982 resultados para SILVER NANOPARTICLE ARRAYS


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Photoactive and electroactive thionine dyes have been introduced in high-surface-area surface-confined Au-nanoparticle superstructures by layer-by-layer deposition techniques.

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Graphite powder-supported cupric hexacyanoferrate (CuHCF) nanoparticles were dispersed into methyltrimethoxysilane based gels to produce a conducting carbon ceramic Composite, which was used as electrode material to fabricate surface- renewable CuHCF-modified electrodes. Electrochemical behavior of the CuHCF-modifled carbon ceramic composite electrodes was characterized using cyclic and square-wave voltammetry. Cyclic voltammograms at various scan rates indicated that peak currents were surface-confined at low scan rates. In the presence of glutathione, a clear electrocatalytic response was observed at the CuHCF-modified composite electrodes. In addition, the electrodes exhibited a distinct advantage of reproducible surface-renewal by simple mechanical polishing on emery paper, as well as ease of preparation, and good chemical and mechanical stability in a flowing stream.

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The photoelectrocatalytic effect for the reduction of CO2 mediated with methylviologen (MV) was studied at mercury, polished silver and roughened silver electrodes using electrochemical and surface-enhanced Raman scattering (SERS) techniques. A large photoelectrocatalytic effect for the reduction of CO2 in the presence of MV was observed at the roughened silver electrode, whereas there was only a very small photoelectrocatalytic current at a more negative potential on mercury and polished silver electrodes. The SERS spectra of MV in the presence and absence of CO2, along with the electrochemical results, demonstrate that the surface adsorbed complexes, MV+ -Ag and MV0-Ag, played a role as the mediator for photoinduced electron transfer to CO2 in the solution. The results also suggest that the surface plasmon resonance of the nanoscale silver particle contributes to the overall photoelectrocatalytic effect on a roughened silver electrode.

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Large, monodisperse core-shell Au-Ag nanoparticles with Ag-like optical properties have been prepared by the seeding growth method in micellar media.

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The Langmuir-Blodgett (LB) composite films, ferric oxide nanoparticle composite with tris-(2,3-di-t-amylphenoxy)-(8-quinolinolinolyl) copper phthalocyanine (CuPcA(2)), were obtained by capped type and alternated type and characterized by X-ray photoelectron spectroscopy (XPS) and visible spectra. The gas sensitivity of the composite films and the pure ferric oxide and pure CuPcA(2) LB films to ammonia and ethanol were measured at room temperature. The composite films could be used as the C2H5OH sensors in the range of 2-8 or 100-200 ppm. The XPS data suggested that the adduct complex NH3-CuPcA(2) was formed after the capped film was exposed to the detected gas of ammonia. (C) 2000 Elsevier Science B.V. All rights reserved.

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Platinum nanoparticles were electrocrystallized on a 4-aminophenyl monolayer-grafted carbon substrate. These Pt-modified surfaces were characterized by scanning tunneling microscopy (STM). The characterization by STM revealed that the platinum nanoparticles obtained had good size monodispersity and were well separated from one another on HOPG surfaces. (C) 2000 Elsevier Science S.A. All rights reserved.

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In this presentation, a reverse micelle technique was described to create colloid gold nanoparticles and their self-organization into superlattices. Gold nanoparticles were prepared by the reduction of HAuCL4 in CTAB/octane + 1-butanol/H2O reverse micelle system using NaBH4 as reducing agent. Dodecanethiol (C12H25SH) was used to passivate the gold nanoparticles immediately after formation of the gold colloid. After re-dispersing in toluene under ultrasonication, a supernatant containing nearly monodispersed dodecanethiol-capped gold nanoparticles was obtained. Self-organization of the gold nanoparticles into 1D, 2D and 3D superlattices was observed on the carbon-coated copper grid by TEM. UV-vis absorption spectra were also used to characterize the gold colloids with and without dodecanethiol capping. (C) 2001 Elsevier Science B.V. All rights reserved.

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It was found that microperoxidase-ll (MP-II) can undergo photoreduction at the bale roughened silver electrode. No photoreduction happens at the roughened silver electrode modified with mercaptoundecanoic carboxylic acid/poly-lysine. The photoreduction mechanism is discussed.

