Stability of Montmorillonite Edge Faces Studied Using First-Principles Calculations
Stability of Montmorillonite Edge Faces Studied Using First-Principles Calculations
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DOI：
10.1346/ccmn.2017.064062
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发表时间：
2017-08
影响因子：
2.2
通讯作者：
H. Sakuma;Y. Tachi;K. Yotsuji;S. Suehara;T. Arima;N. Fujii;K. Kawamura;A. Honda
中科院分区：
文献类型：
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作者：
H. Sakuma;Y. Tachi;K. Yotsuji;S. Suehara;T. Arima;N. Fujii;K. Kawamura;A. Honda
膨胀粘土矿物边面的反应性和稳定性可以通过层电荷和堆积结构来改变；然而，由于实验的限制，人们对这些影响知之甚少。采用基于密度泛函理论的第一性原理计算方法，研究了层电荷y=0.5 0或y=0.33(e−/Si4O10)的蒙脱石{110}、{0 10}、{10 0}和{130}晶面的结构和稳定性。对堆积模型和单层模型进行了测试和比较，以了解堆积对蒙脱石边面稳定性的影响。大多数堆叠层通过在层之间创建氢键来稳定边面；因此，堆叠层模型中层的表面能低于单层模型中的层。这表明在估算边面表面能时应考虑膨胀条件。在化学吸附水分子存在的情况下，计算了这些边面的负表面能。与0.33的低层电荷相比，0.50的高层电荷降低了表面能。镁与铝的类质同晶取代提高了层间钠离子位置的稳定性，钠离子位置稳定在与镁离子相邻的三角环中。{010}和{130}边面的最低表面能是由于边面的局部负电荷而具有较强的阳离子吸附中心的镁离子的存在。与无水的层间相比，吸附在这些边面上的阳离子周围的O原子配位数较小。
The reactivity and stability of the edge faces of swelling clay minerals can be altered by layer charge and the stacking structure; however, these effects are poorly understood due to experimental limitations. The structure and stability of the montmorillonite {110}, {010}, {100}, and {130} edge faces with a layer charge of either y = 0.50 or y = 0.33 (e−/Si4O10) were investigated using first-principles calculations based on density functional theory. Stacked- and single-layer models were tested and compared to understand the effect of stacking on the stability of montmorillonite edge faces. Most stacked layers stabilize the edge faces by creating hydrogen bonds between the layers; therefore, the surface energy of the layers in the stacked-layer model is lower than in the single-layer model. This indicates that the estimates of edge face surface energy should consider the swelling conditions. Negative surface energies were calculated for these edge faces in the presence of chemisorbed water molecules. A high layer charge of 0.50 reduced the surface energy relative to that of the low layer charge of 0.33. The isomorphic substitution of Mg for Al increased the stability of interlayer Na ion positions, which were stable in the trigonal ring next to the Mg ions. The lowest surface energies of the {010} and {130} edge faces were characterized by the presence of Mg ions on edge faces, which had a strong cation adsorption site due to the local negative charge of the edges. The coordination numbers of O atoms around cations adsorbed to these edge faces were small in comparison to interlayers without water.