonding between the ceramic substrate and the functional layer through chemical modification (such as silane coupling agent). For example, in 2014, Yu et al. reported the use of 3-glycidyloxypropyltrimethoxysilane (GPTMS) to modify the ceramic support and deposit GO by dip coating to prepare a composite membrane for dye removal, but this method did not involve salt retention, and the acid, alkali / solvent resistance was not fully verified. A 2018 paper described the use of spin coating to deposit GO on a GLYMO-modified volcanic ash-based ceramic membrane and thermally reduce it to rGO, with a high water flux (2-75L / m 2 ·h·bar), but cross-flow filtration was not used, the membrane uniformity was poor, and there was a lack of durability data. In 2021, a study used octadecyltrichlorosilane (ODTS) to modify a ceramic membrane and deposit GO by immersion, with a flux of up to 520L / m 2 ·h·bar, but they are mainly targeted at tetracycline adsorption, with limited retention performance, and the deposition method does not optimize the order of the GO layer. The common problem of these existing technologies is the lack of efficient GO deposition methods to form ordered nanostructures, making it difficult to achieve high flux, high retention rate, and strong durability at the same time.

[0005] In response to the above problems, there is an urgent need to develop a GO ceramic composite nanofiltration membrane with simple preparation process and excellent performance to meet the requirements of high desalination rate, high flux and resistance to strong acid / alkali and organic solvents. Summary of the Invention

[0006] The present invention aims to overcome the defects of the prior art and provide a method for preparing a graphene oxide ceramic composite nanofiltration membrane.

[0007] The technical solutions of the present invention are as follows:

[0008] A method for preparing a graphene oxide ceramic composite nanofiltration membrane comprises the following steps:

[0009] (1) preparing a graphene oxide aqueous solution with a concentration of 2-4 mg / mL;

[0010] (2) soaking the porous ceramic membrane support in a sodium hydroxide solution to obtain an activated ceramic membrane support;

[0011] (3) immersing the activated ceramic membrane support obtained in step (2) in a 3-aminopropyldiethoxysilane ethanol solution and reacting at room temperature to obtain a grafted ceramic membrane support;

[0012] (4) diluting the graphene oxide aqueous solution obtained in step (1) at room temperature, and performing a cross-flow filtration reaction on the surface of the grafted ceramic membrane support obtained in step (3) for 4-6 minutes, with a cross-flow pressure of 0.2-0.4 MPa and a surface cross-flow rate of 0.2-0.4 m / s; after the reaction, rinsing with RO water to remove unreacted graphene oxide dispersion;

[0013] (5) heat-treating the material obtained in step (4) to obtain the graphene oxide ceramic composite nanofiltration membrane.

[0014] In the present invention, graphene oxide can be arranged in an orderly and uniform manner on the ceramic membrane support after activation and grafting modification through a cross-flow filtration method to form a graphene oxide membrane layer with a compact structure; through heat treatment, the oxygen-containing functional groups on the graphene oxide and the functional groups on the ceramic membrane support after activation and grafting modification are chemically bonded to form a stable graphene oxide nanofiltration membrane layer with excellent desalination performance and acid and alkali resistance.

[0015] In a preferred embodiment of the present invention, step (2) comprises: selecting a porous ceramic membrane support with a pore size of 95-105 nm and a length of 45-55 cm, ultrasonically treating it for 4-6 hours, soaking it in a 1.8-2.2 mol / L sodium hydroxide solution for 20-25 hours, drying it at 95-100°C for 8-12 hours, then rinsing it with ethanol and deionized water several times in sequence, drying it at 95-100°C for 10-14 hours, and then cooling it in the furnace to obtain an activated ceramic membrane support.

[0016] In a preferred embodiment of the present invention, step (3) comprises: immersing the activated ceramic membrane support obtained in step (2) in a 3-aminopropyldiethoxysilane ethanol solution with a concentration of 4-6 mmol / L, reacting at room temperature for 10-12 hours, then rinsing with ethanol and deionized water several times, drying at 145-150°C for 10-14 hours and then cooling with the furnace to obtain a grafted ceramic membrane support.

