Functional ceramic materials database: an online resource for materials research

We present work on the creation of a ceramic materials database which contains data gleaned from literature data sets as well as new data obtained from combinatorial experiments on the London University Search Instrument. At the time of this writing, the database contains data related to two main groups of materials, mainly in the perovskite family. Permittivity measurements of electroceramic materials are the first area of interest, while ion diffusion measurements of oxygen ion conductors are the second. The nature of the database design does not restrict the type of measurements which can be stored; as the available data increase, the database may become a generic, publicly available ceramic materials resource.     

Facile aqueous synthesis and stabilization of nearly monodispersed gold nanospheres by poly(L‐proline)

A facile strategy is developed to synthesize Au nanoparticles (Au‐NPs) using water‐soluble poly(L ‐proline) (PLP). The synthesized NPs were characterized by TEM, FTIR and NMR spectroscopy, thermogravimetric analysis, and circular dichroism. It was found that PLP has a “dual” role as an efficient reductant of Au(III) and simultaneously as a stabilizing agent of Au‐NPs. The influence of PLP molecular weight, temperature, initial Au(III) concentration, and Au(III)/PLP molar ratio on the size and dispersity of Au‐NPs is examined. It was found that the unique extended secondary structure of PLP II resulted in the facile formation of highly crystalline Au‐NPs in water at a very low Au(III)/PLP molar ratio. These Au‐NPs have the smallest dimensions and size distributions among NPs synthesized so far by polymeric materials in aqueous media, and exhibit enduring colloidal stability. Therefore, by utilizing biocompatible and benign materials in water, we managed to obtain Au‐NPs, so as the final product is ready‐to‐use for biomedical applications. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

IMENSE: An e-infrastructure environment for patient specific multiscale data integration,modelling and clinical treatment

Secure access to patient data and analysis tools to run on that data will revolutionize the treatment of a wide range of diseases, by using advanced simulation techniques to underpin the clinical decision making process. To achieve these goals, suitable e-Science infrastructures are required to allow clinicians and researchers to trivially access data and launch simulations. In this paper we describe the open source Individualized MEdiciNe Simulation Environment (IMENSE), which provides a platform to securely manage clinical data, and to perform wide ranging analysis on that data, ultimately with the intention of enhancing clinical decision making with direct impact on patient health care. We motivate the design decisions taken in the development of the IMENSE system by considering the needs of researchers in the ContraCancrum project, which provides a paradigmatic case in which clinicians and researchers require coordinated access to data and simulation tools. We show how the modular nature of the IMENSE system makes it applicable to a wide range of biomedical computing scenarios, from within a single hospital to major international research projects.     

"Squaring the clusters": a Mn(III)4Ni(II)4 molecular square from nickel(II)-induced structural transformation of a Mn(II/III/IV)12 cage

A Mn(III)(4)Ni(II)(4) molecular square exhibiting slow magnetization relaxation has been prepared from the reaction of a Mn(II)(4)Mn(III)(6)Mn(IV)(2) cluster and a simple Ni(II) source.     

Partial and complete reduction of O2 by hydrogen on transition metal surfaces

The metal-catalyzed reduction of di-oxygen (O₂) by hydrogen is at the heart of direct synthesis of hydrogen peroxide (HOOH) and power generation by proton exchange membrane fuel cells. Despite its apparent simplicity, how the reaction proceeds on different metals is not yet well understood. We present a systematic study of O₂ reduction on the (111) facets of eight transition metals (Rh, Ir, Ni, Pd, Pt, Cu, Ag, and Au) based on periodic density functional theory (DFT-GGA) calculations. Analysis of ten surface elementary reaction steps suggests three selectivity regimes as a function of the binding energy of atomic oxygen (BE_O), delineated by the opposite demands to catalyze O–O bond scission and O–H bond formation: The dissociative adsorption of O₂ prevails on Ni, Rh, Ir, and Cu; the complete reduction to water via associative (peroxyl, peroxide, and aquoxyl) mechanisms prevails on Pd, Pt, and Ag; and HOOH formation prevails on Au. The reducing power of hydrogen is decreased electrochemically by increasing the electrode potential. This hinders the hydrogenation of oxygen species and shifts the optimal selectivity for water to less reactive metals. Our results point to the important role of the intrinsic reactivity of metals in the selectivity of O2 reduction, provide a unified basis for understanding the metal-catalyzed reduction of O₂ to H₂O and HOOH, and offer useful insights for identifying new catalysts for desired oxygen reduction products.     

Hydrogen adsorption,absorption and diffusion on and in transition metal surfaces: A DFT study

Periodic, self-consistent DFT-GGA(PW91) calculations are used to study the interaction of hydrogen with different facets of seventeen transition metals—the (100) and (111) facets of face-centered cubic (fcc) metals, the (0001) facet of hexagonal-close packed (hcp) metals, and the (100) and (110) facets of body-centered cubic (bcc) metals. Calculated geometries and binding energies for surface and subsurface hydrogen are reported and are, in general, in good agreement with both previous modeling studies and experimental data. There are significant differences between the binding on the close-packed and more open (100) facets of the same metal. Geometries of subsurface hydrogen on different facets of the same metal are generally similar; however, binding energies of hydrogen in the subsurface of the different facets studied showed significant variation. Formation of surface hydrogen is exothermic with respect to gas-phase H₂ on all metals studied with the exception of Ag and Au. For each metal studied, hydrogen in its preferred subsurface state is always less stable than its preferred surface state. The magnitude of the activation energy for hydrogen diffusion from the surface layer into the first subsurface layer is dominated by the difference in the thermodynamic stability of these two states. Diffusion from the first subsurface layer to one layer further into the bulk does not generally have a large thermodynamic barrier but still has a moderate kinetic barrier. Despite the proximity to the metal surface, the activation energy for hydrogen diffusion from the first to the second subsurface layer is generally similar to experimentally-determined activation energies for bulk diffusion found in the literature. There are also some significant differences in the activation energy for hydrogen diffusion into the bulk through different facets of the same metal.     

