Graphene, a single atomic layer of sp²-bonded carbon, has been of significant interest to basic sciences and engineering. Among its unique properties are exceptional mechanical strength, from the strong carbon-carbon bond; high in-plane thermal conductivity; high carrier mobilities, since electrons and holes travel through graphene as mass-less Dirac fermions; and quantum effects (such as the quantum Hall effect), which can be observed at room temperature. In 2009, Li et al., of Professor Ruoff's research group at the University of Texas at Austin, published a seminal paper detailing the production of fairly high quality graphene grown on copper foils using chemical vapor deposition (CVD). The potential for scalability of graphene CVD processing is extremely attractive, and this is currently the most promising method for its commercial viability, particularly for transparent conductive electrodes (TCEs). Here, graphene-based TCEs are compared with TCEs made with multi-walled carbon nanotubes (MWCNTs). A novel technique to reduce the sheet resistance of MWCNT-based TCEs in half is described in detail. Even with these improvements, graphene-based TCEs outperform MWCNT-based TCEs. The decomposition of copper oxides at high temperatures in an oxygen deficient environment is characterized. The ability for the oxygen evolved from the copper foil during this decomposition to react with carbon on the surface of the copper substrate is verified. This phenomenon was used to develop a technique for getting clean pre-graphene growth copper substrates and allowing repeatable graphene nucleation results. A technique for growing large graphene domains inside a copper vapor trapping 'copper enclosure' is described. The quality of the graphene grown inside the copper enclosure is characterized and shown to be of very high quality. This technique can grow graphene domains over 0.5 mm across. Finally, a possible cause of graphene ad-layer growth on the copper surface is suggested. It is proposed that gas diffusing through the copper substrate at high temperature delaminates the graphene from the copper surface in some regions. This then allows carbon containing molecules to diffuse under the graphene and grow new graphene layers. The increased ad-layer growth in the presence of helium supports this. / text

Nanographene oxide particles (NGO) were produced via oxidative exfoliation of graphite. Three different sizes of NGO (300 nm, 200 nm and 100 nm) have been separated by using probe sonication and sucrose density gradient centrifugation. There is great interest in functionalized NGO as a nanocarrier for in vitro and in vivo drug delivery, in order to improve dispersibility and stability of the nanocarrier platforms in physiological media. In this study, the NGO particles were covalently functionalized with zero generation polyamidoamide (PAMAM-G0) and with gelatin via noncovalent interaction. Spectroscopic techniques have been used to discriminate the chemical states of NGO prior and after functionalization. The X-ray photoelectron spectroscopy (XPS) revealed a clear change in the chemical state of NGO after functionalization, for both covalent and noncovalent approaches. Raman spectroscopy gave obvious insight after oxidation of graphite and functionalization of NGO particles depending on the variation of intensity ratios between D, G and 2D bands. The Fourier transform infrared spectroscopy (FTIR) exhibited the presence of oxygen containing functional groups distributed onto graphene sheets after oxidation of graphite. Furthermore, the FTIR is complementary with the XPS which performed a strong reduction in the oxygen contents after functionalization. UV visible spectroscopy was used to understand the binding capacity of gelatin coated NGO particles. The Microscopy tools, scanning electron microscopy (SEM) and atomic force microscopy (AFM) are used to estimate the dimensions of NGO particles (thickness and lateral width). The nanohybrid systems (NGO-PAMAM and Gelatin-NGO) loaded with carboplatin (CP) were sought for anticancer activity investigation in HeLa and neuroblastoma cancer cells respectively. Mesenchymal stem cells (hMSCs) were used as a model of normal cells. On HeLa cells, the pristine NGO particles with average widths of 200 nm and 300 nm showed a cytotoxic effect at low (50 g.ml−1) and high (100 g.ml−1) concentrations. While the pristine NGO sample with an average width of 100 nm revealed no significant cytotoxicity at 50 g.ml−1, and only recorded a 10% level at 100 g.ml−1. The mesenchymal stem cells showed less than 35% viability for all size distributions. After functionalization with PAMAM, the carrier was found to be able to deliver carboplatin to the cancer cells, by enhancing the drug anticancer efficiency. Moreover, the carboplatin loaded NGO carrier shows no significant effect on the viability of hMSCs even at high concentration (100 g.ml−1). On neuroblastoma cells, the cell viability assay validated gelatin-NGO nanohybrids as a useful nanocarrier for CP release and delivery, without obvious signs of toxicity. The nano-sized NGO (200 nm and 300 nm) did not enable CP to kill the cancer cells efficiently, whilst the CP loaded gelatin-NGO 100 nm resulted in a synergistic activity through increasing the local concentration of CP inside the cancer cells.