[0017] In a preferred embodiment of the present invention, step (4) comprises: diluting the graphene oxide aqueous solution obtained in step (1) at room temperature, and then performing a cross-flow filtration reaction on the surface of the grafted ceramic membrane support obtained in step (3) for 5 minutes, with a cross-flow pressure of 0.3 MPa and a surface cross-flow rate of 0.3 m / s; after the reaction, rinsing with RO water to remove unreacted graphene oxide dispersion.

[0018] Further preferably, the step (4) comprises: diluting the graphene oxide aqueous solution obtained in step (1) to 20-40 mg / L at room temperature.

[0019] In a preferred embodiment of the present invention, the step (5) comprises: placing the material obtained in step (4) in a cool place to air-dry, heat-treating it at 80-120° C. for 2-4 hours, and then cooling it in the furnace to obtain the graphene oxide ceramic composite nanofiltration membrane.

[0020] In a preferred embodiment of the present invention, the porous ceramic membrane support is made of alumina, titanium oxide or zirconium oxide.

[0021] More preferably, the porous ceramic membrane support is made of alumina.

[0022] The beneficial effects of the present invention are:

[0023] 1. The present invention forms an ordered GO functional layer by depositing graphene oxide on a porous ceramic support modified by a silane coupling agent using cross-flow filtration. After heat treatment, the pure water flux of the membrane reaches 19.5-22 L / m at 0.6 MPa. 2 ·h, the retention rate of 0.2wt% magnesium sulfate solution is as high as 92%-95.2%, which is significantly better than the comparative example (retention rate 13%-52%).

[0024] 2. The graphene oxide ceramic membrane prepared by the present invention has stable performance under extreme conditions (pH = 0 nitric acid, pH = 12 sodium hydroxide, soaked at 85°C for 168 hours; acetone, tetrahydrofuran and other organic solvents, soaked at 85°C for 10 days), with flux and retention rate changes of less than 5%, showing excellent resistance to strong acids, strong alkalis and organic solvents, and is suitable for harsh environments such as industrial wastewater treatment.

[0025] 3. The present invention adopts cross-flow filtration technology instead of traditional dipping or spin coating to avoid disordered accumulation of GO layers and ensure the uniformity and bonding strength of the film layer; the process parameters (such as GO concentration, cross-flow pressure, and heat treatment temperature) are optimized and easy to control, making it suitable for large-scale production.

[0026] 4. The structure of the graphene oxide ceramic membrane prepared by the present invention combines the mechanical strength of the ceramic support and the nano-scale separation performance of GO, and is suitable for various separation needs in the fields of seawater desalination, water purification, pharmaceuticals and petrochemicals. DETAILED DESCRIPTION

[0027] The technical solution of the present invention is further illustrated and described below through specific implementation methods.

[0028] The method for preparing graphene oxide by the improved Hummers method in the following examples and comparative examples specifically includes:

[0029] (1) Wash and dry a 1000 mL beaker, add 3 g of flake graphite, and slowly add 360 mL of concentrated sulfuric acid (98% H2SO4) and 40 mL of concentrated phosphoric acid (95% H3PO4) under magnetic stirring. Then slowly add 18 g of potassium permanganate (KMnO4) in batches. Move the beaker to a 50°C oil bath and stir for 12 hours. Remove the beaker and allow it to cool naturally to room temperature. Slowly pour the reaction solution onto ice cubes in 400 mL of dilute hydrogen peroxide (containing 18 ml of 30% H2O2). The solution turns bright yellow.

