Synthesis, Characterization, And Photocatalytic Activity Of The TiO₂ Mesocrystals With Exposed {001} Facets

Due to its unique physical and chemical characteristics, such as nontoxicity, stability, high photoelectric conversion efficiency and high reaction activity, TiO2 materials show promising applications in many fields that are related with environment and energy, such as photoelectric conversion and photocatalysis.Currently, most theoretical and experimental studies suggest that anatase TiO2 materials with largely exposed {001} facets have higher photocatalytic activity than the conventional TiO2 materials(which are usually with largely exposed {101} facets). In addition to whether the {001} facets are exposed, the photocatalytic activity is also related to crystallite size and specific surface area of the material. Mesocrystals are a new class of solid materials, which are built of crystallographically oriented nanocrystals. Due to the unique structure, a mesocrystalline material may has a high crystallization degree and a large specific surface area as well. Both of them are beneficial to improve photocatalytic activity of a material.This paper includes three parts.(1) Synthesis of NH4TiOF3 crystals. The reaction between NH4 OH and(NH4)2TiF6 was first developed and used to prepare NH4TiOF3 crystals. The influence of the reactant ratio, reaction time and reaction temperature on the products was investigated.(2) Conversion from NH4TiOF3 to TiO2. Topotactic transformation reaction of NH4TiOF3 to TiO2 was used to prepare TiO2 mesocrystals. The influence of sintering temperature and time on morphology and composition was investigated.(3) Photocatalytic activity. The influence of different reaction conditions on photocatalytic activities of the products was investigated. The results indicate: our method is totally novel, extremely easy, much greener and low cost in comparison with other popular methods; our products are built of TiO2 nanocrystals with similar crystallographic orientation and largely exposed {001} facets; the optimized photocatalytic activity is about twice as commercial used catalyst P25.