CN111470499B - Method for electrochemically preparing graphene - Google Patents
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Abstract
The invention belongs to the technical field of inorganic material preparation, and particularly relates to a preparation method of graphene, which comprises the following steps: preparing a graphite material into an electrode; preparing an electrolyte from ammonium salt, pretreating an electrode under the condition of an external voltage, adding ammonia water, and carrying out electrolytic stripping on a graphite anode at a certain temperature; carrying out solid-liquid separation and drying on the electrolysis product to obtain graphene with different qualities; by accurately controlling the parameters of the alternating current, the intercalation stripping of the graphene can be realized, and the oxidation of the graphene in the intercalation process can be effectively avoided; meanwhile, the problem of low intercalation efficiency caused by contribution of electrode capacitance capacity in the intercalation of general alternating current is solved; in addition, the graphene is prepared by using conventional chemical raw materials, so that the raw materials are low in cost and easy to obtain, and the method is convenient for industrialization.
Description
Technical Field
The invention belongs to the technical field of inorganic material preparation, and particularly relates to a method for electrochemically preparing graphene.
Background
The low-cost large-scale preparation of the graphene is a key technical problem which needs to be solved by exerting excellent electric conduction and heat conduction characteristics of the graphene and promoting the graphene to be applied to the fields of electric heating, sensing, energy storage and the like. The most important technical route for preparing graphene is to take cheap graphite as a raw material and perform intercalation and stripping between graphite layers. For the technical route, high quality is a precondition for realizing various applications of the method, and environmental protection and safety of a preparation system and a preparation process are considered. However, the development of a preparation strategy with high quality, high yield and environmental friendliness still faces challenges, and the realization of low-cost large-scale preparation of graphene through principle innovation and process technology improvement is still an important research topic in the field of graphene materials. The preparation of graphene by an electrolytic method is widely concerned due to the characteristics of rapidness, relative environmental friendliness and the like.
There are a number of reports on methods for preparing graphene by electrolysis, such as: CN108675287A mentions that graphene can be obtained by performing electrochemical anode stripping in liquid molten salt, and the temperature is required to reach a certain condition; in CN107628609A, expanded graphite is used as a negative electrode and an anode, an acidic electrolyte is used, a bidirectional alternating pulse voltage is applied between the negative electrode and the anode, and an agglomerated graphene oxide mixed solution is obtained through electrolysis; parvez (ACS Nano 2013,7,3598) and the like use acidic dilute sulfuric acid as electrolyte to obtain oxidized graphene with high oxidation degree and thick layers; muratlu (Carbon, 2012, 50, 142) et al prepared oxidized graphene having a thickness of about 1.2nm using sodium dodecyl sulfate as an electrolyte; song et al (Journal of Power Sources 2014, 249, 48-58) used a potassium nitrate solution as an electrolyte under neutral conditions and controlled the lower potential to reduce the number of layers from which graphene is exfoliated. However, at lower pH, nitrate also produces a thicker and more oxidized graphite nanolayer, consistent with the exfoliation process at tetrabutylammonium hydrogen sulfate; meanwhile, Zeng et al (ChemSusChem 2011,4,1587) also prepare graphene oxide with higher oxidation degree by electrochemical stripping in phosphate. Therefore, the electrochemical method for stripping graphene is very dependent on the electrolyte, and actually, the graphene obtained under the acidic condition has a high oxidation degree due to the action of the acidic condition, so that a subsequent further reduction process is required to obtain high-quality intrinsic graphene on the basis.
At present, no report on a method for preparing graphene by an asymmetric alternating current electrolysis method is seen.
