Photocatalytic and sonocatalytic degradation procedures of methylene blue dye using a ZnO nanostructured powders

Abstract

The elimination of organic pollutants from wastewater is an important procedure in environmental protection. Dyestuffs and other commercial pigments have emerged as a focus of environmental recovery efforts. Various chemical and physical processes, such as chemical precipitation and separation of pollutants, coagulation, and elimination by adsorption on activated carbon are applied for elimination of organic pollutants. The main disadvantage of these methods is that they only change the contamination from one phase to another. In recent years, semiconductorassisted photocatalysis and sonocatalysis has been extensively investigated, primarily due to its capability to degrade a great number of chemicals in gaseous or aqueous systems, through relatively in-expensive procedures. In this work we have investigated heterogenic photocatalytic and sonocatalytic degradation of methylen blue (MB) aqueous solution, as a common organic pollutant, in the presence of nanosized ZnO powder as a catalyst. The phase composition of synthesized ZnO nanopowder was identified by XRD, particles morphology was characterized by FE–SEM. The optical properties of ZnO nanocrystals were investigated by ultraviolet–visible (UV–Vis) diffuse reflectance spectroscopy (DRS). Concentration of the MB dye in the water solution containing ZnO nanoparticles before and after photocatalytic or sonocatalytic degradation was calculated according to the absorbance maxima value at 665 nm characteristic for MB. The experiments were performed on a UV–Vis spectrophotometer in the wavelength range of 300–800 nm.