Browsing by Author "Zarate, Ximena"

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    A Computational Chemistry Approach to the Molecular Design of SiO2 Nanoparticles Coated with Stearic Acid and Sodium Stearate in Ethanol Solvent.
    (2023) Galarza-Acosta, Gabriela L.; Parra, Jose G.; Hernandez-Bravo, Raiza; Iza, Peter; Schott, Eduardo; Zarate, Ximena; Castillo, Jimmy; Mujica, Vladimiro
    Preparation of hydrophobic SiO2 nanoparticles (NPs) coated with different surfactants is important due to their potential application in different fields of chemistry. In this work, a combined experimental and Molecular Dynamics (MD) simulation approach, is advanced to characterize the adsorption process, in ethanol as a solvent, of stearic acid and sodium stearate on SiO2 spherical NPs with different ionization degrees (0%, 10%, and 23.3%). The main objective is to gain molecular insight into the factors involved in the preparation of hydrophobic coated NPs, which involves the intervention of ion-dipole, electrostatic, and hydrogen bond-type interactions depending on the surfactants and the nature SiO2 NPs. Our results demonstrate that the SiO2 NPs have a good affinity for ethanol solvent medium., as confirmed through the analysis of the Radial Distribution Functions (RDFs)), which indicates that hydrogen bonds are formed at a distance of similar to 0.192 nm between ethanol and SiO2 NPs. The presence of Na+ ions reduce the electrostatic repulsion between the -COO- and -SiO- groups in NPs with degrees of ionization of 10% and 23.3%, because it acts as a bridge and thus favors the adsorption between the silanol and carboxylic groups. The investigation of the Potentials of Mean Force (PMFs) suggests that the adsorption on these NPs, is a spontaneous process compared with the case with 0% ionization degree. The experimental coating of the NPs was studied using Atomic Force Microscopy (AFM), a technique that allows the indirect measure of the Work of Adhesion (W-adh), a key quantity to estimate the energy needed to separate the interfaces AFM tip-sample. The experimental values of W-adh for the pure SiO2 NPs and two modified SiO2 NPs correspond to 2.01 J/m(2), 1.72 J/m(2) and 1.43 J/m(2), respectively. The main conclusion is that the interaction energies between surfactants and SiO2 NPs, estimated from MD simulations, and the W-adh obtained from AFM measurements are correlated, in the sense that the reduction in the W-adh, in a solvent-free environment, corresponds to an increment of the interaction energy in the presence of the solvent. This reduction in W-adh is also associated with the fact that the nature of the coating of the SiO2 NPs surfaces increases the NPs hydrophobicity. Our analysis provides a path for the computational design and the prediction of hydrophobicity of coated NPs, which is the main focus of our work.
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    A DFT/TDDFT Study of Porphyrazines and Phthalocyanine Oxo-Titanium Derivatives as Potential Dyes in Solar Cells
    (2011) Zarate, Ximena; Schott Verdugo, Eduardo Enrique; Arratia Pérez, Ramiro
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    A new zero-dimensional (0D) hybrid bismuth (III) halide: Synthesis, crystal structure, thermal analysis, photophysical properties and DFT calculations
    (2024) Msaoura, Selma; Benito, Monica; Molins, Elies; Khirouni, Kamel; Zarate, Ximena; Saavedra-Torres, Mario; Schott, Eduardo; Houas, Ammar; Rayes, Ali
    Low-dimensional organic-inorganic hybrid Bi(III) halides, with organic N, O-heterocycles, are promising solid -state photoluminescent materials, but are underexplored. In this work, we present the synthesis and charac-terization of a novel bismuth (III) hybrid salt, namely (C8H12NO)(4)[Bi2Cl10] (referred as (1)). (1) was synthesized using a solvent-evaporation method and extensively characterized using various techniques. The crystal structure of (1) was determined to be zero-dimensional (0D). In this structure, the individual bioctahedral [Bi2Cl10](4-) dimers, which share edges, are completely isolated from each other. These dimers are separated by large 4-methoxybenzylammonium cations (C8H12NO)(+). The latter are crucial for the crystal structural stability by balancing [Bi2Cl10](4-) dimer charges and maintaining overall integrity. Solid-state diffuse reflectance UV-Vis spectrum demonstrates that (1) is a semiconductor with a band gap of 3.32 eV. Its photoluminescence spectrum exhibits intense blue emission when exposed to UV light, with CIE chromaticity coordinates of (0.22, 0.21). Theoretical calculations suggest that the emission with multiple centers originates both from a charge transition between (C8H12NO)(+) and Bi2Cl104- ions and from excited-state proton transfer (ESPT) processes related to fluo-rescence properties. These ESPT processes occur through C-H center dot center dot center dot pi and C-H center dot center dot center dot O intermolecular hydrogen bonding between the organic cations.
