CN113666366A - Method for preparing graphene through electrochemical anode stripping - Google Patents
Method for preparing graphene through electrochemical anode stripping Download PDFInfo
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- CN113666366A CN113666366A CN202010401630.5A CN202010401630A CN113666366A CN 113666366 A CN113666366 A CN 113666366A CN 202010401630 A CN202010401630 A CN 202010401630A CN 113666366 A CN113666366 A CN 113666366A
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Abstract
The invention provides a method for preparing graphene by electrochemical anode stripping, which comprises the following steps: taking a molybdate aqueous solution as an electrolyte, respectively taking two pieces of graphite paper as an anode and a cathode, connecting the anode and the cathode with two poles of a direct current power supply, placing the anode and the cathode in the electrolyte, and electrifying to carry out electrochemical anode stripping to obtain an electrolytic solution containing a graphene precursor; and purifying the electrolytic solution containing the graphene precursor to obtain the graphene dispersion liquid. The invention provides a novel method for preparing graphene by electrochemical anode stripping, which introduces molybdate aqueous solution as electrolyte for electrochemical stripping for the first time, has the advantages of simple and convenient operation, few steps, safety, controllability, environmental friendliness, low cost, strong repeatability and the like, and is suitable for large-scale production. And 76% of the obtained graphene sheet layers do not exceed five layers, can be uniformly dispersed in water, and has good water solubility and stability.
Description
Technical Field
The invention relates to the technical field of graphene preparation, in particular to a method for preparing graphene through electrochemical anode stripping.
Background
Graphene is a carbon material with a two-dimensional structure, and is formed by sp2The hybridized carbon atoms are arranged in a shape of a plane six square grid. Since 2004, it was discovered that graphene has been widely used in the fields of transistors, batteries and supercapacitors, biomedicine, biosensors, electrothermal films and catalysis due to its excellent electrical, thermal and mechanical properties. Graphene is two-dimensionalIn the research work on the carbon nano material, how to well prepare the graphene becomes the first problem on the application road.
Through continuous trial and search, the existing graphene preparation methods include mechanical exfoliation, Chemical Vapor Deposition (CVD), epitaxial growth, chemical oxidation-reduction, and liquid-phase exfoliation. Among them, the mechanical exfoliation method can theoretically obtain graphene without crystal defects, but the yield of graphene is generally very low. Although the vapor deposition method and the epitaxial growth method can prepare graphene with a larger lamellar, the vapor deposition method requires harsh conditions, and the epitaxial growth method generally needs to transfer a graphene sample to other substrates, which is high in cost. The redox method is low in cost, but a large amount of strong oxidant and toxic substances involved have great harm to the environment. The liquid phase stripping method can basically obtain high-quality graphene, but the yield of the graphene is limited, and the used high-boiling-point organic solvent still has the defects of high toxicity and high cost.
On the basis, the electrochemical stripping preparation of the graphene is expected to become one of better methods for realizing large-scale production of the graphene due to the advantages of simple process, environment friendliness and the like. During electrochemical anode exfoliation, anions originally present in the electrolyte or formed during the application of a voltage are intercalated into the anode graphite layers by the action of an electric field force, which results in the weakening of van der waals forces between the graphite layers, thereby causing the anode graphite to be exfoliated by expansion. Therefore, the electrolyte used in electrochemical anodic stripping has a great influence on the stripping efficiency and the quality of the obtained graphene. The graphene electrochemical anode stripping methods reported so far are roughly classified into those performed in an organic solvent, an ionic liquid, and an aqueous electrolyte. The graphene obtained by stripping the ionic liquid has few defects and is thin, but the ionic liquid is complex in preparation process and high in price, and is difficult to realize large-scale use. Electrochemical anode stripping in organic solvents is usually performed by adding auxiliary agents to improve the yield, but the use of a large amount of organic solvents brings great danger to the operation process.
