Carbonized organic precursors such as wood, shells and some plant seeds are very porous. They are nanostructured and tend to be hard, but have pure mechanical properties as a result of their porosities. An attempt was made to carbonize an organic precursor to produce a bulk material with much less porosity for possible use in structural applications such as reinforcement in metal and polymer matrices. A bulk nanocarbon (BNC) material was synthesized using high energy ball milling and the carbonization of corn cob. Corn cob was mechanically milled for up to 20 hours by applying high energy ball milling to produce the milled powder. The milled powder was cold-compacted and carbonized at up to 1500°C to fabricate the BNC material. The material revealed both micro and nano-porosities; the porosities decreased with carbonizing temperature and hold time. Micropores were mostly closed for samples carbonized above 1300oC, whereas they formed interconnected network at lower carbonization temperatures. BNC has a young's modulus of 120 GPa, about ten times that of extruded graphite. / Master of Science / Wood, shells, and plant seeds are examples of organic precursors. When organic precursors are carbonized, they can become very porous, nanostructured, and hard, but deliver pure mechanical properties because of their porosities. A selected organic precursor was carbonized, in an attempt, to produce a bulk material with much less porosity for possible use in structural applications such as reinforcement in metal and polymer matrices. A bulk nanocarbon (BNC) material was made using high energy ball milling and the carbonization of corn cob (the selected organic precursor). This bulk material revealed both micro and nano-porosities, and a young's modulus of 120 GPa, about ten times that of extruded graphite.

Acid oxidation of multi-walled carbon nanotubes (MWCNTs) introduced carboxylic acid sites onto the MWCNT surface, which permitted further functionalization. Derivatization of carboxylic acid sites yielded amide-amine and amide-urea functionalized MWCNTs from oxidized precursors. Conventional MWCNT characterization techniques including X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and Raman spectroscopy supported successful MWCNT functionalization. Incorporation of MWCNTs functionalized with hydrogen bonding groups into a segmented polyurethane matrix led to an increase in mechanical properties at optimized MWCNT loadings, in contrast with non-functionalized MWCNTs that resulted in mechanical property decreases across all loadings. Dynamic mechanical analysis (DMA) demonstrated an increase in the polyurethane-MWCNT composite flow temperature with increasing hydrogen bonding MWCNT incorporation, as opposed to non-functionalized MWCNT composites which displayed no significant change in flow temperature. Variable temperature Fourier transform infrared spectroscopy (VT FT-IR) probed temperature-dependent hydrogen bonding in the polyurethane-MWCNT composites and revealed a significant impact on composite hydrogen bonding interactions upon MWCNT incorporation, which was amplified in composites formed using hydrogen bonding functionalized MWCNTs. Acid oxidation of carbon nanohorns (CNHs) yielded carboxylic acid functionalized CNHs, providing sites for further reaction with histamine to afford histamine-functionalized CNHs (His-CNHs). Raman spectroscopy, XPS and TGA confirmed successful functionalization. Transmission electron microscopy (TEM) demonstrated that His-CNHs efficiently complex quantum dots (QDs) through imidazole-Zn interactions. Combination of His-CNHs, QDs, and a poly(oligo-(ethylene glycol9) methyl ether methacrylate)-block-poly(4-vinyl imidazole) copolymer using an interfacial complexation technique afforded stable ternary nanocomplexes with average hydrodynamic diameters under 100 nm. These ternary nanocomplexes represent promising materials for photothermal cancer theranostics due to their size and stability. The efficient reaction of 2-isocyanatoethyl methacrylate with amines afforded urea-containing methacrylic monomers, where the amine-derived pendant groups determined the polymer Tg. Reversible addition-fragmentation chain-transfer (RAFT) polymerization enabled the synthesis of ABA triblock copolymers with urea-containing methacrylic outer blocks and poly(2-ethylhexyl methacrylate) inner blocks. These ABA triblocks copolymers displayed composition dependent phase-separated morphologies and desirable mechanical properties. The urea-containing polymers efficiently complexed gold nanoparticles through urea-gold interactions. Furthermore, urea-containing methacrylic polymers served as a useful matrix for incorporation of silica-coated upconverting nanoparticles, affording upconverting nanoparticle composite films.The novel ionene monomer N1,N2-bis(3-(dimethylamino)propyl)oxalamide permitted synthesis of novel oxalamide-containing ammonium ionenes. The hydrogen bonding, charge density, and counter anion tuned the ionene mechanical properties. The ionene structure also influenced water uptake and conductivity. The differences in physical properties correlated well with the morphology observed in small-angle X-ray scattering. The oxalamide-containing ionenes greatly enhance mechanical properties compared to typical ammonium ionenes, and further expand the library of ionene polymers. / Ph. D.

