A method for preparing a self-supporting sponge-like pore structure graphene oxide composite film

Abstract

The present application discloses a method for preparing a self-supporting sponge-like pore structure graphene oxide composite film, comprising the following steps: preparing silicon-doped carbon nanofibers, preparing a graphene oxide / silicon-doped carbon nanofiber dispersion, vacuum filtration to form a film and drying the dispersion at room temperature, and high-temperature calcination in an air atmosphere to remove the mixed cellulose base film to obtain a silicon-doped carbon nanofiber / graphene oxide composite film. The method is easy to operate, low in cost and highly efficient, does not require the use of additional modification chemical reagents, and is environmentally friendly and pollution-free. Vacuum filtration is used to intercalate the carbon nanofibers into the graphene oxide to form a composite film, and self-polymerization is used to make the carbon nanofiber / graphene oxide film more tightly bonded, thereby enhancing the mechanical properties of the composite film, forming a sponge-like pore structure, and increasing the water channel and permeation flux of the graphene oxide composite film. High-temperature calcination is used to make the carbon nanofiber / graphene oxide composite film self-supporting, thereby providing a method for preparing a self-supporting graphene oxide film.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil-water separation membrane preparation, and in particular relates to a method for preparing a self-supporting graphene oxide composite film with a sponge-like pore structure. Background Art

[0002] Currently, several methods for wastewater purification exist, including adsorption combustion, membrane separation, and photocatalytic degradation. Membrane separation has proven to be one of the most promising methods for effective wastewater treatment due to its high efficiency, lack of secondary pollution, and ease of operation. Graphene oxide (GO) is a two-dimensional sheet formed by the oxidation and exfoliation of graphite. It possesses oxygen-containing functional groups on both its basal surface and its edges, making it hydrophilic and highly chemically active. Stacked pure GO membranes, traditionally prepared by simple solution filtration methods, exhibit a smooth, dense laminated structure but are not directly suitable for water separation because GO nanosheets are extremely hydrophilic and easily rupture. Furthermore, the channels in GO-based membranes are typically too narrow, preventing them from achieving high permeation flux. Therefore, addressing the shortcomings of GO-based membranes in water treatment and enabling their effective application in oily wastewater treatment is a key research topic in the field.

[0003] In recent years, to achieve efficient separations in GO-based membranes, researchers have conducted research on how to couple GO-based membranes with nanomaterials to synergistically regulate the channel structure for water transport and enhance membrane stability. The paper "SWCNT-intercalated GO ultrathin films for ultrafast separation of molecules. J. Master. Chem. A, 2015, 36649-6654" reports the preparation of a single-walled carbon nanotube-intercalated GO-based membrane via vacuum filtration, which enables rapid water transport. However, while the nanomaterial-intercalated GO membrane reported in the aforementioned paper can improve the permeation flux of pure GO membranes, the GO on the membrane surface may be lost over time, leading to a decrease in membrane performance. Furthermore, the membranes are not stable enough to be reused. The paper "One-step preparation of GO / SiO2 membrane for highly efficient separation of oil-in-water emulsion. Journal of Membrane Science, 2018, 0376-7388" reports a method for preparing GO / SiO2 composite membranes via vacuum filtration. However, the dispersion process of SiO2 in the GO / SiO2 membrane reported in the above literature has uniformity problems, which affects the stability of the composite membrane and the spacing between GO layers, thereby affecting the separation performance of GO / SiO2; in addition, the composite membrane is a non-self-supporting membrane, and the separation process relies on a mixed cellulose base membrane, which is not conducive to the further promotion and application of GO / SiO2.

[0004] Self-supporting GO is of great significance for oil-water separation. Foreign patent KR1020230084575A discloses a method for preparing a self-supporting graphene oxide or reduced graphene oxide (rGO) film. The method is carried out by depositing an aqueous dispersion containing GO or rGO on a flat substrate of a polymer film that is soluble in an organic solvent and insoluble in water, and finally pickling the polymer film with an organic solvent to dissolve the polymer film to obtain a self-supporting GO film. However, the preparation method of this patent is complicated and dangerous to operate, and polymer molecules will be adsorbed during the dissolution of the polymer film. The use of organic solvents and acids will cause pollution. The mechanical properties of the GO membrane are poor, and it is difficult to apply to the field of oil-water separation. Therefore, it is of great significance to develop a self-supporting GO membrane with good mechanical properties and separation properties and apply it to the field of oil-water separation. Summary of the Invention

[0005] Technical issues solved:

[0006] In response to technical problems in the prior art such as poor permeability and poor bending performance of graphene oxide films, this application provides a method for preparing a self-supporting graphene oxide composite film with a sponge-like pore structure, and prepares a self-supporting graphene oxide film with a bend-resistant and sponge-like pore structure.

