Carbon nanomaterials, such as carbon nanotubes and graphene, have attracted significant interest over the past several years due to their outstanding and unusual combination of physical properties. These properties can be modified in a controllable way by chemical functionalization in order to enable specific technological applications. One example is hydrogenation, achieved by the exposure of these materials to a source of atomic hydrogen. This process has been considered for hydrogen storage purposes and for the control of the band gap of these materials for applications in carbon-based electronics. Hydrogen atoms are chemisorbed onto the surface of these materials, introducing sp3-hybridized C–C bonds in a structure originally formed by delocalized sp2 C–C bonding. This bonding transition causes severe structural and morphological changes to the graphene layers/walls. Also, it has been demonstrated that the exposure of multi-walled carbon nanotubes (MWCNTs) to a H2 plasma leads to the formation of diamond nanocrystals embedded within the nanotube walls. This thesis presents a computational analysis of the effects of hydrogen chemisorption on the structure and morphology of graphene and single-walled carbon nanotubes (SWCNTs), as well as of the different nanostructures that can be generated upon formation of inter-shell and inter-layer sp3 C–C bonds in MWCNTs and few-layer graphene (FLG), respectively. The analysis is based on a synergistic combination of atomic-scale modeling tools, including first-principles density functional theory (DFT) calculations and classical molecular-dynamics (MD) and Monte Carlo (MC) simulations. The results demonstrate that SWCNTs and graphene swell upon hydrogenation and provide interpretations to experiments reported in the literature; this swelling depends strongly on the hydrogen surface coverage. A MC/MD-based compositional relaxation procedure generates configurations whose arrangements of H atoms are in excellent agreement with experimental observations. Detailed structural analysis of the hydrogenated surfaces is carried out, providing information which cannot be extracted easily from conventional experimental techniques. The findings of the analysis are used to explain the limitations on the maximum H storage capacity of SWCNT bundles upon their exposure to an atomic H flux. Furthermore, it is demonstrated that the structures resulting from formation of inter-shell or inter-layer C-C bonds are stable and provide seeds for the nucleation of crystalline carbon phases embedded into the shells and layers of the MWCNT and FLG structures, respectively. The key parameter that determines the type and size of the generated nanocrystals is the chiral-angle difference between adjacent layers/walls in the original structure. A novel type of carbon structure, consisting of fullerene-like caged configurations embedded within adjacent graphene layers, has been discovered for the case where the graphene layers are rotated with respect to each other; interestingly, one class of these structures retains the unique and desired electronic properties of single-layer graphene.

L'écotoxicité de différentes nanoparticules de carbone (NPC) a été évaluée chez des organismes aquatiques, en particulier chez Xenopus laevis. Il a été montré que la surface des NPC est le paramètre le plus pertinent pour décrire l'inhibition de croissance chez le xénope, indépendamment de leur forme allotropique et de leur état de dispersion. L'induction des micronoyaux a aussi été étudiée chez le xénope, et l'oxyde de graphène (GO) s'est révélé génotoxique à faible dose, résultat corroboré par l'étude de l'expression des gènes. Les mécanismes de toxicité impliqués seraient notamment liés aux fonctions oxygénées de la particule. De plus, le GO a aussi entrainé de la génotoxicité chez Pleurodeles waltl. et de la tératogénicité, des retards de développement et de l'inhibition de croissance chez Chironomus riparius. La mise en interaction de ces organismes au sein d'un mésocosme a également conduit à l'observation de génotoxicité chez le pleurodèle en présence de GO. / The ecotoxicity of different carbon-based nanoparticles (CNPs) was assessed in freshwater organisms, especially in Xenopus laevis. The surface of the CNPs was shown to be the more relevant parameter to describe the growth inhibition in Xenopus, regardless of their allotropic form and their state of dispersion. Micronucleus induction was also studied in Xenopus and graphene oxide (GO) was found genotoxic at low dose. This result was in compliance with the study of genes expression. The involved toxicity mechanisms would be related to the oxidized functions of the CNP. Moreover, GO was also found responsible for genotoxicity in Pleurodeles waltl. and for teratogenicity, development delay and growth inhibition in Chironomus riparius. These organisms have finally been put together in a mesocosm, which has also led to genotoxicity in Pleurodeles in the presence of GO.