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Origin of NMR Spectral Features in MCM-41 at Low HydrationsNiknam, Mohamad 17 August 2010 (has links)
Although extensive literature exists on NMR of water in MCM-41, the origin of a number of NMR spectral features in this material had not been understood. Specifically, the
OH proton resonance observed in the dry material disappears completely as it is hydrated to 0.2 mono-layer hydration level. The purpose of this study was to gain insight into the physical basics for these spectral features and in the process broaden our understanding of behaviour/interactions of water molecules in porous material. First, measurements of MAS spectra as a function of temperature and hydration, at very low hydrations, made possible a definitive spectral peak assignment. Second, using 1D and 2D selective inversion recovery and magnetization exchange experiments, as well as MAS and non-MAS techniques, magnetization exchange between the water protons and surface OH group protons was quantified. The present results lead to the conclusion that chemical exchange is not responsible for producing the observed changes in proton spectra in MCM-41 as this material is hydrated up to the 0.2 mono-layer hydration level. This represents an important result as it is at odds with what is assumed in the literature in this connection and means that previous conclusions about hydration dynamics in this material need to be revisited. A dynamics model of water interaction with the surface OH hydration sites was introduced to explain the observed proton spectra. The model can successfully predict the observed chemical shifts and temperature dependent changes of proton spectra in the very low hydration MCM-41.
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Origin of NMR Spectral Features in MCM-41 at Low HydrationsNiknam, Mohamad 17 August 2010 (has links)
Although extensive literature exists on NMR of water in MCM-41, the origin of a number of NMR spectral features in this material had not been understood. Specifically, the
OH proton resonance observed in the dry material disappears completely as it is hydrated to 0.2 mono-layer hydration level. The purpose of this study was to gain insight into the physical basics for these spectral features and in the process broaden our understanding of behaviour/interactions of water molecules in porous material. First, measurements of MAS spectra as a function of temperature and hydration, at very low hydrations, made possible a definitive spectral peak assignment. Second, using 1D and 2D selective inversion recovery and magnetization exchange experiments, as well as MAS and non-MAS techniques, magnetization exchange between the water protons and surface OH group protons was quantified. The present results lead to the conclusion that chemical exchange is not responsible for producing the observed changes in proton spectra in MCM-41 as this material is hydrated up to the 0.2 mono-layer hydration level. This represents an important result as it is at odds with what is assumed in the literature in this connection and means that previous conclusions about hydration dynamics in this material need to be revisited. A dynamics model of water interaction with the surface OH hydration sites was introduced to explain the observed proton spectra. The model can successfully predict the observed chemical shifts and temperature dependent changes of proton spectra in the very low hydration MCM-41.
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Theoretical Investigations on Nanoporpus Materials and Ionic Liquids for Energy StorageMani Biswas, Mousumi 2011 December 1900 (has links)
In the current context of rapidly depleting petroleum resources and growing environmental concerns, it is important to develop materials to harvest and store energy from renewable and sustainable sources. Hydrogen has the potential to be an alternative energy source, since it has higher energy content than petroleum. However, since hydrogen has very low volumetric energy density, hence it is important to design nano porous materials which can efficiently store large volumes of hydrogen gas by adsorption. In this regard carbon nanotube and Metal Organic Framework (MOFs) based materials are worth studying.
Ionic liquids (IL) are potential electrolytes that can improve energy storage capacity and safety in Li ion batteries. Therefore it is important to understand IL's thermodynamic and transport properties, especially when it is in contact with electrode surface and mixed with Li salt, as happens in the battery application. This dissertation presents computation and simulation based studies on:
1. Hydrogen storage in carbon nanotube scaffold.
2. Mechanical property and stability of various nanoporous Metal Organic Frameworks.
3. Thermodynamic and transport properties of [BMIM][BF4] ionic liquid in bulk, in Li Salt mixture, on graphite surface and under nanoconfinement.
In the first study, we report the effects of carbon nanotube diameter, tube chirality, tube spacer distance, tube functionalization and presence of Li on hydrogen sorption capacity and thermodynamics at different temperature and pressure. In the second one, we observe high pressure induced structural transformation of 6 isoreticular MOFs: IRMOF-1. IRMOF-3, IRMOF-6, IRMOF-8, IRMOF-10 and IRMOF-14, explore the deformation mechanism and effect of Hydrogen inside crystal lattice. In the third study, we observe the equilibrium thermodynamic and transport properties of [BMIM][BF4] ionic liquid. The temperature dependence of ion diffusion, conductivity, dielectric constant, dipole relaxation time and viscosity have been observed and found similar behavior to those of supercooled liquid. The ion diffusion on graphite surfaces and under nanoconfinement was found to be higher compared to those in bulk.
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