Dynamics and structure of liquids under special conditions: water confined in giant polyoxometalates and co2-brine mixtures

L'estructura i la dinàmica dels líquids varien sota determinades condicions, tals com sota confinament o en presència d'ions. Aquesta tesi es divideix en dues parts. En la primera part, s'han estudiat l'estructura i la dinàmica d'aigua confinada en polyoxomolibdats gegants, per mitjà de simulacions de dinàmica molecular (DM) a condicions normals de temperatura i pressió. Els resultats obtinguts mostren que l'aigua tendeix a organitzar-se en capes concèntriques de la família de les buckyball. Les posicions d'aquestes capes coincideixen amb resultats experimentals de raigs X per aquest sistema a baixa temperatura. S'han calculat un gran nombre de propietats estructurals i dinàmiques, algunes de les quals s'han comparat amb dades experimentals i de simulació per micel•les reverses de grandària similar amb un resultat satisfactori. La segona part de la tesi es centra en el càlcul de la difussivitat del diòxid de carboni (CO2) en salmorra sota les condiciones termodinàmiques representatives d’aqüífers salins subterranis mitjançant simulacions de dinàmica molecular. S'han calculat els coeficients de difusió màssics i d'autodifusió del CO2, la conductivitat elèctrica de la barreja, així com els temps de relaxació rotacional del CO2 per totes les condicions. Aquests resultats constitueixen la primera estimació de coeficients de difusió màssics i temps de relaxació rotacional del CO2 en aqüífers salins subterranis.The structure and dynamics of liquids are distorted under special conditions, such as under confinement, or in the presence of ions. This thesis is divided into two parts. In the first part, we have studied the structure and dynamics of water confined in giant polyoxomolybdate molecular clusters by means of molecular dynamics (MD) simulations at ambient conditions. We observe that water organizes in concentric layered structures of the buckyball family, which agree with X-ray data for these systems at low temperature. Several structural and dynamical data are provided and compared to experimental and theoretical analyses for reverse micelles of similar size, where qualitative agreement is observed. The second part of the thesis is devoted to the calculation of the diffusivity of carbon dioxide (CO2) in brine under the thermodynamic conditions representative of deep saline aquifers through MD simulations. We have calculated CO2 mass and self diffusion coefficients, electrical conductivities, as well as rotational relaxation times. These results are the first estimation of mass diffusion and rotational relaxation times of CO2 in deep saline aquifers

La pintura mural a la Catalunya interior al segle XX

La pintura mural en el siglo XX en la Catalunya interior definió un período prolífico y productivo durante la segunda mitad del siglo, debido al proceso de reconstrucción de la postguerra y a la recuperación de la disciplina en tiempos de la Transición democrática. Tenemos pocos ejemplos del Modernismo y del Novecentismo y solamente podemos hablar de algunos artistas emblemáticos de dichas corrientes que, como Francesc Galí, Miquel Farré o Josep Obiols, realizaron proyectos murales en una cronología posterior. Si lo comparamos con el muralismo de postguerra, el impacto global de dichos precedentes resulta desproporcionado. Los años cincuenta, especialmente, significaron un salto cuantitativo que se desarrolló por la geografía de Lleida a cargo de los artistas plásticos, que intentaban profesionalizarse, como fue el caso de Jaume Minguell, Lluís Trepat, Miquel Roig Nadal o Víctor P. Pallarés. En los años ochenta, una vez pasado el proceso reconstructivo, el muralismo perdió su presencia, hasta que el pintor Josep Minguell delimitó, a través de su reivindicación ética y estética, una reconstrucción disciplinaria

Electrochemical Effects at Surfactant–Platinum Nanoparticle Interfaces Boost Catalytic Performance

Nanoparticles are applied in a variety of industrially relevant transformations as heterogeneous catalysts typically with the help of an external force (pressure, temperature, or voltage) to steer the chemistry. The modification of platinum nanoparticles by a phosphate–amino surfactant enables catalysis without external energy supply in the hydrogenation of nitrobenzene to aniline. This can be attributed to the complex surfactant/metal interface which is able to split hydrogen into protons and electrons. The subsequent hydrogenation process mimics the electrochemical reduction described by Haber. The surfactant decorated Pt catalyst is two orders of magnitude more active than the state-of-the-art Pb-poisoned Pt catalyst. Our study provides a new approach to understand the functionality of emerging catalytic systems and can be applied to design new materials with optimal interfaces

Shape control in concave metal nanoparticles by etching

The shape control of nanoparticles constitutes one of the main challenges in today’s nanotechnology. The synthetic procedures are based on trial-and-error methods and are difficult to rationalize as many ingredients are typically used. For instance, concave nanoparticles exhibiting high-index facets can be obtained from Pt with different HCl treatments. These structures present exceptional capacities when are employed as catalysts in electrochemical processes, as they maximize the activity per mass unit of the expensive material. Here we show how atomistic simulations based on density functional theory that take into account the environment can predict the morphology for the nanostructures and how it is even possible to address the appearance of concave structures. To describe the control by etching, we have reformulated the Wulff construction through the use of a geometric model that leads to concave polyhedra, which have a larger surface-to-volume ratio compared to that for nanocubes. Such an increase makes these sorts of nanoparticles excellent candidates to improve electrocatalytic performanc