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A graphite carbon nitride (g-C3N4) modified Bi4O5I2 composite was successfully prepared in-situ via the thermal treatment of a g-C3N4/BiOI precursor at 400℃ for 3 hr.The as-preparedg-C3N4/Bi4O5I2 showed high photocatalytic performance in Methyl Orange (MO) degradationunder visible light.The best sample presented a degradation rate of 0.164 min-1,which is3.2 and 82 times as high as that of Bi4O5I2 and g-C3N4,respectively.The g-C3N4/Bi4O5I2 wascharacterized by X-ray powder diffractometer (XRD),scanning electron microscopy (SEM),transmission electron microscopy (TEM),Raman,X-ray photoelectron spectroscopy(XPS),ultraviolet-visible diffuse reflectance spectra (DRS),electrochemical impedancespectroscopy (EIS) and transient photocurrent response in order to explain the enhancedphotoactivity.Results indicated that the decoration with a small amount of g-C3N4influenced the spedfic surface area only slightly.Nevertheless,the capability for absorbingvisible light was improved measurably,which was beneficial to the MO degradation.On topof that,a strong interaction between g-C3N4 and Bi4O5I2 was detected.This interplaypromoted the formation of a favorable heterojunction structure and thereby enhanced thecharge separation.Thus,the g-C3N4/Bi4O5I2 composite presented greater charge separationefficiency and much better photocatalytic performance than Bi4O5I2.Additionally,g-C3N4/Bi4O5I2 also presented high stability.·O-2 and holes were verified to be the main reactivespecies.