Electroless synthesis of multibranched gold nanostructures encapsulated by poly(o-phenylenediamine) in Nafion Subramani Thangavel, Ramasamy Ramaraj ⇑ Centre for Photoelectrochemistry, School of Chemistry, Madurai Kamaraj University, Madurai 625 021, India article info Article history: Received 18 August 2010 Accepted 10 December 2010 Available online 15 December 2010 Keywords: Polymer–metal nanocomposite Gold nanostructure Polyelectrolyte Conductive polymer Oxygen reduction Modified electrode abstract Multibranched gold (Au) nanocomposite materials encapsulated by poly(o-phenylenediamine) (PoPD) (Au@PoPD) were synthesized in a Nafion polymer film through the electroless synthetic route. The micro-heterogeneous structured Nafion film acted as a reaction vessel and as the template for the forma- tion of Au@PoPD nanocomposite materials leading to the formation of highly uniform distribution of high density of the polymer–gold nanocomposite material. The formation of Au@PoPD nanomaterials at the GP/Nf surface was scrutinized by recording in situ absorption spectra and was characterized. The forma- tion of the (1 1 1) plane of gold was dominant at the Au@PoPD nanocomposite. The ratio of the benzenoid and quinoid units of the PoPD (ca. 1.65) observed for the Au@PoPD confirmed that the micro-heteroge- neous structure of Nf film acted as a reaction vessel and as template for the formation of Au@PoPD nano- composite material. Both PoPD and Au at the Au@PoPD nanocomposite showed electrochemical activities at the GC/Nf–Au@PoPD modified electrode. The electrocatalytic activity of the GC/Nf–Au@PoPD modified electrode was studied for oxygen reduction reaction (ORR). Ó 2010 Elsevier Inc. All rights reserved. 1. Introduction Polymer nanocomposites are a combination of polymer matrix and additives that have at least one dimension in the nanometer range. The additives can be three-dimensionally arranged metal nanoparticles and such materials are called polymer–metal nano- composite materials [1]. Polymer–metal nanocomposite materials act as novel materials in the fields of photonic [2,3] and optoelec- tronic systems [3] and electrochemical sensors [4,5]. In particular, the introduction of metal nanoclusters into the conductive poly- mer moiety is known to enhance the electrical conductivity [6–8] and the electrocatalytic activity [9,10] of the conductive polymers. The conducting polymers are termed as the fourth generation of polymeric materials due to their conductive nature [11]. The con- ductivity can be switched into the full range from insulator to metallic by the introduction of suitable doped materials [12]. Con- ductive polymer–metal nanocomposite materials are known to be highly stable [13,14]. The electronic, magnetic and optical and catalytic properties of gold nanoparticles depend on their size (quantum size effect) and shape [15–17]. It is well known that uncovered metal nanoparticles suspension is easily aggregated [15–17]. A variety of methods have been developed to modify gold nanoparticles to prevent the aggregation of nanoparticles [16]. Gold nanoparticle–polymer composites were synthesized by surface-initiated cationic polymerization, reduction of the metal salts dissolved in the polymer matrix, deposition of metal on the polymer surface [16,18–22] and encapsulation by polymerization around the metal nanoparticles [23]. Conducting polyaniline (PANI) and Au nano –PANI nanocomposite particles dispersed in aqueous medium was synthesized by single pot synthesis [24]. In general, p-conjugated polymers act as one-dimensional semiconductor and used in the easy fabrication of large-area devices [25]. Composites of metal nanoparticles and p-conjugated polymers are key materials for wide ranges of applications [13]. Oxidative polymerization of aromatic diamines can be achieved by using suitable oxidants, such as metal salts [26,27]. Colloidal polymer–metal nanocomposite materials require additional steps to fabricate solid supported devices. Consequently, we need a simple and direct synthetic methodology to synthesize tunable and stable polymer–metal nanocomposites in suitable so- lid polymer matrix, which will enable the fabrication of devices. Previous reports show that the plain gold nanoparticles are pre- pared in Nafion film [9,28,29]. The preparation of gold nanoparti- cles encapsulated in conducting polymers are also reported [24,30–32]. However, the gold nanoparticles-conducting polymer nanocomposite materials incorporated in Nafion film and the corresponding modified electrode is not reported. The in situ formation of multibranched Au@PoPD nanocomposite material in the Nafion film is a new methodology and enables one to follow the in situ formation by spectral method. In the present methodol- ogy, the electroless synthesis of a poly(o-phenylenediamine) 0021-9797/$ - see front matter Ó 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2010.12.035 ⇑ Corresponding author. E-mail address: ramarajr@yahoo.com (R. Ramaraj). Journal of Colloid and Interface Science 355 (2011) 293–299 Contents lists available at ScienceDirect Journal of Colloid and Interface Science www.elsevier.com/locate/jcis