CN110282619B - Method for reducing and peeling graphene oxide by lithium-assisted microwave thermal expansion method - Google Patents
Method for reducing and peeling graphene oxide by lithium-assisted microwave thermal expansion method Download PDFInfo
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- CN110282619B CN110282619B CN201910539112.7A CN201910539112A CN110282619B CN 110282619 B CN110282619 B CN 110282619B CN 201910539112 A CN201910539112 A CN 201910539112A CN 110282619 B CN110282619 B CN 110282619B
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Abstract
The invention relates to the field of preparation of nano carbon materials, in particular to a method for reducing and stripping graphene oxide by a lithium-assisted microwave thermal expansion method. The preparation of the lithium-assisted microwave reduction graphene is completed under the conditions of ultrasonic treatment, blast drying and microwave heating, in the microwave heating process, oxygen-containing functional groups on the graphene oxide are separated and released as gas, pressure is generated, thermal expansion is generated between graphene layers to peel off, and high-quality graphene is prepared at low temperature and normal pressure. In the microwave heating process, the decomposition rate of the oxygen-containing functional group in the graphene oxide is greater than the diffusion rate of the generated gas, and van der waals force capable of overcoming the combination of graphene sheets is generated, so that reduction and stripping are realized. And the original electronic structure is broken through by the existence of lithium, so that the graphene sheet layers can be peeled off more conveniently. The preparation method has the advantages of simple process, high preparation speed and low cost, and can be used for large-scale production, and the product is black floccule.
Description
Technical Field
The invention relates to the field of preparation of nano carbon materials, in particular to a method for reducing exfoliated graphene oxide by a lithium-assisted microwave thermal expansion method.
Background
The graphene is formed by combining carbon atoms arranged in a hexagonal honeycomb lattice, has excellent electrical, optical, thermal and mechanical properties, and is an ideal carbon nano material. The application research of graphene is rising, and the graphene has wide application prospects in various aspects including low-cost seawater desalination, high-strength composite bearing materials, high-frequency transistors, solar cells, sensors, catalysis, lithium ion batteries, super capacitors and the like. Therefore, the preparation of high-quality graphene is imperative. Graphene can be prepared by ultrasonically exfoliating or ball milling expanded graphite, but the degree of thermal expansion and thus the thickness of the obtained sheet layer are influenced by the intercalation process of graphite species and an expanding agent, and the thickness of the sheet layer is generally thicker, so that single-layer or few-layer graphene is difficult to obtain.
The conventional thermal expansion method needs to be carried out at high temperature and high pressure, needs harsh preparation conditions, has high energy consumption and few products, so that a large amount of high-quality graphene needs to be prepared, and a novel preparation method is imperative.
Disclosure of Invention
The invention aims to solve the problems in the prior art, and the graphene oxide is used as a raw material, and high-quality graphite is rapidly prepared at a lower temperature and with lower energy consumption through ultrasonic treatment, impregnation and microwave heating.
The invention is realized by the following technical scheme: a method for reducing exfoliated graphene oxide by a lithium-assisted microwave thermal expansion method comprises the following steps:
dissolving a lithium salt in deionized water, uniformly stirring, then uniformly mixing and stirring graphene oxide powder and the lithium salt solution, performing ultrasonic treatment for 30min, and drying the mixed solution after ultrasonic treatment in a vacuum oven to obtain a lithium-assisted microwave reduction graphene precursor; then grinding the lithium-assisted microwave reduction graphene precursor, placing the ground precursor into a corundum crucible with a cover, placing the corundum crucible into an inner bin of a microwave oven, turning on a vacuum pump until the pressure in the microwave oven is-0.05 MPa, turning on cooling circulating water of the microwave oven, turning on a microwave switch, and adjusting power to enable the temperature in the microwave oven to reach 200 ℃; and (3) closing a microwave switch after the cover of the corundum crucible is popped out from a visible window of the microwave oven, naturally cooling the temperature in the oven to 50 ℃, closing cooling circulating water, introducing nitrogen until the pressure in the oven is restored to normal pressure, and opening a cabin door to obtain the lithium-assisted microwave reduction graphene.
As a further improvement of the technical scheme of the invention, the temperature in the vacuum oven is 65 ℃, and the drying time is 12 hours.
As a further improvement of the technical scheme of the invention, the mass ratio of the lithium salt to the graphene oxide powder is 1.
As a further improvement of the technical scheme of the invention, the lithium salt is lithium nitrate or lithium carbonate.
