Synthesis of reduced graphene-based nickel oxide hybrid material for ammonia sensing

Abstract The reduced graphene oxide (rGO)-based nickel oxide (NiO) hybrid material holds significant potential for advancing ammonia sensing technology due to its synergistic properties, enabling high sensitivity, selectivity, and rapid response. In this study, rGO-based nickel oxide hybrid materials were hydrothermally synthesized with varying concentrations of rGO (5 wt%, 10 wt%, and 15 wt%) to evaluate their response to ammonia gas exposure. The as-synthesized hybrid structures were characterized using x-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and energy-dispersive x-ray spectroscopy (EDS) to determine their crystalline structure, morphology, and elemental composition. Diffuse reflectance spectroscopy (DRS) revealed that increasing the graphene content decreased the bandgap to 3.18 eV for 15 wt% of rGO, compared to NiO’s bandgap of 3.6 eV. X-ray photoelectron spectroscopy (XPS) provided insights into the chemical composition of rGO and the electronic states of nickel. A four-probe IV analysis was conducted to investigate conductivity and ammonia-sensing behavior. Exposure of pure nickel oxide to ammonia gas increased the material’s current and resistance from 400 nA to 1 mA and 250 MΩ to 1 kΩ, respectively. When hybrid structures with 15 wt% rGO were used to detect ammonia gas, the current and resistance changed from 16 μA to 19 mA and 62.5 kΩ to 52.6 Ω, respectively. The hybrid sensing layer demonstrated a significantly more desirable response than pure NiO. Therefore, the sample with 15 wt% rGO exhibited optimal conductivity and sensing capabilities.