Room-temperature noble gas trapping with nanocages: size selectivity and retention longevity

Noble gases are a valuable but difficult to isolate natural resource with uses ranging from medical applications to detection of nuclear byproducts. Their industrial separation uses cryogenic distillation, an expensive and energy-intensive approach, creating interest in room-temperature noble gas trapping. Previous work established noble gas trapping in hexagonal prism-shaped silica cages supported on Ru via an activated encapsulation mechanism. However, only relatively large noble gases (Xe, Kr, and Ar) were trapped. Here we investigate the role of the relative sizes of nanocages and gas atoms for trapping. We deposited near monolayer coverages of either hexagonal prism or cubic silica cages on a Ru(0001) crystal using a Langmuir-Blodgett trough, removed the precursor’s organic moieties by calcining, and then reduced the metal. The cages were then exposed to a noble gas plasma, and the trapping was assessed using x-ray photoelectron spectroscopy. A comparison of noble gas retention longevity over a week shows that while both cubic and hexagonal cages trap and retain argon, xenon is excluded from the cubic cages, revealing size selectivity effects. These results are of interest to the development of room-temperature nanocage-based noble gas separation technologies.