Effect of the Support on the Formation of FeCo Alloy Nanoparticles in an SBA-16 Mesoporous Silica Matrix: An X-ray Absorption Spectroscopy Study

A series of nanocomposites consisting of FeCo alloy nanoparticles supported on a three-dimensional cubic mesoporous silica matrix (SBA-16) were prepared by wet impregnation of the matrix with a solution of Fe and Co nitrates. FeCo alloy nanoparticles were obtained by heat treatment at 800 °C in reducing atmosphere of the impregnated SBA-16 previously calcined at 500 °C. Three different SBA-16 types were used as a support of the nanophase. The influence of the matrix on the absorption of Fe and Co ions was investigated using X-ray diffraction and X-ray absorption spectroscopy. In particular, extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) techniques at the Fe and Co K-edges were used in order to identify the intermediate products before reduction and to study the formation of the bcc FeCo alloy, which cannot be assessed unambiguously using X-ray diffraction. An important influence of the matrix has been observed in the phases formed before reduction, in the size of nanoparticles, and in the oxidation of the FeCo alloy nanoparticles

An X-ray absorption investigation of the formation of cobalt ferrites nanoparticles in an aerogel silica matrix

X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) techniques at both Fe and Co K-edges were used to investigate the formation of CoFe2O4 nanoparticles embedded in a silica aerogel matrix as a function of calcination temperature and CoFe2O4 content. In particular, nanocomposite aerogels containing relative CoFe2O4 amounts of 5 and 10 wt % and calcined at 450, 750, and 900 degrees C were studied. The evolution of the nanophase with calcination temperatures depends on the composition. In the sample containing 10 wt % of nanophase, results indicate that CoFe2O4 nanocrystals were formed after calcination at 750 degrees C, whereas in the sample containing 5 wt % of nanophase, they were obtained only after calcination at 900 degrees C. Quantitative determination of the distribution of the iron and cobalt phase in the octahedral and tetrahedral sites of the spinel structure shows that cobalt ferrite prepared by sol-gel has a partially inverted spinel structure with a degree of inversion around 0.70