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M Infas H Mohideen,
Bo Xiao,
Paul S Wheatley,
Alistair C McKinlay,
Yang Li,
Alexandra M Z Slawin,
David W Aldous,
Naomi F Cessford,
Tina Düren, Xuebo Zhao,
Rachel Gill,
K Mark Thomas,
John M Griffin,
Sharon E Ashbrook,
Russell E Morris
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ABSTRACT: Formed by linking metals or metal clusters through organic linkers, metal-organic frameworks are a class of solids with structural and chemical properties that mark them out as candidates for many emerging gas storage, separation, catalysis and biomedical applications. Important features of these materials include their high porosity and their flexibility in response to chemical or physical stimuli. Here, a copper-based metal-organic framework has been prepared in which the starting linker (benzene-1,3,5-tricarboxylic acid) undergoes selective monoesterification during synthesis to produce a solid with two different channel systems, lined by hydrophilic and hydrophobic surfaces, respectively. The material reacts differently to gases or vapours of dissimilar chemistry, some stimulating subtle framework flexibility or showing kinetic adsorption effects. Adsorption can be switched between the two channels by judicious choice of the conditions. The monoesterified linker is recoverable in quantitative yield, demonstrating possible uses of metal-organic frameworks in molecular synthetic chemistry as 'protecting groups' to accomplish selective transformations that are difficult using standard chemistry techniques.
Nature Chemistry 04/2011; 3(4):304-10. · 20.52 Impact Factor
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Sheng-Chang Xiang,
Zhangjing Zhang,
Cong-Gui Zhao,
Kunlun Hong, Xuebo Zhao,
De-Rong Ding,
Ming-Hua Xie,
Chuan-De Wu,
Madhab C Das,
Rachel Gill,
K Mark Thomas,
Banglin Chen
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ABSTRACT: Separation of acetylene and ethylene is an important industrial process because both compounds are essential reagents for a range of chemical products and materials. Current separation approaches include the partial hydrogenation of acetylene into ethylene over a supported Pd catalyst, and the extraction of cracked olefins using an organic solvent; both routes are costly and energy consuming. Adsorption technologies may allow separation, but microporous materials exhibiting highly selective adsorption of C(2)H(2)/C(2)H(4) have not been realized to date. Here, we report the development of tunable microporous enantiopure mixed-metal-organic framework (M'MOF) materials for highly selective separation of C(2)H(2) and C(2)H(4). The high selectivities achieved suggest the potential application of microporous M'MOFs for practical adsorption-based separation of C(2)H(2)/C(2)H(4).
Nature Communications 02/2011; 2:204. · 7.40 Impact Factor
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ABSTRACT: Polychlorinated dibenzo-p-dioxin and polychlorinated dibenzofuran species are classes of extremely toxic compounds generated in very low concentrations in postcombustion gases and these may be removed by adsorption on porous carbons. Their extreme toxicity and very low volatility prevent detailed study of their adsorption characteristics, and therefore, models for dioxins have been used in this study. Chlorobenzene, 2-chlorotoluene, 1,3-dichlorobenzene, and 2-chloroanisole were used as models to investigate factors influencing the adsorption characteristics of dioxins on porous carbons. Adsorption studies were carried out under conditions of very low concentration and temperatures up to 453 K, which simulate those found in dioxin abatement systems. Adsorption of 2-chloroanisole on three carbons with various micro/mesoporous structures showed that microporous structure was a critical adsorbent characteristic under these conditions. A microporous activated carbon was selected for detailed thermodynamic and kinetic studies of adsorption of chloroaromatic species in relation to adsorbate structure and adsorbent surface functional groups. Virial equation analysis of adsorption isotherms was used to determine the Henry’s Law constants and isosteric enthalpies of adsorption at zero surface coverage to compare adsorbate−adsorbent interactions. The van’t Hoff equation was used to determine the enthalpy of adsorption as a function of surface coverage. The role of surface functional groups on adsorption thermodynamics was investigated by oxidizing and reducing the carbon in nitric acid and hydrogen, respectively. The important factor influencing adsorption at very low concentrations is the adsorbate adsorbent interaction. Oxidation of the carbon adsorbent only has a small effect on the isosteric enthalpy of adsorption. The adsorption kinetics for each isotherm pressure increment were described by the stretched exponential equation. The activation energies and enthalpies of activation were calculated as a function of surface coverage for adsorption kinetics of chloroaromatic species. The planar molecules studied had lower activation energies and enthalpies of activation than isosteric enthalpy of adsorption indicating that a site-to-site surface hopping mechanism is the main factor in determining the adsorption kinetics. In comparison, 2-chloroanisole is nonplanar with a methoxy group giving rise to a larger minimum cross-section size and higher barrier to diffusion than isosteric enthalpy of adsorption at low surface coverage leading to the adsorption kinetics being mainly determined by diffusion through constrictions in the porous structure under these conditions. The isosteric enthalpies of adsorption initially increase with increasing surface coverage and this is attributed to π−π interactions of planar aromatic molecules confined in microporosity. The trends in the kinetic barriers and isosteric enthalpies of adsorption with surface coverage for 2-chlorotoluene are similar irrespective of adsorbent oxidation/reduction, indicating that surface functional groups only have a relatively small effect on adsorption characteristics.
