Browsing by Author "Florez, Jiress"

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    Furanyl chalcone derivatives as efficient singlet oxygen quenchers. An experimental and DFT/MRCI study
    (PERGAMON-ELSEVIER SCIENCE LTD, 2020) Diaz Uribe, Carlos; Vallejo, William; Florez, Jiress; Trilleras, Jorge; Gutierrez, Margarita; Rodriguez Serrano, Angela; Schott, Eduardo; Zarate, Ximena
    This study reports the antioxidant activity against singlet oxygen (O-1(2)) of five newly synthesized furanyl chalcones (FCs) (E)-3 (5-(4 chlorophenyl)furan-2-yl)-1-arylprop-2-en-1-ones (3a-e). Their structural difference is based on the aryl substituent as follows (Ar): 3a = -C6H4-OCH3, 3b = -C6H3-(1,2-OCH3), 3c = -C6H4OC6H4, 3d = - C10H6-(OCH3) and 3e = -C4H3O. We used a Claisen-Schmidt condensation involving a 5-(4-chlorophenyl)furan-2-carbaldehyde and the corresponding ketones under ultrasonic irradiation. Their property to O-1(2) quenching was analyzed in terms of the rate constant for the process (k(Q) at 25 degrees C) determined by the Stern-Volmer model in ethanol. For the compounds 3c, 3d and 3e, the k(Q) values are slightly larger respect to 3a and 3b. The FCs 3c behaves as the best quencher (k(Q )of 8.44 (+/- 0.09) x 10(7) M-1 s(-1)). Geometry analysis and electronic structure calculations have been performed in the framework of Density Functional Theory (DFT) and DFT/Multi-Reference Configuration Interaction (DFT/MRCI) methods. According to DFT/MRCI, a physical quenching of O-1(2) from the ground states of the FCs may not likely induce a spontaneous energy transfer processes but a chemical quenching mechanism may dominate the kinetics. (C) 2020 Elsevier Ltd. All rights reserved.
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    Removal and photocatalytic degradation of methylene blue on ZrO2 thin films modified with Anderson-Polioxometalates (Cr3+, Co3+, Cu2+): An experimental and theoretical study
    (2024) Díaz-Uribe, Carlos; Florez, Jiress; Vallejo, William; Duran, Freider; Puello, Esneyder; Roa, Vanesa; Schott, Eduardo; Zarate, Ximena
    In this work, several ZrO2 thin films modified with Anderson-type polyoxomolybdates (POMs) with general formula (NH4)6-n[XMo6O24H6]-6+n where X = Co3+, Cr3+ and, Cu2+ were prepared. Thin films were characterized through SEM and EDX assay, UV–Vis diffuse reflectance and Fourier Transform Infrared (FTIR) assay. The optical bandgap of ZrO2 thin films was determined to be 3.25 eV, while the modified thin films showed a red shift in the optical activity compared with bare ZrO2 thin films. Methylene Blue (MB) adsorption studies showed that Freundlich isotherm describes properly the experimental data for modified-ZrO2 thin films. Besides, the kinetic results showed the MB adsorption of modified-ZrO2 thin films was superior to bare ZrO2 thin film. The adsorption rate values (K2) of the pseudo-second order model follow these trend ZrO2/CrPOM > ZrO2/CoPOM > ZrO2/CuPOM > ZrO2. The photocatalytic activity of the thin films for MB decomposition under UV and Visible irradiation was studied. Among all the catalysts, the ZrO2 thin films showed the lowest photocatalytic degradation rate kap value (kap = 1.5 × 10−3 min−1), while the best result was obtained for ZrO2/CrPOM thin films (kap = 5.7 × 10−3 min−1) under UV irradiation. Besides, this was the only catalyst efficiently active in MB degradation under visible irradiation, these materials reach 10.4 % after 100 min under visible irradiation. Finally, chemical calculations supported the observed results, by means of TDDFT, EDA analysis, Fukui function and periodic DFT calculations.
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    Study of methylene blue removal and photocatalytic degradation on zirconia thin films modified with Mn-Anderson polyoxometalates
    (2024) Florez, Jiress; Díaz Uribe, Carlos; Vallejo, William; Duran, Freider; Puello, Esneyder; Salazar Canas, Javier Antoni; Zarate, Ximena; Schott Verdugo, Eduardo Enrique
    Recalcitrant pollutants are challenging to degrade during water treatment processes. Methylene blue (MB), a cationic dye, is particularly resistant to degradation and is environmentally persistent. Heterogeneous photocatalysis has emerged as a suitable strategy for removing such pollutants from water. In this work, ZrO2 thin films were modified with Anderson-type Mn-polyoxometalate (MnPOM) ((NH4)3[MnMo6O24H6]), and the efficiency of MB removal from water was studied. ZrO2 was synthesized by a sol-gel method, with thin films deposited using the doctor blade method, and ZrO2 thin films were modified using chemisorption method. The synthesized materials were characterized using SEM, EDX, UV-Vis diffuse reflectance spectroscopy and FTIR. The adsorption kinetics and isotherms for MB were studied for both bare ZrO2 and ZrO2/MnPOM composites. Optical characterization showed a band gap energy of 4.02 eV for bare ZrO2, while the ZrO2/MnPOM composite exhibited a band gap of 3.7 eV. Furthermore, ZrO2 showed lower MB removal capacity (similar to 8%) than ZrO2/MnPOM thin films (similar to 29%). The isothermal adsorption studies indicated that MB adsorption onto both bare ZrO2 and ZrO2/MnPOM followed the Langmuir adsorption model (qm = 20.6 mg g-1 for ZrO2 and qm = 62.9 mg g-1 for ZrO2/MnPOM). Furthermore, the adsorption kinetics of MB were well described by a pseudo-second-order model. Photocatalytic testing under UV irradiation showed an apparent rate constant (kap) of 2 x 10-3 min-1 for bare ZrO2 and a value of kap 5.4 x 10-3 min-1 for ZrO2/MnPOM after 100 minutes. TD-DFT calculations revealed an LMCT interaction between the ZrO2 nanoparticle and the MnPOM, which likely contributes to the enhanced photocatalytic activity of the ZrO2/MnPOM composite.