Graphene oxide as an optimal candidate material for methane storage

Methane, the primary constituent of natural gas, binds too weakly to nanostructured carbons to meet the targets set for on-board vehicular storage to be viable. We show, using density functional theory calculations, that replacing graphene by graphene oxide increases the adsorption energy of methane by 50%. This enhancement is sufficient to achieve the optimal binding strength. In order to gain insight into the sources of this increased binding, that could also be used to formulate design principles for novel storage materials, we consider a sequence of model systems that progressively take us from graphene to graphene oxide. A careful analysis of the various contributions to the weak binding between the methane molecule and the graphene oxide shows that the enhancement has important contributions from London dispersion interactions as well as electrostatic interactions such as Debye interactions, aided by geometric curvature induced primarily by the presence of epoxy groups. (C) 2015 AIP Publishing LLC.

Molecular mechanism of water permeation in a helium impermeable graphene and graphene oxide membrane

Layers of graphene oxide (GO) are found to be good for the permeation of water but not for helium (Science, 2012, 335(6067), 442-444) suggesting that the GO layers are dynamic in the formation of a permeation route depending on the environment they are in (i.e., water or helium). To probe the microscopic origin of this observation we calculate the potential of mean force (PMF) of GO sheets (with oxidized and reduced parts), with the inter-planar distance as a reaction coordinate in helium and water. Our PMF calculation shows that the equilibrium interlayer distance between the oxidized part of the GO sheets in helium is at 4.8 angstrom leaving no space for helium permeation. In contrast, the PMF of the oxidized part of the GO in water shows two minima, one at 4.8 angstrom and another at 6.8 angstrom, corresponding to no water and a water filled region, thus giving rise to a permeation path. The increased electrostatic interaction between water with the oxidized part of the sheet helps the sheet open up and pushes water inside. Based on the entropy calculations for water trapped between graphene sheets and oxidized graphene sheets at different inter-sheet spacings, we also show the thermodynamics of filling.

Estimation of mechanical properties of single wall carbon nanotubes using molecular mechanics approach

Molecular mechanics based finite element analysis is adopted in the current work to evaluate the mechanical properties of Zigzag, Armchair and Chiral Single wall Carbon Nanotubes (SWCNT) of different diameters and chiralities. Three different types of atomic bonds, that is Carbon Carbon covalent bond and two types of Carbon Carbon van der Waals bonds are considered in the carbon nanotube system. The stiffness values of these bonds are calculated using the molecular potentials, namely Morse potential function and Lennard-Jones interaction potential function respectively and these stiffness's are assigned to spring elements in the finite element model of the CNT. The geometry of CNT is built using a macro that is developed for the finite element analysis software. The finite element model of the CNT is constructed, appropriate boundary conditions are applied and the behavior of mechanical properties of CNT is studied.

Generation of Temperature Dependent Transversely Isotropic Properties for Zigzag and Armchair Single-Walled Carbon Nanotubes

Finite element analysis has been carried out to obtain temperature dependent transversely isotropic properties of the single-walled carbon nanotubes (SWCNTs). Finite element models of SWCNTs are generated by specifying the C-C bond rigidities. The five independent transversely isotropic properties for different chiralities are evaluated using the stress fields of thick-walled cylinders and the elastic deformations of SWCNTs subjected to pure extension, internal pressure and pure torsion loads. Empirical relations are provided for the five independent elastic constants useful to armchair and zigzag SWCNTs.

