ChemInform Abstract: Composite Pd-Ag Particles in Aqueous Solution

Autor: Paul Mulvaney, Arnim Henglein, Matthias Michaelis
Rok vydání: 2010
Předmět:
Zdroj: ChemInform. 25
ISSN: 0931-7597
0022-3654
DOI: 10.1002/chin.199444031
Popis: published in Advance ACS Abstracts, May 15, 1994. 0022-3654/94/2098-62 12%04.50/0 palladium concentration was 1.2 X 10-4 M as determined by atomic emission spectroscopy. In the silver deposition experiments, the palladium solution was diluted by roughly a factor of 4. Experiments were also carried out to reduce Pd(I1) in the absence of the stabilizing PVS. Under these circumstances, the loss of reduced palladium was much greater than in the presence of PVS. This polymer is not removed by the treatment of the solution with Amberlite (in fact, when a pure PVS solution was treated with Amberlite, the conductivity actually increased, because the K+ ions of PVS were exchanged for free H+ ions). In order to coat the Pd colloids, two methods were used to reduce Ag+ ions. First, the radiolytic method was tried, which in many other cases has been quite useful for preparing concentric bimetallic particles. NaAg(CN)2 was added to the palladium colloid as well as 0.5 M propanol-2 and 0.1 M acetone. As described previously,4b exposure to y-rays leads to the formation of organic radicals that transfer electrons to the Pd particles. The Pd particles are polarized cathodically, and the stored electrons reduce the silver-cyano complexon thesurface of the Pd particles, which leads to a silver mantle. However, it was found that part of the radicals reduced the complexed silver ions directly in solution, the result being that individual silver particles were also formed. Second, formaldehyde was used as the reducing agent. When Ag+ ions are reduced by formaldehyde in the absence of colloidal palladium, an induction period of several minutes is observed. However, when Pd particles are present, the reduction occurs practically instantaneously and individual silver particles are not produced. This method was then applied in all experiments. In detail, the procedure was as follows: 2 X 10-4 M formaldehyde was added to 75 mL of Pd solution (at pH = 11). The solution was in a round flaskunder nitrogen, which had a side arm carrying a 1-cm optical cuvette and a septum. Several milliliters of deaerated AgC104 solution ( 5 X 10-5 to 2 X 10-3 M) was slowly injected (less than 1 mL per minute) under strong stirring. The total injection time was about 8 min. During the injection, the spectral changes took place immediately. This means that the stationary concentration of Ag+ ions was low during the injection, which is the reason why practically no spontaneous nucleation of individual Ag, particles occurred. The palladium concentration in the final solution was 2.9 X le5 M, and the total concentration of added silver varied between 2.2 X 10-6 and 2.0 X 10-4 M.
Databáze: OpenAIRE
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