Atomic-scale structures of interfaces between phyllosilicate edges and water
Atomic-scale structures of interfaces between phyllosilicate edges and water
复制标题
DOI：
10.1016/j.gca.2011.12.009
复制
发表时间：
2012-03
影响因子：
5
通讯作者：
Xiandong Liu;Xiancai Lu;E. Meijer;Rucheng Wang;Huiqun Zhou
中科院分区：
文献类型：
--
作者：
Xiandong Liu;Xiancai Lu;E. Meijer;Rucheng Wang;Huiqun Zhou
我们报告了关于页硅酸盐边缘和水之间界面结构的第一原理分子动力学（FPMD）研究。使用 FPMD，可以在相同的第一原理水平上模拟基材和溶剂，并通过分子动力学对热运动进行采样。考虑中性和带电硅酸盐骨架，对于带电情况，考虑八面体（Mg 代替 Al）和四面体（Al 代替 Si）取代。对于所有框架，我们重点关注常见的 (010) 和 (110) 型边缘表面。利用约束FPMD，计算了八面体阳离子配位水的离开过程的自由能；因此，这些边缘阳离子的配位状态被确定。对于 (010) 型边缘，Al 的 5 重配位态和 6 重配位态都是稳定的，并且以相似的概率出现，而对于 Mg 阳离子，只有 5 重配位态是稳定的。对于(110)型边缘，只有Al阳离子的6重态是稳定的。然而，对于 Mg 阳离子，两种配位状态都是稳定的。在 5 倍情况下，溶剂水分子与桥接氧原子（即 MgOSi）形成氢键。自由能结果表明，界面处应该存在相当数量的五重配位八面体位点（即 MgOH/AlOH）。通过详细的氢键分析确定界面结构和酸/碱基团。 (1)桥接氧位点。对于（010）边缘，桥接氧原子不是有效的质子接受位点，因为它们无法从溶剂中接近。对于 (110) 边，中性和八面体取代骨架（即 MAl/Mg 的 MOSi）的氧原子是质子接受位点。对于 T-sheet 取代的情况，桥接氧位点通过捕获质子而成为供质子基团（即 AlOHSi）。 (2) T 片组。所有 T 片边缘基团均为 MOH (MSi/Al)，并充当质子供体和受体。 (3) O 形片组。对于具有 6 倍 Al 的 (010) 边缘，活性表面基团包括 Al(OH)(H2O) 和 Al(OH)2，而对于 Mg 阳离子，边缘基团为 Mg(OH2)2。对于 5 重配位，活性基团是 AlOH。在(110)边缘，供质子位点包括AlOH、AlOH 2 和MgOH 2 基团。总的来说，我们的结果揭示了同构取代对界面结构的显着影响，并且该模型为理解相关界面过程提供了分子水平的基础。
We report first-principles molecular dynamics (FPMD) studies on the structures of interfaces between phyllosilicate edges and water. Using FPMD, the substrates and solvents are simulated at the same first-principles level, and the thermal motions are sampled via molecular dynamics. Both the neutral and charged silicate frameworks are considered, and for charged cases, the octahedral (Mg for Al) and tetrahedral (Al for Si) substitutions are taken into account. For all frameworks, we focus on the commonly occurring (010)- and (110)-type edge surfaces. With constrained FPMD, we calculated the free energy of the leaving processes of coordinated water of octahedral cations; therefore, the coordination states of those edge cations are determined. For (010)-type edges, both the 5- and 6-fold coordination states of Al are stable and occur with a similar probability, whereas only the 5-fold coordination is stable for Mg cations. For (110)-type edges, only the 6-fold states of Al cations are stable. However, for Mg cations, both coordination states are stable. In the 5-fold case, the solvent water molecules form H-bonds with the bridging oxygen atoms (i.e., MgOSi). The free energy results indicate that there should be a considerable number of 5-fold coordinated octahedral sites (i.e., MgOH/AlOH) at the interfaces. The interfacial structures and acid/base groups were determined by detailed H-bonding analyses. (1) Bridging oxygen sites. For (010) edges, the bridging oxygen atoms are not effective proton-accepting sites because they are inaccessible from the solvent. For (110) edges, the oxygen atoms of neutral and octahedrally substituted frameworks (i.e., MOSi for MAl/Mg) are proton-accepting sites. For T-sheet substituted cases, the bridging oxygen site becomes a proton-donating group (i.e., AlOHSi) through the capture of a proton. (2) T-sheet groups. All T-sheet edge groups are MOH (MSi/Al) and act as both proton donors and acceptors. (3) O-sheet groups. For (010) edges with 6-fold Al, the active surface groups include Al(OH)(H2O) and Al(OH)2, whereas for Mg cations, the edge group is Mg(OH2)2. For 5-fold coordination, the active groups are AlOH. At (110) edges, proton-donating sites include AlOH, AlOH2and MgOH2groups. Overall, our results reveal the significant effects of isomorphic substitutions on the interfacial structures, and the models provide a molecular-level basis for understanding relevant interfacial processes.