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 (NkH2O2), O2 production (NkO2), benzoic acid degradation (NkBA), and hexachloroethane degradation (NkHCA) 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.