Tuning electronic and magnetic properties through disorder in V2O5 nanoparticles.

We report on the synthesis and characterization of V2O5 nanoparticles grown using a sol-gel method at different calcination temperatures. We observed a surprising reduction in the optical band gap from 2.20 to 1.18 eV with increasing calcination temperature from 400 to 500 °C. Raman and X-Ray diffraction measurements indicated slight changes in the lattice parameters induced by the growth process. However, density functional theory calculations of the Rietveld-refined and pristine structures revealed that the observed optical gap reduction could not be explained by structural changes alone. By introducing oxygen vacancies to the refined structures, we could reproduce the reduction of the band gap. Our calculations also showed that the inclusion of oxygen vacancies at the vanadyl position creates a spin-polarized interband state that reduces the electronic band gap and promotes a magnetic response due to unpaired electrons. This prediction was confirmed by our magnetometry measurements, which exhibited a ferromagnetic-like behavior. Our findings suggest that oxygen vacancies play a crucial role in band gap reduction and the promotion of a ferromagnetic-like response in an otherwise paramagnetic material. This provides a promising route to engineer novel devices.

Sulfur-Doped g-C3N4 Heterojunctions for Efficient Visible Light Degradation of Methylene Blue.

The discharge of synthetic dyes from different industrial sources has become a global issue of concern. Enormous amounts are released into wastewater each year, causing concerns due to the high toxic consequences. Photocatalytic semiconductors appear as a green and sustainable form of remediation. Among them, graphitic carbon nitride (g-C3N4) has been widely studied due to its low cost and ease of fabrication. In this work, the synthesis, characterization, and photocatalytic study over methylene blue of undoped, B/S-doped, and exfoliated heterojunctions of g-C3N4 are presented. The evaluation of the photocatalytic performance showed that exfoliated undoped/S-doped heterojunctions with 25, 50, and 75 mass % of S-doped (g-C3N4) present enhanced activity with an apparent reaction rate constant (kapp) of 1.92 × 10-2 min-1 for the 75% sample. These results are supported by photoluminescence (PL) experiments showing that this heterojunction presents the less probable electron-hole recombination. UV-vis diffuse reflectance and valence band-X-ray photoelectron spectroscopy (VB-XPS) allowed the calculation of the band-gap and the valence band positions, suggesting a band structure diagram describing a type I heterojunction. The photocatalytic activities calculated demonstrate that this property is related to the surface area and porosity of the samples, the semiconductor nature of the g-C3N4 structure, and, in this case, the heterojunction that modifies the band structure. These results are of great importance considering that scarce reports are found concerning exfoliated B/S-doped heterojunctions.

Structurally defined graphene nanoribbons with high lateral extension.

Oxidative cyclodehydrogenation of laterally extended polyphenylene precursor allowed bottom-up synthesis of structurally defined graphene nanoribbons (GNRs) with unprecedented width. The efficiency of the cyclodehydrogenation was validated by means of MALDI-TOF MS, FT-IR, Raman, and UV-vis absorption spectroscopies as well as investigation of a representative model system. The produced GNRs demonstrated broad absorption extended to near-infrared region with the optical band gap of as low as 1.12 eV.

High quality dispersions of hexabenzocoronene in organic solvents.

