Ultrafast spectroscopy and coherent acoustic phonons of Au-Ag core-shell nanorods

We performed the first investigations of coherent acoustic phonons in Au-Ag core-shell nanorods, which were compared with the results of parental Au nanorods. Both breathing and extensional modes were observed in Au-Ag core-shell nanorods with ~11 nm Ag shell while only extensional modes were detected in other core-shell nanorods with 4-7 nm Ag shell. Young's modulus estimated from the oscillation period of extensional modes was found to be larger for Au-Ag core-shell nanorods with ~4 nm Ag shell, as compared with that of Au nanorods. The value of Young's modulus decreases with the increase of the Ag shell thickness and finally becomes smaller than that of Au nanorods. This phenomenon is interpreted in terms of the surface effects and the existence of grain boundaries in the lattice structure of Ag shell.     

Synthesis, characterization and SERS activity of Au-Ag nanorods

The formation mechanism and morphology of Au-Ag bimetallic colloidal nanoparticles depend on the composition. Ag coated Au colloidal nanoparticles have been prepared by deposition of Ag through chemical reduction on performed Au colloid. The composition of the Au(100-x)-Ag(x) particles was varied from x=0 to 50. The obtained colloids were characterized by UV-vis spectroscopy and transmission electron microscopy (TEM). The Au(80)-Ag(20) colloid consists of alloy nanorods with dimension of 25nmx100nm. The activity of these nanorods in surface enhanced Raman spectroscopy (SERS) was checked by using sodium salicylate as an adsorbate probe. Intense SERS bands are observed indicating its usefulness as a SERS substrate in near infrared (NIR) laser excitation.     

Synthesis of SnSe in various alkaline media under mild conditions

The synthesis of SnSe was systematically investigated in various alkaline media and at various temperatures with SnCl2.2H2O and selenium as source materials. The basicity of the alkaline media and the reaction temperature are two key factors considered in our process. The synthesis of SnSe in sodium hydroxide solution and aqueous ammonia is limited to a narrow temperature range, while the synthesis in hydrazine hydrate and ethylenediamine proceeds over a wider range. The final products were characterized by X-ray diffraction pattern (XRD), energy dispersive X-ray (EDX), and transmission electron microscopy (TEM). TEM results showed a variation of crystal morphology of SnSe obtained in different media. Two simple chemical mechanisms for the formation of SnSe are presented.     

Epitaxial growth triggered core-shell Pd@RuP nanorods for high-efficiency electrocatalytic hydrogen evolution

Ru with Pt-like hydrogen bond strength,knockdown cost(～1/3 of Pt),and eximious stability is a competitive replacement for Pt-based catalysts towards the hydrogen evolution reaction(HER) in water splitting.The design of Ru-based catalysts via interface construction,crystal phase control,and specific light element doping to realize the impressive promotion of limited activity and stability remains challenging.Herein,we report the fabrication of Pd@RuP core-shell nanorods(NRs) via an epitaxial grow...     

同晶外延生长法合成MFI型核壳复合分子筛

采用二次热液结晶法,以四丙基氢氧化铵水溶液预处理过的低硅ZSM-5分子筛为晶核,通过调控p H值、水量和晶化时间等二次结晶条件,在晶核上外延生长了高硅ZSM-5壳,制备了MFI/MFI核壳型复合分子筛。通过X射线衍射、扫描电镜、能量色散谱仪、透射电子显微镜、N2吸附-脱附和NH3-程序升温脱附等手段表征了所合成的核壳分子筛的晶体结构、表面形态及核/壳界面,并对它们的结构参数以及酸性进行了初步评估。结果表明,核壳复合分子筛的壳层由多层200 nm的MFI沸石晶粒组成;高硅ZSM-5分子筛壳层的生成,引入了介孔结构,显著增大了外比表面积;同时,核壳结构的形成降低了复合分子筛酸性和外表面的酸密度,但增加了弱酸量。当二次晶化母液p H值为8.5,H2O/SO2物质的量比为30,晶化时间为24 h时,高硅分子筛壳层更易可控生长。     

Synthesis of dumbbell-shaped manganese oxide nanocrystals

Dumbbell-like homogeneous MnO nanocrystals are obtained for the first time via the pyrolysis of manganese formate in trioctylamine/oleic acid media and the orientation aggregation mechanism is proposed for this 1D growth route.     

