Graphene oxide separation membrane with multilevel structure as well as preparation method and application of graphene oxide separation membrane

Abstract

The invention provides a graphene oxide separation membrane with a multilevel structure as well as a preparation method and application of the graphene oxide separation membrane. The preparation method comprises the following steps: step 1, preparing a large graphene oxide dispersion liquid and a small graphene oxide dispersion liquid; step 2, carrying out hydrothermal reflux treatment on the large graphene oxide dispersion liquid; 3, sequentially loading the treated large graphene oxide and small graphene oxide on a hydrophilic ultrafiltration membrane or an ultrafiltration membrane subjected to hydrophilization treatment to obtain a composite membrane; and 4, carrying out plasma treatment on the composite membrane obtained in the step 3, and carrying out third spraying on the composite membrane to load small pieces of graphene oxide so as to obtain the graphene oxide separation membrane with the multilevel structure. The preparation method provided by the invention solves the problem of mutual restriction of separation performance and permeability of the graphene oxide membrane, so that the composite membrane has the advantages of good permeability, developed pore structure, small volume density, large specific surface area and pore volume and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of nano material thin films, and in particular to a graphene oxide separation membrane with a multi-level structure, and a preparation method and application thereof. Background Art

[0002] Membrane technology is widely used in the field of water treatment as a separation technology that is efficient, environmentally friendly and can achieve selective transfer of substances. Water filtration membranes can effectively remove harmful pollutants such as microorganisms, suspended matter, organic matter, heavy metals, etc. in water through physical or chemical methods, achieve water purification and purification, and thus obtain cleaner and safer drinking water and industrial water. However, the conventional separation membrane production process often requires the use of a large amount of volatile organic solvents, which may further aggravate environmental pollution. Nanomaterials have broad application prospects in the field of membrane materials due to their unique structure and characteristics. The application of nanomaterials in membrane technology can effectively improve the separation performance, anti-pollution performance and service life of the membrane, thereby improving the efficiency and quality of water treatment. Water-dispersible nanomaterials can form a separation layer with nano or sub-nano pores through the assembly process of the water phase, and play a desalination and pollution resistance function. Graphene oxide, as a unique nanomaterial, has unique advantages and potential in the field of water filtration membrane materials. Graphene oxide has an extremely high specific surface area and pore structure, which is conducive to improving the separation performance and permeability of the membrane, thereby achieving a more efficient water filtration process. Its unique structure makes the membrane have excellent stability and anti-pollution performance, which can effectively prevent pollutants such as microorganisms, organic matter, bacteria, etc. from penetrating the membrane surface. In addition, graphene oxide also has excellent chemical inertness and mechanical strength, which can effectively extend the service life of the membrane and reduce maintenance costs.

[0003] There are also some problems with graphene oxide separation membranes. First, graphene oxide is stacked layer by layer, forming long and tortuous water transmission channels through the gaps between sheets. The narrower and denser the gaps, the stronger the separation performance and the lower the water permeability, that is, there is a trade-off between the water flux and the separation performance of the membrane. Secondly, the less porous / non-porous graphene oxide directly covers the base membrane, blocking the pores on the base membrane, affecting the transmission of water molecules, and increasing the energy consumption of water permeation. In addition, the tortuous channels between the sheets of water molecules increase the interlayer spacing at the subnanometer level and weaken the interlayer bonding effect; the graphene oxide sheets cover the pores of the base membrane, and the transmission of water at the base membrane-graphene oxide interface is blocked. After continuous pressurization, water forcibly enters between graphene oxide and the base membrane, weakening the bonding effect between graphene oxide and the base membrane. In actual tests, graphene oxide-graphene oxide and graphene oxide-base membrane are easy to detach from each other and peel off. The subnanometer transmission pores are tortuous, and the recovery rate of permeability performance is low after the membrane is fouled and cleaned. In order to solve the above problems, ion bombardment, electron bombardment and other methods can be used to etch small holes of less than 1nm on graphene oxide sheets, which can expand water permeation channels. However, due to high precision and complex operation process, it is difficult to apply them on a large scale. Therefore, it is of great significance to design material structure to break through the technical bottleneck of graphene oxide separation membrane preparation and prepare a durable graphene oxide separation membrane with both high separation performance and permeability. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing a graphene oxide separation membrane with a multi-level structure, in view of the fact that the water flux, separation performance and durability of the graphene oxide separation membrane existing in the prior art are difficult to be taken into account at the same time.

[0005] Another object of the present invention is to provide a graphene oxide separation membrane with a multi-level structure prepared by the preparation method.

[0006] Another object of the present invention is to provide an application of the graphene oxide separation membrane with a multi-level structure.

[0007] The technical solution adopted to achieve the purpose of the present invention is:

[0008] A method for preparing a graphene oxide separation membrane with a multi-level structure comprises the following steps:

[0009] Step 1, dispersing a large piece of monolayer graphene oxide and a small piece of monolayer graphene oxide in water to obtain a large piece of graphene oxide dispersion and a small piece of graphene oxide dispersion respectively;

[0010] Step 2, subjecting the large-scale graphene oxide dispersion to a hydrothermal reflux treatment;

[0011] Step 3, taking a hydrophilic ultrafiltration membrane or a hydrophilized ultrafiltration membrane as a base membrane, performing a first spraying, loading the large graphene oxide flakes after the heat treatment in step 2 on the base membrane, and then performing a second spraying, loading the small graphene oxide flakes on the base membrane loaded with the large graphene oxide flakes to obtain a composite membrane;

[0012] Step 4, plasma treating the composite membrane obtained in step 3, and then spraying it for a third time to load small pieces of graphene oxide, so as to obtain the graphene oxide separation membrane with a multi-level structure.

[0013] In the above technical solution, the size of the large single-layer graphene oxide sheet is 40-50 μm, and the size of the small single-layer graphene oxide sheet is 5-8 μm.

