O2Activation over Ag-Decorated CeO2(111) and TiO2(110) Surfaces: A Theoretical Comparative Investigation

Periodic spin-polarized hybrid density functional theory calculations have been performed to investigate the reactivity of pristine, O-defective, and Ag-decorated CeO2(111) and TiO2(110) surfaces with a small Ag10 cluster toward O2. The adsorption of O2 and its subsequent dissociation have been studied in order to provide a better understanding of the role of the oxide, the metallic nanoparticle, and their interaction in the reactivity of composite metal/metal oxide materials toward O2, as potential catalysts to this reaction. Structural, energetic, electronic, and vibrational properties of all species involved in the different reaction paths considered have been fully characterized. On the stoichiometric surfaces, Ag10 is oxidized and reduces surface Ce4+/Ti4+ ions, while on the O-defective surfaces, the adhesion of silver is promoted only on CeO2 but unfavored on TiO2. On the other hand, on the silver-free supports, O2 strongly adsorbs at vacancies and preferentially reduces to peroxide. When no O vacancies are considered on the Ag10-decorated supports, the net positive charge on Ag10 actually prevents the adsorption and reduction of O2. Instead, when O vacancies are included, two reaction pathways are observed; oxygen molecules can weakly absorb on the silver cluster as a superoxide moiety or strongly adsorb at the vacancy as peroxide. The dissociation of the O-O bond of the peroxide is favored both from the thermodynamic and kinetic points of view in silver-decorated surfaces, in contrast with the silver-free cases. In addition, Ag10/CeO2 shows higher activity toward the O2 adsorption and dissociation than Ag10/TiO2, which can be related both to the higher ionicity and superior electron storage/release ability of ceria with respect to titania, thus leading to the weakening of the O-O bond and providing lower activation barriers for oxygen reduction. These results deepen the current understanding of the reactivity of metal/metal oxide composites toward O2, especially elucidating how the surface stoichiometry affects the charge state of the metal clusters, and hence the reactivity of these interfaces toward O2, with potential important consequences when such composites are considered for catalytic applications

Toward a new hybrid proton conductor: lanthanum niobate layered perovskites as a source of tailorable surfaces

The modification of metal oxide surfaces with organic moieties has been widely studied as a method of preparing organic-inorganic hybrid materials for various applications. Among inorganic oxides, the ion-exchangeable layered perovskites [1], materials composed by perovskite-like slabs and intercalated cations, stimulated authors\u2019 interest in reason of some encouraging electronic and reactive properties. In particular it is well known that the interlayer surface of such materials in their protonated form can be easily functionalized with organic groups (such as alcohols [2-3] or organophosphonic acids [4]) thus allowing the production of stable hybrid materials with new electronic and reactive features. As a first step to design a new inorganic-organic hybrid proton conductor, a comprehensive theoretical investigation of the MLaNb2O7 (M=H, Li, Na, K, Rb and Cs) series of ion-exchangeable layered perovskite is presented. In particular, their structural and electronic properties have been investigated by periodic calculations in the framework of DFT. A general very good agreement with the available experimental data has been found. The protonated compound (HLaNb2O7) has been then functionalized with imidazole trying two different settings: in the first arrangement the molecule is adsorbed on the layered oxide exposing the interlayer surface, in the second the organic moiety is just put between two perovskites slabs. This latter model, including the effect of the confinement, allowed to better reproduce the experimental structural XRD data and 13C-NMR measurements of the hybrid system. [1] Schaak, R. E. and Mallouk T. E., Chem. Mat. 2002, 14, 1455-1471. [2] Takahashi S. et al., Inorg. Chem. 1995, 34, 5065-5069. [3] Suzuki H. et al., Chem. Mater. 2003, 15, 636-641. [4] Shimada, A. et al., Chem. Mat. 2009, 21, 4155-4162

Ligand exchange on CdSe nanoplatelets for the solar light sensitization of TiO2 and ZnO nanorod arrays

In quantum dot (QD) solar cells, the ex situ sensitization of wide band gap semiconductors (WBSCs) makes it possible to control the shape and the passivation of the nanosized sensitizer. Hence, ex situ techniques can be used to investigate how the band gap of the sensitizers affects the performance of quantum dot solar cells. The latter can be precisely controlled in 1D confined structures such as quasi-2D nanoplatelets (NPLs), the thickness of which is defined with an atomic precision. In this work, we tested and thoroughly characterized the attachment of 7, 9 and 11 monolayers thick CdSe NPLs (as well as QDs for the sake of comparison) to ZnO and to TiO2 nanorods. A crucial point of the ex situ techniques is the choice of bifunctional ligands that link the nanosized sensitizers to the WBSCs. Besides the well-known mercaptopropionic acid, we also studied two ‘atomic linkers’ (OH− and SH−) to minimize the distance between the sensitizer and the oxide. The as-prepared systems have been analyzed by UV/VIS absorption and Raman spectroscopy. Among them, SH− was found to be the most versatile linker that enabled the efficient attachment of all types of CdSe nanocrystals on ZnO and TiO2 nanorods.Fil: Szemjonov, A.. PSL Research University; Francia. Centre National de la Recherche Scientifique; FranciaFil: Tasso, Mariana Patricia. Laboratoire de Physique Et D'etude Des Materiaux; Francia. Centre National de la Recherche Scientifique; Francia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Ithurria, S.. Laboratoire de Physique Et D'etude Des Materiaux; FranciaFil: Ciofini, I.. PSL Research University; Francia. Centre National de la Recherche Scientifique; FranciaFil: Labat, F.. PSL Research University; Francia. Centre National de la Recherche Scientifique; FranciaFil: Pauporté, T.. PSL Research University; Francia. Centre National de la Recherche Scientifique; Franci

