A comparative study of graphene oxide reduction in vapor and liquid phases

Graphene oxide (GO) was reduced by formaldehyde or formic acid in vapor or liquid phases below 200 °C. The influence of the concentrations of reducing agents, reaction temperature and time on the electrical conductivity of the reduced graphene oxide (rGO) was investigated. The rGOs were characterized by XRD, XPS and Raman spectroscopy. Results show that the optimum reaction temperatures are 150 and 175 °C in the vapor phase and the liquid phase, respectively, based on the electrical conductivities of the rGOs. The ratio of the areas of the C1s peaks related to the C-C and C-O (Rcc/co) from XPS decreases with reaction time from 9 to 24 h in the vapor phase, and increases from 2 to 24 h in the liquid phase, which are in agreement with the electrical conductivities and Raman results. Gasification of carbon atoms in GO sheets may be responsible for the decrease of Rcc/co with prolonged reaction time in the vapor phase.