A comparative study on the photocatalytic behavior of graphene-TiO2 nanostructures: Effect of TiO2 dimensionality on interfacial charge transfer

A series of graphene-TiO 2 nanocomposites (GR-TiO 2 ) with different TiO 2 dimensionalities (including TiO 2 nanoparticles, nanotubes and nanosheets) and GR weight ratios have been prepared via the analogous in-situ synthesis approach. For the first time, a systematic comparison among GR-TiO 2 NP, GR-TiO 2 NT and GR-TiO 2 NS composite photocatalysts toward ultraviolet-driven CO 2 reduction and visible-light-induced benzylamine oxidation has been carried out based on a reasonable benchmark framework. The influences of TiO 2 dimensionalities and GR weight ratios on photocatalytic redox reactions are systematically investigated. Moreover, direct comparisons among GR-TiO 2 NP, GR-TiO 2 NT and GR-TiO 2 NS composites are also conducted in terms of reactive species generation, transient photocurrent response and interfacial charge-transfer kinetics. Due to intimate interfacial contact between graphene and two-dimensional (2D) TiO 2 nanosheets, 2D-2D GR-TiO 2 NS nanocomposites possess superior electronic coupling compared to 2D-0D GR-TiO 2 NP and 2D-1D GR-TiO 2 NT samples, which results in rapid photoinduced charge-transfer and remarkably improved photocatalytic activity for CO 2 reduction under ultraviolet irradiation. On the other hand, because of large BET surface area, GR-TiO 2 NT composites possess stronger adsorption for benzylamine and the resulting visible-light absorption, leading to greater photocatalytic activity toward selective oxidation of benzylamine under visible light illumination. Overall, the results suggest that TiO 2 nanomaterial dimensionality plays the key role in determining the interfacial charge-transfer and reaction specificity of GR-TiO 2 composite photocatalysts.