Structure and reactivity of the Ru(0 0 0 1) electrode towards fuel cell electrocatalysis

The reactivity of the Ru(0 0 0 1) electrode towards the adsorption and electrooxidation of CO and methanol has been studied by variable-temperature in situ FTIR spectroscopy in both perchloric acid and sodium hydroxide solution, and the results interpreted in terms of the surface chemistry of the Ru(0 0 0 1) electrode. Both linear (CO) and threefold hollow (CO) binding CO adsorbates (bands at 1970-2040 and 1770-1820 cm, respectively) were observed on the Ru(0 0 0 1) electrode in both 0.1 M HClO and 0.1 M NaOH solutions from the CO adsorption. In the acid solution, CO was detected as the main adsorbed species on Ru(0 0 0 1) surface over all the potential region studied. In contrast, in the alkaline solution, more CO than CO was detected at lower potentials, whilst increasing the potential resulted in the transformation of CO to CO. At higher potentials, the oxidation of the adsorbed CO took place via reaction with the active (1 × 1)-O oxide/hydroxide. It was found that no dissociative adsorption or electrooxidation of methanol took place at the Ru(0 0 0 1) at potentials below 900 mV vs Ag/AgCl in perchloric acid solution at both 20 and 55°C. However, in the alkaline solution, methanol did undergo dissociative adsorption, to form linearly adsorbed CO (CO) with little or no CO adsorbed at threefold hollow sites (CO) at both 20 and 55°C. Increasing the temperature from 20 to 55°C clearly facilitated the methanol dissociative adsorption to CO and also enhanced the electrooxidation of the CO. At the higher potentials, significant oxidation of methanol to CO and methyl formate in acid solution and to bicarbonate and formate in alkaline solution, was observed, which was attributed to the formation of an active RuO phase on the Ru(0 0 0 1) surface, in agreement with our previous studies. © 2003 Elsevier Ltd. All right reserved.

Structure and dynamics of dextran in binary mixtures of a good and a bad solvent

The structure and dynamics of the common polysaccharide dextran have been investigated in mixed solvents at two different temperatures using small-angle X-ray scattering (SAXS) and viscosity measurements. More specifically, binary mixtures of a good solvent (water, formamide, dimethylsulfoxide, ethanolamine) and the bad solvent ethanol as the minority component have been considered. The experimentally observed effects on the polymer conformation (intrinsic viscosity, coil radius, and radius of gyration) of the bad solvent addition are discussed in terms of hydrogen bonding density and are correlated with the Hansen solubility parameters and the surface tension of the solvent mixtures. Hydrogen bonding appears to be an important contributor to the solubility of dextran but is not sufficient to capture the dextran coil contraction in the mixtures of good+bad solvents.

Structure and thermal properties of salicylate-based-protic ionic liquids as new heat storage media. COSMO-RS structure characterization and modeling of heat capacities

During this research, we present a study on the thermal properties, such as the melting, cold crystallization, and glass transition temperatures as well as heat capacities from 293.15 K to 323.15 K of nine in-house synthesized protic ionic liquids based on the 3-(alkoxymethyl)-1H-imidazol-3-ium salicylate ([H-Im-C₁OC_n][Sal]) with n = 3–11. The 3D structures, surface charge distributions and COSMO volumes of all investigated ions are obtained by combining DFT calculations and the COSMO-RS methodology. The heat capacity data sets as a function of temperature of the 3-(alkoxymethyl)-1H-imidazol-3-ium salicylate are then predicted using the methodology originally proposed in the case of ionic liquids by Ge et al. 3-(Alkoxymethyl)-1H-imidazol-3-ium salicylate based ionic liquids present specific heat capacities higher in many cases than other ionic liquids that make them suitable as heat storage media and in heat transfer processes. It was found experimentally that the heat capacity increases linearly with increasing alkyl chain length of the alkoxymethyl group of 3-(alkoxymethyl)-1H-imidazol-3-ium salicylate as was expected and predicted using the Ge et al. method with an overall relative absolute deviation close to 3.2% for temperatures up to 323.15 K.

Exchange between sub-surface and surface oxygen vacancies on CeO2(111):a new surface diffusion mechanism

Using first principles calculations for O vacancy diffusion on CeO2(111), we locate a surface diffusion mechanism, the two-step O vacancy exchange one, which is more favored than the most common hopping mechanism. By analyzing the results, we identify quantitatively the physical origin of why the two-step exchange mechanism is preferred.

