Chemical, electrochemical, theoretical (DFT & MEP), thermodynamics and surface morphology studies of carbon steel during gas and oil production using three novel di-cationic amphiphilies as corrosion inhibitors in acidic medium

Article abstract of DOI:10.1016/j.molliq.2021.116541

Three di-cationic amphiphilies were synthesized and characterized by FTIR, (¹H & ¹³C) NMR spectroscopies. These compounds are tested as corrosion inhibitors for CS in 1 M HCl by weight loss (WL), EIS, potentiodynamic polarization (PP) techniques, and surface morphology (SEM & AFM). Surface tension results exhibited that these surfactants are a good surface attitude in their aqueous media. The gained results exhibited that the di-cationic surface-active agents are stellar deterioration inhibitors for CS in 1 M HCl. A discouragement efficacy augmented with increment of the inhibitor concentration. Adsorption of CSI, CSII & CSIII on CS in 1 M HCl was established to comply with Langmuir's adsorption isotherm. SEM & AFM photos exhibit a good CS surface in presence of CSI, CSII & CSIII in opposite of the absence of them. The inhibition mechanism is suggested on the thermodynamic factors. The inhibitive impact of the explored surfactants against the corrosion of the CS surface was implied by DFT/6-31G(d,p) computations.

Full text of DOI:10.1016/j.molliq.2021.116541

Journal of Molecular Liquids 337 (2021) 116541
Contents lists available at ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Chemical, electrochemical, theoretical (DFT & MEP), thermodynamics
and surface morphology studies of carbon steel during gas and oil
production using three novel di-cationic amphiphilies as corrosion
inhibitors in acidic medium
b
c
d
M.A. Hegazy a, , M.M. Hegazy , M.K. Awad , M. Shawky
⇑
a Egyptian Petroleum Research Institute (EPRI) Nasr City, Cairo, Egypt
b Chemistry Dept., Faculty of Science, Helwan University, Cairo, Egypt
c Theoretical Applied Chemistry Unit, Chemistry Department, Faculty of Science, Tanta University, Tanta, Egypt
d General Petroleum Company (GPC), Cairo, Egypt
a r t i c l e i n f o
a b s t r a c t
Three di-cationic amphiphilies were synthesized and characterized by FTIR, (1H & 13C) NMR spectro-
scopies. These compounds are tested as corrosion inhibitors for CS in 1 M HCl by weight loss (WL),
EIS, potentiodynamic polarization (PP) techniques, and surface morphology (SEM & AFM). Surface tension
results exhibited that these surfactants are a good surface attitude in their aqueous media. The gained
results exhibited that the di-cationic surface-active agents are stellar deterioration inhibitors for CS in
Article history:
Received 21 February 2021
Revised 3 May 2021
Accepted 18 May 2021
Available online 21 May 2021
1
M HCl. A discouragement efficacy augmented with increment of the inhibitor concentration.
Keywords:
Di-cationic surfactant
EIS
Tafel
SEM
AFM
Adsorption of CSI, CSII & CSIII on CS in 1 M HCl was established to comply with Langmuir’s adsorption
isotherm. SEM & AFM photos exhibit a good CS surface in presence of CSI, CSII & CSIII in opposite of
the absence of them. The inhibition mechanism is suggested on the thermodynamic factors. The inhibi-
tive impact of the explored surfactants against the corrosion of the CS surface was implied by DFT/6-31G
(d,p) computations.
Molecular modeling
DFT
Ó 2021 Elsevier B.V. All rights reserved.
1. Introduction
keeps metal verse corrosion [5]. The adsorption process relies on
the nature of a metal surface, type of corrosive environment, and
In the oil field, there is an acidizing process involves the injec-
tion of chemicals to improve the flow of reservoir fluids, usually
HCl (strong acid) is used to dissolve rock formations [1]. During
the acetification operation, it is needful to clean off the isolated
oxide but the metal is more susceptible to corrosion after the pick-
ling process so it is very important to use corrosion inhibitors [2,3].
CS has been commonly utilized in oil and gas production like
recovery tubes, flux pipelines, and shipping lines [4]. Preventing
the corrosion of CS is very important in numerous manufactures.
Many studies are offered effective methods for the suppression of
corrosion. The cationic surfactants reduce a metal dissolution rate
where the action of the cationic surfactants in an acidic medium is
adsorption onto a steel surface. The technique of corrosion discour-
agement depends on an adsorption of a surfactant on metallic sur-
faces. Then substitution water by inhibitor to form a layer which
chemical composition of the CSI, CSII & CSIII. Adsorption places
because of the interrelation between the free & electron of inhi-
bitor and orbitals of metallic surface atoms. This interrelation exhi-
bits a good adsorption of an inhibitor onto a metallic face leads to a
composition of a protective layer. The high suppression perfor-
mance of the CSI, CSII & CSIII comes from the switching of distinct
p
heteroatoms (ex. N, O, Cl and Br) and a subsistence of p-electrons
in their structures. These compounds form a very thin layer and
adsorbed layer that lead to a reduction in the corrosion rate [6].
The election of an inhibitor is controlled by its capability to damp
corrosion on a metal face and its environmental impacts. They are
organic materials that contain N, S, O, and P to reduce a corrosion
attack on CS [7]. The cationic surfactants lowering the corrosion
rate by adsorbing on a metal surface, and prohibit the active sites
insecure with a corrosive media on the metal surface [8,9].
Exploratory methods are valuable in clarifying the mechanism
of inhibition yet they are regularly costly and tedious. Continuous
equipment and programming propels have opened the entryway
for ground-breaking utilization of computational chemistry in
⇑
Corresponding author.
E-mail address: mohamed_hgazy@yahoo.com (M.A. Hegazy).
https://doi.org/10.1016/j.molliq.2021.116541
0167-7322/Ó 2021 Elsevier B.V. All rights reserved.

