Structure and contribution to photocatalytic activity of the interfaces in nanofibers with mixed anatase and TiO 2(B) phases

Abstract

Fibril photocatalyst of mixed TiO 2(B) and anatase phases, pure TiO 2(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 TiO 2(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 TiO 2 photocatalysts but also for understanding the photocatalysis process.