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摘要
Effective separation of lithium isotopes is of strategic value which attracts growing attention worldwide. This study reports a new class of macrocyclic ligand decorated ordered mesoporous silica (OMS) with large-pore and short-channel characteristics, which holds the potential to effectively separate lithium isotopes in aqueous solutions. Initially, a series of benzo-15-crown-5 (B15C5) derivatives containing different electron-donating or -withdrawing substituents were synthesized. Extractive separation of lithium isotopes in a liquid-liquid system was comparatively studied, highlighting the effect of the substituent, solvent, counter anion and temperature. The optimal NH2-B15C5 ligands were then covalently anchored to a short-channel SBA-15 OMS precursor bearing alkyl halides via a post-modification protocol. Adsorptive separation of the lithium isotopes was fully investigated, combined with kinetics and thermodynamics analysis, and simulation by using classic adsorption isotherm models. The NH2-B15C5 ligand functionalized OMSs exhibited selectivity to lithium ions against other alkali metal ions including K(I). Additionally, a more efficient separation of lithium isotopes could be obtained at a lower temperature in systems with softer counter anions and solvents with a lower dielectric constant. The highest value separation factor (alpha = 1.049 +/- 0.002) was obtained in CF3COOLi aqueous solution at 288.15 K. Moreover, theoretical computation based on the density functional theory (DFT) was performed to elucidate the complexation interactions between the macrocyclic ligands and lithium ions. A suggested mechanism involving an isotopic exchange equilibrium was proposed to describe the lithium isotope separation by the functionalized OMSs.
- 出版日期2016
- 单位清华大学; 中国石油大学（北京）
