Surface Acid–Base Properties of Anion-Adsorbed Species at Pt(111) Electrode Surfaces in Contact with CO2-Containing Perchloric Acid Solutions

Carbonate and bicarbonate adsorption on Pt(111) electrodes from CO2-saturated acidic solutions is investigated by cyclic voltammetry and Fourier transform infrared reflection absorption spectroscopy (FT-IRRAS). Spectroscopic results show carbonate and bicarbonate adsorption even at pH = 1, where bulk concentration of these anions is negligible. Moreover, analysis of the potential dependence of band intensities corresponding to adsorbed carbonate and bicarbonate reveals an effect of the electrode potential on the surface acid–base equilibrium. In this regard, increasing potentials favor bicarbonate deprotonation, leading to carbonate formation. A tentative thermodynamic analysis is given to rationalize these trends.Support from MINECO (Spain) through project CTQ2013-44083-P is greatly acknowledged. RMH thankfully acknowledges support from Generalitat Valenciana under the Santiago Grisolía Program (GRISOLIA/2013/008)

In situ Fourier transform infrared reflection absortion spectroscopy study of adenine adsorption on gold electrodes in basic media

In situ Fourier transform infrared reflection absortion spectroscopy (FT-IRRAS) has been used in the external (SNIFTIRS method) and the internal (ATR-SEIRAS) reflection configurations to determine the pH influence, in the neutral and basic range, on the adsorption of adenine on Au(111) and gold nanofilm electrodes from D2O and H2O solutions. In D2O solutions, the main adsorbate band around 1640 cm−1,due to a ring stretching mode, shows different characteristics in the spectra collected at pH values at which the neutral and the basic adenine forms predominate in solution. The analysis of these differences, in comparison with the respective spectra of adenine in solution, permits us to conclude that both forms of adenine can adsorb chemically. The high sensitivity of the ATR-SEIRAS method has been used to analyze the contribution to the spectra of each form of adsorbed adenine as a function of the pH of the solution. The pKa2 obtained for the adsorbed species from this analysis is almost coincident with the pKa2 reported for adenine in solution, indicating that the coordination to the electrode and the second acid-base equilibrium involves different atoms of the adenine molecule. This result confirms the previously proposed adsorption model for adenine, implying the bonding of adenine to the electrode by the amine nitrogen (N10) and either the ring nitrogens N1 or N7, while the second acid-base equilibrium of adenine involves the ring nitrogen N9. Comparison of the 3400-3600 cm−1 region of the ATR-SEIRAS spectra of adenine obtained in H2O solutions at different pH values, which corresponds to the characteristic–OH stretching mode of the interfacial water molecules, permits us to discard the co-adsorption of water molecules in neutral and basic media, contrary to the case of adenine adsorption from acid media.Financial support from the Spanish Ministry of Science and Technology (CTQ2010-19823 and a FPU-grant to JAM), from the Junta de Andalucia (PAI FQM202) and University of Alicante

ATR-SEIRAS study of CO adsorption and oxidation on Rh modified Au(111-25 nm) film electrodes in 0.1 M H2SO4

Rh modified Au(111-25 nm) electrodes, prepared by electron beam evaporation and galvanostatic deposition, were employed to study adsorption and electro-oxidation of CO on Rh in 0.1 M sulfuric acid solution by in situ attenuated total reflection surface enhanced infrared absorption spectroscopy (ATR-SEIRAS). The results of ATR-SEIRAS experiments were compared with those obtained by infrared reflection absorption spectroscopy on three low-index Rh single crystal surfaces. The Rh film deposited on Au(111-25 nm) electrode consists of 3D clusters forming a highly stepped [n(111) × (111)]-like surface with narrow (111) terraces. When CO was dosed at the hydrogen adsorption potential region, CO adsorbed in both atop (COL) and bridge (COB) configurations, as well as coadsorbed water species, were detected on the Rh film electrode. A partial interconversion of spectroscopic bands due to the CO displacement from bridge to atop sites was found during the anodic potential scan, revealing that there is a potential-dependent preference of CO adsorption sites on Rh surfaces. Our data indicate that CO oxidation on Rh electrode surface in acidic media involves coadsorbed water and follows the nucleation and growth model of a Langmuir-Hinshelwood type reaction.The work was supported by the Research Center Jülich, the University of Bern, Swiss National Science Foundation (200020_144471, 200021-124643), the Spanish Ministerio de Economía y Competitividad (project CTQ2013-44083-P) and University of Alicante. QX acknowledges fellowships of the Research Center Jülich; IP acknowledges support by COST Action TD 1002; and AK acknowledges the financial support by CTI Swiss Competence Centers for Energy Research (SCCER Heat and Electricity Storage)

