Application of carbon nanotubes (CNTs) in various fields demands a thorough investigation of their stability under irradiation. Open structure, ability to reorganize and heal defects, and large surface-to-volume ratio of carbon nanotubes affect materials' radiation response so that it differs from their bulk counterparts. Despite the work conducted to this date, radiation damage and mechanisms governing the evolution of CNTs under irradiation are still deficient in fundamental understanding. This dissertation is aimed to comprehend and characterize radiation response and crystalline-to-amorphous transition in ion and electron irradiated carbon nanotubes using various techniques, including but not limited to, transmission electron microscopy (TEM) and Raman spectroscopy. It shows that ion irradiation can be used to engineer properties of nanotubes in a controllable manner and significantly improve thermal diffusivity and conductivity of the material. This work also establishes the role of nuclear and electronic stopping powers in thermal diffusivity enhancement: thermal properties of irradiated CNTs are governed by nuclear stopping power of bombarding species. The change of thermal properties with irradiation is driven by two competing mechanisms: inter-tube displacement-mediated phonon transport and defect-induced phonon scattering. In addition to experiments, molecular dynamic simulations are used to confirm validity of the obtained results. Radiation damage in CNTs at various temperatures as a function of ion energy, flux and fluence is examined. Mechanisms governing crystalline-to-amorphous transition under electron and ion irradiations are explored, applicability of previously suggested models discussed, and new models introduced. The results show enhanced defect annealing at elevated irradiation temperatures, which delays the formation of amorphous regions. Investigation of nanotube stability after various processing techniques and irradiation indicated that radiation response of CNTs in a composite is similar to that of individual nanotubes.

El progreso de la nanociencia y la nanotecnología está haciendo posible generar nuevos materiales basados en estructuras de carbono con propiedades únicas y con numerosas aplicaciones tecnológicas. Entre estas aplicaciones se encuentra la mejora de los biosensores, dispositivos capaces de realizar análisis químicos con gran rapidez.Las propiedades mecánicas y eléctricas extraordinarias de los nanotubos de carbono han estimulado extensamente su investigación a lo largo de todo el mundo desde su descubrimiento por Sumio Iijima en 1991. En esta tesis, el estudio del comportamiento electrocatalítico de nanotubos de carbono y al mismo tiempo el diseño de nuevos (bio)sensores electroquímicos han sido el principal objetivo, haciendo uso de diferentes alternativas de integración dentro de los sistemas de (bio)detección, basadas en modificaciones de las superficies del electrodo con nanotubos de carbono, o en el uso de nanotubos de carbono basados en (bio)compositos. / The extraordinary mechanical properties and unique electrical properties of carbon nanotubes (CNTs) have stimulated extensive research activities across the world since their discovery by Sumio Iijima in 1991. The range of applications for CNTs is indeed wide ranging from nanoelectronics, with quantum wire interconnects and field emission devices to composites, chemical sensors and biosensors. The application of CNTs to design novel and improved (bio)sensors is the principal objective of this thesis. Different alternatives for CNTs integration into (bio)sensing systems have been developed and the results obtained including some previous theoretical introduction, the state of the art in the field, conclusions and future prospects are presented through the 7 chapters of this PhD thesis.

With the rapid proliferation of carbon nanotube technologies and consumer products comes a need to research the toxicological and ecotoxicological effects of these materials. This research attempted to develop a baseline knowledge of the effects of bulk, unmodified multi-walled carbon nanotubes on commonly studied soil toxicology test organisms: earthworms, springtails, and agricultural plants. In order to minimize confounding factors in the study, a slurry composed of bulk multi-walled carbon nanotubes, silica sand, and water was used to amend test soil without the use of surfactants or functionalization. Analysis of data produced by these experiments showed no significant trends resulting from the exposure of the test organisms to artificial soil amended by the multi- walled carbon nanotube slurry. It was observed, however that carbon nanotubes accumulated in the gut of the earthworm Eisenia andrei and were expelled as castings in the test soil.

