pubs.acs.org/cm Published on Web 10/07/2009 r 2009 American Chemical Society 5170 Chem. Mater. 2009, 21, 5170–5175 DOI:10.1021/cm9021134 Synthesis of Ultrathin Hexagonal Palladium Nanosheets Prem F. Siril, †,^ Laurence Ramos, ‡ Patricia Beaunier, § Pierre Archirel, † Arnaud Etcheberry, ) and Hynd Remita* ,† † Laboratoire de Chimie Physique, UMR 8000-CNRS, Universit e Paris-Sud 11, 91405 Orsay, France, ‡ Laboratoire des Colloı¨des, Verres et Nanomat eriaux, UMR 5587-CNRS, Universit e Montpellier II, 34095 Montpellier Cedex 05, France, § Laboratoire de R eactivit e de Surface, UMR 7197-CNRS, Universit e Paris-VI, 75252 Paris Cedex 05, France, and ) Institut Lavoisier de Versailles, ILV UMR 8180-CNRS, Universit e Versailles Saint-Quentin-en-Yvelines, 45 rue des Etats-Unis, 78035 Versailles Cedex, France. ^ Present address: Chemistry Department, National Institute of Technology, Hamirpur-177 005, Himachal Pradesh, India. Received July 13, 2009. Revised Manuscript Received September 23, 2009 Ultrathin palladium hexagonal nanosheets were synthesized in emulsions constituted of droplets of toluene containing Pd complexes in water and stabilized by CTAB as surfactant and in quaternary mesophases formed by water, toluene containing Pd complexes, CTAB, and a cosurfactant. We have identified slow reduction and nucleation provided by CO and adsorption at the CTAB interface as key factors for the formation of Pd nanosheets. These nanosheets exhibit a broad absorption band from the visible to the near-infrared region. I. Introduction Nanomaterials often exhibit remarkable properties when compared to bulk materials. 1 Exceptional mag- netic, 2 optical, 3 electronic, 4 and catalytic 5 properties can be exploited for numerous technological applications. Properties such as catalytic and electrocatalytic activities could strongly depend on the size and shape of the metal nanoparticles. 6 Therefore synthesis of nanoparticles that could exhibit well-controlled shapes and sizes has been explored to enhance their performances. 7 Pd is a versatile catalyst for a large number of industrially important reactions such as hydrogenation of unsaturated organic compounds 6d,8 and a number of important C-C coupling reactions. 9 Pd is also a performing material for hydrogen storage and sensing. 10 Pd nanoparticles show high catalytic activity for ethanol electrooxidation in basic media, and its electroactivity is even higher than that of Pt. 11 Pd nanoparticles with different shapes have been synthesized by controlled growth on specific crystallo- graphic faces or by templating methods. 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