Document Type : Original Article (Special Issue)

Author

Department of Chemistry, College of Science, University of Thi-Qar, Iraq

Abstract

The electrochemical manner was investigated for poly vinyl alcohol -g- succinic acid by using the cyclic voltammetry mechanism. Such an investigation mostly concentrates on the expected properties of the doped polymers with different doping ratios of Malachite green (0.03, 0.06, 0.09, 0.12, and 0.15) %wt. This is specific by the electrons transmit between the dopants and both polymers, which visibly show the appearance of oxidation- reduction peak accompanied log increase in electrical current Ip as applied potential changer. The heights of Ip oscillate due to the change in see rate ν. The results of linear of relationships between Ip and ν1/2specificed that the electron transfer was a process of one electron transfer

Graphical Abstract

Electrochemical Investigation of Poly Vinyl Alcohol-G-Succinic Acid Doped with Malachite Green

Keywords

Main Subjects

Introduction

Cyclic voltammetry is a very important electrochemical technique. It can be used to study the redox manner of compounds and probe coupled chemical reactions, in particular to determine mechanisms and rates of oxidation-reduction reactions.

The study of cyclic voltammetry with different scan rates offers much acquaintance about electron transfer, kinetics, and transport properties of electrolysis reaction. The current labor is considered as a function of the linear potential applied. Such a current divergence that results, when the electrode potential is numerous, can provide a valuable prudence into the reactions that occur at the electrode surface [1].

Cyclic voltammetry is a method for the electrochemical manner of a system. It was first reported in 1938 and described theoretically by Randles [2].

Cyclic voltammetry is the most vastly used technicality to acquire qualitative information about electrochemical reactions. The power of cyclic voltammetry results from its ability to rapidly provide considerable information on the thermodynamics of redox processes, on the kinetics of heterogeneous electron-transfer reactions, and uncoupled chemical reactions, or adsorption processes. Cyclic voltammetry is often the initial experimental approach performed in an electro analytical study, since it offers rapid location of redox potentials of the electro active species and convenient evaluation of the effect of media upon the redox [3-4].

The cyclic voltammetry (scanning in forward and back directions) and linear voltammetry (scanning in one direction) are the most widely used techniques to investigate electrode reaction mechanisms. They are easy to apply experimentally and readily available in commercial instruments, and also provide a wealth of mechanistic information. In such experiments, the potential of working electrode is controlled by a potential ramp or one or more potential triangle.

The peak current in a cyclic voltammogram containing only one species is described by Sevcik- Randles [5]:

IP=(2.69x105)n3/2AD1/2ѵ1/2 C*                                 (1)

at 25 °C, where Ip is the peak current, n is the number of electrons transferred, A is the electrode area, D is the diffusion of species, v is the scan rate, and C* is the bulk concentration of species. If the diffusion constants for the oxidized and reduced species are similar, the Eo value (formal potential) can be estimated from the average of Epa and Epc, where Epa is the potential of anodic peak current and Epcis the potential of the cathodic current [6].

Cyclic voltammetry is a useful technique for probing the probing the processes that occur at the electrode-solution interface. This technique is not generally well understood in comparison to other instrumental methods such as spectroscopy and chromatography. It is not uncommon for the experimenter who is performing CV to have a poor understanding of the basic concepts of the technique, such as why the voltammograms have their peculiar shapes [7].

Materials and Methods

The materials tested in this study were polyvinyl alcohol, succinic acid, hydrochloric acid, and malachite green.

Preparation of poly vinyl alcohol copolymer succinic acid (PVA-g-SA)

In a round flask of 250 mL capacity, (13.328 g, 0.0136 mol) of polyvinyl alcohol (PVA) was put which dissolved in 70 mL distilled water, and then (1.6 g, 0.0136 mol) of succinic acid and 2 mL of 1N hydrochloric acid were added and the mixture was stirred at 70 °C for 8 hours [8], after the reaction was completed, we noticed the formation of white color polymer, and the yield was 82% (Scheme 1).

Doping of PVA-g-SA

Doping PVA-g-SA with dye malachite green was carried out by adding the weighted dye to the appropriate weight of polymer (1g), and  then the mixture was dissolved in dimethyl formamide DMF after the prepared directly to give a polymer/dye system containing  (0.03, 0.06, 0.09, 0.12, and 0.15) g wt% of doping reagent malachite green [9]. The mixture was stirred well for 20 minutes to guarantee that the homogenous distribution of dye in the polymer matrix.

