Selective extraction of lithium isotopes using B15C5 derivatives modified with different groups: Experimental and theoretical perspectives

Abstract

Lithium isotope separation is pivotal for advancing nuclear energy applications. Crown ethers (CEs) offer unique advantages due to their selective coordination capabilities. However, the influence of side group modifications on CE performance remains unclear, hindering the development of tailored extractants. This study systematically investigates the extraction and separation of lithium isotopes using B15C5 derivatives through experimental and DFT approaches. Results reveal that electronic effects significantly dictate extraction and separation performance: strong electron-donating derivatives (e.g., 4-NH2-B15C5: χM=2.52 eV, E=24.94%, α=1.022) outperform those with electron-withdrawing groups (e.g., 4-NO2-B15C5: χM =4.34 eV, E=21.75%, α=1.016). Moreover, hydrophilic/hydrophobic properties also play a critical role. 4-CH2OH-B15C5’s high hydrophilicity (log P=-2.51, S=6.85 mg L⁻¹) results in a low separation factor (α=1.007). Notably, 4-tBu-B15C5, combining strong electron-donating (χM =2.86 eV) and hydrophobic (log P=0.397, S=0.503 mg L⁻¹) characteristics, achieves optimal performance (E=23.41%, α=1.026). DFT calculations confirm that electron-donating groups enhance the Mayer bond order of neighboring O atoms and increase the charge density at the ether ring center, thereby improving Li+ coordination. Conversely, electron-withdrawing groups weaken this process. This study elucidates the extraction mechanisms of B15C5 derivatives, providing a theoretical foundation for designing efficient CEs for lithium isotope separation and advancing their application in nuclear energy.