N doped ZnO/C-dots nanoflowers as visible light driven photocatalyst for the degradation of malachite green dye in aqueous phase

In an attempt to fabricate potent visible light driven photocatalyst, we have synthesized N-ZnO/C-dots via facile hydrothermal technique. The prepared N-ZnO/C-dots sample was characterized in detail by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDX), Fourier transmission infra-red spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), photoluminescence spectroscopy (PL), UV-diffuse reflectance spectroscopy (UV-DRS) and thermogravimetric analysis (TGA). The results confirmed the presence of nitrogen and successfully introduction of C-dots onto the surface of the N-ZnO. The photocatalytic activity of the prepared nanoflowers was investigated by photocatalytic decomposition of MG dye under visible light. About 85% of MG dye was degraded with N-ZnO/C-dots, higher than that of N-ZnO (75%), pure ZnO (65%) and other commercially available photocatalysts (TiO2 PC 50 (20%) and PC 500 (30%)) under visible light irradiation. The as synthesized N-ZnO/C-dots nanoflowers also exhibited excellent visible light driven photocatalysis towards levofloxacin drug. The effect of operational parameters such as initial dye concentration, pH and catalyst dose on degradation was also studied. The photocatalytic degradation of MG dye was found to be fit with pseudo first order kinetics. Scavenger studies were carried out to investigate the role of reactive radical species in photocatalytic process. The improved photocatalytic activity was accredited to the adequate separation efficiency of the photogenerated electrons and holes, which is accountable to the presence of C-dots as it served as a main role in accepting the photogenerated electrons.