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Synthesis and Characterization of Polypyrrole-Palladium Nanocomposite-Coated Latex Particles and Their Use as a Catalyst for Suzuki Coupling Reaction in Aqueous Media Syuji Fujii,* Soichiro Matsuzawa, Yoshinobu Nakamura, Atsushi Ohtaka, and Takuto Teratani Department of Applied Chemistry, Osaka Institute of Technology, 5-16-1 Ohmiya, Asahi-ku, Osaka 535-8585, Japan
Kensuke Akamatsu, Takaaki Tsuruoka, and Hidemi Nawafune Department of Nanobiochemistry, Frontiers of Innovative Research in Science and Technology (FIRST), Konan University, 7-1-20 Minatojimaminami, Chuo-ku, Kobe 650-0047, Japan Received October 19, 2009. Revised Manuscript Received December 8, 2009 Polypyrrole-palladium (PPy-Pd) nanocomposite was deposited in situ from aqueous solution onto micrometer-sized polystyrene (PS) latex particles. The PS seed particles and resulting composite particles were extensively characterized with respect to particle size and size distribution, morphology, surface/bulk chemical compositions, and conductivity. PPy-Pd nanocomposite loading onto the PS seed latex particles was systematically controlled over a wide range (10-60 wt %) by changing the weight ratio of the PS latex and PPy-Pd nanocomposite. Pd loading was also controlled between 6 and 33 wt %. The conductivity of pressed pellets increased with the PPy-Pd nanocomposite loading and four-point probe measurements indicated conductivities ranging from 3.0 10-1 to 7.9 10-6 S cm-1. Hollow capsule and broken egg-shell morphologies were observed by scanning/transmission electron microscopy after extraction of the PS component from the composite particles, which confirmed a PS core and PPy-Pd nanocomposite shell morphology. X-ray diffraction confirmed that the production of elemental Pd and X-ray photoelectron spectroscopy indicated the existence of elemental Pd on the surface of the composite particles. Transmission electron microscopy confirmed that nanometer-sized Pd particles were distributed in the shell. The nanocomposite particles functioned as an efficient catalyst for Suzuki-type coupling reactions in aqueous media for the formation of carbon-carbon bonds.
Introduction There have been numerous reports on the deposition of air-stable conducting organic polymers such as polypyrrole (PPy), polyaniline (PANI), or poly(3,4-ethylenedioxythiophene) (PEDOT) onto *To whom correspondence should be addressed. E-mail:
[email protected]. ac.jp. (1) (a) Wiersma, A. E.; vd Steeg, L. M. A. Eur. Patent No. 589529, 1993. (b) Wiersma, A. E.; vd Steeg, L. M. A.; Jongeling, T. M. J. Synth. Met. 1995, 71, 2269. (c) Huijs, F.; Lang, J. Colloid Polym. Sci. 2000, 278, 746. (2) Kao Co. Ltd. Japanese Patent No. H4-41410, 1992. (3) (a) Burchell, M. J.; Cole, M. J.; Lascelles, S. F.; Khan, M. A.; Barthet, C.; Wilson, S. A.; Cairns, D. B.; Armes, S. P. J. Phys D: Appl. Phys. 1999, 32, 1719. (b) Burchell, M. J.; Willis, M. J.; Armes, S. P.; Kahn, M. A.; Percy, M. J.; Perruchot, C. Planet. Space Sci. 2002, 50, 1025. (c) Fujii, S.; Armes, S. P.; Jeans, R.; Devonshire, R.; Warren, S.; McArthur, S. L.; Burchell, M. J.; Postberg, F.; Srama, R. Chem. Mater. 2006, 18, 2758. (4) Yassar, A.; Roncali, J.; Garnier, F. Polym. Commun. 1987, 28, 103. (5) (a) Yoshino, K.; Yin, X. H.; Morita, S.; Nakanishi, Y.; Nakagawa, S.; Yamamoto, H.; Watanuki, T.; Isa, I. Jpn J. Appl. Phys. 1993, 32, 979. (b) Omastova, M.; Pionteck, J.; Kosina, S. Eur. Polym. J. 1996, 32, 681. (6) (a) Lascelles, S. F.; Armes, S. P. Adv. Mater. 1995, 7, 864. (b) Lascelles, S. F.; Armes, S. P. J. Mater. Chem. 1997, 7, 1339. (c) Lascelles, S. F.; Armes, S. P.; Zhdan, P.; Greaves, S. J.; Brown, A. M.; Watts, J. F.; Leadley, S. R.; Luk, S. Y. J. Mater. Chem. 1997, 7, 1349. (7) (a) Barthet, C.; Armes, S. P.; Lascelles, S. F.; Luk, S. Y.; Stanley, H. M. E. Langmuir 1998, 14, 2032. (b) Barthet, C.; Armes, S. P.; Chehimi, M. M.; Bilem, C.; Omastova, M. Langmuir 1998, 14, 5032. (8) (a) Khan, M. A.; Armes, S. P. Langmuir 1999, 15, 3469. (b) Khan, M. A.; Armes, S. P.; Perruchot, C.; Ouamara, H.; Chehimi, M. M.; Greaves, S. J.; Watts, J. F. Langmuir 2000, 16, 4171. (c) Khan, M. A.; Armes, S. P. Adv. Mater. 2000, 12, 671. (9) (a) Cairns, D. B.; Khan, M. A.; Perruchot, C.; Riede, A.; Armes, S. P. Chem. Mater. 2003, 15, 233. (b) O.-Prout, J.; Dupin, D.; Armes, S. P.; Foster, N. J.; Burchell, M. J. J. Mater. Chem. 2009, 19, 1433. (10) Okubo, M.; Fujii, S.; Minami, H. Colloid Polym. Sci. 2001, 279, 139. (11) Mangeney, C.; Fertani, M.; Bousalem, S.; Zhicai, M.; Ammar, S.; Herbst, F.; Beaunier, P.; Elaissari, A.; Chehimi, M. M. Langmuir 2007, 23, 10940.
