Browsing by Subject "Liquid crystalline templating-sol-gel processing"

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    Silver nitrate-oligo (ethylene oxide) surfactant mesoporous nanocomposite films and monoliths
    (2000-09) Samarskaya, Ol'ga
    The purpose of this work is to improve and simplify the method of synthesis of metal functionalized mesoporous materials. This study has two particular goals. The first goal is to incorporate silver in its ionic form and to achieve its homogeneous distribution within the pores of meso-silicon oxide. The second goal is to establish the influence of concentration of silver present in the system on structure of the porous silica materials. Silver nitrate salt dissolved in hexagonal mesophase of polyoxyethylene 10 lauryl ether (non-ionic PEO-type surfactant) was evenly distributed within silica framework which is tailored through liquid crystalline templating-sol-gel processing. In this approach, lyotropic liquid crystalline mixture containing silver ion and amphiphilic oligo (ethylene oxide) precursor organizes in hexagonal phase in the presence of nitric acid and water at room temperature. This preformed silver containing LC mesophase is utilized as a template for subsequent condensation-polymerization reacting of Si (OCH subscript 3) subscript 4) which results in formation of silicon oxide matrix as a direct cast mesophase formed by the template. The amount of silver nitrate homogeneously mixed in LC hexagonal phase of oligo-ethylene oxide/water system alters the mesophase. The template, lyotropic hexagonal mesophase made up by silver nitrate which is dissolved in PEO-type surfactant/water system in the certain concentration range, can be used to synthesize silver containing silica-based mesoporous materials. It is determined that C subscript 12 E subscript 10:H subscript 2 0 (50 wt%):HNO subscript 3 system preserves its hexagonal LC phase in the presence of Ag ions up to 0.9 silver to surfactant molar ratios. Higher concentrations of silver nitrate in surfactant mesophase induce formation of white soft solid phase, which is assigned to the Ag ion/surfactant/ nitrate ion complex. The template mixtures of 0.1-0.7 silver nitrate to surfactant molar ratios yield silver containing 3D-hexagonal meso-silicon oxide. However, at higher silver nitrate concentration amorphous disordered materials form. Homogeneously distributed Ag ions were successfully reduced to Ag nunoclusters on both internal and external surface of mesoporous silica materials by hydrazine in the gas phase.