Surface-passivation modulated oxygen vacancies in plasmonic semiconductor Cs-doped WO _{3− <i>x</i>} nanosheets for efficient methyl orange photodegradation

As a transition-metal oxide semiconductor with variable tungsten valence states and abundant oxygen vacancies, WO_3-<i>x</i>has attracted broad interest because its localized surface plasmon resonance performance can be tuned via controlling the concentration of oxygen vacancies. In this work, Cs-doped WO_3-<i>x</i>nanosheets (Cs-WO_3-<i>x</i>) were synthesized by solvothermal method. Subsequently, Cs-WO_3-<i>x</i>were further annealed in hydrogen and air atmosphere, respectively, forming a compact, highly crystalline surface layer (with thickness of ∼14 nm) on the surface while retaining abundant oxygen vacancy defects in the center region (denoted as a-Cs-WO_3-<i>x</i>). As a proof-of-concept, the as-prepared nanosheets were employed as light harvesting materials in photocatalytic degradation of methyl orange (MO), a-Cs-WO_3-<i>x</i>nanosheets demonstrate significantly improved degradation efficiency with respect to WO_3-<i>x</i>and Cs-WO_3-<i>x</i>counterparts. The enhanced performance can be attributed to the hot-carrier transfer routes, which relies on not only direct electron transfer but also the more efficient plasmon-induced resonant energy transfer pathway. This work develops new pathway and provides important insights into the regulation of oxygen vacancies.