Turkevich process

In aqueous solutions, the most common method used to stabilize nanostructures is the use of organic capping ligands. For instance, the Turkevich process, which dates back to early colloidal growth of the 1950s, uses sodium citrate (I) to entrain the reduced gold nuclei. 

Turkevich, J., Stevenson, P.C. and Hillier, J. (1951) A study of the nucleation and growth processes in the synthesis of colloidal gold. Discussions of the Faraday Society, 11, 55-75. 

Various scenarios for the deposition of silver onto colloidal nuclei can be considered. The process could be diffusion-controlled as suggested by Matejec and by Turkevich et al. [36]. In this case the rate was found to be proportional to the radius of the growing spherical nucleus so that ... 

Decationation of the process of conversion of the Bronsted to Lewis acid sites that takes place in the temperature range of 400-500° as a result of the evolution of water can be visualized as shown in Fig. 8. The Bronsted acid sites are shown by (A), the Bronsted base by (B), and the Lewis acid site by (C). The specific molecular locale of the Lewis acid site is the three-coordinated aluminum. It can act as an acceptor of H or of one electron. As an acceptor of the H ion it may play an important role in initiating the carbonium type of reactions of the hydrocarbons by facilitating carbonium ion formation. On the other hand, it is also an electron acceptor. Turkevich and Stamires have shown this when they studied the ESR of triphenylamine (an electron donor) on a variety of zeolites. They found that the amount of electron transfer increased... 

In considering the properties of the solid surface and its influence on the chemistry of the reactants, I should like to recall to your attention papers by Harrison and McDowell (9) which merit, I believe, a measure of careful consideration. The authors were principally concerned with a detailed and quantitative examination of the phenomenon published in 1941 by Turkevich and Selwood. These authors had found that a mixture of zinc oxide and a,a-diphenyl- 3-picrylhydrazyl was much more powerfully a converter of para- to orthohydrogen than would be concluded on the basis of the mixture law and their separate activities in the conversion process. This phenomenon can be rationalized on the basis of concepts developed by Wigner. The more recent paper of Harrison and McDowell demonstrates, however, that, whereas neither the hydrazyl nor zinc oxide has any marked ability to produce the hydrogen-deuterium exchange reaction at 77° K, the reaction proceeds on the mixture at a rapid and reproducible rate, 2.4 times faster than the parahydrogen conversion on the mixture at the same temperature ( ) and 81 times faster than it would have occurred on the zinc oxide constituent. 

Detailed studies of size-selective syntheses of transition metal coUoids in a systematic manner are not as common as one would wish [1, 2]. In a series of dassical papers Turkevich postulated that the relative rates of two crudal processes, namely... 

The third important concept introduced by Taylor was the use of model reactions, "yard sticks" to determine the mode of activation of molecules by surfaces. For hydrogen activation, Taylor(15) proposed the conversion of ortho to para hydrogen as a measure of the catalytic activity of a surface. This turned out to be more complicated than was first realized. A physical magnetic effect was also operative as was shown among others by Diamond and Taylor(27) for the case of rare earths and by Turkevich and Selwood.(25) Later Laroche and Turkevlch(29) used magnetic resonance to quantify the catalytic effect of charcoal and to differentiate it from dissociative process. The discovery of deuterium opened up the use of isotope exchange reactions as delicate "model reactions" for elucidation of the activation of molecules. Immediately after H. Urey announced the discovery of heavy water in 1932, Taylor(30) realized its potential as a tool in catalytic research and engaged in a massive production in Princeton of heavy water. 

Turkevich, J. 1951. A study of the nucleation and growth processes in the synthesis of colloidal gold. 

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