γ-Ray-Assisted Synthesis of a Pt-Sn Bimetallic Composite Loaded on Graphene-Graphitic Carbon Nitride Hybrid: A Cocktail Electrocatalyst for the Methanol Oxidation Reaction.

The composite of Pt with transition metals is viewed as the most promising anode material for direct methanol fuel cell (DMFC) applications. Besides the decrease in the Pt loading, these multimetallic structures help in circumventing CO poisoning issues associated with a Pt catalyst. Herein, we prepared and loaded Pt-Sn bimetallic nanoparticles on an electron-rich and stable substrate consisting of graphitic nitride (GCN) and graphene oxide (GO)/reduced graphene oxide (r-GO) hybrid composites. The γ-radiolysis method was employed for coreduction of metal salts to deposit the binary composite of metal nanoparticles over the substrates. These structures were tested as the anode material for the methanol oxidation reaction (MOR). Among various possible combinations, Pt-Sn-loaded rGO-GCN (Pt-Sn/rGO-GCN) demonstrated the current density of ca. 2.4 A/mgPt. To the best of our knowledge, this value is among the highest ones, reported for similar systems in the acidic pH. Furthermore, these composites demonstrated excellent stability in the repeated cycle test. The improved performance is associated to the plenty of -OH groups provided by the Sn counterpart and a large number of adsorption sites from the electron-reached GCN counterpart.

Covalent conjugation of single-walled carbon nanotube with CYP101 mutant for direct electrocatalysis.

Covalent linkage between the single-walled carbon nanotube (SWCNT) and CYP101 through a specific site of the enzyme can provide a novel method of designing efficient enzyme electrodes using this prototype cytochrome P450 enzyme. We have chemically modified the SWCNT with linker 4-carboxy phenyl maleimide (CPMI) containing maleimide functional groups. The enzyme was covalently attached on to the SWCNT through the maleimide group of the linker (CPMI) to the thiolate group of the surface exposed Cys 58 or Cys 136 of the CYP101 forming a covalently immobilized protein on the nanotube. Thin film of the modified SWCNT-CPMI-CYP101conjugate was made on a glassy carbon (GC) electrode. Direct electrochemistry of the substrate (camphor)-bound enzyme was studied using this immobilized enzyme electrode system and the redox potential was found to be -320mV vs Ag/AgCl (3 M KCl), which agrees with the redox potential of the substrate bound enzyme reported earlier. The electrochemically driven enzymatic mono-oxygenation of camphor by this immobilized enzyme electrode system was studied by measurement of the catalytic current at different concentrations of camphor. The catalytic current was found to increase with increasing concentration of camphor in presence of oxygen. The product formed during the catalysis was identified by mass-spectrometry as hydroxy-camphor.

High sensitive determination of dopamine through catalytic oxidation and preconcentration over gold-multiwall carbon nanotubes composite modified electrode.

Electrochemical properties of dopamine, uric acid and ascorbic acid have been investigated using gold nano particles (AuNPs) decorated functionalized multiwall carbon nanotubes (MWCNTs) nano composite modified electrode. MWCNTs were acid functionalized to introduce -COOH functionalities. The functionalized MWCNTs were used as support materials and were decorated with gold nano particles of 20 nm in size. The nano composite materials thus prepared have been named as f-MWCNTs/AuNPs composite. The composite material was characterized using FTIR, RAMAN, TEM, UV-VIS spectroscopy and atomic force microscopy measurements. Electrochemical investigations on the composite modified glassy carbon electrode for dopamine was investigated in presence of interfering agents like ascorbic acid and uric acid. The modified electrode showed sensitivity of 0.002 µAnM-1 for dopamine with the detection limit of 35 nM. Present electrode showed high selectivity for dopamine as the oxidation peak of dopamine and uric acid were very well resolved. The analytical method was found to be suitable for the simultaneous determination of dopamine and uric acid using the modified electrode. Method was applied in spiked real serum sample for the determination of dopamine.

Boosting the Efficiency of Quantum Dot-Sensitized Solar Cells through Formation of the Cation-Exchanged Hole Transporting Layer.

