Low-temperature and high-selectivity Ag/Co3O4 toluene sensor based on lattice oxygen and d-band and investigation of response behavior shifts induced by Ag nanoparticles

Currently, the sensing mechanism of toluene remains controversial. The sensing action of toluene is often attributed to adsorbed oxygen based on acknowledged Wolkenstein model. However, the role of lattice oxygen often remains neglected. To investigate toluene sensing mechanism, Ag quantum dot-modified Co3O4 were successfully synthesized by the thermal method. X-ray photoelectron spectroscopy (XPS) of Ag-Co3O4 before and after exposure to toluene reveal the role of lattice oxygen, and Gas Chromatography-Mass Spectrometry (GC-MS) and Density Functional Theory (DFT) reveal the catalytic role of Ag particles. Ag particles caused the upshift of Co D-band, more readily hybridizing the s and p orbitals in the toluene and O2 molecules, possibly contributing to the enhanced catalytic and adsorption activity of the materials. Moreover, Ag-induced response behaviors switching from oxidation-reduction transitions were found and explained. Excitingly, the synthesized 16 at% Ag-Co3O4 has good selectivity for toluene at 180 °C. And the response of 16 at% Ag-Co3O4 to 100 ppm toluene reached 2113% with a detection limit 100 ppb. This work provides a novel insight into the toluene sensing mechanism, aiding the design of high-performance toluene sensors.