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Exposure to high impact velocity is the principle limiting factor of material performance in ballistic applications for use in civilian and defense industries. Graphene has emerged as a material of scientific interest due to its exceptional mechanical and thermal properties. When incorporated appropriately in a polymer matrix, graphene can significantly improve properties of polymers at small loading, while preserving the integrity of the polymer. Graphene based polymer nanocomposites provide a novel approach for material design for ballistic applications. The reliability of graphene/polymer nanocomposites on end use applications depends on understanding the effect of structure-property relationship of nanocomposite. A first approach to engineering nanocomposite for ballistic applications requires thorough understanding of physical properties change with incorporation of nanofillers in polymer matrix. One significant class of properties tremendously affected by inclusion of nanofiller is thermodynamic properties. Therefore, a first investigative study, we explore non-linear elastic behavior of graphene using first principle method, specifically Density-Functional Theory (DFT), and atomistic simulation. Using DFT, we calculated the equation of state (EOS) and elastic constants of graphene. The results are in agreement with experimental and other theoretical studies using DFT. However, accuracy of atomistic simulations is limited by empirical potentials. Nevertheless, general anisotropic, non-linear mechanical behavior of graphene is evident on both approaches. Additionally we use molecular dynamics (MD) simulations to study effect of graphene nanofiller on thermo‑mechanical properties of polyurethane. We have calculated thermodynamic, structural and mechanical properties of the amorphous polyurethane and its graphene nanocomposite. Our results show significant enhancement of thermal-mechanical properties. The final part of this dissertation, we used non-equilibrium molecular dynamics (NEMD) simulations to investigate dynamic response behavior of polyurethane and its graphene nanocomposite. Calculation of Hugoniot states of polyurethane agrees with experimental studies. However, a phase change phenomenon observed in experimental work was not visible in the present work. This is due to bond breaking and formation, which is a clear characterization of phase changes. Graphene-polyurethane nanocomposites demonstrate similar shock wave propagation illustrating characteristics of impeding shock wave when subjected to different particle velocities. This is due to graphene inducing stress concentrations in the composite, which may increase yield strength.

