Experimental and quantum chemical analysis of 2-amino-3-((4-((S)-2-amino-2-carboxyethyl)-1H-imidazol-2-yl)thio) propionic acid as new and green corrosion inhibitor for mild steel in 1?M hydrochloric acid solution

Article abstract of DOI:10.1016/j.molliq.2016.11.011

A new corrosion inhibitor namely, 2-amino-3-((4-((S)-2-amino-2-carboxyethyl)-1H-imidazol-2-yl)thio)propionic acid (AIPA) has been synthesized and its inhibition action on corrosion of mild steel in 1?M HCl has been investigated using Electrochemical impedance spectroscopy (EIS),Potentiodynamic polarization, Scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX) and Atomic force microscopy(AFM) methods. The results obtained from above methods reveal that AIPA is an excellent inhibitor. It gives a maximum inhibition efficiency of 96.52% at 0.456?mM/L (125?ppm; 125?mg?L^??1) and inhibits corrosion by adsorbing at the mild steel surface. Polarization study suggested that AIPA acts as mixed type inhibitor with some cathodic predominance. SEM and AFM analyses showed improved morphology of the mild steel surface in presence AIPA. Quantum chemicals parameters such as E_HOMO, E_LUMO, ΔE, global hardness and softness, electronegativity and fraction of electron transfer (ΔN) were calculated using DFT method to correlate the electronic properties with the adsorption and inhibition behavior of AIPA.

Full text of DOI:10.1016/j.molliq.2016.11.011

Experimental and quantum chemical analysis of 2-amino-3-((4-((S)-2-amino-
2-carboxyethyl)-1H-imidazol-2-yl)thio) propionic acid as new and green
corrosion inhibitor for mild steel in 1 M hydrochloric acid solution
Jiyaul Haque, Vandana Srivastava, Chandrabhan Verma, M.A. Quraishi
PII:
DOI:
Reference:
S0167-7322(16)33229-9
doi:10.1016/j.molliq.2016.11.011
MOLLIQ 6553
To appear in:
Journal of Molecular Liquids
Received date:
Revised date:
Accepted date:
19 October 2016
4 November 2016
5 November 2016
Please cite this article as: Jiyaul Haque, Vandana Srivastava, Chandrabhan Verma, M.A.
Quraishi, Experimental and quantum chemical analysis of 2-amino-3-((4-((S)-2-amino-2-
carboxyethyl)-1H-imidazol-2-yl)thio) propionic acid as new and green corrosion inhibitor
for mild steel in 1 M hydrochloric acid solution, Journal of Molecular Liquids (2016),
doi:10.1016/j.molliq.2016.11.011
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Experimental and quantum chemical analysis of 2-amino-3-((4-((S)-2-amino-
2-carboxyethyl)-1H-imidazol-2-yl) thio) propionic acid as new and green
corrosion inhibitor for mild steel in 1M hydrochloric acid solution
Jiyaul Haque, Vandana Srivastava, Chandrabhan Verma, M.A. Quraishi*,
Department of Chemistry, Indian Institute of Technology, Banaras Hindu University, Varanasi
*Corresponding author: Phone +91-9307025126; Fax: +91- 542- 2368428
E-mail: maquraishi.apc@itbhu.ac.in; maquraishi@rediffmail.com
Abstract:
A new corrosion inhibitor namely, 2-amino-3-((4-((S)-2-amino-2-carboxyethyl)-1H-
imidazol-2-yl) thio)propionic acid (AIPA) has been synthesized and its inhibition action on
corrosion of mild steel in 1M HCl has been investigated using Electrochemical impedance
spectroscopy (EIS),Potentiodynamic polarization, Scanning electron microscopy (SEM),
Energy-dispersive X-ray spectroscopy (EDX) and Atomic force microscopy(AFM) methods.
The results obtained from above methods reveal that AIPA is an excellent inhibitor. It gives a
maximum inhibition efficiency of 96.52% at 0.456 mM/L (125 ppm; 125 mgL-1) and inhibits
corrosion by adsorbing at the mild steel surface. Polarization study suggested that AIPA acts as
mixed type inhibitor with some cathodic predominance. SEM and AFM analyses showed
improved morphology of the mild steel surface in presence AIPA. Quantum chemicals
parameters such as EHOMO, ELUMO, ΔE, global hardness and softness, electronegativity and
fraction of electron transfer (ΔN) were calculated using DFT method to correlate the electronic
properties with the adsorption and inhibition behavior of AIPA.
Keywords: Cysteine-Histidine, Green inhibitor, Electrochemical impedance spectroscope,
Atomic Force Microscopy, Density Functional Theory

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1. Introduction
Corrosion is a major problem in several industries. It causes enormous wastage of
metallic materials. The global economic loss due to corrosion is approximately $2.5 trillion
estimated by National association of corrosion engineer in 2016 that is about 3.5 % of world
GDP. Mild steel is most important of engineering material particular for structural,
instrumental, industrial and automobile applications due to its low cost and excellent
mechanical properties. However, it is severely attacked in acid solutions in contact with HCl in
various industries during pickling cleaning of industrial equipment of oil well etc. Inhibited acid
solutions are commonly used to reduce the corrosive attack of acid on metals. The use of
inhibitors is specific for different systems, and thus it needs to be studied thoroughly. Most of
the synthetic organic inhibitors are hazardous to health and cause adverse effect on
environment,1-3 The increasing ecological awareness and strict environmental regulations has
led to the development of green and environmentally benign corrosion inhibitors.4-6 Amino
acids have been recently reported as green corrosion inhibitors. They are naturally occurring
chemicals and display wide range of pharmaceutical and biological activities.7,8
A number of earlier reports have shown the application of amino acids as green
corrosion inhibitors, but they exhibit low inhibition efficiency (IE) at higher concentration if
they are used alone. It is reported that histidine alone exhibits 93.4 % IE on mild steel in 1 M
HCl at 10 mM/L and cysteine gives 85.6 % IE on mild steel in 1 M HCl at 4.1 mM/L.9,10 In
addition to this, the inhibition effect of cysteine on Cu–30Ni alloy corrosion in aerated 0.5 M
sulphuric acid was also studied by Saifi et al.11 using electrochemical and scanning electron
microscopic methods. These authors found that cysteine exhibits maximum efficiency of 91% at
1 mM concentration. Zhang et al.12 reported the inhibition effect of glutamic acid on corrosion

