The separation of molecules with similar size and shape is an important technological challenge. For example, rare gases can pose either an economic opportunity or an environmental hazard and there is a need to separate these spherical molecules selectively at low concentrations in air. Radon gas, which occurs naturally in a radioactive form (222Rn), can accumulate in buildings, and is a leading cause of lung cancer, accounting for around 21,000 deaths per year in the USA alone. Rare gases are difficult to be separated from one another due to their lack of reactivity and the small size difference between the higher-mass rare gases, such as xenon (4.10 Å) and radon (4.17 Å). It can be a greater challenge to capture the rare gases from air, in which they are commonly encountered at concentrations of only a few parts per million (with the exception of argon). Likewise, many chemical analyses rely on the separation of complex mixtures by chromatography, which is an important process for characterizing and purifying organic molecules, but some mixtures remain challenging to separate.
Here we show that a porous organic cage molecule has unprecedented performance in the solid state for the separation of rare gases, such as krypton and xenon. The selectivity arises from a precise size match between the rare gas and the organic cage cavity, as predicted by molecular simulations. Breakthrough experiments demonstrate real practical potential for the separation of krypton, xenon, and radon from air at concentrations of only a few parts per million. We also show that porous organic cage-coated capillary columns can perform gas chromatography separations of organic molecules, such as alkanes, aromatic compounds, and racemic mixtures. The solution processability of porous organic cages, combined with the ability to tailor their pore size by modular assembly, makes them interesting as promising stationary phase for otherwise difficult separations...
Session: G15 - Gaseous Compounds Separation
Day: 13 October 2016
Time: 14:45 - 16:00 h