Características hidroquímicas de un acuífero kárstico sobreexplotado: el caso del Cabeçó d’Or (SE de España)

The karstic system of the Cabeçó d’Or is a small overexploited aquifer where water level declined by more than 200 m from the early sixties to 1987. After this year the water level has recovered 20 m and it has been almost stabilized. The waters of this aquifer are calcium-sulphate type and show a clear thermal positive anomaly. Mineralization has been related to the presence at depth of evaporite deposits (Keuper facies) rich in gypsum. The processes occurring in the aquifer include the dissolution of gypsum, calcite and dolomite, and the precipitation of calcite. Lower concentration in sodium than chloride shows a cation exchange processes between water and clay minerals. These processes could be favoured by the input of CO2. The content of carbon-13 could be related to the deep CO2 inputs. Fractures within the study area appear to be responsible for the temperature and CO2 anomalies, as well as for the elevated concentrations of radon and radium encountered in these waters. Oxygen-18 and carbon-13 have remained relatively constant, reflecting the relatively stable hydrogeochemical conditions. This hydrogeochemical stability over time is interpreted as an indication that overexploitation of the aquifer has not induced any significant deterioration in water quality. The thermal anomaly of groundwater can be responsible of a mixing processes what prevent a vertical hydrogeochemical zoning.El sistema kárstico del Cabeçó d’Or es un pequeño acuífero sobreexplotado donde los niveles han descendido más de 200 m entre los años 60 y 1987. Después de ese año los niveles han recuperado 20 m y se han estabilizado. Las aguas de este acuífero son sulfatadas cálcicas y presentan un claro carácter termal. Su mineralización ha sido relacionada con la presencia de rocas evaporíticas (facies Keuper rica en yesos) en profundidad. Algunos de los procesos que tienen lugar en el seno del acuífero son la disolución de yeso, calcita, dolomita y precipitación de calcita. Las menores concentraciones de sodio que de cloruro apuntan a procesos de intercambio iónico entre el agua con minerales de la arcilla. Estos procesos podrían estar favorecidos por la entrada de CO2. Los contenidos de carbono-13 parecen estar relacionados con la existencia de aportes de CO2 de origen profundo. Las fracturas de gran envergadura existentes en el área de estudio parecen ser las responsables del ascenso calorífico, del CO2, así como de las elevadas concentraciones de radón y radio encontradas en estas aguas. Los contenidos de oxígeno-18 y carbono-13 han permanecido relativamente constantes, lo que manifiesta unas condiciones hidrogeológicas e hidrogeoquímicas bastante estables. La relativa estabilidad hidrogeoquímica a lo largo del tiempo se manifiesta como un indicador de que la sobreexplotación del acuífero no ha originado cambios significativos en el deterioro de la calidad del agua. La anomalía termal del agua subterránea de este acuífero puede ser responsable de los procesos de mezcla, lo que dificulta la existencia de una zonación hidrogeoquímica en la vertical.This work was carried out within the framework of the projects AMB95-0493 and HID99-0597 (CICYT)

Establishing the nature of X-ray binaries through infrared spectroscopy

European Space Agency's INTEGRAL (International Gamma-Ray Astrophysics Laboratory) satellite have discovered new X-ray sources due to its sensitivity above 20 keV. Most of these sources suffer from high absorption and the classical blue band spectral classification region is normally not accessible. This can be overcome, however, through infrared spectroscopy. The characterisation of these systems can influence the population synthesis models currently in use. In this work, we present the first H and K band spectra for three INTEGRAL sources using the NICS instrument mounted on the Telescopio Nazionale Galileo (TNG) 3.5-m telescope. This study was complemented with infrared photometry from UKIDSS, 2MASS, WISE and NEOWISE databases. Our spectra show all the significant features in emission and are, thus, consistent with a Be nature of the companions. Owing to their X-ray characteristics, these systems were classified as Be X-ray binaries. This allowed us to refine its distances to the sources using suitable calibrations that take into account the contamination by the circumstellar disk.This work was supported partially by the project ESP2017-85691-P AM acknowledges the support by the VIDI de la UA under visiting programme INV17-26

