A simple cation exchange approach to Bi-doped ZnS hollow spheres with enhanced UV and visible-light photocatalytic H2-production activity

Abstract

Bi-doped ZnS hollow spheres were successfully synthesized by a facile cation exchange reaction between ZnS hollow spheres and Bi(NO₃)₃. The samples were characterized by X-ray diffraction, scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, N₂ adsorption–desorption isotherms, UV-vis absorption spectroscopy as well as transient photocurrent responses. The photocatalytic H₂-production activity was investigated by using Na₂S and Na₂SO₃ as sacrificial reagents in water. Even without a Pt cocatalyst, the as-prepared Bi-doped ZnS hollow spheres exhibited significant visible-light and UV-light photocatalytic activity and good stability for H₂-production. The optimal content of Bi dopant was determined to be about 0.3 at% and the corresponding H₂-production rate was 1030 and 134 μmol h⁻¹ g⁻¹ under UV and visible-light irradiation, respectively. The apparent quantum efficiency was 0.99% at 420 nm and 4.0% at 365 nm. It is suggested that doping Bi into ZnS generated an isolated state originating from Bi 6s above the top of the valence band of ZnS, and the electron excitation from Bi 6s state to the conduction band occurred upon irradiation with visible light. Furthermore, the UV-light photocatalytic H₂ evolution activity over Bi-doped ZnS hollow spheres is even higher than that of Pt/ZnS counterparts. This is ascribed to the fact that the Bi doping facilitates the separation of photogenerated electron–hole pairs and reduces their recombination rate.