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.

Observation of magnetic edge state in graphene nanoribbons

"The electronic structure and spin magnetism for few-layer-graphene nanoribbons synthesized by chemical vapor deposition have been investigated using near-edge x-ray absorption fine structure (NEXAFS) and electron-spin resonance (ESR). For the pristine sample, a prepeak was observed below the pi* peak close to the Fermi level in NEXAFS, indicating the presence of additional electronic states close to the Fermi level. The intensity of this prepeak decreased with increasing annealing temperature and disappeared after annealing above 1500 degrees C. The ESR spectra, which proved the presence of localized spins, tracked the annealing-temperature-dependent behavior of the prepeak with fidelity. The NEXAFS and ESR results jointly confirm the existence of a magnetic edge state that originates from open nanographene edges. The disappearance of the edge state after annealing at higher temperatures is explained by the decrease in the population of open edges owing to loop formation of adjacent graphene edges.

Effect of graphene oxide on bacteria and peripheral blood mononuclear cells

"Background Driven by the potential biological applications of graphene, many groups have studied the response of cells exposed to graphene oxide (GO). In particular, investigations of bacteria indicate that there are 2 crucial parameters, which so far have only been investigated separately: GO size and exposure methodology. Our study took into account both parameters. We carefully characterized the samples to catalog sizes and structural properties, and tested different exposure methodologies: exposure in saline solution and in the presence of growth media. Furthermore, we performed experiments with peripheral blood mononuclear cells exposed to our GO materials. Methods Atomic force microscopy, scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy were used to characterize the morphology and composition of different samples of GO: GO-H2O, GO-PBS and GO-MG. Our samples had 2D sizes of ?100 nm (GO-H2O and GO-PBS) and >2 µm (GO-MG). We tested antibacterial activity and cytotoxicity toward peripheral blood mononuclear cells of 3 different GO samples. Results A size-dependent growth inhibition of Escherichia coli (DH5 ?) in suspension was found, which proved that this effect depends strongly on the protocol followed for exposure. Hemocompatibility was confirmed by exposing peripheral blood mononuclear cells to materials for 24 hours; viability and apoptosis tests were also carried out. Conclusions Our experiments provide vital information for future applications of GO in suspension. If its antibacterial properties are to be potentiated, care should be taken to select 2D sizes in the micrometer range, and exposure should not be carried out in the presence of grow media.

Synthesis and characterization of doped single-walled carbon nanotubes and graphitic nanoribbons.

Tesis (Doctorado en Nanociencias y Materiales)"Este trabajo concentra resultados experimentales de la síntesis de nanotubos de carbono de pared sencilla (SWNTs) y de nanolistones grafíticos, así como una extensiva caracterización de los mismos. El método de síntesis de SWNTs utilizado consiste en la deposición química de vapores (CVD) asistido por aerosol con catalizador flotante. Para el dopaje de SWNTs se eligieron compuestos precursores que contienen al elemento dopante y se agregaron en diferentes concentraciones a soluciones de ferroceno (Fe(C5H5)2) y etanol (C2H6O). Los precursores con los que se trabajó son: tiofeno (C4H4S), trifenilfosfina ((C6H5)3P), bencilamina (C7H7NH2), pirazina (C4H4N2) y metoxitrimetilsilano (CH3OSi(CH3)3). Los nanotubos de pared sencilla y los co-productos obtenidos fueron estudiados por SEM, TEM, EELS, EDX y espectroscopia Raman. Nuestros experimentos con bajas concentraciones de tiofeno nos condujeron a la síntesis de nanolistones de carbono. Una completa caracterización mediante las técnicas SEM, TEM, EDX, XPS, XRD, TGA, y espectroscopia Raman se realizó para el material puro, es decir sin tratamientos posteriores a la síntesis.Se realizaron tratamientos térmicos en hornos de grafito hasta temperaturas de 2800 ºC. Los materiales tratados térmicamente fueron evaluados mediante SEM, TEM, XRD, TGA y espectroscopia Raman en bulto y a nivel individual. Se encontró que el material sufre un proceso de cristalización y, arriba de 1500 ºC, las orillas de las hojas grafíticas adyacentes encuentran una configuración más estable al formar uniones. También se realizaron experimentos de calentamiento de Joule (Joule heating), los resultados prueban que esta técnica permite formar tanto uniones como terminaciones armchair y zigzag dependiendo de las condiciones del experimento.""An aerosol-assisted chemical vapor deposition technique was used to produce doped SWNTs and graphitic nanoribbons. The doping elements were introduced to the system by means of precursor compounds, added to ferrocene (Fe(C5H5)2) – ethanol (C2H6O) solutions at different concentrations. Thiophene (C4H4S), triphenylphosphine ((C6H5)3P), benzylamine (C7H7NH2), pyrazine (C4H4N2) and methoxytrimethylsilane (CH3OSi(CH3)3) were the precursors used in this work. The materials thus produced were analyzed with SEM, TEM, EDX, EELS and Raman spectroscopy. Our experiments with low concentrations of thiophene triggered the synthesis of a new carbon nanostructure: graphitic nanoribbons. Such pristine nanoribbons have been carefully characterized by SEM, TEM, XRD, XPS, TGA, EDX and Raman spectroscopy. The nanoribbons were annealed up to 2800 ºC in graphitic furnaces. Characterization of the heat treated samples includes TEM and SEM observation, XRD, TGA and bulk and individual nanoribbon Raman spectroscopy. Our TEM observations revealed that under heat treatments a crystallization process occurs, and above 1500 ºC, the adjacent graphitic sheets find a more stable configuration by forming loops. Single, double and multiple loops are formed at different stages of the heat treatments. Joule heating experiments were also carried out. Our results show that an intense irradiaton of the electron beam, prior to the experiment, results in the formation of sharp zigzag and armchair edges; while the experiment of an as-produced nanoribbon results in multiple-loop formation due to the high temperatures that are achieved in the experiment.

