Photophysical, electronic, and compositional properties of single-walled carbon nanotubes (SWCNTs) and bulk nanotube samples were investigated together with graphene oxide photoluminescence. First, we studied the effect of external electric fields on SWCNT photoluminescence. Fields of up to 10 7 V/m caused dramatic, reversible decreases in emission intensity. Quenching efficiency was proportional to the projection of the field on the SWCNT axis, and showed inverse correlation with optical band gap. The magnitude of the effect was experimentally related to exciton binding energy, as consistent with a proposed field-induced exciton dissociation model. Further, the electronic composition of various SWCNT samples was studied. A new method was developed to measure the fraction of semiconducting nanotubes in as- grown or processed samples. SWCNT number densities were compared in images from near-IR photoluminescence (semiconducting species) and AFM (all species) to compute the semiconducting fraction. The results provide important information about SWCNT sample compositions that can guide controlled growth methods and help calibrate bulk characterization techniques. The nature of absorption backgrounds in SWCNT samples was also studied. A number of extrinsic perturbations such as extensive ultrasonication, sidewall functionalization, amorphous carbon impurities, and SWCNT aggregation were applied and their background contributions quantified. Spectral congestion backgrounds from overlapping absorption bands were assessed with spectral modeling. Unlike semiconducting nanotubes, metallic SWCNTs gave broad intrinsic absorption backgrounds. The shape of the metallic background component and its absorptivity coefficient were determined. These results can be used to minimize and evaluate SWCNT absorption backgrounds. Length dependence of SWCNT optical properties was investigated. Samples were dispersed by ultrasonication or shear processing, and then length-fractionated by gel electrophoresis or controlled ultrasonication shortening. Fractions from both methods showed no significant absorbance variations with SWCNT length. The photoluminescence intensity increased linearly with length, and the relative quantum yield gradually increased, approaching a limiting value. Finally, a strong pH dependence of graphene oxide photoluminescence was observed. Sharp and structured excitation/emission features resembling the spectra of molecular fluorophores were obtained in basic conditions. Based on the observed pH-dependence and quantum calculations, these spectral features were assigned to quasi-molecular fluorophores formed by the electronic coupling of oxygen-containing addends with nearby graphene carbon atoms.

Single-walled carbon nanotubes (SWNTs) are one of the leading candidate materials to realize novel nanoscale photonic devices. In order to assess their performance characteristics as optoelectronic materials, it is crucial to examine their optical properties in highly non-equilibrium situations such as high magnetic fields, low temperatures, and under high photoexcitation. Therefore, we present our latest result on the magnetic susceptibility anisotropy of metallic carbon nanotubes due to the Aharonov-Bohm effect. Here, we performed magnetic linear dichroism on a metallic-enriched HiPco SWNT sample utilizing a 35 T Hybrid Magnet to measure absorption with light polarization both perpendicular and parallel to the magnetic field. By relating these values with the nematic order parameter for alignment, we found that the metallic carbon nanotubes do not follow a strict diameter dependence across the 7 chiralities present in our sample. In addition to the studying the absorption properties exhibited at high magnetic field, we performed temperature-dependent (300 K to 11 K) photoluminescence (PL) on HiPco SWNTs embedded in an ι -carrageenan matrix utilizing intense fs pulses from a wavelength-tunable optical parametric amplifier. We found that for each temperature the PL intensity saturates as a function of pump fluence and the saturation intensity increases from 300 K to a moderate temperature around 100-150 K. Within the framework of diffusion-limited exciton-exciton annihilation (EEA), we successfully estimated the density of 1D excitons in SWNTs as a function of temperature and chirality. These results coupled with our results of magnetic brightening, or an increase in PL intensity as a function of magnetic flux through each SWNT due to the Aharonov-Bohm effect, yield great promise that in the presence of a high magnetic field the density of excitons can be further increased.

