Fluorinated pore walls boost PFAS capture in mechanochemically synthesized covalent organic frameworks

Per- and polyfluoroalkyl substances (PFAS) are persistent water contaminants that require robust, high-affinity sorbents. Covalent organic frameworks (COFs) provide chemically stable, modular platforms for capturing PFAS and mechanochemical synthesis offers an environmentally friendly, scalable method of production. In this study, we use mechanochemistry to quickly produce an isoreticular series of large-pore imine COFs (TAPB-TA, TAPB-DFTA and TAPB-DMTA) with systematically varied pore-wall functionality, which is optimised for PFAS adsorption. The fluorinated TAPB-DFTA COF exhibits the greatest crystallinity, the highest BET surface area (1237 m² g^-1) and the greatest thermal stability. These properties result in superior uptake of PFOA, PFOS and short-chain analogues compared to the methylated and unsubstituted analogues in batch adsorption experiments across a broad concentration range. The three COFs achieve near-quantitative PFOS removal within minutes, while TAPB-DFTA maintains significantly higher PFOA removal even at a feed concentration of 100 mg L^-1. These findings indicate that mechanochemical synthesis combined with pore wall modification offers a possible approach for tuning COF adsorption sites for PFAS uptake.