Catalyzed H₂O₂ decomposition over iron oxides and oxyhydroxides: Insights from oxygen production and organic degradation

Iron minerals, such as iron oxides and iron oxyhydroxides, are the main influential soil components in catalyzed hydrogen peroxide propagation (CHP). Due to their dual effects on H₂O₂ activation to produce reactive oxygen species (ROS) and invalid consumption to produce oxygen, the intrinsic reactivity of iron minerals toward H₂O₂ decomposition requires comprehensive investigations. Herein, six iron minerals (hematite, magnetite, maghemite, goethite, feroxyhyte, and ferrihydrite) for H₂O₂ decomposition were investigated by a combination of normalized kinetic rate constants of H₂O₂ decomposition (Nk_H2O2), O₂ production (Nk_O2), benzoic acid degradation (Nk_BA), and hexachloroethane degradation (Nk_HCA) over the surface area of each mineral. The results indicate H₂O₂ decomposition over iron minerals is a surface-related heterogeneous process. Hematite and goethite are the most promising minerals for environmental cleanup in terms of ROS production, because their H₂O₂ utilization efficiency for benzoic acid (BA) degradation (0.138 and 0.024 mol BA/mol H₂O₂ for hematite and goethite, respectively) are highest among the six iron minerals. Magnetite and maghemite are highly active for both H₂O₂ decomposition and O₂ production at neutral and basic pHs. The presence of organic compounds suppresses O₂ production by more than 60%, which favors H₂O₂ utilization. Ferrihydrite and feroxyhyte are considered as the problematic mineral for CHP due to that the two minerals acquire a high O₂ production and negligible ROS generation at all pHs. The results of this study provide new insights to increase the understandings of H₂O₂-iron mineral systems and guide the application of iron minerals in chemical oxidation technologies.