NiO/ZnO composite decorated on rGO for detection of NO2

The rGO-NiO/ZnO composites were successfully synthesized by hydrothermal and hydrazine hydrate reduction methods and were used to detect NO2. The structure and morphology of the composites were characterized using spectrum techniques. The sensing tests showed that the triadic composite of rGO (0.5 wt%)-NiO/32ZnO exhibits a liner response toward NO2 in the concentration range of 0.5–3 ppm and the highest response reaches 75.3 to 2 ppm NO2 at 140 °C, which is 4.55 times and 1.38 times higher than that of pure ZnO and binary composite of NiO/32ZnO, respectively. The composite also exhibits a fast response of 39 s and a low detection limit of 46 ppb. The improvement mechanism is ascribed to the formation of p-n heterojunction that benefits from the formation of an additional depletion layer at the junction interface and the decoration of rGO increases surface active sites and accelerates electron transfer.