Aggregation effects on pigment coatings: Pigment red 179 as a case study

Here, we have studied, with a combined experimental and computational approach, the effect of the crystal environment and aggregation on the electronic properties of Pigment Red 179, which affect both its color and optical energy gap. Spectra acquired in the near-infrared and visible range of energies suggest that this molecule is indeed a "cool" dye, which can be employed as a red pigment that provides effective color coverage to different substrates without contributing to their heating during light irradiation. Spectra acquired on different polymer mixtures at different pigment concentrations (i.e., 2.5-10 wt %) suggest that absorption features depend on chromophoric arrangements promoted by the strong intermolecular I -\u3c0interactions. Calculations, performed at the time-dependent density functional theory level, allowed to both attribute the nature of the electronic transitions causing the observed spectra involved and understand the effect of the environment. Indeed, the visible spectra of the pigment is dominated by two localized transitions, with negligible charge transfer for both a dye monomer and dimer either in vacuum or acetonitrile solution. Instead, models including the crystal environment of the pigment show the presence of a high-wavelength S1 \ue2 S0 charge transfer transition between two adjacent molecules, in quantitative agreement with the experimental absorption energy of the crystal pigment

The endothelial mineralocorticoid receptor regulates vasoconstrictor tone and blood pressure

Pathophysiological aldosterone (aldo)/mineralocorticoid receptor (MR) signaling has significant effects on the cardiovascular system, resulting in hypertension and cardiovascular remodeling; however, the specific contribution of the vascular MR to blood pressure regulation remains to be established. To address this question, we generated a mouse model with conditional overexpression of the MR in endothelial cells (MR-EC). In basal conditions, MR-EC mice developed moderate hypertension that could be reversed by canrenoate, a pharmacological MR antagonist. MR-EC mice presented increased contractile response of resistance arteries to vasoconstrictors (phenylephrine, thromboxane A(2) analog, angiotensin II, and endothelin 1) in the absence of vascular morphological alterations. The acute blood pressure response to angiotensin II or endothelin 1 infusion was increased in MR-EC mice compared with that in littermate controls. These observations demonstrate that enhanced MR activation in the endothelium generates an increase in blood pressure, independent of stimulation of renal tubular Na(+) transport by aldo/MR or direct activation of smooth muscle MR and establish one mechanism by which endothelial MR activation per se may contribute to impaired vascular reactivity

In‐situ Bragg coherent X‐ray diffraction during tensile testing of an individual Au nanowire

Nanomechanical testing methods have drawn significant attention in both scientific and industrial research fields owing to unique deformation mechanisms in constrained volumes that underpin new property regimes. In-situ imaging equipment is now routinely employed to monitor the live evolution of material response during mechanical loading, with many of the testing developments tailored for electron microscopes (EMs). More recently, progress towards quantitative in-situ testing at synchrotron beamlines1–3 enabled by innovations in source brightness, focusing optics, and large size detectors has been made. Novel techniques such as Bragg coherent X-ray diffraction promise 3D information with phase information related to displacement fields (elastic strain, defects) within the material. However, despite the rich information that can be collected, many challenges arise in the realization of in-situ imaging of single nanostructures using such methods, including meticulous sample preparation and complex data analysis in retrieving phase information. In this work, we present the first successful systematic single nanowire tensile test while simultaneously recording 3D Bragg peaks using coherent X-rays. Defect free single crystalline \u3c110\u3e oriented Au nanowires were grown by physical vapor deposition4 and a 100 nm nanowire was harvested from the substrate and transferred to a nanotensile stage within a microelectromechanical system chip, which can be mounted to a coherent X-ray beamline. 3D Bragg peaks were recorded with nanofocused beam combined with 2D detector at each displacement step to discuss the evolution of strain and rotation of the nanowire during the tensile test. The movement of the peak sensitively depicted evolution of the deformation of the nanowire. In addition, the 3D Bragg coherent X-ray diffraction followed by phase retrieval has shown to reveal the internal strain state of nanostructure5 and this advanced technique is expected to reveal unique surface effects that mediate the overall mechanical performance of nano-scaled materials. 1. Cornelius, T. W. et al. In situ three-dimensional reciprocal-space mapping during mechanical deformation. J. Synchrotron Radiat. 19, 688–694 (2012). 2. Ren, Z. et al. Scanning force microscope for in situ nanofocused X-ray diffraction studies. J. Synchrotron Radiat. 21, 1128–1133 (2014). 3. Leclere, C. et al. In situ bending of an Au nanowire monitored by micro Laue diffraction. J. Appl. Crystallogr. 48, 291–296 (2015). 4. Richter, G. et al. Ultrahigh strength single crystalline nanowhiskers grown by physical vapor deposition. Nano Lett. 9, 3048–3052 (2009). 5. Haag, S. et al. Anomalous coherent diffraction of core-shell nano-objects: A methodology for determination of composition and strain fields. Phys. Rev. B 87, 35408 (2013)