Graphene oxide film with wrinkle structure as well as preparation method and application of graphene oxide film

Abstract

The invention belongs to the technical field of functional materials, and particularly relates to a graphene oxide film with a wrinkle structure and a preparation method and application thereof. The preparation method of the graphene oxide film with the wrinkle structure comprises the following steps: mixing a graphene oxide dispersion liquid and a cation salt solution, and then carrying out hydrothermal reduction reaction to obtain a cation-induced graphene oxide solution; preparing a graphene oxide film with a wrinkle structure through vacuum filtration; wherein cations in the cation salt solution comprise one or more of Na < + >, K < + >, NH4 < + >, Cs < + >, Mg < 2 + >, Ca < 2 + >, Pb < 2 + >, Sr < 2 + > or Al < 3 + >. Compared with the prior art, the graphene oxide membrane with the wrinkle structure prepared by the invention has considerable pollutant removal capacity on a sewage system containing micro-plastics and heavy metals, and has a good application prospect in the field of water treatment.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional materials, and particularly relates to a graphene oxide membrane with a wrinkled structure, a preparation method thereof, and an application thereof. Background Art

[0002] In the comprehensive treatment of water environment, microplastics and heavy metal pollution have been listed as the key targets of "new pollutant treatment".

[0003] At present, common methods for removing microplastics (such as catalysis, biodegradation, and adsorption, etc.) and heavy metals (such as chemical precipitation, adsorption, ion exchange, etc.) have the disadvantages of low efficiency, high cost, difficulty in effectively removing small-sized pollutants, and generating secondary pollution. In contrast, membrane separation technology has been favored due to its high efficiency, simple operation, and environmental friendliness. However, traditional membrane materials have problems such as poor anti-fouling ability, difficulty in separating small-sized particles, and poor mechanical strength. In view of this, it has become particularly important to develop a new type of membrane material with high flux, high rejection rate, strong stability, and capable of effectively removing small-sized pollutants.

[0004] Graphene is considered an ideal membrane material due to its unique physical and chemical properties. However, the narrow and tortuous mass transfer path in the unmodified or non-functionalized graphene-based membrane usually leads to extremely high mass transfer resistance, reducing the membrane permeability and limiting the practical application of graphene-based membranes. The wrinkled structure, which has been long neglected in layered two-dimensional nano-separation membranes, can provide additional mass transfer channels, providing an important opportunity to solve the above problems. Common methods for constructing wrinkles on the surface of graphene-based membranes include pre-stretching method, solvent-induced method, rapid drying method, and pH adjustment method, etc. Among them, although the pre-stretching method and the rapid drying method have simple preparation processes, the physical stretching and rapid drying processes are likely to damage the inherent interlayer structure of the layered two-dimensional nano-separation membrane; the pH adjustment method is only applicable to single-layer graphene and is not suitable for constructing wrinkles on multi-layer graphene membranes; the solvent-induced method requires the introduction of additional organic solvents, which can construct wrinkles on the membrane, but the improvement of the membrane permeability is extremely limited.

[0005] CN 113522059 B discloses a wrinkled graphene oxide membrane and its preparation method, which can be used in related fields such as water purification. The preparation method is as follows: uniformly disperse graphene oxide in a first organic solvent to obtain a graphene oxide dispersion; then pour the graphene oxide dispersion onto a porous support and perform suction filtration to obtain a graphene oxide membrane adhered to the porous support; then remove the first organic solvent in the graphene oxide membrane; then place the graphene oxide membrane from which the first organic solvent has been removed in a second organic solvent, and finally remove the second organic solvent to obtain a wrinkled graphene oxide membrane. However, the above preparation method of the wrinkled graphene oxide membrane has the following disadvantages: high-boiling organic solvents such as dimethyl sulfoxide, N-methylformamide, and N,N-dimethylformamide need to be used, with a high toxicity risk and harm to the human body; the recovery cost is high, and it is difficult to recover after the solvent evaporates, increasing the production cost; the residue of the organic solvent may lead to a decrease in the chemical stability and separation performance of the membrane material, resulting in its separation flux being 1-2 orders of magnitude lower than that of this project; the prepared wrinkled structure is formed by solvent replacement-induced stress, and the uniformity of the wrinkles is highly dependent on the matching degree of the solvents, and the polarity difference between the two solvents needs to be precisely controlled.

