A graphene oxide composite nanofiltration membrane and its preparation method and application

Abstract

The present invention provides a graphene oxide composite nanofiltration membrane and a preparation method and application thereof. The graphene oxide composite nanofiltration membrane comprises: a base membrane, and a graphene oxide nanofiltration membrane embedded with a polymer nanomaterial on the surface of the base membrane; wherein the graphene oxide nanofiltration membrane embedded with the polymer nanomaterial is obtained by embedding the polymer nanomaterial between the sheets of graphene oxide materials by cross-linking. The preparation method of the composite nanofiltration membrane comprises: applying a mixed solution containing graphene oxide materials, polymer nanomaterials and a cross-linking agent to the surface of the base membrane, and performing a cross-linking reaction to obtain the graphene oxide composite nanofiltration membrane. The present invention provides the application of the graphene oxide composite nanofiltration membrane in treating high-salt wastewater containing dyes. The graphene oxide composite nanofiltration membrane of the present invention has a simple preparation process, is easy to mass produce, has a stable structure, stable performance, and has excellent inorganic salt / dye separation performance.

Description

Technical Field

[0001] The invention relates to a graphene oxide composite nanofiltration membrane and a preparation method and application thereof, belonging to the technical field of nanofiltration membranes. Background Art

[0002] The processing, weaving and printing and dyeing processes of cotton products are very complicated and each process will add and produce different pollutant components. In particular, the wastewater discharged from the printing and dyeing process contains a large amount of salt (usually including one or more of NaCl, Na2CO3, Na2SO4, etc.), undyed dyes and their hydrolysis products. The dyeing wastewater has high salinity and high chroma, and is difficult to treat biochemically. The traditional method for treating this part of the wastewater is to mix it with the wastewater generated by other production links, dilute the salt content and chroma, and then deeply treat it through physicochemical treatment, biochemical treatment or physicochemical-biochemical combination, and then discharge it in compliance with the standards. If the wastewater that meets the discharge standards needs to be reused, it still needs to undergo advanced oxidation or activated carbon adsorption to completely decolorize and meet the requirements for reuse. However, these steps will inevitably bring secondary pollution to the environment.

[0003] Loose nanofiltration is a membrane separation technology with a pore size between ultrafiltration and nanofiltration. On the basis of ensuring high retention of organic dyes, it can allow most inorganic salts to pass through the membrane, thereby achieving efficient separation of organic dyes / brine water in printing and dyeing wastewater, which has high economic value and research significance. However, most commercial nanofiltration membranes are organic membranes. Due to the inherent properties of the polymer network chain structure, the pore size of organic membranes is relatively wide, the selectivity is poor, and the pollution resistance is poor. When the organic membrane is used to treat high-salinity and high-chroma wastewater, if a high dye retention rate is required, the pore size of the organic membrane is required to be small. At this time, it also has a certain retention of salt. Due to the osmotic pressure of this part of the retained salt, the flux of the membrane is very small, so it is difficult to obtain high flux and dye retention rate at the same time.

[0004] Graphene oxide is a derivative of graphene and is also a single-layer two-dimensional sheet carbon material. Recent studies have shown that water molecules can flow quickly on the surface of graphene oxide, and it has excellent separation properties. The surface of graphene oxide is rich in oxygen-containing functional groups such as hydroxyl, carboxyl, epoxy and carbonyl, and has good hydrophilicity. Therefore, it is easy to disperse in water to form a uniform dispersion and easy to prepare into graphene oxide film.

[0005] At present, graphene oxide nanofiltration membranes can be prepared by vacuum filtration, dip coating, spray coating, layer-by-layer self-assembly, coating and other methods, and exhibit excellent salt / dye separation performance. CN110523297A discloses a graphene oxide composite nanofiltration membrane and a preparation method thereof. The preparation method comprises the following steps: using a coating rod to uniformly coat a graphene oxide dispersion on one side of a base film, and then drying and partially reducing it by ultraviolet irradiation to obtain a graphene oxide composite nanofiltration membrane. CN111821867A discloses a self-supporting reduced graphene oxide nanofiltration membrane and a preparation method and application thereof. The preparation method comprises the following steps: uniformly coating a graphene oxide slurry on a polymer substrate, and then reducing it by ultraviolet irradiation to obtain a self-supporting reduced graphene oxide nanofiltration membrane.

[0006] Although the above documents provide a trial plan for the mass production of graphene oxide nanofiltration membranes, there is a lack of rigid support between graphene oxide sheets, and the water channels between sheets will change with the external environment. On the one hand, since the surface of graphene oxide contains a large number of carboxyl, hydroxyl and epoxy groups, it has good hydrophilicity. After the graphene oxide membrane prepared by the above documents comes into contact with water, the interlayer spacing increases, the interception rate decreases, and the graphene oxide membrane expands after soaking for a long time, and the membrane will be damaged or even disintegrated. On the other hand, when the graphene oxide membrane comes into contact with a reducing agent, the oxygen-containing groups decrease; or after acid treatment, the carboxyl groups are protonated, and the interlayer spacing between graphene oxide sheets decreases, resulting in a significant decrease in flux. Therefore, the graphene oxide membrane prepared by the above method does not have practical application value.

[0007] Therefore, developing a graphene oxide nanofiltration membrane that is simple to prepare, easy to mass produce, has a stable structure, stable performance, and has good salt / dye separation performance has become one of the urgent problems to be solved in this field. Summary of the invention

[0008] In order to solve the above technical problems, the purpose of the present invention is to provide a graphene oxide composite nanofiltration membrane and a preparation method and application thereof. The graphene oxide composite nanofiltration membrane of the present invention has a stable structure and has better salt / dye separation performance.

[0009] In order to achieve the above-mentioned purpose, the first aspect of the present invention provides a graphene oxide composite nanofiltration membrane, which comprises: a base membrane, and a graphene oxide nanofiltration membrane embedded with polymer nanomaterials on the surface of the base membrane; wherein the graphene oxide nanofiltration membrane embedded with polymer nanomaterials is obtained by embedding polymer nanomaterials between the flakes of graphene oxide materials by cross-linking.

[0010] In the above-mentioned graphene oxide composite nanofiltration membrane, preferably, the graphene oxide nanofiltration membrane embedded with polymer nanomaterials is arranged on one surface of the base membrane.

[0011] In the above-mentioned graphene oxide composite nanofiltration membrane, preferably, the thickness of the graphene oxide nanofiltration membrane embedded with polymer nanomaterials is 5-2000 nm, more preferably 50-500 nm.

[0012] In the above-mentioned graphene oxide composite nanofiltration membrane, preferably, the interlayer spacing between the graphene oxide material sheets in the graphene oxide nanofiltration membrane embedded with polymer nanomaterials is 0.8-2.0 nm.

[0013] In the above-mentioned graphene oxide composite nanofiltration membrane, preferably, the molecular weight cutoff of the graphene oxide nanofiltration membrane embedded with polymer nanomaterials is 500-3000 Daltons, more preferably 800-3000 Daltons.

