Enhanced photocatalytic Hg0 removal over Z-scheme CeO2/Bi5O7I nanorod composite under fluorescent light irradiation

Abstract

Novel CeO2 modified Bi5O7I nanorod composites were synthesized via a coprecipitation subsequent calcination method, which were employed to oxidize gaseous Hg0 in a photocatalytic bubbling reactor. The porosity properties, crystal structures, morphologies, elemental composition and optical absorption properties of the composites were investigated using various characterization methods. CeO2/Bi5O7I showed a significantly improved photoactivity of Hg0 removal under fluorescent light irradiation. The optimal mass percentage of CeO2 to CeO2–Bi5O7I was 10% and its photocatalytic removal efficiency of Hg0 reached as high as 97%. In comparison to NO, SO2 exhibited significant inhibition on Hg0 removal because of its easy reactivity with active species. The XRD, HRTEM and XPS results indicated the tight contact between Bi5O7I and CeO2, implying that a heterojunction between Bi5O7I and CeO2 was produced. The UV–vis DRS, PL and transient photocurrent test demonstrated that an enhanced activity of 10% CeO2/Bi5O7I for Hg0 removal could be assigned to the broad visible-light-absorption property, much superior separation of photoexcited electron-hole pairs. The scavenging experiments exhibited the superoxide radicals (•O2−) was the major oxidants in the process of Hg0 removal. Moreover, a proposed Z-scheme charge transfer path in CeO2/Bi5O7I nanorod composite was put forward according to the characterization and DFT calculation results.