We have studied the exfoliation and dispersion of hexabenzocoronene (HBC) in 28 different solvents. We see a wide range of dispersed concentrations and aggregation states, all of which can be related to the solvent properties. To a first approximation, the dispersed concentration is maximized for solvents with Hildebrand solubility parameter close to 21 MPa(1/2), similar to graphitic materials such as nanotubes and graphene. We have also studied the concentration dependence of the absorbance and photoluminescence of HBC for both a good solvent, cyclohexyl pyrrolidone (CHP), and a poor solvent, tetrahydrofuran (THF). In both cases, we observe features that can be associated with either individual molecules or aggregates, allowing us to establish metrics both for aggregate and individual molecule content. While the aggregate content always increases with concentration, good solvents disperse individual molecules at relatively high concentrations while poor solvents display aggregation even at low concentrations. Using these metrics, we determine that large populations of individual molecules are present at low concentrations in certain solvents with Hildebrand solubility parameters close to 21 MPa(1/2). However, the aggregation state of HBC is considerably more sensitive to solvent Hildebrand parameter for halogenated solvents than for amide solvents. We find a combination of high overall concentrations and large populations of individual molecules in four solvents: cyclohexyl pyrrolidone, 1-chloronaphthalene, 1-bromonaphthalene, and 1,2,4-trichlorobenzene. Scanning tunnelling microscopy (STM) measurements show the formation of self-assembled monolayers at the interface between a HBC-solvent dispersion and a highly oriented pyrolytic graphite (HOPG) substrate. Similar structures were observed on ultrathin supports by aberration-corrected transmission electron microscopy (TEM). Also observed were graphitic objects of size ~1 nm consistent with monomers or aggregated stacks of very few monomers. We believe this is strong evidence of the presence of individual molecules in dispersions prepared with appropriate solvents.

From nanographene and graphene nanoribbons to graphene sheets: chemical synthesis.

Graphene, an individual two-dimensional, atomically thick sheet of graphite composed of a hexagonal network of sp(2) carbon atoms, has been intensively investigated since its first isolation in 2004, which was based on repeated peeling of highly oriented pyrolyzed graphite (HOPG). The extraordinary electronic, thermal, and mechanical properties of graphene make it a promising candidate for practical applications in electronics, sensing, catalysis, energy storage, conversion, etc. Both the theoretical and experimental studies proved that the properties of graphene are mainly dependent on their geometric structures. Precise control over graphene synthesis is therefore crucial for probing their fundamental physical properties and introduction in promising applications. In this Minireview, we highlight the recent progress that has led to the successful chemical synthesis of graphene with a range of different sizes and chemical compositions based on both top-down and bottom-up strategies.

Flexible, transparent, conducting films of randomly stacked graphene from surfactant-stabilized, oxide-free graphene dispersions.

Graphite is exfoliated in water to give dispersions of mono- and few-layer graphene stabilized by surfactant. These dispersions can be used to form thin, disordered films of randomly stacked, oxide-free, few-layer graphenes. These films are transparent with a direct current conductivity of up to 1.5 x 10(4) S m(-1). The conductivity is stable under flexing for at least 2000 cycles. The electrical properties are limited by disorder and aggregation suggesting future routes for improvement.

Measurement of multicomponent solubility parameters for graphene facilitates solvent discovery.

We have measured the dispersibility of graphene in 40 solvents, with 28 of them previously unreported. We have shown that good solvents for graphene are characterized by a Hildebrand solubility parameter of delta(T) approximately 23 MPa(1/2) and Hansen solubility parameters of delta(D) approximately 18 MPa(1/2), delta(P) approximately 9.3 MPa(1/2), and delta(H) approximately 7.7 MPa(1/2). The dispersibility is smaller for solvents with Hansen parameters further from these values. We have used transmission electron microscopy (TEM) analysis to show that the graphene is well exfoliated in all cases. Even in relatively poor solvents, >63% of observed flakes have <5 layers.

Rational Design of Photo-Electrochemical Hybrid Devices Based on Graphene and Chlamydomonas reinhardtii Light-Harvesting Proteins.

Dye-sensitized solar cells (DSSCs) have been highlighted as the promising alternative to generate clean energy based on low pay-back time materials. These devices have been designed to mimic solar energy conversion processes from photosynthetic organisms (the most efficient energy transduction phenomenon observed in nature) with the aid of low-cost materials. Recently, light-harvesting complexes (LHC) have been proposed as potential dyes in DSSCs based on their higher light-absorption efficiencies as compared to synthetic dyes. In this work, photo-electrochemical hybrid devices were rationally designed by adding for the first time Leu and Lys tags to heterologously expressed light-harvesting proteins from Chlamydomonas reinhardtii, thus allowing their proper orientation and immobilization on graphene electrodes. The light-harvesting complex 4 from C. reinhardtii (LHC4) was initially expressed in Escherichia coli, purified via affinity chromatography and subsequently immobilized on plasma-treated thin-film graphene electrodes. A photocurrent density of 40.30 ± 9.26 µA/cm2 was measured on devices using liquid electrolytes supplemented with a phosphonated viologen to facilitate charge transfer. Our results suggest that a new family of graphene-based thin-film photovoltaic devices can be manufactured from rationally tagged LHC proteins and opens the possibility to further explore fundamental processes of energy transfer for biological components interfaced with synthetic materials.

