Importance of trivalency and the e(g)(1) configuration in the photocatalytic oxidation of water by Mn and Co oxides.

Prompted by the early results on the catalytic activity of LiMn2O4 and related oxides in the photochemical oxidation of water, our detailed study of several manganese oxides has shown that trivalency of Mn is an important factor in determining the catalytic activity. Thus, Mn2O3, LaMnO3, and MgMn2O4 are found to be very good catalysts with turnover frequencies of 5 × 10(-4) s(-1), 4.8 × 10(-4) s(-1), and 0.8 × 10(-4) s(-1), respectively. Among the cobalt oxides, Li2Co2O4 and LaCoO3--especially the latter--exhibit excellent catalytic activity, with the turnover frequencies being 9 × 10(-4) s(-1) and 1.4 × 10(-3) s(-1), respectively. The common feature among the catalytic Mn and Co oxides is not only that Mn and Co are in the trivalent state, but Co(3+) in the Co oxides is in the intermediate t2g(5)e(g)(1) state whereas Mn(3+) is in the t2g(3e(g)(1) state. The presence of the e(g)(1) electron in these Mn and Co oxides is considered to play a crucial role in the photocatalytic properties of the oxides.

Noteworthy performance of La(1-x)Ca(x)MnO3 perovskites in generating H2 and CO by the thermochemical splitting of H2O and CO2.

Perovskite oxides of the composition La1-xCaxMnO3 (LCM) have been investigated for the thermochemical splitting of H2O and CO2 to produce H2 and CO, respectively. The study was carried out in comparison with La1-xSrxMnO3, CeO2 and other oxides. The LCM system exhibits superior characteristics in high-temperature evolution of oxygen, and in reducing CO2 to CO and H2O to H2. The best results were obtained with La0.5Ca0.5MnO3 whose performance is noteworthy compared to that of other oxides including ceria. The orthorhombic structure of LCM seems to be a crucial factor.

Chemical storage of hydrogen in few-layer graphene.

Birch reduction of few-layer graphene samples gives rise to hydrogenated samples containing up to 5 wt % of hydrogen. Spectroscopic studies reveal the presence of sp(3) C-H bonds in the hydrogenated graphenes. They, however, decompose readily on heating to 500 °C or on irradiation with UV or laser radiation releasing all the hydrogen, thereby demonstrating the possible use of few-layer graphene for chemical storage of hydrogen. First-principles calculations throw light on the mechanism of dehydrogenation that appears to involve a significant reconstruction and relaxation of the lattice.

Enhanced thermoelectric properties of In-filled Co4Sb12 by dispersion of reduced graphene oxide.

Uniform dispersion of nanosized secondary phases in bulk thermoelectric materials has proven to be an effective strategy to reduce the lattice part of thermal conductivity and improve the thermoelectric efficiency. In this work, reduced graphene oxide (rGO) was uniformly dispersed in the In0.5Co4Sb12 bulk material by ultrasonication. The formation of impurity phases of InSb and CoSb2 in the In-filled Co4Sb12 is inevitable, as observed from XRD and EPMA analyses. The Raman spectra of the nanocomposites showed broad peaks suggesting phonon softening and additional peaks corresponding to rGO. Electron transport was not affected by rGO addition, resulting in little change in the electrical resistivity and Seebeck coefficient. The lattice thermal conductivity of the bulk material was significantly reduced by the addition of a small amount of rGO, primarily attributed to the interface scattering of phonons. Hence, the highest zT of ∼1.53 at 773 K was achieved for the In0.5Co4Sb12/0.25 vol% rGO composite in the temperature range from 723 K to 773 K.

Unipolar assembly of zinc oxide rods manifesting polarity-driven collective luminescence.

Oriented assemblies of small crystals forming larger structures are common in nature and crucial for forthcoming technologies as they circumvent the difficulties of structural manipulation at microscopic scale. We have discovered two distinctive concentric assemblies of zinc oxide rods, wherein each rod has an intrinsically positive and a negative polar end induced by the noncentrosymmetric arrangement of Zn and O atoms. All the rods in a single assembly emanate out of a central core maintaining a single polar direction. Due to growth along the two polar surfaces with different atomic arrangements, these assemblies are distinct in their intrinsic properties and exhibit strong UV luminescence in the exterior of Zn-polar assemblies, unlike the O-polar assemblies. Although novel applications can be envisioned, these observations suggest that hierarchical organization with respect to internal asymmetry might be widespread in natural crystal assemblies.

Highly effective visible-light-induced H(2) generation by single-layer 1T-MoS(2) and a nanocomposite of few-layer 2H-MoS(2) with heavily nitrogenated graphene.

Two sorts of MoS2 : A single-layer, metallic form of MoS2 (1T-MoS2 ) and a nanocomposite of a second form of MoS2 (few-layer 2H-MoS2 ) with heavily nitrogenated reduced graphene oxide (NRGO; N content ca. 15 %) show outstanding performance in the production of H2 under visible-light illumination.

New strategies for the enrichment of metallic single-walled carbon nanotubes.

