Tratamiento de nanotubos de carbono y hollín grafítico con vapor de agua: Análisis comparativo por espectroscopía óptica y tamaño de partícula

Los nanotubos de carbono constan de uno o varios cilindros de carbono con semiestructuras de fullerenos en sus extremos. Así, se clasifican en nanotubos de una sola pared (SWCNTs – Single-Walled Carbon Nanotubes) y de pared múltiple (MWCNTs – Multi-Walled Carbon NanoTubes). La purificación trata de eliminar las impurezas producidas durante la síntesis, tales como carbono amorfo, fullerenos, partículas grafíticas y partículas metálicas. En este contexto, el objetivo de este trabajo es el estudio experimental del tratamiento de SWCNTs y hollín grafítico con vapor de agua en un reactor tubular de cuarzo a presión atmosférica en un intervalo de temperaturas de 560 a 760°C. Este método de purificación se basa en la hipótesis de que los nanotubos de carbono tienen menor reactividad que las impurezas de carbono frente al vapor de agua a alta temperatura. Se lleva a cabo un análisis de termogravimetría (TGA) para conocer el comportamiento de las muestras en atmosfera inerte. Además, se pone en marcha la instalación experimental para alcanzar las condiciones de trabajo ideales mostradas en el TGA. Los principales productos de gasificación se estudian mediante espectroscopía UV-VIS y NIR, y tamaño de partícula, siendo dispersados con anterioridad en una disolución acuosa de un tensoactivo. Mediante estos estudios se evalúa la influencia de la temperatura como variable de operación. Además, se realiza un análisis comparativo con otras muestras comerciales y modificadas de SWCNTs y MWCNTs con la intención de obtener una visión más general. Se detecta que en las muestras de SWCNTs tratadas no existe una oxidación preferencial de las impurezas con respecto a los nanotubos de carbono. Además, a partir de una temperatura aproximada de 622°C, la compactación de las partículas predomina por encima de la rotura de los enlaces haciendo que el tamaño de partícula aumente en vez de disminuir. En la comparación con las muestras comerciales y modificadas se observa que la pureza de partida de la muestra SWCNT es más baja y no mejora con el tratamiento. Este hecho podría estar provocado precisamente por un contenido de nanotubos inicial bajo. La obtención de mayores o menores tamaños de partícula no guarda una relación clara con los distintos métodos de síntesis y tratamientos de las muestras

Preparación y caracterización de tintas conductoras y electrodos para la producción de hidrógeno con nanotubos de carbono

El método más utilizado para dispersar nanotubos de carbono en medios acuosos es a través de la aplicación de ultrasonidos. Sin embargo, existen estudios que indican que este método presenta ciertos inconvenientes como el acortamiento de los nanotubos, así como daño estructural. Resulta posible dispersar nanotubos de carbono en medios acuosos mediante agitación durante un tiempo prolongado (Lukasczuk et al, 2010).En este trabajo se ha realizado un estudio en el que se han caracterizado y comparado dispersiones de nanotubos de carbono del tipo SWCNT (Single-Walled Carbon Nanotubes) y del tipo MWCNT (Multi-Walled Carbon Nanotubes) realizadas mediante el método de ultrasonidos y el método agitación. Se ha demostrado que el método de preparación de dispersiones de nanotubos de carbono en un medio acuoso mediante agitación resulta satisfactorio para obtener dispersiones estables con un alto grado de nanotubos en dispersión.En la comparativa entre ambos métodos, se observó que los SWCNT mostraron valores similares de dispersabilidad, mientras que los MWCNT preparados por agitación mostraron una dispersabilidad algo peor en comparación con el método de ultrasonidos. No obstante, el estudio de viscosidad indicó que el método de agitación sería menos invasivo y permitiría obtener dispersiones con nanotubos con una mayor relación deaspecto (relación entre la longitud del nanotubo y el diámetro).Una vez estudiadas las dispersiones, fueron empleadas a modo de “tintas” para elaborar películas conductoras sobre vidrio, las cuales se usaron como soporte para la preparación de electrodos el óxido de titanio.Finalmente, con los electrodos de óxido de titanio que se prepararon se realizó un experimento fotoelectroquímico irradiando con un simulador solar de laboratorio. En este experimento se pudo comprobar que todos los electrodos preparados mostraron un cierto grado de fotoactividad.<br /

Procesado químico-físico de nanomateriales de carbono para la preparación de tintas y películas funcionales

