The adsorption sites of Cs on montmorillonite clays were investigated by theoretical ¹³³Cs chemical shift calculations, ¹³³Cs magic-angle-spinning nuclear magnetic resonance (MAS NMR) spectroscopy, and X-ray diffraction under controlled relative humidity. The theoretical calculations were carried out for structures with three stacking variations in the clay layers, where hexagonal cavities formed with Si–O bonds in the tetrahedral layers were aligned as monoclinic, parallel, alternated; with various d-spacings. After structural optimization, all Cs atoms were positioned around the center of hexagonal cavities in the upper or lower tetrahedral sheets. The calculated ¹³³Cs chemical shifts were highly sensitive to the tetrahedral Al (Al^T)-Cs distance and d-spacing, rather than to the Cs coordination number. Accordingly, three peaks observed in our theoretical spectra were interpreted to be adsorbed Cs around the center of hexagonal cavity with or without Al^T and on the surface in the open nanospace. In a series of ¹³³Cs MAS NMR spectral changes for partial Cs substituted samples, the Cs atoms are preferentially adsorbed at sites near Al^T for low Cs substituted montmorillonites. The presence of nonhydrated Cs was also confirmed in partially Cs substituted samples, even after being hydrated under high relative humidity.

中文翻译：

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从¹³³ Cs固态NMR和密度泛函理论计算看蒙脱土上Cs的吸附新见解。

通过理论¹³³ Cs化学位移计算，¹³³ Cs魔角旋转核磁共振（MAS NMR）光谱和在相对湿度受控下的X射线衍射研究了Cs在蒙脱土粘土上的吸附位置。对在粘土层中具有三个堆积变化的结构进行了理论计算，其中四面体层中由Si-O键形成的六边形空腔被排列为单斜，平行，交替排列。具有各种d-间距。经过结构优化后，所有Cs原子都位于上或下四面体片材的六边形腔体中心附近。计算出的¹³³ Cs化学位移对四面体Al（Al^T）-Cs距离和d-间距，而不是Cs协调数。因此，在我们的理论光谱中观察到的三个峰被解释为在具有或不具有Al ^T的六方腔中心周围以及在开放纳米空间的表面上吸附的Cs 。在针对部分Cs取代的样品的一系列¹³³ Cs MAS NMR光谱变化中，对于低Cs取代的蒙脱土，Cs原子优先吸附在Al ^T附近的位置。即使在高相对湿度下水合后，在部分被Cs取代的样品中也证实了非水合Cs的存在。