Successful Decontamination of 99TcO4− in Groundwater at Legacy Nuclear Sites by a Cationic Metal‐Organic Framework with Hydrophobic Pockets

99 Tc contamination at legacy nuclear sites is a serious and unsolved environmental issue. The selective remediation of 99 TcO4- in the presence of a large excess of NO3- and SO42- from natural waste systems represents a significant scientific and technical challenge, since anions with a higher charge density are often preferentially sorbed by traditional anion-exchange materials. We present a solution to this challenge based on a stable cationic metal-organic framework, SCU-102 (Ni2 (tipm)3 (NO3 )4 ), which exhibits fast sorption kinetics, a large capacity (291 mg g-1 ), a high distribution coefficient, and, most importantly, a record-high TcO4- uptake selectivity. This material can almost quantitatively remove TcO4- in the presence of a large excess of NO3- and SO42- . Decontamination experiments confirm that SCU-102 represents the optimal Tc scavenger with the highest reported clean-up efficiency, while first-principle simulations reveal that the origin of the selectivity is the recognition of TcO4- by the hydrophobic pockets of the structure.