Redox property of coordinated iron ion enables activation of O via in-situ generated HO and additionally added HO in EDTA-chelated Fenton reaction.

The Fenton system was a generation system of reactive oxygen species via the chain reactions, which employed HO and O as radical precursors and Fe/Fe as electron-donor/acceptor for triggering or terminating the generation of radicals. Recent work mainly emphasized the Fe- activated HO and the application of in-situ generated OH, while neglecting other side-reactions. In this work, EDTA (Ethylene diamine tetraacetic acid) was employed as a chelating agent of iron ions, which simultaneously changed the redox property of coordinated iron. The Fe-EDTA complexes in the presence of dissolved oxygen enabled the two-electron transfer from Fe to O and the in-situ production of HO, which further activate HO for yielding OH. Meanwhile, coordinated Fe exhibited non-negligible reactivity toward HO, which was higher than that of free Fe in the traditional Fenton system. The complexation of EDTA with Fe could enhance the Fe generation reaction by the HO, accompanied by the O formation. The enhancement of O formation and Fe-EDTA regeneration induced the subsequent HO activation by Fe-EDTA, thus accelerating the Fe-EDTA/Fe-EDTA cycle for simultaneously producing O and OH. To sum up, the EDTA-chelated Fenton system extended the applicable pH range to circumneutral/alkaline level and tuned the redox property of coordinated iron for diversifying the OH production routes. The research reinterpreted the chain reactions in the Fenton system, revealing another way to enhance the radical production or other property of the Fenton/Fenton-like system.