Hydroxyl radical generation in peroxymonocarbonate/Co2+ systems: kinetic and mechanistic insights.

This study investigates the generation of hydroxyl radicals (˙OH) in a peroxymonocarbonate (PMC)-based advanced oxidation process (AOP) catalyzed by Co2+. Steady-state ˙OH concentrations ([˙OH]ss) were quantified using terephthalic acid (TA) as a probe. The presence of PMC alone had negligible effect on ˙OH production, whereas Co2+ markedly enhanced radical formation. Specifically, [˙OH]ss increased from 4.03 × 10-17 M in the H2O2-only system to 2.25 × 10-16 M in H2O2 + Co2+, and from 2.26 × 10-17 M in PMC-only to 3.38 × 10-16 M in PMC/Co2+. This enhancement is attributed to a Fenton-like mechanism involving Co2+. Kinetic analysis revealed first-order dependence on TA concentration (R 2 ≈ 0.99), Langmuir-type dependence on PMC concentration, and linear correlation with Co2+ concentration. Inorganic anions exhibited diverse roles, with Cl- enhancing ˙OH generation by ∼26%, whereas SO4 2- and HPO4 2- suppressed it by ∼35 and ∼25%, respectively. A kinetic model describing radical generation agreed well with experimental data, offering valuable mechanistic insights and highlighting practical applicability of PMC-based AOPs for controlled ˙OH generation.