In this study, a comparison between two methods of synthesis of Bi2O3-ZnO composite deposited on glass wool (GW) was conducted via the layered double hydroxide (LDH) synthesis route followed by treatment at 450 °C. The obtained materials were characterized by TGA, XDR, SEM, BET, XPS and UV–visible DRS. Characterization results showed two structures identified as LDH and (BiO)2CO3 with and without GW before heat treatment. Bi2O3-ZnO composite was obtained after treatment at 450 °C; however, solvothermal synthesis with GW would appear to be better than that of hydrothermal. Indeed, the material prepared by solvothermal with GW then treated at 450 °C has good crystallinity, high specific surface and lowest band gap energy compared to materials synthesized by hydrothermal. Furthermore, this material showed photocatalytic efficiency of 20 min for a total discoloration of the indigo carmine (IC), this was the best time of discoloration obtained compared to other materials and others from the literature. Identification of the responsible species for the photo-discoloration was conducted and the result showed that the species responsible for the dye discoloration was the radical superoxide anion with a small contribution of the e−/h+ pair. It appears that the hydroxyl radical didn't contribute in this discoloration mechanism.