Producción de nanoestructuras de carbono con morfología controlada y sus aplicaciones

Tesis (Doctorado en Nanociencias y Nanotecnología)"En este trabajo se reportan los resultados de la síntesis y caracterización de diferentes nanoestructuras de carbono con morfología controlada mediante la modificación de los parámetros involucrados en el método deposición química de vapor (CVD): la solución precursora, temperatura, flujo de gas, arreglo experimental y sustrato. En esta tesis se abarcan tres proyectos sobre nanoestructuras de carbono con morfología controlada sintetizadas por modificación en CVD. El primero consiste en la síntesis y caracterización de nanotubos de carbono multicapa dopados con nitrógeno (CNx) con múltiples defectos, realizando la modificación del líquido usado en el burbujeador de la zona de salida: se utilizaron soluciones acuosas de NaCl a diferentes concentraciones en peso en vez de acetona (generalmente utilizada en la configuración usada). La caracterización del material resultante reveló CNx altamente defectuosos, con modificaciones en la morfología del hueco, ramificaciones, aglomerados de nanopartículas en las paredes y estructuras puntiagudas. En el segundo proyecto también se sintetizaron CNx crecidos en sustrato de silicio, modificando la configuración de la zona de salida y se exploraron las dos caras del sustrato. El resultado de esta combinación en el estudio de los parámetros fue una morfología tipo pino en los CNxMWCNT, generada en una región confinada por la parte inferior del sustrato y el arco formado por el tubo de cuarzo en donde se colocaron los sustratos para recoger la muestra. Las estructuras tipo pino están formadas por nanotubos de carbono de diferentes longitudes formando un microarreglo colocado de forma aleatoria. Estas estructuras mostraron buenas propiedades de emisión de campo gracias a su microestructura jerárquica con forma cónica compuesta por CNxMWCNT. El tercer proyecto consistió en la síntesis de nanolistones de grafito dopados con nitrógeno NxGNR. En esta ocasión se modificó la solución precursora. Se adicionaron precursores de nitrógeno como pirazina a la solución usada para sintetizar nanolistones de grafito prístinos. La morfología de los nanolistones de grafito perdió un poco su estructura corrugada, usualmente observada en los GNR. En los nanolistones dopados se observó que en sus bordes, las capas grafíticas tienden a cerrarse adyacentemente, en multicapa o simplemente se curvan a mayores concentraciones de pirazina. El análisis mediante XPS revelo que el dopaje tuvo lugar en forma grafítica o sustitucional.""In this work we report the results of the synthesis and characterization of different carbon nanostructures with controlled morphology by modified chemical vapor deposition (CVD). The CVD modifiable parameters are: the precursor solution, temperature, gas flow, substrate and experimental setup. This thesis covers three projects on carbon nanostructures with controlled morphology synthesized by CVD modification. The first one involves the synthesis and characterization of nitrogen doped multi-walled carbon nanotubes (CNx) performing the modification of one of the components of the experimental arrangement in CVD, which is the exhaust zone. In the exhaust zone it is placed a container which is usually filled with acetone. In this experiment, water and aqueous solutions with different weight concentrations of NaCl were used instead acetone. The characterization of resulting material revealed highly defective CNx with morphology changes in the hollow core and presenting branches, agglomerates of nanoparticles on the walls and sharp structures. In the second project also synthesized CNx on silicon substrate; however the configuration of the exhaust zone was modified and explored both sides of the substrate. The result of this combination in the study was CNxMWCNT with pinelike morphology generated in a confined region bordered by the bottom of the substrate and the arc formed by the quartz tube, where the substrates were placed to collect the sample. It was observed that the distribution of pine-like structures depend strongly on the region confinement. Pine-like structures are formed by carbon nanotubes of varying lengths forming a microarray organized randomly. These structures exhibited good field emission properties due to its cone shaped hierarchical microstructure, composed by CNxMWCNT. The third project involved the synthesis of nitrogen doped graphite nanoribbons NxGNR. In this experiment, the precursor solution was modified. Nitrogen precursors such as pyrazine were added to the solution used to synthesize pristine graphite nanoribbons. At increasing the precursor, the morphology lost gradually its rippled structure, usually observed in GNR. Additionally, the edges formed loops, closed in different fashion: the graphitic layers tend to close adjacently, multilayered or just forming curled edges at higher pyrazine concentrations. The XPS analysis revealed that N-doping was possible substitutionally.