The graphene prepared by stripping in the aqueous electrolyte is relatively safe. The aqueous electrolyte includes an aqueous solution of an acidic or alkaline reagent such as sulfuric acid, nitric acid, perchloric acid, and sodium hydroxide, a salt thereof, and a partial oxidizing agent. For example, Tian et al (chem.Mater.2017,29,15, 6214-. The graphene stripped by the method has uniform transverse dimension (2-6 mu m), few structural defects and high conductivity, but the electrolyte used by the method relates to a strong oxidant, namely hydrogen peroxide, with high concentration, the risk coefficient is large, and the obtained graphene has good dispersibility in an organic solvent, namely NMP. Khaled Parvez et al (Journal of the American Chemical Society,2014,136(16): 6083-. The safety of the electrolyte in the method is better, but the dispersion concentration of the obtained graphene in an organic solvent DMF is higher, so that the uniform dispersion of the graphene in water cannot be realized, and the quality of the graphene still needs to be improved.
Disclosure of Invention
In view of this, the present application provides a method for preparing graphene by electrochemical anode stripping, and the method of the present invention is simple in operation, safe, controllable, environment-friendly, low in cost, high in efficiency, and excellent in water solubility of the obtained graphene.
The invention provides a method for preparing graphene by electrochemical anode stripping, which comprises the following steps:
taking a molybdate aqueous solution as an electrolyte, and taking two pieces of graphite paper as an anode and a cathode respectively to form an electrolytic system, electrifying, and carrying out electrochemical anode stripping to obtain an electrolytic solution containing a graphene precursor;
and purifying the electrolytic solution containing the graphene precursor to obtain the graphene dispersion liquid.
Preferably, the molybdate is one or more of sodium molybdate and ammonium molybdate.
Preferably, the concentration of molybdate in the molybdate aqueous solution is 0.015 to 1.0M.
Preferably, the graphite paper is cleaned with absolute alcohol before being used as an anode and a cathode respectively.
Preferably, the anode and the cathode are arranged in the electrolyte in parallel and are connected with two poles of a direct current power supply to form an electrolytic system; the voltage of the direct current power supply ranges from +9V to + 10V.
Further preferably, the time for stripping the electrochemical anode is 1.5-8 h.
Preferably, the purification is specifically: and carrying out solid-liquid separation and washing on the electrolyte solution containing the graphene precursor to obtain a precipitate, ultrasonically dispersing the precipitate in water, and centrifuging to obtain an upper layer liquid to obtain a graphene dispersion liquid.
Preferably, the electrolyte solution containing the graphene precursor is subjected to short-time ultrasound before solid-liquid separation; the solid-liquid separation adopts a centrifugal mode, and then residual inorganic salt particles in the electrolytic solution are washed and removed to obtain precipitates.
Preferably, the solid-liquid separation comprises multiple times of centrifugation, wherein the rotating speed of each time of centrifugation is 10000-12000 rpm, and the time of each time of centrifugation is 5-15 min.
Preferably, the supernatant obtained by centrifugation is specifically: centrifuging at the rotating speed of 5000-9000 rpm for 5-20 min, and taking supernatant to obtain the stable graphene dispersion.
Compared with the prior art for preparing graphene by electrochemical anode stripping, the method has the advantages that the graphite paper is stripped in molybdate aqueous solution; when positive potential is applied to the anode graphite paper, the edge and the grain boundary of the anode graphite paper are oxidized, namely the edge area of the anode graphite paper is opened, a large number of molybdate ions, water molecules and hydroxide ions generated in the water electrolysis process enter between the graphite layers, so that the graphite paper is gradually expanded, and finally, by means of oxygen released in the water electrolysis process, the graphite layers are peeled off by overcoming the action of van der waals force, and then the graphene is obtained through purification. The graphite paper electrode adopted by the invention is low in price and convenient and easy to obtain; the electrolyte does not have strong acid, strong base and oxidizing reagent, molybdate aqueous solution is introduced as the electrolyte for the first time, the innovativeness is high, and molybdate remained on the graphene precursor is easy to remove; no toxic gas is generated in the electrolysis process, and only a simple water electrolysis reaction is performed to generate hydrogen and oxygen, so that the method is green and pollution-free. In addition, 76% of graphene sheets obtained by the method do not exceed five layers, can be uniformly dispersed in water, and has good water solubility and stability. The whole process is simple to operate, environment-friendly, pollution-free, safe, non-toxic, low in cost and energy consumption, and compared with the traditional electrochemical anode stripping method, the method is more suitable for industrial production.