<p>Single-walled carbon nanotubes (SWNT) are highly ordered filamentous nanocarbon structures. As their commercial and industrial use becomes more widespread, it is anticipated that SWNT will enter the environment through waste streams and product degradation. Because of their highly hydrophobic nature, SWNT aggregate and settle out of aqueous environments, especially in saline environments such as estuaries. Therefore, sediments are a likely environmental sink for SWNT once released. It is important to understand how these materials will impact benthic estuarine systems since they are the probable target area for SWNT exposure in addition to containing many lower trophic level organisms whose survvial and contaminant body burdens can have a large impact on the overall ecosystem. Disruptions in lower trophic level organism survival can have negative consequences for higher trophic levels, impacting the overall health of the ecosystem. It is also important to consider contaminant bioaccumulation, trophic transfer and biomagnification. If SWNT are taken up by benthic invertebrates, there is the possibility for trophic transfer, increasing the exposure of SWNT to higher trophic level organisms that otherwise would not have been exposed. If this type of transfer occurs in environmentally important species, the potential for human exposure may increase. My research aims to determine the magnitude of the toxicity and bioaccumulation of SWNT in benthic estuarine systems, as well as determine how they interact with other contaminants in the environment. This research will contribute to the knowledge base necessary for performing environmental risk assessments by providing information on the effects of SWNT to benthic estuarine systems. </p><p> Before investigating the environmental effects of SWNT, it is imperative that a measurement method is established to detect and quantify SWNT once they enter the environment. This research utilized pristine, semiconducting SWNT to develop extraction and measurement methods to detect and quantify these specific materials in environmental media using near infrared fluorescence (NIRF) spectroscopy. Semiconducting SWNT fluoresce in the near infrared (NIR) spectrum when excited with visible&ndashNIR light. This unique optical property can be used to selectively measure SWNT in complex media. </p><p> The fate, bioavailability, bioaccumulation and toxicity of SWNT have not been extensively studied to date. Pristine SWNT are highly hydrophobic and have been shown to strongly associate with natural particulate matter in aquatic environments. In light of this, I have focused my research to examine the influence of sediment and food exposure routes on bioavailability, bioaccumulation, and toxicity of structurally diverse SWNT in several ecologically-important marine invertebrate species. No significant mortality was observed in any organism at concentrations up to 1000 mg/kg. Evidence of biouptake after ingestion was observed for pristine semiconducting SWNT using NIRF spectroscopy and for oxidized <super>14</super>C&ndashSWNT using liquid scintillation counting. After a 24 hour depuration period, the pristine semiconducting SWNT were eliminated from organisms to below the method detection limit (5 &mug/mL), and the <super>14</super>C&ndashSWNT body burden was decreased by an order of magnitude to a bioaccumulation factor (BAF) of <0.01. Neither pristine SWNT nor oxidized <super>14</super>C&ndashSWNT caused environmentally relevant toxicity or bioaccumulation in benthic invertebrates. Overall, the SWNT were not bioavailable and appear to associate with the sediment.</p><p> In addition to investigating the toxicity and bioaccumulation of SWNT as an independent toxicant, it is important to consider how they will interact with other contaminants in the environment (i.e., increase or decrease toxicity and bioaccumulation of co&ndashcontaminants, alter the environmental transport of co&ndashcontaminants, induce degradation of co&ndashcontaminants, etc.). I wanted to investigate the effects of SWNT on a complex mixture of contaminants already present in a natural system. New Bedford Harbor (NBH) sediment, which is contaminated with polychlorinated biphenyls (PCBs), was amended with pristine SWNT to determine if the presence of SWNT would mitigate the toxicity and bioaccumulation of the PCBs in deposit-feeding invertebrates. A dilution series of the NBH sediment was created using uncontaminated Long Island Sound (LIS) sediment to test 25% NBH sediment, 50% NBH sediment, 75% NBH sediment, and 100% NBH sediment. The results of this work showed increased organism survival and decreased bioaccumulation of PCBs in treatments amended with SWNT, with the greatest reduction observed in the 25% NBH sediment treatment group amended with 10 mg SWNT/g dry sediment. Polyethylene (PE) passive samplers indicated a reduction of interstitial water (ITW) PCB concentration of greater than 90% in the 25% NBH sediment + 10 mg SWNT/g dry sediment amendment. The ITW concentration was reduced because PCBs were not desorbing from the SWNT. Lower bioavailability leads to reduced potential for toxic effects, supporting the observation of increased survival and decreased bioaccumulation. Once in the sediment, not only are SWNT not bioavailable, they act as a highly sorptive phase, such as black carbon (BC), into which hydrophobic organic contaminants (HOCs), such as PCBS and polycyclic aromatic hydrocarbons (PAHs), can partition, thereby reducing the toxicity and bioavailability of co-occurring HOCs.</p><p> To more fully understand the impact of SWNT in this environment, their biodegradability also needs to be investigated. Biodegradation of SWNT could lead to release and/or transformation of sorbed HOCs as well as a change in the inherent transport, toxicity, and bioaccumulation of SWNT in the estuarine environment. Because the persistence of SWNT will be a primary determinant of the fate of these materials in the environment, I conducted experiments to determine if the fungus <italic>Trametes versicolor</italic>, the natural bacterial communities present in NBH sediment, and municipal wastewater treatment plant sludge could degrade or mineralize oxidized <super>14</super>C&ndashSWNT. Over a six month time period, no significant degradation or mineralization was observed. In all treatments, approximately 99% of the 14C-SWNT remained associated with the solid phase, with only approximately 0.8% of added <super>14</super>C present as dissolved species and only 0.1% present as <super>14</super>CO₂. These small pools of non-SWNT <super>14</super>C were likely due to trace impurities, as no differences in production were observed between treatments and abiotic (killed) controls.</p> / Dissertation

