Uphill diffusion and overshooting in the adsorption of binary mixtures in nanoporous solids.
Uphill diffusion and overshooting in the adsorption of binary mixtures in nanoporous solids.
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DOI：
10.1038/ncomms8697
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发表时间：
2015-07-16
影响因子：
16.6
通讯作者：
Kärger J
中科院分区：
文献类型：
--
作者：
Lauerer A;Binder T;Chmelik C;Miersemann E;Haase J;Ruthven DM;Kärger J
在一定条件下，二元混合物在纳米多孔介质中吸附时，其中一种组分的浓度可能会暂时超过其平衡值。这意味着，与菲克定律相反，分子必须以增加而不是减少浓度的方向扩散。虽然这种“超调”现象以前已经被观察到，但直到最近，使用微成像技术，纳米多孔材料内部的扩散通量才可以直接观察到。在这里，我们报告了干涉显微镜的应用，以监测“上坡”通量，涵盖了从开始到最终平衡的整个超调期。结果表明，单组分扩散系数和二元吸附平衡数据可以很好地预测剖面的演化。所研究的客体分子（二氧化碳、乙烷和丙烯）和宿主材料（ZSM-58或DDR）对发展动态选择性吸附分离过程具有实际意义。在二元混合物在纳米多孔介质中的瞬态吸附过程中，其中一种组分的浓度可能会暂时超过其平衡值，分子沿浓度增加的方向扩散。在这里，作者使用微成像来检查这一过程在一个真实的系统。
Under certain conditions, during binary mixture adsorption in nanoporous hosts, the concentration of one component may temporarily exceed its equilibrium value. This implies that, in contrast to Fick's Law, molecules must diffuse in the direction of increasing rather than decreasing concentration. Although this phenomenon of ‘overshooting' has been observed previously, it is only recently, using microimaging techniques, that diffusive fluxes in the interior of nanoporous materials have become accessible to direct observation. Here we report the application of interference microscopy to monitor ‘uphill' fluxes, covering the entire period of overshooting from initiation until final equilibration. It is shown that the evolution of the profiles can be adequately predicted from the single-component diffusivities together with the binary adsorption equilibrium data. The guest molecules studied (carbon dioxide, ethane and propene) and the host material (ZSM-58 or DDR) are of practical interest in relation to the development of kinetically selective adsorption separation processes. During the transient adsorption of a binary mixture in a nanoporous host, the concentration of one component may temporarily exceed its equilibrium value, with molecules diffusing in the direction of increasing concentration. Here, the authors use microimaging to examine this process in a real system.