Selective synthesis of zigzag-type aligned carbon nanotubes on SiC (0 0 0 −1) wafers

Zigzag-type carbon nanotubes have been selectively produced by surface decomposition of a well-polished SiC single crystal. The SiC wafer was heated to 1500 °C at a very small heating rate under vacuum. Transmission electron microscopy (TEM) and electron diffraction patterns revealed that almost all the well-aligned carbon nanotubes formed perpendicular to the SiC (0 0 0 −1) surface were double-walled and of zigzag type. The results of high-resolution electron microscopy (HREM) indicate that the zigzag type structure evolves from the Si–C hexagonal networks in the SiC crystal by the collapse of carbon layers remaining after the process of decomposition.     

Electrocatalysis on gold nanostructures: Is the {1 1 0} facet more active than the {1 1 1} facet?

The anisotropic electrocatalytic properties of gold nanobelts and nanoplates enclosed by either {1 1 0} or {1 1 1} facets were studied. Different strategies were used to synthesize these materials. It was found that the {1 1 0} surface of gold does not necessarily show a higher electrocatalytic activity than the {1 1 1} surface. The {1 1 0} surface of gold is more active than the {1 1 1} surface for glucose oxidation in both, neutral and alkaline media. However, for methanol oxidation in alkaline solution, the {1 1 0} surface shows a lower activity than the {1 1 1} surface, which is contrary to the general belief that {1 1 0} facet is the most active surface among the three basal planes. The possible mechanisms are discussed.     

Thermally-driven processes on rutile TiO2(1 1 0)-(1 × 1): A direct view at the atomic scale

The technological importance of TiO₂ has led to a broad effort aimed at understanding the elementary steps that underlie catalytic and photocatalytic reactions. The most stable surface, rutile TiO₂(1 1 0), in particular, has became a prototypical model for fundamental studies of TiO₂. In this critical review we have selected oxygen, water, and alcohols to evaluate recent progress relevant for applications in the areas of water splitting and oxidation of organic contaminants. We first focus on the characterization of defects and the distribution of excess charge that results from their formation. The subsequent section concentrates on the role of individual surface sites and the effect of available charge in the adsorption processes. The discussion of adsorbate dynamics follows, providing models for intrinsic and extrinsic diffusion processes as well as rotational dynamics of anchored alkoxy species. The final section summarizes our current understanding of TiO₂(1 1 0) catalyzed reactions between water, oxygen, and their dissociation products.     

Spectral,electrochemical and computational investigations on the host–guest interaction of Coumarin-460 with <Emphasis Type="Italic">p</Emphasis>-sulfonatocalix[4]arene

The supramolecular host–guest investigation of Coumarin 460 (C460), a salient coumarin family dye molecule is studied with a noteworthy host molecule, p-sulfonatocalix[4]arene (p-SC4). The investigation is carried out by both experimental and theoretical approach. The binding affinity of C460 with p-SC4 is experimentally studied using absorption, emission, excited state lifetime and Cyclic Voltammetry methods. The binding constant is around 10³ M^??1, which shows potent binding. The binding stoichiometry is 1:1. The binding orientations and binding energies are studied using computational simulations. The mode of binding is also established using NMR spectral techniques.     

Reactive epitaxy of beryllium on Si(1 1 1)-(7×7)

Scanning tunneling microscopy (STM) and photoelectron spectroscopy (PES) have been used to investigate the nucleation, growth, and structure of beryllium on Si(1 1 1)-(7×7). STM indicates that a chemical reaction occurs at temperatures as low as 120 K, resulting in a nano-clustered morphology, presumed to be composed of a beryllium silicide compound. Upon annealing to higher temperatures, PES data indicate that beryllium diffuses into the selvage region. High temperature annealing (∼1175 K) results in the formation of a universal ring cluster structure suggesting a Be–Si bond length less than 2.5 Å, in agreement with previous calculations regarding hypothetical Be₂Si.     

Are dispersive forces relevant for CO adsorption on the MgO(0 0 1) surface?

Periodic ab initio B3-LYP calculations on the MgO(0 0 1)/CO system underestimate the CO binding energy value with respect to experiment. The flaw is in the B3-LYP functional, unable to compute dispersive interactions. Here we show how to evaluate this contribution by adopting a two-layer ONIOM scheme in which the B3-LYP crystal energy is improved by the MP2 energy computed on the Mg₉O₉/CO cluster. The final complete basis set extrapolated (MP2/∞:B3-LYP/VTZ) CO/Mg(0 0 1) binding energy of 13 kJ/mol is in good agreement with experiment, with about 7 kJ/mol deriving from dispersive interactions.     

