Browsing by Author "Schott, Eduardo"

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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 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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    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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    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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    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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    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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    Furfural adsorption on V2O5 surface: A combined experimental-theoretical study
    (2024) Lizana, Ignacio; Schott, Eduardo; Saavedra-Torres, Mario; Hidalgo-Rosa, Yoan; Pecchi, Gina; Karelovic, Alejandro; Zarate, Ximena
    The adsorption of furfural on the V 2 O 5 surface was investigated using experimental and theoretical methods. In situ Diffuse Reflectance Infrared Fourier-Transform Spectroscopy results show the presence of physi- and chemisorption phenomena, where trans -furfural is mostly chemisorbed at the beginning of the adsorption process. These results are in agreement with theoretical DFT results, as the most thermodynamically favored configurations corresponds to the chemisorbed trans -furfural (T1) and cis -furfural (C1) with binding energies of -1.83 and -2.05 eV.
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    High Performance of Mn2O3 Electrodes for Hydrogen Evolution Using Natural Bischofite Salt from Atacama Desert: A Novel Application for Solar Saline Water Splitting
    (2024) Galleguillos-Madrid, Felipe M.; Salazar-Avalos, Sebastian; Fuentealba, Edward; Leiva-Guajardo, Susana; Caceres, Luis; Portillo, Carlos; Sepulveda, Felipe; Brito, Ivan; Cobos-Murcia, Jose Angel; Rojas-Moreno, Omar F.; Jimenez-Arevalo, Victor; Schott, Eduardo; Soliz, Alvaro
    Solar saline water splitting is a promising approach to sustainable hydrogen production, harnessing abundant solar energy and the availability of brine resources, especially in the Atacama Desert. Bischofite salt (MgCl26H2O) has garnered significant attention due to its wide range of industrial applications. Efficient hydrogen production in arid or hyper arid locations using bischofite solutions is a novel and revolutionary idea. This work studied the electrochemical performance of Mn2O3 electrodes using a superposition model based on mixed potential theory and evaluated the superficial performance of this electrode in contact with a 0.5 M bischofite salt solution focusing on the hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) that occur during saline water splitting. The application of the non-linear superposition model provides valuable electrochemical kinetic parameters that complement the understanding of Mn2O3, this being one of the novelties of this work.
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    Highly efficient hydrogen evolution reaction, plasmon-enhanced by AuNP-l-TiO2NP photocatalysts
    (2020) Castillo-Rodriguez, Judith ; Ortiz, Pedro D. ; Isaacs, Mauricio ; Martinez, Natalia P. ; O’Shea, James N. ; Hart, Jack ; Temperton, Robert ; Zarate, Ximena ; Contreras, David ; Schott, Eduardo
    A set of AuNPs-l-TiO2NP nanoaggregates which showed efficient covering of the semiconductor's surface by AuNPs, as well as appropriate AuNP sizes for effective sensibilization were used as photocatalysts for the hydrogen evolution reaction (HER). Three aliphatic short-chain linkers: 3-mercaptopropionic acid (MPA), thioglycolic acid (TGA) and thiolactic acid (TLA) were used as stabilizing agents. The slight structure variations of the linkers did not produce differences in the AuNP size and morphology. However, it was interesting to show how the photocatalytic performance of the nanoaggregates is dependent on the linker present, as well as to determine the influence of the Au/TiO(2)ratio. It was found that TGA gave the best performance at a longer irradiation time, though high amounts of H(2)were also obtained for the other two linkers. Furthermore, for all samples large amounts of hydrogen were obtained, which are significantly higher than that usually obtained with plasmon-sensitized TiO(2)nanostructures. In addition, high amounts of H(2)were obtained after five catalytic cycles for all samples, showing the suitability of these nanoaggregates for the photoinduced HER.