Low Dimensional Nanostructures: Measurement and Remediation Technologies Applied to Trace Heavy Metals in Water

A nanostructure is a system in which at least one external dimension is in the nanoscale, it means a length range smaller than 100 nm. Nanostructures can be natural or synthetic and determine the physicochemical properties of bulk materials. Due to their high surface area and surface reactivity, they can be an efficient alternative to remove contaminants from the environment, including heavy metals from water. Heavy metals like mercury (Hg), cadmium (Cd), arsenic (As), lead (Pb), and chromium (Cr) are highly poisonous and hazardous to human health due to their non-biodegradability and highly toxic properties, even at trace levels. Thus, efficient, low-cost, and environmentally friendly methodologies of removal are needed. These needs for removal require fast detection, quantification, and remediation to have heavy metal-free water. Nanostructures emerged as a powerful tool capable to detect, quantify, and remove these contaminants. This book chapter summarizes some examples of nanostructures that have been used on the detection, quantification, and remediation of heavy metals in water

Hojas de Warmi (no. 16)

Hojas de Warmi es una referencia ya indispensable en el haber historiográfico de los estudios de género y la investigación feminista, y significada en su proyección sobre América Latina. Publicación ciertamente única en el panorama académico español que es editada por el Seminario Interdisciplinar Mujeres y Sociedad, SIMS, de la L'Universitat de Barcelona y dirigida por su fundadora Lola G. Luna, profesora titular de Historia Contemporánea de América desde 1977 y emérita a partir de 2008 en la misma universidad

Heterogeneous contributions of change in population distribution of body mass index to change in obesity and underweight NCD Risk Factor Collaboration (NCD-RisC)

From 1985 to 2016, the prevalence of underweight decreased, and that of obesity and severe obesity increased, in most regions, with significant variation in the magnitude of these changes across regions. We investigated how much change in mean body mass index (BMI) explains changes in the prevalence of underweight, obesity, and severe obesity in different regions using data from 2896 population-based studies with 187 million participants. Changes in the prevalence of underweight and total obesity, and to a lesser extent severe obesity, are largely driven by shifts in the distribution of BMI, with smaller contributions from changes in the shape of the distribution. In East and Southeast Asia and sub-Saharan Africa, the underweight tail of the BMI distribution was left behind as the distribution shifted. There is a need for policies that address all forms of malnutrition by making healthy foods accessible and affordable, while restricting unhealthy foods through fiscal and regulatory restrictions

Retrospective evaluation of whole exome and genome mutation calls in 746 cancer samples

Funder: NCI U24CA211006Abstract: The Cancer Genome Atlas (TCGA) and International Cancer Genome Consortium (ICGC) curated consensus somatic mutation calls using whole exome sequencing (WES) and whole genome sequencing (WGS), respectively. Here, as part of the ICGC/TCGA Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium, which aggregated whole genome sequencing data from 2,658 cancers across 38 tumour types, we compare WES and WGS side-by-side from 746 TCGA samples, finding that ~80% of mutations overlap in covered exonic regions. We estimate that low variant allele fraction (VAF < 15%) and clonal heterogeneity contribute up to 68% of private WGS mutations and 71% of private WES mutations. We observe that ~30% of private WGS mutations trace to mutations identified by a single variant caller in WES consensus efforts. WGS captures both ~50% more variation in exonic regions and un-observed mutations in loci with variable GC-content. Together, our analysis highlights technological divergences between two reproducible somatic variant detection efforts

Magnetic and Electrical Properties of Nitrogen-Doped Multiwall Carbon Nanotubes Fabricated by a Modified Chemical Vapor Deposition Method

Chemical vapor deposition (CVD) is a preferential method to fabricate carbon nanotubes (CNTs). Several changes have been proposed to obtain improved CNTs. In this work we have fabricated nitrogen-doped multiwall carbon nanotubes (N-MWCNTs) by means of a CVD which has been slightly modified. Such modification consists in changing the content of the by-product trap. Instead of acetone, we have half-filled the trap with an aqueous solution of NaCl (0–26.82 wt.%). Scanning electron microscope (SEM) characterization showed morphological changes depending upon concentration of NaCl included in the trap. Using high resolution transmission electron microscopy several shape changes on the catalyst nanoparticles were also observed. According to Raman spectroscopy results N-MWCNTs fabricated using pure distillate water exhibit better crystallinity. Resistivity measurements performed on different samples by physical properties measurement Evercool system (PPMS) showed metallic to semiconducting temperature dependent transitions when high content of NaCl is used. Results of magnetic properties show a ferromagnetic response to static magnetic fields and the coercive fields were very similar for all the studied cases. However, saturation magnetization is decreased if aqueous solution of NaCl is used in the trap

