Several 2:1 layer silicates comprising di- and trioctahedral smectites of different layer charge between 0.2 and 0.4 per formula unit and a trioctahedral vermiculite were studied by an in situ method that allowed Fourier transform infrared spectroscopy (FTIR) spectra and water vapor sorption isotherms to be obtained simultaneously. The particle size and shape of the selected materials were determined using X-ray diffraction and gas adsorption analyses, which provided an estimate of the particle size with resulting edge site proportion. The aim of this study was to elucidate the hydration mechanism in 2:1 layer silicates during desorption and adsorption of water vapor. Domains in the desorption and adsorption of water vapor of the smectite samples with a slightly increasing slope were explained by a heterogeneous layer charge distribution, which enables the coexistence of different hydration states even under controlled conditions. Whereas hysteresis was observed over the entire isothermal range of the smectites, the isotherm of the vermiculite sample only showed hysteresis in the transition from the monohydrated state (1W) to the bihydrated state (2W). We also revealed that hysteresis is a function of the layer charge distribution, the achieved water content, and the particle size with resulting edge site contribution. Increasing the edge site proportions led to an increased hysteresis. The findings from the experimental FTIR/gravimetric analysis showed that the transition from 2W to 1W and backward is visible using infrared spectroscopy. The shifting of δ(H–O–H) was influenced by the layer charge and octahedral substitutions. As a final point, we use water as a sensor molecule to describe the OH groups of the octahedral sheet and show that the observed shifts result from a change in the tilting angle. Our experimental results were supported by ab initio thermodynamic simulations that revealed the different shifting behavior of δ(H–O–H) and δ(M^x+–OH–N^y+) related to the differences in surface charge density and octahedral compositions.

中文翻译：

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本征结构性质对2：1层硅酸盐水合的影响

通过原位研究了几种2：1层硅酸盐，这些层硅酸盐包含每层配方单元电荷在0.2和0.4之间的不同层数的二和三八面体蒙脱石和三八面体ver石。允许同时获得傅里叶变换红外光谱（FTIR）光谱和水蒸气吸附等温线的方法。使用X射线衍射和气体吸附分析确定所选材料的粒径和形状，这提供了对粒径的估计以及产生的边缘部位比例。这项研究的目的是阐明水蒸气解吸和吸附过程中2：1层硅酸盐的水合机理。坡度略有增加的绿土样品的水蒸气解吸和吸附域由不均匀的层电荷分布来解释，即使在受控条件下，该分布也可以使不同水化状态共存。尽管在蒙皂石的整个等温范围内都观察到了磁滞现象，ul石样品的等温线在从一水合态（1W）到二水合态（2W）的转变中仅显示出滞后现象。我们还发现，磁滞现象是层电荷分布，所达到的水含量和颗粒尺寸以及所产生的边缘位点贡献的函数。边缘部位比例的增加导致磁滞的增加。FTIR /重量分析实验的结果表明，使用红外光谱仪可以看到从2W到1W以及向后的跃迁。δ（H–O–H）的移动受层电荷和八面体取代的影响。最后，我们使用水作为传感器分子来描述八面体薄片的OH基团，并表明观察到的位移是由倾斜角的变化引起的。我们的实验结果得到了以下方面的支持从头开始的热力学模拟揭示了δ（H–OH–H）和δ（M ^{x +} –OH–N ^{y +}）的不同迁移行为，这与表面电荷密度和八面体组成的差异有关。