This thesis investigates the chemistry of graphene from its basic synthesis to further modulation of its structure, geometry and surface chemical functional groups. A series of wet chemistry and dry chemistry experiments were performed. The wet chemistry includes the diazonium salt functionalization, graphene oxidation and reduction, nanotube unzipping chemistry, graphite intercalation and exfoliation. The dry chemistry includes chemical vapor deposition and solid carbon source synthesis of graphene, the control of domain size and stacking order, graphene hydrogenation and lithographically patterned graphene superlattices. With all these chemical approaches, graphene's electrical and optical properties, solubility in organic solvents, crystallography, and chemical reactivity were carefully investigated and discussed. In addition to the fundamental chemistry of graphene, the bio- and environmental impact of this new material was also taken into consideration and investigated.

京都大学 / 新制・課程博士 / 博士(エネルギー科学) / 甲第23295号 / エネ博第420号 / 新制||エネ||80(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻 / (主査)教授 萩原 理加, 教授 野平 俊之, 教授 坂口 浩司 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DFAM

Graphene is a two-dimensional carbon structure that exhibits remarkable structure-property relations. Consequently, there has been immense effort undertaken towards developing methods for graphene synthesis. Chemical vapor deposition (CVD) and chemical exfoliation from colloidal suspensions are two common methods used for obtaining graphene films. However, the underlying experimental conditions have to be carefully optimized in order to obtain graphene films of controllable thickness and morphology. In this context, a significant part of this dissertation was devoted towards developing and improving current CVD-based and chemical exfoliation based methods for synthesizing high quality graphene films. Specifically, in the CVD based procedure for growing graphene on copper, the effect of surface pretreatment of copper was investigated and the quality of graphene grown using two different pretreatment procedures was compared and analyzed. In particular, graphene grown on electropolished copper (EP-Cu) was analyzed with respect to its surface morphology, surface roughness and thickness, and compared with graphene grown on as cold-rolled acetic acid cleaned copper (AA-Cu). It was shown that electropolishing of the Cu substrates prior to graphene growth greatly enhanced the ability to obtain flat, uniform, predominantly single layer graphene surface coverage on copper. The reported surface roughness of the graphene on EP-Cu was found to be much lower than for previously reported systems, suggesting that the electropolishing procedure adopted in this work has great promise as a pretreatment step for Cu substrates used in CVD growth of graphene. Obtaining graphene from colloidal suspensions of graphitic systems was also examined. In this work, an acid (H₂SO₄ + HNO₃) treatment process for intercalating natural graphite flakes was examined and the ability to reversibly intercalate and deintercalate acid ions within graphitic galleries was investigated. More importantly, a rapid-thermal expansion (RTP) processing was developed to thermally expand the acid-treated graphite, followed by exfoliation of predominantly bilayer graphene as well as few layer graphene flakes in an organic solvent (N, N-Dimethylformamide - DMF). The developed method was shown to provide bilayer and few layer graphene flakes in a reliable fashion. Fullerene is another carbon nanostructure that has garnered attention due to unique structure and chemical properties. Recently, there has been increased focus towards harnessing the properties of fullerenes by synthesizing fullerene self-assemblies in the form of extended rods, tubes and more complex shapes. Current methods to synthesize these self-assemblies are either cumbersome, time consuming or expensive. In this context, an alternate, straightforward dip-coating procedure technique to self-assemble equal-sized, faceted, polymerized fullerene nanorods on graphene-based substrates in a rapid fashion was developed. By suitably modifying the kinetics of self-assembly, the ability to reliably control the spatial distribution, size, shape, morphology and chemistry of fullerene nanorods was achieved.

Pour améliorer les performances des batteries au lithium, des ruptures technologiques sont nécessaires. Ceci impose que les aspects fondamentaux liés au fonctionnement de ces dispositifs électroniques soient reconsidérés. Dans cette optique, les méthodes de la chimie quantique peuvent apporter une aide précieuse, notamment pour comprendre les phénomènes électroniques microscopiques, à l'origine du stockage de l'énergie. Établir une relation directe entre la nature de la liaison chimique (microscopique) et les propriétés physico-chimiques (macroscopiques) des matériaux d'électrode pour batteries Li-Ion est donc l'objectif dans lequel s'inscrivent les travaux exposés dans cette thèse. Ce travail explore à la fois des aspects méthodologiques et des applications. Il vise à proposer des méthodologies d'analyse simples permettant de traiter les réactions électrochimiques d'un point de vue théorique et de déterminer les mécanismes microscopiques mis en jeu au cours des cycles de charge et de décharge des batteries. Les systèmes étudiés sont les composés d'insertion du graphite (Li-GICs) et un matériau hybride de type MOFs (« Metal Organic Framework ») basé sur l'ion ferrique (MIL-53(Fe)). Pour les Li-GICs, une nouvelle méthode couplant des calculs premiers principes DFT à un modèle statistique dérivé du modèle de Bethe-Peierls a été développée pour rendre compte des effets d'entropie (de configuration) dans leur diagramme de phase. Les résultats obtenus apportent un nouveau regard sur les processus électrochimiques induits par le lithium, ouvrant des perspectives technologiques intéressantes pour remédier aux problèmes de sécurité posés par ce type d'électrode. Pour le MIL-53(Fe), la méthode DFT+U a été utilisée pour rendre compte des effets de corrélation électronique et pour reproduire l'état fondamental complexe de ce système. Les résultats obtenus ont permis de comprendre l'origine de la faible capacité de ce matériau vis-`a-vis du lithium.