Maria L. Sushko

Sodium ion insertion in hollow carbon nanowires for battery applications.

Hollow carbon nanowires (HCNWs) were prepared through pyrolyzation of a hollow polyaniline nanowire precursor. The HCNWs used as anode material for Na-ion batteries deliver a high reversible capacity of 251 mAh g(-1) and 82.2% capacity retention over 400 charge-discharge cycles between 1.2 and 0.01 V (vs Na(+)/Na) at a constant current of 50 mA g(-1) (0.2 C). Excellent cycling stability is also observed at an even higher charge-discharge rate. A high reversible capacity of 149 mAh g(-1) also can be obtained at a current rate of 500 mA g(-1) (2C). The good Na-ion insertion property is attributed to the short diffusion distance in the HCNWs and the large interlayer distance (0.37 nm) between the graphitic sheets, which agrees with the interlayered distance predicted by theoretical calculations to enable Na-ion insertion in carbon materials.

High‐Performance LiNi0.5Mn1.5O4 Spinel Controlled by Mn3+ Concentration and Site Disorder

The complex correlation between Mn(3+) ions and the disordered phase in the lattice structure of high voltage spinel, and its effect on the charge transport properties, are revealed through a combination of experimental study and computer simulations. Superior cycling stability is achieved in LiNi(0.45)Cr(0.05)Mn(1.5)O(4) with carefully controlled Mn(3+) concentration. At 250th cycle, capacity retention is 99.6% along with excellent rate capabilities.

Computational Techniques at the Organic−Inorganic Interface in Biomineralization

Just over ninety years ago, the first edition of D’Arcy Thompson’s book On Growth and Form appeared. Much of it is long out of date, but D’Arcy Thompson makes a point of fundamental importance in his discussion of the morphology of inorganic crystals in biological systems. He points out that the deposition of minerals in the living body, the complex shapes and symmetries often seen, cannot be explained by simple ideas of crystal packing. He speculates (and in 1919 it could be no more than speculation) on the importance of “directing forces”, using the analogy of ordering in liquid crystals discussed in the work of Lehman. In some cases, it was already clear that a pre-existing template controlled the growth of the inorganic material and D’Arcy Thompson shows how the complex forms of the silicate skeletons of sponges and radiolarians can be explained using simple models based on froths and bubbles that somehow constrain the growth of the inorganic material in their interstices. This presence of some controlling growth mechanism distinguishes two kinds of biomineralization process. Biologically induced mineralization occurs when minerals form as a byproduct of the activity of cells or their interaction with the surrounding environment. The morphologies and phases observed are usually similar to those seen in nonbiological systems. Biologically controlled mineralization is regulated by the organism, and the resulting structures have a physiological function (or sometimes functions). In this review, we are concerned only with the second case, biologically controlled mineralization. * Address for corresponding author: Department of Engineering Materials, Sir Robert Hadfield Building, University of Sheffield, Mappin St., Sheffield S1 3JD, U.K. Telephone: +44 114 222 5957. Fax: +44 114 222 5943. E-mail: j.harding@sheffield.ac.uk. Chem. Rev. 2008, 108, 4823–4854 4823

Functionalized Graphene Sheets as Molecular Templates for Controlled Nucleation and Self‐Assembly of Metal Oxide‐Graphene Nanocomposites

Graphene sheets have been extensively studied as a key functional component of graphene-based nanocomposites for electronics, energy, catalysis,and sensing applications. However, fundamental understanding of the interfacial binding and nucleation processes at graphene surfaces remains lacking, and the range of controlled structures that can be produced are limited. Here, by using a combination of theoretical and experimental approaches, we demonstrate that functionalized graphene sheets (FGS) can function as a new class of molecular templates to direct nucleation and self-assembly and produce novel, three-dimensional nanocomposite materials. Two key aspects are demonstrated: First, the functional groups on FGS surface determine the nucleation energy, and thus control the nucleation sites and nucleation density, as well as the preferred crystalline phases. Second, FGS can function as a template to direct the self-assembly of surfactant micelles and produce ordered, mesoporous arrays of crystalline metal oxides and composites.

Zirconium-based metal-organic framework for removal of perrhenate from water

The efficient removal of pertechnetate (TcO4(-)) anions from liquid waste or melter off-gas solution for an alternative treatment is one of the promising options to manage (99)Tc in legacy nuclear waste. Safe immobilization of (99)Tc is of major importance because of its long half-life (t1/2 = 2.13 × 10(5) yrs) and environmental mobility. Different types of inorganic and solid-state ion-exchange materials have been shown to absorb TcO4(-) anions from water. However, both high capacity and selectivity have yet to be achieved in a single material. Herein, we show that a protonated version of an ultrastable zirconium-based metal-organic framework can adsorb perrhenate (ReO4(-)) anions, a nonradioactive surrogate for TcO4(-), from water even in the presence of other common anions. Synchrotron-based powder X-ray diffraction and molecular simulations were used to identify the position of the adsorbed ReO4(-) (surrogate for TcO4(-)) molecule within the framework.

Ionic asymmetry and solvent excluded volume effects on spherical electric double layers: a density functional approach.

