Synergistic light-thermal-mass engineering of metal-coordinated covalent organic framework membranes for water purification

Abstract

Membrane-based photothermal evaporation and separation offer a sustainable solution for both clean water access and environmental remediation. Covalent organic framework (COF) membranes are highly attractive due to their ordered porosity and chemical tunability, yet efficient light-to-heat-to-mass conversion at the interface remains challenging. Here we present a synergistic light-thermal-mass engineering strategy to overcome this limitation by utilizing cation-coordinated COF membranes. Through interfacial polymerization, we synthesized a photothermal COF with abundant nitrogen and oxygen chelating sites, followed by coordination with various divalent cations. Experimental and simulation results reveal that atomic dispersion of Co centers within a COF layer facilitates steeper interfacial gradients under one-sun irradiation, driving intensified buoyant convection to enhance mass transport and evaporation. The representative cobalt-COF (Co-COF) membrane achieves an extraordinary 99.996% ion removal, which meets stringent WHO standards. Complementary frontier molecular orbital analysis indicates substantial shifts in the HOMO and LUMO energy levels, resulting in a pronounced near-infrared redshift of the optical absorption edge. This substantially increases the photon budget for highly efficient photothermal and photocatalytic processes, conferring a high removal efficiency of volatile organic contaminants. This work underscores how precise metal ion coordination within COF structures significantly boosts both photothermal and photocatalytic efficiencies for sustainable water treatment.