| While graphite resources are huge in China,it is indiscriminately mined and abused,export at low price and import at high price under mismanagement,so the further processing of graphite becomes a particularly important way to protect our resources.Aimed at the downstream products of graphite-graphite oxide,graphene oxide and graphene,this acticle studied new preparation methods to increase production,simplify the operation process,reduce pollution and save energy.The main research includes the following two aspects:(1)Improve the Hummers process,design orthogonal experiment,study the factors:dosage of potassium permanganate and concentrated sulfuric acid,reacting time and reacting temperature,then get the optimal reaction conditions as follows:graphite:potassium permanganate = 1:3,graphite:concentrated sulfuric acid = 1:50,the reacting time is 3 h and reacting temperature is 60 ?,find carbon-oxygen ratio of graphite oxide is 0.79,and the sulfur content is 3.54 wt%.The high temperature reaction stage was omitted,the preparation process was simplified,the risk of the experiment was reduced,and the cost was saved compared with the Hummers method.Comparing the graphite oxides prepared by the two methods before and after improvement,it was found that the product of improved method was added more epoxy groups,which resulted a high degree of oxidation.The interlayer spacing of 0.94 nm was slightly larger than that of Hummers' 0.796 nm,and it was easier to be exfoliated.The hydrothermal reduction results showed that the oxygen-containing functional groups of the one-step method can be removed totally,and the reduction effect is better than that of Hummers',and there are more bulky structure and larger pores in three-dimensional graphene.The specific surface area was 147 m2/g,which was larger than that of Hummers' 135 m2/g,good mechanical stress,resistance of 11 ? was better than Hummers' 17 ?.The absorption capacity for safranine O was 980 mg/g,also better than that of Hummers' 860 mg/g.(2)Purification of graphite,preparation of graphene oxide and graphene were studied by electrochemical method.In the graphite crucible,alkaline electrolyte was used to purify the graphite powder,removing impurities such as S,Si,etc.and some small molecular volatiles contained in the graphite sheet layer,and regulate the conjugated structure of the aromatic ring to facilitate the subsequent processing and use of the graphite.The graphene oxide was prepared in the H-type electrolytic cell,it showed that the oxidation degree of the product was high,the carbon-oxygen ratio was 1.47.The products contained various oxygen-containing functional groups,the number of layers was small,and the size of the sheet was about 500nm.Compared with the chemical oxidation method,the use of hazardous oxidants is not required,and a large number of cleaning processes are also omitted.Compared with the conventional electrochemical method,the degree of oxidation is greatly improved,thus it is a promising new technology solution.In the process of preparing graphene,the using of alternating current can maximize the reducing effect of hydrogen and reduce the oxidation degree of graphene.It was found that the degree of oxidation decreased with the decrease of alternating cycle of currents,the size of average sheet also decreased,the sheets became thinner,and the defects decreased;when increase electrolysis time,the yield of graphene increased and the size of average sheet decreased,the sheets became thinner,the degree of oxidation and the defects were basically unchanged.When alternating cycle was 1 min and electrolysis time was 5 h,the C/O ratio of graphene was as high as 19.23,the concentration was 1.66 mg/ml,the size of average sheet was 128 nm.98%of the sheets were monolayer,double-layer and tri-layer graphene with a little of defects compared with direct stripping products,and a large number of graphene quantum dots were found in the product,opening up a new simple and efficient way for the preparation of quantum dots. |
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