Enrichment of metallic single-walled carbon nanotubes (SWNTs) has been accomplished by several means, including new extraction and synthetic procedures and by interaction with metal nanoparticles as well as electron donor molecules. In the presence of Fe(CO)5, the arc discharge method yields nearly pure metallic nanotubes. Fluorous chemistry involving the preferential diazotization of metallic SWNTs offers a good procedure of obtaining the pure metallic species. Interaction of gold or platinum nanoparticles as well as of electron-donor molecules such as aniline and tetrathiafulvalene (TTF) transform semiconducting SWNTs into metallic ones. Raman and electronic spectroscopies provide ideal means to monitor enrichment of metallic SWNTs.

A study of the synthetic methods and properties of graphenes.

Graphenes with varying number of layers can be synthesized by using different strategies. Thus, single-layer graphene is prepared by micromechanical cleavage, reduction of single-layer graphene oxide, chemical vapor deposition and other methods. Few-layer graphenes are synthesized by conversion of nanodiamond, arc discharge of graphite and other methods. In this article, we briefly overview the various synthetic methods and the surface, magnetic and electrical properties of the produced graphenes. Few-layer graphenes exhibit ferromagnetic features along with antiferromagnetic properties, independent of the method of preparation. Aside from the data on electrical conductivity of graphenes and graphene-polymer composites, we also present the field-effect transistor characteristics of graphenes. Only single-layer reduced graphene oxide exhibits ambipolar properties. The interaction of electron donor and acceptor molecules with few-layer graphene samples is examined in detail.

Graphene: the new two-dimensional nanomaterial.

Every few years, a new material with unique properties emerges and fascinates the scientific community, typical recent examples being high-temperature superconductors and carbon nanotubes. Graphene is the latest sensation with unusual properties, such as half-integer quantum Hall effect and ballistic electron transport. This two-dimensional material which is the parent of all graphitic carbon forms is strictly expected to comprise a single layer, but there is considerable interest in investigating two-layer and few-layer graphenes as well. Synthesis and characterization of graphenes pose challenges, but there has been considerable progress in the last year or so. Herein, we present the status of graphene research which includes aspects related to synthesis, characterization, structure, and properties.

Novel vapor phase reactions for the synthesis and modification of carbon nanotubes and inorganic nanowires.

Several vapor phase methods have been developed for the preparation and modification of carbon nanotubes and inorganic nanowires. Thus, nebulized spray pyrolysis has been employed for the synthesis of carbon nanotubes and metal nanowires. Multi-walled carbon nanotubes (MWNTs) with fairly uniform diameters and aligned nanotube bundles have been obtained by nebulized spray pyrolysis using solutions of organometallics such as ferrocene in hydrocarbon solvents. Single-crystalline nanowires of zinc, cadmium, cobalt, and lead are obtained by the decomposition of metal acetates. By reacting acid-treated carbon nanotubes with vapors of metal halides, followed by reaction with water and calcination chemically-bonded oxide layers can be obtained on the nanotubes. A similar procedure has been employed to prepare chemically-bonded oxide layers on Al2O3, ZnO, and silicon nanowires by the reaction of the metal halides with the surface hydroxyl groups present on these nanowire surfaces.

Ethanol and hydrogen sensors based on ZnO nanoparticles and nanowires.

Hydrogen sensing characteristics of thick films of nanoparticles of ZnO and 3% Mn or Co doped ZnO with and without impregnation of 1% Pt have been investigated over a wide concentration range. The sensor characteristics of the Pt impregnated ZnO and 3% Mn or Co-doped ZnO nanoparticles are found to be excellent with the sensitivity reaching values in the 1000-1500 range for 1000 ppm of H2 at 125 degrees C or lower. The sensitivity is quite high even for 10 ppm of H2. The response and recovery times are generally less than 10 s in the region of high sensitivity. These films exhibit very good sensing characteristics for ethanol, the sensitivity being well above 2000 at 50 degrees C for 1000 ppm of vapour. Nanowires of Pt-impregnated ZnO also exhibit satisfactory sensing characteristics, but the values of the sensitivity are somewhat lower. Humidity has negligible effect on the performance of these sensors.

In vitro Thrombolytic Potential of Actinoprotease from Marine Streptomyces violaceus VITYGM.

Back ground: One of the most prevailing diseases that required effective drug as therapeutic purposes is cardiac related illness includes myocardial infarction Current scenario makes enzyme to raises their sector towards therapeutic as effective active component for such diseases. OBJECTIVES: The main aim of the study was to isolate, screen, characterize and produce an extracellular thrombolytic protease from marine actinomycetes. METHODS: Marine actinomycete was isolated and characterized on the basis of morphological, biochemical, and molecular characterization. The primary screening for protease activity was done by casein hydrolysis method followed by radial caseinolytic assay. The actinoprotease was partially purified using ammonium sulfate precipitation technique followed by dialysis and Sephadex G-50 gel permeation chromatography. RESULTS: 16srDNA sequencing and BLAST search analysis of the sequence revealed close affiliation with Streptomyces genera and identified as Streptomyces violaceus VITYGM with 99% similarity. The specific activity of purified protease was found to be 1437 units/mg along with purification fold up to 1.5 times. The blood clot lysis activity was compared with the standard and found to lyse the blood clot with 97.43%. Till now very less evidences have been reported on actinoprotease. A single peak at retention time 0.9 min observed on high performance liquid chromatography (HPLC) confirmed the homogeneity of the preparation. CONCLUSION: This is the first study to report on actinoprotease from Streptomyces violaceus VITYGM. This study emphasizes the potency of novel actinoproteases as active compound in drugs for the treatment of cardiovascular diseases.

