**2.3 PPy-metal composite films**

134 Electropolymerization

PPy films is achieved in only one step using an aqueous medium containing saccharin and Py. Similarly, Bazzaoui et al. (2006b) obtained PPy coating on Fe by the use of an aqueous

Various techniques have been employed to prepare composite films of PPy with pure metals, oxides (pure as well as mixed valence ones), anions (simple as well as complex ones), etc. It is difficult to to describe all of them here. However, efforts would be made to include as much as possible those techniques which have repeatedly been used in

The functionalized PPy films can be obtained in mainly two ways. The first involves the polymerization of a functionalized monomeric molecule. The second technique makes use of

The functionalization of a monomer Py molecule can be carried out by introducing a substituent on the nitrogen atom or on its 3, 4 positions. N-substituted pyrroles are excellent electropolymerizable monomers for the preparation of polymer films containing active centres. A series of Py-substituted pyridine, 2,2'-bipyridine, l,l0-phenanthroline and 2,2':6-2" terpyridine ligands and their corresponding Ru(II), Fe(II), Re(I), Cu(I), Cu(II), Co(II), Ni(II), Rh(III), Mn(III), Pd(II), Zn(II), Ag(I) and Ir(III) complexes have been synthesized. In most cases, films of PPy bearing these complexes can be obtained by anodic electropolymerization of the monomer. There are also two types of Py-substituted metallic tetraphenylporphyrins (M=Ni+, Zn+, Co+, Cu2+, Mn+2); one involving the connection of the Py group directly on the phenyl group, the other through a flexible chain. The efficiency of electropolymerization seems to be lower for complexes in which the Py is connected directly to the macrocycle. With this configuration, steric hindrance and mesomeric effects limit the efficiency of the electrochemical polymerization process (Deronzier & Moutet, 1996). Recently, Diab and Schuhmann (2001) synthesized Mn+2-meso-tetracarboxyphenylporphyrin linked via a spacer chain to a Py unit using electropolymerization method. Abrantes et al. (2000) prepared substituted Mn and Fe metalloporphyrins with two Py groups bonded in lateral chains through the

The literature suggests that 3-substituted Py molecules would require a less anodic potential for their oxidation and would be more conductive than the N-substituted PPy. However, Py monomers substituted at the 3-position with metallic complexes are limited in literature; only two examples are cited here, the first one involves ferrocene derivatives, and the

The functionalized PPy films can also be obtained by carrying out electropolymerization of Py in a medium containing an anionic species as the supporting electrolyte. Following this procedure PPy has been doped by several metallic tetraphenylporphyrin, tetrasulphonates or carboxylates (CoII, FeII, MnII) and metallic phthalocyanine, mono and tetrasulphonates (CoII, FeII, CuII). Some other complexes have also been incorporated by this technique. For instance, PPy films containing cobalt salts, thiomolybdate anions, nickel and palladium complexes of maleonitriledithiol, heteropolyanions, a chromium oxalate complex, an iron trisphenanthroline sulphonic acid complex or ferri/ferrocyanide and Prussian blue have been prepared by electropolymerization in a medium containing these anions as supporting electrolyte. All these works has been cited in (Deronzier & Moutet, 1996). It is expected that the polymer frame would be formed around the trapped anion and retains it strongly.

second one an entwining phenanthroline Cu(I) complex (Deronzier & Moutet, 1996).

solution of 0.1M sodium saccharinate and 0.5M Py.

the anion exchange properties of the oxidized form of the polymer.

electropolymerization under potentiodynamic condition.

preparation of different composites.

**2.2 Functionalized PPy film** 

Several methods have been reported on modification of conducting PPy by metal catalysts (Juttner et al., 2004). They can be put into the following four main categories:


Methods, 2 and 3, results a homogeneous distribution of the metal within the whole PPy film.

4. PPy-metal nanoparticle composites were electro-co-deposited from a solution containing Py, metal salt as source of metal ions, a suitable neutral salt as supporting electrolyte and small amount of a suitable additive to achieve stability of the metal complex salt. For examples, PPy-Au (Rapecki et al., 2010), PPy/Ni (Haseko et al., 2006), PPy/Fe (Chipara et al., 2007), PPy/Co (Ikeda et al., 1983) and Pd/PPy/foam-Ni (Sun et al., 2010) are some examples of nano composites obtained by this technique.