Thermoanalytical investigations on the sol-gel synthesis of YBa2Cu3O72212;δ

The high temperature superconducting compound YBa₂Cu₃O_72212; (Y-123) is synthesised by sol-gel process using various precursors viz., acetate, acetate-citrate, nitrate-citrate and acrylamide. The phase purity of the final product depends on the homogeneity of the gels which intern depends on the bonding of the metal ions in the gels. The samples prepared by acrylamide and nitrate-citrate gel routes yielded phase pure Y-123 compound with better superconducting properties. The mechanism of formation of Y-123 in all these four gel routes is established by characterising the gels and intermediate phases using TG, DTA and XRD techniques. Kinetic analysis is carried out on the mass loss data using the method proposed by Phadni's and Deshpande. Avrami-Erofeev nuclei growth in case of acrylamide, diffusion controlled process in nitrate-citrate and phase boundary reaction mechanisms in case of acetate-citrate gels are found to be responsible for the formation of Y-123 phase.The authors are grateful to Dr. Baldev Raj, Director, Metals and Materials Group, for his constant encouragement and support. We thank Prof. G. V. Subba Rao, Director, Central Electrochemical Research Institute, Karaikudi for his keen interest in this work. Thanks are also due to Dr. Sundaram, CECRI, Karaikudi for his help in thermal analysis experiments.     

First-principles study on the geometries,stabilities and electronic properties of yttrium–silicon clusters (Y2Si n ; 1 ≤ n ≤ 12)

Structural Chemistry - The geometries, growth patterns, relative stabilities and electronic properties of yttrium-doped silicon clusters Y2Si n (n&nbsp;=&nbsp;1–12) are systematically...     

A thermodynamic study on solubility and liquid−liquid phase behaviour for 2,2,2-trifluoroethanol + cyclohexane + 1-butanol at three temperatures and pressure 101.3 kPa

This study demonstrates the course of solubility and (liquid + liquid) equilibrium (LLE) for the system (cyclohexane + 1-butanol + 2,2,2-trifluoroethanol) at temperatures of (288.15, 298.15, and 308.15) K and pressure 101.3 kPa. The titration method was used to assess solubility (binodal) curves, while a direct analytical method to acquire tie lines.The consistency of the binodal curves and phase diagrams data were well calculated by Hand and Othmer–Tobias empirical equations. The NRTL and UNIQUAC thermodynamic models gave accurate tie-line values for the systems. Plait-point, distribution coefficient, solvent selectivity, and NRTL and UNIQUAC binary interaction parameters were obtained.The immiscibility region of the system decreases significantly with increasing temperature. The results present an overview of the high efficiency of liquid extraction using 2,2,2-trifluoroethanol as solvent to yield pure cyclohexane from its 1-butanol azeotrope mixture at ambient temperatures.     

Study on the effect of Li doping in spinel Li4+xTi5−xO12 (0 ⩽ x ⩽ 0.2) materials for lithium-ion batteries

The effect of Li doping in spinel Li_4+xTi_5−xO₁₂ (0 ⩽ x ⩽ 0.2) materials on the structural and electrochemical properties were investigated. The ratio of the capacity in the voltage plateau (1.5 V) to the overall discharge capacity for Li_4.1Ti_4.9O₁₂ (x = 0.1) and Li_4.2Ti_4.8O₁₂ (x = 0.2) were higher than that of Li₄Ti₅O₁₂ especially at high current rates due to their enhanced lithium-ion and electronic conductivity by the substitution of Ti atoms by Li atoms. With the increasing of Li doping amount, lithium-ion and electronic conductivity of Li_4+xTi_5−xO₁₂ increased, however its cycling stability was depressed when the Li doping was of x = 0.2. The Li doping of x = 0.1, the appropriate Li doping amount, showed improved rate capability and better high rate performance comparing to undoped Li_4+xTi_5−xO₁₂ (x = 0).     

A single crystal X-ray and powder neutron diffraction study on NASICON-type Li1+xAlxTi2−x(PO4)3 (0 ≤ x ≤ 0.5) crystals: Implications on ionic conductivity

Single crystals of NASICON-type material Li_1+xTi_2−xAl_x(PO₄)₃ (LATP) with 0 ≤ x ≤ 0.5 were successfully grown using long-term sintering techniques. Sample material was studied by chemical analysis, single crystal X-ray and neutron diffraction. The Ti⁴⁺ replacement scales very well with the Al³⁺ and Li⁺ incorporation. The additional Li⁺ thereby enters the M3 cavity of the NASICON framework at x, y, z ∼ (0.07, 0.34, 0.09) and is regarded to be responsible for the enhanced Li⁺ conduction of LATP as compared to Al-free LTP. Variations in structural parameters, associated with the Ti⁴⁺ substitution with Al³⁺ + Li⁺ will be discussed in detail in this paper.     

A new accurate calorimetric method for the enthalpy of fusion measurements up to 1000 °C

A new metrological approach is proposed by the Laboratoire National de Metrologie et d’Essais to lower the uncertainty of measurements of enthalpy of fusion from 23 to 1000 °C. It consists, as in our previous works, in putting the studied sample inside a calibration crucible and in performing the heat calibration of the calorimeter by electrical substitution at two temperatures before and after the temperature of fusion of the sample during the same low-rate heating run. The novelty lies in the “electrical compensation” of the endothermic reaction of fusion. The quantification of the electrical energy needed to melt the sample, which can be measured with high accuracy, and the integrated remaining heat flow rate divided by the calibration factor (sensitivity) of the calorimeter at the temperature of fusion, leads to the determination of the enthalpy of fusion of the sample with low uncertainty. This methodology reduces the influence of the uncertainty component associated with the area of the peak of fusion by comparison with the former procedure when no electrical compensation was applied. The relative expanded uncertainty (k = 2) associated with the enthalpy of fusion measurements, performed using this facility and this new procedure, has been assessed to be < 0.2% for tin and indium and to be about 0.3% in the case of silver.