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Nanosized ZnS doped with different concentrations of Eu3+ were prepared and analyzed by x-ray diffraction technique. The experimental results show that ZnS belongs to the cubic structure. From the photoluminescence (PL) emission spectra, it can be seen that the ratio of the emission intensity of Eu3+ 616 nm to that at 590 nm increases as the increasing of Eu3+. This phenomenon reveals that the site symmetry of Eu3+ reduces as the increasing of Eu3+.

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TiO2 nanoparticle film catalysts with different thicknesses were prepared by plasma-enhanced chemical vapor deposition(PECVD) method and the surfaces were subsequently treated by TiCl4 or O-2 plasma. Two kinds of TiO2 films with different surface properties were obtained. Their surface microstructures and energy levels of surface states were tested by AFM, XRD, SPS, The photocatalytic activities of the catalysts were determined via photodegradation experiments of phenol. The results demonstrated that photocatalytic activities of samples whose surface was treated by O-2 plasma were greater than those treated by TiCl4 plasma. Moreover, photodegradation ratio of phenol during the first hour catalyzed by 0. 17 mu m thickness TiO2 nanoparticle film was greater than other samples. Especially, the difference of photocatalytic activities of TiO2 nanoparticle films treated by TiCl4 or O-2 plasma was respectively explained by energy band theory.

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Photoelectrochemical reduction of nitrite and nitrate was studied on the surface of an electrochemically roughened silver electrode. The dependence of the photocurrent on photon energy, applied potential, and concentration of nitrite was determined. It was concluded that the photoelectrochemical reduction proceeds via a photoemission process followed by the capture of hydrated electrons by electron accepters. The excitation of plasmon resonances in nanosize metal structures produced during the roughening procedure resulted in the enhancement of the photoemission process. Ammonia was detected as one of the final products in this reaction. Mechanisms for the photoelectrochemical reduction of nitrite and nitrate are proposed.

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Multilayer assemblies of silver doped ZnS colloid and polycation were fabricated by a self-assembly technique exploiting electrostatic interaction. UV/Vis spectra showed the uniform deposition process and X-ray photoemission spectroscopy (XPS) confirmed the coexistence of silver. It was found that the emission spectra of the silver doped ZnS colloid red-shifted to 528 nm comparing with undoped ZnS colloid. However, the most important finding was that the luminescence intensity of doped ZnS assembled in films was much stronger than that of undoped ZnS in films and that of doped ZnS in the spin-casting film. The mechanism of the enhancement luminescence was discussed. (C) 1998 Elsevier Science S.A. All rights reserved.

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A successful analysis of silver was reported utilizing laser desorption/ionization time-of-flight mass spectrometry (LDI/TOF-MS) in this paper, The silver cluster ions Ag-n(+) and AgnO+ (n=2 similar to 5) were formed during laser desorption/ionization. In the presence of I-, K+ and Na+, the peaks corresponding, to the cluster ions [AgnIn-1](+) (n=2 similar to 6) and the adduct ions [AgI](+), [AgI]Na+ and [AgI]K+ were observed in the positive ion spectrum; the peaks corresponding to [AgnIn+1](-) (n=1 similar to 3) were found in the negative ion spectrum, all of which accompanied by sliver isotope distribution, The formation of silver cluster ions was accomplished through two-stage reaction: the first step was the generation of clusters, which was followed by the processes of photoionization and ion/molecule reaction.

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Three new compounds AgLnMo(2)O(8) (Ln = Eu, Gd, Tb) crystallize with a tetragonal scheelite-type structure characterized by MoO4 tetrahedra. The IR spectra show three absorption bands, which correspond respectively to the nu(1), nu(2), and nu(3) modes of the tetrahedral-MoO42- groups. The emission of AgGdMo2O8 shows the band of the MoO42- groups around 600 nm wavelength with very weak intensity. Both AgEuMo2O8 and AgTbMo2O8 emit intensely, and the concentration quenchings of both Eu3+ and Tb3+ luminescences are very weak. For all compounds, Ag+ luminescence is not observed. (C) 1996 Academic Press, Inc.