[0014] In the above-mentioned graphene oxide composite nanofiltration membrane, preferably, the weight ratio of the polymer nanomaterial to the graphene oxide material in the graphene oxide nanofiltration membrane embedded with the polymer nanomaterial is 0.125-16, more preferably 0.5-8.

[0015] In the above-mentioned graphene oxide composite nanofiltration membrane, preferably, the polymer nanomaterial includes polymer nanofibers and / or polymer nanocrystals, etc. More preferably, the polymer nanofibers have a diameter of 10-50nm and an aspect ratio of 10-100. More preferably, the polymer nanocrystals have a diameter of 2-20nm and an aspect ratio of 10-100. More specifically, the polymer nanomaterial includes one or a combination of cellulose nanofibers, cellulose nanocrystals, chitin nanofibers, chitin nanocrystals, chitosan nanofibers, chitosan nanocrystals, lignin nanofibers, lignin nanocrystals, etc.

[0016] In the above-mentioned graphene oxide composite nanofiltration membrane, preferably, the graphene oxide material includes graphene oxide and / or modified graphene oxide. More preferably, the graphene oxide material is graphene oxide. The graphene oxide and the modified graphene oxide can be a single-layer two-dimensional sheet structure. The modified graphene oxide can include various modified graphene oxides in the prior art, such as but not limited to carboxyl-modified graphene oxide and / or amine-modified graphene oxide, etc.

[0017] In the above-mentioned graphene oxide composite nanofiltration membrane, preferably, the flake size of the graphene oxide and the modified graphene oxide is 0.5-500 μm, more preferably 2-50 μm.

[0018] In the above-mentioned graphene oxide composite nanofiltration membrane, preferably, the material of the base membrane includes one or a combination of nylon (PA), polyvinylidene fluoride (PVDF), polysulfone (PSF), polyethersulfone (PES), polyacrylonitrile (PAN) and cellulose acetate (CA).

[0019] In the above-mentioned graphene oxide composite nanofiltration membrane, preferably, the average pore size of the base membrane is 0.02-10 μm, more preferably 0.1-0.22 μm, and further preferably 0.1 μm and / or 0.22 μm.

[0020] In the above-mentioned graphene oxide composite nanofiltration membrane, preferably, the base membrane includes a positively charged modified nylon microfiltration membrane. The positively charged modified nylon microfiltration membrane can be obtained by commercial purchase or prepared by a method disclosed in the prior art, and the present invention does not specifically limit it. The present invention preferably uses a positively charged modified nylon microfiltration membrane as the base membrane, the surface of which carries positive charge, and can be combined with the negatively charged graphene oxide material by electrostatic force, hydrogen bond and van der Waals force, etc., to enhance the bonding force between the graphene oxide nanofiltration membrane embedded with polymer nanomaterials and the base membrane, and avoid the graphene oxide nanofiltration membrane from falling off from the base membrane during membrane filtration.

[0021] In the above-mentioned graphene oxide composite nanofiltration membrane, preferably, the thickness of the base membrane is 50-200 μm.

[0022] In the above-mentioned graphene oxide composite nanofiltration membrane, preferably, the graphene oxide nanofiltration membrane embedded with polymer nanomaterials is obtained by using a cross-linking agent to carry out a cross-linking reaction to embed the polymer nanomaterials between the sheets of graphene oxide materials. More preferably, the graphene oxide nanofiltration membrane embedded with polymer nanomaterials is obtained specifically by the following method: a mixed solution containing graphene oxide materials, polymer nanomaterials and a cross-linking agent is applied to the surface of a base film, and a cross-linking reaction is carried out, and the polymer nanomaterials are embedded between the sheets of graphene oxide materials by cross-linking, and at the same time, the graphene oxide nanofiltration membrane embedded with polymer nanomaterials is formed on the surface of the base film.

[0023] In the above-mentioned graphene oxide composite nanofiltration membrane, preferably, the cross-linking agent includes a carboxyl cross-linking agent and / or a hydroxyl cross-linking agent, etc.; more preferably, the carboxyl cross-linking agent includes an aziridine cross-linking agent and / or a polycarbodiimide cross-linking agent, etc.; more preferably, the hydroxyl cross-linking agent includes an isocyanate cross-linking agent and / or a polyaldehyde cross-linking agent, etc., more specifically, the polyaldehyde cross-linking agent includes glyoxal and / or glutaraldehyde, etc.

[0024] In the above-mentioned graphene oxide composite nanofiltration membrane, preferably, the amount of the cross-linking agent is 0.1%-30% of the total weight of the graphene oxide material and the polymer nanomaterial, more preferably 0.5%-10%, and further preferably 1%-8%.

[0025] In the above graphene oxide composite nanofiltration membrane, preferably, the temperature of the cross-linking reaction is 20-100° C., more preferably 50-70° C.; preferably, the time of the cross-linking reaction is 2 minutes to one week. The cross-linking reaction can be carried out by natural drying or heating cross-linking.

[0026] The surface of the polymer nanomaterial selected by the present invention contains a large number of carboxyl groups and / or hydroxyl groups, and the surface of the graphene oxide material also contains abundant carboxyl groups and hydroxyl groups. The present invention adopts a carboxyl crosslinker and / or a hydroxyl crosslinker to crosslink the graphene oxide material and the polymer nanomaterial together through the carboxyl groups and / or hydroxyl groups on the graphene oxide material and the polymer nanomaterial, and embed the polymer nanomaterial between the sheets of the graphene oxide material; on the one hand, a rigid support is provided to maintain the water channel between the layers of the graphene oxide material, thereby avoiding the decrease of the membrane flux in practical applications, and on the other hand, the structural stability of the membrane is improved. The preferred technical solution of the present invention can break through the trade-off relationship between the permeability and selectivity of the graphene oxide nanofiltration membrane by optimizing the content of the polymer nanomaterial and the crosslinker, thereby achieving a double increase in the flux and the dye interception rate.

[0027] According to a specific embodiment of the present invention, preferably, the flux of the graphene oxide composite nanofiltration membrane filtering a 2000ppm sodium sulfate solution is 5-30L / (m 2 ·H·Bar), the desalination rate is 50-95%. The desalination rate is the interception rate of inorganic salt (here refers to sodium sulfate), which is calculated by the conventional calculation method in the art.

[0028] According to a specific embodiment of the present invention, preferably, the flux of the graphene oxide composite nanofiltration membrane filtering a 2000ppm active dye solution is 5-30L / (m 2 ·H·Bar), interception rate>98%. Wherein, the reactive dye is a reactive dye conventionally used in the textile field, mainly used for cotton dyeing. More specifically, the reactive dye includes but is not limited to one or a combination of TQ Blue, BlueR, Yellow 3RF, Red E7B, Everzol Blue BB and Novacron Red EC-2BL.

[0029] According to a specific embodiment of the present invention, preferably, the flux of the graphene oxide composite nanofiltration membrane filtering a mixed solution of 70 g / L sodium sulfate and 2 g / L active dye is 3-10 L / (m2 ·H·Bar), dye retention rate is 95%-99.9%, and desalination rate is <15%.

