CN113479868A - Method for preparing graphene through bipolar electrochemical stripping of organic acid ammonium fused salt - Google Patents
Method for preparing graphene through bipolar electrochemical stripping of organic acid ammonium fused salt Download PDFInfo
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- 239000010439 graphite Substances 0.000 claims abstract description 111
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- VZTDIZULWFCMLS-UHFFFAOYSA-N ammonium formate Chemical compound [NH4+].[O-]C=O VZTDIZULWFCMLS-UHFFFAOYSA-N 0.000 claims abstract description 33
- USFZMSVCRYTOJT-UHFFFAOYSA-N Ammonium acetate Chemical compound N.CC(O)=O USFZMSVCRYTOJT-UHFFFAOYSA-N 0.000 claims abstract description 29
- 239000005695 Ammonium acetate Substances 0.000 claims abstract description 29
- 229940043376 ammonium acetate Drugs 0.000 claims abstract description 29
- 235000019257 ammonium acetate Nutrition 0.000 claims abstract description 29
- XJMWHXZUIGHOBA-UHFFFAOYSA-N azane;propanoic acid Chemical compound N.CCC(O)=O XJMWHXZUIGHOBA-UHFFFAOYSA-N 0.000 claims abstract description 28
- 238000005868 electrolysis reaction Methods 0.000 claims abstract description 21
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- 238000010438 heat treatment Methods 0.000 claims description 13
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- ZMXDDKWLCZADIW-UHFFFAOYSA-N N,N-Dimethylformamide Chemical compound CN(C)C=O ZMXDDKWLCZADIW-UHFFFAOYSA-N 0.000 claims description 6
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
- C01B32/15—Nano-sized carbon materials
- C01B32/182—Graphene
- C01B32/184—Preparation
- C01B32/19—Preparation by exfoliation
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B2204/00—Structure or properties of graphene
- C01B2204/20—Graphene characterized by its properties
- C01B2204/32—Size or surface area
Abstract
The invention discloses a method for preparing graphene by bipolar electrochemical stripping of organic acid ammonium fused salt. The method comprises the following steps: the method comprises the following steps of (1) constructing an electrochemical reaction system by taking liquid molten salt as electrolyte and graphite electrodes as a cathode and an anode respectively, wherein the electrolyte comprises organic acid ammonium liquid molten salt; electrifying the electrochemical reaction system for electrolysis, applying a voltage of 1-30V for electrolysis for 1-100 min to obtain expanded graphite, and then carrying out ultrasonic treatment to obtain graphene. The organic acid ammonium liquid fused salt comprises ammonium formate, ammonium acetate, ammonium propionate and the like. The method can realize the stripping of the anode and the cathode simultaneously, organic acid ammonium can be inserted into the graphite interlayer after forming molten salt, and decomposed into gas under the driving of voltage, so that the graphite interlayer expands to generate graphene; the operation is simple, and the required organic acid ammonium fused salt is environment-friendly, low in price, good in reproducibility and convenient for industrial popularization.
Description
Technical Field
The invention relates to a preparation method of graphene, in particular to a method for preparing graphene by bipolar electrochemical stripping of organic acid ammonium fused salt, and belongs to the technical field of nano materials.
Background
Graphene is composed of a single layer of carbon atoms and has excellent physical and chemical properties. And has potential application in the fields of photoelectric devices, catalysis, biosensing, transparent conductive films, energy storage and the like. Development of scalability and low-cost production of high-quality graphene is an urgent requirement for realization of commercialization and large-scale application thereof. However, the conventional methods are lacking in competitiveness in terms of yield, scale, cost effectiveness, and environmental acceptability. For example, chemically reducing graphite oxide requires the use of strong acids, strong oxidants, and toxic substances in large quantities to produce single-layer and few-layer graphene, and the produced graphene contains a large number of defects. In addition, electrochemical stripping has become a potentially scalable process due to its advantages of easy handling, easy solution processing, environmental friendliness, low cost effectiveness, and easy control. During electrochemical exfoliation of graphite, a voltage is applied across the graphite electrode, where a current drives the migration of ions or charged molecules into the graphite interlayer channels. The graphite sheet structure is then expanded and then exfoliated into graphene sheets. Electrochemically driven stripping can be performed in an anodic oxidation or cathodic reduction process.
