Unraveling the generation mechanism of singlet oxygen in Bi₂W_xMo_1-xO₆ solid solution and roles in photocatalytic degradation of gaseous toluene under visible-light irradiation

Photocatalytic degradation volatile organic compounds (VOCs) represent an appealing strategy since the inexhaustible solar energy and facile reaction condition. In this work, a flower-like microsphere Bi2WxMo1-xO6 solid solution photocatalysts with abundant oxygen vacancies (OVs) were prepared via HTAB-assisted hydrothermal method. The mole ratio of W and Mo atoms were regulated by adjusting the stoichiometric ratio of their precursor. The optimized Bi2W0.25Mo0.75O6 presented outstanding photocatalytic performance with 96.8% of toluene degradation rate after 180 min of irradiation under visible light (>420 nm), which was 13.76 times higher than that of pure Bi2MoO6 and 10.32 times higher than that of pure Bi2WO6, respectively. The enhanced photocatalytic activity of Bi2W0.25Mo0.75O6 was attributed to the optimized band structure and efficient separation efficiency of carriers as well as the participation of singlet oxygen (O-1(2)) radicals. Free radical trap experiments and electron spin resonance investigations revealed that O-1(2), hydroxyl radical, and holes were the predominated reactive oxygen species (ROSs) in toluene degradation. Meanwhile, the generation of O-1(2) was related to abundant OVs of Bi2W0.25Mo0.75O6 solid solution. This work suggested that solid solution with abundant OVs was an effective photocatalyst to improve the VOCs degradation activity under visible-light irradiation.