[0007] Technical solution:

[0008] To achieve the above objectives, this application is implemented through the following technical solutions:

[0009] A method for preparing a self-supporting sponge-like pore structured graphene oxide composite film comprises the following steps:

[0010] Step one: preparing hydrophilic carbon nanofibers;

[0011] Step 2: preparing graphene oxide / carbon nanofiber / dopamine hydrochloride dispersion;

[0012] Step 3: vacuum filtration and drying at room temperature to form a film;

[0013] The fourth step is to remove the filter membrane: remove the base membrane by high-temperature calcination in an air atmosphere to obtain a self-supporting graphene oxide composite film.

[0014] Furthermore, the first step of preparing silicon-doped carbon nanofibers is an electrospinning method, and the specific steps are:

[0015] S1: Using polyacrylonitrile as the spinning polymer and tetraethyl orthosilicate liquid or silica as the silicon source, wherein the amount of tetraethyl orthosilicate or silica nanoparticles added is 15-30% of the mass of the polyacrylonitrile; adding the silicon source and the spinning polymer to a solvent containing a catalyst, wherein the catalyst is glacial acetic acid, and the amount of the glacial acetic acid added is 0.01-6.25% of the solvent volume; electrospinning is performed in a multi-nozzle electrospinning machine using a non-woven fabric as a receiving substrate; the electrospinning process parameters are: spinning voltage 25kV, injection speed 1mL / h, receiving distance 20cm, ambient temperature 25±3℃, ambient humidity 50±5%, to prepare the required nanofiber membrane raw materials;

[0016] S2: Cutting the nanofiber membrane into pieces and placing it into a blender for high-speed blending at a speed of 8000-15000 r / min for 20 minutes to obtain nano short fibers, wherein the length of the nano short fibers is 30-100 μm; then placing the nano short fibers into an oven to completely dry them, placing the dried nano short fibers into a glass container, and finally placing the nano short fibers into a blast oven and heating them to 240° C. at a speed of 5° C. / min. After keeping the temperature for 120 minutes, taking them out and letting them cool naturally to room temperature to obtain nano short fibers after pre-oxidation heat treatment;

[0017] S3, carbonization treatment: the nano short fibers after pre-oxidation heat treatment are placed in a vacuum tube furnace, and the temperature is raised to 800-1000°C at 5°C / min under the protection of high-purity nitrogen, and maintained for 120 minutes. During this period, the high-purity nitrogen flow rate is 2 ml / min, and the vacuum tube furnace outlet valve is kept half open. After cooling to room temperature, hydrophilic carbon nano short fibers CNF are obtained.

[0018] Furthermore, the preparation method of the graphene oxide / carbon nanofiber short / dopamine hydrochloride dispersion in the second step is:

[0019] Step 1: 0.3 g of dopamine hydrochloride and 0.4 g of Tris were added to 60 ml of aqueous solution at a concentration of 5 mg / ml to prepare a dopamine hydrochloride mixed solution with a pH between 8 and 9;

[0020] Step 2: The solid content of graphene oxide and / or hydrophilic carbon nanofibers CNF is fixed at 0.5 mg / ml, and the mass ratio of GO and / or CNF is changed to add them to the dopamine hydrochloride mixed solution of step 1 to obtain a suspension, and then ultrasonicate the suspension for 120 minutes using an ultrasonic cell stirrer or stir the suspension at 10,000 rpm for 10 minutes using a high-speed disperser to obtain a graphene oxide / hydrophilic carbon nanofiber / dopamine hydrochloride dispersion.

[0021] Furthermore, the specific method of the third step is a vacuum filtration film-forming method; specifically, filter paper is placed between the filtration cup and the filter head, and then the dispersion obtained in the second step is poured into the filtration cup, and a circulating water vacuum filtration pump is connected to filter the graphene oxide / hydrophilic carbon nanofiber / dopamine hydrochloride dispersion to obtain a wet graphene oxide / carbon nanofiber / filter paper composite film, and finally the composite film is placed at room temperature for natural drying or dried in a vacuum drying oven at 60°C for 120 minutes to completely dry the composite film; during the drying process, the dopamine remaining in the composite film undergoes self-polymerization to form polydopamine, which acts as a bonding agent; the filter paper is made of a thermosetting resin substrate, and the membrane pore size is 0.22 to 0.45 μm; the maximum vacuum degree of vacuum filtration is 0.098 MPa.

