One-step synthesis of band-tunable N, S co-doped commercial TiO2/graphene quantum dots composites with enhanced photocatalytic activity

N, S co-doped commercial TiO2/N, S-GQDs graphene quantum dots (NSTG) composites with band tunability are synthesized via a facile solvothermal treatment in the presence of thiourea, which acts as a precursor for the dopants. The as prepared nanocomposites are characterized via X-ray diffraction (XRD), Raman spectroscopy (Raman), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform-infrared spectroscopy (FT-IR) and UV-vis diffuse reflectance spectroscopy (UV-vis DRS). The photocatalytic activity of NSTG is evaluated through the degradation of methylene blue (MB) under visible light irradiation (l > 400 nm). Compared with commercial TiO2 (P25) and N, S co-doped TiO2 (NST), the NSTG composites exhibit the highest photodegradation efficiency. The apparent rate constant of NSTG is about 2.4 times and 50.7 times higher than that of NST and commercial TiO2, respectively. Furthermore, the band gaps of the NSTG composites can be tuned by changing the molar ratio of citric acid (CA) : thiourea. Our work demonstrates that this innovative synthetic approach could provide an effective approach for industrial applications due to its low cost and scalability. Furthermore, the NSTG composites are a more promising photocatalytic material than the well studied N doped TiO2 for potential applications in environmental protection.