DigitalUM :: Browsing by browse.metadata.contributordepartment "Química Física"

Browsing by browse.metadata.contributordepartment "Química Física"

Now showing 1 - 20 of 35

Open Access
A study of the catalyst layer morphology generated by electrospray: effect of the voltage and catalyst ink aging on its performance in a proton electrolyte membrane fuel cell
(Elsevier, 2024-11-26) Gómez, Modesto A.; Navarro, Andrés J.; López-Sicilia, Irene; Fernández-Romero, Antonio J.; Santos, Florencio; Molina-García, Ángel; Hernández Cifre, José G.; López-Cascales, José J.; Química Física
Proton electrolyte membrane fuel cells are gaining relevance in different energy sectors as a viable alternative to the use of fossil fuels. Among others, the automotive industry is one of the sectors that has focused a special interest on this technology with the aim of reducing its gas emissions. Thus, with the increase in the production to great scale of proton exchange membrane fuel cells (PEMFC), the amount of catalyst demanded is expected that increase accordingly. In this context, the optimization of both, the composition of the catalyst ink used, and the technique employed for the fabrication of the catalyst layers (CL), are two of the main challenges to be solved in this field. Electrospray is an optimized technique to prepare catalyst layers (CL) for fuel cells. However, aspects such as the voltage applied in the electrospray and the aging of the catalyst inks until its use for the catalyst layer preparation, are some of the key aspects to be studied because they can significantly alter their fuel cell performance. Therefore, this work was focused on studying by cyclic voltammetry, how the voltage used in the electrospray and the ink aging alter the morphology of the catalyst layer and, consequently, their performance in a fuel cell.
Open Access
Aggregation behaviour of gold nanoparticles in saline aqueous media
(Springer, 0001-04-14) Ramón Pamiés; José Ginés Hernández Cifre; Vanesa Fernández Espín; Mar Collado-González; Francisco Guillermo Díaz Baños; José García de la Torre; Química Física; Facultades de la UMU
The evaluation of the effect of saline aqueous media in the aggregation of colloidal gold nanoparticles (AuNP) suspensions has been followed by means of both dynamic light scattering and UV–Vis spectroscopy techniques. A wide range of ionic strengths from 0 to 1 M has been covered for suspensions of AuNPs with a hydrodynamic radius of 6.5 nm. The growth of the clusters over time is described by a power law whose exponent varies with the ionic strength. Two main aggregation regimes are found in qualitative agreement with predictions of the DLVO theory. At low ionic strength, AuNPs form small aggregates that are long-term stable. When a critical electrolyte concentration is exceeded, big clusters are formed rapidly and then colloidal suspension becomes unstable and precipitation occurs. That so-called critical coagulation concentration was estimated by analyzing the time evolution of both the nanoparticle size (determined by DLS) and the plasmon peak (determined by UV–Vis spectroscopy), thus showing the validity of both techniques for such a purpose. The stability is also studied in terms of the zeta potential which approaches zero when salt concentration is above the critical coagulation concentration.
Open Access
Aggregation of gold nanoparticles in presence of the thermoresponsive cationic ciblock copolymer PNIPAAM48-b-PAMPTMA6
(MDPI, 2021-11-23) Herrera Robalino, David; Durán del Amor, María del Mar; Almagro Gómez, Carmen María; Hernández Cifre, José G.; Química Física
The adsorption of the thermoresponsive positively charged copolymer poly(N-isopropylacr ylamide)-block-poly(3-acrylamidopropyl)trimethylammonium chloride, PNIPAAM48-b-PAMPTMA6(+), onto negatively charged gold nanoparticles can provide stability to the nanoparticles and make the emerging structure tunable by temperature. In this work, we characterize the nanocomposite formed by gold nanoparticles and copolymer chains and study the influence of the copolymer on the expected aggregation process that undergoes those nanoparticles at high ionic strength. We also determine the lower critical solution temperature (LCST) of the copolymer (around 42 ºC) and evaluate the influence of the temperature on the nanocomposite. For those purposes, we use dynamic light scattering, UV-vis spectroscopy and transmission electron microscopy. At the working PNIPAAM48-b-PAMPTMA6(+) concentration, we observe the existence of copolymer structures that trap the gold nanoparticles and avoid the formation of nanoparticles aggregates. Finally, we discuss how these structures can be useful in catalysis and nanoparticles recovery.
