Facile fabrication of 3D spherical Ag2WO4 doped BiOI/BiOCl double S-scheme heterojunction photocatalyst with efficient activity for mercury removal

The novel ternary Ag 2 WO 4 /BiOI/BiOCl microspherical photocatalysts were successfully fabricated by a facile one-pot coprecipitation method to accelerate the separation performance of photogenerated electron-hole (e – -h + ) pairs of BiOCl and BiOI materials. The as-prepared materials were characterized by multiple methods, and the effects of various parameters such as Ag 2 WO 4 content, fluorescent light irradiation, pH value and inorganic anions on photocatalytic removal of Hg 0 were studied in detailed. The characterization results showed that the three-dimensional (3D) microspherical BiOI/BiOCl composite provided a suitable carrier for Ag 2 WO 4 , and Ag 2 WO 4 material was evenly dispersed on the Ag 2 WO 4 /BiOI/BiOCl surface. The ternary composite possessed a larger surface area than Ag 2 WO 4 and BiOI/BiOCl with the addition of Ag 2 WO 4 . Meanwhile, the separation efficiency of e – -h + pairs in Ag 2 WO 4 /BiOI/BiOCl composite was greatly enhanced. The experimental results showed that Ag 2 WO 4 content, fluorescent light irradiation, CO 3 2− and SO 2 all exhibited remarkable influences in the photocatalytic process. The Hg 0 removal efficiency of Ag 2 WO 4 /BiOI/BiOCl photocatalyst was still up to 94% after four cycles, indicating a superior stability of photocatalyst. Superoxide radical ( • O 2 – ) and hole (h + ) were proved to be the main reaction substances for Hg 0 removal. In view of the characterization analysis, free radicals capture test results and Density Functional Theory (DFT) calculation, the charge transfer route of Ag 2 WO 4 /BiOI/BiOCl composite and its mechanism for gaseous Hg 0 removal were proposed with a double S-scheme mode. • Ag 2 WO 4 /BiOI/BiOCl was prepared via one-pot coprecipitation method. • The optimal photocatalytic Hg 0 removal efficiency can reach up to 98%. • The enhanced activity was attributed to an effective separation of carriers. • The mechanism of a double S-scheme mode was proposed.