High-Performance Adsorption of Chromate by Hydrazone-Linked Guanidinium-Based Ionic Covalent Organic Frameworks: Selective Ion Exchange

Abstract In consideration of the serious environmental issues caused by heavy metals, novel nanomaterials have been developed and applied as highly selective adsorbents with the capacity to eliminate heavy metal ions in ambient ecosystems. Ionic covalent organic frameworks (I-COFs) serve as an emerging species of functional nanomaterials that inherently possess ionic interfaces that interact strongly with oppositely charged ionic species. In this work, a guanidinium-based COF with a β-ketoenamine linkage (Tp-DGCl) was synthesized using a solvothermal method. The obtained Tp-DGCl colligated four advantages, namely easy synthesis, high selectivity (for Cr (VI)), excellent adsorption (360.02 mg/g calculated by Langmuir model), and good recyclability (five cycles), which enables it to serve as a reliable sorbent for wastewater treatment. Owing to the stable and selective binding affinities between tetrahedral oxoanions and diiminoguanidinium groups, Tp-DGCl exhibited an outstanding adsorption capacity for Cr (VI). Subsequent to five cycles, the adsorption performance of Tp-DGCl remained at a high level (85%), which demonstrated an excellent regenerative capacity by supplementing Cl- to the Tp-DGCl after adsorption. Consequently, Tp-DGCl revealed a strong potential for broad applications in wastewater remediation.