CN114105127A

CN114105127A - Method for preparing graphene

Info

Publication number: CN114105127A
Application number: CN202210034039.XA
Authority: CN
Inventors: 杨盛贤
Original assignee: Qujing Huajin Rainforest Technology Co ltd
Current assignee: Qujing Huajin Rainforest Technology Co ltd
Priority date: 2022-01-14
Filing date: 2022-01-14
Publication date: 2022-03-01

Abstract

The invention discloses a method for preparing graphene, and belongs to the technical field of nano materials. The reduction degree of the graphene is not good enough, the dispersion is difficult, the purification is difficult, and the application of the graphene is limited. According to the method, firstly, the graphene oxide is subjected to chemical reduction, most of oxygen-containing functional groups are removed, and then the residual oxygen-containing functional groups are further reduced by electrochemical reduction, so that the reduction degree of the graphene is improved. And then, adding a dispersing agent to react with the electrochemically reduced graphene solution, and dispersing and maintaining the graphene by using a reaction product, so that the agglomeration of the graphene is avoided, and the graphene is uniformly dispersed in the solution. And finally, filtering through different solvents to remove various impurities, and uniformly dispersing the graphene in various inorganic solvents and organic solvents. The method has the advantages of simple process, high repeatability and application and popularization possibility.

Description

Method for preparing graphene

Technical Field

The invention belongs to the technical field of new material preparation, and particularly provides a method for preparing graphene.

Background

Graphene is a single-layer two-dimensional material consisting of close packing of carbon atoms. The carbon atom having 4 valence electrons, 3 of which are sp²Hybridization forms sigma bond, and the 4 th un-bonded electron forms pi bond with the plane through the sigma bond and other three carbon atoms connected into a hexagonal structure. Based on a unique crystal structure, graphene has excellent optical, thermal, electrical, magnetic and mechanical properties, such as super-strong mechanical properties, extremely high carrier mobility, extremely high heat conductivity, good electromagnetic shielding performance, good optical properties and the like. Although graphene has many excellent properties, three main difficulties have hindered the scaling of grapheneApplication is carried out. The first difficulty is how to improve the reduction degree of graphene; secondly, how to uniformly disperse the graphene in the solvent; and the difficulty is three, how to purify the prepared graphene.

At present, the graphene oxide is usually produced in a large scale by an oxidation graphite method, and then the graphene oxide is reduced to obtain the graphene. The graphene reduced by the chemical reagent can only remove part of oxygen-containing functional groups, recover part of structures and part of performances, and has poor reduction effect.

The reason why the graphene is difficult to disperse in the solvent is that pi-pi interaction between carbon atoms and van der waals interaction between sheets make the graphene easily agglomerated and difficult to disperse, which is an inherent property of the graphene. Pure graphene is prone to agglomeration, resulting in significant reduction or even disappearance of many of the properties that are excellent at the nanoscale as graphene lamellae are agglomerated. Due to the hydrophobic and oleophobic characteristics of the graphene, the graphene cannot be dispersed in water, cannot be widely dispersed in various organic solvents, and can be only dispersed in a part of organic solvents in a small amount and unstably, so that the application is greatly limited. Therefore, the research and development of the uniformly dispersed graphene solution have important significance and are important conditions for promoting the application and development of graphene.

A large amount of impurities can be introduced in the preparation process of the graphene, the quality of the graphene can be reduced by the residual impurities, the application of the graphene is seriously influenced, and the difficulty in purification is always a great difficulty in hindering the application of the graphene. When graphene is prepared, graphene oxide is usually produced by using reagents such as graphite powder, sulfuric acid, nitrate, chlorate, potassium permanganate, hydrochloric acid, phosphoric acid and the like, and the graphene oxide is reduced to obtain graphene, so that impurity elements such as sodium, potassium, manganese, sulfur, nitrogen, chlorine, phosphorus and the like and a large amount of residual reducing agents are inevitably introduced into the graphene. Many downstream applications have high requirements on the purity of graphene, and the impurity content in graphene needs to be strictly controlled, so that purification is very important.

Most of the existing purification modes are purification in the production stage of graphene oxide through dialysis, centrifugation, suction filtration, precipitation and other modes. However, these processes all suffer from various disadvantages including: high cost, long time, poor effect, complex equipment, high content of residual impurities and the like. The removal of impurities in graphene is very difficult in the industry, and no effective method is available at present, which is an important difficulty in restricting the preparation and application of graphene. Therefore, on the basis of the prior art, a person skilled in the art needs to research an efficient, convenient and low-cost method, and the following three points are achieved simultaneously in the process of preparing graphene: (1) the reduction degree of the graphene is improved; (2) various impurities in the graphene are removed efficiently; (3) so that the graphene is uniformly dispersed in various solutions.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to provide a method for preparing graphene, which has better reduction effect, can efficiently and quickly remove various impurities and uniformly disperse graphene in various solvents.

The specific operation principle of the present invention is as follows.

The principle of the invention for improving the reduction degree of graphene is as follows: after chemical reduction, partial oxygen-containing functional groups remain on the surface of the graphene. And then reducing by using an electrochemical reaction, obtaining electrons from the residual oxygen-containing functional groups on the cathode to separate from the graphene, and further reducing the graphene. The reduction degree of the graphene can be controlled and the structural defects can be regulated and controlled by controlling the voltage, the current and the reduction time. Therefore, the reduction degree of the graphene can be improved by combining chemical reduction and electrochemical reduction.

The principle of uniformly dispersing graphene in the solution is as follows: (1) after electrochemical reduction, unreacted reducing agents, chemical reduction products, electrochemical reduction products and other small molecules are adsorbed on the surface of the graphene through the interaction of hydrogen bonds, van der waals force, intermolecular force and the like, so that the agglomeration of the graphene is avoided, the graphene is uniformly dispersed in a solution, and the common small molecules are as follows: ascorbic acid, dehydroascorbic acid, oxalic acid, glucose; (2) when the electrolyte contains water and the voltage applied by the electrochemical reaction exceeds the electrochemical stability window voltage of the water, hydrogen is generated on the cathode and is adsorbed on the surface of the graphene after the hydrogen is generated, so that the agglomeration of the graphene is avoided and the graphene is uniformly dispersed in the solution; (3) after chemical and electrochemical reduction, a dispersing agent is added into the graphene solution, the dispersing agent reacts with unreacted reducing agent, a chemical reduction product and an electrochemical reaction product to generate gas, and the generated gas is adsorbed on the surface of the graphene, so that the agglomeration of the graphene is avoided, and the graphene is uniformly dispersed in the solution. The gas generated by the invention is one or the mixture of two gases as follows: oxygen, carbon dioxide; (4) after various small molecules adsorbed on the surface of the graphene react with the dispersing agent, the adsorption is desorbed from the surface of the graphene and dissolved in the solution, and the adsorption is replaced by gas. After the dispersing agent is added, the substances for keeping the graphene uniformly dispersed are changed into gas from various small molecules.