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of copper in 0.5 M hydrochloric acid. These authors have found that glutamic acid gives
maximum inhibition efficiency of 90.4% at 1.0 mM/L concentration. Methionine exhibited 84%
inhibition efficiency on mild steel corrosion in 0.5 M sulphuric acid solution at 10 mM
concentration.13 The inhibition effect of methionine and its two derivatives namely, L-
14
methionine sulphoxide and L-methionine sulphone is also investigated by K. F. Khaled on
mild steel corrosion using Monte Carlo simulations method. The methionine, L-methionine
sulphoxide and L-methionine sulphone exhibited maximum efficiencies of 93.2%, 94.0%, and
98.2% at 50 mM concentration, respectively. Zhang et al.15 also investigated inhibition effect of
two amino acids namely, DL-alanine and DL-cysteine on copper corrosion in 0.5 M aerated
hydrochloric acid solution using weight loss and electrochemical measurements. These amino
acids exhibited maximum efficiencies of 42.7% and 58.7% at 0.01 mM concentration. Several
attempts to improve their inhibition efficiency of amino acids have been made but no significant
enhancement in the inhibition efficiency was observed by synergizing them using the halides
and surfactants.10,16,17 It is reported that the condensation products of amino acids with
aldehydes give relatively better inhibition efficiency as compared to individual components.18,19
In view of the above observations and in continuation of our work on development of
green inhibitors, we report here the synthesis of condensation product of histidine and cysteine
namely 2-amino-3-((4-((S)-2-amino-2-carboxyethyl)-1H-imidazol-2-yl) thio) propionic acid
(AIPA) and its evaluation as corrosion inhibitor on mild steel corrosion in 1 M HCl using
weight loss, electrochemical impedance spectroscopy (EIS), potentiodynamic polarization,
scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), atomic
force microscopy (AFM) and quantum chemical methods. The chemical structure of the
inhibitor is given in Fig.1, which reveals the presence of π electrons and heteroatoms such as N,

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O and S in its structure through which it adsorbs on steel surface and is likely to give effective
corrosion inhibition. To the best of our knowledge no work has been reported on application of
2-amino-3-((4-((S)-2-amino-2-carboxyethyl)-1H-imidazol-2-yl) thio) propionic acid as
corrosion inhibitor.
2. Experimental section
2.1. Materials and test solution
All the gravimetric, electrochemical and surface studies were performed on mild steel
specimens, having chemical composition (wt %) C 0.31%, Si 0.19% Mn 0.92%, P 0.01%, S
0.008% and Cr 0.2% and Fe in balance. Mild steel coupons with dimensions 2.5 cm × 2.0 cm ×
0.025 cm and 8.0 cm × 1.0 cm × 0.025 cm were used for gravimetric and electrochemical
experiments, respectively. The test samples were prepared following the previously reported
method.20 The test solution (1 M HCl) was prepared using hydrochloric acid (HCl, 37 %, Fisher
Scientific) and double distilled water.
2.2. Synthesis of inhibitor
The investigated AIPA inhibitor was synthesized using the previously reported method
of Irene Erdelmeier et al.21 The formation of AIPA compound was confirmed by its melting
point, IR and NMR spectra (supporting information). The synthetic scheme of AIPA is shown
in Fig. 1, and other relevant information about AIPA is given in Table 1.
2.3. Corrosion tests
2.3.1 Gravimetric tests

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Gravimetric tests were performed at different concentration (0.091- 0.456 mM/L) and
temperatures (308-338 K) on mild steel in 1M HCl with and without AIPA inhibitor for 3 hrs,
by the previously reported method.22 The corrosion rate (CR), inhibition efficiency (η) and
surface coverage (θ) were calculated at different concentration and temperature by using the
following equations:
W
CR 
At
(1)
(2)
(3)
CR C
% 
R(i) 100
CR
CR CR(i)
 
CR
Where, W is the weight loss of specimen (mg), A is the area of specimen (cm2), t is the exposure
time (h), CR and CR(i) are the corrosion rates in the absence and presence of the inhibitor
molecules.
2.3.2Electrochemical tests
Electrochemical experiments were performed by using a conventional three-electrode
glass cell connected with Gamry Potentiostat/Galvanostat (Model G-300) instrument. Gamry
Echem Analyst 5.0 software package was used for fitting and analysis of data. The mild steel
specimens with 1 cm2 exposure area were used as working electrode. A platinum foil and a
saturated calomel electrode (SCE) were used as auxiliary and reference electrodes, respectively.
All the electrochemical experiments were performed at room temperature (308 +2K) using 100
ml of 1M HCl solution with and without AIPA inhibitor. Prior to each experiment, the working

