Journal of Physical Chemistry B, Vol.106, No.34, 8547-8554, 2002
Preparation of Rh-graphite and Rh-clay nanocomposites: Model substances for nanographite and induced magnetization in 4d transition metals
Rh nanoparticles in a graphite lattice have been prepared by reduction of a RhCl3-graphite intercalation compound by hydrogen gas at high temperatures (I) or at room temperature by Li-diphenylide (II). In all cases, the reduction was complete. All four samples (natural graphite and HOPG) showed a full set of fcc Rh reflections by selected-area electron diffraction. This indicates a particle thickness from at least four layers. Only in the case of the samples reduced by (II) can additional very strong reflections can be observed. They seem to be due to the occurrence of 2D Rh structures with (2 x a(graphite)) and (3 x a(graphite)) superstructures. For a (2 x a(graphite)) Rh superstructure on graphite or expanded multilayers of fcc Rh, an induced magnetic moment was theoretically predicted. Bright-field electron microscopy shows particles in the size ranges 11-106 nm (I) and 1.5-37.5 nm (II). The magnetism of Rh-Gr is related to the detail of Rh nanoparticles and nanographites, depending on the condition of reduction. Short-range magnetic order is observed in Rh nanoparticles for the sample with uncommon spacings. However, Curie-like susceptibility is observed at low temperatures for all samples. This is due. to nanographites with zigzag edges. As reference substances, Rh nanoparticles were generated in bentonite and on kaolin by polyol reduction of Rh-acetate hydrate. The size range in bentonite was 2.1-60 nm; the kaolin samples showed Rh particles from 5.3-52.5 nm. Electron diffraction patterns gave no evidence of an expanded lattice in those Rh particles.