Three novel indole-bearing porous organic polymers for efficient iodine capture from both vapor and organic phases

Abstract

Herein, a mild and convenient strategy for the preparation of p-di(bis-indolyl-methane)benzene (Ph-TIn) using iodine as a catalyst was proposed. On this basis, three novel indole-bearing porous organic polymers (InPOPs) with different morphologies were successfully synthesized via Friedel–Crafts alkylation and oxidative coupling reactions. The obtained InPOPs (InPOP-1, InPOP-2 and InPOP-3) were applied for iodine adsorption in the cases of both an organic medium and vapor phase. Among them, InPOP-1 exhibits the best adsorption performance in iodine/cyclohexane solution. The thermodynamic and kinetic analysis reveals that the adsorption behavior of InPOP-1 is represented by Freundlich and pseudo-second-order models, respectively. Besides, the adsorption rate is influenced by both liquid-film diffusion and intra-particle diffusion. In addition, the results of thermodynamic calculations indicate that the adsorption of iodine on InPOP-1 is a spontaneous, endothermic and entropy-increasing process. However, InPOP-3 displays the highest capacity of removing iodine vapor. Furthermore, the recycling evaluations and spectral evidence of I₂@InPOP-1 and I₂@InPOP-3 demonstrate that the iodine adsorption process is influenced by both physisorption and chemisorption, whether in an organic medium or vapor phase. Most importantly, we draw a conclusion that both porosity and morphology of InPOPs significantly influence the behavior of iodine adsorption in organic media, whereas the larger average pore size is favorable to the adsorption of iodine in the vapor phase. This study will serve as a guide for future inventions of porous organic polymers in the field of radioactive iodine capture.