Preparation And Photocatalytic Performannce Of Graphene Based-TiO₂Composites

Titanium dioxide has become the most potential photocatalyst for its high stability,excellent photocatalytic performance and nontoxicity. However, it also presents somedrawbacks, such as poor photocatalytic performence and low absorption ablility for solarenergy. The strong Van der Waals interactions among the graphene sheets results in theirtendency to aggregate. It could prevent the aggregation of graphene sheets by binding titaniumdioxide particles onto graphene. The combination and interaction between titanium dioxideparticles and graphene may impart novel properties in such composites. An attractivealternative to graphene is graphene oxide, which has adequate functional groups such ashydroxyl, carboxy, carbonyl, and so on. Such functional groups are benefical for the in situgrowth of nanoparticles on the surface of graphene oxide. In this paper, graphene-based TiO₂composites were prepared by molten-salt reaction method and hydrothermal method. Theidiographic work is as follows:1. Graphene based-TiO₂composites were prepared through molten-salt reaction andoxidition process using four different structures of graphene based materials and titaniumpowder. The effects of reaction temperature, reaction time and the molar ratio of graphenebased materials to titanium powder as well as oxidation temperature on the microstructure,morphology of titanium carbide （TiC） and titanium dioxide （TiO₂） coatings were investigated.The as-prepared composites were characterized by X-ray diffraction, scanning electronmicroscopy, transmission electron microscopy, Raman spectroscopy and X-ray photoelectronspectroscopy. The photocatalytic activity was evaluated by degradation of methylene blue（MB） under visible light illumination. The structure and performance of the graphene based-TiO₂composites prepared with four different graphene based materials as carbon source andsupport were compared. The main results are as follows:（1） Molten salt reaction temperatureand molar ratio of graphene to titanium （nC/nTi） were crucial factors to determine thestructure composition, morphology and performance of the final photocatalyst. The oxidationtemperature has a great influence on the structure and component of the graphene based-TiO₂composites. The increase of oxidation temperature can promote the formation of crystalnucleus and crystal grain growth of TiO₂. But high temperature will result in thetransformation of crystalline phase. Compared with P25, the GO-TiO₂composites showobviously enhanced visible light catalytic activity.（2） Four different structures of graphenebased materials have certain reactivity differences with titanium powder. The graphenebased-TiO₂composites show an enhanced visible light photodegradation efficiency. Theadsorption rate and degradation rate of graphene based-TiO₂composites with different structures have certain differences.2. Partially reduced graphene oxide/titanium dioxide （RGO/TiO₂） composite wassynthesized using tetrabutyl titanate and graphite oxide as the starting materials byhydrothermal method. The effects of reaction temperature and the amount of graphite oxide onthe the crystal phase composition and the microstructures of TiO₂were investigated. The mainresults are as follows: the crystal phase and dispersity of titanium oxide in the composite canbe controlled by varying the reaction temperature and the amount of graphite oxide. Thephotocatalytic activities of partially reduced graphene oxide/titanium dioxide compositesunder both visible and UV light irradiation are higher than that of pure TiO₂. Partially reducedgraphene oxide may act as the support and the electron acceptor, and can shift the absorptionband edge and strengthen the absorbance of TiO₂in the visible light region, which willeffectively enhance the adsorbability and the photocatalytic activity.