Synthesis of ZnO/NiO nanocomposites for the rapid detection of ammonia at room temperature

This paper presents the facile synthesis of pure ZnO nanoparticles (NPs) and ZnO/NiO nanocomposites (NCs) and their ammonia sensing properties. The synthesis of ZnO/NiO NCs was done via a simple two-step process (co-precipitation followed by sol-gel method). Structural analysis of the prepared samples revealed the existence of hexagonal wurtzite structured ZnO and face center cubic structured NiO in ZnO/NiO sample. Surface morphological studies of the fabricated sensors show the porous nature, which further helps in enhanced sensing response. X-ray photoelectron spectroscope (XPS) results of ZnO/NiO NCs revealed the valence states of Ni (+2) and Zn (+2). Superior gas sensing response of the ZnO/NiO sensor towards ammonia at room temperature was observed from the gas sensing studies. The response of ZnO/NiO (~1208) was nearly 80 times higher than pristine ZnO (~15) towards 100 ppm ammonia at room temperature. Low detection limit was obtained for ZnO/NiO sensor (8.27–1 ppm ammonia). The response and recovery times of ZnO/NiO were 5 s and 8 s respectively. The p-n junction formed between p-NiO and n-ZnO, and chemical sensitization and catalytic activity of the NiO contributed to the enhanced sensing performance of NiO/ZnO sensor.