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.