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Desulfurization of liquid and gas phase sulfur compounds has been receiving dramatic attention since sulfur compounds cause environmental damages (especially acid rain) and pose industrial challenges (i.e. corrosion of equipment and deactivation of catalysts). This thesis has focused on the removal of liquid phase aromatic sulfur compounds (i.e. thiophene or dibenzothiophene (DBT)), as well as on the removal of gas phase hydrogen sulfide (H2S) through adsorption method by metal oxide/graphene composites. More specifically, the effects of graphene (or reduced graphite oxide) as a substrate were thoroughly investigated. For liquid phase sulfur removal, graphene which possesses π orbitals can adsorb aromatic sulfur compounds through π-π interactions. In addition, depending on the synthesis methods, higher quality graphene (i.e. thinner or larger graphene) could be obtained; and it improved the amount of DBT adsorption. For gas phase desulfurization (i.e. H2S adsorption), zinc oxide (ZnO) and reduced graphite oxide (rGO) composites have been studied. This study highlights the critical role of rGO as a substrate to enhance the H2S adsorption capacity. The presence of rGO with ZnO increases the surface area compared with pure ZnO since the oxygen functional groups on rGO prevent the aggregation of nano-sized ZnO particles for mid temperature sulfidation processes. The average particle size for pure ZnO was increased from 110 nm to 201 nm during the adsorption process while that for ZnO/rGO was maintained as 95 nm even after adsorption at 300°C. This contributes to explain that the presence of rGO with ZnO can enhance the H2S adsorption capacity from 31.7 mg S/g ads (for pure ZnO) to 172.6 mg S/g ads (for ZnO/rGO), that is more than a 5-fold increase. Morever, the presence of rGO with ZnO considerably improves the stability of the adsorbent; for multiple regeneration cycles at 600°C (in N2 environment), the adsorption capacity for ZnO/rGO stabilized at 93.1 mg S/g ads after the 8th cycle, while that for pure ZnO was nil after 5 cycles. The effects of copper (5, 10, 15, 20 and 25 mol%) with zinc oxide (ZnO) and reduced graphite oxide (rGO) composite on the hydrogen sulfide (H2S) adsorption capacity have also been studied. It was found that depending on the copper loading, the H2S adsorption capacity has been increased by up to 18 times compared to pure ZnO. In order to investigate the oxidation changes on copper and zinc oxides, crystallite analysis by XRD and chemical state analysis by XPS were performed. It was confirmed that the 2D rGO substrate, containing abundant oxygen functional groups, promoted the metal oxide dispersion and increased the H2S adsorption efficiency by providing loosely bonded oxygen ions to the sulfur molecules. In addition, it was determined that the optimum content of copper was 15 mol% relative to ZnO for maximizing the H2S adsorption. The 15% copper with ZnO/rGO led to the highest portion of zinc ions located in the Zn-O lattice; and led to the co-existence of Cu1+ and Cu2+ ions with ZnO. The H2S exposure at 300°C produces metal sulfides (i.e. zinc sulfide and copper sulfide) and sulfate ions.

Low dimensional carbon allotropes presently provide an unparalleled platform to explore novel electronic properties, and with tremendous progress may one day supplant entrenched materials within the semiconductor industry. In order for graphene to continue on its extraordinary scientific and technological trajectories, many hurdles must be overcome such as reliable bandgap engineering, advances in processability, removal or mitigation of defects and so on. Noncovalent chemical modification of graphene offers a pathway to address many of these concerns and furthermore provides an opportunity to graft new functionality onto this unique material. In this work, the effects of noncovalent modification of graphene by simple polyaromatic molecules – rubrene and tetracene – are investigated. By exploiting π π interactions between the two highly conjugated systems, a simple approach to functionalize graphene devices has been developed. Optical and electron-beam lithography are used to fabricate graphene field effect transistors, which can be subsequently modified either in their entirety or in a site specific manner. In order to better understand the resulting graphene/rubrene structure, a suite of analytical tools has been employed. Raman spectroscopy and microscopy confirm the presence of the rubrene and spatially correlate observed electronic changes with surface modification while polarized Raman spectroscopy is used to investigate any long range order of rubrene on the graphene surface. Photoluminescence measurements show that rubrene emission is not quenched, and spectral analysis offers insight into rubrene film characteristics. Atomic force microscopy provides detailed information as to film thickness, and suggests that rubrene film morphology is largely disordered. Due to the simplicity of this functionalization procedure, a rubrene-based motif could be widely expanded allowing researchers to explore grafting new chemical moieties onto graphene and enabling new device opportunities. Transport measurements reveal the effects of rubrene on the graphene electronic properties. Modified devices display increased conductivity, a substantial shift in Dirac point and a moderate decrease in carrier mobility, all of which are consistent with an electronic doping mechanism whereby the rubrene acts as a hole dopant. Preliminary photoresponse measurements suggest that this graphene-molecular hybrid could act as a potential photodetector. / Graduate