Hydrothermal deoxygenation of graphene oxide in sub- and supercritical water

Abstract

Graphene oxide (GO), an oxidized form of graphene, exhibits immense potential for a wide range of applications owing to its rich chemistry. This work reports the controlled deoxygenation of GO under sub- and supercritical hydrothermal conditions, which are considered to be foremost green, environmentally-friendly and economically viable. The remarkable thermo-physical and chemical properties of water, monitored by temperature (373–653 K) and pressure (0.04–22.75 MPa), facilitate the deoxygenation of GO. The gradual chemical and structural changes in GO in hydrothermal reactions, over a wide range of temperature and pressure are elucidated using XPS, FTIR, Raman, XRD, and HRTEM analyses. Plausible deoxygenation mechanisms, particularly elimination of hydroxyl, epoxide, carboxyl, and carbonyl groups and repairing of the π-conjugated network are discussed on the basis of spectroscopic analyses. The addressed hydrothermal route not only avoids the use of toxic and hazardous chemicals as reducing agents but also regulates the deoxygenation events.