Investigations On The Synthesis Of Carbon Nanotube And Graphene By A Hydrogen-free Chemical Vapor Deposition Process

Due to their excellent mechanical strength,thermal conductivity,conductivity and chemical properties,single walled carbon nanotubes and graphene have numerous potential applications in different fields.Since 1990s,researches on single walled carbon nanotubes and graphene have been thriving.However,the practical applications of single walled carbon nanotubes and graphene remain scarce.There are many hurdles on the road for their practical applications,such as the low purity,low yield,and complex structure of raw materials.Since the carbon nanomaterial structure governs their properties and the preparation thus determines the future.Consequently,there is still plenty of room for regulating the properties of carbon nanotubes and graphene,and the preparation of high-quality single walled carbon nanotubes and graphene with controlled structure and properties is the prerequisite for their "killer" application.Among many methods have been developed for preparing single walled carbon nanotubes and graphene,chemical vapor deposition have many advantages over other techniques,such as low cost,high yield and strong controllability.Therefore,it is the most promising method for synthesizing single walled carbon nanotubes and graphene.Based on extensive investigations,this thesis explores the structure-controlled synthesis of single walled carbon nanotubes(SWNTs)and graphene by chemical vapor deposition method.The main results are as follows:(1)A solid iridium(Ir)catalyst was developed for the success growth of SWNTs.Firstly,Ir nanoparticles with uniform size were prepared by a microwave reduction method,and were subsequently applied to catalyze SWNTs growth using CO as carbon source.The morphology and structure of the product were systematically characterized by different techniques,which showed that SWNTs could be grown efficiently at 1000? for 60 min.The nucleation and growth of SWNTs follow a perpendicular mode,resulting in a bicentric diameter distribution of SWNTs.Molecular dynamics and DFT calculations show that Ir nanoparticles preserve solid state under the reaction conditions,the(111)surface of which serves as a template for the nucleation and growth of structure-specific SWNTs.The structural symmetry of SWNTs should match the six-fold symmetry of Ir(111)crystal plane.The theoretical results explain the growth of SWNTs with radius close to 0.61 nm and 0.88 nm,agrees with the bicentric diameter distribution observed in experiments.(2)Horizontally aligned small-diameter SWNTs arrays were prepared on ST-cut quartz substrate using CO as the carbon source and iron(Fe)nanoparticles as the catalyst.Systematic characterizations revealed that the orientation of SWNTs is sensitive to SWNT diameter.SWNTs with small diameters have strong SWNT-substrate interactions,which guide the SWNT growth along certain crystal orientation.The hydrogen-free atmosphere not only prevents the etching of small diameter SWNTs with high curvature radius,but also facilitates the SWNTs nucleation by a perpendicular mode.Grounded on the understanding of the SWNT growth and orientation mechanism.Horizontally aligned SWNTs with small diameters were synthesized by optimizing the experimental conditions.(3)CO was applied to grow graphene by chemical vapor deposition.Particularly,adlayer-free monolayer graphene was obtained with 300 sccm CO at 900? for 60 min.Because CO disproportionation does not generate hydrogen,which could etch the graphene substrate interface and cause the formation of adlayer.Therefore,is the use of CO as the carbon source is crucial for the growth of adlayer-free monolayer graphene.Besides,graphene grown on foamed copper was primarily applied for seawater desalination,marine pollution control and other fields without further operations.