Multifunctional covalent organic framework membranes with an ultrathin recycled palladium nanolayer for efficient water decontamination

Palladium recycling offers a sustainable and economic approach to meet the rising global demand of this precious yet naturally scarce metal. Here, we demonstrate a new recovery concept that utilizes a bipyridine-based adsorptive membrane (AM) based on covalent organic frameworks (COFs). This approach enables selective recovery of palladium via local coordination and electrostatic interaction, followed by in situ reduction to form a palladium nanolayer within the COF AM. Simulation and experimental results demonstrate that palladium nanoparticles with narrow size distributions were evenly enriched and localized within the continuous, 33-nm-thick COF nanofilm. This palladium enrichment step further provided high catalytic activity (99.9 % conversion of 4-nitrophenol) to the nanofilms, which maintained an ultrahigh water permeability (226.0 L m−2 h−1 bar−1). These multifunctional properties outperform state-of-the-art catalytic membranes. This study opens new directions in recovering and repurposing palladium waste into catalytic membranes, using COF membranes that efficiently decontaminate water.