Preparation of new magnetic nanocatalysts based on TiO2 and ZnO and their application in improved photocatalytic degradation of dye pollutant under visible light

摘要

Photocatalytic degradation of methyl orange (MO) as a model of an organic pollution was accomplished with magnetic and porous TiO_2/ZnO/Fe _3O_4/PANI and ZnO/Fe_3O_4/PANI nanocomposites under visible light irradiation. The structures of nanocomposites were characterized by various techniques including UV-Vis absorption spectroscopy, XRD, SEM, EDS, BET and TGA. Optical absorption investigations show two λ_(max) at 450 and 590 nm for TiO_2/ZnO/Fe _3O_4/PANI nanocomposites respectively possessing optical band gaps about 2.75 and 2.1 eV smaller than that of the neat TiO_2 and ZnO nanoparticles. Due to these optical absorptions, the nanocomposites can be considered promising candidates as visible light photocatalysts to produce more electron-hole pairs. The degradation of MO, extremely increased using polymeric photocatalysts and decolorization in the presence of visible light achieved up to 90% in less than 20 min in comparison with the neat nanoparticles (about 10%). All these advantages promise a bright future for these composites as useful photocatalysts. The degradation efficiency of MO using stable nanocomposites was still over 70% after ten times reusing. The highest decolorizing efficiencies were achieved with 0.75 g L~(-1) of catalyst and 10 mg L~(-1) of MO at natural pH under visible light irradiation in less than 20 min. The three and four component nanocomposites (TiO _2/ZnO/Fe_3O_4/PANI and ZnO/Fe_3O _4/PANI), for the degradation of MO as an azo dye at the presence of visible light were used. The results demonstrate that the synthesized nanocomposites are useful for the degradation of water pollutions and may be used for several times without appreciable loss of activity.