M.A. Hegazy, M.M. Hegazy, M.K. Awad et al.
Journal of Molecular Liquids 337 (2021) 116541
corrosion hindrance research. In this way, a few quantum chemical
strategies and modeling displaying methods have been acted as
correspond the inhibition efficacy of the properties of substances
[10-13]. The utilization of hypothetical quantum parameters
exhibit two principal focal points: firstly, the materials with their
different sections and substituents can be straightforwardly
described based on their molecular constructions just; and sec-
ondly, the suggested reaction mechanization of association can
be straightforwardly represented regarding the synthetic reactivity
of compounds [14]. A few examinations have demonstrated that
the hindrance of corrosion is essentially portrayed by an arrange-
ment of contributor donor–acceptor face buildings betwixt free
ylmethylene)amino)-N,N-dimethylethan-1-amine (viscous and
black color), N,N-dimethyl-2-(((1E,2E)-3-phenylallylidene)amino)
ethan-1-amine (semi-liquid and black red color), and (E)-2-((4-m
ethoxybenzylidene)amino)-N,N-dimethylethan-1-amine
liquid and black red color) respectively, as in Scheme 1.
The second step:
(semi-
Reaction (8.914 g, 0.1 mol) 2-(Dimethylamino)ethan-1-ol and
(24.923 g, 0.1 mol) 1-bromododecane in 100 ml absolute ethanol
at 70 °C for two days. The products recrystallized by hot ethanol
and purified by diethyl ether. The product N-(2-hydroxyethyl)-N,
N-dimethyldodecan-1-aminium bromide (white powder) is shown
in Scheme 2.
The third step:
or
p ꢀ electrons of a surfactant, generally comprising N, S, or O
Reaction (33.837 g, 0.1 mol) N-(2-hydroxyethyl)-N,N-
dimethyldodecan-1-aminium bromide and (9.449 g, 0.1 mol)
Chloroacetic acid in 100 ml xylene till percent of water which cal-
culated is trapped. And evaporate xylene from a mixture then let
the mixture cool down, and finally N-(2-(2-chloroacetoxy)ethyl)-
N,N-dimethyldodecan-1-aminium bromide (honey color- viscous
liquid) as in Scheme 2.
particles, and goofy d-orbital of a metal [15-17]. Di-cationic surfac-
tants which are significant mixtures in numerous scopes have been
accounted for before as consumption inhibitors for a metal [18].
The target of research is to explore the influence of three di-
cationic surfactants namely: (E)-N-(2-(2-((2-((furan-2-ylmethy
lene)amino)ethyl)dimethylammonio)acetoxy)ethyl)-N,N-dimethyl
dodecan-1-aminium bromide chloride (CSI), N-(2-(2-(dimethyl(2-
(((1E,2E)-3-phenylallylidene) amino)ethyl)ammonio)acetoxy)ethy
l)-N,N-dimethyldodecan-1-aminium bromide chloride (CSII),
(E)-N-(2-(2-((2-((4-methoxybenzylidene)amino)ethyl)dimethylam
monio)acetoxy)ethyl)-N,N-dimethyldodecan-1-aminium bromide
chloride (CSIII) on CS in 1 M HCl medium through chemical (WL)
and electrochemical (PP & EIS) procedures. We study surface
parameters to determine the optimum dose of inhibitors. We study
the inhibition behavior of di-cationic amphiphilies on the CS face
through thermodynamic parameters to understanding the corro-
sion suppression technique and interactivity betwixt the inhibitor
molecules and CS surface. Surface inspection (SEM & AFM) is used
for the examination of the steel surface with and without CSI, CSII
& CSIII. The relationship between the structural parameters and
corrosion inhibition of those compounds has not been studied
yet. Therefore the task of this paper is to correlate the quantum
chemical parameters and the observed inhibition efficiency of the
investigated surfactant inhibitors. The inhibitive impact of the
explored surfactants against the corrosion of the surface of CS
was implied by DFT/6-31G(d,p) computations. The determined
quantum parameters associated with the restraint effectiveness
are lowest unoccupied molecular orbitalðLUMOÞ, highest occupied
The fourth step:
Reaction of (41.485 g, 0.1 mol) N-(2-(2-chloroacetoxy)ethyl)-N,
N-dimethyldodecan-1-aminium bromide and (16.622 g, 0.1 mol)
(E)-2-((furan-2-ylmethylene)amino)-N,N-dimethylethan-1-amine,
(20.230 g, 0.1 mol) N,N-dimethyl-2-(((1E,2E)-3-phenylallylidene)a
mino)ethan-1-amine, and (20.629 g, 0.1 mol) (E)-2-((4-methoxy
benzylidene)amino)-N,N-dimethylethan-1-amine in 100 ml abso-
lute ethanol at 70 °C for two days.
Then evaporate ethanol from the mixture and let the
mixture to cool-down. To produce (E)-N-(2-(2-((2-((furan-2-
ylmethylene)amino)ethyl)dimethylammonio)acetoxy)ethyl)-N,N-
dimethyldodecan-1-aminium bromide chloride (CSI) (black-brown
viscous), N-(2-(2-(dimethyl(2-(((1E,2E)-3-phenylallylidene)amino)
ethyl)ammonio)acetoxy)ethyl)-N,N-dimethyldodecan-1-aminium
bromide chloride (CSII) (black-brown semi-liquid), and (E)-N-(2-
(2-((2-((4-methoxybenzylidene)amino)ethyl)dimethylammonio)
acetoxy)ethyl)-N,N-dimethyldodecan-1-aminium bromide chloride
(CSIII) (black-brown semi-liquid) as in Scheme 3.
2.2. Surface tension
molecular orbital ðHOMOÞ, separation gap ð
ðDMÞ, softness ð Þ, total negative charge ðTNCÞ, molecular volume
ðMVÞ, chemical potential ð Þ, and electronegativet ð Þ. A decent
DE), dipole moment
Surface properties is evaluated via utilizing Kruss K6 tensiome-
r
ter for CSI, CSII & CSIII with a concentration of (5 ꢁ 10ꢀ5
–
l
v
1 ꢁ 10ꢀ3M) at 25 °C.
relationship was found between the exploratory and hypothetical
examinations. The relationship betwixt the parameters and corro-
sion restraint of those compounds has not been performed at this
point. The undertaking of this search is to relate the quantum vari-
ables and the noticed corrosion hindrance proficiency of the exam-
ined surfactants.
2.3. Weight loss technique
Analytical balance, (KERN Pattern: ABJ 320-4NM), was used for
weight loss evaluation. The CS coupons of 6 ꢁ 3 ꢁ 0.4 CM were
rubbed off with emery sheets (degree 320–400–600–800–1000–1
200–2500) then wash out by DW, acetone, and lastly dry with
air. After carefully weighing, coupons are placed in 100 ml volume
1 M HCl medium in occurrence & absenteeism of various concen-
trations of surfactants at varied temperatures. Temperatures of
weight loss evaluations were stripped by water bath supplied by
thermostat 0.5 °C. The CS coupons were taken out after 24 h then
immersed in inhibited 15% HCl solution to remove corrosion prod-
ucts then immersed in saturated sodium bicarbonate for one min-
ute to equalize the acid, then wash with distilled water to cut off
the neutralizer, then wash the coupons in acetone, and dry the cou-
pons with dry air. Finally, weight and record the results in mg. The
chemical structure of AISI 1018 mild/low CS specimen has a fol-
lowing percentage of elements: C (0.14–0.20), Mn (0.60–0.90),
P ꢂ 0.040, S 0.050, Fe (98.81–99.26% as remainder).
2. Experimental methods and materials
2.1. Synthesis
Three di-cationic surfactants (CSI, CSII & CSIII) applied in a
search were produced through four steps:
The first step:
Three Schiff bases were synthesized by reaction (8.815 g,
0.1 mol) N1,N1-dimethylethane-1,2-diamine with (9.609 g,
0.1 mol) Furan-2-carbaldehyde, (13.216 g, 0.1 mol) Cinnamalde-
hyde, and (13.615 g, 0.1 mol) 4-methoxybenzaldehyde in 100 ml
absolute ethanol at 70 °C for 6 h. Then evaporate the amount of
ethanol. The products were recrystallized by hot ethanol. The prod-
ucts purified by diethyl ether [19] to produce (E)-2-((furan-2-
2

M.A. Hegazy, M.M. Hegazy, M.K. Awad et al.
Journal of Molecular Liquids 337 (2021) 116541
Scheme 1.
2.4. Electrochemical measurements
2.6. Theory and computational details:
The electrochemical studies are achieved in a suitable three-
electrode cell with a platinum counter electrode (CE) and a satu-
rated calomel electrode (SCE) as a reference electrode. The working
electrode (WE) is a rod of CS included in PVC holder utilizing
Teflon. Therefore, a regular face was the lone uncovered face in
the electrode. Uncovered area is 0.7 cm2 for working. Such region
is rubbed off with an emery sheet (degree 320–400–600–800–10
00–1200–2500) on the test surface, and then immersed in DW,
then acetone, and lastly drying with dry atmosphere.
Prior evaluation, the electrode is sunken in a test solution at
(OCP) for half hour until a steady state was attained. All electro-
chemical evaluations were accomplished by utilizing a Volta Lab
40 (PGZ 301 & Volta master 4) - (Radiometer Analytical - FRANCE)
at 25 °C. The potentiodynamic polarization measures were
acquired by alteration the electrode potential from ꢀ800 to
ꢀ200 mV versus SCE at 25 °C. EIS measurements were applied in
the frequency range of 100 kHz – 30 mHz at a little alternating
voltage perturbation (10 mV) at 20 °C.
The molecular structures of the investigated di- cationic surfac-
tants were optimized with the DFT/6-31G (d,p) method. A vibra-
tional investigation of the structures is executed by Gaussian 09
program package [20] to decide if they match to a maximal or a
minimal on a potential energy bend and found imaginative was
determined, showing minimum energy structure. The matters
were worked with the GaussView 5.0 executed in Gaussian 09.
Molecular orbitals ðHOMOandLUMOÞ could be utilized to antici-
pate the center of adsorption of the inhibitors. For ordinary
exchange of electrons, adsorption ought to happen at the piece of
a particle where the softnessðrÞ, which is a property that has the
most elevated worth.
3. Results and discussion
3.1. Chemical structure validation
The chemical structure was established by FTIR, 1HNMR &
13CNMR spectroscopies.
2.5. SEM and AFM image
3.1.1. Confirmation of Schiff bases structure
FTIR of Schiff base (I) exhibited the following absorption sects
at 1011.93 cmꢀ1 (CAN stretch), 1378.4 cmꢀ1 (CAH rock),
1462.47 cmꢀ1 (CAH bend), 1664.85 cmꢀ1 (C@N stretch),
2859.5 cmꢀ1 (CAH stretch), 2941.4 cmꢀ1 (@CAH stretch) as dis-
played in (Supplementary materials, Fig. 1).
SEM (Inspect S, Manufacturer FEI Company, Netherlands) and
Atomic Force Microscope (AFM, MFP, Asylum Research) that give
3-D photo are used as a powerful tool in the morphological exam-
inations for CS surface immersed for one day in 1 M HCl in an
absenteeism and an existence of 1 ꢁ 10ꢀ3M of CSI, CSII & CSIII at
25 °C.
FTIR of Schiff base (II) exhibited the following absorption sects
at 1035.29 cmꢀ1 (CAN stretch), 1381.34 cmꢀ1 (CAH rock),
3

