Solar photocatalytic degradation of RB5 by ferrite bismuth nanoparticles synthesized via ultrasound

► RB5 was completely destroyed under sunlight irradiation in acidic medium (50min). ► Degradation of RB5 proceeded by different paths in acidic and basic media. ► The photocatalytic degradation of RB5 proceeded via direct reactions with holes and OH ► The catalyst exhibited no significant loss of activity after consecutive cycles. ► BFO synthesized with ultrasound had higher photocatalytic activity than sol–gel method. In this paper, the photocatalytic degradation of Reactive Black 5 (RB5) was investigated with ferrite bismuth synthesized via ultrasound under direct sunlight irradiation. The intensity of absorption peaks of RB5 gradually decreased by increasing the irradiation time and finally vanished in 50min in acidic medium. 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 considered during the experiment in acidic and basic media. The effects of various parameters such as amount of catalyst, concentration 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 addition, the stability and reusability of the catalyst were examined in this work.