Investigating Catalytic Properties of Composite Nanoparticle Assemblies
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Investigating Catalytic Properties of Composite Nanoparticle Assemblies M.M. MAYE, J. LUO, Y. LOU, N. K. LY, W.-B. CHAN, E. PHILLIP, M. HEPELa, C.J. ZHONG* Department of Chemistry, State University of New York at Binghamton, Binghamton, NY 13902. (a) Department of Chemistry, State University of New York at Potsdam, Potsdam, NY 13676. (*) [email protected]
ABSTRACT We present herein recent findings of an investigation of catalyst assembly and activation using metallic nanoparticles encapsulated with organic monolayers. Gold nanocrystals (2~5 nm) encapsulated with thiolate monolayers assembled on electrode surfaces, were found to be catalytically active towards electrooxidation of CO and MeOH upon activation. The activation involved partial removal of the encapsulating thiolates and the formation of surface oxygenated species. A polymeric film was also used as a substrate for the assembly of the nanoparticle catalysts. When the polymer matrix was doped with small amounts of Pt, a remarkable catalytic activity was observed. These catalysts were characterized utilizing cyclic voltammetry and atomic force microscopy. INTRODUCTION The pioneer work of two-phase synthesis of gold nanoparticles with a few nm core size stabilized by alkanethiolate monolayers has led to increasing research and development interest in the field of composite nanomaterials [1]. The possibility of further processing of these particles into highly monodispersed, larger sized, and stable nanoparticles has enabled the ability to probe size-dependent reactivity, as recently demonstrated in our laboratory [2]. These nanoparticles can be effectively linked to form thin films using molecular crosslinking agents. There are several routes reported for crosslinking. One involves a stepwise "layer-by- layer" assembly method [3], and another involves one step “exchange-crosslinking-precipitation” route developed recently in our laboratory [4]. The nanostructured thin films have potential applications in microelectronics, optics, biomimetics, molecular recognition, drug delivery, chemical and environmental sensing, and catalysis [5,6,7]. Gold is traditionally considered as catalytically inert. The recent finding by Haruta and co-workers [8] demonstrated that the catalytic ability for gold increases as the size is reduced to nanometer scales [9]. Gold nanoparticles supported on oxides show high catalytic activity to CO oxidation. Although the idea of using small sized particles as catalysts has been known for a long time, problems faced when using bare nanoparticles include aggregation, short life times, and propensity of poisoning. We recently hypothesized that the core-shell nanoparticles (CSNs) could be used to solve some of these problems. Part of the concept is related to the high stability and the reactivity of CSNs by which they can be assembled in a controllable way. While the use of surface protected nanoparticles as catalysts has the effect of preventing particles from aggregation, catalytic activity may become hindered due to possible inhibitin
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