A graphene-based composite electrode and its preparation method and application

Abstract

The present invention provides a graphene-based composite electrode and a preparation method and application thereof, belonging to the field of electrode material technology. The present invention uses an amino modifier to modify GO, expand the interlayer distance of GO, form a modified graphene with a three-dimensional network structure, so that the modified graphene has a larger specific surface area and better conductivity; and the N in the amino modifier can improve the adsorption capacity for sodium ions; the present invention uses ultrasound to break the activated carbon powder into nanocrystalline carbon, so that it is dispersed between the modified graphene sheets, and the conductivity of the electrode is improved; at the same time, it has a stronger adsorption capacity for sodium ions. Since the graphene-based composite material prepared by the present invention has excellent conductivity and adsorption capacity for sodium ions, the graphene-based composite electrode prepared by mixing it with a conductive agent, a binder and an organic solvent and then coating it on conductive paper has excellent adsorption capacity for sodium ions when it is assembled into a CDI device for seawater desalination.

Description

Technical Field

[0001] The present invention relates to the technical field of electrode materials, and in particular to a graphene-based composite electrode and a preparation method and application thereof. Background Art

[0002] With the growth of population and the development of industry, the shortage of fresh water resources has become an important factor limiting human progress. Seawater desalination is one of the effective methods to replenish fresh water. Among the many seawater desalination technologies, capacitive deionization (CDI) technology has the characteristics of renewability, simple operation, low cost and low energy consumption, and is considered to be a very promising seawater desalination technology. In CDI technology, electrode materials and operating conditions jointly control the desalination effect. Good electrode materials should have good conductivity, large specific surface area, good wettability and good stability. Therefore, carbon-based materials with the above characteristics are often used as CDI electrode materials.

[0003] Common carbon electrode materials include activated carbon, graphene, carbon fiber / nanotubes, etc. Among them, graphene is sp 2 Hybrid nanosheets with two-dimensional planar structures have high specific surface areas and excellent electrochemical properties, which determine their potential application as CDI electrodes. Graphene oxide (GO) is a precursor of graphene. Due to its rich oxygen-containing functional groups, it can be modified while maintaining its advantages. However, most reported carbon-based electrode materials have the following problems that need to be improved: (1) The electrode polarization caused by excessive specific surface area may lead to an increase in the applied voltage, thereby increasing additional energy consumption; (2) The low conductivity that occurs during the modification process such as calcination will limit the charge efficiency, thereby affecting the CDI electrode adsorption performance of the CDI electrode; (3) High-temperature calcination is an effective method to obtain a porous electrode structure, but the preparation conditions are harsh and the operation is complicated, and it will also increase the uncertainty of material preparation, thereby affecting the electrosorption performance of the CDI electrode.

[0004] Therefore, there is an urgent need to provide a simple, green method for preparing a graphene-based composite electrode that can achieve high electrosorption performance. Summary of the invention

[0005] The purpose of the present invention is to provide a graphene-based composite electrode and a preparation method and application thereof. The preparation method provided by the present invention is simple to operate, green and has high electrical adsorption performance. When it is used for CDI electrode for seawater desalination, it has excellent adsorption for sodium ions.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing a graphene-based composite electrode, comprising the following steps:

[0008] (1) mixing graphene oxide, an amino modifier and a first organic solvent to perform a covalent bond reaction to obtain modified graphene;

[0009] (2) mixing the modified graphene obtained in step (1) with activated carbon powder and a solvent and then subjecting the mixture to ultrasonic compounding to obtain a graphene-based composite material;

[0010] (3) mixing the graphene-based composite material obtained in step (2) with a conductive agent, a binder and a second organic solvent to obtain a mixed slurry;

[0011] (4) The mixed slurry obtained in step (3) is coated on conductive paper, and a graphene-based composite electrode is obtained after drying.

[0012] Preferably, the amino-modifying agent in step (1) includes aminoacetaldehyde dimethyl acetal, aminoacetaldehyde diethyl acetal, 2-amino-1,3-propanediol or 3-aminoglutaric acid.

[0013] Preferably, the mass ratio of graphene oxide to amino modifier in step (1) is (0.1-0.5):(0.5-1).

[0014] Preferably, the temperature of the covalent bond reaction in step (1) is 90 to 130° C.; and the time of the covalent bond reaction is 10 to 15 hours.

[0015] Preferably, the mass ratio of the modified graphene to the activated carbon powder in step (2) is (1-5):(5-9).

[0016] Preferably, the ultrasonic power of the ultrasonic compounding in step (2) is 100 to 200 W, and the ultrasonic time of the ultrasonic compounding is 1 to 3 hours.

[0017] Preferably, the conductive agent in step (3) comprises one or more of acetylene black, conductive carbon black, conductive graphite and Ketjen black.

[0018] Preferably, in step (3), the mass ratio of the graphene-based composite material, the conductive agent and the binder is (5-8):1:(1-4).

[0019] The present invention also provides a graphene-based composite electrode prepared by the preparation method described in the above technical solution.

[0020] The present invention also provides the application of the graphene-based composite electrode described in the above technical solution in seawater desalination.