[0006] Therefore, in view of the problems existing in the existing preparation method of the above-mentioned wrinkled graphene oxide membrane, such as the need to use a large amount of organic solvents and the difficulty in controlling the uniformity of the wrinkles, it is urgent to develop a new method for constructing wrinkles on the surface of the graphene-based membrane to significantly improve the membrane separation performance. Summary of the Invention

[0007] The purpose of the present invention is to provide a graphene oxide membrane with a wrinkled structure, its preparation method and application, in order to overcome at least one defect existing in the prior art, such as the need to use a large amount of organic solvents and the difficulty in controlling the uniformity of the wrinkles.

[0008] The purpose of the present invention can be achieved through the following technical solutions:

[0009] The present invention first provides a preparation method of a graphene oxide membrane with a wrinkled structure, and the preparation method includes the following steps:

[0010] Mix the graphene oxide dispersion with a salt ion solution and then perform hydrothermal reduction reaction to obtain a cation-induced graphene oxide solution; prepare a graphene oxide membrane with a wrinkled structure through vacuum suction filtration.

[0011] Among them, the cations in the cation salt solution include Na + , K + , NH4 + , Cs + , Mg 2+ , Ca 2+ , Pb 2+ , Sr 2+ or Al3+ One or more of those in

[0012] Furthermore, the anions in the cationic salt solution include F - , Cl - , Br - , I - , OH - , NO3 - or SO4 2- One or more of those in

[0013] Furthermore, the final concentration range of the graphene oxide in the mixed solution is 0.01 - 1 g / L.

[0014] Furthermore, the final concentration range of the cation in the mixed solution is 0.01 - 0.5 mol / L.

[0015] Furthermore, the temperature of the hydrothermal reduction reaction is 10 - 90 °C.

[0016] Furthermore, the time of the hydrothermal reduction reaction is 0.05 - 5 h.

[0017] Furthermore, the pH during the hydrothermal reduction reaction is controlled at 3 - 13.

[0018] The present invention also provides a graphene oxide film with a wrinkled structure prepared by the above preparation method.

[0019] Furthermore, the wrinkled structure formed on the graphene oxide film includes any one of ridge-like, fishbone-like, and interlaced network-like.

[0020] Furthermore, there is a cation-π electron interaction between the cation and the aromatic ring structure of the graphene oxide, which induces the formation of a wrinkled structure on the graphene surface by enhancing the electrostatic attraction and van der Waals force between the graphene oxide sheets.

[0021] Furthermore, the average surface roughness of the graphene oxide film is at least 20 nm.

[0022] Furthermore, the content of the metal element or non-metal element introduced on the surface of the graphene oxide film accounts for 1 - 10% of the total content of all elements on the surface of the graphene oxide film.

[0023] The present invention also provides an application of the graphene oxide film with a wrinkled structure in sewage treatment.

[0024] Furthermore, the graphene oxide film can be used as a separation membrane to intercept microplastics and / or heavy metal ions in sewage.

[0025] Furthermore, the graphene oxide membrane can retain microplastic particles with a particle size not greater than 2.5 μm and a concentration not greater than 50 mg / L.

[0026] Furthermore, the shapes of the microplastic particles include, but are not limited to, rhombus, spherical, and square.

[0027] Furthermore, the heavy metal elements that the graphene oxide membrane can retain include Fe, Cu, Co, and Cr, and the concentration of heavy metal salts in the sewage is not greater than 50 mg / L.

[0028] In the present invention, since the formation of the wrinkled structure is essentially due to the action of anisotropic forces, the present invention uses a cationic solution to assist in the hydrothermal reduction of graphene oxide dispersion to prepare graphene separation membranes with different wrinkled structures and roughnesses. By changing the type and concentration of cations, the cation-π interaction and cation-oxidation group interaction can be affected, etc., to effectively adjust the degree of wrinkling on the graphene membrane, increase the water molecule transport channels, and be used for the rapid and efficient removal of microplastics and heavy metals in sewage, having good application prospects in the field of environmental governance.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] (1) The present invention uses a cationic solution to assist in the hydrothermal reduction of graphene oxide dispersion to prepare a series of graphene separation membranes with different wrinkled structures and roughnesses, which can effectively adjust the degree of wrinkling on the graphene membrane, increase the water molecule transport channels, and be used for the rapid and efficient removal of microplastics and heavy metals in sewage.

