Anchorage of small cluster of manganese oxide, zinc oxide and silver on nitrogen doped and functionalized carbon nanotubes

Tesis (Maestría en Nanociencias y Nanotecnología)"Los nanotubos de carbono de pared múltiple (MWCNTs) exhiben excelentes propiedades mecánicas y electrónicas. Debido a su estructura y tamaño, los MWCNTs podrían ser utilizados como sustratos para la deposición de nanopartículas metálicas u óxidos metálicos que permitan el desarrollo de novedosos materiales compuestos. Estos materiales podrían ser utilizados como catalizadores, adsorbedores de gases, intercambiadores de iones, sensores químicos, bio-marcadores, etc. En este trabajo se presentan los resultados obtenidos al utilizar los MWCNTs como sustratos para el crecimiento de nanopartículas de óxido de zinc (ZnO), óxido de manganeso (III) (-Mn2O3) y plata (Ag). Nanopartículas de ZnO han sido eficiente y homogéneamente ancladas en dos tipos de nanotubos de carbono. Hemos utilizado como sustrato a nanotubos de carbono dopados con nitrógeno (CNx-MWNTs) y nanotubos de carbono funcionalizados con grupos carbonilo e hidroxilo (COx-MWNTs). El tamaño de partícula más pequeño fue obtenido utilizando los COx-MWNTs con un diámetro medio de partícula de 4.1 nm. Posteriormente, se desarrolló una novedosa metodología que nos permitió recubrir eficientemente a los MWCNTs con -Mn2O3 (tamaño de partícula desde 6 a 10 nm), sin emplear reactivos costosos y/o peligrosos. Finalmente, se diseñó un proceso sencillo para el anclaje de partículas de plata en diferentes tipos de nanotubos de carbono. Este método permite depositar nanopartículas de Ag (con un tamaño de partícula de 3 a 7 nm) sin el uso de agentes reductores externos, en este caso los MWCNTs podrían actuar como agentes reductores.""Multi-walled carbon nanotubes (MWCNTs) exhibit outstanding mechanical and electronic properties. Due to their structure, the MWCNTs could also play an important role as substrates for the deposition of metal and metal oxide nanoparticles that allow the development of novel composite materials. These materials could be used as catalysts, gas sensors, ion-exchange materials, gas adsorbers, biomarkers, drugs delivery systems, etc. The results obtained from the use of the MWCNTs as substrates for metal and metal oxide (e.g. ZnO, -Mn2O3 and Ag) nanoparticles are presented in this work. ZnO nanoparticles have been efficiently and homogeneously anchored on the surfaces of two types of carbon nanotubes. We use nitrogen-doped (CNx-MWNTs) and functionalized carbon nanotubes with oxygen groups (COx-MWNTs) as substrate. The smallest particles were deposited on the COx-MWNTs with a mean size of 4.1 nm. Furthermore, we developed a novel methodology that allows us to coat efficiently carbon nanotubes with -Mn2O3 nanoparticles (particle size from 6 to 10 nm) without employing expensive and hazardous chemicals. Finally, we developed a simple process able to anchor efficiently small Ag nanoparticles on different carbon nanotubes. This method is able to attach Ag particles (ranging from 3 to 7 nm in size) without any external reducing agent. In this case, the CNTs could act as reducing agents for the silver ions.

Loop formation in graphitic nanoribbon edges using furnace heating or Joule heating

"Here the authors report the use of either furnace heating or Joule heating to pacify the exposed graphene edges by loop formation in a novel graphitic nanoribbon material, grown by chemical vapor deposition. The edge energy minimization process involves the formation of loops between adjacent graphene layers within the nanoribbons. A comparison is made of the similarities and differences between the loop structures formed using these two methods. An estimation of the temperature of these graphitic nanoribbons during Joule heating is also reported based on the melting and evaporation of Pt nanoparticles.

