Abstract: In this paper, a series of pure-phase Bi₂Fe₄O₉ nanocrystals were synthesized by adding different content of FeCl₂ in the process of hydrothermal method, and the lower valence iron ions were successfully introduced into Bi₂Fe₄O₉. The UV-visible absorption spectrum data proves that the addition of FeCl₂ reduces the optical band gap of Bi₂Fe₄O₉ from 2.06 eV to 1.96 eV. Both the scanning electron microscope images and X-ray diffraction patterns prove that the synthesized samples are pure-phase square flakes Bi₂Fe₄O₉ nanocrystals. Three synthesized Bi₂Fe₄O₉ nanocrystal samples (S1, S2, S3, the FeCl₂ content of the three samples increased from 0 during the synthesis process, corresponding to x=0, 0.2 mmol, 0.4 mmol, respectively) were used for photocatalytic degradation of methyl orange solutions under a 500 W mercury lamp irradiation. It is found that the photocatalytic degradation rate of the three samples is the fastest when 20 μL of hydrogen peroxide is added, and the photocatalytic degradation rate of the S3 sample is faster than that of S1 and S2. In the case of appropriate addition of hydrogen peroxide, the addition of FeCl₂ can improve the performance of Bi₂Fe₄O₉ in photocatalytic degradation of dye molecules.

Key words: FeCl₂, Bi₂Fe₄O₉, hydrothermal method, photocatalysis, methyl orange, H₂O₂