TiO2 mesocrystals: Synthesis, formation mechanisms and applications

Mesocrystals, which are assemblies of crystallographically oriented nanocrystals, have received increasing attention due to their unique properties such as high crystallinity, high porosity, oriented subunit alignment, and similarity to highly sophisticated biominerals. However, the controlled synthesis of TiO2 mesocrystals has not been realized until recently, probably because of the difficulty in accurately controlling the reaction processes that produce TiO2 crystals. In this review, recent advances in the synthesis and applications of TiO2 mesocrystals are summarized with particular attention paid to the mechanisms of their formation. Three typical pathways for the preparation of TiO2 mesocrystals are discussed, namely topotactic transformation, direct synthesis in solution, and growth on supports. The potential applications of TiO2 mesocrystals in lithium ion batteries, photocatalysis, enzyme immobilization, and antireflection materials are also described.