The principle of removing impurities in the graphene solution is as follows: the gas adsorbed on the surface keeps the dispersion of the graphene, the solvent can smoothly flow through the graphene interlayer, and various impurities in the solution are taken away during filtering, so that pure graphene uniformly dispersed in the solution is obtained. The impurities removed include: (1) impurities contained in the graphite powder; (2) sodium, potassium, manganese, sulfur, nitrogen, chlorine, phosphorus and other impurity elements are introduced by sulfuric acid, nitrate, chlorate, potassium permanganate, hydrochloric acid, phosphoric acid and other reagents used in the preparation of graphene oxide; (3) unreacted reducing agent, chemical reduction products, electrochemical reduction products. The method is simple, rapid and efficient, and is beneficial to reducing the production cost of the graphene.

The principle that the graphene can be uniformly dispersed in different solvents is as follows: and (3) uniformly dispersing the graphene solution in the first solvent by utilizing the intersolubility of the solvents, and replacing by using a second solvent to obtain the graphene solution uniformly dispersed in the second solvent.

The principle that the concentration of the graphene solution can be adjusted is as follows: for the graphene solution which is uniformly dispersed, a certain amount of solvent is newly added, or the redundant solvent is removed by filtration, so that the concentration of the graphene solution can be conveniently adjusted. Wherein the concentration of the single-layer graphene solution is generally 0.1 mg/mL to 10 mg/mL, the concentration of the few-layer graphene solution is generally 1 mg/mL to 20 mg/mL, and the concentration of the multi-layer graphene solution is generally 5mg/mL to 200 mg/mL. By measuring the concentration of the graphene solution, it can be seen that the dispersion uniformity of graphene in the solvent is good.

The invention is realized by the following technical scheme, which comprises the following steps:

firstly, mixing a graphene oxide solution with a reducing agent and then reacting to obtain a chemically reduced graphene solution;

secondly, placing the graphene solution subjected to chemical reduction into an electrolytic cell, and further reducing the graphene solution by utilizing an electrochemical reaction to improve the reduction degree of the graphene so as to obtain the graphene solution subjected to electrochemical reduction;

thirdly, adding a dispersing agent into the graphene solution subjected to electrochemical reduction, mixing and reacting to obtain a uniformly dispersed graphene solution;

and fourthly, adding the uniformly dispersed graphene solution into a solvent, filtering, and removing impurities in the graphene solution to obtain the graphene solution uniformly dispersed in the solvent, wherein the solvent is an inorganic solvent or an organic solvent.

Preferably, the first step is to prepare graphene oxide using a prior art publication, which includes: chemical oxidation, electrochemical stripping, and the like.

Preferably, the concentration of the graphene oxide solution in the first step is 0.05-50 mg/mL, and is usually 0.05 mg/mL, 0.1 mg/mL, 0.2 mg/mL, 0.5 mg/mL, 1 mg/mL, 2 mg/mL, 5 mg/mL.

Preferably, the graphene oxide in the first step is used in a mixture of one or more of the following: single-layer graphene oxide, few-layer graphene oxide and multilayer graphene oxide.

Preferably, the solvent for the reaction in the first step is an inorganic solvent and an organic solvent. The solvent is one or more of water, acid solution, alkali solution, salt solution, hydrocarbon solvent, alcohol solvent, ether solvent, amide solvent, ketone solvent, ester solvent, phenol solvent, and nitrile solvent.

Preferably, the reducing agent in the first step is a mixture of one or more of: organic acid, borohydride, citrate, ascorbate, hydrohalic acid, alcohol, sugar, amino acid, sulfur-containing reducing agent, nitrogen-containing reducing agent, and reducing plant extract. The organic acids include: ascorbic acid, oxalic acid, gallic acid, citric acid, tannic acid, tartaric acid, formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, oxalic acid, malonic acid, succinic acid, adipic acid, maleic acid, benzoic acid, phenylacetic acid, phthalic acid, terephthalic acid, fatty acid, acrylic acid, trifluoroacetic acid, dehydroascorbic acid, gulonic acid, threonic acid; the borohydride includes: lithium borohydride, sodium borohydride, potassium borohydride, rubidium borohydride, aluminum borohydride, beryllium borohydride, calcium borohydride, zinc borohydride, magnesium borohydride, cesium borohydride, strontium borohydride, barium borohydride, cuprous borohydride, titanium borohydride, zirconium borohydride, yttrium borohydride, manganese borohydride, iron borohydride, nickel borohydride, and borane borohydride; the citrate salt comprises: lithium citrate, sodium citrate, potassium citrate, calcium citrate, magnesium citrate, copper citrate, nickel citrate; the ascorbate comprises: lithium ascorbate, sodium ascorbate, potassium ascorbate, magnesium ascorbate, calcium ascorbate, and iron ascorbate; the halogen acid comprises: hydrofluoric acid, hydroiodic acid, hydrobromic acid, hydrochloric acid; alcohols include: methanol, benzyl alcohol, ethanol, ethylene glycol, propanol, isopropanol, butanol, sorbitol; the saccharides include: monosaccharides (glucose, fructose, galactose), disaccharides (sucrose, lactose, maltose), oligosaccharides (cyclodextrin), polysaccharides (chitosan); the amino acids include: l-cysteine, L-glutathione; the sulfur-containing reducing agent comprises: thiourea, thiourea dioxide, ethanethiol and thiophene; nitrogenous reducing agents include: ammonia, hydrazine (hydrazine), hydrazine hydrate (hydrazine hydrate), phenylhydrazine, nitrite, urea, hydroxylamine hydrochloride, pyrrole, pyridine, benzylamine, p-phenylenediamine, ethylenediamine, dimethylketoxime; the reducing plant extract comprises: tea extract, rose extract, folium aconiti szechenyiani extract, orange peel extract, and ginkgo leaf extract.