Los nanotubos de carbono (CNT de las siglas en inglés carbon nanotubes) se están abriendo paso como componentes en aplicaciones electrónicas como sensores, pantallas táctiles o dispositivos de energía, convirtiéndose así en una realidad comercial. En este ámbito, los principales retos a los que se enfrentan los CNT son: conseguir niveles de dopado controlables, estables y prolongados en el tiempo; la pureza, la escalabilidad y el costo de la separación de CNT en metálicos y semiconductores; el procesado y el depósito controlado de CNT sobre sustratos flexibles. La presente Tesis Doctoral se centra en el uso de nanotubos de carbono de pared única (SWCNT de las siglas en inglés de single-walled carbon nanotubes) y de otros nanomateriales de carbono, en concreto nanohorns de carbono (CNH de las siglas en inglés de carbon nanohorns), en polvo para preparar tintas y con ellas fabricar películas con propiedades moduladas y controladas a través de tratamientos fisicoquímicos para su potencial aplicación en una de las áreas de mayor relevancia tecnológica: la optoelectrónica. En primer lugar, se presentan las modificaciones realizadas a los SWCNT y los CNH en polvo a través de estrategias de funcionalización química que resultan en un control preciso de las propiedades electrónicas. Posteriormente se dispersan en agua estos materiales de SWCNT en polvo para conseguir tintas estables purificadas por ultracentrifugación con control específico de las propiedades coloidales. Además, el método de separación por columna cromatográfica permite la obtención de tintas de SWCNT enriquecidas en SWCNT metálicos y semiconductores. Las tintas de SWCNT resultantes de estos procesos se emplean para preparar películas que posteriormente se someten a tratamientos electroquímicos y procesado por láser, obteniéndose destrucción selectiva de SWCNT y control de los niveles de dopado. Se ha estudiado además la realización de tratamientos químicos a películas de SWCNT en sustratos flexibles para mejorar la adhesión y conseguir películas robustas, conductoras, transparentes y flexibles. Se acompaña toda esta investigación de estudios completos de caracterización por medio de técnicas coloidales, eléctricas, espectroscópicas, electroquímicas y microscópicas. Toda la metodología experimental se ha planificado y llevado a cabo teniendo en mente que se buscan procesos que puedan ser aplicados a nivel industrial para futuras aplicaciones comerciales. Por tanto los resultados que se presentan combinan ciencia básica centrada en generar nuevo conocimiento, junto con interés aplicado de esta ciencia básica que podría servir para desarrollar aplicaciones electrónicas y mejorar el desarrollo de dispositivos electrónicos basados en el uso de SWCNT y CNH.<br /

Purification of surface-modified arc-discharge single-walled carbon nanotubes by centrifugation processes

Talk delivered at GDR-I GNT2013 conference, held at Guidel-Plages (France), from 8th-12th April 2013.Arc-discharge single-walled carbon nanotubes (SWCNTs) demonstrate well-defined spectroscopic responses and a high structural quality. In addition, the arc-discharge technique allows the synthesis of relatively large amounts of material, and the product is available at moderate prices. However, pristine arc-discharge SWCNTs contain large amounts of impurities, including catalyst metals, graphitic particles, and amorphous carbon. Well-purified commercial samples are expensive since current purification processes are time consuming and have low yields. Liquid media, which are necessary for the purification, change the physical aggregation of the SWCNTs or modify its chemical reactivity. Therefore, chemical studies on high-purity arc-discharge SWCNTs are limited. In this communication, we present our results on SWCNT purification by centrifugation or ultracentrifugation in aqueous media. More specifically, we study the influence of surface chemistry on the separation of arc-discharge SWCNTs from their impurities during the centrifugation. The results of processing chemically modified materials are analyzed in terms of graphitic and amorphous carbon impurities, residual metal content, and SWCNT spectral characteristics.Peer reviewe

Hydrothermal synthesis of 1D TiO2 nanostructures for dye sensitized solar cells

El pdf del artículo es la versión pre-print.Mono-dimensional titanium oxide nanostructures (multi-walled nanotubes and nanorods) were synthesized by the hydrothermal method and applied to the construction of dye sensitized solar cells (DSCs). First, nanotubes (TiNTs) and nanotubes loaded with titanium oxide nanoparticles (TiNT/NPs) were synthesized with specific surface areas of 253 m2/g and 304 m2/g, respectively. After that, thermal treatment of the nanotubes at 500 °C resulted in their transformation into the corresponding anatase nanorods (TiNT-Δ and TiNT/NPs-Δ samples). X-ray diffraction and Raman spectroscopy data indicated that titanium oxide in the pristine TiNT and TiNT/NP samples was converted into anatase phase TiO2 during the heating. Additionally, specific surface areas and water adsorption capacities decreased after the heat treatment due to the sample agglomeration and the collapse of the inner nanotube channels. DSCs were fabricated with the nanotube TiNT and TiNT/NP samples and with the anatase nanorod TiNT-Δ and TiNT/NPs-Δ samples as well. The highest power conversion efficiency of η = 3.12% was obtained for the TiNT sample, despite its lower specific surface compared with the corresponding nanoparticle-loaded sample (TiNT/NP). © 2011 Elsevier B.V. All rights reserved.This work was funded by the Government of Aragon and La Caixa (project ref. GA-LC-041/2008) and by the Spanish MICINN (projects ref. EUI2008-00152 and ENE2008-04373). We thank the Spanish National Research Council (CSIC) for the JAE-Doc contracts awarded to Y.Y. and A.A. To the Xarxa de Referència en Materials Avanc¸ ats per a l’Energia, XaRMAE (Reference Center for Advanced Materials for Energy) of the Catalonia Government.Peer Reviewe