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Hoy en día, la necesidad de monitorizar y controlar el medio ambiente es a cada vezmás importante debido al creciente nivel de gases tóxicos que provienen de la expansiónde las actividades industriales, amenazando así el medio ambiente y la salud humana. Eldesarrollo de la nano-tecnología ha permitido fabricar sensores de gases portables,altamente sensibles, selectivos, de bajo coste y de bajo consumo de potencia.Los nanotubos de carbono (NTC) están ganando un interés a cada vez más considerablepor parte de la comunidad científica debido a su geometría y morfología únicas y susexcelentes propiedades electrónicas, mecánicas, térmicas i ópticas. Esto hace de ellosunos candidatos prometedores para un amplio rango de aplicaciones como por ejemplonuevos sensores de gases con propiedades mejoradas. En este contexto, mediante lapresente tesis, se ha realizado un profundo estudio para explorar las propiedades dediferentes sensores basados en nano-materiales híbridos constituidos por nanotubos decarbono junto a otros materiales con el fin de detectar gases tóxicos de manera eficiente.El trabajo realizado consistió en el diseño, la fabricación, la caracterización, y laoptimización de nanosensores híbridos.Esta tesis fue financiada en el marco del proyecto Europeo "Nano2hybrids", cuyoobjetivo era de diseñar la interfaz de las nano-partículas del metal con los nanotubos decarbono a través del control de los defectos estructurales y químicos producidos por ladescarga de un plasma de radiofrecuencia y aplicarlo a la detección de gases. Elbenceno fue elegido como gas principal, debido a sus graves efectos tóxicos a niveles depocas ppb y también debido a la no existencia en el mercado de un detector de bajocoste para benceno. De hecho, no hay en el estado de la técnica, un sensor de gas quepuede detectar de forma selectiva este gas a nivel operativo de ppb y trabajando atemperatura ambiente. Así, el reto de esta tesis era obtener un sensor altamente sensible,selectivo y estable, portátil y de bajo coste para la detección de benceno.En este sentido, se estudiaron exhaustivamente diferentes materiales basados ennanotubos de carbono funcionalizados, decorados con nanopartículas de metal o biendecorados o mezclados con óxidos metálicos, en términos de su adecuación para ladetección de gases (por ejemplo, sus sensibilidad, selectividad, estabilidad, y elmecanismo de detección, etc.). En particular se estudió la detección de diferentes gasescomo (benceno (C6H6 ), monóxido de carbono (CO), dióxido de nitrógeno (NO2), eletileno (C2H4), el sulfuro de hidrógeno (H2S), amoníaco (NH3) y agua (H2O)). Nuestrastareas consistieron en investigar experimentalmente y teóricamente el efecto de lascondiciones de preparación de los materiales (p.e. el tratamiento con plasma, lanaturaleza del precursor y tamaño de las nanoparticulas de metales), fabricación delsensor (p.e., técnica de deposición, el efecto del tipo de metal del los electrodos delsensor), y de las condiciones de caracterización del sensor (p.e., temperatura deoperación, flujo de gas,) sobre las propiedades sensoras de los mismos. Todo ello hapermitido adquirir conocimientos, explicar los mecanismos de funcionamiento en elsensado de gases de los diferentes materiales investigados y con ello desarrollar unsensor de gases adecuado para la detección de benceno.Hemos encontrado que los materiales híbridos que consisten en nanotubos tratados conplasma de oxígeno y decorados con diferentes nanopartículas de metal, muestran unamayor capacitad de detección a temperatura ambiente respecto a los nanotubos decarbono en bruto o los funcionalizados sólo con plasma. Las propiedades interfacialesde los materiales híbridos resultantes pueden ser adaptadas, lo que ofrece una enormeflexibilidad para el ajuste de sus propiedades sensoras. Cuando se combinaron en unamatriz de micro-sensores que opera a temperatura ambiente, nanotubos decorados condiferentes metales, de forma que unos resulten sensibles al benceno y otros insensibles,esto permitió por primera vez la realización de un prototipo de bajo coste capaz dedetectar selectivamente y a temperatura ambiente el benceno presente a nivel de trazas(por debajo de 50 ppbs) en una mezcla de gases. El prototipo realizado presenta unostiempos de respuesta y de recuperación de 60 s y 10 minutos respectivamente además deuna buena estabilidad y reproducibilidad. Este prototipo se encuentra protegido por unapatente que ha sido licenciada a una compañía que se encargará de la comercializaciónindustrial del producto.In the last few years, there has been a growing demand for monitoring the environment,especially with the increasing concern by the release of toxic gases emitted by manmadeactivities. The development of nanotechnology has created a huge potential for buildinghighly sensitive, selective, low cost, and portable gas sensors with low powerconsumption.Nowadays, carbon nanotubes are receiving an intense interest from the scientificcommunity, due to their unique geometry, morphology, electronic, mechanical, thermaland optical