Determination of the surface chemistry of ozone-treated carbon fibers by highly consistent evaluation of X-ray photoelectron spectra

Room-temperature ozone treatment is a promising technique for functionalization of carbon materials: it is fast, well controllable, and leads to oxygen uptakes of up to 15 at.% on carbon fiber surfaces. We investigated the surface chemistry of untreated and room-temperature ozone-treated polyacrylonitrilebased carbon fibers using X-ray photoelectron spectroscopy (XPS). By identifying two different nitrogen species (graphitic and pyridine-like) we developed a new constraint for fitting the C 1s spectra. This approach ensured high consistency between measured elemental concentrations and elemental concentrations calculated from fitted functional group peaks. It also revealed a different relative ordering of functional group concentrations than previously reported for ozone-treated carbons. The results of this new fitting procedure were cross-checked with chemical derivatization XPS measurements, resulting in a good correlation for hydroxyl and carbonyl groups. Examination of single fiber cross-sections using energy-dispersive X-ray spectroscopy in a transmission electron microscope showed that even after intense treatments oxygen can mainly be found in the topmost 40 nm-50 nm, stressing the importance of surface sensitive techniques such as XPS. Furthermore, XPS results suggested only a minor surface degradation caused by the ozone treatment. This was corroborated by atomic force microscopy results. (c) 2019 Elsevier Ltd. All rights reserved.