Atomic and molecular adsorption on Pd(111)

The adsorption properties of a variety of atomic species (H, O, N, S, and C), molecular species (N₂, HCN, CO, NO, and NH₃) and molecular fragments (CN, NH₂, NH, CH₃, CH₂, CH, HNO, NOH, and OH) are calculated on the (111) facet of palladium using periodic self-consistent density functional theory (DFT–GGA) calculations at ¼ ML coverage. For each species, we determine the optimal binding geometry and corresponding binding energy. The vibrational frequencies of these adsorbed species are calculated and are found to be in good agreement with experimental values that have been reported in literature. From the binding energies, we calculate potential energy surfaces for the decomposition of NO, CO, N₂, NH₃, and CH₄ on Pd(111), showing that only the decomposition of NO is thermochemically preferred to its molecular desorption.     

A new class of ferromagnetically-coupled mixed valence vanadium(IV/V) polyoxometalates

Reaction of [V(VI)OCl(2)(thf)(2)] with a bidentate nitrogen-donor ligand (L: phen=1,10-phenanthroline, 5-mephen=5-methyl-1,10-phenanthroline, bipy=2,2'-bipyridine, 5,5'-me(2)bipy=5,5'-dimethyl-2,2'-bipy) in methyl alcohol, in the presence of triethylamine, leads to the formation of hexameric [V(2) (IV)V(4) (V)] oxo-alkoxo-vanadates of the general formula [V(6)O(12)(mu(2)-OCH(3))(4)(L)(4)].x H(2)O [L=phen (1.4 H(2)O), 5-mephen (2.6 H(2)O), bipy (3.4 H(2)O), 5,5'-me(2)bipy (4.H(2)O)]. X-ray structure analysis of 1.2 H(2)O and 4.8 CH(3)OH revealed a pair of V(3)O(13)N(4) trimeric units sharing two corners, with a centrosymmetric planar V(6)-core. In addition, a fully oxidized V(V) species [V(V) (4)O(8)(OCH(3))(2)(mu(3)-OCH(3))(2)(5,5'-me(2)bipy)(2)].3 CH(3)OH (5.3 CH(3)OH) was isolated from the reaction mixture used for the synthesis of 4.H(2)O. The crystal structure of 5.3 CH(3)OH revealed a dicubane-like framework with two missing vertices. Electron paramagnetic resonance (EPR) and variable temperature magnetic susceptibility studies for the hexamers 1.4 H(2)O and 3.4 H(2)O showed the complete localization of the single 3d electrons on the V(IV) ions and unusual ferromagnetic interaction between the two paramagnetic vanadium(IV) ions separated by a distance of about 5.1 A. Furthermore, intermolecular antiferromagnetic interactions through pi-contacts of phenyl rings were observed for these species below 8 K. The ferromagnetic exchange coupling observed in the hexanuclear compounds 1.4 H(2)O and 3.4 H(2)O is also discussed using ab initio UHF calculations on a model compound. The value of the exchange coupling constant (3.7 cm(-1)) for this model compound, calculated using the broken symmetry approach, is in good agreement, both in sign and magnitude, with the experimental J values (6.00 cm(-1) for 1.4 H(2)O and 8.54 cm(-1) for 3.4 H(2)O).     

Mixed-metal pt monolayer electrocatalysts for enhanced oxygen reduction kinetics

We have synthesized a new class of electrocatalysts for the O2 reduction reaction, consisting of a mixed monolayer of Pt and another late transition metal (Ir, Ru, Rh, Re, or Os) deposited on a Pd(111) single crystal or on carbon-supported Pd nanoparticles. Several of these mixed monolayer electrocatalysts exhibited very high activity and increased stability of Pt against oxidation, as well as a 20-fold increase in a Pt mass-specific activity, compared with state-of-the-art all-Pt electrocatalysts. Their superior activity and stability reflect a low OH coverage on Pt, caused by the lateral repulsion between the OH adsorbed on Pt and the OH or O adsorbed on neighboring, other than Pt, late transition metal atoms. The origin of this effect was identified through a combination of experimental and theoretical methods, employing electrochemical techniques, in situ X-ray absorption spectroscopy, and periodic, self-consistent density functional theory calculations. This new class of electrocatalysts promises to alleviate some major problems of existing fuel cell technology by simultaneously decreasing materials cost and enhancing performance. Our studies suggest a new way of synthesizing improved ORR catalysts through the modification and control of the surface reactivity of Pt-based mixed monolayers supported on transition metals other than Pt. In addition to improving the ORR catalysts, co-depositing oxophilic metals may be a promising possibility for improving a variety of other catalysts.     

Surface segregation energies in low-index open surfaces of bimetallic transition metal alloys

We present a database of 24 × 24 segregation energies of single transition metal impurities in low-index surfaces of transition metal hosts, calculated using the localized self-consistent Green’s function (LSGF) method, in combination with the atomic sphere approximation including a multipole correction to the electrostatic potential and energy. The surface energies of facets for fcc and bcc transition metals, and the more stable of the two facets of hcp transition metals are also calculated and compared with available theoretical results. Insights derived should be useful for determining the nature of active sites in a variety of catalytic reactions employing bimetallic catalysts.