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    In situ formation of sub nanometer cobalt particle with platinum nanocrystal for high performance oxygen reduction reaction electrocatalyst
    (2024) Khalid, Mohmmad; Honorato, Ana Maria Borges; Zarate, Ximena; Zaman, Shahid; Schott, Eduardo; Shahgaldi, Samaneh
    Hitherto, platinum (Pt) is the most active electrocatalyst for the oxygen reduction reaction (ORR) of the proton exchange membrane fuel cells (PEMFCs). Enhancing the performance and reducing the use of costly Pt is of great significance for the wider adoption of PEMFCs. The present research demonstrates in situ synthesized Pt nanocrystal immobilized with sub nanometer sized cobalt (Co) particles (<= 0.3 nm) loaded on ketjenblack carbon (KB) support via a simple polyol method as a highly active ORR electrocatalyst. The as synthesized Pt4.1Co/KB catalyst featured a more positive halfwave potential of 0.925 V with a resultant of 1.8 times higher mass activity than Co free Pt/KB catalyst at 0.9 V in 0.1 M HClO4 and insignificant decay in ORR performance after 30,000 potential cycles. The excellent electrocatalytic performance of Pt4.1Co/KB has also been proven in a practical H2/ air fuel cell, demonstrating a maximum peak power density of 1.08 W/cm2, comparable to the standard Pt/CTKK (47 %) catalyst. The improved ORR performance of Pt4.1Co/KB is attributed to the incorporation of sub nanometer sized Co particles, which synergistically enhance the activity and stability. Computational studies using periodic density functional theory calculations also suggest that the integration of ultrafine Co nanoparticles shifted the Pt contribution to the density of states towards higher energy levels, thereby facilitating the ORR process for the Pt4.1Co/KB catalyst. This work provides a distinctive development of an efficient and robust ORR catalyst for advancing PEMFCs.
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    Methylxanthines for halogen bonded cocrystals with 1,4-diiodotetrafluorobenzene: green synthesis, structure, photophysics and DFT studies
    (2024) Benito, Monica; Nunez, Rosario; Sinha, Sohini; Roscini, Claudio; Hidalgo-Rosa, Yoan; Schott, Eduardo; Zarate, Ximena; Molins, Elies
    Four new halogen-bonded cocrystals of biological methylxanthines, named caffeine, theophylline and theobromine, have been prepared with 1,4-diiodotetrafluorobenzene as a halogen bond donor by mechanochemical and solution processes. For theophylline, N & ctdot;I and N & ctdot;O interactions were observed, while for caffeine and theobromine, only N & ctdot;I was detected. The solids were characterized by PXRD, SC-XRD, FTIR and thermal methods (TGA-DSC analyses). In addition, the solid-state photoluminescence properties of the methylxanthines and their respective cocrystals have been studied and quantum chemistry calculations have been performed to rationalise and understand the electronic and optical properties of all compounds. This work provides a triad of natural methylxanthines capable of forming halogen-bonded multicomponent systems that can give rise to a cocrystal-to-crystal transformation with off-on luminescence activation.
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    Organic radicals stabilization in natural rubber: Discerning the influence of thermo-oxidation using chemically modified or unmodified lignin as antioxidant
    (2024) Troncoso-Ortega, Eduardo; Castano-Rivera, Patricia; Romero, Romina; Henriquez, Adolfo; Mendez, Camila; Schott, Eduardo; Contreras, David
    We have implemented a lignin compatibilization strategy through silylation and elaborated NR compounds with lignin and silylated lignin. Then, the lignin's contribution to the preservation of physico-mechanical properties and stability of the materials obtained against thermo-oxidation was studied. Thus, our work considered the indirect study of the antioxidant activity on NR compounds by determining the physico-mechanical properties before and after accelerated thermo-oxidative aging, which allowed us to determine that the increase in crosslinking density during the initial hours of accelerated aging was the main observed cause associated with a higher tensile strength retention rate (TSRR: 13.4 %) in NR compound with 5 phr of lignin (CL5) versus a TSRR: 4.7 % for the compound with 5 phr of silylated lignin (CL5Si1). On the other hand, the direct study of the antioxidant capacity by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) using oxygen atmosphere indicated greater thermal stability in NR compounds when lignin is not silylated. The maximum degradation temperature for the CL5 compound was 341.6 degrees C, while for the CL5Si1 compound it was 328.6 degrees C. The oxidation induction temperature (OITtemp) in the CL5 compound was 190.9 degrees C with a peak at 221.0 degrees C, while for CL5Si1 it was 170.3 degrees C with a peak at 194.1 degrees C, indicating again that unsilylated lignin is more suitable as an antioxidant. Finally, through Electron Paramagnetic Resonance (EPR), we determined that the radical quenching effect due to the presence of lignin was significant as the lignin content increases, with a reduction in radical presence close to 50 % compared to a reference compound without lignin.