[0022] Furthermore, in the fourth step, the high-temperature calcination step is to place the graphene oxide / hydrophilic carbon nanofiber / filter paper base membrane composite film in a crucible, place it in a muffle furnace, and heat it to 300°C at a heating rate of 15°C / min and keep it warm for 10 minutes until the filter paper base membrane is completely decomposed, and finally naturally cool it to room temperature to obtain a self-supporting sponge-like pore structure graphene oxide composite film.

[0023] Furthermore, the mass fraction of polyacrylonitrile in S1 is 12 wt % of the total mass of the solution.

[0024] Furthermore, the solvent in S1 is a mixture of one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

[0025] Furthermore, in step 2, the mass ratios of GO and / or CNF are 1:0, 2:1, 1:1, and 2:1, respectively.

[0026] Principle explanation: This patent mainly utilizes GO, which has oxygen-containing functional groups on its base and edges, is hydrophilic, has high chemical activity, and forms a uniform dispersion after high-speed dispersion in water and can form an oil-water separation membrane under the action of filtration. However, the current GO membrane has shortcomings such as poor water flux, i.e., permeability, inability to be self-supporting, and poor bending resistance. Therefore, by preparing flexible hydrophilic carbon nanofibers, they can be intercalated between GO sheets under the pressure of vacuum filtration. Furthermore, because CNF and GO cannot form a membrane smoothly by relying solely on filtration and have poor mechanical properties, dopamine hydrochloride is used as a binder for the two. The self-polymerization of dopamine enables GO and CNFS to be effectively bonded together. In addition, dopamine also contains hydrophilic groups that will not significantly affect the hydrophilicity of the membrane. Moreover, under the intercalation of CNF, the vertical spacing between GO layers is significantly expanded, making it easier for water to penetrate through the layered membrane structure. Hydrophilic CNFs are hydrophilic, thermally stable, and chemically inert, and combined with GO make the composite membranes an ideal choice for energy-saving oil-water separation technologies (such as gravity-driven separation), where CNFs show high reinforcement ability and improve the mechanical properties of the nanocomposite membranes.

[0027] Beneficial effects:

[0028] This application provides a method for preparing a self-supporting sponge-like pore structured graphene oxide composite film, which has the following beneficial effects compared with the prior art:

[0029] 1. The hydrophilic carbon nanofibers of this application are made flexible by the introduction of silicon dioxide into the fibers. Vacuum filtration and intercalation of silicon dioxide into the graphene oxide film, combined with the self-polymerization and bonding effect of dopamine, enhance the bending resistance of the hydrophilic carbon nanofiber / graphene oxide composite film.

[0030] 2. This application introduces hydrophilic carbon nanofibers between GO sheets to form a sponge-like pore structure, expanding the vertical interlayer nanochannels, thereby improving water permeability. At the same time, the presence of hydrophilic carbon nanofibers and dopamine also makes the composite film superhydrophilic and underwater superoleophobic, preventing oil droplets from penetrating through the membrane;

[0031] 3. The hydrophilic carbon nanofiber / graphene oxide composite film can be made self-supporting by high-temperature calcination, which provides a new approach for the preparation of self-supporting graphene oxide films.

[0032] 4. The technology of the present invention is easy to operate, low in cost and highly efficient, does not require the use of additional modifying chemical reagents, and is environmentally friendly and pollution-free. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The cross-sectional SEM images of the GO / CNF=1:1 film of the present application, wherein (a) is a 500x image and (b) is a 5kx image;

[0034] Figure 2 : These are water contact angle measurements of GO / CNF composite films with different ratios in this application, where (a) is the water contact angle measurement of pure GO, (b) is the water contact angle measurement of a composite film with a GO / CNF addition ratio of 2:1, (c) is the water contact angle measurement of a composite film with a GO / CNF addition ratio of 1:1, and (d) is the water contact angle measurement of a composite film with a GO / CNF addition ratio of 1:2;

[0035] Figure 3 The following are photos of the bending resistance test of the GO / CNF composite film of the present application, wherein (a) is a test diagram of the bending resistance of the GO film, and (b) is a test diagram of the bending resistance of the GO / CNF=1:1 composite film;

[0036] Figure 4 This is a graph showing the change in pure water flux of different GO / CNF composite films in this application. DETAILED DESCRIPTION

[0037] Below in conjunction with specific embodiment, further set forth the present invention.Should be understood that these embodiments are only used to illustrate the present invention and are not used in limiting the scope of the present invention.In addition, should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall equally within the scope limited by the appended claims of the application.

