Gold nanoparticles anchored reduced graphene oxide as catalyst for oxygen electrode of rechargeable Li-O-2 cells

Gold nanoparticles decorated reduced graphene oxide (Au-RGO) catalyst for O-2 electrode is prepared by in situ reduction of Au3+ ions and graphene oxide dispersed in water. The Au nanoparticles are uniformly distributed on the two-dimensional RGO layers. Li-O-2 cells assembled in a non-aqueous electrolyte using Au-RGO catalyst exhibit an initial discharge capacity as high as 5.89 mA h cm-(2) (5230 mA h g(-1))at a current density of 0.1 mA cm(-2). The voltage gap between the charge and discharge curves is less for Li-O-2(Au-RGO) cell in comparison with Li-O-2(RGO) cell. The Li-O-2(Au-RGO) cells are cycled over about 120 charge-discharge cycles. The results suggest that Au-RGO is a promising catalyst for rechargeable Li-O-2 cells.

Platinum Ion-Doped TiO2: High Catalytic Activity of Pt2+ with Oxide Ion Vacancy in Ti1-x4+Ptx2+O2-x Compared to Pt4+ without Oxide Ion Vacancy in Ti1-x4+Ptx4+O2

Ti0.97Pt0.032+O1.97 and Ti0.97Pt0.034+O2 have been synthesized by a solution combustion method using alanine and glycine as the fuels, respectively. Both crystallize in anatase TiO2 structure with 15 nm average crystallite size. X-ray photoelectron spectroscopy (XPS) confirmed Pt ions are in the 2+ state in Ti0.97Pt0.03O1.97 (alanine) and 4+ state in Ti0.97Pt0.03O2 (glycine). The rate of CO oxidation occurring over Ti0.97Pt0.032+O1.97 (0.76 mu mol.g(-1).s(-1)) is similar to 10, times more than that over Ti0.97Pt0.034+O2 at 60 degrees C (0.08 mu mol.g(-1).s(-1)). A large shift in 100% hydrocarbons conversion to lower temperature was observed for Pt2+ ion-substituted TiO2 relative 10 that for Pt4+ ion-substituted TiO2. After reoxidation of the reduced compound by H-2 as well as CO, Pt ions are stabilized in mixed valences, 2+ and 4+ states. The role of oxide ion vacancy has been demonstrated by CO oxidation and H-2 + O-2 recombination reactions in the presence and absence of O-2. We analyze the activated lattice oxygens upon substitution of Pt2+ and Pt4+ ions in TiO2, using first-principles density functional theory (DFT) calculations with supercells of Ti31Pt1O63, Ti30Pt2O62, and Ti29Pt3O61 for Pt2+ ion substitution and Ti31Pt1O64, Ti30Pt2O62, and Ti29Pt3O61 for Pt4+ ion substitution in TiO2. We find that the local structure of Pt2+ ion has a distorted square planar geometry and that of Pt4+ ion has an octahedral geometry similar to that of Ti4+ ion in pure TiO2. The change in coordination of Pt2+ ion gives rise to weakly bonded oxygens, and these oxygens are involved in high rates of catalytic reaction. Thus, the high catalytic activity results from synergistic roles of Pt2+ ion and oxide ion vacancy and weakly bonded lattice oxygen.

Morphological and electrochemical characterization of electrodeposited Zn-Ag nanoparticle composite coatings

Silver nanoparticles with an average size of 23 nm were chemically synthesized and used to fabricate Zn-Ag composite coatings. The Zn-Ag composite coatings were generated by electrodeposition method using a simple sulfate plating bath dispersed with 0.5, land 1.5 g/l of Ag nanoparticles. Scanning electron microscopy, X-ray diffraction and texture co-efficient calculations revealed that Ag nanoparticles appreciably influenced the morphology, micro-structure and texture of the deposit. It was also noticed that agglomerates of Ag nanopartides, in the case of high bath load conditions, produced defects and dislocations on the deposit surface. Ag nanoparticles altered the corrosion resistance property of Zn-Ag composite coatings as observed from Tafel polarization, electrochemical impedance analysis and an immersion test. Reduction in corrosion rate with increased charge transfer resistance was observed for Zn-Ag composite coatings when compared to a pure Zn coating. However, the particle concentration in the plating bath and their agglomeration state directly influenced the surface morphology and the subsequent corrosion behavior of the deposits. (C) 2013 Elsevier Inc. All rights reserved.

