Comparative study of fluorinated single- and few-wall carbon nanotubes by X-ray photoelectron and X-ray absorption spectroscopy

Abstract

Pristine and ball-milled samples containing single-wall carbon nanotubes (SWCNTs) and few-wall carbon nanotubes (FWCNTs) have been fluorinated at room temperature using gaseous BrF 3 as a fluorinating agent. X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy were used to estimate the chemical composition and to probe the electronic structure of the fluorinated CNTs. Analysis of the XPS C 1s spectra revealed that fluorinated carbon atoms in SWCNTs are bounded with one CF-group at least while most of the fluorinated carbon atoms in FWCNTs are surrounded by bare carbon atoms only. The ball-milling of the samples during 1 hour has insignificant effect on CNT length and more likely produces defects in CNT surface layers. These defects increase fluorination ability of CNTs and provide access for fluorine atoms to the subsurface layers of FWCNTs. NEXAFS investigation revealed that some of CNTs, which probably constitute interior of FWCNTs or CNT ropes, are not fluorinated during the conditions used and the fluorine atoms interact more strongly with CNT surfaces having a larger curvature.