The efficient removal of pertechnetate (TcO4-) anions from liquid waste or melter off-gas solution for an alternative treatment is one of the promising options to manage Tc-99 in legacy nuclear waste. Safe immobilization of Tc-99 is of major importance because of its long half-life (t(1/2) = 2.13 X 10(5) yrs) and environmental mobility. Different types of inorganic and solid-state ion-exchange materials have been shown to absorb TcO4- anions from water. However, both high capacity and selectivity have yet to be achieved in a single material. Herein, we show that a protonated version of an ultrastable zirconium-based metal-organic framework can adsorb perrhenate (ReO4-) anions, a nonradioactive surrogate for TcO4-, from water even in the presence of other common anions. Synchrotron-based powder X-ray diffraction and molecular simulations were used to identify the position of the adsorbed ReO4- (surrogate for TcO4-) molecule within the framework.