Preferably, the mass ratio of the graphene oxide to the reducing agent in the first step is 1: (1-200), wherein the common mass ratio is 1: 5. 1: 7.5, 1: 10. 1: 15. 1: 20. 1: 25. 1: 30. 1: 35. 1: 40.

preferably, the chemical reduction reaction in the first step needs stirring, and the stirring speed is 0-3000 r/min. The usual rotational speeds are: 0 r/min (standing), 10 r/min, 20 r/min, 30 r/min, 40 r/min, 50 r/min, 60 r/min, 70 r/min, 80 r/min, 90 r/min, 100 r/min, 110 r/min, 120 r/min, 130 r/min, 140 r/min, 150 r/min, 180 r/min, 200 r/min, 240 r/min, 300 r/min, 500 r/min, 600 r/min, 700 r/min, 800 r/min, 900 r/min, 1000 r/min.

Preferably, the chemical reduction reaction time in the first step is 0 to 120 hours. It is usually 0 hour (i.e., electrochemical reduction reaction is carried out immediately after addition of the reducing agent), 5 minutes, 10 minutes, 30 minutes, 60 minutes, 90 minutes, 2 hours, 4 hours, 6 hours, 10 hours, 12 hours, 24 hours, 36 hours, 48 hours, 72 hours, 96 hours, 120 hours.

Preferably, the chemical reduction reaction temperature in the first step is-10 ℃ to 100 ℃, and the chemical reduction reaction temperature is commonly-5 ℃, 0 ℃, 5 ℃, 10 ℃, 15 ℃, 20 ℃, 25 ℃, 50 ℃, 85 ℃, 90 ℃ and 95 ℃.

Preferably, the chemical reduction reaction in the first step can adjust related parameters of reducing agent species, reducing agent quality, stirring speed, reaction time and reaction temperature in the experimental process.

Preferably, the electrolyte used in the electrochemical reduction reaction in the second step is an aqueous electrolyte or a non-aqueous electrolyte, the pH is between 0 and 14, and the common pH values are 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11.

Preferably, the electrolyte used in the electrochemical reduction reaction in the second step should be an acid, a base, a salt with chemical and electrochemical stability, in a mixture of one or more of the following: organic acid, inorganic acid, organic salt, inorganic salt and inorganic base. Common organic acids include: ascorbic acid, oxalic acid, gallic acid, citric acid, tannic acid, tartaric acid, formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, oxalic acid, malonic acid, succinic acid, adipic acid, maleic acid, benzoic acid, phenylacetic acid, phthalic acid, terephthalic acid, fatty acid, acrylic acid, trifluoroacetic acid, dehydroascorbic acid, gulonic acid, threonic acid; common inorganic acids include: sulfuric acid, hydrofluoric acid, hydroiodic acid, hydrobromic acid, hydrochloric acid, phosphoric acid, nitric acid, carbonic acid; common organic salts include: lithium citrate, sodium citrate, potassium citrate, calcium citrate, magnesium citrate, copper citrate, nickel citrate, lithium ascorbate, sodium ascorbate, potassium ascorbate, magnesium ascorbate, calcium ascorbate, and ferric ascorbate; common inorganic salts include: lithium sulfate, sodium sulfate, magnesium sulfate, aluminum sulfate, potassium sulfate, lithium nitrate, sodium nitrate, magnesium nitrate, aluminum nitrate, potassium nitrate, lithium chloride, sodium chloride, magnesium chloride, aluminum chloride, potassium chloride, lithium borohydride, sodium borohydride, potassium borohydride, lithium carbonate, sodium carbonate, potassium carbonate, ammonium carbonate, lithium bicarbonate, sodium bicarbonate, potassium bicarbonate, magnesium bicarbonate, ammonium bicarbonate; the inorganic base includes: lithium hydroxide, sodium hydroxide, potassium hydroxide and ammonia water.

Preferably, the electrolyte used in the electrochemical reduction reaction in the second step further comprises a reducing agent used in the chemical reduction in the first step and oxidation products thereof. After the reducing agent reacts with the graphene oxide, the graphene oxide is oxidized to generate a new product, and the oxidized product and the unreacted reducing agent are dissolved in the solution and are also components of the electrolyte.

Preferably, the concentration of the electrolyte in the electrochemical reduction reaction solution in the second step is 0.05-10.00 mol/L, and the commonly used concentrations are 0.1 mol/L, 0.15 mol/L, 0.2 mol/L, 0.25 mol/L, 0.3 mol/L, 0.35 mol/L, 0.4 mol/L, 0.45 mol/L and 0.5 mol/L.

Preferably, the electrode material used in the electrochemical reduction reaction in the second step is chemically and electrochemically stable metal and alloy or non-metal conductor material, and commonly used materials are platinum, gold, silver, copper, nickel, titanium, lead, copper alloy, titanium alloy, nickel alloy, lead alloy and graphite.

Preferably, the electrochemical reduction reaction in the second step uses a constant voltage power supply, wherein the constant voltage interval is 1-40V, and the common constant voltage is 1.2V, 1.3V, 1.4V, 1.5V, 1.6V, 1.7V, 1.8V, 1.9V, 2V, 2.5V, 3V, 3.5V, 4V, 4.5V, 5V, 6V, 7V, 8V, 9V, 10V, 12V, 15V, 18V, 20V, 25V, 30V.

Preferably, the duration of the electrochemical reduction reaction in the second step is 10 seconds to 48 hours. It is usually 10 seconds, 1 minute, 2 minutes, 5 minutes, 10 minutes, 30 minutes, 60 minutes, 90 minutes, 2 hours, 3 hours, 6 hours, 12 hours, 18 hours, 24 hours, 36 hours.

Preferably, the electrochemical reduction reaction in the second step requires stirring, the stirring speed is 0-3000 r/min, and the common speed is: 0 r/min (standing), 10 r/min, 20 r/min, 30 r/min, 40 r/min, 50 r/min, 60 r/min, 70 r/min, 80 r/min, 90 r/min, 100 r/min, 110 r/min, 120 r/min, 130 r/min, 140 r/min, 150 r/min, 180 r/min, 200 r/min, 240 r/min, 300 r/min, 500 r/min, 600 r/min, 700 r/min, 800 r/min, 900 r/min, 1000 r/min.

Preferably, the electrochemical reduction reaction temperature in the second step is-10 ℃ to 90 ℃, and the electrochemical reduction reaction temperature is commonly-5 ℃, 0 ℃, 5 ℃, 10 ℃, 15 ℃, 20 ℃, 25 ℃, 30 ℃, 35 ℃, 40 ℃, 45 ℃, 50 ℃, 80 ℃, 85 ℃ and 90 ℃.