M.A. Hegazy, M.M. Hegazy, M.K. Awad et al.
Journal of Molecular Liquids 337 (2021) 116541
Scheme 2.
1453.62 cmꢀ1 (CAH bending), 1634.93 cmꢀ1 (C@N stretch),
1672.17 cmꢀ1 (C@C stretch), 2859.34 cmꢀ1(CAH stretch),
2943.52 cmꢀ1(@CAH stretch) as shown in (Supplementary mate-
rials, Fig. 2).
FTIR of Schiff base (III) exhibited the following absorption sects
at 1032.24 cmꢀ1 (CAN stretch), 1379.59 cmꢀ1 (CAH rock),
1461.77 cmꢀ1 (CAH bend), 1645.26 cmꢀ1 (C@N stretch),
2833.4 cmꢀ1 (CAH stretch), 2941.45 cmꢀ1 (@C-H stretch) as shown
in (Supplementary materials, Fig. 3).
1464.7 cmꢀ1 (CAH bend), 1197.84 cmꢀ1 (CAO stretch),
1747.33 cmꢀ1 (C@O stretch), 2853.47 cmꢀ1 (CAH stretch). The FTIR
assured the predicted function groups in the step (3) product as
shown in (Supplementary materials, Fig. 5).
1HNMR of step (3) product exhibited different sects at
d = 0.85 ppm (t, 3H, NCH2(CH2)nCH2CH3); d = 1.22 ppm (m, 6H,
NCH2(CH2)nCH2CH3); d = 1.22 ppm (m, 5H, NCH2(CH2)nCH2CH3);
d = 1.52 ppm (NCH2(CH2)n CH2CH3); d = 2.73 ppm (s, 1H, NCH3);
d = 2.49 ppm (t, 3H, ClCH2COOCH2CH2N), d = 3.04 ppm (t, 3H,
ClCH2COOCH2CH2N), d = 3.46 ppm ((s, 1H, ClCH2COOCH2CH2N)
as shown in (Supplementary materials, Fig. 6).
3.1.2. Validation of monomeric surfactant (product of step 2)
FTIR of step (2) product exhibited the following absorption
sects at 1084.87 cmꢀ1 (CAN stretch), 1378.34 cmꢀ1 (CAH rock),
1468.37 cmꢀ1(CAH bend), 2853.54 cmꢀ1(CAH stretch),
3398.3 cmꢀ1 (OAH stretch) as shown in (Supplementary materi-
als, Fig. 4).
13CNMR of step (3) product exhibited various sects at
d = 13.97 ppm (NCH2(CH2)nCH2CH2CH3); d = 22.12 ppm (NCH2(-
CH2)nCH2CH2CH3);
d = 31.33 ppm (NCH2(CH2)nCH2CH2CH3);
d = 28.99 ppm (NCH2(CH2)nCH2CH2CH3); d = 68.54 ppm (NCH2
1HNMR of step (2) product exhibited different beaks at
(CH2)nCH2CH2CH3);
d
=
54.22 ppm (NCH3);
d = 68.54 ppm
d = 0.85 ppm (t, 3H, NCH2(CH2)nCH2CH3); d = 1.27 ppm (m, 6H,
NCH2(CH2)nCH2CH3); d = 1.25 ppm (m, 5H, NCH2(CH2)nCH2CH3);
d = 1.65 ppm (s, 3H, NCH2(CH2)nCH2CH3); d = 3.29 ppm (s,1H,
NCH3); d = 3.12 ppm (t, 3H, HOCH2CH2N), d = 3.38 ppm (m, 4H,
HOCH2CH2N), d = 5.26 ppm (t, 3H, HOCH2CH2N) as shown in Fig. 1.
(ClCH2COOCH2CH2N),
d
=
59.58 ppm (ClCH2COOCH2CH2N),
d = 168.56 ppm (ClCH2COOCH2CH2N), d = 48.24 ppm (ClCH2-
COOCH2CH2N) as shown in Fig. 2.
3.1.4. Validation of CSI, CSII & CSIII
FTIR of (ꢀC1SI) exhibited the following absorption sects at
1465.75 cmꢀ1 (CAH bend), 1149.24 cmꢀ1 (CAO stretch),
1660.35 cmꢀ1 (C@O stretch), 2854.13 cmꢀ1 (CAH stretch),
3.1.3. Validation of the product of step 3
1077.67 cm
(CAN stretch), 1378.01 cmꢀ1 (CAH rock),
FTIR of step (3) product exhibited the following absorption
sects at 1073.64 cmꢀ1(CAN stretch), 1400.27 cmꢀ1 (CAH rock),
4

M.A. Hegazy, M.M. Hegazy, M.K. Awad et al.
Journal of Molecular Liquids 337 (2021) 116541
Scheme 3.
Fig. 1. 1HNMR of step (2) product.
5

M.A. Hegazy, M.M. Hegazy, M.K. Awad et al.
Journal of Molecular Liquids 337 (2021) 116541
Fig. 2. 13CNMR of step (3) product.
2925.14 cmꢀ1 (@CAH stretch) as shown in (Supplementary mate-
rials, Fig. 7).
1HNMR of (CSII) exhibited different sects at d = 0.86 ppm (t, 3H,
NCH2(CH2)nCH2CH3), d = 1.23 ppm (m, 6H, NCH2(CH2)nCH2CH3),
d = 1.54 ppm (m, 5H, NCH2(CH2)nCH2CH3), d = 3.01 ppm (t, 3H,
NCH2(CH2)nCH2CH3), d = 3.03 ppm (s, 1H, NCH3), d = 3.09 ppm (t,
3H, NCH2COOCH2CH2N), d = 3.97 ppm (t, 3H, NCH2COOCH2CH2N),
d = 3.47 ppm (s, 1H, NCH2COOCH2CH2N), d = 3.03 ppm (t, 3H,
FTIR of (CSII) exhibited the following absorption sects at
1071.90 cmꢀ1 (CAN stretch), 1378.25 cmꢀ1 (CAH rock),
1463.66 cmꢀ1 (CAH bend), 1648.43 cmꢀ1 (C@C stretch),
1152.31 cmꢀ1 (CAO stretch), 1744.7 cmꢀ1(C@O stretch),
2853.76 cmꢀ1(CAH stretch), 2924.95 cmꢀ1(@CAH stretch) as
shown in (Supplementary materials, Fig. 8).
Ar-CH@CHCH@NCH2CH2N),
d
=
1.8 ppm (t, 3H, Ar-CH@
FTIR of (CSIII) exhibited the following absorption sects at
CHCH@NCH2CH2N),
d
= 7.89 ppm (d, 2H, Ar-CH@CHCH@
1034.61 cmꢀ1 (CAN stretch), 1374.69 cꢀm1ꢀ1 (CAH rock),
NCH2CH2N), d = 7.14 ppm (t, 3H, Ar-CH@CHCH@NCH2CH2N),
1512.41 cmꢀ1 (CAH bend), 1168.95 cm
(CAO stretch),
d = 7.29 ppm (d, 2H, Ar-CH@CHCH@NCH2CH2N) as shown in Fig. 4.
1HNMR of (CSIII) exhibited different sects at d = 0.85 ppm (t, 3H,
1744.55 cmꢀ1 (C@O stretch), 2853.54 cmꢀ1 (CAH stretch),
2925.45 cmꢀ1 (@CAH stretch) as shown in (Supplementary mate-
rials, Fig. 9).
NCH2(CH2)nCH2CH3), d = 1.22 ppm (m, 6H, NCH2(CH2)nCH2CH3),
1HNMR of (CSI) exhibited different sects at d = 0.88 ppm (t, 3H,
d
=
1.58 ppm (m, 5H, NCH2(CH2)nCH2CH3),
d = 2.95 ppm
(t, 3H, NCH2(CH2)nCH2CH3), 3.1 ppm (s, 1H, NCH3),
d
=
NCH2(CH2)nCH2CH3), d = 1.3 ppm (m, 6H, NCH2(CH2)nCH2CH3),
d = 1.7 ppm (m, 5H, NCH2(CH2)nCH2CH3), d = 3.2 ppm (t, 3H, NCH2(-
CH2)nCH2CH3), d = 3.3 ppm (s, 1H, NCH3), d = 3.5 ppm (t, 3H, NCH2-
COOCH2CH2N), d = 4.2 ppm (t, 3H, NCH2COOCH2CH2N), d = 3.9 ppm
(s, 1H, NCH2COOCH2CH2N), d = 3.2 ppm (t, 3H, Ar-CH@N CH2-
COOCH2CH2N), d = 1.9 ppm (t, 3H, Ar-CH@NCH2COOCH2CH2N),
d = 7.9 ppm (s, 1H, Ar-CH@N CH2COOCH2CH2N) as shown in Fig. 3.
d = 3.45 ppm (t, 3H, NCH2COOCH2CH2N), d = 3.85 ppm (t, 3H,
NCH2COOCH2CH2N), d = 3.71 ppm (s, 1H, NCH2COOCH2CH2N),
d
=
2.95 ppm (t, 3H, Ar-CH@NCH2CH2N),
(t, 3H, Ar-CH@NCH2CH2N), 8.3 ppm (s, 1H,
Ar-CH@NCH2CH2N), d = 3.78 ppm (s, 1H, OCH3) as shown in Fig. 5.
d = 3.73 ppm
d
=
6