properties, which make them a promising candidate for many industrialapplications including new gas sensors for the detection of toxic species. In this context,in this thesis a deep study is devoted to explore the sensing properties of differenthybrid nanomaterials based on carbon nanotubes for an efficient detection of toxicgases. The design, fabrication, characterization, and optimization of gas sensors usinghybrid materials have been carried out.This thesis was financially supported by the European project "Nano2hybrids", whichexploits the interface design of metal nanocluster-carbon nanotube hybrids via controlof structural and chemical defects in a plasma discharge, for designing gas sensors withsuperior performance. Benzene was chosen as the principal target gas due to its serioustoxic effects at low ppb levels and the fact that there are no reliable, low cost andselective benzene detectors in the market. In fact, no gas sensor able to selectivelydetect this gas at ppb levels and operating at ambient temperature has been reported upto now in the literature. So, the challenge of the project was to fabricate sensitive,highly selective, stable, portable, and low cost benzene gas sensor employing hybridnanomaterials.Herein, functionalized MWCNTs, metal decorated MWCNTs, and metal oxidedecorated MWCNTs or metal oxide and MWCNT mixtures were deeply investigated interms of their gas sensing performances (e.g, sensitivity, selectivity, stability, detectionmechanism,. etc) towards the detection of different gases (benzene (C6H6), carbonmonoxide (CO), nitrogen dioxide (NO2), ethylene (C2H4), hydrogen sulfide (H2S),ammonia (NH3), and water (H2O)). Our tasks were to investigate experimentally andtheoretically the effects of material preparation conditions (e.g., plasma treatment,nanocluster precursor and size), sensor fabrication (e.g., deposition technique,electrodes sensor metal), and sensor characterization conditions (e.g., operatingtemperature, gas flow) on the gas sensing properties of our devices, and to acquireknowledge in order to develop a selective benzene detector. Based on experimental andtheoretical results, different mechanisms for the interaction between gases and thehybrid materials tested have been proposed.We found that hybrid materials consisting of oxygen plasma treated multiwalled carbonnanotubes decorated with different metal nanoparticles showed room temperaturesensing capability. Responsiveness to gases of these hybrid materials was higher thanthat of pristine or plasma functionalized carbon nanotubes. Metal decoated CNTs can betailored for the recognition of different gases and vapors with different reactivities,which offers enormous flexibility for tuning the interfacial properties of the resultinghybrid materials and thus, of their sensing properties. When combined in a microsensorarray operating at room temperature, the use of benzene-sensitive and benzeneinsensitivemetal-decorated multiwalled carbon nanotubes, allowed for the first time theimplementation of a low cost detector prototype, which can selectively detect benzenewhen present at trace levels (below 50 ppb) in a gas mixture. Sensors present responseand recovery times of 60 s and 10 min respectively, good stability and reproducibility.This type of sensors are protected by a patent, and licensed to a company for industrialcommercialization.

Composites are multiphasic materials with individual constituent parts that work cooperatively to produce some desired result. For the common case of structural composites, the use of nanoscale additives does not always yield a predictable outcome due to the complex interactions that occur in the interfacial region where a reinforcing filler meets the supporting matrix. It stands to reason, however, that the thoughtful and deliberate exploitation of unusual effects in this region could lead to the development of nanocomposite materials with extraordinary properties. In this thesis work, I will introduce two such responses in a compliant nanocomposite consisting of highly-aligned carbon nanotubes (CNTs) encased within a poly(dimethylsiloxane) (PDMS) matrix. It is first demonstrated that the material exhibits extremely anisotropic dynamic mechanical behavior. The composite will behave in a way that is evocative of the neat polymer when deformed orthogonal to the CNT alignment direction, yet will exhibit strain softening when cyclically compressed along their axis due to the collective buckling of the nanotube struts. Next, it is shown that this nanocomposite material has the ability to respond and adapt to applied loads. Independent, yet complimentary tests reveal that the structure of the polymer in the presence of nanoscale interstitials will evolve during dynamic stressing, an effect that was predicted nearly 50 years ago. With support from both recent and established literature, an updated mechanism is proposed. Collectively, these results provide insight into the complicated mechanics between polymer matrices and embedded nanoparticles, and assist in the design of advanced synthetic materials with unique physical properties.