[0030] The second aspect of the present invention provides a method for preparing the above-mentioned graphene oxide composite nanofiltration membrane, which comprises the following steps: applying a mixed solution containing graphene oxide materials, polymer nanomaterials and a cross-linking agent to the surface of a base membrane, and performing a cross-linking reaction, embedding the polymer nanomaterials between the sheets of the graphene oxide materials by cross-linking, and simultaneously forming a graphene oxide nanofiltration membrane embedded with the polymer nanomaterials on the surface of the base membrane, thereby obtaining the graphene oxide composite nanofiltration membrane.

[0031] In the above preparation method, preferably, in the mixed solution, the weight ratio of the polymer nanomaterial to the graphene oxide material is 0.125-16, more preferably 0.5-8.

[0032] In the above preparation method, preferably, in the mixed solution, the amount of the crosslinking agent is 0.1%-30% of the total weight of the graphene oxide material and the polymer nanomaterial, more preferably 0.5%-10%, and further preferably 1%-8%.

[0033] In the above preparation method, preferably, in the mixed solution, the content of the graphene oxide material is 0.5-10 g / L, more preferably 1-4 g / L.

[0034] In the above-mentioned preparation method, preferably, the coating method includes one or a combination of conventional coating processes such as wire bar coating, slit coating and micro-concave coating, as long as the mixed liquid is evenly coated on the base film.

[0035] In the above preparation method, the mixed solution of graphene oxide material, polymer nanomaterial and crosslinking agent is coated on the surface of the base film. It can be coated on one side of the base film or on both sides of the base film, and is preferably coated on one side of the base film.

[0036] In the above preparation method, preferably, the temperature of the cross-linking reaction is 20-100°C, more preferably 50-70°C; preferably, the time of the cross-linking reaction is 2 minutes to one week. The cross-linking reaction can be carried out by natural drying or heating cross-linking. The polymer nanomaterial is embedded in the interlamellar of the graphene oxide material through the cross-linking reaction, and during the cross-linking reaction, the graphene oxide nanofiltration membrane embedded with the polymer nanomaterial is formed on the surface of the base film.

[0037] A third aspect of the present invention provides an application of the above-mentioned graphene oxide composite nanofiltration membrane in treating high-salt wastewater containing dyes.

[0038] According to a specific embodiment of the present invention, preferably, the application is the use of the graphene oxide composite nanofiltration membrane in the decolorization treatment of the dye-containing high-salt wastewater.

[0039] In the above application, preferably, the salt concentration in the high-salt wastewater containing dye is 20-200 g / L, and the dye concentration is 0.2-5 g / L. Wherein, the salt may include NaCl and / or Na2SO4, etc. The salt concentration is the total concentration of inorganic salts in the wastewater. The dye may include reactive dyes. The reactive dyes are conventionally used in the textile field and are mainly used for cotton dyeing. More specifically, the reactive dyes include but are not limited to one or a combination of TQ Blue, BlueR, Yellow3RF, Red E7B, Everzol Blue BB and Novacron Red EC-2BL, etc.

[0040] In the above application, preferably, the flux of the graphene oxide composite nanofiltration membrane for treating the dye-containing high-salt wastewater is 2.5-10 L / (m 2 ·H·Bar), the dye interception rate is 90%-99.9%, and the desalination rate is <15%. The graphene oxide composite nanofiltration membrane of the present invention can be used to filter high-salt wastewater containing dyes, can efficiently remove dyes, and allow most inorganic salts to pass through.

[0041] The inventors of this case have discovered through a large number of experimental studies that the salt retention rate of the unique graphene oxide composite nanofiltration membrane of the present invention decreases with the increase of salt content. Specifically, in some specific embodiments of the present invention, the graphene oxide composite nanofiltration membrane has a high salt retention rate (more than 50%, more specifically 50-95%) for low-salt solutions (such as 2g / L Na2SO4 solution), but has almost no retention (retention rate less than 15%) for salt solutions with a concentration exceeding 20g / L. According to a specific embodiment of the present invention, the flux and desalination rate of filtering aqueous solutions of different contents of sodium sulphate (i.e., Na2SO4) using the graphene oxide composite nanofiltration membrane of the present invention are as follows: Figure 1As shown. In addition, in some specific embodiments of the present invention, when the graphene oxide composite nanofiltration membrane filters a mixture of dyes and high-concentration salts, the interception rate of salts will also be reduced to less than 15%, but the interception rate of dyes can still be maintained at a high level, and the dye interception rate reaches 95%-99.9%. In other words, the graphene oxide composite nanofiltration membrane of the present invention has a high interception rate for low-concentration salts and dyes of unlimited concentrations, and is therefore not suitable for separating systems containing dyes and low-concentration salts (such as 2g / L Na2SO4+1g / L active dye solution). However, the graphene oxide composite nanofiltration membrane of the present invention can efficiently separate dyes and high-concentration salts in the system (such as 50g / LNa2SO4+1g / L active dye solution). When the graphene oxide composite nanofiltration membrane of the present invention is used to filter a system containing dyes and high-concentration salts, the salt retention rate is very low (less than 15%), but the dyes can still be efficiently retained (the dye retention rate is 95%-99.9%), so that low-chroma salt water can be obtained, thereby achieving decolorization treatment of high-salt wastewater containing dyes and recycling inorganic salts.

[0042] A fourth aspect of the present invention provides a wastewater treatment system, which includes the above-mentioned graphene oxide composite nanofiltration membrane.

[0043] According to a specific embodiment of the present invention, preferably, the wastewater treatment system comprises: a pH adjusting unit, a coarse filtration unit, an ultrafiltration unit and a nanofiltration unit; the inlet of the pH adjusting unit is connected to a wastewater delivery pipeline, the outlet of the pH adjusting unit is connected to the inlet of the coarse filtration unit through a pipeline, the outlet of the coarse filtration unit is connected to the inlet of the ultrafiltration unit through a pipeline, the outlet of the ultrafiltration unit is connected to the inlet of the nanofiltration unit through a pipeline, the water production port of the nanofiltration unit produces recycled water; wherein, the nanofiltration unit comprises the graphene oxide composite nanofiltration membrane.

[0044] In the above wastewater treatment system, preferably, the pH value adjusting unit comprises a pH value adjusting tank for adjusting the pH value of the wastewater to neutral. The pH value adjusting tank used can be a conventional pH value adjusting tank in the art.

[0045] In the above wastewater treatment system, preferably, the coarse filtration unit includes one or a combination of a sand filter, a filter bag, and a security filter. More preferably, the coarse filtration unit includes a sand filter and a filter bag connected in series, or a sand filter and a security filter connected in series. The sand filter, filter bag, and security filter used can all be conventional filtration devices in the art.

[0046] In the above wastewater treatment system, preferably, the ultrafiltration unit comprises a hollow fiber ultrafiltration membrane or a tubular ceramic ultrafiltration membrane. More preferably, the pore size of the ultrafiltration unit is 10-100 nm.

