Introduction to the preparation and characterization of graphene redox method

Using the Hummers method, in the presence of concentrated sulphuric acid, potassium permanganate and other oxidants, the graphite powder is oxidized to form graphene oxide, the graphite oxide is dissolved in water, and then the graphene oxide is reduced by hydrazine hydrate to prepare graphene. The obtained graphene oxide and graphene were characterized by infrared spectroscopy, ultraviolet spectroscopy and transmission electron microscopy. The results show that graphene oxide and graphene are prepared and both have been sufficiently stripped.

The University of Manchester physicist Andre Heim and Konstantin Novoselov successfully separated graphene from graphite. After winning the Nobel Prize in Physics in 2010, the world set off a wave of research on graphene. Graphene is a kind of new carbon material in which carbon atoms are closely packed into a single-layer two-dimensional honeycomb lattice structure. The thickness of the graphene crystal film is only 0.335 nm, which is one hundred thousandth of the hair diameter. The most intensive material in the world is the basic unit for the construction of other dimensions of carbonaceous materials, with excellent crystallinity and electrochemical properties. Because of its excellent performance, low cost and good processability, graphene has great application prospects in the fields of electronics, information, energy, materials and biomedicine.

At present, the preparation methods of graphene can be generally divided into two types, namely, chemical method for preparing graphene and physical method for preparing graphene. The physical method is obtained from graphite or a similar material having high lattice perfection, and the obtained graphene has a scale of 80 nm or more. Physical methods include mechanical exfoliation, orientation epitaxy, heated SiC, explosion, etc.; and chemical methods are prepared by small molecule synthesis or solution separation to obtain graphene scales below 10 nm. Chemical methods include graphite intercalation, thermal expansion stripping, electrochemical, chemical vapor deposition, ball milling, graphite oxide reduction, and the like.

The graphite oxide reduction method is currently the most popular method for preparing graphene. The graphite reacts with a strong oxidant under certain conditions in concentrated sulfuric acid, and is oxidized to carry a group such as a carbonyl group, a hydroxyl group or an epoxy group between the sheets. The graphite layer pitch is increased to become graphite oxide. After appropriate sonication, the graphite oxide is easily dispersed into a uniform single or double layer graphene oxide solution in water or an organic solvent, and finally the remaining oxygen-containing functional group is removed by hydrazine hydrate reduction. Although graphite which has been completely oxidized by a strong oxidizing agent may not be completely reduced, resulting in some physical and chemical properties being lowered, the method is simple and low in cost, and a large amount of graphene can be prepared. Graphene is prepared by a graphite oxide reduction method.

1, the experimental part

1.1, reagents and instruments

Graphite powder (200 mesh sieve, Shanghai Reagent Factory), concentrated sulfuric acid (95% ~ 98%), potassium permanganate, sodium nitrate, hydrogen peroxide (30%), hydrochloric acid, hydrazine hydrate (80%), etc. are all analytically pure The test water is a second sub-boiling distilled water, BrukerTensor27 infrared spectrometer, UV-2550PCUV-visiblespectrometer ultraviolet spectrometer, PhilipsTECNAI-12 transmission electron microscope.

1.2, Preparation of graphene oxide

Graphene oxidation was prepared from graphite by the Hummers method.

The graphite is first chemically oxidized to obtain a carboxyl group having a carboxyl group and a hydroxyl group at the edge and an oxygen-containing group such as an epoxy group and a carbonyl group is intercalated between the layers. This process can increase the distance between the graphite layers from 0.34 nm to about 0.78 nm, and then peel off by external force (for example). Ultrasonic stripping) yields a graphene oxide having a single atomic layer thickness. The specific experimental steps are as follows:

Add 70mL concentrated sulfuric acid to a 250mL beaker, put it into the ice water bath, add a suitable mixture of graphite powder and 1g sodium nitrate under magnetic stirring, and then add 6g potassium permanganate separately, control the reaction temperature ≤20°C, reaction 1.5h . Then, the temperature of the water bath was controlled at 35 ° C to stir the reaction for 40 min, and then slowly add 90 mL of deionized water, the reaction temperature was controlled at 90-98 ° C, the reaction was stirred for 30 min, then 7 mL of 30% H 2 O 2 was added to reduce the residual oxidant, and the reaction was carried out for 10 min, and then added. 55 mL of deionized water was reacted for 5 min. It was filtered while hot and washed with a dilute hydrochloric acid solution and deionized water at a volume ratio of 1:10 until no sulfate was detected in the filtrate. The product was thoroughly dried in a vacuum oven at 60 ° C for 2 to 3 days and stored for later use.

1.3. Preparation of reduced graphene

Weighed 150 mg of GO and added 150 mL of water. After sonication for 1 h, it was placed in a 250 mL three-necked flask, 0.3 g of KOH was added, and 2 mL of hydrazine hydrate was added. After refluxing at 98 ° C for 24 hours, the reaction solution was cooled, centrifuged (10000 rpm, 20 min), and washed, centrifugation, 3 times in a row, and 1 time in ethanol. The solid product was dried under vacuum at 60 °C.

2, results and discussion

2.1, infrared characterization

The infrared spectrum of graphene oxide and graphene is shown in Fig. 1.

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Fig.1 Infrared spectrum of graphene oxide (GO) and graphene (GN)

It can be seen from Fig. 1 that a series of infrared absorption peaks appear after the oxidation of graphite, and a broad and strong absorption peak appears in the range of 3000 to 3700 cm-1, which is attributed to the stretching vibration peak of -OH; The absorption peaks appearing at 1723, 1382, 1221 and 1055 cm-1 are respectively attributed to the -C=O stretching vibration peak, the O-H deformation vibration peak, and the C-OH and C-O stretching vibration peaks. These results indicate that the GO surface already contains different kinds of oxygen-containing functional groups. When GO is reduced to GN, the characteristic absorption of -C=O disappears, and the deformation vibration peak of O-H at 1382 and the stretching vibration peak of 1055 become very weak. This result indicates that most of the oxygen-containing functional groups on the surface of the graphene oxide have been removed, and graphene has been successfully prepared.

2.2, UV characterization

The prepared GO and GN were confirmed by ultraviolet spectroscopy (Fig. 2).

Figure 2 Ultraviolet absorption curves of graphene oxide (GO) and graphene GN

It can be seen from Fig. 2 that the characteristic absorption peak of graphene oxide GO appears at 232 nm and 301 nm, and when GO is reduced to GN with hydrazine hydrate, GN does not have any ultraviolet absorption peak, indicating that GO has been reduced to GN.

2.3, TEM characterization

The sample was characterized by dissolving graphite, graphene oxide and graphene in a solvent, dropping it on the surface of the copper mesh, drying it by infrared light, and then characterizing it on a transmission electron microscope. Figure 3 is a TEM image of graphite, graphene oxide and graphene, respectively.

Figure 3 TEM image of graphite (A), graphene oxide (B), graphene (C)

The topography of graphite, graphene oxide and graphene can be seen from Fig. 3. Graphite is a large block structure, and graphene oxide and graphene are separated single-layered sheet structures. Double-layer, single-layer graphene oxide and graphene can be observed by electron microscopy, indicating graphene oxide and graphite. The olefin has been well detached after repeated ultrasound.

3. Conclusion

Graphene is prepared by the Hummers method, and graphene is obtained by reducing the graphene oxide with hydrazine hydrate. It is proved by various characterization methods that the surface of GO contains a large number of oxygen-containing functional groups, which provides a theoretical basis for the modification of nanocomposites for the preparation of graphene.

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