Removal of iodine from water in seconds using nonporous naphthobipyrrole-based organic cages
The rapid and efficient removal of radioactive iodine species from water is critical for nuclear waste treatment, particularly given the short half-life of 131I (8.02 days). Traditional porous inorganic materials exhibit low uptake capacities (<1 g g−1), while porous frameworks such as MOFs and COFs achieve high capacities (>5 g g−1) but suffer from slow removal kinetics, often requiring hours to capture 80% of iodine. This study introduces nonporous naphthobipyrrole-based organic cages (NBP-Cages) that demonstrate ultrafast iodine removal from water. Among the materials tested, type-II Me-NBP-Cage and Et-NBP-Cage, prepared via reprecipitation, exhibit amorphous morphology with small particle sizes (2–6 μm) and low BET surface areas (33.4 and 2.3 m2 g−1, respectively). Despite their nonporosity, these materials achieve >99% iodine removal within seconds, outperforming previously reported sorbents. The adsorption performance correlates with particle size and morphology: amorphous, small particles with effective surface gaps show superior kinetics. The materials are recyclable; for instance, Et-NBP-Cage can be regenerated by washing with acetonitrile, maintaining removal efficiency over five cycles. This work highlights the potential of nonporous organic cages as high-performance iodine sorbents, addressing the critical need for materials that combine high uptake capacity with rapid removal kinetics.