Electroanalytical studies on the corrosion inhibitionbehavior of guava (Psidium guajava) leaves extracton mild steel in hydrochloric acid

K. K. Anupama • Joseph Abraham

Received: 21 August 2012 / Accepted: 10 November 2012

� Springer Science+Business Media Dordrecht 2012

Abstract Corrosion inhibition behavior of the extract of guava (Psidium guajava)

leaves towards mild steel in HCl media have been studied by polarization, EIS,

adsorption and surface studies at different temperatures. Polarization studies showed

that this extract has good inhibition efficiency (IE) and acts as a mixed-type

inhibitor. As the concentration of the extract increases, the IE also increases,

whereas with respect to temperature the corrosion inhibition shows a reverse trend.

Keywords Mild steel � Acid solutions � EIS � Polarization � Acid inhibition

Introduction

Mild steel being a low cost material is widely used in industries. In petrochemical

industries, corrosion of mild steel is a major problem due to severe attack by

hydrochloric acid when used as a cleaning agent, through chemical reactions [1].

The use of acid is inevitable in industries, as acid solutions are generally used for the

removal of undesirable scale and rust in several industrial processes [2]. Corrosion

inhibition of these metals is mainly achieved through the use of inhibitors. The

inhibitory action of any inhibitor compound is decided by factors such as the

presence of heteroatoms, electronegative functional groups, conjugated double

bonds, presence of aromatic rings, etc. [3].

However, the use of corrosion inhibitors has several limitations as it may be

hazardous when they have to be used somewhere like in a pipeline. The toxic effect

does not only affect living organisms but also poison the environment [2]. The

inhibition performance of plant extracts is normally ascribed to the presence in their

composition of complex organic species such as tannins, alkaloids, nitrogen base,

K. K. Anupama � J. Abraham (&)

Department of Chemistry, University of Calicut, Calicut University P O, Calicut, Kerala, India

e-mail: drabrahamj@gmail.com

123

Res Chem Intermed

DOI 10.1007/s11164-012-0923-0

carbohydrates, and proteins [4, 5]. Several authors have investigated and reported

natural corrosion inhibitors like Areca catechu [1], Clematis gouriana [3], olive

leaves [6], henna [7], Rauvolfia serpentina [8], Andrographis paniculata [9],

Oxandra asbeckii [10], Mentha leaves [11], Zenthoxylum alatum [12], Iris tenuifolia[13], Spondias mombin [14], Spirulina platensis [15], Withania somnifera [16],

Piper guineense [17], Buddleia perfoliata [18], Lavandula multifida [19], and argan

hulls [20].

The present work is devoted to examining the extract of guava (Psidium guajava)

leaves as an inhibitor for corrosion of mild steel in HCl media. The guava plant

(P. guajava L.; Myrtaceae) is widely cultivated in tropical and temperate regions of the

O

O

Fig. 1 Structure of typicalflavonoid

Fig. 2 Polarization curves of mild steel corrosion in a 0.5 N, b 1 N, c 1.5 N, d 2 N HCl in absence andpresence of different concentrations of P. guajava water extract at 30 �C

K. K. Anupama, J. Abraham

123

world. Native to Central America, they are small trees with reddish-brown bark and

tough leaves [21]. Phytochemical screening has shown that the extract contains an

appreciable amount of flavonoids and tannins amongst others [22]. Recent phytochem-

ical screening of P. guajava leaves showed tannins in aqueous extract, and anthocyans,

alkaloids, flavonoids (Fig. 1), and steroids/terpenoids in ethanol extract [23].

Experimental

Inhibitor preparation

Fresh guava leaves were collected and identified. They were then sun-dried for

7 days and made into a fine powder. A sample of 2.5 g of powdered leaves were

then extracted with 500 ml of double-distilled water to make P. guajava water

extract. A second sample of 2.5 g of powdered guava leaves were also extracted

with 500 ml of distilled ethanol.