Scheme 1: Preparation of poly vinyl alcohol Graft succinic acid (PVA-g-SA)

Electrochemical measurements

Cyclic voltammetry (CV) was carried out in a thermo stated one compartment three -electrode cell. The working electrode was a platinum wire of nominal area 0.0785 cm2. This was controlled by silver-silver chloride as a reference electrode through which no current flows. The auxiliary (secondary) electrode was a platinum wire. Cyclic voltammetry was performed with a DY 2300 Series Potentiostat/Bipotentiostat, potentiostate-galvanostate fully computerized in the processed data analysis.

In cyclic voltammetry (CV), the voltage is linearly varied from initial to final potential values as required, and then directly swept back at the same sweep rate to the initial one. The current response is plotted as a function of voltage rather than time. The species were reduced and oxidized in the manner of reversible reactions. During all measurements Bu4NBF4 was used as a supporting electrolyte.

In cyclic voltammetry, the negative initial potential value was set mostly equal to the final positive one. The scan rate (ν) was varied from 0.1 to1 Vs-1, while the voltage was canned between -2 to 2V. The molar concentration of supporting electrolyte Bu4NBF4 was 0.15 M. The solutions of pure PVA-g-SA and the doped solutions with different weight ratios of malachite green (0.03, 0.06, 0.09, 0.12, and 0.15) wt% were all subjected to cyclic voltammogram, to achieve a comparison with the measured precursor cyclic voltamograms of pure solutions. All measurements were performed at room temperature.

Results and Discussion

The electrochemical behavior of the PVA-g-SA and its doping ratios were established by cyclic voltammetry (CV) for oxidation and reduction at a platinum electrode in DMF at scan rates that ranged from 0.1 to 1 Vs-1 at a potential range of 2 to -2V. At scan rate (ν) 0.05 Vs-1, as an example, one reduction peak was clearly obtained for PVA-g-SA at Epred1=-0.8 V corresponding to the cathodic peak current Ipred1=1.2×10-5A. At the same scan rate and potential range, the cyclic voltammogram shows also a oxidation peak at Epox1=-0.82V corresponding to the cathodic peak current Ipox1=1.5×10-5 A, as displayed in Figure 1.

It is obvious that the reduction and oxidation peaks were shifted to more negative potential values as ν increases accompanied by an increase in the current peak. This behavior is indicated and confirmed by Sevcik-Randles Equation 1.

According to the same Equation 1, which presented the relationship between the peak current Ip and the square root of the scan rate ν½, the following graphic relations are established:

Ip&ν½

Fp&ν

Where, Fp=Ip / ν½ and it is known as current function. Thus, both Fpred (reduction) and Fpox (oxidation) can be computed. Table (1) illustrates the obtained data for the reduction and oxidation states of the PVA-g-SA. Figure 2 represents a linear relationship between Ipred and Ipox with ν½ of PVA-g-SA indicating that the electron transfer is a process of one electron transfer. Figure 3 shows the plot of Fpred and Fpox vs. ν from which it is clear that the Fpred and Fpox are essentially invariant with ν provided that ν>0.1 Vs-1 a condition which isolates the primary electron transfer from the subsequent chemical step. The Fp independence is a diagnostic signal of diffusion-controlled electron transfer at specified potentials beyond the peak potential [10,11].

Figure 1: Cyclic voltammogram for PVA-g-SA at scan rates: (a) 0.05Vs-1, (b) 0.1 Vs-1, (c) 0.2 Vs-1, and (d) 0.5 Vs

 

Table 1: Cyclic voltammogram data of PVA-g-SA at different scan rates

νV.sec-1

ν (Vs-1)1/2

Ipred1 A (10-5)

Fpred1 A/(V.s-1)1/2 (10-5)

Ipox1A (10-5)

Fpox1 A/(V.s-1)1/2 (10-5)

0.05

0.223

1.2

5.381166

1.5

6.726457

0.1

0.316

1.3

4.113924

2

6.329114

0.2

0.447

1.5

3.355705

2.5

5.592841

0.5

0.707

1.8

2.545969

3.7

5.23338

Figure 2: Ipred1 and Ipox1 peaks of reduction and oxidation vs. ν1/2 for PVA-g-SA

Figure 3: Current function Fpred1 and Fpox1 vs. scan rate for PVA-g-SA

Upon doping PVA-g-SA with the dye malachite green, two oxidation peaks and one cathodic peak appeared at the sometime for all doping ratios. It was noticed that the peaks increase in current values as the doping ratios increase. This is probably due to the transfer of electrons from the valence band to the conduction band which causes current growth in value as ν increase [12-13].