Drawings
FIG. 1 is a low-power transmission electron micrograph of graphene obtained in example one;
FIG. 2 is a high-resolution TEM image of the graphene obtained in the first example;
FIG. 3 is a high resolution TEM image of the graphene obtained in the first example;
FIG. 4 is a high resolution TEM image of the graphene obtained in the first example;
FIG. 5 is a photo of the graphene dispersion dispersed in deionized water obtained in the first example, wherein the left and right sides are compared before and after being placed for two months;
FIG. 6 is a comparison of the electrode conditions before and after electrolysis for the first example and the third comparative example.
Detailed Description
The technical solutions in the embodiments of the present invention are clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The embodiment of the invention provides a method for preparing graphene by electrochemical anode stripping, which comprises the following steps:
taking a molybdate aqueous solution as an electrolyte, respectively taking two pieces of graphite paper as an anode and a cathode, connecting the anode and the cathode with two poles of a direct current power supply, placing the anode and the cathode in the electrolyte to form an electrolytic system, and electrifying to strip the electrochemical anode to obtain an electrolytic solution containing a graphene precursor;
and purifying the electrolytic solution containing the graphene precursor to obtain the graphene dispersion liquid.
Aiming at the problems in the prior art, on one hand, the preparation of the graphene at present requires simple operation, environment-friendly process, no pollution, safe and controllable steps, low cost and high efficiency, and has potential possibility of large-scale preparation; on the other hand, the high quality of the obtained graphene, namely, the number of layers is small, the number of sheets is thin, the transverse size is large, and good dispersibility and stability can be realized in water. The invention provides a novel method for preparing graphene by electrochemical stripping, which has the characteristics of simplicity and convenience in operation, safety, controllability, environmental friendliness, lower cost and the like, and the obtained graphene has excellent water-solubility and other qualities.
The invention adopts molybdate aqueous solution as electrolyte, wherein the molybdate is preferably one or more of sodium molybdate and ammonium molybdate, and more preferably sodium molybdate. Firstly, preparing a molybdate aqueous solution, and dissolving molybdate in water to prepare an electrolyte (namely the molybdate aqueous solution); the electrolyte adopted by the invention does not contain strong acid, strong base and oxidizing reagent, and is safer and more environment-friendly. The water involved in the scheme of the invention is generally deionized water; the concentration of molybdate in the molybdate aqueous solution can be 0.015 to 1.0M. In some preferred embodiments of the present invention, the concentration of the sodium molybdate in the electrolyte is 0.05-1.0M, such as any one of 0.05M, 0.1M, 0.5M, and 1.0M. In other preferred embodiments of the present invention, the ammonium molybdate is ammonium heptamolybdate, and the concentration of the ammonium heptamolybdate can be 0.015-1.0M; the concentration of the amount of the substance of ammonium heptamolybdate was 0.015M (since the heptamolybdate ion is converted to the molybdate ion in the deionized water, in order to control the content of the molybdenum element in the electrolyte to be 0.1M, the concentration of the amount of the substance of ammonium heptamolybdate was set to be 0.015M).
In the embodiment of the invention, two pieces of graphite paper are respectively taken as an anode and a cathode and are correspondingly connected with the positive pole and the negative pole of a direct current power supply, and then the two graphite paper electrodes are put into a prepared electrolyte in parallel to form the electrolysis device.
Wherein the graphite paper is a flake graphite material. The embodiment of the invention adopts low-price commercial flexible graphite paper as stripping raw material, is convenient and easy to obtain, and greatly reduces the production cost. In a preferred embodiment of the present invention, the graphite paper is a commercial graphite material, and has high purity (carbon content greater than 99.5%), and good graphitization degree (the peak of (002) crystal plane at 26.5 ° 2 θ in XRD result is strong); specifically, the thickness of the graphite paper can be 0.05cm, the taking length is 5cm, the width is 2cm, and the surface of the graphite paper is simply wiped and cleaned by using absolute ethyl alcohol before taking, so that the cleaning is convenient and quick. In some embodiments of the invention, the graphite paper can be fixed in the electrolyte by means of clamps such as crocodile clip wires when being put into the electrolyte; when the two graphite paper electrodes are placed in the electrolyte in parallel, the distance between the two graphite paper electrodes is 4cm, the length of the two graphite paper electrodes partially immersed in the electrolyte is 4cm, and the width of the two graphite paper electrodes is 2 cm.
