Facile fabrication of ZnO nanocrystalline-modified graphene hybrid nanocomposite toward methane gas sensing application

In this paper, we synthetized a hybrid composite of zinc oxide (ZnO) nanocrystalline-decorated reduced graphene oxide (rGO) via a facile hydrothermal process, and fabricated a methane gas sensor by using the ZnO–rGO hybrid composite as sensing film coated on a ceramic tube with Ni–Cr heater. The presence of nanorod-shaped ZnO nanocrystalline and rGO nanosheets was characterized by scanning electron microscopy, X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy, UV–Vis diffuse reflectance and photoluminescence spectra measurement. The sensing properties of the ZnO–rGO film sensor were investigated by exposing to various concentration of methane gas at different temperature. It was found that the presented sensor exhibited unique advantages in methane gas sensing with concentration spanning from 100 to 4000 ppm, such as outstanding repeatability, fast response-recovery time as well as good selectivity, at an optimal operating temperature of 190 °C. The gas response of the ZnO–rGO hybrid composite was superior to that of the pure ZnO and rGO counterpart in methane gas sensing. The possible and proposed sensing mechanism for the sensor is mainly attributed to its nano-hybrid structure and special interactions at p–n heterojunction. This observed results highlight the ZnO–rGO hybrid composite as a candidate material for constructing methane gas sensors.