Figure 4 shows the cyclic voltammogram of (0.03%) doping of PVA-g-SA at a potential range of 2 to -2V at different scan rates. At scan rate 0.05 Vs-1 the ratio exhibited two oxidation peaks, the first oxidation peak appeared at Epox1= -0.45V corresponding to anodic peak current Ipox1=1.8 x 10-5 A, while the second peak Epox2 = -1V was corresponded to the anodic peak current Ipox2=3×10-5 A. At the same scan rate and potential range, the cyclic voltammogram shows also are reduction peak at Epred= -0.9V with peak cathodic current of Ipred=1.3× 10-5A, and at scan rate of 0.2 Vs-1, 0.5 Vs-1, and 1Vs-1, a new oxidation peak was observed at Epox= -0.0.45V with anodic peak current of Ipox=(2-3.5)×10-5A shifted to higher values as ν increases. It is obvious that the oxidation potential peaks are shifted to more positive values as ν increases.

Figure 4: Cyclic voltammogram for 0.03% doping of PVA-g-SA at scan rates: (a) 0.05Vs-1, (b) 0.1 Vs-1, (c) 0.2 Vs-1, and (d) 0.5 Vs-1

The results are presented in Table 2. A linear relationship was obtained between Ip and ν1/2 indicating one electron transfer [14-15], as shown in Figures 5 and 6. While Figures 7 and (8) reveal the relationship between Fpox vs. ν indicating the same condition Figure 3 for isolation between the primary electron transfer and that of subsequent chemical step.

Table 2: Cyclic voltammogram data of 0.03% doping of PVA-g-SA at different scan rates

νV.sec-1

ν (Vs-1)1/2

Ipred1 A (10-5)

Fpred1 A/(V.s-1)1/2 (10-5)

Ipox1A (10-5)

Fpox1 A/(V.s-1)1/2 (10-5)

Ipox2A (10-5)

Fpox2 A/(V.s-1)1/2 (10-5)

0.05

0.223

1.3

5.829596

1.8

8.071749

3

13.45291

0.1

0.316

1.6

5.063291

2

6.329114

3.7

11.70886

0.2

0.447

1.7

3.803132

2.6

5.816555

4.5

10.06711

0.5

0.707

2

2.828854

3.5

4.950495

6.3

8.910891

 

Figure 5: Ipred1 peak of reduction vs. ν1/2 for 0.03% doping of PVA-g-SA

 

Figure 6: Ipox1 and Ipox2 peaks of oxidation vs. ν1/2 for 0.03% doping of PVA-g-SA

 

Figure 7: Current function Fpred1 vs. scan rate for 0.03% doping of PVA-g-SA

Figure 8: Current function Fpox1 and Fpox2 vs. scan rate for v0.03% doping of PVA-g-SA

The cyclic voltammogram of (0.06%) doping of PVA-g-SA in DMF at scan rate 0.05 Vs-1 and potential range from 2 to -2. Figure (9) shows two oxidation peaks at Epox1= -0.4V and Epox2= -1.2V with peak oxidation current of Ipox1 = 2×10-5A and Ipox2 = 3.3×10-5A, respectively. Also, there is a decreased peak at Epred= -0.74V with a peak reduction current of Ipred = 2.2×10-5A.

Figure 9: Cyclic voltammogram for 0.06% doping of PVA-g-SA at scan rates: (a) 0.05Vs-1, (b) 0.1 Vs-1, (c) 0.2 Vs-1, and (d) 0.5 Vs-1

 

As mentioned before, the same trend was obtained at other scan rates, 0.1V-1, 0.2V-1, and 0.5Vs-1 a new oxidation peak observed at Epox= -0.5V with anodic peak current Ipox=(2.2-4.2) × 10-5A. The oxidation peaks potential are shifted to more positive values as ν increases, while the reduction peak shifted to higher negative values, as displayed in Figure 9.

The corresponding results were summarized in Table 3, again a linear relationships between both Ipred and Ipox with ν1/2 were detected, that the electron transfer is a process of one electron as shown in Figures 10 and 11, while Figures 12 and 13 indicate the relationships between Fp with ν for both oxidation and reduction conforming the same characteristics as mentioned before 0.03%.