Preferably, in the electrochemical reduction reaction in the second step, a diaphragm is used in the electrolytic cell, and the diaphragm is one or more of the following: cation exchange membrane, anion exchange membrane, proton exchange membrane. The diaphragm separates the cathode from the anode region of the cell, preventing the electrolysis products from contacting and chemically reacting. The graphene solution is positioned on one side of the cathode, and the graphene solution is separated from the anode by the diaphragm.

Preferably, the electrochemical reduction reaction in the second step can adjust the relevant parameters of pH value, electrolyte type, electrolyte concentration, reaction voltage, reaction time, stirring speed and reaction temperature in the experimental process.

Preferably, in the third step, the dispersant is one of peroxide, percarbonate, persulfate, permanganate and permanganate, ferrate and ferrate, chlorate, carbonate and bicarbonate, or a mixture of two or more of these agents. The peroxide comprises: hydrogen peroxide, lithium peroxide, sodium peroxide, potassium peroxide, calcium peroxide, magnesium peroxide, zinc peroxide, strontium peroxide, barium peroxide and organic peroxide; percarbonates include: lithium percarbonate, sodium percarbonate, potassium percarbonate, ammonium percarbonate, calcium percarbonate, aluminum percarbonate, magnesium percarbonate; permanganic acid and permanganate include: permanganic acid, lithium permanganate, sodium permanganate, potassium permanganate, ammonium permanganate, calcium permanganate, zinc permanganate and magnesium permanganate; ferrate and ferrate include: ferrate, lithium ferrate, sodium ferrate, potassium ferrate; persulfates include: lithium persulfate, sodium persulfate, potassium persulfate and ammonium persulfate; chloric acid and chlorate salts include: perchloric acid, chloric acid, chlorous acid, hypochlorous acid, lithium perchlorate, sodium perchlorate, potassium perchlorate, magnesium perchlorate, ammonium perchlorate, lithium chlorate, sodium chlorate, potassium chlorate, magnesium chlorate, ammonium chlorate, lithium chlorite, sodium chlorite, potassium chlorite, magnesium chlorite, ammonium chlorite, lithium hypochlorite, sodium hypochlorite, potassium hypochlorite, magnesium hypochlorite, ammonium hypochlorite, chlorine dioxide; the carbonate includes: lithium carbonate, sodium carbonate, potassium carbonate, ammonium carbonate, calcium carbonate, magnesium carbonate, aluminum carbonate, iron carbonate, copper carbonate, silver carbonate; the bicarbonate includes: lithium bicarbonate, sodium bicarbonate, potassium bicarbonate, magnesium bicarbonate, calcium bicarbonate, barium bicarbonate and ammonium bicarbonate.

Preferably, the reaction in the third step needs stirring, the stirring speed is 0-3000 r/min, usually 0 r/min (standing), 10 r/min, 20 r/min, 30 r/min, 40 r/min, 50 r/min, 60 r/min, 70 r/min, 80 r/min, 90 r/min, 100 r/min, 110 r/min, 120 r/min, 130 r/min, 140 r/min, 150 r/min, 180 r/min, 200 r/min, 240 r/min, 300 r/min, 500 r/min, 600 r/min, 700 r/min, 800 r/min, 900 r/min, 1000 r/min.

Preferably, the reaction in the third step needs stirring, the stirring speed is 0-3000 r/min, and the stirring speed is usually 0 r/min (namely standing), 10 r/min, 20 r/min, 30 r/min, 60 r/min, 100 r/min, 150 r/min, 200 r/min, 300 r/min, 500 r/min, 800 r/min and 1000 r/min.

Preferably, the reaction time in the third step is 1 minute to 120 hours, and 5 minutes, 10 minutes, 30 minutes, 60 minutes, 90 minutes, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 12 hours, 18 hours, 24 hours, 36 hours, 48 hours, 72 hours, 96 hours, 120 hours are commonly used.

Preferably, the reaction temperature in the third step is-10 ℃ to 90 ℃, and the reaction temperature is commonly-5 ℃, 0 ℃, 5 ℃, 10 ℃, 15 ℃, 20 ℃, 25 ℃, 30 ℃, 35 ℃ and 40 ℃.

Preferably, the dispersant in the third step is capable of reacting with the reduced graphene oxide solution containing impurities, and the reaction product contains gas, and the gas is one or a mixture of two of the following: oxygen and carbon dioxide react together to form soluble products. Gas generated by the reaction is adsorbed on the surface of the graphene, so that the agglomeration of the graphene is avoided, and the graphene is uniformly dispersed in the solution. The first commonly used is ascorbic acid as the reducing agent and hydrogen peroxide as the dispersing agent, the products being: oxygen, water, dehydroascorbic acid, diketogulonic acid, oxalic acid, threonic acid; in a second common use, the reducing agent is ascorbic acid, the dispersing agent is sodium percarbonate, and the compositions are: oxygen, carbon dioxide, water, dehydroascorbic acid, diketogulonic acid, threonic acid, oxalic acid, sodium oxalate, carbonic acid, sodium carbonate; the third is commonly used: the reducing agent is ascorbic acid, the dispersing agent is hydrogen peroxide and sodium carbonate, and the composition comprises: oxygen, carbon dioxide, water, dehydroascorbic acid, diketogulonic acid, threonic acid, oxalic acid, sodium oxalate, carbonic acid; the fourth is commonly used: the reducing agent is ascorbic acid, the dispersing agent is sodium carbonate, and the composition comprises the following components: carbon dioxide, water, sodium ascorbate, oxalic acid, sodium oxalate and carbonic acid.

Preferably, the reaction in the third step can adjust related parameters of the type of the dispersing agent, the quality of the dispersing agent, the stirring speed, the reaction time and the reaction temperature in the experimental process.

Preferably, the filtering device in the fourth step uses a filtering net, the number of the filtering net is 10-5000 meshes, and 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800 and 1000 meshes are commonly used according to different sheet diameters and layer numbers of graphene.

Preferably, the filtering in the fourth step removes impurities in the graphene solution, the removal of impurities being marked by an impurity content of the filtrate being equal to an impurity content of the filtration solvent.