Specimen preparation

Mild steel specimens of composition C (0.2 %), Mn (1 %), P (0.03 %), S (0.02 %),

and Fe (98.75 %) were used. The steel specimens with an exposed area of 1 cm2

were used for electrochemical studies.

Fig. 3 Polarization curves of mild steel corrosion in a 0.5 N, b 1 N, c 1.5 N, d 2 N HCl in absence andpresence of different concentrations of P. guajava alcohol extract at 30 �C

Electroanalytical studies on the corrosion inhibition behaviour

123

Medium

The medium for the study was made using reagent grade HCl (Merck, Germany)

and distilled water. All tests were performed in aerated medium at room temperature

and atmospheric pressure.

Electrochemical measurements

The electrochemical studies were made using a three-electrode cell assembly at room

temperature. Mild steel of 1 cm2 exposed surface area was the working electrode.

Platinum sheet with 1 cm2 surface area was used as the auxiliary electrode and

saturated calomel electrode as the reference electrode. All the electrochemical

measurements were carried out using a Gill AC computer controlled work station

(model no: 1475; ACM, UK). Prior to the electrochemical measurements, a

stabilization period of 60 min was allowed, to attain a stable value of Ecorr [9].

Table 1 Polarization data for mild steel corrosion in different concentrations of HCl without and with

P. guajava water extract

Acid

concentration

(N)

Inhibitor

concentration

(ml)

-Ecorr

(mV)

ba

(mv/dec)

bc

(mv/dec)

Icorr

(mA cm-2)CR

(mm/year)

%IE

0.5 Blank 443.20 108.74 156.52 2.31 26.75 –

2 452.93 89.43 193.96 1.04 12.04 55

4 460.76 78.48 129.3 0.37 4.30 83.9

6 458.69 52.69 87.85 0.36 4.18 84.4

8 465.30 54.61 103.72 0.27 3.10 88.4

10 469.40 59.51 105.93 0.25 2.87 89.3

1 Blank 479.15 168.95 228.11 3.37 39.02 –

2 477.03 160.08 225.15 2.89 33.55 14

4 494.85 81.14 149.09 0.56 6.48 83.4

6 510.35 42.95 75.63 0.26 3.00 92.3

8 507.10 60.44 115.56 0.08 0.88 98

10 497.92 71.58 134.86 0.27 3.11 92

1.5 Blank 459.24 56.92 117.78 0.69 8.05 –

2 468.19 49.44 91.04 0.51 5.88 26.8

4 480.49 48.66 82.61 0.45 5.19 35.3

6 474.97 51.40 78.43 0.30 3.53 56.2

8 477.25 29.94 49.57 0.23 2.66 56.9

10 476.53 44.79 83.49 0.14 1.67 79.2

2 Blank 437.40 80.14 232.3 1.49 17.38 –

2 448.90 68.53 134 1.32 15.35 11.7

4 451.00 70.28 367.6 0.88 10.25 41

6 448.50 64.15 150.7 0.74 8.62 50.4

8 454.80 57.36 134.3 0.63 7.33 57.8

10 456.01 57.93 185.6 0.50 5.81 66.4

K. K. Anupama, J. Abraham

123

The linear polarization study was carried out from a cathodic potential -250 mV

versus Ecorr to an anodic potential of ?250 mV versus Ecorr with a scan rate of

1 mV/s. The linear Tafel segments of the anodic and cathodic curves were

extrapolated to corrosion potential to obtain the corrosion current densities using

which inhibition efficiency (IE) was calculated.

EIS measurements were carried out with amplitude of 10 mV in a frequency

range from 10 kHz to 0.1 Hz. The impedance diagrams are given in the form of

Nyquist plots. The charge transfer resistance values were obtained from the

diameter of the semicircles of the Nyquist plots.