[0047] In the above wastewater treatment system, preferably, the nanofiltration unit comprises a first-stage nanofiltration membrane element and a second-stage nanofiltration membrane element connected in series, the outlet of the ultrafiltration unit is connected to the inlet of the first-stage nanofiltration membrane element through a pipeline, the water outlet of the first-stage nanofiltration membrane element is connected to the inlet of the second-stage nanofiltration membrane element through a pipeline, and the water outlet of the second-stage nanofiltration membrane element produces recycled water; wherein, the first-stage nanofiltration membrane element and the second-stage nanofiltration membrane element are both membrane elements made of the graphene oxide composite nanofiltration membrane roll. The method of rolling the nanofiltration membrane into a membrane element can be carried out according to conventional methods in the art, and the present invention does not specifically limit it.

[0048] In the above-mentioned wastewater treatment system, preferably, the nanofiltration unit further includes a first concentrated water return pipeline, which is used to return part of the concentrated water generated after being treated by the first-stage nanofiltration membrane element, and treat it again by the first-stage nanofiltration membrane element.

[0049] In the above-mentioned wastewater treatment system, preferably, the nanofiltration unit further includes a second concentrated water return pipeline, and the second concentrated water return pipeline is used to return the concentrated water generated after being treated by the second-stage nanofiltration membrane element, and treat it again by the first-stage nanofiltration membrane element.

[0050] The method for treating wastewater using the wastewater treatment system of the present invention may include the following steps: allowing the wastewater to enter the pH value adjustment unit, adjusting the pH value of the wastewater with acid in the pH value adjustment unit to obtain wastewater with a neutral pH value; then subjecting the wastewater with a neutral pH value to treatment by the coarse filtration unit to remove large particles and / or fine substances therein, and obtain wastewater after coarse filtration; then subjecting the wastewater after coarse filtration to treatment by the ultrafiltration unit to further remove fine substances and / or part of COD therein, and obtain wastewater after ultrafiltration treatment; then subjecting the wastewater after ultrafiltration treatment to treatment by the nanofiltration unit to intercept the dye therein and allow most of the inorganic salts to pass through, and obtain recycled water. Preferably, the wastewater includes high-salt wastewater containing dyes.

[0051] The wastewater treatment system and method of the present invention are particularly suitable for treating high-salt wastewater containing dyes, especially high-salt and high-chroma wastewater. High-salt wastewater containing dyes contains a large amount of inorganic salts such as sodium sulfate (i.e., sodium sulfate) and / or sodium carbonate, as well as dyes, and is therefore alkaline. According to a specific embodiment of the present invention, the wastewater treatment system and method of the present invention first use a pH adjustment unit to adjust the wastewater to neutrality using acid (preferably sulfuric acid), and sodium carbonate is converted into sodium sulfate, and then large particles and / or fine suspended matter in the wastewater are removed by a coarse filtration unit, and then the fine matter and / or part of COD in the wastewater are further removed by an ultrafiltration unit, and the graphene oxide composite nanofiltration membrane of the subsequent nanofiltration unit is finely protected at the same time, and the wastewater after the last ultrafiltration treatment is treated by a two-stage graphene oxide composite nanofiltration membrane, and the dye is intercepted, and most of the inorganic salts such as sodium sulfate are allowed to pass through, and finally a low-color or colorless salt solution is obtained, i.e., recycled water, which can be reused in the dyeing process of textiles.

[0052] The present invention provides a graphene oxide composite nanofiltration membrane and a preparation method and application thereof. The preparation method of the graphene oxide composite nanofiltration membrane is to apply a mixed solution containing graphene oxide materials, polymer nanomaterials and a crosslinking agent to the surface of a base film, and to carry out a crosslinking reaction, so that the polymer nanomaterials are embedded between the sheets of the graphene oxide materials by crosslinking, and at the same time, a graphene oxide nanofiltration membrane embedded with the polymer nanomaterials is formed on the surface of the base film to obtain the graphene oxide composite nanofiltration membrane. The present invention embeds the polymer nanomaterial membrane between the sheets of the graphene oxide materials by crosslinking, on the one hand, provides rigid support, can maintain the water channel between the layers of the graphene oxide materials, and avoid the decrease of the membrane flux in practical applications, on the other hand, due to the crosslinking structure between the polymer nanomaterial and the graphene oxide materials, the structural stability of the membrane is improved. In addition, the preferred technical scheme of the present invention can break through the trade-off relationship between the permeability and selectivity of the graphene oxide nanofiltration membrane by optimizing the content of the polymer nanomaterial and the crosslinking agent, and realize the double increase of the flux and the dye interception rate. In addition, the present invention preferably uses a positively charged modified nylon microfiltration membrane as the base membrane, the surface of which carries positive charge and can be combined with the negatively charged graphene oxide material through electrostatic force, hydrogen bond and van der Waals force, thereby enhancing the binding force between the graphene oxide nanofiltration membrane embedded with polymer nanomaterials and the base membrane, and preventing the graphene oxide nanofiltration membrane from falling off from the base membrane during the membrane filtration process.

[0053] The graphene oxide composite nanofiltration membrane provided by the present invention has a simple preparation process, is easy to mass produce, has a stable structure, stable performance, and has excellent inorganic salt / dye separation performance. The graphene oxide composite nanofiltration membrane provided by the present invention is particularly suitable for decolorizing high-salt wastewater containing dyes, including high-salt and high-chroma industrial wastewater, and has the advantages of large flux and high dye interception rate, and can efficiently remove chroma and recycle inorganic salts. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 The graph is a graph of flux and desalination rate of a graphene oxide composite nanofiltration membrane in a specific embodiment of the present invention filtering aqueous solutions of different contents of sodium sulphate.

[0055] Figure 2 This is an optical image of the graphene oxide composite nanofiltration membrane of Example 1.

[0056] Figure 3 The electron microscope images of the graphene oxide composite nanofiltration membranes prepared with the isocyanate crosslinking agent content of 0.1 mg / mL and the chitin nanofibers content of 0, 0.5, 1, 2, 4 and 8 mg / mL in Table 1.

[0057] Figure 4 This is an optical comparison diagram of the graphene oxide composite nanofiltration membrane obtained without using chitin nanofibers and isocyanate crosslinking agent in Example 1 and the graphene oxide composite nanofiltration membrane obtained with chitin nanofibers and isocyanate crosslinking agent after application testing.

[0058] Figure 5 This is a cross-sectional view of the graphene oxide nanofiltration membrane embedded with lignin nanofibers in the graphene oxide composite nanofiltration membrane of Example 3.

[0059] Figure 6 A schematic diagram of the structure of a wastewater treatment system provided for an application example.

[0060] Figure 7 An optical image of a membrane element made of a graphene oxide composite nanofiltration membrane roll in a wastewater treatment system according to an application example.

[0061] Figure 8 The optical images are of actual high-salt wastewater containing dyes before and after being treated by the wastewater treatment system of the application embodiment, as well as a comparison diagram of recycled sodium sulfate being reused for dyeing and directly using fresh sodium sulfate for dyeing.

