Fabrication of TiO2(B)/anatase heterophase junctions in nanowires via a surface-preferred phase transformation process for enhanced photocatalytic activity

Abstract

Heterojunction fabrication is one of the most effective strategies for enhancing the photocatalytic performance of semiconductor photocatalysts. Here, TiO2(B)/anatase nanowires with interfacial heterostructures were prepared through a three-step synthesis method, including hydrothermal treatment, H+ exchange, and annealing. The phase structures of the nanowires in the bulk and on the surface during the annealing process were monitored by XRD and UV-Raman spectroscopy, respectively. SEM and TEM results indicate that the TiO2(B) nanowires partially collapse and transform into anatase during the annealing process and the heterophase junction structure is formed simultaneously. On the basis of the phase structure together with morphology data, a phase-transformation mechanism was proposed. Photocatalytic activity was evaluated by hydrogen production and pollutant-degradation assays. The optimized structure of the photocatalyst contains 24% TiO2(B) in the bulk and 100% anatase on the surface. The charge-carrier behavior during the photocatalytic process was investigated by photocurrent, electrochemical impedance spectroscopy (EIS), and photoluminescence (PL) spectroscopy, which revealed that the heterophase-junction structure in the bulk was responsible for the highly efficient charge separation and transportation, etc.; the anatase on the surface took control of the high surface-reaction activity.