Open Access
Analytical theory for ion transfer-electron transfer coupled reactions at redox layer/thick film-modified electrodes
(Elsevier, 2020-02) Laborda, Eduardo; González Sánchez, Joaquín; Molina, Angela; Química Física
Electrodes modified by liquid films or plasticized polymeric membranes containing a redox species offer valuable alternatives for the study of ion transfers and bimolecular electron transfers at liquid|liquid interfaces with conventional electrode arrangements and stable interfaces. The ion-to-electron (or electron-to-electron) transducer affects the electrochemical signal, complicating the accurate analysis of experimental data. This can be reduced through the use of an electrode surface-attached redox species of well-defined electrochemical behaviour. As will be demonstrated, the voltammetry of these systems show significant deviations with respect to individual charge transfers, which must be considered for appropriate diagnosis and quantitative analysis. For this, a simple analytical theory is presented here, deducing mathematical expressions for the current-potential response, as well as for the potential difference at the two polarized interfaces, the surface excess of the redox species and the ion interfacial concentrations.
Open Access
Calculation of the friction, diffusion and sedimentation coefficients of nanoplatelets of arbitrary shape
(Elsevier, 2022-12-02) Hernández Cifre, José G.; Rodríguez Schmidt, Ricardo; Almagro Gómez, Carmen M.; García de la Torre, José; Química Física
We have developed a computational scheme for the calculation of the hydrodynamic properties of nanoplatelets – or flat sheets – of arbitrary shape based on the bead-modeling methodology. The procedure has been implemented in computer codes that interface with the public-domain HYDRO++ program. When the friction coefficient calculated for the model is normalized to the value of an infinitely thin disk having the same surface area, its dependence on thickness normalized to a characteristic length of the platelet surface is very weak and depends just on the shape of the particle and not on its size. This allows for a simplified, general treatment of the dependence on thickness. In addition to examples with various peculiar shapes, we have calculated the friction coefficient of elliptical particles as well as some regular polygons. The results are presented in the form of simple equations relating the friction coefficient to the particle dimensions. The results for the friction coefficient are applied to the formulation of the experimentally measurable diffusion and sedimentation coefficients. The diffusion coefficient has a very weak dependence on thickness so that it can be employed to analyze the geometry of the surface even if the thickness is not precisely determined. However, the sedimentation coefficient depends appreciably on thickness and can be used for its precise determination. A joint analysis of diffusion and sedimentation can provide a complete determination of the nanoplatelet shape, dimensions and mass.
Open Access
Complex polysaccharide-based nanocomposites for 2 oral insulin delivery
(MDPI (Basel, Switzerland), 2020-01-15) Collado-González, Mar; Freitas, Alessandra R.; Santos, Ana Claudia; Ferreira, Nuno F.; Ferreri, Maria Cristina; Sequeira, Joana A.D.; Díaz Baños, F. Guillermo; Víllora, Gloria; Veiga, Francisco; Ribeiro, Antonio; Carissimi, Guzmán; Química Física
Polyelectrolyte nanocomposites rarely reach a stable state and aggregation often occurs. Here, we report the synthesis of nanocomposites for the oral delivery of insulin composed of alginate, dextran sulfate, poly-(ethyleneglycol) 4000, Poloxamer 188®, chitosan, and BSA. Chitosan seems to be essential for the final size of the nanocomposites. When the chitosan concentration used in the synthesis is 10-4 gcm-3, nanocomposites, microcomposites and milimetric composites are obtained. Reducing the chitosan concentration to 10-5 or 10-7 gcm-3 yields nanocomposites of 400-600 nm or 800-900 nm hydrodynamic diameter, respectively, measured by DLS. According to our results, the molecular weight of chitosan has little influence on the size of the composites. The enhanced stability of the newest nanocomposites synthesized was assessed with LUMiSizer®. The rounded shapes of the nanocomposites were confirmed by scanning electron microscopy. Analysis by HPLC revealed that, after loaded with insulin, about 80% of the drug was released from our nanocomposites.