Scanning electron microscopy (SEM)

The specimens for surface morphological examination were immersed in acid

containing an optimum concentration of inhibitors and blank solution for 4 h. Then,

they were removed, rinsed quickly with acetone, and dried. The analysis was

Table 2 Polarization data for mild steel corrosion in different concentrations of HCl without and with

P. guajava alcohol extract

Acid

concentration

(N)

Inhibitor

concentration

(ml)

-Ecorr

(mV)

ba

(mv/dec)

bc

(mv/dec)

Icorr

(mA cm-2)

CR

(mm/year)

%IE

0.5 Blank 443.2 108.74 156.52 2.31 26.75 –

2 454.4 84.31 160.96 0.92 10.64 60.2

4 470.1 78.24 169.13 0.57 6.62 75.3

6 464.3 69.73 172.81 0.45 5.17 80.7

8 471.9 63.80 156.62 0.16 1.90 92.9

10 473.6 66.90 157.33 0.13 1.47 94.5

1 Blank 479.1 168.9 228.11 3.37 39.02 –

2 481.4 88.7 195.57 1.87 21.68 44.4

4 465.4 75.49 174.91 0.95 11.05 71.7

6 473.6 77.80 175.75 0.77 9.03 77.1

8 470.2 62.42 154.44 0.37 4.36 89.0

10 482 53.58 140.97 0.18 2.14 94.6

1.5 Blank 459.2 56.92 117.78 0.69 8.05 –

2 490.2 46.20 86.73 0.44 5.49 37.2

4 456.2 48.9 136.38 0.30 3.50 56.5

6 473.3 52.40 133.6 0.19 2.24 72.2

8 458.5 50.10 91.73 0.18 2.06 74.3

10 475.2 43.86 101.6 0.16 0.88 76.6

2 Blank 437.4 80.14 232.39 1.49 17.38 –

2 448.5 61.85 172.20 1.01 11.64 32.9

4 454.1 58.45 513.40 0.93 10.8 37.9

6 445.6 61.95 158.30 0.75 8.75 49.6

8 444.3 59.3 147.30 0.49 5.76 66.8

10 450.4 49.02 203.50 0.25 2.89 83.3

Electroanalytical studies on the corrosion inhibition behaviour

123

performed on a scanning electron microscope (model SU6600, serial no. HI-2102-

0003) at an accelerating voltage 20.0 kV. All micrographs of the specimen were

taken at 9500 magnification.

Atomic force microscopy (AFM)

Mild steel strips of size 4.8 9 1.9 cm2 were used for AFM studies. The specimens

were immersed in blank solution and also in 1 N HCl containing an optimum

concentration of inhibitors, for 4 h. The specimens were cleaned and dried before

conducting AFM studies.

Results and discussion

Potentiodynamic polarization measurements

The potentiodynamic polarization curves for steel corrosion in HCl having different

concentrations, without and with the inhibitor, i.e. P. guajava water and alcoholic

extracts at 30 �C, are shown in Figs. 2 and 3. The corrosion parameters obtained

from polarization curves such as corrosion potential (Ecorr), corrosion current

Fig. 4 Nyquist plots for mild steel corrosion in a 0.5 N, b 1 N, c 1.5 N, d 2 N HCl in the absence andpresence of different concentrations of P. guajava water extract at 30 �C

K. K. Anupama, J. Abraham

123

densities (Icorr), and anodic and cathodic Tafel slopes (ba and bc) are given in

Tables 1 and 2.

IEs were calculated using the equation,

% IE ¼ Icorr � Icorr�Icorr

� 100 ð1Þ

where Icorr and Icorr� are the uninhibited and inhibited corrosion current densities,

respectively.

From Tables 1 and 2, it can be seen that Icorr values are decreasing with

increasing inhibitor concentration, which evidently shows corrosion inhibition.

From Figs 2 and 3, it is evident that P. guajava extracts retard both cathodic and

anodic processes, which is also supported by the data given in Tables 1 and 2. Both

ba and bc values have changed, and it can be seen that there is no regular

displacement pattern in the Ecorr values which shows that both the inhibitors act as

mixed type. According to Ferreira and others [24, 25], if the displacement in

corrosion potential is more than 85 mV with respect to the corrosion potential of the

blank, the inhibitor can be seen as a cathodic or anodic type [26].

