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 Co 3 O 4 were successfully synthesized by the thermal method. X-ray photoelectron spectroscopy (XPS) of Ag-Co 3 O 4 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 O 2 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-Co 3 O 4 has good selectivity for toluene at 180 °C. And the response of 16 at% Ag-Co 3 O 4 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. • Ag quantum dot leads to the upward shift of Co d-band on Co 3 O 4 , activating toluene and oxygen. • Ag quantum dot modified Co 3 O 4 transfers lattice defect and reduces adsorbed oxygen. • Excess Ag particles led to a switch in the response behavior of CO 3 O 4. • Lattice oxygen has an essential role in the toluene sensing reaction. [ABSTRACT FROM AUTHOR]