Co–Fe–oxide nanoparticles supported on the various highly dispersed matrices: the effect of the carrier on structural and magnetic properties

Abstracts A series of mixed oxides was synthesized by deposition of the guest phase on the highly dispersed oxide matrix. Fumed nanooxides SiO 2 , Al 2 O 3 , SiO 2 /Al 2 O 3 , and SiO 2 /Al 2 O 3 /TiO 2 with the specific surface area of 65–91 m 2 /g were selected as highly dispersed matrices. Co–Fe mixed oxides with the general formula Co 4x Fe x O y (Co: Fe = 4: 1) were deposited as the guest oxides using the two-step method: (i) solvate-stimulated modification of the surface of fumed nanocarriers with the mixture of cobalt nitrate (II) and iron (III) formate and (ii) subsequent heat treatment up to 600 °C to form Co 4x Fe x O y . The aim of this paper was to study the influence of the composition and structure of fumed oxide matrices and deposited guest phase on the morphology of the resulting composites in the gaseous and aqueous media using the XRD, XPS, FTIR, nitrogen adsorption and SEM/EDX, as well as quasi-elastic light scattering (QELS) methods. The low-temperature nitrogen adsorption isotherms have a sigmoidal shape with a narrow hysteresis loop characteristic of mesoporous materials. The specific surface area ( S BET ) of the composites varies from 48 to 82 m 2 /g, showing a tendency towards a decrease in the S BET values by 10–26% in comparison with the initial nanocarriers. The SEM data show the denser aggregate structure of nanocomposites compared to the initial carriers. The primary particle size was in the 30–60 nm range and the EDX data confirm the formation of a guest phase on the mixed aluminosilicate carriers, mainly in the surface patches corresponding to the alumina structure. According to the QELS data, there is a tendency to form aggregates of 100–10 μm in size in the aqueous media. The XRD method shows that the deposited metal oxides are in the form of crystalline phases of Co 3 O 4 with the crystallites of 25–26 nm in size for the individual SiO 2 and Al 2 O 3 nanocarriers and 34–37 for the mixed ones, but the iron oxide reflections were not identified for the composites. XPS observation demonstrates the signal of Fe 2p electrons as the form of Fe 2 O 3 oxide in the surface layer of nanocomposites as well as Co 2p as the Co 3 O 4 and Co(OH) 2 .