[0030] (2) The solution obtained in step (1) is subjected to cross-flow filtration with a tubular ceramic membrane having a pore size of 0.05 μm to remove impurities, thereby obtaining a graphene oxide solution after impurities removal; the basic principle is to utilize the pore screening effect of the tubular ceramic membrane, that is, the filtration pore size of the tubular ceramic membrane is smaller than the size of the GO sheet, so that the GO sheet cannot flow out through the tubular ceramic membrane, but flows back to the feed liquid barrel with the circulation of the liquid in the pipeline, which neither blocks the membrane pores nor ensures the smoothness of the membrane pores, and also crushes and peels off the larger GO sheets; the filtration pore size of the tubular ceramic membrane is larger than the impurity ion size of the GO solution, so that H + , K + 、Mn 2+ Acid radicals and metal ions can easily pass through the pores of the ceramic tubular membrane and be discharged. This cycle is repeated to achieve the separation of GO and waste acid, K + , and Mn 2+ The separation of metal ions and the collection of GO solution complete the washing and impurity removal of GO;

[0031] (3) Diluting or concentrating according to the required concentration to obtain graphene oxide aqueous solutions of different concentrations.

[0032] Example 1

[0033] (1) Using the modified Hummers method described above, a graphene oxide aqueous solution with a concentration of 3 mg / mL was prepared;

[0034] (2) After cutting the alumina ceramic membrane tube with a length of about 50 cm and a pore size of 100 nm, ultrasonically treat it for 5 hours, soak it in 2 mol / L sodium hydroxide for 24 hours, dry it at 100°C for 10 hours, and then rinse it with ethanol and deionized water several times. Then, put it in an oven with a temperature setting of 100°C and dry it for 12 hours. After that, cool it in the oven to obtain an activated ceramic membrane support body.

[0035] (3) Soaking the activated ceramic membrane support obtained in step (2) in a 5 mmol / L 3-aminopropyldiethoxysilane ethanol solution, reacting for 12 h at room temperature, then rinsing with ethanol and deionized water several times, placing in an oven at a temperature setting of 150° C. and drying for 12 h, and then cooling in the oven to obtain a grafted ceramic membrane support;

[0036] (4) At room temperature, the grafted ceramic membrane support obtained in step (3) is positioned, the graphene oxide aqueous solution obtained in step (1) is diluted to 20 mg / L, and a cross-flow filtration reaction is performed on the surface of the grafted ceramic membrane support obtained in step (3) for 5 minutes, the cross-flow pressure is 0.3 MPa, and the surface cross-flow rate is 0.3 m / s; after the cross-flow filtration reaction is completed, it is rinsed with RO water to remove the unreacted graphene oxide aqueous solution;

[0037] (5) The material obtained in step (4) was placed in a cool place to air-dry and then placed in an 80° C. oven for heat treatment for 3 h, and then cooled in the oven to obtain a graphene oxide ceramic composite nanofiltration membrane.

[0038] Membrane tube performance test: The graphene oxide ceramic composite nanofiltration membrane prepared in this example was tested at room temperature and a pressure of 0.6 MPa. The pure water flux was 22 LHM, and the rejection rate of 0.2 wt % magnesium sulfate solution was 92%.

[0039] Acid and alkali resistance test: After the graphene oxide ceramic composite nanofiltration membrane prepared in this example was immersed in a nitric acid solution with a pH of 0 and a sodium hydroxide solution with a pH of 12 at 85°C for 168 hours, the pure water flux was 23 and 22.5 LHM, respectively, and the retention rates of 0.2 wt% magnesium sulfate solution were 92.5% and 93%, respectively, and the performance remained basically unchanged.

[0040] Solvent resistance test: The graphene oxide ceramic composite nanofiltration membrane prepared in this example was immersed in acetone, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide and acetonitrile solutions, respectively. After immersion at 85°C for 10 days, the retention rates of 0.2 wt% magnesium sulfate solution were 93%, 91.5%, 90%, 93.5% and 91.8%, respectively, and the performance remained basically unchanged.