In search of a viable way to enhance the power conversion efficiency (PCE) of quantum dot-sensitized solar cells, we have designed a method by introducing a hole transporting layer (HTL) of p-type CuS through partial cation exchange process in a postsynthetic ligand-assisted assembly of nanocrystals (NCs). High-quality CdSe and CdSSe gradient alloy NCs were synthesized through colloidal method, and the charge carrier dynamics was monitored through ultrafast transient absorption measurements. A notable increase in the short-circuit current concomitant with the increase in open-circuit voltage and the fill factor led to 45% increment in PCE for CdSe-based solar cells upon formation of the CuS HTL. Electrochemical impedance spectroscopy further revealed that the CuS layer formation increases recombination resistance at the TiO2/NC/electrolyte interface, implying that interfacial recombination gets drastically reduced because of smooth hole transfer to the redox electrolyte. Utilizing the same approach for CdSSe alloy NCs, the highest PCE (4.03%) was obtained upon CuS layer formation compared to 3.26% PCE for the untreated one and 3.61% PCE with the conventional ZnS coating. Therefore, such strategies will help to overcome the kinetic barriers of hole transfer to electrolytes, which is one of the major obstacles of high-performance devices.

CZTS x Se1-x nanocrystals: Composition dependent method of preparation, morphological characterization and cyclic voltammetry data analysis.

In this article, synthesis procedures of preparation of copper zinc tin sulpho-selenide (CZTS x Se1-x ) alloy nanocrystals and the data acquired for the material characterization are presented. This data article is related to the research article doi: http://dx.doi.org/10.1016/j.solmat.2016.06.030 (Jadhav et al., 2016) [1]. FTIR data have been presented which helped in confirmation of adsorption of oleylamine on CZTS x Se1-x . Transmission electron microscopy (TEM), Field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) data have been presented which have been used to reveal the morphological details of the nanocrystals. The Energy dispersive X-ray analysis (EDAX) based elemental mapping data has been presented to confirm the elemental composition of nanocrystals. Procedure for the preparation of CZTS x Se1-x based working electrode for the CV measurements have been given. The summary table for the optical, electrochemical band gaps, valance and conduction band edges as a function of composition are listed for the ready reference.

Electrocatalyst on insulating support?: Hollow silica spheres loaded with Pt nanoparticles for methanol oxidation.

Electrocatalytic oxidation of methanol on silica hollow spheres, loaded with platinum nanoparticles (Pt-SiO2-HS), is reported. The functionalized hollow silica spheres were prepared by the surfactant (lauryl ester of tyrosine) template-assisted synthesis. These spheres were loaded with platinum nanoparticles by γ-radiolysis. Energy-dispersive X-ray analysis (EDAX) and X-ray photoelectron spectroscopy (XPS) analyses confirmed presence of Si and Pt in the composite. High-resolution transmission electron microscopy showed the formation of uniformly deposited Pt nanoparticles over the hollow spheres with a predominant Pt(111) lattice plane on the surface. In spite of the poor conducting nature of the silica support, the oxidation potential and current density per unit mass for methanol oxidation were noted to be ca. 0.72 V vs NHE and 270 mA mg(-1), respectively, which are among the best values reported in its class. The composite did not show any sign of a degradation even after repeated use. In fact, the anodic current was found to increase under constant polarization, which is attributed to a facile reaction between adsorbed CO with a surface hydroxyl group present on the silica support. These results are in favor of Pt-SiO2-HS as a promising electrocatalyst material in the direct methanol fuel cell (DMFC) applications.

Outer sphere electroreduction of CCl4 in 1-butyl-3-methylimmidazolium tetrafluoroborate: an example of solvent specific effect of ionic liquid.

Electrodics of CCl4 reduction in 1-butyl-3-methylimmidazolium tetrafluoroborate [BMIM][BF4] room temperature ionic liquid (RTIL) is reported. A convolutive analysis of the cyclic voltammograms suggests that CCl4 electroreduction follows stepwise (outer sphere) dissociative electron transfer pathway, rather than the sticky dissociative (inner sphere) electron transfer, as in the case of conventional organic solvents. This difference in the mechanism of electron transfer initiated bond cleavage is attributed to the solvent specific effects, namely, stabilization of CCl4*- intermediate radical anion in RTIL, which in turn decreases the electron transfer rate and thus the carbon-halogen bond cleavage rates. Electroreduction of CCl4 in RTIL through outer sphere electron transfer would be a promising pathway for its direct conversion to methane.