[0021] The invention provides a method for preparing a graphene-based composite electrode, comprising the following steps: mixing graphene oxide, an amino modifier and a first organic solvent, performing a covalent bond reaction to obtain modified graphene; mixing the modified graphene with activated carbon powder and a solvent, and then performing ultrasonic compounding to obtain a graphene-based composite material; mixing the graphene-based composite material with a conductive agent, a binder and a second organic solvent to obtain a mixed slurry; coating the mixed slurry on conductive paper, and obtaining a graphene-based composite electrode after drying. The invention obtains modified graphene by covalently reacting an amino modifier with graphene oxide. In the process, the amino functional group of the amino modifier and the carboxyl group and the ether oxygen bond on the graphene oxide undergo amination and nucleophilic addition and other covalent bond reactions, so that the amino modifier is loaded on the graphene oxide, the interlayer distance of the graphene oxide is enlarged, and the modified graphene with a three-dimensional network structure is formed, which not only enables the modified graphene to have a larger specific surface area, but also has better conductivity; and N in the amino modifier can adsorb sodium ions, thereby improving the adsorption capacity of the composite electrode for sodium ions; the invention mixes the modified graphene with activated carbon powder and a solvent and then performs ultrasonic compounding, and the ultrasound can break the activated carbon powder into nanocrystalline carbon, expose micropores, improve adsorption sites, and have stronger adsorption capacity for sodium ions; meanwhile, both the nanocrystalline carbon and the modified graphene are nanomaterials, and the binding force between the two is relatively strong, and the nanocrystalline carbon is dispersed between the modified graphene sheets through adsorption, so as to form more abundant conductive paths and improve the conductivity of the electrode. Since the graphene-based composite material prepared by the present invention has excellent conductivity and adsorption capacity for sodium ions, the graphene-based composite electrode prepared by mixing it with a conductive agent, a binder and an organic solvent and coating it on a conductive paper is assembled into a CDI device and then used for seawater desalination, and has excellent adsorption capacity for sodium ions. The results of the embodiment show that after the graphene-based composite electrode prepared by the present invention is assembled into a CDI device, adsorption is carried out in a 50 mg / L NaCl solution, and the electrosorption capacity (SAC) can reach 17.89 mg / g, which has excellent adsorption. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 SEM and TEM images of GO, ADMA-GO and GMAC1 prepared in Example 1 of the present invention;

[0023] Figure 2 FT-IR spectra of ADMA used in the present invention and AC, GO, ADMA-GO and GMAC1 prepared in Example 1;

[0024] Figure 3 Raman spectra of AC, GO, ADMA-GO and GMAC1 prepared in Example 1 of the present invention;

[0025] Figure 4XRD patterns of AC, GO, ADMA-GO and GMAC1 prepared in Example 1 of the present invention;

[0026] Figure 5 XPS graphs of GO and ADMA-GO prepared in Example 1 of the present invention;

[0027] Figure 6 The nitrogen adsorption / desorption curves of AC, ADMA-GO and GMAC1 prepared in Example 1 of the present invention are shown;

[0028] Figure 7 The pore size distribution curves of AC, ADMA-GO and GMAC1 prepared in Example 1 of the present invention are shown;

[0029] Figure 8 The conductivity change curve of ADMA-GO prepared in Example 1 of the present invention at different voltages;

[0030] Fig. 9 The conductivity change curves of AC, ADMA-GO and GMAC1, GMAC2, GMAC3, GMAC4 and GMAC5 at a voltage of 1.6V were prepared for the present invention. DETAILED DESCRIPTION

[0031] The present invention provides a method for preparing a graphene-based composite electrode, comprising the following steps:

[0032] (1) mixing graphene oxide, an amino modifier and a first organic solvent to perform a covalent bond reaction to obtain modified graphene;

[0033] (2) mixing the modified graphene obtained in step (1) with activated carbon powder and a solvent and then subjecting the mixture to ultrasonic compounding to obtain a graphene-based composite material;

[0034] (3) mixing the graphene-based composite material obtained in step (2) with a conductive agent, a binder and a second organic solvent to obtain a mixed slurry;

[0035] (4) The mixed slurry obtained in step (3) is coated on conductive paper, and a graphene-based composite electrode is obtained after drying.

[0036] The invention mixes graphene oxide, an amino modifier and a first organic solvent, and performs a covalent bond reaction to obtain modified graphene.

[0037] The present invention has no particular limitation on the preparation method of graphene oxide, and any preparation method well known to those skilled in the art or any commercially available product may be used.

[0038] In the present invention, the method for preparing graphene oxide is preferably a modified Hummers method, and the modified Hummers method preferably comprises the following steps:

[0039] (a) Add P to the concentrated sulfuric acid solution under stirring. 2 O 5 and K 2 S 2 O 8 , after heating to 80°C, a mixed solution is obtained;

[0040] (b) adding graphite powder to the mixed solution obtained in step (a), cooling the solution to 30° C. after the liquid becomes a black viscous substance, washing the solution with water and drying the solution to obtain pre-oxidized graphite;

[0041] (c) adding the pre-oxidized graphite obtained in step (b) to a concentrated sulfuric acid solution in an ice-water bath and under stirring to obtain a mixed slurry; then adding KMnO 4 , heat to 35°C, stir for 2h, add deionized water for dilution, then add 30% hydrogen peroxide, let stand for 24h, take out the lower precipitate for dialyzation to obtain graphene oxide.

[0042] The present invention preferably adds P to the concentrated sulfuric acid solution under stirring conditions. 2 O 5 and K 2 S 2 O 8 After heating to 80°C, a mixed solution is obtained. 2 O 5 and K 2 S 2 O 8 An oxidizing solution is formed.

[0043] In the present invention, the volume of the concentrated sulfuric acid solution, P 2 O 5 The quality and K 2 S 2 O 8 The mass ratio of is preferably 30mL:10mg:10mg. In the present invention, the concentration of the concentrated sulfuric acid solution is preferably 98%.

[0044] After obtaining the mixed solution, the present invention preferably adds graphite powder to the mixed solution, and after the liquid becomes a black viscous substance, the temperature is cooled to 30° C., washed with water and dried to obtain pre-oxidized graphite. The present invention achieves pre-oxidation of graphite powder by adding graphite powder to the mixed solution and waiting for the liquid to become a black viscous substance.

[0045] In the present invention, the graphite powder is preferably natural graphite with a mesh size of 400. In the present invention, when the volume of the concentrated sulfuric acid solution is 30 mL, the mass of the graphite powder is preferably 20 g.

[0046] The present invention has no special limitation on the operation method of water washing and drying, and the water washing and drying methods well known to those skilled in the art can be used. The present invention purifies the black viscous substance by water washing and drying to obtain pre-oxidized graphite.

[0047] After obtaining the pre-oxidized graphite, the present invention preferably adds the pre-oxidized graphite into a concentrated sulfuric acid solution under ice-water bath and stirring conditions to obtain a mixed slurry.

[0048] In the present invention, the ratio of the mass of the pre-oxidized graphite to the volume of the concentrated sulfuric acid solution is preferably 20 g:460 mL.

[0049] In the present invention, when the mass of the pre-oxidized graphite is 20g, the KMnO 4 The mass of the present invention is preferably 60g. 4 , and stirred at 35 °C for 2 h to deeply oxidize the pre-oxidized graphite.

