Purification Of Single-walled Carbon Nanotubes

Single-walled carbon nanotubes(SWCNTs)exhibiting well-defined hollow tubular structure are one-dimensional carbon nanomaterials.In addition to the amazing mechanical and electronic properties,SWCNTs possess good biocompatibility with living systems.As a result,SWCNTs are considered to be excellent candidates for many potential applications,including nanoelectronic devices,composite materials,energy storage media,catalyst,catalyst supports,sensors,field emitters,conductive films,and bio-nanomaterials.However,only some of these properties and applications have been verified due to the difficulties in getting high purity SWCNTs.Since as-prepared SWCNTs are usually accompanied by carbonaceous or metallic impurities,purification is an essential issue for their application.Up to date,considerable progress for the purification of SWCNTs has been made and a number of purification methods have been developed for obtaining SWCNTs with high purity,including chemical oxidation,physical separation,and combinations of chemical and physical techniques.Although considerable progress has been achieved,it is still difficult to find a simple method that can purify SWCNTs effectively.Moreover,since the quality and accompanying impurities of as-prepared SWCNTs strongly depend on the synthesis method and experimental conditions,the purification strategy must vary according to the features of the raw SWCNTs and their target applications.It is hard to propose a universal method.To this end,this paper focuses on the purification of single-walled carbon nanotubes,in order to explore a simple,efficient and universal purification process.The main content of this paper can be summarized as follows:Chapter 1:This chapter briefly introduce the research history,structure,properties,applications,synthesis methods and growth mechanisms of SWCNTs.The purification methods of SWCNTs have been summarized in detail.Finally we explained the basis and significance of the topic.Chapter 2:Based on our previous studies for the dispersion and function of carbon-based materials in solvated electron system,we proposed a unique SWCNTs reduction purification method.The OCSiAl SWCNTs were subjected to reduction purification experiments.The residual metal content of the sample was decreased from 18.7 wt%to 8.8 wt%,and the yield of the reduction purification process was up to 85 wt%.The purity and yield were higher than those obtained by the conventional air oxidation purification method.Moreover,the reduction purification method has little damage to the structure of SWCNTs,and the degree of crystallization of the sample is high.Chapter 3:Aiming at the problems existing in the gas phase oxidation purification method of SWCNTs,a unique SWCNTs gradient oxidation purification process was proposed,and the SWCNTs were subjected to gradient oxidation purification experiments.The combination of low-temperature strong oxidation and high-temperature weak oxidation,exerts the advantages of both,and the gradient oxidation purification is performed to obtain a pure SWCNTs sample.The residual metal catalyst content of the sample can be remarkably dec,reased to 0.2 wt%,the purity is up to 99 wt%,and the purification yield is?40 wt%.The method has little damage to the structure of SWCNTs,and the purified sample has a high degree of crystallization and an increase in thermal stability of about 100 ?.This gradient oxidation purification method is a low cost,high efficiency the structure of SWCNTs purification method.Chapter 4:In this chapter,the universality of the gradient oxidation method of SWCNTs was studied.The gradient oxidation purification experiments were carried out on single-walled carbon nanotubes mainly composed of metal impurities and carbon impurities.The SWCNTs mainly composed of metal impurities were purified by gradient oxidation,and the residual content of the sample metal catalyst was remarkably decreased from 29.5 wt%to 2.1 wt%,and the purity was 98 wt%.Sample impurities were purified by gradient oxidation of SWCNTs with carbon impurities such as amorphous carbon and nano-graphite sheets.The amorphous carbon impurities in the sample were significantly reduced,and the residual metal content of the sample was decreased from 8.9 wt%to 2.9 wt%and the purity was over 95 wt%.The SWCNTs sample obtained by the gradient oxidation purification process has improved graphitization degree,reduced defects and improved thermal stability of 100 ? or more.This proves that the gradient oxidation purification method can effectively remove carbon impurities such as amorphous carbon,fullerene and nano-graphite sheets as well as metal impurities,which embodies the universality of the gradient oxidation purification method.Chapter 5:This chapter summarizes the main content of the dissertation and gives a prospect of the future work.