Anodic stripping in mineral acids, inorganic salts, ionic liquids and eutectic solvents has been extensively studied, where production rate, throughput and product quality depend on the graphite source, electrolyte and applied voltage. For example, anodic stripping in high conductivity aqueous sulfate solutions has higher yields and efficiencies than other electrolytes due to their efficient intercalation and gas expansion. In addition, exfoliation using graphite flakes can yield few layers of graphene with high yield (75%) and 5.5% oxygen content, and with good yield (over 10g h)-1) While the yield with graphite powder is lower than 40%, the oxygen content is higher (21.0%), the graphite rods are 17% and 28.3% respectively, the treatment time is also up to 12 hours (chem. commun.52: 5714-5717.). As for the influence of the applied voltage, the low voltage can obtain enough anion intercalation and slow exfoliation of graphene, thereby obtaining high yield of few-layer graphene, almost no defects, but lower production efficiency. Increasing the voltage can improve yield, but can result in more defects in the prepared graphene. In summary, the anodic oxidation can achieve high exfoliation efficiency, but at high voltage, graphite inevitably forms certain defects on its surface.
The cathode stripping is to insert cations into the graphite cathode, so that oxygen function on graphene is avoided in the stripping processAnd (4) forming clusters. The cathodic exfoliation technique of graphene is often studied in organic solvents (Carbon 127: 392-403) and ionic liquids (electrochim. acta 113: 9-16) containing lithium or quaternary ammonium salts. Graphite rods in Tetraalkylammonium (TAA) salts/N-methylpyridinone (NMP) or graphite flakes in (Li)++Et3NH+) Cathodic disbonding in Dimethylsulfoxide (DMSO) organic solvents usually takes several minutes, increasing the oxygen content by no more than 3%. The exfoliation efficiency is limited because large cations or solvated ions readily exfoliate the graphite into thick sheets, and therefore, most of the sheets do not intercalate sufficiently away from the graphite cathode.
In summary, graphite (whether anode or cathode) can be electrochemically exfoliated to yield graphene. For anode exfoliation, several layers of nanosheets with a certain degree of oxidation can be obtained with high efficiency and high yield, and the degree of oxidation and defect density can be tailored by varying different parameters. In contrast to the anode, cathodic intercalation and/or exfoliation of the graphite electrode will prevent oxidation of the exfoliated graphene. High quality non-oxidized graphene can be prepared by this method, however, cathodic intercalation occurs mainly in organic electrolytes. Cost, safety and efficiency issues need to be addressed before further development can be achieved.
Disclosure of Invention
The invention mainly aims to provide a method for preparing graphene by bipolar electrochemical stripping of organic acid ammonium fused salt, so as to overcome the defects in the prior art.
In order to achieve the purpose, the technical scheme adopted by the invention comprises the following steps:
the embodiment of the invention provides a method for preparing graphene by bipolar electrochemical stripping of organic acid ammonium molten salt, which comprises the following steps:
the method comprises the following steps of (1) constructing an electrochemical reaction system by taking liquid molten salt as electrolyte and graphite electrodes as a cathode and an anode respectively, wherein the electrolyte comprises organic acid ammonium liquid molten salt;
electrifying the electrochemical reaction system for electrolysis, and applying a voltage of 1-30V for electrolysis for 1-100 min to obtain expanded graphite;
and carrying out ultrasonic treatment on the expanded graphite to obtain the graphene.
Furthermore, the graphene has a size of 1-5 μm and a thickness of less than 5 nm.
In some embodiments, the liquid fused salt of ammonium organate comprises any one or a combination of two or more of ammonium formate, ammonium acetate, ammonium propionate, and the like.
In some embodiments, the distance between the cathode and the anode is 1cm to 5cm, and the depth of insertion into the electrolyte is lcm to 10 cm.
