**2.6 Adsorption of methylene blue (MB) dye**

24 Electropolymerization

constituents. The deposited polymer film was subjected to different experimental tests to

Scanning electron microscopic (SEM) analysis was carried out on the as-prepared polymer film deposited on Pt-working electrode surface using a JSM-T20 Electron Probe Microanalyzer (JEOL, Tokyo, Japan). The X-ray diffraction analysis (XRD) (Philips 1976 Model 1390, Netherlands) was operated under the following conditions that were kept constant for all the analysis processes: X-ray tube, Cu; scan speed, 8 deg min-1; current, 30

The amount of polymer electrodeposited on the electrode surface can be determined directly from the peak current density (ip) [Sayah et al, 2010] therefore, The peak current density (ip) is proportional to the electropolymerization rate (RP,E) at a given concentration of the monomer and H2SO4. The kinetic equation was calculated from the value of anodic peak current density (ip) measured at each concentration during the electroformation of polymer. In this case, we used the value of (ip) instead of (RP,E). Therefore, the kinetic rate law can be

 RP,E = ip= kE [Acid]a[Monomer]b (1) where a and b are the reaction orders with respect to acid and monomer concentrations respectively, and kE is the kinetic rate constant calculated from the electrochemical

The electropolymerization were performed with a three-electrode system mention above in section. Using a potential range -0.2 ~ +0.9V (vs.SCE) with a scan rate of 25 mVs-1. Finally, a POCP modified Pt-electrode was ready for further experiments. the thickness of the polymer films were controlled by varying the no of repetitive cycles from 3 to 15 cycles as the thickness of polymer films were positively correlated with the no of repetitive cycles.

**2.4 Determination of the kinetic rate law of the electropolymerization reaction** 

**H-NMR spectroscopy, TGA and elemental analysis**  UV-vis. absorption spectra of the prepared polymer sample was measured using Shimadzu UV spectrophotometer (M160 PC) at room temperature in the range 200-400 nm using dimethylformamide (DMF) as a solvent and reference. IR measurements were carried out using shimadzu FTIR-340 Jasco spectrophotometer (Japan) by KBr pellets disk technique. 1H-NMR measurements were carried out using a Varian EM 360 L, 60-MHz NMR spectrometer. NMR signals of the electropolymerized sample were recorded in dimethylsulphoxide (DMSO) using tetramethylsilane as internal standard. TGA of the obtained polymer was performed using a Shimadzu DT-30 thermal analyzer (Shimadzu, Kyoto, Japan). The weight loss was measured from ambient temperature up to 600 ºC, at the rate of 20 ºC min-1 and nitrogen 50cc min-1 to determine the degradation rate of the polymer. Elemental analysis was carried out in the micro-analytical center at Cairo University (Cairo,

**2.3 Characterization of the electro-prepared polymers** 

Egypt) by oxygen flask combustion and dosimat E415 titrator (Metrohm).

**2.3.2 Scanning electron microscopy and X-ray diffraction** 

mA; voltage, 40 kV; preset time, 10 s.

**2.5 Potentiometric data and pH measurements** 

expressed as follows

measurements.

characterize it.

**2.3.1 UV-vis, IR and 1**

Different concentrations of MB solution was added to 0.05gm of POHP previously deposited potentiodynamically on Pt electrode surface in 50 ml measuring flask and with continuous stirring for 2 h and then filtration. The concentration of dye in the filtrate was determined at different time intervals by using UV-Vis spectrophotometer at 664 nm for MB dye, the equilibrium uptake was calculated according to the following equation:

$$\mathbf{Q} \mathbf{\bar{c}} = (\mathbf{C}\_o \mathbf{\bar{c}} \mathbf{C}\_e) \mathbf{V} \;/\; W \tag{2}$$

Where Qe is the amount adsorbed at equilibrium, Co is the initial concentration of dye, Ce is the equilibrium conc. of the dye solution, V is volume of solution (L) and W is the mass of polymer taken for the experiment (mg)

The percentage removal of dye was calculated as

$$\text{Percentage removal} = 100 \left( \text{C}\_{\text{o}} \text{-C}\_{\text{e}} \right) / \text{ C}\_{\text{o}} \tag{3}$$

Electropolymerization of Some Ortho-Substituted Phenol Derivatives on Pt-Electrode from

SEC where the presence of (Cl and OH) make the oxidation process difficult.

Aqueous Acidic Solution; Kinetics, Mechanism, Electrochemical Studies and Characterization of… 27

other monomer molecule via head-to-tail coupling to form predominantly a para-linked dimeric radical and so on to form oligomer and polymer film; this film is a chain of isolated aromatic rings (polyethers) without π-electrons delocalization between each unit as shown in schemes (1 and 2). The oxidation occurs at more positive values ~ + 863 and +622 mV vs.

On reversing the potential scan from, the reversing anodic current is very small indicating the presence of polymer layer adhered to the Pt-surface [Sayyah et al, 2010]. One cathodic peak (II') was found which could be ascribed to the reduction of the formed polymer films. The effects of repetitive cycling on Pt- electrode in aqueous solution containing 0.6M H2SO4 with and without monomer at 303 K are shown in Fig. 4 (a-c). The data reveal that, in absence of monomer, the repetitive cycling show the oxidation peak (I) only. The current of this peak (ipI) is almost the same and not affected with cycling up to 6 cycles (c.f. fig. 4 (a)).

Fig. 4. Repetitive cycling of electropolymerization from solution containing 0.6M H2SO4 at

303 K with scan rate 25 mVs-1
