Ag Colloidal Particles Research Articles

Surface-Enhanced Resonance Raman Scattering from Copper(II) 5,10,15,20-Tetrakis(1-methyl-4-pyridyl)porphyrin Adsorbed on Aggregated and Nonaggregated Silver Colloids

Surface-enhanced resonance Raman scattering (SERRS) from copper(II) 5,10,15,20-tetrakis(1-methyl-4-pyridyl)porphyrin (CuTMPyP(4)) adsorbed on a borohydride-reduced silver colloid was studied as a function of CuTMPyP(4) concentration ranging from 1 × 10-9 to 1 × 10-6 M, using the 441.6 nm excitation line of a He−Cd laser. The OH stretching band of bulk water was employed as an internal intensity standard for normalization of the porphyrin SERRS spectra. The surface coverage of Ag colloidal particles by porphyrin molecules as well as the surface plasmon absorption (SPA) and morphology of the Ag colloid/CuTMPyP(4) systems in dependence on the total porphyrin concentration in the systems were investigated and related to the concentration dependence of the SERRS signal. The plots of the intensities of 12 SERRS spectral bands of the A1g porphyrin modes against the porphyrin concentration are found to be fairly linear for systems with the total porphyrin concentrations 1 × 10-8 to 2 × 10-7 M, in which all porphy...

ラマン分光法によるウランの吸着挙動に関する研究 銀コロイドおよび金コロイドへの吸着

Raman spectra of uranium loaded Ag and Au colloidal particles have been measured. It was observed that Raman active symmetric stretching frequency of uranyl ion at 870cm-1 shifts to smaller wavenumber when adsorbed onto Ag and Au particles. The shift depends on pH of the solution for Ag particles, but not for Au particles. The notion that uranium adsorption involves ligand liberation was thus confirmed for Ag particles, while it was discounted for Au particles.

Tailoring particle size and morphology of colloidal Ag particles via chemical precipitation for Ag-BSCCO composites

The chemical precipitation of silver particles is an effective method for tailoring the particle size and morphology. This article investigates a chemical precipitation method for producing silver colloids, and how processing parameters affected particle size, morphology and adherence. Decreasing the silver nitrate concentration during precipitation with sodium borohydride decreased the colloidal silver particle size. Decreasing the addition rate of the reducing agent produced faceted particles. Reversing the reactant addition order also changed the particle size and the morphology. Precipitated colloids demonstrated a difference between the growth-dominated and the equilibrium structures. Co-dispersing Bi-based superconducting platelets during precipitation allowed Ag colloids to preferentially nucleate on the platelets and to remain adhered even after the additional processing.

Chemical and Electrochemical Ag Deposition onto Preformed Au Colloid Monolayers: Approaches to Uniformly-Sized Surface Features with Ag-Like Optical Properties

Two approaches to preparation of Ag-clad Au colloid monolayers are described. Each begins with a preformed monolayer of colloidal Au particles on glass, Au-coated quartz, or In-doped SnO2. Chemical reduction of Ag+ from a commercial Ag coating formulation (LI Silver) or electrochemical reduction of Ag+ leads to surfaces for which the amount of Ag deposited can be controlled. On transparent substrates, Ag deposition can be followed in real time by UV−visible spectroscopy. When the substrate is an electrode, electrochemical deposition can be monitored by coulometry; for the chemical process, anodic stripping voltammetry yields accurate values of the amount of Ag present, as confirmed by quartz crystal microgravimetry (QCM). Chemical reduction yields surfaces that are extremely enhancing for surface enhanced Raman scattering (SERS), although the deposition process required must be precisely tuned. In contrast, electrochemical deposition, while affording more accurate control of the reduction rate, produces only mildly enhancing surfaces. Atomic force microscopy (AFM) images of electrochemically-produced surfaces show formation of very large nonuniform Ag particles that are distinct from the Au colloid monolayer, while those prepared by LI Silver show both growth of Ag on Au and formation of smaller colloidal Ag particles attached to Ag-coated Au particles.

