Specific Ion Effects in Lanthanide–Amphiphile Structures at the Air–Water Interface and Their Implications for Selective Separation
Specific Ion Effects in Lanthanide–Amphiphile Structures at the Air–Water Interface and Their Implications for Selective Separation
复制标题
空气-水界面上镧系元素-两亲结构的特定离子效应及其对选择性分离的影响
DOI：
10.1021/acsami.1c24008
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发表时间：
2022
影响因子：
9.5
通讯作者：
Dutta, Pulak
中科院分区：
文献类型：
--
作者：
Yoo, Sangjun;Qiao, Baofu;Douglas, Travis;Bu, Wei;Olvera de la Cruz, Monica;Dutta, Pulak
使用表面活性剂将溶解的离子吸引到水表面和界面是基于溶剂和无溶剂的分离过程中的重要步骤。研究了亚水相中镧系离子与磷酸双十六烷基酯在气-水界面上的相互作用。在亚相中有较重的镧系元素（原子序数Z ≥ 65）时，浮层可以被压缩到分子横截面的一半，表明形成了双层。X射线荧光和反射率数据支持这一结论。在较轻的镧系元素（Z< 65）的存在下，仅观察到单层。使用Er 3+（较重）和Nd 3+（较轻）镧系元素的亚相浓度依赖性研究显示了一个阶梯式的进展，只有当溶液浓度>3 × 10- 7 M时，离子才会附着在单层上。高于10 ~（-5）M时，双层形成，但仅在较重的镧系元素存在下。掠入射X-射线衍射表明，在双层结构，但不是在单层的横向离子-离子相关性的证据。显式溶剂全原子分子动力学模拟证实了双层系统中离子-离子关联的升高。这种双层结构从水溶液中分离较重的镧系元素，但不分离较轻的镧系元素，因此是选择性分离较重的镧系元素的潜在机制。
The use of surfactants to attract dissolved ions to water surfaces and interfaces is an essential step in both solvent-based and solvent-free separation processes. We have studied the interactions of lanthanide ions in the aqueous subphase with monolayers of dihexadecyl phosphate at air–water interfaces. With heavier lanthanides (atomic numberZ≥ 65) in the subphase, the floating layer can be compressed to an area/molecule of about half the molecular cross section, indicating bilayer formation. X-ray fluorescence and reflectivity data support this conclusion. In the presence of lighter lanthanides (Z< 65), only monolayers are observed. Subphase-concentration-dependent studies using Er3+(heavier) and Nd3+(lighter) lanthanides show a stepwise progression, with ions attaching to the monolayer only when the solution concentration is >3 × 10–7M. Above ∼10–5M, bilayers form but only in the presence of the heavier lanthanide. Grazing incidence X-ray diffraction shows evidence of lateral ion–ion correlations in the bilayer structure but not in monolayers. Explicit solvent all-atom molecular dynamics simulations confirm the elevated ion–ion correlation in the bilayer system. This bilayer structure isolates heavier lanthanides but not lighter lanthanides from an aqueous solution and is therefore a potential mechanism for the selective separation of heavier lanthanides.