Investigation of the supercritical deposition of platinum nanoparticles into carbon aerogels Carl D. Saquing a , Dafei Kang b , Mark Aindow b , Can Erkey a, * a Environmental Engineering Program, Department of Chemical Engineering, University of Connecticut, 191 Auditorium Road, Storrs, CT 06269, USA b Department of Materials Science and Engineering, Institute of Materials Science, University of Connecticut, Storrs, CT 06269-3136, USA Received 28 July 2004; received in revised form 8 November 2004; accepted 8 November 2004 Available online 12 January 2005 Abstract The preparation of platinum/carbon aerogel (CA) nanocomposites by the supercritical deposition method was investigated. CAs were impregnated with dimethyl(cyclooctadiene)platinum, CODPtMe 2 , from supercritical carbon dioxide (scCO 2 ) solutions and the resulting CODPtMe 2 /CA composites were converted to Pt/CA composites. The adsorption isotherms of CODPtMe 2 on CAs were measured and could be represented by the Langmuir model. The results indicated a strong interaction between CODPtMe 2 mole- cules and the CA surface and that a substantial fraction of the surface of the CAs was covered with CODPtMe 2 molecules at rel- atively low concentrations. Four different reduction methods were used to convert the CODPtMe 2 impregnated CAs which were: (1) thermal reduction at atmospheric pressure in an inert atmosphere; (2) thermal reduction in scCO 2 ; (3) chemical reduction in scCO 2 with hydrogen; and (4) chemical reduction at atmospheric pressure with hydrogen. Method 1 gave highly dispersed Pt nanoparticles (1–3 nm) at loadings ranging from 10 to 40 wt.%. The use of hydrogen in Method 4 increased the average particle size by a factor of 2 over Method 1 at the same Pt loading, but the particles still had a narrow unimodal size distribution. When the thermal reduction was carried out in scCO 2 , loadings as high as 73% could be obtained. Method 3 generated a composite having a disordered columnar Pt coating and equiaxed particles 1 lm in diameter on the external surface of the monolith and dispersed Pt nanoparticles in the interior. The analysis of the reaction products in scCO 2 indicated an autocatalytic reaction. Increasing the Pt loading was found to decrease the surface area of the CA, primarily through blockage of the micropores. Ó 2004 Elsevier Inc. All rights reserved. Keywords: Carbon aerogel; Platinum; Supercritical deposition; Microporosity; Nanocomposite 1. Introduction The synthesis of nanoscale composite materials has attracted a great deal of attention due largely to their unique physical and chemical properties, which are suit- able for a wide range of industrial applications [1–3]. In particular, nanoparticulate metals of uniform and con- trollable size and composition contained in an appropri- ate porous support find uses in areas as diverse as catalysis, microelectronics, magnetics, electrochemistry and optics [4–7]. Frequently, the special properties exhibited by these materials in such applications depend strongly on the size, spatial distribution and specific con- centration of the metal clusters within the host porous matrix [1,4,7], as well as the properties of the support. Metal-support interactions may play an important role in catalysis; and the effect of the size of metal nanopar- ticles on catalytic activity is an ongoing area of research [8], especially for structure-sensitive reactions [9]. One group of materials that can be used as substrates for metal nanoparticles are carbon aerogels (CAs). CAs are mesoporous materials with unique properties such as 1387-1811/$ - see front matter Ó 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.micromeso.2004.11.019 * Corresponding author. Tel.: +1 860 486 4601; fax: +1 860 486 2959. E-mail address: cerkey@engr.uconn.edu (C. Erkey). www.elsevier.com/locate/micromeso Microporous and Mesoporous Materials 80 (2005) 11–23