Understanding the toxicity of carbon nanomaterials, such as carbon nanotubes and graphenes, is important for the development of nanotechnology. Studies have shown that surface redox capability is an important factor for toxicity of carbon nanomaterials. We have measured the surface reductive capacity for a number of carbon nanomaterials in previous studies, but the effects of various engineering processes on surface redox capability have not been investigated until this study. In this study, commercially available carbon black, carbon nanotubes, standard reference materials, fullerenes, graphenes and acetylene soot generated in the lab were used. The carbon nanomaterials were subjected to heating at various temperatures in various atmospheres up to 500 ˚C, and soaking in water at room temperature under various atmospheres, and weathering in the powder form at room temperature under various atmospheres. The redox capability of the carbon nanomaterials was quantified in terms of the reductive capacity towards Fe3+ ions (RCFI). The RCFI values of the asreceived nanomaterials and that of the nanomaterials after various treatments were compared. The carbon nanomaterials were also characterized using x-ray photoelectron spectroscopy (XPS), for understanding the surface chemistry mechanisms of RCFI and the effects of various treatments. In general, heating induced a significant increase in RCFI, regardless of the atmosphere under which the nanomaterials were heated. On the other hand, aging in O2- containing atmospheres brought about significant decrease in RCFI, either in water suspension or in the powder form. Water vapor enhanced the aging effect of O2. CO2 was found to affect the RCFI and the aging of carbon nanomaterials. The extent of RCFI change due to heating or aging was dependent on the type of material. According to the XPS results, the RCFI of some carbon nanomaterials such as carbon black may be correlated with the C-O surface functional groups. However, the definitive correlation between the oxygen-containing surface functional group and RCFI for all carbon nanomaterials couldn’t be determined by the XPS result. This indicates that the RCFI changes of carbon nanomaterials after treatments mainly derived from the factors such as the active sites of edges other than the oxygen-containing surface functional group changes as other studies show. This suggests that the RCFI measurement cannot be replaced by XPS analysis. The effects of heating and aging on RCFI, and more generally the surface redox capability of carbon nanomaterials, reveals that various engineering and environmental processes may significantly change the toxicity of carbon nanomaterials. The findings of this study suggest that it is important to take into account the effects of engineering and environmental processes when assessing the toxicity of carbon nanomaterials.

