Chromium (VI) photo-reduction under visible and sunlight irradiation over bismuth-ferrites Bi2Fe4O9 photo-catalyst
Abstract
The photo-catalytic reduction of Cr(VI) in aqueous solution was investigated over spinel ferrites Bi2Fe4O9 photo-catalyst under both visible and solar light irradiation. The material was prepared by a low-cost method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersive x-ray (EDX), Fourier transform infrared spectroscopy (FTIR), and diffuse reflectance spectroscopy (DRS). Electrochemical and photo-electrochemical studies of the material were also explored. The Bi2Fe3O9 structure had a small band gap (2.05 eV), which allowed the material to absorb more visible light. The photo-electrochemical characterization in the presence of Na2SO4 indicated that Bi2Fe4O9 is a n-type semi-conductor with a flat band of 0.77 V. The influence of the catalyst dose (0.25–1.5 g L−1), the initial concentration of Cr(VI) (25–125 mg L−1), and the irradiation source parameters on the photo-catalytic performance of Bi2Fe4O9 were studied at pH 2. The results indicated that the reduction rate of Cr(VI) depended on the catalyst's mass and the initial concentration of Cr(VI). By comparing the photo-reduction activity under visible, ultrasonic, and solar irradiation, it became apparent that the presence of solar light increased the reduction efficiency. The Cr(VI) reduction rate was remarkably different when a combination of sonication and photo-catalysis was utilized. This work indicated that Bi2Fe4O9 can serve as a promising photo-catalyst for the photo-reduction of Cr(VI) under visible light irradiation.
