Effective adsorption and visible light driven enhanced photocatalytic degradation of rhodamine B using ZnO nanoparticles immobilized on graphene oxide nanosheets

Abstract

In this study, graphene oxide (GO), ZnO nanoparticles (NPs) and GO based ZnO nanocomposites (GO-ZnO) have been successfully synthesized by modified Hummer’s method, chemical co-precipitation method and ultrasonication method, respectively. Powder X-ray diffraction (PXRD), transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy were employed to study the crystallographic structure, phase, surface micro-morphology and different functional groups in the prepared catalysts. The optical band gap of pristine ZnO NPs was found in the UV region (3.2 eV), whereas the ZnO NPs immobilized on GO nanosheets possesses it in the visible wavelength region (2.67 eV). GO-ZnO catalysts demonstrate excellent degradation efficiency (97.7 %) within just 85 min due to its effective adsorption and visible light driven photocatalytic activity in the degradation of rhodamine B (RhB) dye. The adsorption capacity of GO-ZnO catalysts was found ∼ 24 times higher with the second order kinetic rate constant as low as 0.0014 min ∙ g/mg and the visible light driven photocatalytic activity was ∼ 9 times faster when compared to unmodified ZnO catalyst. Effect of GO-ZnO catalyst dosages in the degradation of RhB was also conducted. The scavenger test firmly evidenced that super oxide radicals (•O2–) play the lead role in RhB dye degradation process by GO-ZnO nanocomposites. Reusability studies of GO-ZnO catalysts demonstrate more than 91 % degradation efficiency up to 4 back-to-back cycles along with retaining the crystal structure. These findings suggest the viable application of GO-ZnO catalysts for the degradation of RhB dye in wastewater.