[0014] In the above technical solution, the concentration of large single-layer graphene oxide in the large graphene oxide dispersion in step 1 is 0.08-0.25 g·L -1 The concentration of the small monolayer graphene oxide sheets in the small graphene oxide dispersion is 0.08-0.25 g·L -1 ;

[0015] In the step 2, the temperature of the hydrothermal reflux is 80-100° C., and the time of the hydrothermal reflux is 0.5-1 h.

[0016] In the above technical solution, the hydrophilic ultrafiltration membrane is a flat ultrafiltration membrane or a curved ultrafiltration membrane of polysulfone, polyethersulfone, or cellulose acetate;

[0017] The hydrophilized ultrafiltration membrane is one of polyvinyl chloride, polytetrafluoroethylene, polyvinylidene fluoride, polyacrylonitrile, polypropylene, polyethylene, polyurethane, polycaprolactam flat ultrafiltration membrane or curved ultrafiltration membrane soaked in ethanol or isopropanol.

[0018] In the above technical solution, the spraying speed of the first spraying is 0.2-0.5s·cm -2 The spraying pressure is 0.1-0.2MPa, and the spraying amount per unit area is 30-40mg·m -2 ;

[0019] The spraying speed of the second spraying is 0.2-0.5s·cm -2 The spraying pressure is 0.1-0.2MPa, and the spraying amount per unit area is 30-40mg·m -2 .

[0020] In the above technical solution, the processing power of the plasma treatment is 20-100W, and the processing time is 5-600s.

[0021] In the above technical solution, the spraying speed of the third spraying is 0.2-0.5s·cm -2 The spraying pressure is 0.1-0.2MPa, and the spraying amount per unit area is 30-50mg·m -2 .

[0022] Another aspect of the present invention provides a graphene oxide separation membrane with a multi-level structure, which is prepared by the preparation method.

[0023] In the above technical solution, the initial desalination rate of the graphene oxide separation membrane is not less than 90%, the dye interception rate is not less than 99.5%, and the initial water flux is not less than 10L·m -2 ·h -1 bar -1 .

[0024] Another aspect of the present invention provides an application of the graphene oxide separation membrane with a multi-level structure in water treatment.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The preparation method of the present invention is precise and controllable, less time-consuming and energy-consuming, and solves the problem of mutual restriction between the separation performance and permeability performance of graphene oxide membrane. The preparation method of the present invention prepares a multi-level structure material, so that the composite membrane has the advantages of good permeability, developed pore structure, low volume density, large specific surface area and pore volume, breaking the limitation of the single pore structure of traditional single-level structure materials. At the same time, through a simple and scalable spraying method and plasma treatment film making, the problems of complex preparation process, high preparation cost, and difficult to control pore structure that may exist in multi-level structure membrane materials are avoided.

[0027] 2. The graphene oxide separation membrane with a multi-level structure of the present invention is divided into three layers: a loose and porous lower layer, a dense and porous middle layer and a dense upper layer. The hydrothermal reflux treatment of large pieces of graphene oxide can partially reduce the graphene oxide and etch holes on the nanosheets, and the large pieces are overlapped to form a loose and porous lower layer. Plasma treatment can etch nanoscale holes in the small pieces of graphene oxide middle layer. A dense upper layer is formed by spraying small pieces of graphene oxide on the plasma-treated middle layer. Compared with conventional homogeneous graphene oxide membranes, the graphene oxide separation membrane of the present invention has controllable structure, scalable membrane formation, good structural and performance stability, high retention rate for multivalent salt ions and macromolecular organic matter, high water flux, and excellent performance recovery ability. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the preparation process of graphene oxide multi-level structure membrane;

[0029] Figure 2The scanning electron microscope images of the large and small graphene oxide flakes and the large graphene oxide flakes after hydrothermal treatment in Example 1 of the present invention are shown;

[0030] Figure 3 Electron microscope images of the film surfaces after different plasma treatment times in Example 1 and Example 5 of the present invention;

[0031] Figure 4 This is a comparison diagram of the internal structure and water molecule transport of graphene oxide multi-level structure membrane and conventional single-level structure membrane. DETAILED DESCRIPTION

[0032] The present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0033] A method for preparing a graphene oxide separation membrane having a multi-level structure, such as Figure 1 As shown, the following steps are included:

[0034] Step 1: Dispersing large monolayer graphene oxide and small monolayer graphene oxide sheets in water to obtain large monolayer graphene oxide dispersion and small monolayer graphene oxide dispersion, respectively. The large monolayer graphene oxide has a size of 40-50 μm, the small monolayer graphene oxide has a size of 5-8 μm, and the concentration of the large monolayer graphene oxide in the large monolayer graphene oxide dispersion is 0.08-0.25 g·L -1 The concentration of the small monolayer graphene oxide sheets in the small graphene oxide dispersion is 0.08-0.25 g·L -1 ;

[0035] Step 2, subjecting the large graphene oxide dispersion to a hydrothermal reflux treatment, wherein the hydrothermal reflux temperature is 80-100° C., and the hydrothermal reflux time is 0.5-1 h;

[0036] Step 3, taking a hydrophilic ultrafiltration membrane or a hydrophilized ultrafiltration membrane as a base membrane, performing a first spraying to load a large piece of graphene oxide on the base membrane, and then performing a second spraying to load a small piece of graphene oxide on the base membrane loaded with a large piece of graphene oxide to obtain a composite membrane, wherein the hydrophilic ultrafiltration membrane is a flat ultrafiltration membrane or a curved ultrafiltration membrane of polysulfone, polyethersulfone, and cellulose acetate; the hydrophilized ultrafiltration membrane is a polyvinyl chloride, polytetrafluoroethylene, polyvinylidene fluoride, polyacrylonitrile, polypropylene, polyethylene, polyurethane, polycaprolactam flat ultrafiltration membrane or a curved ultrafiltration membrane soaked in ethanol or isopropanol, and the spraying speed of the first spraying is 0.2-0.5s·cm -2 The spraying pressure is 0.1-0.2MPa, and the spraying amount per unit area is 30-40mg·m -2The spraying speed of the second spraying is 0.2-0.5s·cm -2 The spraying pressure is 0.1-0.2MPa, and the spraying amount per unit area is 30-40mg·m -2 ;

[0037] Step 4, plasma treating the composite membrane obtained in step 3, and then spraying it for a third time to load small pieces of graphene oxide, so as to obtain the graphene oxide separation membrane with a multi-level structure, wherein the processing power of the plasma treatment is 20-100W, the processing time is 5-600s, and the spraying speed of the third spraying is 0.2-0.5s·cm -2 The spraying pressure is 0.1-0.2MPa, and the spraying amount per unit area is 30-50mg·m -2 .