In the embodiment of the invention, a direct-current power supply is turned on, electrochemical anode stripping is started and timing is carried out, and the stripping is finished until the part of the anode graphite paper in the electrolyte is completely stripped, so that the electrolyte solution containing the graphene precursor is obtained. In some preferred embodiments of the present invention, the dc power voltage is +9V to +10V, for example +9V or + 10V; the time for stripping the electrochemical anode is 1.5-8 h.
In the invention, when positive potential is applied to the anode graphite paper, the edge and the grain boundary of the anode graphite paper are oxidized, so that the edge area of the anode graphite paper is opened, a large amount of molybdate ions, water molecules and hydroxide ions generated in the water electrolysis process enter between the graphite layers, so that the graphite paper is gradually expanded, and finally, the graphite layers are peeled off by overcoming the action of van der Waals force by virtue of oxygen released in the water electrolysis process, so that the graphene is obtained. What is important in the process is that molybdate ions can enter between graphite layers and prop open graphite sheets, and many other ions cannot enter between the graphite sheets due to the factors such as the self three-dimensional structure, the charge-mass ratio and the like, or can enter into the graphite sheets but cannot prop open the graphite sheets, so that van der waals force between the graphite layers cannot be damaged, and van der waals force cannot be damaged, namely, the graphite sheets cannot be peeled off, and thus peeling fails.
Wherein, the electrolytic voltage has certain influence on the stripping speed; the stripping speed is higher as the voltage is higher, so that the time for oxidizing the edges of the graphite sheet layers is shortened, and the oxygen content in the obtained graphene is slightly reduced. In addition, the degree of oxidation during the stripping process determines the solubility and stability of graphene in water. In the molybdate stripping process, the graphite sheet layer is oxidized to a greater degree before being stripped, so that the obtained graphene has greater solubility in water and better stability.
In addition, the electrolysis process of the invention is only simple water electrolysis reaction, hydrogen and oxygen are generated, no toxic gas is generated, and the invention is green and pollution-free.
According to the embodiment of the invention, the graphite paper electrode is taken down, the stripped electrolyte and the obtained graphene precursor are subjected to post-treatment to purify the sample, wherein molybdate remained on the graphene precursor is easily removed, so that the graphene dispersion liquid is obtained. Preferably, the purification specifically comprises: removing residual inorganic salt in the electrolyte by performing solid-liquid separation and washing on the electrolyte solution containing the graphene precursor to obtain a precipitate; the sediment is ultrasonically dispersed in water, so that the thickness of a sheet layer can be reduced, and the yield of graphene can be increased; and then centrifuging to obtain supernatant, thereby ensuring that the thickness of the obtained graphene sheet is relatively thin.
In the embodiment of the invention, the electrolyte solution containing the graphene precursor (containing the graphene precursor and the stripped electrolyte) is subjected to short-time ultrasonic treatment, and then solid-liquid separation operation and washing are carried out; in a preferred embodiment of the present invention, the short ultrasonic time of the stripped electrolyte and the graphene precursor may be 1 min. The solid-liquid separation is preferably operated by adopting a multi-centrifugation mode, wherein the rotating speed of each centrifugation can be 10000-12000 rpm, and the time of each centrifugation can be 5-15 min. In a preferred embodiment of the present invention, the solid-liquid separation is performed by centrifuging at 11000rpm for 10min, removing the supernatant, oscillating and dispersing with deionized water, washing, centrifuging at 11000rpm for 10min again, and repeating the step for four times to wash away the residual inorganic salt particles in the electrolyte. The centrifugal operation in the solid-liquid separation and washing process is to wash away residual ions in the solution as much as possible without losing graphene precursors, so that the rotation speed is relatively high and appropriate as much as possible.
The precipitate is placed in deionized water for ultrasonic redispersion, and finally supernatant liquid is obtained through centrifugation, so that the stable graphene dispersion liquid is obtained. In a preferred embodiment of the present invention, the placing the precipitate in deionized water for ultrasonic redispersion specifically comprises: the resulting precipitate was placed in 50mL deionized water and ultrasonically dispersed for 40 min. If the ultrasonic time is too short, the graphene precursor is not completely dispersed, and the obtained graphene has low yield and thicker lamella; and the graphene sheet layer obtained when the ultrasonic time is too long is too small to reach the required micron level. Preferably, the supernatant liquid is obtained by centrifuging at the rotating speed of 5000-9000 rpm for 5-20 min, so that a large and thick graphene sheet layer can be removed, and the dispersibility and stability of the graphene product in water can be effectively improved. In a preferred embodiment of the present invention, the centrifugation is performed at 8000rpm for 10min, and then 80% of the supernatant is obtained, so as to obtain the stable graphene dispersion.