Due to the aggressive downscaling of the CMOS technology, power and current densities are increasing inside the chip. The limiting current conduction capacity(106 Acm−2)and thermal conductivity(201Wm−1K−1 for Al and 400 Wm−1K−1 for Cu) of the existing interconnects materials has given rise to different electro-thermal issues such a shot-spot formation, electromigration, etc. Exploration of new materials with high thermal conductivity and current conduction has thus attracted much attention for future integrated circuit technology. Among all the elemental materials, carbon nanomaterials (graphene and carbon nanotube) possess exceptionally high thermal (600-7000 Wm−1K−1) and current( ~108 -109 Acm−2)conduction properties at room temperature, which makes them potential candidate for interconnect materials. At the same time development of efficient energy harvesting techniques are also becoming important for future wireless autonomous devices. The excess heat generated at the hot-spot location could be used to drive an electronic circuit through a suitable thermoelectric generator. As the See beck coefficient of graphene is reported to be the highest among all elementary semiconductors, exploration of thermoelectric properties of graphene is very important. This thesis investigates the electrothermal and thermoelectric properties of metallic single walled carbon nanotube (SWCNT) and single layer graphene (SLG) for their possible applications in thermal management in next generation integrated circuits. A closed form analytical solution of Joule-heating equation in metallic SWCNTs is thus proposed by considering a temperature dependent lattice thermal conductivity (κ) on the basis of three-phonon Umklapp, mass-difference and boundary scattering phenomena. The solution of which gives the temperature profile over the SWCNT length and hence the location of hot-spot(created due to the self-heating inside the chip) can be predicted. This self-heating phenomenon is further extended to estimate the electromigration performance and mean-time-to-failure of metallic SWCNTs. It is shown that metallic SWCNTs are less prone to electromigration. To analyze the electro-thermal effects in a suspended SLG, a physics-based flexural phonon dominated thermal conductivity model is developed, which shows that κ follows a T1.5 and T−2 law at lower(<300 K) and higher temperature respectively in the absence of isotopes(C13 atoms). However in the presence of isotopic impurity, the behavior of κ sharply deviates from T−2 at higher temperatures. The proposed model of κ is found to be in excellent match with the available experimental data over a wide range of temperatures and can be utilized for an efficient electro-thermal analysis of encased/supported graphene. By considering the interaction of electron with in-plane and flexural phonons in a doped SLG sheet, a physics-based electrical conductance(σ) model of SLG under self-heating effect is also discussed that particularly exhibits the variation of electrical resistance with temperature at different current levels and matches well with the available experimental data. To investigate the thermoelectric performance of a SLG sheet, analytical models for See beck effect coefficient (SB) and specific heat (Cph) are developed, which are found to be in good agreement with the experimental data. Using those analytical models, it is predicted that one can achieve a thermoelectric figure of merit(ZT) of ~ 0.62 at room temperature by adding isotopic impurities(C13 atoms) in a degenerate SLG. Such prediction shows the immense potential of graphene in waste-heat recovery applications. Those models for σ, κ, SB and Cph are further used to determine the time evolution of temperature distribution along suspended SLG sheet through a transient analysis of Joule-heating equation under the Thomson effect. The proposed methodology can be extended to analyze the graphene heat-spreader theory and interconnects and graphene based thermoelectrics.

