Radical-Integrated Phosphorus-Containing Ionic Organic Cage for Efficient Gold Recovery From Complex Liquids

The development of advanced adsorbents for the selective and efficient recovery of gold from complex aqueous matrices is of paramount importance for sustainable resource recycling. Here, we report a phosphorus-functionalized, quaternized ammonium cages (Phos-QA-Cage-Cl) featuring multiple integrated binding sites, which delivers exceptional Au(III) uptake of up to 2331 mg g^{- 1}. The intrinsically cationic skeleton and Au-affinitive phosphorus sites synergistically capture AuCl₄ ^- through combined electrostatic and coordination interactions. Thermal activation generates persistent radicals within the cage, which further enhance Au uptake by reducing Au(III) to nanoparticles, followed by halide-promoted ripening of the nascent Au species. DFT calculations reveal the cooperative roles of noncovalent interactions, coordination bonding and radical-assisted redox chemistry in driving efficient Au(III) capture. As a result, the cage exhibits rapid adsorption kinetics, high selectivity, and good recyclability in complex aqueous matrices. Leveraging its solution processability, a mixed-matrix membrane based on polyvinylidene fluoride is fabricated, enabling efficient filtration and recovery of Au(III) (up to 95%) from dilute solutions, with a high permeate flux (87 L m^{- 1} h^{- 1} bar^{- 1}). This work introduces a new class of functionalized porous cages for precious metal recovery and highlights the potential of integrating molecular design with solution processibility for environmental applications.