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electrode was immersed in the test solution for 30 minutes and allowed to corrode freely until
the steady state of open circuit potential (OCP) corresponding to the corrosion potential (Ecorr)
of the working electrode was obtained. During the polarization measurement, cathodic and
anodic slopes were recorded by sweeping the electrode potential from -0.25 V and +0.25 V vs
corrosion potential (Ecorr) at a constant sweep rate 1 mV/s. The corrosion current density (Icorr)
and other relevant parameters were obtained by the extrapolation of the linear segment of
cathodic and anodic Tafel slopes. The corrosion inhibition efficiency (η%) was calculated from
the Icorr values by using the following equation:23
ic0orr ii
% 
corr 100
ic0orr
(4)
Where the i0corr and iicorr are the corrosion current densities in the absence and presence of AIPA,
respectively. EIS experiments were performed in the frequency range 100 KHz to 0.01 Hz at
open circuit potential (Ecorr) with an amplitude of 10 mV AC signal. By accurately fitting
Nyquist plot, charge transfer resistance (Rct), double layer capacitance (Cdl) and other
parameters were calculated. The inhibition efficiency (η%) was calculated by applying the
following equation:
Rpi  Rp0
%
10
(5)
Rpi
Where R0 and Rip are the polarization resistances without and with AIPA, respectively.
p
2.3.3. Surface study (AFM, SEM and EDX):
For the surface study, the mild steel specimens were cleaned and immersed in the 1 M
HCl solution for 3 hrs with and without optimum concentration of AIPA. After the immersion

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period, the mild steel specimens were taken out; washed, dried and fresh specimens were
employed for AFM, SEM and EDX analysis. The SEM Ziess Evo 50 XVP instrument model
was used to examine the micromorphology of mild steel surface at 2000× magnification. The
SEM coupled EDX detector was used to investigate the chemical composition of inhibited and
uninhibited specimens. The surface analysis through the AFM was carried out using the NT-
MDT multimode AFM, Russia, 111 controlled by Solver scanning probe microscope
controller. The single beam cantilever having resonance frequency in the range of 240–255
kHz in semi-contact mode with corresponding spring constant of 11.5Nm−1 containing NOVA
program was used for image interpretation.
3. Results and discussions
3.1. Weight loss measurements
3.1.1 Influence of concentration:
Table 2 represents corrosion parameters obtained from weight loss data for AIPA at
different concentrations. Careful inspection of the results revealed that inhibition performance
of the AIPA increases with increasing its concentrations and maximum inhibition efficiency of
96.52% was obtained at 0.456 mM/L concentration. The increased inhibition efficiency of the
AIPA on increasing its concentration is attributed to increased surface coverage.24 The high
inhibition efficiency of the investigated AIPA at relatively low concentration is attributed to
the presence of several heteroatoms in the form of polar functional groups such as –NH2, -S-
and -COOH and hetero-aromatic imidazole ring which act as adsorption centers and enhance
the inhibition efficiency of the AIPA molecule. Furthermore, the presence of polar functional
groups such as –NH2 and –COOH increases the solubility of the investigated inhibitor which in
turn also enhances the effectiveness of the inhibitor molecule.

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3.1.1.Influence of temperature:
Table 3 shows the variation in the values of corrosion rate (CR) and percentage
inhibition efficiency (η%) of investigated inhibitor at its optimum concentration with solution
temperature. From the results represented in Table 3, it can be seen that inhibition efficiency of
AIPA decreases with increasing solution temperature which might be attributed to increased
kinetic energy of the inhibitor which decrease the intermolecular force of interaction between
adsorbate (AIPA) and adsorbent (metallic surface).25 Further, molecular rearrangement, rapid
etching, and molecular decomposition may also decrease the inhibition performance of the
inhibitor.26 The effect of temperature on the corrosion inhibition efficiency of the AIPA can be
best represented by Arrhenius equation which represents the natural logarithm of corrosion rate
(log CR) as a linear function of 1/T:27
Ea
2.303RT
log(CR )
log
(6)
Where, A is the Arrhenius pre-exponent, CR is the corrosion rate (mgcm-2h-1), T is the
absolute temperature and R is the universal gas constant. The slope ( Ea 2.303R ) values of
Arrhenius plots shown in Fig. 2 were employed in order to obtain the values of Ea in the
absence and presence of optimum concentration of the studied inhibitor. The calculated values
of Ea were 28.48 kJmol-1 and 91.70 kJmol-1 in the absence and presence of AIPA, respectively.
The increased value of Ea in presence of AIPA is attributed to increased energy barrier for mild
steel corrosion in acid solution in presence of inhibitor.28 Generally, an organic inhibitor forms
surface metal-inhibitor complex which acts as barrier for corrosion process and thereby
increases the value of activation energy (Ea).29

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3.1.2. Adsorption isotherm:
Adsorption isotherm is the most important parameter in the field of corrosion study as it
provides structural as well as thermodynamic information about electric double layer formed
over the metallic surface. Furthermore, adsorption isotherm also gives information about nature
and effectiveness of adsorption of inhibitor molecule on the metallic surface. In the present
study, the Temkin, Frumkin, and Langmuir adsorption isotherms were tested. The criterion for
selection of best isotherm was the value of regression coefficient which was closest to one for
Langmuir adsorption isotherm which suggests that the adsorption of AIPA on mild steel
surface obeyed the Langmuir adsorption isotherm. However, from Langmuir isotherm plot for
studied inhibitor shown in Fig. 3, it can be seen that the value of slope was much deviated from
unity. The deviation from ideal Langmuir adsorption behavior of studied inhibitor molecule
might be attributed to intermolecular interactions of the adsorbed inhibitor molecules over the
metallic surface which resulted into mutual attraction and/ or repulsion.30,31 The Langmuir
isotherm can be represented by following equation:

