Nuclear energy is among the most viable alternatives to our current fossil fuel-based energy economy. The mass deployment of nuclear energy as a low-emissions source requires the reprocessing of used nuclear fuel to recover fissile materials and mitigate radioactive waste. A major concern with reprocessing used nuclear fuel is the release of volatile radionuclides such as xenon and krypton that evolve into reprocessing facility off-gas in parts per million concentrations. The existing technology to remove these radioactive noble gases is a costly cryogenic distillation; alternatively, porous materials such as metal–organic frameworks have demonstrated the ability to selectively adsorb xenon and krypton at ambient conditions. Here we carry out a high-throughput computational screening of large databases of metal–organic frameworks and identify SBMOF-1 as the most selective for xenon. We affirm this prediction and report that SBMOF-1 exhibits by far the highest reported xenon adsorption capacity and a remarkable Xe/Kr selectivity under conditions pertinent to nuclear fuel reprocessing.

The cryogenic separation of noble gases is energy-intensive and expensive, especially when low concentrations are involved. Metal-organic frameworks (MOFs) containing polarizing groups within their pore spaces are predicted to be efficient Xe/Kr solid-state adsorbents, but no experimental insights into the nature of the Xe-network interaction are available to date. Here we report a new microporous MOF (designated SBMOF-2) that is selective toward Xe over Kr under ambient conditions, with a Xe/Kr selectivity of about 10 and a Xe capacity of 27.07 wt % at 298 K. Single-crystal diffraction results show that the Xe selectivity may be attributed to the specific geometry of the pores, forming cages built with phenyl rings and enriched with polar -OH groups, both of which serve as strong adsorption sites for polarizable Xe gas. The Xe/Kr separation in SBMOF-2 was investigated with experimental and computational breakthrough methods. These experiments showed that Kr broke through the column first, followed by Xe, which confirmed that SBMOF-2 has a real practical potential for separating Xe from Kr. Calculations showed that the capacity and adsorption selectivity of SBMOF-2 are comparable to those of the best-performing unmodified MOFs such as NiMOF-74 or Co formate.

Used nuclear fuel reprocessing represents a unique challenge when dealing with radionuclides such as isotopes of Kr andI due to their volatility and long half-life. Efficient capture of I ( t = 15.7 × 10 years) from the nuclear waste stream can help reduce the risk of releasing I radionuclide into the environment and/or potential incorporation into the human thyroid. Metal organic frameworks have the reported potential to be I adsorbents but the effect of water vapor, generally present in the reprocessing off-gas stream, is rarely taken into account. Moisture-stable porous metal organic frameworks that can selectively adsorb I in the presence of water vapor are thus of great interest. Herein, we report on the I adsorption capacity of two microporous metal organic frameworks at both dry and humid conditions. Single-crystal X-ray diffraction and Raman spectroscopy reveal distinct sorption sites of molecular I within the pores in proximity to the phenyl- and phenol-based linkers stabilized by the I···π and I···O interactions, which allow selective uptake of iodine.

The adsorption mechanism of ethane, ethylene and acetylene (C 2 H n ; n=2, 4, 6) on two microporous metal organic frameworks (MOFs) is described here that is consistent with observations from single crystal and powder X-ray diffraction, calorimetric measurments and gas adsorption isotherm measurements. Two calcium-based MOFs, designated as SBMOF-1 and SBMOF-2 (SB: Stony Brook), form three-dimensional frameworks with one-dimensional open channels. As determined form single crystal diffraction experiments channel geometries of both SBMOF-1 and SBMOF-2 provide multiple adsorption sites for hydrocarbon molecules trough C-H … π and C-H … O interactions, similarly to interactions in the molecular and protein crystals. Both materials selectively adsorb C 2 hydrocarbon gases over methane as determined with IAST and breakthrough calculations as well as experimental breakthrough measurements, with C 2 H 6 /CH 4 selectivity as high as 74 in SBMOF-1.

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