Calix[4]pyrrole-Crosslinked Porous Polymeric Networks for Micropollutant Removal from Water.

Three calix[4]pyrrole-based porous organic polymers (P1-P3) have been prepared with the goal of removing organic micropollutants from water. A bowl-shaped α,α,α,α-tetraalkynyl calix[4]pyrrole and diketopyrrolopyrrole monomer were crosslinked via Sonogashira coupling to produce a three-dimensional network polymer P1. This polymer, which proved too hydrophobic for use as an adsorbent, was converted to the corresponding neutral polymer P2 (containing carboxylic acid groups) and its anionic derivative (polymer P3 containing carboxylate anion groups) through post-polymerization structural modification of the pendent tert-butyl esters. The anionic polymer P3 outperformed its precursor neutral polymer P2 as determined from screening studies involving a variety of model organic micropollutants of different charge, hydrophilicity and functionality, including dyes, simple aromatics, and two cationic pesticides. Polymer P3 proved particularly effective for cationic micropollutants. The theoretical maximum adsorption capacity (qmax,e) of P3 determined from the corresponding Langmuir isotherms reached 454 mg g-1 for the dye methylene blue, 344 mg g-1 for the pesticide paraquat, and 495 mg g-1 for diquat, respectively. These uptake values are significantly higher than those of most synthetic adsorbent materials reported to date. The present findings thus lend support to the conclusion that calix[4]pyrrole-based porous organic polymers may have a role to play in water purification.