1
KadsC 
(7)
Where, Kads represents the equilibrium constant for adsorption-desorption processes taking
place on the metallic surface, C is the concentration and θ is the surface coverage. From the
intercept of the Langmuir plot, values of Kads at different studied temperatures were calculated
and by employing which values of standard free energy of adsorption (ΔG0ads) were derived
using following relationship:
Gaοds  RT ln(55.5Kads )
(8)

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In the above equation, 55.5 denotes the concentration (in mole) of water in acid solution.
The derived values of Kads and ΔG0ads at different studied temperatures are given in the Table 4.
Literature survey revealed that value of ΔG0ads is associated with the nature of adsorption. In
general, -20 kJmol-1 or more positive value of ΔG0ads is related with electrostatic interactions
between oppositely charged inhibitor molecule and metallic surface,32 and -40 kJmol-1or more
negative value of ΔG0ads is related to electron sharing between inhibitor and metallic surface.33
In the present case, the values of ΔG0ads varied from 34.96 kJmol-1 to -38.19 kJmol-1 indicating
that interaction of AIPA on mild steel surface in acid solution involves the both physisorption
and chemisorption i.e. AIPA behaves as mixed type.34-37
3.2 Electrochemical studies
3.2.1. Potentiodynamic polarization studies
Potentiodynamic polarization behavior of mild steel corrosion without and with different
concentrations of AIPA is shown in Fig. 4 and various potentiodynamic polarization
parameters such as corrosion current density (icorr), anodic and cathodic Tafel slopes (βa and
βc), surface coverage and corrosion potential (Ecorr) are presented in Table 5. Inspection of the
results depicted in Table 5 and Fig. 4 showed that in presence of AIPA, corrosion current
density decreased significantly indicating the formation of a protective film by the inhibitor
molecules. Moreover, it can also be seen that the decrease in current density is more
pronounced at higher inhibitor concentration. From Fig. 4 it is seen that shape of Tafel curves
for inhibited and uninhibited mild steel specimens are similar indicating that presence of AIPA
inhibits the metallic corrosion by adsorbing on metallic surface without changing the
mechanism of metallic corrosion. Change in both anodic and cathodic slopes without

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appreciable change in the shape of Tafel slopes is attributed due to formation of mild steel-
AIPA or mild steel-OH-AIPA complex that isolates metals and inhibits from corrosion as
reported earlier.38 Further, it can be seen from the results that values of both βa and βc are
affected in the presence of the inhibitor molecules. However, the values of βc are more affected
as compared to the value of βa indicating that the investigated inhibitor predominantly acts as a
cathodic inhibitor. Moreover, the nature of inhibitor can also be determined by the variation in
the value of corrosion potential with and without inhibitor. If the change in Ecorr value in
presence of inhibitor is greater than 85 mV as compared to the Ecorr value of blank, then the
inhibitor can be categorized as anodic or cathodic type.39,40 However, if the change in Ecorr
value is less than 85 mV, associated with mixed type inhibitor39,40. In the present case, the
maximum change in the Ecorr value is 66 mV indicating that the investigated inhibitor acts as
mixed type inhibitor with slight cathodic predominance.
3.1.2. Electrochemical impedance spectroscopy study
The Nyquist and Bode plots for mild steel corrosion in the absence and presence of
different concentrations of inhibitor are shown in Figs. 5 and 6. The Nyquist plots with and
without inhibitor consists of a single capacitive loop indicating the charge transfer mechanism
which is further supported by a single maxima in the corresponding Bode plots. A careful
visualization of the Nyquist plots showed that the diameter of the semicircle capacitive loop
increases in presence of increasing concentration of inhibitor. During analysis of Nyquist
plots, the difference in the real impedance at lower and higher frequencies is generally termed
as charge transfer resistance (Rct). However, in our present study, the difference in the real
impedance at lower and higher frequencies is considered as polarization resistance (Rp) rather
than charge transfer resistance as reported earlier.41-44 In a typical metal corroding system,

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polarization resistance (Rp) includes charge transfer resistance (Rct), the resistance due to
accumulated species at metal/ electrolyte interface i.e. accumulation resistance (Ra), diffusion
layer resistance (Rd), and the resistance caused by inhibitor film (Rf) at metal surface (Rp= Rct
+ Ra + Rd + Rf).42,44,45 This finding suggests the polarization resistance increases in presence of
inhibitor which is attributed to the formation of a protective film by inhibitor molecules over
the metal/ electrolyte interface.46 Various electrochemical impedance parameters such as
solution resistance (Rs), charge transfer resistance (Rp), double layer capacitance (Cdl), phase
shift (n) and corresponding corrosion inhibition efficiency (η%) were determined with the
42,44
help of equivalent circuit described elsewhere
and are given in the Table 6. Generally,
CPE is used in a model at the place of a capacitor to compensate for non-homogeneity in the
system. In the present case, impedance of CPE (ZCPE) can be represented according to the
following equation:
 
1
n 1
ZCPE

( j)

 
(9)
Y0
 
In the above equation, Y0 represents the CPE constant, ω represents the angular
frequency, n is the phase shift which provides information about the surface inhomogeneity
and j represents the imaginary number. In general, a higher value of n related with lower
surface roughness and vice versa. Moreover, the nature of impedance spectra for metal
corroding in acid solution can also be explained with the help of n value. For example, n = 0
represents the resistance, n = 1 represent the capacitance, n = -1 represents the inductance and
n = 0.5 represents the Warburg impedance. In our present study, values of n in the absence
and presence of inhibitor molecule range from 0.827 to 0.893. The deviation from unity (ideal

