The Effect Of Graphene Reduction Methods On Structure And Electrical Properties

Graphene is a kind of hexagon-shaped honeycomb structure which is made up of single layer of carbon atoms that is sp2 hybridized, and its thickness is 0.34 nm. That graphene oxide(GO) is as raw material, using chemical or thermal reduction is a common way of reduced graphene oxide(RGO) preparation. There are many different types and numerous oxygen-containing groups on GO, what kind of reduction process can most effectively remove the oxygen-containing groups, to ensure high-performance graphene has not been reported. In this paper, a variety of oxidation-reduction methods are used to make graphene. Researching the morphology and structure characterization of the graphene by XRD, SEM, Raman, XPS, and chemical titration, and then exploring the conductivity of graphene samples to illustrate the different reduction methods reduction ability on different kinds of oxygen-containing groups.This paper combines chemical reduction with thermal reduction method and designes one-step and two-step reduction processes. One-step reduction processes include direct thermal reduction, vitamin C microwave-assisted reduction, hydrazine reduction and sodium borohydride reduction. Two-step reduction include vitamin C/thermal reduction, hydrazine/ thermal reduction. The research indicates that direct thermal reduction, hydrazine reduction and two step-reduction method can get morphology of gossamer layer of graphene. In three kinds of RGO reduction process which involve thermal reduction, the reduction result(C/O ratio and carbon network structure percent) increase with annealed temperature. When it is 1000℃, the C/O of samples which from direct reduction and vitamin C/thermal reduction reach 46.62 and 46.31 respectively, while hydrazine/thermal reduction is 23.82. All reduction processes can cause defects and disorder in graphene layers. At the same time, chemical titration analysis obtains that direct thermal reduction causes an increase in carbonyl content, vitamin C/thermal reduction can reduce hydroxyl group effectively.The electrical measurement shows that the conductivity of annealed samples with reduction temperature. There is a certain gap between the maximum conductivity of graphene in this issue is 17038S/m, and the theoretical conductivity of graphene(6× 105S/m). Chemical reduction pretreatment can improve the electrical conductivity of graphene. Different mathods of reduction have different influence on conductivity. The ranking of average conductivity: hydrazine/thermal reduction one > VC/thermal reduction one > direct thermal reduction one. The conductivity also increases with C/O and sp2 percent.Chemical titration has measured that there are more carboxyl and carbonyl in samples reduced from direct thermal reduction, and samples reduced from VC/thermal have more ester and hydroxyl group. Combined with simulation results, we propose that 1) carbonyl and carboxyl located in the edge of the graphene with wider bandgap have larger influence on electrical conductivity; 2) the bandgap of graphene linked hydroxyl and epoxy group is narrow, and these groups have less impact on the electrical conductivity.