[0041] Example 2

[0042] (1) Using the modified Hummers method described above, a graphene oxide aqueous solution with a concentration of 3 mg / mL was prepared;

[0043] (2) After cutting the alumina ceramic membrane tube with a length of about 50 cm and a pore size of 100 nm, ultrasonically treat it for 5 hours, soak it in 2 mol / L sodium hydroxide for 24 hours, dry it at 100°C for 10 hours, and then rinse it with ethanol and deionized water several times. Then, put it in an oven with a temperature setting of 100°C and dry it for 12 hours. After that, cool it in the oven to obtain an activated ceramic membrane support body.

[0044] (3) Soaking the activated ceramic membrane support obtained in step (2) in a 5 mmol / L 3-aminopropyldiethoxysilane ethanol solution, reacting for 12 h at room temperature, then rinsing with ethanol and deionized water several times, placing in an oven at a temperature setting of 150° C. and drying for 12 h, and then cooling in the oven to obtain a grafted ceramic membrane support;

[0045] (4) At room temperature, the grafted ceramic membrane support obtained in step (3) is positioned, the graphene oxide aqueous solution obtained in step (1) is diluted to 40 mg / L, and a cross-flow filtration reaction is performed on the surface of the grafted ceramic membrane support obtained in step (3) for 5 minutes, the cross-flow pressure is 0.3 MPa, and the surface cross-flow rate is 0.3 m / s; after the cross-flow filtration reaction is completed, it is rinsed with RO water to remove the unreacted graphene oxide aqueous solution;

[0046] (5) The material obtained in step (4) was placed in a cool place to air-dry and then placed in an 80° C. oven for heat treatment for 3 h, and then cooled in the oven to obtain a graphene oxide ceramic composite nanofiltration membrane.

[0047] Membrane tube performance test: The graphene oxide ceramic composite nanofiltration membrane prepared in this example was tested at room temperature and a pressure of 0.6 MPa. Its pure water flux was 21 LHM, and its rejection rate for 0.2 wt % magnesium sulfate solution was 93.5%.

[0048] Acid and alkali resistance test: After the graphene oxide ceramic composite nanofiltration membrane prepared in this example was immersed in a nitric acid solution with a pH of 0 and a sodium hydroxide solution with a pH of 12 at 85°C for 168 hours, the pure water flux was 21 and 20.8 LHM, respectively, and the retention rate of 0.2 wt% magnesium sulfate solution was 94% and 94.8%, respectively, and the performance remained basically unchanged.

[0049] Solvent resistance test: The graphene oxide ceramic composite nanofiltration membrane prepared in this example was immersed in acetone, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide and acetonitrile solutions, respectively. After immersion at 85°C for 10 days, the retention rates of 0.2 wt% magnesium sulfate solution were 92.8%, 94%, 92%, 95% and 93.5%, respectively, and the performance remained basically unchanged.

[0050] Example 3

[0051] (1) Using the modified Hummers method described above, a graphene oxide aqueous solution with a concentration of 3 mg / mL was prepared;

[0052] (2) After cutting the alumina ceramic membrane tube with a length of about 50 cm and a pore size of 100 nm, ultrasonically treat it for 5 hours, soak it in 2 mol / L sodium hydroxide for 24 hours, dry it at 100°C for 10 hours, and then rinse it with ethanol and deionized water several times. Then, put it in an oven with a temperature setting of 100°C and dry it for 12 hours. After that, cool it in the oven to obtain an activated ceramic membrane support body.

[0053] (3) Soaking the activated ceramic membrane support obtained in step (2) in a 5 mmol / L 3-aminopropyldiethoxysilane ethanol solution, reacting for 12 h at room temperature, then rinsing with ethanol and deionized water several times, placing in an oven at a temperature setting of 150° C. and drying for 12 h, and then cooling in the oven to obtain a grafted ceramic membrane support;

[0054] (4) At room temperature, the grafted ceramic membrane support obtained in step (3) is positioned, the graphene oxide aqueous solution obtained in step (1) is diluted to 40 mg / L, and a cross-flow filtration reaction is performed on the surface of the grafted ceramic membrane support obtained in step (3) for 5 minutes, the cross-flow pressure is 0.3 MPa, and the surface cross-flow rate is 0.3 m / s; after the cross-flow filtration reaction is completed, it is rinsed with RO water to remove the unreacted graphene oxide aqueous solution;

[0055] (5) The material obtained in step (4) was placed in a cool place to air-dry and then placed in a 120° C. oven for heat treatment for 3 h, and then cooled in the oven to obtain a graphene oxide ceramic composite nanofiltration membrane.

