Viologen functionalized C-C bonded cationic polymers for oxo-anion pollutant removal from aqueous medium

Abstract

Three cationic viologen functionalized polymers (IISERP-POF9, POF10 and POF11) have been synthesized based on metal catalyst-free Bakelite chemistry. They exhibit high stability in organic or aqueous medium and possess high thermal stability too. Their microporous frameworks capture Cr2O72− and MnO4− from water even in low concentrations (2.5 × 10−4 M) and is rapid (< 1 min). The polymers exhibit exchange capacities (Dt) 77, 78 and 81% for Cr2O72− capture and 99, 97 & 98% for MnO4− capture. The capture capacities (qt) are also remarkable in such a low concentration of oxo-anion solutions (60.16 mg g−1, 54.31 mg g−1 and 61.14 mg g−1 for Cr2O72− capture and 39.28 mg g−1, 38.72 mg g−1and 40.07 mg g−1 for MnO4− capture). These viologen-based cationic polymers exhibit imposing oxo-anion selectivity even in the presence of 40-fold excess interfering anions (Cl−, ClO4−, CO32−, PO43− and SO42−). Moreover, the polymers are able to capture the oxo anions at a wide pH range (pH = 1-12). Cyclability has been performed with the best performing polymer (IISERP-POF11) and it shows retention of activity even after five cycles of exchange. The capture mechanism follows a pseudo-second-order kinetics which corroborates to the selectivities observed for oxo-anions over other interfering anions.