Synthesis and Characterization of Graphene Oxide and Reduced Graphene Oxide and its Use in Flexible Photovoltaic Cells

El óxido de grafeno (OG) y el óxido de grafeno reducido (OGR) fue sintetizado empleando el método de exfoliación por oxidación exhaustiva o método de Hummers, empleando grafito de partida comercial tipo UF4 (>10 μm) y grafito triturado por molienda tipo GR5 (< 5 μm). Las imágenes por SEM permiten distinguir, que a pesar de que las partículas de GR5 son más pequeñas que las tipo UF4, el OG y el OGR resultantes de las partículas GR5 son mucho más grandes que el OG y OGR de tipo F4, formando material laminar con áreas de hasta 0.5 μm x 1.0 μm. La caracterización por TEM muestra que tanto el OG y el OGR provenientes del GR5, presentan partículas en monocapa, comportamiento que permite tener buenas propiedades eléctricas comparadas con el OG y el OGR tipo UF4. El análisis de difracción de rayos-x DRX, corrobora que el OG GR5 después del proceso de reducción con hidracina permite la obtención de laminas de grafeno individuales altamente orientadas. Sin embargo, hay zonas del material donde se encuentran partículas con varias capas siendo un material no homogéneo. Espectroscopía FTIR y de absorción UV fueron empleadas para corroborar la presencia de grupos funcionales. La resistencia de hoja es 0,028 kΩ/cuadrado en PET, comparado con 0.160 kΩ/cuadrado en vidrio, siendo este material el más apropiado para ser empleado como contra-electrodo en células solares sensibilizadas con colorantes o tipo Grätzel, sí es comparado con el OGR, el cual es 0.391 kΩ/cuadrado en PET y 0.413 kΩ/cuadrado en vidrio. En condiciones estándar de iluminación se alcanzo una eficiencia de conversión igual a 0.25% (una capa de TDBR) para una célula tipo PET/TiO2/TBDR/(I2/I-3)/GO/PET y una eficiencia de 0.20% (tres capas de TDBR) para una célula tipo PET/TiO2/TBDR/(I2/I-3)/RGO/PET. Las suspensiones de OG y OGR obtenidas son bastante estables en agua, evitándose el proceso de precipitación; siendo estas suspensiones de bastante interés para la industria de semiconductores impresos en sustratos flexibles

CTZS Thin Films Grown by a Sequential Deposition of Precursors

A comparative study of the structural, optical and morphological properties of Cu2ZnSnS4 (CZTS) thin films prepared by two different techniques was performed. One consists of sequential evaporation of the elemental metallic precursors under a flux of sulphur supplied by evaporation from an effusion cell (physical vapor deposition-PVD) and the second one is a solution-based chemical route where thin layers of CuS, SnS and ZnS are deposited sequentially by diffusion membrane- assisted chemical bath deposition techniques; the membranes are used to optimize the kinetic growth through a moderate control of the release of the metal into CBD solution by osmosis. The present comparative study is helpful to the synthesis of kesterite nanostructured thin films.Comment: Published 201

Estado actual de las celdas solares basadas en capas absorbentes de bajo costo Cu2ZnSnS4, perspectivas y nuevos aportes realizados

En este artículo se hace una revisión exhaustiva y completa del estado actual de las celdas solares que emplean el compuesto se- miconductor Cu2ZnSnS4 como capa absorbente siguiendo los procesos de manufactura de tecnología de película delgada. Como complemento se hace un resumen de los aportes más significativos hechos dentro del grupo de Materiales Semiconductores y Energía Solar de la Universidad Nacional de Colombia correspondientes a la síntesis y caracterización del compuesto Cu2ZnSnS4

IoT-WLAN Proximity Network for Potentiostats

© 2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.[EN] The implementation of potentiostats as portable and communicated devices has reached significant progress to benefit research, industry, and education. The Internet of Things (IoT) is a good opportunity to interconnect devices such as the potentiostats together with electronics, communication technologies, and chemistry into a single system. This work proposes a network for potentiostats using machine-to-machine (M2M) protocols, modifying its functioning mechanism in the broker to check the payload of the message that passes through it and synchronize the sensors depending on its content. Although one sensor can be synchronized directly to another, the broker decides which sensor to pair. This modification was made in the M2M protocol algorithm, both in the Broker and in the Client (sensor). In addition to this, the network uses an interconnection architecture of IoT smart networks of proximity with centralized management. The results of the tests carried out showed that the use of a modified M2M such as the one proposed in the architecture allows synchronization and comparison of the measurements of several sensors in real-time.González, P.; Lloret, J.; Tomás Gironés, J.; Rodríguez, O.; Hurtado, M. (2020). IoT-WLAN Proximity Network for Potentiostats. IEEE. 94-99. https://doi.org/10.1109/FMEC49853.2020.9144776S949