[0050] The present invention has no special limitation on the amount of deionized water, which can be adjusted as needed.

[0051] In the present invention, when the mass of the pre-oxidized graphite is 20 g, the amount of the 30% hydrogen peroxide added is preferably 100 mL. The present invention promotes the exfoliation of oxidized graphite by adding 30% hydrogen peroxide to generate gas through the reaction of hydrogen peroxide.

[0052] The present invention has no particular limitation on the method and frequency of dialysis, which can be adjusted as needed to fully remove impurities in graphene oxide.

[0053] The present invention adopts the above-mentioned improved Hummers method to prepare graphene oxide, which is more conducive to obtaining graphene oxide with a better degree of exfoliation.

[0054] In the present invention, the amino modifier preferably includes aminoacetaldehyde dimethyl acetal, aminoacetaldehyde diethyl acetal, 2-amino-1,3-propylene glycol or 3-aminoglutaric acid, and more preferably aminoacetaldehyde dimethyl acetal. The present invention can modify graphene oxide with amino groups by using amino modifiers, expand the interlayer spacing of graphene oxide, form modified graphene with a three-dimensional network structure, improve the specific surface area and conductivity of the modified graphene, and can use N to improve the adsorption capacity of sodium ions.

[0055] In the present invention, the mass ratio of the graphene oxide to the amino modifier is preferably (0.1-0.5):(0.5-1), and more preferably 0.3: 1. When the mass ratio of the graphene oxide to the amino modifier is controlled within the above range, the graphene oxide can be fully modified.

[0056] In the present invention, the first organic solvent is preferably N,N-dimethylformamide, dimethyl sulfoxide or N-methyl-2-pyrrolidone. When the present invention uses the above organic solvent, the amino modifier can be dissolved and the graphene oxide can be well dispersed, which is more conducive to the full covalent bond reaction. The present invention has no special limitation on the amount of the first organic solvent, which can be adjusted according to experimental needs.

[0057] The present invention does not specifically limit the method for mixing the graphene oxide, the amino modifier and the first organic solvent, as long as the above components can be fully mixed and uniform. In the present invention, the method for mixing the graphene oxide, the amino modifier and the first organic solvent is preferably: dispersing the graphene oxide in the first organic solution to obtain a dispersion; heating the dispersion to the temperature of the covalent bond reaction, and then dropping the amino modifier solution under stirring. In the present invention, the concentration of the amino modifier solution is preferably 0.1g / mL. The present invention can make the covalent bond reaction more sufficient and uniform through the above mixing method, ensure that the graphene sheets are loaded with the amino modifier, and then the graphene oxide is fully modified into modified graphene.

[0058] In the present invention, the temperature of the covalent bond reaction is preferably 90 to 130° C., more preferably 100 to 120° C.; the time of the covalent bond reaction is preferably 10 to 15 hours, more preferably 10 to 12 hours. The present invention can promote the covalent bond reaction more fully at the above temperature and time.

[0059] After the covalent bond reaction is completed, the present invention preferably performs suction filtration, washing and drying on the system obtained after the covalent bond reaction in sequence to obtain modified graphene. The present invention does not specifically limit the operation methods of the suction filtration, washing and drying, and the operation methods of suction filtration, washing and drying well known to those skilled in the art can be used. In the present invention, the washing reagent is preferably a mixed solution of N, N-dimethylformamide and ethanol, and the volume ratio of N, N-dimethylformamide and ethanol is preferably 1:1; the drying temperature is preferably 60°C, the drying time is preferably 24h, and the drying device is preferably an oven. The present invention can remove unreacted amino modifiers and organic solvents in modified graphene by suction filtration, washing and drying.

[0060] After the modified graphene is obtained, the modified graphene is mixed with activated carbon powder and a solvent and then ultrasonically compounded to obtain a graphene-based composite material.

[0061] The present invention does not specifically limit the particle size of the activated carbon powder, and ordinary commercially available activated carbon powder can be used. In the present invention, the activated carbon powder is preferably a pretreated commercially available activated carbon powder. In the present invention, the pretreatment method is preferably: ultrasonically disperse the commercially available activated carbon powder in ultrapure water for 1 hour to obtain an activated carbon dispersion, transfer the activated carbon dispersion to a round-bottom flask, heat it in an oil bath at 100°C, condense and reflux for 2 hours, then filter and wash it with ultrapure water several times, and dry it at 60°C to obtain an activated carbon powder. The present invention can remove pigments and other impurities in commercially available activated carbon powder by adopting the above-mentioned pretreatment method.

[0062] In the present invention, the mass ratio of the modified graphene to the activated carbon powder is preferably (1-5):(5-9), and more preferably (2-4):(6-8). When the mass ratio of the modified graphene to the activated carbon powder is controlled within the above range, the activated carbon powder can be fully dispersed in the modified graphene network to construct a rich conductive path.

[0063] In the present invention, the solvent is preferably ethanol, dimethyl sulfoxide, or ethylene glycol, more preferably ethanol. The use of the above solvents is more conducive to the full dispersion of modified graphene and activated carbon powder. The present invention has no special limitation on the amount of the solvent, which can be adjusted as needed.

[0064] The present invention has no particular limitation on the method for mixing the modified graphene with the activated carbon powder and the solvent, as long as the above components can be mixed uniformly. In the present invention, the method for mixing the modified graphene with the activated carbon powder and the solvent is preferably to stir and mix the modified graphene and the activated carbon powder, and then mix them with the solvent.

[0065] In the present invention, the ultrasonic power of the ultrasonic compound is preferably 100-200W, more preferably 150-180W; the ultrasonic time of the ultrasonic compound is preferably 1-3h, more preferably 1-2h. The present invention can break the activated carbon powder into nanocrystalline carbon by performing ultrasonic compounding under the above ultrasonic parameters, and the micropores are exposed, which has more adsorption sites; and the binding force between the nanocrystalline carbon and the modified graphene is strong, and the nanocrystalline carbon can be dispersed between the graphene sheets through adsorption.

[0066] In the present invention, the mixed solution obtained after the ultrasonic compounding is preferably dried to obtain the graphene-based composite material. In the present invention, the drying is preferably natural air drying.

[0067] After obtaining the graphene-based composite material, the present invention mixes the graphene-based composite material with a conductive agent, a binder and a second organic solvent to obtain a mixed slurry.