[0062] Description of reference numerals:

[0063] 11: pH value adjustment unit; 12: coarse filtration unit; 13: ultrafiltration unit; 14: nanofiltration unit; 141: first stage nanofiltration membrane element; 142: second stage nanofiltration membrane element; 143: first concentrate return pipeline; 144: concentrate discharge pipeline; 145: second concentrate return pipeline; 146: first water production pipeline; 147: second water production pipeline. DETAILED DESCRIPTION

[0064] In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be construed as limiting the applicable scope of the present invention.

[0065] Example 1

[0066] This embodiment provides a graphene oxide composite nanofiltration membrane, which is prepared by the following steps:

[0067] (1) adding graphene oxide (sheet size of 5-50 μm), chitin nanofibers (average diameter of 30 nm, aspect ratio of 10-20), and 4,4'-diphenylmethane diisocyanate to deionized water, and stirring them uniformly with a stirrer to obtain a mixed solution, in which the content of graphene oxide is 2 mg / mL, and the contents of chitin nanofibers and isocyanate crosslinking agent are as shown in Table 1;

[0068] (2) laying a positively charged modified nylon microfiltration membrane with an average pore size of 0.1 μm and a thickness of 50-200 μm on an automatic coating machine, and uniformly coating the mixed solution prepared in step (1) on one side of the nylon microfiltration membrane using a micro-concave coating method to form a wet film containing graphene oxide, chitin nanofibers and 4,4'-diphenylmethane diisocyanate, the thickness of the wet film being 40 μm, thereby obtaining a base film coated with the wet film;

[0069] (3) The base film coated with the wet film obtained in step (2) is placed in an oven and dried at 80° C. for 2 hours, and the chitosan nanofibers are embedded between the graphene oxide layers through a cross-linking reaction. At the same time, a graphene oxide nanofiltration membrane embedded with chitosan nanofibers is formed on the surface of the base film, thereby obtaining the graphene oxide composite nanofiltration membrane.

[0070] The graphene oxide composite nanofiltration membrane of this embodiment includes: a positively charged modified nylon microfiltration membrane with an average pore size of 0.1 μm and a thickness of 50-200 μm, and a graphene oxide nanofiltration membrane with chitosan nanofibers embedded on the surface of the positively charged modified nylon microfiltration membrane; wherein the thickness of the graphene oxide nanofiltration membrane (dry membrane) embedded with chitosan nanofibers is about 240 nm.

[0071] The graphene oxide composite nanofiltration membrane of this embodiment is used to filter a 2 g / L (ie, 2000 ppm) sodium sulfate solution, and the sodium sulfate retention rate (ie, desalination rate) is greater than 60%.

[0072] The graphene oxide composite nanofiltration membrane of this embodiment was used to filter a 70 g / L sodium sulfate solution, and the retention rate of sodium sulfate was lower than 15%.

[0073] The graphene oxide composite nanofiltration membrane of this embodiment was used to filter a 2 g / L dye BlueR solution, and the retention rate of the dye was greater than 99%.

[0074] The graphene oxide composite nanofiltration membrane of this embodiment was used to filter a mixed solution of 70 g / L sodium sulfate and 2 g / L dye BlueR. The flux and dye retention rate results are shown in Table 1. The retention rate of sodium sulfate was <15%.

[0075] Table 1 Flux and dye retention rate of graphene oxide composite nanofiltration membrane prepared from mixed solutions with different chitin nanofiber contents and isocyanate crosslinking agent contents.

[0076] It should be noted that the graphene oxide composite nanofiltration membrane prepared with chitosan nanofiber content and isocyanate crosslinking agent content outside the scope of the present invention in Table 1 is for comparison, not an embodiment of the present invention. It can be seen from Table 1 that with the increase of the crosslinking agent content, the flux of the membrane decreases and the dye retention rate increases; with the increase of the chitosan nanofiber content, the flux of the membrane increases and the dye retention rate decreases. The present invention optimizes the content of the two, so that the weight ratio of polymer nanomaterials and graphene oxide is 0.5-8, and the amount of crosslinking agent is 0.5%-10% (more preferably 1%-8%) of the total weight of graphene oxide and polymer nanomaterials, which can achieve an increase in both flux and retention rate, breaking through the trade-off relationship between the permeability and selectivity of the separation membrane.

[0077] The preparation process of the graphene oxide composite nanofiltration membrane of this embodiment is simple and easy to mass produce. The optical image of the graphene oxide composite nanofiltration membrane is as follows: Figure 2 As shown, it shows photos of graphene oxide composite nanofiltration membrane rolls and rolled membrane elements. Figure 3 The isocyanate crosslinking agent content in Table 1 is 0.1 mg / mL, and the chitin nanofibers are 0( Figure 3 a), 0.5( Figure 3 b) in the above formula, 1( Figure 3 c), 2( Figure 3 d), 4( Figure 3 e) and 8mg / mL( Figure 3 f) Electron micrograph of the prepared graphene oxide composite nanofiltration membrane. Figure 4This is an optical comparison chart of a graphene oxide composite nanofiltration membrane obtained without using chitin nanofibers and isocyanate crosslinking agent and a graphene oxide composite nanofiltration membrane obtained with chitin nanofibers and isocyanate crosslinking agent after application testing. Figure 4 It can be seen that due to the effects of chitin nanofibers and cross-linking agent, the graphene oxide composite nanofiltration membrane will not be damaged at the place where it contacts the rubber ring after testing, indicating that the structural stability of the membrane is greatly improved.

[0078] The graphene oxide composite nanofiltration membrane prepared with an isocyanate crosslinking agent content of 0.1 mg / mL and chitin nanofibers of 4 mg / mL in this embodiment, and the graphene oxide composite nanofiltration membrane prepared without chitin nanofibers and isocyanate crosslinking agent as a comparison, were treated with acid or reducing agent, and then filtered for a mixed solution of 70 g / L sodium sulfate and 2 g / L dye BlueR, and the results are shown in Table 2. The acid solution used hydrochloric acid with a pH of 3, and the treatment method was soaking for 8 hours; the reducing agent used 1% hydroiodic acid, and the treatment method was soaking for 8 hours.

[0079] Table 2

[0080]

[0081] It can be seen from Table 2 that the graphene oxide composite nanofiltration membrane obtained by using chitosan nanofibers and isocyanate crosslinking agent in this embodiment does not show significant attenuation in flux after being treated with acid or reducing agent, indicating that the performance stability of the membrane is greatly improved.

[0082] Example 2

[0083] This embodiment provides a graphene oxide composite nanofiltration membrane, which is prepared by the following steps:

[0084] (1) adding graphene oxide (sheet size of 5-50 μm), cellulose nanocrystals (average diameter of 10 nm, aspect ratio of 20-50), and glutaraldehyde to deionized water, and stirring them uniformly with a stirrer to obtain a mixed solution, wherein the content of graphene oxide is 1 mg / mL, the content of cellulose nanocrystals is 8 mg / mL, and the content of glutaraldehyde is 0.72 mg / mL;

[0085] (2) laying a positively charged modified nylon microfiltration membrane with an average pore size of 0.22 μm on an automatic coating machine, and uniformly coating the mixed solution prepared in step (1) on one side of the nylon microfiltration membrane using a wire rod coating method to form a wet film containing graphene oxide, cellulose nanocrystals and glutaraldehyde, the thickness of the wet film being 10 μm, thereby obtaining a base membrane coated with the wet film;

[0086] (3) The base film coated with the wet film obtained in step (2) is placed under room temperature and dried naturally for three days, and the cellulose nanocrystals are embedded between the graphene oxide layers through a cross-linking reaction, and a graphene oxide nanofiltration membrane embedded with cellulose nanocrystals is formed on the surface of the base film to obtain the graphene oxide composite nanofiltration membrane.

