Preparation of polymer-covered metal nanorods and metal microcrystals by intrinsic two-dimensional crystalline lattice t
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Miguel J. Yacaman Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712-0231; and Texas Materials Institute, University of Texas at Austin, Austin, Texas 78712-1063
John T. McDevitt Department of Chemistry and Biochemistry, University of Texas at Austin, Austin, Texas 78712-0165; Center for Nano- and Molecular Science and Technology, University of Texas at Austin, Austin, Texas 78712-1063; and Texas Materials Institute, University of Texas at Austin, Austin, Texas 78712-1063 (Received 25 April 2005; accepted 2 August 2005)
Two-dimensional layered ceramics, highly anisotropic materials in terms of structure and properties, were used to produce polymer-covered metal nanorods and metal microcrystals. The procedure took advantage of the intrinsic planar, layered ordering of the metal cations suitable to be reduced and could be further used to engineer one-dimensional metal alloy nanostructures by appropriate doping of the initial layered ceramic lattice with suitable cationic species. The procedure involved the formation in an intermediate step of a polymer-intercalated ceramic nanocomposite, highly porous to the diffusion of the polymerizable reducing agent, pyrrole. Two structurally similar layered bismuthates, Bi2Sr2CaCu2O8+␦ and Bi6Sr2CaO12 and a partially Rh-substituted ceramic, Bi4Rh2Sr2CaO12 were used as the precursor layered ceramics and the reducible metal cations were Cu2+, Bi3+, and Rh3+, respectively. The formation of the polymer-covered metal nanorods and metal microcrystals took place at relatively high temperatures of reaction (325 °C) and long reaction times (10–12 days).
I. INTRODUCTION
Layered inorganic lattices have been used as host materials for guest organic monomers in intercalation reactions,1,2 with the goal to create homogeneous nanocomposites that exhibit an improved set of physical and chemical properties when compared to the individual parent compounds, and that can be subsequently implemented in the targeted practical applications.3 The planar, intrinsic 2-D ordering of the constituent, reducible cations can be used as a template for the 1-D metal nanostructure formation, based on a surface area minimization effect. The two layered bismuthates used in this study belong to different classes in terms of electronic conductivity, Bi2Sr2CaCu2O8+␦ is a high-temperature superconductor (Tc ⳱ 85 K), while Bi6Sr2CaO12 is a room temperature insulating oxide that exhibits ionic
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0377 3034
J. Mater. Res., Vol. 20, No. 11, Nov 2005
conductivity at high temperatures (over 700 °C). They are related through similar cationic composition and the presence of van der Waals gaps between Bi–O···Bi–O consecutive layers, which can host a monolayer of iodine atoms and a sterically constrained monolayer of polypyrrole chains.4,5 Appropriate doping of the Bi6Sr2CaO12 can lead to engineered lattices that present more than one reducible metal cation per formula unit, within the same
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