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Noble gas xenon (Xe) is an excellent anesthetic gas, but its rarity, high cost and constrained production prohibits wide use in medicine. Here, we have developed a closed‐circuit anesthetic Xe recovery and reusage process with highly effective CO2‐specific adsorbent CUPMOF‐5 that is promising to solve the anesthetic Xe supply problem. CUPMOF‐5 possesses spacious cage cavities interconnected in four directions by confinement throat apertures of ~3.4 Å, which makes it an ideal molecular sieving of CO2 from Xe, O2, N2 with the benchmark selectivity and high uptake capacity of CO2. In situ single‐crystal X‐ray diffraction (SCXRD) and computational simulation solidly revealed the vital sieving role of the confined throat and the sorbent‐sorbate induced‐fit strengthening binding interaction to CO2. CUPMOF‐5 can remove 5 % CO2 even from actual moist exhaled anesthetic gases, and achieves the highest Xe recovery rate (99.8 %) so far, as verified by breakthrough experiments. This endows CUPMOF‐5 great potential for the on‐line CO2 removal and Xe recovery from anesthetic closed‐circuits. [ABSTRACT FROM AUTHOR]

Stimuli‐responsive physisorbents that undergo reversible structural transformations induced by external stimuli (e.g. light, guests, or heat) offer the promise of utility in gas storage and separation. Whereas reports on guest or light‐responsive sorbents have increased in recent years, we are unaware of reports on sorbents that exhibit both light and guest‐induced structural transformations. Herein, we report that the square lattice, sql, topology coordination network Zn(fba)(bis) ⋅ 2DMF (sql‐5,6‐Zn‐α, 5=trans‐4,4′‐bis(1‐imidazolyl)stilbene=bis, 6=2,2‐bis(4‐carboxyphenyl)hexafluoropropane=H2fba) underwent single‐crystal‐to‐single‐crystal transformation (SCSC) upon activation, affording nonporous sql‐5,6‐Zn‐β. Parallel alignment at 3.23 Å of olefinic moieties on adjacent bis ligands in sql‐5,6‐Zn‐α enabled SCSC [2+2] photocycloaddition upon exposure to UV light (365 nm) or sunlight. sql‐5,6‐Zn‐α thereby transformed to mot‐5,6‐Zn‐α, which was subsequently activated to the narrow pore phase mot‐5,6‐Zn‐β. sql‐5,6‐Zn‐β and mot‐5,6‐Zn‐β both exhibited S‐shaped adsorption isotherms characteristic of guest‐induced structural changes when exposed to CO2 at 195 K (type‐F–IV and type F–I, respectively). Cycling experiments conducted upon sql‐5,6‐Zn‐β reduced particle size after cycle 1 and induced transformation into a rare example of a shape memory coordination network, sql‐5,6‐Zn‐γ. Insight into this smorgasbord of SCSC phase changes was gained from in situ PXRD, single crystal XRD and 1H NMR spectroscopy experiments. [ABSTRACT FROM AUTHOR]

We report that linker ligand substitution involving just one atom induces a shape‐memory effect in a flexible coordination network. Specifically, whereas SIFSIX‐23‐Cu, [Cu(SiF6)(L)2]n, (L=1,4‐bis(1‐imidazolyl)benzene, SiF62−=SIFSIX) has been previously reported to exhibit reversible switching between closed and open phases, the activated phase of SIFSIX‐23‐CuN, [Cu(SiF6)(LN)2]n (LN=2,5‐bis(1‐imidazolyl)pyridine), transformed to a kinetically stable porous phase with strong affinity for CO2. As‐synthesized SIFSIX‐23‐CuN, α, transformed to less open, γ, and closed, β, phases during activation. β did not adsorb N2 (77 K), rather it reverted to α induced by CO2 at 195, 273 and 298 K. CO2 desorption resulted in α′, a shape‐memory phase which subsequently exhibited type‐I isotherms for N2 (77 K) and CO2 as well as strong performance for separation of CO2/N2 (15/85) at 298 K and 1 bar driven by strong binding (Qst=45–51 kJ/mol) and excellent CO2/N2 selectivity (up to 700). Interestingly, α′ reverted to β after re‐solvation/desolvation. Molecular simulations and density functional theory (DFT) calculations provide insight into the properties of SIFSIX‐23‐CuN. [ABSTRACT FROM AUTHOR]

Although pyrazine‐linked hybrid ultramicroporous materials (HUMs, pore size <7 Å) are benchmark physisorbents for trace carbon dioxide (CO2) capture under dry conditions, their affinity for water (H2O) mitigates their carbon capture performance in humid conditions. Herein, we report on the co‐adsorption of H2O and CO2 by TIFSIX‐3‐Ni—a high CO2 affinity HUM—and find that slow H2O sorption kinetics can enable CO2 uptake and release using shortened adsorption cycles with retention of ca. 90 % of dry CO2 uptake. Insight into co‐adsorption is provided by in situ infrared spectroscopy and ab initio calculations. The binding sites and sorption mechanisms reveal that both CO2 and H2O molecules occupy the same ultramicropore through favorable interactions between CO2 and H2O at low water loading. An energetically favored water network displaces CO2 molecules at higher loading. Our results offer bottom‐up design principles and insight into co‐adsorption of CO2 and H2O that is likely to be relevant across the full spectrum of carbon capture sorbents to better understand and address the challenge posed by humidity to gas capture. [ABSTRACT FROM AUTHOR]

