The mechanism of surface
functionalization is the formation of Fe−O−Si bond between
the nanoparticles and silane ligand, very similar to the siloxane
layer formation on silica. However, accurate control of the layer
quality has been a difficult task.8,11,20−22 Silane attachment may
exist in physisorption, hydrogen bonding, or electrostatic
attachment besides covalent linkage.20 Even for covalently
linked ligands, complications may be present in monolayer and
multilayer formation.23