Use of fluorous chemistry in the solubilization and phase transfer of nanocrystals, nanorods, and nanotubes.

Fluorous chemistry, involving the use of a fluorous label for the functionalization of a substrate and a fluorous solvent for extraction of the functionalized substrate, is shown to be effective in solubilizing gold and CdSe nanoparticles in a fluorous medium, through phase transfer from an aqueous or a hydrocarbon medium. While these nanoparticles were functionalized with a fluorous thiol, single-walled carbon nanotubes and ZnO nanorods could be solubilized in a fluorous medium by reacting them with a fluorous amine. Fluorous chemistry enables the solubilization of the nanostructures in the most nonpolar liquid medium possible.

GaS and GaSe nanowalls and their transformation to Ga2O3 and GaN nanowalls.

Two-dimensional nanowalls of GaS and GaSe are obtained by thermal exfoliation around 900 degrees C, and transformed to Ga2O3 and GaN nanowalls upon reaction with air and ammonia respectively at 800 degrees C, while maintaining dimensional integrity.

Synthesis and characterization of germanium oxide nanowires.

Germanium oxide (GeO2) nanowires have been prepared by heating a mixture of Ge powder and carbon in an Ar + O2 mixture at 900 degrees C. The nanowires have been characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and spectroscopic measurements. The nanowires are single crystalline with diameters in the 15-250-nm range. They exhibit characteristic blue luminescence.

Nanotubes.

Carbon nanotubes were discovered soon after the successful laboratory synthesis of fullerenes. Since their discovery in 1991, there has been intensive research activity in the area of carbon nanotubes, not only because of their fascinating structural features and properties, but also because of their potential technological applications. There is increasing experimental evidence to show that carbon nanotubes may find use in nanoelectronic devices, displays, and in hydrogen storage. In this article, we discuss various important aspects related to the synthesis, structure, characterization, and mechanism of formation of multi-walled and single-walled carbon nanotubes, followed by a presentation of the important electronic, mechanical, hydrogen storage, and other properties of the nanotubes. Doping, as well as other chemical manipulations with boron and nitrogen, bring about significant changes in the properties of the nanotubes. Carbon nanotubes also serve as useful templates to make other nanostructures. Layered metal chalcogenides, boron nitride, and other materials form nanotubes and provide considerable scope for study.

Optical spectra of nanowires of Cu and Zn chalcogenides.

Nanowires of CuS, ZnS, CuSe, and ZnSe, with diameters in the 5-150-nm range and high aspect ratios, have been prepared with the use of surfactants and characterized by X-ray diffraction and electron microscopy. Electronic absorption spectra and photoluminescence spectra of chalcogenide nanowires have been studied. The spectra show blue-shifts compared with those of bulk samples.

Single crystal GaN nanowires.

Single crystal gallium nitride nanowires have been obtained by heating gallium acetylacetonate in the presence of carbon nanotubes or activated carbon in NH3 vapor at 910 degrees C. GaN nanowires also were obtained when the reaction of gallium acetylacetonate with NH3 was carried out over catalytic Fe/Ni particles dispersed over silica. The former procedure with carbon nanotubes is preferable because it avoids the presence of metal particles in the nanowire bundles.

A Raman study of CdSe and ZnSe nanostructures.

Raman studies have been carried out on CdSe nanotubes and ZnSe nanorods produced by surfactant-assisted synthesis. The Raman spectrum of CdSe nanotubes shows modes at 207.5 and 198 cm-1; the former arises from the longitudinal optic phonon mode red-shifted with respect to the bulk mode because of phonon confinement, and the latter is the l = 1 surface phonon. Analysis based on the phonon confinement model demonstrates that the size of the nanoparticle responsible for the red-shift is about 4 nm, close to the estimate from the blue-shift of the photoluminescence. The Raman spectrum of ZnSe nanorods shows modes at 257 and 213 cm-1, assigned to longitudinal and transverse optic phonons, blue-shifted with respect to the bulk ZnSe modes because of compressive strain. The mode at 237 cm-1 is the surface phonon.

A study of polyaniline-carbon nanotube composites.

Composites of polyaniline (PANI) have been prepared with pristine multiwalled and single-walled nanotubes as well as nanotubes subjected to acid treatment and subsequent reaction with thionyl chloride. The composites have been characterized by various techniques, including X-ray diffraction, electron microscopy, as well as infrared and Raman spectroscopy. Electrical resistivities of the PANI-nanotube composites have been measured and compared with those of the nanotubes and PANI.