Stabilizing Oxygen Vacancies in Plasmonic WO _3‐x Semiconductor Nanosheets via Surface Reconstruction Approach

ABSTRACT Plasmonic semiconductors have attracted extensive interest in optoelectronics and photocatalysis due to their broadened absorption spectral range, hot‐electron injection, and near‐field enhancement. Among various plasmonic semiconductors, WO _3‐x allows high concentrations of oxygen vacancies (O _V ) and pronounced localized surface plasmon resonance (LSPR) effects, enabling continuous tuning of optical and electronic properties. However, the LSPR effect in WO _3‐x depends critically on O _V concentration and their stability. Herein, a surface reconstruction approach (structural rearrangement forming a dense surface layer with altered stoichiometry) was employed to synthesize WO _3‐x nanosheets consisting of an inner layer with rich O _V concentration and a dense WO ₃ surface passivation layer, which suppresses O _V healing and thereby allows stable O _V concentration during exposure in ambient atmosphere conditions or photocatalytic reactions. The as‐synthesized plasmonic WO _3‐x semiconductor exhibits enhanced LSPR effect due to the formation of a dense WO ₃ passivation layer on the surface, which significantly improves the efficiency and stability of photocatalytic degradation of methyl orange under visible‐near‐infrared light illumination. This study provides a novel approach to improve the O _V stability in plasmonic WO _3‐x semiconductors, offering important insights for stabilizing O _V concentrations in various plasmonic semiconductors. This advancement facilitates the application of plasmonic semiconductors in fields such as photocatalysis and nano‐optoelectronics.