Marathe R P
Department of Chemical and Biomolecular Engineering, National University of Singapore, 4 Engineering Drive 4, Singapore 117576.
J Colloid Interface Sci. 2005 Oct 1;290(1):69-75. doi: 10.1016/j.jcis.2005.04.009.
Energetic heterogeneity has been investigated for Engelhard titanium silicate Na-ETS-4 adsorbent and its Sr-exchanged variant, Sr-ETS-4. Na-ETS-4 was nearly homogeneous, while Sr exchange seemed to induce some degree of energetic heterogeneity in the sample, which diminished upon dehydration at higher temperature. Analysis of the entropy change during adsorption showed that the adsorbate molecules at low as well as moderate loading possess entropy greater than that predicted by the 2-D mobile film model, the excess being attributed to vibrational freedom. The wavelength of this vibration decreased with increasing coverage, as expected. For oxygen, the observed entropy drops in Na-ETS-4 and in Sr-ETS-4 are comparable, whereas, for nitrogen and methane, Sr exchange resulted in a greater entropy drop than in Na-ETS-4, suggesting greater restriction to movement in the Sr-exchanged sample. This study presents a simplistic yet effective understanding of the energetic behavior of the adsorbed molecules in ETS-4 adsorbent. This is vital to a thorough energetic characterization and study of the adsorption phenomenon in these new, promising adsorbents.
对恩格尔哈特钛硅酸盐Na-ETS-4吸附剂及其锶交换变体Sr-ETS-4的能量异质性进行了研究。Na-ETS-4几乎是均匀的，而锶交换似乎在样品中诱导了一定程度 的能量异质性，这种异质性在较高温度下脱水时会减弱。吸附过程中熵变的分析表明，低负载和中等负载下的吸附质分子的熵大于二维移动膜模型预测的熵， 多余的熵归因于振动自由度。如预期的那样，这种振动的波长随着覆盖率的增加而减小。对于氧气，在Na-ETS-4和Sr-ETS-4中观察到的熵降相当，而对于氮 气和甲烷，锶交换导致的熵降比在Na-ETS-4中更大，这表明在锶交换样品中分子运动受到的限制更大。这项研究对ETS-4吸附剂中吸附分子的能量行为提出了 一种简单而有效的理解。这对于全面表征这些新型有前景吸附剂的能量特性以及研究其吸附现象至关重要。
