Guanidinium-Based Hydrophobic Ionic Covalent Organic Network for Rapid and Selective Entrapment of Iodine and Toxic Oxoanions

Abstract Rapid industrialization and energy production have intensified water pollution, making it a global issue that poses serious threats to human health and the ecosystem. The presence of radioactive pollutants and heavy metal-based toxic oxoanions in water systems, has severely compromised the easy availability of clean and safe drinking water. Ionic covalent organic networks (iCONs) provide an effective approach for water purification owing to their multiple binding sites and ion-exchange capabilities, which facilitate the efficient removal of ionic contaminants through electrostatic interactions. In this work, physicochemically stable iCON-7 was synthesized via a facile Schiff-base polycondensation reaction and applied for the efficient removal of toxic iodine species present in multiple phases (vapor, aqueous, and organic), along with hazardous oxoanions (CrO42– and MnO4–) from water via ion-exchange. iCON-7 demonstrated rapid adsorption kinetics and high uptake capacities for multiple oxoanion pollutants [MnO4– (692.8 mg/g) and CrO42– (393.1 mg/g)], as well as for toxic iodine species (2.79 g/g in the vapor phase at 350 K and 1.59 g/g in the aqueous phase at 298 K). The presence of competing anions had a negligible effect on the adsorption efficiency of iCON-7, suggesting its excellent selectivity toward the target pollutant. iCON-7 can be reused for up to five consecutive cycles with no loss of adsorption efficiency, and it has been shown to perform consistently in various water collected from various sources (e.g., sea, river, and tap water), indicating its real-world applicability. Furthermore, density functional theory (DFT) supported the electrostatic and hydrogen-bonding interactions between iCON-7 and anionic pollutants, providing detailed insights into the preferential binding sites and associated binding energies for pollutants capture. Hence, iCON-7 has the potential as an economical, versatile and efficient alternative to the existing adsorbent materials for the sequestration of multiple anionic pollutants from wastewater.