CSIRO PUBLISHING Rapid Communication www.publish.csiro.au/journals/ajc Aust. J. Chem. 2008, 61, 833–836 Formation and Stabilization of Anisotropic Palladium and Platinum Nanoparticles in Aqueous Polymer Solution Using Microwave Irradiation Angshuman Pal, A Sunil Shah, A Debjani Chakraborty, A and Surekha Devi A,B A Department of Chemistry, Faculty of Science,The Maharaja Sayajirao University of Baroda, Vadodara 390002, Gujarat, India. B Corresponding author. Email: surekha_devi@yahoo.com Anisotropic palladium and platinum nanoparticles were synthesized by reduction of the corresponding metal ions with hydrazine using polyacrylamide as a stabilizing agent in aqueous medium under microwave irradiation. The formation of particles was confirmed by UV-visible spectroscopy.The size and shape of the particles were determined using trans- mission electron microscopy. Rapid microwave heating resulted in ‘star-shaped’palladium nanoparticles, but platinum nanoparticles were observed to be spherical with a distinctly visible 3–4 nm coating of polyacrylamide on their surface, which was not observed for the palladium particles. The Pt nanoparticles were used as a catalyst in the redox reaction. Manuscript received: 10 October 2007. Final version: 23 September 2008. The past couple of decades have witnessed worldwide exponen- tial growth of activities in the field of nanoscience, driven both by the excitement of understanding new science and by the potential hope for newer applications and economic impacts. The largest activity in this field at present is in the synthesis of nanoparti- cles of different sizes and shapes, e.g., by bottom-up or top-down techniques. Although many future applications such as sensors, medical diagnosis, and homogeneous catalysis will make use of the specific properties of the individual nanoparticles, they can also be used in nanoelectronics, optoelectronics, photonics, and heterogeneous catalysis. Interest in colloidal noble metal nanoparticles protected by polymers is increasing, as these mate- rials offer options to combine properties that originate from both the nanoparticles and the polymers. [1–3] Polymer-protected noble metal colloids are usually prepared from suitable metal precur- sors by various in-situ reactions in the presence of the protective polymer. Through suitable choice of the precursors, reduction conditions, and protective polymer, it is possible to control not only the particle size but also the particle shape and morphology, which can be an additional tool to engineer the optical or cat- alytic properties. [1] Tristany et al. [4] have reported the synthesis of Pt nanoparticles organised in rod or wire-shaped superstruc- tures that result from the combination of an organometallic route, which leads to size-controlled nanoparticles, with the use of a fluorinated aniline as a stabilizing agent. Among all the metals, Pd and Pt nanoparticles have their own place because of their unique catalytic activity and their use in other appli- cations. Palladium nanoparticles serve as the primary catalyst for the low temperature reduction of pollutants emitted from automobiles [5,6] and in organic reactions, such as Suzuki, Heck, and Stille couplings. [7–11] By tailoring the size and/or shape, one can, in principle, enhance their catalytic performance in a range of applications. [12,13] Pd nanoparticles of various morphologies have also been prepared in the presence of surfactant, [14,15] with the mediation of RNAs, [16] through the thermal decomposition of a Pd–surfactant complex, [17] and via use of a coordinating ligand. [18] Platinum is a catalyst for several significant reactions, including evolution of hydrogen, reduction of oxygen, oxidation of hydrogen, oxidation of methanol, and hydrogenation. [19–22] Recent developments in the synthesis of Pt nanoparticles with surface capping agents [23,11] permitted control over the nanopar- ticles’ size, shape, and crystallinity and, therefore, opened the possibility for systematic studies of nanometer-scale catalysis. El-Sayed and co-workers have synthesized polyacrylate-capped Pt nanocrystallites in cubic, tetrahedral, octahedral, and various other shapes. [24] Here in this communication we report ‘star’-shaped Pd nanoparticles and spherical Pt nanoparticles synthesized by microwave irradiation. To our knowledge, this is the first report for the anisotropic synthesis of Pd and Pt nanoparticles using polyacrylamide as a stabilizing agent and hydrazine as a reduc- ing agent under microwave irradiation. Chlorides of palladium and platinum were taken as metal precursors and hydrazine hydrate (0.25 M) was used for the reduction of the metal ions. An aqueous polyacrylamide (0.1%, v/v) solution was used as a sta- bilizing agent and a 0.01 M concentration was used for both the metal ions. A typical reaction volume that contained 10 mL of 0.1% (v/v) polyacrylamide solution, with 3 × 10 −4 M metal and 2.5 × 10 −3 M reducing agent was irradiated with microwaves in an LG make MG 605AP microwave oven for 5 min at grill con- ditions. Over the conventional synthesis methods, microwave- mediated syntheses have the advantage of improved kinetics of the reaction generally by one or two orders of magnitude, because of rapid initial heating and the generation of local- ized high-temperature zones at reaction sites. This may be because all the species involved in the nanoparticle formation reaction are simultaneously thermally excited within a very short time. © CSIRO 2008 10.1071/CH07353 0004-9425/08/110833