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

Abstract

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 (λ > 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.