Ir nanoparticles-anchored reduced graphene oxide as a catalyst for oxygen electrode in Li-O-2 cells

Iridium nanoparticles-anchored reduced graphene oxide (Ir-RGO) was prepared by simultaneous reduction of graphene oxide and Ir3+ ions and its catalytic activity for oxygen electrode in Li-O-2 cells was demonstrated. Ir particles with an average size of 3.9 nm were uniformly distributed on RGO sheets. The oxygen reduction reaction (ORR) was studied on an Ir-RGO catalyst in non-aqueous electrolytes using cyclic voltammetry and rotating disk electrode techniques. Li-O-2 cells with Ir-RGO as a bifunctional oxygen electrode catalyst were subjected to charge-discharge cycling at several current densities. A discharge capacity of 9529 mA h g(-1) (11.36 mA h cm(-2)) was obtained initially at a current density of 0.5 mA cm(-2) (393 mA g(-1)). A decrease in capacity was observed on increasing the current density. Although there was a decrease in capacity on repeated discharge-charge cycling initially, a stable capacity was observed for about 30 cycles. The results suggest that Ir-RGO is a useful catalyst for rechargeable Li-O-2 cells.

High aspect ratio, processable coordination polymer gel nanotubes based on an AIE-active LMWG with tunable emission

A new TPE based low molecular weight gelator (LMWG) which displays both AIE and MCIE phenomena in gel state has been synthesized. LMWG self-assembles to form 1D nanofibers which undergo morphology transformation to coordination polymer gel (CPG) nanotubes upon metal ion coordination. CPG shows enhanced mechanical stability along with tunable emission properties.

New physical insights into the electromagnetic shielding efficiency in PVDF nanocomposites containing multiwall carbon nanotubes and magnetic nanoparticles

This work attempts to bring critical insights into the electromagnetic shielding efficiency in polymeric nanocomposites with respect to the particle size of magnetic nanoparticles added along with or without a conductive inclusion. To gain insight, various Ni-Fe (NixFe1-x; x = 10, 20, 40; Ni: nickel, Fe: iron) alloys were prepared by a vacuum arc melting process and different particle sizes were then achieved by a controlled grinding process for different time scales. Poly(vinylidene fluoride), PVDF based composites involving different particle sizes of the Ni-Fe alloy were prepared with or without multiwall carbon nanotubes (MWNTs) by a wet grinding approach. The Ni-Fe particles were thoroughly characterized with respect to their microstructure and magnetization; and the electromagnetic (EM) shielding efficiency (SE) of the resulting composites was obtained from the scattering parameters using a vector network analyzer in a broad range of frequencies. The saturation magnetization of Ni-Fe nanoparticles and the bulk electrical conductivity of PVDF/Ni-Fe composites scaled with increasing particle size of NiFe. Interestingly, the PVDF/Ni-Fe/MWNT composites showed a different trend where the bulk electrical conductivity and SE scaled with decreasing particle size of the Ni-Fe alloy. A total SE of similar to 35 dB was achieved with 50 wt% of Ni60Fe40 and 3 wt% MWNTs. More interestingly, the PVDF/Ni-Fe composites shielded the EM waves mostly by reflection whereas, the PVDF/Ni-Fe/MWNT shielded mostly by absorption. A minimum reflection loss of similar to 58 dB was achieved in the PVDF/Ni-Fe/MWNT composites in the X-band (8-12 GHz) for a particular size of Ni-Fe alloy nanoparticles. This study brings new insights into the EM shielding efficiency in PVDF/magnetic nanoparticle based composites in the presence and absence of conducting inclusion.

Iridium-decorated multiwall carbon nanotubes and its catalytic activity with Shell 405 in hydrazine decomposition

Iridium-functionalized multiwalled carbon nanotubes (Ir-MWNT) are the future catalyst support material for hydrazine fuel decomposition. The present work demonstrates decoration of iridium particle on iron-encapsulated multiwalled carbon nanotubes (MWNT) by wet impregnation method in the absence of any stabilizer. Electron microscopy studies reveal the coated iridium particle size in the range of 5-10 nm. Elemental analysis by energy dispersive X-ray diffraction confirms 21 wt% of Ir coated over MWNT. X-ray photoelectron spectroscopy (XPS) shows 4f(5/2) and 4f(7/2) lines of iridium and confirms the metallic nature. The catalytic activity of Ir-MWNT/Shell 405 combination is performed in 1 N hydrazine micro-thrusters. The thruster performance shows increase in chamber pressure and decrease in chamber temperature when compared to Shell 405 alone. This enhanced performance is due to high thermal conducting nature of MWNTs and the presence of Ir active sites over MWNTs.

