Stabilization of Unsupported Nanoparticles

In order to study the reactivity of organometallic complexes with unsupported monometallic nanoparticles, it is necessary to prepare these nanoparticles in a very efficient manner. 

Napper [175] was the first to study the adsorphon of nanopartides in polymers and since then, different types of polymers Hke vinyl polymers with polar side groups such as poly(vinyl)pyrrolidone (PVP) and poly (vinyl) alcohol (PVA) have been applied [69, 176-179]. 

Nanoparticles can be protected by the HDA (hexadecyiamine) ligand to prevent reactions between each other and in order to stabilize them in solution [69]. This stabilization mode presents several advantages such as their behavior as molecular systems, control of the size, size distribution and adjustment of the surface state (Fig. 18.13). Solution C NMR studies evidenced a fast exchange on the NMR time scale between amine ligands free and coordinated to mthenium . In this section, the preparation of HDA-protected ruthenium nanoparticles, the study of the size of the nanoparticles and their characterization will be described. 

The Ru/HDA particles are prepared by decomposition of the mthenium precursor Ru(COD)(COT) with 3 bar of dihydrogen at 293 K in the presence of 0.2eq HDA in THF. The particles are monocrystalline, as evidenced by HREM analysis (Fig. 18.14) and a careful observation of some electron micrographs reveals the presence of spherical nanoparticles which are in the process of coalescing. The size could be determined as about 1.9 nm. 

The possible organisation of the amines in THF could influence the growth of the ruthenium particles in the solution and their tendency to present different forms such as spherical particles and nanorods. In the case ofO.leq HDA/Ru the particles are spherical, while with 0.2 eq HDA/Ru the beginning of the formation of elongated particles can be observed, continuing with time with 0.5 eq H DA/Ru, nanorods were present. 

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