Macrocycle polymeric networks based on a chair-like calix[4]pyrrole for the rapid and efficient adsorption of iodine from water

Abstract

We report two macrocycle-containing polymeric networks (MPNs), C[4]P-TEPM and C[4]P-HEPM, that incorporate calix[4]pyrrole subunits. These networks were prepared by Sonogashira cross-coupling reactions between a chair-like diiodo trans-C[4]P precursor and tetraphenylmethane or 1,4-ditritylbenzene. Both MPNs contain a large number of presumed absorption sites reflecting the presence of the calix[4]pyrrolic π-electron rich cavities, as well as multiple phenyl rings and ethynyl bonds. C[4]P-TEPM and C[4]P-HEPM exhibited iodine uptake capacities of 3.67 g g⁻¹ and 4.07 g g⁻¹, respectively, from saturated aqueous iodine solutions, and high adsorption capacities of 4.02 and 4.45 g g⁻¹ from saturated aqueous KI/I₂ at RT. Moreover, C[4]P-TEPM and C[4]P-HEPM showed fast iodine adsorption rates with k_obs of 8.54 and 10.21 g g⁻¹ min⁻¹ being seen in the case of a saturated iodine aqueous solution. Flow-through type adsorption studies revealed iodine removal efficiencies as high as 92.2% and 94.5% for C[4]P-TEPM and C[4]P-HEPM, respectively, at a saturated iodine aqueous flow rate of 10 mL min⁻¹. To the best of our knowledge, the two MPNs reported here have the highest adsorption capacities and display the fastest adsorption rates for aqueous iodine capture among all adsorbent materials reported to date.