PDF(Pubmed)
Abstract：
Type III porous liquids (PLs) consist of porous solid particles dispersed in a size-excluded liquid phase and are attracting much attention as novel media for applications such as gas separation. However, the effects of fundamental variables such as particle size on their physical properties are currently largely unknown. Here we study the effects of particle size in a series of porous liquids based on solid Al(OH)(fumarate) (a microporous metal-organic framework, MOF) with particle sizes of 60 nm, 200-600 nm, or 800-1000 dispersed in liquid polydimethylsiloxane (PDMS). Properties examined include physical stability of the dispersion, viscosity, total CO2 uptake, and kinetics of CO2 uptake. As expected, both physical stability and viscosity decreased with increasing particle size. Unexpectedly, total gravimetric gas uptake also varied with particle size, being greatest for the largest particles, which we ascribe to larger particles having a lower relative content of surface-bound FMA ligands. Various models for the gas uptake kinetic data were considered, specifically adsorption reaction models such as pseudo-first-order, pseudo-second-order, and Elovich models. In contrast to pure PDMS, which showed first-order kinetics, all PLs fit best to the Elovich model confirming that their uptake mechanism is more complex than for a simple liquid. Adsorption diffusion models, specifically Weber and Morris\' intraparticle model and Boyd\'s model, were also applied which revealed a three-step process in which a combination of diffusion through a surface layer and intraparticle diffusion were rate-limiting. The rate of gas uptake follows the order PDMS < PL1 < PL2 < PL3, showing that the porous liquids take up gas more rapidly than does PDMS and that this rate increases with particle size. Overall, the study suggests that for high gas uptake and fast uptake kinetics, large particles may be preferred. Also, the fact that large particles resulted in low viscosity may be advantageous in reducing the pumping energy needed in flow separation systems. Therefore, the work suggests that finding ways to stabilize PLs with large particles against phase separation could be advantageous for optimizing the properties of PLs toward applications.
摘要：
III型多孔液体(PL)由分散在尺寸排除的液相中的多孔固体颗粒组成,并且作为用于诸如气体分离的应用的新型介质吸引了很多关注。然而,颗粒大小等基本变量对其物理性质的影响目前在很大程度上是未知的。在这里，我们研究了基于固体Al（OH）（富马酸酯）（一种微孔金属有机骨架，MOF)粒径为60nm,200-600nm,或800-1000分散在液体聚二甲基硅氧烷（PDMS）。检查的性质包括分散体的物理稳定性，粘度,总CO2吸收，和二氧化碳吸收动力学。不出所料,物理稳定性和粘度均随粒径的增加而降低。出乎意料的是,总重量气体吸收也随颗粒大小而变化，对最大的粒子来说是最大的，我们将其归因于具有较低相对含量的表面结合的FMA配体的较大颗粒。考虑了气体吸收动力学数据的各种模型，特别是吸附反应模型，如伪一级，伪二阶，还有Elovich的模特.与纯PDMS相比,显示了一级动力学，所有PLs最符合Elovich模型，证实它们的摄取机制比简单液体更复杂。吸附扩散模型，特别是韦伯和莫里斯的内部模型和博伊德的模型，也被应用，这揭示了一个三步过程，其中通过表面层的扩散和粒子内扩散的组合是限速的。气体吸收速率遵循PDMS
