Intramolecular generation of endogenous Cu(III) for selectively self-catalytic degradation of Cu(II)-EDTA from wastewater by UV/peroxymonosulfate

Abstract

HO^•/SO₄^•--based advanced oxidation processes for the decomplexation of heavy metal-organic complexes usually encounter poor efficiency in real scenarios. Herein, we reported an interesting self-catalyzed degradation of Cu(II)-EDTA with high selectivity in UV/peroxymonosulfate (PMS). Chemical probing experiments and competitive kinetic analysis quantitatively revealed the crucial role of in situ formed Cu(III). The Cu(III) species not only oxidized Cu(II)-EDTA rapidly at ∼3 × 10⁷ M^-1 s^-1, but also exhibited 2-3 orders of magnitude higher steady-state concentration than HO^•/SO₄^•-, leading to highly efficient and selective degradation of Cu(II)-EDTA even in complex matrices. The ternary Cu(II)-OOSO₃^- complexes derived from Cu(II)-EDTA decomposition could generate Cu(III) in situ via the Cu(II)-Cu(I)-Cu(III)-Cu(II) cycle involving intramolecular electron transfer. This method was also applicable to various Cu(II) complexes in real electroplating wastewater, demonstrating higher energy efficiency than commonly studied UV-based AOPs. This study provids a proof of concept for efficient decomplexation through activating complexed heavy metals into endogenous reactive species.

Keywords: Cu valence cycle; Cu(III); Endogenous reactive species; Self-catalytic decomplexation; UV/PMS.