[0038] Example 1

[0039] This embodiment relates to a graphene oxide separation membrane with a multi-level structure and a preparation method thereof, which specifically comprises the following steps:

[0040] Step 1, preparation of graphene oxide dispersion: select large single-layer graphene oxide with a size of about 40-50 μm and small single-layer graphene oxide nanosheets with a size of about 5-8 μm, and add 0.08 g·L -1 The concentration of is ultrasonically dispersed in water;

[0041] Step 2, pretreatment of large flake graphene oxide: subjecting the large flake graphene oxide dispersion to hydrothermal reflux treatment, the hydrothermal reflux temperature being 80° C., and the hydrothermal reflux time being 0.5 h;

[0042] Step 3, selecting a polysulfone ultrafiltration membrane as a base membrane, performing a first spraying, loading the large graphene oxide flakes after the heat treatment in step 2 on the base membrane, and then performing a second spraying, loading the small graphene oxide flakes on the base membrane loaded with the large graphene oxide flakes to obtain a composite membrane, the spraying speed of the first spraying and the second spraying is 0.2 s·cm -2 The spraying pressure is 0.1MPa and the spraying amount per unit area is 30mg·m -2 ;

[0043] Step 4: Plasma treatment of the composite film, with a treatment power of 100 W and a treatment time of 600 s. A third spraying is performed to load small pieces of graphene oxide, with a spraying speed of 0.2 s·cm -2 The spraying pressure is 0.1MPa and the spraying amount per unit area is 50mg·m -2 , and finally a graphene oxide separation membrane with a multi-level structure was obtained.

[0044] Figure 2 The scanning electron microscope images of large and small graphene oxide flakes and large graphene oxide flakes after hydrothermal treatment in the embodiments of the present invention are shown in FIG. The large graphene oxide flakes after hydrothermal treatment have darkened in color due to partial reduction and etching, but the overall size remains at 40-50 μm.

[0045] The water flux and salt rejection rate of the prepared graphene oxide composite nanofiltration membrane were evaluated using a cross-flow membrane filtration device. The concentration of methyl blue dye solution was 1 g·L -1 Under the conditions of , the rejection rate of the membrane prepared by the spray coating method in this embodiment is 99.8%; under the operating pressure of 5 bar and the concentration of Na2SO4 solution of 1 g·L -1 Under the condition of -2 ·h -1 bar -1 , the salt rejection rate was 96.0%. After 400h of continuous testing, the water flux of the membrane dropped to 10.0L·m -2 ·h -1 bar -1 The salt rejection rate dropped to 93.0%. After cleaning, the water flux of the membrane recovered to 12.0 L·m -2 ·h -1 bar -1 , the salt rejection rate was restored to 95.0%. It demonstrated the superior separation performance, structural and performance stability, and performance recovery ability of the hierarchical structure membrane after cleaning.

[0046] Example 2

[0047] This embodiment relates to a graphene oxide separation membrane with a multi-level structure and a preparation method thereof, which specifically comprises the following steps:

[0048] Step 1, preparation of graphene oxide dispersion: select large single-layer graphene oxide with a size of about 40-50 μm and small single-layer graphene oxide nanosheets with a size of about 5-8 μm, and add 0.08 g·L -1 The concentration of is ultrasonically dispersed in water;

[0049] Step 2, pretreatment of large flake graphene oxide: subjecting the large flake graphene oxide dispersion to hydrothermal reflux treatment, the hydrothermal reflux temperature being 100° C., and the hydrothermal reflux time being 1 h;

[0050] Step 3, selecting a polysulfone ultrafiltration membrane as a base membrane, performing a first spraying, loading the large graphene oxide flakes after the heat treatment in step 2 on the base membrane, and then performing a second spraying, loading the small graphene oxide flakes on the base membrane loaded with the large graphene oxide flakes to obtain a composite membrane, the spraying speed of the first spraying and the second spraying is 0.2 s·cm -2The spraying pressure is 0.1MPa and the spraying amount per unit area is 30mg·m -2 ;

[0051] Step 4: Plasma treatment of the composite film, with a treatment power of 100 W and a treatment time of 600 s. A third spraying is performed to load small pieces of graphene oxide, with a spraying speed of 0.2 s·cm -2 The spraying pressure is 0.1MPa and the spraying amount per unit area is 50mg·m -2 , and finally a graphene oxide separation membrane with a multi-level structure was obtained.

[0052] The water flux and salt rejection of the prepared graphene oxide composite nanofiltration membrane were evaluated using a cross-flow membrane filtration device. -1 Under the conditions of , the rejection rate of the membrane prepared by the spray coating method in this embodiment is 99.8%; under the operating pressure of 5 bar and the concentration of Na2SO4 solution of 1 g·L -1 Under the condition of -2 ·h -1 bar -1 , the salt rejection rate was 95.0%. After 400h of continuous testing, the water flux of the membrane dropped to 14.5L·m -2 ·h -1 bar -1 The salt rejection rate dropped to 91.5%. After cleaning, the water flux of the membrane recovered to 17.5L·m -2 ·h -1 bar -1 , the salt rejection rate was restored to 94.5%. It demonstrated the superior separation performance, structural and performance stability, and performance recovery ability of the hierarchical structure membrane after cleaning.

