A transparent TiO₂-C@TiO₂-graphene free-standing film with enhanced visible light photocatalysis

A transparent TiO₂-C@TiO₂-graphene free-standing film has been synthesized by electrostatical self-assembling GO nanosheets on a cellulose-TiO₂@TiO₂ film prepared by a one-step hydrothermal method followed by thermal annealing at 500°C. Scanning and transmission electron microscope observations have shown graphene wrapped flower-like micro/nanostructure TiO₂ particles uniformly distribute on TiO₂-C fibers that are interconnected with each other to form a 3D reticulate microstructure. X-ray photoelectron spectra have demonstrated that interaction between the TiO₂ and graphene facilitates the generation of O-Ti³⁺ species and Ti-O-C bonds. As a result, the TiO₂-C@TiO₂-graphene film exhibits a significant enhancement of light absorption within the visible region as compared to the TiO₂-C@TiO₂ film. Meanwhile, the introduction of a graphene layer slows the recombination of photogenerated electron-hole pairs, increasing the charge transfer rate of electrons. Thus, in the photocatalytic degradation reaction of methylene blue, the photodegradation rate constant for the TiO₂-C@TiO₂-graphene film is 2.2 times higher than that of the TiO₂-C@TiO₂ film obtained from thermal treatment of the cellulose-TiO₂@TiO₂ film. The enhanced photocatalytic property is well consistent with the photoelectrical responses, electrochemical impedance spectroscopy analyses and photoluminescence spectra results. This work may provide a rational and convenient strategy to construct transparent free-standing films with visible light photocatalysis toward environmental purification.