Modifications in structural, morphological, optical and photocatalytic properties of ZnO:Mn nanoparticles by sol-gel protocol

ZnO:Mn nanoparticles with different Mn concentrations (0, 1 and 3 at%) have been produced by sol-gel wet chemical route. The effect of manganese doping on the structural, micro-structural, optical and photocatalytic properties of zinc oxide nanoparticles (ZnO NPs) has been investigated. X-ray diffraction and Raman investigations confirmed high quality monophase wurtzite hexagonal structure of pure and Mn-doped ZnO NPs; and no separate phase of dopant has been found. The chemical composition of Mn-doped ZnO NPs has been confirmed by X-ray photoelectron spectroscopic measurements. Additionally, the presence of Mn 2p3/2 peak at 640 eV in XPS spectra confirmed the addition of Mn in ZnO host matrix. TEM micrograph showed spherical shaped NPs with an average size in the range of 21-35 nm. The high resolution TEM images exhibit the highly crystalline nature and the inter-planar distances of hexagonal wurtzite ZnO:Mn nanoparticles. Raman study also confirmed the hexagonal wurtzite structure of ZnO:Mn (0, 1 and 3 at%) NPs. Optical absorption spectra showed a red shift in the absorbance band edge with increasing Mn doping in ZnO. The increasing doping level of Mn in ZnO resulted in the narrowing of bandgap and the increasing of visible light absorption. For photocatalytic behavior, the methylene blue (MB) decolorization efficiency in the very presence of synthesized pure and Mn-doped ZnO NPs has been studied under visible light irradiation. Photoluminescence measurements showed that the band edges of ultraviolet and green emissions are slightly red shifted; and PL intensity decreases with the increasing concentration of Mn in ZnO NPs. The significantly enhanced photocatalytic activity of Mn doped ZnO NPs is because of the increase in light absorption and the effective separation between photogenerated electron-hole pairs.