Colloidal silver particles

Moreover, according to this general schematic mechanism, a more detailed picture of the particle formation has been tentatively given in two particular cases (1) synthesis of colloidal silver particles, and (2) formation of bimetallic ferromagnetic metal particles. 

Fig. 9.2.19 High-resolution TEM image of a colloidal silver particle observed along [111] and its schematic model. (From Ref. 39.)...

The detection of sharp plasmon absorption signifies the onset of metallic character. This phenomenon occurs in the presence of a conduction band intersected by the Fermi level, which enables electron-hole pairs of all energies, no matter how small, to be excited. A metal, of course, conducts current electrically and its resistivity has a positive temperature coefficient. On the basis of these definitions, aqueous 5-10 nm colloidal silver particles, in the millimolar concentration range, can be considered to be metallic. Smaller particles in the 100-A > D > 20-A size domain, which exhibit absorption spectra blue-shifted from the plasmon band (Fig. 80), have been suggested to be quasi-metallic [513] these particles are size-quantized [8-11]. Still smaller particles, having distinct absorption bands in the ultraviolet region, are non-metallic silver clusters. 

The hydroxyl radical reacts with 2-propanol to form 2-hydroxypropan-2-yl radicals, which transfers electrons, in turn, to the colloidal silver particles ... 

Equilibrium was reached in the addition of N (Eq. 26) when the accumulated negative charge in the interior of the silver particles precluded further electron transfer. Addition of N to metallic colloidal silver particles also shifted the Fermi potential to a more negative value (see top part of Fig. 84) [531]. 

Fig. 84 (Upper) Schematic presentation of surface complexation (preoxidation) by a nucleophilic reagent N and final oxidation of the silver particle by oxygen. (Lower) Chemisorption of a complex AgN and final reduction of the silver ions in chemisorbed AgN by excess electrons deposited by reducing radicals. In both parts of the figure, the changes in the position of the Fermi level in the colloidal silver particles are indicated [531]...

Velikov, K.P., Zegers, G.E., and van Blaaderen, A. (2003) Synthesis and Characterization of Large Colloidal Silver Particles. Langmuir 19 1384-1389. 

T. Linnert P. Mulvaney A. Henglein, Photochemistry of colloidal silver particles The effects of N2O and adsorbed CN. Ber. Bunsenges. Phys. Chem. 1991, 95, 838-841. 

Kneipp, K., Pohle, W., and Fabian, H. (1991) Surface enhanced Raman spectroscopy on nucleic adds and related compounds adsorbed on colloidal silver particles. Journal of Molecular Structure, 244,183-192. 

Fig. 2 Arrangement for the development of Si nuclei to colloidal silver particle.

Reglinski et al,106 reported the use of Tm and Tz anions as surface modifiers for colloidal silver particles for the production of novel soft coating. The use of these species in surface-enhanced resonance Raman spectra has been described. 

When silver alginate was irradiated at room temperature, two kinds of singlet spectra were observed, one of which (g = 2.0033, line-width a few gauss) might be attributed to colloidal silver particles. 

A dissolution of the complex in ethanol (Fig. 2a) and DMF (Fig. 2b) (1 mg/ml) results in its destruction accompanied by oxidation of pyrocatechol and reduction of silver with formation of colloid. Silver particles were adsorbed on the positively charged surface of the substrate. Particle size can be varied between —20 nm in ethanol and -50 nm in DMF. 

In the silver halides Mott and Gurney suggested a mechanism for the formation of colloidal Ag [167]. A conduction-band electron produced by irradiation is first trapped at a lattice imperfection which may be a silver atom or ion, a chemical impurity, or a trapping site along a dislocation. The trapped electron then attracts a Ag interstitial ion to form a Ag atom. Following this, electrons and Ag " interstitials are trapped at the site in proper sequence to cause the buildup of a colloidal silver particle. This mechanism requires the presence and mobility of silver ions, and it is further required that the hole motion be sufficiently small that trapped electrons are not annihilated by electron-hole recombinations. 

Kim K. J., Chen V., Fane A.G. (1993), ultrafiltration of colloidal silver particles flux, rejection, and fouling,), of Colloid and Interface Science, 155, 347-359. 

Obtaining normal solution Raman spectra of some anabolic agents is impossible, because of its very low solubility in water. However, vibrational spectra of these compounds have been obtained by means of SERS in the presence of colloidal silver particles The anabolic DES shows at 8 x 10 M bulk concentration a very strong Raman scattering with enhanced bands at 1174, 1468 and 1606 cm . ... 

There is evidence that the extreme enhancement of the Raman signal on a silver deposit comes from colloidal silver particles. Considering the special situation of a silver nucleus with adsorbed CN" ions, other explanations of the Raman results are possible, e.g., an adsorption of CN" on clusters of different sizes and charges. ... 

The presence of direct proportionality of refractive index of developed RM, containing colloid silver particles, on developed silver concentration, is confirmed by measurements of... 

F. Strelow and A. Henglein, Time resolved chemisorption of f and SH on colloidal silver particles (a stopped-flow study), / Phys. Chem. 99,11834-11838 (1995). 

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