In the graphene dispersion liquid obtained by the embodiment of the invention, the graphene sheets are thin, and 76% of the graphene sheets do not exceed five layers; the obtained graphene dispersion liquid is uniform and good in stability. The whole process is simple to operate, environment-friendly, pollution-free, safe, non-toxic, low in cost and low in energy consumption; compared with the traditional electrochemical anode stripping method, the method is more suitable for industrial production.
In order to further understand the present application, the following specifically describes the method for preparing graphene by electrochemical anodic stripping provided in the present application with reference to the examples. It should be understood, however, that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention, which is defined by the following examples.
The following raw materials are all commercially available products. Wherein, the carbon content of the used graphite paper is more than 99.5% (JB/T9141.6-1999), the graphite paper is purchased from Qingdateng Hengda carbon machinery company, model TSD, and is pressed by natural crystalline flake graphite powder (the crystalline flake graphite powder is from Navilla graphite ore in Qingdao Lexi city, has complete crystallization, thin sheet, good resistance, excellent physical and chemical properties, and has good temperature resistance, self-lubricating property, conductivity, corrosion resistance and other properties); tensile strength: greater than 4.5MPa (JB/T9141.8-1999); sulfur content: less than 800ppm (JB/T7758.3-2008).
In an X-ray powder diffraction (XRD) pattern of the original graphite paper, a peak of (002) crystal plane at 26.5 ° 2 θ is very strong; the intensity ratio of the D peak to the G peak on the Raman diagram is 0.15, which indicates that the graphite paper has good graphitization degree. It should be noted that, here, the results of XRD and raman detection are summarized, and the detection diagram is not shown.
Example one
The graphene is prepared by electrochemical stripping sequentially through the following steps:
(1) 2.4195g of sodium molybdate dihydrate were weighed and dissolved in 100mL of deionized water with stirring to obtain 0.1M sodium molybdate electrolyte.
(2) The thickness of the used graphite paper is 0.05cm, two pieces with the length of 5cm and the width of 2cm are cut, the surface of the graphite paper is cleaned by absolute ethyl alcohol, then the graphite paper is respectively used as an anode and a cathode and is connected with two poles of a direct current power supply, the two graphite paper electrodes are parallelly placed into the electrolyte in the step (1), the distance between the two pieces of graphite paper is 4cm, the length of the two pieces of graphite paper partially immersed into the electrolyte is 4cm, and the width of the two pieces of graphite paper is 2 cm.
(3) And (3) turning on a direct current power supply, starting electrochemical anode stripping and timing, and taking 4 hours after the anode graphite paper is completely stripped in the electrolyte.
(4) And taking off the graphite paper electrode, carrying out short-time ultrasonic treatment on the stripped electrolyte and the graphene precursor for 1min, then repeating the operation of centrifuging for 10min at 11000rpm for four times, and washing with deionized water to wash away residual inorganic salt ions in the electrolyte. And placing the obtained precipitate in 50mL deionized water, performing ultrasonic dispersion for 40min, and finally centrifuging at 8000rpm for 10min to obtain 80% of upper layer liquid to obtain a stable graphene dispersion liquid.
Fig. 1 to 4 show the transmission electron microscope results of the graphene obtained in the first embodiment of the present invention, where fig. 1 shows the size of the graphene sheet layer, and a distinct wrinkle state can be seen, and fig. 2 to 4 show the number of layers of different graphene sheet layers, which are two layers, three layers, and four layers, respectively. The sample preparation step of the electron microscope shooting comprises the following steps: and (3) taking a small amount of graphene dispersion liquid, diluting to a proper concentration, dripping the graphene dispersion liquid on a special copper net for electron microscope testing, and naturally airing to be tested. The graphene sheets on the copper mesh can approximately represent the sheets of the whole graphene dispersion liquid, so that the size and the number of the layers of the graphene sheets on the copper mesh can be approximately considered as the size and the number of the layers of the whole graphene dispersion liquid through statistical analysis.
Fig. 2 to 4 are high-resolution observations of different graphene sheets on a copper mesh during shooting, which clearly show that the number of different graphene sheets is 2, 3, or 4 graphene sheets are present in the obtained graphene dispersion.
