Synthesis and photocatalytic properties of fibrous titania by solvothermal reactions

Fibrous titania was synthesized by the solvothermal reactions of fibrous H2Ti4O9·0.25H2O precursor in different media. H2Ti4O9·0.25H2O transformed in steps to H2Ti8O17, monoclinic TiO2, anatase and rutile. The phase transformation temperature and microstructure of the products changed significantly, depending on the heating environment. The critical temperature at which anatase appeared in liquid media was much lower than that in air, indicating that the phase transformation of the monoclinic TiO2 to anatase proceeded by the dissolution–precipitation mechanism. Nanosize crystals of TiO2 possessing high crystallinity could be obtained by the solvothermal reactions using water and methanol as reaction media. The crystallite size of the titania could be decreased using methanol as a reaction medium. The photocatalytic activity of titania changed with heat treatment media in the following sequence: methanol>water⪢air. The effects of the phase composition and microstructure of the TiO2 powders on photocatalytic activity were also investigated. Titania powders crystallized by the solvothermal reaction in methanol possessed excellent photocatalytic activity and thermal stability.