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Aberration-corrected transmission electron microscopy of the atomic structure of diamond–graphite interface after Ni-induced catalytic transformation reveals graphitic planes bound covalently to the diamond in the upright orientation. The covalent attachment, together with a significant volume expansion of graphite transformed from diamond, gives rise to uniaxial stress that is released through plastic deformation. We propose a comprehensive model explaining the Ni-mediated transformation of diamond to graphite and covalent bonding at the interface as well as the mechanism of relaxation of uniaxial stress. We also explain the mechanism of electrical transport through the graphitized surface of diamond. The result may thus provide a foundation for the catalytically driven formation of graphene–diamond nanodevices.

Graphene oxide is a complex material whose synthesis is still incompletely understood. To study the time evolution of structural and chemical properties of oxidized graphite, samples at different temporal stages of oxidation were selected and characterized through a number of techniques: X-ray photoelectron spectroscopy for the content and bonding of oxygen, X-ray diffraction for the level of intercalation, Raman spectroscopy for detection of structural changes, electrical resistivity measurements for probing charge localization on the macroscopic scale, and scanning 2 transmission electron microscopy for the atomic structure of the graphene oxide flakes. We found a non-linear behavior of oxygen uptake with time where two concentration plateaus were identified: uptake reached 20 at.% in the first 15 minutes, and after one hour a second uptake started, reaching a highest oxygen concentration of more than 30 at.% after two hours of oxidation. At the same time, the interlayer distance expanded to more than twice the value of graphite and the electrical resistivity increased by 7 orders of magnitude. After four days of chemical processing, the expanded structure of graphite oxide became unstable and spontaneously exfoliated; more than two weeks resulted in a significant decrease of the oxygen content accompanied by re-aggregation of the GO sheets. These correlated measurements allow us to offer a comprehensive view into the complex oxidation process.

Carbon nanomaterials such as nanodiamond (ND) and graphene oxide (GO) attract increasing attention for biomedical applications due their unique and adjustable properties. Here we report on antibacterial activity of NDs and GO as evaluated by bacterial colony counting. ND and GO were used in oxidized (O-ND, GO) or reduced (H-ND, rGO) forms. ND or GO are mixed in Mueller-Hinton (MH) broth with Escherichia coli at the concentration of 1 mg ml À1 . The resulting suspensions were cultivated for 5 and 24 h at 37 8C in a shaker. After each period, a sample of the suspension was spread on the MH agar and cultivated for 24 h at 378 C. The effect of nanomaterials on colony forming ability (CFA) of E. coli was evaluated and compared with the negative control sample. The most noticeable effect was that after 5 h H-ND decreased the CFA of E. coli in the MH broth by 60% and GO by 50%. After 24 h, H-ND decreased CFA by 50%. Other nanomaterials had no statistically significant antibacterial effect. Factors influencing ND and GO antibacterial activity against the E. coli and possibly against other bacteria are discussed.