     

Vibrational relaxation rates for H on a Si(1 0 0):(2×1) surface: a two-dimensional model

The results of calculations based on perturbation theory of vibrational relaxation rates due to coupling to substrate phonons for hydrogen atoms adsorbed on a Si(1 0 0):(2×1) surface are presented. For this purpose a two-dimensional model is adopted in which both the H–Si stretching and bending motions are included. It is shown that within this model the multiphonon emission and absorption processes play a negligible role. The calculated lifetimes agree well with available experimental data.     

Doping effects on mixed-phase crystalline perovskite AxSr1−xFeO3−δ (A = Pr,Sm; 0 ≤ x ≤ 0.8) nanoparticles and their application for photodegradation of rhodamine B

Research on Chemical Intermediates - A series of doped perovskite AxSr1?xFeO3?δ (A?=?Pr, Sm; 0?≤?x?≤?0.8) nanoparticles were...     

Theoretical investigations of TTR derived aggregation-prone peptides’ potential to biochemically attenuate the amyloidogenic propensities of V30 M TTR amyloid fibrils

Transthyretin (TTR) is a cerebrospinal fluid and plasma prevalent protein implicated in heritable and sporadic amyloidosis. Numerous mutations and a wide range of phenotypes have been associated with TTR-mediated amyloidosis. Among these, V30 M is the most predominant point mutation, inculpated with familial amyloid polyneuropathy (FAP), a life-threatening autosomal dominant genetic disorder characterized by the deposition of amyloid fibrils in crucial areas. Hence, efficacious therapeutics against this detrimental disorder is warranted. Lately, several peptide-based analeptics, especially the ones that are aggregation-prone and the ones derived from aggregation hotspots of amyloidogenic proteins are being increasingly proffered against the amyloid fibrils. In the present study, as an effective precursor to in vitro investigations, we examined and assessed the therapeutic potentials of aggregation-prone peptides (APPs) derived from TTR, against V30 M TTR amyloid fibrils, computationally. Out of five experimentally corroborated APPs availed for this study, molecular dynamics simulation analysis endorses APP TAVVTN to be an effective beta-sheet breaker against V30 M TTR amyloid fibrils. Furthermore, consistent findings from various molecular trajectory analyses, residual frustration analysis and simulated thermal denaturation have indicated that APP TAVVTN could effectually relater the structural dynamics of V30 M TTR amyloid fibrils, to conformationally digress it away from its amyloidogenic propensities. Hence, based on consistent unvarying findings from numerous adept computational pipelines, APP TAVVTN could be an efficacious analeptic to therapeutically intervene and mitigate the amyloidogenic propensities of V30 M TTR amyloid fibrils, thereby ameliorating the pathological ramifications due to FAP.     

Thermochemical behaviour of crown ethers in the mixtures of water with organic solvents. Part IX. Effect of base–acid properties of {(1 − x)AN + xH2O} on the solution enthalpy of cyclic ethers in this mixed solvent at T = 298.15 K

The enthalpies of solution of cyclic ethers: 1,4-dioxane, 12-crown-4 and 18-crown-6 in {(1 ? x)AN + xH₂O} have been measured over the whole mole fraction range at T = 298.15 K. Based on the results obtained, the effects of base–acid properties of mixed solvent and the number of –CH₂CH₂– groups in cyclic ethers molecules on the solution enthalpy of cyclic ethers in {(1 ? x)AN + xH₂O} have been analyzed.     

Investigation on graphitic carbon foams – LiNiyPO4 (y = 0.8–1.0) composites

Graphitic carbon foams coated with olivine-structured lithium nickel phosphate (LiNi_yPO₄) (y = 0.8–1.0) as possible cathode materials for 5 V applications are investigated. The composites are prepared by soaking the foams into solutions containing lithium, nickel ions and phosphates, treated in flowing air then in flowing nitrogen. The structural, morphological and electrochemical properties are strongly dependent upon the Ni-content. The X-ray diffractograms, performed on powders prepared under very similar conditions, showed the formation of LiNiPO₄ phase with Li₄P₂O₇ and Li₂Ni₃(P₂O₇)₂. The morphological investigation revealed a dramatic change of the layer by decreasing the Ni-content. The voltammetric curves show values of the mean peak maxima in the anodic region between 5.1 and 5.2 V and in the cathodic region between 4.88 for (y = 1.0) and ∼5.18 V for (y = 0.9 and 0.8) respectively. The specific capacity of the composites (at the first cycle, a discharge rate of C/10 and room temperature) increases by decreasing the nickel content into the cathode material reaching a maximum of 122 mAh g⁻¹ for y = 0.8.