Volume 19 Paper 45
Lawsonia Extract as a Green Corrosion Inhibitor for Copper in Nitric Acid Solution
K. K. Patel and R. T. Vashi
Keywords: Corrosion, Copper, Lawsonia extract, Nitric acid, Inhibitor
The inhibition effect of henna leaves (Lawsonia inermis) extract for the corrosion of copper in nitric acid solution has been studied by using weight loss, potentiodynamic polarization and electrochemical impedance spectroscopic methods at different temperature. The effect of inhibitor concentrations on different acid concentrations was investigated. The present study revealed that the percentage of inhibition efficiency is enhanced with increase of inhibitor concentration and decrease with increase in temperature. The inhibitive action of the extract is discussed in view of adsorption of Lawsonia molecules on the metal surface. It was found that this adsorption follows Langmuir adsorption isotherm in all tested systems. Tafel plot of polarization study indicates that the extract acts as a mixed type inhibitor. It was found that the extract acts as a good corrosion inhibitor for all the tested systems and the inhibition efficiency was obtained up to 98%.
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Corrosion Inhibition of Copper in Nitric Acid Using
Lawsonia Extract as Green Inhibitor
K. K. Patel, R. T. Vashi*
Department of Chemistry, Navyug Science College, Surat, Gujarat-395009, India
For correspondence: Email: email@example.com (K.K.Patel)
The inhibitive action of henna leaves (Lawsonia Inermis) extract on corrosion of copper in nitric
acid solution was investigated through weight loss, potentiodynamic polarization and
electrochemical impedance spectroscopic methods at different temperature. The effect of
inhibitor concentrations on different acid concentrations was investigated. The present study
revealed that the percentage of inhibition efficiency is enhanced with increase of inhibitor
concentration and decrease with increase in temperature. The inhibitive action of the extract is
discussed in view of adsorption of Lawsonia molecules on the metal surface. It was found that
the adsorption follows Langmuir adsorption isotherm. Tafel plot of polarization study indicate
that the Lawsonia extract acts as a mixed type inhibitor. Inhibition efficiency of Lawsonia
extract was found up to 98%.
Keywords: Corrosion; Copper; Lawsonia extract; Nitric acid; Inhibitor.
Corrosion of metal can be defined as the deterioration of materials due to their reaction with
the environment. Copper and its alloys are widely used material for its excellent electrical and
thermal conductivities in many industrial applications such as electronics and in the
manufacture of integrated circuits. Copper is a relatively noble metal, requiring strong
oxidants for its corrosion or dissolution; its corrosion resistance becomes less while the
aggressive solution concentration increases [1, 2]. Copper corrosion in nitric acid solution
induced a great deal of research [3, 4]. It is noticed that presence of heteroatom such as
nitrogen [5, 6], oxygen [7, 8], phosphorus  and sulphur [10, 11] in the organic compound
molecule improves its action as corrosion inhibition. However, as a result of their high cost,
toxicity and increasing awareness of health and ecological risks, attention is being drawn
towards finding highly efficient, cheaper and non-toxic inhibitors. The present trend in
research on environmental friendly corrosion inhibitors is concentrating on products of natural
origin due principally to their low cost and eco-friendliness.
The aim of the present work is to develop eco-friendly corrosion inhibitors, with good
inhibition efficiency (IE) at low risk of environmental pollution . From many decades, plant
extracts have attracted attention in the field of corrosion inhibition. As natural products, they
are a source of non-toxic, eco-friendly, bio-degradable and of potentially low cost inhibitors
for preventing metal corrosion . Most of the naturally occurring substances are safe and
can be extracted by simple procedure. The inhibitive action of leaves extract of Azadirachta
indica on copper corrosion in HNO3 solutions was studied using weight loss and
electrochemical techniques . The results obtained indicated that the extracts functioned as
good inhibitors in HNO3 solutions.