The Model of Linear Aggregate of Ag Colloidal Particles with Variable Inter-Particle Distances

A simplified method of calculation of the surface plasmon energy states of the Ag colloidal aggregates characterized by varying inter-particle (inter-sphere) distance has been developed. Ag colloidal aggregate is approximated by a linear (one-dimensional) assembly of N silver spheres (of identical radii r and identical inter-sphere distances D) mutually interacting by a dipole-dipole interaction. The calculations use the following parameters: N from 1 to 25, r = 2, 5 and 10 nm, D = 0, 0.5, 1 and 2 nm, water and/or vacuum embedding media. The perturbation energies Vmin (stabilization energy) and Vmax (destabilization energy) of the excited plasmon state of a linear aggregate of N spheres interacting by the dipole-dipole interaction were calculated as the eigenvalues of perturbation matrix using the above-mentioned parameters. The stabilization energy Vmin increases with increasing number of spheres in the aggregate and with increasing sphere radius, while it decreases with increasing inter-particle (inter-sphere) distance. Calculations of the square values of the eigenvector coefficients show that the contribution of a particular single sphere to the total energy of the aggregate is the highest for the central sphere in the odd-N aggregates and for the two central spheres in the even-N aggregates. The results of the model calculations support the hypothesis that the differences between the surface plasmon absorption curves of the Ag colloid/monomeric adsorbate and of the Ag colloid/polymeric (oligomeric) adsorbate systems have their origin in the difference in the inter-particle distance distributions.

Processing with colloidal Ag particles in hot forged Ag-coated BSCCO-2223 composites

Multilayer Ag-BSCCO-2223 composites have been fabricated by open-die hot forging to study the role of Ag in densification and microstructural development. The composite microstructures were produced using Ag-coated BSCCO particles produced from a chemical precipitation technique. Grain alignment and Ag microstructure effects were characterized via optical and electron microscopy.

Surface-Enhanced Raman Scattering (SERS) Spectroscopy with Borohydride-Reduced Silver Colloids: Controlling Adsorption of the Scattering Species by Surface Potential of Silver Colloid

Formation of Ag colloid/adsorbate SERS-active systems (upon adsorption of the selected adsorbates on the surface of Ag colloidal particles) as a function of (i) NaBH4 to AgNO3 molar ratio in the preparation protocol of Ag colloid, and (ii) aging of the colloid has been investigated by Surface-enhanced Raman scattering (SERS) spectroscopy. Oligomeric synthetic polypeptides, bovine serum albumin, phosphate coadsorbed with CuTMePyP [copper(II) derivative of 5,10,15,20-tetrakis-(N-methylpyridinium-4-yl)porphyrin chloride] and borates in systems with N-containing bases were selected as model adsorbates. Both (i) a decrease of NaBH4 to AgNO3 molar ratio upon preparation and (ii) aging of Ag colloid affect adsorption of the adsorbates and consequently, their SERS spectra, in the same manner. Aging of Ag colloid is thus viewed as a slow hydrolysis of BH4- anions. The actual concentration of BH4- in the system is identified as the most important factor controlling adsorption of all the selected adsorbates on the surface of Ag colloid. As this factor can be related to the surface potential, the conditions controlling adsorption of the selected adsorbates are specified in terms of a more negative and/or more positive surface potential of Ag colloidal particles. A more positive surface potential promotes adsorption of polypeptides, bovine serum albumin and phosphate while observation of spectral features of borates in the SERS spectra of N-containing bases in alkaline solutions is conditioned by a more negative surface potential.

Surface-enhanced Raman spectra of 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin/silver colloid system: what information about the porphyrin do we obtain?

Porphyrins, both as free bases and as metal complexes, are involved in many important biological functions (photosynthesis, metabolic redox reactions, oxygen transport, photodynamic processes, etc.). Vibrational spectroscopy of these large but highly symmetric molecules is a very sensitive probe of their structure in various types of environment. However, the generally low oscillator strengths of vibrational transitions in porphyrins make their infrared (IR) and Raman measurements at low (physiological) concentrations difficult. Surface-enhanced Raman scattering (SERS) spectroscopy overcomes this problem by the 10{sup 4}-10{sup 6} enhancement of Raman scattering upon adsorption of the molecular species studied on a roughened surface of the particular metal. Nevertheless, a specific chemical interaction of the species with the metal surface may affect the relevancy of the structural information about the species itself provided by SERS. Classification of the possible structural changes induced by adsorption of porphyrins onto the metal surface thus becomes a crucial point in the interpretation of the SERS spectra of porphyrin-containing systems. In this paper, the authors address this basic problem for the water-soluble free base 5, 10, 15, 20-tetrakis(4-carboxyphenyl)porphyrin (TPPC4) adsorbed on the surface of Ag colloidal particles.

