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The interaction between carbon nanotubes (CNTs) and biological molecules of diagnostic and therapeutic interest, as well as the internalization of the CNTs-biomolecules complexes in different types of cell, has been extensively studied due to the potential use of these nanocomplexes as multifunctional nanoplatforms in a great variety of biomedical applications. The effective use of these nanobiotechnologies requires broad multidisciplinary studies of biocompatibility, regarding, for example, the in vitro and in vivo nanotoxicological assays, the capacity to target specific cells and the evaluation of their biomedical potential. However, the first step to be reached is the careful obtainment of the nanoplatform and the understanding of the actual surface composition and structural integrity of the complex system. In this work, we show the detailed construction of a nanoplatform created by the noncovalent interaction between oxidized multi walled carbon nanotubes (MWCNTs) and a DNA aptamer targeting tumor cells. The excess free aptamer was removed by successive washes, revealing the actual surface of the nanocomplex. The MWCNT-aptamer interaction by π-stacking was evidenced and shown to contribute in obtaining a stable nanocomplex compatible with aqueous media having good cell viability. The nucleotide sequence of the aptamer remained intact after the functionalization, allowing its use in further studies of specificity and binding affinity and for the construction of functional nanoplatforms.

The functionalization of graphene oxide with organosilanes is an important strategy to yield graphene-silica composites as well as to create nanomaterials for use as reinforcement in polymer nanocomposites and corrosion-inhibiting coatings for metals, among other uses. However, depending on the reaction conditions used, the organosilanes tend to self-condense, encapsulating the graphene oxide in a silica-like layer which can impair its properties by hiding its real surface and two-dimensionality. In this paper we describe a facile route for the functionalization of commercial graphene oxide with (3-aminopropyl) triethoxysilane using low concentrations and mild reaction conditions, and yielding amine and silanol surface-modified graphene nanohybrids while preserving its two-dimensional characteristics. The material obtained was characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), potentiometric titration, thermogravimetric analysis and electronic microscopy, evidencing the covalent and superficial nature of the functionalization.

This work describes the production of carbon xerogel/TiO2 nanocomposites by sol-gel polymerization of resorcinol-formaldehyde in the presence of K2TiF6 inorganic titanium salt as TiO2 precursor. The effects of different starting C/Ti molar ratios in the morphology, surface property, and photocatalytic activity on the decomposition of acetaminophen (APP) were investigated. The materials were characterized by thermogravimetric analysis, Fourier transforms infrared spectroscopy, scanning and transmission electron microscopy, X-ray diffractometry, and textural properties. The composites presented heterogeneous structure, and presence of two phases for the introduction of TiO2. A region was formed by amorphous carbon and carbon spheres, where Ti is detected only immersed in the amorphous carbon particles, in the anatase phase. CXTi-4.5 (adopted nomenclature CXTi-n, where n is the number of mmol of titanium salt inserted) composite presented the highest efficiency in the removal of the APP in the aqueous medium, as well as acceptable reusability properties after the washing step.

The production and use of graphene-based nanomaterials is rapidly increasing. However, few data are available regarding the toxicity of these nanomaterials in aquatic organisms. In the present study, the toxicity of few-layer graphene (FLG) (obtained by chemical exfoliation) was evaluated in different tissues of the shrimp Litopenaeus vannamei following exposure to FLG through a diet for four weeks. Transmission electron microscopy and dynamic light scattering measurements showed a distribution of lateral sheet sizes between 100 and 2000 nm with the average length and width of 800 and 400 nm, respectively. Oxidative stress parameters were analyzed, indicating that FLG exposure led to an increase in the concentration of reactive oxygen species, modulated the activity of antioxidant enzymes such as glutamate cysteine ligase and glutathione-S-transferase, and reduced glutathione levels and total antioxidant capacity. However, the observed modulations were not sufficient to avoid lipid and DNA damage in both gill and hepatopancreas tissues. Furthermore, graphene exposure resulted in morphological changes in hepatopancreas tissues. These results demonstrate that exposure to FLG through the diet induces alterations in the redox state of cells, leading to a subsequent oxidative stress situation. It is therefore clear that nanomaterials presenting these physico-chemical characteristics may be harmful to aquatic biota.