[0087] The graphene oxide composite nanofiltration membrane of this embodiment includes: a positively charged modified nylon microfiltration membrane with an average pore size of 0.22 μm, and a graphene oxide nanofiltration membrane embedded with cellulose nanocrystals on the surface of the positively charged modified nylon microfiltration membrane; wherein the thickness of the graphene oxide nanofiltration membrane embedded with cellulose nanocrystals (dry membrane) is about 90 nm.

[0088] The graphene oxide composite nanofiltration membrane of this embodiment was used to filter a 2 g / L sodium sulfate solution, and the flux was 8.35 L / (m 2 ·h·Bar), the retention rate of sodium sulfate is 82%.

[0089] The graphene oxide composite nanofiltration membrane of this embodiment was used to filter 70 g / L sodium sulfate solution, and the flux was 4.87 L / (m 2 ·h·Bar), the retention rate of sodium sulfate was 9.2%.

[0090] The graphene oxide composite nanofiltration membrane of this embodiment was used to filter 2g / L dye BlueR solution, and the flux was 7.46L / (m 2 ·h·Bar), the dye retention rate is 99.9%.

[0091] The graphene oxide composite nanofiltration membrane of this embodiment was used to filter a mixed solution of 70 g / L sodium sulfate and 2 g / L dye BlueR, and the flux was 4.64 L / (m 2 ·h·Bar), the retention rate of dye is 99.2%, and the retention rate of sodium sulfate is 13.2%.

[0092] Example 3

[0093] This embodiment provides a graphene oxide composite nanofiltration membrane, which is prepared by the following steps:

[0094] (1) adding graphene oxide (sheet size of 5-50 μm), lignin nanofibers (average diameter of 30 nm, aspect ratio of 20-50), and aziridine crosslinking agent (Youen Chemical SAC-100) to deionized water, stirring evenly with a stirrer to obtain a mixed solution, in which the content of graphene oxide is 3 mg / mL, the content of lignin nanofibers is 2 mg / mL, and the content of aziridine crosslinking agent is 0.06 mg / mL;

[0095] (2) laying a positively charged modified nylon microfiltration membrane with an average pore size of 0.1 μm on an automatic coating machine, and uniformly coating the mixed solution prepared in step (1) on one side of the nylon microfiltration membrane using a micro-concave coating method to form a wet film containing graphene oxide, lignin nanofibers and an aziridine crosslinking agent, the thickness of the wet film being 10 μm, thereby obtaining a base film coated with the wet film;

[0096] (3) The base film coated with the wet film obtained in step (2) is placed in an oven and dried at 70° C. for 15 minutes, and the lignin nanofibers are embedded between the graphene oxide layers through a cross-linking reaction. At the same time, a graphene oxide nanofiltration membrane embedded with lignin nanofibers is formed on the surface of the base film, thereby obtaining the graphene oxide composite nanofiltration membrane.

[0097] The graphene oxide composite nanofiltration membrane of this embodiment comprises: a positively charged modified nylon microfiltration membrane with an average pore size of 0.1 μm, and a graphene oxide nanofiltration membrane with lignin nanofibers embedded on the surface of the positively charged modified nylon microfiltration membrane; wherein the thickness of the graphene oxide nanofiltration membrane with lignin nanofibers embedded (dry membrane) is about 40 nm. The cross-sectional view of the graphene oxide nanofiltration membrane with lignin nanofibers embedded in the graphene oxide composite nanofiltration membrane of this embodiment is as shown in FIG. Figure 5 shown.

[0098] The graphene oxide composite nanofiltration membrane of this embodiment was used to filter a 2 g / L sodium sulfate solution, and the flux was 16.3 L / (m 2 ·h·Bar), the retention rate of sodium sulfate is 91%.

[0099] The graphene oxide composite nanofiltration membrane of this embodiment was used to filter 70 g / L sodium sulfate solution, and the flux was 9.82 L / (m 2 ·h·Bar), the retention rate of sodium sulfate was 11.2%.

[0100] The graphene oxide composite nanofiltration membrane of this embodiment was used to filter 2g / L dye BlueR solution, and the flux was 14.2L / (m 2 ·h·Bar), the dye retention rate is 99.8%.

[0101] The graphene oxide composite nanofiltration membrane of this embodiment was used to filter a mixed solution of 70 g / L sodium sulfate and 2 g / L dye BlueR, and the flux was 9.04 L / (m 2 ·h·Bar), the retention rate of dye is 96.3%, and the retention rate of sodium sulfate is 11.2%.

[0102] Application Examples

[0103] This application example provides the use of the graphene oxide composite nanofiltration membrane of Example 1 (a graphene oxide composite nanofiltration membrane prepared with an isocyanate crosslinking agent content of 0.1 mg / mL and chitin nanofibers of 4 mg / mL in the mixed liquid) to decolorize high-salt wastewater containing dyes and recycle salt (especially alum).

[0104] This application embodiment provides a wastewater treatment system, the structure of which is as follows: Figure 6 As shown, the wastewater treatment system includes: a pH value adjustment unit 11, a coarse filtration unit 12, an ultrafiltration unit 13 and a nanofiltration unit 14;

[0105] The nanofiltration unit 14 includes a first-stage nanofiltration membrane element 141 and a second-stage nanofiltration membrane element 142 connected in series, as well as a first concentrated water return pipeline 143, a concentrated water discharge pipeline 144, a second concentrated water return pipeline 145, a first produced water pipeline 146 and a second produced water pipeline 147;

[0106] The inlet of the pH value adjusting unit 11 is connected to a wastewater delivery pipeline, the outlet of the pH value adjusting unit 11 is connected to the inlet of the coarse filtration unit 12 through a pipeline, the outlet of the coarse filtration unit 12 is connected to the inlet of the ultrafiltration unit 13 through a pipeline, the outlet of the ultrafiltration unit 13 is connected to the inlet of the first-stage nanofiltration membrane element 141 through a pipeline, the water production port of the first-stage nanofiltration membrane element 141 is connected to the inlet of the second-stage nanofiltration membrane element 142 through the first water production pipeline 146, and the water production port of the second-stage nanofiltration membrane element 142 is connected to the second water production pipeline 147 for producing high-salinity reuse water with no or low color;

[0107] The first concentrated water return pipeline 143 is connected to the concentrated water outlet of the first-stage nanofiltration membrane element 141, and is used to return part of the concentrated water produced after being treated by the first-stage nanofiltration membrane element 141, and treat it again by the first-stage nanofiltration membrane element 141, and the other part of the concentrated water is discharged through the concentrated water discharge pipeline 144;

[0108] The second concentrated water return pipeline 145 is connected to the concentrated water outlet of the second-stage nanofiltration membrane element 142, and is used to return the concentrated water produced after being treated by the second-stage nanofiltration membrane element 142, and to be treated again by the first-stage nanofiltration membrane element 141;

[0109] Wherein, the pH value adjusting unit 11 includes a pH value adjusting tank, which is used to adjust the pH value of the wastewater to neutral; the pH value adjusting tank used can be a conventional pH value adjusting tank in the art;

[0110] The coarse filtration unit 12 includes a sand filter and a filter bag connected in series; the sand filter and the filter bag used can be conventional filtration devices in the art;

[0111] The ultrafiltration unit 13 includes a hollow fiber ultrafiltration membrane, the pore size of which is 10 nm;

[0112] The first-stage nanofiltration membrane element 141 and the second-stage nanofiltration membrane element 142 are both membrane elements made of the graphene oxide composite nanofiltration membrane roll provided in Example 1 (rolled in a conventional manner).

