Tuning the gating energy barrier of metal-organic framework for molecular sieving

•Distinguishing gating and pore-opening actions of flexible adsorbents•Tuning energy barrier avoiding pore opening for molecular sieving•Molecular sieving CO2/N2 CO2/CH4•Role host-guest interaction at the moment Molecular sieving, relying on simple size exclusion mechanism, is ideal adsorptive separation. While guest diffusion are generally judged by pore/aperture molecule sizes, precise determination these parameters impossible due to quantum effect unavoidable flexibility system. The action, a classic type adsorbent based structural transformation equilibrium states, has been regarded as strategy achieving but its role performance controversial, particularly co-adsorption problem. an unconventional transient variation non-equilibrium important in narrow pores usually overlooked. We show that can be controlled also important. separation controversial. Here, we flexibility, used achieve sieving. Two isostructural metal-organic frameworks possessing quasi-discrete/gating designed synthesized, which allow CO2 adsorption from extremely low pressures. Adding amino group organic ligand strengthens intra-framework hydrogen bonding, increases completely block N2 CH4 with larger giving record-high CO2/CH4 selectivities. C2 C3 hydrocarbons than induce significantly different pressures implying C2H4/C2H6 C3H6/C3H8 Quantitative mixture breakthrough experiments first example switchable preference, reveal co-adsorption. Computational simulation situ single-crystal/powder X-ray diffraction absence presence responsible co-adsorption, respectively. Offering ultrahigh selectivity,1Barrer R. Zeolites & Clay Minerals Sorbents Sieves. Academic Press, 1978Google Scholar,2Yang R.T. Adsorbents: Fundamentals Applications. John Wiley Sons, Inc., 2003Crossref Google Scholar solving chemical challenges.3Sholl D.S. Lively R.P. 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Note conventional there no rational Ea.35Evans construct MOF [Zn3(OH)2(pzdc)(tz)]·DMA (1·DMA, H3pzdc = 3,5-pyrazoledicarboxylic acid, Htz 1,2,4-trizole, DMA N,N-dimethylacetamide) quasi-discrete 2A; Table S1), testing concept 1, two crystallography independent Zn2+ ions adopt either tetrahedral trigonal bipyramidal geometry. Each tz?, pzdc3?, OH? coordinates three, five, ions, respectively, complicated three-dimensional (3D) network, topological analysis. Alternatively, network might described parallelly aligned Zn2(pzdc) ribbons interconnected Zn(OH)2 units tz? ligands S1). There cavities (8.4 × 7.0 4.2 Å3) small apertures (4.0 2.1 Å2 along a-axis 3.6 2.4 b-axis) 1 S2). accommodate while serve gates diffusion.33Zhang Scholar,39Gu Considering abundant polar sites surface introducing hydrogen-bonding functional groups this increase attraction enhance barrier. adding convenient approach, amino-functionalized [Zn3(OH)2(pzdc)(atz)]·DMA (2?DMA, Hatz 3-amino-1,2,4-trizole) was successfully synthesized (cavity 7.8 6.8 4.4 Å3, 4.0 3.7 1.3 Å2, Figure 2C; Tables S1 Thermogravimetry, powder (PXRD), single-crystal (SCXRD) studies showed 1·DMA retained (Figures 2B S2–S4; unit-cell volume just 1.3% 1?DMA (Table contrast, gives guest-free [Zn3(OH)2(pzdc)(atz)] (2?) 18.7% reduced 7.5 4.8 3.8 2.5 1.0 0.8 Figures 2D, S4–S6; S2), accompanying reconstitution bonds S7). bond formed –NH2 2? 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Karakoti Bahadur Yi Zhao AlBahily Vinu Emerging trends conversion.Chem. 49: 4360-4404Crossref uptakes arise rather thermodynamic effect. indicate action. expand 2 adsorbing suitably guests, it comparing actions. Single-component C2H4, C2H6, C3H6, C3H8 measured 4A S39). C3H8, largest, excluded, C3H6 typical isotherm shapes (two steps) characteristic nonporous/small-pore state large-pore state,25Wang being quite (one step) stays small-pore state. inflection points 26, 15, kPa, could almost reach atm. Furthermore, smallest, adsorbed below point, although slope small. context diameter, C2H4 N2/CH4, indicates requires and/or furnish adsorption. Grand canonical Monte Carlo (GCMC) simulations, omit diffusion/kinetic processes, CO2, molecules S4), consistent well low-pressure slopes C3H8. inconsistencies results experimental should attributed On hand, 2, 2?, confirming expansion prerequisite Periodic density theory (PDFT) calculations normal binding orders > N2/CH4 2?. follows C2H6 S4). 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SCXRD sealed S55 S56; S57). confirm CO2/CH4/N2 behaviors C2H4/C2H6/C3H6/C3H8 2. study actual quantitative column performed 10:90 CO2/N2, CO2/He mixtures 5). experiment three times, gave overlapped curves indicative stability S58). outflow beginning together, occurs later 5), ignored like non-adsorbing He. calculated 1.556(2) 1.556(1) g?1, S7), matching 0.1 (1.55 g?1). 0.002(6) 0.009(10) CO2/CH4. purity before 99.999%+ S59), given adsorbents. decrease 273–298 (the usual trend physisorption) (temperature-dependent diffusion-controlled sorption), optimum uptake, Nevertheless, since already near saturation, lowering cannot selectivity. Using same column, further 50:50 pure 6). time ? < simulations. 0.71 1.35 6A), C2H6/C2H4 1.9 showing preferential over C2H4.48Lin Tang X.L. Gao Cui Boosting ethane/ethylene within isoreticular 12940-12946Crossref (237) Scholar,49Li R.-B. 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More importantly, contrasting demonstrated possibility effect, ones. noted values electrons less nature molecules/materials. radii, distance useful determinative references judging critical evaluating diffusion, adsorption, principle, play role. measurement/simulation still challenging. integrated MOF, selectively activated pressure. separation, simulation, convincing evidences existence opening, comprehensive exclusion, shed utilization