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capacitive behavior) is attributed to the presence of surface inhomogeneity and surface
roughness.47 The value of double layer capacitance (Cdl) can be derived using following
equation:
n-1
Cdl = Y0 (ωmax
)
(10)
Where, ωmax represents the frequency at which the imaginary part of impedance is maximum
(rads-1). A careful inspection of the results depicted in the Table 6 shows that the values of Rct
increase and that of Cdl decrease with increase in the inhibitor concentration which results in
an increased thickness of electric double layer due to adsorption of inhibitor molecules on the
metallic surface and/ or decreased value of dielectric constant due to replacement of water
molecules by the inhibitor.47,48
The increased surface smoothness in presence of inhibitor can also be supported by Bode
plots. The ideal capacitor is characterized by a constant slope value of –1 and phase angle of -
900. However, this deviation from ideal capacitive behavior is attributed to surface
roughness.48 One can see from the Bode plots with and without inhibitor that the deviation
from the ideal capacitive behavior is more effective in the absence of inhibitor. The slope and
phase angle values significantly increased in presence of inhibitor owing to the formation of a
protective film. Moreover, the increased values of phase angles are more effective at high
inhibitor concentrations.
3.2. Surface analysis
3.2.1 Scanning electron microscopy (SEM)

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Scanning electron micrographs of the mild steel specimens in the absence and presence
of optimum concentration of the studied inhibitor after 3 h immersion time are shown in the
Fig. 7. Fig. 7a shows the micrograph of uninhibited mild steel specimen which is
characterized by a highly rough surface owing to the acid corrosion of the specimen in the
absence of inhibitor. However, the micrograph of inhibited mild steel specimen (Fig.7b) was
relatively smoother indicating that the inhibitor has formed a protective film over the metallic
surface which protects metal from corrosion.
3.3.2. Energy dispersive X-ray analysis (EDX)
The elemental composition of iron and other elements on the surface of mild steel in 1M
HCl after immersion for 3h in the presence and absence of optimum concentration of AIPA
can be seen in Fig. 8. The EDX spectrum of uninhibited mild steel specimen (Fig.8a) shows
signals corresponding to iron (Fe), carbon (C) and oxygen (O) only. Presence of signal for
oxygen in uninhibited mild steel specimen is attributed due to formation of ferrous and ferric
oxide due to atmospheric oxidation of iron during SEM/EDX analyses. However, the EDX
spectrum of inhibited mild steel specimen (Fig. 8b) shows two additional signals
corresponding to N and S, indicating that these elements were also present on the inhibited
mild steel specimen. Moreover, the spectra of inhibited sample of mild steel show that the
peak of Fe-atom is suppressed significantly and more intense peaks of O-atom, when
compared to the spectra in the absence of inhibitor has appeared which further supports that

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the inhibitor forms a protective film on mild steel surface. The percentage elemental
composition of inhibited and uninhibited mild steel specimens is given in Table 7.
3.3.3. Atomic force microscopy
The AFM micrographs of inhibited and uninhibited mild steel specimens after 3 h
immersion time are shown in Fig.9. The mild steel surface was highly corroded and damaged
in the absence of inhibitor (Fig. 9a) with average surface roughness of 392 nm. However, in
presence of inhibitor at its optimum concentration, the surface morphology of the mild steel
specimen was significant improved. The increased surface smoothness in presence of inhibitor
is attributed to retardation of corrosion processes. In presence of inhibitor the calculated
surface roughness was 96 nm.
3.4 Quantum chemical calculations
The quantum chemical calculations were performed in order to support the experimental
findings. The optimized molecular structure and highest occupied molecular orbital and
lowest unoccupied molecular electron density distribution of the studied inhibitor are shown
in Figs. 10 and 11, respectively and important quantum chemical parameters such as EHOMO
,
ELUMO, ΔE, global hardness (ρ), global softness (σ), electronegativity (χ), fraction of electron
transfer (ΔN) and dipole moment are presented in Table 8. In general, a high value of EHOMO
represents a higher electron donating ability of the inhibitor and therefore high bonding
tendency between the metal and the inhibitor. Similarly, a lower value of ELUMO represents the
higher electron accepting tendency of the inhibitor from the metal surface. And therefore it
can be concluded that the higher value of EHOMO and lower value of ELUMO facilitate the
inhibitor bonding between metal and inhibitor. Similarly, a lower value of ΔE is associated

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with a high chemical reactivity and therefore high inhibition efficiency. Moreover, lower
electronegativity (χ), higher softness (σ) and higher value of fraction of electron transfer (ΔN)
represent the greater electron donating ability of the inhibitor. While, higher value of global
hardness (η) and electronegativity decreases the electron donating ability of the inhibitor
molecule. In the present study, the AIPA showed a comparatively high value of EHOMO (-
5.581eV) and low value of ELUMO (-0.574 eV) signifying that it has strong electron donating
(donation) as well as electron accepting (retro-donation) tendencies resulting into strong
bonding between inhibitor and metal surface. Further, a very small value of ΔE (5.008 eV) of
AIPA in comparison to that of cysteine (5.352 eV) and Histidine (5.662 eV) in the present
study indicated that it is highly reactive and acted as a good corrosion inhibitor. Similarly, the
values of hardness and electronegativity were very low as 2.503 eV and 3.077 eV respectively
suggesting that the inhibitor has a very high electron donating ability. This finding was further
supported by a high value of global softness (σ) and electron transfer (∆N). Moreover, a
higher value of dipole moment (4.17 Debye) as compared to the dipole moment of water (1.85
Debye) indicates that the inhibitor has a strong tendency to replace water molecules from the
metallic surface.
4. Conclusions
From weight loss, electrochemical, surface and quantum chemical studies, it is
concluded that the investigated compound acts as a good corrosion inhibitor for mild steel in
acid solution and its inhibition efficiency increases with increasing concentration. Maximum
inhibition efficiency of 96.52% was obtained at 0.456 mM/L concentration. Adsorption of the
compound on mild steel surface obeyed the Langmuir adsorption isotherm. Potentiodynamic
polarization study revealed the AIPA acted as a mixed type inhibitor with cathodic