Plasmonic Spherical Nanoparticles Coupled with Titania Nanotube Arrays Prepared by Anodization as Substrates for Surface-Enhanced Raman Spectroscopy Applications: A Review

As surface-enhanced Raman spectroscopy (SERS) continues developing to be a powerful analytical tool for several probes, four important aspects to make it more accessible have to be addressed: low-cost, reproducibility, high sensibility, and recyclability. Titanium dioxide nanotubes (TiO2 NTs) prepared by anodization have attracted interest in this field because they can be used as safe solid supports to deposit metal nanoparticles to build SERS substrate nanoplatforms that meet these four desired aspects. TiO2 NTs can be easily prepared and, by varying different synthesis parameters, their dimensions and specific features of their morphology can be tuned allowing them to support metal nanoparticles of different sizes that can achieve a regular dispersion on their surface promoting high enhancement factors (EF) and reproducibility. Besides, the TiO2 photocatalytic properties enable the substrate’s self-cleaning property for recyclability. In this review, we discuss the different methodological strategies that have been tested to achieve a high performance of the SERS substrates based on TiO2 NTs as solid support for the three main noble metal nanoparticles mainly studied for this purpose: Ag, Au, and Pt

Effect of Graphene Oxide on Bacteria and Peripheral Blood Mononuclear Cells

"Background Driven by the potential biological applications of graphene, many groups have studied the response of cells exposed to graphene oxide (GO). In particular, investigations of bacteria indicate that there are 2 crucial parameters, which so far have only been investigated separately: GO size and exposure methodology. Our study took into account both parameters. We carefully characterized the samples to catalog sizes and structural properties, and tested different exposure methodologies: exposure in saline solution and in the presence of growth media. Furthermore, we performed experiments with peripheral blood mononuclear cells exposed to our GO materials. Methods Atomic force microscopy, scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy were used to characterize the morphology and composition of different samples of GO: GO-H2O, GO-PBS and GO-MG. Our samples had 2D sizes of ?100 nm (GO-H2O and GO-PBS) and >2 µm (GO-MG). We tested antibacterial activity and cytotoxicity toward peripheral blood mononuclear cells of 3 different GO samples. Results A size-dependent growth inhibition of Escherichia coli (DH5 ?) in suspension was found, which proved that this effect depends strongly on the protocol followed for exposure. Hemocompatibility was confirmed by exposing peripheral blood mononuclear cells to materials for 24 hours; viability and apoptosis tests were also carried out. Conclusions Our experiments provide vital information for future applications of GO in suspension. If its antibacterial properties are to be potentiated, care should be taken to select 2D sizes in the micrometer range, and exposure should not be carried out in the presence of grow media.