Photoelectrocatalytic reduction of hexavalent chromium by Ti-doped hydroxyapatite thin film

Abstract

Ti-doped hydroxyapatite (TiHAP) is a novel photocatalyst with high adsorption capacity. It shows high photocatalytic activity for the degradation of organic pollutants and sterilization than conventional semiconductors. In this study, highly efficient TiHAP film and fluorine-doped TiHAP (TiFHAP) film were prepared on ITO glass by sol-gel method to investigate their photocatalytic (PC) and photoelectrocatalytic (PEC) reduction towards hexavalent chromium (Cr(VI)). Field emission scanning electronic microscope (FESEM), UV–vis spectrophotometry, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques were used to characterize the morphologies, structure and composition of the samples. In the conditions of 0.5mol/L Na2SO4, 0.5mmol/L citric acid, 0.34mmol/L Cr(VI) and pH=3.4, the PC and PEC conversion rates of Cr(VI) over TiHAP film can achieve 70% and 84% under 90min UV illumination, respectively, which were both higher than TiO2 film. Fluorine-doped TiHAP film (TiFHAP) showed enhanced PC and PEC activities than TiHAP film, with 5.6wt% F-doping being the best. A two-compartment system was employed to study the reaction mechanism of the PEC process. Different from the traditional knowing that Cr(VI) would be reduced on photocathode by photoinduced electrons transferred from anode photocatalyst, the result suggested that it was on the surface of TiHAP photoanode where Cr(VI) was mainly reduced.