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 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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    New Pillar-MOF with Nitrogen-Donor Sites for CO2 Adsorption
    (2024) Lancheros Sánchez, Andrés Fernando; Goswami, Subhadip; Zarate, Ximena; Blanco, Elodie; Schott Verdugo, Eduardo Enrique; Hupp, Joseph T.
    A new pillar-MOF [Zn2(L)(DABCO)] was solvo-thermally synthesized by using a new linker (L = 4,4′-(1,4-phenylenebis(3,5-dimethyl-1H-pyrazole-4,1-diyl))dibenzoic acid),Zn(NO3)2·6H2O, and triethylenediamine (DABCO) as pillarlinker. It was characterized using single-crystal X-ray diffraction,powder X-ray diffraction (PXRD), thermogravimetric analysis(TGA), and scanning electron microscopy (SEM) and tested forCO2 adsorption. It exhibits dinuclear paddle−wheel nodes wherethe Zn(II) cations are coordinated by four equatorial L linkersgenerating two-dimensional sheets. DABCO acted as a pillarbinding the sheets to obtain a neutral three-dimensional frameworkthat shows one-dimensional square channels. The new pillar-layered MOF presents micro- and mesopores, and its crystallinity is preserved after activation at 160 °C × 16 h and adsorption ofCO2. Due to the presence of the pyrazole nitrogen atoms in the framework, which have an increased affinity toward CO2, this newmaterial exhibited a reasonable CO2 uptake capacity and a low isosteric enthalpy of adsorption (Hads)
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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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    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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    Tunning the optical properties of a photocatalytic metal-organic framework by means of molecular modelling
    (2023) Treto-Suarez, Manuel A.; Hidalgo-Rosa, Yoan; Ulecia, Karel Mena; Paez-Hernandez, Dayan; Koivisto, Bryan D.; Zarate, Ximena; Schott, Eduardo
    A theoretical study of reported isostructural metal-organic frameworks (MOFs) based on MIL-125-Ti4+ was performed to understand the optical properties and facilitate the rational design of new materials with potentially improved features as photocatalysts. The experimentally tested MOFs (MIL-125-Ti4+ labeled as M) were functionalized with -NH2, -CH3, and -OH substituents on the 1,4-benzene-dicarboxylate (BDC) linker (labeled as M-NH2, M-CH3, and M-OH, respectively), generating a broadened light-harvesting of the MOF and an improvement of the N-2 conversion rate. The M-NH2 showed the highest visible light absorption and N-2 photocatalysis efficiency experimentally. This substituent effect was theoretically studied via Density Functional Theory (DFT) calculations on the ground singlet (S-0) and first excited state (singlet and triplet) using Time-Dependent Density Functional Theory (TD-DFT), the Morokuma-Ziegler energy decomposition scheme, and Natural Orbital of Chemical Valence (NOCV) analysis. These tools allowed for the reproduction of the optical properties and performance in good agreement with the experiment and highlight that the N-2 conversion rate increases as the donor character of the R group improve. This effect is a result of the stabilization of the Occupied Molecular Orbitals (localized on the BDC linker), a decrease in the charge recombination, and by an increase of charge flow to the metal center favoring the photocatalytic Ti4+/Ti3+ reduction (via ligand to metal charge transfer (LMCT) transition). These systems also display a metal-ligand charge transfer (MLCT) process in the excited state favoring the emission localized in the BDC linker, which was confirmed via Complete Active Space Self-Consistent Field (CASSCF) calculation. Finally, through CASSCF, it was possible to propose two new isoreticular structures, with the -SH and -NO2 substituents (labeled as M-SH and M-NO2), with the -SH variant exhibiting optical and photocatalytic properties that could rival M with -NH2 substitution.