Intrinsic and Selective Activity of Functionalized Carbon Nanotube/Nanocellulose Platforms Against Colon Cancer Cells

[Abstract] Given their large surface area and versatile chemical reactivity, single-walled carbon nanotubes (SWCNTs) are regarded as the basis of new pharmacological complexes. In this study, SWCNTs are chemically functionalized with fluorescein, folic acid, and capecitabine, a drug that is commonly used against colorectal cancer. These functionalized SWCNTs are dispersed in water by taking advantage of their synergistic interaction with type-II nanocrystalline cellulose (II-NCC), and the resulting colloidal system is tested in vitro on both normal (differentiated) and cancerous (proliferative) human colon cells (Caco-2). The functionalized SWCNT/II-NCC hybrids show a higher activity than the reference (capecitabine) against the Caco-2 cancer cell line. However, this effect appears to be intrinsically associated with the SWCNT/II-NCC complex, particularly boosted by fluorescein, as the presence of capecitabine is not required. In addition, confocal microscopy fluorescence imaging using cell cultures highlights the enormous potential of this nanohybrid platform for colon cancer theranostics.This research was funded by the regional government of Aragón, DGA (Grupos Reconocidos DGA-T03_17R, DGA-T03_20R and DGA-A20_20R), together with associated EU Regional Development Funds, and also the Spanish MINEICO through a “Juan de la Cierva Incorporación” contract, and their associated research funds (ref. IJCI-2016–27789). A.C. thanks the Xunta de Galicia for an “Atracción de Talento” research grant (no. ED431H 2020/17)Gobierno de Aragón; DGA-T03_17RGobierno de Aragón; DGA-T03_20RGobierno de Aragón; DGA-A20_20RXunta de Galicia; ED431H 2020/1

Epoxy composites with covalently anchored amino-functionalized SWNTs: Towards the tailoring of physical properties through targeted functionalization

First published on the web August 24th, 2011Functionalization of single-walled carbon nanotubes (SWNTs) with covalently grafted amine moieties provides reactive fillers with potential for covalent anchoring to an epoxy matrix. Manufacturing and characterization of a high performance epoxy system reinforced with as-grown and aminated SWNTs are presented through four different approaches. Epoxy composite materials incorporating SWNTs aminated through sidewall addition reactions present enhanced mechanical, thermal and electrical properties, beyond the effect of unfunctionalized SWNTs. The functionalization pathways studied here lead to a composite with specific improvements in some of the physical properties of the epoxy matrix, which enables the tailored design of the composite's properties through functionalization. The amination via diazonium reaction with 4-aminobenzylamine is especially effective in enhancing the tensile and impact properties of the epoxy composites (44% improvement in impact strength at 0.1 wt% loading) and leads to the highest increase in elastic modulus reported so far for the integration of aminated nanotubes into epoxy resin. Composites incorporating aminated SWNTs throughout the 1,3-dipolar cycloaddition reaction stand out for their thermo-oxidative stability and thermomechanical properties. The incorporation of as-produced arc-discharge SWNTs into the TGAP/DDS epoxy matrix leads to composite materials with the highest electrical conductivity among all the studied samples. This journal is © The Royal Society of Chemistry.The present work was carried out with financial support from the NRC-CSIC collaboration project and fellowships from MICINN Spanish Ministry (FPU grant) and CAI-DGA and Europa XXI programmes. J.M.G.D. would like to thank Dr Benoit Simard and Dr Yadienka Martinez of SIMS-NRC for their close collaboration. Special thanks go to Prof. Maurizio Prato for kindly allowing a short research stay in his group, and his entire team. Epoxy reagents were received as a gift from Huntsman, which is gratefully acknowledged.Peer Reviewe