[0113] Figure 7 This is an optical picture of the membrane element made of graphene oxide composite nanofiltration membrane roll in the wastewater treatment system of this application example. The two on top are used two-stage membrane elements, and the two on the bottom are unused membrane elements.

[0114] The high-salt wastewater containing dyes treated in this application example contains a large amount of sodium sulfate (ie, sodium carbonate) and dyes, and is therefore alkaline.

[0115] The method for treating wastewater using the wastewater treatment system of the present application embodiment may include the following steps: allowing high-salt wastewater containing dyes to enter the pH value adjustment unit 11, adjusting the pH value of the wastewater to neutrality using sulfuric acid in the pH value adjustment unit 11, and converting sodium carbonate into sodium sulfate to obtain wastewater with a neutral pH value; then subjecting the wastewater with a neutral pH value to treatment by the coarse filtration unit 12, removing large particles and / or fine suspended matter therein, and obtaining coarsely filtered wastewater; then subjecting the coarsely filtered wastewater to treatment by the ultrafiltration unit 13, so as to further remove fine matter and part of COD therein, and at the same time play a role in finely protecting the graphene oxide composite nanofiltration membrane of the subsequent nanofiltration unit 14, so as to obtain ultrafiltration-treated wastewater; then subjecting the ultrafiltration-treated wastewater to treatment by the nanofiltration unit 14, intercepting the dye therein and allowing most of the sodium sulfate to pass through, so as to obtain a low-color or colorless sodium sulfate solution, i.e., recycled water, which can be reused in the dyeing process of textiles.

[0116] Application comparison

[0117] This application comparative example provides the use of a traditional commercial loose nanofiltration membrane (Suez, product model Suez GK) to decolorize high-salt wastewater containing dyes and recycle salt (especially sodium sulfate).

[0118] The wastewater treatment system of this application comparison example is basically the same as that in the above-mentioned application embodiment, except that the first-stage nanofiltration membrane element 141 and the second-stage nanofiltration membrane element 142 in the application embodiment are replaced by membrane elements made of commercial loose nanofiltration membrane rolls in this application comparison example.

[0119] Test Case

[0120] A mixed solution of 70 g / L sodium sulfate and 2 g / L dye Blue R was filtered using a membrane element rolled up with the graphene oxide composite nanofiltration membrane provided in Example 1 (a graphene oxide composite nanofiltration membrane prepared with an isocyanate cross-linking agent content of 0.1 mg / mL and chitin nanofibers of 4 mg / mL in the mixed solution) and a membrane element rolled up with the commercial loose nanofiltration membrane in the comparative example. The results are shown in Table 3.

[0121] Table 3

[0122]

[0123] Actual high-salt wastewater containing dyes was treated by the wastewater treatment systems of the above application examples and comparative examples, and the results are shown in Table 4. The concentration of sodium sulfate in the high-salt wastewater containing dyes was 20-100 g / L, and the concentration of dyes was 0.2-2 g / L.

[0124] Table 4

[0125]

[0126] The conventional commercial loose nanofiltration membrane has a retention rate of only 85-88% for dyes in dyeing wastewater, and a flux of 2L / (m 2 In actual applications, at a water recovery rate of 85% for membrane elements, the stable flux is only 0.5-1.5 L / (m 2 ·h·Bar), a single-stage nanofiltration membrane can only remove 65-75% of the dye. After two-stage nanofiltration membrane treatment of dyeing wastewater, only 90% of the dye can be removed. Subsequently, it is necessary to further remove the remaining dyes through activated carbon adsorption or advanced oxidation technology and reuse the output water containing sodium sulfate, which greatly increases the treatment cost.

[0127] The graphene oxide composite nanofiltration membrane of the present invention has a unique advantage in separating salt and dye in the process of treating high-salt wastewater containing dye. The flux of the graphene oxide composite nanofiltration membrane of the present invention is 3-10L / (m 2 ·h·Bar) is about 2-4 times that of commercial loose nanofiltration membranes, and the retention rate of dyes (>95%) is much better than that of commercial loose nanofiltration membranes. In practical applications, at a membrane element water recovery rate of 85%, the stable flux is 2.5-3.6L / (m 2 ·h·Bar), the dye retention rate of each stage of nanofiltration membrane is more than 90%. After the dyeing wastewater is treated by two-stage graphene oxide composite nanofiltration membrane, more than 99% of the dye can be removed, and the output water containing sodium sulfate can be reused without post-treatment.

[0128] Figure 8The optical images of the actual high-salt wastewater containing dyes before and after being treated by the wastewater treatment system (two-stage graphene oxide composite nanofiltration membrane) of the above application embodiment ( Figure 8 a) in the figure and the comparison between the recycled sodium sulfate used for dyeing and the direct use of fresh sodium sulfate for dyeing ( Figure 8 b) in Figure 8 It can be seen that the recycled sodium sulfate is reused for dyeing, and the fabric has no obvious color difference. Therefore, the membrane element made of the graphene oxide composite nanofiltration membrane roll of the present invention is used to separate the actual high-salt dyeing wastewater, with large membrane flux and excellent separation effect, and can efficiently decolorize the high-salt dyeing wastewater, and the sodium sulfate recycling rate is high (more than 85%), and the recycled sodium sulfate is reused in the textile dyeing process with excellent dyeing effect.

[0129] In summary, the graphene oxide composite nanofiltration membrane provided by the present invention has a simple preparation process, is easy to mass produce, has a stable structure, stable performance, and has excellent inorganic salt / dye separation performance. The graphene oxide composite nanofiltration membrane provided by the present invention is particularly suitable for decolorizing high-salt and high-chroma industrial wastewater, has the advantages of large flux and high dye interception rate, can efficiently remove chroma, and recycle inorganic salts such as sodium sulfate.