[0056] Membrane tube performance test: The graphene oxide ceramic composite nanofiltration membrane prepared in this example was tested at room temperature and a pressure of 0.6 MPa. Its pure water flux was 19.5 LHM, and its rejection rate for 0.2 wt % magnesium sulfate solution was 95.2%.

[0057] Acid and alkali resistance test: After the graphene oxide ceramic composite nanofiltration membrane prepared in this example was immersed in a nitric acid solution with a pH of 0 and a sodium hydroxide solution with a pH of 12 at 85°C for 168 hours, the pure water flux was 20 and 19.5 LHM, respectively, and the retention rate of 0.2 wt% magnesium sulfate solution was 95% and 96.2%, respectively, and the performance remained basically unchanged.

[0058] Solvent resistance test: The graphene oxide ceramic composite nanofiltration membrane prepared in this example was immersed in acetone, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide and acetonitrile solutions, respectively. After immersion at 85°C for 10 days, the retention rates of 0.2 wt% magnesium sulfate solution were 96%, 95%, 94.5%, 93% and 96.2%, respectively, and the performance remained basically unchanged.

[0059] Comparative Example 1

[0060] (1) Using the modified Hummers method described above, a graphene oxide aqueous solution with a concentration of 3 mg / mL was prepared;

[0061] (2) After cutting the alumina ceramic membrane tube with a length of about 50 cm and a pore size of 100 nm, ultrasonically treat it for 5 hours, soak it in 2 mol / L sodium hydroxide for 24 hours, dry it at 100°C for 10 hours, and then rinse it with ethanol and deionized water several times. Then, put it in an oven with a temperature setting of 100°C and dry it for 12 hours. After that, cool it in the oven to obtain an activated ceramic membrane support body.

[0062] (3) Soaking the activated ceramic membrane support obtained in step (2) in a 5 mmol / L 3-aminopropyldiethoxysilane ethanol solution, reacting for 12 h at room temperature, then rinsing with ethanol and deionized water several times, placing in an oven at a temperature setting of 150° C. and drying for 12 h, and then cooling in the oven to obtain a grafted ceramic membrane support;

[0063] (4) At room temperature, the grafted ceramic membrane support obtained in step (3) is positioned, the graphene oxide aqueous solution obtained in step (1) is diluted to 30 mg / L, and a dead-end filtration reaction is performed for 5 minutes at a surface cross-flow rate of 0.3 m / s; after the cross-flow filtration reaction is completed, the solution is rinsed with RO water to remove unreacted graphene oxide aqueous solution;

[0064] (5) The material obtained in step (4) was placed in a cool place for air drying and then placed in an oven at 80°C for heat treatment for 3 hours, and then cooled in the oven to obtain a comparison film.

[0065] Membrane tube performance test: The comparative membrane prepared in this comparative example was tested at room temperature and a pressure of 0.6 MPa. The pure water flux was 12 LHM, and the rejection rate of 0.2 wt % magnesium sulfate solution was 13%.

[0066] Acid and alkali resistance test: After the comparative membrane prepared in this comparative example was immersed in a nitric acid solution with a pH of 0 and a sodium hydroxide solution with a pH of 12 at 85°C for 168 hours, the pure water flux was 11 and 12 LHM, respectively, and the retention rate of 0.2wt% magnesium sulfate solution was 12.5% ​​and 13.2%, respectively, and the performance remained basically unchanged.

