Phase transition and morphological evolution of titania/titanate nanomaterials under alkalescent hydrothermal treatment

A systematic morphological phase diagram of titania/titanate was determined by the most important synthesis parameters of reaction temperature and NaCl concentration via a facile one-step alkalescent approach. X-Ray diffraction and Raman spectroscopy were used to generally assess the phase composition and crystallite size of different titania/titanate samples, which were also used to investigate the phase transition behavior in connection with the synthesis parameters. Scanning/transmission electron microscopy was employed to characterize the morphology, size, and lattice plane, and to further elucidate the morphological evolution of the resulting products. According to the Ostwald's step rule, a phase transition mechanism was proposed based on our current systematic experimental results, which reveals the phase transitions from layered hydrogen titanate to anatase or brookite under hydrothermal treatment. The brookite-anatase composite exhibited excellent photocatalytic activity in the photodegradation of methyl orange, phenol and salicylic acid solution under UV irradiation.