[0053] Example 3

[0054] This embodiment relates to a graphene oxide separation membrane with a multi-level structure and a preparation method thereof, which specifically comprises the following steps:

[0055] Step 1, preparation of graphene oxide dispersion: select large single-layer graphene oxide with a size of about 40-50 μm and small single-layer graphene oxide nanosheets with a size of about 5-8 μm, and add 0.08 g·L -1 The concentration of is ultrasonically dispersed in water;

[0056] Step 2, pretreatment of large flake graphene oxide: subjecting the large flake graphene oxide dispersion to hydrothermal reflux treatment, the hydrothermal reflux temperature being 80° C., and the hydrothermal reflux time being 1 h;

[0057] Step 3, selecting a polysulfone ultrafiltration membrane as a base membrane, performing a first spraying, loading the large graphene oxide flakes after the heat treatment in step 2 on the base membrane, and then performing a second spraying, loading the small graphene oxide flakes on the base membrane loaded with the large graphene oxide flakes to obtain a composite membrane, the spraying speed of the first spraying and the second spraying is 0.2 s·cm -2 The spraying pressure is 0.1MPa and the spraying amount per unit area is 30mg·m -2 ;

[0058] Step 4: Plasma treatment of the composite film, with a treatment power of 100 W and a treatment time of 600 s. A third spraying is performed to load small pieces of graphene oxide, with a spraying speed of 0.2 s·cm -2 The spraying pressure is 0.1MPa and the spraying amount per unit area is 50mg·m -2 , and finally a graphene oxide separation membrane with a multi-level structure was obtained.

[0059] The water flux and salt rejection of the prepared graphene oxide composite nanofiltration membrane were evaluated using a cross-flow membrane filtration device. -1 Under the conditions of , the rejection rate of the membrane prepared by the spray coating method in this embodiment is 99.8%; under the operating pressure of 5 bar and the concentration of Na2SO4 solution of 1 g·L -1 Under the condition of -2 ·h -1 bar -1 , the salt rejection rate was 96.0%. After 400h of continuous testing, the water flux of the membrane dropped to 12.5L·m -2 ·h -1 bar -1 The salt rejection rate dropped to 93.0%. After cleaning, the water flux of the membrane recovered to 15.0 L·m -2 ·h -1 bar -1 , the salt rejection rate was restored to 95.0%. It demonstrated the superior separation performance, structural and performance stability, and performance recovery ability of the hierarchical structure membrane after cleaning.

[0060] Example 4

[0061] This embodiment relates to a graphene oxide separation membrane with a multi-level structure and a preparation method thereof, which specifically comprises the following steps:

[0062] Step 1, preparation of graphene oxide dispersion: select large single-layer graphene oxide with a size of about 40-50 μm and small single-layer graphene oxide nanosheets with a size of about 5-8 μm, and add 0.08 g·L -1 The concentration of is ultrasonically dispersed in water;

[0063] Step 2, pretreatment of large flake graphene oxide: subjecting the large flake graphene oxide dispersion to hydrothermal reflux treatment, the hydrothermal reflux temperature being 100° C., and the hydrothermal reflux time being 0.5 h;

[0064] Step 3, selecting a polysulfone ultrafiltration membrane as a base membrane, performing a first spraying, loading the large graphene oxide flakes after the heat treatment in step 2 on the base membrane, and then performing a second spraying, loading the small graphene oxide flakes on the base membrane loaded with the large graphene oxide flakes to obtain a composite membrane, the spraying speed of the first spraying and the second spraying is 0.2 s·cm -2 The spraying pressure is 0.1MPa and the spraying amount per unit area is 30mg·m -2 ;

[0065] Step 4: Plasma treatment of the composite film, with a treatment power of 100 W and a treatment time of 600 s. A third spraying is performed to load small pieces of graphene oxide, with a spraying speed of 0.2 s·cm -2 The spraying pressure is 0.1MPa and the spraying amount per unit area is 50mg·m -2 , and finally a graphene oxide separation membrane with a multi-level structure was obtained.

[0066] The water flux and salt rejection of the prepared graphene oxide composite nanofiltration membrane were evaluated using a cross-flow membrane filtration device. -1 Under the conditions of , the rejection rate of the membrane prepared by the spray coating method in this embodiment is 99.8%; under the operating pressure of 5 bar and the concentration of Na2SO4 solution of 1 g·L -1 Under the condition of -2 ·h -1 bar -1 , the salt rejection rate was 96.0%. After 400h of continuous testing, the water flux of the membrane dropped to 12.5L·m -2 ·h -1 bar -1 The salt rejection rate dropped to 93.0%. After cleaning, the water flux of the membrane recovered to 15.0 L·m -2 ·h -1 bar -1 , the salt rejection rate was restored to 95.0%. It demonstrated the superior separation performance, structural and performance stability, and performance recovery ability of the hierarchical structure membrane after cleaning.

[0067] Example 5

[0068] This embodiment relates to a graphene oxide separation membrane with a multi-level structure and a preparation method thereof, which specifically comprises the following steps:

[0069] Step 1, preparation of graphene oxide dispersion: select large single-layer graphene oxide with a size of about 40-50 μm and small single-layer graphene oxide nanosheets with a size of about 5-8 μm, and add 0.08 g·L -1 The concentration of is ultrasonically dispersed in water;

[0070] Step 2, pretreatment of large flake graphene oxide: subjecting the large flake graphene oxide dispersion to hydrothermal reflux treatment, the hydrothermal reflux temperature being 80° C., and the hydrothermal reflux time being 0.5 h;

[0071] Step 3, selecting a polysulfone ultrafiltration membrane as a base membrane, performing a first spraying, loading the large graphene oxide flakes after the heat treatment in step 2 on the base membrane, and then performing a second spraying, loading the small graphene oxide flakes on the base membrane loaded with the large graphene oxide flakes to obtain a composite membrane, the spraying speed of the first spraying and the second spraying is 0.2 s·cm -2 The spraying pressure is 0.1MPa and the spraying amount per unit area is 30mg·m -2 ;

[0072] Step 4: Plasma treatment of the composite film, with a treatment power of 20 W and a treatment time of 5 s. A third spraying is performed to load small pieces of graphene oxide, with a spraying speed of 0.2 s·cm -2 The spraying pressure is 0.1MPa and the spraying amount per unit area is 50mg·m -2 , and finally a graphene oxide separation membrane with a multi-level structure was obtained.