[0068] In the present invention, the conductive agent preferably includes one or more of acetylene black, conductive carbon black, conductive graphite and Ketjen black, and more preferably acetylene black. The present invention can improve the cycle performance, discharge performance and reduce the internal resistance by adding the conductive agent, thereby improving the performance of the electrode.

[0069] In the present invention, the binder preferably includes one or more of polytetrafluoroethylene, polyvinylidene fluoride, polyacrylic acid and polyacrylate, and more preferably polytetrafluoroethylene. The present invention can bond the graphene-based composite material and the conductive agent by adding the binder.

[0070] In the present invention, the mass ratio of the graphene-based composite material, the conductive agent and the binder is preferably (5-8):1:(1-4), and more preferably (6-8):1:(1-3). Since the graphene-based composite material prepared in the present invention has excellent conductivity and adsorption, it can still have excellent conductivity and adsorption when less conductive agent is added.

[0071] In the present invention, the second organic solvent is preferably ethanol. The addition of the second organic solvent is more conducive to the full dispersion of the graphene-based composite material, the conductive agent and the binder. The present invention has no special limitation on the amount of ethanol used, and it can be adjusted according to the viscosity of the slurry to make it more conducive to coating.

[0072] The present invention has no particular limitation on the method of mixing the graphene-based composite material with the conductive agent, the binder and the second organic solvent, as long as the graphene-based composite material, the conductive agent and the binder are fully dispersed in the second organic solvent to form a dispersed slurry. In the present invention, the method of mixing the graphene-based composite material, the conductive agent and the binder is preferably ultrasound; and the ultrasound time is preferably 2 hours.

[0073] After obtaining the mixed slurry, the present invention coats the mixed slurry on conductive paper and obtains a graphene-based composite electrode after drying.

[0074] In the present invention, the conductive paper is preferably graphite paper. In the present invention, the graphite paper is preferably commercially available conductive graphite paper cut into a suitable size and ultrasonically washed in acetone, ethanol or ultrapure water, and then dried for standby use. The present invention uses conductive paper to carry graphene-based composite materials, conductive agents and binders to form a composite electrode.

[0075] The present invention has no special restrictions on the method and coating amount of the mixed slurry on the conductive paper, as long as the weight of the mixed slurry on the conductive paper after drying reaches the required weight.

[0076] The preparation method provided by the present invention is simple to operate and can obtain a graphene-based composite electrode with high conductivity and adsorption capacity without high-temperature treatment. It can solve the problem of complex operation and increased uncertainty of electrode materials caused by the need for high-temperature treatment in the prior art to prepare porous structure electrodes.

[0077] The present invention also provides a graphene-based composite electrode prepared by the preparation method described in the above technical solution.

[0078] The graphene-based composite electrode prepared by the present invention has a three-dimensional network composite structure, the broken nano-crystalline carbon is evenly distributed in the three-dimensional network structure of the modified graphene, and has a multi-level pore structure.

[0079] The present invention also provides the application of the graphene-based composite electrode described in the above technical solution in seawater desalination.

[0080] In the present invention, the method for applying the graphene-based composite electrode in seawater desalination preferably comprises: assembling the graphene-based composite electrode into a CDI device, and then using the CDI device to desalinate seawater.

[0081] The present invention does not specifically limit the assembly method of the CDI device, and the assembly method of the CDI device well known to those skilled in the art can be used. In the present invention, the assembly method of the CDI device preferably includes: stacking and sealing a polytetrafluoroethylene plastic base plate, a rubber gasket, a graphene-based composite electrode and a plastic pressing sheet in sequence to obtain an anode of the CDI device; applying vaseline between the polytetrafluoroethylene plastic base plate, the rubber gasket, the graphene-based composite electrode and the plastic pressing sheet, and pressing a conductive copper sheet on the 2 o'clock direction of the graphene-based composite electrode; in the present invention, the CDI device adopts a symmetrical electrode design, and the cathode of the CDI device is assembled in the same way; a gauze spacer is added between the anode and the cathode and assembled and fixed with screws to obtain a CDI device.

[0082] Since the prepared graphene-based composite material has excellent electrical conductivity and adsorption capacity for sodium ions, the graphene-based composite electrode prepared by mixing the graphene-based composite material with a conductive agent, a binder and a second organic solvent and coating the mixed graphene-based composite electrode on conductive paper has excellent adsorption capacity for sodium ions when seawater is desalinated after being assembled into a CDI device. Therefore, when adsorbing in a low-concentration NaCl solution, the composite electrode has a higher electrical adsorption capacity and excellent adsorption.

[0083] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0084] Example 1

[0085] A method for preparing a graphene-based composite electrode, comprising the following steps:

[0086] (1) 0.3 g of graphene oxide (GO) was dispersed in 150 mL of organic solvent (DMF), and ultrasonicated for 6 h to obtain a GO dispersion. The GO dispersion was transferred to a round-bottom flask and heated to 120 °C. 1 g of an amino modifier (aminoacetaldehyde dimethyl acetal, referred to as ADMA) was dispersed in 10 mL of DMF to obtain an ADMA solution. The ADMA solution was placed in a constant pressure dropping funnel and dripped into the flask at a rate of 1 to 2 drops per second. The mixture was then stirred at 120 °C for 10 h to perform a covalent bond reaction. After the reaction was completed, the mixture was filtered and washed with a mixed solution of DMF and ethanol in a volume ratio of (1:1). The obtained solid was then dried in a vacuum oven at 60 °C for 24 h to obtain modified graphene, referred to as ADMA-GO. The mass ratio of GO to ADMA was 0.3:1.

