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The capture of the xenon and krypton from nuclear reprocessing off‐gas is essential to the treatment of radioactive waste. Although various porous materials have been employed to capture Xe and Kr, the development of high‐performance adsorbents capable of trapping Xe/Kr at very low partial pressure as in the nuclear reprocessing off‐gas conditions remains challenging. Herein, we report a self‐adjusting metal‐organic framework based on multiple weak binding interactions to capture trace Xe and Kr from the nuclear reprocessing off‐gas. The self‐adjusting behavior of ATC‐Cu and its mechanism have been visualized by the in‐situ single‐crystal X‐ray diffraction studies and theoretical calculations. The self‐adjusting behavior endows ATC‐Cu unprecedented uptake capacities of 2.65 and 0.52 mmol g−1 for Xe and Kr respectively at 0.1 bar and 298 K, as well as the record Xe capture capability from the nuclear reprocessing off‐gas. Our work not only provides a benchmark Xe adsorbent but proposes a new route to construct smart materials for efficient separations. [ABSTRACT FROM AUTHOR]

Xenon is known to be a very efficient anesthetic gas, but its cost prohibits the wider use in medical industry and other potential applications. It has been shown that Xe recovery and recycling from anesthetic gas mixtures can significantly reduce its cost as anesthetic. The current technology uses series of adsorbent columns followed by low-temperature distillation to recover Xe; this method is expensive to use in medical facilities. Herein, we propose a much simpler and more efficient system to recover and recycle Xe from exhaled anesthetic gas mixtures at room temperature using metal-organic frameworks (MOFs). Among the MOFs tested, PCN-12 exhibits unprecedented performance with high Xe capacity and Xe/O2, Xe/N2 and Xe/CO2 selectivity at room temperature. The in situ synchrotron measurements suggest that Xe is occupies the small pockets of PCN-12 compared to unsaturated metal centers (UMCs). Computational modeling of adsorption further supports our experimental observation of Xe binding sites in PCN-12. [ABSTRACT FROM AUTHOR]

Considering the rapidly rising CO2 level, there is a constant need for versatile materials which can selectively adsorb CO2 at low cost. The quest for efficient sorptive materials is still on since the practical applications of conventional porous materials possess certain limitations. In that context, we designed, synthesized, and characterized two novel supramolecular organic frameworks based on C-pentylpyrogallol[4]arene (PgC5) with spacer molecules, such as 4,4′-bipyridine (bpy). Highly optimized and symmetric intermolecular hydrogen-bonding interactions between the main building blocks and comparatively weak van der Waals interactions between solvent molecules and PgC5 leads to the formation of robust extended frameworks, which withstand solvent evacuation from the crystal lattice. The evacuated framework shows excellent affinity for carbon dioxide over nitrogen and adsorbs ca. 3 wt % of CO2 at ambient temperature and pressure. [ABSTRACT FROM AUTHOR]

The effective separation of small hydrocarbon molecules (C1– C4) is an important process for the petroleum industry, determining the end price of many essential commodities in our daily lives. Current technologies for separation of these molecules rely on energy-intensive fractional distillation processes at cryogenic temperature, which is particularly difficult because of their similar volatility. In retrospect, adsorptive separation using solid-state adsorbents might be a cost-effective alternative. Several types of solid-state adsorbents (e.g., zeolite molecular sieves) were tested for separation of small hydrocarbon molecules as a function of pressure, temperature, or vacuum. Among different types of plausible adsorbents, metal organic frameworks (MOFs), a class of porous, crystalline, inorganic-organic hybrid materials, is particularly promising. In this brief comment article, we discuss the separation properties of different types of solid-state adsorbents, with a particular emphasis on MOF-based adsorbents for separation of C2hydrocarbon molecules. [ABSTRACT FROM AUTHOR]

