Water Adsorption on Clay Minerals As a Function of Relative Humidity: Application of BET and Freundlich Adsorption Models
Water Adsorption on Clay Minerals As a Function of Relative Humidity: Application of BET and Freundlich Adsorption Models
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DOI：
10.1021/la2042873
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发表时间：
2012-01-24
期刊：
影响因子：
3.9
通讯作者：
Baltrusaitis, Jonas
中科院分区：
文献类型：
--
作者：
Hatch, Courtney D.;Wiese, Jadon S.;Baltrusaitis, Jonas
使用配备流通池的水平衰减全反射 (HATR) 傅立叶变换红外 (FTIR) 光谱，研究了室温 (298 K) 下高岭石、伊利石和蒙脱石粘土上的水吸附与相对湿度 (RH) 的函数关系。使用 Brunauer、Emmett 和 Teller (BET) 和 Freundlich 吸附等温线模型对含水量与 RH 的关系进行建模，以提供粘土吸水量的补充多层吸附分析。报告了模型拟合完整性的详细分析。根据 BET 与实验数据的拟合，确定了单层 (ML) 水覆盖率下三种粘土中每种粘土的水含量，并发现与之前报道的重量数据一致。然而，BET 分析未能充分描述高岭石、伊利石和蒙脱石粘土在 RH 值分别大于 80%、50% 和 70% RH 时的吸附现象。 Freundlich 吸附模型被发现可以很好地拟合所研究的整个 RH 值范围内的数据，并揭示了两种不同的水吸附模式。从 Freundlich 模型获得的数据表明，相对于高岭石和伊利石粘土，蒙脱石在 RH 值大于 19%（即高于 ML 水吸附量）时具有最高的水吸附强度和最高的吸附容量。三种粘土之间观察到的水吸附行为的差异归因于基于可用吸附位点分布的不同吸水机制。这表明不同的特性在不同的吸附机制下驱动水的吸附，导致吸水机制的广泛变化。
Water adsorption on kaolinite, illite, and montmorillonite clays was studied as a function of relative humidity (RH) at room temperature (298 K) using horizontal attenuated total reflectance (HATR) Fourier transform infrared (FTIR) spectroscopy equipped with a flow cell. The water content as a function of RH was modeled using the Brunauer, Emmett, and Teller (BET) and Freundlich adsorption isotherm models to provide complementary multilayer adsorption analysis of water uptake on the clays. A detailed analysis of model fit integrity is reported. From the BET fit to the experimental data, the water content on each of the three clays at monolayer (ML) water coverage was determined and found to agree with previously reported gravimetric data. However, BET analysis failed to adequately describe adsorption phenomena at RH values greater than 80%, 50%, and 70% RH for kaolinite, illite, and montmorillonite clays, respectively. The Freundlich adsorption model was found to fit the data well over the entire range of RH values studied and revealed two distinct water adsorption regimes. Data obtained from the Freundlich model showed that montmorillonite has the highest water adsorption strength and highest adsorption capacity at RH values greater than 19% (i.e., above ML water adsorption) relative to the kaolinite and illite clays. The difference in the observed water adsorption behavior between the three clays was attributed to different water uptake mechanisms based on a distribution of available adsorption sites. It is suggested that different properties drive water adsorption under different adsorption regimes resulting in the broad variability of water uptake mechanisms.