Interfacial charge transfer mechanism in bismuth oxide/tungsten oxide p-n heterojunction photocatalyst for methylene blue degradation

In this study, tungsten trioxide (WO 3 ) photocatalysts were synthesized through a hydrothermal process, utilizing sodium tungstate (Na 2 WO 4 ) as the starting material in the presence of polyvinylpyrrolidone (PVP) at different heat-treatment temperatures (180°C, 190°C, and 200°C). The 190°C sample exhibited a hybrid rod-sheet morphology, achieving the highest methylene blue (MB) degradation (47.6% in 60 min under light). In order to improve the activity, the molar ratio of Bi 2 O 3 /WO 3 was adjusted and the Bi 2 O 3 /WO 3 p-n heterojunction was constructed. The ratio critically governed both morphology and charge dynamics: increasing Bi 2 O 3 content promoted the growth of spherical Bi 2 O 3 particles on WO 3 rods/sheets, optimizing interfacial contact and light harvesting. When the molar ratio of Bi 2 O 3 /WO 3 was 60%, the composite photocatalyst displayed the greatest photocatalytic property, the first-order reaction rate constant of 0.0100 min -1 , it was 3.6 times of WO 3 . The Mott-Schottky curve indicated that p-n heterojunctions were formed between Bi 2 O 3 and WO 3 , and the internal electric field (IEF) at the interface effectively promoted the separation of charge carriers. During illumination, photogenerated electrons in the conduction band (CB) of Bi 2 O 3 migrate to the CB of WO 3 , and holes in the valence band (VB) of WO 3 migrate to the VB of Bi 2 O 3 , enhancing the utilization of charge carriers.