Dextran templating for the synthesis of metallic and metal oxide sponges

Abstract

Silver or gold-containing porous frameworks have been used extensively in catalysis, electrochemistry, heat dissipation and biofiltration^1,2,3. 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 m² g⁻¹, which is typically higher than that obtained for pure metal powders or foils prepared electrolytically⁴ or by infiltration and thermal decomposition of insoluble cellulose supports⁵. Starch gels have been used in association with zeolite nanoparticles to produce porous inorganic materials with structural hierarchy⁶, 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 °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.