The high energy footprint of commodity gas purification and increasing demand for gases require new approaches to gas separation. Kinetic separation of gas mixtures through molecular sieving can enable separation by molecular size or shape exclusion. Physisorbents must exhibit the right pore diameter to enable separation, but the 0.3–0.4 nm range relevant to small gas molecules is hard to control. Herein, dehydration of the ultramicroporous metal–organic framework Ca‐trimesate, Ca(HBTC)⋅H2O (H3BTC=trimesic acid), bnn‐1‐Ca‐H2O, affords a narrow pore variant, Ca(HBTC), bnn‐1‐Ca. Whereas bnn‐1‐Ca‐H2O (pore diameter 0.34 nm) exhibits ultra‐high CO2/N2, CO2/CH4, and C2H2/C2H4 binary selectivity, bnn‐1‐Ca (pore diameter 0.31 nm) offers ideal selectivity for H2/CO2 and H2/N2 under cryogenic conditions. Ca‐trimesate, the first physisorbent to exhibit H2 sieving under cryogenic conditions, could be a prototype for a general approach to exert precise control over pore diameter in physisorbents. [ABSTRACT FROM AUTHOR]

Purification of the C8 aromatics (xylenes and ethylbenzene) is particularly challenging because of their similar physical properties. It is also relevant because of their industrial utility. Physisorptive separation of C8 aromatics has long been suggested as an energy efficient solution but no physisorbent has yet combined high selectivity (>5) with high adsorption capacity (>50 wt %). Now a counterintuitive approach to the adsorptive separation of o‐xylene from other C8 aromatics involves the study of a known nonporous layered material, [Co(bipy)2(NCS)2]n (sql‐1‐Co‐NCS), which can reversibly switch to C8 aromatics loaded phases with different switching pressures and kinetics, manifesting benchmark o‐xylene selectivity (SOX/EB≈60) and high saturation capacity (>80 wt %). Structural insight into the observed selectivity and capacity is gained by analysis of the crystal structures of C8 aromatics loaded phases. [ABSTRACT FROM AUTHOR]

Abstract: Removal of CO2 from CO gas mixtures is a necessary but challenging step during production of ultra‐pure CO as processed from either steam reforming of hydrocarbons or CO2 reduction. Herein, two hybrid ultramicroporous materials (HUMs), SIFSIX‐3‐Ni and TIFSIX‐2‐Cu‐i, which are known to exhibit strong affinity for CO2, were examined with respect to their performance for this separation. The single‐gas CO sorption isotherms of these HUMs were measured for the first time and are indicative of weak affinity for CO and benchmark CO2/CO selectivity (>4000 for SIFSIX‐3‐Ni). This prompted us to conduct dynamic breakthrough experiments and compare performance with other porous materials. Ultra‐pure CO (99.99 %) was thereby obtained from CO gas mixtures containing both trace (1 %) and bulk (50 %) levels of CO2 in a one‐step physisorption‐based separation process. [ABSTRACT FROM AUTHOR]

Porous materials capable of selectively capturing CO2 from flue-gases or natural gas are of interest in terms of rising atmospheric CO2 levels and methane purification. Size-exclusive sieving of CO2 over CH4 and N2 has rarely been achieved. Herein we show that a crystal engineering approach to tuning of pore-size in a coordination network, [Cu(quinoline-5-carboxyate)2] n ( Qc-5-Cu) ena+bles ultra-high selectivity for CO2 over N2 (SCN≈40 000) and CH4 (SCM≈3300). Qc-5-Cu-sql-β, a narrow pore polymorph of the square lattice ( sql) coordination network Qc-5-Cu-sql-α, adsorbs CO2 while excluding both CH4 and N2. Experimental measurements and molecular modeling validate and explain the performance. Qc-5-Cu-sql-β is stable to moisture and its separation performance is unaffected by humidity. [ABSTRACT FROM AUTHOR]

Sequestration of CO2, either from gas mixtures or directly from air (direct air capture, DAC), could mitigate carbon emissions. Here five materials are investigated for their ability to adsorb CO2 directly from air and other gas mixtures. The sorbents studied are benchmark materials that encompass four types of porous material, one chemisorbent, TEPA-SBA-15 (amine-modified mesoporous silica) and four physisorbents: Zeolite 13X (inorganic); HKUST-1 and Mg-MOF-74/Mg-dobdc (metal–organic frameworks, MOFs); SIFSIX-3-Ni, (hybrid ultramicroporous material). Temperature-programmed desorption (TPD) experiments afforded information about the contents of each sorbent under equilibrium conditions and their ease of recycling. Accelerated stability tests addressed projected shelf-life of the five sorbents. The four physisorbents were found to be capable of carbon capture from CO2-rich gas mixtures, but competition and reaction with atmospheric moisture significantly reduced their DAC performance. [ABSTRACT FROM AUTHOR]

Organic polymers are usually amorphous or possess very low crystallinity. The metal complexes of organic polymeric ligands are also difficult to crystallize by traditional methods because of their poor solubilities and their 3D structures can not be determined by single-crystal X-ray crystallography owing to a lack of single crystals. Herein, we report the crystal structure of a 1D ZnII coordination polymer fused with an organic polymer ligand made in situ by a [2+2] cycloaddition reaction of a six-fold interpenetrated metal-organic framework. It is also shown that this organic polymer ligand can be depolymerized in a single-crystal-to-single-crystal (SCSC) fashion by heating. This strategy could potentially be extended to make a range of monocrystalline metal organopolymeric complexes and metal-organic organopolymeric hybrid materials. Such monocrystalline metal complexes of organic polymers have hitherto been inaccessible for materials researchers. [ABSTRACT FROM AUTHOR]