Controllable Preparation Of Doped Graphene Quantum Dots And Investigation Of Their Photoluminescence And Electrocatalysis

Graphene quantum dots（GQDs）has obvious quantum confinement effect,boundary effect and good biocompatibility,showing great application prospect in the field of fluorescence labeling,micro nano sensor,targeted medicine,biological tracer and electrocatalysis.Doping can change the photoluminescence and electrocatalytic properties of graphene quantum dots by effectively regulating their crystal and electronic structure.At present,there are still many problems preventing the industrialization of graphene quantum dots,such as controllable preparation,modification and low cost production.In this paper,carbon fibers and graphite powders were used as raw materials to prepare graphene quantum dots by strong oxidation etching separating method,proposing a general system which can significantly improve the doping level of graphene based materials,that is bestraddle doping method.Doped graphene quantum dots and their nanocomposites successfully prepared by this law were applied to photoluminescence and electrocatalysis.The main research work was carried out as the follows:1.Controllable preparation of graphene quantum dots.Carbon fibers and graphite powders were used as raw materials to prepare graphene quantum dots by strong oxidation etching separating method.The experimental results show that the sizes of both graphene quantum dots are below 6 nm,and the fluorescence quantum yield was 2%and 1%respectively（quinine sulfate as reference）,demonstrating obvious excitation wavelength dependent fluorescence.2.Doping of graphene quantum dots.Firstly fluorine doped GQDs（F-GQDs）was prepared to increase the concentration of internal defects of GQDs,then nitrogen doping of F-GQDs was carried out in ammonia under high temperature.The experimental results show that when the mass ratio of fluoride to GQDs was 5:1 and the heat treatment temperature was 700℃,the F doping ratio of F-GQDs was 23%and the N doping ratio of the resultant N-GQDs was up to 4.25%,whereas the non-fluorinated N-GQDs sample’s ratio was only 1.6%,demonstrating the bestraddle doping method with preferential fluorine doping can significantly improve the doping amount of nitrogen.3.Properties of doped graphene quantum dots.（1）Photoluminescence properties:the fluorescence spectrum of N-GQDs showed a blue shift of 20 nm compared with undoped GQDs,the quantum yield was increased by a factor of 1.5,and the emission color changed from yellow to yellow green under UV irradiation,the fluorescence intensity of N-GQDs decreases remarkably with the increase of Fe³⁺ concentration.（2）Electrocatalytic properties:the half wave potential and the limiting current density of N-GQDs 700 under 0.1M KOH alkaline conditions were 0.76 V and 3.69 mA cm^-2 respectively(catalyst loading was 600 μg cm^-2),after 2500 cycles,the two separately reduced 2.4 and 2.7 percent;By the use of a one-step solvothermal method,Co₃O₄ compound with N-GQDs（Co₃O₄@N-GQDs）was prepared.The half wave potential and the limiting current density of Co₃O₄@N-GQDs 450 under 0.1M KOH alkaline conditions were 0.77 V and 5.48 mA cm^-2(catalyst loading was 600 μg cm^-2)respectively,after 2500 cycles,the half wave potential only decreased by 0.7 percent yet the limiting current density decreased slightly,showing enhanced catalytic activity and improved stability compared with the N-GQDs 700 catalyst.This paper provides new ideas for the photoluminescence application of doped graphene quantum dots in biomedical field.A low cost and efficient non-metallic oxygen reduction reaction catalyst was developed,providing theoretical basis and technical support for the utilization of doped graphene quantum dots in the field of energy materials.