Liquid phase production of graphene by exfoliation of graphite in surfactant/water solutions.

We have demonstrated a method to disperse and exfoliate graphite to give graphene suspended in water-surfactant solutions. Optical characterization of these suspensions allowed the partial optimization of the dispersion process. Transmission electron microscopy showed the dispersed phase to consist of small graphitic flakes. More than 40% of these flakes had <5 layers with approximately 3% of flakes consisting of monolayers. Atomic resolution transmission electron microscopy shows the monolayers to be generally free of defects. The dispersed graphitic flakes are stabilized against reaggregation by Coulomb repulsion due to the adsorbed surfactant. We use DLVO and Hamaker theory to describe this stabilization. However, the larger flakes tend to sediment out over approximately 6 weeks, leaving only small flakes dispersed. It is possible to form thin films by vacuum filtration of these dispersions. Raman and IR spectroscopic analysis of these films suggests the flakes to be largely free of defects and oxides, although X-ray photoelectron spectroscopy shows evidence of a small oxide population. Individual graphene flakes can be deposited onto mica by spray coating, allowing statistical analysis of flake size and thickness. Vacuum filtered films are reasonably conductive and are semitransparent. Further improvements may result in the development of cheap transparent conductors.

Carbon-nanotube-polymer nanocomposites for field-emission cathodes.

The electron field-emission (FE) characteristics of functionalized single-walled carbon-nanotube (CNT)-polymer composites produced by solution processing are reported. It is shown that excellent electron emission can be obtained by using as little as 0.7% volume fraction of nanotubes in the composite. Furthermore by tailoring the nanotube concentration and type of polymer, improvements in the charge transfer through the composite can be obtained. The synthesis of well-dispersed randomly oriented nanotube-polymer composites by solution processing allows the development of CNT-based large area cathodes produced using a scalable technology. The relative insensitivity of the cathode's FE characteristics to the electrical conductivity of the composite is also discussed.

Preparation of buckypaper-copper composites and investigation of their conductivity and mechanical properties.

Buckypaper-metal composites are prepared by substrate-enhanced electroless deposition of copper onto strips of buckypaper (see picture). Electrical conductivity and mechanical properties of these buckypaper-copper composites at different copper content are investigated. The conductivity is shown to increases by up to 350 %, and the Young's modulus and the ultimate tensile strength of the composites by 282 % and 290 % respectively over pristine buckypaper.

Panorama de la investigación en fonoaudiología: tendencias en Colombia / Overview of research in speech therapy: trends in Colombia

El objetivo de este artículo es analizar el panorama investigativo disciplinar desde la producción académica nacional, para identificar poblaciones, áreas, enfoques de investigación, de esta manera reconocer necesidades y retos para la investigación formativa de la fonoaudiología en Colombia. Se analizó información proveniente de proyectos de investigación de pregrado y posgrado de 13 programas de formación en Fonoaudiología del país, entre 2010 y 2019, reportados por las instituciones de educación superior. Se recolectó información de informes y documentos de investigación (N=638). En primer lugar, se observa un incremento en la producción investigativa entre 2010 (4,9%) y 2019 (18,3%). El 85% de la investigación se identificó en pregrado y el 15% en postgrado. El enfoque predominante fue cualitativo (55,3%), el que, junto con el alcance descriptivo (77,8%) que representan la mayoría de productos de investigación. El escenario relacionado con el ámbito de salud clínico asistencial lidera la investigación (52,9%). Las áreas predominantes en este escenario investigativo son Lenguaje (29,1%) y Audición (27,4%) en poblaciones de adultos (56,7%) e infantil (28,52%). Se concluye que la producción investigativa desde la academia, específicamente desde los programas de formación de fonoaudiólogos en Colombia, evidencian la necesidad de fomentar la investigación de tipo experimental y analítica, con poblaciones de neonatos y lactantes, en áreas relacionadas con la función oralfaríngea y en escenarios inéditos. Además, es necesario incluir el uso de tecnologías y nuevos enfoques de intervención para aportar al abordaje basado en la evidencia. Futuras investigaciones deben permitir comparar la investigación antes y después de la pandemia, dada la virtualización y la inclusión de la fonoaudiología en escenarios como las unidades de cuidado crítico y cuidado paliativo.