Caracterización fisicoquímica del sistema Mo/CuInS2/Zn(O,OH)S/ZnO por medio de espectroscopía fotoelectrónica XPS y AES

Volume and surface spectroscopy techniques are reliable analytical methods to characterize thin films of different materials. This paper presents results related to the composition of the absorbing film (CuInS2) and the Zn(O,OH)S buffer film within the Mo/CuInS2/Zn(O,OH)S/ZnO system. CuInS2 and ZnS films were synthesized per co-evaporation and chemical bath deposition (CBD) respectively. The system was characterized through an X-ray photoelectron spectroscopy (XPS) and studied through the Auger electron spectroscopy (AES). The results of the XPS indicated that the buffer film covered uniformly the CuInS2 surface, and we were able to verify that this film is created by a mixture of different compounds. Finally, the AES characterization allowed us to determine the composition of each one of the films of the photovoltaic system.Las técnicas de espectroscopía en volumen y superficie son métodos analíticos muy confiables para realizar la caracterización de películas delgadas de diferentes materiales; en este trabajo se presentan resultados relacionados con la composición de la capa absorbente (CuInS2) y la capa buffer Zn(O,OH)S en el sistema Mo/CuInS2/Zn(O,OH)S/ZnO.Las capas de CuInS2 y ZnS fueron sintetizadas por co-evaporación y deposición de baño químico (CBD) respectivamente, el sistema fue caracterizado por medio de espectroscopia fotoelectrónica de rayos X (XPS) y todo el sistema fue estudiado por medio de espectroscopia electrónica Auger (AES). Los resultados de XPS indicaron que la capa buffer cubrió uniformemente la superficie de CuInS2, además se verificó que la capa buffer esta compuesta por una mezcla de diferentes compuestos. Finalmente la caracterización por AES en profundidad permitió determinar la composición de cada una de las películas del sistema fotovoltáico

Microstructural Evolution as a Function of Increasing Aluminum Content in Novel Lightweight Cast Irons

In the context of the development of new lightweight materials, Al-alloyed cast irons have a great potential for reducing the weight of the different part of the vehicles in the transport industry. The correlation of the amount of Al and its effect in the microstructure of cast irons is not completely well established as it is affected by many factors such as chemical composition, cooling rate, etc. In this work, four novel lightweight cast irons were developed with different amounts of Al (from 0 wt. % to 15 wt. %). The alloys were manufactured by an easily scalable and affordable gravity casting process in an induction furnace, and casted in a resin-bonded sand mold. The microstructural evolution as a function of increasing Al content by different microstructural characterization techniques was studied. The hardness of the cast irons was measured by the Vickers indentation test and correlated with the previously characterized microstructures. In general, the microstructural evolution shows that the perlite content decrease with the increment of wt. % of Al. The opposite occurs with the ferrite content. In the case of graphite, a slight increment occurs with 2 wt. % of Al, but a great decrease occurs until 15 wt. % of Al. The addition of Al promotes the stabilization of ferrite in the studied alloys. The hardness obtained varied from 235 HV and 363 HV in function of the Al content. The addition of Al increases the hardness of the studied cast irons, but not gradually. The alloy with the highest hardness is the alloy containing 7 wt. % Al, which is correlated with the formation of kappa-carbides and finer perlite.This work has been partially funded by the Basque Government through the project Elkartek LION: KK-2019/0004

Comparative study of ZnO thin films doped with transition metals (Cu and Co) for methylene blue photodegradation under visible irradiation