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    A theoretical study of substituted indeno[1,2b]fluorene compounds and their possible applications in solar cells
    (2015) Martinez, Ivan; Zarate, Ximena; Schott Verdugo, Eduardo Enrique; Morales Verdejo, César Aarón; Castillo Suzarte, Francisco Javier; Manriquez, Juan Manuel; Chávez Madariaga, Ivonne; Martinez, Ivan; Zarate, Ximena; Schott Verdugo, Eduardo Enrique; Morales Verdejo, César Aarón; Castillo Suzarte, Francisco Javier; Manriquez, Juan Manuel; Chávez Madariaga, Ivonne
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    Adsorption and Photocatalytic Degradation of Methylene Blue on TiO2 Thin Films Impregnated with Anderson-Evans Al-Polyoxometalates: Experimental and DFT Study
    (2023) Duran, Freider; Diaz-Uribe, Carlos; Vallejo, William; Munoz-Acevedo, Amner; Schott, Eduardo; Zarate, Ximena
    In this work, we fabricated a TiO2 thin film,and thesame film was modified with an Anderson aluminum polyoxometalate (TiO2-AlPOM). Physical-chemical characterization of thecatalysts showed a significant change in morphological and opticalproperties of the TiO2 thin films after surface modification.We applied the kinetic and isothermal models to the methylene blue(MB) adsorption process on both catalysts. The pseudo-second ordermodel was the best fitting model for the kinetic results; qe (mg/g) was 11.9 for TiO2 thin films and 14.6for TiO2-AlPOM thin films, and k (2) (g mg(-1) min(-1)) was 16.3 x10(-2) for TiO2 thin films and 28.2 x10(-2) for TiO2-AlPOM thin films. Furthermore,the Freundlich model was suitable to describe the isothermal behaviorof TiO2, K (F) (5.42 mg/g), and1/n (0.312). The kinetics of photocatalytic degradationwas fitted using the Langmuir-Hinshelwood model; k (ap) was 7 x 10(-4) min(-1) for TiO2 and 13 x 10(-4) min(-1) for TiO2-AlPOM. The comparative studyshowed that TiO2 thin films reach a 19.6% MB degradationunder UV irradiation and 9.1% MB adsorption, while the TiO2-AlPOM thin films reach a 32.6% MB degradation and 12.2% MB adsorptionon their surface. The surface modification improves the morphological,optical, and photocatalytic properties of the thin films. Finally,the DFT study supports all the previously shown results.
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    Adsorption properties of M-UiO-66 (M = Zr(iv); Hf(iv) or Ce(iv)) with BDC or PDC linker
    (2024) Gonzalez, Diego; Pazo-Carballo, Cesar; Camu, Esteban; Hidalgo-Rosa, Yoan; Zarate, Ximena; Escalona, Nestor; Schott, Eduardo
    The increasing CO2 emissions and their direct impact on climate change due to the greenhouse effect are environmental issues that must be solved as soon as possible. Metal-organic frameworks (MOFs) are one class of crystalline adsorbent materials that are thought to have enormous potential in CO2 capture applications. In this research, the effect of changing the metal center between Zr(iv), Ce(iv), and Hf(iv), and the linker between BDC and PDC has been fully studied. Thus, the six UiO-66 isoreticular derivatives have been synthesized and characterized by FTIR, PXRD, TGA, and N2 adsorption. We also report the BET surface area, CO2 adsorption capacities, kinetics, and the adsorption isosteric heat (Q(st)) of the UiO-66 derivatives mentioned family. The CO2 adsorption kinetics were evaluated using pseudo-first order, pseudo-second order, Avrami's kinetic models, and the rate-limiting step with Boyd's film diffusion, interparticle diffusion, and intraparticle diffusion models. The isosteric heats of CO2 adsorption using various MOFs are in the range 20-65 kJ mol(-1) observing differences in adsorption capacities between 1.15 and 4.72 mmol g(-1) at different temperatures due to the electrostatic interactions between CO2 and extra-framework metal ions. The isosteric heat of adsorption calculation in this report, which accounts for the unexpectedly high heat released from Zr-UiO-66-PDC, is finally represented as an increase in the interaction of CO2 with the PDC linker and an increase in Q(st) with defects.
