Magnetic iron oxide–silica nanocomposites. Synthesis and characterization
Composite materials containing nanoparticles of maghaemite (γ-Fe2O3) dispersed in a silica matrix have been made by polymerizing a silica precursor (triethoxysilane or silicic acid) inside an aqueous sol of maghaemite particles. After gelation, the examination of xerogels by electron microscopy does not reveal noticeable aggregation of particles. The structure and composition of the silica matrices were deduced from 29Si MAS NMR spectroscopy. Thermal analysis, FTIR and NIR spectroscopic studies showed that the particles and silanol groups of the matrix remain solvated in the composite materials. No Si–O–Fe bonds are formed in the xerogels and the dispersion of particles in the matrix seems to result from the mutual solvation of particle surfaces and remaining silanol groups, as indicated by strongly associated hydrogen-bonded water molecules.