Open Access
Density, refractive index and volumetric properties of water-ionic liquid binary systems with imidazolium-based cations and tetrafluoroborate, triflate and octylsulphate anions at T=293 to 343 K and p=0.1 MPa
(ACS Publications, 2019) Carissimi, Guzman; Montalbán, Mercedes G.; Díaz Baños, F. Guillermo; Víllora, Gloria; Química Física
The density and refractive index of ionic liquids (ILs) + water binary mixtures were determined as a function of temperature (from 293.15 to 343.15 K) at atmospheric pressure over the whole composition range in which the mixtures were miscible. To carry out a systematic study, all the ILs selected are imidazolium-based ILs with a different number of carbons in the alkyl chain of the cation and also different anions (tetrafluoroborate, triflate and octylsulphate). Specifically, the studied ILs were 1-ethyl-3-methylimidazolium tetrafluoroborate [emim][BF4], 1-butyl-3-methylimidazolium tetrafluoroborate [bmim][BF4], 1-hexyl-3-methylimidazolium tetrafluoroborate [hmim][BF4], 1-methyl-3-octylimidazolium tetrafluoroborate [omim][BF4], 1-ethyl-3-methylimidazolium triflate [emim][TfO], 1-butyl-3-methylimidazolium triflate [bmim][TfO] and 1-butyl-3-methylimidazolium octylsulphate [bmim][OcSO4]. The excess molar volumes and the deviation in the molar refraction of the binary mixtures were calculated for a better understanding of the interactions that take place between the components and successfully correlated by the Redlich-Kister empirical correlations. Bahe-Varela model, which has a more physical meaning, was also used to successfully correlate the excess molar volume values. Volumetric properties, such as apparent molar volumes, partial molar volumes, isobaric thermal expansion coefficients, partial molar volumes at infinite dilution and excess partial molar volumes at infinite dilution were also calculated in order to obtain information about the influence of composition and temperature on the thermodynamic behavior of the selected ILs and water in the mixture. The results are discussed in order to understand the formation of hydrogen bonds between components of the mixture and the possible packing effects that take place in the mixing process. Density and refractive index experimental data were correlated by the Lorentz-Lorenz, Wiener, Dale-Gladstone and Eykman equations to determine the relationship between both parameters, and a good agreement between the experimental and calculated refractive index values was obtained.
Open Access
Electrochemical determination of kinetic parameters of surface confined redox probes in presence of intermolecular interactions by means of Cyclic Voltammetry. Application to TEMPO monolayers in gold and platinum electrodes
(Elsevier, 2021-01-01) González Sánchez, Joaquín; Sequí Castellano, Alfonso; Química Física
Application of Cyclic Voltammetry to the characterisation of redox kinetics of surface confined redox probes is usually based on the linear regression of the peak potentials versus the logarithm of the scan rate under fully irreversible redox conditions by following the well-known method due to E. Laviron. This method implicitly assumes the Butler-Volmer formalism under ideal conditions, a fact that, in spite of the broad use of this method, strongly restrict its applicability. Here, we propose a combination of the Marcus-Hush-Chidsey formalism and the presence of intermolecular interactions in order to extract kinetic information of the CV curves. Full-width at half-maximum (fwhm) and its correlation with the peak potentials reveals to be very useful to evaluate both kinetics and interactions influences with high sensitivity and accuracy. Experimental analysis of the CV curves of electroactive monolayers of the persistent radical TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) directly attached to gold and platinum electrodes in two aprotic solvents (Ethanol and Propylene Carbonate) have been carried out.
Open Access
Exploring the physicochemical and antimicrobial properties of gold-chitosan hybrid nanoparticles composed of varying chitosan amounts.
(Elsevier, 2020) Mohamady Hussein, Mohamed A.; Díaz Baños, F. Guillermo; Grinholc, Mariusz; Abo Dena, Ahmed S.; El-Sherbiny, Ibrahim M.; Megahed, Mosaad; Química Física
A green synthesis method for gold-chitosan hybrid nanoparticles (Au-CS hNPs) using different concentrations of CS as a capping/reducing agent is reported to investigate the effect of CS concentration on the physicochemical properties as well as the antimicrobial activity of the developed Au-CS hNPs. The as-synthesized Au-CS hNPs were characterized using visible spectrophotometry, FTIR, dynamic light scattering, DSC, XRD, SEM-EDX and TEM. The size of the formed hNPs ranges from 16.9 ± 3.9 nm (highest CS concentration) to 34.7 ± 7.6 nm (lowest CS concentration). It was noticed that increasing the amount of CS increases the ζ-potential from +25.1 to +53.1 mV and enhances the 6-months stability of the produced Au-CS hNPs. Furthermore, the obtained results indicated that the antimicrobial activity, in terms of MIC and CFU assays, is directly proportional to the amount of CS used in the preparation procedure. FTIR analysis revealed that the mechanism of formation of the Au-CS hNPs may involve complexation of CS with Au ions via its NH2 and OH groups followed by the chemical reduction of Au ions to metallic Au NPs. Eventually, higher amounts of CS are necessary for synthesizing highly stable Au-CS hNPs with small size, homogeneous shape and potent antibacterial/antifungal properties.
