School of Chemistry and Chemical Engineering, Queen's University Belfast, David Keir Building, Stranmillis Road, Belfast BT9 5AG, UK.
School of Mathematics and Physics, Queen's University Belfast, University Road, Belfast BT7 1NN, UK.
Nature. 2015 Nov 12;527(7577):216-20. doi: 10.1038/nature16072.
Porous solids such as zeolites and metal-organic frameworks are useful in molecular separation and in catalysis, but their solid nature can impose limitations. For example, liquid solvents, rather than porous solids, are the most mature technology for post-combustion capture of carbon dioxide because liquid circulation systems are more easily retrofitted to existing plants. Solid porous adsorbents offer major benefits, such as lower energy penalties in adsorption-desorption cycles, but they are difficult to implement in conventional flow processes. Materials that combine the properties of fluidity and permanent porosity could therefore offer technological advantages, but permanent porosity is not associated with conventional liquids. Here we report free-flowing liquids whose bulk properties are determined by their permanent porosity. To achieve this, we designed cage molecules that provide a well-defined pore space and that are highly soluble in solvents whose molecules are too large to enter the pores. The concentration of unoccupied cages can thus be around 500 times greater than in other molecular solutions that contain cavities, resulting in a marked change in bulk properties, such as an eightfold increase in the solubility of methane gas. Our results provide the basis for development of a new class of functional porous materials for chemical processes, and we present a one-step, multigram scale-up route for highly soluble 'scrambled' porous cages prepared from a mixture of commercially available reagents. The unifying design principle for these materials is the avoidance of functional groups that can penetrate into the molecular cage cavities.
多孔固体，如沸石和金属有机骨架，在分子分离和催化中很有用，但它们的固态可能会带来限制。例如，液体溶剂而不是多孔固体，是最成熟的燃烧后二氧化碳捕集技术，因为液体循环系统更容易改装到现有的工厂。固体多孔吸附剂具有重大优势，例如在吸附-解吸循环中能量损失较低，但它们在传统的流动工艺中很难实施。因此，结合流动性和永久孔隙率的材料可能具有技术优势，但永久孔隙率与传统液体无关。在这里，我们报告了能够自由流动的液体，其整体性质由其永久孔隙率决定。为了实现这一目标，我们设计了笼状分子，这些分子提供了明确的孔径，并且在其分子过大而无法进入孔的溶剂中具有很高的溶解度。因此，未占据笼的浓度可以比其他含有空腔的分子溶液高约 500 倍，从而导致整体性质发生明显变化，例如甲烷气体的溶解度增加八倍。我们的研究结果为化学过程中开发一类新的功能性多孔材料提供了基础，并提出了一种从商业可得试剂的混合物中制备高溶解度“混合”多孔笼的一步、多克规模放大途径。这些材料的统一设计原则是避免能够穿透分子笼腔的功能基团。