In this article, we present a classical density functional theory for electrical double layers of spherical macroions that extends the capabilities of conventional approaches by accounting for electrostatic ion correlations, size asymmetry, and excluded volume effects. The approach is based on a recent approximation introduced by Hansen-Goos and Roth for the hard sphere excess free energy of inhomogeneous fluids [J. Chem. Phys. 124, 154506 (2006); Hansen-Goos and Roth, J. Phys.: Condens. Matter 18, 8413 (2006)]. It accounts for the proper and efficient description of the effects of ionic asymmetry and solvent excluded volume, especially at high ion concentrations and size asymmetry ratios including those observed in experimental studies. Additionally, we utilize a leading functional Taylor expansion approximation of the ion density profiles. In addition, we use the mean spherical approximation for multi-component charged hard sphere fluids to account for the electrostatic ion correlation effects. These approximations are implemented in our theoretical formulation into a suitable decomposition of the excess free energy which plays a key role in capturing the complex interplay between charge correlations and excluded volume effects. We perform Monte Carlo simulations in various scenarios to validate the proposed approach, obtaining a good compromise between accuracy and computational cost. We use the proposed computational approach to study the effects of ion size, ion size asymmetry, and solvent excluded volume on the ion profiles, integrated charge, mean electrostatic potential, and ionic coordination number around spherical macroions in various electrolyte mixtures. Our results show that both solvent hard sphere diameter and density play a dominant role in the distribution of ions around spherical macroions, mainly for experimental water molarity and size values where the counterion distribution is characterized by a tight binding to the macroion, similar to that predicted by the Stern model.

Interface Promoted Reversible Mg Insertion in Nanostructured Tin–Antimony Alloys

An interface promoted approach is developed for guiding the design of stable and high capacity materials for Mg batteries using SnSb alloys as model materials. Experimental and theoretical studies reveal that the SnSb alloy has exceptionally high reversible capacity (420 mA h g(-1)), excellent rate capability, and good cyclic stability for hosting Mg ions due to the stabilization/promotion effects of the interfaces between the multicomponent phases generated during repeated magnesiation-demagnesiation.

Numerical Solution of 3D Poisson-Nernst-Planck Equations Coupled with Classical Density Functional Theory for Modeling Ion and Electron Transport in a Confined Environment

We have developed efficient numerical algorithms for the solution of 3D steady-state Poisson-Nernst-Planck equations (PNP) with excess chemical potentials described by the classical density functional theory (cDFT). The coupled PNP equations are discretized by finite difference scheme and solved iteratively by Gummel method with relaxation. The Nernst-Planck equations are transformed into Laplace equations through the Slotboom transformation. Algebraic multigrid method is then applied to efficiently solve the Poisson equation and the transformed Nernst-Planck equations. A novel strategy for calculating excess chemical potentials through fast Fourier transforms is proposed which reduces computational complexity from O(N2) to O(NlogN) where N is the number of grid points. Integrals involving Dirac delta function are evaluated directly by coordinate transformation which yields more accurate result compared to applying numerical quadrature to an approximated delta function. Numerical results for ion and electron transport in solid electrolyte for Li ion batteries are shown to be in good agreement with the experimental data and the results from previous studies.

Nanomechanics of organic/inorganic interfaces: a theoretical insight

Microfabricated arrays of cantilevers coated with active layers represent ultrasensitive devices for the label-free detection of chemical and biochemical reactions. The development of these sensors for practical applications requires an understanding of the mechanism of transduction of chemical or physical changes in the active layer of the cantilever into its mechanical bending. In order to eliminate non-specific effects, differential detection with respect to reference cantilevers with an inert coating is used. However, the convolution of different specific effects leading to cantilever bending does not allow their direct decoupling based on experiments alone. We propose a quantitative mesoscopic model showing that there are two competing components to the differential deflection: the component associated with specific chemical or physical reaction on the active cantilever and the component due to a difference in elastic properties of the active and reference coatings. We apply the model to study the origin of the chemomechanical response in cantilever arrays for experimentally studied reactions, including deprotonation of pH sensitive self-assembled monolayers, DNA hybridization and swelling of polyelectrolyte brushes. We show that for all these diverse systems the theoretical model gives good quantitative agreement with the experimental data and provides a guide for designing cantilever sensors with significantly improved sensitivity.

The role of correlation and solvation in ion interactions with B-DNA

The ionic atmospheres around nucleic acids play important roles in biological function. Large-scale explicit solvent simulations coupled to experimental assays such as anomalous small-angle x-ray scattering can provide important insights into the structure and energetics of such atmospheres but are time- and resource intensive. In this article, we use classical density functional theory to explore the balance among ion-DNA, ion-water, and ion-ion interactions in ionic atmospheres of RbCl, SrCl2, and CoHexCl3 (cobalt hexamine chloride) around a B-form DNA molecule. The accuracy of the classical density functional theory calculations was assessed by comparison between simulated and experimental anomalous small-angle x-ray scattering curves, demonstrating that an accurate model should take into account ion-ion correlation and ion hydration forces, DNA topology, and the discrete distribution of charges on the DNA backbone. As expected, these calculations revealed significant differences among monovalent, divalent, and trivalent cation distributions around DNA. Approximately half of the DNA-bound Rb(+) ions penetrate into the minor groove of the DNA and half adsorb on the DNA backbone. The fraction of cations in the minor groove decreases for the larger Sr(2+) ions and becomes zero for CoHex(3+) ions, which all adsorb on the DNA backbone. The distribution of CoHex(3+) ions is mainly determined by Coulomb and steric interactions, while ion-correlation forces play a central role in the monovalent Rb(+) distribution and a combination of ion-correlation and hydration forces affect the Sr(2+) distribution around DNA. This does not imply that correlations in CoHex solutions are weaker or stronger than for other ions. Steric inaccessibility of the grooves to large CoHex ions leads to their binding at the DNA surface. In this binding mode, first-order electrostatic interactions (Coulomb) dominate the overall binding energy as evidenced by low sensitivity of ionic distribution to the presence or absence of second-order electrostatic correlation interactions.