Synthesis, characterization and photocatalytic activity of MnO2/Al2O3/Fe2O3 nanocomposite for degradation of malachite green

New nanocomposite MnO2/Al2O3/Fe2O3 photocatalyst was successfully synthesized by sol-gel method using metal salts as precursors in the presence of acid catalyst. The as-synthesized samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), atomic absorption spectroscopy (AAS) and UV-Vis diffuse reflectance spectroscopy. Elemental analyses of the as-synthesized samples were similar to those expected from the initial concentrations of the solutions used during synthesis. The x-ray diffraction pattern indicated that all as-synthesized samples had a crystal size with a rhombohedral structure and finest particle size of the catalyst (20.096 nm) was obtained at 400°C calcination temperature. The band gap energy of the MnO2/Al2O3/Fe2O3 photocatalyst was calculated to be 1.97 eV and indicated that the as-synthesize sample had high photoabsorption property in the visible light region. Fourier transform infrared spectra confirmed the presence of hydroxyl group and Fe-O bond vibration in the catalyst. Experimental result of the MnO2/Al2O3/Fe2O3 photocatalyst calcined at 400°C in 180 min (the molar ratio of 10 wt% Mn/15 wt% Al/75 wt% Fe) exhibited high photocatalytic activity of 92.89% under visible light irradiation. This may be due to the coupling effect of semiconductors, small particle size of catalyst and low electron-hole pair recombination on the surface of the catalyst. The pseudo-first-order rate constants of MG dye degradation in the presence of the catalyst were calculated as 4 × 10-4, 6.56 × 10-3 and 1.0 × 10-2 min-1 under no light irradiation, UV and visible light irradiation, respectively. Key words: Malachite green, nanoparticles, photocatalysis, sol-gel synthesis, ternaryoxides.