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

Abstract

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 as-prepared samples are present as square-section nanorods, and the length and sectional size of the CeVO₄ NRs are found to be ∼1.5 μm and ∼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 °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 O₂ (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.