M.A. Hegazy, M.M. Hegazy, M.K. Awad et al.
Journal of Molecular Liquids 337 (2021) 116541
Fig. 3. 1HNMR of CSI.
Fig. 4. 1HNMR of CSII.
7

M.A. Hegazy, M.M. Hegazy, M.K. Awad et al.
Journal of Molecular Liquids 337 (2021) 116541
Fig. 5. 1HNMR of CSIII.
70
60
50
40
30
20
I
II
III
11
10
9
8
7
6
5
4
3
2
-ln (C, M)
Fig. 6. Curve of surface tension (
c
) against logarithm concentration (ln C) of the CSI, CSII & CSIII.
8

M.A. Hegazy, M.M. Hegazy, M.K. Awad et al.
Journal of Molecular Liquids 337 (2021) 116541
Table 1
Surface tension parameters of di-cationic surfactants in double distilled water at 25 °C.
Inhibitor
Ccmc ꢁ 103 (M)
ccmc (mN mꢀ1
)
pcmc (mN mꢀ1
)
Cmax ꢁ 1010 (mol cmꢀ2
)
Amin (nm2)
CSI
CSII
CSIII
4.95
4.02
3.91
29
27
27
42
45
46
1.01
1.05
1.07
1.65
1.58
1.55
Table 2
Weight loss data for CS in 1 M HCl in the absence and presence of different concentrations of di-cationic surfactants at different temperatures.
Inh. name Inh. conc. (M) 25 °C
k (mg cmꢀ2hꢀ1
0.5304
40 °C
w (%) k (mg cmꢀ2hꢀ1
1.1676
55 °C
w (%) k (mg cmꢀ2hꢀ1
2.2146
70 °C
)
h
g
)
h
g
)
h
g
w (%) k (mg cmꢀ2hꢀ1
)
h
g
w (%)
Abs.
CSI
0
–
–
–
–
–
–
4.0294
–
–
5 ꢁ 10ꢀ5
1 ꢁ 10ꢀ4
5 ꢁ 10ꢀ4
1 ꢁ 10ꢀ3
5 ꢁ 10ꢀ5
1 ꢁ 10ꢀ4
5 ꢁ 10ꢀ4
1 ꢁ 10ꢀ3
5 ꢁ 10ꢀ5
1 ꢁ 10ꢀ4
5 ꢁ 10ꢀ4
1 ꢁ 10ꢀ3
0.0781
0.0535
0.0330
0.0248
0.0739
0.0488
0.0304
0.0217
0.0704
0.0404
0.0265
0.0203
0.85 85.27
0.90 89.91
0.94 93.78
0.95 95.33
0.86 86.07
0.91 90.80
0.94 94.27
0.96 95.91
0.87 86.72
0.92 92.38
0.95 95.00
0.96 96.18
0.2298
0.1571
0.0986
0.0860
0.2037
0.1423
0.0918
0.0729
0.1824
0.1045
0.0804
0.0556
0.80 80.32
0.87 86.54
0.92 91.56
0.93 92.63
0.83 82.55
0.88 87.82
0.92 92.14
0.94 93.76
0.84 84.38
0.91 91.05
0.93 93.11
0.95 95.24
0.4804
0.3583
0.2602
0.2088
0.4570
0.3498
0.2375
0.1908
0.3954
0.2852
0.1947
0.1456
0.78 78.31
0.84 83.82
0.88 88.25
0.91 90.57
0.79 79.37
0.84 84.20
0.89 89.28
0.91 91.39
0.82 82.14
0.87 87.12
0.91 91.21
0.93 93.42
1.0104
0.8790
0.6330
0.5208
0.9387
0.7562
0.5588
0.4344
0.7996
0.5854
0.4625
0.3591
0.75 74.92
0.78 78.19
0.84 84.29
0.87 87.07
0.77 76.70
0.81 81.23
0.86 86.13
0.89 89.22
0.80 80.16
0.85 85.47
0.89 88.52
0.91 91.09
CSII
CSIII
1 M HCl
0.00005 M
0.0001 M
0.0005 M
0.001M
250
200
150
100
50
0
0
100
200
300
400
500
600
Z
real (ohm.cm2)
Fig. 7. Nyquist plot for CS in 1 M HCl in existence and absenteeism of varied concentrations of CSIII.
3.2. Surface tension
Surface tension (c) reductions linearly with augmentation of
concentration (ꢀ ln C) of CSI, CSII & CSIII until Ccmc Then stability
occurs after that as in Fig. 6. The existence of surfactants in med-
ium provide us with data about effectiveness (pcmc), area/molecule
at an air–water interface (Amin), and surface excess concentration
(Tmax) of CSI, CSII & CSIII. Ccmc data gained from the breakpoint of
c
ꢀ ln C curve as in Table 1. By comparison, Ccmc for the three CSI,
CSII & CSIII, it was observed that the increment in hydrophobicity
of dicationic surfactants molecules leading to lowering Ccmc values.
This is attributed to 4-methoxy benzyl > cinnamyl > furanyl
according to the total hydrophobicity. Therefore, CSI, CSII & CSIII
Fig. 8. Equivalent circuit used to pattern impedance measurements calculated for
CS in 1 M HCl in existence and absenteeism of varied concentrations of CSI, CSII &
CSIII.
9