[0087] The preparation method of GO is:

[0088] (a) Place a 500 mL clean beaker in a water bath, take 30 mL of concentrated sulfuric acid and place it in the beaker. Stir the solution with a stirring paddle and slowly add 10 g of P 2 O5 and 10gK 2 S 2 O 8 , slowly raise the temperature to 80°C to obtain a mixed solution;

[0089] (b) adding 20 g of natural graphite (400 mesh) to the mixed solution obtained in step (a), and after the liquid in the beaker becomes a black viscous substance, turning off the water bath heating, waiting for the temperature to cool to 30° C., washing the crude product with water, filtering under reduced pressure, and drying in a vacuum oven at 60° C. for 24 h to obtain pre-oxidized graphite;

[0090] (c) In an ice-water bath and under stirring, 20 g of the pre-oxidized graphite obtained in step (b) was added to 460 mL of concentrated sulfuric acid solution, and then 60 g of KMnO 4 , heat to 35°C, stir for 2h, add deionized water dropwise along the inner wall of the beaker until no white mist appears, then continue stirring for 15min, then add 3L deionized water, and then slowly add 100mL 30% hydrogen peroxide, the solution turns yellow, and naturally settle for 24h, pour out the supernatant, repeat 4 to 5 times, transfer the bottom precipitate to a dialysis bag and start a 30-day dialysis, dry the viscous substance, grind it in a mortar to obtain graphene oxide.

[0091] (2) 0.1000 g of the ADMA-GO obtained in step (1) and 0.9000 g of activated carbon (AC) powder were mixed, added to 15 mL of ethanol, ultrasonically composited at 180 W for 1 h in an ice water bath, and then naturally air-dried to obtain a graphene-based composite material, referred to as GMAC1; wherein the mass ratio of ADMA-GO to AC was 1:9;

[0092] The preparation method of AC is as follows: commercial activated carbon powder is ultrasonically dispersed in ultrapure water for 1 hour, the dispersion is transferred to a round-bottom flask, heated in an oil bath at 100°C, condensed and refluxed for 2 hours, then filtered and washed with ultrapure water, and dried in a vacuum oven at 60°C to obtain AC;

[0093] (3) 0.0800 g of the GMAC1 obtained in step (2), 0.0100 g of acetylene black and 0.0150 g of PTFE () solution (66 wt%) were mixed to obtain a mixture, ethanol was added to immerse the mixture, and then ultrasonicated for 2 h to obtain a mixed slurry; the mass ratio of the graphene-based composite material, the conductive agent and the binder was 8:1:1;

[0094] (4) Take a 60 mm × 60 mm graphite paper, cut out a 30 mm × 30 mm area, and evenly apply the mixed slurry obtained in step (3) on the working area of ​​the graphite paper, and then place it in an oven and dry it at 40° C. for 24 h to obtain a graphene-based composite electrode, referred to as GMAC1 composite electrode.

[0095] Example 2

[0096] A method for preparing a graphene-based composite electrode, which is different from that in Example 1, in that step (2) is: 0.2000 g of ADMA-GO obtained in step (1) and 0.8000 g of AC are mixed, added to 15 mL of ethanol, ultrasonically composited at 180 W for 1 h in an ice-water bath, and then naturally air-dried to obtain a graphene-based composite material, referred to as GMAC2; wherein the mass ratio of ADMA-GO to AC is 2:8; the remaining steps are the same as in Example 1, and the obtained graphene-based composite electrode is referred to as GMAC2 composite electrode.

[0097] Example 3

[0098] A method for preparing a graphene-based composite electrode, which is different from that in Example 1, in that step (2) is: 0.3000 g of the ADMA-GO obtained in step (1) and 0.7000 g of AC are mixed, added to 15 mL of ethanol, ultrasonically composited at 180 W for 1 h in an ice-water bath, and then naturally air-dried to obtain a graphene-based composite material, referred to as GMAC3; wherein the mass ratio of ADMA-GO to AC is 3:7; the remaining steps are the same as in Example 1, and the obtained graphene-based composite electrode is referred to as GMAC3 composite electrode.

[0099] Example 4

[0100] A method for preparing a graphene-based composite electrode, which is different from that in Example 1, in that step (2) is: 0.4000 g of ADMA-GO obtained in step (1) and 0.6000 g of AC are mixed, added to 15 mL of ethanol, ultrasonically composited at 180 W for 1 h in an ice-water bath, and then naturally air-dried to obtain a graphene-based composite material, referred to as GMAC4; wherein the mass ratio of ADMA-GO to AC is 4:6; the remaining steps are the same as in Example 1, and the obtained graphene-based composite electrode is referred to as GMAC4 composite electrode.

[0101] Example 5

[0102] A method for preparing a graphene-based composite electrode, which is different from that in Example 1, in that step (2) is: 0.5000 g of the ADMA-GO obtained in step (1) and 0.5000 g of AC are mixed, added to 15 mL of ethanol, ultrasonically composited at 180 W for 1 h in an ice-water bath, and then naturally air-dried to obtain a graphene-based composite material, referred to as GMAC5; wherein the mass ratio of ADMA-GO to AC is 5:5; the remaining steps are the same as in Example 1, and the obtained graphene-based composite electrode is referred to as GMAC5 composite electrode.

[0103] Comparative Example 1

[0104] A method for preparing a graphene-based composite electrode, comprising the following steps:

[0105] (1) Take 300 mg of GO, place it in a beaker, add 150 mL of DMF, and sonicate for 6 h to obtain a GO dispersion;

[0106] (2) 1 g of ADMA was ultrasonically dispersed in 10 mL of DMF, mixed with the GO dispersion in step (1), placed in a polytetrafluoroethylene reactor, and subjected to hydrothermal reaction at 120 °C for 10 h. After the reaction was completed, the obtained product was filtered and washed with DMF and ethanol, and dried in a vacuum oven at 60 °C for 24 h to obtain ADMA-GO;

[0107] (3) According to the steps (3) to (4) in Example 1, an ADMA-GO electrode was obtained.

[0108] Comparative Example 2

[0109] A method for preparing a graphene-based composite electrode, comprising the following steps:

[0110] (1) The commercially available activated carbon powder was ultrasonically dispersed in ultrapure water for 1 h, the dispersion was transferred to a round-bottom flask, heated in an oil bath at 100 °C, condensed and refluxed for 2 h, then filtered and washed with ultrapure water, and dried in a vacuum oven at 60 °C to obtain AC;

[0111] (2) 0.0800 g of the AC obtained in step (1), 0.0100 g of acetylene black and 0.0150 g of PTFE () solution (66 wt%) were mixed to obtain a mixture, ethanol was added to immerse the mixture, and then ultrasonicated for 2 h to obtain a mixed slurry; the mass ratio of the graphene-based composite material, the conductive agent and the binder was 8:1:1;

[0112] (3) Take a 60 mm × 60 mm graphite paper, cut out a 30 mm × 30 mm area, apply the mixed slurry obtained in step (2) to the working area of ​​the graphite paper, and then place it in an oven and dry it at 40° C. for 24 hours to obtain a graphene-based composite electrode, referred to as an AC composite electrode.

