Ce3+/Ce4+ redox-mediated defect engineering in ZnO/CeO2 heterojunctions: Theoretical and experimental elucidation of enhanced xylene sensing

Abstract

The development of efficient sensors for detecting volatile organic compounds (VOCs) like xylene is critical to mitigating health risks in household environments. This study presents a simple synthetic method and a rapid detection process for a xylene gas sensor. By employing a hydrothermal method, CeO₂ nano-spheres were loaded onto flower-like ZnO, creating a ZnO/CeO₂ heterojunction with a larger specific surface area and higher reactive oxygen content compared to pure ZnO. At an optimal operating temperature of 240 °C, the sensor demonstrates better xylene response, rapid response/recovery kinetics (2 s/3 s), excellent cyclability, and long-term stability. Combined experimental characterization (XPS, TEM) and DFT calculations reveal threefold enhancement mechanisms. The work function disparity between CeO₂ and ZnO drives interfacial charge redistribution, inducing band bending and electron depletion layer formation at the heterojunction interface. Ce³⁺/Ce⁴⁺ redox cycling promotes oxygen vacancy formation, and hierarchical porosity optimizes gas diffusion and active site exposure. The heterojunction engineering strategy not only improves xylene selectivity but also establishes a generalizable approach for designing MOS-based sensors through synergistic interface and defect modulation. This work offers new insights into the design of MOS-based selective xylene detection materials through heterojunction engineering.