Effect of large graphene particle size on structure, optical property and photocatalytic activity of graphene-titanate nanotube composites

In this work we investigate the crystal transformation and optical properties of hydrothermal titania nanotube (TNT) when combining with large size of exfoliated graphene achieved by electrochemical process (EC-Gr). The TNT monoclinic structure has been changed to TiO2 anatase phase when TNT was grown in the presence of graphene dispersion. The effect of graphene on the evolution of TNT crystal could be understood by the interaction of carbon elements in graphene and Ti4+ ions in the titania structure. Due to the carrier separation which reduced recombination rate of excited photoelectrons and holes revealed by photoluminescence characterizations, the visible light photocatalytic activity in degradation of methylene blue in solution of the composite was enhanced. The photocatalytic enhancement was discussed and clarified based on UV–vis diffuse absorption spectra and time-resolved photoluminescence investigation. •The TNT@EC-Gr photocatalyst was successfully synthesized by a facile hydrothermal method.•TNT was transformed from monoclinic to anatase phase in nanocomposite.•MB dye degradation performance under sunlight was improved in nanocomposite.•Compositing with graphene reduced the band gap and prolonged the carriers' lifetime.•The bandgap diagram was proposed to elucidate the photocatalytic mechanism.