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

KEYWORDS:

• Dipyridyl-derived bis(pyrazole) ligands
• Americium
• Europium
• Solvent extraction
• Complexation

Acknowledgments

The comprehensive training platform of a specialized laboratory (College of Chemistry, Sichuan University) is acknowledged for ESI-MS, ¹H NMR, and FT-IR analyses.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/07366299.2023.2173014

Additional information

Funding

This work was supported by the National Science Foundation of China (Grant numbers 11975161, 11675115, and U2167219) and the Fundamental Research Funds for the Central Universities (Grant numbers 20826041D4117).