Doping & decoration of carbon based nanoparticles: applications in flame retardancy and catalysis

Mención Internacional en el título de doctorThe present work involves two main parts that will be explained after introduction. A brief introduction about history, properties, synthesis and characterization of carbon nanotubes, graphene and their nanocomposites and nanohybrides will be presented. The first part of the thesis is focused on the synthesis of different types of nanotubes: pristine carbon nanotubes (CNT), oxygen doped carbon nanotubes (COx), and nitrogen doped carbon nanotubes (CNx) by CVD method. The structure of the nanotubes were confirmed by XRD, XPS, SEM, TEM, TGA and Raman spectroscopy (Chapter 2). The most important difference between the synthesized nanotubes was their aspect ratio which is calculated from 1500-3000 for CNx to COx. Pristine CNT shows the aspect ratio about < 2000. Subsequently, the epoxy nanocomposites at 2 wt.% constant loading of carbon nanotubes (CNT, COx and CNx) and Diglycidyl ether bisphenol-A (DGEBA) as a good example of thermosetting polymer were have been prepared by three roll milling and cured by 4,4′- Diamio diphenyl sulfone (DDS) as a hardener. The thermal degradation of epoxy nanocomposites as well as glass transition temperatures and elastic moduli were measured by TGA, DSC and DMTA. The flammability of epoxy nanocomposites was studied by microscale combustion calorimetry (MCC) and limiting oxygen index (LOI) determination. Results showed that the fire retardant properties of nanocomposites improved significantly specially for COx, which presented a very high LOI (35%) and a homogeneous and uniform surface after burning. This effect was attributed to the very high aspect ratio of COx tubes. The results showed that introduction of the nanofillers at 2 wt.% loading caused the earlier initial decomposition of the nanocomposites, an increased char yield, and a reduction of the degradation rate of in comparison with pure epoxy. The influence of addition of nanofillers on the relaxational and mechanical behavior of nanocomposites was evaluated by DSC and DMTA. No significant variations in Tg, storage modulus or loss tangent width were detected, indicating that the addition of nanofillers does not negatively affect the relaxational and mechanical response of the nanocomposites (Chapter4). In the second part of our work, different copper nanocomponents were synthesized and decorated on graphene oxide by our microwave-assisted method. Copper hydroxyl nitrate double salt (DS) (Cu2(OH)3(NO3) and cuprous oxide (Cu2O) by changing the solvent in a very simple procedure were obtained from copper nitrate. Copper nitrate (CuO) and metallic copper can prepared from heating and reduction by ascorbic acid of DS, respectively. The four copper salts have been decorated on graphene oxide GO following the same microwave-assisted method. (Chapter 3) The performance of copper salts/GO nanohybrids as photocatalyst in degradation of one common dyes (Rhodamine B) has been studied. As we expected, incorporation of copper oxides (copper with different oxidation number) onto GO via our method resulted in enhancing the properties of initial metal oxides and it was comparable with the CuO and Cu2O/GO hybrids produced of conventional methods Photocatalytic activity of DS alone and decorated on GO has been reported for the first time in this work. In the last part of the thesis, we have checked the performance of decorated copper salts as catalyst in some common organic reactions like: C-C , C-N, and C-S coupling and oxidation of aldehyde (Chapter 6). The catalytic application of DS is introduced for the first time here. The results open up the possibility of a more thorough study of the catalytic performance of the supported copper double salt in other conditions which may be applied in the future for different catalytic and consecutive processes of organic synthesis.El presente trabajo incluye dos bloques principales que se explicarán después de la introducción. Empezaremos con una breve introducción sobre la historia, propiedades, síntesis y caracterización de los nanotubos de carbono, el grafeno y sus nanocompuestos y nanohíbridos. La primera parte de la tesis se centra en la síntesis de diferentes tipos de nanotubos: nanotubos de carbono prístinos (CNT), nanotubos de carbono dopados con oxígeno (COx) y nanotubos de carbono dopados con nitrógeno (CNx) por el método CVD. La estructura de los nanotubos se confirmó mediante espectroscopía XRD, XPS, SEM, TEM, TGA y Raman (Capítulo 2). La diferencia más importante entre los nanotubos sintetizados fue su relación de aspecto que se calcula de 1500-3000 para CNx y COx. Los CNT prístinos muestra una relación de aspecto de <2000. Posteriormente como un buen ejemplo de polímero termoestable se prepararon los nanocompuestos epoxídicos de diglicidil éter de bisfenol-A (DGEBA) a una carga constante del 2% en peso de nanotubos de carbono (CNT, COx y CNx). Se dispersaron por calandrado y se curaron con 4 , 4′- diamio difenil sulfona (DDS). Se midieron la degradación térmica de los nanocompuestos epoxi, las temperaturas de transición vítrea y los módulos elásticos mediante las técnicas de TGA, DSC y DMTA. La inflamabilidad de los nanocompuestos epoxi se estudió mediante calorimetría de combustión a micro escala (MCC) e índice limitante de oxígeno (LOI). Los resultados mostraron que las propiedades ignífugas de los nanocompuestos mejoraron significativamente especialmente para COx, que presentó una LOI muy alta (35%) y una superficie homogénea y uniforme después de la quema. Este efecto se atribuyó a la muy alta relación de aspecto de los tubos COx. Los resultados mostraron que la introducción de nanofillers a una carga del 2% en peso causó la descomposición inicial más temprana de los nanocompuestos, un mayor rendimiento de producción de ceniza y una reducción de la tasa de degradación en comparación con el epoxi puro. La influencia de la adición de nanofillers en las propiedades de relajación y mecánicas de los nanocompuestos fue evaluada por DSC y DMTA. No se detectaron variaciones significativas en la Tg, el módulo de almacenamiento o el ancho de la tangente de pérdida, lo que indica que la adición de nanofillers no afecta negativamente a la respuesta de relajación y mecánica de los nanocompuestos (Capítulo 4). En la segunda parte de nuestro trabajo, diferentes nanoderivados de cobre se sintetizaron y anclaron a óxido de grafeno mediante un método propio asistido por microondas. Mediante un procedimiento muy simple partiendo de nitrato de cobre y modificando el disolvente de reacción se obtuvieron preferentemente la sal doble de nitrato-hidróxido de cobre (DS) (Cu2(OH)3(NO3) ó el óxido cuproso (Cu2O). El nitrato de cobre (CuO) y el cobre metálico pueden prepararse a partir del calentamiento y la reducción por ácido ascórbico de DS, respectivamente. Las cuatro sales de cobre se han depositado sobre óxido de grafeno GO siguiendo el mismo método asistido por microondas. (Capítulo 3) Se ha testado el rendimiento de las sales de cobre / nanohíbridos GO como fotocatalizadores en la degradación de un colorante común (rodamina B). Como esperábamos, la incorporación de óxidos de cobre (cobre con diferente número de oxidación) en GO a través de nuestro método derivó en la mejora de las propiedades de los óxidos metálicos iniciales y fue comparable con los híbridos CuO y Cu2O / GO producidos por métodos convencionales. La actividad fotocatalítica de la DS sola y soportadas en GO ha sido obtenida por primera vez en este trabajo. En la última parte de la tesis, hemos comprobado la eficacia de las sales de cobre soportadas en GO como catalizadores de algunas reacciones orgánicas comunes : acoplamiento de C-C, C-N y C-S y oxidación del aldehído (Capítulo 6). La aplicación catalítica de DS se estudia en este trabajo por primera vez . Los resultados obtenidos abren la posibilidad a nuevos estudios, más exhaustivo, del rendimiento catalítico de la doble sal de cobre soportada en otras reacciones de química orgánica que pueden plantearse en el futuro.Programa de Doctorado en Ciencia e Ingeniería de Materiales por la Universidad Carlos III de MadridPresidente: Ester Vázquez Fernández-Pacheco.- Secretario: María Crespo Ribadeneyra.- Vocal: María González Gonzále