6230 DOI: 10.1021/la9039545
polymeric colloidal substrates.1-14 The synthesis of conducting polymer-coated colloidal particles has attracted much interest, due to the increasing applicability of these particles in antistatic and/or anticorrosion coatings,1 in pigments,2 and as synthetic mimics for micrometeorites.3 One of the first reports in this area was by Yassar et al., who described the synthesis of PPy-coated sulfonated polystyrene (PS) latex particles.4 Another early example included the deposition of PPy onto relatively large (noncolloidal) polyolefin-based particles of 10-35 μm in diameter, where the coated particles were mixed with uncoated polyolefin-based particles to produce electrically conductive composites that exhibited relatively low conductivity percolation thresholds after melt-processing.5 More recently, Armes’ group conducted a series of studies on the synthesis of PPy-, PANI-, and PEDOT-coated polymer latexes.6-9 In most cases sterically stabilized latex particles were employed as colloidal substrates, and care was taken to ensure that the thickness of the deposited conducting polymer overlayer did not exceed the steric stabilizer layer thickness for maximum colloidal stability. Okubo et al. succeeded in the synthesis of PANI-coated PS latex particles by chemical oxidative seeded dispersion polymerization and hollow PANI microspheres by extraction of the PS core.10 Mangeney et al. described the synthesis of magnetic, reactive PS/PPy core/shell latex particles, of which the core consists of a PS microsphere containing γ-Fe2O3 superparamagnetic (12) Kim, B. J.; Oh, S. G.; Han, M. G.; Im, S. S. Polymer 2002, 43, 111. (13) Bremer, L. G. B.; Verbong, M. W. C. G.; Webers, M. A. M.; van Doorn, M. A. M. M. Synth. Met. 1997, 84, 355. (14) Slimane, A. B.; Chehimi, M. M.; Vaulay, M.-J. Colloid Polym. Sci. 2004, 282, 314.
Published on Web 02/10/2010
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nanoparticles, and the shell is composed of reactive N-carboxylic acid-functionalized PPy.11 Despite a significant amount of work on the synthesis and characterization of colloidal particles coated with various conductive polymer shells and their corresponding hollow capsules, there are only a limited number of reports on conducting polymer-noble metal nanocomposite-coated latex particles. The main benefit from the introduction of noble metal nanoparticles to spherical surfaces is to avoid the spread of the nanoparticles to the environment. Conducting polymer-noble metal nanocomposites provide an exciting system to investigate the possibility of designing device functionality15 and also exhibit enhanced sensing and catalytic capabilities, compared with those of the pure conducting polymer.16 Armes and co-workers17 synthesized PPy-Au nanocomposite-coated latex particles by electroless deposition of Au via redox interaction between Au(III) ions and a PPy overlayer on the PS particles. Mangeney et al.18 described a method involving the electrostatic assembly of negatively charged Au nanoparticles onto positively charged PS/PPy core/shell particles bearing surface-protonated N-propylamino groups. The synthesis of such conducting polymer-metal nanocomposite-coated particles typically requires three steps: (i) preparation of seed particles, (ii) coating of the seed colloidal particles with a conductive polymer, and (iii) application of metal nanoparticles onto the conducting polymer shell. Recently, it was reported that conducting polymer-noble metal nanocomposites can be synthesized by a one-step chemical oxidative polymerization using metal salts as an oxidant.19-23 It was demonstrated that chemical oxidative polymerization using metal salts such as tetrachloroaurate, silver nitrate, and palladium(II) chloride (PdCl2), which act both as oxidant and as a source of metal atoms, yielded well-dispersed metal nanoparticles in bulk conducting polymers. Selvan et al.19 polymerized pyrrole with tetrachloroauric acid as an oxidant in the presence of PS-b-poly(2-vinylpyridine) copolymer micelles dispersed in toluene, which led to the fabrication of PPy-Au nanocomposites. Chen et al.20 and the present authors21 have demonstrated a onestep facile and versatile synthetic route to PPy-Ag nanocomposites by chemical oxidative polymerization using silver nitrate as an oxidant in aqueous media. Freund et al.22 suggested that PdCl2 acts as an efficient oxidant for pyrrole to form PPy-Pd composite in aqueous media. More recently, Vasilyeva et al.23 described the synthesis of PPy-Pd nanocomposites via direct redox reaction between Pd(II) acetate and pyrrole in acetonitrile. In the present work, a new approach to the synthesis of PPy-noble metal nanocomposite-coated latex particles is developed; we describe the one-step facile coating of PS seed particles (15) Gangopadhyay, R.; De, A. Chem. Mater. 