Catalytic effect of silver nanoparticle on electron transfer reaction: Reduction of [Co(NH3)5Cl](NO3)2 by iron(II)

Silver nanoparticle was synthesized by chemical reduction method and stabilized in a series of non-ionic Tween surfactants. Its size and shape vary with the chain length, head group size and concentration of surfactants. The rate of electron transfer reaction between [Co-III(NH3)(5)Cl](NO3)(2) and Mohr's salt (Fe-II) was investigated in presence of different sizes of silver nanoparticles. The reaction is second order: first order in each [Co(NH3)(5)Cl](NO3)(2) and Mohr's salt in presence of silver nanoparticles. Silver nanoparticle enhances the rate about two to three times. The ionic strength does not influence the rate significantly in presence of silver nanoparticle, possibly of significant catalytic effect of nanoparticle. Thermodynamic activation parameters (Delta H-double dagger degrees and Delta S-double dagger degrees) were determined from variable temperature kinetic Studies. The negative values of Delta S-double dagger degrees indicate that the reactions proceed through an associative inner sphere mechanism. All kinetic and thermodynamic activation parameters Support an electron transfer from Fe-II to Co-III through the chloro bridge on the surface of silver nanoparticle within the stern layer. (C) 2009 Elsevier B.V. All rights reserved.