Carbon nanomaterials (CNM), such as graphene oxide (GO), have been the focus of study in several areas of science mostly due to their physical-chemical properties. However, data concerning the potential toxic effects of these CNM in bivalves are still scarce. When present in the aquatic systems, the combination with other contaminants, as well as pH environmental variations, can influence the behavior of these nanomaterials and, consequently, their toxicity. Thus, the main goal of this study was to evaluate the effect of exposure of clam Ruditapes philippinarum to GO when acting alone and in the combination with copper (Cu), under two pH levels (control 7.8 and 7.3). A 28-day exposure was performed and metabolism and oxidative stress-related parameters were evaluated. The effects caused by GO and Cu exposures, either isolated or co-exposed, showed a direct and dependent relationship with the pH in which the organisms were exposed. In clams maintained at control pH (7.8), Cu and GO + Cu treatments showed lower lipid peroxidation (LPO) and lower electron transport system (ETS) activity, respectively. In clams maintained at low pH, glutathione-S-transferases (GSTs) activities were increased in Cu and Cu + GO treatments, whereas reduced glutathione (GSH) levels were increased in Cu treatment and ETS activity was higher in GO + Cu. Thus, it can be observed that clams responses to Cu and GO were strongly modulated by pH in terms of their defense system and energy production, although this does not result into higher LPO levels.

Xerogeis de carbono (CXs) sao materiais constituidos por uma estrutura tridimensional formada por esferas nanometricas interligadas e poros interconectados. Diversos trabalhos apresentam os CXs como suporte para utilizacao em catalise. A principal vantagem destes suportes e que suas propriedades fisicas e quimicas superficiais podem ser adaptadas as exigencias cataliticas. Neste trabalho, compositos CX/TiO2 foram sintetizados em etapa unica, por polimerizacao/condensacao sol-gel de solucao formaldeido e resorcinol, com simultânea adicao de nanoparticulas de TiO2 ou Ti(IV), seguido de secagem e tratamento termico. Os compositos foram caracterizados por analise termogravimetrica (TG), difratometria de raios X (DRX), microscopia eletronica de varredura (MEV), espectroscopia Raman e isotermas de adsorcao de nitrogenio (N2) com determinacao de area superficial (BET) e volume de poros (Vp). Os resultados mostraram a presenca de uma mistura das fases anatase e rutilo do TiO2 nos compostos obtidos. Atraves das imagens de MEV verificou-se grande homogeneidade na distribuicao das particulas de TiO2 no suporte de CX. As propriedades fotocataliticas dos compositos foram investigadas para fotodegradacao de azul de metileno (AM). A cinetica de degradacao de azul de metileno ajustou-se ao modelo de pseudo primeira ordem. Observou-se um efeito sinergico entre os solidos, com um aumento da atividade fotocatalitica nos compositos de CX/TiO2, em relacao ao TiO2. Palavras-chave: carbono xerogel, fotocatalise, oxido de titânio.

The influence of extensive purification on oxidized multiwalled carbon nanotube surface composition was studied through the characterization and differentiation of the actual surface submitted to three oxidation methods: microwave-assisted acid oxidation, hydrogen peroxide reflux, and Fenton reaction. The oxidized samples were purified by a multi-step procedure including the sequential use of basic reflux and dispersion in dimethylformamide (DMF). The results showed a significant increase in the amount of oxidation debris with hydrogen peroxide and Fenton reaction times longer than 8 h and strong surface characteristic modification. With regard to sample purification, basic reflux led to a reduction in oxygenated group concentration of only 10% in the samples treated by acid oxidation. On the other hand, the subsequent use of DMF led to a further decrease in concentration of 39%, proving to be a more efficient method for the removal of oxidation debris.

Graphene has been shown to induce toxicity in mammals and marine crustaceans; however, information regarding oxidative stress in fish is scarce. The aim of this study was to evaluate the mechanism of graphene toxicity in different tissues of Danio rerio, considering different parameters of stress. Animals were injected intraperitoneally (i.p.) with 10 μL of suspensions containing different graphene concentrations (5 and 50 mg/L); the gills, intestine, muscle and brain were analysed 48 h later. There was no significant difference in the expression of the gclc (glutamate cysteine ligase catalytic subunit) and nrf2 (nuclear factor (erythroid-derived 2)-like 2) genes after exposure. In contrast, glutamate cysteine ligase (GCL) and glutathione-S-transferase (GST) activities were modulated and the glutathione (GSH) concentration was reduced in different tissues and at different concentrations. Lipid damage was observed in the gills. Histological analyses were performed to observe if the exposure could induce pathological damage in these tissues. The results showed pathological effects in all tissues, excluding the intestine, after exposure to both concentrations. Overall, these results indicate that graphene induces different grades of toxicological effects that are dependent on the analysed organ, with distinct pathological effects on some and oxidative effects on others. However, the brain and gills seem to be the primary target organs for graphene toxicity.