We synthesized and characterized both Co-doped ZnO (ZnO:Co) and Cu-doped ZnO (ZnO:Cu) thin films. The catalysts’ synthesis was carried out by the sol–gel method while the doctor blade technique was used for thin film deposition. The physicochemical characterization of the catalysts was carried out by Raman spectroscopy, scanning electron microscopy (SEM), X-ray diffraction, and diffuse reflectance measurements. The photocatalytic activity was studied under visible irradiation in aqueous solution, and kinetic parameters were determined by pseudo-first-order fitting. The Raman spectra results evinced the doping process and suggested the formation of heterojunctions for both dopants. The structural diffraction patterns indicated that the catalysts were polycrystalline and demonstrated the presence of a ZnO wurtzite crystalline phase. The SEM analysis showed that the morphological properties changed significantly, the micro-aggregates disappeared, and agglomeration was reduced after modification of ZnO. The ZnO optical bandgap (3.22 eV) reduced after the doping process, these being ZnO:Co (2.39 eV) and ZnO:Co (3.01 eV). Finally, the kinetic results of methylene blue photodegradation reached 62.6% for ZnO:Co thin films and 42.5% for ZnO:Cu thin films.Fil: Vallejo Lozada, William Andrés. Universidad del Atlantico. Facultad de Cs. Basicas. Prog. de Química; ColombiaFil: Cantillo, Alvaro. Universidad del Atlantico. Facultad de Cs. Basicas. Prog. de Química; ColombiaFil: Salazar, Briggitte. Universidad del Atlantico. Facultad de Cs. Basicas. Prog. de Química; ColombiaFil: Diaz Uribe, Carlos Enrique. Universidad del Atlantico. Facultad de Cs. Basicas. Prog. de Química; ColombiaFil: Ramos Cervantes, Wilkendry. Universidad del Atlantico. Facultad de Cs. Basicas. Prog. de Química; Colombia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Romero, Eduard. Universidad Nacional de Colombia. Sede Bogotá; ColombiaFil: Hurtado, Mikel. Universidad Minuto de Dios; Colombia. Universidad Central; Colombi

Cyanobacterial biomass pigments as natural sensitizer for tio2 thin films

In this work, we studied the effect of TiO2 sensitization with dry biomass extracted of cyanobacteria on the degradation of methylene blue dye (AM). Cyanobacterial cultures isolated from water samples were collected from the swamp of Malambo in Colombia; two main genera of cyanobacteria were identified, and they were cultivated with BG-11 culture medium. The concentrations of chlorophyll a in the exponential and stationary phases of growth were measured; the phycobilin content was quantified by spectrophotometry. Thin films of TiO2 were deposited by a doctor blade method, and they were sensitized by wet impregnation. Furthermore, a methylene blue (MB) photodegradation process was studied under visible light irradiation on the cyanobacterial biomass sensitized TiO2 material (TiO2/sensitizer); besides, the pseudo-first-order model was used to obtain kinetic information about photocatalytic degradation. The results showed that the BG-11+ treatment reported a higher amount of dry biomass and phycobiliproteins. After the sensitization process, the TiO2/sensitizer thin films showed a significant red shift in the optical activity; besides the thin film roughness decreasing, the TiO2/sensitizer showed photocatalytic activity of 23.2% under visible irradiation, and besides, the kinetic () constant for TiO2/sensitizer thin films was 3.1 times greater than the value of TiO2 thin films. Finally, results indicated that cyanobacterial biomass is a suitable source of natural sensitizers to be used in semiconductor sensitization.Universidad del Atlántico, Universidad de la Costa, Institución Universitaria Politécnico Gran Colombiano, Universidad Central, Universidad Minuto de Dios, Pontificia Universidad Católica de Chile, Millennium Nuclei on Catalytic Processes towards Sustainable Chemistry

Distribution and demographic parameters of the Peregrine falcon Falco peregrinus L., 1756 in Gipuzkoa

Gathering information on the distribution and population size is crucial in order to develop precise conservation actions, especially in threatened species or those of special concern. The aim of the present article is to update the population status and the breeding parameters of the Peregrine falcon Falco peregrinus L., 1756 in Gipuzkoa. We also used data obtained from previous studies in order to estimate population trends in the region (2000-2017). In 2017, 35 territories were detected. During the period from 1990 to 2000, the mean breeding population size increased 79.4%, but from 2000 to 2017, the increase was just 3.2%. However, the latter increase was not statistically significant. Therefore, it can be concluded that the population has remained stable for the last two decades. The Peregrine falcon is well distributed in Gipuzkoa, except for the central-eastern part of the region. The nests were found on inland cliffs (48.6%), marine cliffs (25.7%), quarries (22.9%) and buildings (2.9%). The breeding parameters in 2017 (productivity: 1.72 ± 1.36 offspring/breeding pair, n = 35; flight rate: 2.50 ± 0.83 offspring/nest, n = 24; breeding success, 92%) did not differ significantly from previous years within the region. In conclusion, the peregrine falcon population in Gipuzkoa has remained constant during the last two decades (from 2000 to 2010, and up to 2017), with one of the highest breeding densities in Spain. Breeding parameters are also high and, overall, the conservation status of the population is apparently good in Gipuzkoa