Strongly enhanced persulfate activation by bicarbonate accelerated Cu(iii)/Cu(i) redox cycles

Abstract

In advanced oxidation systems, the promoting effect of bicarbonate is relatively overlooked. Bicarbonate, as an inorganic anion widely present in natural waters, is extremely important for water treatment. Therefore, bicarbonate was added to a PDS/Cu²⁺ system to investigate the degradation mechanisms of organic contaminants. The generation of alkyl radicals in the PDS/Cu²⁺/HCO₃⁻ system was first demonstrated through Electron Paramagnetic Resonance (EPR) testing. This study reveals that the introduced bicarbonate ions undergo transformation into alkyl radicals. The presence of alkyl radicals promotes the cycling of monovalent, divalent, and trivalent copper ions, facilitating the degradation of contaminants. The production of monovalent and trivalent copper ions in the reaction system was confirmed through UV-vis absorption spectroscopy and quenching experiments. Furthermore, the change in the oxidation state of copper ions was further confirmed through EPR testing. These findings not only shed new light on the degradation mechanism of the PDS/Cu²⁺ system in the presence of bicarbonate but also open up new avenues for the further application of bicarbonate in advanced oxidation processes.