EDTA enhanced heterogeneous Fenton oxidation of dimethyl phthalate catalyzed by Fe3O4: Kinetics and interface mechanism

• EDTA(aq) introduced enhanced homogeneous reaction by promoting Fe3O4 dissolution.
• The adsorbed EDTA could also enhance DMP removal probably by efficient use of ROS.
• Asorbed EDTA competed with H2O2 for active sites, inhibiting H2O2 decomposition.
• DMP in close proximity to the catalyst surface was probably oxidized.

It has been noticed that some chelating agents can enhance heterogeneous Fenton reactions, as well as homogeneous Fenton reactions. However, the mechanism of the enhanced heterogeneous Fenton reactions remains speculative, due to the ambiguous concurrence of homogeneous and heterogeneous reactions. In the present work, ethylene diamine tetraacetic acid (EDTA) was introduced to study the role of the chelating agent in the oxidation of dimethyl phthalate (DMP) in nano-Fe3O4/H2O2 system. The addition of EDTA in solution dramatically accelerated DMP removal partly due to the induced homogeneous Fenton reaction by enhanced dissolution of Fe3O4. Meanwhile, the adsorbed EDTA on the catalyst could also enhance DMP removal. Effects of EDTA surface loadings, initial H2O2 concentrations, initial DMP concentrations, and initial pHs on the reaction kinetics in EDTA modified Fe3O4/H2O2 system were investigated, together with the reusability of the EDTA modified Fe3O4. Results showed that the surface complexed EDTA (FeII/III-EDTA) inhibited H2O2 decomposition by competition for surface active sites. However, the generation of OH and HO2/O2−was not suppressed according to the ESR results. The enhanced DMP removal by FeII/III-EDTA was probably due to the efficient use of reactive oxygen species (ROS). A possible EDTA enhanced heterogeneous Fenton mechanism was further proposed.

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