Ultra-sensitive and selective p-xylene gas sensor at low operating temperature utilizing Zn doped CuO nanoplatelets: Insignificant vestiges of oxygen vacancies

p-xylene is a harmful volatile organic compound that needs to be tested for indoor air quality detection. We report on the sensing characteristics of CuO and Zn doped CuO nanoplatelets of various concentrations that were prepared by hydrothermal synthesis, against nine different gases. These CuO and Zn based nanoplatelets were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, photoluminescence emission and vibrating sample magnetometer measurements. CuO and 0.1 at. % Zn doped CuO samples were most sensitive and selective to p-xylene gas with relatively high responses (Ra/Rg ratio) of about 42 and 53 at an operating temperature of 150 °C, respectively. These responses were about six times higher compared to the other 8 tested interfering gases. All these samples further exhibited a paramagnetic behaviour at room temperature, due to small traces of point defects, such as oxygen vacancies. Both these sensor materials did not show green luminescence at room temperature that is normally associated with oxygen vacancies. However, temperature dependent photoluminescence (PL) measurements for the 0.1 at. % Zn doped CuO showed broad visible emission, including green luminescence, which increased with temperature up to 150 °C and coincided with the gas sensing temperature. The pure CuO, however, showed a rapid quenching in PL emission with an increase in the temperature up to 150 °C. Nevertheless, both pure CuO and 0.1 at. % Zn doped CuO based sensors were highly sensitive to the p-xylene gas. The mechanism associated to the xylene superior sensing was considered in terms of point defects and surface area as active sites for adsorption of gas molecules.