Truncated octahedral particles

So-called superlattices of 5mn alkylthiolate protected silver particles having truncated octahedral shapes as well as thiol-stabilized 5 6 mn gold particles can be obtained from solution. Fractional crystallization is a very usual method to separate chemical compounds from other compounds and impurities. Mixtures of thiolate stabilized gold nanoparticles between 1.5 and 3.5 nm could successfully be fractioned into real monodisperse species containing 140, 225, 314, and 459 atoms. 2D assemblies have also become available of these fcc-structured nanoparticles. The decisive criterion to successhilly fraction and crystallize metal nanoparticles is to protect them perfectly by strongly bound ligand molecules in order to avoid coalescence. 

In a modification of the synthetic procedure described above, Tao et al. reported a procedure in which nanocrystals with regular polyhedral shapes, bounded entirely by either the 100 or 111 facets, were produced [102]. In this case the metal salt was reduced by a diol solvent at near-reflux temperatures in the presence of PVP. By extending the polyol reaction for a given period of time, it was possible to obtain cubes, trancated cubes, cubo-octahedra, truncated octahedra and octahe-dra in high yield, as shown in Figure 3.15. It should be mentioned here that the authors stated that the stability of both 100 and 111 planes in the presence of PVP, especially for the cubo-octahedral and octahedral particles, indicated that shape control may not be exphcitly dictated by the capping polymer. Rather, preferential growth would be favored by a kinetically limited equUibrium influenced by the reaction conditions. 

The octahedral shape of 10-20-nm particles on MgO is limited by eight (111) faces, truncated asymmetrically by (001) faces at the top and at the interface and by (100) faces less extended at the corners. The ratio of the height to the diameter of 0.46. 

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