Nucleation of iron oxy-hydroxide nanoparticles by layer-by-layer polyionicassemblies

We report here the growth and characterization of iron oxide nanoparticles by polyionic multilayers assembled by electrostatic layer-by-layer adsorpti on. The polyions poly(diallyldimethylammonium) chloride (PDDA) and polystyr enesulfonate (PSS) were used for the layer-by-layer assembly of the polyion s. Nanoparticle nucleation was achieved by a cyclic repetition of Fe oxidat ive hydrolysis under an inert atmosphere. We employed UV-vis analysis for b oth monitoring the multilayer assembly process and ascertaining the influen ce of the Fe oxidative hydrolysis process on the integrity of the polymer f ilm. No degradation of the multilayers due to the particle growth procedure was observed. The nucleation and growth of needle-shaped nanoparticles wit h a length of about 100 nm and a width of about 10 nm were detected by tran smission electron microscopy (TEM). The void volume of the polymer matrix p rovided an upper limit to the particle size. As shown by selective area ele ctron diffraction (SAED), the polycrystalline particles were identified as beta-FeOOH (akaganeite), a result confirmed by reflection-absorption IR spe ctroscopy.