Silver 2,4'-Bipyridine Coordination Polymer for the High-Capacity Trapping of Perrhenate, A Pertechnetate Surrogate

Pertechnetate, the most stable form of the radionuclide ⁹⁹Tc in aerobic aqueous systems, is a hazardous anion present in nuclear waste. Its high mobility in water makes the remediation of the anion challenging. In the past decade, significant effort has been placed into finding materials capable of adsorbing this species. Here, we present the synthesis and high-resolution crystal structure of the coordination polymer [Ag(2,4'-bipyridine)]NO₃, which is capable of sequestering perrhenate─a pertechnetate surrogate─through anion exchange to form another new coordination polymer, [Ag(2,4'-bipyridine)]ReO₄. Both the beginning and end structures were solved by single-crystal X-ray diffraction and the adsorption reaction was monitored through inductively coupled plasma-optical emission spectroscopy and UV-vis spectroscopy. The exchange reaction follows a pseudo-second-order mechanism and the maximum adsorption capacity is 764 mg ReO₄/g [Ag(2,4'-bipyridine)]NO₃, one of the highest recorded for a coordination polymer or metal-organic framework. A solvent-mediated recrystallization mechanism was determined by monitoring the ion-exchange reaction by scanning electron microscopy-energy-dispersive spectroscopy and powder X-ray diffraction.