[0067] Solvent resistance test: The comparative membrane prepared in this comparative example was immersed in acetone, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide and acetonitrile solutions, respectively. After immersion at 85°C for 10 days, the retention rates of 0.2wt% magnesium sulfate solution were 11.5%, 12.2%, 11%, 12% and 12.6%, respectively, and the performance remained basically unchanged.

[0068] Comparative Example 2

[0069] (1) Using the modified Hummers method described above, a graphene oxide aqueous solution with a concentration of 3 mg / mL was prepared;

[0070] (2) After cutting the alumina ceramic membrane tube with a length of about 50 cm and a pore size of 100 nm, ultrasonically treat it for 5 hours, soak it in 2 mol / L sodium hydroxide for 24 hours, dry it at 100°C for 10 hours, and then rinse it with ethanol and deionized water several times. Then, put it in an oven with a temperature setting of 100°C and dry it for 12 hours. After that, cool it in the oven to obtain an activated ceramic membrane support body.

[0071] (3) Soaking the activated ceramic membrane support obtained in step (2) in a 5 mmol / L 3-aminopropyldiethoxysilane ethanol solution, reacting for 12 h at room temperature, then rinsing with ethanol and deionized water several times, placing in an oven at a temperature setting of 150° C. and drying for 12 h, and then cooling in the oven to obtain a grafted ceramic membrane support;

[0072] (4) At room temperature, the grafted ceramic membrane support obtained in step (3) is positioned, the graphene oxide aqueous solution obtained in step (1) is diluted to 30 mg / L, and a cross-flow filtration reaction is performed on the surface of the grafted ceramic membrane support obtained in step (3) for 5 minutes, the cross-flow pressure is 0.3 MPa, and the surface cross-flow rate is 0.3 m / s; after the cross-flow filtration reaction is completed, it is rinsed with RO water to remove the unreacted graphene oxide aqueous solution;

[0073] (5) The material obtained in step (4) was placed in a cool place for air drying and then placed in an oven at 180°C for heat treatment for 3 hours, and then cooled in the oven to obtain a comparison film.

[0074] Membrane tube performance test: The comparative membrane prepared in this comparative example was tested at room temperature and a pressure of 0.6 MPa. The pure water flux was 14.5 LHM, and the rejection rate of 0.2 wt % magnesium sulfate solution was 24%.

[0075] Acid and alkali resistance test: After the comparative membrane prepared in this comparative example was immersed in a nitric acid solution with a pH of 0 and a sodium hydroxide solution with a pH of 12 at 85°C for 168 hours, the pure water flux was 14 and 13 LHM, respectively, and the retention rate of 0.2wt% magnesium sulfate solution was 23% and 23.5%, respectively, and the performance remained basically unchanged.

[0076] Solvent resistance test: The comparative membrane prepared in this comparative example was immersed in acetone, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide and acetonitrile solutions, respectively. After immersion at 85°C for 10 days, the retention rates of 0.2wt% magnesium sulfate solution were 23%, 25%, 24.4%, 23.5% and 22.8%, respectively, and the performance remained basically unchanged.

[0077] Comparative Example 3

[0078] (1) Using the improved Hummers method described above to prepare a graphene oxide aqueous solution with a concentration of 3 mg / mL;

[0079] (2) An alumina ceramic membrane tube with a pore size of 100 nm and a length of about 50 cm after cutting was ultrasonically treated for 5 h, then soaked in 2 mol / L sodium hydroxide for 24 h, dried at 100°C for 10 h, then washed with ethanol and deionized water several times, and dried in an oven at a temperature setting of 100°C for 12 h and then cooled with the oven to obtain an activated ceramic membrane support;

[0080] (3) The activated ceramic membrane support obtained in step (2) was soaked in a 3-aminopropyl diethoxysilane ethanol solution with a concentration of 5 mmol / L, reacted at room temperature for 12 h, then washed with ethanol and deionized water several times, and dried in an oven at a temperature setting of 150°C for 12 h and then cooled with the oven to obtain a grafted ceramic membrane support;

