Enhanced reduction of graphene oxide by high-pressure hydrothermal treatment

Abstract

A high-pressure assisted hydrothermal treatment is proposed as a facile, green and efficient route for the reduction of aqueous dispersions of graphene oxide. Reactions were performed in an autoclave at mild temperature (180 °C) using only water and nitrogen or hydrogen gas. No further separation or purification of the reduced products was required. X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction and thermogravimetric analysis revealed that the application of high pressure significantly enhanced oxygen removal. The C/O atomic ratio of the graphene oxide sheets increased from 1.65 to 5.29 upon conventional hydrothermal treatment using autogenous pressure. Higher C/O ratios of 6.35 and 7.93 were obtained for graphene oxides that were reduced under high-pressure of nitrogen and hydrogen, respectively. Specifically, the use of high-pressure hydrogen improved the removal of oxygen double-bonded to carbon. The introduction of covalently bonded heteroatoms, which is commonly observed for the use of reductants such as hydrazine, was not detected. Furthermore, high-pressure reduction led to a better restoration of the sp² conjugation than was obtained by conventional hydrothermal treatment, as determined by XPS and Raman spectroscopies. These findings illustrate the promise of high-pressure hydrothermal treatments for the eco-friendly mass production of reduced graphene oxide.