Novel preparation method of well-defined mesostructured nanoaluminas via carbon–alumina composites

Carbon-embedded boehmite and alumina nanoparticles have been obtained through microemulsion-mediated hydrolysis of aluminum alkoxide, hydrothermal treatment and surfactant decomposition in inert atmosphere steps. The rod-shaped alumina nanoparticles, of around 5–15 nm in length and 1 nm in width, were relatively uniformly dispersed into the carbon matrix. The phase transition of the carbon-embedded boehmite to γ-Al2O3 was observed to take place for T ⩾ 600 °C. On the other hand, the γ- to α-phase transition for the alumina nanoparticles dispersed into carbon matrix could not be observed even at temperatures as high as 1340 °C. Energetically restrictions have been invoked to explain this new phenomenon. The alumina nanoparticles of the composite material have been conveniently recovered by air calcination at various temperatures. The morphology of the alumina nanoparticles was preserved after the removal of carbon matrix by air calcination at T ⩽ 800 °C. The carbon-free material showed a mesoporosity (centered at 3.1 nm) formed through scaffold-like aggregation of γ-Al2O3 nanoparticles with rod-like shapes. Higher calcination temperatures (i.e., 900 °C) led to larger, tri-dimensionally developed γ-Al2O3 nanoparticles (diameter 3–9 nm). Consequently, the monomodal pore size distribution was shifted to larger values, centered at 8.1 nm.