Important contribution of Cu(III)-peroxo species to As(III) oxidation in the Cu(II)-S(IV) system

Sulfate radical (SO4 center dot-) is always thought to be an important oxidizing species in the metal-sulfite [S(IV)] systems, however, the oxidizing species correlated with the metal species have rarely been mentioned. In this study, the oxidizing species that oxidize arsenite [As(III)] in the Cu(II)-S(IV) system were investigated under alkaline conditions. Kinetic results indicate that complexation between Cu(II) and S(IV) is the pre-requisite to initiate various oxidizing species, followed by internal electron transfer from S(IV) to Cu(II) with the formation of SO3 center dot- and the Cu-I(SO3)(n)(-2n+1) complexes. Quenching experiments rule out contributions of SO5 center dot-, peroxymonosulfate (HSO5-, PMS), hydroxyl radical ((OH)-O-center dot), superoxide radical (O-2(center dot-)) and singlet oxygen (O-1(2)) to As(III) oxidation in the Cu(II)-S(IV) system and indicate that some kinds of peroxo species contribute. On the other side, apart from the oxidizing species such as SO5 center dot-, PMS and SO4 center dot- generated via a series of reactions between SO3 center dot- and O-2, the Cu-I(SO3)(n)(-2n+1) complexes also react with O-2 to form CuII-O-2(center dot-)-(SO32-)(n) superoxo species and Cu-III-O-2(2-)-(SO32-)(n) peroxo species, as revealed by Raman analysis. UV-vis spectrum further confirms the presence of Cu(III) in the Cu(II)-S(IV) system. We therefore suggest that both SO4 center dot- and the Cu(III)-peroxo species play important roles in the oxidation of As(III) in the Cu(II)-S(IV) system. This study enriches our understanding on the diversity of oxidizing species in the metal-S(IV) systems under alkaline conditions.

Automated summary

This study reveals that both Cu(III)-peroxo species and SO4 center dot- play important roles in the oxidation of As(III) in the Cu(II)-S(IV) system, enriching our understanding of the diversity of oxidizing species in metal-S(IV) systems under alkaline conditions.