Gas sensing performance of Ni-doped CuO/ZnO p–n heterostructures for ethanol detection: high sensitivity, selectivity and stability

The gas sensitive characteristics of pure, 4 and 6 wt% Ni-doped CuO/ZnO nanocomposites toward ethanol gas were studied for industrial and safety applications. The X-ray diffraction analysis verified that the pure, 4 and 6 wt% Ni-doped CuO/ZnO nanocomposites were composed of monoclinic CuO and hexagonal ZnO phases without existence of any impurities. The scanning electron microscope image of pure CuO/ZnO powder shows the formation of uniform and well distribution spherical particles. Owing to incorporation of Ni ions, some rods particles were formed besides major fine semi-spherical grains. Pure CuO/ZnO exhibits two band gap energies with value of 1.4 and 3.2 eV which can be exactly indexed to CuO and ZnO components, respectively. Upon doping by Ni ions, the band gap of p-type CuO was blue shifted, while the band gap of the n-type ZnO was red shifted. The gas sensing performance of CuO/ZnO heterostructure shows a maximum sensitivity at 250 °C towards 100 ppm ethanol gas while Ni-doped CuO/ZnO nanocomposites attain a maximum sensitivity at 225 °C. The measurements revealed that the 4 wt% Ni-doped CuO/ZnO possesses superior gas sensing characteristics including high response, fast response and recovery times as well as good stability towards 100 ppm ethanol gas. Besides, this sensor exhibits high selectivity for ethanol gas in presence of many volatile organic compounds such as acetone, formaldehyde, methanol and propanol as well as carbon dioxide. This work indicates that Ni-doped CuO/ZnO heterojunction is a highly promising sensitive structure for ethanol gas detection.