Impact of Ag2O on the gas sensing properties of the star-shaped BaTiO3/ ZnO heterostructures

In this work, star-shaped heterostructures of Ag2O/BaTiO3/ZnO were proposed as resistive-type gas sensors. Through combined analyzes of XRD, SEM, and EDS, the structure, surface morphology, and the elemental composition of the synthesized materials were confirmed. The star-shaped morphology of BaTiO3/ZnO was found to be intact even after loading with different quantities of Ag2O, as revealed by the SEM analysis. The impact of loading different amounts of Ag2O (ranging from 1 % to 3 %) on the sensors' ability to detect volatile organic compounds (VOCs) and carbon dioxide (CO2) was concretely gauged by their response, response/recovery times, selectivity, and long-term stability. For the detection of ethanol/acetone, CO2, and methanol, a 1:2 M ratio of BaTiO3/ZnO with 1 % and 2 % Ag2O, and a 1:3 M ratio of BaTiO3/ZnO with 1 % Ag2O were determined as the optimum content, respectively. From the gas sensing analysis, Ag2O/BaTiO3/ZnO sensors with different amounts of Ag2O additive gave different optimal temperatures for different target gases. Lower operating temperatures, i.e. 180 degrees C, and 260 degrees C for CO2 and VOCs, respectively, rapid responsivity with a response time of <1 s for VOCs, and fast recovery times (as low as 10, 13, and 6 s for ethanol, acetone, and methanol vapors, respectively) were observed. More importantly, the sensor exhibited good selectivity for several possible interferences. The underlying reasons for the acceleration of the gas molecules adsorption, hence the fast sensor response, are the high specific surface area established by the star-shaped morphology, and compatible energy band alignment at the p/n interface coupled with the catalytic effect induced by Ag2O.