Highly functionalized epoxy macromolecule as an anti-corrosive material for carbon steel: Computational (DFT, MDS), surface (SEM-EDS) and electrochemical (OCP, PDP, EIS) studies

Article abstract of DOI:10.1016/j.molliq.2020.112535

In present study, a tetra-functionalized aromatic epoxy pre-polymer namely, 4,4′-oxybis(N,N-bis(oxiran-2-ylmethyl)aniline) (AA2) was synthesized and established as corrosion inhibitor for carbon steel corrosion in 1 M HCl medium. The prepolymer was charac

Full text of DOI:10.1016/j.molliq.2020.112535

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Highly functionalized epoxy macromolecule as an anti-corrosive
material for carbon steel: Computational (DFT, MDS), surface
(SEM-EDS) and electrochemical (OCP, PDP, EIS) studies
O. Dagdag, Zaki Safi, Nuha Wazzan, H. Erramli, Lei Guo, Ahmed
M. Mkadmh, Chandrabhan Verma, E.E. Ebenso, L. El Gana, A. El
Harfi
PII:
S0167-7322(19)36479-7
DOI:
https://doi.org/10.1016/j.molliq.2020.112535
MOLLIQ 112535
Reference:
To appear in:
Journal of Molecular Liquids
Received date:
Revised date:
Accepted date:
25 November 2019
6 January 2020
18 January 2020
Please cite this article as: O. Dagdag, Z. Safi, N. Wazzan, et al., Highly functionalized
epoxy macromolecule as an anti-corrosive material for carbon steel: Computational (DFT,
MDS), surface (SEM-EDS) and electrochemical (OCP, PDP, EIS) studies, Journal of
Molecular Liquids(2020), https://doi.org/10.1016/j.molliq.2020.112535
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Highly functionalized epoxy macromolecule as a anti-corrosive material for
carbon steel: Computational (DFT, MDS), surface (SEM-EDS) and
electrochemical (OCP, PDP, EIS) studies
O. Dagdag1,2, Zaki Safi3, Nuha Wazzan4, H. Erramli5 Lei Guo6, Ahmed M. Mkadmh7,
ChandrabhanVerma8,9,10*, E. E. Ebenso9, 10, L. El Gana 11 and A. El Harfi 1
1Laboratory of Agroresources, Polymers and Process Engineering (LAPPE), Department of Chemistry,
Faculty of Science, Ibn Tofail University, BP 133, 14000 Kenitra, Morocco.
2Laboratory of Industrial Technologies and Services(LITS), Department of Process Engineering,
Height School of Technology, Sidi Mohammed Ben Abdallah University, P.O. Box 2427, 30000, Fez,
Morocco.
3Al Azhar University-Gaza, Chemistry Department, Faculty of Science, P.O Box 1277, Gaza, Palestine
4King Abdulaziz University, Chemistry Department, Faculty of Science, P.O Box 42805, Jeddah,
21589, Saudi Arabia.
5Laboratory of Materials, Electrochemistry and Environment, Department of Chemistry, Faculty of
Sciences, Ibn Tofail University, Kenitra, Morocco.
6School of Materials and Chemical Engineering, Tongren University, Tongren, 554300, China.
7Chemistry Department, Faculty of Applied Science, Al Aqsa University, Gaza, Palestine
8Center of Research Excellence in Corrosion, Research Institute, King Fahd University of Petroleum
and Minerals, Dhahran 31261, Saudi Arabia
9Material Science Innovation & Modelling (MaSIM) Research Focus Area, Faculty of Natural and
Agricultural Sciences, North-West University, Private Bag X2046, Mmabatho 2735, South Africa
10Department of Chemistry, Faculty of Natural and Agricultural Sciences, School of Chemical and
Physical Sciences, North-West University, Private Bag X2046, Mmabatho 2735, South Africa.
11Laboratory of Optoelectronics, Physical Chemistry of Materials and Environment, Department of
Physics, Faculty of Science, Ibn Tofail University, BP 133, 14000 Kenitra, Morocco.
*Corresponding
author
E-mails:
chandraverma.rs.apc@itbhu.ac.in,
cbverma38@gmail.com (CV)
Abstract
In present study, a tetra-functionalized aromatic epoxy pre-polymer namely, 4,4'-
oxybis(N,N-bis(oxiran-2-ylmethyl)aniline) (AA2) was synthesized and established as
corrosion inhibitor for carbon steel corrosion in 1 M HCl medium. The prepolymer
was characterized by proton nuclear magnetic resonance (1H NMR) and Fourier-
transform infrared spectroscopy (FT-IR) spectral techniques and its inhibition
property was demonstrated using electrochemical open circuit potential (OCP),
potentiodynamic polarization(PDP) and electrochemical impedance spectroscopy
(EIS), surface scanning electron microscopy (SEM) analysis coupled with energy
dispersive spectroscopy (EDS) analysis and computational density functional theory

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(DFT) and molecular dynamic (MD) simulations methods. Electrochemical studies
demonstrate that AA2 acts as sensibly good inhibitor for carbon steel in 1 M HCl
medium and showed highest efficiency of as high as 91.3% at 10-3M.The PDP results
show that AA2 behaves as predominantly cathodic type of inhibitor.SEM analysis
coupled with EDS showed that AA2 forms surface protective films and isolates the
metal from aggressive solution. DFT studies suggest that both neutral as well as
cationic forms of the AA2 strongly interact with metallic surface using two aromatic
and four oxirane rings. Molecular dynamic simulations (MDS) study showed that
AA2 adsorb strongly on metallic surface using their electron rich centers and acquires
the parallel or flat orientation. Outcomes of the experimental (SEM-EDS, OCP, EIS
and PDP) and computational (DFT and MDS) studies were in excellent concurrence.
Keywords: Epoxy prepolymer inhibitor, electrochemical, cathodic inhibitor, Langmuir
adsorption isotherm and computational studies.
1. Introduction
Steel alloys have constantly been the materials of enormous significance for an
assortment of engineering applications for the reason that of their fashionable and
outstanding mechanical properties[1,2].However, they suffer severe attack in
corrosive environments (acid solutions) especially HCl and H2SO4 solutions which
are repeatedly being utilized in acid pickling, acid descaling, acid cleaning, etc.
processes [3,4].Therefore, these engineering and industrial processes require the
addition of corrosion inhibitors in aggressive solutions[5, 6].Use of organic
compounds as corrosion inhibitors is one of frequent methods against the corrosion
because of their economic and inhibition effectiveness along with ease of synthesis
and application. These compounds adsorb on metallic surface through their polar
functional groups including amines, amides, diamines, polyols, diols, ketones,
aromatic rings, etc. [7-9]. Here, we demonstrated the anti-corrosive property of an
aromatic epoxy prepolymer namely, 4,4'-oxybis (N,N-bis(oxiran-2-ylmethyl)aniline)
(AA2) on acidic dissolution of carbon steel using several experimental and
computational techniques. The organic aromatic epoxy prepolymer contains several
electron rich sites in the form of nitrogen (N), oxygen (O) and π-electrons through
which AA2 can adsorbs effectually and slowdown or retards the corrosion attack
thereafter. Owing to its high molecular size, AA2 covers larger surface area and
behaves as good anti-corrosive compound. Four peripheral polar groups enhance the