Fig. 5 is a comparison of the resulting graphene dispersion before and after two months of standing, the right side being a stable dispersion after two months of standing, no agglomeration occurred.
In the process of shooting by an electron microscope, 50 graphene sheets are randomly selected for high-resolution observation, the number of the graphene sheets is counted, and finally summary calculation is carried out, so that 76% of the graphene sheets are not more than five.
In the preferred embodiment of the present application (0.1M sodium molybdate solution, 10V), the obtained graphene dispersion is freeze-dried to remove water, so that about 160mg of graphene powder can be obtained. The mass of the original graphite paper was about 400mg, and the yield was 38%. The method can be used for batch preparation by parallel electrolysis or enlarging graphite paper.
Example two
The graphene is prepared by electrochemical stripping sequentially through the following steps:
(1) 2.4195g of sodium molybdate dihydrate were weighed and dissolved in 100mL of deionized water with stirring to obtain 0.1M sodium molybdate electrolyte.
(2) The thickness of the used graphite paper is 0.05cm, two pieces with the length of 5cm and the width of 2cm are cut, the surface of the graphite paper is cleaned by using absolute ethyl alcohol, then the graphite paper is respectively used as an anode and a cathode and is connected with two poles of a direct current power supply, then the two graphite paper electrodes are parallelly placed into the electrolyte in the step (1), the distance between the two pieces of graphite paper is 4cm, the length of the two pieces of graphite paper partially immersed into the electrolyte is 4cm, and the width of the two pieces of graphite paper is 2 cm.
(3) And (3) turning on a direct current power supply, starting electrochemical anode stripping and timing, and taking 5.5 hours after the anode graphite paper is completely stripped in the electrolyte.
(4) And taking off the graphite paper electrode, carrying out short-time ultrasonic treatment on the stripped electrolyte and the graphene precursor for 1min, then repeating the operation of centrifuging for 10min at 11000rpm for four times, and washing with deionized water to wash away residual inorganic salt ions in the electrolyte. And placing the obtained precipitate in 50mL deionized water, performing ultrasonic dispersion for 40min, and finally centrifuging at 8000rpm for 10min to obtain 80% of upper layer liquid to obtain a stable graphene dispersion liquid.
EXAMPLE III
The graphene is prepared by electrochemical stripping sequentially through the following steps:
(1) 1.2098g of sodium molybdate dihydrate were weighed and dissolved in 100mL of deionized water with stirring to obtain 0.05M sodium molybdate electrolyte.
(2) The thickness of the used graphite paper is 0.05cm, two pieces with the length of 5cm and the width of 2cm are cut, the surface of the graphite paper is cleaned by using absolute ethyl alcohol, then the graphite paper is respectively used as an anode and a cathode and is connected with two poles of a direct current power supply, then the two graphite paper electrodes are parallelly placed into the electrolyte in the step (1), the distance between the two pieces of graphite paper is 4cm, the length of the two pieces of graphite paper partially immersed into the electrolyte is 4cm, and the width of the two pieces of graphite paper is 2 cm.
(3) And (3) turning on a direct current power supply, starting electrochemical anode stripping and timing, and taking 6 hours after the anode graphite paper is completely stripped in the electrolyte.
(4) And taking off the graphite paper electrode, carrying out short-time ultrasonic treatment on the stripped electrolyte and the graphene precursor for 1min, then repeating the operation of centrifuging for 10min at 11000rpm for four times, and washing with deionized water to wash away residual inorganic salt ions in the electrolyte. And placing the obtained precipitate in 50mL deionized water, performing ultrasonic dispersion for 40min, and finally centrifuging at 8000rpm for 10min to obtain 80% of upper layer liquid to obtain a stable graphene dispersion liquid.
Example four
The graphene is prepared by electrochemical stripping sequentially through the following steps:
(1) 12.0975g of sodium molybdate dihydrate were weighed and dissolved in 100mL of deionized water with stirring to obtain 0.5M sodium molybdate electrolyte.
(2) The thickness of the used graphite paper is 0.05cm, two pieces with the length of 5cm and the width of 2cm are cut, the surface of the graphite paper is cleaned by using absolute ethyl alcohol, then the graphite paper is respectively used as an anode and a cathode and is connected with two poles of a direct current power supply, then the two graphite paper electrodes are parallelly placed into the electrolyte in the step (1), the distance between the two pieces of graphite paper is 4cm, and the length and the width of the part of the two pieces of graphite paper, which is immersed into the electrolyte, are both 4 cm.