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predominance. EIS results showed that the presence of inhibitor molecule decreased the value
of Cdl and increased the value of Rct which indicated its adsorption over the metal/ electrolyte
interface. SEM and AFM analyses showed the existence of protective film of inhibitor
molecule over the metallic surface. Quantum chemical study confirmed the experimental
results and showed that the investigated inhibitor has a strong tendency of adsorption over the
metallic surface.
References:
[1] C. Verma, A. Singh, G. Pallikonda, M. Chakravarty, M.A. Quraishi, I. Bahadur, E.E.
Ebenso, Aryl sulfonamidomethylphosphonates as new class of green corrosion inhibitors
for mild steel in 1 M HCl: Electrochemical, surface and quantum chemical investigation,
J. Mol. Liq., 209 (2015) 306–319.
[2] C. Verma, P. Singh, I. Bahadur, E.E. Ebenso, M.A. Quraishi, Electrochemical,
thermodynamic, surface and theoretical investigation of 2-aminobenzene-1,3-
dicarbonitriles as green corrosion inhibitor for aluminum in 0.5 M NaOH, J. Mol. Liq.,
209 (2015) 767–778.
[3] Y. Tang, X. Yang, W. Yang, Y. Chen, R. Wan, Experimental and molecular dynamics
studies on corrosion inhibition of mild steel by 2-amino-5-phenyl-1,3,4-thiadiazole,
Corros. Sci., 52 (2010) 242–249.
[4] K.M. Ismail, Evaluation of cysteine as environmentally friendly corrosion inhibitor for
copper in neutral and acidic chloride solutions, Electrochimi. Acta. 52 (2007) 7811–
7819.

ACCEPTED MANUSCRIPT
[5] Bobina, M. Kellenberger, A. Millet, J.-P.C. Muntean, N. Vaszilcsin, Corrosion resistance
of carbon steel in weak acid solutions in the presence of l-histidine as corrosion
inhibitor, Corros. Sci., 69 (2013) 389–395.
[6] H. Zhao, X. Zhang, L. Ji, H. Hud, Q. Li, Quantitative structure–activity relationship
model for amino acids as corrosion inhibitors based on the support vector machine and
molecular design, Corros. Sci., 83 (2014) 261–271.
[7] K.F. Khaled, Corrosion control of copper in nitric acid solutions using some amino acids
– A combined experimental and theoretical study, Corros. Sci., 52 (2010) 3225–3234.
[8] R. A. Sheldon, Green and sustainable manufacture of chemicals from biomass: state of
the art, Green Chem., 16 (2014) 950–963.
[9] J. Fu, S. Li, Y. Wang, L. Cao, L. Lu, Computational and electrochemical studies of some
amino acid compounds as corrosion inhibitors for mild steel in hydrochloric acid
solution, J. Mater. Sci., 45 (2010) 6255–6265.
[10] M. Mobin, S. Zehra, M. Parveen, L-Cysteine as corrosion inhibitor for mild steel in
1MHCl and synergistic effect of anionic, cationic and non-ionic surfactants, J. Mol. Liq.,
216 (2016) 598–607.
[11] H. Saifi, M.C. Bernard, S. Joiret, K. Rahmouni, H. Takenouti, B. Talhi, Corrosion
inhibitive action of cysteine on Cu–30Ni alloy in aerated 0.5M H2SO4, Mater. Chem.
Phys., 120 (2010) 661–669.
[12] Da-Quan Zhang, Qi-Rui Cai, Li-Xin Gao, Kang Yong Lee, Effect of serine, threonine
and glutamic acid on the corrosion of copper in aerated hydrochloric acid solution,
Corros. Sci., 50 (2008) 3615–3621.
[13] M. Ozcan, F. Karadag, I. Dehri, Investigation of adsorption characteristics of methionine
at mild steel/sulfuric acid interface: An experimental and theoretical study, Colloids
Surf. A Physicochem. Eng. Asp., 316 (2008) 55–61.
[14] K. F. Khaled, Monte Carlo simulations of corrosion inhibition of mild steel in 0.5 M
sulphuric acid by some green corrosion inhibitors, J. Solid State Electr., 13 (2009)
1743–1756.
[15] Da-Quan Zhang, Li-Xin Gao, Guo-Ding Zhou, Inhibition of copper corrosion in aerated
hydrochloric acid solution by amino-acid compounds, J. Appl. Electrochem., (2005)
35:1081–1085

