Thermal annealing-induced self-junction of hydrothermal titanate nanotubes/TiO nanoparticles with enhanced photocatalytic activity.

This work investigates the effect of thermal annealing on the crystalline structure and optical properties of hydrothermal titanate nanotubes (TNTs). It shows that subjecting TNTs to air at 400 °C can be used to form a junction between TNTs and TiO nanoparticles. Furthermore, the TNT microstructure is transformed from monoclinic to anatase phase by the annealing process. As a result of the self-junction formation, the visible photocatalytic activity in the degradation of methylene blue is enhanced in the thermal annealed sample in which the pseudo-first-order model fits well with the kinetic reaction rates of the TNTs and thermal TNTs with values of 0.0034 and 0.0082 min, respectively. Insights into the improvement in photocatalytic activity are revealed by ultraviolet-visible diffuse reflectance and photoluminescence emission spectroscopies.