Serr evidence for enzymatic reduction of cytochrome c 3 adsorbed on Ag colloids

Surface-enhanced resonance Raman (SERR) spectra are reported for cytochrome c 3 (Cyt-C 3) adsorbed on colloidal Ag particles. The adsorbed Cyt-C 3 could be reduced by hydrogen in the presence of hydrogenase but not in its absence, providing direct evidence that the physiological function of Cyt-C 3 and hydrogenase in bulk are preserved in the adsorbed state. An adsorption-induced partial transition from the low-spin to the high-spin state occurs in both the oxidized and reduced forms. The spin transition is temperature-dependent and reversible.

ChemInform Abstract: Production of Ultrafine Gold and Silver Particles by Means of a Gas Evaporation and Solvent Trap Technique.

AbstractUltrafine colloidal Au and Ag particles suspended in ethanol are obtained by the title method.

Surface‐enhanced Raman scattering (SERS) of aromatic amino acids and their glycyl dipeptides in silver sol

AbstractThe surface‐enhanced Raman (SER) spectra of aromatic amino acids (L‐phenylalanine, L‐tyrosine and tryptophan) and their glycyl dipeptides (glycyl‐L‐phenylalanine, glycyl‐L‐tyrosine and glycyl‐L‐tryptophan) adsorbed on Ag colloidal particles have been obtained. The surface‐enhanced and ordinary Raman spectra show satisfactory correlations. The most prominent features in the SER spectra of all compounds are the strongly enhanced peaks at about 930 and 1390 cm−1 due to the CCOO− stretching and COO− symmetric stretching vibrational modes, respectively. This is interpreted as suggesting that the above compounds are adsorbed on the Ag surface through the carboxylate group. In the SER spectrum of glycyl‐L‐phenylalanine, the amide I and II bands are observed at about 1670 and 1520 cm−1, respectively.

Aggregation and migration of ion-implanted silver in lithia-alumina-silica glass

The near-surface nucleation and crystallization behavior of Ag+ ion-implanted lithia-alumina-silica glasses has been studied. For room-temperature Ag implants, crystallization of the glass ceramic phase was prevented by dissolution of Ag precipitates and migration of Ag atoms at temperatures below that necessary for formation of the glass ceramic phase. Crystallization was demonstrated after low-temperature or low-dose-rate implantations. Optical spectroscopy was used to monitor the size of colloidal Ag particles and to detect the presence of the crystalline phase. Rutherford backscattering spectroscopy (RBS) was used to obtain the depth distribution of Ag atoms in the glass and thus monitor Ag migration. For samples implanted at room temperature and at relatively high dose rates (∼1 μA/cm2), aggregation of the Ag atoms into colloids occurred during implantation and also during subsequent annealing to temperatures ?350 °C. The RBS spectra indicate some migration of the Ag to the surface at these temperatures. For annealing temperatures ≳350 °C, both optical and RBS measurements show that Ag is lost from the glass surface. The initial spatial distribution of the Ag for these high-dose-rate room-temperature implantations was distorted by interactions with the associated damage and possibly by local electric fields caused by neutralization of the implanted ions. It was possible to obtain dispersed Ag nuclei by implanting at low sample temperatures (80 K) or at low beam current (∼200 nA/cm2) to reduce ion-beam heating. Although some migration to the surface was seen in these samples, it occurred at higher temperatures and crystalline precipitation was achieved by annealing at 500 °C.

Optical absorption of silver colloids in KCl crystals at low temperature

The observed increase in the intensity of the optical absorption curve at low temperature, due to Ag colloidal particles in KCl crystals, is quantitively explained by the effect of temperature on the collision frequency of the free electrons with electrons and phonons in silver.