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    Photocatalytic Degradation of Methylene Blue under Visible Light Using TiO2 Thin Films Impregnated with Porphyrin and Anderson-Type Polyoxometalates (Cu and Zn)
    (2022) Sanguino, Alexander; Diaz-Uribe, Carlos; Duran, Freider; Vallejo, William; Guzman, Leidy; Ruiz, Daniela; Puello, Esneyder; Quinones, Cesar; Schott, Eduardo; Zarate, Ximena
    In this work, tetra(4-carboxyphenyl)porphyrin (TCPP) and two Anderson-type polyoxomolybdates (containing Cu and Zn, respectively; CuPOM, ZnPOM) were synthesized and deposited on TiO2 thin films. The properties of the obtained materials were characterized through UV-vis spectroscopy, Fourier transform infrared spectroscopy (FT-IR), diffuse reflection spectroscopy, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The adsorption and photodegradation under the visible light irradiation of methylene blue (MB) were studied for TiO2, TCPP/TiO2, TCPP/CuPOM/TiO2 and TCPP/ZnPOM/TiO2 thin films in aqueous solution. The results of the diffuse reflectance showed two bands in the visible light spectrum for the TCPP/POM/TiO2 systems compared to unmodified TiO2 that does not show any bands in the same region of the spectrum. The TCPP/POM/TiO2 systems showed a higher removal of MB, with an adsorption rate near to 31% for the TCPP/CuPOM/TiO2 film compared to 9% adsorption on the TiO2 film. The kinetic results show that the pseudo-second order model was the best fitting model for the MB adsorption process onto fabricated materials. The photodegradation studies under visible light showed a better performance on TCPP/POM/TiO2 thin films, with an efficiency in the MB photodegradation of near 49% and 44% in aqueous solution for TCPP/CuPOM/TiO2 and TCPP/ZnPOM/TiO2, respectively. The reusability test indicated that the porphyrin films are moderately stable after the performed cycles.
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    Photocatalytic study of TiO2 thin films modified with Anderson-type polyoxometalates (Cr, Co and Ni): Experimental and DFT study
    (2023) Diaz-Uribe, Carlos; Duran, Freider; Vallejo, William; Puello, Esneyder; Zarate, Ximena; Schott, Eduardo
    In this work, three Anderson-type polyoxomolybdates (POMs) with general formula (NH4)6-n[XMo6O24H6]- 6+n where X = Co3+, Cr3+, and Ni2+ were deposited on TiO2 thin films Furthermore, the methylene blue (MB) dye adsorption capacity and photocatalytic degradation were studied. Morphological results show that the POMs/TiO2 films have a more heterogeneous surface in terms of particle size and distribution than bare TiO2 films. Optical characterization indicated that the CrMo6/TiO2 material had the lowest band gap energy with a value of 2.8 eV. The adsorption results show that the maximum percentage of MB adsorption was 37 % for NiMo6/TiO2 while bare TiO2 has only 9.2 %. The MB adsorption on POMs-TiO2 was modeled using and the Freundlich model showed the best fit in all studied films for MB removal. The MB photodegradation values shows this tendency 12 % for bare TiO2, 55 % for NiMo6/TiO2, 73 % for NiMo6/TiO2 and, 83 % for CrMo6/ TiO2. Finally, DFT calculations were performed to characterize the geometry and electronic structure of the all compounds studied in this work, with the aim to explain the observed experimental results.
