Zinc oxide-nickel oxide-copper oxide mixed nanocomposite thin films for ammonia gas sensor applications

Abstract

Mixed metal oxides are emerging materials in the gas-sensing industry because of their superior gas-sensing characteristics. ZnO-based ternary mixed-metal oxide nanocomposites were sprayed on glass substrates using the spray pyrolysis method with optimized deposition conditions by changing NiO and CuO molar concentrations. Microstructural, topographical, and chemical studies of synthesised thin films were conducted using XRD, Raman spectroscopy, TEM, FESEM, and XPS, respectively. The XRD studies showed that ZnO is hexagonal, NiO particles are cubic, and CuO has monoclinic structures. Using the Scherrer formula, the crystallite sizes of the nanocomposites were calculated and found to be in the range of 8 nm–10 nm. FESEM results indicate that the synthesised films show a uniform distribution of particles with a good porous nature. Raman spectroscopy and TEM results agree with the studies of XRD. XPS analysis also confirms the formation of ZnO-NiO-CuO composites. Using a static method, gas sensing studies were conducted towards different ammonia concentrations, starting from 5 ppm to 20 ppm, at room temperature. A ternary composite sprayed with a molar concentration of 50 wt% ZnO – 30 wt% NiO- 20 wt% CuO showed superior gas sensing properties compared to other samples with response and recovery times of 59 s and 66 s, respectively, towards 5 ppm of ammonia at room temperature due to uniformly distributed spherical nanoparticles with a highly porous and rough surface made it strong interparticle interactions, making it ideal for ammonia sensing applications.