Silver or gold-containing porous frameworks have been used extensively in catalysis, electrochemistry, heat dissipation and biofiltration. These materials are often prepared by thermal reduction of metal-ion-impregnated porous insoluble supports (such as alumina and pumice), and have surface areas of about 1 m(2) g(-1), which is typically higher than that obtained for pure metal powders or foils prepared electrolytically or by infiltration and thermal decomposition of insoluble cellulose supports. Starch gels have been used in association with zeolite nanoparticles to produce porous inorganic materials with structural hierarchy, but the use of soft sacrificial templates in the synthesis of metallic sponges has not been investigated. Here we demonstrate that self-supporting macroporous frameworks of silver, gold and copper oxide, as well as composites of silver/copper oxide or silver/titania can be routinely prepared by heating metal-salt-containing pastes of the polysaccharide, dextran, to temperatures between 500 and 900 degrees C. Magnetic sponges were similarly prepared by replacing the metal salt precursor with preformed iron oxide (magnetite) nanoparticles. The use of dextran as a sacrificial template for the fabrication of metallic and metal oxide sponges should have significant benefits over existing technologies because the method is facile, inexpensive, environmentally benign, and amenable to scale-up and processing.
High surface area ceramic films and biopolymer films were fabricated by precipitation at room temperature of a reagent aerosol composed of approximately 1 μm diameter microdroplets laid onto a reactive receiver solution using a completely enclosed system. Calcium phosphate films of up to 340 μm in thickness composed of hollow microspheres were generated by gradual settling and precipitation of the reagent microdroplets on the receiver solution surface. Suitability of the ceramic film as a drug support using alendronate as an example was investigated. Chitosan/alginate biopolymer films were similarly prepared and precipitation with limitation to the air/water interface promoted a wire form copper oxide precursor. Zirconia microspheres were prepared without use of surfactant or template via precursor precipitation in a stirred receiver solution. Additional components could be readily incorporated and the flexibility of the novel approach is consistent with a new general strategy for the preparation of thin films and hollow microspheres of nanostructured materials.
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