Electrochemical Synthesis Of Nano-carbon Spheres And Graphene

Compared with the traditional chemical methods,electrochemical methods has many advantages on the preparation of nano-carbon material.For example,the driving force of electrochemical reaction relys mainly on electrical energy,so it dose not involve strong acids and other irritating chemicals,but also simplifies the removal process after the reaction.The high efficiency and low cost characteristics of the electrochemical method are expected to achieve the industrial production and use of nano-carbon materials such as nano-carbon spheres and graphene.However,electrochemical methods still have many shortcomings.For example,the electrochemical preparation of nano-carbon spheres has not been fully studied and its synthesis mechanism has not been unified.At the same time,the morphology and yield of nanocarbon spheres can’t be freely controlled.Although the electrochemical preparation of graphene,to some extent,improves the production efficiency of graphene,but the quality of the prepared graphene is generally lower.In this paper,we prepared nano-carbon spheres and graphenes through electrochemical method.The electrochemical synthesis mechanism of carbon nano-carbon spheres and the effects of electrolysis parameters on morphology and yield of nano-carbon spheres were studied.At the same time,to improve the quality of graphene prepared by electrochemical preparation,we explored the impact of operation of reversing the positive and negative poles of DC on the number of layers and defects of graphene,the specific contents are as follows:(1)In this paper,pure water was used as electrolyte,DC power was supplied on two artificial and high purity graphite plates which were parallel to each other to prepare nanocarbon spheres.Through a series of experimental analysis methods,we concluded that the synthesis process was as follows: water firstly oxidized the edge or defective positions of graphite plate under the external application of electric field,so that the graphite sheets space was increased,then water molecules entered into the graphite sheets and further oxidized the graphite sheets,so that the van der Waals forces between the graphite sheets were destroyed by oxidation of water molecules,at the same time,the oxygen was produced through the oxidation of water.The corresponding phenomenon was that the graphite sheets continued to expand and became loose and falled off continuously.In order to obtain the most stable state,the exfoliated graphite sheet was wrapped in a spontaneous curl to form a nano-carbon spheres.(2)In the experiment of electrochemical preparation of nano-carbon spheres,the influence of some experimental parameters on the yield and morphology of carbon spheres were studied,such as electrolysis times,current densities,plate spacing and reverse of poles.We concluded that as the electrolysis time increased,the carbon content of electrolyte gradually increased,but the rate of increase decreased.The size of carbon spheres became uneven with the prolongation of electrolysis time,and the size of carbon spheres produced in the later stage of electrolysis was smaller.The higher the current density,the higher the electrolysis efficiency,but the current density had little effect on the size of carbon spheres.With the increase of the plate spacing,the carbon content of electrolyte first increased and then decreased,and the carbon content of electrolyte was the largest when the plate spacing was 2mm.Carbon spheres diameter was also increased and then decreased.1mm was the most suitable spacing for the growth of carbon spheres.Within a single cycle of reverse of poles,as the time of negative potential prolongs,The carbon content of electrolyte and the size of carbon spheres gradually decreased,the particles size uniformity improved.On the premise of keeping the same electrolysis time of the positive and negative potential.With the increase of frequency of reverse of poles,the carbon content of electrolyte gradually decreased and the particle size firstly decreased then kept constant when the time of negative potential was too short in single cycle of reverse of poles.(3)The metal ions were used as precipitant to extract the carbon spheres.It was found that the higher valence state of metal ions,the better the extraction effect of carbon spheres.Under the same valence state,the higher the ion concentration,the better the extraction effect of carbon spheres.For the high-valent metal ions,when the concentration of ions is only 0.02 M,the extraction rate can up to 80%.In this paper,the method of two-steps suction filtration effectively removed most of the amorphous graphite in the electrolyte.But they could not be completely removed.(4)In this paper,sodium sulfate was used as electrolyte,graphene layers with a number of 4 to 5 layers and a size of 1 to 2 μm were successfully prepared by electrolysis of expanded graphite paper in a DC constant voltage mode.The operation of cyclically reverse the positive and the negative poles of the DC effectively reduced the defects of graphene and the number of oxygen-containing functional groups on the graphene,so that the C/O of the graphene could be as high as 20.05 These improvements effectively improved the conductivity of graphene.But there would also be issues such as increased thickness of graphene,decreased production rates,and so on.Therefore,there was still room for the improvement of this method.