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Selective Binding of O2 over N2 in a RedoxÐActive MetalÐOrganic Framework with Open Iron(II) Coordination Sites, E.D. Bloch, L.J. Murray, W.L. Queen, S, Chavan, S.N. Maximoff, J.P. Bigi, R. Krishna, V.K. Peterson, F. Grandjean, G.J. Long, B. Smit, S. Bordiga, C.M. Brown, and J.R. Long. JACS 2011
Associating binding sites with increased enthalpy of adsorption
Refining the models from our earlier observations in this new redox-active framework
Hydrogen Adsorption in the Metal-Organic Frameworks Fe2(dobdc) and Fe2(O2)(dobdc), W.L. Queen, E.D. Bloch, C.M. Brown, M.R. Hudson, J.A. Mason, L.J. Murray, A.J. Ramirez-Cuesta, V.K. Peterson, J.R. Long. dalton Trans. 2012
Associating binding sites with increased enthalpy of adsorption
A couple of our early papers really pin-pointed the increased enthalpy of adsorption in certain types of coordination-polymers (metal-organic frameworks - MOFs) being due to hydrogen interaction with unsaturated metal sites. Our most recent work on the Fe-BTT compound has given us remarkable clarity on the adsorption sites, and lead to the shortest M-D2. interaction distance so-far determined.
Hydrogen Storage and Carbon Dioxide Capture in an Iron-Based Sodalite-Type Metal-Organic Framework (Fe-BTT) Discovered via High-Throughput Methods, K. Sumida, S. Horike, S. S. Kaye, Z. R. Herm, W. L. Queen, C. M. Brown, F. Grandjean, G. J. Long, A. Dailly and J. R. Long, J. Chemical Science, 2010
Hydrogen Storage in a microporous metal-organic framework with exposed Mn2+ coordination sites, M. Dinca, W. S. Han, Y. Liu, A. Dailly, C. M. Brown, and J. R. Long, J. Am. Chem. Soc., 2006, 128, 51, 16876.
Observation of CuII-H2 interactions in a fully-desolvated, sodalite-type metal-organic framework, M. Dinca, A. Dailly, Y. Liu, C. M. Brown, D. A. Neumann and J. R. Long, Angewandte Chemie, 2007, 46, 1419.
Neutron powder diffraction study of D2 sorption in Cu3(1,3,5-benzenetricarboxylate)2, V. K. Peterson, Y. Liu, C. M. Brown and Cameron Kepert, J. Am. Chem. Soc., 2006, 128, 15578.
Increasing the density of adsorbed hydrogen
It turns out that not only do the unsaturated metals in MOFs increase the enthalpy of adsorption, but can increase the packing density of the H2 as well!
Increasing the density of adsorbed hydrogen with coordinately unsaturated metal centers in metal-organic frameworks, Y. Liu, H. Kabbour, C. M. Brown, D. A. Neumann, and C. C. Ahn, Langmuir, 2008, 24, 4772.
Breathing MOFs are cool...
We figured out that MIL-53 changes it's pore size just on cooling (it was known to respond to solvents by the Ferey group). This is a bit of a problem when you do hydrogen isotherm measurements at 77 K, but need to reference the helium volume from room temp! We are working on getting the response with hydrogen in publishable form, should be out soon.
A reversible structural transition of MIL-53 with temperature hysteresis, Y. Liu, J.-H. Her, A. Dailly, A. J. Ramirez-Cuesta, D. A. Neumann and C. M. Brown, J. Am. Chem. Soc. 2008, 130, 11813.
Understanding Inelastic Neutron Scattering Spectra (INS) of hydrogen in materials
We know that hydrogen has quantum rotational levels that are barely perturbed when adsorbed on various carbons, but the levels are razed with stronger interactions. There is some assumption in the literature that the measured energy levels are related to the enthalpy of adsorption. The most commonly cited relationship is the lower the vibrational frequency the higher the enthalpy of adsorption - something that I really doubt in the cases of H2-MOFs. For instance, take HKUST-1. It has available copper ions when activated, but the adsorption enthalpy is not much better than a good carbon. Working with Taner Yildrim for bit more of a theoretical basis on this we can easily explain the INS at low coverages and attribute most of the interaction of Cu-H2 as Coulombic interactions and observe no H--H elongation.
The nature of adsorbed hydrogen in HKUST-1: a Combined Inelastic Neutron Scattering and First-Principles Study, C. M. Brown, Y. Liu, T. Yildirim, V. K. Peterson, and C. J. Kepert, Nanotechnology, 2009, 20, 4025.
Spillover hydrogen of Pd-nanofibers
Turns out that it is pretty hard to find solid signatures of atomic species in carbon materials. We have had some mild success using an indirect observation or the reduction in the hydrogen rotational line and some increase in the higher energy densities of states for Pd/carbon nanofiber materials with ORNL researchers.
Detection of Hydrogen Spillover in Palladium-Modified Activated Carbon Fibers During Hydrogen Adsorption,, C. I. Contescu, C. M. Brown, Y. Liu, V. V. Bhat and C. Gallego, J. Phys. Chem. 2009, 113, 5886.
Past Highlights from the NCNR Annual Report
2009 (page 30-31) Toward an Improved Understanding of Hydrogen Interactions with Coordinated Metals2008 (page 35-36) Dense hydrogen upon adsorption in MOF-74
2006 (page 12-13) Hydrogen adsorption in Mn based MOF
2001, Phonon softening in alpha-Uranium
2000, Ligand dynamics in Metal-organic framework
2000, Molten globule-native protein dynamics