Determination of band structure parameters and the quasi-particle gap of CdSe quantum dots by cyclic voltammetry.

Band structure parameters such as the conduction band edge, the valence band edge and the quasi-particle gap of diffusing CdSe quantum dots (Q-dots) of various sizes were determined using cyclic voltammetry. These parameters are strongly dependent on the size of the Q-dots. The results obtained from voltammetric measurements are compared to spectroscopic and theoretical data. The fit obtained to the reported calculations based on the semi-empirical pseudopotential method (SEPM)-especially in the strong size-confinement region, is the best reported so far, according to our knowledge. For the smallest CdSe Q-dots, the difference between the quasi-particle gap and the optical band gap gives the electron-hole Coulombic interaction energy (J(e1,h1)). Interband states seen in the photoluminescence spectra were verified with cyclic voltammetry measurements.

Synthesis and characterization of uncapped gamma-Fe2O3 nanoparticles prepared by flame pyrolysis of ferrocene in ethanol.

Nanoparticles of iron(III) oxide were synthesized by spontaneous combustion of ferrocene in ethanol solution using a simple spirit lamp. X-ray powder diffraction and electron diffraction analysis of the powder suggested the formation of gamma-Fe2O3 (Maghemite phase) having lattice constant 8.3539 +/- 0.0209 A. Transmission Electron Micrograph suggested the formation of spherical particles with an average diameter of 24.7 +/- 1.6 nm. A sextet with an isomeric shift of 0.328 mm s(-1) seen in the Mossbauer spectrum recorded at room temperature, further supports the formation of gamma-Fe2O3. The particles were dispersed freely in the polar solvents like ethanol, dimethyl sulfoxide, and water. Infra Red spectrum gave bands at 400, 432, 565, and 638 cm(-1), which confirms the presence of gamma-Fe2O3 phase.

Synthesis and characterization of stable organosols of silver nanoparticles by electrochemical dissolution of silver in DMSO.

Stable organosols of silver nanoparticles (AgNPs) without any capping agents have been synthesized by an electrochemical dissolution of a sacrificing silver electrode in dimethyl sulfoxide (DMSO). The peak at 425 +/- 5 nm observed in the UV-vis spectra was attributed to the surface plasmon resonance for silver. The formation of nanoparticles of silver was confirmed by X-ray diffraction analysis (XRD). In TEM, three ranges of particle size were observed, namely, 3.75 +/- 0.8, 6.25 +/- 0.5, and 9.25 +/- 0.3 nm. The correlation among these sizes was explained by a new model based on a droplet coalition. Based on that, sizes correlation fits very well in the empirical formula 5d(1)(3)n' + (3 - n')d(2)(3) = d(3)(3) where d(1), d(2), and d(3) are three sizes of particles and n' is an integer having values 0, 1, 2, 3, .... The sols prepared in DMSO were stable against flocculation for months. An unusual solution stability without any capping agents was attributed to the formation of Ag(I)DMSO complex on particle surface, which was confirmed by FTIR, fluorescence spectroscopy, and thermal analysis.

Electrochemistry and electrogenerated chemiluminescence from silicon nanocrystal quantum dots.

Reversible electrochemical injection of discrete numbers of electrons into sterically stabilized silicon nanocrystals (NCs) (approximately 2 to 4 nanometers in diameter) was observed by differential pulse voltammetry (DPV) in N,N'-dimethylformamide and acetonitrile. The electrochemical gap between the onset of electron injection and hole injection-related to the highest occupied and lowest unoccupied molecular orbitals-grew with decreasing nanocrystal size, and the DPV peak potentials above the onset for electron injection roughly correspond to expected Coulomb blockade or quantized double-layer charging energies. Electron transfer reactions between positively and negatively charged nanocrystals (or between charged nanocrystals and molecular redox-active coreactants) occurred that led to electron and hole annihilation, producing visible light. The electrogenerated chemiluminescence spectra exhibited a peak maximum at 640 nanometers, a significant red shift from the photoluminescence maximum (420 nanometers) of the same silicon NC solution. These results demonstrate that the chemical stability of silicon NCs could enable their use as redox-active macromolecular species with the combined optical and charging properties of semiconductor quantum dots.