Interparticle distance, control

The hydrogen-bond mediated self-assembly of nanoparticles and polymers provides a versatile and effective method to control interparticle distances, assembly shapes, sizes, and anisotropic ordering of the resultant nanocomposites. This approach presents the bottom-up strategy to fabricate nanomaterials from molecular building blocks, which have great potential for assembling and integrating nanoscale materials and particles into advanced structures, systems, and devices. 

In the model catalysts described so far, the interparticle distances were more or less random, governed by the separation of substrate defects which control the nucleation and growth process of the metal particles (74,101). The position and separation of metal particles can be controlled accurately by electron beam lithography (EBL) (which has also been used to fabricate model catalysts), but the minimum size of the metal aggregates is currently still approximately lOnm. Figure 3g shows an example of a platinum nanoparticle array on Si02 (mean size 28 nm interparticle separation 200 nm) (53,106,107). 

One of the main problems of traditional metal catalysts is that they are fairly ill-defined, in that the shapes of the metal particles on the supports are often irregular, that their particle size distributions are broad, and that no strict control can be exerted on interparticle distances. Recent developments in material technologies promise to provide new metallic materials, new supports, and new methodologies for the fabrication of better defined catalysts. 

There is no agreement in the literature on the role of the catalyst particle size for methanol oxidation. Two main evidences have been reported one is related to the presence of a maximum in the mass activity as a function of particle size located, for some authors [40], at 3nm and at 2nm for others [41] moreover, for some authors there is no influence of the interparticle distance and particle size on specific activity. If these parameters are not controlling, an increase in mass activity should be observed as the metal surface area is increased [42]. In this context, the metal-... 

Dabbousi, B. O., Murray, C. B., Rubner, M. F., and Bawendi, M. G., Langmuir-Blodgett manipulation of size-selected CdSe nanocrystaliites, Chem. Mater., 6, 216-219 (1994). Kotov, N. A., Meldrum, F. C., and Fendler, J. H., Monoparticulate layers at titanium dioxide nanocrystaliites with controllable interparticle distances, J. Phvs. Chem., 98, 8827-8830 (1994). 

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