[0031] (2) The present invention uses graphite as a raw material, synthesizes graphene oxide dispersion based on the Hummers method, and uses a cationic solution to assist in the hydrothermal reduction of graphene oxide dispersion. The prepared graphene-based separation membrane has a controllable degree of wrinkling and roughness.

[0032] (3) The wrinkled structure of the cation-induced graphene oxide membrane in the present invention provides a large number of water molecule transport channels, significantly improving the membrane permeability, which is much higher than the reported membrane separation fluxes currently: such as the flux of the PAN membrane is about 98 LMH bar -1 [Polymer 114, 64 - 72(2017)]; the flux of the PES membrane is about 120 LMH bar -1 [Chem.Eng.J.450 138484(2022)]; the flux of the GO-PVA membrane is about 179 LMH bar -1 [J.Water Process Eng.52 103554(2023)].

[0033] (4) The graphene oxide membrane with a wrinkled structure of the present invention can achieve high-throughput permeation for extremely difficult-to-treat small-sized microplastic (below 500 nm) sewage while still maintaining an extremely high rejection rate, and can efficiently remove pollutants from a complex sewage system containing both microplastics and heavy metals, showing good application prospects in the field of environmental governance.

[0034] (5) The preparation steps of the graphene oxide membrane with a wrinkled structure of the present invention are simple, without the need for complex equipment and harsh conditions, without secondary pollution, and without the use of a large amount of toxic and difficult-to-recycle organic solvents, showing good application prospects in the treatment of microplastic and heavy metal sewage.

[0035] (6) The preparation method of the graphene oxide membrane with a wrinkled structure of the present invention can effectively overcome many disadvantages of traditional methods for constructing wrinkles on the surface of graphene-based membranes. For example, although the pre-stretching method and the rapid drying method have simple preparation processes, the physical stretching and rapid drying processes are likely to damage the inherent interlayer structure of the layered two-dimensional nano-separation membrane; the pH adjustment method is only applicable to single-layer graphene and is not suitable for constructing wrinkles on multi-layer graphene membranes; the solvent induction method requires the introduction of additional organic solvents, which can construct wrinkles on the membrane but has extremely limited improvement in the membrane's permeation performance. Description of the Drawings

[0036] Figure 1 Photograph of the physical object of the graphene oxide membrane with a wrinkled structure induced by Na in Example 1. +

[0037] Figure 2 SEM characterization diagram of the graphene oxide membrane with a wrinkled structure induced by Na in Example 1; +

[0038] Figure 3 Atomic force microscopy image of the graphene oxide membrane with a wrinkled structure induced by Na in Example 1; +

[0039] Figure 4 SEM characterization diagram of the graphene oxide membrane with a wrinkled structure induced by NH4 in Example 2; +

[0040] Figure 5 Atomic force microscopy image of the graphene oxide membrane with a wrinkled structure induced by NH4 in Example 2; +

[0041] Figure 6 SEM characterization diagram of the graphene oxide membrane with a wrinkled structure induced by K in Example 3; +

[0042] Figure 7SEM characterization diagram of the graphene oxide membrane without cation induction prepared in Comparative Example 1;

[0043] Figure 8 Atomic force microscope image of the graphene oxide membrane without cation induction prepared in Comparative Example 1;

[0044] Figure 9 For the Na prepared in Example 1 + Interception performance test diagram of the graphene oxide membrane with a wrinkled structure induced by Na for microplastic sewage of different sizes;

[0045] Figure 10 For the Na prepared in Example 1 + Interception performance test diagram of the graphene oxide membrane with a wrinkled structure induced by Na for microplastic sewage of different concentrations;

[0046] Figure 11 Interception performance test comparison diagram of the graphene oxide membranes with a wrinkled structure induced by different cations in Examples 1-3 and the graphene oxide membrane prepared in Comparative Example 1 for microplastic sewage;

[0047] Figure 12 For the Na composed of different anions prepared in Example 4 + Interception performance test diagram of the graphene oxide membrane with a wrinkled structure induced by Na for microplastic sewage;

[0048] Figure 13 Interception performance test comparison diagram of the graphene oxide membranes prepared from different hydrothermal reduction reaction times in Example 1 and Comparative Example 2 for microplastic sewage;

[0049] Figure 14 For the Na prepared in Example 1 + Interception performance test diagram of the graphene oxide membrane with a wrinkled structure induced by Na for heavy metal sewage;

[0050] Figure 15 For the Na prepared in Example 1 + Interception performance test diagram of the graphene oxide membrane with a wrinkled structure induced by Na for pollutants in a complex sewage system. Detailed implementation mode

[0051] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. These embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operation processes are given, but the protection scope of the present invention is not limited to the following embodiments.