Preferably, the filtration in the fourth step may be carried out with only one solvent or sequentially with a plurality of solvents. By utilizing the intersolubility of solvents, graphene uniformly dispersed in one solvent is fully replaced by different solvents in sequence and uniformly dispersed in other solvents to obtain graphene solutions uniformly dispersed in different solvents in sequence. The solvent used is one or more of the following: water, peroxide solution, acid solution, alkali solution, salt solution, hydrocarbon solvent, alcohol solvent, ether solvent, amide solvent, ketone solvent, ester solvent, phenol solvent and nitrile solvent. Commonly used are: water, hydrogen peroxide solution, methanol, ethanol, propanol, butanol, pentanol, ethylene glycol, polyethylene glycol, acetone, N-dimethylformamide, N-dimethylacetamide, N-methylpyrrolidone, gasoline, kerosene, turpentine, dimethyl carbonate, dipropyl carbonate, tetrahydrofuran, diethyl ether, benzene, toluene, xylene, dimethyl sulfoxide, acetonitrile, methyl acetate, ethyl acetate, propyl acetate, methyl chloride, dichloromethane, trichloromethane, tetrachloromethane, pentane, hexane, N-hexane, octane, petroleum ether, petroleum spirit, formic acid, acetic acid, anisole, methyl formate, ethyl formate, diesel oil, peanut oil, soybean oil, rapeseed oil, olive oil, rapeseed oil, dilute hydrochloric acid, dilute sulfuric acid, dilute nitric acid, lithium hydroxide solution, sodium hydroxide solution, potassium hydroxide solution, ammonia water solution, methanol, ethanol, acetone, N-dimethylformamide, N-dimethylacetamide, N-methylpyrrolidone, hexane, N-hexane, octane, petroleum ether, petroleum spirit, formic acid, acetic acid, anisole, methyl formate, ethyl formate, diesel oil, peanut oil, sodium hydroxide solution, potassium hydroxide solution, ammonium hydroxide, ammonium chloride, ammonium, A lithium chloride solution, a sodium chloride solution, a magnesium chloride solution, an aluminum chloride solution, a potassium chloride solution, a calcium chloride solution, an iron chloride solution, a ferrous chloride solution, an ammonium chloride solution, a lithium sulfate solution, a sodium sulfate solution, a magnesium sulfate solution, an aluminum sulfate solution, a potassium sulfate solution, a ferric sulfate solution, a ferrous sulfate solution, an ammonium sulfate solution, a lithium nitrate solution, a sodium nitrate solution, a magnesium nitrate solution, an aluminum nitrate solution, a potassium nitrate solution, a calcium nitrate solution, an iron nitrate solution, a ferrous nitrate solution, an ammonium nitrate solution, a lithium carbonate solution, a sodium carbonate solution, a potassium carbonate solution, an ammonium carbonate solution, a lithium bicarbonate solution, a sodium bicarbonate solution, a magnesium bicarbonate solution, a potassium bicarbonate solution, a calcium bicarbonate solution, and an ammonium bicarbonate solution.

Preferably, in the method for preparing graphene, in order to meet the requirement of the application on the concentration of the graphene solution, more solvent may be added to the graphene solution, or the extra solvent in the graphene solution may be removed by filtration.

Preferably, in order to meet the requirement of graphene drying in application, the method for electrochemically preparing graphene is dried in a common manner to obtain dried graphene. Common drying means include: forced air drying, natural air drying, freeze drying, vacuum drying, spray drying, microwave drying, and supercritical drying.

Preferably, the graphene prepared by the present invention can be used in the following fields: lithium ion battery, sodium ion battery, potassium ion battery, magnesium ion battery, solid-state battery, conductive agent, graphene paper, super capacitor, solar battery, light-transmitting coating, flexible display device, transparent conductive film, photodetector, heat-dissipating coating, heat sink, heat-generating sheet, conductive coating, conductive ink, conductive adhesive, antistatic coating, antistatic plastic, conductive rubber, conductive thin film, anticorrosive coating, metal composite, cable material, hydrogel, aerogel, 3D printing material, electromagnetic shielding material, chemical sensor, biosensor, blood sensor, gas sensor, drug carrier, medical imaging, building material, wear-resistant coating, reinforced plastic, graphene tire, foam material, water-impermeable plastic, reinforcing material, graphene fiber, graphene brake pad, carbon composite material, sponge oil-absorbing plastic, carbon composite material, and the like, Seawater desalination, sewage purification, seawater uranium extraction, seawater lithium extraction, a separation membrane, an ion sieve, a mask, a catalyst carrier, a hydrogen evolution catalyst and an oxygen evolution catalyst.

The invention has the beneficial effects that: the invention provides a method for preparing graphene, which can improve the reduction effect of graphene, enable the graphene to be uniformly dispersed in various solvents and efficiently and conveniently remove various impurities in the graphene. The solvent for dispersing the graphene includes various inorganic solvents and organic solvents, and the removed impurities include: impurities in graphite powder, impurities introduced during preparation and impurities introduced during reduction. The method is beneficial to improving the quality of the graphene, reducing the production cost of the graphene and conveniently adjusting the concentration of the graphene solution.

The attached drawings of the specification.

Fig. 1 is a scanning electron microscope image of graphene oxide.

Fig. 2 is a scanning electron microscope image of graphene prepared according to the present invention.

Fig. 3 is an X-ray diffraction pattern of graphene oxide.

Fig. 4 is an X-ray diffraction pattern of graphene after chemical reduction in example 1.

Fig. 5 is an X-ray diffraction pattern of graphene after electrochemical reduction in example 1.

Fig. 6 is a measurement value, an average value, and a standard deviation of the concentration of the graphene solution (chemical + electrochemical reduction).

Fig. 7 is a graph of measured values, mean values, and standard deviations of graphene solution (chemical + electrochemical reduction + dispersant) concentrations.

Fig. 8 is a graph of measured values, mean values, and standard deviations of graphene solution (chemical + electrochemical reduction + dispersant + filter displacement) concentrations.

Fig. 9 is a schematic diagram of electrochemical reduction of graphene.

FIG. 10 is a schematic diagram illustrating the steps of the present invention.

Detailed description of the preferred embodiments.

Example 1.

1 g of graphene oxide and 20 g of ascorbic acid are dissolved in 1000 mL of pure water, and the solution with an electrolyte of ascorbic acid and a graphene oxide concentration of 1 mg/mL is formed after ultrasonic stirring for 2 hours.

And standing the solution at 15 ℃ for 24 hours to react to obtain the chemically reduced graphene solution.

And (3) placing the solution in an electrolytic cell, inserting an electrode, and performing electrochemical reduction for 6 hours by applying a constant voltage of 10V by using a constant potential electrochemical method under the standing condition of 15 ℃ to obtain the electrochemically reduced graphene solution.