The successful fabrication and characterization of two chemiresistive platforms for biomolecule detection was demonstrated by this work. The Si/Silica based single walled nanotube thin film (SWNTTF) platform was developed to understand the effect of device geometry on pH and M13 bacteriophage sensing capabilities as well as the underlying mechanisms governing SWNTTF chemiresistive biosensors. The dominant mechanism of sensing switched from direct chemical doping to electrostatic gating when the target analyte changed from H+/OH- ions in pH testing to whole viruses. The experimental limit of detection for M13 for this platform was 0.5pM and an increased sensitivity as well as variability was observed in devices with smaller channel widths. Preliminary device calibration was completed in order to correlate a resistance response to a bulk M13 concentration. The polyethylene terephthalate (PET) based SWNTTF platform was developed to demonstrate the commercial potential of SWNTTF chemiresistive biosensors by detecting relevant concentrations of brain natriuretic peptide (BNP) on economically viable substrates. The pH response of these chemiresistors confirmed that chemical doping was the cause for resistance change in the SWNTTFs. The preliminary results demonstrated successful BNP detection at 50pg/mL using both aptamers and antibodies as recognition elements. Using SWNTTFs as the transducing element of chemiresistors allowed for further understanding of electrical mechanisms of sensing as well as achieving sensitive, real-time and reproducible electrical virus and biomolecule detection. Although these platforms do not achieve ultrasensitive limits of detection, they demonstrate the commercial potential of platforms using SWNTTFs as the transducing element of electrical biomolecule sensors.

In order to find/design porous materials that could be used in practical applications involving adsorption, it is important to investigate the basic properties (i.e. isosteric heat, specific surface area, binding energy, pore size, pore volume, etc.) of each material. With this aim in mind we have looked at three different types of materials: single-walled carbon nanotubes (prepared by the HiPco and laser methods), single-walled nanohorns (dahlia-like and bud-like) and metal-organic frameworks (Cu-BTC and RPM-1). For these substrates we have measured volumetric adsorption isotherms using several gases such as neon, argon, tetrafluoromethane (CF4), xenon, and methane (not all gases for all substrates). Experimental adsorption isotherms were measured using methane, argon, xenon, and neon gases on unpurified single-walled carbon nanotubes prepared by the HiPco method. The main idea behind these experiments was to investigate, using different size gas molecules, the sites available for adsorption on this type of porous material. We found that surface area occupied by these adsorbates on the sample is the same, regardless of their size. This means that all the gases have access to the same group of adsorption sites. Since the biggest adsorbate in this experiment was Xe, and since it is unlikely that it could penetrate the interstitial channels in the nanotube bundles, we conclude that none of the gases, including the smallest one - Ne, are able to adsorb in the interstitial channels in bundles of single-walled carbon nanotubes. For the case of argon on laser produced single-walled carbon nanotubes we measured 21 adsorption isotherms using argon gas temperatures between 40 and 153 K that were used to determine the isosteric heat of adsorption for this system. Our experimental results were compared to the ones from computer simulations performed by J. K. Johnson (from the University of Pittsburgh) for the same gas on heterogeneous and homogenous bundles. It was observed that the isosteric heat data matches better with data computed for heterogeneous nanotube bundles. This indicates that at the lowest pressure and coverages argon might be adsorbing in the defect-induced interstitial channels. We studied Cu3(Benzene-1,3,5-tricarboxylate)2(H2O)3 (abbreviated as Cu-BTC) metal-organic framework with argon to determine the sites available for adsorption on this material. Volumetric adsorption isotherms were measured at temperatures between 66 and 143 K. We found two substeps in the isotherm data, indicating that there are two types of pores present in the material: tetrahedrally-shaped side pockets and the main channels. Our experimental results were compared with data from simulations conducted using the Grand Canonical Monte Carlo method. We determined that the theoretical results match reasonably well with ours if the coverage is scaled down by a factor of 1.6. We explored the potential of two different metal-organic framework materials (Cu-BTC and RPM-1) for gas separation application. We used argon and tetrafluoromethane (CF4) gases to check if this can be achieved through kinetic and steric mechanisms. We found that Cu-BTC has excellent potential in gas separation using a steric mechanism, since argon easily adsorbs into the small pores present in the sample, while CF4 is excluded from them. Adsorption properties of RPM-1 showed that it could be employed in gas separation using a kinetic mechanism - argon gas adsorbs and reaches equilibrium in the pores of the sample more than the order of magnitude faster than CF4. Closed-ended dahlia-like nanohorns were studied with neon and tetrafluoromethane gases. In the first layer of neon and tetrafluoromethane adsorbed on dahlia-like nanohorns we found two substeps. These results were compared with results of computer simulations performed by Prof. M. Calbi. We determined, after comparison with the simulation isotherms, that the lower pressure substeps correspond to adsorption of Ne and CF4 in the narrowest parts of interstitial channels of the aggregates. Surface area calculated from neon isotherms was found to be higher than the one obtained using CF4, meaning that the smaller Ne molecule has the access to the parts of the interstitial channels that are not accessible for the bigger CF4 molecule. Features that appeared in neon adsorption isotherms on bud-like nanohorn aggregates were quite different from the ones on dahlia-like aggregates. We measured neon adsorption isotherms on this type of sample at temperatures between 22 and 49 K. In the monolayer regime we observed one single substep whose origin we can not definitely identify, because the structure of the bud-like nanohorns is not well-known. The binding energy value that was calculated from the isotherm data was lower than the value for neon adsorbed in the grooves of nanotube bundles but higher than for neon on graphite.

