Fast Room-Temperature Synthesis of an Extremely Alkaline-Resistant Cationic Metal-Organic Framework for Sequestering TcO4- with Exceptional Selectivity

Leveraging metal-organic framework (MOF) to eliminate radioactive contaminants has invariably received much attention, but low preparation efficiency and poor selectivity have still limited its actual application. Herein, it is found that a fourfold interpenetrated cationic MOF (Ag-TPPE) can be rapidly synthesized by only mixing, stirring, or sonication at room temperature. More impressively, the preparation process can be completed in <1 min. Up to now, this is the first report that cationic MOFs can be obtained by directly mixing the corresponding raw materials at room temperature. In addition to holding the rare merits of structural stability in extremely strong bases (8 m NaOH), Ag-TPPE can selectively remove TcO4- in the presence of large excess SO42- or NO3-. Based on its ultra-high selectivity, Ag-TPPE exhibits exceptional removal rate for TcO4- from simulated Hanford and Savannah River Site waste streams, which refreshes the record of selective sorption of TcO4- at low solid/liquid ratio, overcoming the drawback of overused sorbent in treatment of radioactive waste solution. Such superior sorption capabilities are thoroughly elucidated by the density functional theory calculations on a molecular level, clearly disclosing that TcO4- can enter into the framework through breathing effect and is trapped in the large cavity through dense hydrogen bonds.