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Free keywords:
XPS; UPS; carbon nanotubes
revealing oxygen functional groups on carbon
Abstract:
A novel composite material consisting of carbon nanofibers (CNF) grown on sintered metal fibers (SMF) filters was modified by H2O2 or plasma-generated O3. Coupling TPD and XPS techniques in the same UHV apparatus allowed the direct correlation between the nature of the created O-functional groups and their evolution as CO and CO2 upon heating. The two oxidative treatments yielded different distributions of O-containing groups. The relative contribution of oxidized carbon was very low in the C1s region, so the functional groups were better analyzed in the O1s region. The quantification of the released oxygen by integration of the TPD CO, CO2 and H2O spectra, compared with the intensity loss of the XPS O1s spectra showed a good agreement. In order to fit the data adequately, the set of O1s spectra was decomposed in at least four peaks for the differently activated samples. Finally, it was shown that functional groups formed by H2O2-treatment (mostly non-phenolic OH groups) are thermally more stable than the ones formed by O3-treatment. The latter treatment increases the concentration of carboxylic functionalities, which decomposes at temperatures < 800 K; O3-activated CNF therefore should show a more pronounced acidic behavior.