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    Photophysical characterization of tetrahydroxyphenyl porphyrin Zn(II) and V(IV) complexes: experimental and DFT study
    (2023) Diaz-Uribe, Carlos; Rangel, Daily; Vallejo, William; Valle, Roger; Hidago-Rosa, Yoan; Zarate, Ximena; Schott, Eduardo
    Photodynamic therapy (PDT) is a promising technique for the treatment of various diseases. In this sense, the singlet oxygen quantum yield (& phi;( increment )) is a physical-chemical property that allows to stablish the applicability of a potential photosensitizers (PS) as a drug for PDT. In the herein report, the & phi;( increment ) of three photosensitizers was determined: metal-free tetrahydroxyphenyl porphyrin (THPP), THPP-Zn and the THPP-V metal complexes. Their biological application was also evaluated. Therefore, the in vitro study was carried out to assess their biological activity against Escherichia coli. The metal-porphyrin complexes exhibited highest activities against the bacterial strain Escherichia coli. at the highest concentration (175 & mu;g/mL) and show better activity than the free base ligand (salts and blank solution). Results indicated a relation between & phi;( increment ) and the inhibitory activity against Escherichia coli, thus, whereas higher is the & phi;( increment ), higher is the inhibitory activity. The values of the & phi;( increment ) and the inhibitory activity follows the tendency THPP-Zn > THPP > THPP-V. Furthermore, quantum chemical calculations allowed to gain deep insight into the electronic and optical properties of THPP-Zn macrocycle, which let to verify the most probable energy transfer pathway involved in the singlet oxygen generation.
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    Polymers of intrinsic microporosity containing aryl-phthalimide moieties: synthesis, modeling, and membrane gas transport properties
    (2023) Rodriguez-Gonzalez, Fidel E.; Soto, Cenit; Palacio, Laura; Montero-Alejo, Ana L.; Escalona, Nestor; Schott, Eduardo; Comesana-Gandara, Bibiana; Terraza, Claudio A.; Tundidor-Camba, Alain
    High-performance polymers for membrane gas separation require the careful design of the structure-porous relationship. In this work, five phthalimide-based polymers of intrinsic microporosity (PIMs) were obtained via the double nucleophilic aromatic substitution with the commercially available 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethylspirobisindane (TTSBI) monomer. The phthalimide monomers were synthesized considering different sizes and positions of the alkyl-substituents to evaluate their influence on the physical properties of the polymers and their potential use as gas separation membranes. Four polymers were soluble in the low-boiling solvents chloroform and tetrahydrofuran, facilitating the casting of self-standing films to evaluate their gas separation properties. The thermally stable membranes showed 5% weight lost between 537 ? and 549 ?. As powders, these four polymers showed apparent BET surface areas ranging from 434 to 661 m(2) g(-1). The experimental BET surface areas correlated with those obtained by molecular simulation models of the synthesized polymers. A linear function is proposed as a tool to predict, with a known uncertainty, the surface area values of this type of polymer from the corresponding computational models. As a trend, increasing the volume of the ortho-substituent in the aryl-phthalimide group increases the permeability of the membranes, reaching generally better performances than Matrimid (R) and close to those of PIM-1, considering their place on the Robeson diagrams of the O-2/N-2, CO2/CH4 and CO2/N-2 gas pairs. Aging studies between 63 and 122 days showed a decrease in permeability, accompanied by the typical increase in selectivity that tends to move the data parallel to the upper Robeson limits.
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    Rare-earth-based metal-organic frameworks with improved visible-light-harvesting properties: a quantum chemistry study
    (2023) Hidalgo-Rosa, Yoan; Saavedra-Torres, Mario; Koivisto, Bryan D.; Treto-Suarez, Manuel A.; Paez-Hernandez, Dayan; Zarate, Ximena; Schott, Eduardo
    This report proves that improving the visible-light-harvesting properties in rare-earth-based metal-organic frameworks (RE-MOFs) (labelled as RE-UiO-66, UiO = University of Oslo MOFs), with the aim of performing as potential visible-light-driven photocatalysts, is achievable. Thus, the design of MOFs with specific applications, especially those involving sunlight and material interactions, represents a growing field, which has been addressed in the herein work using quantum mechanical tools. We achieved to relate the light absorption properties with the structure in systems Y-UiO-66, Sc-UiO-66 and La-UiO-66, by evaluating the inclusion of well-known electron donor substituents in the structure of the 1,4-benzenedicarboxylate (BDC) linker (i.e. BDC-R, R: -CH3, -OH, -SH and -NH2). The electronic structure and optical properties of Y-UiO-66 were rigorously investigated using computational techniques combining molecular and periodic density functional theory (DFT) calculations. As a remarkable result, it was shown that including the groups -SH or -NH2 in the BDC linker, induced a shift in the absorption bands to the visible region (>= 400 nm). Hence, a group of new RE-MOFs materials with optimal structural and photocatalytic properties is proposed. This could encourage researchers to prepare these new materials to be tested in photocatalysis, such as cleaving the C-H bond, water splitting or photocatalytic degradation of organic contaminants.