Orientador: Oswaldo Luiz Alves / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-13T13:25:05Z (GMT). No. of bitstreams: 1 Otubo_Larissa_D.pdf: 20335674 bytes, checksum: e95a782705baee771821f94a195ba7d0 (MD5) Previous issue date: 2009 / Resumo: Neste trabalho foram feitas preparações de nanopartículas de ouro passivadas com diferentes moléculas orgânicas (4,4'-tiobisbenzenotiol, benzenotiol, aminotiofenol e tiocolesterol). Tais moléculas possuem cadeias aromáticas mono ou difuncionalizadas, tendo tióis e aminas como grupamentos terminais. Foram estudados parâmetros como tamanho, estabilidade frente à agregação e coalescência, formação de blocos de agregados de nanopartículas conectadas por moléculas bifuncionais, variações das absorções no UV-Vis frente à sua formação e agregação, mostrando a importância das moléculas passivadoras nas propriedades das nanopartículas. Foram estudados também os efeitos causados pelo tratamento hidrotérmico sobre os agregados de nanopartículas passivadas com mono e ditióis. Tal estudo reforçou a importância das moléculas passivadoras na estabilidade das nanopartículas, sendo que o ditiol utilizado foi capaz de impedir o crescimento e coalescência das nanopartículas. Na segunda parte desta Tese, foram feitas as purificação e modificação química de nanotubos de carbono de parede simples com grupamentos oxigenados, tióis e aminas, visando a sua interação com nanopartículas de ouro. Foram abordados dois métodos de interação dos nanotubos com as nanopartículas de ouro: o in situ e o ex situ. Tais métodos estão relacionados com a redução do ouro e formação das nanopartículas em presença ou não dos nanotubos modificados, respectivamente. Foi observado que o tipo de grupamento na superfície dos nanotubos e o método de interação influenciaram tanto na quantidade de nanopartículas aderidas aos nanotubos, dado as diferenças de afinidade, quanto na distribuição de tamanho / Abstract: In this Thesis, passivated gold nanoparticles were prepared with different types of organic molecules (4,4'-thiobisbenzenethiol, benzenethiol, aminethiophenol e thiocolesterol). These molecules have aromatic chains, mono or difunctionalized, with thiols and amines as terminal groups. Some aspects were studied: size, stability against aggregation and coalescence, formation of blocks of nanoparticles, connected through bifuntional molecules, variations of UV-Vis absorption during aggregation, wich showed the importance of the passivating molecules on the final properties of the nanoparticles. Hydrothermal treatments were also carried out on the nanoparticles aggregates.Such study reinforced the importance of the passivating molecules on the nanoparticles' stabilization, once the dithiol showed to be capable of preventing the growing and coalescence of the nanoparticles. In the second part of this work, single-walled carbon nanotubes were purified and chemically modified. The chemical modification on the surface of the carbon nanotubes were done resulting in oxygenated, thiol and amine groups, aiming their interaction with gold nanoparticles. Two methods of interaction of the carbon nanotubes with gold nanoparticles were used: in situ and ex situ. Such methods are related with the reduction of gold and formation of the nanoparticles in presence or not of the modified nanotubes, respectively. It was observed that the type of surface modification of the nanotubes and the method of interaction influenced not only in the amount of nanoparticles on the surface of the nanotubes, due to different affinity, but also the size distribution / Doutorado / Quimica Inorganica / Doutor em Ciências

