Delivered by Ingenta to: Steven Kuznicki IP : 129.128.32.196 Mon, 02 Mar 2009 19:49:09 COMMUNICATION Copyright © 2009 American Scientific Publishers All rights reserved Printed in the United States of America Journal of Nanoscience and Nanotechnology Vol. 9, 2768–2771, 2009 A Novel Method to Control the Size of Silver Nanoparticles Formed on Chabazite Yan Liu 1 , Fu Chen 2 , Steven M. Kuznicki 1 ∗ , Roderick E. Wasylishen 2 , and Zhenghe Xu 1 1 Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta, T6G 2G6, Canada 2 Department of Chemistry, Gunning/Lemieux Chemistry Centre, University of Alberta, Edmonton, Alberta, T6G 2G2, Canada Highdensity,uniform,surface-supportednanosilverparticlescanbegeneratedonmineralchabazite by thermal reduction of exchanged silver cations. These nanoparticles have properties unique from thoseofbulksilver,includingantimicrobialactivity,whichareafunctionofparticlesize.Inthisstudy, the activation environment is manipulated in order to alter the average size of the silver particles. Nanoparticles with mean diameters of 4.2, 6.1 and 35.0 nm are formed in air, Ar and H 2 at 400  C, respectively. Interaction with the surface of highly polarizing chabazite stabilizes the nanoparticles, and unreduced silver ions on the nanosilver surfaces may play a critical role in determining particle size. Keywords: Nanosilver, Nanometal, Zeolites, Molecular Sieves. Nanotechnology is rapidly altering many disciplines including materials, electronics, and pharmaceuticals. 1 2 Nanotechnology is expected to represent a $1-trillion industry by 2017, with world demand for nanomaterials (largely nano-scale metals and metal oxides) predicted to grow more than five-fold to $3.7 billion in 2008 alone. 1 2 Nano-scale silver has potential antimicrobial and electronic properties that might be exploited by this booming indus- try, if inexpensive nano-silver was readily available. 3–6 It has been reported that silver ions exchanged into mineral chabazite are readily and economically reduced by thermal treatment to form high concentrations of surface-supported silver nanoparticles. 7 Unlike bulk silver, these nanoparticles demonstrate strong antimicrobial activity and can adsorb mercury at high temperature. 7 The chemical properties of nanoparticles vary with particle size, and producing metal nanoparticles of uni- form size in a reproducible manner may influence the purpose-specific utility of the resultant material. 8–12 Sev- eral approaches, including microemulsion techniques and ion implantation in silica, have been reported for con- trolling the size of silver nanoparticles, but the methods suffer from low yields, high energy consumption, irre- producibility, complexity and/or poor control of size and morphology. 13–19 A proven alternative approach is to gener- ate nano-scale silver on mineral chabazite, a highly polar- izing support that can interact with and stabilize the silver ∗ Author to whom correspondence should be addressed. particles. 7 In this method, silver cations are first exchanged into mineral chabazite (MC). Upon thermal reduction, the metal migrates to form high concentrations of supported silver nanoparticles uniformly distributed on the zeolite surface. Controlling the environment in which the ionic silver is reduced could further control the silver parti- cle size by manipulating the surface charge on the parti- cle. In this model, the electrostatic interactions between unreduced silver ions on the nanoparticle surface and the highly polarizing chabazite may prevent aggregation of the silver. Conversely, if all of the silver ions are reduced, the particle–surface interaction may decrease, resulting in larger particles. In this study, the activation environment is manipulated in order to efficiently and reproducibly generate supported silver nanoparticles of controlled size in a potentially eco- nomical manner. We report the formation of silver parti- cles under varying reductive environments and characterize the nanoparticles by X-ray diffraction (XRD), transmission electron microscopy (TEM) and solid-state 109 Ag nuclear magnetic resonance (NMR). The mean diameter of the sil- ver nanoparticles ranges from 4.2 nm for particles formed in an oxidizing environment, to 35.0 nm for particles formed in a reducing environment. Synthesis: The mineral chabazite (MC) used in this study is from the deposit at Bowie, Arizona and was obtained from GSA Resources of Tucson, Arizona. Silver ion-exchanged chabazite, designated Ag-MC, was gener- ated by standard methods. 7 The Ag-MC was subsequently heated to 110  C using a 10  C/min heat ramp under a 2768 J. Nanosci. Nanotechnol. 2009, Vol. 9, No. 4 1533-4880/2009/9/2768/004 doi:10.1166/jnn.2009.446