A tale of two metal ions: contrasting behaviors of high oxidation states of Cu and Mn in a bicarbonate–H2O2 system

Abstract

In this study, the contrasting activities and pathways of Mn²⁺/Cu²⁺–HCO₃⁻ systems for Congo red (CR) dye degradation are presented. The Mn²⁺–HCO₃⁻ system (with the well-known Mn^IVO as the reactive species) did not degrade CR, while the Cu²⁺–HCO₃⁻ system (with high-valent Cu proposed as the reactive species) had a good oxidizing ability for CR. Further, HO radicals in the classic Fenton-like system made no contribution to CR degradation with both Cu and Fe ions as catalysts. The results indicate that reactive species in metal–HCO₃⁻ AOPs need prudent examination and better understanding of the underlying mechanism would benefit the development of more efficient AOPs.