Dual-S-scheme 3D Ag2CO3/BiOI/BiOCl microsphere heterojunction for improving photocatalytic mercury removal

A novel 3D microspherical Ag2CO3/BiOI/BiOCl heterojunction photocatalyst was successfully prepared via a one-pot coprecipitation method. The pore characteristics, morphologies and optical properties of the composite photocatalysts were characterized in detail by means of XRD, FTIR, SEM, TEM, UV-Vis DRS, N2 adsorptiondesorption, XPS, ESR and PL. The effects of the CO32  /Bi3+ molar ratio, pH value, fluorescent lamp irradiation, SO2, NO and scavengers on the wet removal of gaseous Hg0 by the composites were studied through a series of experiments. The results showed that more than 98% of Hg0 from simulated flue gas was removed by the optimized 3% Ag2CO3-BiOI/BiOCl system within 60 min. The photocatalyst had good acid, alkali and NO resistance, but SO2 significantly inhibited it. The specific surface area of the Ag2CO3/BiOI/BiOCl photocatalyst was much higher than that of a single component, which was 6.80 and 1.56 times that of Ag2CO3 and BiOI/ BiOCl, respectively. For 3% Ag2CO3-BiOI/BiOCl, the Hg0 removal efficiency remained at approximately 94% in the sixth cycle. Density functional theory (DFT) revealed that the formation of heterojunctions could enhance the electron transition and efficient separation of photoinduced electron-hole pairs. Furthermore, the free radical capture experiment showed that anionic superoxide radical (& BULL;O2  ) was the main active substance for the removal of Hg0. A reasonable dual-S-scheme charge transfer mechanism for an enhanced photocatalytic removal of Hg0 is proposed.

Automated summary

A 3D microspherical Ag2CO3/BiOI/BiOCl heterojunction photocatalyst was successfully prepared by one-pot coprecipitation method. The composite photocatalysts were characterized by XRD, FTIR, SEM, TEM, UV-Vis DRS, N2 adsorption-desorption, XPS, ESR, and PL. The optimized 3% Ag2CO3-BiOI/BiOCl system showed more than 98% removal efficiency of Hg0 from simulated flue gas within 60 min. The photocatalyst had good acid, alkali, and NO resistance, but was significantly inhibited by SO2. The specific surface area of the Ag2CO3/BiOI/BiOCl photocatalyst was much higher than that of a single component, and the Hg0 removal efficiency remained around 94% even after six cycles.