Opening the Gate:Framework Flexibility in ZIF-8 Explored by Experiments and Simulations

ZIF-8 is a zeolitic imidazole-based metal-organic framework with large cavities interconnected by narrow windows. Because the small size of the windows, it allows in principle for molecular sieving of gases such as H-2 and CH4. However, the unexpected adsorption of large molecules on ZIF-8 suggests the existence of structural flexibility. ZIF-8 flexibility is explored in this work combining different experimental techniques with molecular simulation. We show that the ZIF-8 structure is modified by gas adsorption uptake in the same way as it is at a very high pressure (i.e., 14 700 bar) due to a swing effect in the imidazolate linkers, giving access to the porosity. Tuning the flexibility, and so the opening of the small windows, has a further impact on the design of advanced molecular sieving membrane materials for gas separation, adjusting the access of fluids to the porous network.</p

Selective CO₂ capture in metal-organic frameworks with azine-functionalized pores generated by mechanosynthesis

Two new three-dimensional porous Zn(II)-based metal-organic frameworks, containing azine-functionalized pores, have been readily and quickly isolated via mechanosynthesis, by using a nonlinear dicarboxylate and linear N-donor ligands. The use of nonfunctionalized and methyl-functionalized N-donor ligands has led to the formation of frameworks with different topologies and metal-ligand connectivities and therefore different pore sizes and accessible volumes. Despite this, both metal-organic frameworks (MOFs) possess comparable BET surface areas and CO₂ uptakes at 273 and 298 K at 1 bar. The network with narrow and interconnected pores in three dimensions shows greater affinity for CO compared to the network with one-dimensional and relatively large pores-attributable to the more effective interactions with the azine groups

Three-dimensional lanthanide-organic frameworks based on di-, tetra-, and hexameric clusters

Three-dimensional lanthanide-organic frameworks formulated as (CH3)2NH2[Ln(pydc)2] · 1/2H2O [Ln3+ ) Eu3+ (1a) or Er3+ (1b); pydc2- corresponds to the diprotonated residue of 2,5-pyridinedicarboxylic acid (H2pydc)], [Er4(OH)4(pydc)4(H2O)3] ·H2O (2), and [PrIII 2PrIV 1.25O(OH)3(pydc)3] (3) have been isolated from typical solvothermal (1a and 1b in N,N-dimethylformamide - DMF) and hydrothermal (2 and 3) syntheses. Materials were characterized in the solid state using single-crystal X-ray diffraction, thermogravimetric analysis, vibrational spectroscopy (FT-IR and FT-Raman), electron microscopy, and CHN elemental analysis. While synthesis in DMF promotes the formation of centrosymmetric dimeric units, which act as building blocks in the construction of anionic ∞ 3{[Ln(pydc)2]-} frameworks having the channels filled by the charge-balancing (CH3)2NH2 + cations generated in situ by the solvolysis of DMF, the use of water as the solvent medium promotes clustering of the lanthanide centers: structures of 2 and 3 contain instead tetrameric [Er4(μ3-OH)4]8+ and hexameric |Pr6(μ3-O)2(μ3-OH)6| clusters which act as the building blocks of the networks, and are bridged by the H2-xpydcx- residues. It is demonstrated that this modular approach is reflected in the topological nature of the materials inducing 4-, 8-, and 14-connected uninodal networks (the nodes being the centers of gravity of the clusters) with topologies identical to those of diamond (family 1), and framework types bct (for 2) and bcu-x (for 3), respectively. The thermogravimetric studies of compound 3 further reveal a significant weight increase between ambient temperature and 450 °C with this being correlated with the uptake of oxygen from the surrounding environment by the praseodymium oxide inorganic core

Diffusion of H-2, CO2, and Their Mixtures in the Porous Zirconium Based Metal Organic Framework MIL-140A(Zr): Combination of Quasi-Elastic Neutron Scattering Measurements and Molecular Dynamics Simulations

SSCI-VIDE+ATARI+HJOInternational audienceThe diffusivity of H-2 and CO2 in the small pore Zr based metalorganic framework (MOF) MIL-140A(Zr) has been evaluated using a combination of quasi-elastic neutron scattering measurements and molecular dynamics simulations. These two techniques were used to determine the self-diffusivities of H-2, and the corrected and transport diffusivities of CO2, as single components and binary mixture. H-2 was shown to be the faster of the two gases to diffuse through the narrow triangular channel of MIL-140A(Zr), its self-diffusivity value being 1 order of magnitude higher than that of CO2, at the same temperature. In this case, although no specific interaction sites are present, the CO2 interacts more strongly with the pore wall than H-2, partly a consequence of its greater kinetic radius, which renders it slower than H-2. In the context of a binary mixture, H-2 still diffuses faster between the two, although with a slightly lower self-diffusivity, while that of CO2 increases slightly. However, the difference in terms of order of magnitude is not altered and makes MIL-140A(Zr) a potential candidate for H-2/CO2 separation based on kinetics