The importance of the CTAB surfactant on the colloidal seed-mediated synthesis of gold nanorods

Gold nanorods were synthesized by the colloidal seed-mediated, surfactant-assisted approach [Gou et al., Chem. Mater. 2005, 17, 3668-3672] using CTAB (hexadecylcetyltrimethylammonium bromide) obtained from ten different suppliers. The yield of gold nanorods depended strongly on the CTAB used: with the same recipe, three of the CTABs did not yield nanorods and produced only spherical gold particles, whereas the other CTABs yielded nanorods with nearly 100% yield. These results suggest that an impurity in the CTAB is very important for nanorod formation.     

Silver-nanoparticle-attached indium tin oxide surfaces fabricated by a seed-mediated growth approach

By applying a seed-mediated growth method that had been reported for the chemical synthesis of Ag nanorods and nanowires in aqueous solution, we successfully attached Ag nanosphere and nanorod particles to indium tin oxide (ITO) surfaces. In this method, it is characteristic that the attachment can be performed without using bridging reagents, such as 3-mercaptopropyltrimethoxysilane, but rather through a two-step immersion into the seed solution first and then into the growth solution containing AgNO(3), cetyltrimethylammonium bromide, and ascorbic acid. It was found that the formed nanostructures were very sensitive to the amount of ascorbic acid in the growth solution. Whereas Ag nanoparticles grew on the ITO surface with a moderate dispersion when the concentration of ascorbic acid in the growth solution was 0.64 mM, the formation of nanorods and nanowires was observed when the ascorbic acid concentration was increased to 0.86 mM. The attachment of Ag nanoparticles onto the ITO surfaces was strong enough for further use, e.g., as a working electrode. From electrochemical measurements, it was confirmed that the outer spheres of the Ag nanoparticles involved in the redox reaction show the typical oxidation and reduction waves of Ag. In addition, the redox behavior of [Fe(CN)(6)](3-)/[Fe(CN)(6)](4-) was improved on the Ag-nanoparticle-attached ITO (AgNP/ITO) electrode, reflecting the low electron-transfer resistivity, which is a remarkable advantage of the present fabrication without using bridging reagents. This result indicated that the Ag nanoparticles promote the electron-transfer reactions by being present on the conducting ITO surface. The AgNP/ITO electrode was examined for the reduction of the methyl viologen dication in order to discuss some features of the present fabrication.     

Surface plasmon mapping of dumbbell-shaped gold nanorods: the effect of silver coating

We report on the identification of surface plasmons in individual gold dumbbell-shaped nanoparticles (AuDBs), as well as AuDBs coated with silver. We use spatially resolved electron energy-loss spectroscopy in a scanning electron microscope, which allows us to map plasmon-energy and intensity spatial distributions. Two dominant plasmon resonances are experimentally resolved in both AuDBs and silver-coated AuDBs. The intensity of these features is peaked either at the tips or at the sides of the nanoparticles. We present boundary element method simulations in good agreement with the experiment, allowing us to elucidate the nature of such modes. While the lower-energy, tip-focused plasmon is of longitudinal character for all dumbbells under consideration, the second side-bound plasmon has a more involved symmetry, starting as a longitudinal quadrupole in homogeneous AuDBs and picking up transversal components when silver coating is added. The longitudinal dipolar mode energy is found to blue-shift upon coating with silver. We find that the substrate produces sizable shifts in the plasmons of silver-coated AuDBs. Our analysis portraits a complex plasmonic scenario in metal nanoparticles coated with silver, including a transition from the original homogeneous gold dumbbell plasmons to the modes of homogeneous silver rods. We believe that these findings can have potential application to plasmon engineering.     

Capillary electrophoresis of proteins under alkaline conditions.

Successful separations of proteins by capillary electrophoresis in uncoated fused-silica capillaries is limited by adsorption and variable rates of electroendosmosis, which can compromise quantitative accuracy and precision. Operation at extremes of pH to minimize these problems is useful in special cases but is not a general strategy for protein separations. Three alternative strategies are described: use of capillaries coated with a linear hydrophilic polymer, the use of acidic solutions to wash the capillary between runs, and the incorporation of additives into the electrophoresis buffer to minimize adsorption during analysis. Applications of these techniques to protein samples is demonstrated.     

