El Azrak Anwar, Grekov Denys I, Truche Laurent, Pré Pascaline
IMT Atlantique, GEPEA, UMR CNRS 6144, F-44307 Nantes, France.
Univ. Grenoble Alpes, CNRS, IRD, IFSTTAR, ISTerre, 38000 Grenoble, France.
Molecules. 2024 Dec 20;29(24):6019. doi: 10.3390/molecules29246019.
The textural properties of synthetic and natural clays in the sodium form and exchanged with tetramethylammonium cations (TMA) were characterized using N and Ar physisorption isotherms at cryogenic temperatures. Specific surface areas and micro/mesoporous volumes were determined using the BET and the models. The analysis requires the use of reference isotherms measured at the same temperature on the surface of non-porous materials with an identical chemical composition. In order to better assess the effects of chemical heterogeneities in the clay particles, reference isotherms representative of silica surfaces were taken into account in the analysis of the and corrected to account for variations in curvature at the interface of the film adsorbed in the micropores. In addition, high-resolution Ar adsorption isotherms at 87 K were analyzed using the Derivative Isotherm Summation (DIS) method to quantify the energy contributions of adsorption sites and determine the fractions of basal and lateral surfaces of clay particles. The high-energy adsorption sites, identified in the low-pressure range, were attributed to intra-particle microporosity due to stacking defects and/or open inter-layer spaces. These sites were differentiated from those on the lateral and basal surfaces of the particles. A modification of the DIS method was proposed to measure these contributions and improve the fit with the experimental data. The results show that TMA cation exchange significantly increases the microporosity of clays compared to their sodic form, which can be attributed to the increased contribution of intra-particle adsorption sites due to interlayer expansion.
使用低温下的N和Ar物理吸附等温线对钠型以及与四甲基铵阳离子（TMA）交换后的合成粘土和天然粘土的质地特性进行了表征。使用BET和 模型测定了比表面积以及微孔/介孔体积。 分析需要使用在相同温度下在具有相同化学组成的无孔材料表面上测量的参考等温线。为了更好地评估粘土颗粒中化学不均匀性的影响，在 分析中考虑了代表二氧化硅表面的参考等温线，并进行了校正以考虑微孔中吸附膜界面处曲率的变化。此外，使用导数等温线求和（DIS）方法分析了87K下的高分辨率Ar吸附等温线，以量化吸附位点的能量贡献，并确定粘土颗粒基面和侧面的比例。在低压范围内识别出的高能吸附位点归因于由于堆积缺陷和/或开放层间空间导致的颗粒内微孔率。这些位点与颗粒侧面和基面上的位点区分开来。提出了一种DIS方法的改进方法来测量这些贡献并改善与实验数据的拟合。结果表明，与钠型粘土相比，TMA阳离子交换显著增加了粘土的微孔率，这可归因于层间膨胀导致颗粒内吸附位点的贡献增加。