[0081] (4) The grafted ceramic membrane support obtained in step (3) was positioned, the graphene oxide aqueous solution obtained in step (1) was diluted to 5 mg / L, and a cross-flow filtration reaction was carried out on the surface of the grafted ceramic membrane support obtained in step (3) for 5 min at a cross-flow pressure of 0.3 MPa and a surface cross-flow rate of 0.3 m / s. After the cross-flow filtration reaction was completed, the unreacted graphene oxide aqueous solution was removed by washing with RO water;

[0082] (5) The material obtained in step (4) was placed in a cool place to air dry, then placed in an 80°C oven for heat treatment for 3 h, and then cooled with the oven to obtain the comparative membrane.

[0083] Membrane tube performance test: The comparative membrane prepared in this comparative example was tested at room temperature and a pressure of 0.6 MPa, and had a pure water flux of 24 LHM and a 0.2 wt% magnesium sulfate solution rejection rate of 45%.

[0084] Acid and alkali resistance test: The comparative membrane prepared in this comparative example was immersed in a nitric acid solution with a pH of 0 and a sodium hydroxide solution with a pH of 12 at 85°C for 168 h, and then had a pure water flux of 22.5 and 23.8 LHM, respectively, and a 0.2 wt% magnesium sulfate solution rejection rate of 45.8% and 44%, respectively, and the performance remained basically unchanged.

[0085] Solvent resistance test: The comparative membrane prepared in this comparative example was immersed in acetone, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, and acetonitrile solutions, respectively, at 85°C for 10 days, and then had a 0.2 wt% magnesium sulfate solution rejection rate of 45%, 44%, 44.7%, 43%, and 46%, respectively, and the performance remained basically unchanged.

[0086] Comparative Example 4

[0087] (1) Using the modified Hummers method described above, a graphene oxide aqueous solution with a concentration of 3 mg / mL was prepared;

[0088] (2) After cutting the alumina ceramic membrane tube with a length of about 50 cm and a pore size of 100 nm, ultrasonically treat it for 5 hours, soak it in 2 mol / L sodium hydroxide for 24 hours, dry it at 100°C for 10 hours, and then rinse it with ethanol and deionized water several times in sequence. After drying it in an oven at a temperature setting of 100°C for 12 hours, it was cooled in the oven to obtain an activated ceramic membrane support body;

[0089] (3) Soaking the activated ceramic membrane support obtained in step (2) in a 5 mmol / L 3-aminopropyldiethoxysilane ethanol solution, reacting for 12 h at room temperature, then rinsing with ethanol and deionized water several times, placing in an oven at a temperature setting of 150° C. and drying for 12 h, and then cooling in the oven to obtain a grafted ceramic membrane support;

[0090] (4) At room temperature, the grafted ceramic membrane support obtained in step (3) is positioned, the graphene oxide aqueous solution obtained in step (1) is diluted to 100 mg / L, and a cross-flow filtration reaction is performed on the surface of the grafted ceramic membrane support obtained in step (3) for 5 minutes, the cross-flow pressure is 0.3 MPa, and the surface cross-flow rate is 0.3 m / s; after the cross-flow filtration reaction is completed, it is rinsed with RO water to remove the unreacted graphene oxide aqueous solution;

[0091] (5) The material obtained in step (4) was placed in a cool place for air drying and then placed in an oven at 80°C for heat treatment for 3 hours, and then cooled in the oven to obtain a comparison film.

[0092] Membrane tube performance test: The comparative membrane prepared in this comparative example was tested at room temperature and a pressure of 0.6 MPa. The pure water flux was 20 LHM, and the rejection rate of 0.2 wt % magnesium sulfate solution was 52%.

[0093] Acid and alkali resistance test: After the comparative membrane prepared in this comparative example was immersed in a nitric acid solution with a pH of 0 and a sodium hydroxide solution with a pH of 12 at 85°C for 168 hours, the pure water flux was 18 and 19.2 LHM, respectively, and the retention rate of 0.2 wt% magnesium sulfate solution was 53.2% and 51%, respectively, and the performance remained basically unchanged.

