TiO₂ is the most extensively studied materials for photocatalysts because of its strong oxidizing power, low toxicity, and long-term photostability. TiO₂ exists mainly in four polymorphic forms in nature, anatase, rutile, brookite and TiO₂(B). Generally, anatase phase is considered to have higher photoactivity than other phase. However, it was also found that the TiO₂ powders consisted of mixed anatase and rutile nanocrystals (P25), exhibit a better photoactivity than pure anatase in many reaction systems. This phenomenon has been extensively investigated because it could be important for design of efficient TiO₂ photocatalysts. It is believed that the difference between conduction band edges of the two phases may facilitate irreversible electron transfer from anatase to rutile, and thus reduce the recombination of photo-generated electrons and holes.
In principle, the mechanism of efficient charge separation via irreversible charge transfer should be applicable to other systems of mixed TiO₂ phases as long as there is a difference between the conduction band edges to causing irreversible charge transfer from one phase to another. In the present study, we investigated the photoactivity of a series of nanofibers with mixed TiO₂(B) and anatase phases and verified that the irreversible charge transfer enhanced the photocatalytic activity of the mixed phase nanofibers. The structure of the interfaces between the two phases in nanofibers was investigated in detail, and we found that interfaces formed by well-matched two phases are important for photoactivity of the nanofibers.