[0113] Application Example 1

[0114] Application of a graphene-based composite electrode in seawater desalination, the method comprising:

[0115] (1) Assembly of CDI device: A polytetrafluoroethylene plastic base plate, a rubber gasket, the GMAC1 composite electrode prepared in Example 1 and a plastic pressing sheet are stacked and sealed in sequence to obtain an anode of the CDI device; vaseline is applied between the polytetrafluoroethylene plastic base plate, the rubber gasket, the graphene-based composite electrode and the plastic pressing sheet, and a conductive copper sheet is pressed on the 2 o'clock direction of the GMAC1 composite electrode; the cathode of the CDI device is assembled in the same way; a gauze spacer is added between the anode and the cathode and assembled and fixed with screws to obtain a CDI device;

[0116] (2) At a voltage of 1.6 V, the CDI device assembled in step (1) was used to adsorb a NaCl solution with a concentration of 50 mg / L. Within 20 minutes, the electrosorption capacity (SAC) reached 17.89 mg / g.

[0117] Application Example 2

[0118] (1) The difference from Application Example 1 is that in step (1), the GMAC2 composite electrode prepared in Example 2 is used to assemble the CDI device;

[0119] (2) At a voltage of 1.6 V, the CDI device assembled in step (1) was used to adsorb a NaCl solution with a concentration of 50 mg / L. Within 20 minutes, the SAC reached 17.00 mg / g.

[0120] Application Example 3

[0121] (1) The difference from Application Example 1 is that in step (1), the GMAC3 composite electrode prepared in Example 3 is used to assemble the CDI device;

[0122] (2) At a voltage of 1.6 V, the CDI device assembled in step (1) was used to adsorb a NaCl solution with a concentration of 50 mg / L. Within 20 minutes, the SAC reached 15.61 mg / g.

[0123] Application Example 4

[0124] (1) is different from Application Example 1 in that the GMAC4 composite electrode prepared in Example 4 is used to assemble the CDI device in step (1);

[0125] (2) At a voltage of 1.6 V, the CDI device assembled in step (1) was used to adsorb a NaCl solution with a concentration of 50 mg / L. Within 20 minutes, the SAC reached 14.78 mg / g.

[0126] Application Example 5

[0127] (1) The difference from Application Example 1 is that in step (1), the GMAC5 composite electrode prepared in Example 5 is used to assemble the CDI device;

[0128] (2) At a voltage of 1.6 V, the CDI device assembled in step (1) was used to adsorb a NaCl solution with a concentration of 50 mg / L. Within 20 minutes, the SAC reached 9.2 mg / g.

[0129] Application Example 6

[0130] (1) Assembling a CDI device in the same manner as step (1) of Application Example 1;

[0131] (2) At a voltage of 1.2 V, the CDI device assembled in step (1) was used to adsorb a NaCl solution with a concentration of 50 mg / L. Within 20 minutes, the SAC reached 13.83 mg / g.

[0132] Application Example 7

[0133] (1) Assembling a CDI device in the same manner as step (1) of Application Example 1;

[0134] (2) At a voltage of 1.4 V, the CDI device assembled in step (1) was used to adsorb a NaCl solution with a concentration of 50 mg / L. Within 20 minutes, the SAC reached 15.14 mg / g.

[0135] Comparative application example 1

[0136] (1) The difference from Application Example 1 is that in step (1), the ADMA-GO electrode prepared in Comparative Example 1 is used to assemble the CDI device;

[0137] (2) At a voltage of 1.6 V, the CDI device assembled in step (1) was used to adsorb a NaCl solution with a concentration of 50 mg / L. Within 20 minutes, the SAC reached 7.05 mg / g.

[0138] Comparative Application Example 2

[0139] (1) The difference from Application Example 1 is that in step (1), the AC composite electrode prepared in Comparative Example 2 is used to assemble the CDI device;

[0140] (2) At a voltage of 1.6 V, the CDI device assembled in step (1) was used to adsorb a NaCl solution with a concentration of 50 mg / L. Within 20 minutes, the SAC reached 5.08 mg / g.

[0141] Comparative Application Example 3

[0142] (1) Assembling a CDI device in the same manner as step (1) of Application Example 1;

[0143] (2) At a voltage of 0.8 V, the CDI device assembled in step (1) was used to adsorb a NaCl solution with a concentration of 50 mg / L. Within 20 minutes, the SAC reached 4.61 mg / g.

[0144] Comparative Application Example 4

[0145] (1) Assembling a CDI device in the same manner as step (1) of Application Example 1;

[0146] (2) At a voltage of 1.0 V, the CDI device assembled in step (1) was used to adsorb a NaCl solution with a concentration of 50 mg / L. Within 20 minutes, the SAC reached 4.61 mg / g.

[0147] Comparative Application Example 5

[0148] (1) Assembling a CDI device in the same manner as step (1) of Application Example 1;

[0149] (2) At a voltage of 1.8 V, the CDI device assembled in step (1) was used to adsorb a NaCl solution with a concentration of 50 mg / L. Within 20 minutes, the SAC reached 8.03 mg / g.

[0150] Test Example 1

[0151] (1) GO, ADMA-GO and GMAC1 prepared in Example 1 were tested by scanning electron microscopy and transmission electron microscopy, respectively, and the SEM and TEM images were obtained as shown in the figure. Figure 1 As shown. Figure 1 In the figure, a and b are SEM images of GO at different magnifications, d and e are SEM images of ADMA-GO at different magnifications, g and h are SEM images of GMAC1 at different magnifications, c is TEM image of GO, f is TEM image of DMA-GO, and i is TEM image of GMAC1. Figure 1 As can be seen from a and b, GO exhibits a regular and smooth plane, which results in a limited specific surface area and pore size structure. This undesirable electro-adsorption structure is caused by graphene stacking. Figure 1 As can be seen from d and e, the GO modified by ADMA exhibits a sheet-like uncovered structure, which indicates that the molecules covalently bonded to the graphene have a certain supporting effect on its interlayer; Figure 1 As can be seen from graphs g and h, GMAC exhibits a morphology in which GO is tightly packed with AC particles. The co-filling of AC particles and graphene sheets leads to a larger specific surface area and more electrical adsorption sites. Figure 1 The dark cluster morphology in (i) indicates that AC is successfully bound to GO, and the light silk stretched film background shows that the aggregation of GO is effectively inhibited.

