Coordination engineering upcycles hazardous nickel complexes into FO draw solutes: Proof-of-concept for...

Nickel-ethylenediamine complexes ubiquitously present in electroplating effluents are highly toxic and recalcitrant contaminants hindering conventional wastewater treatment. To mitigate these severe environmental risks and bypass energy-intensive ligand-destruction processes, this study advances a closed-loop strategy directly repurposing these hazardous complexes into functional forward osmosis (FO) draw solutes for simultaneous wastewater purification and nickel recovery. Through rational coordination engineering, structurally well-defined nickel-monoethylenediamine (Ni-en) and nickel-triethylenediamine (Ni-3en) complexes were synthesized to systematically regulate their hydration capacity and molecular geometry. The resulting robust three-dimensional hydration network enables a unique size-exclusion mechanism within specialized sub-nanometer polyamide membranes, mitigates the persistent trade-off between osmotic driving force and reverse solute diffusion. Consequently, utilizing the optimized Ni-en draw solute achieved an outstanding pure water flux of 44.9 LMH (120% higher than NaCl) alongside a minimal specific reverse solute flux of 0.09 g L^-1. Furthermore, the system maintained a stable water flux of 26.7 LMH over 36 h of continuous operation when treating a 1000 ppm nickel feed solution. These complexes were efficiently regenerated via a solvent-polarity-controlled phase transition, offering a low-energy recovery alternative. Ultimately, this study provides a proof-of-concept for establishing coordination-regulated complexes as a high-performance draw-solute platform, paving a pathway for hazardous electroplating wastewater valorization.