Fluorescent carbon dots are a new class of carbon nanomaterials that have emerged recently, and have created a lot of interest as a potential competitor to classical semiconductor quantum dots. Carbon dots possess low toxicity, biocompatibility, easy and low-cost synthesis, and good optical properties. They show huge potential as novel and versatile nanomaterials for a wide range of applications such as bioimaging, drug delivery, chemical sensing, photocatalysis, and as sensitizers for photovoltaic solar cells. The main motivation for this research was the need to produce non-toxic, low-cost nanomaterials with good optical and electrical properties for the use in the fabrication of sustainable, inexpensive nanostructured solar cells with good efficiency. The main aims and objectives of this PhD research were: to synthesize fluorescent carbon dots from biomass-derived precursors by using the hydrothermal synthesis method, to understand and explain structural and optical properties of the as-synthesized carbon dots, and to use the carbon dots as sensitizers for nanostructured solar cells. Carbon dots (CDs) were synthesized using hydrothermal synthesis method from polysaccharides (chitosan and chitin), monosaccharide (D-glucose), amino acids (L-arginine and L-cysteine), and from real food waste in the form of lobster shells. Carbon dots were thoroughly characterized to obtain the information about their structural and optical properties. The as-synthesized carbon dots showed polydispersity and quasi-spherical morphology, with particle sizes ranging from 5-17 nm. Carbon dots showed predominantly amorphous nature, and the functional groups from the starting precursors were successfully incorporated into the as-synthesized carbon dots. Diluted solutions of carbon dots were transparent under daylight and showed blue-green photoluminescence emission under UV excitation. All carbon dots showed excitation-dependent photoluminescence emission which was more pronounced for excitation wavelengths larger than 320 nm. Chitosan CDs, L-cysteine CDs and lobster CDs also showed excitation-independent emission for excitation wavelength in the range of 200 - 320 nm. The highest fluorescence quantum yield of (43.3 ± 2.1) % was calculated for L-arginine CDs. It was concluded that the origin of light emission in carbon dots must be governed by the interplay between the absorption due to the carbon cores and the surface functional groups. Considering the application of the as-synthesized carbon dots, two types of solar cells were fabricated. Carbon dots were used as sensitizers for ZnO-nanorod-based and for TiO2-based nanostructured solar cells. Three types of carbon dots (chitosan CDs, chitin CDs and D-glucose CDs) were used as sensitizers for ZnO-nanorod-based solar cells. ZnO nanorods were successfully coated with carbon dots, and the chitosan-CDs-sensitized solar cells showed the efficiency of 0.061 %. When using layer-by-layer coating method, solar cells with combination of chitosan- and chitin-CDs as sensitizers showed the efficiency of 0.077 %. All six types of carbon dots (chitosan CDs, chitin CDs, D-glucose CDs, L-arginine CDs, L-cysteine CDs, and lobster CDs) were used as sensitizers for TiO2-based nanostructured solar cells. TiO2-based solar cells sensitized with carbon dots showed much higher efficiency compared to the ZnO-nanorod-based solar cells. L-arginine-CDs sensitized TiO2-based solar cells showed the highest efficiency of (0.362 ± 0.007) %, which was the best efficiency of all fabricated solar cells. By surveying a range of biomass-derived carbon dots, and demonstrating a clear link between functionalisation and solar cell performance, this PhD research project provides a guide to direct future development of low-cost, biomass-derived sensitizers for nanostructured solar cells.

This dissertation primarily documents the quantification of the interfacial behavior of carbon based nanomaterials, which includes two categories, one is the nanofriction properties evaluation of aligned carbon nanotube carpets, few-layer graphene as well as three types of functionalized graphene nanoribbons, the second is the mechanical characterization of individual functionalized carbon nanofibers and the interfacial fracture toughness quantification in carbon nanotube/polymer derived ceramics nanocomposite. The aligned carbon nanotube carpets have a highly anisotropic friction behavior, which means the friction force are lower for transversely aligned CNTs side than for vertically aligned CNTs surface. We can also tune the friction properties of graphene ribbons by grafting different functional groups. In addition, two narrow angular regions with high friction, separated by a wide angular interval with low friction, were identified between graphene and highly oriented pyrolytic graphite. The distance between the two friction peaks is 61◦, which corresponds well with the 60◦ symmetry of individual atomic layers in the graphite lattice. The technique that involves the usage of mcirodevices and nanoidenter was used to conduct tensile tests on pristine, fluorinated and amino-functionalized carbon nanofibers, which were found to exhibit varied load-bearing abilities and unique fracture modes. The technique was also used to perform single fiber pullout experiments to study carbon nanotube/polymer derived ceramic interface.

