Study On High-Resolution And Mass Chirality Separation Of Single-Wall Carbon Nanotubes

A Single-wall carbon nanotube(SWCNT)is conceptually a one-dimensional cylindrical molecular formed by rolling up a graphene sheet.SWCNTs not only have prominent properties similar to graphene,such as excellent mechanical properties,extremely high carrier mobility,and chemical stability,but also possess tunable photoelectric properties and good characteristics of gate control,giving them a promising prospect in the fields of engineering material,electronic device,photoelectronics,biomedicine and many other fields.However,the structure of a SWCNT determines its properties.And,slight differences in structure lead to spectacular diversity in properties.For instance,SWCNTs with different structures may exhibit metallic or semiconducting priorities;Morever,the energy band gap of semiconducting SWCNTs is approximately inversely proportional to their diameters.Applications of SWCNTs with different properties should be different.However,at present,the SWCNTS syntheized with various techniques are usually mixtures containing many chiralities and various structures.Due to the unpredictable properties of the mixtures,they are difficult to be applied directly,especially in the field of photoelectronic.In recent years,various post-processing separation techniques have been developed to realize the separation of metallic/semiconducting SWCNTs,single-chirality species and even their enantiomers.Among these separation techniques,gel chromatography has the advantages of simplicity,high-efficiency,low-cost and easy to avhieve automatic separation,and has been developed to be one of the main techniques for separating SWCNTs.However,the separation of small chiral angles(chiral angles < 20 °)and large diameters(> 1.2 nm)still remain challenges.Moreover,due to the low separation efficiency and demands for high-quality raw materials,the yield of single-chirality SWCNTs is still hard to meet the needs of their practical applicationsIn this dissertation,to overcome the problems of the present separation techniques,gel chromatography was modified to achieve high-efficiency separation of SWCNTs with small chiral angles(chiral angles < 20 °)and large diameters(> 1.2 nm).Besides,we developed a novel technique to prepare high-concentration mono-dispersion of SWCNTs,which greatly improved the efficiency and yield of single-chiality separation.The details are as follows:(1)In order to overcome the difficulty in the single-chirality separation of small-chiral-angle SWCNTs(chiral angeles < 20 °),we empolyed temperature and co-surfactants to tune the interactions between SWCNTs and dextran-based gel to enhance the selective adsorption of SWCNTs to the gel by chiral angles.With this technique,we enlarged the interaction differences of different SWCNTs with the gel by chiral angles and diameters,and thus enhancing the recognition of gel to the chiral structures of SWCNTs.Through successive separation by diameters and chiral angles,fifteen high-purity distinct(n,m)single-chirality species and even their enatiomers were extracted from raw materials in a large scale.Among them,11 species are of small-chiral-angle ones,which are difficultly separated by the traditional techniques.The chiral purities of 10 types of species are higher than 90%,and that of only one type of species is lower than 80%.(2)As the diameters of SWCNTs increase,the population of SWCNT species with similar diameter increases.Morever,large-diamter SWCNTs are easy to be oxidized and surfactant molecules prefer to adsorb on their surfaces,leading to their weak interactions with gel,which hinders their structure separation.In view of this difficulty,we designed and developed NaOH-assisted gel chromatography,in which NaOH was introduced to suppress the oxidation and promote the reduction of the oxidized large-diameter SWCNTs,thus to finely tune their interactions with gel and enlarge the interaction difference among different species with the gel.On this basis,a two-step method was developed to simultaneously achieve high-purity metallic/semiconducting separation,diameter separation and even chirality separation of large-diameter SWCNTs(1.2-1.7 nm)in a large scale.(3)In view of the low separation efficiency of SWCNTs,we developed an innovative method to prepare high-concentration mono-dispersion of SWCNTs.With this technique,we improved the separation efficiency by at least 300%,which dramatically improves the separation efficiency and yield of single-chirality SWCNT species.More importantly,we firstly achived the mass separation of at least ten different(n,m)species of high-purity SWCNTs with diameter less than 1 nm and also the diameter separation of other large-diameter semiconducting SWCNTs(> 1.1 nm)in a large scale when this method has been applied to the raw SWCNTs with no structural selectivity.The separation yield has been increased by more than one order of magnitude.By employing the SWCNTs with no structural selectivity as raw materials,we not only reduced the separation cost,but also can separate various SWCNTs what we want,laying a foundation for the industrial separation of high-purity semiconducting SWCNTs and effectively promoting the practical applications of SWCNTs.In general,to improve disadvanteges of the present separation techqniue,we have systematically designed different research schemes to dramatically improve the resolution and separation efficiency of gel chromatography.The mass separation of SWCNTs with small chiral angles and large diameters were achieved successfully.The separation efficiency and yield of SWCNs were further improved by developing the method of high-concentration mono-dispersion of SWCNTs.These achievements will greatly promote the industrial separation of high-purity semiconducting and even single-chiraliy SWCNTs by gel chromatography.