Twofold Interpenetrated Cationic Metal-Organic Framework with Hydrophobic Channels for Effectively Trapping Toxic Oxo-Anions.

Sequestration of toxic oxo-anions (such as 99TcO4- and ClO4-) from wastewater has received constant attention due to the existing serious threat to public health and the sustainability of the environment. In view of the low energy of hydration of TcO4- and ClO4-, cationic metal-organic framework (MOF) materials with the hydrophobic microenvironment are preferred in the selection of sorbents. Herein, a twofold interpenetrated cationic MOF (ZJU-X15) with double-helical chains was constructed by tetrakis[4-(pyridin-4-yl)phenyl]ethene (TPPE) and Cd2+ for the elimination of 99TcO4- and ClO4-. Profiting from hydrophobic channels, ZJU-X15 could remove most of ReO4- (a surrogate for 99TcO4-) and ClO4- in less than 10 and 20 min, respectively. As the result of batch experiments, ZJU-X15 could capture 356 mg of ReO4- and 221 mg of ClO4- per 1 g of sorbent, showcase decent selectivity, and still maintain high removal efficiency for anions after four recycles. Furthermore, the process of anion-exchange was confirmed by ion chromatography, Fourier-transform infrared spectroscopy, scanning electron microscopy combined with an energy-dispersive X-ray spectrometer, and X-ray photoelectron spectroscopy, indicating that target anions successfully entered into the body of ZJU-X15 through anion exchange.