Simultaneous purification and functionalization of carbon nanotubes using chlorination
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obert Pełech Faculty of Chemical Engineering, Institute of Organic Chemical Technology, West Pomeranian University of Technology in Szczecin, 70-310 Szczecin, Poland (Received 6 March 2012; accepted 25 June 2012)
Multiwalled carbon nanotubes (MWCNTs) obtained using ethylene as a carbon source and nanocrystalline iron as a catalyst were used as the initial material. The functionalization of MWCNTs was carried out using chlorine in the liquid and gas phase. In the second case, the reaction was conducted in the temperature range from 50 to 450 °C for 2 h. The presence of chlorine species on the surface of chlorinated samples was confirmed by x-ray photoelectron spectroscopy (XPS). A quantitative analysis of metal impurity content was validated by means of thermogravimetric analysis. Better results of metal removal were achieved when the chlorination process was conducted in the gas phase and the ratio of metal in samples amounted from 2.3% to 5.1%. I. INTRODUCTION
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.243
the sake of comparison, chlorination was also performed using chlorine gas. It was concluded that this method gives functionalized SWCNTs in the range of 0.3–3.5% wt% of fluorine and 5.5–17.5 wt% of chlorine and it was proved that liquid materials containing halogen are more effective as functionalizing agents than gases. Direct fluorination of CNTs was carried out using hydrofluoric acid10 or fluorine gas.11–13 However, this process can lead to products that hardly allow any further reactions.11 Chlorine addition to MWCNTs was performed by Kónya et al.14 The authors reported that ball milling induces functionalization of MWCNTs in reactive atmospheres giving rise to formation of short CNTs containing different chemical functional groups, including chlorine. A method to purify MWCNTs involving chlorine water and ammonia water treatment was described in.15 The authors indicated that catalyst particles, amorphous carbon and carbon particles were almost completely eliminated and some carboxyl group and C–Cl bonds were introduced. Functionalized CNTs with dichlorocarbene (CCl2)16 and thionyl chloride17,18 can be converted with other chemical agents to add the corresponding functional group. Tang et al.19 used CNTs together with nickel oxide (Ni2O3) to reduce flammability of propylene. In this article, we present a functionalization of CNTs’ surface using chlorination method, which enables a simultaneous purification of MWCNTs from metal impurities. Details regarding the influence of experimental conditions (liquid or gas phase) and in the case of the gas phase—the effect of temperature, on the removal degree of metal particles and the amount of chlorine is presented. A quantitative analysis of metal impurity content was validated by means of thermogravimetric analysis (TGA). The presence of chlorine species on the surface of chlorinated
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Ó Materials Research Society 2012
Carbon nanotubes (CNTs) have potential applications in many fields, e.g., as electron emitters in t
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