Constructing a phenyl bridged switch in porous aromatic frameworks for enhancing the adsorption capacity of volatile iodine

Radioactive iodine extensively discharged from nuclear fission is considered the most dangerous substance. Microsized cavities have been substantiated as efficient containers due to their strong capillary action. However, its relatively small space is easy to fill, resulting in limited uptake capacity. Herein, a carbazole-based monomer with a settled angle (∼88°) is selected as the building unit, which distorts the porous network during skeletal extension and generates a flexible architecture with meso-sized apertures (5.3 nm). Based on this specified structure, additional phenyl fragments serving as π-π cross-linked bridges are introduced into the carbazole-based porous aromatic framework (PAF) to divide the large pores (5.3 nm) into small cavities (2.7 nm). These newly formed 2.7-nanometer-sized pores adsorb iodine molecules through the cooperation of capillary action and Lewis acid-base interactions; as the box is filled, the π-π linked bridges are gradually dissociated, which enlarges the accommodation space for capturing iodine molecules. Accordingly, the resulting porous network shows excellent iodine adsorption performance with a maximum capacity of 2.85 g g−1, achieving the highest level among all porous solids reported to date. This work provides valuable guidance for the design and construction of breathing architecture for high-performance iodine enrichment.