Green Routes for Graphene Oxide Reduction and Self- Assembled Graphene Oxide Micro- and Nanostructures Production

Graphene-derived materials are currently studied because of their actual and projected applications. Among them, graphene oxide (GO) promises for outstanding applications as it can be prepared at large scale by simple, scalable, and low-cost techniques. The existent chemical methods based on the graphite exfoliation (phase solution and Hummers based) produce highly functionalized graphene, i.e., GO-like materials that converts into reduced GO (rGO) after a reduction treatment. The present work presents the current scenario on the GO green reduction methods, on the development of hierarchical carbon-based structures by the self-assembly of GO sheets at interfaces, and on rGO-based hybrid nanocomposites. It is worth noting that, to date, the production and application of graphene-related materials are the fastest-growing research areas

Synthesis and Magnetic Characterization of Graphite-Coated Iron Nanoparticles

Graphite-coated iron nanoparticles were prepared from magnetite nanoparticles by chemical vapour deposition (CVD) under methane and hydrogen atmosphere. After being purified from carbon excess, graphite-coated iron nanoparticles were tested for morphological and magnetic properties. It was found that, during the thermal process, magnetite nanoparticles 6 nm in size coalesce and transform into graphite-coated iron 200 nm in size, as revealed by scanning electron microscopy (SEM). Raman characterization assessed that high-quality graphite coats the iron core. Magnetic measurements revealed the phase change (magnetite to iron) as an increase in the saturation magnetization from 50 to 165 emu/g after the CVD process

Development of highly faceted reduced graphene oxide-coated copper oxide and copper nanoparticles on a copper foil surface

This work describes the formation of reduced graphene oxide-coated copper oxide and copper nanoparticles (rGO-Cu2ONPs, rGO-CuNPs) on the surface of a copper foil supporting graphene oxide (GO) at annealing temperatures of 200–1000 °C, under an Ar atmosphere. These hybrid nanostructures were developed from bare copper oxide nanoparticles which grew at an annealing temperature of 80 °C under nitrogen flux. The predominant phase as well as the particle size and shape strongly depend on the process temperature. Characterization with transmission electron microscopy and scanning electron microscopy indicates that Cu or Cu2O nanoparticles take rGO sheets from the rGO network to form core–shell Cu–rGO or Cu2O–rGO nanostructures. It is noted that such ones increase in size from 5 to 800 nm as the annealing temperature increases in the 200–1000 °C range. At 1000 °C, Cu nanoparticles develop a highly faceted morphology, displaying arm-like carbon nanorods that originate from different facets of the copper crystal structure

Nanostructured PbSe Films Deposited by Spray Pyrolysis Using PbSe Colloidal Solutions

This work describes the spray pyrolysis deposition of PbSe films, using as-prepared PbSe colloids as the starting solution. The PbSe colloids were prepared by using the alkahest approach, where Pb and Se precursors were made to react with the following green polyols: glycerin, ethylene glycol, and propylene glycol, to subsequently spray them onto glass substrates. The results of the characterization indicated that amine or thiol groups-free and single-phase rock-salt cubic PbSe powder was obtained, producing nanocrystals 16–30 nm in size. X-ray diffraction also showed that the PbSe films containing PbSeO3 and PbO·xH2O as impurity phases were produced during the deposition. The morphology of the powders and films was developed by a self-assembly process, in which the primary PbSe nanoparticles self-assemble to produce peanut-like microstructures. Additionally, a non-continuous and porous feature was formed in the thick films. Certain films revealed optical structures characterized by broad- and low-intensity bands resembling an exciton-like behavior. This could be attributed to the presence of nanocrystals with a size less than the Bohr radius, indicating reminiscent quantum effects. The results suggest that the usage of colloidal dispersions as spray solutions represents an effective approach to forming PbSe films, as well as that the synthesis method allows for the elimination of thiol and amine groups before deposition, significantly simplifying the process

Reversiones parciales y totales: muestra-comparativo en igualación a la muestra con consecuencias diferenciales y no diferenciales

Se evaluaron los efectos de los cambios parciales y totales de las relaciones de contingencia muestra-comparativo en una tarea de igualación a la muestra con consecuencias diferenciales y no diferenciales. Se formaron cuatro grupos de diez estudiantes cada uno, dos grupos fueron entrenados en un procedimiento de igualación a la muestra con consecuencias no diferenciales, mientras que los otros dos fueron entrenados en uno con consecuencias diferenciales. Concluida la fase de entrenamiento, a un grupo de consecuencias no diferenciales y a un grupo de consecuencias diferenciales se les cambiaron totalmente las relaciones de contingencia muestra-comparativo, mientras que a los otros dos grupos únicamente se les cambió una de las relaciones muestra-comparativo. Durante la fase de entrenamiento se observó que los grupos entrenados con consecuencias diferenciales obtuvieron porcentajes de respuestas correctas más altos que los grupos entrenados con consecuencias no diferenciales; durante la fase de reversión se observó que en los cuatro grupos hubo una disminución en el porcentaje de respuestas correctas siendo mayor en los grupos que fueron entrenados con consecuencias no diferenciales

Optical and structural characterization of oleic acid-stabilized CdTe nanocrystals for solution thin film processing

This work presents results of the optical and structural characterization of oleic acid-stabilized cadmium telluride nanocrystals (CdTe-NC) synthesized by an organometallic route. After being cleaned, the CdTe-NC were dispersed in toluene to obtain an ink-like dispersion, which was drop-cast on glass substrate to deposit a thin film. The CdTe-NC colloidal dispersion as well as the CdTe drop-cast thin films were characterized with regard to the optical and structural properties. TEM analysis indicates that the CdTe-NC have a nearly spherical shape (3.5 nm as mean size). Electron diffraction and XRD diffraction analyses indicated the bulk-CdTe face-centered cubic structure for CdTe-NC. An additional diffraction line corresponding to the octahedral Cd3P2 was also detected as a secondary phase, which probably originates by reacting free cadmium ions with trioctylphosphine (the tellurium reducing agent). The Raman spectrum exhibits two broad bands centered at 141.6 and 162.3 cm−1, which could be associated to the TO and LO modes of cubic CdTe nanocrystals, respectively. Additional peaks located in the 222 to 324 cm−1 range, agree fairly well with the wavenumbers reported for TO modes of octahedral Cd3P2