A waste graphite-derived SG / GO composite layered membrane, its preparation method and application

Abstract

This invention discloses a waste graphite-derived SG / GO composite layered membrane, its preparation method, and its applications, relating to the field of separation membrane materials technology. The invention involves homogenizing a mixture of waste graphite-derived functional graphene and GO, followed by vacuum filtration to form a membrane. In the resulting composite layered membrane, GO sheets provide continuous coverage to seal defects, while SG sheets are inserted into the interlayer to construct water channels. This significantly increases water flux without significantly increasing membrane thickness and effectively inhibits solute reverse osmosis. The composite layered membrane of this invention exhibits excellent permeation / nanofiltration performance in the separation of high osmotic pressure and large organic molecules, achieving an organic combination of waste resource utilization and high-performance separation membrane development.

Description

Technical Field

[0001] This invention relates to the field of separation membrane materials technology, and in particular to a waste graphite-derived SG / GO composite layered membrane, its preparation method, and its application. Background Technology

[0002] Two-dimensional layered membranes, with their adjustable interlayer spacing, abundant surface functional groups, and selective mass transfer at the molecular scale, have been widely used in water treatment and solute separation. Among them, graphene oxide (GO) membranes, due to their advantages such as good aqueous dispersibility, scalable preparation, and regular layered structure, have shown good application potential in permeation / nanofiltration separation. However, in high-osmotic-pressure systems (such as high-concentration sugar solutions and salt solutions) and in the separation of macromolecular organic matter, pure GO membranes have significant drawbacks: First, GO sheets are prone to changes in interlayer spacing and structural rearrangement due to hydration, resulting in unstable membrane structure and separation performance; second, the dense interlayer channels of pure GO membranes lead to high resistance to water molecule transport, resulting in a decrease in effective transmembrane driving force and significant flux attenuation under high osmotic pressure; third, during membrane formation, layer stacking, edge defects, and local aggregation can easily generate non-selective permeation channels, reducing separation selectivity and long-term operational reliability.

[0003] Currently, the preparation of graphene and its derivative materials mostly adopts high-purity graphite raw materials and oxidation exfoliation processes, which not only results in high raw material costs but also brings pressure from the discharge of acid and alkaline waste liquids, hindering large-scale and green applications. With the development of industries such as lithium batteries, metallurgy, lubrication, and conductive materials, the output of waste graphite resources such as waste graphite powder and waste anode materials continues to grow, and their resource utilization value is becoming increasingly prominent. However, the current related utilization technologies have obvious limitations: waste graphite is widely available and inexpensive, making it a highly promising carbon-based resource utilization raw material. Its large-scale accumulation not only causes resource waste but also brings environmental pressure. Existing waste graphite recycling is mostly limited to carbon material recovery or low-value-added filler preparation, and the technology to directly convert it into two-dimensional sheet materials for membrane separation and construct high-performance layered membranes is relatively scarce.

[0004] In addition, although functionalized graphene (SG) made from waste graphite has a high specific surface area and excellent water flux, making it suitable for high osmotic pressure system applications, its small sheet size and numerous edge sites make it easy to form non-selective defect channels when forming films alone, leading to problems such as solute back osmosis and poor separation selectivity, which makes it difficult to meet the requirements of engineering applications.

[0005] Therefore, there is an urgent need to develop a composite separation membrane preparation technology that can realize the resource utilization of waste graphite while possessing both high throughput and structural stability. This technology can reduce raw material costs while solving the technical problems of insufficient throughput of pure GO membranes and easy leakage and poor stability of pure graphite-based membranes, thus achieving the dual goals of resource recovery and performance improvement. Summary of the Invention

[0006] The purpose of this invention is to provide a waste graphite-derived SG / GO composite layered membrane, its preparation method, and its application, in order to overcome the shortcomings of existing technologies such as low flux and high cost of pure GO membranes, difficulty in directly utilizing waste graphite, and easy leakage of pure SG membranes. This invention provides a waste graphite-derived SG / GO composite layered membrane that achieves resource utilization of waste graphite while obtaining a low-cost, high-flux, and structurally stable composite separation membrane.

