Nanocasting of Hierarchically porous Co3O4, Co, NiO, Ni, and Ag Monoliths: Impact of processing conditions on fidelity of replication

Franchessa M. Sayler, Amy J. Grano, Jan-Henrik Smått, Mika Lindén, Martin G. Bakker

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    Hierarchically porous silica monoliths with a bicontinuous pore structure at the micrometer length scale and 3.4 nm surfactant templated mesopores were used as hard templates for preparing Co3O4, NiO, as well as cobalt, nickel and silver metal monoliths. Aqueous solutions of metal nitrates were repeatedly infiltrated into the porous silica templates after which the nitrate salts were thermally decomposed. Thermal decomposition in air or nitrogen produced porous NiO and Co3O4 oxide monoliths, while thermal decomposition under an atmosphere of 5% hydrogen in 95% nitrogen produced porous monoliths of nickel, cobalt and silver. Removal of the silica template using potassium hydroxide solutions produced free-standing hierarchically porous Co3O4, NiO, cobalt, nickel and silver monoliths. The surface areas of the materials determined by nitrogen adsorption were 141 m2/g for Co3O4, 42 m2/g for cobalt, 32 m2/g for NiO, 13.7 m2/g for nickel and 2.2 m2/g for silver. The impact of an additional annealing step was also assessed. The differences in the surface area, pore size distribution, morphology between the samples as well as the fidelity of the replication are discussed within the framework of a comprehensive model for nanocasting within porous monoliths. From this model, it is evident that the final replica structure is strongly dependent on the wettability of the metal oxide or metal on silica and the increased mobility at elevated temperatures, as the non-wetting metals typically displayed a higher migration out of the mesopores giving rise to a lower surface area compared to the metal oxides.
    Original languageUndefined/Unknown
    Pages (from-to)141–150
    JournalMicroporous and Mesoporous Materials
    Publication statusPublished - 2014
    MoE publication typeA1 Journal article-refereed

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