01/2011;
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Bo Xiao,
Peter J Byrne,
Paul S Wheatley,
David S Wragg, Xuebo Zhao,
Ashleigh J Fletcher,
K Mark Thomas,
Lars Peters,
John S O Evans,
John E Warren,
Wuzong Zhou,
Russell E Morris
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ABSTRACT: Metal organic frameworks (MOFs) are among the most exciting materials discovered recently, attracting particular attention for their gas-adsorption and -storage properties. Certain MOFs show considerable structural flexibility in response to various stimuli. Although there are several examples of 'breathing' MOFs, in which structural changes occur without any bond breaking, examples of transformations in which several bonds are broken and made are much rarer. In this paper we demonstrate how a flexible MOF, Cu2(OH)(C8H3O7S)(H2O)2H2O, can be synthesized by careful choice of the organic linker ligand. The flexibility can be controlled by addition of a supplementary coordinating molecule, which increases the thermal stability of the solid sufficiently for direct imaging with electron microscopy to be possible. We also demonstrate that the MOF shows unprecedented low-pressure selectivity towards nitric oxide through a coordination-driven gating mechanism. The chemical control over these behaviours offers new possibilities for the synthesis of MOFs with unusual and potentially exploitable properties.
Nature Chemistry 07/2009; 1(4):289-94. · 20.52 Impact Factor
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Bo Xiao,
Peter J. Byrne,
Paul S. Wheatley,
David S. Wragg, Xuebo Zhao,
Ashleigh J. Fletcher,
K. Mark Thomas,
Lars Peters,
John S. O. Evans,
John E. Warren,
Wuzong Zhou,
Russell E. Morris
[show abstract]
[hide abstract]
ABSTRACT: Metal organic frameworks (MOFs) are among the most exciting materials discovered recently, attracting particular attention for their gas-adsorption and -storage properties. Certain MOFs show considerable structural flexibility in response to various stimuli. Although there are several examples of 'breathing' MOFs, in which structural changes occur without any bond breaking, examples of transformations in which several bonds are broken and made are much rarer. In this paper we demonstrate how a flexible MOF, Cu2(OH)(C8H3O7S)(H2O)2H2O, can be synthesized by careful choice of the organic linker ligand. The flexibility can be controlled by addition of a supplementary coordinating molecule, which increases the thermal stability of the solid sufficiently for direct imaging with electron microscopy to be possible. We also demonstrate that the MOF shows unprecedented low-pressure selectivity towards nitric oxide through a coordination-driven gating mechanism. The chemical control over these behaviours offers new possibilities for the synthesis of MOFs with unusual and potentially exploitable properties.
Nature Chemistry 06/2009; 1(4):289-294. · 20.52 Impact Factor
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ABSTRACT: A rational strategy has been used to immobilize open metal sites in ultramicroporosity for stronger binding of multiple H 2 molecules per unsaturated metal site for H 2 storage applications. The synthesis and structure of a mixed zinc/copper metal-organic framework material Zn 3(BDC) 3[Cu(Pyen)] .(DMF) 5(H 2O) 5 (H 2BDC = 1,4 benzenedicarboxylic acid and PyenH 2 = 5-methyl-4-oxo-1,4-dihydro-pyridine-3-carbaldehyde) is reported. Desolvation provides a bimodal porous structure Zn 3(BDC) 3[Cu(Pyen)] (M'MOF 1) with narrow porosity (<0.56 nm) and an array of pores in the bc crystallographic plane where the adsorbate-adsorbent interactions are maximized by both the presence of open copper centers and overlap of the potential energy fields from pore walls. The H 2 and D 2 adsorption isotherms for M'MOF 1 at 77.3 and 87.3 K were reversible with virtually no hysteresis. Methods for determination of the isosteric enthalpies of H 2 and D 2 adsorption were compared. A virial model gave the best agreement (average deviation <1 standard deviation) with the isotherm data. This was used in conjunction with the van't Hoff isochore giving isosteric enthalpies at zero surface coverage of 12.29 +/- 0.53 and 12.44 +/- 0.50 kJ mol (-1) for H 2 and D 2 adsorption, respectively. This is the highest value so far observed for hydrogen adsorption on a porous material. The enthalpy of adsorption, decreases with increasing amount adsorbed to 9.5 kJ mol (-1) at approximately 1.9 mmol g (-1) (2 H 2 or D 2 molecules per Cu corresponding to adsorption on both sides of planar Cu open centers) and is virtually unchanged in the range 1.9-3.6 mmol g (-1). Virial analysis of isotherms at 87.3 K is also consistent with two H 2 or D 2 molecules being bound to each open Cu center. The adsorption kinetics follow a double exponential model, corresponding to diffusion along two types of pores, a slow component with high activation energy (13.35 +/- 0.59 kJ mol (-1)) for the narrow pores and a faster component with low activation energy (8.56 +/- 0.41 kJ mol (-1)). The D 2 adsorption kinetic constants for both components were significantly faster than the corresponding H 2 kinetics for specific pressure increments and had slightly lower activation energies than the corresponding values for H 2 adsorption. The kD 2/ kH 2 ratio for the slow component was 1.62 +/- 0.07, while the fast component was 1.38 +/- 0.04 at 77.3 K, and the corresponding ratios were smaller at 87.3 K. These observations of kinetic isotope quantum molecular sieving in porous materials are due to the larger zero-point energy for the lighter H 2, resulting in slower adsorption kinetics compared with the heavier D 2. The results show that a combination of open metal centers and confinement in ultramicroporosity leads to a high enthalpy for H 2 adsorption over a wide range of surface coverage and quantum effects influence diffusion of H 2 and D 2 in pores in M'MOF 1.