[0007] To achieve the above objectives, the present invention provides the following solution: This invention provides a method for preparing a waste graphite-derived SG / GO composite layered film, comprising the following steps: (1) Preparation of waste graphite-derived functional graphene: Heat-treated waste graphite is first mixed with concentrated sulfuric acid and potassium permanganate, and then phosphoric acid and carbonate are added for a second mixing to obtain waste graphite-derived functional graphene (SG). (2) Preparation of dispersion: The waste graphite-derived functional graphene was added to deionized water, the pH was adjusted to 8-10, and the supernatant was obtained by ultrasonic dispersion and centrifugation to obtain waste graphite-derived functional graphene dispersion (SG dispersion). (3) Mixing and homogenizing, and filtration to form a film: The waste graphite-derived functional graphene dispersion and graphene oxide (GO) dispersion are mixed to achieve the target SG / GO mass ratio. After ultrasonic homogenization, the mixture is deposited on a porous support membrane by filtration to obtain the waste graphite-derived SG / GO composite layered membrane.

[0008] When using waste graphite as a raw material, its strong interlayer forces, dense agglomeration, and high surface hydrophobicity make it difficult to disperse stably in water and to directly construct a separation layer with uniform structure and high transport efficiency. Therefore, this invention performs derivatization treatment on waste graphite, modifying it into a functionalized graphene material (SG) suitable for preparing separation membranes through steps such as heat treatment, oxidation intercalation, intercalation exfoliation, and functionalization regulation. Heat treatment is used to remove any residual organic impurities from waste graphite and activate defect / edge sites, improving the accessibility and uniformity of subsequent reactions. Oxidation intercalation in a concentrated sulfuric acid-potassium permanganate system weakens van der Waals interactions between sheets and introduces oxygen-containing functional groups such as hydroxyl, epoxy, and carboxyl groups onto the sheet surface / edges, thereby improving the material's hydrophilicity and dispersibility. Phosphoric acid is added to regulate the acidic environment and reaction mildness, promoting a more uniform intercalation oxidation process and reducing the risk of sheet breakage due to over-oxidation. Carbonate treatment terminates the reaction, neutralizes residual acid, promotes the salting of some functional groups and the formation of charge stability, further reducing the tendency to agglomerate. Finally, thorough washing and drying remove residual acid salts and byproducts, yielding a functionalized graphene material SG that is easily dispersed in the aqueous phase and suitable for filtration film formation.

[0009] After the above steps, waste graphite is transformed from a strongly hydrophobic and difficult-to-disperse agglomerate state into a functionalized sheet material (SG) containing certain oxygen-containing functional groups, richer edge sites, and more easily forming stable dispersions in the aqueous phase. This SG provides both a higher specific surface area and water transport potential, and also provides the necessary interfacial interaction basis for subsequent synergistic stacking with GO, thus facilitating the construction of a composite separation layer with a more uniform structure, more efficient water transport, and lower risk of defect penetration.

[0010] Furthermore, the heat treatment is carried out in an inert gas atmosphere; the temperature of the heat treatment is 400-600℃, and the time is 1-3 hours. The inert gas includes nitrogen, argon, etc.

[0011] Furthermore, the mass ratio of the waste graphite, concentrated sulfuric acid and potassium permanganate is 1:(5~15):(1~5); the mass ratio of the waste graphite, phosphoric acid and carbonate is 1:(10~20):(1~5).

[0012] Furthermore, the carbonate is one or more of sodium carbonate, calcium carbonate, potassium carbonate, etc.

[0013] Furthermore, in the waste graphite-derived SG / GO composite layered membrane, the mass fraction of the waste graphite-derived functional graphene is 10-90%, and the mass fraction of the graphene oxide is 10-90%.

[0014] Furthermore, in the waste graphite-derived SG / GO composite layered membrane, the mass fraction of the waste graphite-derived functional graphene is 60-80%, and the mass fraction of the graphene oxide is 20-40%.

[0015] Furthermore, the loading of the waste graphite-derived SG / GO composite layered membrane on the porous support membrane is 50-1000 mg / m³. 2 .

[0016] Furthermore, the temperature of the first mixture is 0°C and the time is 0.5-2 hours; the temperature of the second mixture is 25°C and the time is 2-5 hours.

[0017] Furthermore, the porous support membrane includes PES, PVDF, etc.; the pore size is preferably 0.01-0.22 μm.

