Direct synthesis of highly porous interconnected carbon nanosheets and their application as high-performance supercapacitors

An easy, one-step procedure is proposed for the synthesis of highly porous carbon nanosheets with an excellent performance as supercapacitor electrodes. The procedure is based on the carbonization of an organic salt, i.e., potassium citrate, at a temperature in the 750-900 °C range. In this way, carbon particles made up of interconnected carbon nanosheets with a thickness of <80 nm are obtained. The porosity of the carbon nanosheets consists essentially of micropores distributed in two pore systems of 0.7-0.85 nm and 0.95-1.6 nm. Importantly, the micropore sizes of both systems can be enlarged by simply increasing the carbonization temperature. Furthermore, the carbon nanosheets possess BET surface areas in the ∼1400-2200 m(2) g(-1) range and electronic conductivities in the range of 1.7-7.4 S cm(-1) (measured at 7.1 MPa). These materials behave as high-performance supercapacitor electrodes in organic electrolyte and exhibit an excellent power handling ability and a superb robustness over long-term cycling. Excellent results were obtained with the supercapacitor fabricated from the material synthesized at 850 °C in terms of both gravimetric and volumetric energy and power densities. This device was able to deliver ∼13 Wh kg(-1) (5.2 Wh L(-1)) at an extremely high power density of 78 kW kg(-1) (31 kW L(-1)) and ∼30 Wh kg(-1) (12 Wh L(-1)) at a power density of 13 kW kg(-1) (5.2 kW L(-1)) (voltage range of 2.7 V).

Assessment of the role of micropore size and N-doping in CO2 capture by porous carbons

The role of micropore size and N-doping in CO2 capture by microporous carbons has been investigated by analyzing the CO2 adsorption properties of two types of activated carbons with analogous textural properties: (a) N-free carbon microspheres and (b) N-doped carbon microspheres. Both materials exhibit a porosity made up exclusively of micropores ranging in size between <0.6 nm in the case of the pristine materials and up to 1.6 nm for the highly activated carbons (47% burnoff). The N-doped carbons possess ~3 wt % of N heteroatoms that are incorporated into several types of functional groups (i.e., pyrrole/pyridone, pyridine, quaternary, and pyridine-N-oxide). Under conventional operation conditions (i.e., T ~ 0-25 °C and P(CO2) ~ 0-1 bar), CO2 adsorption proceeds via a volume-filling mechanism, the size limit for volume-filling being ~0.7-0.8 nm. Under these circumstances, the adsorption of CO2 by nonfunctionalized porous carbons is mainly determined by the volume of the micropores with a size below 0.8 nm. It was also observed that the CO2 capture capacities of undoped and N-doped carbons are analogous which shows that the nitrogen functionalities present in these N-doped samples do not influence CO2 adsorption. Taking into account the temperature invariance of the characteristic curve postulated by the Dubinin theory, we show that CO2 uptakes can be accurately predicted by using the adsorption data measured at just one temperature.

Hydrothermal carbons from hemicellulose-derived aqueous hydrolysis products as electrode materials for supercapacitors

Acid pretreatment of lignocellulosic biomass, required for bioethanol production, generates large amounts of by-products, such as lignin and hydrolyzed hemicellulose fractions, which have found so far very limited applications. In this work, we demonstrate how the recovered hemicellulose hydrolysis products can be effectively utilized as a precursor for the synthesis of functional carbon materials through hydrothermal carbonization (HTC). The morphology and chemical structure of the synthesized HTC carbons are thoroughly characterized to highlight their similarities with glucose-derived HTC carbons. Furthermore, two routes for introducing porosity within the HTC carbon structure are presented: i) silica nanoparticle hard-templating, which is shown to be a viable method for the synthesis of carbonaceous hollow spheres; and ii) KOH chemical activation. The synthesized activated carbons (ACs) show an extremely high porosity (pore volume≈1.0 cm(3) g(-1)) mostly composed of micropores (90 % of total pore volume). Because of their favorable textural properties, the ACs are further tested as electrodes for supercapacitors, yielding very promising results (300 F g(-1) at 250 mA g(-1)) and confirming the high suitability of KOH-activated HTC carbons derived from spruce and corncob hydrolysis products as materials for electric double layer supercapacitors.

