Probing the high radiation tolerance of minor actinide selective zirconium phosphonate sorbents

Minor actinide (MA) selective materials that are resistant to radiation are necessary to enable separation of MAs from lanthanides in nuclear wastes. Zirconium(iv) phosphonates (ZrPs) are a class of amorphous coordination polymers with promising applications as a solid-phase sorbent for MA-lanthanide separations. In this study, a zirconium phosphonate sorbent (ZrPTP) that intramolecularly incorporates the MA-selective 2,6-bis(1,2,3-triazol-4-yl)pyridine (PTP) ligand was synthesised and evaluated for radiation tolerance with high energy electron irradiation to doses of 2 MGy. The MA sorption selectivity of ZrPTP before and after irradiation was compared using Am and Eu. ZrPTP demonstrated maintained selectivity for Am over Eu even after a 2 MGy dose. Synchrotron radiation characterisation techniques and solid-state NMR were employed to accurately assess the average local structure before and after irradiation, where minor amounts of Zr-O bonds, aliphatic C-H bonds, and triazole groups were broken, showcasing excellent radiation stability for doses up to 2 MGy. Our results demonstrate the importance of chemistry in ZrP coordination polymers maintaining not only selective separation properties, but also maintaining radiation stability as well.