Surfactant-Engineered Micellar Reactors Intensify Fenton Decomplexation of Cu(II)-Organophosphonates

Recalcitrant copper-organophosphonate complexes in industrial wastewater challenge conventional advanced oxidation because their high stability and rigid coordination geometry limit radical access and utilization. Here we report a surfactant-enhanced Fenton process in which cetyltrimethylammonium bromide (CTAB) self-assembles into cationic micelles that act as supramolecular microreactors to capture and decomplex Cu(II)-hydroxyethylidenediphosphonate (Cu-HEDP). By confining the reaction in micelles, Cu(II)-HEDP was colocalized with the iron catalyst and short-lived •OH, achieving substantial decomplexation (>97%) and nearly complete removal of total phosphorus upon alkalization, markedly outperforming the CTAB-free Fenton process, which only exhibited partial decomplexation and removal of total phosphorus (≈40%) under otherwise identical conditions. Mechanistically, CTAB enriches anionic Cu-HEDP at the micellar interface and reshapes the electron distribution within HEDP, creating electron-deficient sites for •OH attack while promoting intramolecular electron transfer. Meanwhile, the positively charged micellar interface promotes Fe(III)/Fe(II) recycling and helps maintain a high •OH generation. CTAB further acts as a cationic coagulant during precipitation, neutralizing and bridging Fe(OH)₃/Cu(OH)₂ colloids and phosphorus-containing byproducts into settleable flocs. The process also works well for Cu(II) complexes with several other organophosphonates, suggesting a broadly applicable, interface-enabled "capture-and-degrade" approach for charged metal-organic pollutants that conventional AOPs often struggle to remove.