Silver salts, adsorption study

It remains to be determined to what extent the dye adsorption technique is applicable to other substrates. No evidence was obtained for Pseudocyanine adsorption to Mn02, Fe2Os or to pure silver surfaces, although this dye can be bound to mica, lead halides, and mercury salts with formation of a /-band (61). Not only cyanines but other dye classes can yield surface spectra which may be similarly analyzed. This is specifically the case with the phthalein and azine dyes which were recommended by Fajans and by Kolthoff as adsorption indicators in potentio-metric titrations (15, 30). The techniques described are also convenient for determining rates and heats of adsorption and surface concentrations of dyes they have already found application in studies of luminescence (18) and electrophoresis (68) of silver halides as a function of dye coverage. 

Systematic electrosorption studies are not abundant in the literature in that rarely are salt effect simultaneously measured over a large range. What are available are Just millions of adsorption Isotherms under a number of conditions, sometimes in connection with electrokinetlc and/or stability studies. However useful such studies may be, they do not provide enough information to carry out analyses as Intended in the present section. We shall therefore Illustrate the subject matter with two case studies, choosing silver Iodide and oxides as the, rather representative, examples. 

Some of the questions raised are longstanding ones in the field of colloid science, and they will not be addressed in any detail in this review. Synthesis of the colloids is generally performed (in the context of SERS) by reduction of the metal salt. Specific procedures are to be found in each of the reports which pertain to SERS on colloids. The adsorbed molecule for the SERS study can be present during the reduction stage and even participate in it (citrate on silver, for instance). Alternatively, the adsorption may be carried out after the reduction (pyridine on silver and gold, for example). The later procedure often causes noticeable changes in the colloid, such as aggregation and precipitation. 

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