Novel triazole derivatives as ecological corrosion inhibitors for mild steel in 1.0 M HCl: experimental & theoretical approach

Article abstract of DOI:10.1039/d0ra09679b

The present paper illustrates the investigation of two novel ecological triazole derivative corrosion inhibitors, namely ethyl 2-(4-phenyl-1H-1,2,3-triazol-1-yl) acetate [Tria-CO2Et], and 2-(4-phenyl-1H-1,2,3-triazol-1-yl) acetohydrazide [Tria-CONHNH2]. T

Full text of DOI:10.1039/d0ra09679b

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Novel triazole derivatives as ecological corrosion
inhibitors for mild steel in 1.0 M HCl: experimental
Cite this: RSC Adv., 2021, 11, 4147
&
theoretical approach
a
b
b
c
c
b
A. Nahle, * R. Salim, F. El Hajjaji, M. R. Aouad, M. Messali, E. Ech-chihbi,
´
d
b
B. Hammouti and M. Taleb
The present paper illustrates the investigation of two novel ecological triazole derivative corrosion
inhibitors, namely ethyl 2-(4-phenyl-1H-1,2,3-triazol-1-yl) acetate [Tria-CO Et], and 2-(4-phenyl-1H-
]. The studied inhibitors were investigated against the
HCl solution using different electrochemical techniques.
Potentiodynamic polarization experiments indicated that the [Tria-CO Et], and the [Tria-CONHNH
2
1,2,3-triazol-1-yl) acetohydrazide [Tria-CONHNH
2
corrosion of mild steel in 1.0
M
2
2
]
acted as mixed type inhibitors. Electrochemical impedance spectroscopy measurements revealed that
both inhibitors presented a high inhibition performance, achieving an inhibition efficiency of 95.3% for
ꢁ3
[
Tria-CO
2
Et] and 95.0% for [Tria-CONHNH
2
] at a concentration of 1.0 ꢀ 10 M. Based on the Langmuir
Received 13th November 2020
Accepted 28th December 2020
isotherm model and the activation parameters, these triazole derivatives were adsorbed onto a steel
surface by physical and chemical bonds. Density functional theory based on B3LYp6-311G(d,p) was also
carried out to correlate the inhibition efficiencies obtained experimentally with the theoretical
descriptors of the studied molecular structures.
DOI: 10.1039/d0ra09679b
rsc.li/rsc-advances
explained by the adsorption of these molecules on the metal
surface using several heteroatom centers such as N, S, and O
1
. Introduction
Generally, triazole is a ve-membered ring containing three heteroatoms, and p-electrons. Furthermore, this adsorption
nitrogen atoms, and acts as a building block for many can be achieved through physical adsorption, chemisorption, or
7
,8
compounds that have various applications, especially in medi- both (physical and chemical).
cine. These triazole derivative compounds have attracted wide
1
Recently, many researchers have focused on the application
interest from many researchers because of their exceptional of eco-friendly corrosion inhibitors. These compounds can be
properties. They have diverse agricultural, industrial, and bio- considered as ecological inhibitors since they have low toxicity
9,10
logical properties, as well as anti-microbial, anticonvulsant, and characteristics of strong chemical activity. These triazole
anticancer, anti-inammatory, diuretic, antibacterial, hypogly- derivatives are amphoteric in nature, forming salts with acids
2
cemic, antitubercular, and antifungal activities.
and bases, and have special affinity to metal surfaces with
Various industrial elds use construction materials such as moving water molecules on the surface. Moreover, they have
mild steel, since it is of low cost, high availability, and good abundant p-electrons and unshared electron pairs on the
3,4
physicochemical characteristics. However, mild steel can be nitrogen atom that can combine with d-orbitals of the metal to
11,12
easily weakened and causes wide human and economic costs afford a protecting lm.
Therefore, several previous works
when it is in contact with an aggressive acidic solution. There- have focused on the application of 1,2,4-triazole derivatives as
13,14
fore, the best way to protect the steel surface is by applying corrosion inhibitors.