M.A. Hegazy, M.M. Hegazy, M.K. Awad et al.
Journal of Molecular Liquids 337 (2021) 116541
Table 3
EIS parameters for CS corrosion in 1 M HCl in the absence and presence of different concentrations of di-cationic surfactants at 25° C.
Inhibitor name
Tested Solution
Rs (O cm2)
Qdl (mOꢀ1 sn cmꢀ2
)
n
Rct (O cm2)
Cdl
(l
F cmꢀ2
)
Chi-sq
gI (%)
Absence
CSI
1 M HCl
5 ꢁ 10ꢀ5
1 ꢁ 10ꢀ4
5 ꢁ 10ꢀ4
1 ꢁ 10ꢀ3
5 ꢁ 10ꢀ5
1 ꢁ 10ꢀ4
5 ꢁ 10ꢀ4
1 ꢁ 10ꢀ3
5 ꢁ 10ꢀ5
1 ꢁ 10ꢀ4
5 ꢁ 10ꢀ4
1 ꢁ 10ꢀ3
2.06
2.27
2.18
1.92
2.00
2.79
2.83
2.45
2.82
2.99
3.01
2.97
3.07
0.3595
0.0575
0.0455
0.0309
0.0207
0.0392
0.0383
0.0239
0.0196
0.0494
0.0373
0.0213
0.0177
0.85
0.90
0.88
0.87
0.87
0.89
0.87
0.85
0.87
0.87
0.87
0.85
0.87
26.22
165.7
234.3
370.6
490.0
183.7
262.4
407.9
522.9
195.0
306.3
472.8
575.5
64.51
10.34
8.27
5.07
4.33
9.17
7.07
4.37
3.77
9.01
6.12
4.08
3.36
0.00353
0.00476
0.00198
0.00345
0.00315
0.00338
0.00129
0.00133
0.00298
0.00330
0.00161
0.00133
0.00313
–
84.18
88.81
92.92
94.65
85.73
90.01
93.57
94.99
86.55
91.44
94.45
95.44
CSII
CSIII
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
20
1M HCl
0.00005M
0.0001M
0.0005M
0.001M
0
-20
-40
-60
-80
-100
-120
-140
-1.2
-0.2
0.8
1.8
2.8
3.8
4.8
log (f, Hz)
Fig. 9. Bode and Phase angle curve for CS in 1 M HCl in existence and absenteeism of various concentrations of CSIII.
1014
NATmax
gather into masses, where the hydrophilic group is pointed across
water while the hydrophobic group is pointed towards the inside
to form a micelle to obviate a relate with an aqueous medium, that
way lowering the free energy of the structure. Subsequently, by
augmentation hydrophobic group numbers, the tendency of the
surfactants to form micelle augments, consequently Ccmc decreases
[21].
Amin
¼
ð3Þ
where NA is Avogadro’s no.
The values of (Amin) were evaluated and recorded in Table 1. It
observed that Amin value decreases according to the following
order: CSI > CSII > CSIII. Amin value decreases because of increment
in hydrophobicity structure of CSI, CSII & CSIII in solution.
Effectiveness (pcmc) of CSI, CSII & CSIII can be evaluated by the
following eq. [22] and listed in Table 1:
3.3. Weight loss measurements
pcmc
¼
co
ꢀ
c
ð1Þ
Weight loss datum of CS in 1 M HCl in existence & absenteeism
of varied concentrations of CSI, CSII & CSIII were calculated. Then
calculate the inhibition efficiency (gw) as following eq. [25]:
where co
at Ccmc, respectively.
&
c
is surface tension of DW & of CSI, CSII & CSIII solution
Besides, Table 1 records the surface pressure values of cationic
ꢀ
ꢁ
surfactants (
pcmc). It is evident that the effectiveness values
Wcorr ꢀ WcorrðinhÞ
(p
cmc) augment with augmentation of a hydrophobicity of surfac-
gw
¼
ꢁ 100
ð4Þ
Wcorr
tants in aqueous media.
Tmax at the link was evaluated from the following eq. [23]:
where Wcorr and WcorrðinhÞ are the weight loss of CS with and without
the CSI, CSII & CSIII.
The results offer that gw of the CSI, CSII & CSIII increases with
augmentation of CSI, CSII & CSIII concentration. This behavior is
because of surface encasement through adsorption of CSI, CSII &
CSIII.
ꢀ
ꢁ
1
dc
Tmax
¼
ð2Þ
nRT dlnC
where d
c
=dlnC is a slope of straight line before Ccmc of (
c
v
s: ꢀ ln C)
plot and n is no. of species ions in a liquid phase.
Tmax value decreases according to the follows order:
CSIII > CSII > CSI. Tmax augments because of increment in hydropho-
bicity structure of CSI, CSII & CSIII in solution.
Effectiveness of heat on CS in the heat range 25–70 °C in corro-
sive medium in occurrence and absenteeism of various concentra-
tions of the CSI, CSII & CSIII were accomplished by weight loss
technique and shown in (Supplementary materials, Figs. 10–12)
Besides, the Amin was evaluated from the next eq. [24]:
10

M.A. Hegazy, M.M. Hegazy, M.K. Awad et al.
Journal of Molecular Liquids 337 (2021) 116541
looked as the polarization resistance (RP) [26]. RP includes the
resistance of cumulative kinds, the charges transfer resistance
(Rct), and the diffuse layer resistance (Rd). It is established that
Rct increases in existence of CSI, CSII & CSIII further than in absen-
teeism of them. Rct increases as concentration increased. The incre-
ment in Rct is concerning with a slower destroying system, due to
reducing the activated centers, which are needful for the corrosion
reaction. However, CPE used instead of pure capacitance (Cdl). EIS
spectrum is supplied with a convenient equivalent circuit as
Fig. 8. The equivalent circuit consists of Rs, Rct and CPE (constant
phase element) instead of Cdl.
1 M HCl
0.00005 M
0.0005 M
-2
-3
The Cdl values determined by the next formula:
-4
nꢀ1
Cdl ¼ Qdlð
x
maxÞ
ð5Þ
1M HCl
Impedance (ZCPE) is calculated by the following equation:
ꢀ1
0.00005 M
-5
0.001 M
ZCPE ¼ Q ðixmaxÞ ꢀ n
ð6Þ
dl
0.0001 M
x
¼ 2p
fmax
ð7Þ
0.0005 M
-6
where Qdl
,
x
max, fmax, i, n are constant phase element, the angular
0.0001 M
frequency, the frequency at a maximum imaginary element of the
impedance, an imaginary number, and a coefficient of surface inho-
mogeneity, respectively.
0.001 M
EIS variables were evaluated by the equivalent circuit. Table 3
clears that n values are 0.5 to 1, which refers that the adsorption
barrier is considered a capacitive double layer. As shown in Table 3,
Cdl values decrease as the CSI, CSII & CSIII concentration increase.
The Cdl is decreased because the water molecules are replaced by
CSI, CSII & CSIII on CS surface. Therefore Cdl value is smallest in
existence of CSI, CSII & CSIII than in them absenteeism. The adsorp-
tion of CSI, CSII & CSIII maybe raises thickness of the double layer
agreeing to Helmholtz pattern [27]. Bode and Phase curves for CS
in tested medium in absenteeism and existence of CSI, CSII & CSIII
are shown in Fig. 9 & (Supplementary materials, Figs. 15 and 16).
It was established that the impedance value augments with incre-
ment of CSI, CSII & CSIII concentration. Forming of a covering layer
of CSI, CSII & CSIII on a metal face prohibits the degradation of iron
in an acidic medium.
-7
-0.85
-0.65
E vs. SCE (V)
-0.45
-0.25
Fig. 10. Tafel polarization plot for CS gained at 25 °C in 1 M HCl solution in
existence and absenteeism of varied concentrations of CSII.
and recorded in Table 2. Data demonstration that gw slightly
decreases in the following range 25–70 °C. This refers to protection
of CSI, CSII & CSIII to CS face in tested medium maybe tend to
chemical adsorption than physical adsorption.
3.4. Impedance results
The deterioration performance of CS in tested medium in occur-
rence and absenteeism of diversified concentrations of CSI, CSII &
CSIII is assay by EIS at 25 °C. Fig. 7 & (Supplementary materials,
Figs. 13 and 14) show Nyquist curves of CS in tested medium in
occurrence & absenteeism of distinct concentrations of CSI, CSII &
CSIII. Nyquist curves exhibit one capacitive semi-circle. A capaci-
tive loop referred that a suppression of CS in a tested medium
under control by the charge transfer operation. And CSI, CSII & CSIII
form barrier film on CS face in existence of CSI, CSII & CSIII. The
variation in the actual impedance, at low and high frequencies, it
The inhibition efficiency (
eq. [28,29]:
gI) is evaluated according to the next
ꢀ
ꢁ
RctðinhÞ ꢀ Rct
RctðinhÞ
gI
¼
ꢁ 100
ð8Þ
where Rct and RctðinhÞ are the charge transfer resistance in occur-
rence and absenteeism of various concentrations CSI, CSII & CSIII.
gI was recorded in Table 3; and as in Table 3 the inhibition effi-
ciency (gI) augments as CSI, CSII & CSIII concentration increase.
Table 4
Tafel polarization parameters for CS corrosion in 1 M HCl in the absence and presence of different concentrations of di-cationic surfactants at 25 °C.
Inhibitor
Conc. of inhibitor (M)
Ecorr V(SCE)
icorr (mA cmꢀ2
)
ba (V decꢀ1
)
bc (V decꢀ1
)
gp (%)
Absence
CSI
0
ꢀ0.484
ꢀ0.529
ꢀ0.496
ꢀ0.514
ꢀ0.519
ꢀ0.511
ꢀ0.519
ꢀ0.517
ꢀ0.504
ꢀ0.531
ꢀ0.521
ꢀ0.505
ꢀ0.539
0.5465
0.0849
0.0615
0.0375
0.0277
0.0800
0.0589
0.0330
0.0264
0.0781
0.0462
0.0295
0.0247
0.152
0.168
0.180
0.155
0.176
0.165
0.185
0.145
0.187
0.141
0.174
0.178
0.108
ꢀ0.164
ꢀ0.182
ꢀ0.159
ꢀ0.168
ꢀ0.206
ꢀ0.144
ꢀ0.146
ꢀ0.178
ꢀ0.204
ꢀ0.141
ꢀ0.177
ꢀ0.175
ꢀ0.139
–
5 ꢁ 10ꢀ5
1 ꢁ 10ꢀ4
5 ꢁ 10ꢀ4
1 ꢁ 10ꢀ3
5 ꢁ 10ꢀ5
1 ꢁ 10ꢀ4
5 ꢁ 10ꢀ4
1 ꢁ 10ꢀ3
5 ꢁ 10ꢀ5
1 ꢁ 10ꢀ4
5 ꢁ 10ꢀ4
1 ꢁ 10ꢀ3
84.46
88.75
93.14
94.94
85.36
89.22
93.96
95.16
85.71
91.55
94.60
95.49
CSII
CSIII
11

