Preparation And Applications Of Single-walled Carbon Nanotubes With A Narrow Chirality Distribution

Because of their unique structures,single-walled carbon nanotubes(SWCNTs)have excellent properties and many potential applications,such as semiconductor components,optoelectronic devices,nanoelectronic devices,etc.Therefore,SWCNTs have attracted worldwide attention since their dicovery.To realize their practical applications in electronic devices,SWCNTs with controlled density,diameter,electric nature and chirality are required.However,most prepared SWCNTs contain species with different structures and electrical properties.As preparation determines the future,and the synthesis of SWCNTs with a narrow chirality distribution is essential for achieving its killer application in nanoelectronic devices.Among various techniques applied for synthesizing SWCNTs,chemical vapor deposition method is recognized as the most potential technique for large-scale synthesis of SWCNTs with controlled configurationsbecause of its low cost and good controllability.During the growth of SWCNTs,catalyst plays an important role in controlling the nucleation thermodynamics and growth kinetics of SWCNTs.The catalyst serves as the nucleation center for SWCNT growth,which could regulate the SWCNT diameter,chirality and growth rateby modifying the state of the catalyst.Therefore,the development of novel catalyst systems is essential for the preparation of SWCNTs with a narrow chirality distribution.In this thesis,we reported the development of different catalyst systems,which lead to the synthesis of SWCNTs with a narrow chirality distribution by controlling the reaction conditions.The strucutres of SWCNTs were systematically characterized and their applications in seawater desalination were explored.The main research results are as follows:(1)Using iron silicide(FeSi)as the catalyst and carbon monoxide(CO)as the carbon source,SWCNTs with a narrow chirality/diameter distribution were synthesized by chemical vapor deposition.During the growth of SWCNTs,Fe atoms migrate to the surface of FeSi and form Fe nanoparticles of uniform size,which subsequently catalyze the growth of SWCNTs.During the SWCNT growth process,the Fe nanoparticles remain solid and SWCNTs nucleate in a perpendicular mode,facilitating the growth of SWCNTs with a narrow chirality distribution.Based on Raman and absorption spectroscopy characterizations,it was revealed that(12,6)SWCNTs occupy more than 40%of all the SWCNTs grown at 800?.One reason for enriching(12,6)SWCNTs is that most stable Fe catalysts are exposed with(111)planes with quasi-sixfold symmetry,favoring the nucleation of(2n,n)SWCNTs with a matched symmetry.On the other hand,(2n,n)SWCNTs have more active sites on the SWCNT-catalyst interface,and thus a higher growth rate than SWCNTs with other chiral angles.This work first demonstrates the use of silicide for sucessfully growing SWCNTs,which opens up a new way for chirality-selective synthesis of SWCNTs.(2)High quality SWCNTs with a narrow diameter/chirality distribution was realized at a relatively high temperature by the chemical vapor deposition on a porous MgO supported Co catalyst.Under the reaction conditions,only a small amount of Co ions is reduced and migrated to the MgO surface.The reduced Co nanoparticles are well anchored by the unreduced Co ions to form uniform Co nanoparticles,thereby catalyzing the growth of SWCNTs.High-resolution transmission electron microscopy and thermogravimetric analysis characterizations indicate that the synthesizedSWCNTs are of high quality.A shift of the chiral preference from(6,5)to(7,5)by tuning the growth temperature from 700? to 800? was observed,as verified by optical measurements including UV-vis-NIR absorption and photoluminescence spectroscopy.In addition,systematic studies have shown that the content of Co in the catalyst,the calcination time and temperature of the catalyst have little effect on the chirality distribution of the synthesized SWCNTs,confirming the robustness of the MgO-supported Co catalyst.(3)The SWCNT films were prepared from the dispersed SWCNTs were were and tested for seawater desalination.A 1 kW/m2 solar simulation light source was used to illuminate the sample,an evaporation efficiency of 56.6%was achieved for the purified SWCNTs film,which is higher than the untreated SWCNT film,indicating that the purified SWCNTs have better light absorption capabilities and effective light-heat conversion ability.Through the contact angle test,it was found that the SWCNTs dispersed in sodium deoxycholate solution had good lipophilic and hydrophobic properties after suction filtration to form a membrane,which is ideal for ocean oil-water separation and improving seawater desalination efficiency.