In-vitro toxicity of carbon nanotube/polylysine colloids to colon cancer cells

Single-walled carbon nanotubes (SWCNTs) are thoroughly purified and dispersed in an aqueous solution of high molecular weight poly-L-lysine (pLlys). Human intestinal epithelial Caco-2/TC7 cells are incubated with the SWCNT dispersions in pLlys, and their effects on cell viability are studied by image flow cytometry. No significant changes are observed in the cell culture wells up to pLlys concentrations of 10 g mL-1. However, high mortality is detected at pLlys concentrations of 100 g mL-1. The presence of oxygen-free SWCNTs does not modify the effects of pLlys on cell cultures at any of the tested concentrations (£ 1 g mL-1). In addition, SWCNTs having an 8 wt.% of surface oxygen are tested with identical results. Thus, purified SWCNTs, even bearing oxygen functional groups, act as inert particles in the cell culture medium. This result supports the applicability of SWCNTs as carriers in pharmacological formulations against digestive tract diseases.This work was funded by the Spanish Ministry MINECO and the European Regional Development Fund under the projects PRI-PIBAR-2011-1 and ENE2013-48816-C5-5-R, and the Government of Aragon and the European Social Fund (DGA-ESF-T66 Grupo Consolidado and DGA-ESF-B61 Grupo Consolidado).Peer reviewe

Electrochemical behavior of hybrid carbon nanomaterials: the chemistry behind electrochemistry

The unzipping of temperature-induced multi-walled carbon nanotubes (MWCNTs) to yield graphene nanoribbons (GNRs) has been studied. These carbon nanomaterials consisting of MWCNTs and unzipped MWCNTs have been synthesized, thoroughly characterized, and subsequently evaluated for electrochemical sensing. Three temperatures (55, 65 and 75 ºC) yielding three carbon nanomaterial termed as GNR-55, GNR-65 and GNR-75, respectively, were carefully studied. Interestingly, GNR-65 became the most suitable material for the electrochemical sensing of a wide range of model analytes displaying the best electrochemical response with independence of the analysed molecule. This electrochemical behaviour seems to be associated to the progress of the unzipping reaction that influences the balance between the Csp2/Csp3 ratio, the graphitic fraction and the type of functional groups introduced. These results revealed the importance of the temperature in the synthesis process, for tailoring carbon nanomaterials which could be used in a particular molecular detection application opening new opportunities for electrochemical sensing applications.This work has been Financial supported by the Spanish Ministry of Science and Innovation (CTQ2011-28135), the NANOAVANSENS program from the Community of Madrid (S2013/MIT-3029), the Spanish MINECO (ENE2013-48816-C5-5-R), the Government Aragon (Project DGA_ESF-T66 CNN) and the European Social Fund (ESF). D. A. M. acknowledges the FPU fellowship from the Ministry of Education, Culture and Sports. D. M. M.-G. acknowledges the fellowship received from the NANOAVANSENS program.Peer reviewe

Epoxy composites with covalently anchored amino-functionalized SWNTs: Towards the tailoring of physical properties through targeted functionalization

Functionalization of single-walled carbon nanotubes (SWNTs) with covalently grafted amine moieties provides reactive fillers with potential for covalent anchoring to an epoxy matrix. Manufacturing and characterization of a high performance epoxy system reinforced with as-grown and aminated SWNTs are presented through four different approaches. Epoxy composite materials incorporating SWNTs aminated through sidewall addition reactions present enhanced mechanical, thermal and electrical properties, beyond the effect of unfunctionalized SWNTs. The functionalization pathways studied here lead to a composite with specific improvements in some of the physical properties of the epoxy matrix, which enables the tailored design of the composite's properties through functionalization. The amination via diazonium reaction with 4-aminobenzylamine is especially effective in enhancing the tensile and impact properties of the epoxy composites (44% improvement in impact strength at 0.1 wt% loading) and leads to the highest increase in elastic modulus reported so far for the integration of aminated nanotubes into epoxy resin. Composites incorporating aminated SWNTs throughout the 1,3-dipolar cycloaddition reaction stand out for their thermo-oxidative stability and thermomechanical properties. The incorporation of as-produced arc-discharge SWNTs into the TGAP/DDS epoxy matrix leads to composite materials with the highest electrical conductivity among all the studied samples. This journal is © The Royal Society of Chemistry.The present work was carried out with financial support from the NRC-CSIC collaboration project and fellowships from MICINN Spanish Ministry (FPU grant) and CAI-DGA and Europa XXI programmes. J.M.G.D. would like to thank Dr Benoit Simard and Dr Yadienka Martinez of SIMS-NRC for their close collaboration. Special thanks go to Prof. Maurizio Prato for kindly allowing a short research stay in his group, and his entire team. Epoxy reagents were received as a gift from Huntsman, which is gratefully acknowledged.Peer Reviewe