Carbon nanotubes are appealing materials for nanofabrication due to their unique properties and structures. However, for carbon nanotubes to be used in mass-fabricated devices, precise control of nanotube orientation and location on surfaces is critical. I have developed a technique to align single-walled carbon nanotubes (SWNTs) on surfaces from a droplet of nanotube suspension under gas flow. Fluid motion studies indicate that alignment is likely due to circulation of SWNTs in the droplet. My work provides a facile method for generating oriented nanotubes for nanodevice applications. I have also devised an approach for localizing SWNTs onto 1-pyrenemethylamine-decorated DNA on surfaces. I found that 63% of SWNTs on surfaces were anchored along DNA, and these nanotubes covered ~5% of the total DNA length. This technique was an initial demonstration of DNA-templated SWNT localization. In an improved method to localize SWNTs on DNA templates, dodecyltrimethylammonium bromide was utilized to suspend SWNTs in aqueous media and localize them on DNA electrostatically. SWNT positioning was controlled by the surface DNA arrangement, and the extent of deposition was influenced by the SWNT concentration and number of treatments. Under optimized conditions, 83% of the length of surface DNAs was covered with SWNTs, and 76% of the deposited SWNTs were on DNA. In some regions, nearly continuous SWNT assemblies were formed. This approach should be useful for the fabrication of nanotube nanowires in nanoelectronic circuits. Using my improved procedures, I have localized SWNTs on DNA templates across electrodes and measured the electrical properties of DNA-templated SWNT assemblies. When a DNA-templated SWNT was deposited on top of and bridging electrodes, the measured conductance was comparable to literature values. In contrast, SWNTs with end-on contacts to the sides of electrodes had conductances hundreds of times lower than literature values, probably due to gaps between the SWNT ends and the electrodes. This work provides a novel approach for localizing SWNTs across contacts in a controlled manner. These results may be useful in the fabrication of nanoelectronic devices such as transistors with SWNTs as active components. Moreover, this approach could be valuable in arranging SWNTs as electrical interconnects for nanoelectronics applications.

No description available.

Since their discovery over two decades ago, single-walled carbon nanotubes (SWNTs) have become one of the most investigated nanomaterials in materials science. Their exotic optical, electrical, thermal and mechanical properties afford them amazing potential in a variety of different fields. Current SWNT synthetic processes produce heterogeneous mixtures of both semiconducting and metallic SWNTs. The mixed electronic nature of these materials, combined with their limited solubility, has significantly hampered the realization of many applications and necessitates the development of post-synthetic purification techniques. Conjugated polymers offer a significant advantage over other proposed strategies in that not only do they provide a cheaper and scalable route towards the isolation of SWNTs, but they also allow for the preparation of materials with novel properties. Polyfluorenes have been extensively investigated in the literature due to their preference towards dispersing semiconducting SWNTs; however, these dispersions are often quite dilute, and the polyfluorene structure is incompatible with certain device applications for SWNTs. Poly(2,7-carbazole)s offer a viable alternative to polyfluorenes for the purification of bulk SWNT material. At the time of this thesis, there have been relatively few reports investigating the interactions of poly(2,7-carbazole)s with SWNTs, and the majority of examples in the literature have suffered from poor stability and complex dispersal procedures due to the inherent insolubility of the 2,7-carbazole structure. The work presented in this thesis involved the preparation and characterization of a novel poly(2,7-carbazole) structure that displayed excellent solubility in a variety of organic solvents, allowing for the preparation of extremely stable and relatively concentrated dispersions of SWNTs. Thorough characterization of the supramolecular complexes through absorbance, photoluminescence and Raman spectroscopies determined that this polymer preferentially disperses semiconducting SWNTs. A second objective of this work was to investigate how modification of various parameters (including polymer structure, molecular weight and the type of SWNTs) can influence the quality of the resultant composite dispersions. One important study performed was to investigate how the electronic nature of the polymer backbone can affect the separation of SWNTs by electronic type. We demonstrate for the first time that by incorporating an electron-poor functionality into a polyfluorene it is possible to change from dispersing only semiconducting SWNTs to solubilizing both electronic types. This investigation highlights the potential importance of incorporating electron-poor functionalities in the development of polymeric systems that can selectively discriminate metallic SWNTs, which remains a challenging endeavor at the time of this thesis publication. / Thesis / Doctor of Philosophy (PhD)

No description available.