New efficient p-n heterojunction of BiOI/TiO2nanotube arrays with enhanced visible-light photoelectrocatalytic activities

Abstract

New flake-tube structured p-n heterojunction of BiOI/TiO 2 nanotube arrays (TNTAs) were successfully prepared by loading large amounts of BiOI nanoflakes onto both the outer and inner walls of well-separated TiO 2 nanotubes via anodization followed by sequential chemical bath deposition (S-CBD) method. The as-prepared BiOI/TNTAs samples with different deposition cycles were characterized by X-ray diffraction, electron microscopy, UV-vis diffuse reflectance spectroscopy and nitrogen sorption. The photoelectrocatalytic (PEC) activity of the BiOI/TNTAs samples toward degradation of methyl orange (MO) solutions under visible-light irradiation were further evaluated. The visible-light PEC activity of BiOI/TNTAs samples were further confirmed by the transient photocurrent response test. In this paper, the 5-BiOI/TNTAs sample with the best PEC activity and the highest photocurrent density among all the BiOI/TNTAs samples was chosen as the typical delegates and emphatically discussed. The results from the current study revealed that TNTAs consisting of well-separated nanotubes with large tube spacings were first fabricated via increasing the water proportion in electrolyte to 10 vol. %. The synergetic effects of several factors may contribute to the remarkably enhanced PEC activities of the 5-BiOI/TNTAs sample, including a 3D connected intertube spacing system and open tube-mouth structure, strong visible-light absorption by BiOI, the formation of p-n heterojunction, larger specific surface area, and the impact of the applied external electrostatic field.