Disclosure of Invention
The invention aims to provide a method for electrochemically preparing graphene, which is specifically characterized by comprising the following steps:
(1) preparation of reactants:
pressing a graphite material into a graphite sheet through tabletting equipment, wherein the graphite material is one or more of graphite paper, crystalline flake graphite, graphite powder and graphite foil, and the tabletting thickness is 2-5 mm and is used as an electrode reactant A during electrolysis;
selecting ammonium salt as electrolyte to prepare 0.1-3mol/L of the electrolyte as ammonium salt solution B;
the ammonium salt is selected from tetrabutylammonium hydrogen sulfate (TBAHSO)4) Tetrabutylammonium sulfate ((TBA)2SO4) Tetraethylammonium hydrogen sulfate (TEAHSO)4) Tetraethylammonium sulfate ((TEA)2SO4) One or more of;
adding ammonia water into the solution B, adjusting the pH value of the solution B to 8-14, and uniformly mixing the mixed solution to obtain an alkaline electrolyte solution C;
(2) and (3) reactive stripping:
placing an electrolyte device in a constant temperature environment of 0-5 ℃, wherein in the step (1), the graphite flakes are respectively used as an electrode M and an electrode N to be electrolyzed, the solution B is used as electrolyte, and the electrolyte is stably kept for 1-3 h under the direct current voltage of 2.5-3.5V;
and then transferring the electrode to an alkaline electrolyte solution C, stripping by using an alternating voltage with the following control time parameters, stabilizing at 5-15V, continuously electrifying for 0.5-2 h according to the set parameters, and obtaining a precipitate at the bottom of the solution C, wherein the alternating voltage controls the parameters: two electrodes are named as an electrode M and an electrode N, and voltages are applied to the two electrodes according to the following parameters:
| electrode M | Electrode N | Voltage of | Time | |
| Stage one | + | - | 5～15V | 30-300s |
| Stage two | - | + | 5～15V | 5-25s |
| Stage three | + | - | 5～15V | 30-300s |
| Stage four | - | + | 5～15V | 5-25s |
| Stage five | + | - | 5～15V | 5-25s |
| Stage six | - | + | 5～15V | 30-300s |
| Stage seven | + | - | 5～15V | 5-25s |
| Stage eight | - | + | 5～15V | 30-300s |
| Go back to stage one and cycle | + | - | 5～15V | 30-300s |
The time ratio of the first stage to the second stage, the third stage to the fourth stage, the sixth stage to the fifth stage, and the eighth stage to the seventh stage is selected from 1: 1-60: 1, preferably 4: 1-30: 1, more preferably 10: 1-20: 1, and precipitates are obtained at the bottom of the solution C.
Preferably, step (1) is preferably one or more of the following:
the thickness of the graphite sheet is preferably 2-3 mm;
the concentration of the ammonium salt solution is 0.2-1mol/L, and more preferably 0.2-0.5 mol/L;
and further adding ammonia water into the solution B, adjusting the pH value of the solution B to 9-10, and uniformly mixing the mixed solution to obtain an alkaline electrolyte solution C.
Preferably, said step (2) is preferably one or more of the following:
placing an electrolyte device in a constant temperature environment of 0-5 ℃, wherein in the step (1), the graphite flake is used as an electrode M and an electrode N to be electrolyzed, the solution B is used as electrolyte, and the electrolyte is stably kept for 1-2 hours under the direct current voltage of 2.5-3V;
and then transferring the electrode to an alkaline electrolyte solution C, stripping by using an alternating voltage with the following control time parameters, stabilizing the voltage by 10-15V, continuously electrifying for 1-1.5 h according to the set parameters, and obtaining a precipitate at the bottom of the solution C, wherein the alternating voltage controls the parameters: two electrodes are named as an electrode M and an electrode N, and voltages are applied to the two electrodes according to the following parameters:
| electrode M | Electrode N | Voltage of | Time | |
| Stage one | + | - | 10～15V | 30-300s |
| Stage two | - | + | 10～15V | 5-25s |
| Stage three | + | - | 10～15V | 30-300s |
| Stage four | - | + | 10～15V | 5-25s |
| Stage five | + | - | 10～15V | 5-25s |
| Stage six | - | + | 10～15V | 30-300s |
| Stage seven | + | - | 10～15V | 5-25s |
| Stage eight | - | + | 10～15V | 30-300s |
| Go back to stage one and cycle | + | - | 10～15V | 30-300s |
The time ratio of the first stage to the second stage, the third stage to the fourth stage, the sixth stage to the fifth stage, and the eighth stage to the seventh stage is selected from 4: 1-30: 1, and preferably 10: 1-20: 1, and precipitates are obtained at the bottom of the solution C.
More preferably, the step (2) is preferably one or more of the following:
placing an electrolyte device in a constant temperature environment of 0 ℃, wherein in the step (1), the graphite flake is taken as an electrode M and an electrode N to be electrolyzed, the solution B is taken as electrolyte, and the electrolyte is stably kept for 2 hours under the direct current voltage of 3V;
transferring the electrode into an alkaline electrolyte solution C, stripping by using an alternating voltage with the following control time parameters, stabilizing 10V, continuously electrifying for 1-1.5 h according to the set parameters, and obtaining a precipitate at the bottom of the solution C, wherein the alternating voltage controls the parameters: two electrodes are named as an electrode M and an electrode N, and voltages are applied to the two electrodes according to the following parameters:
a precipitate was obtained at the bottom of solution C.
Preferably, the alkaline electrolyte solution C in the step (1) is preferably added into the solution B according to a volume ratio of 1-5%, namely 1-5 mL of 30% ammonia water by mass fraction is added into each 100mL of the solution B, preferably 2-3% by volume ratio, the pH value of the solution B is regulated to 8-14, and the mixed solution is uniformly stirred for 15-20 minutes; and performing ultrasonic treatment at room temperature under 30-60W for 1-10 min, preferably 50-60W for 5-10 min to obtain electrolyte solution C.
