The Experts below are selected from a list of 25929 Experts worldwide ranked by ideXlab platform
Omar M Yaghi - One of the best experts on this subject based on the ideXlab platform.
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extra adsorption and Adsorbate superlattice formation in metal organic frameworks
Nature, 2015Co-Authors: Hae Sung Cho, Hexiang Deng, Keiichi Miyasaka, Zhiyue Dong, Minhyung Cho, Alexander V Neimark, Jeung Ku Kang, Omar M YaghiAbstract:Metal-organic frameworks (MOFs) have a high internal surface area and widely tunable composition, which make them useful for applications involving adsorption, such as hydrogen, methane or carbon dioxide storage. The selectivity and uptake capacity of the adsorption process are determined by interactions involving the Adsorbates and their porous host materials. But, although the interactions of Adsorbate molecules with the internal MOF surface and also amongst themselves within individual pores have been extensively studied, Adsorbate-Adsorbate interactions across pore walls have not been explored. Here we show that local strain in the MOF, induced by pore filling, can give rise to collective and long-range Adsorbate-Adsorbate interactions and the formation of Adsorbate superlattices that extend beyond an original MOF unit cell. Specifically, we use in situ small-angle X-ray scattering to track and map the distribution and ordering of Adsorbate molecules in five members of the mesoporous MOF-74 series along entire adsorption-desorption isotherms. We find in all cases that the capillary condensation that fills the pores gives rise to the formation of 'extra adsorption domains'-that is, domains spanning several neighbouring pores, which have a higher Adsorbate density than non-domain pores. In the case of one MOF, IRMOF-74-V-hex, these domains form a superlattice structure that is difficult to reconcile with the prevailing view of pore-filling as a stochastic process. The visualization of the adsorption process provided by our data, with clear evidence for initial Adsorbate aggregation in distinct domains and ordering before an even distribution is finally reached, should help to improve our understanding of this process and may thereby improve our ability to exploit it practically.
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extra adsorption and Adsorbate superlattice formation in metal organic frameworks
Nature, 2015Co-Authors: Hexiang Deng, Keiichi Miyasaka, Zhiyue Dong, Alexander V Neimark, Jeung Ku Kang, Omar M Yaghi, Osamu TerasakiAbstract:Metal-organic frameworks have a porous structure that has useful applications in gas adsorption; here, small-angle X-ray scattering is used to visualize the process of adsorption as gas pressure increases, revealing that Adsorbate molecules interact across pore walls in a way that allows extra Adsorbate domains to be created in the framework and to form superlattices, before the Adsorbate settles down into a more uniform distribution. Porous materials are widely used for gas adsorption in clean energy, catalysis and other applications. Here Osamu Terasaki and colleagues use small-angle X-ray scattering to visualize the process of adsorption of gases (Ar, CO2 and N2) into/onto porous metal-organic frameworks (MOFs), specifically five members of the mesoporous MOF-74 series. The data reveal that collective Adsorbate–Adsorbate interactions occur across the pore network in a way that allows extra Adsorbate domains to be created in the framework and to form superlattices, before the Adsorbate adopts a more uniform distribution. The superlattice structure is difficult to reconcile with the prevailing view of pore filling as a stochastic process. Metal-organic frameworks (MOFs) have a high internal surface area and widely tunable composition1,2, which make them useful for applications involving adsorption, such as hydrogen, methane or carbon dioxide storage3,4,5,6,7,8,9. The selectivity and uptake capacity of the adsorption process are determined by interactions involving the Adsorbates and their porous host materials. But, although the interactions of Adsorbate molecules with the internal MOF surface10,11,12,13,14,15,16,17 and also amongst themselves within individual pores18,19,20,21,22 have been extensively studied, Adsorbate–Adsorbate interactions across pore walls have not been explored. Here we show that local strain in the MOF, induced by pore filling, can give rise to collective and long-range Adsorbate–Adsorbate interactions and the formation of Adsorbate superlattices that extend beyond an original MOF unit cell. Specifically, we use in situ small-angle X-ray scattering to track and map the distribution and ordering of Adsorbate molecules in five members of the mesoporous MOF-74 series along entire adsorption–desorption isotherms. We find in all cases that the capillary condensation that fills the pores gives rise to the formation of ‘extra adsorption domains’—that is, domains spanning several neighbouring pores, which have a higher Adsorbate density than non-domain pores. In the case of one MOF, IRMOF-74-V-hex, these domains form a superlattice structure that is difficult to reconcile with the prevailing view of pore-filling as a stochastic process. The visualization of the adsorption process provided by our data, with clear evidence for initial Adsorbate aggregation in distinct domains and ordering before an even distribution is finally reached, should help to improve our understanding of this process and may thereby improve our ability to exploit it practically.