The objective of this article is to analyze the disciplinary research landscape from the national academic production, to identify populations, areas, research approaches, in this way identify needs and challenges for formative research of speech therapy in Colombia. Information from undergraduate and graduate research projects of 13 training programs in Speech Therapy in the country, between 2010 and 2019, reported by higher education institutions, was analyzed. Information was collected from reports and research papers (N=638). First, there was an increase in research production between 2010 (4.9%) and 2019 (18.3%). 85% of the researchwas identified in undergraduate and 15% in postgraduate. The predominant approach was qualitative (55.3%), which, together with the descriptive scope (77.8%) that represent the majority of research products. The scenario related to the field of clinical health care leads the research (52.9%). The predominant areas in this research scenario are Language (29.1%) and Hearing (27.4%)in adult (56.7%) and child (28.52%) populations. It is concluded that the research production from the academy, specifically from the trainingprograms of speech therapists in Colombia, evidences the need to promote experimental and analytical research, with populations of neonates and infants, in areas related to oral function and in unprecedented scenarios. Besides, it is necessary to include the use oftechnologies and new intervention approaches to contribute to the evidence-based approach. Future research should allow comparison of research before and after the pandemic, given the virtualization and the inclusion of speech therapy in settings such as critical careand palliative care units.

Synthesis of structurally well-defined and liquid-phase-processable graphene nanoribbons.

The properties of graphene nanoribbons (GNRs) make them good candidates for next-generation electronic materials. Whereas 'top-down' methods, such as the lithographical patterning of graphene and the unzipping of carbon nanotubes, give mixtures of different GNRs, structurally well-defined GNRs can be made using a 'bottom-up' organic synthesis approach through solution-mediated or surface-assisted cyclodehydrogenation reactions. Specifically, non-planar polyphenylene precursors were first 'built up' from small molecules, and then 'graphitized' and 'planarized' to yield GNRs. However, fabrication of processable and longitudinally well-extended GNRs has remained a major challenge. Here we report a bottom-up solution synthesis of long (>200 nm) liquid-phase-processable GNRs with a well-defined structure and a large optical bandgap of 1.88 eV. Self-assembled monolayers of GNRs can be observed by scanning probe microscopy, and non-contact time-resolved terahertz conductivity measurements reveal excellent charge-carrier mobility within individual GNRs. Such structurally well-defined GNRs may prove useful for fundamental studies of graphene nanostructures, as well as the development of GNR-based nanoelectronics.

Electrochemically exfoliated graphene as solution-processable, highly conductive electrodes for organic electronics.

Solution-processable thin layer graphene is an intriguing nanomaterial with tremendous potential for electronic applications. In this work, we demonstrate that electrochemical exfoliation of graphite furnishes graphene sheets of high quality. The electrochemically exfoliated graphene (EG) contains a high yield (>80%) of one- to three-layer graphene flakes with high C/O ratio of 12.3 and low sheet resistance (4.8 kΩ/□ for a single EG sheet). Due to the solution processability of EG, a vacuum filtration method in association with dry transfer is introduced to produce large-area and highly conductive graphene films on various substrates. Moreover, we demonstrate that the patterned EG can serve as high-performance source/drain electrodes for organic field-effect transistors.

Porous iron oxide ribbons grown on graphene for high-performance lithium storage.