Tsunami audiovisual resources on the Internet

Presentamos una selección de páginas web que contienen recursos audiovisuales sobre tsunamis (esquemas, mapas, animaciones, vídeos, imágenes de satélite, fotografías, etc.). Este material gráfico puede ser utilizado por los docentes, como complemento a las tradicionales clases teóricas, para la preparación de seminarios, talleres, presentaciones por ordenador, entre otros. La avalancha de información publicada en Internet sobre el tsunami del Índico de 2004 ha puesto de manifiesto el gran potencial que tiene en la docencia de las Ciencias de la Tierra.We present a web site selection which contains audiovisual resources on tsunamis (diagrams, maps, animations, videos, satellite images, photographs, etc.). This graphic material can be used by lecturers as a complement to traditional theory classes, in order to prepare seminars, workshops, computer-aided presentations, etc. The enormous amount of information published about the 2004 Indian Ocean tsunami on the Internet reveals the great potential of this resource in teaching Earth Sciences

Hydroxyurea electrooxidation at gold electrodes. In situ infrared spectroelectrochemical and DFT characterization of adsorbed intermediates

The oxidation of hydroxyurea (H2NCONHOH, HU) at Au(100), Au(111) and Au(111)–25 nm thin film electrodes is studied spectroelectrochemically in perchloric acid solutions. HU, which in agreement with DFT results interacts weakly with the gold surfaces, oxidizes irreversibly at gold electrodes irrespective of the surface orientation. The in situ infrared external reflection spectra prove the formation of dissolved carbon dioxide and adsorbed cyanate as products of the HU electrooxidation reaction. A band at ca. 2230 cm−1 can be related both to dissolved isocyanic acid coming from the protonation of adsorbed cyanate or to nitrous oxide coming from the oxidation of hydroxylamine, which is formed (together with adsorbed cyanate) upon the chemical decomposition of hydroxyurea. ATR-SEIRAS experiments allow the observation of other adsorbate bands that can be tentatively ascribed to reaction intermediates that conserve the NCN skeleton and are bonded to the metal by the nitrogen atoms at near on-top positions. Bonding to the surface can be either unidentate or bidentate, involving covalent-type bonds or dative bonding through the lone pairs of the N atoms. Some of the signals of the experimental spectra, in particular those appearing around 1800 cm−1, can be assigned to the CO stretch of adsorbed intermediates having a nitrosyl group formed by oxidation of the NOH moiety (namely, adsorbed nitrosoformamide or its deprotonated form). The bands observed around 1650 cm−1 can correspond either to the NO stretching mode of the former species or to the CO stretching modes of adspecies conserving the NOH group.The authors acknowledge the funding by Ministerio de Economía y Competitividad through projectsCTQ2016-76221-P (AIE/FEDER, UE) and CTQ2016-76231-C2-2-R (AEI/FEDER, UE) and by the University of Alicante (VIGROB-263). William Cheuquepán is grateful for the award of a F.P.I. grant associated to project CTQ2009-13142

On the electrochemical behavior of formamidine disulfide on gold electrodes in acid media

The adsorption and reactivity of formamidine disulfide (FDS) were studied at gold single crystal and thin film electrodes in perchloric acid solutions and the results of cyclic voltammetry and in situ infrared spectroscopy (SNIFTIR and ATR-SEIRAS) experiments compared with those previously obtained with thiourea (TU). In addition, optimized geometries and theoretical harmonic vibrational frequencies were obtained for adsorbed FDS, TU and thioureate from plane-wave DFT calculations using periodic surface models. These results were compared in the case of TU and thioureate to those previously obtained with a model Au cluster surface with (111) orientation. In the case of FDS, weak adsorption takes place with the S–S bond essentially parallel to the metal surface. No specific bands for adsorbed FDS can be identified in the experimental ATR-SEIRA spectra. These latter spectra suggest that adsorbed thioureate species are spontaneously formed upon dissociative adsorption of FDS when dosing this molecule at open circuit. Some of the adsorbed thioureate species undergo reductive protonation giving rise to a mixed adlayer formed by adsorbed thioureate and thiourea in a surface process which is faster when a controlled potential of 0.70 V is applied. In agreement with the observations reported when dosing TU, the ratio between TU and thioureate adsorbates is found to depend on the electrode potential, being higher for potentials close to the hydrogen evolution limit and decreasing for higher potential values.The authors acknowledge the finance by Ministerio de Economía y Competitividad (project CTQ2013-44083-P) and the University of Alicante. William Cheuquepán is grateful for the award of a F.P.I. grant associated to project CTQ2009-13142

La cestería decorada de la cueva de los Murcíélagos (Albuñol, Granada)

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