Carbon nanotubes (CNT) are promising materials for biomedical applications, especially in the field of neuroscience; therefore, it is essential to evaluate the neurotoxicity of these nanomaterials. The present work assessed the effects of single-walled CNT functionalized with polyethylene glycol (SWCNT-PEG) on the consolidation and retrieval of contextual fear memory in rats and on oxidative stress parameters in the hippocampus. SWCNT-PEG were dispersed in water at concentrations of 0.5, 1.0, and 2.1 mg/mL and infused into the rat hippocampus. The infusion was completed immediately after training and 30 min before testing of a contextual fear conditioning task, resulting in exposure times of 24 h and 30 min, respectively. The results showed that a short exposure to SWCNT-PEG impaired fear memory retrieval and caused lipid peroxidation in the hippocampus. This response was transient and overcome by the mobilization of antioxidant defenses at 24 h. These effects occurred at low and intermediate but not high concentration of SWCNT-PEG, suggesting that the observed biological response may be related to the concentration-dependent increase in particle size in SWCNT-PEG dispersions.

Exposure to ionizing radiation has been found to induce changes in poly(vinylidene fluoride) (PVDF) homopolymers. The high dose gamma irradiation process induces the formation of C=C and C=O bonds in its [CH2-CF2]n main chain. The irradiation also provokes crosslinking and chain scission. All these radio-induced defects lead to changes in the PVDF crystalline structure. As a consequence, it is common to observe a decrease in the melting temperature (TM) and melting latent heat (LM) and some changes in its ferroelectric features. We have investigated the possibility of preparing nanocomposites of PVDF with graphene oxide (GO) through the radio-induction of molecular bonds. In this work, we discuss how the gamma radiation interacts with the nanocomposite crystalline structure., {"references":["G. Botelho, S. Lanceros-Mendez, A.M. Gonçalves, V. Sencadas, J.G. Rocha, \"Relationship between processing conditions, defects and thermal degradation of poly(vinylidene fluoride) in the β-phase\" in Journal of Non-Crystalline Solids, vol. 354, 2008, pp.72-78.","M. Celina, T.R. Dargaville, R. A. Assink, J. W. Martín, \"Selection and optimization of piezoelectric polyvinylidene fluoride polymers for adaptive optics in space environments\" in High Performance Polymers, vol. 17, 2005, pp. 575-593.","R. D. Dreyer, S. Park, C. W. Bielawski, R. S. Ruoff, \"The chemistry of graphene oxide\" in Chemical Society Reviews, vol. 39, 2010, pp. 228-240.","C. Yu, D. Li, W. Wu, C. Luo, Y. Zhang, C. Pan, \"Mechanical property enhancement of PVDF/graphene composite based on a high-quality graphene\" in Journal Materials Science, vol. 49, 2014, pp. 8311-8316.","I. Boullier, S. Esnouf, A. L. Moël, \"Radiooxidation of fluoropolymers: identification of oxidation products\" in \"Journal of Polymer Science Part B Polymer Physics, vol. 41, 2003, pp. 1509 – 1517."]}

The production and use of graphene-based nanomaterials is rapidly increasing. However, few data are available regarding the toxicity of these nanomaterials in aquatic organisms. In the present study, the toxicity of few-layer graphene (FLG) (obtained by chemical exfoliation) was evaluated in different tissues of the shrimp

The combination of the properties of graphene oxide (OG) and PVDF homopolymer makes their combined composite materials as multifunctional systems with great potential. Knowledge of the molecular structure is essential for better use. In this work, the degradation of PVDF polymer exposed to gamma irradiation in oxygen atmosphere in high dose rate has been studied and compared to degradation of PVDF/OG composites. The samples were irradiated with a Co-60 source at constant dose rate, with doses ranging from 100 kGy to 1,000 kGy. In FTIR data shown that the formation of oxidation products was at the both samples with formation of carbonyl and hydroxyl groups amongst the most prevalent products in the pure PVDF samples. In the other hand, the composites samples exhibit less presence of degradation products with predominant formation of carbonyl groups, these results also seen in the UV-Vis analysis. The results show that the samples of composites may have greater resistance to the irradiation process, since they have less degradation products than pure PVDF samples seen by spectroscopic techniques.

