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    Ion Limited Charging of Nanoparticle Thin Films

    Year: 2008

    Journal: J. Phys. Chem. C, 2008, 112 (40), pp 15637–15642, 20111221

    Authors: Timo Laaksonen, Virginia Ruiz, Peter Liljeroth and Bernadette M. Quinn

    Organizations: Division of Pharmaceutical Technology, Faculty of Pharmacy, University of Helsinki, P.O. Box 56, FIN-00014 University of Helsinki, Finland, Department of Engineering Physics, Helsinki University of Technology, P.O. Box 5100, FIN-02015 HUT, Finland, Condensed Matter and Interfaces, Debye Institute for Nanomaterials Science, University of Utrecht, P.O. Box 80000, 3508 TA Utrecht, The Netherlands, and Department of Chemistry, Helsinki University of Technology, P.O. Box 6100, FIN-02015 HUT, Finland

    This article reports on the charging behavior of thin films of alkanethiol protected gold nanoparticles, so-called monolayer protected clusters (MPCs), immersed in aqueous solution. We demonstrate that the oxidation of the MPCs is controlled by the transfer of counter-ions across the aqueous/MPC film interface. A model is developed to describe this and its predictions compared with experiment. Langmuir-Schaefer MPC thin films were transferred to a glassy carbon electrode and film charging behavior investigated in a series of aqueous solutions comprised of different base electrolyte anions. The dependence of peak current on film thickness and peak position on anion lipophilicity for MPC oxidative charging can all be accounted for with the ion-transfer limited model. The impact of ion partitioning into the film at equilibrium is also discussed and the effect of the aqueous phase cation is theoretically considered. In addition, the effect of co-transported water with hydrophilic ions transferring into the film on film charging is rationalized.