Analysis of Anhydrous and Hydrated Surface Energies of gamma-Al2O3 by Water Adsorption Microcalorimetry
Analysis of Anhydrous and Hydrated Surface Energies of gamma-Al2O3 by Water Adsorption Microcalorimetry
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DOI：
10.1021/jp309319j
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发表时间：
2012-11-22
影响因子：
3.7
通讯作者：
Quach, Dat V.
中科院分区：
文献类型：
--
作者：
Castro, Ricardo H. R.;Quach, Dat V.
表面能在催化、晶体生长等方面具有重要意义。烧结、多态等诸多领域。在处理纳米结构材料时，其重要性更为关键，因为纳米结构材料的表面体积比相当高，表面项也相当大。占总自由能的很大一部分。在这里，我们提出了一种新的方法来实验评估氧化物的平均无水和水合表面能，并使用该方法来确定，γ氧化铝的表面能。该方法使用了一个水吸附装置与微量计相结合，吸附热可以作为吸附量的函数来监测。这就是液态水形态存在的点的定义（在高相对湿度下）。该信息允许使用吸附量热数据计算室温下任何覆盖状态下的表面能。对于gamma氧化铝，观察到水吸附行为与表面能之间的密切关系，证明较高的表面能与水的高能量解离行为有关，并且在水吸附时表面能持续下降。结合吸附等温线和微量热数据，可以清楚地观察到三个吸附阶段，与所提出的模型一致。
Surface energies have postulated importance to catalysis, crystal growth,. sintering, polymorphism, and many other fields. importance is even more critical when dealing with nanostructured materials, where the surface-to-volume ratio is considerably higher and the surface term. accounts for a much larger fraction of the total free energy. Here we present a novel approach to experimentally assess the average anhydrous and hydrated surface energies of oxides, and used the method to determine, the surface energy of gamma alumina The method uses a water adsorption setup combined with a microcalorimeter where the heat of adsorption can be monitored as a function of the adsorbed amount Maintaining a closed system, the approach enables the correlation of the molecular configuration of absorbed water with the thermodynamic data, and hence the definition of the point where a liquid water configuration exists (at high relative humidity). This information allows the calculation of the surface energy at room temperature for any coverage state by using the adsorption calorimetric data For gamma alumina, a close relationship between the water adsorption behavior and the surface energy was observed, evidencing that higher surface energies are associated with highly energetic dissociative behaviors of water and a continuous surface energy decrease upon water adsorption. Three adsorption stages were clearly observed from the combination of adsorption isotherm and microcalorimetric data, consistently with presented models.