Green synthesis of ZnO-TiO2-reduced graphene oxide composite for the photocatalytic removal of organic dye

Abstract

There has been a growing interest in gathering together photocatalysis of semiconductors, like ZnO, TiO2 and the excellent electron transmittability of graphene to produce a graphene-based semiconductor for photocatalytic degradation. In this regard, a simple in-situ rGO supported ZnO, TiO2 and ZnO-TiO2 nanostructures were successfully synthesized by microwave assisted reduction of graphene oxide (GO) in presence of ZnO and TiO2 suspension respectively. Structural and morphological features of prepared samples are systematically characterized by X-ray Diffraction Spectroscopy (XRD), Field Emission Scanning Electron Microscope (FESEM), Photoluminescence (PL) spectroscopy, UV-Visible spectroscopy (UV-vis) and Fourier Transform Infrared Spectroscopy (FTIR) analysis. The XRD results indicate that ZnO-rGO, TiO2-rGO and ZnO-TiO2-rGO composite are free of any impurity phase and crystalline in structure. FTIR results showed that the reduction of GO into rGO was successful without and with metal oxides. Synthesized ternary ZnO-TiO2-rGO nanocomposite showed 99.58% adsorption assisted photocatalytic activity under UV light irradiation whereas dye adsorption capacity was only 56% from aqueous solution containing 20 ppm methylene blue (MB) dye at 120 min. It was compared with pure ZnO which shows only 0% adsorption and 31% photocatalytic activity. The nanocomposite ZnO-TiO2-rGO showed an excellent adsorption assisted photocatalytic performance up to 100% for MB dye via sunlight irradiation within 5 min. The photocatalytic efficiency as well as dye adsorption capacity is very high for the cationic dye MB compared to anionic dye methyl orange (MO). The effect of catalyst dose, initial concentration of dye on photodegradation were thoroughly investigated. The mechanism of the enhanced photocatalytic efficiency of ZnO-TiO2-rGO nanocomposite propose that the stronger adsorption on photocatalyst for the targeted molecules of pollutant is achieved by the incorporation of the rGO, due to their large specific surface area and high quality active sites. The results suggest that ZnO-TiO2-rGO nanocomposite prepared by microwave assisted method can be developed as an economically feasible and environmentally friendly method to degrade dye containing wastewater using UV and natural sun light irradiation.