Browsing by Author "Kailasam, Kamalakannan"

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    Synthesis and characterization of mesoporous silica and metal oxide based stationary phase materials
    (2008) Kailasam, Kamalakannan; Müller, Klaus (Prof. Dr.)
    The development of covalently bonded alkyl stationary phases is one of the most important advances in the field of chromatography that lead to the growth of reversed-phase high-performance liquid chromatography (RP-HPLC) as a widely used separation technique. In this dissertation, conventional amorphous and ordered MCM-41 silica, metal oxides (titania, hafnia, alumina, and zirconia) and silica-zirconia mixed oxides were grafted with octadecyl chains, using different silylating agents and employing various preparation routes. Several physico-chemical techniques were employed to determine the mesoporosity, morphology, grafting and organization of alkyl chains on these inorganic oxide substrates. From small angle X-ray scattering experiments and nitrogen sorption isotherms the pore size, pore volume and surface area were derived. Scanning electron microscopy measurements provided the morphological features of the particles. The elemental composition was determined by elemental and XPS analysis. Solid-state 29Si NMR spectroscopy was employed to probe the grafting and degree of cross-linking of the alkyl chains on these substrates. Recent studies have cleared that the conformation features, chain dynamics and their concomitant effects on retention and selectivity depend on various factors such as alkyl chain lengths, surface coverage, supporting material, temperature and pressure, etc. The conformational order, chain length and chain packing of the n-alkyl chains are known to play a dominant role in determining the separation performance of the chromatographic phases. Therefore, Fourier transform infrared spectroscopy - through analysis of the symmetric and antisymmetric CH2 stretching bands - was used to get information about the conformational order of the alkyl chains. In addition, solid-state 13C NMR spectroscopy provided independent information about the conformation and mobility of the surface-attached alkyl ligands and other organic components.