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.