[0152] (2) The FT-IR spectra of ADMA used in the present invention and AC, GO, ADMA-GO and GMAC1 prepared in Example 1 are as follows: Figure 2 As shown. Figure 2 It can be seen that the infrared absorption peak of GO is distributed at 3324 cm -1 、1734cm -1 and 1050cm -1 , corresponding to -OH, -OC=O and COC functional groups, respectively. The appearance of these oxygen-containing functional groups indicates that GO was successfully synthesized from graphite; at 3300 cm -1 The broad peak near 3372 cm indicates the intermolecular hydrogen bonding between water molecules adsorbed by the material and carboxyl groups; for ADMA, 3372 cm -1 and 1542cm -1 The peak belongs to the stretching and bending vibration of NH bond at 2935cm -1 、1190cm-1 and 1050cm -1 The peaks at 1646 cm-1 indicate that the material contains CH, CN and COC bonds; the peaks at 1646 cm-1 for ADMA-GO -1 and 1373cm -1 There are absorption peaks, representing carbonyl and CN bonds, at 3194 cm -1 The broad peak and blue shift of carbonyl functional group indicate that the small molecule has been successfully loaded onto GO; ADMA is loaded onto GO mainly through the amination and nucleophilic addition reaction between the amino functional group and the carboxyl group and ether oxygen bond on GO. In addition, AC, ADMA-GO and GMAC1 all have the peaks at 1550cm -1 and 1050cm -1 The absorption peaks are shown, corresponding to the stretching vibration peaks of C=C and COC on the aromatic ring; GMAC1 is at 3418cm -1 2700~2000cm -1 The broad peaks near 1193 cm-1 are mainly generated by oxygen-rich functional groups and aromatic rings in AC; most importantly, GMAC1 -1 The CN peak derived from ADMA-GO is shown at 3300 cm -1 The blue-shifted hydroxyl peak at shows a blue-shifted hydroxyl peak, indicating the intermolecular forces between AC and ADMA-GO, such as intermolecular hydrogen bonds. This result proves the structural morphology of GMAC1 tightly surrounded by AC particles and provides a theoretical basis for constructing a three-dimensional porous structure.

[0153] (3) Raman spectra of AC, GO, ADMA-GO and GMAC1 prepared in Example 1 are shown in Figure 3 As shown. Figure 3 It can be seen that AC, GO, ADMA-GO and GMAC1 have -1 With 1580cm -1 There are absorption peaks at all locations, which correspond to the D (defect) peak and the G (graphic) peak. The D peak refers to the structural defect peak of the material, which to a certain extent represents the degree of chaotic defects in the material; the G peak represents the regular structure of the material, which is mainly manifested as the complete sp 2 Hybrid conjugated structure. Therefore, the ratio of D and G peak intensities (I D / I G ) can be used to compare the structural defects and flatness of materials. The larger the ratio, the more defects the material has. Figure 3 It can be seen that the I of GO D / I G The value is the smallest, which is 0.99, indicating that the surface of unmodified GO is very regular and orderly due to the π-π conjugated structure; the I D / IG The value is 1.18, which is due to the successful modification of small molecules, which makes the GO sheets open and increases the degree of defects in the material, which is conducive to the formation of electrical adsorption sites; the I D / I G The values ​​are 1.16 and 1.15 respectively, which indicates that the composite material GMAC1 forms more electrical adsorption sites, which is more conducive to the formation of an electrical double layer (EDL), and is an ideal electrode that can be used for capacitive deionization (CDI) applications.

[0154] (4) The XRD patterns of AC, GO, ADMA-GO and GMAC1 prepared in Example 1 are shown in Figure 4 As shown. Figure 4 It can be seen that the curve of GO is a typical hydration characteristic line: 2θ=10°, representing the successful synthesis of GO; other samples have absorption peaks at 2θ=26°, which is the (002) characteristic peak of carbon; in addition, ADMA-GO shows a shifted diffraction peak of GO at 2θ=14°, which represents the successful modification of the material; GMAC1 and AC show diffraction peaks at 2θ=44°, which is the (101) characteristic peak of carbon and is a disordered structure.

[0155] (5) The molecular structure, atomic valence, elemental composition and content of GO and ADMA-GO prepared in Example 1 were analyzed by XPS. Figure 5 As shown. Figure 5 a It can be seen that the peaks at 284.5eV and 532.5eV are derived from the C1s orbital and the O1s orbital. The new peak at 398.5eV is attributed to N1s, proving the successful functionalization of GO and the successful doping of N. Figure 5 As shown in Figure 2b, the C 1s peak can be divided into four small peaks, namely 284.2 eV for CC / C=C bond, 284.8 eV for C-OH bond, 286.2 eV for COC and 288.4 eV for C(O)-O. Figure 5 As shown in Figure c, compared with GO, two new peaks of C 1s at 285.5 eV and 287.8 eV can be separated on ADMA-GO, corresponding to CN and -NC=O bonds, respectively. The disappearance of the C(O)-O bond at 288.4 eV means that the amino group of ADMA forms a new chemical bond with the carboxyl group of GO. Figure 5 d is the peak of N1s, which can be divided into three peaks at 399.3 eV, 400.3 eV and 401.7 eV, corresponding to CN, NC(O) and C-NH 3+ This indicates that ADMA is successfully modified onto GO through nucleophilic addition reaction, amidation reaction and electrostatic self-assembly process, which is consistent with Figure 4 The analysis of the FT-IR spectrum corresponds to that of the