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AA2 solubility in the electrolyte (1M HCl). Inhibition effect of the AA2 was
investigated using computation and experimental techniques and the results were in
good agreement.
2. Experimental
2.1. Materials and methods
The materials used in this study such as 4,4'-oxydianiline (purity of 97%),
epichlorohydrin (purity of 99%) and triethylamine (purity of ≥99.5%) were purchased
from Sigma-Aldrich. Carbon steel strips containing C 0.11 wt.%, Si 0.24 wt. %, Mn
0.47 wt.%, Cr 0.12 wt. %, Mo 0.02 wt.%, Ni 0.1 wt.%, Al 0.03 wt.%, Cu 0.14, Co
<0.0012 wt. %, V <0.003 wt.%, W 0.06 wt. %[10].
The corrosive solution of 1 M HCl was prepared by diluting the appropriate amount
of concentrated HCl (37%) with distilled water. The range of concentration for the
tested inhibitor was from 10-3 to 10-6 mol L-1.This range of concentrations was
determined after the study of the solubility of the tetra-functional epoxy
macromolecule (AA2) in the corrosive medium.
2.2. Chemical synthesis of AA2
A mixture of organic compound (aromatic diamine) (2.0 x 10-2 mol) and ethanol (20
mL) was put in a bicol equipped with a condenser and a dropping funnel. After
dissolving the aromatic diamine, 4 mL of epichlorohydrin was poured with invariable
magnetic thrilling. The resulting reaction mixture was heated at 70 °C for 4 h. Then,
5mL of triethylamine was added to the reaction mixture. Stirring was continued for a
further 3 hours at 40 °C. Viscous resin was obtained by concentrating the resulting
solution on a rotary evaporator. Scheme for AA2 synthesis is given Fig. 1. TheAA2
1
synthesis was verified by H NMR (using Bruker AVANCE 300 MHz)and FT-IR
spectroscopic methods and corresponding spectra are given in Figs. SI 1 and SI2and
Table SI 1.
2.3. Electrochemical test
Electrochemical study of carbon steel dissolution in 1M HCl in the absence and
presence of AA2was performed using Potentiostat SP 200 device as described in our
previous studies [11, 12]. The device is connected by means of a three-electrode
arrangement consisting of pure Pt as the auxiliary or assisting electrode (CE),
saturated calomel the same as the reference electrode (SCE) and carbon steel panels
the same as the working electrode (WE). Prior to starting the electrochemical

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experiments, the WE permitted to corrode liberally with and without AA2 for 1800
second in order to acquire the establishment of OCP (open circuit potential). The EIS
measurements were performed over a frequency range of 100 kHz to 10 mHz, using
10 mV amplitude. The PDP curves were measured at a scan rate of 1 mV/s from −800
to 0 mV versus SCE.
2.4. SEM characterization
SEM-EDS study was carried out using model S3000H, Hitachi-Field Emission for
carbon steel surfaces corrode for 12 h in 1M HCl solution.
2.5. Theoretical study
DFT calculations were accomplished with the Gaussian 09 program. Geometry
optimization in the aqueous phase for the AA1 was completely optimized atB3LYP/6-
31G (d, p) level of the theory[13].
The molecular dynamics (MD) simulation was performed using Forcite module of
Materials Studio 8.0 program developed by BIOVIA Inc. It was carried out in a
simulation box (2.48 nm × 2.48 nm × 4.71 nm) with periodic boundary conditions.
The box consisted of a lower Fe slab and a upper solvent layer (containing 800 water
molecules and one inhibitor molecule)[14].
3. Result and discussion
3.1. Electrochemical Study
Open circuit potential (OCP) can be defined the same as “potential originated over the
working electrode (carbon steel in this case) without applying any external current or
potential”. Fig. 2, represents the OCP versus time curves for WE corrosion of the bare
carbon steel substrate and presence the different concentrations of AA2.For better
interpretation and reliability of the OCP curves, the OCP studies for carbon steel
dissolution in 1M HCl were carried out for 1800 s. Generally, straight OCP versus
time curves suggest the dissolution of surface metal oxide layer(s) and adsorption of
the corrosion inhibitor(s) that interface of metal and electrolyte [15]. From Figure 2, it
can be clearly seen that OCP versus time curves are almost straight throughout the
experiments for different concentrations AA2 in their absence. This observation
suggests that shift in OCP versus time curves of inhibited specimens with respect to
the uninhibited once gives information about the nature of corrosion inhibitor.
Visualization show that OCP versus time curves for the metallic specimens inhibited
by AA2 are shifted towards more negative (cathodic) direction which reveals that
AA2 is mainly acts as cathodic type of corrosion inhibitors [16].

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Tafel curves and respective polarization indices are shown in Fig. 3and Table 1,
respectively. Using icorr, efficiency of protection (ηPDP %) was determined by the
following Eq. (1) :
푖푐표푟푟
푖푐0표푟푟
( )
휂푃퐷푃 % = (1 −
) × 100 (1)
Whereas, i0corrand icorr are the current densities for steel corrosion in the absence and
presence of AA2 in HCl solution, respectively.
Inspection showed that icorr value decreased from 916.6 to 81.66 μ.cm−2in the
presence of 10-3 M concentration of AA2.The decrease in icorr value in the presence of
AA2 is attributed to the blocking of the surface active sites [13]. Presence of
peripheral polar groups, nitrogen and oxygen atoms enhance the adsorption of AA2
on the metallic surface. More so, presence of these hydrophilic moieties enhances the
solubility in the polar electrolytic solution of 1M HCl.
Nyquist plots for steel acidic dissolution in 1M HCl is shown in Fig. 4. Formation of
single semicircle with and without AA2 suggests that dissolution of the working
electrode is a charge transfer process [17]. Surface heterogeneity causes the
imperfection in the semicircle. Increased diameter of semicircle also indicates that
AA2 adsorbs at metal/ electrolyte interfaces and acts as interface type of inhibitor.
Equivalent circuit engaged intended for appropriately analyzing the EIS data is shown
in Fig. 5. The CPE is defined as the below Eq. (2) [18]:
1
( )
2
푍퐶푃퐸
=
훼
(
)
푌 푗휔
0
Here, symbols have their typical meaning [19].The capacitance values (Cdl) is
calculated using Eq. (3) [20] :
(
)
푛−1( )
퐶푑푙 = 푌 휔푚푎푥 3
0
The polarization resistance parameters were used to calculate the corrosion inhibition
efficiency (ηEIS%) based on the following Eq (4):
푅푃0
( )
휂퐸퐼푆 % = (1 − ) × 100 (4)
푅푃
Results showed that presence of AA2 enhances the polarization resistance value and
corresponding increase in the inhibition efficiency [21]. AA2 showed highest value
of91.3 % at 10-3M concentration. Decrease in the values of Cdl in the presence of AA2

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suggests that surface smoothness is increasing because of the AA2 adsorption at the
interfaces[22]. This assumption was further supported by increased value of phase
angle values in the Bode plots (Fig. 6) for steel acidic dissolution [22].
3.2. Morphological analysis
SEM-EDS images for the working electrode surfaces are presented in Fig. 7.It can be
seen that without AA2 surface was highly damaged and corroded with very high
surface imperfection. However, in the presence of AA2 surface morphology is greatly
improved due to AA2 adsorption over the metallic surface.
3.3. Adsorption studies
Nature of carbon steel and AA2 interaction can be demonstrated using
adsorption isotherm and Langmuir adsorption isotherm is best model that can be
presented as follows[23].
퐶ꢀ푛ℎ
1
( )
+ 퐶ꢀ푛ℎ 5
=
휃
퐾푎푑푠
All symbols have their typical meaning. Graphs between Cinh and Cinh /θ is shown in
Fig. SI3. The ΔGads are calculated using Eq. (6) [24] :
1
−∆퐺푎푑푠
푅푇
( )
) 6
퐾푎푑푠
=
푒푥푝 (
55.5
It is well known that value of ΔGads the order of lower than −40 kJ/mol were reported
as chemisorption owing to the formation of covalent bond between organic inhibitors
and to the metallic surface [25]. If the ΔGads value is around or higher than −20
kJ/mol indicates a physisorption [26]. Results revealed that AA2 adsorption mainly
obeyed the chemisorption (Table SI2).
3.4. Effect of temperature
The PDP study was conducted at 298, 308, 318 and 328 K temperature and
corresponding outcomes are given in Fig. 8 and Table 3. Effect of temperature can be
presented as follows Eqs (7) and (8)[27]:
퐸푎
( )
푖푐표푟푟 = 퐴. 푒푥푝 (− ) 7
푅푇

