Double Z-scheme system of silver bromide@bismuth tungstate/tungsten trioxide ternary heterojunction with enhanced visible-light photocatalytic activity.

The ternary heterojunction of silver bromide@bismuth tungstate/tungsten trioxide (AgBr@Bi2 WO6 /WO3 ) was designed and synthesised by hydrothermal and deposition-precipitation approaches. The composites were characterised by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy (XPS). The photoabsorption range and bandgaps of the photocatalysts were analysed by ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS). Compared with Bi2 WO6 /WO3 or AgBr alone, the AgBr@Bi2 WO6 /WO3 composites displayed higher visible-light photocatalytic performance for degrading rhodamine B (RhB). AgBr@Bi2 WO6 /WO3 with 40% AgBr concentration was optimum for photocatalytic activity. Radical-trapping experiments revealed that superoxide anion radicals (O2 - ) and holes (h+ ) were the active species during photocatalytic degradation and that O2 - was the dominant active species. Therefore, the increased photocatalytic activity of AgBr@Bi2 WO6 /WO3 was attributed to the atypical double Z-scheme system, which effectively improved the transfer and separation of electron-hole pairs in ternary heterojunction structures.