Effects of functionalization and doping in carbon nanotubes for fabricating field effect transistors and cluster-nanotube systems: theory and experiment

Tesis (Doctorado en Nanociencias y Materiales)"Este trabajo concentra resultados teóricos y experimentales sobre nanotubos de carbono modificados con diferentes grupos funcionales, dopados o decorados con distintas nanopartículas, lo cual modifica sus propiedades y su interacción con el medio circundante. Iniciamos, estudiamos el transporte electrónico y las propiedades de efecto de campo de redes aleatorias formadas por nanotubes de carbono de pared sencilla con diferentes grupos funcionales. Hemos confirmado la importancia de la funcionalización química en las propiedades eléctricas de redes de nanotubes de carbono. Además, se demostró la construcción y el buen funcionamiento de un transistor de efecto de campo fabricado con los nanotubos estudiados. Los materiales compuestos como los nanotubos decorados con nanopartículas metálicas pueden mostrar propiedades mejoradas o únicas para su uso en sensores de gases. Por esta razón, hemos propuesto el uso de nanotubos de pared múltiple dopados con nitrógeno y decorados con nanopartículas de plata como sensores para disulfuro de carbono. Los resultados muestran que al modificar la temperatura de operación es posible incrementar la sensibilidad y la selectividad sobre moléculas especificas. Este trabajo, también se enfocó a estudiar las propiedades electrónicas y estructurales de nanotubos de carbono de pared simple dopados con nitrógeno. Se realizaron cálculos basados en la teoría funcional de la densidad. Los resultados muestran que, los nanotubos pueden ser modificados de semiconductores a metálicos al variar la concentración y posición de los átomos de nitrógeno. Finalmente, materiales compuestos como los nanotubos de carbono decorados con nanopartículas metálicas o semiconductoras pueden ser utilizados en una gran cantidad de aplicaciones, sin embargo las interacciones entre las nanopartículas y los nanotubos no están completamente claras. Nosotros presentamos la síntesis de nanotubos de carbono a los cuales depositamos nanopartículas de óxido de zinc. Realizamos cálculos basados en la teoría funcional de la densidad para comprender el proceso de anclaje del óxido de zinc al nanotubo de carbono, además de estudiar el rol del azufre en la estabilización de las nanopartículas.""This Thesis work has the experimental and theoretical results on modified carbon nanotubes with different functional groups, doped or decorated with nanoparticles, which modify their properties and interaction with the surrounded environment. In chapter 2, we studied the electrical transport and field-effect properties of random networks made of single walled carbon nanotubes with different functional side groups. We confirmed the important role of chemical functionalization on the electrical properties of nanotube networks. In addition, we also have successfully demonstrated the construction of entirely functionalized carbon nanotube field-effect transistors. Hybrid materials, consisting of nanotubes decorated with nanoparticles shows unique or enhanced sensitivity toward gaseous species when compared to pure nanotubes gas sensors. For this reason, in chapter 3, we propose the use of nitrogen-doped multiwalled carbon nanotubes decorated with silver nanoparticles as carbon disulfide gas sensors. Our results demonstrate that the mechanism of gas detection can be tuned from physisorption, at room temperature, to chemisorption at higher temperature. We demonstrated that the used of nanotube decorated with silver nanoparticles can significantly improve the signal response when compared to those materials without nanoparticles. We also studied in chapter 4, the electronic and structural properties of nitrogendoped (10,0) single walled carbon nanotubes using first-principles density functional theory. Our results demonstrated that carbon nanotubes could be changed from semiconductor to metallic, when modifying the concentration and position of nitrogen atoms. Composite materials such as metal or metal oxide decorated carbon nanotubes could be used in many applications, but the understanding of the interactions between nanoparticles and the carbon nanotubes has not been fully addressed. Along these lines, in chapter 5, we use nitrogen doped multiwalled carbon nanotubes as an efficient substrate for the deposition of zinc oxide nanoparticles. We also performed first-principles density functional calculations to understand the anchorage process of the zinc oxide to the nitrogen-doped carbon nanotubes, and the role of sulfur in the stabilization of nanoparticles.

Electron transport study on functionalized armchair graphene nanoribbons: DFT calculations

"Quantum transport studies are performed on doped and functionalized 8- and 11-armchair graphene nanoribbons (aGNRs) by means of density functional theory. Substitutional doping is performed by introducing boron, nitrogen, oxygen, silicon, phosphorus, and sulfur atoms within the lattice of the aGNRs. Other functional groups such as borane, amine, hydroxyl, thiol, silane, silene, phosphine, and phosphorane groups are also introduced at the nanoribbon's edge. The dopant position and the nanoribbon's width strongly influence the current–voltage characteristics, and generally, the narrow 8-aGNRs and edge-doped 11-aGNRs show deteriorated transport properties, mainly due to the formation of irregular edges that create highly localized states disrupting several conducting bands. On the other hand, the inside-doped 11-aGNRs are barely affected, mainly because these systems preserve the edge's structure, thus edge conduction bands still contribute to the electron transport. Our results suggest that wider graphene nanoribbons could be functionalized at the inner sections without significantly compromising their transport characteristics while retaining the chemical reactivity that characterize doped nanocarbons. Such characteristics are highly desirable in fuel cells where doped graphene is used as a catalyst support or as a metal-free catalyst.