Still further, the method comprises the steps of:
(3) cleaning and extracting:
dissolving the precipitate obtained by the stripping reaction in the step (2) in an organic solvent, and carrying out ultrasonic treatment for 20-40 minutes at the power of 180-240W at room temperature to obtain a solution D;
centrifuging the solution D at 2000-4000rpm for 20-40 minutes;
washing and recovering the centrifuged lower-layer precipitate, and reusing the lower-layer precipitate for preparing the positive electrode reactant A in the step (1);
and (4) carrying out suction filtration and cleaning on the centrifuged supernatant for 5-10 times by using deionized water to obtain a separated solid.
Preferably, the organic solvent in the step (3) is one or more of N-N dimethylformamide, N-methylpyrrolidone and isopropanol; the amount of the organic solvent is 1-2 ml/mg of the precipitate obtained by the stripping reaction in the step (2).
Still further, the method comprises the steps of:
(4) and (3) drying: and (4) drying the solid separated in the step (3) to obtain the graphene.
Preferably, the drying method in the step (4) is one of air drying, spray drying, oven drying or freeze drying.
The invention also relates to graphene prepared by any one of the methods, wherein the graphene is not graphene oxide but low-oxidation-degree graphene, the oxygen content of the graphene is low, and the proportion of oxygen element relative to the total mass of the graphene is not more than 10%; the prepared graphene is large in size and not smaller than 3 mu m; the number of layers is less than 8.
The alternating current of the invention is controlled by artificial means and is non-periodic alternating current.
Compared with the prior art, the invention has the beneficial effects that:
(1) during reaction, the graphene prepared by selecting ammonium salt as electrolyte is more completely stripped, and the number of layers is less. When the anode is intercalated, the graphite at the anode is intercalated by utilizing the larger ion volume of sulfate radicals; when the cathode is intercalated, the intercalation stripping effect of the graphite material is improved by utilizing the larger volume of the ammonium cation for intercalation;
(2) compared with the existing mass-produced graphene, the maximum oxygen content of the low-oxidation-degree graphene is not more than 10%, the size of the low-oxidation-degree graphene exceeds 2 microns, and the number of layers is less than 8, so that the low-cost large-scale preparation of the graphene is favorably realized;
(3) the graphene is prepared by using conventional chemical raw materials, so that the raw materials are easy to obtain, the cost is low, and the industrialization is facilitated;
(4) by controlling the time of alternating current turning over the two electrodes, the intercalation ion in the electrolyte is repeatedly intercalated to the electrodes.
By accurately controlling the parameters of the asymmetric alternating current, the intercalation stripping of the graphene can be realized, and the oxidation of the graphene in the intercalation process can be effectively avoided; meanwhile, the problem of low intercalation efficiency caused by contribution of electrode capacitance capacity in the intercalation of general alternating current is solved; the method helps to improve the size of the product graphene by regulating and controlling parameters such as pH value, electrolyte, voltage and the like during electrolysis, and is more favorable for improving the quality of the graphene.
Drawings
The invention is further described below with reference to the accompanying drawings.
FIG. 1 is a schematic diagram of AC electrolysis according to the present invention.
Detailed Description
The present invention will be further described with reference to the following examples. The described embodiments and their results are only intended to illustrate the invention and should not be taken as limiting the invention described in detail in the claims.
Example 1
A preparation method of graphene is characterized by comprising the following steps:
(1) preparation of reactants: pressing graphite powder into graphite flakes through tabletting equipment, wherein the thickness of the pressed graphite flakes is 3mm, and the thickness of the pressed graphite flakes is the electrode M and the electrode N; selecting tetrabutylammonium hydrogen sulfate (TBAHSO)4) To prepare 0.5mol/L solution B; adding 3mL of 30% ammonia water into the solution B according to the volume ratio of 3%, namely adding 3mL of 30% ammonia water into each 100mL of the solution B, regulating the pH value of the solution B to 9, and mixingUniformly stirring the mixed solution for 15 minutes; carrying out ultrasonic treatment for 5 minutes at the power of 50W at room temperature to obtain an electrolyte solution C;
(2) and (3) reactive stripping: placing an electrolyte device in a constant temperature environment of 0 ℃, taking the graphite sheet as an electrode in the step (1) and the solution B as electrolyte, and stably keeping for 2 hours under the direct current voltage of 3V; then transferring the electrode into an electrolyte solution C, stripping by using an alternating voltage with the following control time parameters, stabilizing at 10V, continuously electrifying for 1h according to the set parameters, and obtaining a precipitate at the bottom of the solution C; alternating voltage control parameters: the voltage is applied to the electrode M and the electrode N according to the following parameters:
| electrode M | Electrode N | Voltage of | Time | |
| Stage one | + | - | 10V | 45s |
| Stage two | - | + | 10V | 10s |
| Stage three | + | - | 10V | 45s |
| Stage four | - | + | 10V | 10s |
| Stage five | + | - | 10V | 10s |
| Stage six | - | + | 10V | 45s |
| Stage seven | + | - | 10V | 10s |
| Stage eight | - | + | 10V | 45s |
| Go back to stage one and cycle | + | - | 10V | 45s |
(3) Cleaning and extracting: dissolving the precipitate obtained by the reaction in the step (2) in N-N dimethylformamide, wherein the addition amount of the N-N dimethylformamide is 1ml/mg of the precipitate; performing ultrasonic treatment for 30 minutes at the power of 240W at room temperature to obtain a solution D, centrifuging the solution D at the speed of 3000rpm for 30 minutes, cleaning and recycling the lower-layer precipitate after centrifugation, and reusing the lower-layer precipitate for preparing the positive electrode reactant A in the step (1); filtering and washing the centrifuged supernatant for 10 times by using deionized water to obtain separated solids;
(4) and (3) drying: freeze-drying the solid separated in the step (3) to obtain graphene; the obtained graphene has an oxygen content of about 8%, a size of more than 3 μm, and a number of layers of less than 8.
