Nanoarchitectonics of bridged palladium-polyelectrolyte colloidal complexes via reversible coordination-driven assembly and disassembly for closed-loop recovery.

Palladium (Pd) is a critical element in modern technologies, yet it faces supply risks and is often lost in industrial wastewater. In this study, a cystamine-modified polyacrylic acid (Cyst-PAA) was developed for rapid and targeted Pd recovery via S/N cooperative coordination. Binding of Pd(II) through amide N, amine N, and disulfide S atoms triggers intermolecular bridging, crosslinking polymer chains into a three-dimensional network within seconds that enables spontaneous precipitation and achieves over 93% removal by microfiltration in single-metal systems, delivering a water flux 77.5 times higher than that of conventional ultrafiltration. In the presence of eight competing metal ions, Cyst-PAA exhibits excellent selectivity, achieving >96% removal of Pd(II) while the co-removal of most coexisting metals remains below 10%, with only Fe(III) slightly exceeding 10%. A closed-loop system integrating microfiltration enrichment with electrochemical regeneration achieved over 85% Pd recovery and simultaneous polymer regeneration, enabled by pH-controlled disassembly of the polymer-Pd complexes. Validated with real industrial wastewater, the system maintained stable performance over four cycles (average: 93% removal and 85% recovery). A comparative analysis with reported materials reveals that Cyst-PAA exhibits superior kinetics, capacity, selectivity, regenerability, and economic feasibility. This work provides a sustainable closed-loop strategy for recovering critical metals from challenging waste streams.