Osamu Terasaki - One of the best experts on this subject based on the ideXlab platform.
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extra adsorption and Adsorbate superlattice formation in metal organic frameworks
Nature, 2015Co-Authors: Hexiang Deng, Keiichi Miyasaka, Zhiyue Dong, Alexander V Neimark, Jeung Ku Kang, Omar M Yaghi, Osamu TerasakiAbstract:Metal-organic frameworks have a porous structure that has useful applications in gas adsorption; here, small-angle X-ray scattering is used to visualize the process of adsorption as gas pressure increases, revealing that Adsorbate molecules interact across pore walls in a way that allows extra Adsorbate domains to be created in the framework and to form superlattices, before the Adsorbate settles down into a more uniform distribution. Porous materials are widely used for gas adsorption in clean energy, catalysis and other applications. Here Osamu Terasaki and colleagues use small-angle X-ray scattering to visualize the process of adsorption of gases (Ar, CO2 and N2) into/onto porous metal-organic frameworks (MOFs), specifically five members of the mesoporous MOF-74 series. The data reveal that collective Adsorbate–Adsorbate interactions occur across the pore network in a way that allows extra Adsorbate domains to be created in the framework and to form superlattices, before the Adsorbate adopts a more uniform distribution. The superlattice structure is difficult to reconcile with the prevailing view of pore filling as a stochastic process. Metal-organic frameworks (MOFs) have a high internal surface area and widely tunable composition1,2, which make them useful for applications involving adsorption, such as hydrogen, methane or carbon dioxide storage3,4,5,6,7,8,9. The selectivity and uptake capacity of the adsorption process are determined by interactions involving the Adsorbates and their porous host materials. But, although the interactions of Adsorbate molecules with the internal MOF surface10,11,12,13,14,15,16,17 and also amongst themselves within individual pores18,19,20,21,22 have been extensively studied, Adsorbate–Adsorbate interactions across pore walls have not been explored. Here we show that local strain in the MOF, induced by pore filling, can give rise to collective and long-range Adsorbate–Adsorbate interactions and the formation of Adsorbate superlattices that extend beyond an original MOF unit cell. Specifically, we use in situ small-angle X-ray scattering to track and map the distribution and ordering of Adsorbate molecules in five members of the mesoporous MOF-74 series along entire adsorption–desorption isotherms. We find in all cases that the capillary condensation that fills the pores gives rise to the formation of ‘extra adsorption domains’—that is, domains spanning several neighbouring pores, which have a higher Adsorbate density than non-domain pores. In the case of one MOF, IRMOF-74-V-hex, these domains form a superlattice structure that is difficult to reconcile with the prevailing view of pore-filling as a stochastic process. The visualization of the adsorption process provided by our data, with clear evidence for initial Adsorbate aggregation in distinct domains and ordering before an even distribution is finally reached, should help to improve our understanding of this process and may thereby improve our ability to exploit it practically.
Angelika Kuhnle - One of the best experts on this subject based on the ideXlab platform.
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repulsive interaction and contrast inversion in noncontact atomic force microscopy imaging of Adsorbates
Physical Review B, 2008Co-Authors: Philipp Rahe, Ralf Bechstein, Jens Schutte, Frank Ostendorf, Angelika KuhnleAbstract:To understand contrast formation in atomic resolution noncontact atomic force microscopy (NC-AFM), we investigate whether or not repulsive tip-sample interaction contributes to contrast formation. We relate attractive and repulsive interactions to contrast features depending on both oscillating amplitude and measured detuning. Simulations based on a Morse potential illustrate the mechanism behind contrast inversion due to repulsive interactions above an Adsorbate on the surface. Experimental NC-AFM images of Adsorbates on mica and TiO(2) surfaces confirm our simulations. Furthermore, we discuss the influence of the topography feedback loop on contrast formation above Adsorbates, which illustrates that data interpretation can become rather delicate for constant-detuning images.
