conducting polymer-silver composite (review)

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It is an review article on conducting polymer metal composites

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  • Chemical Papers 67 (8) 814848 (2013)DOI: 10.2478/s11696-012-0304-6

    REVIEW

    Conducting polymersilver composites

    Jaroslav Stejskal*

    Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, 162 06 Prague 6, Czech Republic

    Received 10 July 2012; Revised 22 October 2012; Accepted 25 October 2012

    Preparations of hybrid composites composed of two conducting components, a conducting polymerand silver, are reviewed. They are produced mainly by the oxidation of aniline or pyrrole withsilver ions. In another approach, polyaniline or polypyrrole are used for the reduction of silverions to metallic silver. Other synthetic approaches are also reviewed. Products of oxidation ofaniline derivatives, including phenylenediamines, are considered. Morphology of both the conductingpolymers and the silver in composites displays a rich variety. Conductivity of the composites seldomexceeds 1000 S cm1 and seems to be controlled by percolation. Interfacial eects are also discussed.Potential applications of hybrid composites are outlined; they are likely to extend especially toconducting inks, printed electronics, noble-metal recovery, antimicrobial materials, catalysts, andsensors.c 2012 Institute of Chemistry, Slovak Academy of Sciences

    Keywords: polyaniline, polypyrrole, poly(o-phenylenediamine), poly(p-phenylenediamine), silver,silver nanoparticles, hybrid composites, conductivity

    Introduction 815Polyanilinesilver composites 816Oxidation of aniline with silvercompounds 816Physical acceleration 817Chemical acceleration 818Morphology of composites 818

    Reduction of silver ions with PANI 820Eect of counter-ions 821Silver complexes 821Morphology of PANI 821PANI lms and coatings 821

    Preparation of PANI in the presence ofsilver particles 822Reduction of silver ions with externalreductants in the presence of PANI 823Mixing of PANI and silver particles 823More complex systems 823Two reductants of silver ions 823Two oxidants of aniline 824Ternary composites 824Colloids 824

    Polypyrrolesilver composites 824

    Oxidation of pyrrole with silvercompounds 824Morphology of composites 825

    Reduction of silver ions with PPy 826Preparation of PPy in the presenceof silver particles 827Reduction of silver ions with externalreductants in the presence of PPy 827Mixing of PPy and silver particles 827More complex systems 827Multiple reactants 827Ternary composites 827Colloids 828

    Related polymersilver composites 828Poly(p-phenylenediamine) 829Poly(m-phenylenediamine) 829Poly(o-phenylenediamine) 829Substituted polyanilines 830Polymethylanilines 830Poly(o-methoxyaniline) 830Poly(2,5-dimethoxyaniline) 830Poly(4-aminodiphenylamine) 830Sulfonated polyaniline 830

    *Corresponding author, e-mail: stejskal@imc.cas.cz

  • J. Stejskal/Chemical Papers 67 (8) 814848 (2013) 815

    Aniline oligomers 830Other related systems 831

    Conductivity 831Conductivity of polyanilinesilvercomposites 832Direct preparation 832Reduction with polyaniline 833Other syntheses 833

    Conductivity of polypyrrolesilvercomposites 834Direct preparation 834Reduction with polypyrrole 834

    Conductivity of other systems 834

    Temperature dependenceof conductivity 835Deprotonation phenomena 835

    Applications 835Antimicrobial activity 835Bioapplications 836Catalysis and electrocatalysis 836Conducting composites 836Sensors 837Silver recovery and water-treatment 837Surface-enhanced Raman scattering 837Other uses 837

    Conclusions 837References 838

    Introduction

    Composites of conducting polymers, such as poly-aniline (PANI) and polypyrrole (PPy), and silver con-tain two types of electric conductors. Conductingpolymers are organic semiconductors, silver is a metal-lic conductor. Such composites are called here as hy-brid because they combine dierent electrical featuresof the parent constituents. Both the conducting poly-mers and silver display a variety of morphologies onthe nanoscale. Their nature, distribution within thecomposites, and interfacial phenomena are expectedto control or aect their electrical properties. In addi-tion to electrical features, many potential applicationsrely on chemical, electrochemical, optical, and otherphysical properties.Early studies on polyacetylene have illustrated the

    potential of conducting polymers to compete withmetals in the conduction of electric current, and con-ductivities comparable to those of metals have beenreported. Limited stability of polyacetylene under am-bient conditions shifted the research interest to otherconducting polymers. Most of the currently-used con-ducting polymers, such as PANI or PPy, have a typi-cal conductivity of the order of 1 S cm1 (Stejskal &Gilbert, 2002; Blinova et al., 2007b), i.e. at the semi-conductor level, four to ve orders of magnitude lowercompared with metals such as mercury, copper, sil-ver, or gold. Various ways to further enhance the con-ductivity have therefore been sought. Processing ofPANI in m-cresol in the presence of camphorsulfonicacid leads to the conductivity exceeding 1000 S cm1

