Carbon quantum dots/KNbO3 hybrid composites with enhanced visible-light driven photocatalytic activity toward dye waste-water degradation and hydrogen production

In this work, a new visible-light driven photocatalyst, carbon quantum dots (CQDs)/KNbO3 composite, is successfully prepared via hydrothermal and mixed-calcination methods Multiple techniques, such as X-ray diffraction (XRD) spectroscopy, scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray (EDX) spectroscopy, fourier-transform infrared (FT-IR) spectroscopy, UV-vis diffuse reflectance spectroscopy and photoluminescence (PL) spectroscopy, are applied to investigate the morphologies, structures and optical properties of the prepared CQDs/KNbO3 composites. The photocatalytic activity of CQDs/KNbO3 composites is evaluated via degradation of crystal violet dye as target organic pollutant with simultaneous hydrogen production under visible-light irradiation. The results show that the CQDs/KNbO3 composites exhibit much higher photocatalytic activity than the KNbO3. It is ascribed to the presence of the CQDs as co-catalyst on the surface of KNbO3 particles, forming much more active sites for trapping electrons and promoting the separation of photo-generated electron-hole pairs. In addition, the CQDs can absorb visible-lights and emit the ultraviolet-lights to activate the wide band-gap KNbO3. The study of reusability shows that the CQDs/KNbO3 can be effectively recycled for four repetitive cycles and maintain a higher level of photocatalytic activity. In conclusion, the present work designs an effectively visible light driven photocatalyst, which can be applied in photocatalytic degradation of organic pollutants with simultaneous hydrogen evolution. (C) 2017 Elsevier B.V. All rights reserved.