[0018] The present invention also provides a waste graphite-derived SG / GO composite layered membrane prepared by the above preparation method.

[0019] The composite layered membrane of this invention is constructed by mixing waste graphite-derived SG sheets and graphene oxide (GO) sheets in a specific mass ratio, forming a unique layered stacked structure. In this structure, the GO sheets play a role in "continuous coverage and pore sealing," utilizing their large-diameter characteristics to provide a continuous cover layer and seal defects; while the SG sheets play a role in "intercalation and channel enhancement," inserting into the gaps between or between GO sheets, effectively increasing the channels for water molecule transport, while inhibiting excessive densification of the layered stack. This synergistic construction mechanism of SG and GO achieves complementary and enhanced performance. (1) High flux: Without significantly increasing the membrane thickness, the resistance to water molecule transport is significantly reduced. Compared with pure GO membrane, the water flux of the composite membrane can be increased by several times under the same test conditions.

[0020] (2) High selectivity and stability: The large-diameter layered coverage of GO and the optional GO sealing structure effectively suppress the non-selective defects caused by the small diameter of SG, thereby eliminating the phenomenon of solute reverse osmosis.

[0021] The composite layered membrane of this invention successfully balances high water flux and separation stability, and is particularly suitable for high osmotic pressure systems and permeation / nanofiltration separation applications of macromolecular organic matter.

[0022] The present invention further provides the application of the above-mentioned waste graphite-derived SG / GO composite layered membrane as a separation membrane material.

[0023] This invention obtains SG material with good hydrophilicity and easy film formation by derivatizing waste graphite; after compounding SG with GO, a structurally complete composite separation layer can be formed on the surface of the supporting membrane, realizing the high-value resource utilization of waste graphite, and solving the technical problems in the prior art. The specific technical effects are as follows: (1) Realize the resource utilization of waste graphite: This invention uses waste graphite, which is widely available and inexpensive, as raw material and transforms it into high-performance membrane material through derivation and modification. This not only solves the resource waste and environmental problems caused by the accumulation of waste graphite, but also significantly reduces the raw material cost of separation membrane, which is conducive to large-scale application.

[0024] (2) Solving the inherent defects of pure SG membrane and pure GO membrane: Compared with pure SG membrane, the composite membrane of the present invention can effectively block the non-selective defect channels generated during the formation of pure SG membrane by introducing GO, avoid solute leakage and reverse osmosis, and significantly improve the structural stability and separation integrity of the separation membrane; compared with pure GO membrane, the present invention can widen the water transport channels of the separation layer by introducing SG, and significantly improve the water flux of the membrane.

[0025] (3) Adjustable flux and synergistic effect: Experiments show that by adjusting the ratio of SG to GO, the water flux of the composite membrane can be flexibly adjusted, which can meet the needs of different separation scenarios.

[0026] The composite layered membrane prepared by this invention has the advantages of low cost, high flux, and high stability, and solves the technical problems of high cost, low flux, poor stability, and difficulty in resource utilization of waste graphite in existing separation membranes. It has important industrial application value.

[0027] The present invention discloses the following technical effects: This invention successfully solves the flux-selectivity trade-off problem faced by traditional graphene membranes in the separation of high osmotic pressure and large organic molecules by constructing a composite structure of waste graphite-derived SG sheets and GO sheets. Utilizing the large-diameter layered coverage and pore-sealing effect of GO sheets, the non-selective defect penetration caused by the small-diameter SG sheets is effectively suppressed, thereby significantly reducing solute reverse osmosis and greatly improving membrane selectivity and operational stability. Simultaneously, the insertion of SG sheets not only increases the effective channels for water molecule transport but also significantly improves water flux without significantly increasing membrane thickness, achieving a performance breakthrough of several times the original value.

[0028] The composite layered membrane of this invention provides an ideal solution for the efficient permeation / nanofiltration separation of high osmotic pressure systems and macromolecular organic matter. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a SEM morphology characterization image of the pure SG material prepared in Comparative Example 1 of this invention.

[0031] Figure 2 This is a SEM morphology characterization image of the pure GO material prepared in Comparative Example 2 of this invention.

[0032] Figure 3 This is a schematic diagram illustrating the preparation of the SG / GO composite layered membrane according to the present invention.