Compared with the prior art, the invention has the advantages that:
according to the method for preparing graphene by bipolar electrochemical stripping of organic ammonium fused salt, provided by the invention, stripping of a cathode and an anode can be realized simultaneously, organic ammonium can be inserted into the graphite interlayer after forming fused salt, and decomposed into gas under the drive of voltage, so that the graphite interlayer expands to generate graphene. Because the conductivity of the molten salt is high, enough ions can be embedded between graphite layers, and efficient stripping can be realized at low voltage. In the stripping process, fewer oxidizing groups are generated, so that high-quality thin-layer graphene is obtained; the method for preparing the graphene only needs a power supply and electrolysis equipment, is simple to operate, and the required organic acid ammonium electrolyte is environment-friendly, low in price, good in reproducibility and convenient for industrial popularization.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments described in the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a Scanning Electron Microscope (SEM) image of graphene obtained in example 1 of the present invention;
FIG. 2 is a Scanning Electron Microscope (SEM) image of graphene obtained in example 2 of the present invention;
FIG. 3 is an X-ray diffraction (XRD) pattern of graphene obtained in example 3 of the present invention;
FIG. 4 is an Atomic Force Microscope (AFM) image of graphene obtained in example 4 of the present invention;
FIG. 5 is a Raman spectrum (Raman) chart of graphene obtained in example 5 of the present invention;
FIG. 6 is a Transmission Electron Microscope (TEM) image of graphene obtained in example 6 of the present invention;
FIG. 7 is a Transmission Electron Microscope (TEM) image of graphene obtained in example 7 of the present invention;
FIG. 8 is a High Resolution Transmission Electron Microscope (HRTEM) image of graphene obtained in example 8 of the present invention;
fig. 9 is an electron diffraction pattern of graphene obtained in example 9 of the present invention.
Detailed Description
In view of the deficiencies in the prior art, the inventors of the present invention have made extensive studies and extensive practices to provide technical solutions of the present invention. The technical solution, its implementation and principles, etc. will be further explained as follows.
One aspect of the embodiment of the invention provides a method for preparing graphene by bipolar electrochemical stripping of organic acid ammonium molten salt, which comprises the following steps:
the method comprises the following steps of (1) constructing an electrochemical reaction system by taking liquid molten salt as electrolyte and graphite electrodes as a cathode and an anode respectively, wherein the electrolyte comprises organic acid ammonium liquid molten salt;
electrifying the electrochemical reaction system for electrolysis, applying a voltage of 1-30V for electrolysis for 1-100 min, and forcing the graphite electrode to expand and peel to obtain expanded graphite;
and carrying out ultrasonic treatment on the expanded graphite to obtain the graphene.
Furthermore, the graphene has a size of 1-5 μm and a thickness of less than 5 nm.
In some embodiments, the liquid fused salt of ammonium organate includes any one or a combination of two or more of ammonium formate, ammonium acetate, ammonium propionate, and the like, but is not limited thereto.
In some embodiments, the method comprises: at least one or more than two kinds of organic ammonium are heated to be melted and evenly stirred to obtain the organic ammonium liquid molten salt.
In some specific preferred embodiments, the method for preparing graphene by bipolar electrochemical stripping of ammonium organic acid fused salt comprises the following steps:
(1) weighing one or more than two organic acids according to the mass fraction ratio, heating to melt the organic acids, and uniformly stirring by magnetic force to obtain liquid molten salt of the organic acids; the organic acid ammonium fused salt is ammonium formate, ammonium acetate and ammonium propionate;
(2) taking two graphite electrodes as a cathode and an anode respectively, taking organic acid ammonium fused salt as electrolyte, and inserting the graphite electrodes into the electrolyte (the organic acid ammonium fused salt);
(3) connecting the negative and positive poles of the two graphite with a power supply thereof, applying a voltage of 1-30V for electrolysis for 1-100 minutes, collecting expanded graphite in an electrolyte, washing with distilled water, and cleaning with ethanol;
(4) and dispersing the cleaned expanded graphite in N-methylpyrrolidone (NMP), then carrying out ultrasonic treatment for 5-60 minutes, carrying out suction filtration and ethanol washing on the dispersion liquid, and drying to obtain the graphene.
In some embodiments, the heating temperature range in step (1) is 80-150 ℃, and specifically, the method comprises: heating the organic acid ammonium to 80-150 ℃ to melt the organic acid ammonium.
In some embodiments, when the ammonium organate comprises two or more of ammonium formate, ammonium acetate, and ammonium propionate, the content of any ammonium organate is 5 wt% to 95 wt%.
Further, in the step (1), the organic acid ammonium is mixed according to the mass percentage, when two kinds of organic acid ammonium are mixed, any one kind of organic acid ammonium is 5% -95%, when three kinds of organic acid ammonium are mixed, any one kind of organic acid ammonium is 5% -95%, and the organic acid ammonium fused salt is ammonium formate, ammonium acetate and ammonium propionate.