Nanoparticulate Double-Heterojunction Photocatalysts Comprising TiO2(Anatase)/WO3/TiO2(Rutile) with Enhanced Photocatalytic Activity toward the Degradation of Methyl Orange under Near-Ultraviolet and Visible Light

Nanoparticulate double-heterojunction photocatalysts comprising TiO2(Anatase)/WO3/TiO2(Rutile) were produced by a sol–gel method. The resulting photocatalysts exhibit clear synergistic effects when tested toward the degradation of methyl orange under both UV and visible light. Kinetic studies indicate that the degradation rate on the best double-heterojunction photocatalyst (10 wt % WO3-TiO2) depends mainly on the amount of dye concentration, contrary to pure oxides in which the degradation rate is limited by diffusion-controlled processes. The synergistic effects were confirmed through systematic and careful studies including holes and OH radical formation, X-ray diffraction, electron microscopy, elemental analysis, UV–vis diffuse reflectance spectroscopy, and surface area analysis. Our results indicate that the successful formation of a double heterojunction in the TiO2(Anatase)/WO3/TiO2(Rutile) system leads to enhanced photoactivity when compared to individual oxides and commercial TiO2 P25

Loop formation in graphitic nanoribbon edges using furnace heating or Joule heating

Here the authors report the use of either furnace heating or Joule heating to pacify the exposed graphene edges by loop formation in a novel graphitic nanoribbonmaterial, grown by chemical vapor deposition. The edge energy minimization process involves the formation of loops between adjacent graphene layers within the nanoribbons. A comparison is made of the similarities and differences between the loop structures formed using these two methods. An estimation of the temperature of these graphitic nanoribbons during Joule heating is also reported based on the melting and evaporation of Pt nanoparticles.National Science Foundation (U.S.) (Grant NIRT CTS-05-06830)National Science Foundation (U.S.) (Grant DMR 07-04197)MIT-CONACYT Collaboration Gran

Evaluation of a quality improvement intervention to reduce anastomotic leak following right colectomy (EAGLE): pragmatic, batched stepped-wedge, cluster-randomized trial in 64 countries

Background Anastomotic leak affects 8 per cent of patients after right colectomy with a 10-fold increased risk of postoperative death. The EAGLE study aimed to develop and test whether an international, standardized quality improvement intervention could reduce anastomotic leaks. Methods The internationally intended protocol, iteratively co-developed by a multistage Delphi process, comprised an online educational module introducing risk stratification, an intraoperative checklist, and harmonized surgical techniques. Clusters (hospital teams) were randomized to one of three arms with varied sequences of intervention/data collection by a derived stepped-wedge batch design (at least 18 hospital teams per batch). Patients were blinded to the study allocation. Low- and middle-income country enrolment was encouraged. The primary outcome (assessed by intention to treat) was anastomotic leak rate, and subgroup analyses by module completion (at least 80 per cent of surgeons, high engagement; less than 50 per cent, low engagement) were preplanned. Results A total 355 hospital teams registered, with 332 from 64 countries (39.2 per cent low and middle income) included in the final analysis. The online modules were completed by half of the surgeons (2143 of 4411). The primary analysis included 3039 of the 3268 patients recruited (206 patients had no anastomosis and 23 were lost to follow-up), with anastomotic leaks arising before and after the intervention in 10.1 and 9.6 per cent respectively (adjusted OR 0.87, 95 per cent c.i. 0.59 to 1.30; P = 0.498). The proportion of surgeons completing the educational modules was an influence: the leak rate decreased from 12.2 per cent (61 of 500) before intervention to 5.1 per cent (24 of 473) after intervention in high-engagement centres (adjusted OR 0.36, 0.20 to 0.64; P < 0.001), but this was not observed in low-engagement hospitals (8.3 per cent (59 of 714) and 13.8 per cent (61 of 443) respectively; adjusted OR 2.09, 1.31 to 3.31). Conclusion Completion of globally available digital training by engaged teams can alter anastomotic leak rates. Registration number: NCT04270721 (http://www.clinicaltrials.gov)