William Vallejo

Novel (E)-1-(pyrrole-2-yl)-3-(aryl)-2-(propen-1-one) derivatives as efficient singlet oxygen quenchers: kinetics and quantum chemical calculations

Chalcones constitute an important group of natural and synthetic products that have been screened due to their wide range of pharmacological applications. Herein, we studied the antioxidant activity of five newly synthetized (E)-1-(pyrrole-2-yl)-3-(aryl)-2-(propen-1-one) (PAPs) derivatives against singlet oxygen (1O2). The differences among the compounds are related to aryl substitution in the p-position where: 3a = C6H5, 3b = 4-H3COC6H4, 3c = 4-FC6H4, 3d = 4-ClC6H4, 3e = 4-BrC6H4. The PAPs were synthesized using a Claisen–Schmidt condensation reaction between 2-acetylpyrrole and aromatic aldehydes under ultrasonic irradiation (yields between 79–86%) and were characterized by IR, mass spectrometry, NMR and quantum chemical calculations. The total singlet oxygen quenching rate constants (kQ) of the PAPs were measured spectrophotometrically in ethanol at 25 °C and determined by using the Stern–Volmer model. As the character of the EWGs is increased from 3a to 3e, the kQ diminishes smoothly. The best quencher is found to be the 3a compound (where the aryl group is unsubstituted) with a kQ = 5.71 (±0.21) × 107 M−1 s−1, which is similar to those for other antioxidants e.g. flavonoids. These results suggest these compounds are efficient quenchers of singlet oxygen and their potential applicability in biological systems.

Comparison of two grid connected photovoltaic systems GCPVS with different dimensioning factor DF during three years operation in Bogotá - Colombia

This paper shows the comparison of two grid connected photovoltaic systems GCPVS that are operating in the city of Bogotá - Colombia for more than three years. The systems are constituted by one of 0.8 kWp and the other of 3.6 kWp, they were designed with different dimensioning factor FD. The results revealed that the systems has different performance ratio PR, one of 0,78 for the one of 3,6 kW and 0,5 for the other of 0,8 kW.

Methylene Blue Photocatalytic Degradation under Visible Irradiation on In2S3 Synthesized by Chemical Bath Deposition

In this work, we synthesized In2S3 powder through chemical bath deposition method (CBD) in acid medium; we used thioacetamide as sulphide source and InCl3 as indium ion source. X-ray diffraction, diffuse reflection, and Raman spectroscopy measurements were used for In2S3 powder physicochemical characterization. Optical analysis indicated that In2S3 was active in the visible region of electromagnetic spectrum; it had a band gap of 2.47 eV; the diffraction patterns and Raman spectroscopy suggested that powder had polycrystalline structure. Furthermore, we also studied the adsorption process of methylene blue (MB) on In2S3 powder; adsorption studies indicated that the Langmuir model describes experimental data. Finally, photocatalytic degradation of MB was studied under visible irradiation in aqueous solution; besides, pseudo-first-order model was used to obtain kinetic information about photocatalytic degradation; results indicated that the powder catalyst reduces 26% concentration of MB under visible irradiation.

Methodology for technical analysis to massify PV systems as an option for distributed energy generation in low-voltage systems

This work presents the results for the use of a methodology to predict in a statistically reliable way, the impact of the behavior in steady-state of the massification of Grid-connected photovoltaic system to a low-voltage system. The methodology can be implemented either in common using programming software or using any commercial electric system simulation software. First, a grid-connected photovoltaic model was determined and verified for comparing its behavior with output measured on a real installed system 3.6 kWp. Parallel, atmospheric parameters which affect the PV systems behavior were characterized in statistically way from actual measurements. The solar resource characterized and the photovoltaic system model are integrated in a non-deterministic approach using the stochastic method to estimate the electrical parameters in steady- state, describing the influence of massification of the Grid-connected PV systems in low-voltage grid.

Photocatalytic Activity of Ag-TiO2 Composites Deposited by Photoreduction under UV Irradiation

In this work, we synthesized Ag nanoparticles on TiO2 thin films deposited on soda lime glass substrates. Ag nanoparticles were synthesized by photoreduction under UV irradiation silver nitrate solution. X-ray diffraction, Raman spectroscopy, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) measurements were used for physicochemical characterization. The structural study showed that all samples were polycrystalline, main phases were anatase and rutile, and no additional signals were detected after surface modification. Raman spectroscopy suggested that silver aggregates deposited on the TiO2 films could exhibit the surface plasmon resonance (SPR) phenomenon; XPS and SEM analysis confirmed TiO2 film morphological modification after photoreduction process. Photocatalytic degradation of methylene blue (MB) was studied under UV irradiation in aqueous solution, and, besides, pseudo-first-order model was used to obtain kinetic information about photocatalytic degradation. Results indicated that Ag-TiO2 showed an important increase in photocatalytic activity under UV (from 20% to 35%); finally, Ag-TiO2 thin films had value 2.4 × 10−3 ± 0.003 min−1 of 1.8 times greater than the value 1.3 × 10−4 ± 0.0004 min−1 of TiO2 thin films.

