Study on the separation mechanisms of photogenerated electrons and holes for composite photocatalysts g-C3N4-WO3

The separation mechanisms of photogenerated electrons and holes for composite photocatalysts have been a research focus. In this paper, the composite g-C 3 N 4 -WO 3 photocatalysts with different main parts of C 3 N 4 or WO 3 were prepared by ball milling and heat treatment methods. The photocatalytic performance was evaluated by degradation of methylene blue (MB) and fuchsin (BF) under visible light illumination. The photocatalyst was characterized by X-ray powder diffraction (XRD), UV–vis diffuse reflection spectroscopy (DRS), transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) methods. The separation mechanisms of photogenerated electrons and holes of the g-C 3 N 4 -WO 3 photocatalysts were investigated by electron spin resonance technology (ESR), photoluminescence technique (PL), and determination of reactive species in the photocatalytic reactions. When the main part of the g-C 3 N 4 -WO 3 photocatalyst is WO 3 (namely g-C 3 N 4 /WO 3 ), the transport process of the photogenerated electrons and holes adopts the generic band–band transfer. Meanwhile, g-C 3 N 4 is covered by WO 3 powder, and the role of g-C 3 N 4 can not be played fully. The photocatalytic activity of the photocatalyst is not obviously increased. However, when the primary part of the WO 3 -g-C 3 N 4 photocatalyst is g-C 3 N 4 (namely WO 3 /g-C 3 N 4 ), the migration of photogenerated electrons and holes exhibits a typical characteristic of Z-scheme photocatalyst, and the photocatalytic activity of the photocatalyst is increased greatly.