Electrogenerated hydrophilic carbon nanomaterials with tailored electrocatalytic activity

This work investigates the influence of the type of buffer electrolyte used in the generation of Electrochemical Hydrophilic Carbon (EHC) on their physical-chemical properties and electrocatalytic activity. The EHC nanomaterials were prepared in three different biological buffers, phosphate, glycine and citrate buffers (EHC@phosphate, EHC@glycine, EHC@citrate) and their surface properties were fully characterized by AFM, XPS and Raman. The EHC nanomaterials drop cast onto a glassy carbon electrode were electrochemically characterized in [Fe(CN)6]3-/4- and [Ru(NH3)6]3+/2+ redox probes solutions, and their electrocatalytic activity was investigated towards hydrogen peroxide and oxygen reduction reactions (ORR) in a phosphate buffer solution. It was found that the nature of buffer electrolyte strongly influences the surface chemical state of the EHC materials, disorder degree in the hexagonal sp2 carbon network and oxygen functional groups, affecting both the EHC electrocatalytic activity towards the ORR and H2O2 reduction reaction. The most catalytic material for the ORR was EHC@citrate, whereas EHC@glycine showed the highest oxygen conversion (n ≅ 2.7 to 3). Moreover, it was shown that the content of oxygen singly bonded to carbon correlates strongly with the number of electrons transferred. A very singular behaviour in the electrochemical reduction of hydrogen peroxide was observed on EHC@glycine, qualitatively interpreted as an autocatalytic reaction. In contrast, a blocking-like effect was depicted on EHC@phosphate. These results must have an important impact in the development of materials with peroxidase-like activity and in the design of O2 sensors with non-sensitivity to H2O2.publishe

NEOTROPICAL XENARTHRANS: a data set of occurrence of xenarthran species in the Neotropics

Xenarthrans – anteaters, sloths, and armadillos – have essential functions for ecosystem maintenance, such as insect control and nutrient cycling, playing key roles as ecosystem engineers. Because of habitat loss and fragmentation, hunting pressure, and conflicts with 24 domestic dogs, these species have been threatened locally, regionally, or even across their full distribution ranges. The Neotropics harbor 21 species of armadillos, ten anteaters, and six sloths. Our dataset includes the families Chlamyphoridae (13), Dasypodidae (7), Myrmecophagidae (3), Bradypodidae (4), and Megalonychidae (2). We have no occurrence data on Dasypus pilosus (Dasypodidae). Regarding Cyclopedidae, until recently, only one species was recognized, but new genetic studies have revealed that the group is represented by seven species. In this data-paper, we compiled a total of 42,528 records of 31 species, represented by occurrence and quantitative data, totaling 24,847 unique georeferenced records. The geographic range is from the south of the USA, Mexico, and Caribbean countries at the northern portion of the Neotropics, to its austral distribution in Argentina, Paraguay, Chile, and Uruguay. Regarding anteaters, Myrmecophaga tridactyla has the most records (n=5,941), and Cyclopes sp. has the fewest (n=240). The armadillo species with the most data is Dasypus novemcinctus (n=11,588), and the least recorded for Calyptophractus retusus (n=33). With regards to sloth species, Bradypus variegatus has the most records (n=962), and Bradypus pygmaeus has the fewest (n=12). Our main objective with Neotropical Xenarthrans is to make occurrence and quantitative data available to facilitate more ecological research, particularly if we integrate the xenarthran data with other datasets of Neotropical Series which will become available very soon (i.e. Neotropical Carnivores, Neotropical Invasive Mammals, and Neotropical Hunters and Dogs). Therefore, studies on trophic cascades, hunting pressure, habitat loss, fragmentation effects, species invasion, and climate change effects will be possible with the Neotropical Xenarthrans dataset

Microwave plasmas applied for the synthesis of free standing graphene sheets

The article of record as published may be located at http://dx.doi.org/10.1088/0022-3727/47/38/385501Self-standing graphene sheets were synthesized using microwave plasmas driven by surface waves at 2.45 GHz stimulating frequency and atmospheric pressure. The method is based on injecting ethanol molecules through a microwave argon plasma environment, where decomposition of ethanol molecules takes place. The evolution of the ethanol decomposition was studied in situ by plasma emission spectroscopy. Free gas-phase carbon atoms created in the plasma diffuse into colder zones, both in radial and axial directions, and aggregate into solid carbon nuclei. The main part of the solid carbon is gradually withdrawn from the hot region of the plasma in the outlet plasma stream where nanostructures assemble and grow. Externally forced heating in the assembly zone of the plasma reactor has been applied to engineer the structural qualities of the assembled nanostructures. The synthesized graphene sheets have been analysed by Raman spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy and x-ray photoelectron spectroscopy. The presence of sp3 carbons is reduced by increasing the gas temperature in the assembly zone of the plasma reactor. As a general trend, the number of mono-layers decreases when the wall temperature increases from 60 to 100 ◦C. The synthesized graphene sheets are stable and highly ordered

Influence of oxygen partial pressure on the properties of undoped InOx films deposited at room temperature by rf-PERTE

Transparent and conductive/semiconductive undoped indium oxide (InOx) thin films were deposited at room temperature. The deposition technique used is the radio frequency (rf) plasma enhanced reactive thermal evaporation (rf-PERTE) of indium (In) in the presence of oxygen. The influence of oxygen partial pressure on the properties of these films is presented. The oxygen partial pressure varied between 3 × 10−2 and 1.3 × 10−1 Pa. Undoped InOx films, 100 nm thick, deposited at the oxygen partial pressure of 6 × 10−2 Pa show a conductive behaviour, exhibit an average visible transmittance of 81%, a band gap around 2.7 eV and an electrical conductivity of about 1100 (Ω cm)−1. For oxygen pressures greater than 6 × 10−2 Pa, semiconductive films are obtained, maintaining the visible transmittance. Films deposited at lower pressures are conductive but dark. From XPS data, films deposited at an oxygen partial pressure of 6 × 10−2 Pa show the highest amount of oxygen in the film surface and the lowest ratio between oxygen in the oxide crystalline and amorphous phases

Transparent p-type CuxS thin films

The effect of different mild post-annealing treatments in air, at 270 °C, for 4–6 min, on the optical, electrical, structural and chemical properties of copper sulphide (CuxS) thin films deposited at room temperature are investigated. CuxS films, 70 nm thick, are deposited on glass substrates by vacuum thermal evaporation from a Cu2S:S (50:50 wt.%) sulphur rich powder mixture. The as-deposited highly conductive crystalline CuS (covellite) films show high carrier concentration (∼1022 cm−3), low electrical resistivity (∼10−4 Ω cm) and inconclusive p-type conduction. After the mild post-annealing, these films display increasing values of resistivity (∼10−3 to ∼10−2 Ω cm) with annealing time and exhibit conclusive p-type conduction. An increase of copper content in CuxS phases towards the semiconductive Cu2S (chalcocite) compound with annealing time is reported, due to re-evaporation of sulphur from the films. However, the latter stoichiometry was not obtained, which indicates the presence of vacancies in the Cu lattice. In the most resistive films a Cu2O phase is also observed, diminishing the amount of available copper to combine with sulphur, and therefore the highest values of optical transmittance are reached (65%). The appearance on the surface of amorphous sulphates with annealing time increase is also detected as a consequence of sulphur oxidation and replacement of sulphur with oxygen. All annealed films are copper deficient in regards to the stoichiometric Cu2S and exhibit stable p-type conductivity