Green synthesis of ZnO hollow microspheres and ZnO/rGO nanocomposite using red rice husk extract and their photocatalytic performance

Abstract

ZnO hollow microspheres and ZnO hollow microspheres/reduced graphene oxide (ZnO/rGO) nanocomposites were synthesized for the first time by a completely green method based on red rice husk extract as an effective oxidizing agent as well as a chelating agent and water as a solvent. The green ZnO and ZnO/rGO materials were characterized by x-ray diffraction, scanning electron microscope, FTIR spectroscopy, Raman spectroscopy, BET surface area analyzer and TGA. The results showed that the biosynthesized ZnO and ZnO/rGO has a hollow spherical morphology composed of small ZnO particles with the mean particle size of about 15 nm. The Raman and XRD measurements demonstrated that the as-prepared ZnO structures are of wurtzite hexagonal phase with high crystallinity. The synthesized green ZnO microspheres show high photocatalytic activity for the degradation of malachite green dye as a model pollutant. The photoctalytic activity was further increased in the presence of ZnO/rGO nanocomposite evidencing the role of graphene oxide in capturing the photogenerated electrons and decreasing the electron–hole pair recombination.