Facile synthesis of high surface area of p-n Co3O4-In2O3 heterostructure-based sensor for improved xylene detection at low temperature
Rethabile Makole, Zamaswazi P. Tshabalala, Mudalo Jozela, Franscious Cummings, H.C. Swart, David E. Motaung
Abstract
This study reports on the gas sensing properties of Co3O4 – n-type semiconducting metal oxides (Co-nSMOs) heterostructures, i.e., Co3O4-In2O3 (Co-In), Co3O4-CeO2 (Co-Ce), Co3O4-SnO2 (Co-Sn) and Co3O4-ZrO2 (Co-Zr) synthesized by microwave-assisted hydrothermal synthesis. Structural studies confirmed the formation of Co-nSMO heterostructures. Electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) showed that the Co-In possesses higher surface defects compared to its counterparts. The Co-nSMOs sensors were evaluated towards benzene, toluene, ethylbenzene, and xylene (BTEX) compounds, acetone, and NO2. Amongst the tested sensors, the Co-In heterostructure showed superior selectivity and a response of 36.6 to 100 ppm xylene at an optimum effective temperature of 150 °C. The sensor further showed good sensitivity and a low limit of detection of 0.2 ppm. Moreover, the Co-In-based sensor stored for 5 months, demonstrated excellent long-term stability toward xylene vapour in dry air and under 40 % relative humidity environment. The improved performance was due to the enriched facilitation of surface oxygen adsorption, which resulted in the enhanced catalytic influence of Co3O4 for oxidizing xylene vapour. Additionally, the performance was also associated with the higher surface area, mesoporous behaviour, and biggest pore volume which offered plentiful energetic sites for redox reactions, and synergistic combination of Co3O4 and In2O3 at the nanoscale p-n heterojunction. The xylene sensing mechanisms associated with improved performance were deliberated in detail. These results demonstrated that the Co-In could be utilized to monitor xylene with trivial interference from RH.