Renewable nitrogen-doped hydrothermal carbons derived from microalgae

Nitrogen-doped carbon materials are synthesized via an effective, sustainable, and green one-step route based on the hydrothermal carbonization of microalgae with high nitrogen content (ca. 11 wt %). The addition of the monosaccharide glucose to the reaction mixture is found to be advantageous, enhancing the fixation of nitrogen in the synthesized carbons, resulting in materials possessing nitrogen content in excess of 7 wt %, and leading to promising reaction yields. Increasing the amount of glucose leads to a higher nitrogen retention in the carbons, which suggests co-condensation of the microalgae and glucose-derived degradation/hydrolysis products via Maillard-type cascade reactions, yielding nitrogen-containing aromatic heterocycles (e.g., pyrroles) as confirmed by several analytical techniques. Increasing the HTC processing temperature leads to a further aromatization of the chemical structure of the HTC carbon and the formation of increasingly more condensed nitrogen-containing functional motifs (i.e., pyridinic and quaternary nitrogen).

Signatures of clustering in superparamagnetic colloidal nanocomposites of an inorganic and hybrid nature

The individual and co-operative properties of inorganic and hybrid superparamagnetic colloidal nanocomposites that satisfy all the requirements of magnetic carriers in the biosciences and/or catalysis fields are been studied. Essential to the success of this study is the selection of suitable synthetic routes (aerosol and nanocasting) that allow the preparation of materials with different matrix characteristics (carbon, silica, and polymers with controlled porosity). These materials present magnetic properties that depend on the average particle size and the degree of polydispersity. Finally, the analysis of the co-operative behavior of samples allows for the detection of signatures of clustering, which are closely related to the textural characteristics of samples and the methodology used to produce the magnetic carriers.

Solid-phase synthesis of graphitic carbon nanostructures from iron and cobalt gluconates and their utilization as electrocatalyst supports

We present a novel and facile synthesis methodology for obtaining graphitic carbon structures from Fe(II) and Co(II) gluconates. The formation of graphitic carbon can be carried out in only one step by means of heat treatment of these organic salts at a temperature of 900 degrees C or 1000 degrees C under inert atmosphere. This process consists of the following steps: (a) pyrolysis of the organic gluconate and its transformation to amorphous carbon, (b) conversion of Fe(2+) and Co(2+) ions to Fe(2)O(3) and CoO and their subsequent reduction to metallic nanoparticles by the carbon and (c) conversion of a fraction of formed amorphous carbon to graphitic structures by Fe and Co nanoparticles that act as catalysts in the graphitization process. The removal of the amorphous carbon and metallic nanoparticles by means of oxidative treatment (KMnO(4) in an acid solution) allows graphitic carbon nanostructures (GCNs) to be selectively recovered. The GCNs thus obtained (i.e. nanocapsules and nanopipes) have a high crystallinity as evidenced by TEM/SAED, XRD and Raman analysis. In addition, we used these GCNs as supports for platinum nanoparticles, which were well dispersed (mean Pt size approximately 2.5-3.2 nm). Most electrocatalysts prepared in this way have a high electrocatalytical surface area, up to 90 m(2) g(-1) Pt, and exhibit high catalytic activities toward methanol electrooxidation.