M.A. Hegazy, M.M. Hegazy, M.K. Awad et al.
Journal of Molecular Liquids 337 (2021) 116541
2
1
0
-1
-2
-3
-4
1M HCl
0.0005M
0.00005M
0.001M
0.0001M
3.18
-5
2.88
2.98
3.08
3.28
3.38
(1/T) x 103 (K-1)
Fig. 11. Arrhenius plot (ln k vs. 1/T) for CS degradation in existence and absenteeism of various concentrations of CSIII in 1 M HCl medium.
-4
-5
-6
-7
-8
-9
1M HCl
0.0005M
0.00005M
0.001M
0.0001M
3.18
-10
-11
2.88
2.98
3.08
3.28
3.38
(1/T) x 103 (K-1)
Fig. 12. Transition-state plot (ln k/T vs. 1/T) for CS degradation in existence and absenteeism of varied concentrations of CSIII in 1 M HCl solution.
Table 5
Activation parameters for CS in 1 M HCl in the absence and presence of different concentrations of di-cationic surfactants.
Inhibitor name
Conc. of inhibitor (M)
Ea (kJ molꢀ1
)
D
H* (kJ molꢀ1
)
- D )
S* (J molꢀ1 Kꢀ1
Absence
CSI
0
38.14
47.80
52.26
55.75
56.88
47.88
51.77
54.94
56.51
45.75
51.17
53.65
54.31
35.49
45.15
49.61
53.09
54.23
35.49
45.22
49.11
52.28
43.10
48.52
51.00
51.66
130.33
113.52
102.04
102.04
94.45
113.91
104.35
97.76
5 ꢁ 10ꢀ5
1 ꢁ 10ꢀ4
5 ꢁ 10ꢀ4
1 ꢁ 10ꢀ3
5 ꢁ 10ꢀ5
1 ꢁ 10ꢀ4
5 ꢁ 10ꢀ4
1 ꢁ 10ꢀ3
5 ꢁ 10ꢀ5
1 ꢁ 10ꢀ4
5 ꢁ 10ꢀ4
1 ꢁ 10ꢀ3
CSII
94.99
CSIII
121.52
108.19
103.14
103.54
12

M.A. Hegazy, M.M. Hegazy, M.K. Awad et al.
Journal of Molecular Liquids 337 (2021) 116541
0.001
0.001
0.001
0.001
0.000
0.000
0.000
0.000
0.000
0.000
0.001
0.001
0.001
C (M)
Fig. 13. Langmuir isotherm adsorption pattern of CSIII on CS face in 1 M HCl at varied temperatures.
Table 6
Standard thermodynamic parameters of adsorption on carbon steel surface in 1 M HCl containing different concentrations of di-cationic surfactants.
ꢀ1
ꢀ1
ꢀ1
1
Inhibitors name
CSI
Temp. (C)
Kads (M
)
4Goads (kJ mol
)
4Ho
(kJ molꢀ1
)
4Soads (J mol
Kꢀ
)
ads
25
40
55
70
25
40
55
70
25
40
55
70
129,154
111,517
88,449
ꢀ 39.11
ꢀ 40.70
ꢀ 42.01
ꢀ 43.24
ꢀ 39.19
ꢀ 40.73
ꢀ 42.08
ꢀ 43.41
ꢀ 39.70
ꢀ 41.00
ꢀ 42.40
ꢀ 44.23
ꢀ 11.84
ꢀ 11.37
ꢀ 9.99
91.51
92.19
91.99
91.54
93.36
93.82
93.63
93.41
99.67
99.07
98.79
99.82
69,245
CSII
133,523
113,230
90,659
73,491
CSIII
163,757
125,595
101,811
98,161
3.5. Potentiodynamic polarization
3.6. Dissolution parameters
Fig. 10 & (Supplementary materials, Figs. 17 and 18) show
Tafel plots for CS in tested medium at several concentrations of
CSI, CSII & CSIII at 25 °C. The deterioration current densities
(icorr), deterioration potential (Ecorr), cathodic Tafel slope (bc), and
anodic Tafel slope (ba) which gained are recorded in Table 4. It evi-
dent that the (icorr) minifies with increment of CSI, CSII & CSIII con-
centration. The existence of the CSI, CSII & CSIII gave a little
movement of the (Ecorr) in a positive way. So the CSI, CSII & CSIII
were considered a mixed inhibitor [30]. Besides, (ba andbc) are
lightly changed with increment of the CSI, CSII & CSIII concentra-
tion. This means that CSI, CSII & CSIII prevent deterioration by
deactivation of active sites without change the deterioration mech-
anism. The anodic and cathodic Tafel lines are moved a little to
deterioration current densities. This is due to inhibition activity
of CSI, CSII & CSIII executes by deactivation of active sites of CS face
and reduces the surface region susceptible to the damage [31].
Activation energy (Ea) values are evaluated from Arrhenius
equation as follows [33]:
ꢀ
ꢁ
ꢀEa
k ¼ Aexp
ð10Þ
RT
Enthalpy (
D
Hꢃ) & entropy (
D
Sꢃ) of activation are evaluated from
Wine–Jones–Erying equation [34]:
ꢀ
ꢀ
ꢁ
ꢀ
ꢁꢁ
k
T
R
NAh
D
R
Sꢃ
D
Hꢃ
lnð Þ ¼ ln
þ
ꢀ
RT
ð11Þ
where k is deterioration rate, A is frequency factor, T is absolute
temp., R and h are universal gas and Planck’s constants and NA is
Avogadro’s no.
Arrhenius plots (ln k vs:1=T) for CS dissolution in occurrence
and absenteeism of various concentrations of CSI, CSII & CSIII in
1 M HCl solution is presented in Fig. 11 & (Supplementary mate-
rials, Figs. 19 and 20). Slope of straight lines ¼ ꢀEa=R. Ea values in
the presence of CSI, CSII & CSIII are slightly bigger than that
obtained in HCl solution. This indicates that CSI, CSII & CSIII
adsorption on CS is physical and chemical.
The (gp) was evaluated from the following eq. [32]:
icorr ꢀ icorrðinhÞ
gp
¼
ꢁ 100
ð9Þ
icorr
Fig. 12 & (Supplementary materials, Figs. 21 and 22) repre-
where icorr & icorrðinhÞ are deterioration current densities in occur-
rence & absenteeism of various concentrations of CSI, CSII & CSIII
concentration.
sent Transition-state curves (ln k=T
occurrence and absenteeism of various concentrations of CSI, CSII
vs:1=T) for CS dissolution in
& CSIII in 1 M HCl solution. Slope of straight lines ¼ ꢀ
D
Hꢃ=R and
D D
Hꢃand Sꢃ values are
the intercept =ln ðR=NAhÞ þ ð
D
Sꢃ=RÞ. Ea;
The values of the (
gp) is recorded in Table 4. gp augments with
augmentation of CSI, CSII & CSIII concentration.
recorded in Table 5. The +ve signs of (D
Hꢃ) refer to an endother-
13

