Improvement Of Conductivity Of MWNTs By Cl₂-doping And Research On Conducting Mechanism

Carbon nanotubes(CNTs) are receiving more and more attentions,because of the potential applications of CNTs and relative composites.The electrical properties are influenced by its chirality,form,layers,diameter and defects,etc.The electrical properties of CNTs differ greatly,CNTS with certain properties can't be obtained,because these factors are difficult to be controlled precisely,which gives the applications not an easy way.Doping, as an effective way,was always given to CNTs to control its electrical and other properties,the superiority of doping is controllability.Novel electrical transport properties emerged when CNTs was doped.In this paper,Cl2-doped MWNTs were fabricated,and electrical properties of Cl2-doped Multi-walled nanotubes(MWNTs) were investigated,including the electrical performance and conductive mechanism.The followinges were mainly concluded:1, Fabrication of CI2-doped MWNTsCl2-doped MWNTs were fabricated by gas absorption, Cl2 was produced by the reaction of H2SO4 and Ca (ClO) 2, MWNTs, including unpurified, HNO3-treated and high-temperatured-treated MWNTs, were doped after the gas was dried by silica gel. A series of Cl2-doped MWNTs samples were fabricated under conditions of different doping time, doping temperature and with the radiation of UV light respectively.2, Research on electrical conductivity of Cl2-doped MWNTsFirst, the influence of purification on electrical conductivity of MWNTs were carried out.Then MWNTs were doped by Cl2 under different conditions, we focused on the change of electrical conductivity. The results indicated that high-temperature treatment brought negative effect, causing the electrical conductivity declined and even worse after Cl2-doping,while acid treatment gave a little enhancement on the electrical conductivity, the electrical conductivities of, both unpurified and HNO3-treated MWNTs were improved after Cl2-doping under the conditions of low temperature, high temperature and UV radiation. Compared with the HNO3-treated MWNTs, Unpurified MWNTs improved most, with the conductivity of 1548.3s/m, over five times of that of unpurified MWNTs. 3, Conducting mechanism of Cl2-doped MWNTsThree kinds of Chlorine existed in Cl2-doping MWNTs, as physically absorpted, chemically absorpted and bonded Cl2. The percentage of each kind of Chlorine was investigated by TG and XPS, the results showed that the chemically absorpted Chlorine brought positive influence on the conductivity of MWNTs.The variation of conductivities of Cl2-doped MWNTs with temperature was investigated, the result showed the MWNTs had the characteristics of semiconductor. Analyses of TG, FTIR, Raman, UV-vis and XPS were carried out.The results stated that electrons were transferred from MWNTs to Chlorine, improving the conjugation of MWNTs. Based on these findings, conducting mechanism was presented:Interactions existed between Chlorine and MWNTs,Ï€-electrons were transferred from MWNTs to chlorine, Impurity band came into being between the valence band and conduction band, which lowered their energy gap and enhanced the hopping capability from the valence band to conduction band, making the densities of electrons and holes improved, causing the improvement of the conductivity of Cl2-doped MWNTs.