The combination of multi–walled carbon nanotubes (MWCNTs) with polymers offers an attractive route to reinforce the macromolecular compounds as well as the introduction of new properties based on morphological modifications or electronic interactions between the two constituents. As they are only a few nanometers in dimension, it offers ultra-large interfacial area per volume between the nano-element and polymer matrix. Nevertheless, the use of MWCNTs as a rough material in different applications has been largely limited by their poor processability, insolubility, and infusibility. Studies concerning the nanofiller reinforced polymer composites are justified in an attempt to overcome these limitations. This work presents one preliminary study of MWCNTs dispersion into the PVDF homopolymer. For preparation, the composite components were diluted in n,n-dimethylacetamide (DMAc) with mechanical agitation assistance. After complete dilution, followed by slow evaporation of the solvent at 60°C, the samples were dried. Films of about 80 μm were obtained. FTIR and UV-Vis spectroscopic techniques were used to characterize the nanocomposites. The appearance of absorption bands in the FTIR spectra of nanofilled samples, when compared to the spectrum of pristine PVDF samples, are discussed and compared with the UV-Vis measurements.

This paper presents a novel TiO2-Graphene composite film one-step preparation method by electrochemical synthesis. The films were prepared on a Ti substrate by electrochemical deposition from a GO and Ti (IV) aqueous solution. For comparison, pure TiO2 on a Ti substrate was obtained by the same electrochemical method. The as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy, Raman spectroscopy, photoluminescence and ultravioletevisible spectrophotometry. The photocatalytic properties of the films were investigated for the discoloration of Reactive Yellow 145 dye. The results showed that the TiO2-Graphene oxide composite film presented photocatalytic activity almost twice as high as that observed for the TiO2 film. In addition, the TiO2-Graphene oxide composite film presented better stability and recyclability, retaining its catalytic efficiency (z70%) even after 15 cycles. Published by Elsevier B.V.

A molecule with a π conjugated backbone built from aromatic thiophene and dialkoxyphenylene units and substituted imidazolium groups (TPO) is designed to obtain ultra-stable single walled carbon nanotube (SWCNT) dispersion in aqueous medium. The proposed mechanism of non-covalent interaction is accompanied by individualization of SWCNT and comprises of dominant nondisruptive π-π and cation-π interaction between them and the TPO conjugated oligomer. The individualization of SWCNT and dispersibility and stability of the ultra-stable suspensions were estimated using high resolution transmission electron microscopy, UV-Visible-NIR absorption spectroscopy, Raman spectroscopy, photoluminescence and zeta potential measurement. Nuclear magnetic resonance data provides direct evidence toward possible cation-π interaction.

Carbon nanotubes are promising nanomaterials for the diagnosis and treatment of brain disorders. However, the ability of these nanomaterials to cross cell membranes and interact with neural cells brings the need for the assessment of their potential adverse effects on the nervous system. This study aimed to investigate the biopersistence of single-walled carbon nanotubes functionalized with polyethylene glycol (SWCNT-PEG) directly infused into the rat hippocampus. Contextual fear conditioning, Y-maze and open field tasks were performed to evaluate the effects of SWCNT-PEG on memory and locomotor activity. The effects of SWCNT-PEG on oxidative stress and morphology of the hippocampus were assessed 1 and 7 days after infusion of the dispersions at 0.5, 1.0 and 2.1 mg/mL. Raman analysis of the hippocampal homogenates indicates the biopersistence of SWCNT-PEG in the hippocampus 7 days post-injection. The infusion of the dispersions had no effect on the acquisition or persistence of the contextual fear memory; likewise, the spatial recognition memory and locomotor activity were not affected by SWCNT-PEG. Histological examination revealed no remarkable morphological alterations after nanomaterial exposure. One day after the infusion, SWCNT-PEG dispersions at 0.5 and 1.0 mg/mL were able to decrease total antioxidant capacity without modifying the levels of reactive oxygen species or lipid hydroperoxides in the hippocampus. Moreover, SWCNT-PEG dispersions at all concentrations induced antioxidant defenses and reduced reactive oxygen species production in the hippocampus at 7 days post-injection. In this work, we found a time-dependent change in antioxidant defenses after the exposure to SWCNT-PEG. We hypothesized that the persistence of the nanomaterial in the tissue can induce an antioxidant response that might have provided resistance to an initial insult. Such antioxidant delayed response may constitute an adaptive response to the biopersistence of SWCNT-PEG in the hippocampus.

