Sonochemical synthesis of ZnO hollow microstructure/reduced graphene oxide for enhanced sunlight photocatalytic degradation of organic pollutants

Abstract

ZnO hollow microspheres and ZnO hollow microspheres/reduced graphene oxide nanocomposites (ZnO-rGO) were synthesized through simple and surfactant free sonochemical method at relatively low temperature. The crystalline structure and morphology of the as-prepared hollow microspheres and their nanocomposites were characterized by X-ray diffraction (XRD), Raman spectroscopy, BET surface area analyzer and electron microscopy (SEM, TEM). The photocatalytic performance of the samples was evaluated for the photodegradation of 2,4-dichlorophenoxy acetic acid (2,4-D) under direct sunlight irradiation. The results showed that the synthesized ZnO have porous hollow microspheres structure, which can act as an antenna system transferring the photogenerated electrons within the network structure as compared to the nonporous ZnO nanoparticles. The introduction of graphene oxide is further enhanced the photocatalytic activity evidencing the role of graphene oxide extending the optical absorption to longer wavelength as well as in decreasing the electron-hole pair recombination. The effect of various parameters such as pH and initial concentration of 2,4-D has been also studied. The kinetic parameters have been determined and the underline reaction mechanism has been proposed.