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

Ongezwa Mnethu; Steven S Nkosi; Ioannis Kortidis; David E Motaung; R E Kroon; Hendrik C Swart; Napo G Ntsasa; James Tshilongo; Thomas Moyo

doi:10.1016/j.jcis.2020.05.030

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

J Colloid Interface Sci. 2020 Sep 15:576:364-375. doi: 10.1016/j.jcis.2020.05.030. Epub 2020 May 15.

Authors

Ongezwa Mnethu¹, Steven S Nkosi², Ioannis Kortidis³, David E Motaung⁴, R E Kroon⁵, Hendrik C Swart⁵, Napo G Ntsasa⁶, James Tshilongo⁶, Thomas Moyo⁷

Affiliations

¹ Department of Physics, University of Zululand, Private Bag X1001, KwaDlangezwa 3886, South Africa.
² Department of Physics, University of Zululand, Private Bag X1001, KwaDlangezwa 3886, South Africa. Electronic address: steven.solethu.nkosi@gmail.com.
³ Department of Physics, University of Zululand, Private Bag X1001, KwaDlangezwa 3886, South Africa. Electronic address: gkortidis@gmail.com.
⁴ Department of Physics, University of Limpopo, Private Bag X1106, Sovenga 0727, South Africa.
⁵ Department of Physics, University of the Free State, Bloemfontein, South Africa.
⁶ National Metrology Institute of South Africa (NMISA), CSIR Campus, Building 5, Meiring Naude Road, Brummeria, Pretoria 0182, South Africa.
⁷ School of Chemistry and Physics, Westville Campus, University of KwaZulu-Natal, Private Bag X54001, Durban 4000, South Africa.

PMID: 32460099
DOI: 10.1016/j.jcis.2020.05.030

Abstract

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 (R_a/R_g 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.

Keywords: Oxygen vacancies; Xylene gas sensor; Zn doped CuO nanoplatelets; p-type CuO.