Photocatalytic degradation of azo dye by novel Bi-based photocatalyst Bi4TaO8I under visible-light irradiation

In this work, a novel Bi-based oxyhalide Bi4TaO8I was prepared and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV-vis diffuse reflectance spectroscopy. Photocatalytic activity of this material was evaluated by using methyl orange (MO) as a representative azo dye. It was found that Bi4TaO8I had a visible light absorption, and the band-gap energy was estimated to be 2.43 eV. This material exhibited good photocatalytic activity under both ultraviolet and visible light irradiation. The effects of initial MO concentration, aqueous pH, catalyst dosage and irradiation time on the photocatalytic activity were studied systematically. The photocatalytic degradation of MO by Bi4TaO8I under visible-light irradiation was found to follow the pseudo first-order reaction at the low initial concentrations of MO. Reuse of the catalyst was also examined, and the degradation efficiency of MO was still as high as 60% after 3 cycles 01 28 h visible-light irradiation. Furthermore, it was found that the degradation of MO was also effective under solar irradiation. Five main degradation products were observed by HPLC/MS and their chemical structures were suggested. In order to exclude the photosensitization effect, the photocatalytic degradation efficiency of pentachlorophenol (PCP) by Bi4TaO8I was also determined under visible light irradiation. It is expected that Bi4TaO8I would have potential application in the degradation of azo dye wastewaters under solar irradiation. (C) 2011 Elsevier B.V. All rights reserved.