In some embodiments, the graphite electrode in step (2) comprises a graphite rod, a graphite foil, high-orientation pyrolytic graphite, natural graphite flake or natural graphite flake, or the like. That is, in another aspect, the graphite electrode used in the present invention may be graphite foil, highly oriented pyrolytic graphite, natural graphite flake, and natural graphite powder flake, in addition to the graphite rod.
Further, the distance between the cathode and the anode (namely two graphite electrodes) in the step (2) is kept between 1cm and 5cm, and the depth of the cathode and the anode inserted into the electrolyte is 1cm to 10 cm.
In some embodiments, the power source for applying the voltage in step (3) is a direct current constant voltage, an alternating current power source, a constant current power source, a pulse power source, or the like.
In some embodiments, the method comprises: dispersing the expanded graphite in a solvent, then carrying out ultrasonic treatment for 5-60 min, and then washing and drying to obtain the graphene.
Further, the solvent includes any one or a combination of two or more of N-methylpyrrolidone (NMP), N-dimethylformamide, dimethylsulfoxide, formamide, and the like, but is not limited thereto.
In some embodiments, the ultrasonic treatment in step (3) may be performed by using an ultrasonic cleaning machine or an ultrasonic crusher.
Further, the drying in the step (4) may be atmospheric drying, freeze drying, supercritical drying, or the like.
In conclusion, the method for preparing graphene by bipolar electrochemical stripping of organic ammonium salt fused salt provided by the invention can realize simultaneous stripping of the anode and the cathode, and the organic ammonium salt can be inserted into the graphite interlayer after forming fused salt and decomposed into gas under the drive of voltage, so that the graphite interlayer expands to generate graphene. Because the conductivity of the molten salt is high, enough ions can be embedded between graphite layers, and efficient stripping can be realized at low voltage. During the exfoliation process, fewer oxidized groups are generated, resulting in high quality thin-layer graphene. Meanwhile, the method for preparing the graphene only needs a power supply and electrolysis equipment, is simple to operate, and the required organic acid ammonium electrolyte is environment-friendly, low in price, good in reproducibility and convenient for industrial popularization.
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described below with reference to the following detailed description and accompanying drawings, so that those skilled in the art can implement the present invention with reference to the description. It should be understood that the specific embodiments described herein are merely illustrative of the invention, and that experimental conditions and set parameters therein are not to be considered as limitations of the basic embodiments of the invention. And the scope of the present invention is not limited to the following examples. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
Example 1
(1) Weighing ammonium formate to a certain mass, heating to 120 ℃ to melt the ammonium formate, and magnetically stirring the ammonium formate uniformly to obtain liquid molten salt of the ammonium formate;
(2) taking two graphite rod electrodes as a positive electrode and a negative electrode respectively, taking the ammonium formate molten salt as electrolyte, inserting the graphite rod electrodes into the electrolyte, keeping the distance between the graphite electrodes at 1cm, and keeping the depth of the graphite rod electrodes inserted into the electrolyte at 1 cm;
(3) connecting the anode and cathode of graphite with a direct current power supply, applying a voltage of 1V for electrolysis for 1 minute, collecting expanded graphite in the electrolyte, washing with distilled water, and washing with ethanol;
(4) dispersing the cleaned expanded graphite in N-methylpyrrolidone (NMP), then carrying out ultrasonic treatment for 5 minutes by using an ultrasonic cleaning machine, carrying out suction filtration on the dispersion liquid, washing with ethanol, and drying at normal pressure to obtain graphene, wherein the size of the graphene is 1-5 mu m, and the thickness of the graphene is less than 5 nm.
Example 2
(1) Weighing ammonium formate and ammonium acetate according to the mass fractions of 5% and 95%, heating to 130 ℃ to melt the ammonium formate and the ammonium acetate, and magnetically stirring the ammonium formate and the ammonium acetate uniformly to obtain liquid molten salt;
(2) taking two graphite foil electrodes as a positive electrode and a negative electrode respectively, taking the ammonium formate and ammonium acetate fused salt as electrolyte, inserting the graphite foil electrodes into the electrolyte, keeping the distance between the graphite electrodes at 2cm, and keeping the depth of the graphite foil electrodes inserted into the electrolyte at 2 cm;
(3) connecting the anode and cathode of graphite with a direct current power supply, applying a voltage of 3V for electrolysis for 5 minutes, collecting expanded graphite in the electrolyte, washing with distilled water, and washing with ethanol;
(4) and dispersing the cleaned expanded graphite in N-methylpyrrolidone (NMP), then carrying out ultrasonic treatment for 60 minutes by using an ultrasonic crusher, carrying out suction filtration on the dispersion liquid, washing with ethanol, and carrying out freeze drying to obtain graphene, wherein the size of the graphene is 1-5 mu m, and the thickness of the graphene is less than 5 nm.