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푅푇
∆푆푎
∆퐻푎
( )
) 8
푖푐표푟푟
=
푒푥푝 (
) 푒푥푝 (−
ℎ푁
푅
푅푇
where A is the pre-exponential factor, ΔHa is the enthalpy, ΔSa is the entropy of
activation, T is the absolute temperature in Kelvin, h is the Plank constant, N is the
Avogadro number, and R the molar gas constant. Results are presented in Fig. SI 4and
Table SI 3. Careful observation showed that value of Ea in the presence of the AA2 is
higher than in their absence. The studied AA2 retard corrosion at room temperature,
but inhibition is diminished at an elevated temperature. The decrease in the corrosion
rate is mostly determined by the Ea [28].Moreover, the positive values of ΔHa showed
that the corrosion process is endothermic. The higher value of ΔSa in the presence of
AA2 is attributed to increase in solvent entropy, which drives the adsorption of
inhibitors on the metal surface [29].
4. Theoretical study
Recently, quantum chemical calculation facilitated the development of adequate
corrosion inhibitors. DFT investigates globally and locally all the probable donation
and accepting interaction of the inhibitor molecule as well as every atom in it. DFT
extensively investigated evidence that for an inhibitor might be adsorbed to show
corrosion inhibition characteristic. More specifically, the donation-accepting type
interaction that is accountable for adsorption on the favored surface. So that, DFT
provides the connection of molecular structure or characteristics with the ability of the
inhibitor molecule to inhibit the surfaces from corrosion. Accordingly, for this study,
the global and local quantum chemical calculations have been performed using DFT
method at the B3LYP/6-31+G(d,p) level of theory in aqueous solution using PCM
model.
4.1. Global and Local quantum descriptors of the neutral AA2
The optimized geometrical structure and the electrostatic potential map of the neutral
species of the AA2 molecule are presented in Figure 9. The highest occupied and
lowest unoccupied molecular orbitals (HOMO and LUMO) of the AA2 molecule, as
well as their energy values and the energy gap between them are shown in Figure 10.
The calculated quantum chemical descriptors such as EHOMO and ELUMO, energy gap
(ΔE), dipole moment (μ), electronegativity (χ), hardness (η), softness(S),
electrophilicity (),electron accepting power (-), electron donating power
(+),netelectrophilicity (∆휔±), Charge transfer model for donation and back-donation

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of charges (∆Eb-d), Number of transferred electrons (N110), number of electron
transfer electron from metal to inhibitor(∆Nmax), and the initial molecule-metal
interaction energy() are collected in Table 4. The equations used to calculate the
above mentioned parameters are given as a footnote under Table 4.
Figure 9 shows that the optimized structure of the inhibitor AA2 has a non-planar
geometry in location, indicating that it is not adsorbed in horizontal location on the
metal surface. Hence, the question to be addressed here is how improbable amount of
inhibition efficiency may be expected by the inhibitor AA2. Figure 10affirmed that
electron density of the HOMO is dispersed over the entire molecule, whereas
considerable electron density is distributed in LUMO over the middle part of the
molecule (the two aromatic rings). These observations are also confirmed when the
ESP map is considered (Figure 9).Therefore, the middle part of the molecule shows a
dual behavior; donor-acceptor property, which facilitates the adsorption of the
inhibitor molecule over the metal surface and consequently increases the inhibition
efficiency of the inhibitor molecule[9, 10, 11, 30-36].More specifically, the energy of
the EHOMO is commonly correlated with the ability of the inhibitor molecule to donate
its electrons to the vacant d orbital of the metal. Thus, the higher the EHOMO and the
lower the ELUMO values, the better inhibition efficiency of the inhibitor [37-39]. It is
clearly obvious from Table 4 that the inhibitor molecule has higher EHOMO and lower
ELUMO value compared with those reported for some previously published molecules
[7,30,40]. In order to earn additional information, whether the investigated AA2
molecule adequate to donate the electron or not, the values of EHOMO and ELUMO can
be used to calculate the above mentioned global quantum descriptors [41].One of the
most important global descriptors is the energy gap, which can be used to elucidate
the reactivity of the inhibitor molecule. It was reported that lower values of energy
gap indicates a high chemical reactivity and inhibition efficiencies of the inhibitor
molecules [37-39]. A careful inspection of Table 4 and Figure 10 shows that the value
of energy gap if the titled inhibitor is small (E = 4.405 eV), which displays that the
AA2easily polarized and get adsorbed.
Lower values of electronegativity and hardness also indicate that the inhibitor under
probe is highly reactive molecule and can transfer as well as accept electrons during
metal-inhibitor interactions. According to our results (Table 5), the inhibitor under

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probe has a negative Eback-donation, which demonstrates a highly efficient inhibition. It
is also shown the rest of the quantum global parameters reflect a good inhibition
efficiency of the investigated inhibitor, which is a good agreement with experimental
results. Furthermore, fraction of electron transferred (N110) between the metal
surface and the inhibitor molecule AA2 is calculated using Eq. (9).
(휑퐹푒 − 휒퐹푒)
( )
9
∆푁110
=
2(휂퐹푒 + 휂ꢀ푛ℎ
)
where, ϕ, χinh correspond to work function of iron and electronegativity of the
inhibitor, while ηFe and ηinh corresponds to hardness of Fe and inhibitor molecule,
respectively. It was reported that the obtained DFT derived  values for Fe(100),
Fe(110) and Fe(111) planes are 3.91, 4.82 and 3.88ꢀeV, respectively[42]. For this
study, the Fe(110) plane is treated due to its packed surface and higher stabilization
energy. The results obtained are also listed in Table 4. It is well known that electrons
transfer takes place from AA2 molecule Fe(110) surface when ΔN100ꢀ>ꢀ0 and vice
versa[42-44]. Additionally, it was proposed that the ability of the inhibitor to give
electrons increases when the ΔN100< 3.6 [45].Careful inspection of Table 4 affirms
that the calculated ΔN100 value is positive (0.4177) and less than 3.6. Therefore, the
AA2 inhibitor may transfer its electron to the metallic surface, which in turn
facilitates the adsorption of the AA2 on the Fe(110) surface. Moreover, higher
softness (S) value demonstrates the high inhibition efficiency of the AA2 molecule.
The calculated softness value of the AA2 inhibitor (S = 0.454 eV-1) is quite good
enough compared with those reported for a previously published inhibitors
[7,9,10,30,40,46].
Finally, it was also reported that higher value of dipole moment enhances the dipole-
dipole interactions between the metallic surface and the adsorbed inhibitor, resulting
in better adsorption and, in turn, higher inhibition effect [47].Our results (Table 4)
demonstrate that the dipole moment value of the investigated inhibitor molecule is
0.803 Debye, which is smaller than that of water (1.8546 Debye).These results reveal
that the dipole-dipole interactions between the neutral AA2 and the Fe(110) surface is
week.
4.2. Fukui indices study