Synthesis, characterisation and application of an exfoliated graphite-diamond composite electrode in the electrochemical degradation of trichloroethylene

A composite electrode made up of exfoliated graphite (EG) and diamond was prepared for the electrochemical oxidation of trichloroethylene (TCE). The SEM images of the EG-diamond material showed that diamond powders were dispersed on the surface of EG materials. The N-2 adsorption-desorption isotherm of EG-diamond material resulted in a poor adsorption capability due to the insertion of diamond powders into the porous matrix of EG. Raman spectroscopy revealed the presence of characteristic sp(3) bands of diamond confirming good interaction of diamond with EG. Electrochemical characterisation of EG-diamond in 0.1 M Na2SO4 resulted in an enhanced working potential window. The EG-diamond electrode was employed for the electrochemical oxidation of trichloroethylene (0.2 mM) in a Na2SO4 supporting electrolyte. The EG-diamond, in comparison to the pristine EG electrode, exhibited a higher removal efficiency of 94% (EG was 57%) and faster degradation kinetics of 25.3 x 10(-3) min(-1) showing pseudo first order kinetic behaviour. Under the optimised conditions, 73% total organic content (TOC) removal was achieved after 4 h of electrolysis. The degradation of TCE was also monitored with gas chromatography-mass spectrometry. Dichloroacetic acid (DCAA) was identified as a major intermediate product during the electrochemical oxidation of TCE. The electrochemical degradation of TCE at the EG-diamond electrode represents a cost effective method due to the ease of preparation of EG-diamond composite material without the necessity of diamond activation which is normally achieved through doping.

Preparation of zinc oxide coatings by using newly designed metal-organic complexes of Zn: Effect of molecular structure of the precursor and surfactant over the crystallization, growth and luminescence

We report large scale deposition of tapered zinc oxide (ZnO) nanorods on Si(100) substrate by using newly designed metal-organic complex of zinc (Zn) as the precursor, and microwave irradiation assisted chemical synthesis as a process. The coatings are uniform and high density ZnO nanorods (similar to 1.5 mu m length) grow over the entire area (625 mm(2)) of the substrate within 1-5 min of microwave irradiation. ZnO coatings obtained by solution phase deposition yield strong UV emission. Variation of the molecular structure/molecular weight of the precursors and surfactants influence the crystallinity, morphology, and optical properties of ZnO coatings. The precursors in addition with the surfactant and the solvent are widely used to obtain desired coating on any substrate. The growth mechanism and the schematics of the growth process of ZnO coatings on Si(100) are discussed. (c) 2013 Elsevier B.V. All rights reserved.

Experimental analysis of composite single-lap joints using digital image correlation and comparison with theoretical models

The demand for energy efficient, low weight structures has boosted the use of composite structures assembled using increased quantities of structural adhesives. Bonded structures may be subjected to severe working environments such as high temperature and moisture due to which the adhesive gets degraded over a period of time. This reduces the strength of a joint and leads to premature failure. Measurement of strains in the adhesive bondline at any point of time during service may be beneficial as an assessment can be made on the integrity of a joint and necessary preventive actions may be taken before failure. This paper presents an experimental approach of measuring peel and shear strains in the adhesive bondline of composite single-lap joints using digital image correlation. Different sets of composite adhesive joints with varied bond quality were prepared and subjected to tensile load during which digital images were taken and processed using digital image correlation software. The measured peel strain at the joint edge showed a rapid increase with the initiation of a crack till failure of the joint. The measured strains were used to compute the corresponding stresses assuming a plane strain condition and the results were compared with stresses predicted using theoretical models, namely linear and nonlinear adhesive beam models. A similar trend in stress distribution was observed. Further comparison of peel and shear strains also exhibited similar trend for both healthy and degraded joints. Maximum peel stress failure criterion was used to predict the failure load of a composite adhesive joint and a comparison was made between predicted and actual failure loads. The predicted failure loads from theoretical models were found to be higher than the actual failure load for all the joints.