[0052] Unless otherwise specified, the reagents, methods, instruments and equipment used in the present invention are conventional reagents, methods, instruments and equipment in the art. Unless otherwise specified, the reagents and materials used in the following examples are all commercially available.

[0053] Example 1:

[0054] This example provides a Na + -induced graphene oxide film with a wrinkled structure, and the specific preparation steps are as follows:

[0055] S1. Prepare a graphene oxide dispersion based on the Hummers method:

[0056] 1. Grind 3 g of natural graphite powder and add it to a mixed solution containing 2.5 g of potassium persulfate, 2.5 g of phosphorus pentoxide, and 12 mL of concentrated sulfuric acid after ultrasonic treatment. Perform pre-oxidation at 80 °C, cool it, dilute it with pure water, and let it stand overnight. After pouring off the supernatant, use a vacuum filtration device to filter the precipitate into a solid and dry it in a vacuum drying oven;

[0057] 2. Grind the dried sample and add 120 mL of concentrated sulfuric acid. Slowly add 15 g of potassium permanganate after grinding to the concentrated sulfuric acid. The temperature during this process is always controlled below 6 °C. After adding potassium permanganate, stir the sample at 35 °C for 2 h, slowly add pure water drop by drop, and keep the temperature below 13 °C during this process. After adding pure water, stir the sample at room temperature for 2 h. Then transfer the sample to a 2 L beaker, add 700 mL of pure water while stirring, and immediately add 20 mL of 30% hydrogen peroxide, stir for another half an hour, and then let it stand overnight.

[0058] 3. After removing the supernatant from the standing solution, dilute it with 1 L of pure water, centrifuge it at 8000 rpm for 10 min, pour off the supernatant, collect the precipitate, then wash it with 1:10 hydrochloric acid dilution, centrifuge it at 8000 rpm for 10 min, pour off the supernatant, collect the precipitate, then dilute it with 1 L of pure water, centrifuge it at 10000 rpm for 10 min, pour off the supernatant, and finally collect the precipitated graphene oxide and dilute it to a constant volume with 1 L of pure water. After ultrasonic treatment for half an hour, stir it for standby to obtain a graphene oxide dispersion with a concentration of 5 mg / mL.

[0059] S2. Hydrothermal reduction reaction: Measure 5 mL of the graphene oxide dispersion prepared in S1 and dilute it to 0.5 mg / mL. Mix 2 mL of a sodium hydroxide solution with a concentration of 8 mol / L and 50 mL of the diluted graphene oxide dispersion, and heat and stir at 80 °C for 15 min. After cooling, obtain a Na + -induced graphene oxide solution.

[0060] S3. Prepare a graphene oxide film with a wrinkled structure: Take 400 μL of the prepared graphene oxide solution, dilute it to 15 mL with pure water, and use a vacuum filtration device to filter it into a film on a cellulose substrate. Then dry it at 60 °C for 12 h to obtain a graphene oxide film with a wrinkled structure.

[0061] Figure 1 This is a physical photograph of the graphene oxide film with a wrinkled structure prepared in this example. Figure 2 This is a scanning electron microscope image of the graphene oxide film with a wrinkled structure prepared in this example. As can be seen from the figure, in this example, a graphene oxide film material with a wrinkled structure was prepared under the induction of Na + Under the induction of Na, a graphene oxide film material with a wrinkled structure was prepared, and the surface of the graphene oxide film has an obvious staggered network-like wrinkled structure. This is because in a high-concentration sodium hydroxide solution, there is a significant Na + -π interaction between Na and the aromatic ring structure of graphene. This cation-π electron synergistic effect will significantly enhance the electrostatic attraction and van der Waals force between graphene sheets, thereby inducing a strong wrinkled structure on the surface of graphene. + -π interaction. This cation-π electron synergistic effect will significantly enhance the electrostatic attraction and van der Waals force between graphene sheets, thereby inducing a strong wrinkled structure on the surface of graphene.

