Mechanochemical synthesis of pincer nanotraps for efficient rhodium recovery

The sustainable recycling of platinum group metals (PGMs) from secondary resources requires task-specific adsorbents that offer both high extraction efficiency and environmental compatibility. However, rhodium recovery remains particularly challenging due to the high thermodynamic stability of its chloro-complexes, which hampers ligand exchange with adsorbent binding sites. Here, we report a series of porous organic polymer (POP)-based nanotraps for targeted rhodium extraction, functionalized with pincer-type chelators, whose installation was realized by mechanochemical imine bond formation in a green, solvent-free manner. Among them, POP-Py-OMe bearing electron-donating -OMe groups, exhibits the highest rhodium uptake capacity and the fastest extraction kinetics from aqueous solution, significantly outperforming its -OH and -H analogues. Furthermore, sequential breakthrough experiments employing various task-specific POPs as column packing adsorbents enable the efficient and selective separation of Pt, Pd, and Rh in sequence with high purity, highlighting a practical and modular strategy for comprehensive PGM recovery.