CONICET | Buscador de Institutos y Recursos Humanos

Layer by layer sequential adsorption of polycations and polyanions is a simple and versatile technique for assemblying functional films which can be used to encapsulate enzymes, nanoparticles, etc. In particular, metal complexes coordinated or electro-statically bound to functional polyions (i.e. NH2, COOH, etc) has been a strategy to form nanoparticles by chemical or electrochemical reduction of such ions in the LbL multilayer nanoreactors. In the case of electrochemical reduction of metal ions it is of utmost interest to determine if all metal sites coordinated in the multilayers are accessible for electron transfer. Therefore we have used FTIR spectroelectrochemistry to study a very well known system, namely Fe(CN)63- and Fe(CN)64- exchanged with the as prepared electrostatically self assembled pollyalylamine (PAH) and polyacrylic acid (PAA) LBL film at low pH carrying a positive charge in the NH3+ groups. During the exchange it is expected that the freely diffusing redox ions bind to NH3+ groups by breaking polyion-polyion bonds and forming an extrinsic LbL film. We have used cyclic voltammetry and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) since the CN stretching has a strong signal which depends on the oxidation state of the Fe center. By comparing the number of centers revealed by spectroscopy with the redox charge we can evaluate the fraction of redox sites accessible for electrochemical conversion. We have studied the effect of the number of assembled layers, charge of the outmost layer, concentration of redox species in solution, and ionic strength. We have examined these effects on the formation of metal nanoparticles by ionic exchange and further electro-reduction of metal complex ions such as AuCl4-, PtCl62-, etc.