The synthesis of clusters of iron oxides in mesopores of monodisperse spherical silica particles

The method of obtaining nanoclusters $\alpha$-Fe$_{2}$O$_{3}$ in the pores of monodisperse spherical particles of mesoporous silica ($m$SiO$_2$) by a single impregnation of the pores with a melt of crystalline hydrate of ferric nitrate and its subsequent thermal destruction has been proposed. Fe$_{3}$O$_{4}$ nanoclusters are synthesized from $\alpha$-Fe$_{2}$O$_{3}$ in the pores by reducing in thermodynamically equilibrium conditions. Then particles containing Fe$_{3}$O$_{4}$ were annealed in oxygen for the conversion of Fe$_{3}$O$_{4}$ back to $\alpha$-Fe$_{2}$O$_{3}$. In the result, the particles with the structure of the core-shell $m$SiO$_2$/ Fe$_{3}$O$_{4}$@$m$SiO$_2$/$\alpha$-Fe$_{2}$O$_{3}$ are obtained. The composition and structure of synthesized materials as well as the field dependence of the magnetic moment on the magnetic field strength have been investigated.