Synthesis of nanocrystalline bismuth oxide and its visible photocatalytic activity in the degradation of an organic dye

Bismuth oxide powder was synthesized, characterized and employed as a visible light photocatalyst for the degradation of aqueous solutions of Orange G (OG), a mono azo dye that is a commonly used colouring agent in various industrial applications. A simple combustion method using urea as fuel was employed to synthesize the metal oxide nanopowders. The prepared material was found to be nanocrystalline in nature as confirmed by XRD analysis. The band gap energy of the material is calculated by plotting (Ah nu)(2) vs. h nu from the UV-DRS spectrum and it is found to be 2.7 eV. The surface morphology and roughness of the material was studied by FE-SEM and AFM techniques. XPS and EDAX studies confirmed the elemental purity and presence in the nanomaterial. Preliminary studies were carried out in order to optimize the solution pH, catalyst dosage and initial dye concentration. As the catalyst possessed good activity at all pH values, thereafter all the photocatalytic reactions were carried out at neutral pH to make the process less cumber-some and cost effective. An optimum catalyst dosage of 1.5 g/L was fixed for a dye solution of 5 mg/L concentration. Kinetic studies showed the photo-degradation to follow pseudo-first order kinetics. Studies on the effect of electrolytes in solution showed that there was a decrease in the efficiency of the catalyst in the presence of the electrolytes. Reusability studies were performed on the catalyst to estimate the economic viability of the system.