Negative differential resistance and effect of defects and deformations in MoS2 armchair nanoribbon metal-oxide-semiconductor field effect transistor

In this work, we present a study on the negative differential resistance (NDR) behavior and the impact of various deformations (like ripple, twist, wrap) and defects like vacancies and edge roughness on the electronic properties of short-channel MoS2 armchair nanoribbon MOSFETs. The effect of deformation (3 degrees-7 degrees twist or wrap and 0.3-0.7 angstrom ripple amplitude) and defects on a 10 nm MoS2 ANR FET is evaluated by the density functional tight binding theory and the non-equilibrium Green's function approach. We study the channel density of states, transmission spectra, and the I-D-V-D characteristics of such devices under the varying conditions, with focus on the NDR behavior. Our results show significant change in the NDR peak to valley ratio and the NDR window with such minor intrinsic deformations, especially with the ripple. (C) 2013 AIP Publishing LLC.

Gas sensing response analysis of p-type porous chromium oxide thin films

The ethanol sensing properties of porous Cr2O3 thin films deposited by the ultrasonic nebulized spray pyrolysis of an aqueous combustion mixture is reported. The impact of the precursor selection and various deposition parameters on the film crystallinity, surface morphology and stoichiometry are studied using thermo-gravimetric analysis, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and atomic force microscopy techniques. The film morphology exhibits a highly porous nature, as a result of the exothermic combustion reaction during film deposition. The gas sensing properties of these films are investigated in the temperature range of 200-375 degrees C for ethanol. The films show two different regions of response for ethanol above and below 300 degrees C. A good relationship between the response and the ethanol concentration is observed, and is modeled using an empirical relation. The possible mechanism and the surface chemical reactions of ethanol over the chromium oxide surface are discussed.

Catalytic Reduction of Graphene Oxide Nanosheets by Glutathione Peroxidase Mimetics Reveals a New Structural Motif in Graphene Oxide

A catalytic reduction of graphene oxide (GO) by glutathione peroxidase (GPx) mimics is reported. This study reveals that GO contains peroxide functionalities, in addition to the epoxy, hydroxyl and carboxylic acid groups that have been identified earlier. It also is shown that GO acts as a peroxide substrate in the GPx-like catalytic activity of organoselenium/tellurium compounds. The reaction of tellurol, generated from the corresponding ditelluride, reduces GO through the glutathione (GSH)-mediated cleavage of the peroxide linkage. The mechanism of GO reduction by the tellurol in the presence of GSH involves the formation of a tellurenic acid and tellurenyl sulfide intermediates. Interestingly, the GPx mimics also catalyze the decarboxylation of the carboxylic acid functionality in GO at ambient conditions. Whereas the selenium/tellurium-mediated catalytic reduction/decarboxylation of GO may find applications in bioremediation processes, this study suggests that the modification of GO by biologically relevant compounds such as redox proteins must be taken into account when using GO for biomedical applications because such modifications can alter the fundamental properties of GO.

NOD2-Nitric Oxide-responsive MicroRNA-146a Activates Sonic Hedgehog Signaling to Orchestrate Inflammatory Responses in Murine Model of Inflammatory Bowel Disease

Background: Genetic variants of NOD2 are linked to inflammatory bowel disease (IBD) etiology. Results: DSS model of colitis in wild-type and inducible nitric-oxide synthase (iNOS) null mice revealed that NOD2-iNOS/NO-responsive microRNA-146a targets NUMB gene facilitating Sonic hedgehog (SHH) signaling. Conclusion: miR-146a-mediated NOD2-SHH signaling regulates gut inflammation. Significance: Identification of novel regulators of IBD provides new insights into pathophysiology and development of new therapy concepts. Inflammatory bowel disease (IBD) is a debilitating chronic inflammatory disorder of the intestine. The interactions between enteric bacteria and genetic susceptibilities are major contributors of IBD etiology. Although genetic variants with loss or gain of NOD2 functions have been linked to IBD susceptibility, the mechanisms coordinating NOD2 downstream signaling, especially in macrophages, during IBD pathogenesis are not precisely identified. Here, studies utilizing the murine dextran sodium sulfate model of colitis revealed the crucial roles for inducible nitric-oxide synthase (iNOS) in regulating pathophysiology of IBDs. Importantly, stimulation of NOD2 failed to activate Sonic hedgehog (SHH) signaling in iNOS null macrophages, implicating NO mediated cross-talk between NOD2 and SHH signaling. NOD2 signaling up-regulated the expression of a NO-responsive microRNA, miR-146a, that targeted NUMB gene and alleviated the suppression of SHH signaling. In vivo and ex vivo studies confirmed the important roles for miR-146a in amplifying inflammatory responses. Collectively, we have identified new roles for miR-146a that established novel cross-talk between NOD2-SHH signaling during gut inflammation. Potential implications of these observations in therapeutics could increase the possibility of defining and developing better regimes to treat IBD pathophysiology.

