Electrochemical Preparation And Properties Of Nitrogen-doped Graphene Quantum Dots

Graphene quantum dots(GQDs)are widely used in biology,medicine,energy and other fields because of its high electron mobility,good chemical stability and high biocompatibility.Due to quantum confinement and boundary effect,it also has great potential in optoelectronic equipment and fluorescence imaging.The properties of GQDs can be further improved by doping.For example,the addition of nitrogen atoms helps to enhance the surface polarity of graphene quantum dots and enhance their electrical conductivity.However,how to prepare GQDs with high quality and fluorescence quantum yield is still challenging.In this study,nitrogen-doped graphene quantum dots with high fluorescence quantum yield were prepared by electrochemical process,and the photoluminescence behavior was investigated by changing the preparation conditions.The main research contents and results are as follows:1.Nitrogen-doped carbon nanotubes and nitrogen-doped graphene three-dimensional composites(N-CNT/N-Graphene)was synthesized on nickel substrate by chemical vapor deposition(CVD)with melamine as the source of both carbon and nitrogen.2.Nitrogen-doped graphene quantum dots(N-GQDs)was prepared by electrochemical method using N-CNT/N-Graphene as precursor.The size distribution of the prepared N-GQDs is uniform,the average size of 2 nm,is only composed of 1-3 layers of graphene,and the nitrogen doping level is as high as 18%.In addition,it can maintain high stability under sunlight and UV irradiation,and has the highest fluorescence intensity in pH=2.3.The fluorescence emission behavior was controlled by change the reaction conditions of electrochemical preparation of N-GQDs.The results show that the intensity and position of the emission peak both effected by concentration of electrolyte and current intensity.When the electrolyte concentration is 0.2 mol/L and the current intensity is 0.01 A,the N-GQDs have the highest fluorescence quantum yield(19%).