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As known, the responsible interactions in the inhibition operation are the donor-
acceptor processes. In these interactions, the inhibitor molecules are adsorbed on the
surface of the metal. Hence, it is very valuable to examine the atoms in the molecule
that participate in this type of interaction. For this purposes, the condensed Fukui
functions in a molecule with N electron were proposed by Yang and Mortier [48]. In
the current study, the Fukui Functions (FFs) was used to analyze the reactive sites of
the investigated inhibitor molecule. The Natural Population Analysis (NPA) as
implemented in G09 [49] was adopted to calculate the FFs. All NBO single point
calculations for neutral, cationic and anionic species were performed using
geometrical structures of the studied inhibitors at the same level of theory. The sites
for nucleophilic (푓+) and electrophilic (푓−) can be evaluated in terms of the
푘
푘
electronic populations as Eqs. (10) and (11):
+( )
푓 푘 = 푞푘 푁 + 1 − 푞푘 푁 퐼푛푑푒푥 푓표푟 푎 푛푢푐푙푒표푝ℎ푖푙푖푐 푎푡푡푎푐푘푠 (10)
(
)
( )(
)
푘
−( )
( )
(
)(
)
푓 푘 = 푞푘 푁 − 푞푘 푁 − 1 퐼푛푑푒푥 푓표푟 푒푙푒푐푟표푝ℎ푖푙푖푐 푎푡푡푎푐푘 (11)
푘
Here, all symbols have their usual meaning[50,51].Recently, another descriptor was
introduced, which is a second order FF, also called as “dual descriptor” [50,53]. Dual
descriptor is used to give a simple and instinctive way to chemical reactivity (Eq. (12)
:
2( )
+( )
−( )
푓 푟 ≈ 푓 푟 − 푓 푟 (12)
2( )
It was pointed out that [52,53], the electron acceptor regions are indicated by 푓 푟 >
2( )
0, whereas, the electron donors regions are indicated by 푓 푟 < 0. For better meta-
inhibitor interactions both the regions should be aligned together.
The local softness is defined as the product of the global softness and the condensed
FFs as shown below in Eq. (13):
±( )
±( )
푠푘 푟 = 푆 × 푓 푟 (13)
푘
The calculated Fukui indices and local softness, as well as the dual descriptor (second
order Fukui indices) for the inhibitor molecule under probe are summarized in Table
5.The natural atomic charges of the neutral, anion and cation species of the neutral
AA2 inhibitor are presented in Table SI4of the electronic supplementary material. The
optimized structure of the neutral AA2 with the numbering systems for Fukui indices

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is shown in Figure SI5of the electronic supplementary materials. It can be seen that
the investigated inhibitor possesses the highest values of 푓+ which are located on the
푘
atoms of the aromatic rings (C13, C2, C12, C3, C4, C16, C14 andC6 indicating that
these sites are electron acceptors. These results agree with the electron density
distribution over the LUMO surface whereas N22, N21, O35, C6, C14, C1, C11, C4
and C16act as electron donor. Furthermore, as displayed in Table 5 and Figure 11a,
the dual descriptor index (f2(r)) displays that the locations for the highest electron
acceptor regions are follow the next pattern: C13 > C2 > C12 > C3 > C16 > C4 >
2( )
C14, which indicated by푓 푟 > 0. On the other hand, the atoms that have the highest
electron donating regions are arranged in the following trend: N22 > N21 > O35 > C1
2( )
> C11 > C8, which are indicated by the 푓 푟 < 0. Thus the preferred site for the
accepting electron was found on N22, N21 and O35, respectively.
4.3. Quantum chemical calculations of the protonated form of inhibitor molecule
It is worth to demonstrate how molecular property of the protonated form of the AA2
molecule play important role for the adsorption on the Fe(110) surface. When the
AA2 molecule dissolves in acidic solution, the epoxy group (oxirane ring) is opened
and converted into glycol. The optimized geometric configurations and the
electrostatic potential map (ESP) of the CDR molecule are also shown in Figure 9.
The HOMO and LUMO, as well their energies and the energy gap between them are
also presented in Figure 10. The above mentioned global descriptors for the
protonated form obtained from DFT calculation are also summarized in Table 4.
Careful inspection of Table 4 and Figure 10 shows that the value of EHOMO of the
protonated form is shifted towards the less negative value in comparison to
the EHOMO value of neutral form. These results affirm that the protonated form has a
higher tendency to donate the electrons than the neutral form, which is also supported
by the value of N110. Our results show that the N110 of the protonated form is 0.006
lower than that of the neutral form. On the contrary, ELUMO value tabulated in Table
4 also shifted towards the less negative value compared with that of the neutral form,
which affirms that the ELUMO of the protonated form is larger than that of the neutral
one. It is pointing out that electron acceptance capability in the protonated form is
decreased, and the capability to back-donation interactions is reduced. Our results
show that the electronegativity of the protonated form is 0.053 eV much lower than

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that of the neutral one. Analysis of the energy gap values tabulated in Table 4indicates
that the energy gap of the neutral species is lower than that of the protonated ones,
which indicates that chemical reactivity of the neutral species is higher than that of the
protonated form. Finally, the tabulated results (Table 4) shows that the dipole moment
of the protonated inhibitor is much higher than that of the neutral species, reflecting
that the dipole-dipole interactions between the protonated inhibitor and the metal
surface is much stronger compared with that between the neutral inhibitor and the
metal surface, however, it is important to mention that there isn't a clear relationship
between the inhibition efficiency and the dipole moments. Thus the inhibition
efficiency of the protonated form is higher than that of the neutral one. Analysis of the
results showed neutral form of AA2 acts as better donor and protonated form of AA2
behaves as better acceptor.
4.4. Active sites analysis of protonated form of molecule
±( )
ퟐ( )
The Fukui functions (풇풌+퐚퐧퐝 풇풌−), local softness (풔풌 풓 ) and dual descriptor (풇 풓 )
are also summarized in Table 5 and graphically shown in Figure 11b. The natural
atomic charges of the neutral, anionic and cationic species of the protonated AA2
inhibitor are presented in Table SI4 of the electronic supplementary material. The
optimized structure of the protonated AA2 with the numbering systems for Fukui
indices is shown in Figure SI6of the electronic supplementary materials. According to
Table 5and Figure 11b the C2, C6, C4, C3, C12, C16, C14 and C13 atoms of the
protonated form of the inhibitor molecule having high value of풇풌+, and therefore are
exposed to accept electrons, while, N22, N21, O23, C1, C16, C11, C6, C4, C14 and
C49 atoms having high value of 풇풌−are suspected to transfer their electrons to the
surface of the metal. Therefore, it is shown that in both case, the donor and the
accepted centers of the electron to the meta surface of to the inhibitor molecule,
respectively, are similar, which is totally agree with the electron density distribution
over the HOMO and LUMO surfaces.
5. Molecular dynamics simulation
To get further information about the interaction between the AA2 molecules and
the iron surface, molecular dynamics (MD) simulation was performed. As mentioned
above, AA2 has a great tendency to occur ring-opening reaction under acidic solution.
Thus, the ring open product was used for the simulation. The dynamics process was

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carried out and the whole system reached equilibrium until both temperature and
energy of the system were balance.
The equilibrium configurations (top and side view) of AA2 adsorbed on the
Fe(110) surface are shown in Figure (12a). It can be seen that the inhibitor molecule
adsorb on the metal surface through the N, O atoms as well as the aromatic rings. The
adsorption energy (Eads) for inhibitor adsorption can be calculated as following Eq.
(14):
퐸푎푑푠 = 퐸푡표푡푎푙 − (퐸푠푢푟푓+푤푎푡푒푟 + 퐸ꢀ푛ℎ+푠푢푟푓) + 퐸푤푎푡푒푟 (14)
The symbols have their typical meaning. The adsorption energies in the present work
were calculated from the average adsorption energy of the obtained equilibrium
configurations.
6. Comparative efficiency
Literature study reveals that few of the tetra-functional macromolecular epoxy resins
based organic inhibitors have been evaluated for their anti-corrosive behavior for steel
in 1 M HCl media [7-9, 54]. Inhibition effectiveness of some common representatives
of the similar inhibitors is presented in Table 6.
It can be seen that these types of compounds are acted as good corrosion inhibitors
and their compounds containing two aromatic rings and heteroatoms (N, O, S and P).
6. Conclusions
From above experimental and theoretical studies, it can be concluded that:
1. The highest inhibition efficiency value for AA2 at 10-3 M (optimum
concentration) is 91.3 %.
2. The PDP results show that AA2 behaves a cathodic type of corrosion
inhibitor.
3. The EIS results suggested that, AA2 protect the carbon steel form corrosion by
the formation of a protective film at the metal surface.
4. Adsorption of the tested organic aromatic based multifunctional epoxy
prepolymer molecules obeys Langmuir adsorption isotherm.
5. The ΔGads value for AA2 is superior to 40 kJ/mol, indicating strongly
interaction of AA2 onto the metallic surface.