Dissolution of uranium oxides under alkaline oxidizing conditions

Bench scale experiments were conducted to determine the dissolution characteristics of UO₂, U₃O₈, and UO₃ in aqueous peroxide-containing carbonate solutions. The experimental parameters investigated included carbonate countercation (NH₄ ⁺, Na⁺, K⁺, and Rb⁺) and H₂O₂ concentration. The carbonate countercation had a dramatic influence on the dissolution behavior of UO₂ in 1 M carbonate solutions containing 0.1 M H₂O₂, with the most rapid dissolution occurring in (NH₄)₂CO₃ solution. The initial dissolution rate (y) of UO₂ in 1 M (NH₄)₂CO₃ increased linearly with peroxide concentration (x) ranging from 0.05 to 2 M according to: y = 2.41x + 1.14. The trend in initial dissolution rates for the three U oxides under study was UO₃ ≫ U₃O₈ > UO₂.     

Catalytic cross-coupling of aniline by pyrite and dissolved oxygen under alkaline conditions

Pyrite catalyzes oxidation of various organic contaminants by dissolved oxygen (DO) under acidic conditions; however, the catalytic mechanism under alkaline conditions is still not clear. In this study, we observe increased oxidation rates of aniline with increasing pHs (7.0–11.0). Electron paramagnetic resonance (EPR) analysis and quenching experiments rule out contributions of •OH, O₂^•−, ¹O₂ and Fe (IV) to aniline oxidation and suggest that the Fe (III)–OOH peroxo and/or H₂O₂ are the primary oxidative species in the oxidation of aniline at pH 11.0. In addition, 200 mg L⁻¹ H₂O₂ does not apparently increase the oxidation rate of aniline, which also rules out the predominant contribution of the produced H₂O₂ to aniline oxidation. We therefore suggest that the Fe (III)–OOH peroxo is indeed the primary oxidative species in the pyrite–DO system under alkaline conditions. Analyses of solid total organic carbon (TOC), gas chromatography–mass spectrometry and Fourier-transform infrared spectroscopy further reveal that more than 83.3% aniline has been polymerized to polyaniline, instead of being mineralized into CO₂ and H₂O, indicating that H-abstraction from aniline by the Fe (III)–OOH peroxo is an important step in the oxidation of aniline under alkaline conditions. This study provides new insight into the oxidative species in the pyrite–DO system, and opens a new door for organic degradations under alkaline conditions.     

Rotor-like ZnO by epitaxial growth under hydrothermal conditions

Rotor-like ZnO was grown from a mixture of rod-like ZnO powder and a saturated Zn(OH)(4)(2-) solution under moderate hydrothermal conditions at 100 degree C, in which the precursor rod-like ZnO crystal plane acts as a matrix core, and the branched nanorods showed fast epitaxial growth on the six directions around the prism core.     

Sandwich structures at oil-water interfaces under alkaline conditions

Equilibrium liquid crystal (LC) layer on an interface between crude oils and water was observed at high pH. This layer is composed mainly of sodium naphthenates produced in situ at the water/oil interface. Transient LC layer was also evolved at the interface of aqueous phase of sodium hydroxide solutions and oleic phase of naphthenic acid (NA) solutions as result of a chemical reaction between NaOH and NA. This chemical reaction causes transport process resulting in a disturbance of the interface. Optical observation of this interface disturbance reviled that the interface covered with LC shows considerably lower flexibility as compared to LC free interface. The LC layer eventually dissolves in the water phase at low oil-to-water ratio, while at high oil-to-water ratio it can form an equilibrium phase, which spreads spontaneously at the oil-water interface.     

The catalytic properties of alkaline phosphatases under various conditions

A comparative study was performed to examine the catalytic properties of alkaline phosphatases from bacteria Escherichia coli and bovine and chicken intestines. The activity of enzyme dimers and tetramers was determined. The activity of the dimer was three or four times higher than that of the tetramer. The maximum activity and affinity for 4-nitrophenylphosphate was observed for the bacterial alkaline phosphatase (K _M = 1.7 × 10^?5 M, V _max = 1800 μmol/(min mg of protein) for dimers and V _max = 420 μmol/(min mg of protein) for tetramers). The Michaelis constants were equal for two animal phosphatases in various buffer media (pH 8.5) ((3.5 ± 0.2) × 10^?4 M). Five buffer systems were investigated: tris, carbonate, hepes, borate, and glycine buffers, and the lowest catalytic activity of alkaline phosphatases at equal pH was observed in the borate buffer (for enzyme from bovine intestine, V _max = 80 μmol/(min mg of protein)). Cu²⁺ cations formed a complex with tris-(oxymethyl)-aminomethane (tris-HCl buffer) and inhibited the intestine alkaline phosphatases by a noncompetitive mechanism.     

