Silver, colloidal charge

The excess negative charge located in the interior of metallic silver colloids could also be transferred to other electron acceptors, including methylviologen, nitrobenzene, nitropyridinium oxide, anthracene quinone sulfonic add, and potassium cyanohexaferrate(III)[506, 531], The efficiency and, indeed, the direction of electron transfer were found to depend on the position of the Fermi level of the surface-modified silver particles. For example, chemisorption of AgN to a silver particle is shown to result in a shift of the Fermi level to a more positive potential, as shown in the lower line in Fig. 84. 

The assumption on the electric charge effect of excess electrons on the rate constant of their interfacial transfer is supported by an evident similarity of these semiconductor colloidal systems with metal colloids, for which effect of the charge of electrons captured by the particle is well known and agrees with the microelectrode theory . Moreover, kinetic curves similar to those we found for CdS colloids were observed previously for silver colloids in ref. [17], where the particles charge q was shown to decrease by the law... 

At the time of initial nucleation most spots appear yellow to brown. As the reaction continues in the carbonate solution some proteins stain red or blue, or black while others remain yellow or brown. It is generally accepted that the smaller silver colloidal particle (approximately . 2 urn) are seen as yellow - red coloration and that larger particles (above >. 3um) are blue to black in coloration. The mechanism of different coloration of proteins may be dependent on protein sequence or structure. Thus coalescence of differing amounts of silver colloidal particles onto precipitated proteins is at least one plausible explanation of the colors seen in the gels. Therefore, colors observed in the pro tein pattern are influenced by the chemical environment as well as the charge and steric characteristics of the precipitated protein. 

In view of these results obtained with a rough silver electrode, the Raman scattering from biomolecules absorbed on dispersed silver particles of positively charged silver colloids has been reported From the results of the strong SERS signals of... 

Silver colloid is popular due to the relative ease of manufacture, low cost, and stability. One widely used method of silver colloid preparation is citrate reduction of silver nitrate (Figure 3). This results in an overall net negative charge on the colloid, which is high compared with many preparations (Figure 4). As a result, the colloid is stable for months and even years, and in some cases, with careful attention to detail, quantitative SERRS can be obtained from this colloid with relative standard deviations of less than 5%. There is, however, a change in enhancement with time, and so a standard needs to be used. 

Silver colloids were prepared in the presence of various surfactants by the reduction of silver nitrate with hydrazine. Because of the positively charged hydrophobic nature of Ag nanoparticles, the Ag colloids prepared in aqueous surfactant solutions of sodium dodecyl sulfate (SDS) and Tween 20 showed good stability. But poor colloidal stability was observed in solutions of ce-tyltrimethylammonium bromide (CTAB) and NP-9. The stabilization of Ag colloids by surfactant molecules was explained on the basis of the electrostatic interaction between the Ag particles and surfactants and a stabilization model was proposed. The particle size distribution was investigated by ultraviolet (UV) absorption spectroscopy measurements. The UV absorption spectra showed different patterns depending on the nature of the stabilizers (i.e., sinfactants). In the case of Tween 20 as a stabilizer, the smallest particles, about 11.6 nm in average diameter, were obtained. In the case of CTAB, pearl formation was observed because of the formation of relatively large particles about 300 mn in size. 

Charge alteration on the surfaces of nanosized metallic silver particles has been investigated by simultaneously monitoring absorption and conductivity changes during pulse-radiolytic experiments [506]. Pulse radiolysis of a nitrous-oxide-(N20) saturated aqueous solution of 3.0 nm diameter metallic silver particles containing 0.2 M 2-propanol resulted in electron injection to the colloid. NzO functions to double the yield of hydroxyl radicals ( OH) generated in water... 

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]. 

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