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6. Global quantum descriptors of the neutral and protonated species of the AA2
inhibitor molecule in aqueous solution concluded that the title molecule
behaves as a good inhibitor for the carbon steel surfaces and it may be
physically adsorbed by stacking on carbon steel.
7. The negative values of Eads for AA2 at different temprature suggests a stronger
adsorption strength between an AA2 molecule and metal surface.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements: CV thankfully acknowledges the North-West University
(Mafikeng Campus) for financial support under postdoc fellowship scheme. Nuha
Wazzan gratefully acknowledges King Abdulaziz University's High Performance
Computing Centre (Aziz Supercomputer) (http://hpc.kau.edu.sa) for assisting with the
calculations for this study. This work was sponsored by the National Natural Science
Foundation of China (21706195).
References
1. Akpan, E. D., Isaac, I. O., Olasunkanmi, L. O., Ebenso, E. E., & Sherif, E. S.
M. (2019). Acridine-based thiosemicarbazones as novel inhibitors of mild
steel corrosion in 1 M HCl: synthesis, electrochemical, DFT and Monte Carlo
simulation studies. RSC Advances, 9(51), 29590-29599.
2. Srivastava, M., Srivastava, S. K., Ji, G., & Prakash, R. (2019). Chitosan based
new nanocomposites for corrosion protection of mild steel in aggressive
chloride media. International journal of biological macromolecules, 140, 177-
187.
3. Luo, X., Ci, C., Li, J., Lin, K., Du, S., Zhang, H., ... & Liu, Y. (2019). 4-
aminoazobenzene modified natural glucomannan as a green eco-friendly
inhibitor for the mild steel in 0.5 M HCl solution. Corrosion Science, 151,
132-142.
4. Bentiss, F., Lagrenee, M., Traisnel, M., & Hornez, J. C. (1999). The corrosion
inhibition of mild steel in acidic media by a new triazole derivative. Corrosion
Science, 41(4), 789-803.
5. Jafari, H., & Sayin, K. (2016). Corrosion inhibition studies of N, N′-bis (4-
formylphenol)-1, 2-Diaminocyclohexane on steel in 1 HCl solution
acid. Journal of the Taiwan Institute of Chemical Engineers, 64, 314-324.

Journal Pre-proof
6. Jiang, L., Qiang, Y., Lei, Z., Wang, J., Qin, Z., & Xiang, B. (2018). Excellent
corrosion inhibition performance of novel quinoline derivatives on mild steel
in HCl media: experimental and computational investigations. Journal of
Molecular Liquids, 255, 53-63.
7. Dagdag, O., Safi, Z., Erramli, H., Cherkaoui, O., Wazzan, N., Guo, L., ... & El
Harfi, A. (2019). Adsorption and anticorrosive behavior of aromatic epoxy
monomers on carbon steel corrosion in acidic solution: computational studies
and sustained experimental studies. RSC Advances, 9(26), 14782-14796.
8. Dagdag, O., Safi, Z., Hsissou, R., Erramli, H., El Bouchti, M., Wazzan, N., ...
& El Harfi, A. (2019). Epoxy pre-polymers as new and effective materials for
corrosion inhibition of carbon steel in acidic medium: Computational and
experimental studies. Scientific reports, 9(1), 1-14.
9. Dagdag, O., El Harfi, A., Cherkaoui, O., Safi, Z., Wazzan, N., Guo, L., ... &
Jalgham, R. T. (2019). Rheological, electrochemical, surface, DFT and
molecular dynamics simulation studies on the anticorrosive properties of new
epoxy monomer compound for steel in 1 M HCl solution. RSC advances, 9(8),
4454-4462.
10. Becke, A. D., & Johnson, E. R. (2005). Exchange-hole dipole moment and the
dispersion interaction. The Journal of chemical physics, 122(15), 154104.
11. Dagdag, O., Safi, Z., Erramli, H., Wazzan, N., Obot, I. B., Akpan, E. D., ... &
El Harfi, A. (2019). Anticorrosive property of heterocyclic based epoxy resins
on carbon steel corrosion in acidic medium: Electrochemical, surface
morphology, DFT and Monte Carlo simulation studies. Journal of Molecular
Liquids, 110977.
12. Dagdag, O., El Harfi, A., El Gouri, M., Safi, Z., Jalgham, R. T., Wazzan, N.,
... & Kumar, U. P. (2019). Anticorrosive properties of Hexa (3-methoxy
propan-1, 2-diol) cyclotri-phosphazene compound for carbon steel in 3% NaCl
medium: gravimetric, electrochemical, DFT and Monte Carlo simulation
studies. Heliyon, 5(3), e01340.
13. Frisch, M. J., Trucks, G. W., Schlegel, H. B., Scuseria, G. E., Robb, M. A.,
Cheeseman, J. R., ... & Nakatsuji, H. (2009). Gaussian 2009. Gaussian Inc.:
Wallingford, CT, USA.
14. Dagdag, O., Hanbali, G., Khalaf, B., Jodeh, S., El Harfi, A., & Deghles, A.
(2019). Dual Component Polymeric Epoxy-Polyaminoamide Based Zinc
Phosphate Anticorrosive Formulation for 15CDV6 Steel. Coatings, 9(8), 463.
15. Verma, C., Obot, I. B., Bahadur, I., Sherif, E. S. M., & Ebenso, E. E. (2018).
Choline based ionic liquids as sustainable corrosion inhibitors on mild steel
surface in acidic medium: Gravimetric, electrochemical, surface morphology,
DFT and Monte Carlo simulation studies. Applied Surface Science, 457, 134-
149.
16. Verma, C., Quraishi, M. A., Obot, I. B., & Ebenso, E. E. (2019). Effect of
substituent dependent molecular structure on anti-corrosive behavior of one-
pot multicomponent synthesized pyrimido [2, 1-B] benzothiazoles: Computer

Journal Pre-proof
modelling supported experimental studies. Journal of Molecular Liquids, 287,
110972.
17. Liang, C., Liu, Z., Liang, Q., Han, G. C., Han, J., Zhang, S., & Feng, X. Z.
(2019). Synthesis of 2-aminofluorene bis-Schiff base and corrosion inhibition
performance for carbon steel in HCl. Journal of Molecular Liquids, 277, 330-
340.
18. Wang, C., Lai, C., Xie, B., Guo, X., Fu, D., Li, B., & Zhu, S. (2018).
Corrosion inhibition of mild steel in HCl medium by S-benzyl-O, O'-bis (2-
naphthyl) dithiophosphate with ultra-long lifespan. Results in Physics, 10,
558-567.
19. Zhang, H. H., Chen, Y., & Zhang, Z. (2018). Comparative studies of two
benzaldehyde thiosemicarbazone derivatives as corrosion inhibitors for mild
steel in 1.0 M HCl. Results in Physics, 11, 554-563.
20. Dohare, P., Quraishi, M. A., Verma, C., Lgaz, H., Salghi, R., & Ebenso, E. E.
(2019). Ultrasound induced green synthesis of pyrazolo-pyridines as novel
corrosion inhibitors useful for industrial pickling process: Experimental and
theoretical approach. Results in Physics, 13, 102344.
21. Verma, C., Quraishi, M. A., & Gupta, N. K. (2016). 2-(4-{[4-Methyl-6-(1-
methyl-1H-1,
3-benzodiazol-2-yl)-2-propyl-1H-1,
3-benzodiazol-1-yl]
methyl} phenyl) benzoic acid as green corrosion inhibitor for mild steel in 1
M hydrochloric acid. Ain Shams Engineering Journal.
22. Verma, C., Olasunkanmi, L. O., Bahadur, I., Lgaz, H., Quraishi, M. A.,
Haque, J., ... & Ebenso, E. E. (2019). Experimental, density functional theory
and molecular dynamics supported adsorption behavior of environmental
benign imidazolium based ionic liquids on mild steel surface in acidic
medium. Journal of Molecular Liquids, 273, 1-15.
23. Vinutha, M. R., Venkatesha, T. V., & Nagaraja, C. (2018). Anticorrosive
ability of electrochemically synthesized 2, 2′-disulfanediyldianiline for mild
steel corrosion: electrochemical and thermodynamic studies. International
Journal of Industrial Chemistry, 9(2), 185-197.
24. Chauhan, D. S., Quraishi, M. A., Sorour, A. A., Saha, S. K., & Banerjee, P.
(2019). Triazole-modified chitosan: a biomacromolecule as a new
environmentally benign corrosion inhibitor for carbon steel in a hydrochloric
acid solution. RSC Advances, 9(26), 14990-15003.
25. Das, M., Biswas, A., Kundu, B. K., Mobin, S. M., Udayabhanu, G., &
Mukhopadhyay, S. (2017). Targeted synthesis of cadmium (II) Schiff base
complexes towards corrosion inhibition on mild steel. RSC Advances, 7(77),
48569-48585.
26. Tang, Y., Yang, X., Yang, W., Chen, Y., & Wan, R. (2010). Experimental and
molecular dynamics studies on corrosion inhibition of mild steel by 2-amino-
5-phenyl-1, 3, 4-thiadiazole. Corrosion Science, 52(1), 242-249.
27. Sukul, D., Pal, A., Saha, S. K., Satpati, S., Adhikari, U., & Banerjee, P.
(2018). Newly synthesized quercetin derivatives as corrosion inhibitors for