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    Antimicrobial Activity against Fusarium oxysporum f. sp. dianthi of TiO2/ZnO Thin Films under UV Irradiation: Experimental and Theoretical Study
    (2024) Quinones, Cesar; Posada, Martha; Hormiga, Angie; Pena, Julian; Diaz-Uribe, Carlos; Vallejo, William; Munoz-Acevedo, Amner; Roa, Vanesa; Schott, Eduardo; Zarate, Ximena
    We deposited bare TiO2 and TiO2/ZnO thin films to study their antimicrobial capacity against Fusarium oxysporum f. sp. dianthi. The deposit of TiO2 was performed by spin coating and the ZnO thin films were deposited onto the TiO2 surface by plasma-assisted reactive evaporation technique. The characterization of the compounds was carried out by scanning electron microscopy (SEM) and powder X-ray diffraction techniques. Furthermore, density functional theory (DFT) and time-dependent DFT (TDDFT) calculations were performed to support the observed experimental results. Thus, the removal of methylene blue (MB) by adsorption and posterior photocatalytic degradation was studied. Adsorption kinetic results showed that TiO2/ZnO thin films were more efficient in MB removal than bare TiO2 thin films, and the pseudo-second-order model was suitable to describe the experimental results for TiO2/ZnO (q(e) = 12.9 mg/g; k(2) = 0.14 g/mg/min) and TiO2 thin films (q(e) = 12.0 mg/g; k(2) = 0.13 g/mg/min). Photocatalytic results under UV irradiation showed that TiO2 thin films reached 10.9% of MB photodegradation (k = 1.0 x 10(-3) min(-1)), whereas TiO2/ZnO thin films reached 20.6% of MB photodegradation (k = 3.9 x 10(-3) min(-1)). Both thin films reduced the photocatalytic efficiency by less than 3% after 4 photocatalytic tests. DFT study showed that the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy gap decreases for the mixed nanoparticle system, showing its increased reactivity. Furthermore, the chemical hardness shows a lower value for the mixed system, whereas the electrophilicity index shows the biggest value, supporting the larger reactivity for the mixed nanoparticle system. Finally, the antimicrobial activity against F. oxysporum f. sp. dianthi showed that bare TiO2 reached a growth reduction of 68% while TiO2/ZnO reached a growth reduction of 90% after 250 min of UV irradiation.
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    Assessing the electronic properties of bimetallic complexes with N-M-N-M cycle (M = Ag, Au and Cu)
    (2024) Zarate, Ximena; Treto-Suárez, Manuel A.; Hidalgo-Rosa, Yoan; Schott Verdugo, Eduardo Enrique
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    Bipodal dyes with bichromic triphenylamine architectures for use in dye- sensitized solar cell applications
    (2018) Abdi, Omar K.; Fischer, Benjamin J. D.; Al-Faouri, Tamara; Buguis, Francis L.; Devgan, Hardeep S.; Schott Verdugo, Eduardo Enrique; Zarate, Ximena; Koivisto, Bryan D.
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    Catalytic evaluation of MOF-808 with metallic centers of Zr(IV), Hf(IV) and Ce(IV) in the acetalization of benzaldehyde with methanol
    (Royal Society Chemistry, 2024) Arellano Valderrama, Yazmin Anay; Pazo Carballo, César Alexander; Roa, Vanesa; Hidalgo-Rosa, Yoan; Zarate, Ximena; Llanos, Jaime; Escalona Burgos, Nestor Guillermo; Schott, Eduardo
    In the context of climate change, it is of utmost importance to replace the use of fossil fuels as raw material in areas of industrial interest, for example, in the production of chemical inputs. In this context, a viable option is biomass, since by subjecting it to chemical processes such as pyrolysis, it is possible to obtain platform molecules that are the basis for the generation of value-added chemical products. Acetals are molecules obtained from biomass derIVatIVes, which have various applications in cosmetic chemistry, in the pharmaceutical industry as intermediates or final compounds, food additIVes, among others. Different catalysts have been used in the acetalization reaction, including MOFs, which have the advantage of being porous materials with high surface area values. The large surface area translates into a greater number of catalytically actIVe sites available for the reaction. Among the MOFs that have been used for this purpose is MOF-808, which is characterized by having a lower number of ligands attached to its metal cluster, therefore, it has a greater exposure of the metals that make up its structure. In this context, the work carried out studied the catalytic performance of MOF-808 when its Zr(IV) metal centers are replaced by Hf(IV) and Ce(IV) atoms in the acetalization reaction of benzaldehyde with methanol. The MOFs obtained by solvothermal synthesis were characterized by powder X-ray diffraction, N-2 adsorption and desorption, FT-IR spectroscopy, acid-base potentiometric titration, XPS and thermogravimetric analysis. The results of the catalysis indicate that the MOF with the best performance was MOF-808-Ce, which achieved conversions greater than 80% in a period of ten minutes. MOF-808-Ce exhibits a higher number of defects and therefore a higher availability of catalytic sites for the reaction to occur, which explains the better performance. Finally, the performance of MOF-808 in the acetalization of benzaldehyde with methanol was also supported by density functional theory (DFT) calculations.