 

Table 3: Cyclic voltammogram data of 0.06% doping of PVA-g-SA at different scan rates

νV.sec-1

ν (Vs-1)1/2

Ipred1 A (10-5)

Fpred1 A/(V.s-1)1/2 (10-5)

Ipox1A (10-5)

Fpox1 A/(V.s-1)1/2 (10-5)

Ipox2A (10-5)

Fpox2 A/(V.s-1)1/2 (10-5)

0.05

0.223

2.2

9.865471

2

8.96861

3.3

14.79821

0.1

0.316

2.4

7.594937

2.2

6.962025

4

12.65823

0.2

0.447

3

6.711409

2.8

6.263982

5

11.18568

0.5

0.707

3.8

5.374823

4.2

5.940594

6.7

9.476662

Figure 10: Ipred1 peak of reduction vs. ν1/2 for 0.06% doping of PVA-g-SA

Figure 11: Ipox1 and Ipox2 peaks of oxidation vs. ν1/2 for 0.06% doping of PVA-g-SA

Figure 12: Current function Fpred1 vs. scan rate for 0.06% doping of PVA-g-SA

Figure 13: Current function Fpox1 and Fpox2 vs. scan rate for 0.06% doping of PVA-g-SA

 

Figure 14 displays the cyclic voltammogram of (0.09%) doping of PVA-g-SA at a potential range of 2 to -2Vat different scan rates, while the results of all cyclic voltammogram data are collected in Table 4. It is concluded that as the percentage of doping increases the resultant currents increase gradually indicating more electron transfer occurrence. The cyclic voltammogram of (0.09%) doping of PVA-g-SA in DMF was at scan rate of 0.05 Vs-1 and potential range from 2 to -2. There are two oxidation peaks at Epox1 = -0.6V and Epox2= -1.1V with peak oxidation current Ipox1= 2.4×10-5A and Ipox2 = 3.5×10-5A, respectively. Also, a reduction peak was indicated at Epred= -0.7 V with a peak reduction current Ipred = 2.5×10-5A.

Figure 14: Cyclic voltammogram for 0.09% doping of PVA-g-SA at scan rates: (a) 0.05Vs-1, (b) 0.1 Vs-1, (c) 0.2 Vs-1, and (d) 0.5 Vs-1

As an example, Figures 15 and 16 illustrate once more linear relationships for reduction and oxidation processes giving rise to one electron transfer as well as the same trend exhibited in Figures 17 and 18.

 

Table 4: Cyclic voltammogram data of 0.09% doping of PVA-g-SA at different scan rates

νV.sec-1

ν (Vs-1)1/2

Ipred1 A (10-5)

Fpred1 A/(V.s-1)1/2 (10-5)

Ipox1A (10-5)

Fpox1 A/(V.s-1)1/2 (10-5)

Ipox2A (10-5)

Fpox2 A/(V.s-1)1/2 (10-5)

0.05

0.223

2.5

11.21076

2.4

10.76233

3.5

15.69507

0.1

0.316

3.2

10.12658

2.6

8.227848

4.2

13.29114

0.2

0.447

3.8

8.501119

3

6.711409

5.3

11.85682

0.5

0.707

4.2

5.940594

4.5

6.364922

6.8

9.618105

Figure 15: Ipred1 peak of reduction vs. ν1/2 for 0.09% doping of PVA-g-SA

Figure 16: Ipox1 and Ipox2 peaks of oxidation vs. ν1/2 for 0.09% doping of PVA-g-SA

Figure 17: Current function Fpred1 vs. scan rate for 0.09% doping of PVA-g-SA

Figure 18: Current function Fpox1 and Fpox2 vs. scan rate for 0.09% doping of PVA-g-SA

In comparison with the preceding percentage, the cyclic voltammogram of (0.12%) doping of PVA-g-SA in DMF at scan rate 0.05 Vs-1and potential range from 2 to -2 V indicated two oxidation peaks at Epox1 = -0.5V and Epox2= -1V with peak oxidation current Ipox1 = 2.6×10-5A and Ipox2 = 3.7×10-5A, respectively, as demosntrated in Figure 19. Also, the cyclic voltammogram shows reduction peaks at Epred1= -0.6V with cathodic peak current Ipred = 2.6×10-5A. The oxidation peaks are shifted to more positive values, while the reduction peak shifted to higher negative values as ν increases. This is obvious from figure. The main oxidation and reduction peaks increased linearly as the scan rate was increased from 0.1 to 0.5 Vs-1 indicating more electron transfer on doping. Table 5 illustrates the results of all cyclic voltammogram data of 0.12% doping of PVA-g-SA.

Figures 20 and 21 illustrate the specific relations between Ipred and Ipox with ν1/2 characterized linear relationships, which indicate one electron transfer under a controlled diffusion process. Figures 22 and 23 show the same trend as other preceding percentages between Fpred and Fpox with ν.