Journal Pre-proof
mild steel in 1 M HCl: combined experimental and theoretical
investigation. Physical Chemistry Chemical Physics, 20(9), 6562-6574.
28. Aslam, R., Mobin, M., Aslam, J., & Lgaz, H. (2018). Sugar based N, N′-
didodecyl-N, N′ digluconamideethylenediamine gemini surfactant as corrosion
inhibitor for mild steel in 3.5% NaCl solution-effect of synergistic KI
additive. Scientific reports, 8(1), 3690.
29. Kumar, S., Vashisht, H., Olasunkanmi, L. O., Bahadur, I., Verma, H., Singh,
G., ... & Ebenso, E. E. (2016). Experimental and theoretical studies on
inhibition of mild steel corrosion by some synthesized polyurethane tri-block
co-polymers. Scientific reports, 6, 30937.
30. Erdoğan, Ş., Safi, Z. S., Kaya, S., Işın, D. Ö., Guo, L., & Kaya, C. (2017). A
computational study on corrosion inhibition performances of novel quinoline
derivatives against the corrosion of iron. Journal of Molecular
Structure, 1134, 751-761.
31. Guo, L., Safi, Z. S., Kaya, S., Shi, W., Tüzün, B., Altunay, N., & Kaya, C.
(2018). Anticorrosive effects of some thiophene derivatives against the
corrosion of iron: a computational study. Frontiers in chemistry, 6, 155.
32. Kabanda, M. M., Obot, I. B., & Ebenso, E. E. (2013). Computational study of
some amino acid derivatives as potential corrosion inhibitors for different
metal surfaces and in different media. Int. J. Electrochem. Sci, 8(2013),
10839-10850.
33. Obi-Egbedi, N. O., Essien, K. E., Obot, I. B., & Ebenso, E. E. (2011). 1, 2-
Diaminoanthraquinone as corrosion inhibitor for mild steel in hydrochloric
acid: weight loss and quantum chemical study. Int. J. Electrochem. Sci, 6, 913-
930.
34. Obot, I. B., & Gasem, Z. M. (2014). Theoretical evaluation of corrosion
inhibition performance of some pyrazine derivatives. Corrosion Science, 83,
359-366.
35. Obot, I. B., Kaya, S., Kaya, C., & Tüzün, B. (2016). Density Functional
Theory (DFT) modeling and Monte Carlo simulation assessment of inhibition
performance of some carbohydrazide Schiff bases for steel corrosion. Physica
E: Low-dimensional Systems and Nanostructures, 80, 82-90.
36. Singh, P., Ebenso, E. E., Olasunkanmi, L. O., Obot, I. B., & Quraishi, M. A.
(2016). Electrochemical, theoretical, and surface morphological studies of
corrosion inhibition effect of green naphthyridine derivatives on mild steel in
hydrochloric acid. The Journal of Physical Chemistry C, 120(6), 3408-3419.
37. Kadhim, A., Al-Okbi, A. K., Jamil, D. M., Qussay, A., Al-Amiery, A. A.,
Gaaz, T. S., ... & Nassir, M. H. (2017). Experimental and theoretical studies of
benzoxazines corrosion inhibitors. Results in physics, 7, 4013-4019.
38. Verma, C., Olasunkanmi, L. O., Ebenso, E. E., Quraishi, M. A., & Obot, I. B.
(2016). Adsorption behavior of glucosamine-based, pyrimidine-fused
heterocycles as green corrosion inhibitors for mild steel: experimental and
theoretical studies. The Journal of Physical Chemistry C, 120(21), 11598-
11611.

Journal Pre-proof
39. Qiang, Y., Zhang, S., Guo, L., Zheng, X., Xiang, B., & Chen, S. (2017).
Experimental and theoretical studies of four allyl imidazolium-based ionic
liquids as green inhibitors for copper corrosion in sulfuric acid. Corrosion
Science, 119, 68-78.
40. Singh, A. K., Chugh, B., Saha, S. K., Banerjee, P., Ebenso, E. E., Thakur, S.,
& Pani, B. (2019). Evaluation of anti-corrosion performance of an expired
semi synthetic antibiotic cefdinir for mild steel in 1 M HCl medium: An
experimental and theoretical study. Results in Physics, 102383.
41. Lukovits, I., Kalman, E., & Zucchi, F. (2001). Corrosion inhibitors—
correlation between electronic structure and efficiency. Corrosion, 57(1), 3-8.
42. Saha, S. K., Dutta, A., Ghosh, P., Sukul, D., & Banerjee, P. (2016). Novel
Schiff-base molecules as efficient corrosion inhibitors for mild steel surface in
1 M HCl medium: experimental and theoretical approach. Physical Chemistry
Chemical Physics, 18(27), 17898-17911.
43. Saha, S. K., Dutta, A., Ghosh, P., Sukul, D., & Banerjee, P. (2015).
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. Physical Chemistry Chemical Physics, 17(8), 5679-5690.
44. Saha, S. K., Murmu, M., Murmu, N. C., & Banerjee, P. (2016). Evaluating
electronic structure of quinazolinone and pyrimidinone molecules for its
corrosion inhibition effectiveness on target specific mild steel in the acidic
medium: a combined DFT and MD simulation study. Journal of Molecular
Liquids, 224, 629-638.
45. Awad, M. K., Mustafa, M. R., & Elnga, M. M. A. (2010). Computational
simulation of the molecular structure of some triazoles as inhibitors for the
corrosion of metal surface. Journal of molecular structure: theochem, 959(1-
3), 66-74.
46. Yadav, M., Sarkar, T. K., & Obot, I. B. (2016). Carbohydrate compounds as
green corrosion inhibitors: electrochemical, XPS, DFT and molecular
dynamics simulation studies. RSC Advances, 6(111), 110053-110069.
47. Shahabi, S., & Norouzi, P. (2017). Electrochemical and Quantum Chemical
Assessment of Some Thiosemicarbazide Derivatives as Carbon Steel
Corrosion Inhibitors in HCl; Continuously Monitoring the Current Change by
FFT Voltammetry. INTERNATIONAL JOURNAL OF ELECTROCHEMICAL
SCIENCE, 12(4), 2628-2646.
48. Yang, W., & Mortier, W. J. (1986). The use of global and local molecular
parameters for the analysis of the gas-phase basicity of amines. Journal of the
American Chemical Society, 108(19), 5708-5711.
49. Frisch, M. J., Trucks, G. W., Schlegel, H. B., Scuseria, G. E., Robb, M. A.,
Cheeseman, J. R., ... & Nakatsuji, H. (2009). Gaussian 2009. Gaussian Inc.:
Wallingford, CT, USA.
50. Jafari, H., Danaee, I., Eskandari, H., & RashvandAvei, M. (2013).
Electrochemical and theoretical studies of adsorption and corrosion inhibition
of N, N′-bis (2-hydroxyethoxyacetophenone)-2, 2-dimethyl-1, 2-