For instance, El Belghiti et al. showed
inhibitors that act as a wall between the steel surface and the that two 3,5-bis (disubstituted)-4-amino-1,2,4-triazole deriva-
5
,6
aggressive medium.
Moreover, this lm barrier can be tives (T1 and T2) have a corrosion inhibition efficiency of 86%
ꢁ
3
for mild steel when used at a concentration of 1.0 ꢀ 10 M in
15
a
2 M H
3
PO
4
.
More recently, newly synthesized heterocycles,
Department of Chemistry, College of Sciences, University of Sharjah, P.O.Box: 27272,
Sharjah, United Arab Emirates. E-mail: anahle@sharjah.ac.ae; Fax: +971-6-5053820; namely (1-p-tolyl-1H-1,2,3-triazol-4-yl) methanol (TTM) and 5-
16
17
Tel: +971-6-5166 771
b
hexylsulfanyl-1,2,4-triazole (HST), have been investigated in
inhibiting steel corrosion in 1.0 M HCl. These compounds
displayed excellent inhibition performance. The inhibition
efficiencies reached 97% for HST and 81% for TTM based on
Laboratory of Engineering, Electrochemistry, Modeling and Environment (LIEME),
Faculty of Sciences, University Sidi Mohamed Ben Abdellah, Fez, Morocco
c
Department of Chemistry, College of Science, Taibah University, Al-Madinah Al-
Munawarah 30002, Saudi Arabia
ꢁ
3
d
electrochemical data at 1.0 ꢀ 10 M. In addition, the effect of
Laboratory of Applied Chemistry and Environment (LCAE), Faculty of Sciences,
heteroatoms on the corrosion inhibition of structurally similar
University Mohammed Premier Oujda, Morocco
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Table 1 Percentage inhibition efficiency for some selected triazole derivatives used as corrosion inhibitors against the corrosion of mild steel in
an acidic medium
Triazole derivative
Inhibition efficiency (%)
Medium
Ref.
14
85.05% at 3.2 mM
0.5 M HCl
(3-Bromo-4-uoro-benzylidene)-[1,2,4] triazol-4-yl-amine (BFBT)
72.83% at 3.2 mM
0.5 M HCl
14
(2-Fluoro-4-nitro-benzylidene)-[1,2,4] triazol-4-yl-amine (FNBT)
8
8
6.81% at 1.0 ꢀ 10ꢁ
3
M
M
2 M H
3
PO
4
15
15
3
3
,5-Bis(4-methoxyphenyl)-4-amino-1,2,4-triazole (T1)
,5-Bis(4-chlorophenyl)-4-amino-1,2,4-triazole (T2)
6.20% at 1.0 ꢀ 10ꢁ
3
2 M H
3
PO
4
9.9% at 1.0 ꢀ 10ꢁ
4
M
1.0 M HCl
16
8
3
,5-Bis(3-aminophenyl)-4-amino-1,2,4-triazole (3-APAT)
-Amino-1,2,4-triazole (5-ATA),
2
9
4% at 1.0 ꢀ 10ꢁ
2
M
1.0 M HCl
1.0 M HCl
17
17
5
2% at 1.0 ꢀ 10ꢁ
2
M
5
5
-Amino-3-mercapto-1,2,4-triazole (5-AMT)
-Amino-3-methylthio-1,2,4-triazole (5-AMeTT)
2% at 1.0 ꢀ 10ꢁ
2% at 1.0 ꢀ 10ꢁ
2
M
M
1.0 M HCl
1.0 M HCl
17
17
8
8
2
1
-Amino-3-methylthio-1,2,4-triazole (1-AMeTT)
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Table 2 Abbreviations, structures, and IUPAC names for the studied triazole derivatives
Abbreviations
Structures
IUPAC name
[
Tria-CO
2
Et]
Ethyl 2-(4-phenyl-1H-1,2,3-triazol-1-yl)acetate
2-(4-Phenyl-1H-1,2,3-triazol-1-yl)acetohydrazide
[
2
Tria-CONHNH ]
azomethine-based organic molecules (FMT and TMT) showed
2
. Experimental
ꢁ1
that both molecules had good efficiency (>90%) at 5 mmol L
18
2.1. Inhibitor synthesis
concentration in 1.0 M HCl medium.