[0038] In the following examples, polyacrylonitrile (molecular weight 90,000) used to prepare self-supporting sponge-like pore-structured graphene oxide composite films was purchased from Jiangsu Kunshan Hongyu Plastic Co., Ltd., tetraethyl orthosilicate, silica nanoparticles (7-40 nm), N,N-dimethylformamide, and glacial acetic acid were all purchased from Shanghai MacLean Biochemical Technology Co., Ltd., single-layer graphene oxide was purchased from Suzhou Carbon Feng Technology, dopamine hydrochloride (98%), tris(hydroxymethyl)aminomethane (Tris), and sodium dodecyl sulfate (SDS) were all purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; electrospinning was performed using an HZ-11 multi-nozzle electrospinning machine produced by Qingdao Nuokang Environmental Protection Technology Co., Ltd., and a polypropylene spunbond non-woven fabric with a gram weight of 10 g / m2 was used as the receiving substrate; the contact angle test was performed using an SDC-350 contact angle meter produced by Kunshan Shengding Industrial Intelligent Technology Co., Ltd. When testing the water contact angle, the graphene oxide composite film is first stretched flat with a tension clamp and fixed on a horizontal test table. A 3μL ultrapure water droplet is transferred to the membrane surface using a microsyringe. After the water droplet shape stabilizes, a contact angle photo is taken and measured, and the average value of the results of at least 5 measurements is taken. When measuring the dynamic infiltration time of the droplet on the membrane surface, a high-speed camera is used to shoot the infiltration process of the droplet at a speed of 200 frames / second, and then the complete infiltration time is calculated based on the time required for the droplet contact angle in the captured image to become 0°. The evaluation of the oily wastewater purification performance of the membrane material is based on petroleum ether as an oil pollutant template. Petroleum ether and SDS / deionized water are mixed at a volume ratio of 1:99 and the resulting oil-water mixture is emulsified for 5 minutes using a high-speed disperser at 5000rpm, where the concentration of SDS in water is 100ppm, to prepare a water-in-oil emulsified oil-water mixture. The oil-water separation performance test process of the membrane material is as follows: first, the separation membrane is placed in a commercially available filtration device, and the water-in-oil emulsified oil-water mixture is added to the funnel of the filtration device and the liquid level is maintained at 10 cm. The volume V of the filtrate collected within a unit time t (t = 1 min) is measured, and the membrane separation flux is calculated using the formula P = V / St, where S is the effective working area of ​​the separation membrane; then, the total organic carbon (TOC) value C0 of the oil-water mixture before separation and the TOC value C1 of the filtrate after separation are tested using a total organic carbon analyzer, and the membrane separation efficiency is calculated using the formula: E = (C0-C1) / C0.

[0039] Example 1:

[0040] A method for preparing a self-supporting sponge-like pore structured graphene oxide composite film comprises the following steps:

[0041] The first step is to prepare hydrophilic carbon nanofibers:

[0042] S1: Polyacrylonitrile is used as the spinning polymer, tetraethyl orthosilicate is used as the silicon source, and N,N-dimethylformamide is used as the spinning solvent. The mass fraction of polyacrylonitrile is 12% (3.6 g), and the amount of tetraethyl orthosilicate added is 30% (1.08 g) of the mass of polyacrylonitrile. At room temperature, tetraethyl orthosilicate is first added to N,N-dimethylformamide (26.4 g) containing glacial acetic acid (volume fraction of 6.25%) and magnetically stirred for 30 minutes. Then, polyacrylonitrile is added and the spinning solution is obtained by sufficient stirring. Subsequently, electrospinning is carried out in a multi-nozzle electrospinning machine using non-woven fabric as the receiving substrate. The spinning voltage is 25 kV, the injection speed is 1 mL / h, the receiving distance is 20 cm, the ambient temperature is 25±3°C, and the ambient humidity is 50±5%, to prepare the required raw materials for the nanofiber membrane.