Journal Pre-proof
propanediimine on low carbon steel (API 5L Grade B) in acidic
solution. Industrial & Engineering Chemistry Research, 52(20), 6617-6632.
51. Zarrok, H., Oudda, H., Touir, R., El M'Rabet, M., Warad, I., Guenbour, A., &
Lakhrissi, B. (2017). Experimental and theoretical studies of 5-((4-phenyl-4,
5-dihydro-1H-tetrazol-1-yl) methyl) quinolin-8-ol quinoline derivative as
effective corrosion inhibitor for mild steel in 1.0 M HCl.
52. De Proft, F., Martin, J. M., & Geerlings, P. (1996). Calculation of molecular
electrostatic potentials and Fukui functions using density functional
methods. Chemical physics letters, 256(4-5), 400-408.
53. Geerlings, P., Ayers, P. W., Toro-Labbꢁ, A., Chattaraj, P. K., & De Proft, F.
(2012). The Woodward–Hoffmann rules reinterpreted by conceptual density
functional theory. Accounts of chemical research, 45(5), 683-695.
54. Dagdag, O., Safi, Z., Erramli, H., Wazzan, N., Guo, L., Verma, C., ... & El
Harfi, A. (2020). Epoxy prepolymer as a novel anti-corrosive material for
carbon steel in acidic solution: Electrochemical, surface and computational
studies. Materials Today Communications, 22, 100800.

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Tables
Table 1 Potentiodynamic polarization parameters for carbon steel corrosion in 1 M
HCl solution in the absence and presence of different concentrations of AA2.
Inh
C (M)
Ecorr
(mV)
icorr
βa (mV/dec)
-βc
(mV/dec)
η%
(µA/cm2)
-
-473.80
-482.52
-500.71
-498.75
-419.37
-
Blank
AA2
916.6(1.78) 163.6(1.12) 155(1.63)
81.66(±0.85) 91.5(±0.93) 177.9(±1.66)
94.29(±0.91) 89.4(±0.81) 135.7(±0.95)
126.25(±1.05) 79.9(±0.74) 122.3(±0.81)
227.22(±1.26) 83.9(±0.66) 122.2(±0.82)
10-3
10-4
10-5
10-6
91.0
89.7
86.2
75.2
Table 2 Electrochemical impedance spectroscopy parameters for carbon steel
corrosion in 1 M HCl solution in the absence and presence of different concentrations
of AA2.
Inh
C (M) Rs (Ω.cm2) Rp (Ω.cm2) Cdl (mF/cm2) η%
χ2
-
0.056
0.104
0.220
0.152
0.210
Blank
-
2.15(0.03)
1.56(0.01) 290.1(1.16) 0.077(0.02)
25(1.03)
4.6(0.08)
10-3
10-4
10-5
10-6
91.3
AA2
1.20(0.01) 218.0(1.03) 0.095(0.01) 88.5
86.8
74.5
1.18(0.02) 189.9(0.93) 0.111 (0.01)
0.99(0.01) 098.0(0.56) 0.125(0.03)
Table 3 The influence of temperature on the electrochemical parameters for carbon
steel in 1M HCl and 10-3 M of AA2.
T (K)
Ecorr
icorr
Ect
%
-
91
89
83
80
mV/SCE
µA/Cm2
Blank
- 473
- 459
- 455
- 453
10-3 M of AA2
Blank
916
1390
2700
4100
10-3 M of AA2
-482
-496
-488
-511
81.66
142.75
449.77
806.08
298
308
318
328

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Table 4 Calculated quantum chemical parameters of studied neutral and protonated
forms of the inhibitor molecule.
Theoretical parameters
Energy (hartree)
Neutral inhibitor Protonated inhibitor
-1381.031808
-5.1827
-1722.829448
-5.1607
EHOMO(eV)
-0.777
5.183
0.777
4.405
2.980
2.203
0.454
2.016
0.496
0.4177
1.8341
-0.693
5.161
0.693
4.467
2.927
2.234
0.448
1.918
0.521
0.4237
1.8567
ELUMO (eV)
Ionization energy (I) (eV)
Electron affinity (A) (eV)
Energy gap, E, (eV)
Global Electronegativity, χ (eV)
Global hardness, η (eV)
Global softness, S (eV-1)
Global electrophilicity, w (eV)
Global nucleophilicity,  (eV-1)
Number of transferred electrons, N110
Initial molecule-metal interaction energy,  (eV),
Charge transfer model for donation and back-
donation of charges, ∆Eb-d (eV)
-0.551
-0.558
Electrodonating power (ω-)
3.781326584
0.80124821
4.583
3.660511171
0.733495417
4.394
Eelctroaccepting power, (ω+)
Net electrophilicity, (∆ω±)
Dipole moment (Debye)
0.803
8.536
E=ELUMO-EHOMO, I=-EHOMO, A=-ELUMO, π =-=0.5(I+A), =0.5(I-A), S=1/, =2/2,
=1/, N110=(4.82-inh)/2(inh+Fe), =(Fe-inh)2/4(Fe+inh), Ed-b=-/4, 휔− =
ퟐ
ퟐ
+
±
+
−
(
)
(
)
3푰 + 푨 /16(퐼 − 퐴), 휔 = ( 퐼 + 3퐴 ) /16(퐼 − 퐴), ∆휔 = 휔 + 휔