Detailed mechanism and kinetic study of CO oxidation on cobalt oxide surfaces

Co3O4 catalysts were prepared by combustion synthesis using different fuels glycine (G), ODH (O) and urea (U). Morphological changes of the materials were observed by using different fuels. The prepared catalysts were characterized by XRD, XPS, SEM, TEM, BET and DRIFTS analysis. All compounds showed 100% conversion of CO below 175C. The prepared catalysts exhibited very high stability and conversions did not decrease even after 50 h of continuous operation. The oxygen storage capacity (OSC) of materials was measured by H-2-TPR analysis. Co3O4-O is having high OSC among the synthesized catalysts. The activation energies of these catalysts were found to be in the range of 42.3-64.8 kJ mol(-1). With DRIFTS analysis, the surface carbonates, superoxide anions, adsorbed CO, O-2 species on the catalyst surface were found and this information was used to develop a detailed reaction pathway. A kinetic model was developed with the help of proposed mechanism and used to fit the data. (C) 2014 Elsevier B.V. All rights reserved.

Non-enzymatic electronic detection of glucose using aminophenylboronic acid functionalized reduced graphene oxide

We report the non-enzymatic electronic detection of glucose using field effect transistor (FET) devices made of aminophenylboronic acid (APBA) functionalized reduced graphene oxide (RGO). Detection of glucose molecules was carried out over a wide dynamic range of concentration varying from 100 pM to 100 mM with a detection limit of similar to 2 nM using both covalently and non-covalently functionalized APBA-RGO complex. The normalized change in electrical conductance data shows that the FET devices made of non-covalently functionalized APBA-RGO complex (nc-APBA-RGO) exhibited a linear response to glucose aqueous solution of concentrations varying from 1 nM to 10 mM and showed 4 times enhanced sensitivity over the devices made of covalently functionalized APBA-RGO complex (c-APBA-RGO). Specificity of APBA-RGO complex to glucose is confirmed from the observation of negligible change in electrical conductance after exposure to 0.1 mM of lactose and other interfering factors. (C) 2015 Elsevier B.V. All rights reserved.

A 1 V supercapacitor device with nanostructured graphene oxide/polyaniline composite materials

Polyaniline and graphene oxide composite on activated carbon cum reduced graphene oxide-supported supercapacitor electrodes are fabricated and electrochemically characterized in a three-electrode cell assembly. Attractive supercapacitor performance, namely high-power capability and cycling stability for graphene oxide/polyaniline composite, is observed owing to the layered and porous-polymeric-structured electrodes. Based on the materials characterization data in a three-electrode cell assembly, 1 V supercapacitor devices are developed and performance tested. A comparative study has also been conducted for polyaniline and graphene oxide/polyaniline composite-based 1 V supercapacitors for comprehending the synergic effect of graphene oxide and polyaniline. Graphene oxide/polyaniline composite-based capacitor that exhibits about 100 F g(-1) specific capacitance with faradaic efficiency in excess of 90% has its energy and power density values of 14 Wh kg(-1) and 72 kW kg(-1), respectively. Cycle-life data for over 1000 cycles reflect 10% capacitance degradation for graphene oxide/polyaniline composite supercapacitor.

