Photocatalytic mechanism of Bi 2 Fe 4 O 9 nanoparticles in the degradation of methylene blue

We have investigated the effects of O₂, ethanol, and KI on the photocatalytic efficiency of Bi₂Fe₄O₉ nanoparticles towards the degradation of methylene blue (MB). It is observed that O₂ has a negligible effect on the photocatalytic degradation rate of the dye, whereas ethanol and KI exhibit a strong suppression of the dye degradation, with a stronger effect observed for the latter. Hydroxyl radicals are shown, by the photoluminescence technique using coumarin as a probe molecule, to be produced on the irradiated Bi₂Fe₄O₉, and are scavenged on addition of ethanol and KI. The mechanisms involved are discussed in detail. Based on the experimental results, hydroxyl radicals and photogenerated holes are suggested to be the two main active species in the photocatalytic degradation of MB by Bi₂Fe₄O₉ nanoparticles.