Carbon allotropes have taken central stage of nanotechnology in the last two decades. Today, fullerenes, carbon nanotubes (CNTs), and graphene are essential building blocks for nanotechnology. Their superlative electrical, thermal and mechanical properties make them desirable for a number of technological applications ranging from lightweight strong materials to electrical wires and support for catalysts. However, transferring the exceptional single molecule properties into macroscopic objects has presented major challenges. This thesis demonstrates that carbon nanotubes and graphite dissolve in superacids and these solution can processed into macroscopic objects. Chapter 2 reviews neat CNT fiber literature. Specifically, the two main processing methods —solid– state and solution spinning — are discussed. CNT aspect ratio and fibers structure are identified as the main variables affecting fiber properties. Chapter 3 shows that graphite can be exfoliated into single-layer graphene by spontaneous dissolution in chlorosulfonic acid. The dissolution is general and can be applied to various forms of graphite, including graphene nanoribbons. Dilute solutions of graphene can be used to form transparent conductive films. At high concentration, graphene and graphene nanoribbons in chlorosulfonic acid forms a liquid crystal and can be spun directly into continuous fibers. Chapter 4 describes a solution–based method to form a thin CNT network. This network is an ideal specimen support for electron microscopy. Imaging nanoparticles with atomic resolution and sample preparation from reactive fluids demonstrate the unique feature of solution–based CNT support compared to state–of–the–art TEM supports . Chapter 5 describes CNT liquid crystalline phase. Specifically, CNT nematic droplets shape and merging dynamics are analyzed. Despite nanotube liquid crystals having been reported in various CNT systems, a number of anomalies such as low order parameter and spaghetti–like, nematic droplets are reported. However, CNTs in chlorosulfonic acid show elongated, bipolar droplets typical of other rod–like molecules. Moreover, their large aspect ratio allows capturing the transition from homogeneous to bipolar transition expected from scaling arguments.The equilibrium shape and merging dynamics demonstrate the liquid nature of CNT liquid crystals. Chapter 6 describes the CNT/chlorosulfonic acid fiber spinning. The influence of starting material, spinning dope concentration, spin draw ratio and coagulation on fiber properties is discussed. The linear scaling of fiber strength with CNT aspect ratio is demonstrated experimentally, once the best properties from different batches are compared. Moreover, Successful multi–hole spinning demonstrates the intrinsic scalability of wet spinning to meet the typical production output of industrial–scale spinning. Chapter 7 compares acid–spun CNT fibers to other CNTs fibers as well as existing engineered materials. Acid–spun CNT fibers combine the typical specific strength of high–strength carbon fibers to the thermal and electrical conductivity of metals. These properties are obtained because of a highly aligned, dense structure. The combined strength and electrical conductivity allow acid-spun fibers to be used as structural as well as conducting wire while the combined electrical and thermal properties allow for exceptional field emission properties. In conclusion, we demonstrate that multifunctional properties of carbon nanotubes that have fuelled much of the research in the past 20 years, can be attained on a macroscopic level via rational design of fluid–phase processing.

As pointed out more and more frequently in the literature, there is a pressing need for research into the health and environmental impact of nanoparticles. This work represents a joint effort between scientists in nanotechnology, chemistry and biology to answer this call and to investigate the environmental effects of carbon nantoubes (CNTs) from a brand new aspect. The results showed clearly the dose-dependent effects of single-walled carbon nanotubes (SWNTs) on the ingestion and digestion of bacteria by Tetrahymena thermophila, a ciliated protozoan, propagated to its prey bacteria, Escherichia coli. Investigated by confocal microscopy Tetrahymena were able to internalize large quantities of SWNTs and then excrete SWNTs and undigested bacteria in aggregates. Inhibition of ciliate bacterivory measured by Ciliate Bacterivory assay was evident at far below lethal concentrations. At high tube concentrations (above 6.8 μg∙ml-1), cell viability was affected. In addition, explored by fluorescence microscopy and scanning electron microscopy, SWNTs stimulated Tetrahymena to abnormally egest viable bacteria inside membrane protected structures, which enhanced bacterial survival during antimicrobial treatments, bacteriostatic or bacteriocidal. This phenomenon may have important implications to public health. In general, research on toxicity of nanoparticles is in a very early stage with most studies on direct fatality (kill or not to kill) of a single organism or certain type of cells. This work is believed to be among the first few investigating extrapolated effects. Hopefully, this wok will stimulate a line of research towards better understanding of the effects of nanomaterials on diverse organisms, and stimulate not only toxicology but also ecotoxicology studies.