[0043] S2: Cut the nanofiber membrane into pieces and put them into a blender for high-speed (12000r / min) blending for 20min to obtain nano short fibers; then put the nano short fibers into an oven to completely dry them, put the dried nano short fibers into a glass container, and then put it into a blast oven and heat it to 240°C at 5°C / min. After keeping the temperature for 120min, take it out and let it cool to room temperature naturally to obtain pre-oxidized nano short fibers;

[0044] S3: Carbonization treatment: The nano-short fibers after pre-oxidation heat treatment are placed in a vacuum tube furnace, and the temperature is raised to 1000°C at 5°C / min under the protection of high-purity nitrogen, and maintained for 120 minutes. During this period, the high-purity nitrogen flow rate is 2 ml / min, and the vacuum tube furnace outlet valve is kept half open. After cooling to room temperature, hydrophilic carbon nano-short fibers (CNF) are obtained.

[0045] The second step is to prepare the graphene oxide / carbon nanofiber / dopamine hydrochloride dispersion:

[0046] Step 1: Prepare a dopamine hydrochloride mixed solution by adding 0.3 g of dopamine hydrochloride and 0.4 g of Tris to 60 ml of aqueous solution at a concentration of 5 mg / ml. The pH value of the mixed solution should be between 8 and 9.

[0047] Step 2: The solid content of graphene oxide / hydrophilic carbon nanofibers was fixed at 0.5 mg / ml, and the solid content ratio was GO:CNF = 2:1, that is, 0.02 g GO and 0.01 g CNF were added to the mixed solution of step 1, and then the suspension was stirred at 10,000 rpm for 20 min using a high-speed disperser to obtain a graphene oxide / carbon nanofiber / dopamine hydrochloride dispersion;

[0048] The third step is vacuum filtration and drying to form a film; specifically, filter paper is placed between the filtration cup and the filter head, and then the dispersion obtained in the second step is poured into the filtration cup, and a circulating water vacuum filtration pump is connected to filter the graphene oxide / hydrophilic carbon nanofiber short / dopamine hydrochloride dispersion to obtain a wet graphene oxide / carbon nanofiber short / filter paper composite film, and finally the composite film is placed at room temperature to dry naturally to completely dry the composite film;

[0049] Step 4: Place the graphene oxide / hydrophilic carbon nanofiber composite film in a crucible, place it in a muffle furnace, and heat it to 300°C at a heating rate of 15°C / min and keep it warm for 10 minutes until the filter paper base membrane is completely decomposed. Finally, cool it naturally to room temperature to obtain a self-supporting sponge-like pore structure graphene oxide film.

[0050] A self-supporting sponge-like pore structured graphene oxide composite film is prepared by the above method.

[0051] Example 2:

[0052] A method for preparing a self-supporting sponge-like pore structured graphene oxide composite film comprises the following steps:

[0053] The first step is to prepare silicon-doped carbon nanofibers:

[0054] S1: Polyacrylonitrile was used as the spinning polymer, tetraethyl orthosilicate was used as the silicon source, and N,N-dimethylformamide was used as the spinning solvent. The mass fraction of polyacrylonitrile was 12% (3.6 g), and the amount of tetraethyl orthosilicate added was 30% (1.08 g) of the mass of polyacrylonitrile. At room temperature, tetraethyl orthosilicate was first added to N,N-dimethylformamide (26.4 g) containing glacial acetic acid (volume fraction of 6.25%) and magnetically stirred for 30 minutes. Then, polyacrylonitrile was added and the spinning solution was obtained after sufficient stirring. Subsequently, electrospinning was carried out in a multi-nozzle electrospinning machine using a non-woven fabric as a receiving substrate. The spinning voltage was 25 kV, the injection speed was 1 mL / h, the receiving distance was 20 cm, the ambient temperature was 25±3°C, and the ambient humidity was 50±5%, thereby preparing a nanofiber membrane with uniform thickness.

[0055] S2: Cut the nanofiber membrane into pieces and put them into a blender for high-speed (12000r / min) blending for 20min to obtain nano short fibers; then put the nano short fibers into an oven to completely dry them, put the dried nano short fibers into a glass container, and then put it into a blast oven and heat it to 240°C at 5°C / min. After keeping the temperature for 120min, take it out and let it cool to room temperature naturally to obtain pre-oxidized nano short fibers;

[0056] S3: Carbonization treatment: The nano-short fibers after pre-oxidation heat treatment are placed in a vacuum tube furnace, and the temperature is raised to 1000°C at 5°C / min under the protection of high-purity nitrogen, and maintained for 120 minutes. During this period, the high-purity nitrogen flow rate is 2 ml / min, and the vacuum tube furnace outlet valve is kept half open. After cooling to room temperature, hydrophilic carbon nano-short fibers (CNF) are obtained.