2000, 12, 608. (16) (a) Tian, Z. Q.; Lian, Y. Z.; Wang, J. Q.; Wang, S. J.; Li, W. H. J. Electroanal. Chem. 1991, 308, 357. (b) Drelinkiewicz, A.; Hasik, M.; Kloc, M. Catal. Lett. 2000, 64, 41. (c) Kitani, A.; Akashi, T.; Sugimoto, K.; Ito, S. Synth. Met. 2001, 121, 1301. (d) Radford, P. T.; Creager, S. E. Anal. Chim. Acta 2001, 449, 199. (e) Pillalamarri, S. K.; Blum, F. D.; Tokuhiro, A. T.; Bertino, M. F. Chem. Mater. 2005, 17, 5941. (17) Khan, A. M.; Perruchot, C.; Armes, S. P.; Randall, D. P. J. Mater. Chem. 2001, 11, 2363. (18) Mangeney, C.; Bousalem, S.; Connan, C.; Vaulay, M.-J.; Bernard, S.; Chehimi, M. M. Langmuir 2006, 22, 10163. (19) Selvan, S. T.; Spatz, J. P.; Klok, H.-A.; M€oeller, M. Adv. Mater. 1998, 10, 132. (20) (a) Chen, A.; Kamata, K.; Nakagawa, M.; Iyoda, T.; Wang, H.; Li, X. J. Phys. Chem. B 2005, 109, 18283. (b) Chen, A.; Wang, H.; Li, X. Chem. Commun. 2005, 1863. (21) Fujii, S.; Aichi, A.; Akamatsu, K.; Nawafune, H.; Nakamura, Y. J. Mater. Chem. 2007, 17, 3777. (22) Freund, M. S.; Henry, M. C.; Hsueh, C. C.; Timko, B. P. J. Electrochem. Soc. 2001, 148, D155. (23) Vasilyeva, S. V.; Vorotyntsev, M. A.; Bezverkhyy, I.; Lesniewska, E.; Heintz, O.; Chassagnon, R. J. Phys. Chem. C 2008, 112, 19878.
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Article
Figure 1. Schematic representation of PS latex particle coating with a thin overlayer of polypyrrole-palladium (PPy-Pd) nanocomposite by chemical oxidative polymerization, using PdCl2 salt as an oxidant. Scheme 1. Chemical Oxidative Polymerization of Pyrrole Using Palladium(II) Chloride
with PPy-Pd nanocomposite by chemical oxidative polymerization of pyrrole using PdCl2 as an oxidant in aqueous media (Scheme 1 and Figure 1). To the authors’ knowledge, this is the first report of a one-step coating of polymeric seed particles with conducting polymer-metal nanocomposites. Particular attention is given to characterization of the colloidal stability, nanomorphology, and solid-state conductivity of the core-shell particles, using optical microscopy, laser diffraction particle analysis, electron microscopy, and the four-point probe conductivity measurements. In addition, PPy-Pd nanocomposite hollow capsules were obtained by extraction of the PS core. The activity of the coreshell latex particles containing Pd nanoparticle catalysts in the shell was evaluated using a Suzuki cross-coupling reaction in aqueous media as a model reaction.
Experimental Section Materials. Unless otherwise stated, all materials were guaranteed reagent grade. Poly(N-vinylpyrrolidone) [PNVP; nominal molecular weight = 360 000], palladium(II) chloride (PdCl2, 99.9%), p-methylphenylboronic acid (96%), and p-(trifluoromethyl)phenylboronic acid were obtained from Wako Chemicals. p-Bromoacetophenone (97%), p-bromotoluene (99%), and p-bromoanisole (97%) were obtained from Tokyo Chemical Industry Co., Japan. Styrene, isopropanol (IPA), 2,20 -azobis(isobutyronitrile) (AIBN, 98%), sodium chloride (NaCl, 99.5%), hydrated ferric chloride (FeCl3 3 6H2O), and aluminum oxide (activated, basic, Brockmann 1, standard grade, ∼150 mesh, 58 A˚) were obtained from Sigma-Aldrich and were used without further purification. Pyrrole (98%) was also obtained by Sigma-Aldrich and purified by passing through a column of the activated basic alumina prior to storage at -15 °C before use. Cross-linked PS particles with a number-average diameter of 5.2 μm were purchased from Microbeads, Norway. The cross-linked PS particles are stabilized with an anionic sodium dodecyl sulfate surfactant in combination with a cellulosic stabilizer.24 Deionized water (
