3. Results and discussion3.1. Catalyst characterizationFig. 1 shows electron microscopy characterization of the mate-rials obtained. Diamond-based materials (Dsynand ND) containedspheroid agglomerates about 0.5–1 _m in diameter (Fig. 1a). TEManalysis of these agglomerates, however, showed that ND agglom-erates were built of crystallites smaller than 10 nm (Fig. 1b), whilecrystallites of Dsynwere several orders of magnitude larger, up to1 _m in diameter. Multiwalled carbon nanotubes were 18–25 nm indiameter and more than 5 _m in length (Fig. 1c). Backscatter elec-tron SEM data showed that metal particles were present at the endsof the nanotubes despite of thorough washing, likely due to encap-sulation during the growth. Carbon flakes, both purely carbon CNFand nitrogen-doped CNF-N, had the same morphology and werebuilt of 3–6 layered graphene sheets about 25 by 25 nm (Fig. 1dand e). Fluorinated graphite contained particles 1–10 _m in diam-eter and a lot of partially exfoliated sheets, which were obtained,likely, due to fluorination treatment (Fig. 1f).Fig. 2 shows X-ray diffraction patterns of CNT and ND materials.As expected, the structure of ND corresponds to the sp3-hybridiseddiamond structure. Carbon nanotubes are built of sp2-hybridisedgraphene sheets, so the most intensive reflex agrees with that ofgraphite, while 2 weak reflexes correspond to the molybdenumoxide which is one of the components of the CNT synthesis catalystand was not fully removed from the CNT material. Average crys-tallite size of carbon based materials was about 7 nm for ND, whileit was about 4 nm for CNT, which agrees with the microscopy data(Fig. 1).Table 1 shows the surface properties of the studied carboncatalysts. Surface area of the diamond-based materials (ND andDsyn) differs by an order of magnitude, likely, because agglomer-ates of the ND (below 10 nm) are substantially smaller than that