Surface-Capping Agent

During the past decade, a new focus has developed. It was found that semiconductor particles can be made so small, typically into the nanometer size regime, that a quantum confinement effect occurs [6-15]. Particles of this size are often referred to as nanoclusters, nanoparticles, quantum dots, or Q-particles. The structures of these nanometer-sized semiconductor clusters are usually similar to those of the bulk crystals, yet their properties are remarkably different. With the proper surface-capping agents, clusters of varying sizes can be isolated as powders and redissolved into various organic solvents just like molecules. The availability of this new class of materials allows us to study the transition of a material from molecule to bulk solid, as well as its various properties and applications. 

Zaera et al. successfully tuned the selectivity for the production of cix-olefins by isomerization [47]. They synthesized tetrahedral Pt nanoparticles with Pt(lll) facets using PVP as the surface-capping agent Then, the organic surface layer was ranoved by calcination and subsequent oxidation/reduction cycles in O2 and H2 atmospheres. When the calcination temperature was 475 K, the shape was preserved and the trans to cis formation occurred more frequently, as shown in Fig. 2.12. When the calcination temperature was 575 K, the tetrahedral shape degraded into the spherical shape and the cis to tranx formation occurred more frequently than the trans to dx. ... 

How the Catalytic Activity Can Be Varied by the Surface-Capping Agents... 

Pig. Z15 The effect of the length of the surface-capping agents and the reaction medium... 

We developed a method to synthesize shaped Pt nanocrystals directly on three-dimensional supports without a surface-capping agent. When the Pt precursors were reduced in the presence of carbon supports with high surface areas, nucleation occurred on the supports and the nanoparticle was formed without surface-capping... 

Pig. 2.17 In situ-shaped cubic Pt/C synthesized without a surface-capping agent (adapted from ref. [56])... 

Although the surface-capping agents are usually considered as trouble in catalytic applications, they can actually participate in catalytic reactions. Kim et al. synthesized Pt nanoparticles (1-2 nm in size) by using an enzyme (aminopeptidase) [57]... 

Kim C, Lee H (2009) Change in the catalytic reactivity of Pt nanocubes in the presence of different surface-capping agents. Catal Commun 10 1305-1309... 

Kim C, Min M, Chang YW, Yoo KH, Lee H (2010) Chemical and thermal stability of Pt nanocubes synthesized with various surface-capping agents. J Nanosd Nanotechnol 10 233-239... 

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