Continuous-Flow Adsorption With Imidazolium-Based Porous Organic Polymers Capable of Selective Removal of Chromate Contaminants From Water

Abstract

N-rich triazine core functionalized imidazolium-based porous organic polymers (iPOPs) are developed with exceptional oxoanions sequestration capabilities. Two iPOPs, iPOP-1 and iPOP-2, are synthesized via a facile Radziszewski multicomponent reaction and designed with multiple interaction sites for the electrostatically driven adsorption of toxic oxoanion, chromate (CrO4 2-). The strategic incorporation of methylene spacers in iPOP-1 resulted in a structurally flexible framework, enabling ultrafast capture kinetics with 99% removal of CrO4 2- from a 40 ppm aqueous solution within just 15 sec. In contrast, the structurally rigid iPOP-2, lacking methylene spacer units, exhibits significantly reduced performance, achieving only 25% removal even after 300 seconds of contact time. Notably, iPOP-1 maintained remarkable selectivity, effectively capturing CrO4 2- even in the presence of a 200-fold excess of competing anions (Cl-, Br-, NO3 -, SO4 2-, CO3 2-, H2PO4 -). To evaluate the practical application potential of iPOP-1, continuous-flow CrO4 2- sequestration experiments are conducted using both glass-column chromatography and packed-bed reactor configurations, successfully reducing CrO4 2- concentrations to below 40 ppb, well within World Health Organization (WHO) drinking water safety thresholds. Additionally, iPOP-1 demonstrate excellent recyclability, maintaining high sequestration efficiency through five regeneration cycles. These results offer a robust, selective, and reusable approach for the efficient removal of hazardous oxoanions from industrial wastewater.