A flake-tube structured BiOBr-TiO2 nanotube array heterojunction with enhanced visible light photocatalytic activity

In this study, a new flake-tube structured BiOBr-TiO2 nanotube array (TNTA) heterojunction has been successfully prepared by anodization followed by a sequential chemical bath deposition (S-CBD) method. The as-prepared samples were characterized by X-ray diffraction (XRD), electron microscopy, X-ray photoelectron spectroscopy (XPS) and nitrogen sorption. The photocatalytic activities toward degradation of methyl orange (MO) were evaluated under simulated sunlight. The transient photocurrent response under visible-light irradiation was measured to further confirm the photocatalytic activity enhancement. The results revealed that BiOBr nanoflakes were uniformly dispersed on both inner and outer walls of TiO2 nanotubes, and the BiOBr-TNTAs-2 displayed the best photocatalytic activities, favorable stability and highest photocurrent density among all the BiOBr-TNTAs heterostructured samples. The combined effects of several factors may contribute to the remarkably enhanced photocatalytic activity for the BiOBr-TNTAs-2 sample including an open tube-mouth structure, strong visible-light absorption by BiOBr, the formation of a BiOBrTNTAs heterojunction and a larger specific surface area.