[0062] Figure 3 This is an atomic force microscope image of the graphene oxide film with a wrinkled structure prepared in this example. As can be seen from the figure, the average surface roughness R a of the graphene oxide film prepared in this example is 48.7 nm, corresponding to the formation of a strong wrinkled structure on the surface.

[0063] Example 2:

[0064] This example provides a graphene oxide film with a wrinkled structure induced by NH4 + The specific preparation steps are as follows:

[0065] S1. Prepare a graphene oxide dispersion: Refer to Example 1 to prepare a graphene oxide dispersion.

[0066] S2. Hydrothermal reduction reaction: Use a graduated cylinder to measure 5 mL of the graphene oxide dispersion prepared in S1 and dilute it to 0.1 mg / mL. Mix 30 mL of ammonium hydroxide solution with a mass fraction of 26 wt% and 50 mL of the diluted graphene oxide dispersion, heat and stir at 80 °C for 4 h, then raise the temperature to 90 °C and continue heating for 1 h. After the heating is completed, make up the volume to 100 mL. After cooling, an ammonium hydroxide + induced graphene oxide solution is obtained.

[0067] S3. Prepare a graphene oxide film with a wrinkled structure: Take 10 mL of the prepared graphene oxide solution, use a vacuum filtration device to filter it into a film on a cellulose substrate, and then dry it at 60 °C for 12 h to obtain a graphene oxide film with a wrinkled structure.

[0068] From Figure 4 the SEM image, it can be seen that the surface of the graphene oxide film material prepared in this example has a few scale-shaped wrinkled structures, which is related to the NH4 in the ammonium hydroxide solution used.+ is related to. NH4 + The NH4 + -π interaction with the graphene aromatic ring structure is weaker than that of Na + -π interaction, so the degree of wrinkles formed on the material surface is reduced. From Figure 5 the atomic force microscope images, it can be seen that the average roughness of the surface of the graphene oxide film material with a wrinkled structure induced by NH4 + is 40.3 nm, corresponding to the reduction of its wrinkling degree.

[0069] Example 3:

[0070] This example provides a graphene oxide film with a wrinkled structure induced by K + The specific preparation steps are as follows:

[0071] S1. Prepare a graphene oxide dispersion: Refer to Example 1 to prepare a graphene oxide dispersion.

[0072] S2. Hydrothermal reduction reaction: Use a measuring cylinder to measure 5 mL of the graphene oxide dispersion prepared in S1 and dilute it to 0.5 mg / mL. Mix 2 mL of potassium hydroxide solution with a concentration of 8 mol / L and 50 mL of the diluted graphene oxide dispersion, and then heat and stir at 80 °C for 15 min. After cooling, a graphene oxide solution induced by K + is obtained. After cooling, a graphene oxide solution induced by K + is obtained.

[0073] S3. Prepare a graphene oxide film: Take 400 μL of the obtained graphene oxide solution and use a vacuum filtration device to filter it into a film on a cellulose substrate, and then dry it at 60 °C for 12 h to obtain a graphene oxide film with a wrinkled structure.

[0074] From Figure 6 the SEM images, it can be seen that the surface of the graphene oxide film material prepared in this example has a maze-like wrinkled structure, which is related to the K + in the used potassium hydroxide solution. K + The K + -π interaction with the graphene aromatic ring structure is weaker than that of Na + -π interaction, but stronger than that of NH4 + -π interaction. Therefore, the degree of wrinkles formed on the material surface is equivalent to that of the graphene oxide film induced by Na + , but still much higher than that of the graphene oxide film induced by NH4 + .

[0075] Example 4:

[0076] This example provides a group of Na composed of different anions+ Induced graphene oxide film with a wrinkled structure, and the specific preparation steps are as follows:

[0077] S1. Prepare a graphene oxide dispersion: Refer to Example 1 to prepare a graphene oxide dispersion.