ACCEPTED MANUSCRIPT
[16] M. Mobin, M. Parveen, M.Z.A. Rafiquee, Inhibition of Mild Steel Corrosion Using L-
Histidine and Synergistic Surfactants Additives, J. Mater. Eng. Perf., 22 (2013) 548–
556.
[17] D. Zhang, X. He, Q. Cai, L. Gao, G. S. Kim, pH and iodide ion effect on corrosion
inhibition of histidine self-assembled monolayer on copper, Thin Solid Films, 518
(2010) 2745–2749.
[18] M. A. Quraishi, D. Jamal, The influence of some condensation products on corrosion
inhibition of mild steel in acidic solutions. Anti-Corros. Methods Mater, 47 (2000) 233-
240.
[19] M.A. Quraishi, I. Ahamad, A.K. Singh, S.K. Shukla, B. V. Singh, N-(Piperidinomethyl)-
3-[(pyridylidene)amino]isatin: A new and effective acid corrosion inhibitor for mild
steel. Mater. Chem. Phys., 112 (2008) 1035–1039.
[20] C. Verma, M. A. Quraishi, L. O. Olasunkanmi E.E. Ebenso, L-Proline-promoted
synthesis of 2-amino-4-arylquinoline-3-carbonitriles as sustainable corrosion inhibitors
for mild steel in 1 M HCl: experimental and computational studies, RSC Adv., 5 (2015)
85417-85430.
[21] I. Erdelmeier, S. Daunay, R. Lebel, L. Farescour, Jean-Claude Yadan, Cysteine as a
sustainable sulfur reagent for the protecting-group-free synthesis of sulfur-containing
amino acids: biomimetic synthesis of L-ergothioneine in water, Green Chem., 14 (2012)
2256-2265.
[22] C. Verma, L. O. Olasunkanmi, E. E. Ebenso, M. A. Quraishi, I. B. Obot, Adsorption
Behavior of Glucosamine-Based, Pyrimidine-Fused Heterocycles as Green Corrosion
Inhibitors for Mild Steel: Experimental and Theoretical Studies, J. Phys. Chem. C, 120
(2016) 11598−11611.
[23] M. Yadav, S. Kumar, N. Kumari, I. Bahadur, E.E. Ebenso, Experimental and Theoretical
Studies on Corrosion Inhibition Effect of Synthesized Benzothiazole Derivatives on
Mild Steel in 15% HCl Solutionm, Int. J. Electrochem. Sci., 10 (2015) 602 – 624.
[24] T. Ramdé, S. Rossi, L. Bonou, Corrosion Inhibition Action of Sulfamethoxazole for
Brass in Acidic Media, Int. J. Electrochem. Sci., 11 (2016) 6819 – 6829.

ACCEPTED MANUSCRIPT
[25] P. M. Wadhwani, D. G. Ladha, V. K Panchal, N. K. Shah, Enhanced corrosion inhibitive
effect of p-methoxybenzylidene-4,4′-dimorpholine assembled on nickel oxide
nanoparticles for mild steel in acid medium, RSC Adv., 5 (2015) 7098–7111.
[26] C. Verma, L. O. Olasunkanmi, E. E. Ebenso, M. A. Quraishi, I. B. Obot, Adsorption
Behavior of Glucosamine-Based, Pyrimidine-Fused Heterocycles as Green Corrosion
Inhibitors for Mild Steel: Experimental and Theoretical Studies, J. Phys. Chem. C, 120
(2016) 11598–11611.
[27] A. K. Singh, E. E. Ebenso, Inhibition Effect of Cefradine on Corrosion of Mild Steel in
HCl Solution, Int. J. Electrochem. Sci., 9 (2014) 352 – 364.
[28] K. F. Khaled, O. A. Elhabib, A. El-mghraby, O. B. Ibrahim, A. M. Magdy Ibrahim,
Inhibitive effect of thiosemicarbazone derivative on corrosion of mild steel in
hydrochloric acid solution, J. Mater. Environ. Sci., 1 (2010) 139-150.
[29] S. K. Shukla, E. E. Ebenso, Corrosion Inhibition, Adsorption Behavior and
Thermodynamic Properties of Streptomycin on Mild Steel in Hydrochloric Acid
Medium, Int. J. Electrochem. Sci., 6 (2011) 3277 – 3291.
[30] M. Larouj, H. Lgaza, H. Serrard, H. Zarroka, H. Bourazmib, A. Zarroukc, A. Elmidaouia
A. Guenbour, S. Boukhrisd, H. Oudda, Adsorption properties and inhibition of carbon
steel corrosion in hydrochloric acid solution by Ethyl 3-hydroxy-8-methyl-4-oxo-6-
phenyl-2-(p-toly)-4,6- dihydropyrimido[2,1-b] [1,3]thiazine-7-carboxylate, J. Mater.
Environ. Sci., 6 (2015) 3251-3267.
[31] E. E. Oguzie, B. N. Okolue, E. E. Ebenso, G. N. Onuoha, A. I. Onuchukwu, Evaluation
of the inhibitory effect of methylene blue dye on the corrosion of aluminium in
hydrochloric acid, Mater. Chem. Phys., 87 (2004) 394–401.
[32] S. Issaadi, T. Douadi, A. Zouaoui, S. Chafaa, M. A. Khan G. Bouet, Novel thiophene
symmetrical Schiff base compounds as corrosion inhibitor for mild steel in acidic media,
Corros. Sci., 53 (2011)1484–1488.
[33] R. Solmaz, Investigation of adsorption and corrosion inhibition of mild steel in
hydrochloric acid solution by 5-(4-Dimethylaminobenzylidene) rhodanine, Corros. Sci.,
79 (2014) 169–176.
[34] I. Chakib, H. Elmsellem, N.K. Sebbar, S. Lahmidi, A. Nadeem, E.M. Essassi, Ouzidan,
Y. Abdel-Rahman, I. F. Bentiss, B. Hammouti, Electrochemical, gravimetric and