[0073] Figure 3 The electron microscope images of the film surface after different plasma treatment times in Example 1 and Example 5 of the present invention are shown. Different treatment times do not have a significant impact on the film appearance morphology.

[0074] The water flux and salt rejection of the prepared graphene oxide composite nanofiltration membrane were evaluated using a cross-flow membrane filtration device. -1 Under the conditions of , the rejection rate of the membrane prepared by the spray coating method in this embodiment is 99.8%; under the operating pressure of 5 bar and the concentration of Na2SO4 solution of 1 g·L -1 Under the condition of -2 ·h -1 bar -1 , the salt rejection rate was 98.0%. After 400h of continuous testing, the water flux of the membrane dropped to 6.5L·m -2 ·h -1 bar -1 The salt rejection rate dropped to 94.5%. After cleaning, the water flux of the membrane recovered to 7.5L·m -2·h -1 bar -1 , the salt rejection rate was restored to 96.0%. It demonstrated the superior separation performance, structural and performance stability, and performance recovery ability of the hierarchical structure membrane after cleaning.

[0075] Example 6

[0076] This embodiment relates to a graphene oxide separation membrane with a multi-level structure and a preparation method thereof, which specifically comprises the following steps:

[0077] Step 1, preparation of graphene oxide dispersion: select large single-layer graphene oxide with a size of about 40-50 μm and small single-layer graphene oxide nanosheets with a size of about 5-8 μm, and add 0.08 g·L -1 The concentration of is ultrasonically dispersed in water;

[0078] Step 2, pretreatment of large flake graphene oxide: subjecting the large flake graphene oxide dispersion to hydrothermal reflux treatment, the hydrothermal reflux temperature being 100° C., and the hydrothermal reflux time being 1 h;

[0079] Step 3, selecting a polysulfone ultrafiltration membrane as a base membrane, performing a first spraying, loading the large graphene oxide flakes after the heat treatment in step 2 on the base membrane, and then performing a second spraying, loading the small graphene oxide flakes on the base membrane loaded with the large graphene oxide flakes to obtain a composite membrane, the spraying speed of the first spraying and the second spraying is 0.2 s·cm -2 The spraying pressure is 0.1MPa and the spraying amount per unit area is 30mg·m -2 ;

[0080] Step 4: Plasma treatment of the composite film, with a treatment power of 20 W and a treatment time of 600 s. A third spraying is performed to load small pieces of graphene oxide, with a spraying speed of 0.2 s·cm -2 The spraying pressure is 0.1MPa and the spraying amount per unit area is 50mg·m -2 , and finally a graphene oxide separation membrane with a multi-level structure was obtained.

[0081] The water flux and salt rejection of the prepared graphene oxide composite nanofiltration membrane were evaluated using a cross-flow membrane filtration device. -1 Under the conditions of , the rejection rate of the membrane prepared by the spray coating method in this embodiment is 99.8%; under the operating pressure of 5 bar and the concentration of Na2SO4 solution of 1 g·L -1 Under the condition of -2 ·h -1 bar -1, the salt rejection rate was 96.0%. After 400h of continuous testing, the water flux of the membrane dropped to 13.5L·m -2 ·h -1 bar -1 The salt rejection rate dropped to 93.0%. After cleaning, the water flux of the membrane recovered to 15.5 L·m -2 ·h -1 bar -1 , the salt rejection rate was restored to 95.0%. It demonstrated the superior separation performance, structural and performance stability, and performance recovery ability of the hierarchical structure membrane after cleaning.

[0082] Example 7

[0083] This embodiment relates to a graphene oxide separation membrane with a multi-level structure and a preparation method thereof, which specifically comprises the following steps:

[0084] Step 1, preparation of graphene oxide dispersion: select large single-layer graphene oxide with a size of about 40-50 μm and small single-layer graphene oxide nanosheets with a size of about 5-8 μm, and add 0.08 g·L -1 The concentration of is ultrasonically dispersed in water;

[0085] Step 2, pretreatment of large flake graphene oxide: subjecting the large flake graphene oxide dispersion to hydrothermal reflux treatment, the hydrothermal reflux temperature being 100° C., and the hydrothermal reflux time being 1 h;

[0086] Step 3, selecting a polysulfone ultrafiltration membrane as a base membrane, performing a first spraying, loading the large graphene oxide flakes after the heat treatment in step 2 on the base membrane, and then performing a second spraying, loading the small graphene oxide flakes on the base membrane loaded with the large graphene oxide flakes to obtain a composite membrane, the spraying speed of the first spraying and the second spraying is 0.2 s·cm -2 The spraying pressure is 0.1MPa and the spraying amount per unit area is 30mg·m -2 ;

[0087] Step 4: Plasma treatment of the composite film, with a treatment power of 100 W and a treatment time of 5 s. A third spraying is performed to load small pieces of graphene oxide, with a spraying speed of 0.2 s·cm -2 The spraying pressure is 0.1MPa and the spraying amount per unit area is 50mg·m -2 , and finally a graphene oxide separation membrane with a multi-level structure was obtained.

[0088] The water flux and salt rejection of the prepared graphene oxide composite nanofiltration membrane were evaluated using a cross-flow membrane filtration device. -1Under the conditions of , the rejection rate of the membrane prepared by the spray coating method in this embodiment is 99.8%; under the operating pressure of 5 bar and the concentration of Na2SO4 solution of 1 g·L -1 Under the condition of -2 ·h -1 bar -1 , the salt rejection rate was 96.0%. After 400h of continuous testing, the water flux of the membrane dropped to 13.5L·m -2 ·h -1 bar -1 The salt rejection rate dropped to 93.0%. After cleaning, the water flux of the membrane recovered to 15.5 L·m -2 ·h -1 bar -1 , the salt rejection rate was restored to 95.0%. It demonstrated the superior separation performance, structural and performance stability, and performance recovery ability of the hierarchical structure membrane after cleaning.

