Graphene-wrapped hierarchical TiO2 nanoflower composites with enhanced photocatalytic performance

Graphene-wrapped titanium dioxide nanoflower composites (G-TiO2) consisting of nanosheets and nanoparticles were synthesized using a two-step solvo/hydrothermal process. Materials were characterized using SEM, TEM, high-resolution TEM (HRTEM), XRD, Raman spectroscopy, and FTIR. Further analysis was performed using Branauer-Emmett-Teller (BET) specific surface area analysis, electrochemical impedance spectroscopy (EIS), UV-Vis spectroscopy, and diffuse reflectance UV-Vis spectroscopy. Photocatalytic activity was determined by the photo-degradation of methylene blue under UV irradiation. Results show that the TiO2 nanoflower exhibits a higher photocatalytic activity than commercial P25 by a factor of 1.49. This is attributed to the highly crystalline, hierarchical nature of the nanoflower structure, which provides improved charge transport and a reduced recombination rate of photo-generated electron-hole pairs. After wrapping with graphene, the G-TiO2 composite can further improve the photocatalytic performance by providing a planar conjugated surface for dye adsorption, by further reducing recombination through accepting electrons from TiO2, and by causing a red shift in light absorption. The highest photocatalytic performance was found using a graphene loading of 5 wt%, which outperforms commercial P25 by a factor of 3.4.