Influence of first line treatment in the 5 (5yS) and 10-year (10yS) survival outcomes of patients with gastroenteropancreatic neuroendocrine tumors (GNETs): 2001–2005 Spanish task force GNET group

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Background: Data on incidence, morbidity and mortality of GNETs is limited due to the low frequency of these tumors. However this survival data is critical to design studies with new agents. Methods: Data was obtained from medical records of 262 patients with GNETs and centralized in an online registry at www.retegep.net . Among the study parameters were histology, localization, stage, diagnostic workup, 1st line and subsequent treatments, 5yS and 10yS for the whole dataset and for different stages, tumor types and 1st line systemic treatment. Results: Mean age 58, 58% male. Primary tumors: 49% Carcinoids (C), 19% non-functioning pancreatic tumors (PT), 9% insulinomas, 6% gastrinomas and 8% unknown primary. Localizations: midgut (36%), head (17%) and body of pancreas (10%). Functioning symptoms led to diagnosis in 38% of cases. 4% were associated to MEN1. Stage at diagnosis was advanced (Adv) in 46%, localised (L) in 30% and locorregional (LR) in 13% (unknown in 11%). Diagnostic workup were CT Scan (84%), Octreoscan (52%) and US (52%) and serum hormone tests (65%). Treatments for Adv disease included somatostatin analogues (SA) (47%), surgery (S) (43%), chemotherapy (CT) (35%) and interferon (IFN) (34%), embolization (7%) and radiofrequency ablation (3%). 5yS and 10yS for the whole group was 61.6% (SD: 5.2%) and 49.8% (SD: 7.7%) respectively. 5yS and 10yS for the L/LR and Adv stages were 78.1% (SD: 7.3%) and 71% (SD: 10%), and 48.9% (SD: 7.7%) and 29% (SD: 12.4%), respectively. LR PT and C had similar 5 and 10yS but Adv PT did worse than Adv C (5yS of 36.2% and 61.1%, respectively). 1st line systemic treatment for LR and Adv disease (n=90) included SA (39%), CT (34.4%), IFN (5.6%), combinations of SA+IFN (13.3%), A+CT (4.4%) and other combinations (3.3%), with a 10yS rate of 69%, 79%, 50%, 89%, 66% and 50%, respectively. Adv PT perform worse than C regardless of treatment choice. As second line systemic treatment (n=43) 30% received SA, 30% CT, 26% inmunotherapy and 14% combinations. Conclusions: An extensive use of systemic therapy and a scarce use of non-surgical LR treatments is observed in the Adv stages. Choice of 1st line systemic treatment does not seem to influence survival outcomes.

No significant financial relationships to disclose.

Comparison of benefit to sugarcane plant growth and 15N2 incorporation following inoculation of sterile plants with Acetobacter diazotrophicus wild-type and Nif- mutants strains

The ability of the nitrogen-fixing bacterial endophyte Acetobacter diazotrophicus strain PAl5 to enhance the growth of sugarcane SP70-1143 was evaluated in the growth chamber, greenhouse, and field by comparing plants inoculated with wild-type and Nif mutant MAd3A in two independent experiments. The wild-type and Nif mutant strains colonized sugarcane plants equally and persisted in mature plants. In N-deficient conditions, sugarcane plants inoculated with A. diazotrophicus PAl5 generally grew better and had a higher total N content 60 days after planting than did plants inoculated with mutant MAd3A or uninoculated plants. These results indicate that the transfer of fixed N from A. diazotrophicus to sugarcane might be a significant mechanism for plant growth promotion in this association. When N was not limiting, growth enhancement was observed in plants inoculated with either wild-type or Nif- mutants, suggesting the additional effect of a plant growth promoting factor provided by A. diazotrophicus. A 15N2 incorporation experiment demonstrated that A. diazotrophicus wild-type strains actively fixed N2 inside sugarcane plants, whereas the Nif- mutants did not.

Characterization of a major cluster of nif, fix, and associated genes in a sugarcane endophyte, Acetobacter diazotrophicus

A major 30.5-kb cluster of nif and associated genes of Acetobacter diazotrophicus (syn. Gluconacetobacter diazotrophicus), a nitrogen-fixing endophyte of sugarcane, was sequenced and analyzed. This cluster represents the largest assembly of contiguous nif-fix and associated genes so far characterized in any diazotrophic bacterial species. Northern blots and promoter sequence analysis indicated that the genes are organized into eight transcriptional units. The overall arrangement of genes is most like that of the nif-fix cluster in Azospirillum brasilense, while the individual gene products are more similar to those in species of Rhizobiaceae or in Rhodobacter capsulatus.