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

The novel ternary Ag2WO4/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 Ag2WO4 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 Ag2WO4, and Ag2WO4 material was evenly dispersed on the Ag2WO4/BiOI/BiOCl surface. The ternary composite possessed a larger surface area than Ag2WO4 and BiOI/BiOCl with the addition of Ag2WO4. Meanwhile, the separation efficiency of e(-)-h(+) pairs in Ag2WO4/BiOI/BiOCl composite was greatly enhanced. The experimental results showed that Ag2WO4 content, fluorescent light irradiation, CO32- and SO2 all exhibited remarkable influences in the photocatalytic process. The Hg-0 removal efficiency of Ag2WO4/BiOI/BiOCl photocatalyst was still up to 94 % after four cycles, indicating a superior stability of photocatalyst. Superoxide radical (O-center dot(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 Ag2WO4/BiOI/ BiOCl composite and its mechanism for gaseous Hg-0 removal were proposed with a double S-scheme mode.