[0033] Figure 4 This is a schematic diagram of the flux / reverse osmosis testing device in an embodiment of the present invention.

[0034] Figure 5 The results are the water flux test results of Examples 1-4 and Comparative Examples 1-2 of the present invention.

[0035] Figure 6 This is a diagram of the humic acid (HA) retention experiment at 6h in Example 7 of the present invention. Detailed Implementation

[0036] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0037] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0038] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0039] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0040] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0041] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0042] In this invention, room temperature refers to 25°C.

[0043] In the following embodiments and comparative examples of the present invention, the water flux was tested as follows: A dead-end filtration device was used, with a 2.5M sucrose solution as the feed liquid (osmotic pressure of 61 bar), and the test was conducted at room temperature; the effective membrane area used in the test was 7.854 × 10⁻⁶. -5 •m 2The membrane loading was 0.796 g / m³. 2 The continuous test time was 6 hours; the water flux F was calculated by recording the permeate volume per unit membrane area and per unit time.

[0044] Example 1 This embodiment provides a method for preparing a waste graphite-derived SG / GO composite layered film, the steps of which are as follows: (1) Preparation of SG derived from waste graphite: Waste graphite was placed in a nitrogen atmosphere and heat-treated at 500℃ for 2h; 3g of heat-treated waste graphite was taken and mixed with 9 mL of concentrated sulfuric acid (98% mass concentration) and 3g of potassium permanganate, and stirred for 1h under ice bath conditions. Then 42mL of phosphoric acid and 3g of sodium carbonate were added, and stirring was continued at room temperature for 3h. The product was cleaned and dried to obtain waste graphite-derived functionalized graphene (SG).

[0045] (2) Preparation of SG dispersion: Take 1g of SG prepared in step (1) and add it to 1L of deionized water, adjust the pH to 10; disperse by ultrasonication and centrifuge to remove large aggregates, and take the supernatant to obtain SG dispersion; (3) Preparation of GO dispersion: Graphene oxide (GO) was added to deionized water and ultrasonically treated (200W, 10min) to obtain a stable GO dispersion with a concentration of 1 g / L.

[0046] (4) Mixing and homogenizing, film formation: Under stirring conditions, the GO dispersion was slowly added to the SG dispersion. By controlling the mass ratio of SG dispersion to GO dispersion, the SG in the mixed dispersion accounted for 20% of the total mass of SG and GO. Subsequently, ultrasonic treatment (350W, 15min) was performed to obtain a uniform and stable mixed dispersion. The mixed dispersion was filtered on a PES support membrane with a pore size of 0.03 μm and an effective film diameter of 40 mm, so that SG and GO were deposited on the surface of the support membrane to form a composite separation layer. The total loading of the separation layer was controlled to be 1 mg, thus obtaining an SG / GO composite layered membrane.

[0047] Example 2 The only difference from Example 1 is that in the mixed dispersion in step (4), SG accounts for 40% of the total mass of SG and GO.

[0048] Example 3 The only difference from Example 1 is that in the mixed dispersion in step (4), SG accounts for 60% of the total mass of SG and GO.

[0049] Example 4 The only difference from Example 1 is that in the mixed dispersion in step (4), SG accounts for 80% of the total mass of SG and GO.

[0050] Comparative Example 1 The only difference from Example 1 is that step (4) uses SG dispersion to form a film alone, without adding GO dispersion, that is, the separation layer is pure SG material.

[0051] Comparative Example 2 The only difference from Example 1 is that in step (4), GO dispersion is used to form a film alone, without adding SG dispersion, that is, the separation layer is pure GO material.

[0052] The water flux F detection results of Examples 1-4 and Comparative Examples 1-2 of this invention are shown in Table 1 and 2. Figure 5 As shown.

[0053] Table 1 As shown in Table 1, in Examples 1-4, as the mass fraction of SG in the separation layer increased from 20% to 80%, the water flux F gradually increased from 29.93 to 63.46 ml·h. -1 ·m -2 ·bar -1 The flux of the composite membrane (63.46) showed a clear upward trend. When the mass fraction of SG reached 80%, the water flux of the composite membrane (63.46) was higher than that of the pure SG membrane (Comparative Example 1, 59.75) and the pure GO membrane (Comparative Example 2, 34.46). This indicates that at a higher SG ratio (≥60%), the SG / GO composite layered structure can achieve more efficient water transport (demonstrating enhanced flux synergy), while the flux is lower when the SG ratio is too low (e.g., 20%).

