Mesoporous nanocrystal clusters of anatase TiO2 with large surface area and enhanced photocatalytic activity
have been successfully synthesized. The synthesis involves the self-assembly of hydrophobic TiO2 nanocrystals
into submicron clusters, coating of these clusters with a silica layer, thermal treatment to remove organic ligands
and improve the crystallinity of the clusters, and finally removing silica to expose the mesoporous catalysts.
With the help of the silica coating, the clusters not only maintain their small grain size but also keep their
mesoporous structure after calcination at high temperatures (with BET surface area as high as 277 m2/g). The
etching of SiO2 also results in the clusters having high dispersity in water. We have been able to identify the
optimal calcination temperature to produce TiO2 nanocrystal clusters that possess both high crystallinity and
large surface area, and therefore show excellent catalytic efficiency in the decomposition of organic molecules
under illumination by UV light. Convenient doping with nitrogen converts these nanocrystal clusters into active
photocatalysts in both visible light and natural sunlight. The strategy of forming well-defined mesoporous
clusters using nanocrystals promises a versatile and useful method for designing photocatalysts with enhanced
activity and stability.