A gas sensor based on Ag-modified ZnO flower-like microspheres: Temperature-modulated dual selectivity to CO and CH4

The detection of carbon monoxide (CO) and methane (CH4) is crucial given that CH4 explosions and CO poisoning are two major gas accidents that seriously restrict coal mining safety. In this study, Ag-modified ZnO flower-like microspheres are prepared by a solvothermal method combined with an impregnation route. The techniques of X-ray diffraction characterize the crystallographic information, morphology and surface composition of the samples, field emission scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. The gas sensing measurement results show that a sensor based on 1.5 at.% Ag/ZnO microspheres exhibits temperature-modulated dual selectivity detection for CO at 130°C and CH4 at 200°C. Furthermore, the sensor possesses satisfactory sensing performance with high response, fast response/recovery rate, low detection limit and excellent selectivity. The enhanced sensing properties of ZnO microspheres modified with Ag nanoparticles are mainly attributed to the chemical sensitization of Ag nanoparticles, the formation Schottky barrier between semiconducting ZnO and the noble metal Ag and the p-n heterojunction between Ag2O and ZnO. Our experimental results indicate that the obtained sensor is based on 1.5 at.% Ag/ZnO microspheres have broad application prospects in the detection of coal mine gases.