Example 3
(1) Weighing ammonium formate, ammonium acetate and ammonium propionate according to the mass fractions of 5%, 35% and 60%, heating to 135 ℃ to melt the ammonium formate, and magnetically stirring the ammonium formate, the ammonium acetate and the ammonium propionate uniformly to obtain liquid molten salt;
(2) taking two high-orientation thermal cracking graphite electrodes as a cathode and an anode respectively, taking the ammonium formate, ammonium acetate and ammonium propionate molten salt as electrolyte, inserting the high-orientation thermal cracking graphite electrodes into the electrolyte, keeping the distance between the graphite electrodes at 3cm, and keeping the depth of the graphite electrodes inserted into the electrolyte at 2 cm;
(3) connecting the anode and cathode of graphite with a direct current power supply, applying a voltage of 8V for electrolysis for 25 minutes, collecting expanded graphite in the electrolyte, washing with distilled water, and washing with ethanol;
(4) dispersing the cleaned expanded graphite in N-methylpyrrolidone (NMP), then carrying out ultrasonic treatment for 20 minutes by using an ultrasonic cleaning machine, carrying out suction filtration on the dispersion liquid, washing with ethanol, and carrying out supercritical drying to obtain graphene, wherein the size of the graphene is 1-5 mu m, and the thickness of the graphene is less than 5 nm.
Example 4
(1) Weighing ammonium acetate and ammonium propionate according to the mass fractions of 30% and 70%, heating to 135 ℃ to melt the ammonium acetate and the ammonium propionate, and magnetically stirring the ammonium acetate and the ammonium propionate uniformly to obtain liquid molten salt;
(2) taking two natural graphite flake pressing electrodes as a cathode and an anode respectively, taking the ammonium acetate and ammonium propionate fused salt as electrolyte, inserting the natural graphite flake pressing electrodes into the electrolyte, keeping the distance between the graphite electrodes at 5cm, and keeping the depth of the natural graphite flake pressing electrodes inserted into the electrolyte at 6 cm;
(3) connecting the anode and cathode of graphite with a direct current power supply, applying a voltage of 30V for electrolysis for 100 minutes, collecting expanded graphite in the electrolyte, washing with distilled water, and washing with ethanol;
(4) dispersing the cleaned expanded graphite in N-methylpyrrolidone (NMP), then carrying out ultrasonic treatment for 35 minutes by using an ultrasonic cleaning machine, carrying out suction filtration on the dispersion liquid, washing with ethanol, and drying at normal pressure to obtain graphene, wherein the size of the graphene is 1-5 mu m, and the thickness of the graphene is less than 5 nm.
Example 5
(1) Weighing ammonium propionate to a certain mass, heating to 150 ℃ to melt the ammonium propionate, and magnetically stirring the ammonium propionate uniformly to obtain liquid molten salt of the ammonium propionate;
(2) taking two natural graphite powder tabletting electrodes as a cathode and an anode respectively, taking the ammonium acetate and ammonium propionate molten salt as electrolyte, inserting the natural graphite powder tabletting electrodes into the electrolyte, keeping the distance between the graphite electrodes at 5cm, and keeping the depth of the natural graphite powder tabletting electrodes inserted into the electrolyte at 10 cm;
(3) connecting the anode and cathode of graphite with a direct current power supply, applying a voltage of 30V for electrolysis for 100 minutes, collecting expanded graphite in the electrolyte, washing with distilled water, and washing with ethanol;
(4) and dispersing the cleaned expanded graphite in N-methylpyrrolidone (NMP), then carrying out ultrasonic treatment for 45 minutes by using an ultrasonic crusher, carrying out suction filtration on the dispersion liquid, washing with ethanol, and carrying out freeze drying to obtain graphene, wherein the size of the graphene is 1-5 mu m, and the thickness of the graphene is less than 5 nm.
