Pore Wall Engineered Covalent-Organic Frameworks as Size-Matched Nanotraps Enable Highly Selective Adsorption of Sulfonamide Antibiotics.

Trace-level sulfonamide antibiotics (SAs) in water environments pose disproportionate ecological risks, yet their removal by adsorption remains challenging because widely used sorbents lack sufficient selectivity. Current research mainly focuses on introducing functional groups to enhance affinity, while largely overlooking the cooperative role of pore architecture. Here, we synthesize a series of covalent-organic frameworks (COFs) with different sulfonic acid group densities and pore sizes and evaluate their sulfapyridine (SPY, a representative SA) adsorption performance. TpBD-(SO3H)2, which combines the highest density of sulfonic acid groups with pores comparable to the SPY molecular dimensions (double-lock design concept), achieves 99% SPY removal within 30 min. Its adsorption capacity could attain as high as 235.41 mg/g, outperforming TpBD and TpPa-SO3H, while remaining competitive with previously reported SPY adsorbents. More importantly, TpBD-(SO3H)2 maintains high adsorption performance in complex water matrices, including river water and wastewater, and retains its performance over at least seven regeneration cycles. TpBD-(SO3H)2 exhibited pronounced selectivity toward SAs over other organic micropollutants, driven by a synergistic double-lock mechanism. Molecular dynamics simulations and density functional theory calculations suggested that the double-lock effect likely arises from the concerted enhancement of van der Waals force, electrostatic force, hydrogen bond, hydrophobic, and CH-π interactions between SPY and the framework. This work highlights that synergistic tuning of functional group chemistry and pore architecture is critical for selective adsorption and provides design principles for COFs engineered for the efficient removal of emerging trace organic contaminants from water.