A well-designed nanostructure of transition metal oxides has been regarded as a key to solve their problems of large volume changes during lithium insertion-desertion processes which are associated with pulverization of the electrodes and rapid capacity decay. Here we report an effective approach for the fabrication of porous iron oxide ribbons by controlling the nucleation and growth of iron precursor onto the graphene surface and followed by an annealing treatment. The resultant iron oxide ribbons possess large aspect ratio, porous structure, thin feature and enhanced open-edges. These characteristics are favorable for the fast diffusion of lithium ions and electrons, and meanwhile can effectively accommodate the volume change of iron oxides during the cycling processes. As a consequence, the graphene-induced porous iron oxide ribbons exhibit a high reversible capacity and excellent cycle stability for lithium storage.

Nitrogen-doped graphene and its iron-based composite as efficient electrocatalysts for oxygen reduction reaction.

The high cost of platinum-based electrocatalysts for the oxygen reduction reaction (ORR) has hindered the practical application of fuel cells. Thanks to its unique chemical and structural properties, nitrogen-doped graphene (NG) is among the most promising metal-free catalysts for replacing platinum. In this work, we have developed a cost-effective synthesis of NG by using cyanamide as a nitrogen source and graphene oxide as a precursor, which led to high and controllable nitrogen contents (4.0% to 12.0%) after pyrolysis. NG thermally treated at 900 °C shows a stable methanol crossover effect, high current density (6.67 mA cm(-2)), and durability (∼87% after 10,000 cycles) when catalyzing ORR in alkaline solution. Further, iron (Fe) nanoparticles could be incorporated into NG with the aid of Fe(III) chloride in the synthetic process. This allows one to examine the influence of non-noble metals on the electrocatalytic performance. Remarkably, we found that NG supported with 5 wt % Fe nanoparticles displayed an excellent methanol crossover effect and high current density (8.20 mA cm(-2)) in an alkaline solution. Moreover, Fe-incorporated NG showed almost four-electron transfer processes and superior stability in both alkaline (∼94%) and acidic (∼85%) solutions, which outperformed the platinum and NG-based catalysts.

Graphene nanoribbons as low band gap donor materials for organic photovoltaics: quantum chemical aided design.

Graphene nanoribbons (GNRs) are strips of graphene cut along a specific direction that feature peculiar electronic and optical properties owing to lateral confinement effects. We show here by means of (time-dependent) density functional theory calculations that GNRs with properly designed edge structures fulfill the requirements in terms of electronic level alignment with common acceptors (namely, C(60)), solar light harvesting, and singlet-triplet exchange energy to be used as low band gap semiconductors for organic photovoltaics.

Caracterización del proceso lecto-escrito y su relación con el desempeño escolar en estudiantes de Bogotá / Reading and writing characterization and its relation with the academic performance in students from Bogotá

Un número de investigaciones han estudiado la relación entre la lecto-escritura y el desempeño de los estudiantes. Este artículo describe las características del proceso lecto-escrito y analiza la correlación entre este proceso y el desempeño escolar. En este estudio la muestra fue de 327 estudiantes de los grados quinto y sexto quienes fueron evaluados a través de diferentes tareas. En este estudio descriptivo se aplicaron pruebas de comprensión de lectura y de producción de textos. El análisis de la información mostró un desempeño más alto en los estudiantes de grado sexto en comprensión de lectura y en las conciencias fonológica, morfológica y sintáctica. El análisis identificó una correlación entre el desempeño en matemáticas y las habilidades psicolin-güísticas, además una correlación entre el desempeño en ciencias sociales y habilidades metalin-güísticas, ciencias naturales y habilidades metalingüísticas y artes y habilidades metacognitivas. Los hallazgos brindan luces sobre la importancia de la lecto-escritura en el desempeño escolar y como las diferentes habilidades facilitan el desarrollo de la lecto-escritura. En este sentido, es importante plantear nuevas investigaciones centradas en la promoción de habilidades metalin-güísticas, metacognitivas y psicolingüísticas para el desempeño escolar de los estudiantes.

