Construction of hierarchically porous monoliths from covalent organic frameworks (COFs) and their application for bisphenol A removal

Subject to synthetic conditions, covalent organic frameworks (COFs) are usually in powder form. Herein, taking an azine-linked COF as an example, detailed characterizations indicated that accessible aldehyde groups and hydrazine groups ( C N NH 2 , 88 μmol g −1 ) concurrently existed on its surface. Intrigued by such feature, we have developed an approach based on ring-opening polymerization to shape COF powder into monoliths. The crystallinity and micropore of COF in monoliths were well remained, meanwhile, the ring-opening polymerization remarkably generated macropores ranging from 0.43 to 3.51 μm, indicating a hierarchically porous structure. The BET surface area of resultant monoliths with different COF mass fractions of 16%, 28% and 43% ranged from 105 to 281 m 2  g −1 . Due to the π–π interaction and hydrogen bond interaction, COF-based monoliths exhibited strong retention and rapid adsorption for bisphenol A (BPA) in aqueous medium. When 29 mL BPA solution (22.8 mg L −1 ) passed through COF-based monolith (28%), the adsorption capacity was up to 61.3 mg g −1 . Furthermore, the COF-based monolith demonstrated excellent cycle use for catalyzing Suzuki-Miyaura coupling reaction after being coordinated with palladium acetate.