Carlos E. Diaz-Uribe

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.

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.

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.

Phthalocyanines: Alternative Sensitizers of TiO2 to be Used in Photocatalysis

Currently, titanium dioxide is a most researched semiconductor in photocatalysis field; however, practical applications of TiO2 are limited due to high band gap (3.2 eV). In last decades, researchers implemented several strategies to improve photoactivity of TiO2 in visible electromagnetic spectrum. Titanium dioxide (TiO2) sensitization for absorption of naturals and/or synthetics organic dyes is an important research subject in the field, and it is an efficient method to develop practical application in waste treatment. In this chapter, we review main theoretical aspects of sensitization process of TiO2 by phthalocyanines and its effect in photocatalytic properties. In the last section, we review reports of photocatalytic systems.

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.

Synthesis and characterization of Tio2 thin films doped with copper to be used in photocatalysis

In this work we studied the influence of incorporation of copper into TiO2 thin films on structural, optical and surface properties of TiO2 thin films. The as-grown TiO2 was synthesized by sol gel method using titanium isopropoxide, and the TiO2 thin films were deposited by spin coating method. TiO2 copper-doped (Cu:TiO2) was synthesized by impregnation method using Cu(NO3).H2O as source of Cu(II), the Cu:TiO2 thin films were deposited by spin coating method. The properties of the compounds obtained were evaluated by measurements of X-ray diffraction (XRD) and diffuse reflectance. The XRD results showed that Cu doping change the crystalline phase radio of the films, XRD pattern of TiO2 indicated that films grow with anatase structute, while Cu:TiO2 thin films presented a polycrystalline mixture of anatase/rutile. Reflectance analysis indicated that TiO2 presents an energy band gap of 3.25 eV and the Cu:TiO2 presents a shift-red of the band gap to 2,9 eV. The results suggest that doping with copper improved the harvesting of the TiO2 to visible radiation.