Photo-electrochemical decomplexation of cobalt complexes and enhanced cobalt recovery through electrified membranes

The increasing presence of cobalt-chelated species in semiconductor manufacturing poses significant challenges for wastewater treatment because of their structural stability and high solubility. Efficient decomplexation of these metal–ligand complexes is critical for mitigating heavy metal pollution and enabling resource recovery. This study investigates the (photo)electrochemical decomplexation of cobalt-ethylenediaminetetraacetic acid (Co-EDTA) complexes using a TiO₂-encapsulated electrified carbon membrane, with a focus on cobalt recovery. Compared to electrochemical oxidation alone, the photoelectrochemical (PEC) system with 365 nm UV-LED illumination demonstrated better performance, achieving over 90 % EDTA-Na₂ removal within 20 min and approximately 50 % Co-EDTA decomposition within 180 min. Kinetic analysis confirmed enhanced reaction rates under PEC conditions, and system robustness was validated across varying applied voltages and electrolyte concentrations, as well as real-world semiconductor wastewater. Mechanistic studies revealed that the PEC process is driven by the generation of hydroxyl radicals (•OH), formed through the interaction of photoinduced electron-hole pairs with surface hydroxyl groups on the TiO₂ membrane. These radicals facilitate stepwise decomplexation, breaking down Co-EDTA complexes and releasing cobalt ions. This work highlights the potential of TiO₂ electrified membrane-based photo-electrochemical systems for efficient decomplexation and cobalt recovery, offering a sustainable solution for advanced wastewater treatment and resource recovery.