Example 2
A preparation method of graphene is characterized by comprising the following steps:
(1) preparation of reactants: pressing graphite powder into graphite flakes through tabletting equipment, wherein the thickness of the pressed graphite flakes is 3mm, and the thickness of the pressed graphite flakes is the electrode M and the electrode N; selecting tetrabutylammonium hydrogen sulfate (TBAHSO)4) To prepare 0.5mol/L solution B; adding 3mL of 30% ammonia water in the solution B according to the volume ratio of 3% in the solution B, namely adding 3mL of 30% ammonia water in each 100mL of the solution B, regulating the pH value of the solution B to 9, and uniformly stirring the mixed solution for 15 minutes; carrying out ultrasonic treatment for 5 minutes at the power of 50W at room temperature to obtain an electrolyte solution C;
(2) and (3) reactive stripping: placing an electrolyte device in a constant temperature environment of 0 ℃, taking the graphite sheet as an electrode in the step (1) and the solution B as electrolyte, and stably keeping for 2 hours under the direct current voltage of 3V; then transferring the electrode into an electrolyte solution C, stripping by using an alternating voltage with the following control time parameters, stabilizing at 10V, continuously electrifying for 1h according to the set parameters, and obtaining a precipitate at the bottom of the solution C; alternating voltage control parameters: the voltage is applied to the electrode M and the electrode N according to the following parameters:
(3) cleaning and extracting: dissolving the precipitate obtained by the reaction in the step (2) in N-N dimethylformamide, wherein the addition amount of the N-N dimethylformamide is 1ml/mg of the precipitate; performing ultrasonic treatment for 30 minutes at the power of 240W at room temperature to obtain a solution D, centrifuging the solution D at the speed of 3000rpm for 30 minutes, cleaning and recycling the lower-layer precipitate after centrifugation, and reusing the lower-layer precipitate for preparing the positive electrode reactant A in the step (1); filtering and washing the centrifuged supernatant for 10 times by using deionized water to obtain separated solids;
(4) and (3) drying: freeze-drying the solid separated in the step (3) to obtain graphene; the obtained graphene has an oxygen content of about 10%, a size of more than 4 μm, and a number of layers of less than 10.
Example 3
A preparation method of graphene is characterized by comprising the following steps:
(1) preparation of reactants: pressing graphite powder into graphite flakes through tabletting equipment, wherein the thickness of the pressed graphite flakes is 3mm, and the thickness of the pressed graphite flakes is the electrode M and the electrode N; selecting tetrabutylammonium hydrogen sulfate (TBAHSO)4) To prepare 0.5mol/L solution B; adding 3mL of 30% ammonia water in the solution B according to the volume ratio of 3% in the solution B, namely adding 3mL of 30% ammonia water in each 100mL of the solution B, regulating the pH value of the solution B to 9, and uniformly stirring the mixed solution for 15 minutes; carrying out ultrasonic treatment for 5 minutes at the power of 50W at room temperature to obtain an electrolyte solution C;
(2) and (3) reactive stripping: placing an electrolyte device in a constant temperature environment of 0 ℃, taking the graphite sheet as an electrode in the step (1) and the solution B as electrolyte, and stably keeping for 2 hours under the direct current voltage of 3V; then transferring the electrode into an electrolyte solution C, stripping by using an alternating voltage with the following control time parameters, stabilizing at 10V, continuously electrifying for 1h according to the set parameters, and obtaining a precipitate at the bottom of the solution C; alternating voltage control parameters: the voltage is applied to the electrode M and the electrode N according to the following parameters:
(3) cleaning and extracting: dissolving the precipitate obtained by the reaction in the step (2) in N-N dimethylformamide, wherein the addition amount of the N-N dimethylformamide is 1ml/mg of the precipitate; performing ultrasonic treatment for 30 minutes at the power of 240W at room temperature to obtain a solution D, centrifuging the solution D at the speed of 3000rpm for 30 minutes, cleaning and recycling the lower-layer precipitate after centrifugation, and reusing the lower-layer precipitate for preparing the positive electrode reactant A in the step (1); filtering and washing the centrifuged supernatant for 10 times by using deionized water to obtain separated solids;
(4) and (3) drying: freeze-drying the solid separated in the step (3) to obtain graphene; the obtained graphene has an oxygen content of about 6%, a size of more than 3 μm, and a number of layers of less than 9.
