Hierarchically Porous Poly(ionic liquid) – Organic Cage Composite Membrane for Efficient Iodine Capture

The effective capture of iodine with high volatility and poisonousness is significant for reprocessing the spent nuclear fuel. In this article, we report a hierarchically porous poly(ionic liquid)-organic cage composite membrane (PIL@CC3) possessing a gradient content distribution of CC3 cage crystals throughout the membrane to capture iodine vapor. The introduction of microporous CC3 can significantly enhance the uptake capacity of iodine up to 980 mg g⁻¹, which is superior to that of a pristine PIL membrane carrying large meso- and macropores (99 mg g⁻¹), and CC3 crystalline powder (662 mg g⁻¹). Such enhanced performance benefits from the micro-meso-macroporous structure of the PIL@CC3 membrane in which the large meso- and macropores facilitate the mass transfer of iodine molecules from the external environment into the surface of the CC3 crystal, followed by diffusion of iodine molecules from the CC3 surface into the interior and exterior pores of the CC3 crystal. In addition, the asymmetric distribution of CC3 crystals across the PIL@CC3 membrane also displays its advantage in intercepting trace iodine, revealing its great potential for practical application. This study provides an idea for constructing hierarchically porous membrane composites for the removal of toxic vapors.