The role of oxygen adsorption and gas sensing mechanism for cerium vanadate (CeVO4) nanorods

CeVO4 nanorods (NRs) were successfully synthesized via a one-step hydrothermal method using disodium edentate (EDTA) as a chelating agent. The CeVO4 NRs are assigned to the zircon-type tetragonal structure and exhibited pure single-crystals as determined by XRD analysis. FE-SEM images indicate that the asprepared samples are present as square-section nanorods, and the length and sectional size of the CeVO4 NRs are found to be similar to 1.5 mu m and similar to 100 nm, respectively. Moreover, the HRTEM images and SAED diffraction patterns confirm that the main exposed surfaces of the CeVO4 NRs were the (010) and (004) lattice planes with a high exposed percentage (ca. 96.77%) around the NRs and the growth direction was along the (200) lattice plane. The CeVO4 NRs presents a pure phase, with no other impurity phases identified from the FTIR and Raman spectra. XPS results indicate that the vanadium atoms on the surface exhibit a mixture of valence states, i.e., pentavalent state (V5+) and trivalent state (V3+), as dangling bonds around the oxygen vacancies were induced by EDTA desorption during hydrothermal process. An acetone gas sensor based on the CeVO4 NRs was fabricated, which exhibits a significant response (0.5 s) and recovery (80 s) with high selectivity at the optimum working temperature (108 degrees C). This is mainly due to the presence of the trivalent states (V3+), which serve as the active sites and provide a large number of oxygen vacancies (V-o) as identified by XPS and infrabar experiments at 300 ppm O-2 (0.003 atm). Moreover, it has been demonstrated that the response to acetone for the gas sensor was crucially dependent on the adsorbed oxygen (O-ads) on the (010) or (004) facets of the CeVO4 NRs, where the redox reaction with acetone occurred reversibly.