Fig. 5 Nyquist plots for mild sample corrosion in a 0.5 N, b 1 N, c 1.5 N, d 2 N HCl in the absence andpresence of different concentrations of P. guajava alcohol extract at 30 �C

Electroanalytical studies on the corrosion inhibition behaviour

123

Electrochemical impedance spectroscopy

The corrosion behavior of steel in HCl media with different concentrations was also

studied using the EIS technique. Nyquist plots, as can be seen from Figs 4 and 5, are

not perfect semicircles which may be explained as the result of surface

inhomogeneity. The impedance spectra exhibit a single semicircle for a particular

concentration. The diameter of the circle increases with the increase in inhibitor

concentration. The single semicircle indicates that the charge transfer takes place at

the electrode/solution interface, and corrosion of mild steel is increased by the

charge transfer process.

From Tables 3 and 4, it can be seen that Rct values increase with the increase in

inhibitor concentration, showing that the mild steel surface is protected by the

inhibitor. Cdl values show an opposite trend, i.e. a decrease with increasing

thickness of the protective layer formed on the mild steel surface [15]. The

Table 3 Electrochemical impedance data for mild steel corrosion in different concentrations of HCl in

absence and presence of guava–water extract

Acid

concentration (N)

Inhibitor

concentration

(ml)

Rct (X cm2) Cdl

(lF/cm2)

Icorr

(mA cm-2)

CR

(mm/year)

%IE

0.5 Blank 8.03 537 3.24 37.65 –

2 21.12 378 1.23 14.32 61.9

4 30.71 196 0.84 9.84 73.9

6 43.56 185 0.59 6.94 81.6

8 47.17 91.3 0.55 6.41 82.9

10 66.05 81.9 0.39 4.57 87.8

1 Blank 6.54 719 3.98 46.18 –

2 7.55 358 3.45 40.05 13.4

4 35.43 147 0.74 8.53 81.5

6 96.36 143 0.27 3.13 93.2

8 228.1 59.7 0.11 1.33 97.1

10 74.49 138 0.35 4.05 91.2

1.5 Blank 7.91 452 3.29 38.22 –

2 10.80 320 2.41 28.00 26.8

4 12.32 166 2.11 24.54 35.9

6 17.53 220 1.48 17.25 54.9

8 35.66 95.9 0.73 8.49 77.8

10 43.07 13.3 0.61 7.02 81.6

2 Blank 7.88 468 3.31 38.34 –

2 8.91 354 2.93 33.94 11.5

4 13.33 154 1.96 22.68 40.9

6 15.36 275 1.69 19.68 48.7

8 17.99 216 1.45 16.81 56.2

10 22.02 170 1.18 13.73 54.2

K. K. Anupama, J. Abraham

123

maximum IE obtained for both P. guajava water extract and alcohol extract reaches

more than 90 %. It can be seen that these results are in agreement with those

obtained from polarization studies.

IEs were calculated using the equation,

%IE ¼ Rct� � Rct

Rct

� 100 ð2Þ

where Rct and Rct� are the charge transfer resistances in the absence and presence of

inhibitors, respectively.

Observing the results obtained from electrochemical studies, it may be assigned

that the IE increases gradually with the addition of each 2 ml of the extracts up to

the highest concentration of the extracts used, i.e. 10 ml, and that even at the lowest

inhibitor concentration, i.e. 2 ml of the extract, there is considerable IE. Thus,

P. guajava leaves have proven to be a good inhibitor against mild steel corrosion in

HCl. An important fact to be noted is that the quantity of P. guajava leaves used to

Table 4 Electrochemical impedance data for mild steel corrosion in different concentrations of HCl in

absence and presence of guava–alcohol extract

Acid concentration

(N)

Inhibitor concentration

(ml)

Rct

(X cm2)

Cdl

(lF/cm2)