Example 4
A preparation method of graphene is characterized by comprising the following steps:
(1) preparation of reactants: pressing graphite powder into graphite flakes through tabletting equipment, wherein the thickness of the pressed graphite flakes is 3mm, and the thickness of the pressed graphite flakes is the electrode M and the electrode N; selecting tetrabutylammonium hydrogen sulfate (TBAHSO)4) To prepare 0.5mol/L solution B; adding 3mL of 30% ammonia water in the solution B according to the volume ratio of 3% in the solution B, namely adding 3mL of 30% ammonia water in each 100mL of the solution B, regulating the pH value of the solution B to 9, and uniformly stirring the mixed solution for 15 minutes; carrying out ultrasonic treatment for 5 minutes at the power of 50W at room temperature to obtain an electrolyte solution C;
(2) and (3) reactive stripping: placing an electrolyte device in a constant temperature environment of 0 ℃, taking the graphite sheet as an electrode in the step (1) and the solution B as electrolyte, and stably keeping for 2 hours under the direct current voltage of 3V; then transferring the electrode into an electrolyte solution C, stripping by using an alternating voltage with the following control time parameters, stabilizing at 10V, continuously electrifying for 1h according to the set parameters, and obtaining a precipitate at the bottom of the solution C; alternating voltage control parameters: the voltage is applied to the electrode M and the electrode N according to the following parameters:
(3) cleaning and extracting: dissolving the precipitate obtained by the reaction in the step (2) in N-N dimethylformamide, wherein the addition amount of the N-N dimethylformamide is 1ml/mg of the precipitate; performing ultrasonic treatment for 30 minutes at the power of 240W at room temperature to obtain a solution D, centrifuging the solution D at the speed of 3000rpm for 30 minutes, cleaning and recycling the lower-layer precipitate after centrifugation, and reusing the lower-layer precipitate for preparing the positive electrode reactant A in the step (1); filtering and washing the centrifuged supernatant for 10 times by using deionized water to obtain separated solids;
(4) and (3) drying: freeze-drying the solid separated in the step (3) to obtain graphene; the obtained graphene has an oxygen content of about 9%, a size of more than 5 μm, and a number of layers of less than 8.
Example 5
A preparation method of graphene is characterized by comprising the following steps:
(1) preparation of reactants: pressing the flake graphite into a graphite sheet by using a tabletting device, wherein the thickness of the pressed sheet is 4mm for an electrode M and an electrode N; selecting tetrabutyl ammonium sulfate ((TBA)2SO4) To prepare 0.2mol/L solution B; adding 2mL of 30% ammonia water in the volume ratio of 2% into the solution B according to the volume ratio of 2%, namely adding 2mL of 30% ammonia water into each 100mL of the solution B, regulating the pH value of the solution B to 9, and uniformly stirring the mixed solution for 15 minutes; carrying out ultrasonic treatment for 10 minutes at the power of 30W at room temperature to obtain an electrolyte solution C;
(2) and (3) reactive stripping: and (3) placing the electrolyte device in a constant temperature environment of 5 ℃. The graphite flake is taken as an electrode in the step (1), the solution B is taken as an electrolyte, and the graphite flake is stably kept for 2 hours, preferably 2 hours under the direct current voltage of 3V. Then transferring the electrode into an electrolyte solution C, stripping by using an alternating voltage with the following control time parameters, stabilizing at 15V, continuously electrifying for 1.5h according to the set parameters, and obtaining a precipitate at the bottom of the solution C; alternating voltage control parameters: two electrodes are named as an electrode M and an electrode N, and voltages are applied to the two electrodes according to the following parameters:
(3) cleaning and extracting: dissolving the precipitate obtained by the reaction in the step (2) in N-methyl pyrrolidone, wherein the addition amount of the N-methyl pyrrolidone is 1ml/mg of the precipitate; performing ultrasonic treatment for 30 minutes at the power of 240W at room temperature to obtain a solution D, centrifuging the solution D at the speed of 3000rpm for 30 minutes, cleaning and recycling the lower-layer precipitate after centrifugation, and reusing the lower-layer precipitate for preparing the positive electrode reactant A in the step (1); filtering and washing the centrifuged supernatant for 10 times by using deionized water to obtain separated solids;
(4) and (3) drying: freeze-drying the solid separated in the step (3) to obtain graphene; the obtained graphene has an oxygen content of about 8%, a size of more than 4 μm, and a number of layers of less than 10.
