Synergy of first- and second-sphere interactions in a covalent organic framework boosts highly selective platinum uptake

Platinum recovery from waste electrical and electronic equipment (WEEE) in highly acidic solutions is significant to the electronics industry and environmental remediation. However, the lack of ingenious design and synergetic coordination gives rise to unsatisfied PtCl 4 2− extraction capacities and selectivities in most previously reported adsorbents (e.g., polymeric and inorganic materials). Herein, we proposed a synergistic strategy that realizes highly selective PtCl 4 2− uptake through first- and second-sphere coordinations. The proof-of-concept imine-linked covalent organic framework (SCU-COF-3) was found to chelate PtCl 4 2− via the direct N⋯Pt coordination and the synergistically interlaminar N—H⋯Cl hydrogen bonds, which was disclosed by the comprehensive analysis of extended X-ray adsorption fine structure (EXAFS) characterizations and density functional theory (DFT) calculations. The unique adsorption mechanism imparts a superior adsorption capacity (168.4 mg g −1 ) and extraordinary Pt(II) selectivity to SCU-COF-3 under static conditions. In addition, SCU-COF-3 exhibits an upgraded distribution coefficient of 1.62 × 10 5 mL g −1 , one order of magnitude higher than those of reported natural adsorbents. Specifically, SCU-COF-3 can extract PtCl 4 2− quantitatively from a simulated acidic waste solution coexisting with other 12 competitive ions, suggesting its promising application in practical scenarios.