(3) And (3) turning on a direct current power supply, starting electrochemical anode stripping and timing, and taking 1.5 hours after the anode graphite paper is completely stripped in the electrolyte.
(4) And taking off the graphite paper electrode, carrying out short-time ultrasonic treatment on the stripped electrolyte and the graphene precursor for 1min, then repeating the operation of centrifuging for 10min at 11000rpm for four times, and washing with deionized water to wash away residual inorganic salt ions in the electrolyte. And placing the obtained precipitate in 50mL deionized water, performing ultrasonic dispersion for 40min, and finally centrifuging at 8000rpm for 10min to obtain 80% of upper layer liquid to obtain a stable graphene dispersion liquid.
EXAMPLE five
The graphene is prepared by electrochemical stripping sequentially through the following steps:
(1) 24.1950g of sodium molybdate dihydrate were weighed and dissolved in 100mL of deionized water with stirring to obtain 1.0M sodium molybdate electrolyte.
(2) The thickness of the used graphite paper is 0.05cm, two pieces with the length of 5cm and the width of 2cm are cut, the surface of the graphite paper is cleaned by using absolute ethyl alcohol, then the graphite paper is respectively used as an anode and a cathode and is connected with two poles of a direct current power supply, then the two graphite paper electrodes are parallelly placed into the electrolyte in the step (1), the distance between the two pieces of graphite paper is 4cm, the length of the two pieces of graphite paper partially immersed into the electrolyte is 4cm, and the width of the two pieces of graphite paper is 2 cm.
(3) And (3) turning on a direct current power supply, starting electrochemical anode stripping and timing, and taking 1.5 hours after the anode graphite paper is completely stripped in the electrolyte.
(4) And taking off the graphite paper electrode, carrying out short-time ultrasonic treatment on the stripped electrolyte and the graphene precursor for 1min, then repeating the operation of centrifuging for 10min at 11000rpm for four times, and washing with deionized water to wash away residual inorganic salt ions in the electrolyte. And placing the obtained precipitate in 50mL deionized water, performing ultrasonic dispersion for 40min, and finally centrifuging at 8000rpm for 10min to obtain 80% of upper layer liquid to obtain a stable graphene dispersion liquid.
EXAMPLE six
The graphene is prepared by electrochemical stripping sequentially through the following steps:
(1) 1.8538g of ammonium molybdate tetrahydrate were weighed and dissolved in 100mL of deionized water with stirring to give 0.015M ammonium heptamolybdate electrolyte.
(2) The thickness of the used graphite paper is 0.05cm, two pieces with the length of 5cm and the width of 2cm are cut, the surface of the graphite paper is cleaned by using absolute ethyl alcohol, then the graphite paper is respectively used as an anode and a cathode and is connected with two poles of a direct current power supply, then the two graphite paper electrodes are parallelly placed into the electrolyte in the step (1), the distance between the two pieces of graphite paper is 4cm, and the length and the width of the part of the two pieces of graphite paper, which is immersed into the electrolyte, are both 4 cm.
(3) And (3) turning on a direct current power supply, starting electrochemical anode stripping and timing, and taking 8 hours after the anode graphite paper is completely stripped in the electrolyte.
(4) And taking off the graphite paper electrode, carrying out short-time ultrasonic treatment on the stripped electrolyte and the graphene precursor for 1min, then repeating the operation of centrifuging for 10min at 11000rpm for four times, and washing with deionized water to wash away residual inorganic salt ions in the electrolyte. And placing the obtained precipitate in 50mL deionized water, performing ultrasonic dispersion for 40min, and finally centrifuging at 8000rpm for 10min to obtain 80% of upper layer liquid to obtain a stable graphene dispersion liquid.
The second to sixth examples mainly differ in the electrolyte solution, the concentration thereof, and the stripping voltage, and therefore, the time required for stripping differs, and this part is mainly to study the influence of these stripping conditions on the stripping speed. The stripping rate affects the oxygen content of the graphene product, and thus the water solubility. The stripping speed is moderate, the water solubility is good, and the graphene can meet the requirement of subsequent utilization.