Photocatalytic Behavior of Supported Copper Double Salt: The Role of Graphene Oxide

The design of a photocatalyst that may work efficiently with sunlight is a fundamental concern to fight against environmental pollution and electrochemical hydrogen storage devices. In this work, it has been found that the green microwave-assisted decoration of graphene by copper double salt (DS) enhances visible sunlight photocatalysis efficiency. Nanohybrids of graphene oxide decorated with Cu(I) and Cu(II) oxides and copper hydroxy nitrate double salt were selected as photocatalysts for the degradation of rhodamine B in aqueous solution to study the effect of the graphene oxide support. The photodegradation process followed a pseudo–first-order kinetics for the bare catalysts, but the supported catalysts were best fitted to the Langmuir-Hinshelwood model. Supported systems were more efficient in terms of turnover and apparent rate constants. Diffuse reflectance spectroscopy with the use of Kubelka-Munk function allowed to measure bandgap energies. It was found that the absorption edge was reduced about 30% for the supported systems.The authors wish to thank Ministerio de Ciencia, Innovación y Universidades grant MAT2014-57557-R. Additionally, the authors would like to thank to Diogo Videira- Quintela for the invaluable help in the characterization of samples

A critical review of the current progress of plastic waste recycling technology in structural materials

One of the main environmentally threatening factors is plastic waste which generates in great quantity and causes severe damage to both inhabitants and the environment. Commonly, plastic waste generated on the land ends up in water bodies, resulting in detrimental solid impacts on the aquatics via poisoning and flooding the marine ecosystem. Exploring various approaches to convert plastic wastes into new products known as an efficient way to manage them and to enhance the sustainability of the environment, discussed in this article. Moreover, The limitation of the application of plastic waste for construction purposes is also considered. It is wind up that the usage of plastic waste for construction purposes will significantly rectify the sustainability of our environment and also be regarded as a trustworthy source of materials for applying in conventional materials such as concrete and asphalt

Effect of nitrogen and oxygen doped carbon nanotubes on flammability of epoxy nanocomposites

To overcome the flammability of epoxy resins, novel nitrogen (CNₓ) and oxygen (COₓ) doped CNT were synthesized via CVD method and epoxy nanocomposites at 2 wt.%. constant loading were prepared by three roll milling and cured. The structures of the nanotubes were confirmed by XRD, XPS, SEM and Raman and it was found a very high aspect ratio especially for COₓ. Thermal degradation as well as glass transition temperatures and elastic moduli were measured by TGA, DSC and DMTA. The flammability of epoxy nanocomposites was studied by microscale combustion calorimetry (MCC) and limiting oxygen index (LOI) determination. Results showed that the fire retardant properties of nanocomposites improved significantly specially for COₓ, which presented a very high LOI (35%) and a homogeneous and uniform surface after burning. This effect was tentatively attributed to the very high aspect ratio of COₓ tubes.Authors wish to acknowledge financial support from Spanish Ministerio de Economía y Competitividad under grant MAT2014-57557-R. Authors also wish to thank Dr. Sofía M. Vega-Díaz for her invaluable help with XPS interpretatio