Two-Fold Interlocking Cationic Metal-Organic Framework Material with Exchangeable Chloride for...

Albeit reported substantial sorbents for elimination of TcO₄^-, the issue of secondary contamination caused by released counterions (such as NO₃^-) from the cationic metal-organic framework (MOF) has not come into the sufficient limelight for researchers. Herein, our efforts are dedicated to settle the matter through synthesis of NiCl₂ based on the cationic MOF (ZJU-X4). Less harmful chlorides are used as exchangeable anions for replacing hazardous anions. Notably, ZJU-X4 exhibited fast sorption kinetics, high sorption capacity of 395 mg/g, decent selectivity, and excellent reusability in four recycles. The results of ion chromatography revealed that the released chloride ion was equal to sorption of target ions, and pair distribution functions were employed to analyze the changes in ZJU-X4 after sorption of ReO₄^-, clearly elucidating the anion-exchange mechanism. Furthermore, in the dynamic sorption experiments, ReO₄^- could be facilely and effectively removed and recovered, showing the value of practical applications. This work indicated that cationic MOF-based metal chloride salts would be a better choice for anionic sorbents.