Structure and Catalytic Activity of Gold in Low-Temperature CO Oxidation

Structures and catalytic activities of Au thin films supported at anatase TiO(2)(101)) and a Au substrate are studied by using density functional theory calculations. The results show that O(2) can hardly adsorb at flat and stepped Au thin films, even supported by fully reduced TiO(2)(101) that can highly disperse Au atoms and offer strong electronic promotion. Interestingly, in both oxide-supported and pure Au. systems, wire-structured Au can adsorb both CO and O(2) rather strongly, and kinetic analysis suggests its high catalytic activity for low-temperature CO oxidation. The d-band center of Au at the catalytic site is determined to account for the unusual activity of the wire-structured film. A generalized structural model based on the wire-structured film is proposed for active Au, and possible support effects are discussed: Selected oxide surfaces can disperse Au atoms and stabilize the formation of a filmlike structure; they may also serve as a template for the preferential arrangement of Au atoms in a wire structure under low Au coverage.

14C as a tool to trace terrestrial carbon in a complex lake system: implications for food-web structure and carbon cycling

Globally lakes bury and remineralise significant quantities of terrestrial C, and the associated flux of terrestrial C strongly influences their functioning. Changing deposition chemistry, land use and climate induced impacts on hydrology will affect soil biogeochemistry and terrestrial C export¹ and hence lake ecology with potential feedbacks for regional and global C cycling. C and nitrogen stable isotope analysis (SIA) has identified the terrestrial subsidy of freshwater food webs. The approach relies on different ¹³C fractionation in aquatic and terrestrial primary producers, but also that inorganic C demands of aquatic primary producers are partly met by ¹³C depleted C from respiration of terrestrial C, and ‘old’ C derived from weathering of catchment geology. SIA thus fails to differentiate between the contributions of old and recently fixed terrestrial C. Natural abundance ¹⁴C can be used as an additional biomarker to untangle riverine food webs² where aquatic and terrestrial δ ¹³C overlap, but may also be valuable for examining the age and origin of C in the lake. Primary production in lakes is based on dissolved inorganic C (DIC). DIC in alkaline lakes is partially derived from weathering of carbonaceous bedrock, a proportion of which is¹⁴C-free. The low ¹⁴C activity yields an artificial age offset leading samples to appear hundreds to thousands of years older than their actual age. As such, ¹⁴C can be used to identify the proportion of autochthonous C in the food-web. With terrestrial C inputs likely to increase, the origin and utilisation of ‘fossil’ or ‘recent’ allochthonous C in the food-web can also be determined. Stable isotopes and 14C were measured for biota, particulate organic matter (POM), DIC and dissolved organic carbon (DOC) from Lough Erne, Northern Ireland, a humic alkaline lake. Temporal and spatial variation was evident in DIC, DOC and POM C isotopes with implications for the fluctuation in terrestrial export processes. Ramped pyrolysis of lake surface sediment indicates the burial of two C components. ¹⁴C activity (507 ± 30 BP) of sediment combusted at 400˚C was consistent with algal values and younger than bulk sediment values (1097 ± 30 BP). The sample was subsequently combusted at 850˚C, yielding 14C values (1471 ± 30 BP) older than the bulk sediment age, suggesting that fossil terrestrial carbon is also buried in the sediment. Stable isotopes in the food web indicate that terrestrial organic C is also utilised by lake organisms. High winter δ ¹⁵N values in calanoid zooplankton (δ ¹⁵N = 24%¸) relative to phytoplankton and POM (δ ¹⁵N = 6h and 12h respectively) may reflect several microbial trophic levels between terrestrial C and calanoids. Furthermore winter calanoid 14C ages are consistent with DOC from an inflowing river (75 ± 24 BP), not phytoplankton (367 ± 70 BP). Summer calanoid δ ^13C, δ ¹⁵N and ¹⁴C (345 ± 80 BP) indicate greater reliance on phytoplankton.

¹ Monteith, D.T et al., (2007) Dissolved organic carbon trends resulting from changes in atmospheric deposition chemistry. Nature, 450:537-535

² Caraco, N., et al.,(2010) Millennial-aged organic carbon subsidies to a modern river food web. Ecology,91: 2385-2393.