[0078] S2. Hydrothermal reduction reaction: Use a measuring cylinder to measure 5 mL of the graphene oxide dispersion prepared in S1 and dilute it to 0.5 mg / mL, with a total of three portions. After mixing 2 mL of sodium chloride, sodium nitrate, and sodium sulfate solutions with a concentration of 8 mol / L respectively with 50 mL of the diluted graphene oxide dispersion, heat and stir at 80 °C for 15 min. After cooling, a group of Na + -induced graphene oxide solutions are obtained. After cooling, graphene oxide solutions induced by Cl - , NO3 - , and SO4 2- are obtained respectively. + -induced graphene oxide solutions.

[0079] S3. Prepare a graphene oxide film: Take 400 μL of the prepared graphene oxide solution, and use a vacuum filtration device to filter it into a film on a cellulose substrate, and then dry it at 60 °C for 12 h to obtain a Na + -induced graphene oxide film with a wrinkled structure composed of different anions.

[0080] Comparative Example 1:

[0081] This comparative example provides a graphene oxide film without cation induction, and the preparation method is as follows:

[0082] S1: Refer to the preparation of graphene oxide dispersion in Example 1.

[0083] S2: Take 100 μL of the prepared graphene oxide solution, uniformly disperse it into 10 mL of deionized water, use a vacuum filtration device to filter it into a film on a cellulose substrate, and dry it at 60 °C for 12 h to obtain a graphene oxide film.

[0084] As can be seen from Figure 7 , the surface of the graphene oxide film material prepared in this comparative example is smooth without a wrinkled structure. Due to the influence of π-π stacking and van der Waals forces between graphene sheets, the graphene oxide stacks flatly, suppressing the formation of wrinkles.

[0085] As can be seen from Figure 8 the atomic force microscope image, the average roughness of the graphene oxide film material prepared without cation induction is only 18.0 nm, corresponding to its smooth surface and no obvious wrinkled structure.

[0086] Comparative Example 2:

[0087] This comparative example provides the influence of cation-induced graphene oxide membranes prepared under different hydrothermal reduction time conditions on the retention performance of microplastics, which is as follows:

[0088] S1. Prepare the graphene oxide dispersion liquid by referring to S1 in Example 1.

[0089] S2. Refer to the hydrothermal reduction reaction in S2 of Example 1. The hydrothermal reduction reaction conditions in this comparative example are similar to those in Example 1, except that the heating and stirring time is changed to 5 min and 30 min, and no other conditions are changed.

[0090] S3. Prepare the graphene oxide membrane with a wrinkled structure by referring to the vacuum filtration film-forming method in Example 1.

[0091] The graphene oxide membrane with a wrinkled structure prepared in the present invention can be applied to the field of sewage treatment. The graphene oxide membrane with a wrinkled structure can retain microplastics and / or heavy metal ions in sewage.

[0092] Application Example 1:

[0093] In this application example, the graphene oxide membranes of the above-mentioned examples and comparative examples are used as test objects to conduct microplastic retention performance tests.

[0094] The test process is as follows:

[0095] S1. Prepare 250 ml of microplastic solutions with different sizes (30, 100, 200, and 500 nm) at a concentration of 10 mg / L, and 250 ml of microplastic solutions with a size of 200 nm at different concentrations (5, 10, 20, and 50 mg / L).

[0096] S2. After filtering the graphene oxide solution into a film on a cellulose substrate using a vacuum filtration device, conduct separation experiments on microplastic solutions with different concentrations or sizes through a dead-end filter. Record the time required to collect a certain volume of filtrate, and use inductively coupled plasma emission spectroscopy and ultraviolet-spectrophotometer to measure the change in absorbance at the 230 nm characteristic peak of microplastics in the solution before and after filtration to calculate the change in microplastic concentration, so as to test the retention of the prepared membrane material for microplastic sewage.

[0097] It can be seen from Figure 9 that the Na + -induced graphene oxide membrane material with a wrinkled structure prepared in Example 1 has a retention rate of more than 99.0% for microplastics of different sizes such as 30, 100, 200, and 500 nm, and the fluxes are 886.8, 918.9, 963.3, and 1013.7 L m -2 h -1 bar -1The difference in the retention of microplastics of different sizes is related to their particle size. The cation-induced wrinkled graphene oxide membrane has high flux and retention rate for microplastics of the above sizes, because a large number of wrinkled structures have good repulsive effects on microplastics of various sizes and provide more additional water molecule transport paths.

