Growth of hierarchical ZnO nano flower on large functionalized rGO sheet for superior photocatalytic mineralization of antibiotic

In this study, reduced graphene oxide supported mesoporous zinc oxide (rGO@ZnO) was synthesized and applied for the photocatalytic mineralization of ofloxacin, an antibiotic, in the aqueous solution. In-situ rGO@ZnO nano-photocatalysts with different rGO content (0.2%, 0.5%, 1% and 2%) were synthesized using a reflux column method. The nano-photocatalyst was characterized by its structural (crystallinity), morphological, as well as optical properties with the help of powdered X-ray diffraction (P-XRD), field emission-scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Raman spectroscopy, Brauner Emmet Teller (BET), thermo-gravimetric/differential thermal analysis (TGA/DTA) and UV-vis diffuse reflectance spectroscopy (DRS). The influences of pH (5-9) and catalyst dose (400-1400 mg/dm(3)) with irradiation time were studied. At optimum conditions (0.5% rGO@ZnO dose of 1200 mg/dm(3) for ofloxacin, pH = 7, and time = 300 min), ultimate degradation efficiency was found to be 99%, under UV light irradiation. The degradation kinetics fitted well with the first-order kinetic model. The photocatalytic mechanism of the enhanced photo-degradation in the presence of rGO was studied by comparing band structure with the potentials of the main reactive species (O-center dot(2)- and (OH)-O-center dot), which result in the mineralization of ofloxacin. The intermediates and pathways during the mineralization were determined using liquid chromatography, which is coupled with mass spectrometry (LC-MS) analysis and a possible pathway was also proposed on the basis of identified intermediates.