[0089] Example 8

[0090] This embodiment relates to a graphene oxide separation membrane with a multi-level structure and a preparation method thereof, which specifically comprises the following steps:

[0091] Step 1, preparation of graphene oxide dispersion: select large single-layer graphene oxide with a size of about 40-50 μm and small single-layer graphene oxide nanosheets with a size of about 5-8 μm, and add 0.08 g·L -1 The concentration of is ultrasonically dispersed in water;

[0092] Step 2, pretreatment of large flake graphene oxide: subjecting the large flake graphene oxide dispersion to hydrothermal reflux treatment, the hydrothermal reflux temperature being 100° C., and the hydrothermal reflux time being 1 h;

[0093] Step 3, selecting a polysulfone ultrafiltration membrane as a base membrane, performing a first spraying, loading the large graphene oxide flakes after the heat treatment in step 2 on the base membrane, and then performing a second spraying, loading the small graphene oxide flakes on the base membrane loaded with the large graphene oxide flakes to obtain a composite membrane, the spraying speed of the first spraying and the second spraying is 0.2 s·cm -2 The spraying pressure is 0.1MPa and the spraying amount per unit area is 30mg·m -2 ;

[0094] Step 4: Plasma treatment of the composite film, with a treatment power of 100 W and a treatment time of 600 s. A third spraying is performed to load small pieces of graphene oxide, with a spraying speed of 0.2 s·cm -2 The spraying pressure is 0.1MPa and the spraying amount per unit area is 30mg·m -2, and finally a graphene oxide separation membrane with a multi-level structure was obtained.

[0095] The water flux and salt rejection of the prepared graphene oxide composite nanofiltration membrane were evaluated using a cross-flow membrane filtration device. -1 Under the conditions of , the rejection rate of the membrane prepared by the spray coating method in this embodiment is 99.8%; under the operating pressure of 5 bar and the concentration of Na2SO4 solution of 1 g·L -1 Under the condition of -2 ·h -1 bar -1 , the salt rejection rate was 90.0%. After 400h of continuous testing, the water flux of the membrane dropped to 20.0L·m -2 ·h -1 bar -1 The salt rejection rate dropped to 87.5%. After cleaning, the water flux of the membrane recovered to 24.0 L·m -2 ·h -1 bar -1 , the salt rejection rate was restored to 88.5%. It demonstrated the superior separation performance, structural and performance stability, and performance recovery ability of the hierarchical structure membrane after cleaning.

[0096] Comparative Example 1

[0097] This comparative example relates to a graphene oxide separation membrane having a partial multi-level structure and free of a topmost graphene oxide flake, and a preparation method thereof, which specifically comprises the following steps:

[0098] Step 1, preparation of graphene oxide dispersion: select large single-layer graphene oxide with a size of about 40-50 μm and small single-layer graphene oxide nanosheets with a size of about 5-8 μm, and add 0.08 g·L -1 The concentration of is ultrasonically dispersed in water;

[0099] Step 2, pretreatment of large flake graphene oxide: subjecting the large flake graphene oxide dispersion to hydrothermal reflux treatment, the hydrothermal reflux temperature being 100° C., and the hydrothermal reflux time being 1 h;

[0100] Step 3, selecting a polysulfone ultrafiltration membrane as a base membrane, performing a first spraying, loading the large graphene oxide flakes after the heat treatment in step 2 on the base membrane, and then performing a second spraying, loading the small graphene oxide flakes on the base membrane loaded with the large graphene oxide flakes to obtain a composite membrane, the spraying speed of the first spraying and the second spraying is 0.2 s·cm -2 The spraying pressure is 0.1MPa and the spraying amount per unit area is 30mg·m -2 ;

[0101] Step 4, plasma treatment is performed on the composite membrane with a treatment power of 100 W and a treatment time of 600 s, and finally a graphene oxide separation membrane with a partial multi-level structure is obtained.

[0102] The water flux and salt rejection of the prepared graphene oxide composite nanofiltration membrane were evaluated using a cross-flow membrane filtration device. -1 Under the conditions of , the rejection rate of the membrane prepared by the spraying method in this comparative example is 85.0%; under the operating pressure of 5 bar and the concentration of Na2SO4 solution of 1 g·L -1 Under the condition of -2 ·h -1 bar -1 , the salt rejection rate was 70.0%. After 400h of continuous testing, the water flux of the membrane dropped to 25.0L·m -2 ·h -1 bar -1 The salt rejection rate dropped to 66.0%. After cleaning, the water flux of the membrane recovered to 28.0 L·m -2 ·h -1 bar -1 , the salt rejection rate was restored to 68.0%. It demonstrated the superior separation performance, structural and performance stability, and performance recovery ability after cleaning of the fully graded structure membrane.

[0103] Comparative Example 2

[0104] For comparison, this comparative example relates to a method for preparing a graphene oxide separation membrane having no multi-level structure, which specifically comprises the following steps:

[0105] Step 1, preparation of graphene oxide dispersion: select small single-layer graphene oxide nanosheets with a size of about 5-8 μm and add 0.08 g·L -1 The concentration of is ultrasonically dispersed in water;

[0106] Step 2: Select a polysulfone ultrafiltration membrane as a base membrane, and load small pieces of graphene oxide on the base membrane by spraying at a rate of 0.2 s·cm -2 The spraying pressure was 0.1 MPa, and the spraying amount per unit area was 90 mg·m -2 , and finally a graphene oxide separation membrane with a single-level structure was obtained.