[0098] It can be seen from Figure 10 that the Na + -induced graphene oxide membrane material with a wrinkled structure prepared in Example 1 showed a tendency of decreasing water flux for higher-concentration microplastic solutions during the retention test of 200-nm-sized microplastic sewage at different concentrations, but it was still higher than 650 L m -2 h -1 bar -1 . The prepared wrinkled graphene oxide membrane exhibited excellent microplastic retention performance within a wide concentration range.

[0099] In addition, it can be seen from Figure 11 that the Na + , NH4 + and K + -induced graphene oxide membrane materials with a wrinkled structure and the graphene oxide membrane material without cation induction prepared in Example 1, Example 2, Example 3 and Comparative Example 1 had water permeabilities of 963.3, 205.7, 866.8 and 92.9 L m -2 h -1 bar -1 respectively during the retention test of 10-mg / L 200-nm microplastic sewage. The results showed that the graphene oxide membranes induced by different cations (including but not limited to Na + , NH4 + , and K + ) all showed much higher permeabilities than the graphene oxide membrane without cation induction, because the wrinkled structures constructed by the cation-induced graphene oxide membranes provided wider and additional water molecule transport channels, significantly improving the water permeability.

[0100] Furthermore, it can be seen from Figure 12 that the graphene oxide materials induced by different sodium salts of anions in Example 4 had water permeabilities of 956.4, 940.7 and 917.0 L m -2 h -1 bar -1, the rejection rates all remained above 99%, showing high water permeability performance and differences, and the microplastic sewage rejection performance of graphene oxide membranes induced by different sodium anion salts was not significantly different. The results indicate that the types of anions in the cationic solution do not limit the water permeability of the graphene oxide membrane, greatly expanding the applicable range of cationic salt solutions.

[0101] Finally, from Figure 13 it can be seen that for the Na + -induced graphene oxide membranes prepared in Example 1 and Comparative Example 2 with three different hydrothermal reduction times (5, 15, and 30 min), in the microplastic sewage rejection test of 200 nm at a concentration of 10 mg / L, the corresponding water permeabilities were 649.9, 963.3, and 545.2 L m -2 h -1 bar -1 , and the corresponding rejection rates were all above 99%. A hydrothermal reduction time of 30 min would cause a relatively high reduction degree of the graphene oxide membrane, and most of the oxygen-containing functional groups were reduced. At the same time, a large amount of Na + was intercalated between the layers of the graphene oxide membrane, resulting in a narrowing of the channels in the membrane and a decrease in water permeability; a reduction time of 5 min would retain a large number of residual oxygen-containing functional groups in the membrane material, hindering the transport of water molecules. Thus, it can be seen that a moderate degree of hydrothermal reduction is beneficial to ensuring that the finally prepared graphene oxide membrane can maintain good water permeability.

[0102] Application Example 2:

[0103] In this application example, the graphene oxide membrane with a wrinkled structure prepared in Example 1 was used as the test object for heavy metal rejection performance testing.

[0104] The test process is as follows:

[0105] S1: Prepare 250 mL of FeCl3, CuCl2, CoCl2, and CrCl3 solutions with a concentration of 50 mg / L respectively, and 250 mL of a mixed solution containing 10 mg / L of 200 nm-sized microplastics and 50 mg / L of FeCl3, CuCl2, CoCl2, or CrCl3 simultaneously.

[0106] S2: After filtering the graphene oxide solution into a membrane on a cellulose substrate using a vacuum filtration device, conduct a separation experiment of heavy metal ion solutions or microplastic and heavy metal mixed solutions through a dead-end filter, record the time required to collect a certain volume of filtrate, test the change in absorbance at the 230 nm characteristic peak of microplastics in the solution before and after filtration and the change in heavy metal ion concentration, and analyze the rejection of the prepared cation-induced wrinkled graphene oxide membrane for microplastic sewage and complex system sewage.

[0107] From Figure 14It can be seen that the Na prepared in Example 1 + -induced graphene oxide membrane material with a wrinkled structure has a rejection rate of 99.0%, 94.9%, 92.4% and 93.1% for Fe 3+ , Cu 2+ , Co 2+ and Cr 3+ respectively, and the corresponding fluxes are 509.6, 503.2, 393.9 and 366.8 L m -2 h -1 bar -1 , showing that the cation-induced wrinkled graphene oxide membrane has good rejection performance for heavy metal wastewater.