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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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    The development of Au-titania photoanode composites toward semiflexible dye-sensitized solar cells
    (2023) Castillo-Rodriguez, Judith; Ortiz, Pedro D.; Mahmood, Reeda; Gossage, Robert A.; Llanos, Jaime; Espinoza, Dario; Zarate, Ximena; Koivisto, Bryan D.; Schott, Eduardo
    Considering the widespread use of windows in modern urban landscapes, converting these substrates into photovoltaic devices would remarkably impact modern energy generation. A flexible dye-sensitized solar cell (DSSC) architecture is preferred for such applications. A key component of the DSSC is the dye-sensitized photoanode. Herein, we examine different nanoparticle composites within the semiconductor anode formulation and their effect on device performance. Mesoporous titania particles (TiO2) modified with Au-nanoparticles (TiO2@AuNPs) were synthesized using precipitation strategies to assess the solvent effect on the particle size and the efficiency of the devices. The materials were then fully characterized through SEM, XRD, and DRS before and after thermal treatment. A paste prepared from the synthesized semiconductors was applied onto the substrate using the doctor blading technique. The use of high thermal treatment for glass substrates (HTT), low temperature thermal treatment (LTT), and LTT combined with 2 h of UV curing (LTT_UV) was explored. In the case of ITO/PET (flexible substrate) only low temperature thermal treatment were used (LTT and LTT_UV). After characterization (XRD and DRS), the anodes were loaded using a metal-free dye. To complete the comparison, several groups of cells were characterized: considering solvent (EtOH and EtOH:H2O), thermal treatment (HTT, LTT, and LTT_UV), and semiconductor material (TiO2 and TiO2@AuNP). Rigid (glass anode-glass cathode) and semiflexible (flexible anode-glass cathode) DSSCs were obtained with efficiencies from 0.03% to 2.4%, with a substantial performance difference seen using different thermal treatments, and a mild to low effect on semiconductor composition and the used substrate.
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    Thermodynamic Study of Mehtylene Blue Adsorption and Photocatalytic Degradation on The N-Doped TiO2 Thin Films: A DFT and Experimental Study
    (2024) Duran, Freider; Diaz-Uribe, Carlos; Vallejo, William; Vargas, Ximena; Bohorquez, Arnold R. Romero; Schott, Eduardo; Zarate, Ximena
    N-Doped TiO2 coatings (N-TiO2) were synthesized and characterized. The effect of the doping process on the physical-chemical properties and photocatalytic efficiency of Methylene Blue (MB) under visible light irradiation were studied. The bare TiO2 showed only anatase crystalline structure. Furthermore, after the doping process, a slight transition from anatase to rutile was verified. The HRXPS confirmed that the doping process was effective. The N-2 sorption using the BET assay showed a slight increase in surface area after the doping process. MB adsorption kinetic showed also a slight increase for doped TiO2 films, showing as best fitting the Langmuir model. Furthermore, a modification on the electronic structure was observed, showed by the modification of the optical absorption profile in the doped material. The results showed that the MB adsorption on N-TiO2 thin films was endothermic (Delta H=11 kJ mol(-1)) and a spontaneous process (Delta G=-6.45 kJ mol(-1)). We performed DFT calculations to three simulated doped-structures. The Gap value, the global reactivity indexes and, the Fukui function isosurfaces are presented. Finally, the scavenger tests suggested that O-2(center dot) and OH center dot could be the main ROS driving the photocatalytic process.