Copper(II) complexes of N(4)-substituted thiosemicarbazones derived from pyridine-2-carbaldehyde: Crystal structure of a binuclear complex

Ten copper(II) complexes {[CuL1Cl] (1), [CuL1NO3]2 (2), [CuL1N3]2 · 2/3H2O (3), [CuL1]2(ClO4)2 · 2H2O (4), [CuL2Cl]2 (5), [CuL2N3] (6), [Cu(HL2)SO4]2 · 4H2O (7), [Cu(HL2)2] (ClO4)2 · 1/2EtOH (8), [CuL3Cl]2 (9), [CuL3NCS] · 1/2H2O (10)} of three NNS donor thiosemicarbazone ligands {pyridine-2-carbaldehyde-N(4)-p-methoxyphenyl thiosemicarbazone [HL1], pyridine-2-carbaldehyde-N(4)-2-phenethyl thiosemicarbazone [HL2] and pyridine-2-carbaldehyde N(4)-(methyl), N(4)-(phenyl) thiosemicarbazone [HL3]} were synthesized and physico-chemically characterized. The crystal structure of compound 9 has been determined by X-ray diffraction studies and is found that the dimer consists of two square pyramidal Cu(II) centers linked by two chlorine atoms.

Influence of sulphate content on the physico-chemical properties and catalytic activity of some sulphated zirconia systems

The present work attempts a systematic examination of the effect of sulphate content on the physico-chemical properties and catalytic activity of sulphated zirconia and iron promoted sulphated zirconia systems. Sulphate content is estimated by EDX analysis. The amount of sulphate incorporated has been found to influence the surface area, crystal structure and the acid strength distribution. Ammonia TPD and adsorption studies using perylene have enabled the determination of surface acidic properties. The results are supported by the thermodesorption studies using pyridine and 2,6-dimethylpyridine. The catalytic activity towards benzoylation reaction has been correlated with the surface acidity of the systems.

Structure and far-infrared edge modes of quantum antidots at zero magnetic field

We have investigated edge modes of different multipolarity sustained by quantum antidots at zero magnetic field. The ground state of the antidot is described within a local-density-functional formalism. Two sum rules, which are exact within this formalism, have been derived and used to evaluate the energy of edge collective modes as a function of the surface density and the size of the antidot.

Investigations on the structural, optical and Magnetic properties of nanostructured cerium oxide in pure and doped forms and its polymer nanocomposiets

This thesis Entitled INVESTIGATIONS ON THE STRUCTURAL, OPTICAL AND MAGNETIC PROPERTIES OF NANOSTRUCTURED CERIUM OXIDE IN PURE AND DOPED FORMS AND ITS POLYMER NANOCOMPOSITES.Synthesis and processing of nanomatelials and nanostmctures are the essential aspects of nanotechnology. Studies on new physical properties and applications of nanomaterials and nanostructures are possible only when nanostructured materials are made available with desired size, morphology,crystal structure and chemical composition.Recently, several methods have been developed to prepare pure and doped CeO2 powder, including wet chemical synthesis, thermal hydrolysis, flux method, hydrothermal synthesis, gas condensation method, microwave technique etc. In all these, some special reaction conditions, such as high temperature, high pressure, capping agents, expensive or toxic solvents etc. have been involved.Another hi gh-li ght of the present work is room temperature ferromagnetism in cerium oxdie thin films deposited by spray pyrolysis technique.The observation of self trapped exciton mediated PL in ceria nanocrystals is another important outcome of the present study. STE mediated mechanism has been proposed for CeO2 nanocrystals based on the dependence of PL intensity on the annealing temperature. It would be interesting to extent these investigations to the doped forms of cerium oxide and cerium oxide thin films to get deeper Insight into STE mechanism.Due to time constraints detailed investigations could not be canied out on the preparation and properties of free standing films of polymer/ceria nanocomposites. It has been observed that good quality free standing films of PVDF/ceria, PS/C61‘l8, PMMA/ceria can be obtained using solution casting technique. These polymer nanocomposite films show high dielectric constant around 20 and offer prospects of applications as gate electrodes in metal-oxide semiconductor devices.