[0108] It can be seen from Figure 15 that in a complex wastewater system containing both microplastics and heavy metals, the rejection rate of the Na + -induced graphene oxide membrane with a wrinkled structure prepared in Example 1 for microplastics has always remained above 99.0%, and the fluxes for various heavy metal ions are all above 300.0 L m -2 h -1 bar -1 . According to the above results, it can be known that the present invention still has considerable pollutant removal ability for a complex wastewater system in which microplastics and heavy metals coexist.

[0109] In summary, the present invention uses a cation solution to assist in the hydrothermal reduction of graphene oxide dispersion to prepare a series of graphene-based separation membranes with different wrinkled structures and roughnesses. By changing the type and concentration of cations, regulating cation-π interaction and cation-oxidation group interaction, etc., the degree of wrinkling on the graphene membrane is effectively regulated, and the water molecule transport channels are increased for rapid and efficient removal of microplastic particles and heavy metal ions in wastewater.

[0110] The above description of the embodiments is for the convenience of those of ordinary skill in the art to understand and use the invention. Those skilled in the art can obviously make various modifications to these embodiments easily and apply the general principles described herein to other embodiments without creative labor. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a graphene oxide film with a wrinkled structure, characterized in that, The preparation method includes the following steps: Mix the graphene oxide dispersion liquid with the cationic salt solution and then carry out a hydrothermal reduction reaction to obtain a cation-induced graphene oxide solution; Prepare a graphene oxide membrane with a wrinkled structure by vacuum filtration; Wherein, the cations in the cationic salt solution include Na + , K + NH4 + , Cs + Mg 2+ , Ca 2+ , Pb 2+ , Sr 2+ or Al 3+ One or more of .

2. The preparation method of a graphene oxide film with a wrinkled structure according to claim 1, wherein, The anions in the cationic salt solution include OH - , F - , Cl - , Br - , I - , NO3 - or SO4 2- or one or more of them.

3. The preparation method of a graphene oxide film with a wrinkled structure according to claim 1, characterized in that, The final concentration range of the graphene oxide in the mixed solution is 0.01 - 1 g / L, and the final concentration range of the cation is 0.01 - 0.5 mol / L.

4. The preparation method of a graphene oxide film with a wrinkled structure according to claim 1, wherein, The temperature of the hydrothermal reduction reaction is 10 - 90 °C; The time of the hydrothermal reduction reaction is 0.05 - 5 h.

5. The preparation method of a graphene oxide film with a wrinkled structure according to claim 1, characterized in that, The pH during the hydrothermal reduction reaction is controlled at 3 - 13.

6. A graphene oxide film with a wrinkled structure prepared by the preparation method according to any one of claims 1-5, characterized in that, The wrinkled structure formed on the graphene oxide membrane includes any one of ridge-like, fishbone-like, and interlaced network-like; There is a cation-π electron interaction between the cation and the aromatic ring structure of the graphene oxide, which induces the formation of a wrinkled structure on the graphene surface by enhancing the electrostatic attraction and van der Waals force between the graphene oxide sheets.

7. The graphene oxide membrane with a wrinkled structure according to claim 6, characterized in that, The surface average roughness of the graphene oxide membrane is at least 20 nm.

8. The graphene oxide film with a wrinkled structure according to claim 6, wherein The content of the metal element or non-metal element introduced on the surface of the graphene oxide membrane accounts for 1 - 10% of the total content of all elements on the surface of the graphene oxide membrane.

9. Use of the graphene oxide membrane with a wrinkled structure according to claim 6 in sewage treatment, characterized in that, The graphene oxide membrane can be used as a separation membrane to intercept microplastics and / or heavy metal ions in sewage.

10. Use of the graphene oxide membrane with a wrinkled structure according to claim 9 in sewage treatment, characterized in that, The graphene oxide membrane can intercept microplastic particles with a particle size not greater than 2.5 μm and a concentration not greater than 50 mg / L; The heavy metal elements that the graphene oxide membrane can intercept include Fe, Cu, Co, and Cr, and the concentration of the heavy metal salt in the sewage is not greater than 50 mg / L.

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