M.A. Hegazy, M.M. Hegazy, M.K. Awad et al.
Journal of Molecular Liquids 337 (2021) 116541
A
B
C
D
Fig. 14. SEM graphs of CS surface in existence and absenteeism of 1 ꢁ 10–3M of CSI, CSII & CSIII for one day at room temperature.
where C is the CSI, CSII & CSIII concentration.
mic of CS dissolution reaction and refer that the degradation of
CS is hard [35]. Activation entropy (
Sꢃ) has a negative sign. This
indicates that the association rather than dissociation of acti-
vated complex [36].
Curve of C=h against C Fig. 13 & (Supplementary materials,
Figs. 23 and 24) produces a rectum line with slope equivalent
unity. This approves the adsorption of the CSI, CSII & CSIII on the
CS surface track the Langmuir isotherm.
D
Goads) evaluates as the fol-
3.7. Adsorption isotherm
Standard free energy of adsorption (
lowing eq. [40]:
D
CSI, CSII & CSIII prohibit a suppression of CS by adsorption on a
steel – medium link. Adsorption supplies information about inter-
link between adsorbed molecules and electrode face. A grade of
surface covering (h) for varying concentrations of the CSI, CSII &
CSIII in corrosive media has been calculated from the following
eq. [37]:
D
Goads ¼ ꢀRTlnð55:5Kads
Þ
ð14Þ
where Kads is equilibrium const. of CSI, CSII & CSIII adsorption
process.
Negative values of D
Goadsdenotes that the interaction of CSI, CSII
ꢀ
ꢁ
& CSIII on CS face in 1 M HCl is an instant reaction. When
Wcorr ꢀ WcorrðinhÞ
D
Goads values ꢂ -20 kJ/mol refers to physical interlinkage between
h ¼
ð12Þ
Wcorr
the CSI, CSII & CSIII molecules and the charged CS surface.
D
Goads
where Wcorr and WcorrðinhÞ are the weight loss of CS with and without
the CSI, CSII & CSIII.
values ꢄ ꢀ 40 kJ/mol refers to coordination bond of CSI, CSII & CSIII
molecules and CS surface (chemisorption) [41].
D
Goadsvalues are
Langmiur isotherm using equilibrium const. (Kads) characterizes
in the equation [38,39]:
ꢀ39.11, ꢀ 40.70, ꢀ 42,01 and ꢀ 43.24 kJ/mol for CSI, ꢀ39.19,
ꢀ 40.73, 42,08 and ꢀ 43.41 kJ/mol for CSII , ꢀ39.70, ꢀ 41.00,
ꢀ 42.40 and ꢀ 44,23 for CSIII at 25, 40, 55 and 70 °C, respectively.
These values indicate CSI, CSII & CSIII molecules adsorbed on CS
C
1
¼
þ C
ð13Þ
h
Kads
through physical and chemical bond [42]. Great
D
Goads values &
14

M.A. Hegazy, M.M. Hegazy, M.K. Awad et al.
Journal of Molecular Liquids 337 (2021) 116541
their -ve signs are referring to a powerful interlinkage and extre-
mely effective adsorption [43].
3.9. Atomic force microscope (AFM)
Hoads is estimated agreeing to the equation of Van’t Hoff
AFM microscope graphs of CS surface after immersing for one
day without and with 1 ꢁ 10ꢀ3M of CSI, CSII & CSIII at 25 °C are dis-
played in Fig. 15. In a blank sample, the damages and corroding
were apparent. Also, high average roughness (Ra) values
(124.0 nm) in absenteeism CSI, CSII & CSIII might be concerned
to the corrosive species forming on CS substrate during immersed
in corrosive medium. However, these injuries vanished remarkably
after the addition of 1x10ꢀ3M of CSI, CSII & CSIII in a corrosive envi-
ronment. The variations of Ra were mitigated to lower values
(23.1 nm, 19.0, and 17.5 nm) for CSI, CSII & CSIII, respectively).
Additionally, it suggested that the ranking agrees to inhibitory per-
formance of di-cationic surfactants (CSIII > CSII > CSI) which could
protect the CS from corrosion [47,48].
D
[22,29]:
ꢀ
ꢁ
ꢀ
D
Hoads
RT
lnKads
¼
þ constant
ð15Þ
D
Hoadsvalues are ꢀ11.84 kJ/mol for CSI, ꢀ11.37 kJ/mol for CSII
& ꢀ9.99 for CSIII. These values indicate CSI, CSII & CSIII molecules
adsorbed on CS through exothermic reaction [44].
D
Soads was calculated fromthe basic thermodynamic equation[45]:
D
Goads
¼
D
Hoads ꢀ T
D
Soads
ð16Þ
The positive
of CSI, CSII & CSIII molecules on CS surface [46].
The
Gaods Hoads Haods parameters of CSI, CSII & CSIII adsorption
D
Soads values indicate the natural adsorptive ability
D
,
D
, D
at several concentrations and temperatures on MS face in 1 M HCl
are given in Table 6.
3.10. Quantum chemical calculations
It was established experimentally that the carbon steel inhibi-
tion by di-cationic surfactants as inhibitors for the corrosion is in
order:
3.8. Scanning electron microscopy (SEM)
SEM studies are executed to examine if the corrosion inhibition
of CS specimens occurs due forming of a covering layer on a surface
or not. Fig. 14 shows SEM graphs of CS surface in occurrence and
absenteeism of 1x10ꢀ3M of CSI, CSII & CSIII for one day at room
temperature. In the absenteeism of CSI, CSII & CSIII, the damages
and corroding figure were apparent. But, in the presence of CSI, CSII
& CSIII, the smooth and protected surface are present. Furthermore,
SEM photo confirmed the chemical and electrochemical results.
CSIII > CSII > CSI
It was discovered that the explored inhibitor with methoxy
benzylidene stray has higher restraint effectiveness than that with
phenyallylidene and furan-2-ylmethylene groups on a metal face.
The highest hindrance efficacy of CSIII than different inhibitors
has likely alluded to an expanding number of centers of adsorption
Fig. 15. AFM photo of (a) without inhibitor, (b) with CSI, (c) with CSII, and (d) with CSIII.
15

M.A. Hegazy, M.M. Hegazy, M.K. Awad et al.
Journal of Molecular Liquids 337 (2021) 116541
CSI
CSII
CSIII
Fig. 16. Geometrical structure of: (a) CSI, (b) CSII, and (c) CSIII di-cationic surfactants obtained from computational conformation simulation.
Table 7
The calculated quantum chemical parameters obtained from DFT/6-31G (d,p) calculations.
Molecule
HOMO (a.u)
LUMO (a.u)
4E (a.u)
DM (Debye)
g
(a.u)
r
(a.u)ꢀ1
m (a.u)
v
(a.u)
x
TNC (e)
Et (a.u.)
Volume (cm3/mol)
CSI
CSII
CSIII
ꢀ0.357
ꢀ0.357
ꢀ0.353
ꢀ0.256
ꢀ0.253
ꢀ0.255
0.123
0.104
0.098
27.441
27.424
23.091
0.062
0.052
0.049
16.129
19.231
20.408
0.317
0.305
0.304
ꢀ0.317
ꢀ0.305
ꢀ0.304
0.810
0.894
0.943
ꢀ7.976
ꢀ8.118
ꢀ8.503
1448.531
1528.165
1525.957
697.980
795.167
809.158
A ¼ ꢀELUMO
ð18Þ
on the inhibitors and the greater electron densities brought about
by an electron liberation methoxy strays.
l
¼ ꢀ
v
ð19Þ
ð20Þ
In like manner, quantum mechanics computations were exe-
cuted to research the impact of parameters of the structures on
the efficacy of surfactants and explore their mechanism of adsorp-
tion on a metal face. The molecular and electronic properties of the
di-cationic surfactants were determined by enhancement of their
bond lengths, angles, and distortion angles. A calculated structures
with the least energies got from the computations are exhibited in
Fig. 16.
As indicated by Koopman’s hypothesis [49] EHOMOandELUMO of
the inhibitor particle are identified with theionizationpotentialðIÞ,
andtheelectronaffinityðAÞ, respectively other quantum variables
that exhibit significant data about a reactivity of the di-cationic
ðEHOMO þ ELUMO
Þ
l
¼
¼
¼
2
ðELUMO ꢀ EHOMO
Þ
g
ð21Þ
ð22Þ
2
1
g
r
Quantum variables acquired from computations which are
liable to the hindrance of di-cationic surfactants, for example, the
energies of HOMO and LUMO, gap energy
betweenELUMO and EHOMO E, addressing the reactivity, dipole
momentðDÞ, chemical potential Þ, electronegativityð Þ,
hardnessð Þ, softnessð Þ, electrophilicity ð Þ, total negative charge
surfactants,
are
electronegativityð
v
Þ,
chemicalpotentialð
l
Þ,
hardnessð Þand softnessð
g
r
Þare determined by:
;
D
I ¼ ꢀEHOMO
ð17Þ
ð
l
v
g
r
x
16

