A novel cationic organic network for ultra-fast and high-capacity removal of toxic oxo-anions from water

Abstract

Water pollution has become a global concern, especially from toxic metal-derived oxo-anions like CrO₄²⁻, Cr₂O₇²⁻, and TcO₄⁻. Adsorption, particularly ion-exchange-driven adsorption, is a promising remediation approach. In this study, a novel imidazolium-based cationic organic network material, ImCON1, was designed and synthesised. Multiple characterisation techniques were used to analyse its structure and properties, including FTIR, solid-state ¹³C CP-MAS NMR, SEM, TGA, XRD, and XPS. ImCON1 has a cross-linked, irregular spherical morphology, remarkable stability, and an amorphous nature. It shows high-efficiency removal of various toxic oxo-anions, CrO₄²⁻, Cr₂O₇²⁻, and MnO₄⁻ (as a surrogate for TcO₄⁻) from water. The uptake capacities are 259 mg g⁻¹ for CrO₄²⁻, 1118 mg g⁻¹ for Cr₂O₇²⁻, and 694.5 mg g⁻¹ for MnO₄⁻, comparable to or higher than those of previously reported materials. The sorption kinetics follow the pseudo-second-order model, indicating rapid capture. ImCON1 is resistant to a wide pH range and effectively captures oxo-anions even in the presence of competing anions. An ImCON1-packed chromatographic column can efficiently remove oxo-anions from water through an anion exchange mechanism and can be reused for at least ten cycles. This novel cationic organic network material holds great promise for wastewater treatment applications and paves the way for developing high-performance adsorption materials at the molecular scale.