Defective Bi4MoO9/Bi metal core/shell heterostructure: Enhanced visible light photocatalysis and reaction mechanism

Bi4MoO9 is a promising photocatalyst for air pollutant mineralization due to its very positive valance band edge at 3.48 eV. However, its performance usually suffers from its wide band gap and high charge recombination rate, which limits its scaled application. To address these issues, one novel Bi4MoO9/Bi° core/shell heterostructured photocatalyst with considerable number of oxygen vacancies was synthesized through a facile surface chemical reduction treatment over the pre-synthesized Bi4MoO9 microrods in NaBH4 aqueous solution. The combined TEM/HRTEM, UV–vis DRS, PL and ESR study reveals that the construction of Bi4MoO9/Bi° heterojunction in the core/shell structure, the surface plasmon resonance (SPR) of Bi metal and the oxygen vacancy-induced formation of defect states all contribute to an intensified photoabsorption, charge separation efficiency and generation of oxidative radicals. The photocatalytic NO removal test under visible light irradiation shows that Bi4MoO9/Bi°-40 (40 denotes the molar ratio of NaBH4 to Bi4MoO9 is 40/60) presents a maximum NO removal efficiency of 55.4%, much higher than that of the original Bi4MoO9 (12.7%). The reaction pathway of the photocatalytic NO oxidation over the Bi4MoO9/Bi° was examined by in-situ DRFTS and the NO+ species as a kind of intermediate product in NO conversion is detected and critical for the conversion of NO to nitrate. The present work provides a new approach to activate the non-visible-light response semiconductor for efficient visible light photocatalysis.