Comparison study on ZnO and CuO gas sensing characteristics: Temperature modulated-dual selectivity towards benzene and xylene vapours

Abstract

The selective detection of gaseous benzene, toluene, ethylbenzene, and xylene (BTEX) is challenging due to their similar molecular structures. In addition, BTEX vapours are extremely hazardous and carcinogenic. Thus, in the current study, n-type ZnO and p-type CuO nanostructures were synthesized utilizing various bases by a simple hydrothermal method. Among the tested sensors, the ZnO–NaOH-based sensor displayed a temperature dual-mode selectivity toward benzene with responses (Ra/Rg) of 2.5 and 24 at 5 and 100 ppm, respectively at 75 °C, and Ra/Rg ≈ 142 toward xylene vapour at 100 ppm at an operating temperature of 150 °C. While the CuO-based sensors showed poor response, sensitivity and selectivity towards tested analytes. Moreover, the ZnO–NaOH based sensor revealed enormous sensitivity of 1.21 ppm−1 and low limit of detection (LoD) of 0.018 ppm (i.e., 18 ppb) toward xylene. The ultra-sensitivity, selectivity, low LoD of ZnO–NaOH based sensor toward benzene and xylene are associated with the improved VO observed in the in-situ photoluminescence and electron paramagnetic resonance studies, and as well as the x-ray photoelectron spectroscopy analyses. The ZnO–NaOH-based sensor, which was stored for roughly 18 months (547 days), demonstrated a reliable repeatability and long-time operation stability for 22 h exposure to xylene. The superior sensitivity, stability, and selectivity indicate openly that the strategy of using various bases is a striking method for fabricating a temperature dual-mode selectivity for the detection of benzene and xylene vapours.