    (Cao et al., 1993; Pron & Rannou, 2002). Polyani-line produced in emulsion polymerization was also re-ported to reach a room-temperature conductivity ex-ceeding 1000 S cm1 (Lee et al., 2006); the follow-upstudies, however, are missing. Mechanical orientationof conducting-polymer chains is another way demon-strating the potential of conducting polymers as elec-tric conductors. Virtually all papers report the con-ductivity determined in the dry state or at ambienthumidity. It has recently been proposed that, when

    immersed in acidic aqueous media, the eective con-ductivity of PANI may exceed 1000 S cm1 due tothe contribution of proton conduction (Stejskal et al.,2009a).Preparation of composites is an alternative way to

    increase the conductivity of these polymers. For thatreason, organic conducting polymers have been com-bined with inorganic conducting materials, such ascarbon nanotubes, graphene, or graphite (Tchmutinet al., 2003; Konyushenko et al., 2006; Jimnez, et al.,2010; Spitalsky et al., 2010). Noble metals, however,are the most promising candidates for this task. Silverhas received most attention due to its highest conduc-tivity among metals, 5.6 105 S cm1 at room tem-perature, and relatively low cost compared to othernoble metals.Electrical properties of hybrid composites com-

    posed of two conducting components are determined:(i) by composition, i.e. by the mutual proportions ofthe organic semiconductor and the metal; (ii) by themorphology of both components; and (iii) by inter-facial phenomena, such as the presence of insulat-ing barriers between both conducting phases (Efros& Shklovski, 1976; Baibarac et al., 1999; Tchmutinet al., 2003). Conducting polymers generally pro-duce globules, nanobres, nanotubes, microspheres,and various hierarchical nanostructures (Sapurina& Stejskal, 2008, 2010; Stejskal et al., 2010; Zu-jovic et al., 2011b). Silver may be present as micro-spheres, nanocubes, nanobres or nanowires, nanorodsor nanocables, and various two- and three-dimensionalobjects (Nadagouda & Varma, 2007; Chang et al.,2011; Chen & Liu, 2011a). It is of interest to notethat the richness of morphologies displayed is an in-herent feature of both the conducting polymers andsilver. The size of objects becomes important when itdiminishes to the submicrometre level and the interfa-cial area increases. Various interfacial phenomena maythen become important.It has to be stressed, however, that the conduc-

    tivity of composites need not be the primary goalin the potential applications. Conducting polymers

  • 816 J. Stejskal/Chemical Papers 67 (8) 814848 (2013)

    Fig. 1. Oxidation of aniline with silver nitrate in an acidic aqueous medium yields a composite of PANI and silver. Nitric acid isa by-product (Blinova et al., 2009; Bober et al., 2011a).

    are stimuli-responsive. They change their electricaland optical properties depending on external impulses,such as a change in acidity, humidity, temperature, thepresence of oxidants or reductants, etc. The respon-sivity of conducting polymers can be improved by thepresence of noble metals and this property may be-come useful in sensors. Conducting polymers manifestthemselves as oxidants or reductants and can thereforeparticipate in redox reactions. Corrosion protectionand its improvement may serve as such an example(Li et al., 2012b) although the cost of such compos-ites would be rather prohibitive. Widely used catalyticproperties of noble metals can be enhanced by the in-teraction with conducting polymers (Sapurina & Ste-jskal, 2009). Optical properties of metal nanoparticlesare well known since the times of Faraday (Kelly etal., 2003; Stamplecoskie & Scaiano, 2011) and may beaected by the interaction with conducting polymers.Synergetic eect of the two components may becomeimportant in pharmacology and medicine.There are four basic strategies for the prepara-

    tion of the composites of conducting polymers andsilver: (i) a single-step preparation, where a corre-sponding monomer, typically aniline or pyrrole, is ox-idized with a silver cation to produce a composite ofconducting polymer and silver. This is the most im-portant approach; (ii) a conducting polymer is pre-pared by conventional oxidative polymerization andsubsequently used for the reduction of silver salts tosilver; (iii) in another two-step process, the compo-nents are prepared consecutively. Silver particles areprepared at rst, and a conducting polymer is syn-thesized afterwards in their presence. Alternatively,a conducting polymer is synthesized at rst and sil-ver nanoparticles subsequently with the help of ex-ternal reductants; (iv) nally, both components, theconducting polymer and silver particles, are preparedseparately and simply mixed or blended. Some spe-cial approaches

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