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    Comparative study of the anchorage and the catalytic properties of nanoporous tio2 films modified with ruthenium (II) and rhenium (I) carbonyl complexes
    (2018) Oyarzun, Diego P.; Chardon-Noblat, Sylvie; Linarez Perez, Omar E.; Lopez Teijelo, Manuel; Zuniga, Cesar; Zarate, Ximena; Shott, Eduardo; Carreno, Alexander; Arratia-Perez, Ramiro
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    Computational design and properties elucidation of new (FAPbI3)1,x- y(MAPbBr3)y(CsPbBr3)x photoactive systems for their application in perovskite solar cells
    (2023) Borges-Martinez, Merlys; Saavedra-Torres, Mario; Schott, Eduardo; Zarate, Ximena
    The stability and performance of perovskites (PKs) in PK solar cells are a research target, which has been addressed in this work. The theoretical design of new PKs was carried out, based on the different composition of Cs. Specifically, PKs of the type (FAPbI3)1_x-y(MAPbBr3)y(CsPbBr3)x (where MA= methylammonium and FA= formamidinium) with 0
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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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    Effect of triphenylamine as electron-donor evenly spaced in 2, 4, 6 and 8 thiophene units of the main chain : synthesis and properties
    (2015) Salas Sánchez, Cristián Osvaldo; Schott Verdugo, Eduardo Enrique; Zarate, Ximena; Macleod-Carey, D.; Sobarzo Aucal, Patricio Antonio; Gatica, N.; Salas Sánchez, Cristián Osvaldo; Schott Verdugo, Eduardo Enrique; Zarate, Ximena; Macleod-Carey, D.; Sobarzo Aucal, Patricio Antonio; Gatica, N.
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    Evaluation of the affinity of asphaltene molecular models A1 and A2 by the water/oil interfaces based on a novel concept of solubility parameter profiles obtained from MD simulations
    (2023) Parra, Jose G.; Rodriguez, Geraldine; Iza, Peter; Zarate, Ximena; Schott, Eduardo
    Crude oils are formed of asphaltenes that are species soluble in certain solvents such as toluene. The dis-tribution of asphaltene models and their mixtures in water/n-heptane and water/toluene systems were explored with MD simulations. A1 and A2 asphaltene models were used for the exploration of the affinity of these compounds by the water/oil interfaces. For this, a novel concept called solubility parameter pro-files was used to characterize the polarity of the regions present in water/n-heptane and water/toluene systems. Molecules of asphaltene models, n-heptane, and toluene were described with the GROMOS53A6 force field and CHELPG atomic charges, and water molecules with the SPC model. The prediction of the affinity of A1 and A2 asphaltene models at interfaces was determined using the total solubility parameter differences calculated between these species and solvent molecules. Calculated solubility parameters show a good correlation with experimental values. Total solubility parameter differences equal to 6,dtotal = 3.76 MPa0'5 and 6,dtotal = 0.36 MPa0'5 at the water/n-heptane interface suggest that asphaltene models have a good affinity by the water/n-heptane interface in comparison with the water/toluene interface whose values were 6,dtotal = 5.82 MPa0'5 and 6,dtotal = 9.94 MPa0'5 for A1 and A2 asphaltene mod-els, respectively. It was demonstrated that the affinity of asphaltenes by a specific region of the immis-cible system is controlled by the electrostatic and dispersive contributions associated with the solubility parameter profiles.(c) 2023 Elsevier B.V. All rights reserved.
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    Experimental and Theoretical Studies of the ancillary ligand (E)-2-((3-amino- pyridin-4-ylimino)-methyl)-4,6-di-tert-butylphenol in Rhenium(I) core
    (2015) Carreno, Alexander; Gacitua, Manuel; Schott Verdugo, Eduardo Enrique; Zarate, Ximena; Manriquez, Juan Manuel; Preite, Marcelo Daniel; Ladeira, Sonia; Castel, Annie; Pizarro, Nancy; Vega, Andres; Chavez, Ivonne; Arratia-Perez, Ramiro
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    Exploring the relevance of thiophene rings as bridge unit in acceptor-bridge-donor dyes on self-aggregation and performance in DSSCs
    (2018) Zarate, Ximena; Saavedra Torres, Mario; Rodriguez Serrano, Angela; Gomez, Tatiana; Schott Verdugo, Eduardo Enrique