Rational molecular dynamics scheme for predicting optimum concentration loading of nano-additive in phase change materials

The present study deals with the diffusion and phase transition behaviour of paraffin reinforced with carbon nano-additives namely graphene oxide (GO) and surface functionalized single walled carbon nanotubes (SWCNT). Bulk disordered systems of paraffin hydrocarbons impregnated with carbon nano-additives have been generated in realistic equilibrium conformations for potential application as latent heat storage systems. Ab initio molecular dynamics(MD) in conjugation with COMPASS forcefield has been implemented using periodic boundary conditions. The proposed scheme allows determination of optimum nano-additive loading for improving thermo-physical properties through analysis of mass, thermal and transport properties; and assists in determination of composite behaviour and related performance from microscopic point of view. It was observed that nanocomposites containing 7.8% surface functionalised SWCNT and 55% GO loading corresponds to best latent heat storage system. The propounded methodology could serve as a by-pass route for economically taxing and iterative experimental procedures required to attain the optimum composition for best performance. The results also hint at the large unexplored potential of ab-initio classical MD techniques for predicting performance of new nanocomposites for potential phase change material applications. (C) 2015 Author(s).

Copper oxide nanoparticles: an antidermatophytic agent for Trichophyton spp.

Copper oxide (CuO) is one of the most important transition metal oxides due to its unique properties. It is used in various technological applications such as high critical temperature, superconductors, gas sensors, in photoconductive applications and so on. Recently, it has been used as an antimicrobial agent against various pathogenic bacteria. In the present investigation, we studied the structural and antidermatophytic properties of CuO nanoparticles (NPs) synthesized by a precipitation technique. Copper sulfate was used as a precursor and sodium hydroxide as a reducing agent. Scanning electron microscopy (SEM) showed flower-shaped CuO NPs and X-ray diffraction (XRD) pattern showed the crystalline nature of CuO NPs. These NPs were evaluated against two prevalent species of dermatophytes, i.e. Trichophyton rubrum and T. mentagrophytes by using the broth microdilution technique. Further, the NPs activity was also compared with synthetic sertaconazole. Although better antidermatophytic activity was exhibited with sertaconazole as compared to NPs, being synthetic, sertaconazole may not be preferred, as it shows different adverse effects. Trichophyton mentagrophytes is more susceptible to NPs than T. rubrum. A phylogenetic approach was applied for predicting differences in susceptibility of pathogens.

Synthesis, characterization and field emission properties of tin oxide nanowires

Tin oxide (SnO2) nanowires are synthesized by Au catalyzed chemical vapor deposition of Sn and C mixture at 900 degrees C by employing a continuous flow of Ar: O-2 (10:1) for an hour. X-ray diffraction and Raman spectroscopy studies indicate that the as-grown SnO2 nanowires are crystalline in nature with tetragonal rutile phase. Electron microscopy studies reveal towards high aspect ratio of nanowires. The field emission studies show that SnO2 nanowires grown on Si substrate exhibit low turn-on field of 1.75 V/mu m (at 0.1 mu A/cm(2)) and long-term emission stability over a period of more than 50 h with a current density of 4 mu A/cm(2) at a constant electric field of 2.25 V/mu m. Hardly any considerable degradation in the emission current is noticed even after 50 h which may be attributed to the high crystallinity of SnO2 nanowires. (C) 2015 Elsevier B.V. All rights reserved.

The electronic, chemical and electrocatalytic processes and intermediates on iron oxide surfaces during photoelectrochemical water splitting

We re-assess experimental soft X-ray absorption spectra of the oxygen K-shell which we recorded operando from iron oxide during photoelectrochemical water splitting in KOH electrolyte. In particular, we refer to recently reported transitional electron hole states which originate within the charge carrier depletion layer of the iron oxide and on the iron oxide surface. For the latter we find that an intermediate oxy-peroxo species is formed on the iron oxide with increasing bias potential, which disappears upon further polarization of the electrode, concomitantly with the evolution and disappearance of the aforementioned surface state. The oxygen spectra contain also the spectroscopic signatures of the electrolyte water, the position of which changes with increasing bias potential towards lower X-ray energies, revealing the breaking and formation of hydrogen bonds in the water during the experiment. Combined with potential dependent impedance spectroscopy data we are able to sketch the molecular structure of chemical intermediates and their charge carrier dynamics. (C) 2015 Elsevier B.V. All rights reserved.