Fabrication And Applicationof TiO₂Nanotube Arrays Modified With Graphene-based Composites

Photocatalytic degradation of organic pollutants in water is one of the mosteffective methods to solve environmental pollution problems. Titanium dioxide （TiO₂）,as an important inorganic photocatalytic material, has been the most promisingphotocatalyst. However, the widespread pratical application of TiO₂is obstructed byits high recombination rate of the photogenerated electron–hole pairs and wide bandgap.In this work, graphene, as an electronics transporter and storage, was fabricatedon the surface of TiO₂NTs to restrain the recombination of the photogeneratedcarriers and improve the photocatalytic activation. Moreover, the TiO₂NTs modifiedby graphene together with noble metals or semiconductor were investigated. Detailsare given as follows:（1） Ag/RGO–TiO₂NTs: a cyclic voltammetry electrodeposition technique wasproposed for the preparation of high-quality graphene films onto the TiO₂NTssurface. After that, a photoreduction method was used to synthesize Ag NPs.Compared with the unmodified TiO₂NTs, Ag/RGO–TiO₂NTs showed a remarkablyincreased absorption in the visible light region, and a higher photocurrent, indicatingthe reduced recombination rate of the photogenerated electron-hole pairs. After160-min of irradiation, the Ag/RGO–TiO₂NT photocatalyst showed a2,4–D removalefficiency of96.3%, which is about11.3,4.5, and3.3times higher than that over bareTiO₂NTs, Ag–TiO₂NTs and RGO–TiO₂NTs, respectively.（2） Au/RGO–TiO₂NTs: Au-graphene nanocomposite was fabricated on thesurface of TiO₂NTs by one–step cyclic voltammetry electrodeposition technique. Theelectrodeposited graphene and Au particles were assembled into layerednanostructures. The ternary composite showed high photocurrent and photocatalyticactivity. Especially, the simultaneous photocatalytic reduction of Cr（Ⅵ）（nearly100%） and oxidation of2,4-D resulted in a higher photocatalytic efficiency of thecatalyst than the case of only photodegradation of Cr（Ⅵ）（75%） due to the synergisticeffect.（3） CdS/RGO–TiO₂NTs: One-step cyclic voltammetry electrodepositiontechnique was used to prepare CdS-graphene nanocomposite onto the surface of TiO₂NTs. The surface morphology, crystal structure, photocatalytic properties and stabilityof the hybrid material were investigated. After900min, the removal efficiency of CdS/RGO–TiO₂NTs is still nearly100%while that of CdS-TiO₂is only75%（90%at100min） Result shows that CdS/RGO–TiO₂NTs hybrid not only exhibited a highphotocatalytic activity but also an excellent light stability, which would broaden itspractical applications.