Picric Acid Removal from Water Using an Anion-Coordination-Based Supramolecular Organic Framework

In contrast to metal ions that have been routinely used to construct metal-organic frameworks (MOFs), anions have rarely been used as essential coordination centers in supramolecular organic frameworks (SOFs). In this work, we present a SOF, chloride-SOF, based on the coordination of chloride anions and a flexible oligopyrrole. Owing to the multiple interactions between individual oligopyrrole molecules and an A-B-C-style stacking of the 2D honeycomb layers, crystalline chloride-SOF exhibits reasonable thermal stability and retains its structure upon desolvation. Treating contaminated water containing 100 mg L^-1 picric acid (PA) with the desolvated form of chloride-SOF reduced the PA concentration to the low ng L^-1 (ppt) level. Supporting studies provide evidence for the conclusion that the material captures PA through anion exchange and adaptive structural transformation, rather than pore-selectivity. Chloride-SOF thus showcases the potential of SOFs as structurally transformable materials useful for hazardous waste removal.