Synthesis and characterization of pristine and strontium-doped zinc oxide nanoparticles for methyl green photo-degradation application

Herein we describe an effective route for the degradation of methyl green (MG) dye under visible light illumination by pristine and strontium (Sr)-doped zinc oxide (ZnO) photocatalysts (synthesized by the simple chemical precipitation method). The x-ray diffraction structural analysis has confirmed that both photocatalysts exhibit the hexagonal wurtzite structure; without any additional phase formation in Sr-doped ZnO, in particular. The optical properties of the synthesized photocatalysts have been investigated using UV-vis absorption spectroscopy in the wavelength range of 250-800 nm. Through Tauc's plot, the slight decrease from 3.3 to 3.2 eV in band gap energy has been elucidated (in the case of Sr-doped ZnO), which has been further confirmed by the quenching in the intensity of Photoluminescence (PL) emission spectrum. This may be due to sub-band level formation between valence and conduction band, caused by the impregnation of Sr2+ ions into ZnO host. The morphological study has also been performed using Field Emission Scanning Electron Microscope, which indicates nanoparticles (NPs) based surface texture for both photocatalysts. During the photocatalytic activity study, after 30 min irradiation of visible light, similar to 65.7% and similar to 84.8% photocatalytic degradation of MG dye has been achieved for pristine and Sr-doped (2 wt%) ZnO photocatalysts, respectively. The rate of photocatalytic reaction (K) has been observed to be similar to 0.06399 min(-1) for Sr-doped (2 wt%), whereas nearly half magnitude similar to 0.03403 min(-1) has been observed for pristine ZnO, respectively. The significantly improved photodegradation activity may be ascribed to the relatively broader optical absorption capability, surface defects and the enhanced charge separation efficiency of the Sr-doped ZnO photocatalyst.