Hollow spheres of crystalline porous metal oxides: A generalized synthesis route via nanocasting with mesoporous carbon hollow shells

Hollow spheres and shells of crystalline porous metal oxides have been nanocast using hollow spheres of mesoporous carbon as hard template. The metal oxides are fabricated from alkoxide precursors within the pore channels of the carbon templates. Remarkably, only one infiltration cycle was required to introduce (metal alkoxide) molecular precursors into the pores of the carbon templates. Removal of the carbon by calcination (at 500-600 degrees C) results in porous metal oxides with predominantly hollow sphere morphology, thus demonstrating the replication of the hollow sphere morphology from carbon to metal oxide. The metal oxides (titania, zirconia, alumina and magnesia) exhibit highly crystalline frameworks and relatively high surface area. The surface area is particularly high for alumina (gamma-Al2O3, 212 m(2) g(-1)) and titania (anatase, 100 m(2) g(-1)). Mixed (MgO-Al2O3) or binary (MgTiO3) metal oxides with relatively well formed hollow sphere morphology and high surface area (154 m(2) g(-1) for MgTiO3 and 322 m(2) g(-1) for MgO-Al2O3) may also be nanocast.