Noria, a wheely Xe-selective porous cage solid

An interactive visualization of the chemical structure of a Noria molecule [1] is shown on the right. Noria, a white solid at room temperature, is a cyclic oligomer with a hole in its center. The structure of noria resembles a waterwheel; "Noria" is actually Latin for "waterwheel".

The pore in the center of the Noria molecule is so small that only a single gas molecule or atom, such as the noble gas, xenon, can fit inside. Because of favorable interactions with the walls of the pore in Noria, we showed that Noria acts like a sponge for xenon atoms. The pore in the center of Noria happens to be just the right size for snuggly fitting a xenon atom inside. We found that Noria will selectively adsorb xenon over krypton, another noble gas [2]. So, if we have a mixture of xenon and krypton, Noria will soak up the xenon but leave the krypton behind, effectively purifying the mixture. This separation of xenon and krypton is relevant in the reprocessing of used nuclear fuel.

We seek to reprocess used nuclear fuel to recover fissile material for recycling and to mitigate the amount of high-level radioactive waste that needs to be sequestered in some deep geological repository for thousands of years. In this process, radioactive noble gases xenon and krypton-- fission products-- evolve into the off-gases in parts per million concentrations. A material such as Noria may prove useful to selectively capture the xenon from this off-gas.

[1] H. Kudo, R. Hayashi, K. Mitani, T. Yokozawa, N.C. Kasuga, T. Nishikubo. Molecular waterwheel (Noria) from a simple condensation of resorcinol and an alkanedial. (2006) Angewandte Chemie. Full text

[2] R. Patil, D. Banerjee, C. Simon, J. Atwood, P. Thalapally. Noria, a highly Xe-selective Nanoporous Organic Solid. (2016) Chemistry - A European Journal. Full text