Reduction of graphene oxide (GO) to reduced graphene oxide (rGO) at different hydrothermal temperatures and enhanced photodegradation of zinc oxide/rGO composites

Abstract

Scholars are shifting their attention to the development of environmentally friendly materials with a high degradability of environmental pollutants. Among various photocatalytic materials, zinc oxide (ZnO)/reduced graphene oxide (rGO) nanomaterials can meet these requirements. In this study, ZnO/rGO nanomaterials with different hydrothermal temperatures were fabricated through a hydrothermal method. We determined the hydrothermal temperature variations to create different structures and identify the morphologies and sizes of the ZnO/rGO material. The average crystal size of ZnO/rGO nanomaterials decreased from 32.25 nm to 30.30 nm when the hydrothermal temperature was increased from 100 °C to 180 °C. The detailed x-ray diffraction (XRD) study showed that the diffraction peak position of ZnO decreased, the lattice constant increased, and the unit cell volume increased with the increase in hydrothermal temperature. rGO-related diffraction peaks were also observed in the XRD patterns of ZnO/rGO samples, which indicates the formation of a ZnO/rGO crystalline structure. Fourier transform infrared spectra revealed the chemical bonding of ZnO and rGO materials. The photoluminescence (PL) spectra of ZnO/rGO nanocomposites presented two characteristic emission peaks at 383 and 558 nm. The Raman scattering spectra of ZnO/rGO nanomaterials exhibited ZnO-related peaks at 329, 436, and 1123 cm−1 and rGO-related peaks at 1352, 1579, 2706, and 2936 cm−1. The ultraviolet-visible (Vis) absorption spectra of ZnO/rGO nanomaterials manifested the characteristic absorption peaks of ZnO and rGO at 381 and 291 nm, respectively. The photocatalytic properties of ZnO/rGO nanomaterials were studied through the decomposition of methylene blue (MB) under Vis light. The effect of hydrothermal temperature on the properties of ZnO/rGO materials and the photodecomposition mechanism of MB were investigated in detail.