Synthesis and characterization of pristine and Sr-doped ZnO nanostructures for photocatalytic and antimicrobial applications
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Date
2021
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UMT, Lahore
Abstract
Herein this study, we have synthesized pristine Zinc oxide (ZnO) and Strontium (Sr)-doped ZnO (2 and 4 wt.% doping) nano structured photocatalyst by chemical precipitation method. During characterization, structural and optical properties of pristine ZnO and Sr doped-ZnO photocatalyst have been performed using X-Ray Diffraction (XRD) and Ultraviolet-visible (UV-vis) spectroscopy, respectively. The XRD results depict the hexagonal crystalline structure of the synthesized ZnO. Specifically in comparison to XRD pattern of pristine ZnO, no distinct peaks (which may be attributed to Sr doping) have been observed in the XRD patterns of Sr doped ZnO nanostructures. The reason may be two-fold: either because the concentration of strontium doped in the synthesized samples is too low to be measured or that the Sr 2+ has completely doped into the ZnO crystal lattice. Similarly the optical properties of pristine ZnO and Sr-doped ZnO nanomaterials have also been studied and compared. The UV-vis results indicate that absorption of Sr-doped ZnO has been red shifted (i.e., moved towards higher occurrence) as compared to that of pristine ZnO; thereby, resulting in the decrease in optical band gap of Sr doped ZnO photocatalysts. Specifically, the optical band gap of ZnO and Sr doped ZnO (2 and 4 wt.%) has been estimated to be 3.3, 3.2 and 3.1 eV, respectively. The photocatalytic activity of synthesized materials has been performed for the degradation of Methylene Blue (MB) dye. The experimental results indicate that the 2 wt. % Sr doped ZnO photocatalyst has shown the best performance i.e., 95 % degradation of MB dye (degradation rate ~ 0.0263 / min) under 120 mins irradiation by 400W Mercury bulb. We believe that 2 wt. % Sr-doping in ZnO may have resulted in the formation of intermediate energy levels, thereby slowing down the recombination of electron-hole pairs. However, with further Sr doping in ZnO (i.e., 4 wt. %), sunlight utilization may decrease and faster recombination of electron-hole pairs may occur. Furthermore, the antibacterial activity of all the three synthesized nanomaterials has been studied towards S. aureus and E. coli bacteria and compared with the standard antibiotic Ciprofloxacin. We have observed that Sr doped ZnO (4 wt. %) nanostructure have shown excellent bactericidal potential.