Icorr

(mA cm-2)

CR

(mm/year)

%IE

0.5 Blank 8.03 537 3.24 37.65 –

2 17.27 378 1.51 17.51 51.6

4 40.85 196 0.64 7.4 79.5

6 44.85 185 0.58 6.78 81.2

8 149.9 91.3 0.17 2.01 94.4

10 164 81.9 0.16 1.84 94.9

1 Blank 6.54 719 3.98 46.18 –

2 12.63 388 2.06 23.94 48.2

4 23.81 183 1.09 12.7 72.5

6 33.67 150 0.77 8.98 80.6

8 50.74 117 0.51 5.95 87.1

10 105.50 84.6 0.25 2.86 93.8

1.5 Blank 7.91 452 3.29 38.20 –

2 14.79 228 1.76 20.40 46.5

4 22.81 161 1.14 13.20 65.3

6 29.69 151 0.87 10.10 73.4

8 33.66 176 0.77 8.90 76.5

10 41.37 106 0.63 7.30 80.9

2 Blank 7.88 468 3.31 38.34 –

2 11.28 306 2.31 26.80 30.1

4 12.63 212 2.06 23.90 37.7

6 16.04 223 1.62 18.80 50.8

8 22.4 197 1.16 13.40 64.9

10 34.6 130 0.75 8.73 77.2

Electroanalytical studies on the corrosion inhibition behaviour

123

prepare the extract is very small in the whole volume of the solvent (about 2.5 g in

500 ml of double-distilled water and distilled ethanol). The results obtained also

show that the P. guajava alcohol extract exhibits better inhibitive capacity than the

P. guajava water extract, which may be attributed to the nature of the substances

extracted with the solvents [27].

Adsorption studies

Adsorption isotherms provide information regarding the mode of inhibition on the

metal surface. The adsorbed layer combats the action of the corrosive media (HCl)

and enhances the protection of the metal surface [8]. Frequently used isotherms are

the Langmuir, Temkin and Frumkin isotherms. The dependence of h (degree of

surface coverage) as a function of inhibitor concentration was graphically tested for

these isotherms. The best fit was obtained for the Frumkin adsorption isotherm, for

both the inhibitors, with the correlation coefficient (R2) value close to unity (Figs. 6,

7).

The Frumkin isotherm equation (Eq. 3) is obeyed when a plot of log [h/C (1 - h)]

versus h produces a straight line with the slope equal to 2a

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0 R2=0.98653lo

g{ θ

/c(1

-θ)}

θ

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0 R2=0.97803

log

{θ/c

(1- θ

)}

θ

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8R2=0.99866

log

{θ/c

(1-θ

)}

θ

0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.0 0.2 0.4 0.6 0.8 1.0

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0.1 0.2 0.3 0.4 0.5 0.6 0.7

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

R2=0.98783

log

{θ/c

(1-θ

)}

θ

(a) (b)

(c) (d)

Fig. 6 Frumkin adsorption isotherms for mild steel in a 0.5 N, b 1 N, c 1.5 N, d 2 N HCl with differentconcentrations of P. guajava water extract

K. K. Anupama, J. Abraham

123

logh

Cð1� hÞ ¼ 2:303logKFrum þ 2ah ð3Þ

where a is the lateral interaction term describing the molecular interaction in the

adsorbed layer, KFrum is the desorption–adsorption equilibrium constant, and C is

the concentration of the inhibitor. The Frumkin adsorption theory assumes the

adsorption of a multimolecular layer where there is an adsorbate–adsorbent inter-

action. And this fact is almost confirmed from the best fitting isotherm (Figs. 6, 7)

obtained for the P. guajava extract adsorption on mild steel.

The Frumkin adsorption isotherm also accounts for the inhomogeneity on the

surface of the steel specimen, which is an advantage over the Langmuir adsorption

isotherm in explaining the equilibrium reactions.