Henna (Lawsonia Inermis), a herb which has interesting dyeing properties used for centuries in
Asia and North Africa for traditional decoration of the skin and hair. Lawsonia Inermis has
anti-inflammatory, antipyretic and analgesic effect [15-16]. Henna has been used as corrosion
inhibitor for aluminium and steel in aggressive solution , iron in hydrochloric acid  and
aluminium in hydrochloric acid [19-20]. El- Etre A.Y. et al.  studied the inhibiting action of
Lawsonia extract on the corrosion of different metals. The corrosion inhibition efficacy of these
extracts is normally ascribed to the presence, in their composition, of complex organic species
such as tannins, alkaloids and nitrogen bases, carbohydrates and proteins as well as their acid
In the present work, inhibitive action of Lawsonia leaves extract as a cheap, eco friendly and
naturally occurring substance on corrosion behavior of copper in HNO3 solution has been
investigated through weight loss, polarization measurements and electrochemical impedance
2. Experimental section
2.1. Sample and Solution preparation
The copper specimens of the size 4.5 × 2.0 × 0.178 cm having an effective area 0.1988 dm2
with a chemical composition (99.99 % Cu and 0.01% S) was used. The specimens mechanically
abraded using different grades of emery papers, cleaned by washing with distilled water,
degreased with acetone, washed once more with distilled water and finally dried and weighted
by using electronic balance. The corrosive solutions were prepared by dilution of analytical
grade of 69% HNO3 (Merck) using distilled water.
2.2. Extract preparation
Lawsonia inermis leaves were dried, crushed and extracted in boiled water for 2 h. The
extracted solution was then filtered and concentrated until the water from the extract
evaporates . This extract was used to study the corrosion inhibition properties and to
prepare the required concentrations of Lawsonia inermis varied from 0.6, 0.8, 1.0 and 1.2 g/L.
2.3. Weight loss measurement
For weight-loss experiment, the copper coupons were each suspended completely in 0.5, 0.75
and 1.0 M HNO3 solutions without and with different concentrations of Lawsonia extract with
the help of glass hooks at 301±1 K for 24h (1 day). The volume of solution kept 230 ml. The
coupons were retrieved after 24 h, washed by distilled water, dried well and reweighed. From
the weight loss data, corrosion rate in mg/dm2d was calculated.
2.4. Temperature effect
To study the effect of temperature on corrosion rate, the copper coupons were completely
immersed in 230 ml of 1.0 M HNO3 solution without and with different concentrations of
Lawsonia extract at 313, 323 and 333 K for 2h. From the data, inhibition efficiency, energy of
activation (Ea) and heat of adsorption (Qads) were calculated.
2.5. Electrochemical measurements
Electrochemical measurements were carried out by using an electrochemical work station
(CHI608C-series, U.S. Model with CH instrument). In electrochemical experiment Ag/AgCl was
used as a reference electrode, platinum as an auxiliary electrode and copper metal was used as
a working electrode. For polarization study, copper specimens having an area of 1 cm2
exposed to 230 ml 0.5 M HNO3 in absence and presence of Lawsonia extract and allowed to
establish a steady-state open circuit potential (OCP) for about 30 minutes. Test coupons were
then polarized by the application of potential drift of −250 mV cathodically and +250 mV
anodically with respect to the OCP at a scan rate of 5.0 mV/s. The potentiodynamic
polarization plots (Tafel curves) were developed simultaneously. Anodic and cathodic
polarization curves give anodic and cathodic Tafel lines correspondingly. The intersect point of
Tafel lines gives the corrosion potential (Ecorr) and corrosion current (icorr) . The
electrochemical impedance studies were carried out in the same setup using potentiodynamic
polarization studies described above. Impedance studies were carried out at steady-state open
circuit potential (OCP). A small amplitude (5.0 mV) sinusoidal ac Voltage, in wide frequency
range 1 to 100 KHz was applied over the system. A graph was drawn by plotting real
impedance (Z’) versus imaginary impedance (Z″). From the Nyquist plots the charge transfer
resistance (Rct), and double layer capacitance (Cdl) were calculated. Impedance measurements
were carried out both in the absence and presence of Lawsonia extract.
3. Results and discussion
3.1. Weight loss experiment
The corrosion rate of copper in 0.5, 0.75 and 1.0 M of HNO3 solution without and with
different concentration of Lawsonia extract 0.6, 0.8, 1.0 and 1.2 g/L at 301±1 K for an
exposure period of 24h (1 day) was calculated from the weight loss data using following
CR (mg/dm2 d) =
Weight loss (gm ) x 1000
(metal surface area ) dm 2 x day
The Inhibition efficiency (IE) was calculated by using following formula,
W uninh −W inh
where, Wu = Weight loss without inhibitor, Wi = Weight loss with inhibitor.
The degree of surface coverage (θ) for different concentration of the inhibitor in acidic media
have been evaluated from weight loss experiments using this equation,
W uninh −W inh
Table 1. Corrosion rate for copper in various HNO3 concentrations in the absence and presence of
different concentrations of Lawsonia extract from weight loss measurements at 301±1 K.