Example 6
A preparation method of graphene is characterized by comprising the following steps:
(1) preparation of reactants: pressing graphite paper into graphite sheets by using tabletting equipment, wherein the thickness of the pressed graphite sheets is 3.5mm for the electrode M and the electrode N; selecting tetrabutylammonium hydrogen sulfate (TBAHSO)4) To prepare 0.4mol/L solution B; adding 2mL of 30% ammonia water in the solution B according to the volume ratio of 2% in every 100mL of the solution B, regulating the pH value of the solution B to 10, and uniformly stirring the mixed solution for 15 minutes; and at room temperatureCarrying out ultrasonic treatment for 5 minutes under the power of 40W to obtain an electrolyte solution C;
(2) and (3) reactive stripping: and (3) placing the electrolyte device in a constant temperature environment of 3 ℃. Taking the graphite flake as an electrode in the step (1), taking the solution B as electrolyte, and stably keeping the graphite flake for 2 hours under the direct current voltage of 3V; then transferring the electrode into an electrolyte solution C, stripping by using an alternating voltage with the following control time parameters, stabilizing at 9V, continuously electrifying for 1h according to the set parameters, and obtaining a precipitate at the bottom of the solution C; alternating voltage control parameters: two electrodes are named as an electrode M and an electrode N, and voltages are applied to the two electrodes according to the following parameters:
(3) cleaning and extracting: dissolving the precipitate obtained by the reaction in the step (2) in N-N dimethylformamide, wherein the addition amount of the N-N dimethylformamide is 1ml/mg of the precipitate; performing ultrasonic treatment for 30 minutes at the power of 240W at room temperature to obtain a solution D, centrifuging the solution D at the speed of 3000rpm for 30 minutes, cleaning and recycling the lower-layer precipitate after centrifugation, and reusing the lower-layer precipitate for preparing the positive electrode reactant A in the step (1); carrying out suction filtration and cleaning on the centrifuged supernatant for 9 times by using deionized water to obtain a separated solid;
(4) and (3) drying: freeze-drying the solid separated in the step (3) to obtain graphene; the obtained graphene has an oxygen content of about 7%, a size of more than 3 μm, and a number of layers of less than 9.
Example 7
A preparation method of graphene is characterized by comprising the following steps:
(1) preparation of reactants: pressing graphite paper into graphite sheets by using tabletting equipment, wherein the thickness of the pressed graphite sheets is 3.5mm for the electrode M and the electrode N; tetraethylammonium hydrogen sulfate (TEAHSO)4) To prepare 0.4mol/L solution B; in the B solution according to the volume ratio of 2 percentAdding 2mL of 30% ammonia water into every 100mL of the solution B, regulating the pH value of the solution B to 10, and uniformly stirring the mixed solution for 15 minutes; carrying out ultrasonic treatment for 5 minutes at the power of 40W at room temperature to obtain an electrolyte solution C;
(2) and (3) reactive stripping: and (3) placing the electrolyte device in a constant temperature environment of 3 ℃. Taking the graphite flake as an electrode in the step (1), taking the solution B as electrolyte, and stably keeping the graphite flake for 2 hours under the direct current voltage of 3V; then transferring the electrode into an electrolyte solution C, stripping by using an alternating voltage with the following control time parameters, stabilizing at 5V, continuously electrifying for 1h according to the set parameters, and obtaining a precipitate at the bottom of the solution C; alternating voltage control parameters: two electrodes are named as an electrode M and an electrode N, and voltages are applied to the two electrodes according to the following parameters:
| electrode M | Electrode N | Voltage of | Time | |
| Stage one | + | - | 5V | 45s |
| Stage two | - | + | 5V | 10s |
| Stage three | + | - | 5V | 45s |
| Stage four | - | + | 5V | 10s |
| Stage five | + | - | 5V | 10s |
| Stage six | - | + | 5V | 45s |
| Stage seven | + | - | 5V | 10s |
| Stage eight | - | + | 5V | 45s |
| Go back to stage one and cycle | + | - | 5V | 45s |
(3) Cleaning and extracting: dissolving the precipitate obtained in the step (2) in isopropanol, wherein the addition amount of the isopropanol is 1ml/mg of the precipitate; performing ultrasonic treatment for 30 minutes at the power of 240W at room temperature to obtain a solution D, centrifuging the solution D at the speed of 3000rpm for 30 minutes, cleaning and recycling the lower-layer precipitate after centrifugation, and reusing the lower-layer precipitate for preparing the positive electrode reactant A in the step (1); carrying out suction filtration and cleaning on the centrifuged supernatant for 9 times by using deionized water to obtain a separated solid;
(4) and (3) drying: freeze-drying the solid separated in the step (3) to obtain graphene; the obtained graphene has an oxygen content of about 7%, a size of more than 5 μm, and a number of layers of less than 10.