The application of membranes in liquid and gas separation is attractive because of their energy efficiency. Synthesis of membranes with well-defined nanostructure is necessary to achieve highly permeability and selectivity for separation processes. Recently, carbon nanomaterials such as graphene oxide nanoplatelets (GONPs) and carbon nanodots (CNDs) have emerged as an interesting class of nanomaterials due to their unique properties and tailorable functionalities. Incorporation of these nanomaterials in the membranes has been shown to improve membrane selectivity, mechanical robustness, and chemical stability. This dissertation elaborates on developing CNDs or GONPs embedded thin film composite (TFC) membranes using layer-by-layer (LbL) synthesis technique. Regarding the water desalination applications, GONPs were used to enhance the TFC membranes’ selectivity, chlorine resistant properties, and surface hydrophilicity. Incorporation of GONPs in the polyamide layer via LbL method resulted in an increase of surface hydrophilicity and salt rejection properties. Upon exposure to chlorine, GONPs embedded membranes retained salt rejection performance better than the pristine membranes (without GONPs). The LbL assembly was used to synthesize CNDs based TFC membranes for organic solvent nanofiltration (OSN) applications. Using the LbL framework, amineunctionalized CNDs were covalently crosslinked with trimesoyl chloride monomer to obtain nanoscale membranes. The synthesized membranes manifested high selectivity (up to 90%) when tested for dye molecules such as brilliant blue and disperse red in methanol. As the CNDs synthesized here are fluorescent under UV light, the resultant film is also fluorescent. This property can be harnessed for diagnostic purposes, such as tracking mechanical failure and fouling of the membranes. Based on the results, it can be concluded that the incorporation of carbon nanomaterials in the polymeric membranes has enhanced the hydrophilicity, mechanical stability, and chlorine resistant properties of the membranes. Overall, the LbL platform can be considered as a modular method in embedding nanoparticles in TFC membranes.

This dissertation summarises the study of different aspects of the aerosol-assisted chemical vapour deposition (AACVD) technique for the production of multi-wall carbon nanotubes (MWCNTs). Upscaling the synthesis while retaining the quality of MWCNTs has been a prime objective throughout the work. A key aspect of this work was the study of different growth parameters and their influence on the homogeneity of the products across the reactor. The effect of the precursor composition on the yield and quality of MWCNTs were also investigated. It was shown that the synthesis rate can be significantly (60 – 80 %) increased by tuning the composition of the precursor. Moreover, by optimising the synthesis recipe and using a larger reactor, the synthesis rate and efficiency of the precursor were increased fivefold (up to 14 g/hr) and twice (up to 88 %) respectively. Large area (up to 90 cm²), mm-thick carpets of MWCNTs which were both free-standing and on substrate were produced. The carpets could withstand normal handlings without tearing apart, making them suitable for macroscopic characterisations and applications. By in-situ qualitative and quantitative gas analysis of the atmosphere of the reactor, the thermocatalytic cracking behaviour of 25 precursors was investigated and a mechanism for successive formation of different hydrocarbon fragments inside the reactor was proposed. A number of dedicated gas analysis methods and apparatuses such as a probe for zone-by-zone gas analysis of reactor and a heated chamber for preparation of standard gas analysis samples were developed to explore some of the least investigated aspects of the thermocatalytic cracking of precursors. Mapping the reactor revealed that some single-wall and double-wall carbon nanotubes (SWCNTs and DWCNTs) were also produced near the exhaust of the reactor. The SWCNTs were partly covered by fullerene-like species and resembled different forms of carbon nanobuds. In addition, the effect of the electron beam on the interaction of the SWCNTs and the fullerene-like species was studied in situ using high-resolution transmission electron microscopy (HRTEM).

