Heterostructural CuO-ZnO Nanocomposites: A Highly Selective Chemical and Electrochemical NO₂ Sensor

A simple one-step chemical method is employed for the successful synthesis of CuO(50%)-ZnO(50%) nanocomposites (NCs) and investigation of their gas sensing properties. The X-ray diffraction studies revealed that these CuO-ZnO NCs display a hexagonal wurtzite-type crystal structure. The average width of 50-100 nm and length of 200-600 nm of the NCs were confirmed by transmission electron microscopic images, and the 1:1 proportion of Cu and Zn composition was confirmed by energy-dispersive spectra, i.e., CuO(50%)-ZnO(50%) NC studies. The CuO(50%)-ZnO(50%) NCs exhibit superior gas sensing performance with outstanding selectivity toward NO₂ gas at a working temperature of 200 °C. Moreover, these NCs were used for the indirect evaluation of NO₂ via electrochemical detection of NO₂ ^- (as NO₂ converts into NO₂ ^- once it reacts with moisture, resulting into acid rain, i.e., indirect evaluation of NO₂). As compared with other known modified electrodes, CuO(50%)-ZnO(50%) NCs show an apparent oxidation of NO₂ ^- with a larger peak current for a wider linear range of nitrite concentration from 20 to 100 mM. We thus demonstrate that the as-synthesized CuO(50%)-ZnO(50%) NCs act as a promising low-cost NO₂ sensor and further confirm their potential toward tunable gas sensors (electrochemical and solid state) (Scheme 1).