Multifaceted study of the interactions between CPO-27-Ni and polyurethane and their impact on nitric oxide release performance

S.M.V. would like to thank the EPSRC for funding opportunities under grant agreement EP/K005499/1. S.M.V. and D.N.M. would further like to acknowledge the EPSRC Capital for Great Technologies grant (EP/L017008/1) and the EPSRC Strategic Equipment Resource grant (EP/R023751) for funding and supporting electron microscopy facilities at the University of St Andrews. M.J.D. and S.J.W. would like to acknowledge the ProDIA project that has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 685727.A multifaceted study involving focused ion beam scanning electron microscopy techniques, mechanical analysis, water adsorption measurements, and molecular simulations is employed to rationalize the nitric oxide release performance of polyurethane films containing 5, 10, 20, and 40 wt % of the metal-organic framework (MOF) CPO-27-Ni. The polymer and the MOF are first demonstrated to exhibit excellent compatibility. This is reflected in the even distribution and encapsulation of large wt % MOF loadings throughout the full thickness of the films and by the rather minimal influence of the MOF on the mechanical properties of the polymer at low wt %. The NO release efficiency of the MOF is attenuated by the polymer and found to depend on wt % of MOF loading. The formation of a fully connected network of MOF agglomerates within the films at higher wt % is proposed to contribute to a more complex guest transport in these formulations, resulting in a reduction of NO release efficiency and film ductility. An optimum MOF loading of 10 wt % is identified for maximizing NO release without adversely impacting the polymer properties. Bactericidal efficacy of released NO from the films is demonstrated against Pseudomonas aeruginosa, with a >8 log10 reduction in cell density observed after a contact period of 24 h.Publisher PDFPeer reviewe

Adsorption of Small Molecules in the Porous Zirconium-Based Metal Organic Framework MIL-140A (Zr): A Joint Computational-Experimental Approach

International audienceThe adsorption of small molecules (CO2, CO, H-2, CH4, and N-2) in a small pore zirconium terephthalate MOF was explored by combining quantum and force-field-based molecular simulations and experiments. The Density Functional Theory strategy was first validated by a very good agreement between the predicted and the experimental spectroscopic (infrared, NMR) and structural features of the selected MOF. These quantum calculations further predicted the preferential adsorption sites and the strength of the host/guest interactions for all confined molecules. These conclusions were favorably compared to force field-based Monte Carlo simulations and microcalorimetry measurements. The water stability of this hybrid porous solid was equally explored as well as the interaction between the MOF and a well-known gas pollutant, that is, H2S

Exploration of the Long-Chain N-Alkanes Adsorption and Diffusion in the MOF-Type MIL-47 (V) Material by Combining Experimental and Molecular Simulation Tools

International audienceThe adsorption properties of linear long chain alkanes (from n-pentane to n-nonane) within the rigid MOF MIL-47 (V) have been explored by combining gravimetry measurements and molecular simulations. Both experimental absolute isotherms and enthalpies of adsorption for all n-alkanes were compared with those obtained by configurational bias grand canonical Monte Carlo simulations (CB-GCMC) based on two different force fields. From a fair agreement between experimental and simulated data, a further step consisted of investigating the microscopic adsorption mechanism in play to shed some light onto the preferential orientations and conformations of all investigated n-alkanes. Whereas the trans conformation is predominantly observed for all n-alkanes, the proportion of the n-alkane conformations lying parallel to the direction of the tunnel significantly increases with the chain length, emphasizing that the confinement effect is stronger for the longer chain n-alkanes. Finally, molecular dynamics simulations allowed us to emphasize that all n-alkanes follow a pathway along the direction of the tunnel, leading to a 1D type diffusion mechanism, the motions being mainly centered around the middle of the pores at low loading, whereas they are significantly shifted toward the pore wall when the alkane concentration increases

Diffusion of H₂, CO₂, and Their Mixtures in the Porous Zirconium Based Metal–Organic Framework MIL-140A(Zr): Combination of Quasi-Elastic Neutron Scattering Measurements and Molecular Dynamics Simulations

The diffusivity of H₂ and CO₂ in the small pore Zr based metal–organic framework (MOF) MIL-140A­(Zr) has been evaluated using a combination of quasi-elastic neutron scattering measurements and molecular dynamics simulations. These two techniques were used to determine the self-diffusivities of H₂, and the corrected and transport diffusivities of CO₂, as single components and binary mixture. H₂ was shown to be the faster of the two gases to diffuse through the narrow triangular channel of MIL-140A­(Zr), its self-diffusivity value being 1 order of magnitude higher than that of CO₂, at the same temperature. In this case, although no specific interaction sites are present, the CO₂ interacts more strongly with the pore wall than H₂, partly a consequence of its greater kinetic radius, which renders it slower than H₂. In the context of a binary mixture, H₂ still diffuses faster between the two, although with a slightly lower self-diffusivity, while that of CO₂ increases slightly. However, the difference in terms of order of magnitude is not altered and makes MIL-140A­(Zr) a potential candidate for H₂/CO₂ separation based on kinetics