Photocatalysts of quaternary composite, bismuth oxyfluoride/bismuth oxyiodide/ graphitic carbon nitride: Synthesis, characterization, and photocatalytic activity

•The first time, CO2 conversion to CH4 using BiOF/BiOI/Bi26O38F2/g-C3N4.•The quaternary composites exhibit the great photocatalytic activity for CV.•BF2I1–150–7–0.02 was 1.24 times higher than the k value of BF2I1–150–7–0.02.••O2−was the major active species, whereas •OH and h+ were the minor ones.