Abstract
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.
Highlights
Heterogeneous photocatalysis has become an alternative treatment method for degradation of organic pollutants from wastewater, which has the ability to mineralize organic compounds
The photocatalytic activity of the iron oxide is depending on the particle size, which is difficult to synthesize nanosized iron oxide by conventional method and to control its crystal size in the photocatalyst (Park et al, 2010)
One certain way to overcome this drawback is to apply innovative synthetic method of iron oxide nanoparticles of the catalysts that can be dispersed in organic medium and homogenously loaded on to the supported materials
Summary
Heterogeneous photocatalysis has become an alternative treatment method for degradation of organic pollutants from wastewater, which has the ability to mineralize organic compounds. Nano-manganese (IV) oxide (MnO2) has received a great potential application in environmental protection and degradation of organic pollutants in wastewater (Mitta et al, 2009; Su, 2010) It is a promising material for heterogeneous photocatalyst as a new generation environmental friendly catalyst. This is due to its high specific surface area, crystallinity, ability to disintegrate water molecule into hydrogen and hydroxide ions (Kang et al, 2007; Chu and Zhang, 2009). Based on these advantages MnO2 semiconductor was chosen as an assistant component of photocatalyst to improve the photocatalytic activities of binary Al2O3/Fe2O3 nanocomposite.
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