(359e) Characteristics of Self-Assembled Metal Oxide Monolayers On Zeolite Surfaces

Metal oxide -- zeolite nanocomposites are employed as catalysts and adsorbents in organic syntheses, and in waste-water treatment. For example, ruthenium oxide deposited on zeolite-Y is an efficient catalyst for the photochemical reduction of water to hydrogen; and iron oxide ? zeolite-Y composites exhibit high adsorption capacity for Cu2+, Cr3+, and Zn2+ which are commonly found in wastewaters from metal-plating and tanning. Recently, gas separation membranes have been developed by incorporating magnesium oxide -- zeolite composites in polymeric membranes. The presence of MgO nanowhiskers has been shown to significantly improve interfacial adhesion between the zeolite and the polymer, and results in enhanced separation efficiency. Here, we report on the self-assembly of metal oxide nanostructures such as MgO nanowhiskers on zeolite surfaces via hydrothermal treatment starting from aqueous solutions containing magnesium chloride and ammonia. The effect of temperature, pH, time, and reactant concentration on the size and morphology of the deposited MgO have been investigated. Adsorption isotherms were measured to deduce the nature of MgO bonding on the zeolite surface and to determine optimal concentrations, pH, and residence times for monolayer formation. Mechanisms of nanowhisker formation and deposition are postulated.