Spatially Coupled •H-involved Reductive Decomplexation of Cu(II)–EDTA for Sludge-Free Copper Recovery

Abstract

The electrochemical recovery of metals from stable complexes is often limited by the accessibility of coordinated metal centers at the electrode interface. Here, we develop a polyaniline-modified carbon felt (PANI@CF) cathode to regulate the interfacial microenvironment for selective Cu recovery from copper(II)–ethylenediaminetetraacetic acid (Cu(II)–EDTA). The PANI interface couples Cu(II)–EDTA enrichment with •H generation through complementary nitrogen functionalities, thereby promoting Cu(II)–EDTA decomplexation while preserving ligand integrity. Under optimized conditions, PANI@CF achieves high Cu recovery (up to 99.9%) over a broad Cu(II)–EDTA concentration range (0.5–5 mM) and pH range (3–11), with a 32.75-fold enhancement in the apparent reaction rate compared with pristine carbon felt. Mechanistic investigations reveal that imine (–N═) functionalities contribute to interfacial Cu(II)–EDTA enrichment, whereas amine (–NH–) functionalities facilitate N–H activation and •H generation. This spatial coupling promotes interactions between short-lived •H and coordinated Cu centers, weakening Cu(II)–EDTA coordination and facilitating Cu reduction while preserving EDTA integrity. After ten consecutive treatment cycles, the cumulative Cu recovery reached 215.07 mg cm–2, and the PANI@CF electrode was regenerated by mild acid washing. The selective recovery of Cu and EDTA was further demonstrated in actual electroplating wastewater. This work highlights interfacial regulation through spatial coupling as a strategy for overcoming accessibility limitations in the electrochemical transformation of metal–ligand complexes and supports selective resource recovery from complexed industrial effluents.