The main objective of this research was to develop a catalytic thermal conversion process for production of carbon-based nanomaterials (CNs) from kraft lignin. Four specific objectives were to: (1) understand the structural evolution of kraft lignin during its thermal treatment process; (2) investigate effects of temperature, and iron catalyst loading and morphology on the catalytic thermal conversion of kraft lignin to CNs, understand lignin catalytic thermal conversion mechanism; (3) explore potential applications of CNs synthesized from kraft lignin as an adsorbent for lead removing from contaminated water; (4) and propose effective methods for graphene material characterization. Experimental results indicated that the crystallinity of CNs from non-catalytic thermal conversion of kraft lignin increased and amorphous potion in CNs decreased with increased temperature. Specifically, as temperature increased from 500 to 1000 °C, CNs had its lateral crystallite size (La) increased from 6.97 to 13.96 angstrom, its lattice space (d002) decreased from 3.56 to 3.49 angstrom, and its crystallite (Lc) thickness was between 8 to 9 angstrom. The process of catalytic thermal conversion of kraft lignin yielded graphene-based nanomaterials such as multilayer graphene-encapsulated iron nanoparticles (MLGEINs), multilayer graphene (MLG) sheets, and MLG nanoribbons. Producing MLGEINs required a minimum temperature of 750 °C. The minimum temperature for producing MLG sheets and MLG nanoribbons was found to be 600 °C. It was found that carbonous gases from kraft lignin decomposition acted as the carbon source for MLG sheets and MLG nanoribbons formation, and solid carbon from carbonized lignin acted as the carbon source for the formation of MLGEINs. The yield of CNs increased with increased iron loading. Solid iron nanoparticles as a catalyst favor to form MLG nanoribbons, while iron nitrate favors to form MLGEINs. MLGEINs showed a good sorption capacity for aqueous Pb2+. The adsorption mechanism was mainly dominated by ion-exchange reaction. The final lead contains MLGEINs can be rapidly separated from solution through a magnet. FTIR, Raman, and HRTEM techniques are effective tools for characterizing defects in graphene-based materials. XRD technique is useful to evaluate the average structure parameters of graphene-based materials. SEM technique can be used to characterize morphology of graphene-based materials.

Graphene Oxide (GO) has emerged within the last decade as a next generation material for water treatment. Fabrication of graphene oxide membranes has been limited in scale and application due to repulsive hydration forces causing GO layers to electrostatically separate. In this study, chitosan is utilized to increase GO stability in the wet state through interactions with the negatively charged GO sheets (CSGO). This simple aqueous self-assembly allows scalable fabrication and enhanced stability for membrane applications in crosslow. The CSGO membrane’s performance was tested in a crosslow reactor and challenged with methylene blue at concentrations ranging from 1 to 100 ppm at 345 kPa with fluxes ranging from 1 to 4.5 L/(m2 hr) with 100% removal by physical rejection. This work demonstrates that the CSGO composite matrix is a potential alternative to traditional polymeric membranes for water treatment using a renewable biopolymer and minimal chemical input.

No description available.

No description available.

No description available.

THz light has important applications in medical imaging, chemical sensing, industrial quality control, and future wireless communications. However, the widespread adoption of these applications is currently limited by the lack of practical sources of THz radiation that can operate at or near room temperature. Graphene is a promising materials system for basic studies and device applications in THz optoelectronics, with several key functionalities, including photodetection and optical modulation, already demonstrated in recent years. This thesis work is focused on the use of graphene for the THz light emission. In particular, I have demonstrated for the first time the generation of gate-tunable THz radiation from graphene nanoribbons under current injection. The underlying radiation mechanism involves the excitation of graphene plasmonic oscillations by the injected hot carriers and their subsequent radiative decay at the nanoribbon resonance frequency. Combined with suitably designed optical elements, this approach is promising for the development of compact THz sources for imaging and sensing applications. In addition, I have also investigated alternative radiation mechanisms that can provide higher efficiencies but require more complex ultra-high-mobility graphene samples. These mechanisms include Smith-Purcell emission by the graphene electron gas in the vicinity of a periodic grating and interminiband transitions in graphene superlattices produced with a periodic external potential. Finally, I have designed and investigated numerically a graphene-nanoribbon metasurface platform that can provide arbitrary wavefront shaping functionalities for incident THz light, such as beam steering and focusing. Importantly, this device can be actively reconfigured by varying the nanoribbon gate voltages, which makes it particularly attractive for applications in wireless communications beyond 5G.

Even changing one atom in nanoscale materials is expected to alter their properties due to their small physical sizes. Such sensitivity can be utilized to modify materials' properties from bottom up and is essential for the utility of nanoscale materials. As such, the impact of extrinsic atomic adsorbates was measured on pristine graphene and a network of carbon nanotubes using atomic hydrogen, cesium atoms, and dye molecules. In order to further quantify such an atomic influence, the resistance induced by a single potassium atom on metallic and semiconducting carbon nanotubes was measured for the first time. Carbon nanotubes are sensitive to adsorbates due to their high surface-to-volume ratio. The resistance arising from the presence of extrinsic impurity atoms depends on the types of nanotubes. Metallic carbon nanotubes are resilient to a long-ranged, Coulomb-like potential, whereas semiconducting carbon nanotubes are susceptible to these impurities. The difference in the scattering strength originates from the chirality of carbon nanotubes, which defines their unique electronic properties. This difference had not directly measured experimentally because of the issue of contact resistance, the difficulty of chirality identification, and the uncertainty in the number of impurity atoms introduced on carbon nanotubes. We synthesized atomically clean, long ( > 100 ?m) carbon nanotubes, and their chirality was identified by Rayleigh scattering spectroscopy. We introduced potassium atoms on the nanotubes to impose a long-range, Coulomb potential and measured the change in resistivity, excluding the contact resistance, by plotting the resistance as a function of the carbon nanotube length. The flux of potassium atoms coming onto the nanotubes was monitored by quartz crystal microbalance, and the scattering strength of a single potassium atom was deduced from the change in resistivity and the density of potassium atoms on the nanotubes. We found that the scattering strength of potassium atoms on semiconducting nanotubes depends on the charge carrier type (holes or electrons). Metallic nanotubes were found to be less affected by the presence of potassium atoms than semiconducting nanotubes, but the scattering strength showed a large dependence on Fermi energy. These experimental results were compared to theoretical simulations, and we found a good agreement with the experiments. Our findings provide crucial information for the application of carbon nanotubes for electronic devices, such as transistors and sensors.

In this project, different molecules have been investigated with the purpose of creating anohmic contact between metals and carbon nano materials. In particular, we considered simplemolecules connecting a graphene layer and a copper-slab. In order to determine the capability of such systems, the electronic structure was computedusing Density Functional Theory (DFT). Structural relaxation was performed in order to findcandidates where the metal and the graphene binds chemically with the hypothesis that thehybridization of the states will induce more states at the Fermi level. Six different molecularchains were tested and three of them were found to chemisorb to the graphene sheet and thecopper surface simultaneously. The electronic properties for these systems were then furtherinvestigated using the density of states (DOS). An overlap density of states (ODOS) wasdefined in order to evaluate the respective contribution of the graphene, metal and molecule. From the DOS analysis, we report that these systems did not form ohmic contacts as the resultshows too few states close to the Fermi level. The most interesting case was using a hexanolchain which had some partially overlapping states seen from the ODOS of the graphenemoleculeand graphene-Cu at the Fermi level. However, these were only small contributions.Further research is crucial in order to find a more suitable molecular chain between thegraphene and the copper for an ohmic contact.

No description available.

No description available.