Made available in DSpace on 2015-10-21T20:15:10Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-06-17. Added 1 bitstream(s) on 2015-10-22T09:48:16Z : No. of bitstreams: 1 WOS000356518200001.pdf: 803864 bytes, checksum: e41d7e36cd2e1f67d32a7945ba81b594 (MD5) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Gold is a noble metal that, in comparison with silver and copper, has the advantage of corrosion resistance. Despite its high conductivity, chemical stability and biocompatibility, gold exhibits high plasticity, which limits its applications in some nanodevices. Here, we report an experimental and theoretical study on how to attain enhanced mechanical stability of gold nanotips. The gold tips were fabricated by chemical etching and further encapsulated with carbon nanocones via nanomanipulation. Atomic force microscopy experiments were carried out to test their mechanical stability. Molecular dynamics simulations show that the encapsulated nanocone changes the strain release mechanisms at the nanoscale by blocking gold atomic sliding, redistributing the strain along the whole nanostructure. The carbon nanocones are conducting and can induce magnetism, thus opening new avenues on the exploitation of transport, mechanical and magnetic properties of gold covered by sp(2) carbon at the nanoscale. Univ Fed Minas Gerais, ICEx, Dept Fis, BR-31270901 Belo Horizonte, MG, Brazil Penn State Univ, Mat Res Inst, University Pk, PA 16802 USA Univ Fed Minas Gerais, Ctr Microscopia, BR-30123970 Belo Horizonte, MG, Brazil Ctr Desenvolvimento Tecnol Nucl, BR-31270010 Belo Horizonte, MG, Brazil Univ Estadual Campinas, Inst Fis Gleb Wataghin, BR-13083970 Campinas, SP, Brazil Univ Estadual Paulista, UNESP, IGCE, Dept Fis, Rio Claro, SP 13506900, Brazil Univ Estadual Paulista, UNESP, IGCE, Dept Fis, Rio Claro, SP 13506900, Brazil FAPESP: 2013/08293-7 FAPESP: 2011/17253-3 FAPESP: 2013/09536-0

O objetivo deste trabalho é desenvolver uma abordagem simples e reprodutível para experimentos de braquiterapia por HDR que permita estudos de irradiação in vitro com base em parâmetros clínicos. Uma plataforma de acrílico foi desenvolvida para manter frascos de cultura de células T25, placas de cultivo múltiplos poços e cateteres de braquiterapia numa posição fixa e rígida durante o processo de irradiação. Imagens tomográficas de todos os arranjos foram tomadas, para em seguida realizar um planejamento 3D com dose de 550cGy no plano das células tumorais aderentes. A fim de medir a dose recebida pelas células, uma dosimetria com filme radiocrômico foi realizada em todos os arranjos celulares. As incertezas relevantes foram levadas em conta. As células tumorais foram irradiadas duas vezes com um intervalo de 24 horas entre as irradiações. Prova da eficácia do modelo proposto foi obtida por análise de efeitos biológicos utilizando uma linhagem celular humana radiorresistente A431 de carcinoma epidermóide. A proliferação celular e a fase do ciclo celular foram avaliadas por ensaio de exclusão de azul de tripan e análise do conteúdo de DNA por citometria de fluxo, respectivamente. Verificou-se que a distribuição espacial de dose obtida é uniforme em todos os frascos e placas de cultura celular, mas há uma incerteza no valor desta dose. No que se refere aos ensaios in vitro, houve uma diminuição da taxa de proliferação celular das células irradiadas com significância estatística (p

Nanotechnology has been proven to be increasingly compatible with pharmacological and biomedical applications. Therefore, we evaluated the biological interactions of single-wall carbon nanotubes functionalized with polyethylene glycol (SWNT-PEG). For this purpose, we analyzed biochemical, histological, behavioral and biodistribution parameters to understand how this material behaves in vitro and in vivo using the fish Danio rerio (zebrafish) as a biological model. The in vitro results for fish brain homogenates indicated that SWNT-PEG had an effect on lipid peroxidation and GSH (reduced glutathione) content. However, after intraperitoneal exposure, SWNT-PEG proved to be less biocompatible and formed aggregates, suggesting that the PEG used for the nanoparticle functionalization was of an inappropriate size for maintaining product stability in a biological environment. This problem with functionalization may have contributed to the low or practically absent biodistribution of SWNT-PEG in zebrafish tissues, as verified by Raman spectroscopy. There was an accumulation of material in the abdominal cavity that led to inflammation and behavioral disturbances, as evaluated by a histological analysis and an open field test, respectively. These results provide evidence of a lack of biocompatibility of SWNTs modified with short chain PEGs, which leads to the accumulation of the material, tissue damage and behavioral alterations in the tested subjects.

