Navaratnarajah Kuganathan

Structure and Lithium Transport Pathways in Li2FeSiO4 Cathodes for Lithium Batteries

The importance of exploring new low-cost and safe cathodes for large-scale lithium batteries has led to increasing interest in Li(2)FeSiO(4). The structure of Li(2)FeSiO(4) undergoes significant change on cycling, from the as-prepared γ(s) form to an inverse β(II) polymorph; therefore it is important to establish the structure of the cycled material. In γ(s) half the LiO(4), FeO(4), and SiO(4) tetrahedra point in opposite directions in an ordered manner and exhibit extensive edge sharing. Transformation to the inverse β(II) polymorph on cycling involves inversion of half the SiO(4), FeO(4), and LiO(4) tetrahedra, such that they all now point in the same direction, eliminating edge sharing between cation sites and flattening the oxygen layers. As a result of the structural changes, Li(+) transport paths and corresponding Li-Li separations in the cycled structure are quite different from the as-prepared material, as revealed here by computer modeling, and involve distinct zigzag paths between both Li sites and through intervening unoccupied octahedral sites that share faces with the LiO(4) tetrahedra.

Self-assembly of a sulphur-terminated graphene nanoribbon within a single-walled carbon nanotube

The ability to tune the properties of graphene nanoribbons (GNRs) through modification of the nanoribbons width and edge structure widens the potential applications of graphene in electronic devices. Although assembly of GNRs has been recently possible, current methods suffer from limited control of their atomic structure, or require the careful organization of precursors on atomically flat surfaces under ultra-high vacuum conditions. Here we demonstrate that a GNR can self-assemble from a random mixture of molecular precursors within a single-walled carbon nanotube, which ensures propagation of the nanoribbon in one dimension and determines its width. The sulphur-terminated dangling bonds of the GNR make these otherwise unstable nanoribbons thermodynamically viable over other forms of carbon. Electron microscopy reveals elliptical distortion of the nanotube, as well as helical twist and screw-like motion of the nanoribbon. These effects suggest novel ways of controlling the properties of these nanomaterials, such as the electronic band gap and the concentration of charge carriers.

Electride support boosts nitrogen dissociation over ruthenium catalyst and shifts the bottleneck in ammonia synthesis

Novel approaches to efficient ammonia synthesis at an ambient pressure are actively sought out so as to reduce the cost of ammonia production and to allow for compact production facilities. It is accepted that the key is the development of a high-performance catalyst that significantly enhances dissociation of the nitrogen–nitrogen triple bond, which is generally considered a rate-determining step. Here we examine kinetics of nitrogen and hydrogen isotope exchange and hydrogen adsorption/desorption reactions for a recently discovered efficient catalyst for ammonia synthesis—ruthenium-loaded 12CaO·7Al2O3 electride (Ru/C12A7:e−)—and find that the rate controlling step of ammonia synthesis over Ru/C12A7:e− is not dissociation of the nitrogen–nitrogen triple bond but the subsequent formation of N–Hn species. A mechanism of ammonia synthesis involving reversible storage and release of hydrogen atoms on the Ru/C12A7:e− surface is proposed on the basis of observed hydrogen absorption/desorption kinetics.

Interactions and Reactions of Transition Metal Clusters with the Interior of Single-Walled Carbon Nanotubes Imaged at the Atomic Scale

Clusters of transition metals, W, Re, and Os, upon encapsulation within a single-walled carbon nanotube (SWNT) exhibit marked differences in their affinity and reactivity with the SWNT, as revealed by low-voltage aberration-corrected high-resolution transmission electron microscopy (AC-HRTEM). Activated by an 80 keV electron beam, W reacts only weakly with the SWNT, Re creates localized defects on the sidewall, and Os reacts readily causing extensive defect formation and constriction of the SWNT sidewall followed by total rupture of the tubular structure. AC-HRTEM imaging at the atomic level of structural transformations caused by metal-carbon bonding of π- and σ-character demonstrates what a crucial role these types of bonds have in governing the interactions between the transition metal clusters and the SWNT. The observed order of reactivity W < Re < Os is independent of the metal cluster size, shape, or orientation, and is related to the metal to nanotube bonding energy and the amount of electronic density transferred between metal and SWNT, both of which increase along the triad W, Re, Os, as predicted by first-principles density functional theory calculations. By selecting the appropriate energy of the electron beam, the metal-nanotube interactions can be controlled (activated or precluded). At an electron energy as low as 20 keV, no visible transformations in the nanotube in the vicinity of Os-clusters are observed.