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repulsive interaction and contrast inversion in noncontact atomic force microscopy imaging of Adsorbates
Physical Review B, 2008Co-Authors: Philipp Rahe, Ralf Bechstein, Jens Schutte, Frank Ostendorf, Angelika KuhnleAbstract:To understand contrast formation in atomic resolution noncontact atomic force microscopy (NC-AFM), we investigate whether or not repulsive tip-sample interaction contributes to contrast formation. We relate attractive and repulsive interactions to contrast features depending on both oscillating amplitude and measured detuning. Simulations based on a Morse potential illustrate the mechanism behind contrast inversion due to repulsive interactions above an Adsorbate on the surface. Experimental NC-AFM images of Adsorbates on mica and ${\text{TiO}}_{2}$ surfaces confirm our simulations. Furthermore, we discuss the influence of the topography feedback loop on contrast formation above Adsorbates, which illustrates that data interpretation can become rather delicate for constant-detuning images.
Aleksandra Vojvodic - One of the best experts on this subject based on the ideXlab platform.
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an orbital overlap model for minimal work functions of cesiated metal surfaces
Journal of Physics: Condensed Matter, 2012Co-Authors: Sharon H Chou, Johannes Voss, Igor Bargatin, Aleksandra Vojvodic, Roger T Howe, Frank AbildpedersenAbstract:We introduce a model for the effect of cesium Adsorbates on the work function of transition metal surfaces. The model builds on the classical point-dipole equation by adding exponential terms that characterize the degree of orbital overlap between the 6s states of neighboring cesium Adsorbates and its effect on the strength and orientation of electric dipoles along the Adsorbate–substrate interface. The new model improves upon earlier models in terms of agreement with the work function–coverage curves obtained via first-principles calculations based on density functional theory. All the cesiated metal surfaces have optimal coverages between 0.6 and 0.8 monolayers, in accordance with experimental data. Of all the cesiated metal surfaces that we have considered, tungsten has the lowest minimum work function, also in accordance with experiments.
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atomic and molecular adsorption on transition metal carbide 111 surfaces from density functional theory a trend study of surface electronic factors
Journal of Physics: Condensed Matter, 2010Co-Authors: Aleksandra Vojvodic, Carlo Ruberto, Bengt I LundqvistAbstract:This study explores atomic and molecular adsorption on a number of early transition-metal carbides (TMCs) in NaCl structure by means of density-functional theory calculations. The investigated substrates are the TM-terminated TMC(111) surfaces, of interest because of the presence of different types of surface resonances (SRs) on them and because of their technological importance in growth processes. Also, TM compounds have shown potential in catalysis applications. Trend studies are conducted with respect to both period and group in the periodic table, choosing the substrates ScC, TiC, VC, ZrC, NbC, delta-MoC, TaC, and WC (in NaCl structure) and the Adsorbates H, B, C, N, O, F, NH, NH2, and NH3. Trends in adsorption strength are explained in terms of surface electronic factors, by correlating the calculated adsorption-energy values with the calculated surface electronic structures. The results are rationalized by use of a concerted-coupling model (CCM), which has previously been applied successfully to the description of adsorption on TiC(111) and TiN(111) surfaces (Ruberto et al 2007 Solid State Commun. 141 48). First, the clean TMC(111) surfaces are characterized by calculating surface energies, surface relaxations, Bader charges, and surface-localized densities of states (DOSs). Detailed comparisons between surface and bulk DOSs reveal the existence of transition-metal localized SRs (TMSRs) in the pseudogap and of several C-localized SRs (CSRs) in the upper valence band on all considered TMC(111) surfaces. The spatial extent and the dangling bond nature of these SRs are supported by real-space analyses of the calculated Kohn-Sham wavefunctions. Then, atomic and molecular adsorption energies, geometries, and charge transfers are presented. An analysis of the Adsorbate-induced changes in surface DOSs reveals a presence of both Adsorbate-TMSR and Adsorbate-CSRs interactions, of varying strengths depending on the surface and the Adsorbate. These variations are correlated to the variations in adsorption energies. The results are used to generalize the content and applications of the previously proposed CCM to this larger class of substrates and Adsorbates. Implications for other classes of materials, for catalysis, and for other surface processes are discussed.