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Table 5 Fukui functions analysis for both neutral and protonated species.
Neutral inhibitor
푓− 푆푘+
Protonated inhibitor
푓− 푆푘+
푓+
푆푘−
푓+
푆푘−
푓2(푟)
푓2(푟)
푘
푘
푘
푘
C1
C2
C3
C4
C6
C8
-0.00362 0.04884 0.00031 0.02217 -0.05246
0.09954 0.02135 -0.00859 0.00969 0.07819
0.09473 0.02309 -0.00818 0.01048 0.07164
0.08953 0.03830 -0.00773 0.01739 0.05123
0.08945 0.04889 -0.00772 0.02220 0.04056
0.00099 0.02917 -0.00009 0.01324 -0.02818
C1
C2
C3
C4
C6
C8
-0.01965 0.06665 0.00170 0.03026 -0.08630
0.10993 0.02685 -0.00949 0.01219 0.08308
0.09495 0.02472 -0.00819 0.01122 0.07023
0.09603 0.04613 -0.00829 0.02094 0.04990
0.10711 0.04649 -0.00924 0.02111 0.06062
0.00762 0.02782 -0.00066 0.01263 -0.02020
C11 -0.00362 0.04880 0.00031 0.02216 -0.05242
C12 0.09474 0.02308 -0.00818 0.01048 0.07166
C13 0.09955 0.02134 -0.00859 0.00969 0.07821
C14 0.08946 0.04888 -0.00772 0.02219 0.04058
C16 0.08952 0.03828 -0.00773 0.01738 0.05124
C18 0.00099 0.02916 -0.00009 0.01324 -0.02817
N21 0.00836 0.10736 -0.00072 0.04874 -0.09900
N22 0.00836 0.10741 -0.00072 0.04876 -0.09905
C23 -0.00333 -0.01272 0.00029 -0.00577 0.00939
C26 -0.00351 -0.01275 0.00030 -0.00579 0.00924
C29 -0.00334 -0.01273 0.00029 -0.00578 0.00939
C32 -0.00351 -0.01276 0.00030 -0.00579 0.00925
O35 0.02004 0.07296 -0.00173 0.03312 -0.05292
C36 -0.00147 -0.00186 0.00013 -0.00084 0.00039
C37 0.00045 0.00283 -0.00004 0.00128 -0.00238
O38 0.00520 0.01067 -0.00045 0.00484 -0.00547
C42 -0.00152 -0.00192 0.00013 -0.00087 0.00040
C43 0.00036 0.00268 -0.00003 0.00122 -0.00232
O44 0.00530 0.01074 -0.00046 0.00488 -0.00544
C48 -0.00147 -0.00186 0.00013 -0.00084 0.00039
C49 0.00044 0.00284 -0.00004 0.00129 -0.00240
O50 0.00520 0.01067 -0.00045 0.00484 -0.00547
C54 -0.00152 -0.00192 0.00013 -0.00087 0.00040
O55 0.00036 0.00268 -0.00003 0.00122 -0.00232
O56 0.00530 0.01074 -0.00046 0.00488 -0.00544
C11 -0.02358 0.04762 0.00203 0.02162 -0.07120
C12 0.07778 0.01568 -0.00671 0.00712 0.06210
C13 0.07166 0.01715 -0.00618 0.00779 0.05451
C14 0.07368 0.03447 -0.00636 0.01565 0.03921
C16 0.07432 0.04781 -0.00641 0.02171 0.02651
C18 0.00848 0.01859 -0.00073 0.00844 -0.01011
N21 -0.02417 0.12333 0.00209 0.05599 -0.14750
N22 -0.02591 0.15067 0.00224 0.06840 -0.17658
O23 0.00728 0.07369 -0.00063 0.03346 -0.06641
C24 0.00896 -0.02047 -0.00077 -0.00929 0.02943
C25 -0.03331 0.03274 0.00287 0.01486 -0.06605
C26 0.01710 0.00775 -0.00148 0.00352 0.00935
C28 -0.01241 0.01213 0.00107 0.00551 -0.02454
C32 0.00641 -0.02660 -0.00055 -0.01208 0.03301
C33 -0.03201 0.03271 0.00276 0.01485 -0.06472
C36 -0.01010 0.00928 0.00087 0.00421 -0.01938
C40 0.00777 -0.02371 -0.00067 -0.01076 0.03148
C41 -0.03095 0.03092 0.00267 0.01404 -0.06187
C44 -0.01291 0.01223 0.00111 0.00555 -0.02514
C48 0.00879 -0.02130 -0.00076 -0.00967 0.03009
C49 -0.03346 0.03284 0.00289 0.01491 -0.06630
C52 -0.01227 0.01216 0.00106 0.00552 -0.02443
O56 -0.02345 0.02560 0.00202 0.01162 -0.04905
O58 -0.02103 0.01915 0.00181 0.00869 -0.04018
O60 -0.02339 0.02554 0.00202 0.01160 -0.04893
O62 -0.02062 0.01915 0.00178 0.00869 -0.03977
O64 -0.01393 0.02463 0.00120 0.01118 -0.03856
O66 -0.02570 0.02894 0.00222 0.01314 -0.05464
O68 -0.01797 0.02039 0.00155 0.00926 -0.03836
O70 -0.02270 0.02557 0.00196 0.01161 -0.04827

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Table 6: Inhibition efficiency comparisons for some traditional corrosion inhibitors.
Type of corrosion inhibitor
Type of
solution
1M HCl
1M HCl
C
(M)
Type of
substrate
ηMax Ref
(%)
Triglycidyl ether of triethoxy triazine
S, S’-diglycidyl O, O’- dicarbonodithioate of
bisphenol A
10-3 Carbon steel 88.0 [7]
10-3 Carbon steel 96.0 [7]
Octaglycidylether tetra-aniline para
methylene dianiline
1M HCl
1M HCl
10-3 Carbon steel 98.0 [7]
10-3 Carbon steel 91.7 [8]
N1,N1,N2,N2-tetrakis (oxiran-2-ylmethyl)
benzene-1,2-diamine
Tetraglycidyl-1,2-aminobenzamide.
4-methyl-N1,N1,N2,N2-tetrakis (oxiran-2-
1M HCl
1M HCl
10-3 Carbon steel 96.0 [9]
10-3 Carbon steel 92.9 [54]
ylmethyl) benzene-1,2-diamine
Figure

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Figure 1:Schematic outline for the synthesis of AA2
0,60
Blank
10-3 M of AA2
10-4 M of AA2
10-5 M of AA2
10-6 M of AA2
0,55
0,50
0,45
0,40
0
400
800
1200
1600
Time (s)
Figure 2: Evolution of open circuit potential (OCP) versus time for carbon steel in 1
M HCl with different concentrations AA2 at 298 K

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103
102
101
100
10-1
10-2
10-3
10-4
10-5
Blank
10-3 M of AA2
10-4 M of AA2
10-5 M of AA2
10-6 M of AA2
-0,8
-0,7
-0,6
-0,5
-0,4
-0,3
-0,2
-0,1
0,0
E (V/SCE)
Figure 3: Potentiodynamic polarization curves for carbon steel corrosion in 1 M HCl
solution in the absence and presence of different concentrations of AA2
350
50
40
30
20
10
0
Blank
10-3 M of AA2
10-4 M of AA2
10-5 M of AA2
300
250
200
150
100
50
10-6 M of AA2
Fitting data
0
10 20 30 40 50
0
0
50
100
150
200
250
300
350
Z' (.cm2)
Figure 4: Nyquist diagrams for carbon steel in 1 M HCl solution in the absence and
presence of different concentrations of AA2

Journal Pre-proof
Figure 5:Equivalent circuit used for the analysis of the EIS data.
103
Blank
10-3 M of AA2
10-4 M of AA2
10-5 M of AA2
102
10-6 M of AA2
Fitting data
101
100
10-3
10-2
10-1
100
101
102
103
104
105
106
Freq (Hz)
-80
Blank
10-3 M of AA2
10-4 M of AA2
10-5 M of AA2
-70
-60
-50
-40
-30
-20
-10
0
10-6 M of AA2
Fitting data
10-3
10-2
10-1
100
101
102
103
104
105
106
Freq (Hz)
Figure 6: Bode diagrams for carbon steel in 1 M HCl solution in the absence and
presence of different concentrations of AA2

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Figure 7:SEM-EDS micrographs of low carbon steel after 12 h of immersion in 1 M
HCl solution: without inhibitor (a) and with 10-3 M of AA2 (b).
103
102
101
100
10-1
10-2
298 K of AA2
10-3
308 K of AA2
318 K of AA2
328 K of AA2
10-4
-0,8
-0,7
-0,6
-0,5
-0,4
-0,3
-0,2 -0,1 0,0
E (V/SCE)
Figure 8: Potentiodynamic polarization curves of carbon steel in 1 M HCl solution in
the presence of 10-3 M of AA2 at different temperatures.

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Figure 9:Optimized molecular structure and electrostatic potential map (ESP) of the
inhibitor molecule in its neutral (a) and protonated form (b) using DFT/B3LYP/6-
31+G(d,p) in aqueous solution.
Figure 10:Frontier molecular orbitals (HOMO and LUMO) and their energy values,
as well as the energy gap energy diagram of the inhibitor molecule in its neutral (a)
and protonated form (b) using DFT/B3LYP/6-31+G(d,p) in aqueous solution.

Journal Pre-proof
Figure 11:Graphical representation of the second order Fukui function (f2(r)) for
selected atoms in the investigated inhibitors in its (a) neutral forma and (b) protonated
form). The optimized structures of the inhibitor and its protonated form are
superimposed in the figure.
Figure 12: (a) The equilibrium configuration of AA2 adsorbed on Fe(110) surface;
(b) dependence of adsorption energy on the temperature for adsorbed AA2 molecule
on Fe(110).