Crystal-chemical Characteristics Of Graphite In Different Genetic Types And The Influences On Graphene

There is amount of graphite mineral resource in China, which contains kinds of ore types. And natural graphite can be used as the raw material for producing graphene in large scale. Therefore, in this paper, based on the minerological characteristics of graphite mineral samples in different genetic types, reduced graphene oxide(hereinafter referred to as graphene) was prepared from the prepared graphite oxide by oxidation-reduction method. The crystal-chemical characteristics of the graphite samples and their influence on the structure and performance of the sample during the oxidation-reduction progresses were studied systematically. The results have important theoretical and practical significance to realize the industrialization of graphene materials.The results of mineralogical characteristics of graphite samples from typical mines show that these graphite samples produced in China are 2H-graphite, and in certain degree, contain 3R-graphite. Both crystalline and microcrystalline graphite have high graphitization degree. Secondary defects were introduced into graphite structure during the later geological or anthropogenic progresses. Therefor, Oxygen was added to the structure which could lead to bigger cell volume. Because of the difference of the flake diameter, the stability, floatbility, and conductibility of the former are better than those of the latter.Based on the study of mineralogical characteristics of graphite mineral, typical crystalline and microcrystalline graphite samples were chosen as raw materials to prepare graphite oxide by improved Hummers method, and then graphene were prepared from the graphite oxide by thermal exfoliation-reduction method. Kinds of analytical methods were used to study the changes of properties of both kinds of graphite during the oxidation, exfoliation-reduction processes. The results show that the change laws of the structural properties of both graphite are almost same during the preparing proceses, and the graphene prepared from both graphite is a kind of stacking of multi-layers graphene aggregate with lightweight, porous, and high specific surface area. At the same oxidation condition, the structural order degree, electroconductivity of the oxidation production from microcrystalline graphite are lower than those of the oxidation production from crystalline graphite; microcrystalline graphite possesses higher reactivity than crystalline graphite, so the former can be oxided and reduced easier than the latter; compared with oxidation production from cryastalline graphite, there are more COOH, C-OH and less C-O-C groups in the structure of the oxidation production from microcrystalline graphite, and the strippability of graphite oxide from microcrystalline is much lower which leads to the productivity of the graphene oxide is lower yet. The sheet size reduced multiple of graphene oxide is proportion to mean size of crystalline graphite, and the productivity of graphene oxide decrease with the increase of the mean size of crystalline graphite. The structural disorder degree, the content of oxygen containing functional groups and the productivity of graphene oxide increase gradually while the conjugated degree of π system and the electroconductivity decrease gradually with the oxidation degree of both graphite. At the same reduction condition, the expanding volum and the structural disorder degree of the reducted production increase gradually while the interlayer spacing and the electrical resistivity of the graphene stacking decrease with the oxidation degree. The interlayer spacing, the content of oxygen containing groups and the electrical resistivity of the reduced production decrease gradually while the structural disorder degree decrease gradually with the reduction degree.Cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy were used to estimate the supercapacitive performance of the graphene prepared from both kinds of graphite. The results show that the graphene prepared from both kinds of graphite possess electrical double-layer capacitive characteristics. The increasing of the oxidation degree of graphite oxide is beneficial to the supercapacitive perfoemance of the graphene, but the higher oxidation might lead to worse electronical resistivity. At the same oxidation condition, the higher thermal temperature leads to better cycle stability, but the specific capacity could increase fistly and then decrease with the thermal temperature. The supercapacitive performance of graphene prepared from crystalline graphite is slittily better than that of graphene prepared from microcrystalline graphite.The adsorptive property of graphene prepared from both kinds of graphite was studied by the adsorption experiments of methylene blue(MB) onto graphene. The results show that the adsorption of MB onto graphene is a kind iof spontaneous and endothermic reactivity, and the adsorbent force is contributed by the π-π conjugation between graphene and MB molecule. The adsorbing capacity is affected by multy factors such as the initial concentration. The adsorbing capacity and the initial adsorbent rate of graphene prepared from microcrystalline graphite are higher than those of graphene crystalline graphite.