In this paper, the photocata lytic degradation of Reactive Black 5(RB5)was investigated with fe rrite bis- muth synthesized via ultrasound under direct sunlight irradiation.The intensity of absorptio npeaks of RB5 gradually decreased by increasing the irradiation time and finallyvanished in 50 min in acidic med- ium. The formation of new intermediate was observed in basic medium.The relative concentration of RB5 in solution and on the surface of ferrite bismuth (BiFeO3) nanoparticles was consider ed during the exper- iment in acidic and basic media.The effects of various parameters such as amount of catalyst,concentra- tion of dye, and pH of the solution have been studied on the dye degradation.The adsorption isotherm and the kinetic of photocatalytic degradation of RB5 were investigated.The adsorption constants in the dark and in the presence of sunlight irradiation were compared.The photocatalytic degradation mechanism of RB5 has been evaluated through the addition of some scavengers to the solution.In addi- tion, the stability and reusability of the catalyst were examined in this work

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