NO2 Sensing Using Sr-Doped Bi2MoO6 Based on the Synergy of Increased Catalytic Activity and the Cloaking Effect

Abstract Nitrogen dioxide (NO2) serves as a highly reactive atmospheric pollutant that poses significant health risks when inhaled above permissible exposure limits. Here, we present an atomic-level electronic-structure modification technique that generates defect-mediated sub-bandgap states, serving as effective electronic intermediates through the incorporation of Sr2+ ions into environmentally benign Bi2MoO6. These tailored states reduce the bandgap, enhance carrier mobility, and, together with the enlarged grain size that limits the density of grain boundaries and subsequently suppresses carrier scattering, establish a highly favorable charge-transfer pathway. Utilizing NO2 as a target gas, the optimized 1% Sr–Bi2MoO6 sensor exhibits intrinsically selective interaction toward NO2, achieving an experimentally determined detection threshold of 83 ppb and rapid response/recovery characteristics (10/60 s) at a low operating temperature (50 °C). This study describes a generalizable band-structure engineering approach for tuning charge-transfer energetics in oxide semiconductors, providing a materials-driven foundation for selective, energy-efficient NO2 sensing technologies.