[0094] Solvent resistance test: The comparative membrane prepared in this comparative example was immersed in acetone, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide and acetonitrile solutions, respectively. After immersion at 85°C for 10 days, the retention rates of 0.2wt% magnesium sulfate solution were 52.5%, 52%, 51.2%, 50% and 53.1%, respectively, and the performance remained basically unchanged.

[0095] The comparison of the process parameters and technical effects of the above examples and comparative examples are shown in Tables 1 and 2 below respectively:

[0096] Table 1

[0097]

[0098]

[0099] Table 2

[0100]

[0101] The above description is merely a preferred embodiment of the present invention and therefore cannot be used to limit the scope of the present invention. In other words, equivalent changes and modifications made within the scope of the present invention and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A method for preparing a graphene oxide ceramic composite nanofiltration membrane, characterized in that: The steps include: (1) preparing a graphene oxide aqueous solution with a concentration of 2-4 mg / mL; (2) soaking the porous ceramic membrane support in a sodium hydroxide solution to obtain an activated ceramic membrane support; (3) immersing the activated ceramic membrane support obtained in step (2) in a 3-aminopropyldiethoxysilane ethanol solution and reacting at room temperature to obtain a grafted ceramic membrane support; (4) diluting the graphene oxide aqueous solution obtained in step (1) at room temperature, and performing a cross-flow filtration reaction on the surface of the grafted ceramic membrane support obtained in step (3) for 4-6 minutes, with a cross-flow pressure of 0.2-0.4 MPa and a surface cross-flow rate of 0.2-0.4 m / s; after the reaction, rinsing with RO water to remove unreacted graphene oxide dispersion; (5) heat-treating the material obtained in step (4) to obtain the graphene oxide ceramic composite nanofiltration membrane.

2. The preparation method according to claim 1, wherein: The step (2) comprises: selecting a porous ceramic membrane support with a pore size of 95-105 nm and a length of 45-55 cm, ultrasonically treating it for 4-6 hours, soaking it in a 1.8-2.2 mol / L sodium hydroxide solution for 20-25 hours, drying it at 95-100° C. for 8-12 hours, then rinsing it with ethanol and deionized water several times in sequence, drying it at 95-100° C. for 10-14 hours, and then cooling it in the furnace to obtain an activated ceramic membrane support.

3. The preparation method according to claim 1, wherein: The step (3) comprises: immersing the activated ceramic membrane support obtained in the step (2) in a 3-aminopropyldiethoxysilane ethanol solution having a concentration of 4-6 mmol / L, reacting at room temperature for 10-12 hours, then rinsing with ethanol and deionized water several times, drying at 145-150° C. for 10-14 hours, and then cooling in the furnace to obtain a grafted ceramic membrane support.

4. The preparation method according to claim 1, wherein: The step (4) comprises: diluting the graphene oxide aqueous solution obtained in step (1) at room temperature, and then performing a cross-flow filtration reaction on the surface of the grafted ceramic membrane support obtained in step (3) for 5 minutes, with a cross-flow pressure of 0.3 MPa and a surface cross-flow rate of 0.3 m / s; and rinsing with RO water after the reaction to remove unreacted graphene oxide dispersion.

5. The preparation method according to claim 4, wherein: The step (4) comprises: diluting the graphene oxide aqueous solution obtained in the step (1) to 20-40 mg / L at room temperature.

6. The preparation method according to claim 1, wherein: The step (5) comprises: placing the material obtained in the step (4) in a cool place to air-dry, heat-treating it at 80-120° C. for 2-4 hours, and then cooling it in the furnace to obtain the graphene oxide ceramic composite nanofiltration membrane.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The porous ceramic membrane support is made of aluminum oxide, titanium oxide or zirconium oxide.

8. The preparation method according to claim 7, wherein: The porous ceramic membrane support is made of alumina.

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