Radiolysis of diamide phenanthroline in 1-octanol: From the insights into transient processes to a versatile strategy to enhance the radiation-resistance

The ligand of 2,9-Diamide-1,10-phenanthroline (DAPhen), developed for group actinide separation in the past decade, showed excellent extraction and separation performance for various actinides from trivalent lanthanides. However, its radiolysis mechanism remains unclear, restricting its application. Mechanism for the radiolysis of three different DAPhen in 1-octanol was studied by pulse radiolysis, of which the results demonstrated that reductive degradation was the main route of their radiolysis in 1-octanol. Solvated electrons (e sol − ), and α-hydroxyoctyl radicals have been recognized as the most important transient species responsible for DAPhen radiolysis. Rate constants for the reactions of e sol − with N,N′ -diethyl- N,N′ -ditethyl-2,9-diamide-1,10-phenanthroline (Et–Et-DAPhen, EED), N,N′ -dioctyl- N,N′ -ditoctlyl-2,9-diamide-1,10-phenanthroline (Oct-Oct-DAPhen, OOD), and N,N′ -diethyl- N,N′ -ditolyl-2,9-diamide-1,10-phenanthroline (Et-Tol-DAPhen, ETD) were estimated to be 1.9 × 10 9 , 2.3 × 10 9 , and 1.5 × 10 9  L mol −1  s −1 , respectively. Those of α-hydroxyoctyl radicals with EED, OOD, and ETD were approximately 1.1 × 10 8 , 2.1 × 10 8 , and 2.7 × 10 8  L mol −1  s −1 , respectively. The studied DAPhen exhibited high reactivity with e sol − , and α-hydroxyoctyl radicals in 1-octanol, resulting in their vulnerability under irradiation. A versatile strategy was accordingly proposed to enhance their radiation stability based on the insights into transient processes of DAPhen radiolysis. If the HNO 3 -equilibrated organic phase was saturated with nitrous oxide (N 2 O), the reductive species responsible for DAPhen degradation would be scavenged. As a consequence, the radiation-resistance of DAPhen was significantly improved because the key elementary reaction of radiolysis was inhibited by the synergetic effect of N 2 O and HNO 3 .