[0107] The water flux and salt rejection of the prepared graphene oxide composite nanofiltration membrane were evaluated using a cross-flow membrane filtration device. -1Under the conditions of , the rejection rate of the membrane prepared by the spray coating method in this comparative example is 99.8%; under the operating pressure of 5 bar and the concentration of Na2SO4 solution of 1 g·L -1 Under the condition of -2 ·h -1 bar -1 The salt rejection rate was 96.5%. After 400 hours of continuous testing, the water flux of the membrane dropped to 1.2 L·m -2 ·h -1 bar -1 The salt rejection rate dropped to 93.0%. After cleaning, the water flux of the membrane recovered to 2.0 L·m -2 ·h -1 bar -1 , the salt rejection rate was restored to 94.0%. It shows that the hierarchical structure membrane has better separation performance, structural and performance stability, and performance recovery ability after cleaning than the single-stage structure membrane.

[0108] Figure 4 This is a comparison diagram of the internal structure and water molecule transmission of graphene oxide multi-level structure membrane and conventional single-level structure membrane, showing the contribution of the multi-level structure in creating more water transmission channels and avoiding clogging of the pores of the substrate membrane. The spraying amount per unit area in the comparative example of the present invention is consistent with that in Example 8, but the water flux is lower than that in Example 8, which proves that the multi-level structure in the present invention effectively improves the water permeability performance.

[0109] Comparative Example 3

[0110] For comparison, this comparative example relates to a method for preparing a graphene oxide separation membrane having no multi-level structure, which specifically comprises the following steps:

[0111] Step 1, preparation of graphene oxide dispersion: select small single-layer graphene oxide nanosheets with a size of about 5-8 μm and add 0.08 g·L -1 The concentration of is ultrasonically dispersed in water;

[0112] Step 2: Select a polysulfone ultrafiltration membrane as a base membrane, and load small pieces of graphene oxide on the base membrane by spraying at a rate of 0.2 s·cm -2 The spraying pressure is 0.1MPa and the spraying amount is 110mg·m -2 , and finally a graphene oxide separation membrane with a single-level structure was obtained.

[0113] The water flux and salt rejection of the prepared graphene oxide composite nanofiltration membrane were evaluated using a cross-flow membrane filtration device. -1Under the conditions of , the rejection rate of the membrane prepared by the spray coating method in this comparative example is 99.8%; under the operating pressure of 5 bar and the concentration of Na2SO4 solution of 1 g·L -1 Under the condition of -2 ·h -1 bar -1 , the salt rejection rate was 98.0%. After 400h of continuous testing, the water flux of the membrane dropped to 0.8L·m -2 ·h -1 bar -1 The salt rejection rate dropped to 94.0%. After cleaning, the water flux of the membrane recovered to 1.0 L·m -2 ·h -1 bar -1 , the salt rejection rate was restored to 94.5%. It shows that the hierarchical structure membrane has better separation performance, structural and performance stability, and performance recovery ability after cleaning than the single-stage structure membrane.

[0114] Figure 4 This is a comparison diagram of the internal structure and water molecule transmission of graphene oxide multi-level structure membrane and conventional single-level structure membrane, showing the contribution of the multi-level structure in creating more water transmission channels and avoiding clogging of the pores of the substrate membrane. The spraying amount per unit area in the comparative example of the present invention is consistent with that in Examples 1-7, but the water flux is lower than that in Examples 1-7, proving that the multi-level structure in the present invention effectively improves the water permeability.

[0115] Comparative Example 4

[0116] For comparison, this comparative example relates to a method for preparing a graphene oxide separation membrane having no multi-level structure, which specifically comprises the following steps:

[0117] Step 1, preparation of graphene oxide dispersion: select small single-layer graphene oxide nanosheets with a size of about 5-8 μm and add 0.08 g·L -1 The concentration of is ultrasonically dispersed in water;

[0118] Step 2: Select a polysulfone ultrafiltration membrane as a base membrane, and load small pieces of graphene oxide on the base membrane by spraying at a rate of 0.2 s·cm -2 The spraying pressure was 0.1 MPa, and the spraying amount per unit area of ​​the top layer was 50 mg·m -2 , and finally a graphene oxide separation membrane with a single-level structure was obtained.

[0119] The water flux and salt rejection of the prepared graphene oxide composite nanofiltration membrane were evaluated using a cross-flow membrane filtration device. -1Under the conditions of , the rejection rate of the membrane prepared by the spray coating method in this comparative example is 90.0%; under the operating pressure of 5 bar and the concentration of Na2SO4 solution of 1 g·L -1 Under the condition of -2 ·h -1 bar -1 , the salt rejection rate was 80.0%. After 400h of continuous testing, the water flux of the membrane dropped to 2.0L·m -2 ·h -1 bar -1 The salt rejection rate dropped to 70.0%. After cleaning, the water flux of the membrane recovered to 2.2 L·m -2 ·h -1 bar -1 , the salt rejection rate was restored to 73.0%. It shows that the hierarchical structure membrane has better separation performance, structural and performance stability, and performance recovery ability after cleaning than the single-stage structure membrane.

[0120] Comparative Example 5

[0121] For comparison, this comparative example relates to a method for preparing a graphene oxide separation membrane having no multi-level structure, which specifically comprises the following steps:

[0122] Step 1, preparation of graphene oxide dispersion: select small single-layer graphene oxide nanosheets with a size of about 5-8 μm and add 0.08 g·L -1 The concentration of is ultrasonically dispersed in water;

[0123] Step 2: Select a polysulfone ultrafiltration membrane as a base membrane, and load small pieces of graphene oxide on the base membrane by spraying at a rate of 0.2 s·cm -2 The spraying pressure was 0.1 MPa, and the spraying amount per unit area of ​​the top layer was 30 mg·m -2 , and finally a graphene oxide separation membrane with a single-level structure was obtained.