Journal of the American Chemical Society 05/2008; 130(20):6411-23. · 9.91 Impact Factor
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Bo Xiao,
Paul S Wheatley, Xuebo Zhao,
Ashleigh J Fletcher,
Sarah Fox,
Adriano G Rossi,
Ian L Megson,
S Bordiga,
L Regli,
K Mark Thomas,
Russell E Morris
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ABSTRACT: Gas adsorption experiments have been carried out on a copper benzene tricarboxylate metal-organic framework material, HKUST-1. Hydrogen adsorption at 1 and 10 bar (both 77 K) gives an adsorption capacity of 11.16 mmol H2 per g of HKUST-1 (22.7 mg g(-)1, 2.27 wt %) at 1 bar and 18 mmol per g (36.28 mg g(-)1, 3.6 wt %) at 10 bar. Adsorption of D2 at 1 bar (77 K) is between 1.09 (at 1 bar) and 1.20(at <100 mbar) times the H2 values depending on the pressure, agreeing with the theoretical expectations. Gravimetric adsorption measurements of NO on HKUST-1 at 196 K (1 bar) gives a large adsorption capacity of approximately 9 mmol g(-1), which is significantly greater than any other adsorption capacity reported on a porous solid. At 298 K the adsorption capacity at 1 bar is just over 3 mmol g(-1). Infra red experiments show that the NO binds to the empty copper metal sites in HKUST-1. Chemiluminescence and platelet aggregometry experiments indicate that the amount of NO recovered on exposure of the resulting complex to water is enough to be biologically active, completely inhibiting platelet aggregation in platelet rich plasma.
Journal of the American Chemical Society 02/2007; 129(5):1203-9. · 9.91 Impact Factor
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Angewandte Chemie International Edition 12/2006; 45(44):7358-64. · 13.45 Impact Factor
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ABSTRACT: Adsorption and desorption of H(2) and D(2) from porous carbon materials, such as activated carbon at 77 K, are usually fully reversible with very rapid adsorption/desorption kinetics. The adsorption and desorption of H(2) and D(2) at 77 K on a carbon molecular sieve (Takeda 3A), where the kinetic selectivity was incorporated by carbon deposition, and a carbon, where the pore structure was modified by thermal annealing to give similar pore structure characteristics to the carbon molecular sieve substrate, were studied. The D(2) adsorption and desorption kinetics were significantly faster (up to x1.9) than the corresponding H(2) kinetics for specific pressure increments/decrements. This represents the first experimental observation of kinetic isotope quantum molecular sieving in porous materials due to the larger zero-point energy for the lighter H(2), resulting in slower adsorption/desorption kinetics compared with the heavier D(2). The results are discussed in terms of the adsorption mechanism.
The Journal of Physical Chemistry B 06/2006; 110(20):9947-55. · 3.70 Impact Factor
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ABSTRACT: Adsorption and desorption of hydrogen from nanoporous materials, such as activated carbon, is usually fully reversible. We have prepared nanoporous metal-organic framework materials with flexible linkers in which the pore openings, as characterized in the static structures, appear to be too small to allow H2 to pass. We observe hysteresis in their adsorption and desorption kinetics above the supercritical temperature of H2 that reflects the dynamical opening of the "windows" between pores. This behavior would allow H2 to be adsorbed at high pressures but stored at lower pressures.
Science 12/2004; 306(5698):1012-5. · 31.20 Impact Factor
