Enhancing visible light responsive photocatalytic activity by decorating Mn-doped ZnO nanoparticles on graphene

Novel visible-light-responsive Mn-doped ZnO/Graphene nanocomposite photocatalysts were synthesized using a facile single step solvothermal method. A range of techniques including X-Ray diffraction (XRD), a high resolution transmission electron microscope (HR-TEM), a transmission electron microscope (TEM), a scanning electron microscope (SEM) with energy dispersive X-ray analysis (EDX), Fourier transform infrared spectroscopy (FTIR), Brunauer Emmett Teller (BET) surface area analyzer and X-ray photoelectron spectroscopy (XPS) were employed to characterize the as-prepared composites. UV–visible diffuse reflectance spectroscopy (DRS) was used to study the optical properties, which confirmed that the spectral responses of the nanocomposite catalysts were gradually extended to the visible-light region as Mn dosage increased. Fluorescence emission spectra verified that Mn-doped ZnO/Graphene nanocomposites possess enhanced charge separation capability compared to ZnO/Graphene, Mn-doped ZnO and pure ZnO. The photocatalytic activity was investigated by following the degradation of methylene blue (MB), a model dye under visible light irradiation. Chemical oxygen demand (COD) of textile wastewater was also measured before and after the photocatalysis experiment under sunlight to evaluate the mineralization of wastewater. The results demonstrated that Mn-doped ZnO/Graphene nanocomposites efficiently bleached out the MB, showing an impressive photocatalytic enhancement over Mn-doped ZnO and pure ZnO samples. The enhanced activity of composite photocatalysts can be attributed to large adsorption by the dyes, enhanced visible light absorption and efficient charge separation and fast transfer processes.