A novel BiOCl thin film prepared by electrochemical method and its application in photocatalysis

The schematic diagrams of preparation process for BiOCl thin films and the possible synergistic mechanism for electrons and holes transport between BiOCl bulk states and (110) surface states. [Display omitted] ► A novel BiOCl thin film was prepared by electrochemical method for the first time. ► BiOCl with highly exposed (110) plane distributed uniformly on the Ti substrate. ► Synergistic effect of BiOCl bulk and (110) surface states enhanced carrier transport. ► As-prepared thin film exhibited wonderful photocatalytic activity and stability. ► BiOCl film shows a competitive and promising application in photocatalysis field. In this study, a novel BiOCl thin film with flakelike structures has been successfully prepared through electrochemical method composed of a cathodic electrodeposition and an anodic oxidation at room temperature. The samples obtained at the different oxidation voltages were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM), electronic energy spectrum (EDS), and UV–vis diffuse reflectance spectra (UV–vis DRS). The analysis results show that the morphological, structural, and optical characteristics of BiOCl thin films depend markedly on the anode oxidation voltage and the lattice orientation of BiOCl thin film is transformed mainly into (110) surface with the increasing oxidation voltages. The observed results of high-resolution transmission electron microscopy (HRTEM) confirm that pure tetragonal BiOCl thin film with the highly exposed (110) surface is obtained at 2.0V and consists of interlaced nanosheets. First-principles calculations reveal that the existence of BiOCl (110) surface states enhances the electron transition and efficient separation of photo-induced electron–hole pairs. The optimized BiOCl thin film can not only guarantee the intrinsic photochemical properties of BiOCl bulk but also exhibit additional electronic characteristics of BiOCl (110) surface, and consequently the wonderful synergistic effect between BiOCl bulk and BiOCl (110) surface accelerates the efficient separation of electron–hole pairs and produces the high reducing superoxide radicals O2− and strong oxidizing hydroxyl radicals OH required for the degradation of organic compounds. For as-prepared BiOCl thin film, the degradation ratio of methyl orange (MO) reaches 98% under 2.5h UV irradiation at the first cycle and still remains 90% at the fifth cycle, and the COD removal efficiency of 50mg/L MO solution over BiOCl thin film achiev