[0057] The second step is to prepare a graphene oxide / carbon nanofiber / dopamine hydrochloride dispersion;

[0058] Step 1: Prepare a dopamine hydrochloride mixed solution by adding 0.3 g of dopamine hydrochloride and 0.4 g of Tris to 60 ml of aqueous solution at a concentration of 5 mg / ml. The pH value of the mixed solution should be between 8 and 9.

[0059] Step 2: The solid content of graphene oxide / hydrophilic carbon nanofibers was fixed at 0.5 mg / ml, and the solid content ratio was GO:CNF = 1:1, that is, 0.015 g GO and 0.015 g CNF were added to the mixed solution of step 1, and then the suspension was stirred at 10,000 rpm for 20 min using a high-speed disperser to obtain a graphene oxide / carbon nanofiber / dopamine hydrochloride dispersion;

[0060] The third step is vacuum filtration and drying to form a film; specifically, filter paper is placed between the filtration cup and the filter head, and then the dispersion obtained in the second step is poured into the filtration cup, and a circulating water vacuum filtration pump is connected to filter the graphene oxide / hydrophilic carbon nanofiber / dopamine hydrochloride dispersion to obtain a wet graphene oxide / carbon nanofiber / filter paper composite film, and finally the composite film is placed at room temperature to dry naturally to completely dry the composite film;

[0061] Step 4: Place the graphene oxide / hydrophilic carbon nanofiber composite film in a crucible, place it in a muffle furnace, and heat it to 300°C at a heating rate of 15°C / min and keep it warm for 10 minutes until the filter paper base membrane is completely decomposed. Finally, cool it naturally to room temperature to obtain a self-supporting sponge-like pore structure graphene oxide film.

[0062] A self-supporting sponge-like pore structured graphene oxide composite film is prepared by the above method.

[0063] Example 3:

[0064] A method for preparing a self-supporting sponge-like pore structured graphene oxide composite film comprises the following steps:

[0065] The first step is to prepare silicon-doped carbon nanofibers:

[0066] S1: Polyacrylonitrile was used as the spinning polymer, tetraethyl orthosilicate was used as the silicon source, and N,N-dimethylformamide was used as the spinning solvent. The mass fraction of polyacrylonitrile was 12% (3.6 g), and the amount of tetraethyl orthosilicate added was 30% (1.08 g) of the mass of polyacrylonitrile. At room temperature, tetraethyl orthosilicate was first added to N,N-dimethylformamide (26.4 g) containing glacial acetic acid (volume fraction of 6.25%) and magnetically stirred for 30 minutes. Then, polyacrylonitrile was added and the spinning solution was obtained after sufficient stirring. Subsequently, electrospinning was carried out in a multi-nozzle electrospinning machine using a non-woven fabric as a receiving substrate. The spinning voltage was 25 kV, the injection speed was 1 mL / h, the receiving distance was 20 cm, the ambient temperature was 25±3°C, and the ambient humidity was 50±5%, thereby preparing a nanofiber membrane with uniform thickness.

[0067] S2: Cut the nanofiber membrane into pieces and put them into a blender for high-speed (12000r / min) blending for 20min to obtain nano short fibers; then put the nano short fibers into an oven to completely dry them, put the dried nano short fibers into a glass container, and then put it into a blast oven and heat it to 240°C at 5°C / min. After keeping the temperature for 120min, take it out and let it cool to room temperature naturally to obtain pre-oxidized nano short fibers;

[0068] S3: Carbonization treatment: The nano-short fibers after pre-oxidation heat treatment are placed in a vacuum tube furnace, and the temperature is raised to 1000°C at 5°C / min under the protection of high-purity nitrogen, and maintained for 120 minutes. During this period, the high-purity nitrogen flow rate is 2 ml / min, and the vacuum tube furnace outlet valve is kept half open. After cooling to room temperature, hydrophilic carbon nano-short fibers (CNF) are obtained.

