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.