**2.2.2 Procedure**

Potentiodynamic cyclic voltammetry measurements during the formation of the polymer films on the surface of the working electrode was carried out in the electrochemical cell shown in Fig.(1).The cell was filled with the test solution (aqueous solution containing H2SO4 as supporting electrolyte, and monomer). The working and counter electrodes were introduced in the cell. The reference electrode was attached to the cell by U-shaped salt bridge (SB) ended with a fine capillary tip (Luggin –Harber probe)wherein the reference electrode was positioned very closed to the working electrode to minimize the over potential due to electrolyte resistance .The bridge was filled with the test solution. Before and during measurements a current of pure nitrogen gas was bubbled in the test solution to remove dissolved oxygen.

Electrochemical experiments were performed using the potentiostat / Galvanostat Wenking PGS 95. i-E curves were recorded by computer software from the company (Model ECT).

Except otherwise stated ,the potential was swept linearly from the starting potential vs. (SCE) into the positive direction up to a certain anodic potential with a given scan rate and then reversed with the same scan rate up to the starting cathodic potential.

For each run, freshly prepared solutions as well as a cleaned set of electrodes were used. All experiments were conducted at a given temperature (± 0.5 oC) with the help of circular water thermostat. After polymer film formation, the working electrode was withdrawn from the cell, rinsed thoroughly with doubly distilled water to remove any traces of the medium

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

Fig. 2. Two electrode cell used foe potentiometric measurements.

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

 Qe= (Co-Ce) V / W (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

Percentage removal = 100 (Co-Ce) / Co (3)

dye, the equilibrium uptake was calculated according to the following equation:

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

polymer taken for the experiment (mg)

The percentage removal of dye was calculated as

pH 211).

Aqueous Acidic Solution; Kinetics, Mechanism, Electrochemical Studies and Characterization of… 25

Potentiometric data were recorded by using (two electrodes system) shown in Fig.(2). Where the working electrode is the prepared POCP modified Pt-electrode with different thickness and the reference electrode is SCE. The potential of system (the electrode and the tested buffer solution) were recorded after immersion for 5 minute by using Avometer DT3900, then the polymer electrode removed from the solution and rinsed with bidistilled water before immersing in anther buffer solution for the next measurement All pH measurements were performed using the modified electrode as the pH sensor and SCE is the reference electrode. The actual pH of solution was determined by pH meter (HANNA Instruments

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

#### **2.3 Characterization of the electro-prepared polymers 2.3.1 UV-vis, IR and 1 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, Egypt) by oxygen flask combustion and dosimat E415 titrator (Metrohm).

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

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

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

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 expressed as follows

$$\mathbf{R}\_{\rm P,E} = \mathbf{i}\_{\rm P} = \mathbf{k}\_{\rm E} \, [\mathbf{A} \, \text{cid}]^{\rm a} [\mathbf{M} \, \text{monomer}]^{\rm b} \tag{1}$$

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 measurements.

#### **2.5 Potentiometric data and pH measurements**

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.

Potentiometric data were recorded by using (two electrodes system) shown in Fig.(2). Where the working electrode is the prepared POCP modified Pt-electrode with different thickness and the reference electrode is SCE. The potential of system (the electrode and the tested buffer solution) were recorded after immersion for 5 minute by using Avometer DT3900, then the polymer electrode removed from the solution and rinsed with bidistilled water before immersing in anther buffer solution for the next measurement All pH measurements were performed using the modified electrode as the pH sensor and SCE is the reference electrode. The actual pH of solution was determined by pH meter (HANNA Instruments pH 211).

Fig. 2. Two electrode cell used foe potentiometric measurements.