[0156] (6) The nitrogen adsorption / desorption curves of AC, ADMA-GO and GMAC1 prepared in Example 1 were obtained by nitrogen adsorption-desorption experiment. Figure 6 As shown, the pore size distribution curves of AC, ADMA-GO and GMAC1 prepared in Example 1 are as follows Figure 7 As shown. Figure 6 It can be seen that the adsorption and desorption isotherms of AC show the largest N 2 Absorption capacity, thanks to its large specific surface area (749.81m 2 / g), which is a typical type I adsorption isotherm, indicating that there are many microporous structures on AC; ADMA-GO and GMAC1 both show type IV adsorption isotherms, indicating that they have obvious mesoporous structures. 0 When the adsorption isotherm of GMAC1 is >0.7, it shows a more obvious rise than other materials, and an H3 hysteresis loop appears in the intermediate pressure range, indicating that the composite material has a richer and unique pore structure. Figure 7 It can be seen that according to the theoretical calculation of the Barret-Joyner-Halenda (BJH) model, GMAC1 has a wider pore size distribution in the mesoporous range, mainly distributed at 7.89nm and 15.02nm, which indicates that new pores appeared in the composite material after AC and ADMA-GO were treated with ultrasound in water. The addition of more mesoporous structures can promote the transmission of ions between GMAC and electrolyte in the electrode material. Compared with AC, ADMA-GO has a smaller specific surface area (33.01m 2 / g, AC is 749.81m 2 / g, and the pore volume is also smaller (0.0562cm 3 / g, AC is 0.2410cm 3 / g). However, the electrochemical activity of ADMA-GO, such as specific capacitance and CDI performance, is much higher than that of AC. The main reasons are as follows: (1) ADMA-GO has a suitable mesoporous structure (3.26 nm), which can accelerate the Na + and Cl - The transport of hydrated ions is and ); In addition, nitrogen doping also improves its electrochemical performance during electrosorption (2) AC has a larger specific surface area and pore volume, but its microporous structure (1.55nm) hinders the transport and storage of ions, and a common ion effect will occur over time. The underutilized internal space limits the formation of EDL active sites and leads to poor salt adsorption capacity. Similarly, GMAC1 has a larger specific surface area (269.20m 2 / g), pore volume (0.3069cm3 / g) and mesoporous structure (3.03 nm) and can be an optimized electrode for electroselectivity.

[0157] (7) The conductivity change curve of ADMA-GO prepared in Example 1 under different voltages is shown in Figure 8 As shown. Figure 8 It can be seen that all curves within 0 to 10 minutes present a straight line. This is because all materials have a certain physical adsorption effect on the salt ion solution in the environment of solution circulation. This process is different from electrosorption. It is an irreversible process, so we need to experience a physical adsorption platform before all electrode materials are powered on to ensure the accuracy of the electrosorption process. As the applied voltage increases from 0.8V to 1.6V, the smooth conductivity change curve shows that the value of the decrease in the conductivity of the solution within 40min is getting larger and larger, which indicates that within this voltage range, the EDL of the material is formed more fully, the number of electrosorption sites increases, and the salt adsorption capacity increases. When the voltage changes to 1.8V, the conductivity curve shows an upward trend at about 20min, and then becomes stable and no longer decreases, which indicates that other side reactions occur under this voltage condition, generating additional Faraday current, reducing the charge utilization efficiency of the CDI process, so 1.6V can be used as the optimal working voltage for this electrode material and its derivative composite material.

[0158] The conductivity change curves of AC, ADMA-GO and GMAC1, GMAC2, GMAC3, GMAC4 and GMAC5 prepared in Example 1 at a voltage of 1.6 V are shown in FIG. Fig. 9 As shown. Fig. 9 It can be seen that the CDI adsorption curves of NaCl for all materials under the same conditions show the same trend. They all first experience a 10-minute physical adsorption platform and then apply voltage to start the electrical adsorption process. The decrease in conductivity at the end and the instantaneous slope of the curve reflect the electrical adsorption capacity and adsorption rate of the material, respectively. GMAC1 material has the best electrical adsorption characteristics.

[0159] It can be seen from the above experimental results that the present invention adopts the method of organic covalent modification to obtain a modified graphene hybrid functional material with enhanced electrical adsorption performance. The raw materials used in this method are cheap and easy to obtain, the method is simple and convenient, and the prepared electrode material has excellent adsorption performance. When adsorbed in a relatively low concentration NaCl solution, the SAC can reach 17.89 mg / g, which has excellent adsorption.

[0160] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a graphene-based composite electrode, The following steps are involved: (1) mixing graphene oxide, an amino modifier and a first organic solvent to perform a covalent bond reaction to obtain modified graphene; (2) mixing the modified graphene obtained in step (1) with activated carbon powder and a solvent and then subjecting the mixture to ultrasonic compounding to obtain a graphene-based composite material; (3) mixing the graphene-based composite material obtained in step (2) with a conductive agent, a binder and a second organic solvent to obtain a mixed slurry; (4) coating the mixed slurry obtained in step (3) on conductive paper, and obtaining a graphene-based composite electrode after drying; The mass ratio of the modified graphene to the activated carbon powder in the step (2) is (1-5):(5-9); The ultrasonic power of the ultrasonic compound in the step (2) is 100 to 200 W, and the ultrasonic time of the ultrasonic compound is 1 to 3 hours.

2. The method for preparing a graphene-based composite electrode according to claim 1, It is characterized in that The amino modifier in step (1) includes aminoacetaldehyde dimethyl acetal, aminoacetaldehyde diethyl acetal, 2-amino-1,3-propanediol or 3-aminoglutaric acid.

3. The method for preparing a graphene-based composite electrode according to claim 1, It is characterized in that The mass ratio of graphene oxide to amino modifier in step (1) is (0.1-0.5):(0.5-1).

4. The method for preparing a graphene-based composite electrode according to claim 1, It is characterized in that The temperature of the covalent bond reaction in step (1) is 90 to 130° C.; the time of the covalent bond reaction is 10 to 15 hours.

5. The method for preparing a graphene-based composite electrode according to claim 1, It is characterized in that The conductive agent in step (3) includes one or more of acetylene black, conductive carbon black, conductive graphite and Ketjen black.

6. The method for preparing a graphene-based composite electrode according to claim 1 or 5, It is characterized in that The mass ratio of the graphene-based composite material, the conductive agent and the binder in the step (3) is (5-8):1:(1-4).

7. A graphene-based composite electrode prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the graphene-based composite electrode according to claim 7 in seawater desalination.

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