Constructing highly catalytic oxidation over BiOBr-based hierarchical microspheres: Importance of redox potential of doped cations

Abstract

In this work, we prepared BiOBr-based hierarchical microspheres by a simple solvothermal method. The phase structure, morphology and optical properties of catalysts were well characterized by XRD, FESEM, FTIR, UV-DR spectra, XPS valence band and BET surface area analysis. Among the Vis/catalyst/H2O2 system, Cu-BiOBr is found to be the most effective for rhodamine b degradation while Fe-BiOBr exhibits the highest catalytic activity for the mineralization of 2-chlorophenol. Hydroxyl radicals generation rate and H2O2 decomposition rate follow: Fe-BiOBr>BiOBr>Zn-BiOBr=Ni-BiOBr=Ag-BiOBr>Cu-BiOBr, and Cu-BiOBr>Fe-BiOBr>BiOBr=Zn-BiOBr=Ni-BiOBr>Ag-BiOBr, respectively. The catalytic mechanisms under Vis/catalyst/H2O2 systems are proposed and compared, as following: (1) for BiOBr/Zn-BiOBr/Ni-BiOBr/Ag-BiOBr, the activation of H2O2 by photoelectrons to generate hydroxyl radical; (2) for Fe-BiOBr, the reaction of Fe(II) or photoelectrons with H2O2 to produce hydroxyl radical, and Fe(III) is reduced by photoelectrons to Fe(II); (3) for Cu-BiOBr, the activation of H2O2 by photoelectrons to generate hydroxyl radical that probably oxides Cu(II) to Cu(III), and the reaction of Cu(I) with H2O2 to generate Cu(III). The trapping experiments display that holes and hydroxyl radicals (or Cu(III)) have dominant roles.