Optimization of rGO/ZnO and rGO/ZnO-NiO Nanocomposites for Efficient Room Temperature Ammonia Sensors, under DFT simulations

Abstract

Ammonia (NH₃), a hazardous gas associated with respiratory disorders and central nervous system (CNS) impairment, requires reliable room-temperature sensing for environmental monitoring and industrial safety. In this work, binary reduced graphene oxide/zinc oxide (rGO/ZnO, RGZ) and ternary reduced graphene oxide/zinc oxide/nickel oxide (rGO/ZnO/NiO, RGZN) nanocomposites were synthesized using a hydrothermal method to investigate the effect of NiO incorporation on NH₃ sensing performance. The synthesized composites were characterized using UV–Vis spectroscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The formation of the ternary heterostructure was confirmed by the structural and morphological analyses. The sensing performance was evaluated using an electrochemical approach at room temperature. Compared with the binary RGZ composite, the RGZN electrode exhibited enhanced sensing performance owing to the synergistic effect of the conductive rGO network and the ZnO/NiO p–n heterojunction, which facilitates charge transfer and provides abundant active adsorption sites. The RGZN sensor exhibited a maximum response of 180 ppm with a response value of 93%, together with rapid response and recovery times of 45 and 150 seconds respectively. The sensor also demonstrated excellent repeatability and long-term stability, retaining approximately 95% of its initial response after 90 days. Density functional theory (DFT) calculations further supported the experimental observations by revealing changes in the electronic structure upon NH₃ adsorption. These results demonstrate that the RGZN nanocomposite is a promising material for efficient room-temperature ammonia sensing.