Open Access
Extraction of Organic Compounds Involved in the Kinetic Resolution of rac-2-Pentanol from n-Hexane by Imidazolium-based Ionic Liquids: Liquid-Liquid Equilibrium
(Elsevier B.V., 2018) Montalbán, Mercedes G.; Collado-González, Mar; Lozano-Pérez, A. Abel; Díaz Baños, F. Guillermo; Víllora, Gloria; Química Física
This paper focuses on the use of ionic liquids (1-butyl-3-methylimidazolium methylsulphate, [bmim+][MeSO4-], and 1-ethyl-3-methylimidazolium acetate, [emim+][Ac-]) to extract organic compounds involved in the racemic resolution of rac-2-pentanol (rac-2-pentanol, vinyl butyrate, rac-2-pentyl butyrate or butyric acid) from a mixture of one of these organic compounds with n-hexane. Liquid–liquid equilibrium data were experimentally obtained for seven ternary systems comprising an ionic liquid + rac-2-pentanol, vinyl butyrate, rac-2-pentyl butyrate or butyric acid + n-hexane at T=303.15 K and atmospheric pressure. Binodal curves were measured applying the well-known procedure based on the observance of the cloud point while the compositions of the tie lines were calculated from refractive index and density measurements (the phase rich in the ionic liquid) and by gas cromatography (the phase rich in n-hexane). Selectivity values and the solute distribution ratio were utilized to test the possibility of the use of these ionic liquids as extractive solvents of the organic compounds implicated in the kinetic separation of the R- and S-enantiomers of rac-2-pentanol. The liquid-liquid equilibrium data of the ternary systems examined here have not previously been described in the literature.
Open Access
Functionalized Nanoplastics (NPs) Increase the Toxicity of Metals in Fish Cell Lines
(MDPI (Basel, Switzerland), 2021) González Fernández, Carmen; Díaz Baños, F. Guillermo; Esteban Abad, María Ángeles; Cuesta, Alberto; Química Física
Nanoplastics (NPs) are one of the most abundant environment‐threatening nanomaterials on the market. The objective of this study was to determine in vitro if functionalized NPs are cytotoxic by themselves or increase the toxicity of metals. For that, we used 50 nm polystyrene nanoparticles with distinct surface functionalization (pristine, PS‐Plain; carboxylic, PS‐COOH; and amino PS‐NH2) alone or combined with the metals arsenic (As) and methylmercury (MeHg), which possess an environmental risk to marine life. As test model, we chose a brain‐derived cell line (SaB‐1) from gilthead seabream (Sparus aurata), one of the most commercial fish species in the Mediterranean. First, only the PS‐NH2 NPs were toxic to SaB‐1 cells. NPs seem to be internalized into the cells but they showed little alteration in the transcription of genes related to oxidative stress (nrf2, cat, gr, gsta), cellular protection against metals (mta) or apoptosis (bcl2, bax). However, NPs, mainly PSCOOH and PS‐NH2, significantly increased the toxicity of both metals. Since the coexistence of NPs and other pollutants in the aquatic environment is inevitable, our results reveal that the combined effect of NPs with the rest of pollutants deserves more attention.