The successful utilization of carbon nanomaterials in future electron spin-based technologies is highly dependent upon the ability to control their assembly at the nanoscale to form tailored solid-state architectures. Spin active metallofullerenes (MFs), Sc@C₈₂ and La@C<sub>82,/sub>, can be self assembled in 3D fullerene crystals or inside a carbon nanotube to form peapod structures. Single walled carbon nanotubes (SWCNTs) are an architect material to potentially allow the formation of 1-D spin chains. SWCNTs should be optimised to allow formation of spin chains and free of magnetic catalyst and carbon impurities, which have previously limited investigations of SWCNT spin properties. To address this, SWCNTs produced by laser ablation with a non-magnetic PtRhRe catalyst were purified through a multiple step centrifugation process in order to remove amorphous carbon and catalyst impurities. Centrifugation of SWCNT solutions resulted in sedimentation of carbon nanotube bundles containing clusters of catalyst particles, while isolated nanotubes with reduced catalyst particle content remained in the supernatant. Electron paramagnetic resonance (EPR) signals were detected only for samples which contained catalyst particles, with the ultracentrifuged SWCNTs showing no EPR signal at X-band (9.4 GHz) and fields ≤0.4 T. Integration of MFs into future devices requires a clear understanding of the nature of the spin and spin-spin interactions. Evaluating the spin properties of MFs, in both 3D (crystals) and 1D (peapods), will identify the spin-spin interactions and the affect of the surrounding SWCNT. Diluting spin active Sc@C₈₂ and La@C₈₂ MFs in a diamagnetic C₆₀ matrix, between 0.4% and 100%, permitted the tuning of the mean fullerene separation and thus interfullerene spin interactions. In dilute concentrations of MFs the hyper ne structure was resolved in EPR and with increasing concentration exchange narrowing was observed as a single narrow EPR peak. Encapsulation of Sc@C₈₂ MFs, of varying dilutions, into purified SWCNTs allowed formation of highly ordered 1-D array of metallofullerenes. Changing the spin environment from 3D crystal to 1D peapod resulted in the loss of the observed hyperfine structure in EPR. A single narrow peak was observed for Sc@C₈₂:C₆₀ peapods, indicating significant affect of the surrounding SWCNT structure upon the spin interactions of 1D metallofullerenes. Peapods of Ce@C₈₂ showed a similar EPR signal, suggesting that the observed narrow peak arises from charge transfer between the MF cage and the surrounding SWCNT.

The development of enzymatic biosensors and enzymatic biofuel cells (EBFCs) has been a significant area of research for decades. Enzymatic catalysis can provide for specific, reliable sensing of target analytes as well as the continuous generation of power from physiologically present fuels. However, the broad implementation of enzyme-based devices is still limited by low operational/storage stabilities and insufficient power densities. Approaches to improving upon these limitations have focused on the optimization of enzyme activity and electron transfer kinetics at enzyme-functionalized electrodes. Currently, such optimization can be performed through enzyme structural engineering, improvement of enzyme immobilization methodologies, and fabrication of advantageous electrode materials to enhance retained enzyme activity density at the electrode surface and electron transfer rates between enzymes and an electrode. In this work, varying electrode materials were studied to produce an increased understanding on the impacts of material properties on resulting biochemical, and electrochemical performances upon enzyme immobilization and an additional method of electroactive enzyme-based optimization was developed through the use of polymer-based protein engineering (PBPE). First, graphene/single-wall carbon nanotube cogels were studied as supports for membrane- and mediator-free EBFCs. The high available specific surface area and porosity of these materials allowed the rechargeable generation of a power density within one order of magnitude of the highest performing glucose-based EBFCs to date. Second, two additional carbon nanomaterial-based electrode materials were fabricated and examined as EBFC electrodes. Graphene-coated single-wall carbon nanotube gels and gold nanoparticle/multi-wall carbon nanotube-coated polyacrylonitrile fiber paddles were utilized as electroactive enzyme supports. The performance comparison of these three materials provided an increased understanding of the impact of material properties such as pore size, specific surface area and material surface curvature on enzyme biochemical and electrochemical characteristics upon immobilization. Third, PBPE techniques were applied to develop enzyme-redox polymer conjugates as a new platform for enzymatic biosensor and EBFC optimization. Poly(N-(3-dimethyl(ferrocenyl) methylammonium bromide)propyl acrylamide) (pFcAc) was grown directly from the surface of glucose oxidase (GOX) through atom-transfer radical polymerization. Utilization of the synthesized GOX-pFcAc conjugates led to a 24-fold increase in current generation efficiency and a 4-fold increase in EBFC power density compared to native GOX. GOX-pFcAc conjugates were further examined as working catalysts in carbon paper-based enzymatic biosensors, which provided reliable and selective glucose sensitivities and allowed a systematic analysis of sources of instability in enzyme-polymer conjugate-based biosensors and EBFCs. The knowledge gained through these studies and the in-depth characterization of an additional layer of optimization capacity using PBPE could potentially enhance the progress of enzymatic biosensor and EBFC development.