Comparative example 1
A method for preparing graphene, wherein stages 5 to 8 and 1 to 4 are the same as in example 1, the method comprising the steps of:
(1) preparation of reactants: pressing graphite powder into graphite flakes through tabletting equipment, wherein the thickness of the pressed graphite flakes is 3mm, and the thickness of the pressed graphite flakes is the electrode M and the electrode N; selecting tetrabutylammonium hydrogen sulfate (TBAHSO)4) To prepare 0.5mol/L solution B; adding 3mL of 30% ammonia water in the solution B according to the volume ratio of 3% in the solution B, namely adding 3mL of 30% ammonia water in each 100mL of the solution B, regulating the pH value of the solution B to 9, and uniformly stirring the mixed solution for 15 minutes; carrying out ultrasonic treatment for 5 minutes at the power of 50W at room temperature to obtain an electrolyte solution C;
(2) and (3) reactive stripping: placing an electrolyte device in a constant temperature environment of 0 ℃, taking the graphite sheet as an electrode in the step (1) and the solution B as electrolyte, and stably keeping for 2 hours under the direct current voltage of 3V; then transferring the electrode into an electrolyte solution C, stripping by using an alternating voltage with the following control time parameters, stabilizing at 10V, continuously electrifying for 1h according to the set parameters, and obtaining a precipitate at the bottom of the solution C; alternating voltage control parameters: the voltage is applied to the electrode M and the electrode N according to the following parameters:
| electrode M | Electrode N | Voltage of | Time | |
| Stage one | + | - | 10V | 45s |
| Stage two | - | + | 10V | 10s |
| Stage three | + | - | 10V | 45s |
| Stage four | - | + | 10V | 10s |
| Stage five | + | - | 10V | 45s |
| Stage six | - | + | 10V | 10s |
| Stage seven | + | - | 10V | 45s |
| Stage eight | - | + | 10V | 10s |
| Go back to stage one and cycle | + | - | 10V | 45s |
(3) Cleaning and extracting: dissolving the precipitate obtained by the reaction in the step (2) in N-N dimethylformamide, wherein the addition amount of the N-N dimethylformamide is 1ml/mg of the precipitate; performing ultrasonic treatment for 30 minutes at the power of 240W at room temperature to obtain a solution D, centrifuging the solution D at the speed of 3000rpm for 30 minutes, cleaning and recycling the lower-layer precipitate after centrifugation, and reusing the lower-layer precipitate for preparing the positive electrode reactant A in the step (1); filtering and washing the centrifuged supernatant for 10 times by using deionized water to obtain separated solids;
(4) and (3) drying: freeze-drying the solid separated in the step (3) to obtain graphene; the obtained graphene has an oxygen content of about 12%, a size of more than 2 μm, and a number of layers of less than 15.
Claims (16)
1. A method for electrochemically preparing graphene, characterized in that the method comprises the following steps:
(1) preparation of reactants:
pressing a graphite material into a graphite sheet through tabletting equipment, wherein the graphite material is one or more of graphite paper, crystalline flake graphite, graphite powder and graphite foil, and the tabletting thickness is 2-5 mm and is used as an electrode reactant A during electrolysis;
selecting ammonium salt as electrolyte to prepare 0.1-3mol/L of the electrolyte as ammonium salt solution B;
the ammonium salt is selected from one or more of tetrabutylammonium hydrogen sulfate, tetrabutylammonium sulfate, tetraethylammonium hydrogen sulfate and tetraethylammonium sulfate;
adding ammonia water into the solution B, adjusting the pH value of the solution B to 8-14, and uniformly mixing the mixed solution to obtain an alkaline electrolyte solution C;
(2) and (3) reactive stripping:
placing an electrolyte device in a constant temperature environment of 0-5 ℃, wherein the graphite sheets in the step (1) are respectively used as an electrode M and an electrode N to be electrolyzed, the solution B is used as an electrolyte, and the electrolyte is stably kept for 1-3 h under the direct current voltage of 2.5-3.5V;
and then transferring the electrode to an alkaline electrolyte solution C, stripping by using an alternating voltage with the following control time parameters, stabilizing at 5-15V, continuously electrifying for 0.5-2 h according to the set parameters, and obtaining a precipitate at the bottom of the solution C, wherein the alternating voltage controls the parameters: two electrodes are named as an electrode M and an electrode N, and voltages are applied to the two electrodes according to the following parameters:
the time ratio of the first stage to the second stage, the third stage to the fourth stage, the sixth stage to the fifth stage, and the eighth stage to the seventh stage is selected from 1: 1-60: 1, and obtaining a precipitate at the bottom of the solution C.
2. The method of claim 1, wherein the time ratio of stage one to stage two, stage three to stage four, stage six to stage five, and stage eight to stage seven is selected from 4:1 to 30: 1.
