Differential sulfur activity governs electroreductive decomplexation of Cu(II)-EDTA for simultaneous copper and ligand recovery

Sulfur-mediated electroreduction provides an attractive route for the concurrent decomplexation and recovery of persistent Cu(II)-EDTA; however, the intrinsic activity of sulfur sites remains poorly defined. Here, MoS 2 is employed as a model platform to delineate the role of sulfur functionalities by comparing the metallic 1T and semiconducting 2H phases. Studies reveal that sulfur sites promote a direct two-electron reduction pathway from Cu(II) to Cu(0). In the 1T phase, enhanced covalent Cu-S interactions lower the adsorption and activation barriers of Cu(II)-EDTA, while the elevated density of states at the Fermi level facilitates rapid electron transfer. Combined spectroscopic and theoretical analyses further show that sulfur vacancies and distorted octahedral coordination in 1T-MoS 2 modulate the electronic structure of sulfur sites, thereby promoting Cu extraction and lowering the decomplexation barrier. Consequently, 1T-MoS 2 achieves 99.4% Cu recovery with > 99% EDTA preservation, corresponding to an energy efficiency of 198.80 g kWh -1 (at an initial concentration of 100 mg L -1 ), outperforming 2H-MoS 2 (82.85%, 153.43 g kWh -1 ). This sulfur-mediated pathway concurrently enables stable operation over 30 cycles with high selectivity in complex matrices. Moreover, the strategy extends to other metal-EDTA systems ( e.g. , Pb(II), Cd(II)), highlighting the generality of sulfur-active electrocatalysts for coupling ligand preservation with efficient heavy-metal recovery.