Surface and Structural Features of Co‐Fe Oxide Nanoparticles Deposited on a Silica Substrate

Mono‐ and dimetallic cobalt‐ and iron oxide nanoparticles deposited on the surface of a silica substrate have been prepared by an impregnation technique. Both the bulk and surface structures of these particles have been characterised by different physical and chemical techniques. The results provided by X‐ray diffraction, Mössbauer and X‐ray photoelectron spectroscopy show the formation of separate Co 3 O 4 and Fe 2 O 3 nanoparticles in oxide samples, but in no case were cobalt–iron mixed oxides detected. Quantitative data also showed that the dispersion degree of cobalt‐ and iron oxides is rather low. It was also observed that pretreatment of the supported metal oxide nanoparticles under a hydrogen atmosphere does not promote the formation of a metal–support interaction, although a cobalt–iron interaction is observed in the dimetallic systems. The diffraction patterns and photoelectron and Mössbauer spectra of these dimetallic samples provide conclusive proof for the formation of both metallic Co 0 and iron‐cobalt (Co 7 Fe 3 ) alloy phases in the hydrogen‐reduced samples. It was also found that the crystallite size of the alloyed Co 7 Fe 3 phase increases with increasing iron content, i.e. 11 and 23 nm for samples containing 1 % and 5 % Fe added to the base Co sample, respectively, while that of Co 0 was constant (10 nm). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)