Co-reporter:Velencia J. Witherspoon, Lucy M. Yu, Sudi Jawahery, Efrem Braun, Seyed Mohamad Moosavi, Sondre K. Schnell, Berend Smit, and Jeffrey A. Reimer
The Journal of Physical Chemistry C July 20, 2017 Volume 121(Issue 28) pp:15456-15456
Publication Date(Web):May 19, 2017
DOI:10.1021/acs.jpcc.7b03181
We combined nuclear magnetic resonance (NMR) and molecular dynamics (MD) simulation to study xylene behavior in MOF-5, probing the effects of adsorbate geometry in a weakly interacting model isotropic metal organic framework (MOF) system. We employed NMR diffusometry and relaxometry techniques at low field (13 MHz) to quantify the self-diffusion coefficients (Ds) and the longitudinal relaxation times (T1) of xylenes in MOF-5 as a function of temperature at the saturated loading for each xylene. These experiments reveal the translational motion activation energies to be 15.3, 19.7, and 21.2 kj mol–1 and the rotational activation energies to be 47.26, 12.88, and 11.55 for the (p-, m-, o-) xylene isomers, respectively. Paraxylene exhibits faster translational motion, yet shows four times the activation energy barrier for rotational motion vis-à-vis the other isomers. MD simulations performed on these model systems corroborate the findings for paraxylene and suggest that paraxylene has the lower free energy barrier for hopping away from its binding sites, yet has the slowest rotational motion in the plane of the xylene molecule.
Co-reporter:Efrem Braun;Dr. Joseph J. Chen;Dr. Sondre K. Schnell;Dr. Li-Chiang Lin;Dr. Jeffrey A. Reimer;Dr. Berend Smit
Angewandte Chemie International Edition 2015 Volume 54( Issue 48) pp:14349-14352
Publication Date(Web):
DOI:10.1002/anie.201506865
Abstract
Molecular simulations and NMR relaxometry experiments demonstrate that pure benzene or xylene confined in isoreticular metal–organic frameworks (IRMOFs) exhibit true vapor–liquid phase equilibria where the effective critical point may be reduced by tuning the structure of the MOF. Our results are consistent with vapor and liquid phases extending over many MOF unit cells. These results are counterintuitive since the MOF pore diameters are approximately the same length scale as the adsorbate molecules. As applications of these materials in catalysis, separations, and gas storage rely on the ability to tune the properties of adsorbed molecules, we anticipate that the ability to systematically control the critical point, thereby preparing spatially inhomogeneous local adsorbate densities, could add a new design tool for MOF applications.
Co-reporter:Efrem Braun;Dr. Joseph J. Chen;Dr. Sondre K. Schnell;Dr. Li-Chiang Lin;Dr. Jeffrey A. Reimer;Dr. Berend Smit
Angewandte Chemie 2015 Volume 127( Issue 48) pp:14557-14560
Publication Date(Web):
DOI:10.1002/ange.201506865
Abstract
Molecular simulations and NMR relaxometry experiments demonstrate that pure benzene or xylene confined in isoreticular metal–organic frameworks (IRMOFs) exhibit true vapor–liquid phase equilibria where the effective critical point may be reduced by tuning the structure of the MOF. Our results are consistent with vapor and liquid phases extending over many MOF unit cells. These results are counterintuitive since the MOF pore diameters are approximately the same length scale as the adsorbate molecules. As applications of these materials in catalysis, separations, and gas storage rely on the ability to tune the properties of adsorbed molecules, we anticipate that the ability to systematically control the critical point, thereby preparing spatially inhomogeneous local adsorbate densities, could add a new design tool for MOF applications.
Co-reporter:Allison M. Engstrom, Eunhee Lim, Jeffrey A. Reimer, Elton J. Cairns
Electrochimica Acta 2014 Volume 135() pp:249-254
Publication Date(Web):20 July 2014
DOI:10.1016/j.electacta.2014.05.006
A newly formulated four-component modified Butler-Volmer model has been developed to evaluate global oxidation kinetic parameters for the various types of carbon monoxide adsorbates (COads) on a nanoparticle Pt surface determined by the type of bonding as well as the local structure of the adsorption site. Partial coverages of COads were prepared by potentiostatic adsorption of methanol followed by potentiostatic partial oxidation at various elevated potentials and for various durations. Anodic linear sweep voltammetry was then performed, and the COads oxidation peaks were fitted with the model to analyze the kinetics. According to the model, preferential oxidation with respect to COads bonding and Pt substrate structure can be achieved dependent upon the potential and extent of oxidation. Partial oxidation at 450 mV vs. RHE for 60 min. resulted in a majority population of linearly bonded COads on cubic-packed Pt sites; whereas partial oxidation at 650 mV vs. RHE for 220 sec. resulted in a majority population of bridged-bonded COads on close-packed Pt sites.
Co-reporter:Xueqian Kong;Hexiang Deng;Fangyong Yan;Jihan Kim;Joseph A. Swisher;Berend Smit;Omar M. Yaghi
Science 2013 Volume 341(Issue 6148) pp:882-885
Publication Date(Web):23 Aug 2013
DOI:10.1126/science.1238339
Mapping Molecular Linkers
In metal-organic framework compounds, inorganic centers (metal atoms or clusters) are linked by bidentate organic groups. Normally, the same group is used throughout the structure, but recently, synthesis with linkers bearing different functional groups has produced well-defined materials. Kong et al. (p. 882, published online 25 July) combined solid-state nuclear magnetic resonance and molecular simulations to map the distributions of linkers in these materials as random, well-mixed, or clustered.
Co-reporter:Jeffrey A. Reimer
Solid State Nuclear Magnetic Resonance 2010 Volume 37(1–2) pp:3-12
Publication Date(Web):February–April 2010
DOI:10.1016/j.ssnmr.2010.04.001
Nuclear hyperpolarization can be achieved in a number of ways. This article focuses on the use of coupling of nuclei to (nearly) pure quantum states, with particular emphasis on those states obtained by optical excitation in bulk semiconductors. I seek an answer to this question: “What is to prevent the design and analysis of nuclear spintronics devices that use the extremely long-lived hyperpolarized nuclear spin states, and their weak couplings to each other, to affect computation, memory, or informational technology schemes?” The answer, I argue, is in part because there remains a lack of fundamental understanding of how to generate and control nuclear polarization with schemes other than with rf coils.
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