Figure 19: Cyclic voltammogram for 0.12% doping of PVA-g-SA at scan rates: (a) 0.05Vs-1, (b) 0.1 Vs-1, (c) 0.2 Vs-1, and (d) 0.5 Vs-1

 

Table 5: Cyclic voltammogram data of 0.12% doping of PVA-g-SA at different scan rates

νV.sec-1

ν (Vs-1)1/2

Ipred1 A (10-5)

Fpred1 A/(V.s-1)1/2 (10-5)

Ipox1A (10-5)

Fpox1 A/(V.s-1)1/2 (10-5)

Ipox2A (10-5)

Fpox2 A/(V.s-1)1/2 (10-5)

0.05

0.223

2.6

11.65919

2.6

11.65919

3.7

16.59193

0.1

0.316

3

9.493671

2.9

9.177215

4.5

14.24051

0.2

0.447

3.7

8.277405

3.2

7.158837

5.7

12.75168

0.5

0.707

5

7.072136

4.8

6.78925

7

9.90099

Figure 20: Ipred1 peak of reduction vs. ν1/2 for 0.12% doping of PVA-g-SA

Figure 21: Ipox1 and Ipox2 peaks of oxidation vs. ν1/2 for 0.12% doping of PVA-g-SA

Figure 22: Current function Fpred1 vs. scan rate for 0.12% doping of PVA-g-SA

Figure 23: Current function Fpox1 and Fpox2 vs. scan rate for 0.12% doping of PVA-g-SA

The cyclic voltammogram of last percentage (0.15%) doping of PVA-g-SA at a potential range of 2 to -2V at different scan rates show the same behavior as given before, which is abbreviated in Figure 24. All related results are written down in Table 6. Figures 25 and 26 display linear relations between Ipred and Ipox with ν1/2 which indicate once more one electron transfer under a controlled diffusion process, while Figures 27 and 28 indicate the relations between Fpred and Fpox with ν.

Figure 24: Cyclic voltammogram for 0.15% doping of PVA-g-SA at scan rates: (a) 0.05Vs-1, (b) 0.1 Vs-1, (c) 0.2 Vs-1, and (d) 0.5 Vs-1

Table 5: Cyclic voltammogram data of 0.15% doping of PVA-g-SA at different scan rates

νV.sec-1

ν (Vs-1)1/2

Ipred1 A (10-5)

Fpred1 A/(V.s-1)1/2 (10-5)

Ipox1A (10-5)

Fpox1 A/(V.s-1)1/2 (10-5)

Ipox2A (10-5)

Fpox2 A/(V.s-1)1/2 (10-5)

0.05

0.223

2.9

13.00448

2.9

13.00448

3.8

17.04036

0.1

0.316

3.6

11.39241

3.3

10.44304

4.9

15.50633

0.2

0.447

4.3

9.619687

4

8.948546

5.8

12.97539

0.5

0.707

5.2

7.355021

5.3

7.496464

7.5

10.6082

Figure 25: Ipred1 peak of reduction vs. ν1/2 for 0.15% doping of PVA-g-SA

Figure 26: Ipox1 and Ipox2 peaks of oxidation vs. ν1/2 for 0.15% doping of PVA-g-SA

Figure 27: Current function Fpred1 vs. scan rate for 0.15% doping of PVA-g-SA

Figure 28: Current function Fpox1 and Fpox2 vs. scan rate for 0.15% doping of PVA-g-SA

Based on comparison, the effect of the different percentages that have been used, it is concluded that 0.15% is the best one among others. Bulk conductivity in doped polymer material is limited by the need for the electrons to jump from one chain to the next, i.e., in molecular terms an intermolecular charge transfer reaction. It is also limited by macroscopic factors such as bad contacts between different crystalline domains in the material [16].

Conclusion

In the study of cyclic voltammetry, the results of a linear relationship between Ipred and Ipox with ν1/2 of all doped poly vinyl alcohol-g-succinic acid (PVA-g-SA) with different ratios of malachite green that the electron transfer was a process of one electron transfer.

Acknowledgments

I would like to extend my deep appreciation and sincere thanks to Professor AnisA.AlNajar. The same goes to technical staff at the department of chemistry for providing the necessary technical assistance and support in the experimental.

Funding

This research did not receive any specific grant from fundig agencies in the public, commercial, or not-for-profit sectors.

Authors' contributions

All authors contributed to data analysis, drafting, and revising of the paper and agreed to be responsible for all the aspects of this work.

Conflict of Interest

There are no conflicts of interest in this study.

ORCID:

Samah Hussein Kadhim

https://www.orcid.org/0000-0001-8782-1028

HOW TO CITE THIS ARTICLE

Samah Hussein Kadhim, Electrochemical Investigation of Poly Vinyl Alcohol -G- Succinic Acid Doped with Malachite Green. J. Med. Chem. Sci., 2022, 5(7) 1265-1280

https://doi.org/10.26655/JMCHEMSCI.2022.7.16

URL: http://www.jmchemsci.com/article_154650.html

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