Example 6
(1) Weighing ammonium formate and ammonium propionate according to the mass fractions of 45% and 55%, heating to 135 ℃ to melt the ammonium formate and the ammonium propionate, and magnetically stirring the ammonium formate and the ammonium propionate uniformly to obtain liquid molten salt;
(2) taking two high-orientation thermal cracking graphite electrodes as a cathode and an anode respectively, taking the ammonium formate and ammonium propionate fused salt as electrolyte, inserting the high-orientation thermal cracking graphite electrodes into the electrolyte, and keeping the distance between the graphite electrodes at 4cm and the depth of the graphite electrodes inserted into the electrolyte at 5 cm;
(3) connecting the anode and cathode of graphite with a direct current power supply, applying a voltage of 20V for electrolysis for 50 minutes, collecting expanded graphite in the electrolyte, washing with distilled water, and washing with ethanol;
(4) dispersing the cleaned expanded graphite in N-methylpyrrolidone (NMP), then carrying out ultrasonic treatment for 15 minutes by using an ultrasonic crusher, carrying out suction filtration on the dispersion liquid, washing with ethanol, and carrying out supercritical drying to obtain graphene, wherein the size of the graphene is 1-5 mu m, and the thickness of the graphene is less than 5 nm.
Example 7
(1) Weighing ammonium formate and ammonium propionate according to the mass fractions of 65% and 35%, heating to 150 ℃ to melt the ammonium formate and the ammonium propionate, and magnetically stirring the ammonium formate and the ammonium propionate uniformly to obtain liquid molten salt;
(2) taking two high-orientation thermal cracking graphite electrodes as a cathode and an anode respectively, taking the ammonium formate and ammonium propionate fused salt as electrolyte, inserting the high-orientation thermal cracking graphite electrodes into the electrolyte, and keeping the distance between the graphite electrodes at 5cm and the depth of the graphite electrodes inserted into the electrolyte at 10 cm;
(3) connecting the positive and negative electrodes of graphite with a pulse power supply, applying a voltage of 30V for electrolysis for 100 minutes, collecting expanded graphite in the electrolyte, washing with distilled water, and washing with ethanol;
(4) dispersing the cleaned expanded graphite in formamide, then carrying out ultrasonic treatment for 35 minutes by using an ultrasonic cleaning machine, carrying out suction filtration on the dispersion liquid, washing with ethanol, and drying under normal pressure to obtain graphene, wherein the size of the graphene is 1-5 mu m, and the thickness of the graphene is less than 5 nm.
Example 8
(1) Weighing ammonium acetate by a certain mass, heating to 140 ℃ to melt the ammonium acetate, and magnetically stirring the ammonium acetate uniformly to obtain liquid molten salt of the ammonium acetate;
(2) taking two graphite rod electrodes as a cathode and an anode respectively, taking the ammonium acetate fused salt as electrolyte, inserting the graphite rod electrodes into the electrolyte, keeping the distance between the graphite electrodes at 3cm, and keeping the depth of the graphite rod electrodes inserted into the electrolyte at 10 cm;
(3) connecting the anode and cathode of the graphite with a constant current power supply, applying a voltage of 15V for electrolysis for 80 minutes, collecting expanded graphite in the electrolyte, washing with distilled water, and washing with ethanol;
(4) and dispersing the cleaned expanded graphite in dimethyl sulfoxide, then carrying out ultrasonic treatment for 35 minutes by using an ultrasonic cleaning machine, carrying out suction filtration on the dispersion liquid, washing with ethanol, and carrying out freeze drying to obtain graphene, wherein the size of the graphene is 1-5 mu m, and the thickness of the graphene is less than 5 nm.
