Fabrication of platinum nanoparticles in aqueous solution and solid phase using amphiphilic PB-b-PEO copolymer nanoreactors Numan Hoda a, *, Leyla Budama a , Burc ¸in Acar C ¸akır a , O ¨ nder Topel a , Rahmi Ozisik b a Department of Chemistry, Faculty of Sciences, Akdeniz University, 07058 Antalya, Turkey b Department of Materials Science & Engineering and Renssleaer Nanotechnology Center, Rensselaer Polytechnic Institute, Troy, NY 12180, USA 1. Introduction Fabrication of nanoparticles has gained boundless interest in different areas of science due to their size dependent properties, which are different from those of the bulk phase. Nanoparticles of metals, semiconductors, and magnetic crystals are synthesized by several methods including amphiphilic copolymer templating [1]. These kinds of copolymers are able to form micelles in selected solvents in which only one of the blocks is soluble [2]. The soluble block constitutes the corona of the micelle while the insoluble block forms the core. The core of the micelle can then act as a ‘‘nanoreactor’’ in which nanoparticles can be synthesized if metal ions are encapsulated in the core of the micelles by complexation or association, whereas the corona provides stability. Thus, encapsulated metal ions can be easily reduced or oxidized to the corresponding metal or oxide form. Many studies have appeared in the literature about the production of metal and semiconductor nanoparticles using amphiphilic copolymer tem- plates [3–6]. Du et al. synthesized stable gold nanoparticles in N,N- dimethylformamide by using amphiphilic multiblock copolymer (P4VP–PS–P4VP) n which contains multiple trithiocarbonate moieties or amphiphilic triblock copolymer (HS–P4VP–PS– P4VP–SH) with thiol end groups as protecting agents [3]. In fact, the size greatly affects the physical and chemical properties of nanoparticle such as activity, stability and catalytic selectivity in chemical reactions due to surface area and morphological differences (size, shape, etc.) [3–9]. Nanoparticles with narrow size distributions can be synthesized by changing experimental conditions e.g. solvents, precursors, temperature, reaction time, metal-ligand ratio and stabilizing/reducing agents [8,10–13]. During fabrication of nanoparticles in the core of micelles, the size of nanoparticle can be controlled by selection of the block copolymer used, the strength of the reducing agent, and the concentration of the precursor. Papp et al. compared the effects of reducing agents (hydrazine (HA), triethylsilane (TES), and potassium triethylborohydride (PTB)) to prepare gold nanoparti- cles by reduction of HAuCl 4 incorporated in the polar core of poly(styrene)-block-poly(2-vinylpyridine), PS-b-P2VP, copolymer micelles in toluene [14]. The average diameter of the gold nanoparticles prepared by reduction with HA, TES, and PTB were 1.7, 2.6, and 8.0 nm, respectively, which means the strength of the reducing agent plays an important role to determine the size of the gold nanoparticle within micelle core. According to Antonietti et al., the slow reacting triethylsilane (TES) resulted in a single nanoparticle within each micelle, whereas fast reduction with NaBH 4 leads to the formation of many small nanoparticles per micelle. These differing morphologies were termed ‘‘cherry’’ for Materials Research Bulletin 48 (2013) 3183–3188 A R T I C L E I N F O Article history: Received 23 June 2012 Received in revised form 14 January 2013 Accepted 29 April 2013 Available online 15 May 2013 Keywords: A. Composites A. Nanostructures A. Polymer B. Chemical synthesis C. Electron microscopy A B S T R A C T Fabrication of Pt nanoparticles using an amphiphilic copolymer template in aqueous solution was achieved via polybutadiene-block-polyethyleneoxide copolymer micelles, which acted as nanoreactors. In addition, Pt nanoparticles were synthesized using hydrogen gas as the reducing agent in solid state for the first time to compare against solution synthesis. The influences of loaded precursor salt amount to micelles and the type of reducing agent on the size of nanoparticles were investigated through transmission electron microscopy. It was found that increasing the ratio of precursor salt to copolymer and using different type of reducing agent, even in solid phase reduction, did not affect the nanoparticle size. The average size of Pt nanoparticles was estimated to be 1.4  0.1 nm. The reason for getting same sized nanoparticles was discussed in the light of nucleation, growth process, stabilization and diffusion of nanoparticles within micelles. ß 2013 Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: +90 242 3102301; fax: +90 242 2278911. E-mail addresses: nhoda@akdeniz.edu.tr, numanhoda@gmail.com (N. Hoda). Contents lists available at SciVerse ScienceDirect Materials Research Bulletin jo u rn al h om ep age: ww w.els evier.c o m/lo c ate/mat res b u 0025-5408/$ – see front matter ß 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.materresbull.2013.04.091