Synthesis and Characterization of System In(O,OH)S/i-ZnO/n

In this work, we fabricated system In(O,OH)S/i-ZnO/n+-ZnO to be used as potential optical window in thin films solar cells. i-ZnO/n+-ZnO thin films were synthesized by reactive evaporation (RE) method and In(O,OH)S thin films were synthesized by chemical bath deposition (CBD) method; all thin films were deposited on soda lime glass substrates. Thin films were characterized through X-ray diffraction (XRD), atomic force microscopy (AFM), and spectral transmittance measurements. Structural results indicated that both thin films were polycrystalline; furthermore, morphological results indicated that both thin films coated uniformly soda lime glass substrate; besides, optical characterization indicated that system had more than 80% of visible radiation transmittance.

Physicochemical study of synthetic dyes adsorption on TiO2 thin films for dye sensitized solar cells

In this work we study equilibrium and kinetic adsorption process of Methylene Blue (MB) and Copper phthalocyanine (CuPhTh) dyes on TiO2 thin films. We synthesized phthalocyanines through Achar method; dyes were characterized by Fourier-Transform Infrared spectroscopy (FTIR) and Diffuse reflectance. TiO2 thin films were fabricated by Doctor Blade method for using Degussa P25 as TiO2 source. We used Langmuir and Freundlich adsorption models to describe adsorption equilibrium, and besides, we used Largergren model to describe kinetic adsorption process. Characterization results reveal typical signals of phthalocyaninaes, and besides, TiO2 thin films had a polycrystalline structure. Results indicated dyes adsorption to occur through chemisorption process and Langmuir adsorption model describes suitably dye adsorption process on TiO2 thin films.

Technical potential of some Colombian cities for the development of grid connected PV systems through virtual instrumentation

This paper briefly describes the operation curves of some PV modules under actual irradiance conditions and temperature in 10 Colombian cities. Those curves were obtained from a Virtual Instrument (VI) developed in LabVIEW®. With the collected information from the VI, the cities were classified taking into account 5 parameters: solar irradiance, temperature, variability of solar resource, maximum power point and Photovoltaic (PV) modules efficiency in the cities. From the VI, an analytical methodology was developed to identify the technical potential of some regions for the implementation and development of grid connected PV systems. Additionally, users were able to get information on the solar irradiance potential, helping to achieve an accurate design of the PV systems.

Distribución del tamaño de partícula por dispersión dinámica de luz de la tetracarboxifenilporfirina de cobre (II) anclada al dióxido de titanio

La sensibilizacion del dioxido de titanio con porfirinas es esencial para la generacion de especies reactivas del oxigeno inducida con luz visible. Sin embargo, estos sensibilizadores tienden a lixiviarse en el medio de reaccion. La distribucion del tamano de particula es una propiedad fundamental para caracterizar sistemas de particulas en suspension. En este trabajo se estudio la distribucion del tamano de particula de la tetracarboxifenilporfirina de cobre (II) anclada sobre dioxido de titanio por la tecnica de dispersion dinamica de luz. Los resultados indican que la tecnica de dispersion dinamica de luz es adecuada para determinar la estabilidad de estos sistemas, mostrando un solo tipo de particula para el sistema TCPPCu/TiO2 con diametro promedio de 211,1 nm.

Characterization of the solar resource for ten cities in Colombia

The quality of service indicators in distribution networks represents a main concern in the power industry nowadays, and the power quality measurements (PQ) are an important part to obtain these indicators. When a PQ disturbance is detected and measured it has to be characterized to obtain the parametric data related with it; this way, it can be classified according to international standards. To make the characterization process it has been relevant the use of digital signal processing techniques like digital filtering and shifting functions. In this paper digital filters, cancelation filters and delay functions are proposed to characterize PQ disturbances. The results suggest that the developed algorithms can be easily implemented in field instruments due to their simplicity and low computational effort required for his operation. All he developments were made using National Instruments LabVIEW® and conventional PC architectures.