A produção de materiais que apresentem alto desempenho em suas aplicações exige avanços tecnológicos e científicos. Os elevados valores de resistência à tração e módulo de elasticidade, aliados à flexibilidade, baixa densidade e alta razão de aspecto, fazem dos nanotubos de carbono excepcionais candidatos para reforçar compósitos poliméricos. Preparamos por laminação sistemas compósitos ternários à base de resina epóxi/tecidos de fibra de carbono (para os binários), acrescendo nanotubos de carbono para os sistemas ternários. Os parâmetros estequiométricos do sistema epoxídico (valor de Phr) e concentração de nanotubos de carbono empregado nos sistemas compósitos tiveram avaliadas suas morfologias (MEV), propriedades térmicas (TG) e mecânicas (ASTM D790). Embora o sistema epoxídico com Phr 10,0 tenha apresentado uma maior estabilidade térmica, os compósitos ternários produzidos a partir do sistema com Phr 26,6 mostraram valores de tensão máxima e módulo de elasticidade até 8 vezes maiores que aqueles produzidos com o sistema Phr 10. A adição de nanotubos de carbono aos compósitos com Phr 26,6 resultou em ganhos adicionais de aproximadamente 38 e 15% na tensão máxima e no módulo de elasticidade, respectivamente. Esses resultados revelaram a limitação nos métodos de integralização de nanoestruturas a sistemas compósitos, onde as dispersões estão limitadas a uma série de fatores inerentes a interação química e/ou física durante a fabricação dos compósitos nanoestruturados.

Micro-Raman and positron annihilation lifetime spectroscopy (PALS) have been used to investigate the structure of a thermoplastic polyurethane/LiClO4 solid flexible polymer electrolyte at room temperature. Correlation between the free volume and carrier concentration with ionic conductivity was observed. The polyurethane soft phase consisted of a poly(tetramethylene glycol-co-ethylene glycol) copolymer reinforced by condensation with hexamethyldiisocianate. The range of salt concentration between 5 and 35 wt %, which attained the beginning of phase segregation, was also studied by differential scanning calorimetry (DSC), which showed the presence of three thermal events; the soft-phase Tg, a change in heat capacity suggested as the hard-phase Tg, and a hard-phase ordering endotherm. The total ionic conductivity was found to be approximately 4 × 10-6 S cm-1 at 23 °C up to 27 wt % salt, whereas there were pronounced changes observed by the spectroscopic techniques. The PALS measurements indicated a decrease...

We report the preparation of photovoltaic devices using modified single wall carbon nanotubes, SWNTs. Devices are produced stacking on top of fluorine-doped tin-oxide, an electrochemically deposited polybithiophene layer, a layer of SWNT blended with poly(3-octylthiophene) and an evaporated top metal contact, Ca/Al or Al. Ca/Al-top-electrode devices achieve open-circuit voltages of 1.81 V and average power conversion efficiency of 1.48% at irradiance of 15.5 W m–2, spectrally distributed following AM1.5. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

International audience; Negatively charged graphene layers from a graphite intercalation compound spontaneously dissolve in N-methylpyrrolidone, without the need for any sonication, yielding stable, air-sensitive, solutions of laterally extended atom-thick graphene sheets and ribbons with dimensions over tens of micrometers. These can be deposited on a variety of substrates. Height measurements showing single-atom thickness were performed by STM, AFM, multiple beam interferometry, and optical imaging on Sarfus wafers, demonstrating deposits of graphene flakes and ribbons. AFM height measurements on mica give the actual height of graphene (ca. 0.4 nm).

We consider a Volovik's analog model for description of a topological defects in a superfluid and we investigate the scattering of quasiparticles in this background. The analog of the gravitational Aharonov-Bohm in this system is found. An analysis of this problem employing loop variables is considered and corroborates for the existence of the Aharonov-Bohm effect in this system. The results presented here may be used to study the Aharonov-Bohm effect in superconductors., 7 pages, to appear in Europhys. Lett

The IR-active vibrational modes of single-walled carbon nanotubes have been observed by optical transmission through thin films of bundled nanotubes. Because IR-active chemical functional groups, e.g., -COOH, -OH, might be attached to the tube walls and contribute additional spectral features, we have also studied the effects of chemical purification and long-term high-temperature vacuum annealing on the IR spectrum. Through comparison with theory, we are able to assign much of the sharp structure observed in our IR spectra.

CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior Os pontos de carbono (PCs) representam uma classe relativamente nova de nanomateriais de carbono e têm atraído grande interesse devido a propriedades, como alta solubilidade em água, possibilidade de funcionalização, resistência à fotodegradação, baixa toxicidade e excelentes propriedades ópticas com uma fluorescência relativamente alta. As propriedades dos PCs possibilitam sua aplicação em diversas áreas que vão desde a fotocatálise e optoeletrônica, até a bioimagem, além de atuar como sensores para diferentes substâncias, devido à sensibilidade da fotoluminescência na presença de determinados analitos. Neste trabalho, os PCs foram preparados por duas rotas, desidratação ácida e carbonização hidrotérmica, utilizando quitosana e celulose como precursores. A carbonização hidrotérmica mostrou-se uma rota mais adequada para a obtenção de maiores valores de rendimento quântico (RQ). Além disso, a funcionalização dos pontos de carbono foi realizada utilizando amônia, ácido bórico e PEG1500N. Os materiais foram caracterizados por diferentes técnicas de caracterização para investigar as propriedades ópticas e morfológicas dos PCs. A amostra de PC obtida da celulose quando modificada com amônia apresentou aumento no valor RQ de aproximadamente 1,0% (amostra PCCEL) para 6,1% (PCCEL-N). Além disso, a modificação química com o reagente PEG1500N aumentou significativamente o RQ da amostra PCCEL para 5,5%. Com a amostra PC obtida da quitosana, um valor RQ de 9,3% foi obtido para a amostra não modificada enquanto 15,3% de RQ foi obtido após uma modificação simples com amônia. Os PCs que apresentaram maiores valores de RQ foram estudados como sensores para uma série de íons metálicos. Ambos os PCs obtidos da quitosana e da celulose apresentaram seletividade para o íon Fe3+ e as amostras PCCEL-N e PCCEL-PEGN apresentaram os menores limites de detecção, 0,22 e 0,13μM, respectivamente. Carbon dots (PCs) represent a relatively new class of carbon nanomaterials and have attracted great interest due to their interesting properties such as high water solubility, possibility of functionalization, resistance to photodegradation, low toxicity, and excellent optical properties with a relatively high fluorescence. The PCs properties enable their applications in several areas ranging from photocatalysis and optoelectronics, to bioimaging, in addition to acting as sensors for different substances, due to the sensitivity of photoluminescence in the presence of certain analytes. In this work, PCs were prepared by two routes, acid dehydration and hydrothermal carbonization, using chitosan and cellulose as precursors. Hydrothermal carbonization proved to be a more suitable route to obtain higher quantum yield (QY) values. In addition, the functionalization of the carbon dots was performed using ammonia, boric acid and PEG1500N. The materials were characterized by different characterization techniques to investigate the optical and morphological properties of the PCs. The PC sample obtained from cellulose when modified with ammonia, showed an increase in the QY value from ~1.0% (PCCEL sample) to 6.1% (PCCEL-N). Also, the chemical modification with the PEG1500N reagent significantly increased the QY of the PCCEL sample to 5.5%. With the PC sample obtained from chitosan, a QY value of 9.3% was obtained for the unmodified sample whereas 15.3% of QY was obtained after a simple modification with ammonia. The PCs which presented higher QY values were studied as sensors for a series of metallic ions. Both PCs obtained from chitosan and from cellulose showed selectivity for the Fe3+ ion and the samples PCCEL-N and PCCEL-PEGN presented the lowest detection limits, 0.22 and 0.13μM, respectively.