Compared with the background technology, the method has obvious advancement, takes the oxidized graphene as the raw material, fully utilizes the rich oxygen-containing functional groups on the graphene, decomposes the oxygen-containing functional groups into carbon monoxide or carbon dioxide by heating, has higher decomposition rate than the diffusion rate of generated gas, generates Van der Waals force capable of overcoming the combination of graphene sheets together, leads the graphene layer to expand and peel off, and realizes reduction and peeling. Because lithium is small in size and a special electronic structure, the lithium can be inserted between graphene layers, the electronic structure of graphene is changed, the attraction between layers is reduced, the graphene layers can be more favorably peeled off, and meanwhile, rapid heating can be realized by adopting microwave heating. The preparation method has the advantages of advanced process, precise and detailed data, high preparation speed, simple process, low cost, large-scale production, thin yarn-like structure of the product shown by an electron microscope, specific surface area which is about eight times of that of graphene oxide, and high product purity, and is a very effective method for quickly preparing high-quality graphene on a large scale.
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 of 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 transmission electron microscope image of graphene prepared by a lithium-assisted method, and it can be seen that: the graphene is of a transparent yarn-shaped structure and has folds. The material is extremely thin, and graphene oxide is successfully reduced and exfoliated.
Fig. 2 is a graph comparing nitrogen adsorption and desorption curves of graphene oxide, microwave-reduced graphene, and lithium-assisted microwave-reduced graphene, and it can be seen that: the graphene subjected to lithium-assisted microwave reduction has higher gas adsorption capacity.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be described in detail below. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the examples given herein without any inventive step, are within the scope of the present invention.
The technical solution of the present invention will be described in detail below with reference to the accompanying drawings.
The specific implementation uses the following chemical materials: graphite, potassium permanganate, sodium nitrate, lithium carbonate, hydrochloric acid, concentrated sulfuric acid, hydrogen peroxide and deionized water, wherein the preparation dosage is gram, milliliter or centimeter 3 Is a unit of measurement.
Graphite: c solid 2 g. + -. 0.001g
Potassium permanganate: KMnO 4 Solid 7 g. + -. 0.001g
Sodium nitrate: naNO 3 Solid 1.2 g. + -. 0.001g
Lithium nitrate: liNO 3 •H 2 O solid 0.010 g. + -. 0.001g
Lithium carbonate: li 2 CO 3 Solid 0.010 g. + -. 0.001g
Hydrochloric acid: HCl, 300mL +/-10 mL of 37% liquid by mass percentage
Concentrated sulfuric acid: h 2 SO 4 Liquid 100mL +/-10 mL
Hydrogen peroxide: h 2 O 2 50mL +/-10 mL of liquid with volume percentage concentration of 30%
Deionized water: h 2 O liquid 3000 mL +/-50 mL
The preparation method comprises the following steps:
(1) And preparing graphene oxide
(1) Preparing hydrochloric acid aqueous solution
Measuring 10mL +/-0.001 mL of hydrochloric acid and 190 mL +/-0.001 mL of deionized water, adding into a beaker, and stirring for 3min to mix uniformly to obtain a hydrochloric acid aqueous solution;
(2) preparation of graphite oxide
Measuring 40mL +/-0.001 mL of concentrated sulfuric acid, and adding the concentrated sulfuric acid into a 250mL beaker for later use;
weighing 2g +/-0.001 g of graphite powder for later use;
weighing 1.2g of sodium nitrate +/-0.001 g for later use;
weighing 7g of potassium permanganate with the weight of +/-0.001 g for later use;
placing a beaker filled with concentrated sulfuric acid in an ice-water bath, stirring, simultaneously adding weighed graphite powder and sodium nitrate solid, stirring for 5min, slowly adding weighed potassium permanganate solid, controlling the temperature to be not more than 20 ℃, stirring for 5min, then heating to 35 ℃, stirring for 3h at constant temperature, adding 250mL of deionized water for 5 times, finally adding 50mL of +/-0.001 mL of 30% hydrogen peroxide, continuously stirring for 5min, and filtering while the solution is hot;
(3) washing and drying graphite oxide
Washing the filter cake twice with a hydrochloric acid aqueous solution, washing the filter cake three times with deionized water, and then putting the filter cake into a vacuum drying oven at 60 ℃ for drying for 20 hours;
(4) preparation of graphene oxide suspension
Weighing 0.2g +/-0.001 g of graphite oxide, and putting the graphite oxide into a beaker;
measuring 200mL +/-0.001 mL of deionized water, adding the deionized water into a beaker filled with graphite oxide, fully stirring, and carrying out ultrasonic treatment for 1 hour to obtain a graphene oxide suspension;
(5) suction filtering and drying
Placing the graphene oxide suspension subjected to ultrasonic treatment in a Buchner funnel of a filter flask, performing suction filtration by using three layers of medium-speed qualitative filter paper, reserving a product filter cake on the filter paper, and pumping filtrate into the filter flask;
putting the filter cake into a vacuum drying oven at 60 ℃ for drying for 12h;
(2) And preparing lithium-assisted microwave reduction graphene
The preparation of the lithium-assisted microwave reduction graphene is completed under the conditions of ultrasonic treatment, blast drying and microwave heating, and in the microwave heating process, oxygen-containing functional groups on the graphene oxide are released into gas to release, so that pressure is generated, and thermal expansion is generated between graphene layers to peel off. In the present invention, the microwave oven used is NJZ4-3 type microwave high-temperature sintering equipment purchased from Nanjing Jed all microwave Equipment Co. The precursor can also be prepared from commercially available graphene oxide powder or graphene oxide powder prepared by other preparation methods.
