Preparation Of Nitrogen-doped Graphene And Study Of Their Catalytic Activities

Graphene has been the research hot spot since its first preperation by Geim and Novoselov in 2004, the unique physical and chemical properties due to its perfect two-dimensional crystal structure. So far, oxidation-reduction method is the most commonly used preparing method of graphene among various techniques. In oxidation-reduction method, graphite oxide with a variety of oxygen-containing groups, including hydroxyl, carboxyl, the epoxy group and so on. could be obtained by oxidizing graphite chemically. The introduction of these oxygen-containing functional groups not only make graphene has chemical stability, but also enhance the hydrophilicity of graphene. These oxygen-containing functional groups make graphene easier to disperse in water and some organic solvent, and provide more active sites for its further functionalization modification. Recently, the research of carbon-based materials represented by graphene and its derivatives exhibit interesting non-metal catalytic properties is a new hot topic.The amount of active sites of graphene is less, and comparatively its selectivity is also not high. It could not replace noble metal as catalyst as supposed. Thus modification is the only way to overcome these shortcomings. Recently, the doping is a kind of new effective modification methods as reported. The most common doping includes nitrogen-doping, phosphorus-doping, and boron-doping. In this paper, nitrogen-doping was adopted. Study the non-metallic catalytic properties of modificated nitogen-doping graphene systemetically, and put forward a non-metal catalytic mechanism.The main research works can be summarized as followings:(1) Graphene oxide (GO) was prepared by modified Hummers method. The nitrogen-doped graphene (N-RGO) is synthesized by a one-step hydrothermal method from GO and ammonia water (NH3·H2O). The structure of the N-RGO was systematically characterized.Choose the nitrophenol hydrogenation reaction model.The color change during the process of catalyst 4-nitrophenol reduction was observed and analyzed by UV-Vis spectra. The constant of reaction rate was calculated according to the standard first order kinetic reaction equation. With the concentration increase of GO, the apparent rate constant of N-RGO increases first and then decreases. When the concentration of N-RGO is 5 mg/mL, the catalytic reduction activities reach the highest. It can reach a reaction rate constant of 0.34s-1mg-1.(2) N-RGO was added into buffer solution which contains DOPA, ABTS and TMB respectively, and the color changes after reaction was observed by UV-Vis. TMB was chosen as the catalytic system for some reasons. The optimal reaction conditions was explored by measuring catalytic activity of N-RGO under different different pH and temperatures. Furthermore, the mechanism of catalytic oxidation of N-RGO toward TMB was investigated at such a proper reaction condition.(3) Nitrogen doped graphene prepared by using simple hydrothermal synthesis method. After freeze drying can prepare a novel anisotropic nitrogen doped graphene aerogels.N-RGO aerogels were freeze dried and observed by using field emission scanning electron microscope (SEM). It is shown that N-RGO looks like a cylinder consists with a stack of aligned graphene layers along the aperture channel. Equivoluminal of sodium borohydride and 4-nitrophenol was dripped from the upper and side surface (x, y, z axis) respectively to study the influence of surface and structure on catalysis. The most active side was chosen as the contact surface, which opens a new way to improve the catalytic activity.