In-situ nucleation and growth of gamma-FeOOH nanocrystallites in polymericsupramolecular assemblies

This paper reports the nucleation and growth of lepidocrocite (gamma-FeOOH) crystallites in supramolecular polymer multilayers. Organized, polymeric t hin films were formed by the layer by layer deposition technique that consi sted of adsorbing alternate layers of a polycation and a polyanion on a qua rtz substrate. Nucleation of nanoparticles was initiated by absorbing ferri c nitrate in the thin film polymer matrix, followed by hydrolysis with ammo nium hydroxide-1 Repeating the above process resulted in an increase in the density of the nanoparticles initially formed and further growth in the di mensions of the crystallites with the number of absorption and hydrolysis-c ycles;Analysis of the UV-visible absorption spectra of the films revealed t he formation of lepidocrocites, which was confirmed by FTIR and selected ar ea electron diffraction (SAED) studies. An important feature of this work i s that lepidocrocite (gamma-FeOOH) is formed instead of akaganeite (beta-Fe OOH),which is generated when ferrous chloride is used as the starting mater ial and is converted to iron oxyhydroxide through oxidative hydrolysis as r eported in our previous work (Langmuir 1999, 15, 2176). It therefore seems likely that the initial starting material plays a key role in determining t he structural and morphological characteristics of the iron oxyhydroxides a lthough their chemical compositions are the same.