Synthesis of Triazole-Linked Porous Cage Polymers: Modulating Cage Size for Tailored Iodine Adsorption

Abstract

We present the synthesis of two triazole-linked porous cage polymers (pCAGEs) using two D-3h symmetric shape-persistent organic cages of different sizes as monomers. We observed that expanding the size of the cage monomer resulted in an improved surface area, pore volume, and iodine vapor uptake capacity of up to 4.02 g g(-1) at 75 degrees C under ambient pressure. Also, embedding molecular organic cages into pCAGEs boosted their iodine adsorption performances compared to their discrete molecular counterparts, model compounds (mCAGEs), due to their open pore channels, enabling the efficient diffusion of iodine into the binding sites. The pCAGEs showed promising iodine adsorption efficiencies from a concentrated KI/I-2 aqueous solution with a high iodine uptake capacity of up to 3.35 g g(-1). The iodine uptake capacities of pCAGEs differ in vapor and aqueous solutions, which suggests that tuning the cage size allows us not only to control the textural properties of pCAGEs but also to tailor their iodine adsorption performances in vapor and water. Iodine adsorption mechanisms of pCAGEs were investigated using ex situ structural characterization techniques, revealing strong interactions of adsorbed iodine species with nitrogen-rich groups and phenyl rings of the pCAGEs. Notably, pCAGEs demonstrated remarkable regeneration and reusability, maintaining 86% of their initial adsorption capacities over five adsorption/desorption cycles, highlighting their potential for practical applications. These findings contribute to a fundamental understanding of the structure-property relationship for cage-based polymeric materials and provide insights into the development of high-performance adsorbents for iodine capture.