[0124] The water flux and salt rejection of the prepared graphene oxide composite nanofiltration membrane were evaluated using a cross-flow membrane filtration device. -1 Under the conditions of , the rejection rate of the membrane prepared by the spraying method in this comparative example is 70.0%; under the operating pressure of 5 bar and the concentration of Na2SO4 solution of 1 g·L -1 Under the condition of -2 ·h -1 bar -1 , the salt rejection rate was 60.0%. After 400h of continuous testing, the water flux of the membrane dropped to 3.0L·m -2 ·h -1 bar-1 , the salt rejection rate dropped to 50.0%. After cleaning, the water flux of the membrane recovered to 3.5L·m -2 ·h -1 bar -1 , the salt rejection rate was restored to 52.0%. It shows that the hierarchical structure membrane has better separation performance, structural and performance stability, and performance recovery ability after cleaning than the single-stage structure membrane.

[0125] Comparative Example 6

[0126] For comparison, this comparative example involves a permeation separation performance test of a substrate membrane without graphene oxide, specifically including the following:

[0127] Polysulfone ultrafiltration membrane was selected as the test membrane, and the water flux and salt rejection rate were evaluated using a cross-flow membrane filtration device. -1 Under the conditions of , the rejection rate of the membrane prepared by the spray coating method in this comparative example is 40.0%; under the operating pressure of 5 bar and the concentration of Na2SO4 solution of 1 g·L -1 Under the condition of -2 ·h -1 bar -1 , the salt rejection rate was 22.0%. After 400h of continuous testing, the water flux of the membrane dropped to 50.0L·m -2 ·h -1 bar -1 , the salt rejection rate dropped to 20.0%. After cleaning, the water flux of the membrane recovered to 56.0L·m -2 ·h -1 bar -1 , the salt rejection rate was restored to 20.0%, demonstrating the contribution of the graphene oxide separation layer to the membrane separation performance.

[0128]

[0129] Notes: 1. GO, graphene oxide; 2. Test conditions: operating pressure 5 bar, dye and salt solution concentration 1 g·L -1 3. Cleaning conditions: Use deionized water to wash the membrane forward and back for half an hour each at an operating pressure of 10 bar.

[0130] The important parameters and results of the above embodiments and comparisons are summarized in Table 1. From the results, it can be seen that the graphene oxide separation membrane with a multi-level structure of the present invention can take into account both water flux and interception rate, and can restore a higher water flux and retention rate after running for 400 hours and cleaning.

[0131] The above is only a preferred embodiment of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a graphene oxide separation membrane having a multi-level structure, characterized in that: The following steps are involved: Step 1, dispersing a large piece of monolayer graphene oxide and a small piece of monolayer graphene oxide in water to obtain a large piece of graphene oxide dispersion and a small piece of graphene oxide dispersion respectively; Step 2, subjecting the large-scale graphene oxide dispersion to a hydrothermal reflux treatment; Step 3, taking a hydrophilic ultrafiltration membrane or a hydrophilized ultrafiltration membrane as a base membrane, performing a first spraying, loading the large graphene oxide flakes after the heat treatment in step 2 on the base membrane, and then performing a second spraying, loading the small graphene oxide flakes on the base membrane loaded with the large graphene oxide flakes to obtain a composite membrane; Step 4, plasma treating the composite membrane obtained in step 3, and then spraying it for a third time to load small pieces of graphene oxide, so as to obtain the graphene oxide separation membrane with a multi-level structure.

2. The method for preparing a graphene oxide separation membrane having a multi-level structure according to claim 1, wherein: The size of the large single-layer graphene oxide sheet is 40-50 μm, and the size of the small single-layer graphene oxide sheet is 5-8 μm.

3. The method for preparing a graphene oxide separation membrane having a multi-level structure according to claim 1, wherein: The concentration of large single-layer graphene oxide in the large graphene oxide dispersion in step 1 is 0.08-0.25 g·L -1 The concentration of the small monolayer graphene oxide sheets in the small graphene oxide dispersion is 0.08-0.25 g·L -1 ; In the step 2, the temperature of the hydrothermal reflux is 80-100° C., and the time of the hydrothermal reflux is 0.5-1 h.

4. The method for preparing a graphene oxide separation membrane having a multi-level structure as claimed in claim 1, characterized in that: The hydrophilic ultrafiltration membrane is a flat ultrafiltration membrane or a curved ultrafiltration membrane of polysulfone, polyethersulfone, or cellulose acetate; The hydrophilized ultrafiltration membrane is one of polyvinyl chloride, polytetrafluoroethylene, polyvinylidene fluoride, polyacrylonitrile, polypropylene, polyethylene, polyurethane, polycaprolactam flat ultrafiltration membrane or curved ultrafiltration membrane soaked in ethanol or isopropanol.

5. The method for preparing a graphene oxide separation membrane having a multi-level structure according to claim 1, wherein: The spraying speed of the first spraying is 0.2-0.5s·cm -2 The spraying pressure is 0.1-0.2MPa, and the spraying amount per unit area is 30-40mg·m -2 ; The spraying speed of the second spraying is 0.2-0.5s·cm -2 The spraying pressure is 0.1-0.2MPa, and the spraying amount per unit area is 30-40mg·m -2 .

6. The method for preparing a graphene oxide separation membrane having a multi-level structure according to claim 1, wherein: The processing power of the plasma treatment is 20-100W, and the processing time is 5-600s.

7. The method for preparing a graphene oxide separation membrane having a multi-level structure according to claim 1, wherein: The spraying speed of the third spraying is 0.2-0.5s·cm -2 The spraying pressure is 0.1-0.2MPa, and the spraying amount per unit area is 30-50mg·m -2 .

8. A graphene oxide separation membrane having a multi-level structure, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 7.

9. The graphene oxide separation membrane with a multi-level structure according to claim 8, characterized in that: The graphene oxide separation membrane has an initial desalination rate of not less than 90%, a dye interception rate of not less than 99.5%, and an initial water flux of not less than 10 L·m -2 ·h -1 bar -1 .

10. Use of the graphene oxide separation membrane with a multi-level structure as claimed in any one of claims 8 to 9 in water treatment.

Images