Ab initio molecular dynamics study of the interlayer and micropore structure of aqueous montmorillonite clays
Ab initio molecular dynamics study of the interlayer and micropore structure of aqueous montmorillonite clays
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DOI：
10.1016/j.gca.2015.07.013
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发表时间：
2015-11
影响因子：
5
通讯作者：
J. L. Suter;L. Kabalan;M. M. Khader-M.;P. Coveney
中科院分区：
文献类型：
--
作者：
J. L. Suter;L. Kabalan;M. M. Khader-M.;P. Coveney
从头算分子动力学模拟已经进行了充分水化粘土边缘的界面微观结构和反应性的理解。所研究的模型包括层间水和层间水。我们通过解离机制确定酸性位点;所产生的离子可以通过水和层间水来稳定。我们发现粘土边缘具有复杂的两性行为，这取决于所考虑的面和位置的同构取代。对于中性（1 1 0）表面，我们没有观察到任何解离的时间尺度上访问。边缘终止羟基参与水分子的氢键网络，其跨越粘土框架的周期性图像之间的夹层。在四面体层的（1 1 0）粘土边缘的同晶取代，我们发现相邻的暴露的顶端氧的行为作为一个布朗斯特基地和抽象的质子从附近的水分子，这反过来又消除了一个质子从AlOH 2组。在（110）粘土边缘的八面体层中具有同晶取代，相邻暴露的顶端氧原子不从水分子中提取质子，但增加了氢键合的水分子的数量（从一个到两个）。酸处理的粘土可能使两个位点质子化。（0 1 0）表面不具有相同的界面氢键结构;它的稳定性要差得多，我们在模型中观察到一半的末端SiOH基团的解离（三键Sisingle bondO单键H →三键Sisingle bondO−+ H+）。由此产生的阴离子是稳定的溶剂化从两个中间和层间的水分子。这表明，当完全水合时，（0 1 0）表面可以作为布朗斯台德酸，即使在中性pH值下。
Ab initiomolecular dynamics simulations have been performed to gain an understanding of the interfacial microscopic structure and reactivity of fully hydrated clay edges. The models studied include both micropore and interlayer water. We identify acidic sites through dissociation mechanisms; the resulting ions can be stabilized by both micropore and interlayer water. We find clay edges possess a complex amphoteric behavior, which depends on the face under consideration and the location of isomorphic substitution. For the neutral (1 1 0) surface, we do not observe any dissociation on the timescale accessible. The edge terminating hydroxyl groups participate in a hydrogen bonded network of water molecules that spans the interlayer between periodic images of the clay framework. With isomorphic substitutions in the tetrahedral layer of the (1 1 0) clay edge, we find the adjacent exposed apical oxygen behaves as a Brönsted base and abstracts a proton from a nearby water molecule, which in turn removes a proton from an AlOH2group. With isomorphic substitutions in the octahedral layer of the (1 1 0) clay edge the adjacent exposed apical oxygen atom does not abstract a proton from the water molecules, but increases the number of hydrogen bonded water molecules (from one to two). Acid treated clays are likely to have both sites protonated. The (0 1 0) surface does not have the same interfacial hydrogen bonding structure; it is much less stable and we observe dissociation of half the terminal SiOH groups (triple bondSisingle bondOsingle bondH → triple bondSisingle bondO−+ H+) in our models. The resulting anions are stabilized by solvation from both micropore and interlayer water molecules. This suggests that, when fully hydrated, the (0 1 0) surface can act as a Brönsted acid, even at neutral pH.