Open Access
General Explicit Mathematical Solution for the Voltammetry of Nonunity Stoichiometry Electrode Reactions: Diagnosis criteria in Cyclic Voltammetry
(American Chemical Society, 2020-01-31) Gomez-Gil, Jose María; Laborda Ochando, Eduardo; Molina, Angela; Química Física
Electrochemical reactions can effectively follow nonunity stoichiometries as can be found in the electrochemistry of halides, hydrogen and metal complexes. The voltammetric response of these systems shows peculiar deviations with respect to the well-described features of the 1:1 stoichiometry. With the aim of specifying such differences, a rigorous and manageable analytical theory is deduced for the complete characterization of reversible electrode processes with complex stoichiometry in cyclic voltammetry (CV) at macroelectrodes. Particularly, the main features of the CV of 2:1, 1:2, 3:1 and 1:3 processes (that is, the peak currents and potentials and the influence of the scan rate and of the species concentration and diffusion coefficients) are given and compared with the 1:1 case in order to propose unambiguous diagnostic criteria of the stoichiometry of the electrode reaction. Also, expressions for the concentration profiles and surface concentrations of the redox species are given.
Open Access
Guidelines for the Voltammetric Study of Electrode Reactions with Coupled Chemical Kinetics at an Arbitrary Electrode Geometry
(ACS Publications, 2019-04-02) Gómez-Gil, José María; Laborda Ochando, Eduardo; Molina, Angela; Química Física
Open Access
High pressure phase equilibria for binary mixtures of CO2 + 2-pentanol, vinyl butyrate, 2-pentyl butyrate or butyric acid systems
(Elsevier, 2018) Carissimi, Guzman; Montalbán, Mercedes G.; Díaz Baños, F. Guillermo; Víllora, Gloria; Química Física
High pressure phase equilibrium for four binary systems, (CO2 + 2-pentanol, CO2 + vinyl butyrate, CO2 + 2-pentyl butyrate and CO2 + butyric acid), were measured at three temperatures of (313.15, 323.15 and 333.15) K and pressures up to 11 MPa. These four organic compounds are those involved in the kinetic resolution of rac-2-pentanol and their phase equilibria play a significant role in the separation processes of the reaction compounds. Phase behaviour measurements were taken using a synthetic method in a variable volume high-pressure cell. It was checked that the solubility of CO2 in the four systems decreases with increases in temperature at a constant pressure and all systems present type-I phase behaviour within scope of this work. Modifications of Henry's Law and Peng-Robinson and Soave-Redlich-Kwong equations of state combined with the Quadratic mixing rule were used to correlate experimental equilibrium data to determine the phase behaviour of these systems.
Open Access
Hydrodynamic properties of biomacromolecules and macromolecular complexes: concepts and methods. A tutorial mini-review
(Elsevier, 2020-04-17) García de la Torre, José; Hernández Cifre, José G.; Química Física
This article is intended to be an overview of the current possibilities offered by hydrodynamic methods in the calculation of properties and prediction of the behavior of biomacromolecules in solution. First, we briefly cover the experimental techniques, mentioning their fundamentals and current status. Using a tutorial approach, we provide basic hints to understand conceptual aspects of macromolecular hydrodynamics which underlie the instrumental methods and the modeling and computational procedures. The description is focused on the bead model methodology as implemented in the HYDRO suite of computer programs. For rigid particles, we cover simple models, such as ellipsoids and cylinders, to the most detailed models with atomic resolution. The fundamentals and applicability of the basic random coil and wormlike models for flexible particles are also briefly described. In addition to the simple linear, more or less flexible chain, flexibility may appear in other more specific forms. These cases can be treated by Monte Carlo and Brownian simulation methods, for which computational tools are also available. Finally, we present in some detail the applicability of these tools for unfolded and intrinsically disordered proteins. For the particular case of partially disordered proteins comprising both globular domains and flexible linkers or tails, solution properties can be accurately predicted, and this validation makes the methodology quite promising for future work.
