Synthesis, characterization and photocatalytic activity study of synthetic zeolite supported- ZnO-Fe2O3-MnO2 nanocomposite for methylene blue degradation

Abstract

ZnO-Fe2Ü3-Mn02 nanocomposites were synthesized via one step impregnation of Mn02 powder with an aqueous solution of Zn(II) and Fe(III) nitrate salts. Zeolite supported­ ZnO-Fe203-Mn02 composite was prepared by solid state reaction. The morphology, structure and elemental analysis of as-synthesized nanocomposites were studied by using XRD, SEM/EDX, UV-visi ble and AAS spectrophotometry. Photocatalytic degradation activities of as­ synthesized nanocomposites under visible light irradiation have been evaluated in the reduction of aqueous methylene blue (MB) dye solution and real sewage samples collected from Dire Dawa Textile lndustry. Zeolite supported -Zn0-Fe203-Mn02 photocatalyst exhibited effective degradation efficiency of methylene blue (MB) dye and real sewage sample to the extent of approximately 93% and 63%, respecti vely. The photocatalytic efficiency of the naked ZnO­ Fe203-Mn02 nanocomposite was found to be 77% under visible light irrad iation, significantly lower than the supported mixed oxide indicating that zeolite plays a role in the performance of the composite. When the visible light hit the VB of combined sem iconductor, CB electrons can be ejected from the low band gap semiconductor (Fe203) to the high band gap semiconductor (ZnO) and on the contrary, hole transfer can take place from the VB of high band gap semiconductors (ZnO) to the VB of small band gap semiconductor (Fe203). Additionally the presence of electron acceptor Mn(IV) could scavenge the excited electrons and altogether prevent the recombi nation of electron-hole pairs. While these constituents along with the zeolite framework, serve as an electron acceptor and delay the rate of photogenerated electron-hole pairs recombination as well as to increase the surface area that could give more active surface sites to absorb water molecules and to form active hydroxyl radical by trapping the photo­ generated holes. Photocatalytic degradation of methylene blue dye (MB) follows pseudo first order kinetics for all as-synthesized nanocomposites.