A facile template-free approach to metal oxide spheres with well-defined nanopore structures

Nanoporous Al₂O₃ with well-defined pore structure, crystallized framework and spherical morphology has been prepared by a facile template-free approach, which involves the preparation via homogeneous precipitation and subsequent decomposition of spherical basic aluminium sulphate particles. The particle size of the spheres can be tuned by controlling the holding time from the beginning of precipitation, and a proper decomposition temperature is important to get high surface area, high pore volume and well-defined pore structures. By the similar way, nanoporous ZrO₂ and TiO₂ spherical particles can also be prepared. These nanoporous oxides all have moderately high surface area (50–70 m²/g) and well-defined nanopores of around 4–12 nm with very narrow pore size distribution. The frameworks of these oxide spheres consist of many small nanocrystallites, between which the nanopores exist. Compared with the soft and hard template routes, this decomposition strategy of sulphates for nanoporous oxides has the advantages of simplicity and low cost.