Anionic COFs intercalated cationic MOF composites: synergistic adsorption–reduction toward efficient precious metal recovery

Abstract

The selective separation of noble metals from e-waste stands as an acutely urgent and strategically critical challenge. Herein, a COF@MOF hybrid (TpPa-SO₃H@MIL-101(Cr)-NH₂) was fabricated via an electrostatic self-assembly method, and its synergistic adsorption effects toward precious metals were explored. Spectral analysis confirmed that TpPa-SO₃H@MIL-101(Cr)-NH₂ maintained its original framework and mesoporous characteristics while exhibiting a positively charged surface and electron-rich O/N active sites. When applied to simulated wastewater treatment, the maximum equilibrium uptake capacities for Au(III) and Pd(II) reached 1659.6 and 400.5 mg g⁻¹, respectively. Meanwhile, Langmuir isotherm modeling combined with PSO kinetic analysis revealed a chemisorption-dominated monolayer separation process. Furthermore, selectivity studies confirmed that TpPa-SO₃H@MIL-101(Cr)-NH₂ exhibited high selectivity for Au(III)/Pd(II) in the presence of interfering ions. Mechanistic analysis showed that electrostatic attraction and coordination interactions were the primary driving forces for pollutant removal, with partial reduction of Au(III)/Pd(II) to Au(0)/Pd(0) by phenolic hydroxyl groups. Hence, the present study provides a workable methodology for extracting precious metals from e-waste.