[0069] The second step is to prepare the graphene oxide / carbon nanofiber / dopamine hydrochloride dispersion:

[0070] Step 1: Add 0.3 g of dopamine hydrochloride and 0.4 g of Tris to 60 ml of aqueous solution at a concentration of 5 mg / ml to prepare a dopamine hydrochloride mixed solution, the pH of which is between 8 and 9;

[0071] Step 2: The solid content of graphene oxide / hydrophilic carbon nanofibers was fixed at 0.5 mg / ml, and the solid content ratio was GO:CNF = 1:2, that is, 0.01 g GO and 0.02 g CNF were added to the mixed solution of step 1, and then the suspension was stirred at 10,000 rpm for 20 min using a high-speed disperser to obtain a graphene oxide / carbon nanofiber / dopamine hydrochloride dispersion;

[0072] The third step is vacuum filtration and drying to form a film; specifically, filter paper is placed between the filtration cup and the filter head, and then the dispersion obtained in the second step is poured into the filtration cup, and a circulating water vacuum filtration pump is connected to filter the graphene oxide / hydrophilic carbon nanofiber / dopamine hydrochloride dispersion to obtain a wet graphene oxide / carbon nanofiber / filter paper composite film, and finally the composite film is placed at room temperature to dry naturally to completely dry the composite film;

[0073] Step 4: Place the graphene oxide / hydrophilic carbon nanofiber composite film in a crucible, place it in a muffle furnace, and heat it to 300°C at a heating rate of 15°C / min and keep it warm for 10 minutes until the filter paper base membrane is completely decomposed. Finally, cool it naturally to room temperature to obtain a self-supporting sponge-like pore structure graphene oxide film.

[0074] A self-supporting sponge-like pore structured graphene oxide composite film is prepared by the above method.

[0075] Example 4:

[0076] A method for preparing a self-supporting sponge-like pore structured graphene oxide composite film, wherein the steps are different from those in Example 1 in that hydrophilic carbon nanofibers do not need to be prepared. In step 2, 0.3 g GO is added instead, i.e., GO / CNF=1:0. The remaining steps are the same.

[0077] The structure and oil-water selective wettability of the self-supporting sponge-like pore structure graphene oxide composite film prepared in the above examples were evaluated. Figure 1 As shown in FIG, the graphene oxide composite film with hydrophilic carbon nanofibers added presents a distinct sponge-like pore structure, and distinct carbon nanofibers can be seen in the composite film. Figure 2 As shown, a 3 μL water droplet can quickly wet the surface of the graphene oxide composite film prepared in all embodiments, and the static water contact angle of all composite films can be 0°, compared with the pure GO film ( Figure 2 In a), it can be seen that the addition of hydrophilic carbon nanofibers significantly increases the wetting time of water droplets ( Figure 2 b, c, d). Figure 3 As shown in the figure, the pure GO membrane has obvious creases after bending, which affects the subsequent use of the membrane ( Figure 3 a); after adding carbon nanofibers ( Figure 3In b), the composite film remains unchanged after bending, indicating that the addition of carbon nanofibers improves the bending resistance of the graphene oxide composite film. Furthermore, oil-water separation performance tests on the membrane material show that the water flux of the resulting graphene oxide composite film gradually increases with the addition of hydrophilic carbon nanofibers, indicating that the carbon nanofibers effectively expand the water transport channels of graphene oxide and increase water permeability. Furthermore, under an additional pressure of 10 kPa, the separation efficiency of the surfactant-containing oil-in-water mixture can reach over 96%, with a maximum water flux of 2000 Lm -2 h -1 above.

