**2.4 PPy-Oxide composite films**

Sandwich-type composite films of PPy and an oxide (Ox) having composition, PPy/PPy(Ox)/PPy, onto a GC electrode were obtained by a sequential electrodeposition method. For the purpose, two electrolyte solutions (A and B) were used. Solution A contained 0.10M Py and 0.05M K2SO4 and that solution B contained 0.10M Py, 0.05M K2SO4 and 8.33 g L-1 oxide powders. The first layer of PPy (~2.1 μm thick) was obtained onto graphite (G)/GC electrode in solution A by carrying out electrolysis at j (current density) = 5.0 mA cm-2 for 100 s under unstirred condition. After electrolysis, G/PPy electrode was removed from the cell, washed with distilled water, dried in air and then introduced into the cell containing solution B and electrolysis was again carried out at j = 20 mA cm-2 for 200

Polypyrrole Composites: Electrochemical Synthesis, Characterizations and Applications 137

TGA is frequently used to quantify the amount and thermal stability of PPy in the composite and also to know whether there occurs some interaction between PPy and the other constituent of the composite. The TGA curve of the electrochemically synthesized PPy/chitosan composite on Pt electrode in air showed two stages of the weight loss (Yalcinkaya et al., 2010). The first stage of the thermal degradation was observed at 150- 200ºC and was attributed to removal of the dopant molecule (oxalate ion) from the polymer structure. The decomposition of chitosan chain was indicated by minimum weight loss in temperature range 300-370ºC. On the other hand, the maximum weight loss observed at 380- 400ºC was attributed to the degradation and intrerchain crosslink of the composite. The comparison of results of the PPy/chitosan composite with those obtained from chitosan

Similarly, The TGA analysis of SnO2-PPy nanocomposite from 25 to 700ºC exhibited two weight losses (Cui et al., 2011). The first weight loss, in the temperature range of 25-250ºC, attributed to desorption of physisorbed water, while the second in the range of 250-700ºC, attributed to the oxidation of PPy. Bare SnO2 does not show any weight change in the whole temperature range of the investigation, while the pure PPy is burnt off. So, on the basis of weight change before and after the oxidation of PPy, the SnO2 content in the composite was estimated. TGA analyses of the S/PPy composite, bare S and PPy powder indicated (Wang et al, 2006) that S is burnt completely on temperature up to 340ºC, followed by the oxidation of PPy in the second stage on temperature above 340ºC. The weight loss in the second stage was about 40wt% which represents the amount of PPy in the S-PPy composite. TGA measurements were performed in air. The nanocomposites, SnO2-PPy and S/PPy were

The morphology of the composite strongly depends upon the nature as well as the method of preparation. From the SEM analyses of pure PPy and its composites it was observed that morphology of the PPy changed significantly when the composite was formed. As, in the case of the PPy/chitosen composite, the SEM image of composite was significantly different compared to that of PPy (cauliflower-like spherical shape) or chitosan (smooth surface) (Yalcinkaya et al, 2010). On the other hand, HRTEM (High Resolution Transmission Electron Microscope) images of pure PPy and graphene nano sheet (GNS)/PPy composite obtained by chemical method (Zhang et.al., 2011) showed that pure PPy has the amorphous structure, while the PPy is homogenously surrounded by GNS in the composite. The particle size of

The XRD pattern of GNS/PPy exhibited diffraction peaks at 2θ ≈ 24.5°, 26° and 42.8º. The diffraction peaks at 2θ ≈ 24.5° and 42.8º correspond to (002) and (100) planes of graphite like structure while that the peak at 2θ ≈ 26º corresponds to amorphous PPy (Zhang et al., 2011). In the GNS/PPy composite, as GNS percentage increased, the broad peak shifted from 2θ ≈ 26º to 24.8º, implying that interaction occurs between GNS and PPy. The Au/PPy core-shell nanocomposites (Liu and Chuang, 2003) displayed a broad maximum at 2θ ≈ 25.1º (d = 3.5 Å) which was ascribed to the closest distance of approach of the planar aromatic rings of Py

**3. Characterization** 

**3.1 Thermal Gravimetric Analysis (TGA)** 

prepared by chemical polymerization.

**3.2 Scanning Electron Microscopy (SEM)** 

PPy/GNS was found to be smaller than pure PPy.

**3.3 X-Ray Diffraction (XRD)** 

suggests that an interaction occurs between chitosan and PPy.

s under stirred condition so as to obtain a second layer of PPy(Ox) (~16 μm thick). The polymer coated G electrode [G/PPy/PPy(Ox)], so obtained, was washed with distilled water, dried and reintroduced in the former cell containing solution A to electrodeposit the third and final layer of PPy (~4.2 μm thick); electrolysis condition being j = 5.0 mA cm-2, t=200 s, unstirred. Prior to electrodeposition of PPy, the electrolytes (solution A & B) were degassed for 45 min by bubbling Ar and maintained under Ar atmosphere during the electrodeposition process also.

Following similar method several sandwich-type binary composite electrodes of PPy and a mixed oxide belonging to both spinel and perovskite families, namely CoFe2O4 (Singh et al., 2004; Malviya et al., 2005a & b), CuxMn3-xO4 (x = 1.0 – 1.4) (Nguyen Cong et al., 2005; 2002a; 2000), NixCo3-xO4 (x = 0.3 & 1.0) (Nguyen Cong et al., 2002b; 2003, Gautier et al., 2002), La1 xSrxCoO3 (0 ≤ x ≤ 0.4) (Singh et al., 2007a), LaNiO3 (Singh et al., 2007b) and La1-xSrxMnO3 (0 ≤ x ≤ 0.4) (Singh et al., 2007c) were prepared.

#### **2.5 Other composites**

Preparation of PPy/Chitosan: PPy/Chitosan composite films have been electrochemically synthesized on the Pt electrode from an aqueous solution containing 4.0 mg ml-1 chitosan, 0.3M oxalic acid and 5 mmol Py (as monomer) by using cyclic voltammetry method (Yalcinkaya, 2010). A standard 3-electrode cell containing two platinum sheets for use as the counter and working electrodes and an Ag/AgCl (saturated with KCl) electrode as the reference electrode was employed to carry out the electrolysis. The potential was scanned from – 0.60 to + 0.90 V at scan rate of 50 mV s-1. Chitosan is a natural polymer and exhibits characteristic properties, such as chemical inertness, high mechanical strength, biodegradability, biocompatibility, high quality film forming properties and low cost (Yalcinkaya et al., 2010). The proposed structure of the composite is shown in Fig.2.

Preparation of PPy/PANI: 0.02M Py was polymerized in 0.25M H2SO4 solution at 1.0 V under inert atmosphere for 30 min. The electrode was washed with distilled water and dried at 60ºC. 0.1M pure ANI (aniline) was then electrochemically polymerized in 0.25M H2SO4 solution at 0.8 V using PPy coated electrode as working electrode under inert atmosphere for 30 min (Hacaloglu et al., 2009). Similarly, the PANI/PPy composite was prepared. In this case first of all, 0.1M pure ANI solution was polymerized. The polymer films obtained were washed with distilled water several times to remove unreacted monomer as well as the electrolyte and subsequently dried in vacuum.

Fig. 2. Structural representation of the PPy/Chitosan composite