Results showed in Table 1 indicate that as the concentration of acid increases corrosion rate
was increases. The corrosion rate was 90.52, 281.55 and 1030.67 mg/dm2d for 0.5, 0.75 and
1.0 M HNO3 concentrations respectively for an immersion period of 24 h at 301±1 K.
At constant acid concentration, the IE increases with increase Lawsonia extract concentrations,
e.g. Lawsonia extract in 0.5 M HNO3 solution, the IE found to be 77.78, 83.34, 88.89 and
95.56 % with respect to 0.6, 0.8, 1.0 and 1.2 g/L inhibitor concentrations (Table 1). At
constant inhibitor concentration, the IE was decreases as the acid concentration increases, e.g.
for 0.6 g/L Lawsonia extract, the IE was found to be 77.78, 71.43 and 53.66 % with respect to
0.5, 0.75 and 1.0 M HNO3 solution (Table 1).
Table 2. Corrosion rate (log ρ) of copper in 0.5 M HNO3 in absence and presence of Lawsonia extract
for an immersion period of 24 h at 301 ± 1K.
The results obtained were presented in Table 2 and in Fig. 1&2, which indicates that with
increase in inhibitor concentration from 0.6 to 1.2 g/L the corrosion rate was decreased from
20.11 to 4.02 mg/dm2d while IE increases from 77.78 to 95.56 %. It can be concluded that IE
corrosion rate (mg/dm2 d)
is directly proportional to the inhibitor concentration.
Inhibitor concentration (g/L)
Fig.1. Corrosion rate of copper corrosion in 0.5 M HNO3 solution in absence and presence of different
concentration of Lawsonia extract for an immersion period of 24h (1 day).
Inhibitor concentration (g/L)
Fig.2. IE of copper corrosion in 0.5 M HNO3 solution in presence of different concentration of Lawsonia
extract for an immersion period of 24h (1 day).
3.2. Temperature effect
To investigate the influence of temperature on corrosion of copper, the weight-loss
experiments were carried out at temperature 313, 323 and 333K in 1.0 M HNO3 without and
with Lawsonia extract for an immersion period of 2 h. The results in Table 3 shows that
corrosion rate increase with rise in temperature, the corrosion rate was 5309.52, 9050.22 and
23530.58 mg/dm2d with respect to 313, 323 and 333 K. The IE was decrease with increase in
temperature, e.g. for 1.2 g/L Lawsonia extract the IE was 95.45, 90.00 and 82.05 % for 313,
323 and 333 K temperature respectively (Fig. 5). The value of energy of activation (Ea) has been
calculated with the help of following Arrhenius equation .
log ρ2 = 2.303R
�T − T �
where, ρ1 and ρ2 are the corrosion rate at temperature T1 and T2 respectively.
Table 3. Temperature effect on corrosion rate (CR), inhibition efficiency (IE) and activation energy (Ea)
for copper in 1.0 M HNO3 in absence and presence of Lawsonia extract for an immersion period of 2 h.
Energy of activation (Ea)
The value of Ea were also calculated from the slope of the Arrhenius plot (Fig. 3), i.e. log ρ
Versus 1/T ×103 . (ρ=corrosion rate, T=absolute temperature)
It was found that, the values of Ea were found higher in inhibited acid ranging from 89.32 to
125.32 kJ/mol than Ea values for uninhibited acid 65.15 kJ/mol. The higher values of Ea
indicate physical adsorption of the inhibitor on the metal surface and the adsorption of
inhibitor causes an increase in the Ea of the process .
log ρ (CR)
1/T x 1000 K-1
Fig.3. Arrhenius plot for corrosion of copper in 1.0 M HNO3 in absence and presence of different
concentration of Lawsonia extract for an immersion period of 2 h.
The mean value of Ea was 65.15 kJ/mol in uninhibited acid and the value calculated from the
slop of the Arrhenius plot was found 64.33 kJ/mol, which was found almost similar (± 1.0
Fig.4. Effect of temperature on IE for copper corrosion in 1.0 M HNO3 at different concentration of
Lawsonia extract for immersion period of 2 h.
The values of heat of adsorption (Qads) were calculated by following equation .
Qads = 2.303R �log �1−θ2 � − log �1−θ1 �� × �T 1−T2 �
where, θ1 and θ2 are the fraction of the metal surface covered by the inhibitor at temperature T1
and T2 respectively. From Table 4, it is evident that in all cases, the Qads values are negative and
ranging from -51.61 to -96.21 kJ/mol. The negative values shows that the adsorption and
hence the IE decreases with rise in temperature.