Preparing a precursor:
weighing 0.1000g +/-0.001 g of graphene oxide powder, and putting the graphene oxide powder into a 10mL beaker for later use;
weighing 0.0100g +/-0.001 g of lithium salt (lithium nitrate or lithium carbonate), dissolving in 3mL +/-0.001 mL of deionized water, and uniformly stirring;
mixing graphene oxide powder with the solution, stirring uniformly, and carrying out ultrasonic treatment for 30 minutes;
and (4) putting the mixed solution after the ultrasonic treatment into a 65-degree vacuum oven, taking out after 12 hours, and collecting a precursor.
Grinding:
grinding the prepared lithium-assisted microwave reduction graphene precursor by using an agate mortar and a pestle;
microwave thermal expansion:
weighing a ground lithium-assisted microwave reduction graphene precursor, putting the ground lithium-assisted microwave reduction graphene precursor into a corundum crucible with a cover, putting the corundum crucible into an inner bin of a microwave oven, and adjusting the position to obtain an infrared temperature measuring probe for accurately measuring the temperature of the crucible and a sample;
opening a vacuum pump, wherein the pressure in the microwave oven is about-0.05 MPa;
turning on a microwave oven cooling circulating water device, turning on a microwave switch, and adjusting power to rapidly heat the microwave oven cooling circulating water device to about 200 ℃;
after the crucible cover is popped up, the microwave switch is closed, and the temperature begins to be reduced;
closing the cooling circulating water after the temperature in the furnace is reduced to 50 ℃, introducing nitrogen until the pressure in the furnace is recovered to normal pressure, opening a cabin door, and taking out a sample;
save and record
Weighing and recording the prepared lithium-assisted microwave reduced graphene, putting the graphene into a sample bag, sticking a label, marking the date, putting the sample bag into a dryer, and hermetically storing the sample bag;
(3) Detection, analysis, characterization
Detecting, analyzing and representing the morphology and the chemical and physical properties of the prepared graphene;
carrying out appearance analysis on the sample by using a transmission electron microscope;
and (4) conclusion: the lithium-assisted microwave reduction of graphene into loose and flocculent black powder has the product purity of 99.5 percent, and a transparent yarn-shaped structure under a transmission electron microscope shows that the graphene has an extremely thin layer thickness;
carrying out specific surface area test on the sample by using nitrogen adsorption and desorption;
and (4) conclusion: the specific surface area of the lithium-assisted microwave reduction graphene is obviously increased and is 472 m 2 About three and six times as much as graphene oxide.
(4) And preparing microwave reduced graphene
Preparing microwave reduced graphene as a comparison sample, wherein the preparation method is the same as the steps (1) to (2), and lithium salt is not added in the step (2). The following table is a summary table of data such as specific surfaces of graphene oxide, microwave-reduced graphene and lithium-assisted microwave-reduced graphene.
As can be seen from the table: compared with graphene oxide, the specific surface areas of the microwave-reduced graphene and the lithium-assisted microwave-reduced graphene are obviously increased and are respectively about four times and eight times of that of the graphene oxide.
The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily think of the changes or substitutions within the technical scope of the present invention, and shall cover the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.
Claims (2)
1. A method for reducing exfoliated graphene oxide by a lithium-assisted microwave thermal expansion method is characterized by comprising the following steps:
dissolving a lithium salt in deionized water, uniformly stirring, then uniformly mixing and stirring graphene oxide powder and a lithium salt solution, performing ultrasonic treatment for 30min, and drying the mixed solution after ultrasonic treatment in a vacuum oven to obtain a lithium-assisted microwave reduction graphene precursor; then grinding the lithium-assisted microwave reduction graphene precursor, placing the ground precursor into a corundum crucible with a cover, placing the corundum crucible into an inner bin of a microwave oven, turning on a vacuum pump until the pressure in the microwave oven is-0.05 MPa, turning on cooling circulating water of the microwave oven, turning on a microwave switch, and adjusting power to enable the temperature in the microwave oven to reach 200 ℃; the cover of the corundum crucible is popped out from a visible window of the microwave oven, then a microwave switch is closed, the temperature in the microwave oven is naturally cooled to 50 ℃, then cooling circulating water is closed, nitrogen is introduced until the pressure in the microwave oven is restored to normal pressure, and then a cabin door is opened to obtain lithium-assisted microwave reduced graphene;
the temperature in the vacuum oven is 65 ℃, and the drying time is 12 hours; the mass ratio of the lithium salt to the graphene oxide powder is 1.
2. The method of claim 1, wherein the lithium salt is lithium nitrate or lithium carbonate.
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