Activation and splitting of carbon dioxide on the surface of an inorganic electride material

Activation of carbon dioxide is the most important step in its conversion into valuable chemicals. Surfaces of stable oxide with a low work function may be promising for this purpose. Here we report that the surfaces of the inorganic electride [Ca24Al28O64]4+(e−)4 activate and split carbon dioxide at room temperature. This behaviour is attributed to a high concentration of localized electrons in the near-surface region and a corrugation of the surface that can trap oxygen atoms and strained carbon monoxide and carbon dioxide molecules. The [Ca24Al28O64]4+(e−)4 surface exposed to carbon dioxide is studied using temperature-programmed desorption, and spectroscopic methods. The results of these measurements, corroborated with ab initio simulations, show that both carbon monoxide and carbon dioxide adsorb on the [Ca24Al28O64]4+(e−)4 surface at RT and above and adopt unusual configurations that result in desorption of molecular carbon monoxide and atomic oxygen upon heating.

Dinitrogen fixation and activation by Ti and Zr atoms, clusters and complexes

This perspective deals with dinitrogen fixation and activation (a) by complexes of the early transition metals Ti and Zr as synthesized by solution techniques, and (b) by ligand-free Ti and Zr atoms and small clusters as generated using the matrix isolation technique. The two approaches are very different, and not many attempts have yet been made to connect the two different research areas, although a detailed understanding of dinitrogen activation and fixation can only be achieved if all efforts are combined. One of the most striking results that emerged from the research of one of us is that the ligand-free dimer Ti2, which can be stabilized and studied in matrix isolation experiments, is able to cleave the strong NN triple bond without a significant activation barrier in just one step, leading to the cyclic bis-nitrido species Ti(μ-N)2Ti. In this perspective we are discussing possibilities to use this unusually high reactivity for catalytic processes.

Crystal structure of low-dimensional Cu(I) iodide: DFT prediction of cuprophilic interactions

Density functional theory calculations of the crystal structure of copper(I) iodide encapsulated within small diameter single walled nanotubes predict edge sharing tetrahedra of copper atoms, bridged by iodine, with Cu-Cu near neighbour distances varying from 2.42 to 2.72 A indicating a strong closed shell cuprophilic interaction.

Enhanced N2 dissociation on Ru-loaded inorganic electride.

Electrides, i.e. salts in which electrons serve as anions, are promising materials for lowering activation energies of chemical reactions. Ab initio simulations are used to investigate the effect of the electron anions in a prototype mayenite-based electride (C12A7:e(-)) on the mechanism of N2 dissociation. It is found that both atomic and molecular nitrogen species chemisorb on the electride surface and become negatively charged due to the electron transfer from the substrate. However, charging alone is not sufficient to promote dissociation of N2 molecules. In the presence of Ru, N2 adsorbs with the formation of a cis-Ru2N2 complex and the N-N bond weakens due to both the electron transfer from the substrate and interaction with Ru. This complex transforms into a more stable trans-Ru2N2 configuration, in which the N2 molecule is dissociated, with the calculated barrier of 116 kJ mol(-1) and the overall energy gain of 72 kJ mol(-1). In contrast, in the case of the stoichiometric mayentie, the cis-Ru2N2 is ~34 kJ mol(-1) more stable than the trans-Ru2N2, while the cis-trans transition has a barrier of 192 kJ mol(-1). Splitting of N2 is promoted by a combination of the strong electron donating power of C12A7:e(-), ability of Ru to capture N2, polarization of Ru clusters, and electrostatic interaction of negatively charged N species with the surface cations.

Chemical Analysis of Datura Metel Leaves and Investigation of the Acute Toxicity on Grasshoppers and Red Ants

The present study was carried out to analyse the inorganic and organic contents in the leaf of Datura metel and to investigate the acute toxicity at varying concentrations on grasshoppers and red ants. We determined the calcium, magnesium and phosphorous in the ionic state quantitatively and carried out screening tests and solvent extraction using chloroform to find out the presence of organic groups such as alkaloids, flavanoids, saponins and steroids. The concentration of Ca2

High-precision imaging of an encapsulated Lindqvist ion and correlation of its structure and symmetry with quantum chemical calculations

Low-voltage aberration-corrected transmission electron microscopy (AC-TEM) of discrete Lindqvist [W(6)O(19)](2-) polyoxometalate ions inserted from an ethanolic solution of [NBu(4)](2)[W(6)O(19)] into double walled carbon nanotubes (DWNTs) allows a higher precision structural study to be performed than previously reported. W atom column separations within the constituent W(6) tungsten cage can now be visualized with sufficient clarity that reliable correlation with structural predictions from density functional theory (DFT) can be achieved. Calculations performed on [W(6)O(19)](2-) anions encapsulated in carbon nanotubes show good agreement with measured separations between pairs of W(2) atom columns imaged within equatorial WO(6) polyhedral pairs and also single W atom positions located within individual axial WO(6) octahedra. Structural data from the tilted chiral encapsulating DWNT were also determined simultaneously with the anion structural measurements, allowing the influence of the conformation of the encapsulating tubule to be included in the DFT calculation and compared against that of other candidate encapsulating nanotubes. Additional DFT calculations performed using Li(+) cations as a model for the [NBu(4)](+) counterions indicate that the latter may help to induce charge transfer between the DWNT and the [W(6)O(19)](2-) ion and this may help to constrain the motion of the ion in situ.