Large Ultrathin Anatase TiO2 Nanosheets with Exposed {001} Facets on Graphene for Enhanced Visible Light Photocatalytic Activity

Tailored synthesis of well-defined anatase TiO2 nanocrystals with a high percentage of reactive facets has attracted widespread attention due to the scientific and technological importance. Here, high-quality nanosized anatase ultrathin TiO2 nanosheets, mainly dominated by {001} facets, were grown on graphene nanosheets by a simple one-pot solvothermal synthetic route. The obtained samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), ultraviolet-visible (UV-vis) diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of as-prepared TiO2/graphene composites for degradation of methylene blue (MB) under visible-light irradiation at lambda >= 400 nm was investigated. The results show that TiO2/graphene nanocomposites have a higher photocatalytic activity than pure TiO2 and P25. This enhanced photocatalytic activity suggests that the photoinduced electrons in TiO2 prefer transferring to the graphene efficiently. As a consequence, the electron transfer via Ti-O-C between TiO2 and C interaction greatly retards the recombination of photoinduced charge carriers and prolongs the carrier lifetime, thus contributing to the enhancement of photocatalytic performance. The amount of graphene is an important factor affecting the photocatalytic activity of TiO2/graphene nanocomposites. The optimum amount of graphene is ca. 1 wt %, at which the TiO2/graphene sample displays the highest reactivity. Furthermore, the photodegradation rate does not show an obvious decrease during five successive cycles, indicating that our TiO2/graphene nanocomposites are stable visible-light photocatalysts.