Silver, colloidal halides

Adsorption of Ag on the surface of PdO is also an interesting option offered by colloidal oxide synthesis. Silver is a well-known promoter for the improvement of catalytic properties, primarily selectivity, in various reactions such as hydrogenation of polyunsaturated compounds." The more stable oxidation state of silver is -F1 Aquo soluble precursors are silver nitrate (halide precursors are aU insoluble), and some organics such as acetate or oxalate with limited solubility may also be used." Ag" " is a d ° ion and can easily form linear AgL2 type complexes according to crystal field theory. Nevertheless, even for a concentrated solution of AgNOs, Ag+ does not form aquo complexes." Although a solvation sphere surrounds the cation, no metal-water chemical bonds have been observed. 

Different versions of these abbreviations—lower- and upper-case, with or without periods—are used in the literature. The same abbreviations also appear in the form of subscripts, for example, pH,Ep. This notation emphasizes that there are species other than protons that may produce a reversal in sign of the potential, and the concentration of such a species (e.g., a polymer [18,19]) that is required to reverse the sign of the potential can also be termed the lEP. The present book is devoted to pH-dependent surface charging, and there is no need to emphasize repeatedly that the lEP is a pH value. However, in other publications, the abbreviation lEP may refer to species other than protons, and certain situations require a clear indication of which species induced sign reversal. For example, the primary surface charging of silver halide colloids is governed by silver and halide ions in solution, and their lEP is expressed in terms of pAg or pX. One of these... 

The low-frequency modes associated with the halides were seen also in colloidal systems. Wetzel and Gerischer found on a silver sol Raman features at 235, 163, and 112 cm for chloride, bromide, and iodide. Garrel et monitored the replacement of chloride by bromide on a silver colloid. 

Pillai V, Kumar P, Hou M J, Ayyub P, Shah DO (1995) Preparation of Nanoparticles of Silver-Halides, Superconductors and Magnetic-Materials Using Water-in-Oil Microemulsions as Nano-Reactors. Adv Colloid Interface Sci 55 241-269... 

Reaction of 2-thioamidopyridine (L) with silver perchlorate in polar solvents, or by means of the halide complexes K[AgX2] in aqueous ethanol, resulted in the fleeting yellow precipitate which formed first being rapidly reduced to a mixture of colloidal silver and silver sulfide, a... 

In contradistinction to the spectra obtained in the mica dispersion, Pseudocyanine, when added to the colloidal silver and silver halide systems of Figures IB and 1C, yielded no H-bands but formed well defined J-bands. The latter also exhibited a weak secondary peak located near the absorption maximum of dissolved, unperturbed dye. Although the position and intensity of the J-band varied with the substrate (4, 17, 38, 61), the differential spectra obtained in these silver systems exhibited marked similarities. An increase in the concentration of the substrate produced in both cases a monotonic change in the absorbance of the M-... 

The colloidal metallic silver formed in this way is opaque (it would appear black in reflected or transmitted light). The halogen atoms combine with an organic substrate mixed with the silver halide crystals to produce bromides. 

The distillation is continued till the greater part of the liquid has distilled over, and no oily drops are to be seen in the condenser. The residue consisting of a concentrated solution of phosphorus and phosphoric acids in addition to excess of red phosphorus is discarded. The distillate is shaken up with water to remove alcohol, and then with dilute caustic soda to remove free iodine. Enough alkali must be used to render the lower layer of alkyl halide colourless. The latter is then separated ofl, dried over granular calcium chloride (6 gms.) and distilled. The preparation should be kept in the dark in a well-stoppered bottle. If exposed to light, iodine slowly separates, but may be prevented from so doing by adding a small quantity of colloidal silver to the liquid. 

The silver halide crystals can be formed as microscopic grains suspended in a protective colloid, usually gelatin. This dispersion, the photographic emulsion, can be coated on a suitable support to obtain photographic films, plates, and papers. 

Particle electrophoresis studies have proved to be useful in the investigation of model systems (e.g. silver halide sols and polystyrene latex dispersions) and practical situations (e.g. clay suspensions, water purification, paper-making and detergency) where colloid stability is involved. In estimating the double-layer repulsive forces between particles, it is usually assumed that /rd is the operative potential and that tf/d and (calculated from electrophoretic mobilities) are identical. 

Kamat, P. V. Patrick, B. Photochemistry and photophysics of ZnO colloids, in Symp. Electron. Ionic Prop. Silver Halides, vol. 44, B. Levy, J. Deaton, P. V. Kamat, I. Leubner, A. Muenter, L. Slifkin, T. Tani, eds., The Society for Imaging Science and Technology Springfield, VA, 1991, p. 293. 

There are several theories as to the constitution of the silver subhalides in the latent image. The molecular theory regards the subhalides as definite chemical compounds. The adsorption theory regards them as adsorption-compounds of colloidal silver and subhalides. The molecular theory is advocated by Trivelli,1 who considers the colour-changes to indicate the existence of several silver subhalides, which yield solid solutions with each other and with the silver halides. He also regards the mechanism of reduction with ammonium persulphate as favouring the molecular theory. 

The incorporation is of special interest for a variety of applications. One of them has been described in the previous sections, others are the incorporation of semiconductors [38] of metal colloids [39, 29] or silver halides [40]. 

Selective adsorption may also have dramatic consequences for crystal growth if certain crystal planes can be blocked ). Trace amounts of Impurities may in this way determine the eventual crysted shape. This feature plays an Important role in the preparation of (tailor-made) colloids (Volume IV) obviously adsorption kinetics plays an Important role here. Certain substances may of course work the other way around In that they "attack the solid. Examples are some sulfur-containing compounds with silver halides, and chelating agents with haematite (a-Fe O ). 

Pergolese B, Muniz-Miranda M, Bigotto A (2005) Surface enhanced Raman scattering investigation of the halide anion effect on the adsorption of 1,2,3-triazole on silver and gold colloidal nanoparticles. J Phys Chem B 109 9665-9671... 

Colloidal dispersions owe their stability to a surface charge and the resultant electrical repulsion of charged particles. This charge is acquired by adsorption of cations or anions on the surface. For example, an ionic precipitate placed in pure water will reach solubility equilibrium as determined by its solubility product, but the solid may not have the same attraction for both its ions. Solid silver iodide has greater attraction for iodide than for silver ions, so that the zero point of charge (the isoelectric point) corresponds to a silver ion concentration much greater than iodide, rather than to equal concentrations of the two ions. The isoelectric points of the three silver halides are ° silver chloride, pAg = 4, pCl = 5.7 silver bromide, pAg = 5.4, pBr = 6.9 silver iodide, pAg = 5.5, pi = 10.6. For barium sulfate the isoelectric point seems to be dependent on the source of the product and its de ee of perfection. ... 

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