Surface Oxidation of Carbon Nanofibres

Carbon nanofibres of the fishbone and parallel type were surface-oxidised by several methods. The untreated and oxidised fibres were studied with infrared spectroscopy, thermogravimetric analysis and XPS. Oxidation in a mixture of concentrated nitric and sulfuric acid turned out to be the most effective method for creating oxygen-containing surface groups. This treatment results not only in the formation of carboxyl and carboxylic anhydride groups, but also in the formation of ether-type oxygen groups in between graphitic layers that are puckered at their edges. The infrared results clearly show that the formation of oxygen-containing surface groups occurs at defect sites on the carbon nanofibres and that the oxidation proceeds via carbonyl groups and other oxides to carboxyl and carboxylic anhydride groups. Due to the presence of defects, both types of fibre have about the same surface reactivity. With parallel nanofibres, in contrast to fishbone fibres, the macroscopic structure was severely affected by the HNO3/H2SO4 treatment. Finally, the HNO3/H2SO4-treated fibres show a high wettability by water.