Low-operational temperature for selective detection of xylene gas using a p-n CuO-ZnO heterostructure-based sensor

Abstract

Xylene is not just considered detrimental to the environment but also hazardous to humans. Herein we report on xylene vapour detection using CuO-ZnO heterostructures containing various concentrations (0.1–2.0 wt%) of Zn, prepared via hydrothermal synthesis. X-ray diffraction, scanning, and transmission electron microscopy, as well as x-ray photoelectron spectroscopy, validated the formation of the CuO-ZnO heterostructure. Gas detection, sensitivity, selectivity, and stability tests of nine different gases, namely benzene, toluene, ethylbenzene, xylene, ethanol, methane, SO2, NO2, and CO2 at various operational temperatures were subsequently investigated. It was found that a CuO-ZnO heterostructure with 1.0 wt% Zn showed excellent selectivity towards 100 ppm of xylene at 100 °C. The sensor further demonstrated an insignificant cross-sensitivity (Sxylene/Stoluene= 2.7) and (Sxylene/Sbenzene = 8.5) towards toluene and benzene vapour. Additionally, the ultra-low limit of detection of 9.5 ppb and sensitivity of 0.063 ppm−1 were observed towards xylene vapour, which indicated that the CuO-ZnO (1.0 wt%) heterostructure-based sensor can realize sub-ppb-level xylene concentration. The sensor disclosed excellent long-term stability in dry air and 40% relative humidity. The superior gas sensing characteristics could be ascribed to the superior surface area, the creation of p-n heterojunction, the robust chemical affinity, and the catalytic performance of p-type CuO on xylene vapour. The response mechanism towards xylene was also clarified.