How Metal(IV) Phosphonate Local Structure Drives Radiolytic Stability in Sorbents with Novel Minor Actinide-Lanthanide Selectivity

The capture or recovery of f -block metals is an important aspect of reducing waste and improving the sustainability of clean energy solutions including nuclear power, batteries, and catalysis. In nuclear wastes, actinides and lanthanides are present in radioactive, acidic, aqueous solutions, which presents a unique opportunity and challenge for recovery and recycling of these elements. In this study, Zr(IV) and Ti(IV) phosphonate sorbents were prepared with the aminotris(methylenephosphonic acid) ligand (ATMP). The impact of tetravalent metal choice (i.e., Zr or Ti) was then compared. Varying the tetravalent metal had a substantial impact on the morphology, porosity, and local structure, which resulted in considerable differences in sorption performance and degradation mechanisms under ionizing high energy electron radiation. Ti(IV) was significantly less reactive with the phosphonate group, leading to poor ligand loading and inferior sorption of trivalent minor actinides and lanthanides under acidic conditions compared to ZrATMP. Notably, ZrATMP exhibited appreciable selectivity for lanthanides over minor actinides. After irradiation, ZrATMP was damaged via structural rearrangement of its Zr–O–P coordination environment. Conversely, TiATMP degraded via cleavage of its C–N bonds. Our results demonstrate how metal choice in M(IV) phosphonate materials has considerable bearing on their structure, performance, and stability.