Hydrothermal synthesis of perovskite-type MTiO₃(M = Zn, Co, Ni)/TiO₂nanotube arrays from an amorphous TiO₂template

Ordered perovskite-type MTiO3/TiO2 nanotube arrays (NTAs) (M = Zn, Co, Ni) are prepared by a general hydrothermal route based on amorphous TiO2 NTAs via electrochemical anodization of Ti foil. The as-anodized amorphous TiO2 is not stable and can react with H2O in solution producing soluble Ti(OH)62− to form anatase nanoparticles (NPs) via water-induced dissolution and recrystallization. The pH and salt content in the solution play important roles in the morphology and composition of the hydrothermal products. In the presence of a metal acetate, the reaction between Ti(OH)62− and H+ is dramatically restricted and the reaction proceeds preferentially between Ti(OH)62− and M2+ (M = Zn, Co, Ni) to produce insoluble MTiO3 NPs which adhere onto the original architecture in situ to form perovskite-type MTiO3/TiO2 NTAs. This study elucidates the role of the amorphous structure in the formation of MTiO3 and provides a general means of synthesizing nanostructured MTiO3.