And adding 500 mL of 30% hydrogen peroxide solution into the solution, stirring and reacting at 15 ℃ at a rotating speed of 100 r/min for 5 minutes, and standing and reacting for 24 hours to obtain a uniformly dispersed graphene solution.

The solution was filtered through a 350 mesh screen to obtain a black viscous sample.

And adding pure water into the sample for multiple times, and repeatedly filtering until the conductivity of the filtrate is equal to that of the pure water to obtain the graphene solution uniformly dispersed in the pure water.

Example 2.

1 g of graphene oxide and 10 g of ascorbic acid are dissolved in 1000 mL of pure water, and the solution with an electrolyte of ascorbic acid and a graphene oxide concentration of 1 mg/mL is formed after ultrasonic stirring for 2 hours.

And standing the solution at 0 ℃ for reaction for 100 hours to obtain a chemically reduced graphene solution.

And (3) placing the solution in an electrolytic cell, inserting an electrode, applying a constant voltage of 2V by adopting a constant potential electrochemical method under the standing condition of 5 ℃, and carrying out electrochemical reduction for 36 hours to obtain the graphene solution which is uniformly dispersed after the electrochemical reduction.

Adding 250 mL of 30% hydrogen peroxide solution into the solution, stirring and reacting for 5 minutes at the rotation speed of 100 r/min at the temperature of 5 ℃, and standing and reacting for 24 hours to obtain the uniformly dispersed graphene solution.

The solution was filtered through a 300 mesh screen to obtain a black viscous sample.

And adding ethanol into the solution for multiple times, repeatedly filtering, and replacing water with ethanol to obtain the graphene solution uniformly dispersed in the ethanol.

Example 3.

1 g of graphene oxide is dissolved in 1000 mL of pure water, and the solution is ultrasonically stirred for 2 hours to form a solution with the graphene oxide concentration of 1 mg/mL.

After 20 g of ascorbic acid was dissolved in 100 mL of pure water, the above graphene oxide solution was added to form a solution in which the electrolyte was ascorbic acid.

And stirring the solution at the temperature of 20 ℃ and the rotating speed of 300 r/min for reacting for 1 minute to obtain the chemically reduced graphene solution.

And (3) putting the solution into an electrolytic cell, inserting an electrode, applying a constant voltage of 5V by adopting a constant potential electrochemical method at the temperature of 20 ℃, electrochemically reducing for 24 hours, and stirring at the rotating speed of 30 r/min to obtain the electrochemically reduced graphene solution.

And adding 500 mL of 30% hydrogen peroxide solution into the solution, and stirring and reacting at the rotation speed of 30 r/min at 20 ℃ for 24 hours to obtain a uniformly dispersed graphene solution.

And adding methanol into the solution for multiple times, repeatedly filtering, and replacing water with methanol to obtain the graphene solution uniformly dispersed in the methanol.

Example 4.

And (3) placing the solution in an electrolytic cell, inserting an electrode, applying a constant voltage of 15V by adopting a constant potential electrochemical method under the standing condition of 15 ℃, and carrying out electrochemical reduction for 1 hour to obtain the graphene solution subjected to electrochemical reduction.

And adding 500 mL of 30% hydrogen peroxide solution into the solution, stirring and reacting at the rotation speed of 100 r/min for 5 minutes at 20 ℃, and standing and reacting for 24 hours to obtain the uniformly dispersed graphene solution.

The solution was filtered through a 400 mesh screen to obtain a black viscous sample.

And adding ethanol into the sample for multiple times, and repeatedly filtering until the conductivity of the filtrate is equal to that of the ethanol to obtain the graphene solution uniformly dispersed in the ethanol.

Example 5.

And standing the solution at 15 ℃ for reaction for 12 hours to obtain a chemically reduced graphene solution.

And (3) placing the solution in an electrolytic cell, inserting an electrode, applying a constant voltage of 10V by adopting a constant potential electrochemical method under the standing condition of 15 ℃, and carrying out electrochemical reduction for 6 hours to obtain the graphene solution which is uniformly dispersed after the electrochemical reduction.

Adding 250 mL of 30% hydrogen peroxide solution into the solution, and stirring and reacting at 15 ℃ at a rotating speed of 30 r/min for 24 hours to obtain a uniformly dispersed graphene solution.

And adding ethyl acetate into the solution for multiple times, repeatedly filtering, and replacing ethanol with ethyl acetate to obtain the graphene solution uniformly dispersed in the ethyl acetate.

Example 6.

1 g of graphene oxide was dissolved in 1000 mL of pure water, and the mixture was ultrasonically stirred for 2 hours.

Adding a proper amount of ammonia water into the graphene oxide solution, and adjusting the pH =11 to form a solution with the graphene oxide concentration of 1 mg/mL.

And adding 5g of glucose into the solution, and stirring and reacting at 90 ℃ at a rotating speed of 600 r/min for 1 hour to obtain a glucose-reduced graphene solution.

Adding 15g of oxalic acid into the graphene solution reduced by the glucose, stirring and reacting for 2 hours at the temperature of 20 ℃ at the rotating speed of 200 r/min to obtain the graphene solution reduced by the glucose and the oxalic acid together, and the graphene solution is an electrolyte taking the oxalic acid as an electrolyte.

And (3) putting the solution into an electrolytic cell, inserting an electrode, applying a constant voltage of 10V by adopting a constant potential electrochemical method at the temperature of 20 ℃, electrochemically reducing for 2 hours, and stirring at the rotation speed of 200 r/min to obtain the electrochemically reduced graphene solution.

And adding 60 g of sodium percarbonate into the solution, stirring and reacting for 5 minutes at the temperature of 20 ℃ at the rotating speed of 100 r/min, and stirring and reacting for 24 hours at the rotating speed of 10 r/min to obtain the uniformly dispersed graphene solution.

And adding N-methyl pyrrolidone into the solution for multiple times, repeatedly filtering, and replacing ethanol with N-methyl pyrrolidone to obtain the graphene solution uniformly dispersed in N-methyl pyrrolidone.

Example 7.

Adding 300 mL of 30% hydrogen peroxide solution and 10 g of sodium carbonate into the solution, stirring and reacting at 20 ℃ at a rotating speed of 100 r/min for 5 minutes, and standing and reacting for 24 hours to obtain a uniformly dispersed graphene solution.

And adding N, N-dimethylformamide into the solution for multiple times, repeatedly filtering, and replacing water with the N, N-dimethylformamide to obtain the graphene solution uniformly dispersed in the N, N-dimethylformamide.

