Constructing Phenyl -Bridged Switches in Porous Aromatic Frameworks to Achieve Gradually Evolved Capillary Action for High-Performance Iodine Capture

Abstract

Radioactive iodine extensively discharged from nuclear fission, especially 129I and 131I, are considered the most dangerous substance because of the intense radiation and chemical toxicity. Micro-sized (~2 nm) cavity has been substantiated as efficient container due to their strong capillary action. However, its relatively small space is easy to be filled, resulting in a limited uptake capacity. Herein, a carbazole-based monomer with a settled angle (~88 o) is selected as the building unit, which distorts the porous network during the skeletal extension and generates a flexible architecture with meso-sized apertures (5.3 nm). Based on this specified structure, additional phenyl fragments serving as the π-π cross-linked bridges are introduced into the carbazole-based PAF framework to divide the large pores (5.3 nm) into the 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 interaction; as the box is filled, the π-π linked bridges are gradually dissociated, which enlarge the accommodation space for capturing iodine molecules via the extra capillary action. Accordingly, the resulting porous network shows excellent iodine adsorption performance with maximum a capacity of 2.85 g g-1, which surpasses most of the classical porous solids including porous organic frameworks and metal-organic frameworks. This work illustrates valuable guidance for the design and construction of breathing architecture for high-performance iodine enrichment.

Keywords: Iodine capture, Porous aromatic framework, phenyl bridge, on-off switch, π-π dissociation