title: Photocatalytic degradation of methylene blue dye by zinc oxide nanoparticles obtained from precipitation and sol-gel methods.
abstract: Zinc oxide (ZnO) nanoparticles were synthesized by precipitation and sol-gel methods. The aim of this study was to understand how different synthetic methods can affect the photocatalytic activity of ZnO nanoparticles. As-synthesized ZnO nanoparticles were characterized by X-ray diffraction (XRD) and UV-Visible spectroscopic techniques. XRD patterns of ZnO powders synthesized by precipitation and sol-gel methods revealed their hexagonal wurtzite structure with crystallite sizes of 30 and 28 nm, respectively. Their photocatalytic activities were evaluated by photocatalytic degradation of methylene blue, a common water pollutant, under UV radiation. The effects of operational parameters such as photocatalyst load and initial concentration of the dye on photocatalytic degradation of methylene blue were investigated. While the degradation of dye decreased over the studied dye concentration range of 20 to 100 mg/L, an optimum photocatalyst load of 250 mg/L was needed to achieve dye degradation as high as 81 and 92.5 % for ZnO prepared by precipitation and sol-gel methods, respectively. Assuming pseudo first-order reaction kinetics, this corresponded to rate constants of 8.4 × 10-3and 12.4 × 10-3min-1, respectively. Hence, sol-gel method is preferred over precipitation method in order to achieve higher photocatalytic activity of ZnO nanostructures. Photocatalytic activity is further augmented by better choice of capping ligand for colloidal stabilization, starch being more effective than polyethylene glycol (PEG).
authors.affiliation: Chemistry Department, Haramaya University, Post Box 138, Dire Dawa, Ethiopia.
authors.forename: Abebe
authors.initials: A
authors.lastname: Balcha
authors.affiliation: Chemistry Department, Haramaya University, Post Box 138, Dire Dawa, Ethiopia.
authors.forename: Om Prakash
authors.initials: OP
authors.lastname: Yadav
authors.affiliation: Department of Mechanical Engineering, Limerick Institute of Technology, Moylish Park Campus, Limerick, Ireland. taniadey@hotmail.com.
authors.forename: Tania
authors.initials: T
authors.lastname: Dey
mesh_terms: D002384:Catalysis; D011232:Chemical Precipitation; D007700:Kinetics; D008751:Methylene Blue / Q000737:chemistry*; D053758:Nanoparticles / Q000737:chemistry*; D044367:Phase Transition; D010782:Photolysis; D013057:Spectrum Analysis / Q000379:methods; D014961:X-Ray Diffraction; D015034:Zinc Oxide / Q000737:chemistry*
chemical_list: D015034:Zinc Oxide; D008751:Methylene Blue
keywords: Methylene blue; Photocatalyst; Pollutant degradation; XRD; Zinc oxide nanoparticle