Self-assembled Co3O4@WO3 hollow microspheres with oxygen vacancy defects for fast and selective detection of toluene

Abstract As the demand for detecting harmful gases becomes more and more urgent, a potential gas-sensing material with high response and good selectivity based on Co3O4-functionalized WO3 hollow microspheres was successfully synthesized in this study. A variety of techniques were employed to analyze the chemical and structural properties of the samples, involving X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Energy Dispersive Spectrometer (EDS) and X-ray Photoelectron Spectroscopy (XPS). The gas-sensing properties of WO3, Co3O4 and Co3O4-functionalized WO3 hollow spheres towards toluene were investigated to determine the effects of functionalization. In comparison with pure WO3 hollow microspheres, the sensing properties of the complex modified by Co3O4 nanoparticles to toluene were significantly enhanced. The response value of the composite could reach 55.8 to 100 ppm toluene, which was nearly three times higher than that of pure WO3 hollow microspheres. The enhancement of gas sensitivity could be mainly attributed to the catalytic activity of Co3O4 in the process of toluene oxidation, the increase in chemisorbed oxygen species and oxygen vacancies, and the widening in conductive channel as a result of the existence of Co3O4 nanoparticles in the Co3O4-functionalized WO3 composite.