Example 9
(1) Weighing ammonium formate and ammonium acetate according to the mass fractions of 50% and 50%, heating to 80 ℃ to melt the ammonium formate and the ammonium acetate, and magnetically stirring the mixture uniformly to obtain liquid molten salt of the ammonium formate and the ammonium acetate;
(2) taking two natural graphite powder tabletting electrodes as a positive electrode and a negative electrode respectively, taking the ammonium formate and ammonium acetate molten salt as electrolyte, inserting the natural graphite powder tabletting electrodes into the electrolyte, keeping the distance between the graphite electrodes at 5cm, and keeping the depth of the natural graphite powder tabletting electrodes inserted into the electrolyte at 10 cm;
(3) connecting the anode and cathode of graphite with an alternating current power supply, applying voltage of 30V for electrolysis for 100 minutes, collecting expanded graphite in the electrolyte, washing with distilled water, and cleaning with ethanol;
(4) dispersing the cleaned expanded graphite in N, N-dimethylformamide, then carrying out ultrasonic treatment for 35 minutes by using an ultrasonic cleaning machine, carrying out suction filtration on a dispersion liquid, washing with ethanol, and drying at normal pressure to obtain graphene, wherein the size of the graphene is 1-5 mu m, and the thickness of the graphene is less than 5 nm.
Comparative example 1
The inventor also conducted experiments using a mixture of acetamide, urea and salts as an electrolyte according to the method of CN108675287A, but the atom utilization rate is not high, and is far inferior to the above examples of the present invention.
In addition, the inventor also refers to the manner of example 1-example 9, and experiments were carried out on other raw materials and conditions listed in this specification, and the same technical effects can be obtained, stripping of the anode and the cathode can be simultaneously carried out, the organic acid ammonium can be inserted into the graphite interlayer after forming a molten salt, and the molten salt is decomposed into gas under the driving of voltage, so that the graphite interlayer expands to produce graphene. Because the conductivity of the molten salt is high, enough ions can be embedded between graphite layers, and efficient stripping can be realized at low voltage. In the stripping process, fewer oxidizing groups are generated, so that high-quality thin-layer graphene is obtained; the method for preparing the graphene only needs a power supply and electrolysis equipment, is simple to operate, and the required organic acid ammonium electrolyte is environment-friendly, low in price, good in reproducibility and convenient for industrial popularization.
While the invention has been described with reference to illustrative embodiments, it will be understood by those skilled in the art that various other changes, omissions and/or additions may be made and substantial equivalents may be substituted for elements thereof without departing from the spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
Claims (10)
1. A method for preparing graphene by bipolar electrochemical stripping of organic acid ammonium fused salt is characterized by comprising the following steps:
the method comprises the following steps of (1) constructing an electrochemical reaction system by taking liquid molten salt as electrolyte and graphite electrodes as a cathode and an anode respectively, wherein the electrolyte comprises organic acid ammonium liquid molten salt;
electrifying the electrochemical reaction system for electrolysis, and applying a voltage of 1-30V for electrolysis for 1-100 min to obtain expanded graphite;
and carrying out ultrasonic treatment on the expanded graphite to obtain the graphene.
2. The method of claim 1, wherein: the organic acid ammonium liquid fused salt comprises any one or the combination of more than two of ammonium formate, ammonium acetate and ammonium propionate; and/or the graphene has the size of 1-5 mu m and the thickness of less than 5 nm.
3. The method of claim 2, comprising: at least one or more than two kinds of organic ammonium are heated to be melted and evenly stirred to obtain the organic ammonium liquid molten salt.
4. The method of claim 3, comprising: heating the organic acid ammonium to 80-150 ℃ to melt the organic acid ammonium.
5. The method of claim 3, wherein: when the organic acid ammonium comprises more than two of ammonium formate, ammonium acetate and ammonium propionate, the content of any one organic acid ammonium is 5-95 wt%.
6. The method of claim 1, wherein: the graphite electrode comprises a graphite rod, a graphite foil, high-orientation pyrolytic graphite, a natural graphite flake or a natural graphite powder pressing sheet.
7. The method of claim 1, wherein: the distance between the cathode and the anode is 1 cm-5 cm, and the depth of the cathode inserted into the electrolyte is 1 cm-10 cm.
8. The method of claim 1, wherein: the power source for applying voltage includes a direct current constant voltage, an alternating current power source, a constant current power source, or a pulse power source.
9. The method of claim 1, comprising: dispersing the expanded graphite in a solvent, then carrying out ultrasonic treatment for 5-60 min, and then washing and drying to obtain the graphene.
10. The method of claim 9, wherein: the solvent comprises any one or the combination of more than two of N-methyl pyrrolidone, N-dimethylformamide, dimethyl sulfoxide and formamide; and/or, carrying out the ultrasonic treatment by adopting an ultrasonic cleaner or an ultrasonic crusher; and/or, the drying comprises atmospheric drying, freeze drying or supercritical drying.
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