Spectral Migration of Fluorescence in Graphene Oxide Aqueous Dispersions: Evidence for Excited-State Proton Transfer

Aqueous dispersions of graphene oxide (GO) exhibit strong pH-dependent fluorescence in the visible that originates, in part, from the oxygenated functionalities present. Here we examine the spectral migration on nanosecond time-scales of the pH dependent features in the fluorescence spectra. We show, from time-resolved emission spectra (TRES) constructed from the wavelength dependent fluorescence decay curves, that the migration is associated with excited state proton transfer. Both `intramolecular' and `intermolecular' transfer involving the quasi-molecular oxygenated aromatic fragments are observed. As a prerequisite to the time-resolved measurements, we have correlated the changes in the steady state fluorescence spectra with the sequence of dissociation events that occur in GO dispersions at different values of pH.

Supercapacitors based on nitrogen-doped reduced graphene oxide and borocarbonitrides

Nitrogen-doped reduced giaphene oxide (RGO) samples with different nitrogen content, prepared by two different methods, as well as nitrogen-doped few-layer graphene have been investigated as supercapacitor electrodes. Two electrode measurements have been carried out both in aqueous (6 M KOH) and in ionic liquid media. Nitrogen-doped reduced graphene oxides exhibit satisfactory specific capacitance, the values reaching 126 F/g at a scan rate of 10 mV/s in aqueous medium. Besides providing supercapacitor characteristics, the study has shown the nitrogen content and surface area to be important factors. High surface-area borocarbonitrides, BxCyNz, prepared by the urea route appear to be excellent supercapacitor electrode materials. Thus, BC4.5N exhibits a specific capacitance of 169 F/g at a scan rate of 10 mV/s in aqueous medium. In an ionic liquid medium, nitrogen-doped RGO and BC4.5N exhibit specific capacitance values of 258 F/g and 240 F/g at a scan rate of 5 mV/s. The ionic liquid enables a larger operating voltage range of 0.0-2.5 V compared to 0.0-1 V in aqueous medium. (C) 2013 Elsevier Ltd. All rights reserved.

Acoustic emission techniques for NDE & structural health monitoring of advanced composite materials

Structural Health Monitoring (SHM) is an effective extension of NDE to reduce down time and cost of Inspection of structural components. On – line monitoring is an essential part of SHM. Acoustic Emission Techniques have most of the desirable requirements of an effective SHM tool. With the kind of advancement seen in the last couple of decades in the field of electronics, computers and signal processing technologies it can only be more helpful in obtaining better and meaningful quantitative results which can further enhance the potential of AET for the purpose. Advanced Composite materials owing to their specific high performance characteristics are finding a wide range of engineering applications. Testing and Evaluation of this category of materials and SHM of composite structures have been very challenging problems due to the very nature of these materials. Mechanical behaviour of fiber composite materials under different loading conditions is complex and involves different types of failure mechanisms. This is where the potential of AET can be exploited effectively. This paper presents an over view of some relevant studies where AET has been utilised to test, evaluate and monitor health of composite structures.

Fractal dimension method for delamination detection in composite beams

A new delaminated composite beam element is formulated for Timoshenko as well as Euler-Bernoulli beam models. Shape functions are derived from Timoshenko functions; this provides a unified formulation for slender to moderately deep beam analyses. The element is simple and easy to implement, results are on par with those from free mode delamination models. Katz fractal dimension method is applied on the mode shapes obtained from finite element models, to detect the delamination in the beam. The effect of finite element size on fractal dimension method of delamination detection is quantified.