Open Access
Influence of Intermolecular Interactions in the Redox Kinetics Performance of Surface Confined Probes by Square Wave Voltammetry
(2019-10) Gonzalez, Joaquin; Sequí Castellano, Jose Alfonso; Química Física
Analysis of the Square Wave Voltammetry (SWV) responses of surface confined electroactive probes under finite kinetics conditions, by considering the influence of intermolecular interactions on the current, is presented. This non-ideality gives rise to very significant deviations in the most relevant features of the current potential response as compared with predictions of ideal models. The theoretical model does not require that the dependence of the rate constant with the potential (i. e., Butler-Volmer or Marcus-Hush kinetic formalisms) is explicitly established a priori. Both location and height of the Quasi-Reversible Maximum and symmetry of the SWV current-potential curves are strongly affected by the interaction parameters G=aOO+aRR-2aOR and S=aRR-aOO (with aij being the interaction coefficient for species i and j). Quantitative methods for obtaining kinetic and interaction parameters of the redox probes are presented, based on the measurement of the peak currents and potential under quasi-reversible conditions where the current exhibits two asymmetric peaks. A discussion is done concerning the deviations found in the estimation of the rate constants with SWV when intermolecular interactions are not considered. The above methods have been applied to the characterisation of mixed ferrocenylundecanethiol / decanethiol monolayers on gold electrodes at an ethanolic medium for which the SWV is clearly non-ideal
Open Access
Influence of ionic strength on the flexibility of alginate studied by size exclusion chromatography
(Elsevier, 2014-02-15) Díaz Baños, Francisco Guillermo; Díez Peña, Ana I.; Hernández Cifre, José Ginés; López Martínez, M. Carmen; Ortega Retuerta, Álvaro; García de la Torre, José; Química Física
Open Access
Insights into the cyclic voltammetry of surface-confined molecules undergoing two-electron transfers of any reversibility and any ordering of the formal potentials: unravelling the apparent governing factors
(Elsevier, 2023-09-10) López Tenés, Manuela; González Sánchez, Joaquín; Laborda, Eduardo; Molina, Angela; Química Física
The cyclic voltammetry (CV) of surface-immobilized electroactive species undergoing two-electron transfers (so-called surface EE mechanism) is comprehensively studied in this work, considering any electron transfer kinetics (k0′ 1 , k0′ 2 ) and any values of their formal potentials (E0′ 1 , E0′ 2 ). Hence, a large number of possible situations arise, which are systematized through the definition of apparent electrochemical rate constants for both electron transfers (which account for the combined effect of k0′ i (i = 1, 2), ΔE0′ (= E0′ 2 - E0′ 1) and the scan rate), with their values and ratio determining the features of the voltammetric signal. Guidelines are established for the elucidation of the reversibility of the process as a function of the relative values of such apparent rate constants, which reflects on the symmetry of the CV signals in the forward and reverse scans. Thus, as the second transfer is more favorable than the first one, kinetically and/or thermodynamically, the process behaves as more irreversible. Also, simple protocols of quantification of the corresponding kinetic and thermodynamic parameters are given on the basis of the analysis of the height, width, number and position of the CV peaks.
Embargo
Intraresidual correlated motions in peptide chains
(American Chemical Society, 2019-10-31) Bastida, Adolfo; Carmona García, Javier; Zúñiga, José; Requena, Alberto; Cerezo, Javier; Química Física
We investigate the interresidual and intraresidual correlations between dihedral displacements of adjacent residues within model polyalanine peptides by analyzing extensive molecular dynamics trajectories. Correlations are evaluated individually at different residue conformations covering the whole (ϕi ,ψi )-space. From these, we draw maps that unveil an unprecedented strong intramolecular correlation displaying opposite (correlated/anticorrelated) behaviors at different conformations. Both interresidual and intraresidual correlations arise from the propensity of the peptide to minimize the overall atomic displacements.
Open Access
Microelectrode arrays with active-area geometries defined by spatial light modulation
(Elsevier, 2020-10-01) Vogel, Yan B.; Molina, Angela; González Sánchez, Joaquín; Ciampi, Simone; Química Física
Microelectrode arrays form the basis of electrochemical sensing devices because of their unique properties, such as enhanced mass transport and steady-state diffusion currents. However, they demand a predefined and rigid geometry, and require a connecting pad for each element of the array. Here it is reported the formation of microelectrode arrays whose active area geometry is defined by the shape of a light pattern projected on an unstructured silicon electrode with a single electrical connection. Spatiotemporally resolved fluxes of charge carriers are used to confine a model electrochemical reaction only to the illuminated areas. By developing a theoretical model to analyze the current−potential data, it is revealed within which limits spatial light modulation can be used to enhance mass transport in a diffusive redox system on two silicon allotropes. Using this concept microelectrode geometry is adjusted instantaneously and at will by the operator on a homogeneous substrate with a single electrical connection.

Browsing by browse.metadata.contributordepartment "Química Física"

Results Per Page

Sort Options