Studies on Energy Exchange and Upper Ocean Thermat Structure in Arabian Sea and Heat Transport in Northern Indian Ocean

The thesis focused Studies on Energy Exchange and Upper Ocean Thermal Structure in Arabian Sea and Heat Transport in Northern Indian Ocean. The present thesis is an attempt to understand the upper ocean thermal characteristics at selected areas in the western and eastern Arabian Sea in relation to surface energy exchange and dynamics, on a climatological basis. It is also aimed to examine, the relative importance of different processes in the evolution of SST at the western and eastern Arabian Sea. Short-term variations of energy exchange and upper ocean thermal structure are also investigated. Climatological studies of upper ocean thermal structure and surface energy exchange in the western and eastern parts of Arabian Sea bring out the similarities/differences and the causative factors for the observed features. Annual variation of zonally averaged heat advection in north Indian Ocean shows that maximum export of about 100 W/m2 occurs around 15ON during southwest monsoon season. This is due to large negative heat storage caused by intense upwelling in several parts of northern Indian Ocean. By and large, northern Indian Ocean is an area of heat export

Transition metal complexes of some N4-phenylsemicarbazones: crystal structures and spectral studies

The unusual coordination modes of semicarbazones when bound to metals, the wide applications and structural diversity of metal complexes of semicarbazones provoked us to synthesize and characterize the tridentate ONO and NNO-donor semicarbazones and their transition metal complexes. This work is focused on the studies on complexes of three N4-phenylsemicarbazones synthesized by changing the carbonyl compounds. This work is concerned with the studies of two new semicarbazones, 2- formylpyridine-N4-phenylsemicarbazone (HL1) and 3-ethoxysalicylaldehyde- N4-phenylsemicarbazone (H2L2) and a reported semicarbazone 2-benzoylpyridine-N4-phenylsemicarbazone (HL3) [29]. The compositions of these semicarbazones were determined by the CHN analyses and IR, UV and NMR spectral studies were used for the characterization of these compounds. The molecular structure of 3-ethoxysalicylaldehyde-N4-phenylsemicarbazone (H2L2) was obtained by single crystal X-ray diffraction studies. Also, we have synthesized Cu(II), Cd(II), Zn(II) and Ni(II) complexes of these three semicarbazones. The complexes were characterized by various spectroscopic techniques, magnetic and conductivity studies. We could isolate single crystals of some complexes of all metals suitable for X-ray diffraction studies. This thesis is divided into six chapters.

Transition metal complexes derived from ketone based N(4)-substituted thiosemicarbazones: Crystal structures and spectral studies

Thiosemicarbazones have recently attracted considerable attention due to their ability to form tridentate chelates with transition metal ions through either two nitrogen and sulfur atoms, N–N–S or oxygen, nitrogen and sulfur atoms, O–N–S. Considerable interest in thiosemicarbazones and their transition metal complexes has also grown in the areas of biology and chemistry due to biological activities such as antitumoral, fungicidal, bactericidal, antiviral and nonlinear optical properties. They have been used for metal analyses, for device applications related to telecommunications, optical computing, storage and information processing.The versatile applications of metal complexes of thiosemicarbazones in various fields prompted us to synthesize the tridentate NNS-donor thiosemicarbazones and their metal complexes. As a part of our studies on transition metal complexes with these ligands, the researcher undertook the current work with the following objectives. 1. To synthesize and physico-chemically characterize the following thiosemicarbazone ligands: a. Di-2-pyridyl ketone-N(4)-methyl thiosemicarbazone (HDpyMeTsc) b. Di-2-pyridyl ketone-N(4)-ethyl thiosemicarbazone (HDpyETsc) 2. To synthesize oxovanadium(IV), manganese(II), nickel(II), copper(II), zinc(II) and cadmium(II) complexes using the synthesized thiosemicarbazones as principal ligands and some anionic coligands. 3. To study the coordination modes of the ligands in metal complexes by using different physicochemical methods like partial elemental analysis, thermogravimetry and by different spectroscopic techniques. 4. To establish the structure of compounds by single crystal XRD studies

MgO/Ag(001) interface structure and STM images from first principles

The interface of MgO/Ag(001) has been studied with density functional theory applied to slabs. We have found that regular MgO films show a small adhesion to the silver substrate, the binding can be increased in off-stoichiometric regimes, either by the presence of O vacancies at the oxide film or by a small excess of O atoms at the interface between the ceramic to the metal. By means of theoretical methods, the scanning tunneling microscopy signatures of these films is also analyzed in some detail. For defect free deposits containing 1 or 2 ML and at low voltages, tunnelling takes place from the surface Ag substrate, and at large positive voltages Mg atoms are imaged. If defects, oxygen vacancies, are present on the surface of the oxide they introduce much easier channels for tunnelling resulting in big protrusions and controlling the shape of the image, the extra O stored at the interface can also be detected for very thin films.