Characterization of nanosized nickel prepared by surface reactions of Ni-?-organyl complexes on silica: An electron paramagnetic and ferromagnetic resonance study

Abstract

Dispersed atomic nickel(0) is formed during the reaction of the nickel‐σ‐organyl complexes with silanol groups at temperatures below 373 K. That nickel is oxidized to Ni(I) by protons of the silanol groups in a consecutive step. The Ni(I) portion amounts to about 70% w/w of the Ni used. Six different Ni(I) species are detected by electron paramagnetic resonance. They are stabilized by interaction with the silica surface and the organic moieties; they act as anchor ions for the Ni(0) atoms. Ni(0) crystallites stabilized in this way are about 0.5 nm in diameter after a treatment at 373 K. The influence of the Ni(I) ions on the collective, magnetic properties of the clusters is revealed by calculation of ferromagnetic resonance (FMR) spectra using the independent‐grain approach according to Schlömann and Kotyukov. A strain of about 10 GPa is brought about in the nickel crystallites by the interaction with Ni(I) ions. © 1998 John Wiley & Sons, Ltd.

Structural characteristics of oxide nanosphere supported metal nanoparticles

“…After cooling down to room temperature a suspension of the oxide was prepared under argon atmosphere in a solution of THF containing the required quantity of the organometallic complex. The reaction of the metal complexes on oxide nanospheres carried out under anaerobic conditions according to [36,37,64] first resulted in an organometallic surface complex of the type [ " Si-O-MR 2 -O-Si " ] AE Li + as intermediate in the decomposition process induced by reaction with surface hydroxyl groups that finally is leading to metal atoms and metal nanoparticle formation:…”

“…It was used with two different organometallic precursors of Pt and Pd [52,64] for silica as well as for titania nanospheres and mostly produced uniformly arranged metal particles with oxide support coverages between 12 and 30%, mean sizes around 2.5 nm, and narrow size distributions as it is illustrated by TEM images of figure 2. These results are comparable to earlier reports of organometallic nickel complex deposition on silica where Ni nanoparticles of about 1.5 nm mean size have been obtained [37].…”

“…Finely grained polymeric and also inorganic supports dispersed in aqueous solutions can be coated with various metals according to route (c) either by precipitation deposition of an appropriate metal precursor onto the support surface [33,[36][37][38] or by direct surface reactions utilizing specific functional groups to induce coating [7,33,[39][40][41][42][43][44][45][46]. This is usually followed by controlled reduction to create fine metal particles [33,47,48].…”

“…By varying the coating conditions (pH, concentration, temperature and duration of exposure of the metal complex solution) the coverage of the oxide nanospheres and size of metal nanoparticles may be controlled [33]. Permanently anchoring nanoparticles on various oxide nanospheres can be achieved for a number of transition metals by direct reduction of organometallic complexes of the type [Li(THF) 2 ] 2 AE [MR 4 ], with ''THF'' being C 4 H 8 O (tetrahydrofurane), ''M'' being Ni, Pt, Pd, and ''R'' being CH 3 (methyl) or C 6 H 6 (phenyl) ligands, on oxide surfaces of well defined hydroxyl concentration [36,37,52]. Therefore, understanding of structural and functional characteristics of the oxide surface [55][56][57][58][59][60][61] in dependence on pretreatment, modification and metal loading is important.…”