In-Situ Formed Zr-Phosphonate Surface Complex Promotes Peroxymonosulfate Activation of Single-Atom Cu for Efficient Phosphonate Oxidation

Abstract

Phosphonates are recalcitrant water pollutants that trigger eutrophication, and their oxidative transformation into a readily recoverable phosphate is essential for sustainable phosphorus removal. Copper-based advanced oxidation processes (AOPs), such as Cu(II)/peroxymonosulfate (PMS), have been utilized for phosphonate degradation via Cu(III)-mediated oxidation. However, Cu(I) (the crucial intermediate for Cu(III) generation) suffers from sluggish Cu(II) reduction. Herein, we synthesized a copper single-atom catalyst supported on zirconium dioxide (ZrO₂) to achieve superior PMS activation and phosphonate degradation via an in situ-formed Zr-phosphonate surface complex. Cu-ZrO₂/PMS achieved nearly 100% degradation of 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) and 98% conversion to phosphate (PO₄^3-) within 30 min at pH 9, demonstrating high performance and resistance to potential matrix interferences. Experimental results combined with theoretical calculations demonstrated the synergy between Cu and Zr sites, where Cu functioned as PMS activation and Cu(III) generation sites and Zr served as favorable HEDP coordination sites for the formation of complexes. This coordination increased the electron density of Cu sites, facilitating Cu(II) reduction to Cu(I) and subsequent production of Cu(III) via further reaction with PMS. Overall, this study provides a promising coordination strategy to enhance HEDP degradation and fundamentally informs the design of Cu-based catalysts to activate PMS for phosphonate-contaminated wastewater treatment.