In this review, we describe recent efforts to systematically study nano-structured metal organic frameworks (MOFs), also known as metal organic heat carriers, with particular emphasis on their application in heating and cooling processes. We used both molecular dynamics and grand canonical Monte Carlo simulation techniques to gain a molecular-level understanding of the adsorption mechanism of gases in these porous materials. We investigated the uptake of various gases such as refrigerants R12 and R143a. We also evaluated the effects of temperature and pressure on the uptake mechanism. Our computed results compared reasonably well with available measurements from experiments, thus validating our potential models and approaches. In addition, we investigated the structural, diffusive and adsorption properties of different hydrocarbons in Ni2(dhtp). Finally, to elucidate the mechanism of nanoparticle dispersion in condensed phases, we studied the interactions among nanoparticles in various liquids, such asn-hexane, water and methanol. [ABSTRACT FROM PUBLISHER]

Organic solids composed by weak van der Waals forces are attracting considerable attention owing to their potential applications in gas storage, separation and sensor applications. Herein we report a gas-induced transformation that remarkably converts the high-density guest-free form of a well-known organic host (p-tert-butylcalix[4]arene) to a low-density form and vice versa, a process that would be expected to involve surmounting a considerable energy barrier. This transformation occurs despite the fact that the high-density form is devoid of channels or pores. Gas molecules seem to diffuse through the non-porous solid into small lattice voids, and initiate the transition to the low-density kinetic form with ∼10% expansion of the crystalline organic lattice, which corresponds to absorption of CO2 and N2O (refs 4,5). This suggests the possibility of a more general phenomenon that can be exploited to find more porous materials from non-porous organic and metal–organic frameworks that possess void space large enough to accommodate the gas molecules. [ABSTRACT FROM AUTHOR]

Two novel cadmium–organic frameworks containing achiral helical nanotubular channels, [Cd(HImDC)(S)]n(S = Im(1) and Py(2)), have been synthesized and characterized using single crystal X-ray diffraction, in which 1converts to 2upon refluxing 1 in pyridine solution with noticeable porosity and hydrogen uptake at medium pressure. [ABSTRACT FROM AUTHOR]

Herein we followed the structural evolution of a prototypical type of porous organic cage, CC3, as a function of synthesis time. Three distinctive crystal formation stages were identified: at short synthesis times, a rapid crystal growth stage in which amorphous agglomerates transformed into larger irregular particles was observed. At intermediate synthesis times, a decrease in crystal size over time was observed presumably due to crystal fragmentation, redissolution, and/or homogeneous nucleation. Finally, at longer synthesis times, a regrowth process was observed in which particles coalesced through Ostwald ripening leading to a continuous increase in crystal size. Molecular simulation studies, based on the construction of in silico CC3 models and simulation of XRD patterns and nitrogen isotherms, confirm the samples at different synthesis times to be a mixture of CC3α and CC3-amorphous phases. The CC3α phase is found to contract at different synthesis times, and the amorphous phase is found to essentially disappear at the longest synthesis time. Nitrogen and carbon dioxide adsorption properties of these CC3 phases were evaluated, and were highly dependent on synthesis time. [ABSTRACT FROM AUTHOR]

A previously known class of porous coordination polymer (PCP) of formula [Cu(bpy-n)2(SiF6)] (bpy-1 = 4,4'-bipyridine; bpy-2 = 1,2-bis(4-pyridyl)ethene) has been studied to assess its selectivity toward CO2, CH4, N2, and H2O. Gas sorption measurements reveal that [Cu(bpy-1)2(SiF6)] exhibits the highest uptake for CO2 yet seen at 298 K and 1 atm by a PCP that does not contain open metal sites. Significantly, [Cu(bpy-1)2(SiF6)] does not exhibit particularly high uptake under the same conditions for CH4, N2, and, H2O, presumably because of its lack of open metal sites. Consequently, at 298 K and 1 atm [Cu(bpy-1)2(SiF6)] exhibits a relative uptake of CO2 over CH4 of ca. 10.5:1, the highest value experimentally observed in a compound without open metal sites. [Cu(bpy-2)2(SiF6)] exhibits larger pores and surface area than [Cu(bpy-1)2(SiF6)] but retains a high CO2/CH4 relative uptake of ca. 8:1. [ABSTRACT FROM AUTHOR]