Solid peroxides in Fenton-like reactions at near neutral pHs: Superior performance of MgO₂ on the accelerated reduction of ferric species

Fenton-like reactions at near neutral pHs are limited by the slow reduction of ferric species. Enhancing generation of [Formula presented] from solid peroxides is a promising strategy to accelerate the rate-limiting step. Herein, the H₂O₂ release and Fenton-like reactions of four solid peroxides, MgO₂, CaO₂, ZnO₂ and urea hydrogen peroxide (UHP), were investigated. Results indicated that UHP can release H₂O₂ instantly and show a similar behavior as H₂O₂ in the Fenton-like reactions. MgO₂ released H₂O₂ quickly in phosphate buffered solutions, which was comparable to CaO₂ but faster than ZnO₂. Metal peroxides induced higher initial phenol degradation rates than UHP and H₂O₂ when the same theoretic H₂O₂ dosages and Fe(III)-EDTA were used. MgO₂ displayed a superior performance for phenol degradation at pH 5, resulting in more than 93% phenol reduction at 1.5 h. According to kinetic analyses, the generation rate of [Formula presented] in the MgO₂ system was 18 and 3.4 times higher than those in ZnO₂ and CaO₂ systems, respectively. The addition of MgO₂ significantly promoted H₂O₂ based Fenton-like reactions by increasing production of [Formula presented], and the mixture of MgO₂ and H₂O₂ had an improved utilization efficiency of active oxygen than the MgO₂ system. The findings suggested the critical roles of metal peroxides in favoring Fenton-like reactions and inspired strategies to simultaneously accelerate Fenton-like reactions and improve utilization efficiency of active oxygen.