不同物理性质的相互作用对镧系离子分离的挑战--从头算分子动力学和实验研究
Interplay of Physically Different Properties Leading to Challenges in Separating Lanthanide Cations -- an Ab Initio Molecular Dynamics and Experimental Study
摘要：
镧系元素在它们的化学行为中具有充分记载的相似性，这使得有价值的三价镧系元素阳离子（Ln（III））特别难以在水中彼此分离。在这项工作中，我们应用从头算分子动力学模拟，比较自由能（Δ G（ads））与镧系元素阳离子吸附到二氧化硅表面在pH值条件下，其中SiO-基团存在。镥（Lu（III））和铕（Eu（III））的预测Δ G（ads）在统计不确定性范围内相似;这与我们对二氧化硅的批量吸附测量定性一致。这一发现是显著的，因为两种阳离子表现出相差>2 eV的水合自由能（Δ G（hyd））、不同的水合数和远离二氧化硅表面的不同水解行为。我们观察到Lu（III）和Eu（III）Δ G（ads）的相似性是Eu（III）和Lu（III）水合作用的差异（Δ G（hyd））与它们与二氧化硅的结合能差异之间微妙抵消的结果。我们建议在两个端点破坏这种抵消，无论是吸附或完全解吸镧系元素（例如，通过纳米约束或混合溶剂），将导致有效的Ln分离。
英文摘要：
The lanthanide elements have well-documented similarities in their chemical behavior, which makes the valuable trivalent lanthanide cations (Ln(III)) particularly difficult to separate from each other in water. In this work, we apply ab initio molecular dynamics simulations to compare the free energies (Delta G(ads)) associated with the adsorption of lanthanide cations to silica surfaces at a pH condition where SiO- groups are present. The predicted Delta G(ads) for lutetium (Lu(III)) and europium (Eu(III)) are similar within statistical uncertainties; this is in qualitative agreement with our batch adsorption measurements on silica. This finding is remarkable because the two cations exhibit hydration free energies (Delta G(hyd}) that differ by >2 eV, different hydration numbers, and different hydrolysis behavior far from silica surfaces. We observe that the similarity in Lu(III) and Eu(III) Delta G(ads) is the result of a delicate cancellation between the difference in Eu(III) and Lu(III) hydration (Delta G(hyd})), and their difference in binding energies to silica. We propose that disrupting this cancellation at the two end points, either for adsorbed or completely desorbed lanthanides (e.g., via nanoconfinment or mixed solvents), will lead to effective Ln separation.
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