Reduction of free-standing graphene oxide papers by a hydrothermal process at the solid/gas interface

Abstract

Chemical reduction of free-standing graphene oxide papers at a solid/gas interface by a hydrothermal process has been developed. Graphene oxide papers in autoclaves were kept from contacting de-ionized water to form the solid/gas interface between the steam and the graphene oxide papers. Ammonia was also introduced into the hydrothermal system to improve the reduction. The influences of hydrothermal temperature, reducing time and ammonia concentration on the electrical conductivity of reduced GO papers were examined. Reduction under optimum conditions produced a relatively high electrical conductivity of 2283 S m⁻¹. Structural evolution of the reduced GO papers was studied by Fourier-transform infrared spectroscopy, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. The characterizations showed that oxygen functional groups were effectively removed by the interfacial reduction, especially with the addition of ammonia. Fitting results for high-resolution X-ray photoelectron spectra further indicated that doping of N atoms by replacing the C atoms in the skeleton of the graphene sheets was responsible for the further improved electrical conductivity.