3. The method of claim 1, wherein the time ratio of stage one to stage two, stage three to stage four, stage six to stage five, and stage eight to stage seven is selected from 10:1 to 20: 1.
4. The method of claim 1, wherein step (1) is one or more of:
the thickness of the graphite sheet is 2-3 mm;
the concentration of the ammonium salt solution is 0.2-1 mol/L;
and further adding ammonia water into the solution B, adjusting the pH value of the solution B to 9-10, and uniformly mixing the mixed solution to obtain an alkaline electrolyte solution C.
5. The method according to claim 1, wherein the concentration of the ammonium salt solution in the step (1) is 0.2-0.5 mol/L.
6. The method of claim 1, wherein step (2) is one or more of:
placing an electrolyte device in a constant temperature environment of 0-5 ℃, wherein in the step (1), the graphite flake is used as an electrode M and an electrode N to be electrolyzed, the solution B is used as electrolyte, and the electrolyte is stably kept for 1-2 hours under the direct current voltage of 2.5-3V;
and then transferring the electrode to an alkaline electrolyte solution C, stripping by using an alternating voltage with the following control time parameters, stabilizing the voltage by 10-15V, continuously electrifying for 1-1.5 h according to the set parameters, and obtaining a precipitate at the bottom of the solution C, wherein the alternating voltage controls the parameters: two electrodes are named as an electrode M and an electrode N, and voltages are applied to the two electrodes according to the following parameters:
the time ratio of the first stage to the second stage, the third stage to the fourth stage, the sixth stage to the fifth stage, and the eighth stage to the seventh stage is 4: 1-30: 1, and precipitates are obtained at the bottom of the solution C.
7. The method according to claim 5, wherein the time ratio of stage one to stage two, stage three to stage four, stage six to stage five, stage eight to stage seven in step (2) is selected from 10:1 to 20: 1.
8. The method of claim 1, wherein step (2) is one or more of:
placing an electrolyte device in a constant temperature environment of 0 ℃, wherein in the step (1), the graphite flake is taken as an electrode M and an electrode N to be electrolyzed, the solution B is taken as electrolyte, and the electrolyte is stably kept for 2 hours under the direct current voltage of 3V;
transferring the electrode into an alkaline electrolyte solution C, stripping by using an alternating voltage with the following control time parameters, stabilizing 10V, continuously electrifying for 1-1.5 h according to the set parameters, and obtaining a precipitate at the bottom of the solution C, wherein the alternating voltage controls the parameters: two electrodes are named as an electrode M and an electrode N, and voltages are applied to the two electrodes according to the following parameters:
a precipitate was obtained at the bottom of solution C.
9. The method according to claim 1, wherein the alkaline electrolyte solution C in the step (1) is prepared by adding 1-5% by volume of 30% ammonia water to 100mL of the solution B, adjusting the pH value of the solution B to 8-14, and uniformly stirring the mixed solution for 15-20 minutes; and carrying out ultrasonic treatment for 1-10 minutes at the room temperature under the power of 30-60W to obtain an electrolyte solution C.
10. The method of claim 9, wherein the alkaline electrolyte solution C of step (1) is 2-3% by volume in the solution B.
11. The method of claim 9, wherein the electrolyte solution C is obtained by sonication at 50-60W power for 5-10 minutes at room temperature.
12. The method of claim 1, further comprising the step of:
(3) cleaning and extracting:
dissolving the precipitate obtained by the stripping reaction in the step (2) in an organic solvent, and carrying out ultrasonic treatment for 20-40 minutes at the power of 180-240W at room temperature to obtain a solution D;
centrifuging the solution D at 2000-4000rpm for 20-40 minutes;
washing and recovering the centrifuged lower-layer precipitate, and secondarily using the lower-layer precipitate for preparing the electrode reactant A in the step (1);
and (4) carrying out suction filtration and cleaning on the centrifuged supernatant for 5-10 times by using deionized water to obtain a separated solid.
13. The method according to claim 12, wherein the organic solvent in step (3) is one or more of N-N dimethylformamide, N methylpyrrolidone, and isopropanol; the amount of the organic solvent is 1-2 ml/mg of the precipitate obtained by the stripping reaction in the step (2).
14. The method of claim 12, further comprising the step of:
(4) and (3) drying: and (4) drying the solid separated in the step (3) to obtain the graphene.
15. The method of claim 14, wherein the drying method in step (4) is one of forced air drying, spray drying, oven drying, or freeze drying.
16. Graphene prepared by the method according to any one of claims 1 to 15, wherein the obtained graphene is not graphene oxide but low-oxidation-degree graphene, the oxygen content is low, and the proportion of oxygen element relative to the total mass of the graphene is not more than 10%; the prepared graphene is large in size and not smaller than 3 mu m; the number of layers is less than 8.
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