Palladium(II) Modulation Enhances the Water Stability and Aqueous 99TcO4 -/ReO4 - Removal Performance of Metal-Organic Frameworks

Improving the water stability of metal-organic frameworks (MOFs) is essential for their use in water pollution treatment and environmental remediation, though it remains technically challenging. Herein, we report a novel cationic MOF constructed with [Th6O4(OH)(4)(COO)(12)] units and [CoN4<middle dot>Cl-2] units possessing a ftw-type topology (denoted as 1-Th-Co). 1-Th-Co itself exhibited poor water stability but excellent stability following a palladium(II) modulation strategy. Experimental studies reveal that Co(II) ions in 1-Th-Co were replaced by Pd(II) ions through cation exchange in N,N-diethylformamide (yielding 1-Th-Pd). The planar PdN4 units in 1-Th-Pd were responsible for improving the water stability of the framework. As a result, 1-Th-Pd offered excellent stability, fast adsorption kinetics, and high removal ratios for (TcO4-)-Tc-99 and ReO4- (as a (TcO4)-Tc-99 - surrogate) in contaminated water. When used in packed columns, 1-Th-Pd can dynamically capture ReO4 - from groundwater. This work provides a new avenue for improving the water stability of MOFs, offering new vistas for the decontamination of aqueous solutions containing (TcO4-)-Tc-99 and ReO4-.