Nanocelluloses as sustainable membrane materials for separation and filtration technologies: Principles, opportunities, and challenges

Membrane technology is of great interest in various environmental and industrial applications, where membranes are used to separate different mixtures of gas, solid-gas, liquid-gas, liquid-liquid, or liquid-solid. In this context, nanocellulose (NC) membranes can be produced with predefined properties for specific separation and filtration technologies. This review explains the use of nanocellulose membranes as a direct, effective, and sustainable way to solve environmental and industrial problems. The different types of nanocellulose (i.e., nanoparticles, nanocrystals, nanofibers) and their fabrication methods (i.e., mechanical, physical, chemical, mechanochemical, physicochemical, and biological) are discussed. In particular, the structural properties of nanocellulose membranes (i.e., mechanical strength, interactions with various fluids, biocompatibility, hydrophilicity, and biodegradability) are reviewed in relation to membrane performances. Advanced applications of nanocellulose membranes in reverse osmosis (RO), microfiltration (MF), nanofiltration (NF), and ultrafiltration (UF) are highlighted. The applications of nanocellulose membranes offer significant advantages as a key technology for air purification, gas separation, and water treatment, including suspended or soluble solids removal, desalination, or liquid removal using pervaporation membranes or electrically driven membranes. This review will cover the current state of research, future prospects, and challenges in commercializing nanocellulose membranes with respect to membrane applications

Mobility of Heavy Metals in Aquatic Environments Impacted by Ancient Mining-Waste

The mobility of heavy metals in aquatic environments, impacted by discharges from mining waste, is one of the major processes causing metal pollution mainly by arsenic (As), cadmium (Cd), lead (Pb), zinc (Zn) and iron (Fe), which could be risky for biota and human health. The heavy metals contained in mining waste constituted by large amounts of sulfides can reach the aquatic compartments by acid mine drainage and runoff and eventually become deposited in sediments and associated with colloidal material, being this one of the main reservoirs and ways of transport. However, the mobility of heavy metal is influenced by their specific chemical properties and undergo several physicochemical phenomena as sorption, oxidation–reduction, hydrolysis and this can be influenced by water flow, the size and composition of geological material. Hence, this work aims to review the processes and mechanism involved in the fate and transport of heavy metals from mining-waste to aquatic compartments and the methods used for identification of the specific chemical species associated with their mobility and ecological risk

Pine-tree-like morphologies of nitrogen-doped carbon nanotubes: Electron field emission enhancement

"Nitrogen-doped multiwalled carbon nanotube (CNT) bundles exhibiting pine-tree-like morphologies were synthesized on silicon-silicon oxide (Si/SiO2) substrates using a pressure-controlled chemical vapor deposition process. Electron field emission (FE) measurements showed a notable emission improvement at low turn-on voltages for the CNT pine-like morphologies (e.g., 0.59 V/-m) in comparison with standard aligned N-doped CNTs (>1.5 V/-m). We envisage that these pine-tree-like structures could be potentially useful in the fabrication of efficient FE and photonic devices.

Synthesis, characterization and magnetic properties of defective nitrogen-doped multiwall carbon nanotubes encapsulating ferromagnetic nanoparticles

"Nitrogen-doped multi-walled carbon nanotubes (CNxMWNTs) with multiple morphological defects were produced using a modified chemical vapor deposition (CVD) method. In a typical CNxMWNTs synthesis by CVD, an acetone trap is used to catch organic by-products from pyrolysis. In the present work, an aqueous solution of NaCl (26.82 wt%) was used in the trap, instead of acetone. Carbon nanotubes with sharp tips and lumps were found in the products. Scanning electron microscopy (SEM) and high resolution transmission electron microscopy showed the formation of nanoparticles of different shapes inside the nanotubes. The electronic and magnetic properties were studied using a physical properties measurement Evercool system (PPMS). With this simple change in the CVD-trap, it is possible to control the morphology of carbon nanotubes and metallic nanoparticles. Differences in gas flow are proposed as a possible mechanism to produce these changes in both nanoparticles and CNxMWNTs.