A Novel Type of Tetradentate Dipyridyl-Derived Bis(pyrazole) Ligands for Highly Efficient and Selective Extraction of Am3+ Over Eu3+ From HNO3 Solution

ABSTRACT The extraction of Am3+ and Eu3+ with 6,6’-bis(5-alkyl-1H-pyrazol-3-yl)-2,2’-bipyridine (BPzBPy, alkyl = i-Bu, n-Bu, n-Oct) from HNO3 medium and the complexation of BPzBPy with Eu3+ were investigated. By using meta-nitrobenzotrifluoride (F-3) as a diluent, iBu-BPzBPy ligand in combination with 2-bromohexanoic acid was able to extract Am3+ over Eu3+ with the nature of significantly high efficiency, relatively fast extraction kinetics, and easy stripping. Slope analysis showed the formation of a 1:2 metal/ligand extraction species. The analyses of electrospray ionization mass spectrometry (ESI-MS), Fourier transform infrared (FT-IR) and time-resolved laser fluorescence spectrum (TRLFS) revealed that the composition of the extracted complex was [Eu(H2O)L2]A3 (L = ligand; HA = 2-bromohexanoic acid). The complexation of iBu-BPzBPy ligand with Eu3+ was an enthalpy-driven spontaneous, exothermic, and entropy-decreasing process. Besides, the complex stability constants were also obtained via UV–vis spectrophotometric titration. Combining the results of solvent extraction and complexation studies, a cation exchange extraction model was also proposed. GRAPHICAL ABSTRACT