Structure and contribution to photocatalytic activity of the interfaces in nanofibers with mixed anatase and TiO2(B) phases

Fibril photocatalyst of mixed TiO2(B) and anatase phases, pure TiO2(B) and pure anatase are obtained by calcining titanate nanofibers prepared via hydrothermal reaction at different temperatures between 300 and 700 °C. They are used to verify the theory that the difference between the conduction band edges of the two phases may produce charge transfer from one phase to the other, which results in effectively the photo-generated charge separation and thus facilitates the redox reaction involving these charges. Indeed, the mixed-phase nanofibers exhibit higher photocatalytic activity for degradation of sulforhodamine B (SRB) under UV light than the nanofibers of either pure phase alone, or the mechanical mixtures of the two pure phase nanofibers with a similar phase composition. The interfaces between the two phases have a function of preventing charge recombination and enhancing the activity for photocatalytic oxidation. These interfaces are not random contacts between the crystals of the two phases, but form from well-matched lattice planes of the two phases. For instance, (2 0 2) planes in anatase and (2 0 2) planes of TiO2(B) are similar in d-spaces ∼0.18 nm, and they join together to form a stable interface. Such an interface structure is advanced for charge transfer crossing the interfaces, which reduces the recombination between the photo-generated electrons and holes. The knowledge acquired in this study is important not only for design of efficient TiO2 photocatalysts but also for understanding the photocatalysis process.

The interface in mixed phase titania nanofibers is built up by joining (2 0 2) of anatase and (2 0 2) of TiO2(B). The two surfaces are similar in d-spaces ∼0.18 nm. Bonding between the two phases reduces overall energy by removing surface energy associated with unsatisfied bonds. Moreover, such an interface structure provides explanation to the better photocatalytic activity of the mixed-phase nanofibers, compared with that of the mechanical mixtures with a similar phase composition.Figure optionsDownload high-quality image (72 K)Download as PowerPoint slide