Claims

1. A graphene oxide composite nanofiltration membrane, the graphene oxide composite nanofiltration membrane include: A base membrane, and a graphene oxide nanofiltration membrane embedded with polymer nanomaterials on the surface of the base membrane; The graphene oxide nanofiltration membrane embedded with polymer nanomaterials is obtained by using a cross-linking agent to carry out a cross-linking reaction to embed the polymer nanomaterials between the sheets of graphene oxide materials; The polymer nanomaterial includes polymer nanofibers and / or polymer nanocrystals; the polymer nanofibers include one or a combination of cellulose nanofibers, chitin nanofibers, chitosan nanofibers and lignin nanofibers; the polymer nanocrystals include one or a combination of cellulose nanocrystals, chitin nanocrystals, chitosan nanocrystals and lignin nanocrystals; The cross-linking agent includes a carboxyl cross-linking agent and / or a hydroxyl cross-linking agent; the amount of the cross-linking agent is 0.1%-30% of the total weight of the graphene oxide material and the polymer nanomaterial; The temperature of the cross-linking reaction is 20-100°C; the time of the cross-linking reaction is 2 minutes to one week; The thickness of the graphene oxide nanofiltration membrane embedded with polymer nanomaterials is 5-2000 nm; The molecular weight cut-off of the graphene oxide nanofiltration membrane embedded with polymer nanomaterials is 500-3000 Daltons; The weight ratio of the polymer nanomaterial to the graphene oxide material in the graphene oxide nanofiltration membrane embedded with the polymer nanomaterial is 0.125-16; The flux of the graphene oxide composite nanofiltration membrane filtering 2000 ppm sodium sulfate solution is 5-30 L / (m 2 ·h·Bar), the desalination rate is 50-95%; The flux of the graphene oxide composite nanofiltration membrane filtering a 2000 ppm active dye solution is 5-30 L / (m 2 ·h·Bar), retention rate> 98%; The flux of the graphene oxide composite nanofiltration membrane filtering a mixed solution of 70 g / L sodium sulfate and 2 g / L active dye is 3-10 L / (m 2 ·h·Bar), dye retention rate is 95%-99.9%, and desalination rate is <15%.

2. The graphene oxide composite nanofiltration membrane according to claim 1, in, The thickness of the graphene oxide nanofiltration membrane embedded with polymer nanomaterials is 50-500 nm.

3. The graphene oxide composite nanofiltration membrane according to claim 1, in, The weight ratio of the polymer nanomaterial to the graphene oxide material in the graphene oxide nanofiltration membrane embedded with the polymer nanomaterial is 0.5-8.

4. The graphene oxide composite nanofiltration membrane according to claim 1, in, The diameter of the polymer nanofiber is 10-50 nm, and the aspect ratio is 10-100; the diameter of the polymer nanocrystal is 2-20 nm, and the aspect ratio is 10-100.

5. The graphene oxide composite nanofiltration membrane according to claim 1, in, The graphene oxide material includes graphene oxide and / or modified graphene oxide.

6. The graphene oxide composite nanofiltration membrane according to claim 5, in, The graphene oxide material is graphene oxide.

7. The graphene oxide composite nanofiltration membrane according to claim 5, in, The flake size of the graphene oxide and the modified graphene oxide is 0.5-500 μm.

8. The graphene oxide composite nanofiltration membrane according to claim 7, in, The flake size of the graphene oxide and the modified graphene oxide is 2-50 μm.

9. The graphene oxide composite nanofiltration membrane according to claim 1, in, The material of the base film includes one or a combination of nylon, polyvinylidene fluoride, polysulfone, polyethersulfone, polyacrylonitrile and cellulose acetate.

10. The graphene oxide composite nanofiltration membrane according to claim 1, in, The average pore size of the base film is 0.02-10 μm.

11. The graphene oxide composite nanofiltration membrane according to claim 10, in, The average pore size of the base film is 0.1-0.22 μm.

12. The graphene oxide composite nanofiltration membrane according to claim 11, in, The average pore size of the base film is 0.1 μm or 0.22 μm.

13. The graphene oxide composite nanofiltration membrane according to claim 1, in, The base membrane includes a positively charged modified nylon microfiltration membrane.

14. The graphene oxide composite nanofiltration membrane according to claim 1, in, The base film has a thickness of 50-200 μm.

15. The graphene oxide composite nanofiltration membrane according to claim 1, in, The carboxyl crosslinking agent includes an aziridine crosslinking agent and / or a polycarbodiimide crosslinking agent; the hydroxyl crosslinking agent includes an isocyanate crosslinking agent and / or a polyaldehyde crosslinking agent.

16. The graphene oxide composite nanofiltration membrane according to claim 1, in, The amount of the cross-linking agent used is 0.5%-10% of the total weight of the graphene oxide material and the polymer nanomaterial.

17. The graphene oxide composite nanofiltration membrane according to claim 1, in, The temperature of the cross-linking reaction is 50-70°C.

18. A method for preparing the graphene oxide composite nanofiltration membrane according to any one of claims 1 to 17, wherein The following steps are involved: A mixed solution containing graphene oxide materials, polymer nanomaterials and a cross-linking agent is applied to the surface of a base film, and a cross-linking reaction is performed, so that the polymer nanomaterials are embedded between the sheets of the graphene oxide materials by cross-linking, and a graphene oxide nanofiltration membrane embedded with the polymer nanomaterials is formed on the surface of the base film, thereby obtaining the graphene oxide composite nanofiltration membrane; Wherein, in the mixed solution, the weight ratio of the polymer nanomaterial to the graphene oxide material is 0.125-16; the amount of the cross-linking agent is 0.1%-30% of the total weight of the graphene oxide material and the polymer nanomaterial; The temperature of the cross-linking reaction is 20-100° C.; the time of the cross-linking reaction is 2 minutes to one week.

19. The preparation method according to claim 18, in, In the mixed solution, the weight ratio of the polymer nanomaterial to the graphene oxide material is 0.5-8.

20. The preparation method according to claim 18, in, In the mixed solution, the amount of the cross-linking agent is 0.5%-10% of the total weight of the graphene oxide material and the polymer nanomaterial.

21. The preparation method according to claim 18, in, In the mixed solution, the content of the graphene oxide material is 0.5-10 g / L.

22. The preparation method according to claim 21, in, In the mixed solution, the content of the graphene oxide material is 1-4 g / L.

23. The preparation method according to claim 18, in, The coating method includes one or a combination of wire rod coating, slit coating and micro-concave coating.

24. The preparation method according to claim 18, in, The temperature of the cross-linking reaction is 50-70°C.

25. Use of the graphene oxide composite nanofiltration membrane according to any one of claims 1 to 17 in treating high-salt wastewater containing dyes.

26. The use according to claim 25, in, The application is the use of the graphene oxide composite nanofiltration membrane in the decolorization treatment of the dye-containing high-salt wastewater.

27. The use according to claim 25, in, The salt concentration in the dye-containing high-salt wastewater is 20-200 g / L, and the dye concentration is 0.2-5 g / L.

28. The use according to claim 27, in, The salt includes NaCl and / or Na 2 SO 4 .

29. The use according to claim 25, in, The flux of the graphene oxide composite nanofiltration membrane for treating the dye-containing high-salt wastewater is 2.5-10 L / (m 2 ·h·Bar), dye retention rate is 90%-99.9%, and desalination rate is <15%.

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