Synthesis and Enhanced Visible-Light Photoelectrocatalytic Activity ofp−nJunction BiOI/TiO₂Nanotube Arrays

p−n junction BiOI/TiO2 nanotube arrays (NTs) were prepared by coating BiOI on the tube wall of the self-organized TiO2 NTs using a novel impregnating−hydroxylation method. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and UV−vis absorption spectroscopy. The photoelectrocatalytic (PEC) activity toward degradation of methyl orange (MO) aqueous solutions under visible-light irradiation (λ > 420 nm) by p−n junction BiOI/TiO2 NTs was investigated. The results from the current study demonstrate that the as-prepared BiOI/TiO2 junction NTs display much greater PEC activity than the respective pure BiOI and TiO2 counterparts due to the synergetic effects of several factors including the strong visible absorption, the formation of p−n junction, and the impact of external electrostatic field. The proposed mechanism responsible for the enhanced performance was further confirmed by the transient photocurrent response experiments.