Carbetos metálicos são compostos binários (metal-carbono) que apresentam ótimas características físicas e químicas, como resistência a corrosão, estabilidade química em diversos meios, alta dureza e boas propriedades magnéticas e catalíticas. Estes materiais são aplicados como supercapacitores, agentes de contraste em biomedicina, armazenamento magnético e, mais recentemente, como catalisadores ativos ou suportados em remediação ambiental e conversão de energia - por exemplo, em sínteses Fischer-Tropsch e hidrogenação de COx - e como eletrocatalisadores para reações de quebra de água e evolução de hidrogênio e oxigênio. A síntese de carbetos é comumente realizada em fornos, composta de várias etapas e elevadas temperaturas (acima de 800 oC). O grafeno e seus materiais derivados vêm sendo amplamente utilizados como catalisadores ou suporte ativo em catalisadores nanoestruturados em razão de suas propriedades térmicas, elétricas, mecânicas e elevada área de superfície e capacidade de adsorção. Neste trabalho, nanopartículas (NP) de carbetos metálicos MxCy (com M = Fe, Co, Ni, Mo e W) foram quimicamente sintetizadas a 340 oC via reação de decomposição térmica de acetilacetonatos e carbonis metálicos mediada por oleilamina. Os materiais sintetizados foram caracterizados por difração de raios X, microscopia eletrônica de transmissão, magnetometria de amostra vibrante à temperatura ambiente e espectroscopias Raman e infravermelho. As condições de síntese foram estudadas e ajustadas resultando na obtenção de nanopartículas de carbetos de Fe, Co e Ni e nanopartículas ultra-pequenas de carbetos de Mo e W. Para o caso dos precursores de Fe, Co e Ni na forma de acetilacetonatos metálicos, a presença de íons brometo no meio de reação se mostrou essencial para a obtenção da fase carbeto. A presença de íons Ni2+, utilizados na forma de NiBr2 ou Ni(acac)2, favoreceu a formação da fase carbeto de ferro e cobalto, além de apresentar efeito na diminuição do tamanho das nanopartículas, ao contrário do tempo de reação que aumentou o tamanho das nanopartículas. Através de uma pequena modificação neste processo de síntese, foi possível sintetizar materiais híbridos de óxido de grafeno reduzido (rGO): rGO/NP de carbetos (Fe, Co, Ni, Mo e W) ou rGO/NP metálica (Fe, Co e Ni) via redução in situ de óxido de grafeno (GO) a rGO. Duas metodologias de etapa única foram usadas na preparação dos materiais híbridos: syn-grafenização (SG), onde as NP são formadas concomitantemente à redução do GO a rGO, e pós-grafenização (PG), na qual as NP são formadas inicialmente com posterior incorporação das folhas de rGO durante a redução do GO no meio de reação. O método de SG foi eficiente para produzir os materiais híbridos rGO/NP de carbetos de Mo e W. Para Fe, Co e Ni, no entanto, o sistema não mostrou poder redutor e/ou de carburação para promover a redução do GO e a formação da fase carbeto, resultando em materiais híbridos de rGO/NP metálicas de Fe, Co e Ni. A metodologia de PG foi então ajustada para esses três metais, resultando na formação dos materiais híbridos rGO/NP de carbetos de Fe, Co e Ni. Os materiais obtidos apresentam significativa estabilidade e serão testados como catalisadores suportados em trabalhos futuros. Metallic carbides are binary compounds (carbon-metal) that have excellent physical and chemical characteristics such as corrosion resistance, chemical stability in various media, high hardness and good magnetic and catalytic properties. These materials are applied as supercapacitors, contrasting agents in biomedicine, magnetic storage, and more recently, as active catalysts or supported in environmental remediation and energy conversion - for example, in Fischer-Tropsch syntheses, COx hydrogenation - and as electrocalizers for water breakdown and evolution of hydrogen and oxygen reactions. Carbide synthesis is commonly carried out in ovens, involving several steps and high temperatures (above 800oC). Graphene and its derived materials have been widely used as catalysts or active support in nanostructured catalysts due to their thermal, electrical, mechanical properties and high surface area and adsorption capacity. In this work, metal carbides nanoparticles (NP) MxCy (with M = Fe, Co, Ni, Mo and W) were chemically synthesized at 340oC via oleylamine-mediated thermal decomposition reaction of acetylacetonates and metal carbonyls. The synthesized materials were characterized by X-ray diffraction, transmission electronic microscopy, room temperature vibrant sample magnetometry and Raman and infrared spectroscopies. The synthesis conditions were studied and adjusted resulting in carbide nanoparticles of Fe, Co and Ni and ultra-small carbides nanoparticles of Mo and W. For the Fe, Co and Ni precursors, in the form of metal acetylacetonates, the presence of bromide ions in the reaction medium proved to be essential for obtaining the carbide phase. The presence of Ni2+ ions, used in the form of NiBr2 or Ni(acac)2 favored the formation of the iron and cobalt carbides phases, in addition to decreasing the size of the nanoparticles, in contrast to the reaction time which increased the size of the nanoparticles. Through a small modification in this synthesis process, it was possible to synthesize reduced graphene oxide (rGO) hybrid materials: rGO/NP of carbides (Fe, Co, Ni, Mo and W) or metallic rGO/NP (Fe, Co and Ni) via in situ reduction of graphene oxide (GO) to rGO. Two single-step methodologies were used in the preparation of the hybrid materials: syn-graphenization (SG), where NP are formed concomitantly with the reduction of GO to rGO and post-graphenization (PG), in which NP are initially formed with subsequent incorporation in the rGO sheets during GO reduction in the reaction medium. The SG method was efficient to produce the rGO/NP hybrid materials of Mo and W carbides. For Fe, Co and Ni, however, the system did not show reducing and/or carburizing power to promote the reduction of GO and formation of the carbide phase, resulting in rGO/ NP hybrids materials of metallic Fe, Co and Ni. The PG methodology was then adjusted for these three metals, resulting in the formation of the rGO/NP hybrid materials of Fe, Co and Ni carbides. The materials obtained have significant stability and will be tested as supported catalysts in future work.