How to prepare thin paper graphite oxide and graphene and what are its characteristics

The thin paper-like graphite oxide layer was successfully prepared by the modified Hummers method, and the prepared thin paper-like graphite oxide sheet was reduced to graphene nano-material with hydrazine hydrate as a reducing agent. Synthesis products by Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy (RS), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM) the structure and properties were characterized. The results show that the thickness of graphene is 0.36 nm and the number of layers is 3. In addition, the reaction mechanism of the preparation of thin paper-like graphite oxide by a modified Hummers method was discussed, and the chemical reaction process occurred in each reaction stage of the graphite oxidation process.

In 2004, Geim et al. used a mechanical stripping method to prepare a novel two-dimensional atomic crystal, graphene, composed of an sp2 hybrid carbon atom layer. The basic structural unit of graphene is a benzene six-membered ring with a theoretical thickness of only 0.34 nm. Therefore, graphene has many excellent physicochemical properties, such as strength more than 100 times that of steel, up to 130GPa, the carrier mobility of 15000cm2 / (V · s), the thermal conductivity of up to 5000W / (m · K ). In addition, graphene also has special properties such as room temperature quantum Hall effect and room temperature ferromagnetism. At present, the preparation methods of graphene mainly include micro mechanical peeling method, chemical vapor deposition method, chemical oxidation-reduction method, crystal epitaxial growth method, and solvothermal method. Among them, the micro-mechanical stripping method can prepare micron-sized graphene, but the controllability is low, and it is difficult to achieve mass production. The crystal epitaxial growth method is easy to reconstitute due to the surface of the SiC crystal so that it is difficult to obtain graphene having a large area and a uniform thickness. Chemical vapor deposition (CVD) uses a metal single crystal or a metal thin film as a substrate to grow a thin layer of graphene sheets, but graphene is not high in purity and cannot be mass-produced. The solvothermal law has the disadvantages of high temperature and high pressure, and the low conductivity of the product, and does not have the possibility of mass production. The chemical redox method is to prepare graphite oxide by the Hummers method and then prepare graphene by ultrasonic stripping and reduction processes. Due to the short production cycle and high synthetic yield, the method has received extensive attention and research. In the process of preparing graphite oxide by Hummers method, including three stages of low temperature (0 ° C), medium temperature (38 ° C) and high temperature (98 ° C), the oxidant is concentrated H2SO4 and KMnO4. Through the study of the oxidation process of graphite, the Hummers method was modified, that is, the time of the intermediate temperature reaction phase was prolonged, and the high-temperature reaction phase was canceled. Eliminating the reaction process in the high-temperature stage can not only avoid the eruption hazard caused by the sulfuric acid in the high-temperature reaction but also avoid the thermal decomposition reaction in the high-temperature stage and reduce the oxidation degree of the graphite. Theoretically and experimentally, it has been proved that a thin paper-like graphite oxide sheet can be prepared under low temperature, safe and stable conditions. The prepared graphite oxide was reduced by hydrazine hydrate, and the graphene nanomaterials were prepared. The prepared paper-like graphite oxide and graphene materials were characterized.

1, experiment

1.1, raw materials

Flake graphite (particle size: 325 mesh, Xianfeng Nano Technology Co., Ltd.); concentrated sulfuric acid (95% ~ 98%); potassium permanganate, sodium nitrate, hydrogen peroxide (30%), hydrochloric acid, barium chloride, hydrazine hydrate (80 %) and so on are analytically pure. The above drugs are not specifically mentioned, they are all purchased from Shanghai Pharmaceutical Reagent Company of China Pharmaceutical Group. The above reagents are used without treatment.

1.2, sample preparation

1) Preparation of thin paper-like graphite oxide (GO) sheet 230mL (98%) concentrated sulfuric acid was placed in a 1000mL three-necked flask, and a mixture of 5.0 g of NaNO3 and 10.0 g of graphite was added under constant temperature magnetic stirring and ice water bath. Stir for 30 min at a speed and mix thoroughly. 30 g of KMnO4 was gradually added to the mixture, and stirring was continued at 0 ° C for 2 h. The three-necked flask was transferred to a constant temperature water bath adjusted to a temperature of about 38 ° C, and stirring was continued for 30 hours to carry out a medium temperature reaction. After the end of the intermediate temperature reaction, the mixture was transferred to a 2000mL beaker, the reaction solution was diluted to 1000mL with deionized water, and 200mL (5%) of H 2 O 2 was added, at which time the reaction mixture turned golden yellow. Centrifugal separation with a high-speed centrifuge at a speed of 4000 r/min, washing with pre-formed 5% HCl and deionized water until no sulfate was detected in the filtrate, and ultrasonication was carried out for 30 min, and the suspension was transferred to an evaporating dish, 60 dryings in a vacuum at ° C to obtain graphite oxide.

2) Reduction of graphene 100 mg of the above-obtained graphite oxide was dispersed in 100 mL of an aqueous solution to obtain a brownish yellow suspension, which was dispersed under ultrasonic conditions for 2 hours, transferred into a three-necked flask, heated to 90 ° C, and 2 mL of hydrazine hydrate was added thereto. The reaction was filtered for 24 hours, and the obtained product was washed successively with methanol and water and dried under vacuum at 60 ° C to obtain graphene.

1.3, testing and characterization

XRD diffraction analysis was carried out by Japanese RIGAKU D/Max-RB diffractometer (Cu target, Kα radiation, λ=0.154056 nm), scanning range 5°～80°and anfrared spectroscopy (FT-IR) analysis was performed by NNus type of American ThermoNicolet Company. Fourier transform infrared spectrometer, KBr tablet preparation, wavelength range 400 ~ 4000cm-1; Raman analysis (Raman) analysis using British RENISHAW company's INVIA type micro-focus laser Raman spectrometer, the recording range is 100 ~ 3200cm-1, laser wavelength is 785nm, spatial resolution is 1μm horizontal, 1μm in longitudinal direction; scanning electron microscope (SEM) adopts S-4800 FESEM scanning electron microscope; transmission electron microscope (TEM) adopts JEM-2100F field of JEO company of Japan High-resolution transmission electron microscopy was used; the atomic force scanning probe microscope (AFM) used the NanoScope 4 atomic force microscope from Veeco, USA.

In conclusion

A. Through the analysis of the oxidation process of graphite, the reaction time of the intermediate temperature stage was extended, and the modified Hummers method of the high-temperature reaction stage was used to synthesize the thin paper-like graphene oxide. The graphene was obtained by ultrasonic stripping and hydrazine reduction treatment.

b. TEM and AFM test results show that the thickness of graphene is 0.36 nm and the number of layers is 3.

c. The method is safe, simple, large in yield and easy to control. It provides a fast and simple way to prepare thin paper graphene on a large scale, which provides a basis for the commercial application of graphene.

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