Research On The Preparation Of Graphene/Titanium Dioxide Nanocomposites In The Application Of Photocatalytic Degradation Of Organic Pollutant Under Visible Light Irradiation

The development and use of solar energy to solve the environmental pollution and the energy crisis has become an important worldwide issue.Photocatalysis,as a promising and green technology,shows great potential for the applications in the environmental remediation via the conversion of solar energy into chemical energy and electrical energy.However,there are still some disadvantages as follows.Firstly,the widely studied TiO₂ can only be driven by UV light,which results in poor utilization of solar energy.Secondly,the rapid recombination of photo-generated electron-hole pairs severely impair the photocatalytic activity of the catalysts.Finally,the difficulty to recycle the photocatalysts will cause secondary pollution.Therefore,it is very necessary to develop novel kind of photocatalysts with a broad range of visible-light response,superior photocatalytic activity,high photostability,low cost and easily recycling characteristics.In this dissertation,we focus on the development of graphene/titanium dioxide photocatalyst via combined of sol-gel method,hydrothermal method or other methods.The main works are as follows:The binary RGO-TiO₂ and ternary RGO-TiO₂-Cd S nanocomposites were prepared by “one pot” hydrothermal method,and then we investigated the morphology,crystal phase,Uv-vis absorption and photocatalytic activity of the samples.The resulting RGO-TiO₂ sample is composed of spherical TiO₂ particles with the average diameter of 1 mm,and there are obviously flexible thin-sheet among these particles,suggesting the fact that spherical TiO₂ particles are enwrapped by graphene（RGO）.RGO-TiO₂-Cd S sample consists of TiO₂ spheres and RGO framework,whose surface are decorated with some nanoparticles,indicating the in-situ growth of Cd S nanoparticles.Under the illumination of visible-light（λ> 400 nm）for 120 min,the methylene blue or 4-chlorophenol could be effectively degraded.Especially,RGO-TiO₂-0.23 Cd S has the highest photocatalytic activity,indicating that higher Cd S amount could improve the performance of nanocomposite.In addition,the stability of RGO-TiO₂-0.23 Cd S nanocomposite was also studied through the degradation of MB under visible-light illumination,and it retains the photocatalytic efficiency of 81% after four cycling tests.This combination not only expands the optical absorption range and increases the adsorption capacity,but also improves the separation of photo-generated electron-hole pairs.TiO₂-RGO nanocomposites were prepared by ionic liquid-assisted synthesis method,in which the ionic liquid played the role of solvent and templating agent in the process of preparation.On the one hand,GO can be dispersed in ionic liquid because of the van der Waals force of the interface between the ionic liquid and the carbon material.On the other hand,due to the low interfacial tension of the ionic liquid and the interaction of the nanocrystal,TiO₂ were self-assembled on the graphene surface under the mild conditions.Under visible light irradiation,the degradation efficiencies of methylene blue dye and 4-chlorophenol by TiO₂-RGO nanocomposites are much higher than that by the P25,which was mainly due to the expanded photo-absorption range and the significant reduction of the bandgap（2.87 e V）.Importantly,the TiO₂-RGO nanocomposites has good stability.