Example 8.

1 g of graphene oxide, 2g of ascorbic acid and 15g of oxalic acid are dissolved in 1000 mL of pure water, and the solution with the electrolytes of ascorbic acid and oxalic acid and the graphene oxide concentration of 1 mg/mL is formed by ultrasonic stirring for 2 hours.

And (3) placing the solution in an electrolytic cell, inserting an electrode, applying a constant voltage of 4V by adopting a constant potential electrochemical method under the standing condition of 15 ℃, and carrying out electrochemical reduction for 6 hours to obtain the graphene solution which is uniformly dispersed after the electrochemical reduction.

And adding 100 g of sodium carbonate into the solution, and standing at 15 ℃ for 24 hours to react to obtain a uniformly dispersed graphene solution.

And adding gasoline into the solution for multiple times, repeatedly filtering, and replacing ethanol with gasoline to obtain the graphene solution uniformly dispersed in the gasoline.

Example 9.

Adding 5g L-glutathione into the solution, and reacting for 3 hours at 50 ℃ with stirring to obtain the chemically reduced graphene solution.

10 g of ascorbic acid was added to the above solution to form an electrolyte solution using ascorbic acid as an electrolyte.

And (3) putting the solution into an electrolytic cell, inserting an electrode, applying a constant voltage of 5V by adopting a constant potential electrochemical method at the temperature of 20 ℃, electrochemically reducing for 3 hours, and stirring at the rotating speed of 30 r/min to obtain the electrochemically reduced graphene solution.

After the solution is cooled, 300 mL of 30% hydrogen peroxide solution is added, and the mixture is stirred at the rotation speed of 30 r/min at 20 ℃ to react for 24 hours to obtain a uniformly dispersed graphene solution.

And adding acetone into the solution for multiple times, repeatedly filtering, and replacing ethanol with acetone to obtain the graphene solution uniformly dispersed in the acetone.

Example 10.

And adding a proper amount of ammonia water into the graphene oxide solution, and adjusting the pH = 11. The formed electrolyte is ammonia water, and the concentration of graphene oxide is 1 mg/mL.

And adding 12 mL of ethylenediamine into the solution, and reacting for 2 hours at 95 ℃ with stirring to obtain a chemically reduced graphene solution.

To the above solution, 2g of oxalic acid and 2g of ascorbic acid were added to form an electrolytic solution using oxalic acid and ascorbic acid as electrolytes.

And (3) placing the solution in an electrolytic cell, inserting an electrode, applying a constant voltage of 5V by adopting a constant potential electrochemical method under the standing condition of 20 ℃, and carrying out electrochemical reduction for 12 hours to obtain the graphene solution subjected to electrochemical reduction.

Adding 80 mL of 30% hydrogen peroxide solution into the solution, stirring and reacting at the rotation speed of 100 r/min for 5 minutes at 20 ℃, and standing and reacting for 24 hours to obtain the uniformly dispersed graphene solution.

And adding a hydrogen peroxide solution into the solution for multiple times, repeatedly filtering, and replacing water with the hydrogen peroxide solution to obtain the graphene solution uniformly dispersed in the hydrogen peroxide solution.

Example 11.

And (3) dissolving 1 g of graphene oxide in 500 mL of N, N-dimethylformamide, and ultrasonically stirring for 2 hours to form a solution with the graphene oxide concentration of 1 mg/mL.

And adding 1 g of ascorbic acid and 4 g of sodium borohydride into the solution, stirring and reacting for 6 hours at 15 ℃ at a rotating speed of 200 r/min to obtain a chemically reduced graphene solution, and forming an electrolyte solution taking the ascorbic acid and the sodium borohydride as electrolytes.

And (3) placing the solution in an electrolytic cell, inserting an electrode, applying a constant voltage of 2.5V by adopting a constant potential electrochemical method under the standing condition of 20 ℃, and carrying out electrochemical reduction for 12 hours to obtain the graphene solution subjected to electrochemical reduction.

Adding 50 mL of 30% hydrogen peroxide solution into the solution, stirring and reacting at the rotation speed of 200 r/min at 20 ℃ for 5 minutes, and standing and reacting for 24 hours to obtain the uniformly dispersed graphene solution.

And adding N, N-dimethylformamide into the sample for multiple times, repeatedly filtering to remove impurities, and replacing residual water with the N, N-dimethylformamide to obtain a graphene solution uniformly dispersed in the N, N-dimethylformamide.

Example 12.

And adding N, N-dimethylformamide into the solution for multiple times, repeatedly filtering, and replacing ethanol with the N, N-dimethylformamide to obtain the graphene solution uniformly dispersed in the N, N-dimethylformamide.

And adding N-methyl pyrrolidone into the solution for multiple times, repeatedly filtering, and replacing N, N-dimethylformamide with N-methyl pyrrolidone to obtain the graphene solution uniformly dispersed in N-methyl pyrrolidone.

Example 13.

1 g of graphene oxide, 10 g of sodium ascorbate and 10 g of citric acid are dissolved in 1000 mL of pure water, and the solution with electrolytes of sodium ascorbate and citric acid and the concentration of graphene oxide of 1 mg/mL is formed by ultrasonic stirring for 2 hours.

And (3) placing the solution in an electrolytic cell, inserting an electrode, applying a constant voltage of 15V by adopting a constant potential electrochemical method under the standing condition of 15 ℃, and carrying out electrochemical reduction for 2 hours to obtain the graphene solution subjected to electrochemical reduction.

50 mL of 30% hydrogen peroxide solution and 30 g of sodium carbonate are added into the solution, stirred and reacted at the temperature of 20 ℃ for 5 minutes at the rotating speed of 100 r/min, and then the mixture is kept stand and reacted for 24 hours to obtain uniformly dispersed graphene solution.

