Surfactantless synthesis of multiple shapes of gold nanostructures and their shape-dependent SERS spectroscopy

A useful method for the synthesis of various gold nanostructures is presented. The results demonstrated that flowerlike nanoparticle arrays, nanowire networks, nanosheets, and nanoflowers were obtained on the solid substrate under different experimental conditions. In addition, surface-enhanced Raman scattering (SERS) spectra of 4-aminothiophenol (4-ATP) on the as-prepared gold nanostructures of various shapes were measured, and their shape-dependent properties were evaluated. The intensity of the SERS signal was the smallest for the gold nanosheets, and the flowerlike nanoparticle arrays gave the strongest SERS signals.

Noncovalent functionalization of multiwalled carbon nanotubes: Application in hybrid nanostructures

We developed a reproducible, noncovalent strategy to functionalize multiwalled carbon nanotubes (MWNTs) via embedding nanotubes in polysiloxane shells. (3-Aminopropyl)triethoxysilane molecules adsorbed to the nanotube surfaces via hydrophobic interactions are polymerized simply by acid catalysis and form a thin polysiloxane layer. On the basis of the embedded MWNTs, negatively charged gold nanoparticles are anchored to the nanotube surfaces via electrostatic interactions between the protonated amino groups and the gold nanoparticles. Furthermore, these gold nanoparticles can further grow and magnify along the nanotubes through heating in HAuCl4 aqueous solution at 100 degrees C; as a result these nanoparticles are joined to form continuous gold nanowires with MWNTS acting as templates.

Surface-enhanced Raman scattering of silver-gold bimetallic nanostructures with hollow interiors

Surface-enhanced Raman scattering (SERS) activity of silver-gold bimetallic nanostructures (a mean diameter of similar to 100 nm) with hollow interiors was checked using p-aminothiophenol (p-ATP) as a probe molecule at both visible light (514.5 nm) and near-infrared (1064 nm) excitation. Evident Raman peaks of p-ATP were clearly observed, indicating the enhancement Raman scattering activity of the hollow nanostructure to p-ATP. The enhancement factors (EF) at the hollow nanostructures were obtained to be as large as (0.8 +/- 0.3)x10(6) and (2.7 +/- 0.5)x10(8) for 7a and 19b (b(2)) vibration mode, respectively, which was 30-40 times larger than that at silver nanoparticles with solid interiors at 514.5 nm excitation. EF values were also obtained at 1064 nm excitation for 7a and b(2)-type vibration mode, which were estimated to be as large as (1.0 +/- 0.3)x10(6) and (0.9 +/- 0.2)x10(7), respectively. The additional EF values by a factor of similar to 10 for b(2)-type band were assumed to be due to the chemical effect. Large electromagnetic EF values were presumed to derive from a strong localized plasmas electromagnetic field existed at the hollow nanostructures.

Direct patterning of negative nanostructures on self-assembled monolayers of 16-mercaptohexadecanoic acid on Au(111) substrate via dip-pen nanolithography

Both bare and self-assembled monolayer (SAM) protected gold substrate could be etched by allyl bromide according to atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS) and inductively coupled plasma mass spectrometric (ICPMS) analysis results. With this allyl bromide ink material, negative nanopatterns could be fabricated directly by dip-pen nanolithography (DPN) on SAMs of 16-mercaptohexadecanoic acid (MHA) on Au(111) substrate. A tip-promoted etching mechanism was proposed where the gold-reactive ink could penetrate the MHA resist film through tip-induced defects resulting in local corrosive removal of the gold substrate. The fabrication mechanism was also confirmed by electrochemical characterization, energy dispersive spectroscopy (EDS) analysis and fabrication of positive nanopatterns via a used DPN tip.

Hydrothermal growth and gas sensing property of flower-shaped SnS2 nanostructures

Unusual 3D flower-shaped SnS2 nanostructures have been synthesized using a mild hydrothermal treatment in the presence of octyl-phenol-ethoxylate ( Triton X-100) at 160 degrees C. The nanostructures have an average size of 1 mu m, and consist of interconnected nanosheets with thicknesses of about 40 nm. Based on time-dependent experimental results, we ascribe the oriented attachment mechanism to the growth of the SnS2 nanostructures. The nonionic surfactant Triton X-100 plays a key role in the formation of the flower-like morphology. Room temperature gas-sensing measurements show that the 3D SnS2 nanostructures could serve as sensor materials for the detection of NH3 molecules.

Studies of interaction between iron (III) and intermediates of synthetic neuromelanin by means of cyclic voltammetry of Fe(CN)(3-)(6) and dopamine

Neuromelanin is a complex polymer pigment found primarily in the dopaminergic neurons of the human substantia nigra, whose composition is complex including production of dopamine auto-oxidation, glutathione and a variety of amino acid. Neuromelanin forms stable complex with iron (111). We observed that 5,6-dihydroxyindole and its ramification possessed strong ability of chelating iron (111), and they are the production of dopamine auto-oxidation under physiological pH condition. In the present Of L-Cysteine, the relative yields of electrochemical oxidation of dopamine also had strong ability of chelating iron (111). The experimental results suggest that 5,6-dihydroxyindole and 5-S-cysteineldopamine play important roles in the process of synthetic neuromelanin chelating iron (111).