[0078] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various variations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing a self-supporting sponge-like pore structured graphene oxide composite film, characterized in that: The specific steps include: Step one: preparing hydrophilic carbon nanofibers; The method for preparing hydrophilic carbon nanofibers is an electrospinning method, and the specific steps are: S1: Polyacrylonitrile is used as the spinning polymer, and tetraethyl orthosilicate liquid or silica nanoparticles are used as the silicon source, wherein the amount of tetraethyl orthosilicate or silica nanoparticles added is 15-30% of the mass of polyacrylonitrile; the silicon source and the spinning polymer are added to a solvent containing a catalyst, wherein the catalyst is glacial acetic acid, and the amount of glacial acetic acid added is 0.01-6.25% of the solvent volume; electrospinning is performed in a multi-nozzle electrospinning machine using a non-woven fabric as a receiving substrate; the electrospinning process parameters are: spinning voltage 25kV, injection speed 1mL / h, receiving distance 20cm, ambient temperature 25±3℃, ambient humidity 50±5%, to prepare the required nanofiber membrane raw materials; S2: Cut the nanofiber membrane into pieces and put them into a blender for high-speed blending at a speed of 8000-15000 r / min for 20 minutes to obtain nanofibers, wherein the length of the nanofibers is 30-100 μm; The nanofibers were then placed in an oven to completely dry them, and the dried nanofibers were placed in a glass container. The glass container was then placed in a blast oven and heated to 240°C at a rate of 5°C / min. After being kept at this temperature for 120 minutes, the nanofibers were taken out and naturally cooled to room temperature to obtain pre-oxidation heat-treated nanofibers. S3, carbonization treatment: placing the nanofibers after pre-oxidation heat treatment in a vacuum tube furnace, heating them to 800-1000°C at a rate of 5°C / min under high-purity nitrogen protection, and maintaining the temperature for 120 minutes. During this period, the high-purity nitrogen flow rate is 2 ml / min, and the vacuum tube furnace outlet valve is kept half open. After cooling to room temperature, hydrophilic carbon nanofibers CNF are obtained; Step 2: preparing graphene oxide / carbon nanofiber / dopamine hydrochloride dispersion; Step 3: vacuum filtration and drying at room temperature to form a film; The fourth step is to remove the filter membrane: remove the base membrane by high-temperature calcination in an air atmosphere to obtain a self-supporting graphene oxide composite film.

2. The method for preparing a self-supporting sponge-like pore structure graphene oxide composite film according to claim 1, wherein The preparation method of the graphene oxide / carbon nanofiber short / dopamine hydrochloride dispersion in the second step is: Step 1: 0.3 g of dopamine hydrochloride and 0.4 g of Tris were added to 60 ml of aqueous solution at a concentration of 5 mg / ml to prepare a dopamine hydrochloride mixed solution with a pH between 8 and 9; Step 2: The solid content of graphene oxide and / or hydrophilic carbon nanofibers CNF is fixed at 0.5 mg / ml, and the mass ratio of GO and CNF is changed to add them to the dopamine hydrochloride mixed solution of step 1 to obtain a suspension, and then ultrasonicate the suspension for 120 minutes using an ultrasonic cell stirrer or stir the suspension at 10,000 rpm for 10 minutes using a high-speed disperser to obtain a graphene oxide / hydrophilic carbon nanofiber / dopamine hydrochloride dispersion.

3. The method for preparing the self-supporting sponge-like pore structure graphene oxide composite film according to claim 1, characterized in that: The specific method of the third step is a vacuum filtration film-forming method; specifically, filter paper is placed between a filtration cup and a filter head, and then the dispersion obtained in the second step is poured into the filtration cup, and a circulating water vacuum filtration pump is connected to filter the graphene oxide / hydrophilic carbon nanofiber / dopamine hydrochloride dispersion to obtain a wet graphene oxide / carbon nanofiber / filter paper composite film. Finally, the composite film is placed at room temperature for natural drying or dried in a vacuum drying oven at 60°C for 120 minutes to completely dry the composite film; during the drying process, the dopamine remaining in the composite film undergoes self-polymerization to form polydopamine, which acts as a bonding agent; the filter paper is made of a thermosetting resin substrate, and the membrane pore size is 0.22~0.45μm; the maximum vacuum degree of vacuum filtration is 0.098MPa.

4. The method for preparing the self-supporting sponge-like pore structure graphene oxide composite film according to claim 1, characterized in that: In the fourth step, the high-temperature calcination step is to place the graphene oxide / hydrophilic carbon nanofiber / filter paper base membrane composite film in a crucible, place it in a muffle furnace, heat it to 300°C at a heating rate of 15°C / min, and keep it warm for 10 minutes until the filter paper base membrane is completely decomposed, and finally cool it naturally to room temperature to obtain a self-supporting sponge-like pore structure graphene oxide composite film.

5. The method for preparing the self-supporting sponge-like pore structure graphene oxide composite film according to claim 1, characterized in that: The mass fraction of polyacrylonitrile in S1 is 12 wt % of the total mass of the solution.

6. The method for preparing the self-supporting sponge-like pore structure graphene oxide composite film according to claim 1, characterized in that: The solvent in S1 is a mixture of one or more of N,N-dimethylformamide, N,N-dimethylacetamide and dimethyl sulfoxide.

7. The method for preparing the self-supporting sponge-like pore structure graphene oxide composite film according to claim 2, characterized in that: In step 2, the mass ratios of GO and CNF are 1:0, 2:1, 1:1, and 2:1, respectively.

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