The stripping speeds of the sodium molybdate electrolyte at the concentrations of 0.05M, 0.1M, 0.5M and 1.0M are explored, the stripping speed is accelerated when the concentration is increased from visual observation, and the time required for finishing the stripping at the concentrations is respectively 8h, 4h, 1.5h and 1.5 h.
Comparative examples 1 to 3
Respectively comparing with the stripping with sodium chloride, sodium sulfate and ammonium chloride as electrolyte; in the comparative test, the electrode sheet size, the electrolyte concentration and other parameters of the stripping process were all the same as those in example 1 except for the type of the electrolyte (concentration: 0.1M, voltage +10V, post-treatment were the same).
Among them, the stripping effects of sodium chloride and ammonium chloride are weak, and graphene dispersion cannot be obtained.
Sodium sulfate is used as electrolyte, so that the yield of the obtained graphene is low, and the stability of the graphene in water is poor. See figure 6 for a specific peel comparison.
In FIG. 6, part a is a comparison of anodes before and after electrolysis in sodium molybdate, and part b is a comparison of anodes before and after electrolysis in sodium sulfate; the portion of the two portions in which the anode was immersed in the solution was substantially consumed electrolytically, except that the sodium molybdate took 4 hours and the sodium sulfate took 6 hours, so the rate of stripping of the sodium sulfate was slow. Then, through the same post-treatment operation, the graphene powder obtained in comparative example three was about 120mg, with a yield of about 30%, which was 8% lower than that of sodium molybdate.
From the above embodiments, the present invention is a method for preparing graphene by electrochemical anodic stripping in a molybdate aqueous solution, wherein the molybdate aqueous solution is used as an electrolyte, two pieces of graphite paper are used as a cathode and an anode, and a dc power is applied to strip the graphene. The method disclosed by the invention is simple in process, low in cost, low in energy consumption, safe and controllable, and is a green pollution-free graphene preparation method. And 76% of the obtained graphene sheet layers are not more than five, can be uniformly dispersed in water, have good water solubility and stability, and are beneficial to subsequent application.
The above description is only a preferred embodiment of the present invention, and it should be noted that various modifications to these embodiments can be implemented by those skilled in the art without departing from the technical principle of the present invention, and these modifications should be construed as the scope of the present invention.
Claims (10)
1. A method for preparing graphene by electrochemical anode stripping comprises the following steps:
taking a molybdate aqueous solution as an electrolyte, and taking two pieces of graphite paper as an anode and a cathode respectively to form an electrolytic system, electrifying, and carrying out electrochemical anode stripping to obtain an electrolytic solution containing a graphene precursor;
and purifying the electrolytic solution containing the graphene precursor to obtain the graphene dispersion liquid.
2. The method of claim 1, wherein the molybdate is one or more of sodium molybdate and ammonium molybdate.
3. The method of claim 1, wherein the concentration of molybdate in the aqueous molybdate solution is between 0.015 and 1.0M.
4. The method of claim 1, wherein the graphite paper is cleaned with absolute alcohol before being used as the anode and cathode, respectively.
5. The method of claim 1, wherein the anode and the cathode are placed in parallel in the electrolyte and connected to both poles of a dc power source to form an electrolytic system; the voltage of the direct current power supply ranges from +9V to + 10V.
6. The method according to claim 5, wherein the time for electrochemical anodic stripping is 1.5-8 hours.
7. The method according to any one of claims 1 to 6, wherein the purification is in particular: and carrying out solid-liquid separation and washing on the electrolyte solution containing the graphene precursor to obtain a precipitate, ultrasonically dispersing the precipitate in water, and centrifuging to obtain an upper layer liquid to obtain a graphene dispersion liquid.
8. The method according to claim 7, characterized in that the electrolytic solution containing the graphene precursor is subjected to brief ultrasound before solid-liquid separation; the solid-liquid separation adopts a centrifugal mode, and then residual inorganic salt particles in the electrolytic solution are washed and removed to obtain precipitates.
9. The method according to claim 8, wherein the solid-liquid separation comprises multiple centrifugations, wherein the rotating speed of each centrifugation is 10000-12000 rpm, and the time of each centrifugation is 5-15 min.
10. The method according to claim 9, wherein the centrifuging and supernatant extracting are specifically: centrifuging at the rotating speed of 5000-9000 rpm for 5-20 min, and taking supernatant to obtain the stable graphene dispersion.
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