A number of researches have studied the relationship between reading and writing skills and the students school performance. This paper describes the characteristics of reading and writing skills and analyzes the correlation between this process and the academic performance. For this study a total of 327 students from fifth and sixth grade were evaluated through different tasks. In this descriptive study the sample was assessed through reading comprehension and writing production tests. Data analyses showed higher performances in sixth grade students in reading comprehension, and in phonological, morphological and syntactic awareness. The analysis iden-tified correlation between Mathematics performance and Psycholinguistic skills; as well as be-tween Social Science performance and metalinguistic skills, Natural Science performance and metalinguistic skills and Arts performance and metacognitive skills. The findings highlight the importance of reading and writing skills for student's academic performance and how the diffe-rent skills facilitate literacy's development. In this sense, it is important to plan new researches focused on promoting metalinguistic, metacognitive and psycholinguistic skills in the student's academic performance

High-yield production of graphene by liquid-phase exfoliation of graphite.

Fully exploiting the properties of graphene will require a method for the mass production of this remarkable material. Two main routes are possible: large-scale growth or large-scale exfoliation. Here, we demonstrate graphene dispersions with concentrations up to approximately 0.01 mg ml(-1), produced by dispersion and exfoliation of graphite in organic solvents such as N-methyl-pyrrolidone. This is possible because the energy required to exfoliate graphene is balanced by the solvent-graphene interaction for solvents whose surface energies match that of graphene. We confirm the presence of individual graphene sheets by Raman spectroscopy, transmission electron microscopy and electron diffraction. Our method results in a monolayer yield of approximately 1 wt%, which could potentially be improved to 7-12 wt% with further processing. The absence of defects or oxides is confirmed by X-ray photoelectron, infrared and Raman spectroscopies. We are able to produce semi-transparent conducting films and conducting composites. Solution processing of graphene opens up a range of potential large-area applications, from device and sensor fabrication to liquid-phase chemistry.

Tendencias de lainvestigación en la lengua de señas / Research tendencies in sign Language

El objetivo de este artículo fue identificar las tendencias investigativas mundiales de los estu-dios de la Lengua de Señas entre el año 2000 y el 2011 (primer bimestre) a partir de la revisión de 20 revistas indexadas que se encuentran en las bases de datos electrónicas Scielo, Pubmed, y PROQUEST. Los artículos están escritos en diferentes lenguas como Español, Inglés y Por-tugués. Para este propósito cinco variables fueron registradas: a) el nombre de las revistas; b) la producción investigativa por año, c) el porcentaje de autores por artículo, d) los autores más destacados, y e) los temas trabajados. Los resultados muestran 196 artículos de investiga-ción en términos de frecuencia y porcentajes. También hay siete temas: el 25,7% de estos artí-culos se refiere a las características de la lengua de señas; el 24,5% estudia la lengua de señas y la educación; el 22,7% se centra en las variaciones sociolingüísticas de la Lengua de Señas; el 7% se refiere a la comunicación bimodal; el 6% se centra en el proceso lecto-escrito; el 4% estudia el procesamiento psicolingüístico, y el 3% revisa las bases neurológicas de la lengua de señas. Teniendo en cuenta lo anterior, se determinan los siete temas expuestos como las tendencias investigativas en cuanto a la Lengua de Señas. Al finalizar hay algunas propuestas de investigación que pueden ser desarrolladas con el fin de apoyar la comprensión de esta lengua.

The objective of this article was to identify the research world tendencies in Sign Langua-ge studies between 2000 and 2011 (first two months) from the review of 20 indexed journals which are on electronic databases Scielo, Pubmed, and PROQUEST. The articles are written in different languages such as Spanish, English and Portuguese. For this purpose five varia-bles were registered: a) journals' name; b) research production by year; c) authors' percentage by article; d) authors and higher productivity; and e) worked themes. The results show 196 research articles that were analyzed in terms of frequency and percentage. Also there are seven themes: 25,7% of these articles refers to the sign language characteristics; 24,5% studies the sign language and education; 22,7% is focused in sign language and its socio-cultural variables; 7% refers to bimodal communication; 6% is focused in reading-writing process; 4% studies the psycholinguistics processing; and 3% reviews the sign language ́s neurological bases. Given the above, the seven themes were identified as research tendency about Sing Language. At the end, there are some research purposes that can be developed in order to support the understanding of this language.