Preparation of ordered mesoporous crystalline alumina replicated by mesoporous carbon

Ordered mesoporous alumina with crystalline framework walls has been fabricated using a repeated nanocasting strategy. Mesoporous silica and mesoporous carbon were successively employed as the exotemplates. Constrained by the rigid carbon template structure, the alumina precursor in the channels of the carbon template could be well crystallized by elevating the temperature in an inert atmosphere, yielding γ-Al2O3 with ordered mesoporous structure upon the carbon template removal. The resulting alumina sample displays a faithfully negative replication both in the pore arrangement and particle morphology of the carbon template, thus a positive replication of the original silica template. The mean pore sizes of the alumina replicas can be tuned from 4.8 nm to 6.2 nm through choosing mesoporous silicas with different pore sizes as the templates. The ordered structure maintained stable until 750 °C, above which it was significantly destroyed due to the overgrowth of the alumina nanocrystallites and the phase transformation-associated constraint. Besides the hexagonally ordering, a 3D cubic ordered mesoporous alumina with γ-alumina framework walls has also been prepared using cubic CMK-8 as the template.