Scanning electron microscopy (SEM)

Scanning electron microscope images were recorded (Fig. 8) to establish the

interaction of inhibitor molecules with the metal surface. Figure 8a indicates the

finely polished characteristic surface of the mild steel and shows some scratches

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4 R2=0.97121

log

{θ/c

(1- θ

)}

θ

0.0

0.2

0.4

0.6

0.8

1.0

1.2

R2=0.97486

log

{ θ/c

(1-θ

)}

θ

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7 R2=0.9986

log

{θ/c

(1-θ

)}

θ

0.5 0.6 0.7 0.8 0.9 1.0 0.4 0.5 0.6 0.7 0.8 0.9 1.0

0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.3 0.4 0.5 0.6 0.7 0.8

-0.4

-0.2

0.0

0.2

0.4

0.6R2=0.99864

log

{θ/c

(1-θ

)}

θ

(a) (b)

(c) (d)

Fig. 7 Frumkin adsorption isotherms for mild steel in a 0.5 N, b 1 N, c 1.5 N, d 2 N HCl with differentconcentrations of P. guajava alcohol extract

Electroanalytical studies on the corrosion inhibition behaviour

123

which must have arisen during polishing. Figure 8b reveals that the immersed

specimens were highly damaged in the presence of 1 N HCl, due to direct acid

attack. Figure 8c, d shows the formation of a protective film over the metal surface

by P. guajava alcohol and water extracts, respectively. These images well exhibit

the better IE of the P. guajava alcoholic extract when compared to the aqueous one,

agreeing with the results of the electrochemical measurements.

Atomic force microscopy (AFM)

AFM is a powerful technique for surface morphological studies providing

information about the influence of inhibitors on corrosion at the metal–solution

interface. The three-dimensional AFM images are given in Fig. 9a–d. Figure 9a

displays the surface topography of an uncorroded metal surface for which the

average roughness value (Ra) was obtained as 16 nm. Figure 9b displays the

corroded metal surface showing severe damage due to exposure to acid, the Ra value

for which was obtained as 41 nm. Figure 9c, d displays the steel surfaces which

were immersed in 1 N HCl containing optimum concentrations of P. guajavaalcohol and water extracts, respectively. The Ra values obtained for P. guajavaalcohol inhibitor and P. guajava aqueous inhibitor are 12 and 21 nm, respectively,

which are lower than those obtained for the steel surface in the uninhibited

Fig. 8 SEM images of a mild steel, b mild steel in 1 N HCl, c mild steel in 1 N HCl ? 10 ml P. guajavaalcohol extract, and d mild steel in 1 N HCl ? 10 ml P. guajava water extract

K. K. Anupama, J. Abraham

123

environment. This clearly shows that a compact protective film of the inhibitor is

formed on the metal that keeps the surface smooth.

Conclusion

• Psidium guajava acts as a better inhibitor for corrosion of mild steel in HCl

medium. With increasing concentration of the inhibitor, the IE also increases.

• Impedance measurements revealed the increase in charge transfer resistance and

the decrease of double layer capacitance with increasing inhibitor concentration.

• Polarization data suggest that P. guajava acts as a mixed-type inhibitor.

• Adsorption studies revealed that the adsorption pattern of P. guajava inhibitor

obeys the Frumkin adsorption isotherm, suggesting a multimolecular layer

adsorption.

• SEM images shows that a protective layer is formed on the metal surface by the

inhibitor molecules.

Fig. 9 AFM images of a mild steel, b mild steel in 1 N HCl, c mild steel in 1 N HCl ? P. guajavaalcohol extract and d mild steel in 1 N HCl ? P. guajava water extract