The degree of reduction of graphene can be characterized by X-ray diffraction patterns. The surface of the graphene oxide contains a large number of oxygen-containing functional groups, and the oxygen-containing functional groups enable the interplanar spacing of graphene sheets to be increased. After the oxygen-containing functional group is reduced and removed, the interplanar spacing is reduced. The reduction effect can be judged from the interplanar spacing, and the smaller the interplanar spacing, the more oxygen-containing functional groups are removed, and the higher the reduction degree is. Bragg law of X-ray diffraction from crystals: 2dsin theta = n lambda, and the interplanar spacing d can be calculated according to the 2 theta angle of the characteristic peak in the map, so that the reduction effect of the graphene can be judged. The X-ray wavelength used for detection was 0.15406 nm, and the number of diffraction orders n was 1. Fig. 3 is an X-ray diffraction pattern of graphene oxide, 2 θ =12.93 °, and an interplanar spacing d =0.717858 nm. Fig. 4 is an X-ray diffraction pattern after chemical reduction in example 1, 2 θ =25.22 ° and interplanar spacing d =0.352841 nm. Fig. 5 is an X-ray diffraction pattern after electrochemical reduction in example 1, 2 θ =25.80 ° and interplanar spacing d =0.345039 nm. Obviously, the interplanar distance d after electrochemical reduction is further reduced and is smaller than the interplanar distance d after chemical reduction, which shows that most of oxygen-containing functional groups are removed by chemical reduction, more oxygen-containing functional groups are removed by electrochemical reduction, and graphene is further reduced. The X-ray diffraction pattern proves that the reduction degree of the graphene can be improved.

The uniformity of dispersion of graphene in a solution can be judged by measuring the mean and standard deviation of the concentration. A total of 12 groups of samples were measured, 7 samples from each group, and the mean and standard deviation of the concentration were calculated from the measurements. FIG. 6 shows the measurement results of the concentration of graphene solution (chemical + electrochemical reduction), the average value of the sample concentration is 7.33-7.58 mg/mL, and the standard deviation is 0.046-0.112 mg/mL. FIG. 7 shows the measurement results of the concentration of the graphene solution (chemical + electrochemical reduction + dispersant), the average sample concentration is 4.85-5.00 mg/mL, and the standard deviation is 0.043-0.086 mg/mL. FIG. 8 shows the measurement results of the concentration of the graphene solution (chemical + electrochemical reduction + dispersant + filtration displacement), the average value of the sample concentration is 5.38-5.59 mg/mL, and the standard deviation is 0.033-0.078 mg/mL. In consideration of experimental errors, the standard deviation of each sample is very small, and the concentration is very uniform, which indicates that the uniformity of the dispersion of the graphene in the solvent is very good. After the dispersing agent is added, gas is adsorbed on the surface of the graphene, so that the concentration of the solution is lower, which shows that the graphene is more dispersed and looser in the solution, and more space between sheets is provided, thereby being more beneficial for other materials to enter into the sheet layers to form a composite material with the graphene. After the solvent replacement, a small amount of gas escapes, the concentration is slightly increased, and the uniformity of dispersion is unchanged. In conclusion, the uniformity of graphene dispersion in the solution is good before and after the dispersant is added, but after the dispersant is added, graphene lamellar layers are more dispersed, and more solvents are arranged among the lamellar layers, so that the graphene is more beneficial to compounding with other materials. The solvent replacement does not affect the dispersion effect of the graphene, so that the graphene has more application scenes in the downstream industry.

In summary, the present invention provides a method for preparing graphene, which can improve the reduction effect of graphene, so that graphene is uniformly dispersed in various solvents, and various impurities in graphene can be efficiently and conveniently removed. The solvent for dispersing the graphene includes various inorganic solvents and organic solvents, and the removed impurities include: impurities in graphite powder, impurities introduced during preparation and impurities introduced during reduction. The method is beneficial to improving the quality of the graphene, reducing the production cost of the graphene and conveniently adjusting the concentration of the graphene solution.

The invention is not the best known technology.

The above embodiments are merely illustrative of the technical ideas and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing graphene, comprising the following steps:

2. The method for preparing graphene according to claim 1, wherein the reducing agent is one or more of the following: organic acid, borohydride, citrate, ascorbate, hydrohalic acid, alcohol, sugar, amino acid, sulfur-containing reducing agent, nitrogen-containing reducing agent, and reducing plant extract; the mass ratio of the graphene oxide to the reducing agent is 1: (1-200), wherein the reaction time of the chemical reduction is 0-120 hours, the reaction temperature is-10-100 ℃, and the stirring speed of the reaction is 0-3000 r/min.

3. The method for preparing graphene according to claim 1, wherein the electrolyte used in the electrochemical reaction is an aqueous electrolyte or a non-aqueous electrolyte, and the pH is between 0 and 14; the electrolyte used in the reaction is one or more of the following: acid, alkali and salt, wherein the concentration of electrolyte in the solution is 0.01-10.00 mol/L; the cathode is separated from the anode area in the electrolytic cell by using a diaphragm, the graphene solution is positioned at the cathode side, and the diaphragm is one or more of the following: cation exchange membrane, anion exchange membrane, proton exchange membrane.

4. The method for electrochemically preparing graphene according to claim 1, wherein a constant voltage power supply is used for the electrochemical reaction, the constant voltage interval is 1-40V, the reaction time is 10 seconds-48 hours, the stirring speed of the reaction is 0-3000 r/min, and the reaction temperature is-10 ℃ to 90 ℃.

5. The method for preparing graphene according to claim 1, wherein the dispersant is one or more of the following: peroxides, percarbonates, persulfates, permanganic and permanganate salts, ferrates and ferrates, chlorites and chlorates, carbonates, bicarbonates; the dispersing agent can react with the graphene solution after electrochemical reduction, and the reaction product contains gas, so that the graphene is uniformly dispersed in the solution.

6. The method for preparing graphene according to claim 1, wherein the mass ratio of the dispersing agent to the initial graphene oxide is (1-1000): 1, the reaction temperature is-10 ℃ to 90 ℃, the reaction time is 1 minute to 100 hours after the dispersant is added, and the reaction stirring speed is 0 r/min to 3000 r/min.

7. The graphene preparation method of claim 1, wherein the filtering uses one or more of the following combinations: a filter screen, a filter membrane and a filter bag with the mesh number of 10-5000 meshes.

8. The method for preparing graphene according to claim 1, wherein the filtering solvent is one or more of the following: water, peroxide solution, acid solution, alkali solution, salt solution, hydrocarbon solvent, alcohol solvent, ether solvent, amide solvent, ketone solvent, ester solvent, phenol solvent and nitrile solvent.

9. The method for preparing graphene according to claim 1, wherein the removing of impurities from the graphene solution is performed by adding the uniformly dispersed graphene solution into a solvent and filtering until the impurity content of the filtrate is equal to the impurity content of the filtered solvent, so as to obtain the uniformly dispersed graphene solution after removing the impurities.

10. The method for preparing graphene according to claim 1, wherein the graphene solution uniformly dispersed in the first solvent is replaced with the second solvent to obtain a graphene solution uniformly dispersed in the second solvent.