Synthesis and characterization of zinc titanate-graphene oxide composites prepared under ambient and hydrothermal conditions

Abstract

We prepare reduced graphene oxide-zinc titanate (ZTO) composite powders by mixing ZTO with 1 wt% graphene oxide (GO) in solid and liquid states under open environments, and under hydrothermal conditions. The treatment temperature was 400 °C in the first two cases and 180 °C in hydrothermal. Structural and chemical characterizations performed using XRD, SEM, BET, XPS, DRS, and PL are correlated with their photocatalytic performance. Mixing leads to significant structural and chemical changes in GO and ZTO particles but of different natures depending on the process. All the mixing routes reduce GO to r-GO. Unlike hydrothermal mixing, mixing under an open environment converts the rhombohedral ZnTiO₃ to cubic Zn2TiO₄ due to loss of oxygen. However, hydrothermal mixing leads to a loss in crystallinity of the ZnTiO₃ particles resulting into a larger specific surface area. XPS results suggest good binding between the r-GO sheets and the oxide particles. Liquid state mixing leads to the highest reduction in bandgap, probably due to maximal oxygen vacancy formation in this process. Mott-Schottky analysis is done to estimate the charge carrier density in all the samples. EIS shows that the hydrothermally prepared composite has the smallest R_ct. High surface area, less conversion to Zn₂TiO₄, changes in bandgap, good binding of ZTO with GO sheets, and more facile charge transfer in hydrothermally prepared composites have important implications in photocatalytic applications.