Electroanalytical studies on the corrosion inhibition behaviour

123

References

1. K.P. Vinod Kumar, M. Sankara Narayanan Pillai, J. Mater. Sci. 46, 5208 (2011)

2. M. Zinni, L. Majidi, A. Bouyanzer, J. Paolini, J.M. Desjobert, J. Costas, B. Hammouti, Arab.

J. Chem. (2010). doi:10.1016/j.arabjc.2010.09.017

3. M. Gopiraman, P. Sakunthala, R. Kanmani, V. Alex Ramani, N. Sulochana, Ionics. 17, 843 (2011)

4. E.E. Orguzie, Corros. Sci. 50, 2993 (2008)

5. X.-H. Li, S.-D. Deng, H. Fu, J. Appl. Electrochem. 40, 1641 (2010)

6. A.Y. El-Etre, J. Colloid Interface Sci. 314, 578 (2007)

7. A.Y. El-Etre, M. Abdallah, Z.E. El-Tanatwy, Corros. Sci. 47, 385 (2005)

8. P. Bothi Raja, M.G. Sethuraman, JMEPEG. 19, 761 (2010)

9. A. Singh, K. Singh, M.A. Quraishi, Int. J. Corros. (2010). doi:10.1155/2010/275983

10. M. Lebrini, F. Robert, A. Lecante, C. Roos, Corros. Sci. 53, 687 (2001)

11. R. de Oliveira Ramos, A. Battistin, R.S. Goncalves, J. Solid State Electrochem. 16, 747 (2011)

12. G. Gunasekaran, L.R. Chauhan, Electrochem. Acta. 49, 4387 (2004)

13. M.I. Choudhary, S. Hareem, H. Siddiqui, S. Anjum, S. Ali, Atta-ur-Rahman, M.I. Zaidi, Phyto-

chemistry 69, 1880 (2008)

14. N.O. Obi-Egbedi, I.B. Obot, S.A. Umoren, Arab. J. Chem. (2010). doi:10.1016/j.arabjc.2010.09.002

15. C. Kamal, M.G. Sethuraman, Arab. J. Chem. (2010). doi:10.1016/j.arabjc.2010.08.006

16. J. Dubey, N. Jeengar, R.K. Upadhyay, A. Chaturvedi, Res. J. Recent Sci. 1(ISC-2011), 73 (2012)

17. E.E. Oguzie, C.B. Adindu, C.K. Enenebeaku, C.E. Ogukwe, M.A. Chidiebere, K.L. Oguzie, J. Phys.

Chem. 116, 13603 (2012)

18. R. Lopes-Sesenes, J.S. Gonzalez-Rodriguez, G. Francisca, D. Patino, A. Martinez-Villafane,

J. Electrochem. Sci. Eng. 2, 77 (2012). doi:10.5599/jese.2012.0013

19. M. Znini, J. Paolini, L. Majidi, J.-M. Desjobert, J. Costa, N. Lahhit, A. Bouyanzer, Res. Chem.

Intermed. 38, 669 (2012)

20. L. Afia, R. Salghi, E.H. Bazzi, A. Zarrouk, B. Hammouti, M. Bouri, H. Zarrouk, L. Bazzi,

L. Bammou, Res. Chem. Intermed. 38, 1707 (2012)

21. I.A. Ogunwande, N.O. Olawore, K.A. Adeleke, O. Ekundayo, W.A. Koenig, Flavour Fragr. J. 18, 136

(2003)

22. O.S. Adeyemi, M.A. Akanji, S.A. Oguntoye, J. Med. Plants Res. 3, 420 (2009)

23. R.G. Belemtougri, B. Constantin, C. Cognard, G. Raymond, L. Sawadogo, J. Zhejiang Univ. Sci. B.

7, 56 (2006)

24. E.S. Ferreira, C. Giancomelli, F.C. Giacomelli, A. Spinelli, Mater. Chem. Phys. 83, 129 (2004)

25. W.H. Li, Q. He, C.L. Pie, B.R. Hou, J. Appl. Electrochem. 38, 289 (2008)

26. Y. Yan, W. Li, L. Cai, B. Hou, Electrochem. Acta. 53, 5953 (2008)

27. A.M. Al-Turkustani, S.T. Arab, L.S.S. Al-Qarni, J. Saudi Chem. Soc. 15, 73 (2011)

K. K. Anupama, J. Abraham

123