M.A. Hegazy, M.M. Hegazy, M.K. Awad et al.
Journal of Molecular Liquids 337 (2021) 116541
HOMO
LUMO
CSI
CSII
CSIII
Fig. 17. The charge density distribution of (a) HOMO and (b) LUMO levels of the investigated di-cationic surfactants CSI, CSII, and CSIII.
ðTNCÞand total energy ðEtÞare collected in Table 7. The surfactants
may adsorb on a steel face as cation and portion of electrons
betwixt the nitrogen in the surfactant and a metal face. Else chance
is that a di-cationic surfactant may adsorb through electrostatic
association betwixt positively charged surfactant and negatively
charged steel face [50]. It has appeared from the study that the
molecular structures of an explored surfactants are not planar,
Fig. 16. According to the frontier orbital theory, substance reactiv-
drances in numerous structure frameworks. The smaller is the
estimation of E, the more likely that the matter has restraint pro-
D
ficiency [52,53]. It has appeared from the estimations that CSIII has
a littlest HOMO ꢀ LUMO energy gap (0.098 a.u) contrasted and CSII
and CSI (0.104 and 0.123 a.u.) respectively, Table 7. As needs be, it
very well may be normal that CSIII has a wide tendency to adsorb
on a metal face than different inhibitors which concurs well with
the exploratory information. It was discovered that the variety of
the determined LUMO energies among all examined surfactants
hasn’t corresponded with the restraint proficiency, Table 7.
The dipole secondðDÞ, the principal limb of the energy concern-
ing exercised electric field, was utilized to talk about and support
the construction [54]. There is a decent connection between’s D
and hindrance productivity. The particle with the most noteworthy
productivity, CSIII, has the least dipole second, (23.091 D), Table 7.
The sub-atomic volume is else quantum boundary got from the cal-
culation data, Table 7. The slow expansion in the sub-atomic vol-
umes of the surfactant particles suggests that a metal face
territory covered by the particles is progressively expanded by
expanding the hydrophobic chain length. This feedback is equal
to the outcomes acquired from the polarization and impedance
examines. It has appeared from the computations that the CSIII
has the most elevated molecular volume with a worth equivalent
809.158 (cm3/mol) contrasted with CSII and CSI (795.167 and
697.980 cm3/mol), Table 7, which prompts increment its restraint
productivity because of the expansion of the relate zone betwixt
the particle and the metal face. In like manner, the expanding
ity is
a parameter of the interactivity among the orbitals
HOMOandLUMO of the responding kinds [51]. EHOMO shows a
capacity to give electrons to a convenient acceptor with virtual
orbitals and ELUMO demonstrates its capacity to admit electrons.
The lower is the estimation of ELUMO; the more is the capacity to
admit electrons. The greater is an estimation of EHOMO of a surfac-
tant, the more prominent is its simplicity of presenting electrons
to a vacant d-orbital of a steel face, and more noteworthy is its
restraint productivity.
The computations demonstrated that CSIII has most notewor-
thy estimation of EHOMO (ꢀ0.353 a.u) among the examined CSII
and CSI, (ꢀ0.357 and ꢀ0.357 a.u.) respectively, Table 7. This could
clarify the best inclination of CSIII inhibitors to adsorb on a metal
face and likewise has the most noteworthy hindrance effective-
ness. Appropriately, the request for expanding reactivity towards
the surface will be: CSIII > CSII > CSI, which is in a decent concur-
rence with empirical remarks. HOMO ꢀ LUMO gap,
DE, which is a
remarkable evidence for stability, is exercised to create hypotheti-
cal patterns for clarifying the construction and adaptation hin-
17

M.A. Hegazy, M.M. Hegazy, M.K. Awad et al.
Journal of Molecular Liquids 337 (2021) 116541
and subsequently enhance its suppression efficacy. It is concluded
from the above discussion that the optimized parameters confirm
that the inhibitor with a high alkyl chain has the most efficiency
which concurs well with the experimental data. On the other hand,
HOMO level of all cationic surfactants is mostly centralized at the
end of an alkyl chain, which exhibits that the hydrophobic stray is
the favored locales for an electrophilic assault at a steel face,
Fig. 17. This implies that an alkyl chain portion with great coeffi-
cients of HOMO charge density was arranged across a steel face
CSI
and the adsorption most likely happens through the
of it. Additionally, calculations indicated that the charge density
of the LUMO level is restricted on center of particle-
pꢀelectrons
a
a
containing (N) for all explored matters which implies that this por-
tion could be responded to as electrophile (electron acceptor),
Fig. 17.
CSII
The molecular electrostatic potentials are exceptionally useful
in that negative districts may be viewed as nucleophilic centers,
while areas with positive electrostatic potential will be potential
electrophilic destinations. Besides, the electrostatic potential
makes the polarization of the electron density obvious. The com-
putations demonstrated that a hydrophobic chain and the nitro-
gen possess a negative electrostatic potential which implies that
these locales are the dynamic sites for linking to a steel face,
Fig. 18.
4. Mechanism of inhibition
Adsorption of organic molecules on solid faces may be physical
or chemical or both adsorption. A physical adsorption takes place
by electrostatic interlinkage betwixt charged metal face and
charged inhibitor molecule [56]. A chemical adsorption takes place
by interlinkage between free electron pairs of the heteroatoms and
CSIII
p-electrons of multiple bonds [57]. A steel surface in an acidic
medium has a negative charge and a surfactant is positively
charged so electrostatic attraction between a polar head group of
a surfactant and a metal face is arising. Di-cationic surfactant has
a big size and high molecular weight has greater inhibition effi-
ciency [58].
The inhibition efficacy values of the examined di-cationic sur-
factants in1M HCl were in the following order: CSIII > CSII > CSI.
5. Conclusions
Fig. 18. Electron density plots of molecular electrostatic potentials (MEP) of CSI,
CSII, and CSIII di-cationic surfactants.
1. CSI, CSII & CSIII exhibit a perfect inhibitor for corrosion of CS
in 1 M HCl.
2. Active surface properties of three CSI, CSII & CSIII such as
their surface tension, Ccmc, and other parameters in 1 M
HCl at 25 °C were specified and discussed.
3. Inhibition efficacy augments by augmenting concentration
of CSI, CSII & CSIII but slightly increment in temperature of
25–70 °C.
4. Double layer capacitances minimize for blank solution com-
pared to in the existence of CSI, CSII & CSIII. This fact may be
demonstrated by adsorption of the CSI, CSII & CSIII on a
metal face.
5. Tafel polarization plots refer that icorr diminishes and Ecorr
changes a few with adding of the synthesized di-cationic
surfactants, so the CSI, CSII & CSIII are a mixed kind.
6. Activation energy increases with an increment of the CSI,
CSII & CSIII concentration.
7. Adsorption of CSI, CSII & CSIII on CS surface follow Langmuir
isotherm and is mixed kind.
8. Both SEM and AFM techniques confirmed the forming of a
good protective layer.
reactivity will be: CSIII > CSII > CSI which is in a decent concurrence
with the exploratory observations. An ultimate hardness and soft-
ness,
reactivity and stability of a surfactant. A tough one possesses a
huge E and a soft one possesses a little E. Hard compounds
g, r, respectively, are significant properties that assess the
D
D
are very stable than soft matters since soft molecules could
undoubtedly submit electrons to an acceptor. At least difficult
exchange of electrons, adsorption could happen at a piece of an
inhibitor where
r, possesses a greatest value [55]. In a corrosion
system, a surfactant goes about as a Lewis base while a metal goes
about as a Lewis corrosive, respectively. Bulk metals are delicate
acids and hence delicate di-cationic surfactants are best for acidic
corrosion of those metals. Likewise, it is presumed that CSIII with
the most noteworthy
r
esteem (20.408 a.uꢀ1) has the most note-
worthy capacity restraint effectiveness compared to CSII and CSI
(19.231 and 16.129 a.uꢀ1) respectively, Table 7, which is in good
harmony with the experimental data. Also, the computations
exhibited that CSIII has a smallest
vand has a largest xand TNC
(ꢀ0.304 a.u., 0.943 and ꢀ8.503 e), respectively, Table 7, which
drives to augmentation of its donation capability to a steel face
18

M.A. Hegazy, M.M. Hegazy, M.K. Awad et al.
Journal of Molecular Liquids 337 (2021) 116541
Challacombe, P.M.W. Gill, B. Johnson, W. Chen, M.W. Wong, C. Gonzalez, J.A.
Pople, Gaussian 03, Revision B.01, Gaussian Inc, Pittsburgh, PA, 2003.
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9. The computed quantum variables demonstrated a decent
relation of those parameters for the explored di-cationic sur-
factants and their hindrance efficacy for the corrosion of CS.
10. Inhibition efficacy of di-cationic surfactants follows the
order: CSIII > CSII > CSI.
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Declaration of Competing Interest
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared
to influence the work reported in this paper.
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