ACCEPTED MANUSCRIPT
theoretical evaluation of (4Z)-2,5-dimethyl- 4-(4-methylpyrimido[1,2-a]benzimidazol-
2(1H)-ylidene)-2,4-dihydro-3Hpyrazol-3-one (P1) as a corrosion inhibitor for mild steel
in 1 M HCl solution, J. Mater. Environ. Sci., 7 (2016)1866–1881.
[35] R. Solmaz, Investigation of corrosion inhibition mechanism and stability of Vitamin B1
on mild steel in 0.5 M HCl solution, Corros. Sci., 81 (2014) 75–84.
[36] F. Bentiss, M. Lebrini M. Lagrenee, Thermodynamic characterization of metal
dissolution and inhibitor adsorption processes in mild steel/2,5-bis(n-thienyl)-1,3,4-
thiadiazoles/hydrochloric acid system, Corros. Sci., 47 (2005) 2915–2931.
[37] M. A. Amin, M. A. Ahmed, H. A. Arida, T. Arslan, M. Saraçoglu, F. Kandemirli,
Monitoring corrosion and corrosion control of iron in HCl by non-ionic surfactants of
the Triton-X series – Part II. Temperature effect, activation energies and
thermodynamics of adsorption, Corros. Sci., 53 (2011) 540–548.
[38] F. M. Donahue, Ken Nobe, Consecutive Electrode Reactions in the Dissolution Kinetics
of Iron, J. Electrochem. Soc., 114 (1967) 682-685.
[39] A. A. Al-Amiery, F. A. B. Kassim, A. A. H. Kadhum, A. B. Mohamad, Synthesis and
characterization of a novel eco-friendly corrosion inhibition for mild steel in 1 M
hydrochloric acid, Sci. Report., 6 (2016) 19890.
[40] I.O. Arukalam, I. C. Madufo, E.E. Oguzie, E.E. Ebenso, Adsorption and inhibitive
properties of hydroxypropyl Methylcellulose on the acid corrosion of mild steel, Int. J.
Appl. Sci. Eng. Res., 3 (2014) 241-256.
[41] M. Ozcan, I. Dehri, M. Erbil, Organic sulphur-containing compounds as corrosion
inhibitors for mild steel in acidic media: correlation between inhibition efficiency and
chemical structure, Appl. Surf. Sci., 236 (2004) 155–164.
[42] A. Doner, R. Solmaz, M. Ozcan, G. Kardas, Corros. Sci., 53 (2011) 2902–2913.
[43] C. Verma, M.A. Quraishi, E.E. Ebenso, I.B. Obot, A. El Assyry, 3-Amino alkylated
indoles as corrosion inhibitors for mild steel in 1M HCl: Experimental and theoretical
studies, J. Mol. Liq., 219 (2016) 647–660.
[44] R. Solmaz, G. Kardas, M. C¸ ulha, B. Yazıcı, M. Erbil, Investigation of adsorption and
inhibitive effect of 2-mercaptothiazoline on corrosion of mild steel in hydrochloric acid
media, Electrochim. Acta, 53 (2008) 5941–5952.

ACCEPTED MANUSCRIPT
[45] M. Erbil, Determination of corrosion rates by analysis of AC impedance diagrams, Chim.
Acta Turc., 1 (1988) 59–70.
[46] S. K. Saha, A. Dutta, P. Ghosh, D. Sukul, P. Banerjee, Adsorption and corrosion
inhibition effect of Schiff base molecules on the mild steel surface in 1 M HCl medium:
a combined experimental and theoretical approach, Phys, Chem. Chem. Phys., 17 (2015)
5679-5690.
[47] A. Youse, S. Javadian, N. Dalir, J. Kakemam, J. Akbari, Imidazolium-based ionic liquids
as modulators of corrosion inhibition of SDS on mild steel in hydrochloric acid
solutions: experimental and theoretical studies, RSC Adv., 5 (2015) 11697–11713.
[48] C. Verma, M.A. Quraishi, A. Singh, 5-Substituted 1H-tetrazoles as effective corrosion
inhibitors for mild steel in 1 M hydrochloric acid, J. Taibah Univ., 10 (2016) 718–733.

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Fig. 1.: Synthetic scheme for AIPA.
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Blank
-0.2
AIPA
-0.4
-0.6
2.95 3.00 3.05 3.10 3.15 3.20 3.25
[(1/T.103) K-1]
Fig. 2: Arrhenius plots for inhibited and uninhibited mild steel specimens in 1M HCl.

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1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Langmuir adsorption isotherm
AIPA

y = 1.8414x + 7.57
R² = 0.9989
-4.1 -4.0 -3.9 -3.8 -3.7 -3.6 -3.5 -3.4 -3.3
log C(M)
Fig. 3: Langmuir isotherm plots for the adsorption of AIPA on mild steel surface in 1M HCl.

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Fig. 4: Polarization curves for mild steel in absence and presence of different concentrations of
AIPA.

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Fig. 5: Nyquist plot for mild steel in 1 M HCl without and with different concentrations of
AIPA.

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0
Fig. 6: Bode (log f vs log |Z|) and phase angle (log fvsα ) plots for mild steel in 1 M HCl in
absence and presence of different concentrations of AIPA.

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Fig. 7: SEM images of mild steel:(a) in absence of AIPA and (b) in the presence of 0.456 mM/L
concentration of AIPA.

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Fig. 8: EDX spectra of mild steel (a) in absence and (b) in presence of 0.456 mM/L
concentration of AIPA.