Size and composition control of Pt-In nanoparticles prepared by seed-mediated growth using bimetallic seeds

A two-step method has been developed for precise size and composition control of bimetallic Pt-In nanoparticles. Very small (1.62 nm) PtIn seed nanoparticles with 1:1 metal ratio were prepared in the absence of capping agents followed by growth of Pt on their surface in the presence of oleyl amine as reducing and stabilizing agent. Nanoparticles with bulk compositions of Pt(4)In, Pt(3)In, and Pt(2)In could be synthesized with average diameter smaller than 3 nm. TEM, EDX, and XPS provided evidence for homogeneous growth without separate nucleation of pure platinum nanoparticles in the reaction solution. Pt(3)In nanoparticles were deposited onto SiO(2) surface by incipient wetness impregnation. Temperature-induced changes in the particle surface were monitored by in situ IR spectroscopy and CO adsorption. It was found that surface alloy composition of the particles could be tuned by using oxidizing or reducing atmospheres.     

Transformations of secondary diacetylenic alcohols under alkaline isomerization conditions

Summary A study was made of the transformation of secondary diacetylenic alcohols in alkaline medium and the structure of the vinylacetylenic keto alcohols obtained here was proved.Translated from Izvestiya Akademii Nauk SSSR, Khimicheskaya, No. 12, pp. 2215–2216, December, 1965     

Synthesis and thermal properties of new dumbbell-shaped isobutyl-substituted POSSs linked by aliphatic bridges

Five new dumbbell-shaped polyhedral oligomeric silsesquioxanes (POSSs), in which two identical silicon cages are linked to various length aliphatic bridges, were prepared by corner capping reaction between hepta isobutyltricycloheptasiloxane trisilanol (HIBT) and suitable bis(triethoxysilyl) derivatives. The products obtained were characterized by elemental analysis and ¹H NMR spectroscopy, and the results were in very good agreement with the expected ones. Degradations were carried out in flowing nitrogen and in static air atmosphere, and temperatures at 5 % mass loss (T _5 %) and residues at 700 °C were determined to investigate the resistance to the thermal degradation. The T _5 % values were lower in oxidative atmosphere than in inert environment, and increased linearly as a function of organic bridge length in either used atmosphere. The residues at 700 °C were higher in static air than in flowing nitrogen. The results obtained for various dumbbell-shaped POSSs were discussed and compared with each other. A comparison with the results previously obtained with the corresponding un-bridged phenyl, hepta isobutyl-POSSs showed a higher resistance to the thermal degradation of bridged POSSs.     

pH Dependence of the size and crystallographic orientation of the gold nanoparticles prepared by seed-mediated growth

The effect of the pH of the growth solution on the size and crystallographic orientation of gold nanoparticles (GNPs) was studied during the course of the preparation of surface-confined spherical GNPs following a two-step protocol (electrochemical and chemical). GNPs were first electrodeposited onto a clean glassy carbon (GC) electrode and these GNPs were used as seeds. Seed-mediated growth of the electrodeposited GNPs was performed in a solution of H[AuCl(4)] at various pHs (5.0 to 0.5) using NH(2)OH as a reducing agent. The thus-prepared GNPs were characterized by electrochemical, UV-visible absorption spectral, SEM, and TEM studies. The nucleation (i.e., formation of the new seeds) was found to dominate over growth (i.e., enlargement of the seed particles) process at higher pH during NH(2)OH seeding, whereas only growth was recognized at low pH (0.5). Nonspherical byproducts were noticed when the seed-mediated growth was performed at higher pHs, but at pH 0.5 only spherical GNPs were observed. The present method provides a way out for the preparation of GNPs with homogeneous shape resolving the problem of simultaneous formation of nonspherical byproducts during the seed-mediated growth as well as for the preparation of GNPs with a Au(111) facet ratio as high as 97%. On the basis of the obtained results, the mechanism of the growth process at low pH is also discussed. Interestingly, an enhanced electrochemical response was obtained for the oxidation of H(2)O(2) using the GNPs prepared at pH 0.5.