Browsing by Author "Vallejo, William"

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    Cyanobacterial Biomass Pigments as Natural Sensitizer for TiO2 Thin Films
    (2019) Patiño Camelo, Karen; Díaz Uribe, Carlos; Gallego Cartagena, Euler; Vallejo, William; Martínez, Vincent; Quiñones, César; Hurtado, Michel; Schott Verdugo, Eduardo Enrique
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    Cyanobacterial pigment adsorbed on TiO2 thin films
    (2024) Diaz-Uribe, Carlos; Duran, Freider; Arcon, Amado; Vallejo, William; Salazar Canas, Javier Antoni; Schott Verdugo, Eduardo Enrique; Zarate, Ximena
    The rise in toxicity related to cyanobacterial bloom in freshwater is a current problem that perturbs the trophic chain and risks the ecosystems and human health. Currently, the use of biomass as a potential source of value-added bio-products is an important goal to be achieved in the scope of a sustainable bio-economy. Thus, taking advantage of such bacteria is needed. In the present work, we studied the use of cyanobacterial biomass coming from the Malambo swamp in Colombia as a source of Phycocyanobilin (C-PC) and Chlorophyll-a (Chla) which were used as natural pigments for TiO2 thin films. The concentration obtained of C-PC and Chla extracted were 215 μg/mL and 0.417 μg/mL, respectively. We modeled the natural dye adsorption kinetics on TiO2 thin films through three different models. The Langmuir model showed the best fitting, indicating that the pigment extracted from cyanobacterial biomass can sensitize thin TiO2 film through the formation of a monolayer. Furthermore, the TiO2 films present higher adsorption of C-PC (25.8 mg/g) than Chla (23.3 mg/g). Finally, the adsorption modes were assessed using periodic DFT approximations, which is a remarkable method for studying the structure and properties of solid materials. In terms of binding energies, it was found that the dye shows the strongest interaction with TiO2 through the titanium atom. Thus, the main contribution of this work is directed to explore in deep the natural dye adsorption on TiO2 from both experimental and computational point of view.
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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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    Improvement of the photocatalytic activity of TiO2 using Colombian Caribbean species (Syzygium cumini) as natural sensitizers : experimental and theoretical studies
    (2018) Díaz Uribe, Carlos; Vallejo, William; Campos, Karina; Solano, Wilfrido; Andrade, Javier; Muñoz Acevedo, Amner; Schott Verdugo, Eduardo Enrique; Zarate, Ximena
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    Photocatalytic degradation of methylene blue by the Anderson-type polyoxomolybdates/TiO2 thin films
    (2018) Diaz Uribe, Carlos E.; Rodríguez, Angie; Utria, Daniela; Vallejo, William; Puello, Esneyder; Zarate, Ximena; Schott Verdugo, Eduardo Enrique
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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.