In-situ nucleation and growth of γ-FeOOH nanocrystallites in polymeric supramolecular assemblies

This paper reports the nucleation and growth of lepidocrocite (gamma-FeOOH) crystallites in supramolecular polymer multilayers. Organized, polymeric thin films were formed by the layer by layer deposition technique that consisted of adsorbing alternate layers of a polycation and a polyanion on a quartz substrate. Nucleation of nanoparticles was initiated by absorbing ferric nitrate in the thin film polymer matrix, followed by hydrolysis with ammonium hydroxide-1 Repeating the above process resulted in an increase in the density of the nanoparticles initially formed and further growth in the dimensions of the crystallites with the number of absorption and hydrolysis-cycles;Analysis of the UV-visible absorption spectra of the films revealed the formation of lepidocrocites, which was confirmed by FTIR and selected area electron diffraction (SAED) studies. An important feature of this work is that lepidocrocite (gamma-FeOOH) is formed instead of akaganeite (beta-FeOOH),which is generated when ferrous chloride is used as the starting material and is converted to iron oxyhydroxide through oxidative hydrolysis as reported in our previous work (Langmuir 1999, 15, 2176). It therefore seems likely that the initial starting material plays a key role in determining the structural and morphological characteristics of the iron oxyhydroxides although their chemical compositions are the same.