[0054] In some experiments with pure SG membranes, solute cross-leakage / reverse osmosis occurred. The introduction of GO helps to suppress / block non-selective defect channels that may be generated during the formation of pure SG membranes, so that the membrane can maintain high flux while achieving more stable separation layer integrity.

[0055] Example 5 This embodiment provides a method for preparing a waste graphite-derived SG / GO composite layered film, the steps of which are as follows: (1) Preparation of SG derived from waste graphite: Waste graphite was placed in a nitrogen atmosphere and heat-treated at 500℃ for 2h; 3g of heat-treated waste graphite was mixed with 9 mL of concentrated sulfuric acid and 6g of potassium permanganate, stirred for 1h under ice bath conditions, and then 42mL of phosphoric acid and 3g of sodium carbonate were added. Stirring was continued at room temperature for 3h. The product was cleaned and dried to obtain waste graphite-derived functionalized graphene (SG).

[0056] (2) Preparation of SG dispersion: Take 1g of SG prepared in step (1) and add it to 1L of deionized water, adjust the pH to 10; disperse by ultrasonication and centrifuge to remove large aggregates, take the supernatant to obtain SG dispersion with a concentration of 1 g / L. (3) Preparation of GO dispersion: Graphene oxide (GO) was added to deionized water and subjected to gentle ultrasonic treatment to obtain a stable GO dispersion with a concentration of 1 g / L.

[0057] (4) Mixing and homogenizing, film formation: Under stirring conditions, the GO dispersion was slowly added to the SG dispersion. By controlling the mass ratio of the SG dispersion to the GO dispersion, the SG in the mixed dispersion accounted for 80% of the total mass of SG and GO. Then, short-term mild ultrasound was performed to obtain a uniform and stable mixed dispersion. The mixed dispersion was filtered on a PES support membrane with a pore size of 0.03 μm and an effective film diameter of 40 mm, so that SG and GO were deposited on the surface of the support membrane to form a composite separation layer. The total loading of the separation layer was controlled to be 1 mg, thus obtaining an SG / GO composite layered membrane.

[0058] The same test method as in Example 1 was used, and the results showed that the water flux F was 62.53 ml·h. -1 ·m -2 ·bar -1 .

[0059] Comparative Example 3 The only difference from Example 5 is that step (4) uses SG dispersion to form a film alone, without adding GO dispersion, that is, the separation layer is pure SG material.

[0060] The same test method as in Example 1 was used, and the results showed that the water flux F was 55.11 ml·h. -1 ·m -2 ·bar -1 .

[0061] Example 6 This embodiment provides a method for preparing a waste graphite-derived SG / GO composite layered film, the steps of which are as follows: (1) Preparation of waste graphite-derived SG: Waste graphite was placed in a nitrogen atmosphere and heat-treated at 500℃ for 2h; 3g of heat-treated waste graphite was taken and mixed with 9 mL of concentrated sulfuric acid and 9g of potassium permanganate, stirred for 1h under ice bath conditions, then 42mL of phosphoric acid and 3g of sodium carbonate were added, and stirred for 3h at room temperature. The product was cleaned and dried to obtain waste graphite-derived SG.

[0062] (2) Preparation of SG dispersion: Take 1g of the waste graphite-derived SG prepared in step (1) and add it to 1L of deionized water, adjust the pH to 10; disperse by ultrasonication and centrifuge to remove large aggregates, and take the supernatant to obtain SG dispersion; (3) Preparation of GO dispersion: Graphene oxide (GO) was added to deionized water and subjected to gentle ultrasonic treatment to obtain a stable GO dispersion with a concentration of 1 g / L.

[0063] (4) Mixing and homogenizing, film formation: Under stirring conditions, the GO dispersion was slowly added to the SG dispersion. By controlling the mass ratio of the SG dispersion to the GO dispersion, the SG in the mixed dispersion accounted for 80% of the total mass of SG and GO. Then, short-term mild ultrasound was performed to obtain a uniform and stable mixed dispersion. The mixed dispersion was filtered on a PES support membrane with a pore size of 0.03 μm and an effective film diameter of 40 mm, so that SG and GO were deposited on the surface of the support membrane to form a composite separation layer. The total loading of the separation layer was controlled to be 1 mg, thus obtaining an SG / GO composite layered membrane.