The IE was correlated to surface coverage (θ) and a 100 % efficiency suggesting to full coverage
(θ=1). The degree of surface coverage values were used to determine its adsorption
characteristics in HNO3 solution. The plot of Cinh/θ versus Cinh gives straight lines with slope
values equal to unity (Fig. 5). All the regression coefficients are very close to one which
indicates that the inhibitors cover both the anodic and cathodic region through general
adsorption following Langmuir isotherm . This isotherm can be represented as,
where, Kads = equilibrium constant of the adsorption process and Cinh = inhibitor
Fig.5. Langmuir adsorption isotherm for corrosion of copper in 0.5 M HNO3 solution containing
different concentration of Lawsonia extract for an immersion period of 24 h.
Free energy of adsorption (ΔGao) was determined by the Langmuir isotherm was given by a plot
of Cinh/θ Vs Cinh  (Fig. 5). From the intercepts of the straight lines on the Cinh/θ axis, Kads can
be calculated which was related to ΔGao, as given by following equation. The ΔGao value of the
inhibitors on copper surface can be calculated from the following equation [28,29].
ΔGao = -RT ln (55.5 Kads)
where, R is the gas constant, T is the absolute temperature (K), and the value 55.5 in the above
equation is the concentration of water in solution in Molar , Kads is the equilibrium constant
of the adsorption/desorption process. The ΔGa0 values were almost negative in all cases
indicated the spontaneous adsorption of Lawsonia extract on copper surface and strong
interactions between inhibitor molecules and the metal surface. The enthalpy of adsorption
(ΔHao) and entropy of adsorption (ΔSao) were calculated using the equations (8) & (9).
ΔHa0 = Ea – RT
ΔSa0 = ΔHa0 - ∆Ga0/T
Table 4. The values of physical parameters Heat of adsorption (Qads), Free energy of adsorption (∆Ga0),
Enthalpy of adsorption (ΔHa0) and Entropy of adsorption (ΔSa0) for copper in 1.0 M HNO3 in the absence
and presence of different concentration of Lawsonia extract for an immersion period of 2 h.
The results revealed that ΔHao values were positive and increase in presence of inhibitor
indicating a higher degree of surface coverage and higher protection efficiency attained due to
raising the energy barrier for the copper corrosion reaction. The enthalpy change ΔHao was
positive and ranging between 73.98 to 135.10 kJ/mol indicating the endothermic nature of the
reaction suggests that higher temperature favors the corrosion process. Positive value of ΔSao,
lie between 0.27 to 0.45 kJ/mol K indicate the affinity of the adsorbent for the inhibitor and
the corrosion process is thermodynamically favorable.
3.3. Potentiodynamic polarization measurements
Figure 6 represents the Potentiodynamic polarization curves for copper in 0.5 M HNO3 in the
absence and presence of Lawsonia extract. Associated electrochemical parameters such as
corrosion potential (Ecorr), corrosion current (icorr), anodic Tafel slope (βa), cathodic Tafel slope
(βc) and percentage inhibition efficiency were given in Table 5. From Fig. 6 and Table 5, it was
observed that the addition of Lawsonia extract in HNO3 solution, the significant decrease in the
corrosion current density (icorr) and decrease in the corrosion rate with respect to the blank.
There is significant change in the anodic and cathodic slopes after the addition of the inhibitor
and slightly shifted towards cathodic region. This Tafel curves indicate that Lawsonia function
as a mixed-type inhibitor with the predominant cathode effectiveness.
Table 5. Potentiodynamic polarization parameters for copper in 0.5 M HNO3 and in absence and
presence of 1.2 g/L Lawsonia extract.
Inhibition efficiency (IE) from (icorr) was calculated using following equation .
i corr (uninh ) −i corr (inh )
i corr (uninhi )
Fig.6. Potentiodynamic polarization curves for copper in (a) 0.5 M HNO3 and (b) 0.5 M HNO3 containing
1.2 g/L Lawsonia extract.
3.4. Electrochemical impedance spectroscopy (EIS) measurements
Corrosion of copper in 0.5 M HNO3 solution in the presence of Lawsonia extract was
investigated by EIS at room temperature. Nyquist curves for copper obtained in the absence
and presence of extract were shown in Figure 7 and EIS parameters were shown in Table 6. It
was observed from Figure 7 that the impedance diagram is almost semicircular in appearance,
but not perfect semicircle. The difference has been attributed to frequency dispersion. The
semicircular nature of the plots indicates that the corrosion of copper is mainly controlled by
charge transfer process.
Table 6. EIS parameters for the corrosion of copper in 0.5 M HNO3 in absence and presence of 1.2 g/L
IE (%) calculated from
The charge transfer resistance (Rct) values were calculated from the difference in impedance at
lower and higher frequencies. To obtain the double layer capacitance (Cdl), the frequency at
which the imaginary component of the impedance is maximum was found as presented in the
following equation .
