Insight into selectivity: uptake studies of radionuclides ⁹⁰Sr²⁺, ¹³⁷Cs⁺, and ²³³UO₂²⁺ with bis-amidoxime polymers

Uptake characteristics of a bis-amidoximated polymer are presented for 90Sr2+, 137Cs+, and 233UO22+ to assess rational ligand design and polymer engineering efforts applied to selective uranium extraction. Functionalized with the bis-amidoxime diaryl ether ligand at a loading of 1.98 mmol per gram of polymer, the polymer was found to sorb uranium from a pH 6 solution with a separation factor (α) over cesium of 1.2 × 103. Strontium uptake was negligible throughout the pH range studied whereas cesium uptake averaged <30%. Moreover, at near neutral pH, the sorbent was able to purify water to below the United States' set maximum contaminant level for uranium, decreasing the U concentration from 330 ppb to below 3 ppb in 30 minutes. Density functional theory (DFT) calculations, used to probe the nature of the metal-bis-amidoxime interaction, help inform the empirically realized uptake selectivity.