Synthesis Of Hydrogen,Nitrogen-Doped Graphene And Its Electrochemical And Magnetic Properties

Since its discovery,graphene has attracted the attention of many people and became a hot topic in the field of materials science and inorganic chemistry.Graphene's unique two-dimensional crystal structure and long-range?-conjugated electronic structure give it unique and excellent optical,electrical,thermal,and mechanical properties and it can serve as an excellent candidate in the fields of photoelectric conversion,energy storage,semiconductor,catalysis and heat transfer.In recent years,people have been committed to modifying graphene materials by heteroatoms doping to generate some graphene derivatives,so as to make the graphene derivatives have more abundant and extraordinary physical and chemical properties and broaden the application field of graphene.Among the many researches on the properties of doped graphene,magnetic properties and electrochemical properties have attracted people's attention because of their broad application prospects.Doping graphene with heteroatoms can modulate the inherent crystal structure of graphene and introduce the unpaired electrons,so as to form a small amount of magnetic moment in graphene.When the magnetic moment content reaches a certain level and the interaction between the magnetic moments is formed,the resulting long-range magnetic order can make the doped graphene have a strong spontaneous magnetization.The research on the ferromagnetism of doped graphene is helpful to make graphene available in the application fields related to information processing and storage devices.Therefore,it is of great scientific significance to explore the experimental methods of synthesizing doped graphene derivatives and conduct in-depth research on its ferromagnetic properties.Doping heteroatom in the lattice of graphene can also adjust the carrier concentration.Unpaired electrons introduced by heteroatoms can make differences in the electronegativity of graphene surfaces,thus strong polarization occurs in the doped graphene and a certain extra pseudocapacitance is also introduced,which makes graphene have excellent electrochemical performance.The doped graphene has the ability to absorb more electrical charges on the surface which will undergo a redox reaction during charging and discharging.Thus,the energy storage capacity of this material will be considerably enhanced.Furthermore,the heteroatom doped graphene has the characteristic of absorbing electrons quickly,thus giving it the ability to charge and discharge rapidly.In this thesis,hydrogenated graphene and nitrogen doped graphene were prepared by some novel synthetic methods,such as hydrothermal,ultrasonication,and ball-milling,and their electrochemical and magnetic properties were thoroughly investigated.The exfoliating effect of some mechanical exfoliation methods for two-dimensional materials,such as pressure quenching,is also discussed.Some major results have been achieved as follows:(1)Using a relatively mild synthetic method,the hydrothermal approach,graphene oxide and acetic acid were used as raw materials,and nickel foam was used as a catalyst to prepare partially hydrogenated graphene,and its structure and magnetic properties were studied.The results of the study found that as the reaction temperature in the hydrothermal experiment increased,the graphene oxide was reduced by acetic acid,and the hydrogen content of the sample increased.The magnetism of the material changes from paramagnetism to ferromagnetism,and its ferromagnetism comes from the structural integrity and magnetic homogeneity of hydrogenated graphene.(2)A new method for the synthesis of ferromagnetic graphene by nitrogen doping was reported.Nitrogen doped graphene with high nitrogen content was synthesized by heating and ultrasonic method through the expandable graphite and melamine.We fully characterized the materials and discussed the mechanism of nitrogen doping.Subsequently,the magnetic properties of the materials were studied and the origin of the ferromagnetism in nitrogen-doped graphene was in-depth discussed.The results show that with the increase of nitrogen content and the proportion of graphitic N,the saturation magnetization has been enhanced,and it shows a tendency to transform into soft ferromagnetism.(3)Nitrogen doped graphene was prepared from expandable graphite and melamine by heating the mixture of expandable graphite and melamine,which were further exfoliated by ball-milling method.The electrochemical performance of nitrogen doped graphene as supercapacitor electrode material was characterized by the three-electrode configuration.The results show that the specific capacitance of the nitrogen doped graphene electrode is as high as 83.8 m F/cm².Doping of nitrogen atoms introduced pseudocapacitance to the original double-layer capacitance and the redox reaction occurs on the surface of the material.In the meantime,the electrode material also has the characteristics of fast charge and discharge rate and high stability.This method provides a new approach for the introduction of pseudocapacitance into double layer supercapacitors.(4)Using melamine as the raw material,the few-layer carbon nitride(g-C₃N₄)was prepared by the"pressure quenching method".The pressure quenching method is compared with the ball-milling method and ultrasonic method mentioned in this article,and the exfoliating effect of the three methods on two-dimensional materials is compared.