[0064] The same test method as in Example 1 was used, and the results showed that the water flux F was 42.93 ml·h. -1 ·m -2 ·bar -1 .

[0065] Comparative Example 4 The only difference from Example 3 is that in step (4), SG dispersion is used to form a film alone, without adding GO dispersion, that is, the separation layer is pure SG material.

[0066] The same test method as in Example 1 was used, and the results showed that the water flux F was 46.87 ml·h. -1 ·m -2 ·bar -1 .

[0067] Example 7 To prepare a 20 mg / L humic acid (HA) aqueous solution, the same method was used. Figure 4 The dead-end filtration device shown uses the SG / GO composite layered membrane prepared in Example 4 as the separation membrane. The water on the left side is replaced with the prepared HA solution, and a 2.5 M sucrose solution is used as the high osmotic pressure driving phase. The feed side is the above-mentioned humic acid solution. The permeate volume per unit membrane area and per unit time are recorded, and the HA concentration in the feed solution before and after the experiment is measured using a UV spectrophotometer. The apparent retention rate of HA in the feed solution is calculated according to the law of conservation of mass, and the membrane's retention performance for humic acid is evaluated.

[0068] Figure 6The figure shows the 6-hour retention test of humic acid (HA) in Example 7 of the present invention. The results show that the membrane has an apparent retention rate of 97.96% for HA in the feed solution.

[0069] Comparative Example 5 The only difference from Example 7 is that the separation experiment was performed using the pure GO layered membrane of Comparative Example 2.

[0070] The results of the 6-hour retention experiment showed that the apparent retention rate of HA in the feed liquid was 97.38%.

[0071] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a waste graphite-derived SG / GO composite layered film, characterized in that, Includes the following steps: (1) Preparation of waste graphite-derived functional graphene: Heat-treated waste graphite is first mixed with concentrated sulfuric acid and potassium permanganate, and then phosphoric acid and carbonate are added for a second mixing to obtain waste graphite-derived functional graphene. (2) Preparation of dispersion: The waste graphite-derived functional graphene is added to deionized water, the pH is adjusted to 8-10, and the supernatant is collected by ultrasonic dispersion and centrifugation to obtain the waste graphite-derived functional graphene dispersion. (3) Mixing and homogenizing, and filtration to form a film: The waste graphite-derived functional graphene dispersion and the graphene oxide dispersion are mixed to achieve the target mass ratio, and then ultrasonically homogenized and deposited on a porous support membrane by filtration to obtain the waste graphite-derived SG / GO composite layered membrane.

2. The preparation method according to claim 1, characterized in that, The heat treatment is carried out in an inert gas atmosphere; the temperature of the heat treatment is 400-600℃, and the time is 1-3h.

3. The preparation method according to claim 1, characterized in that, The mass ratio of the waste graphite, concentrated sulfuric acid and potassium permanganate is 1:(5~15):(1~5); the mass ratio of the waste graphite, phosphoric acid and carbonate is 1:(10~20):(1~5).

4. The preparation method according to claim 1, characterized in that, In the waste graphite-derived SG / GO composite layered membrane, the mass fraction of the waste graphite-derived functional graphene is 10-90%, and the mass fraction of the graphene oxide is 10-90%.

5. The preparation method according to claim 4, characterized in that, In the waste graphite-derived SG / GO composite layered membrane, the mass fraction of the waste graphite-derived functional graphene is 60-80%, and the mass fraction of the graphene oxide is 20-40%.

6. The preparation method according to claim 1, characterized in that, The loading of the waste graphite-derived SG / GO composite layered membrane on the porous support membrane is 50-1000 mg / m³. 2 .

7. The preparation method according to claim 1, characterized in that, The first mixture is mixed under ice bath conditions and then stirred at 20-40°C; the temperature of the second mixture is 20-40°C.

8. The waste graphite-derived SG / GO composite layered membrane prepared by the preparation method according to any one of claims 1-7.

9. The application of the waste graphite-derived SG / GO composite layered membrane as described in claim 8 as a separation membrane material.

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