Cdl = 2πf
Where fmax is the frequency at maximum height of the semicircle on the imaginary axis .
Fig.7. Nyquist plot for copper in (a) 0.5 M HNO3 alone and (b) 0.5 M HNO3 containing
1.2 g/L Lawsonia extract.
Inhibition efficiency from Rct values was calculated by using the following equation .
R ct (inh ) −R ct (uninh )
R ct (inh )
The addition of inhibitor, increase Rct value while decreases in Cdl values which is due to the
adsorption of inhibitor on the metal surface. The above results can be explained on the basis
that the electrostatic adsorption of inhibitor species at the metal surface leads to form a
physical protective film that retards the charge transfer process and therefore inhibits the
corrosion reactions, leading to increase Rct values. Moreover, the adsorbed inhibitor species
decrease the electrical capacity of electrical double layer values at the electrode/solution
interface and therefore decrease the values of Cdl .
From the result, IE of Lawsonia extract for copper in HNO3 solution obtained by weightloss,
polarization and EIS methods were almost similar.
Fig. 8. Comparison of inhibition efficiency (IE) values obtained by weight loss, polarization and EIS
method for copper in 0.5 M HNO3 solution containing 1.2 g/L Lawsonia extract.
3.5. Mechanism of corrosion
Being a strong oxidizing agent, HNO3 is capable of attacking copper. Copper is corroded to
Cu+2 in HNO3 solution and no oxide film is formed to protect the surface from the attack of the
corrosive medium. The electrochemical reaction for copper in HNO3 solution may be described
Cu ( s ) + 4HNO 3 ( a q ) → Cu(NO 3 ) 2 ( a q ) + 2NO 2 ( g ) + 2H 2 O ( l )
Cu → Cu + 2 + 2e -
NO 3 - + 3H + + 2e - → HNO 2 + H 2 O
NO 3 - + 4H + + 3e - → NO + 2 H 2 O
+ 4H + + 4e - → 2 H 2 O
3.6. Mechanism of inhibition
It was reported that Lawsonia inermis leaves extract contain soluble matter, lawsone (2-
Hydroxy-1, 4-naphthoquinone), resin and tannin, coumarins, gallic acid and sterols . The
main components of Lawsonia inermis extract are hydroxy aromatic compounds such as
tannin and lawsone.
The main constituent of the extract is lawsone (Fig. 9) which is present in a relatively higher
amount. Lawsone amounts to 1.02 % in the leaves . The coloring matter is quinone.
Lawsone molecule is a ligand that can chelate with various metal cations forming complex
compounds. Therefore, the formation of insoluble complex compounds, by combination of the
metal cations and the lawsone molecules adsorbed on the metal surface , is a probable
interpretation of the observed inhibition action of lawsone. In the acidic medium,
delocalization of the lone pair of electrons on hydroxyl group takes place resulting in the
rearrangement shown in Fig. 11. Such a rearrangement, in the presence of metal cations,
enhances the complex formation reaction Fig. 10. This could be the reason for the observed
high inhibition efficiencies in the acidic medium.
Fig.9. Structure of Lawsone.
Fig.10. Forms of M-Lawsonia complexes. M is Cu.
Fig.11. Process of delocalization on Lawsone molecule.
The inhibitive action of tannin was attributed to the formation of a passivating layer of
tannates on the metal surface [36,37]. Tannins are also known to form complex compounds
with different metal cations, especially in the basic media. It can be concluded then, due to the
higher amount of lawsone in Lawsonia inermis extract, it can be attributed to the main
constituent is responsible for inhibition. Moreover, in the presence of henna extract the values
of corrosion potential Ecorr are nearly constant; therefore, henna extract could be classified as a
mixed type inhibitor with the predominant cathode effectiveness.
The present study shows that Lawsonia was found to be a good eco-friendly inhibitor for the
corrosion control of copper in HNO3 solution. Corrosion rate increases as HNO3 concentration
increase. The inhibition efficiency increases with increase in Lawsonia extract concentration.
Lawsonia adsorbed on metal surface follows Langmuir adsorption isotherm. Tafel plot
indicates Lawsonia acts as a mixed type inhibitor. AC impedance spectra reveal that a
protective film is formed on the metal surface. All three techniques give almost identical values
of inhibition efficiency for copper in HNO3 solution.
The authors are thankful to the Department of Chemistry, Navyug Science College, Surat for
providing laboratory facilities.
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