Understanding the Adsorption Mechanism of Xe and Kr in a Metal-Organic Framework from X-ray Structural Analysis and First-Principles Calculations.

Enhancement of adsorption capacity and separation of radioactive Xe/Kr at room temperature and above is a challenging problem. Here, we report a detailed structural refinement and analysis of the synchrotron X-ray powder diffraction data of Ni-DODBC metal organic framework with in situ Xe and Kr adsorption at room temperature and above. Our results reveal that Xe and Kr adsorb at the open metal sites, with adsorption geometries well reproduced by DFT calculations.

Potential of metal-organic frameworks for separation of xenon and krypton.

CONSPECTUS: The total world energy demand is predicted to rise significantly over the next few decades, primarily driven by the continuous growth of the developing world. With rapid depletion of nonrenewable traditional fossil fuels, which currently account for almost 86% of the worldwide energy output, the search for viable alternative energy resources is becoming more important from a national security and economic development standpoint. Nuclear energy, an emission-free, high-energy-density source produced by means of controlled nuclear fission, is often considered as a clean, affordable alternative to fossil fuel.

Separation of rare gases and chiral molecules by selective binding in porous organic cages.

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. Likewise, chiral molecules are important building blocks for pharmaceuticals, but chiral enantiomers, by definition, have identical size and shape, and their separation can be challenging.

Enhanced noble gas adsorption in Ag@MOF-74Ni.

Various amounts of Ag nanoparticles were successfully deposited in porous MOF-74Ni (or Ni/DOBDC) by an auto-reduction method. An optimized silver-loaded MOF-74Ni was shown to have an improved Xe adsorption capacity (15% more) at STP compared to the MOF without silver nanoparticles. The silver-loaded sample also has a higher Xe/Kr selectivity.

Switching Kr/Xe selectivity with temperature in a metal-organic framework.

Krypton (Kr) and xenon (Xe) adsorption on two partially fluorinated metal-organic frameworks (FMOFCu and FMOFZn) with different cavity size and topologies are reported. FMOFCu shows an inversion in sorption selectivity toward Kr at temperatures below 0 °C while FMOFZn does not. The 1D microtubes packed along the (101) direction connected through small bottleneck windows in FMOFCu appear to be the reason for this peculiar behavior.