hcp and fcc Nickel Nanoparticles Prepared from Organically Functionalized Layered Phyllosilicates of Nickel(II)
journal contributionposted on 20.02.2007, 00:00 by Mireille Richard-Plouet, Murielle Guillot, Serge Vilminot, Cédric Leuvrey, Claude Estournès, Mohamedally Kurmoo
We report on the formation of air-stable fcc Ni nanoparticles via the rarely observed metastable hcp Ni from two organically modified layered Ni(II) phyllosilicates at a moderately low temperature of less than 573 K in an inert atmosphere. The presence of hcp Ni as an intermediate is related to the organization of the nickel atoms within the layers of the phyllosilicates, which is a triangular network with Ni−Ni distances of 3.2 Å protected by a strong covalent Si−O network on each surface. Characterizations of the products were performed by TG-DTA coupled to mass spectroscopy, in situ X-ray diffraction, electron microscopy, infrared, and in situ magnetization measurements. TEM shows that the fcc Ni particles are spherical and that the size (average of ca. 20 nm) depends on the starting phyllosilicate. Given that the amount of reduced Ni is proportional to the organic content and not to the Ni content of the phyllosilicates when the atmosphere is inert, we propose that the reduction takes place by the gases produced during the decomposition of the organic moiety. The stabilization of the hcp Ni phase depends on the percentage of Si−O coverage of the surface.