Synthesis and optical properties of TiO₂/TiOF₂ composite powder with controlled phase fractions via an ultrasonic spray pyrolysis process

Photoelectron-hole separation efficiency plays an important role in the enhancement of the photocatalytic activity of photocatalysts towards the degradation of organic molecules. In this study, TiO₂/TiOF₂ heterostructured composite powders with suitable band structures, which structures are able to separate photoelectron-hole pairs, have been synthesized using a simple and versatile ultrasonic spray pyrolysis process. In addition, their phase volume fractions have been controlled by varying the pyrolysis temperature from 400 °C to 800 °C. The structural and optical properties of the synthesized powders have been characterized by X-ray diffraction, scanning electronic microscopy and UV-vis spectroscopy. The powder with a phase volume ratio close to 1, compared with single TiOF₂ and other composite powders with different phase volume fractions, was found to have superior photocatalytic activity for the degradation of rhodamine B. This result shows that the TiO₂/TiOF₂ heterostructure promotes the separation of the photoinduced electrons and holes and that this powder can be applicable to environmental cleaning applications.