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atomic and molecular adsorption on transition metal carbide 111 surfaces from density functional theory a trend study of surface electronic factors
arXiv: Materials Science, 2010Co-Authors: Aleksandra Vojvodic, Carlo Ruberto, Bengt I LundqvistAbstract:This study explores atomic and molecular adsorption on a number of early transition-metal carbides (TMC's) by means of density-functional theory calculations. Trend studies are conducted with respect to both period and group in the periodic table, choosing the substrates ScC, TiC, VC, ZrC, NbC, delta-MoC, TaC, and WC and the Adsorbates H, B, C, N, O, F, NH, NH2, and NH3. Trends in adsorption strength are explained in terms of surface electronic factors, by correlating the calculated adsorption energy values with the calculated surface electronic structures. The results are rationalized with use of a concerted-coupling model (CCM), which has previously been applied succesfully to the description of adsorption on TiC(111) and TiN(111) surfaces [Solid State Commun. 141, 48 (2007)]. First, the clean TMC(111) surfaces are characterized by calculating surface energies, surface relaxations, Bader charges, and surface-localized densities of states (DOS's). Detailed comparisons between surface and bulk DOS's reveal the existence of transition-metal localized SR's (TMSR's) in the pseudogap and of several C-localized SR's (CSR's) in the upper valence band on all considered TMC(111) surfaces. Then, atomic and molecular adsorption energies, geometries, and charge transfers are presented. An analysis of the Adsorbate-induced changes in surface DOS's reveals a presence of both Adsorbate--TMSR and Adsorbate--CSR's interactions, of varying strengths depending on the surface and the Adsorbate. These variations are correlated to the variations in adsorption energies. The results are used to generalize the content and applications of the previously proposed CCM to this larger class of substrates and Adsorbates. Implications for other classes of materials, for catalysis, and for other surface processes are discussed.
Dionisios G. Vlachos - One of the best experts on this subject based on the ideXlab platform.
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scaling relationships and theory for vibrational frequencies of Adsorbates on transition metal surfaces
Nature Communications, 2017Co-Authors: Joshua L Lansford, Alexander V Mironenko, Dionisios G. VlachosAbstract:Adsorbate vibrational excitations are an important fingerprint of molecule/surface interactions, affecting temperature contributions to the free energy and impacting reaction rate and equilibrium constants. Furthermore, vibrational spectra aid in identifying species and adsorption sites present in experimental studies. Despite their importance, knowledge of how Adsorbate frequencies scale across materials is lacking. Here, by combining previously reported experimental data and our own density-functional theory calculations, we reveal linear correlations between vibrational frequencies of Adsorbates on transition metal surfaces. Through effective-medium theory, linear muffin-tin orbital theory, and the d-band model, we rationalize the squares of the frequencies to be fundamentally linear in their scaling across transition metal surfaces. We identify the Adsorbate-binding energy as a descriptor for certain molecular vibrations and rigorously relate errors in frequencies to errors in adsorption energies. We also discuss the impact of scaling on surface thermochemistry and Adsorbate coverage.
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The role of molecular interactions and interfaces in diffusion: transport diffusivity and evaluation of the Darken approximation.
The Journal of chemical physics, 2005Co-Authors: Mark Snyder, Dionisios G. VlachosAbstract:Kinetic Monte Carlo (KMC) simulations are carried out to directly study diffusion of benzene through thin (37–100nm) NaX zeolite membranes under a gradient in chemical potential. Nonlinearities in Adsorbate loading near the membrane boundaries are shown to arise from the difference in Adsorbate density between the zeolite and adjacent fluid phase. Direct extraction of the transport diffusivity from gradient KMC simulations enables testing of the Darken approximation. This rigorous approach reveals limitations of the Darken approximation and, for the first time, the potentially complex nonunique functionality and multiplicity of the transport diffusivity for strongly interacting Adsorbates. In the companion paper we explore these nonlinear interfacial effects in the context of permeation through both single-crystal and polycrystalline membranes.