Novel method of square wave voltammetry for deposition of Bi2S3 thin film: Photocatalytic reduction of hexavalent Cr in single and binary mixtures.

In this work a new method of square‒wave voltammetry was performed for electrodepositing of Bi2S3 film on the stainless steel mesh surface as low-cost and effective substrate in visible light harvesting. First, the obtained porous film was characterized by X‒ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), atomic force microscopy (AFM), and Raman analysis. In following, photocatalytic activity of film for reduction of hexavalent Cr was evaluated under sunlight irradiation. Results suggested that the presence of voids having several nanometers to 2 μm diameters on the film surface plays key role in photocatalytic processes. Indeed, surface voids as trapping cites and producing routs leads to multiple scattering of visible light. It can be noted that morphology of thin film, substrate structure, and diameters of voids are the main parameters to achieving the high reduction efficiency. Cr(VI) was completely reduced within 100  min under sunlight irradiation. Photoreduction mechanistic studies induced by Bi2S3 film suggested that active oxygen species such as HOO• and O2 have significant role in photocatalytic reaction. Finally, the evaluation of simultaneous photocatalytic process of binary mixture (Cr(VI) and Rhodamin B) was shown synergistic improvement of Cr(VI) and Rhodamin B degradation due to rapid surface reactions.