Room-temperature strategy for networked nonspherical gold nanostructures from Au(III)-[G-2]-CO2H dendrimer complex

The present work describes a convenient approach to fabricate networked nonspherical gold nanostructures by using [G-2]-CO2H dendrimer and toluene as capping and bridging agents in a CH2Cl2 and H2O biphasic system. A controlled linear assembly is achieved without the use of any catalyst at room temperature. UV-vis spectrum, transmission electron microscopy (TEM), selected area electron diffraction (SAED), and X-ray diffraction (XRD) analysis show that the product is well networked nanostructures with diameter of 4-10 nm and consists of coalesced face-centered cubic gold nanocrystals. Extended experiments reveal that both benzene and dimethylbenzene can also inhabit the gold ions to make them crosslinked, prolong the nucleation points and eventually facilitate the formation of the networks.

Electron effect of p-substituent on iron(II) and cobalt(II) pyridinebisimine catalyst for ethylene polymerization

A series of 2,6-bis(imino)pyridyl iron and cobalt complexes bearing p-substituent [2,6-(ArN=CMe)(2)C5H3N]-MCl2 (Ar=2,6-Me2C6H3, 2,4,6-Me3C6H2, 2,6-Me-2-4-BrC6H2, 2,6-Me-2-4-ClC6H2, 2,4-Me-2-6-BrC6H2, 2,4-Me-(2)-6-ClC6H2, while M=Fe, Co) have been synthesized and investigated as catalysts for ethylene polymerization in the presence of modified methylaluminoxane as a cocatalyst. The electron effect and positions of the substitueni of pyridinebisimine ligands were observed to affect considerably catalyst activity and polymer property.

Assembly of multilayer films containing iron(III)- substituted Dawson-type heteropolyanions and its electrocatalytic properties: cyclic voltammetry, electrochemical impedance spectroscopy and UV-Vis spectrometry

Ultrathin multilayer films have been prepared by means of alternate adsorption of iron(Ill)-substituted heteropolytungstate anions and a cationic redox polymer on the 4-aminobenzoic acid modified glassy carbon electrode surface based on electrostatic layer-by-layer assembly. Cyclic voltammetry, electrochemical impedance spectroscopy and UV-Vis absorption spectrometry have been used to easily monitor the uniformity of thus-formed multilayer films. Especially, the electrochemical impedance spectroscopy is successfully used to monitor the multilayer deposition processes and is a very useful technique in the characterization of multilayer films because it provides valuable information about the interfacial impedance features. All these results reveal regular film growth with each layer adsorption. The resulting multilayer films can effectively catalyze the reduction of H2O2,NO2- and BrO3-.

Structure of Cyclic Aryl Thioester Dimer Based on o-Phthaloyl Dichloride and Bis(4-mercaptophenyl) Sulfide

A cyclic aryl thioester dimer was prepared by the reaction of o-phthaloyl dichloride and his (4-mercaptophenyl) sulfide in good yield under pseudo-high dilution conditions via interfacial polycondensation. The structure of the cyclic dimer was confirmed by a combination of MALDI-TOF-MS, FTIR, gel permeation chromatography and MM analyses. The X-ray diffraction study of the single crystal of cyclic thioester dimer obtained from two solutions reveals no severe internal strain on the cyclic structure.

One-pot synthesis and characterization of novel silver-gold bimetallic nanostructures with hollow interiors and bearing nanospikes

One-pot preparation of shell-type silver-gold bimetallic nanostructures with hollow interiors and bearing nanospikes, based on colloid seed-engaged replacement reaction and colloid-mediated deposition reactions, has been reported. Heating-induced evolution of Ag-Au bimetallic nanoshells can lead to spontaneous production of nanospikes on the colloid surface. The hollow interior structure and bimetallic nature of the as-prepared colloids are characterized by transmission electron microscopy (TEM), UV-vis spectroscopy, and X-ray photoelectron spectroscopy (XPS).

Synthesis, characterization and fabrication on a glassy carbon electrode of a tetra-iron substituted sandwich-type pentadecatungstodiarsenate heteropolyanion

A novel sandwich-type compound, Na-12[Fe-4(H2O)(2)(As2W15O56)2].41H(2)O, has been synthesized. The compound was well-characterized by means of IR, UV-vis, W-183 NMR and elemental analyses. The compound crystallizes in the triclinic, P (1) over bar symmetry group. The structure of the compound is similar to that of Na-16[M-4(H2O)(2)(As2W15O56)(2)].nH(2)O (M = Cu, Zn, Co, Ni, Mn, Cd), and consists of an oxo-aqua tetranuclear iron core, [(Fe4O14)-O-III(H2O)(2)], sandwiched by two trivacant alpha-Wells-Dawson structural moieties, alpha-[As2W15O56]. Redoxelectrochemistry of the compound has been studied in buffer solutions at pH = 4.7 using polarography and cyclic voltammetry ( CV). The compound exhibited four one-electron couples associated with the Fe(III) center followed by three four-electron redox processes attributed to the tungsten-oxo framework. The compound-containing monolayer and multilayer films have been fabricated on a 4-aminobenzoic acid modified glassy carbon electrode surface by alternating deposition with a quaternized poly(4-vinylpyridine) partially complexed with [Os(bpy)(2)Cl](2+/-). CV, X-ray photoelectron spectroscopy (XPS), UV-vis spectroscopy and atomic force microscopy (AFM) have been used to characterize the multilayer films.