Hierarchically porous monoliths of carbon and metal oxides with ordered mesopores

Hierarchically porous carbon and metal oxide materials offer great benefits in separations, catalysis and renewable energy. We have here used hierarchically porous silica monoliths with ordered mesopores as hard templates to produce nanocast carbon, Co₃O₄, and NiO monoliths with similar structures. Besides providing the materials with more well-defined physicochemical properties, the ordered mesopore structure also offers an excellent model system for investigating the nanocasting process in detail. The mesopores of the silica monoliths were first infiltrated with furfuryl alcohol or metal nitrate precursor solutions, which subsequently could be thermally converted to carbon or the corresponding metal oxides. After the silica scaffolds have been removed by etching in base solutions, the resulting replica monoliths display macroscopic morphology and macropore structure similar to the original silica template. However, while the carbon and Co₃O₄ materials both display a well-organized nanowire structure, giving rise to high surface area and narrow pore size distribution, the NiO monoliths exhibit a significantly lower surface area and less well-defined mesopore structure implying that only part of the silica mesopores has been replicated. We believe this apparent difference between the two metal oxides is a consequence of differences in mass transport.