Many authors have reported that the quantum chemical The click coupling of phenylacetylene (1) with ethylazidoacetate
calculations can offer broad information about structural (2), in the presence of sodium ascorbate and copper sulfate as
properties and relate inhibitors' adsorption ability with their a catalyst in a mixture of t-BuOH : H O (1 : 1), gave the targeted
2
19
20
structural aspects. Y. El Aour et al. have established ethyl 2-(4-phenyl-1H-1,2,3-triazol-1-yl) acetate (1) with 96% yield
a correlation between two 1,2,4-triazole derivatives (TR8 and aer stirring at room temperature for 4 h.
TR10) and their electronic properties. This investigation
conrmed the strong adsorption of these inhibitors on the mild on its spectral data (IR, and H and C-NMR). Its H-NMR
The structure of the 1,2,3-triazole (3) was elucidated based
1
13
1
steel surface through active centers distributed over the triazole spectrum revealed the absence of the characteristic alkyne
moiety and the carbon chain of the studied compounds. In proton (^CH) and the presence of a distinct singlet at dH
¼
addition, some other authors have used quantum chemistry 8.50 ppm assigned to the triazolyl C –H proton, conrming the
5
calculations (density functional theory, DFT) to understand success of the 1,3-dipolar cycloaddition reaction. The spectrum
21–24
inhibitor interactions with the metal surface.
As an example, also revealed the presence of a triplet at 1.24 ppm and a quartet
Table 1 reports the percentage inhibition efficiency for some at 4.18–4.22 ppm attributed to the ethyl ester protons (CH ) and
3
1
3
selected triazole derivatives used as corrosion inhibitors against (OCH ), respectively. In the C-NMR spectrum, the carbon
2
the corrosion of mild steel in an acidic medium.
In this work, we have investigated the effect of two novel 14.78, 51.31, and 63.40 ppm, respectively. The sp -carbons were
synthesized compounds derived from triazole, namely ethyl 2- recorded at their appropriate chemical shis. Thermal hydra-
3 2
signals belonging to CH , NCH and OCH2 resonated at dC
2
(
4-phenyl-1H-1,2,3-triazol-1-yl) acetate [Tria-CO
2
Et], and 2-(4- zinolysis of the resulting 1,2,3-triazole based-ester (3), with
], hydrazine hydrate for 4 h, afforded the corresponding acid
phenyl-1H-1,2,3-triazol-1-yl) acetohydrazide [Tria-CONHNH
2
as corrosion inhibitors. This investigation was performed on hydrazide (4) in excellent yield (90%) (Scheme 1). The success of
mild steel substrates using various electrochemical techniques, the hydrazinolysis reaction has been clearly evidenced based on
such as electrochemical impedance spectroscopy (EIS) and the spectral data of compound (4), which revealed the disap-
potentiodynamic polarization (PDP). DFT based calculations in pearance of the ethyl ester protons and carbons of its starting
1
the gaseous as well as in the aqueous phase were executed to material (3). The H-NMR spectrum also conrmed the pres-
correlate the quantum chemical descriptors of the triazole- ence of the diagnostic hydrazide NH and NH protons as two
2
derived compounds used and their experimental inhibition singlets at dH 4.62, and 9.58 ppm, respectively. All carbon
efficiency.
signals related to the proposed structure of compound (4)
Scheme 1 Synthesis of the 1,2,3-triazole based-ester and/or hydrazide (3)/(4).
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25
resonated in their appropriate regions. The structures and the a three-electrode glass cell. Platinum as the counter electrode, Ag/
IUPAC names of the studied compounds are given in Table 2. AgCl as a reference electrode, and mild steel samples as the
The measurement of the melting points was performed with working electrode. The surface area of the steel electrode used for
2
a Stuart Scientic SMP1. The functional groups were identied the electrochemical tests was 1.00 cm , and the volume of the
using a SHIMADZU FTIR-Affinity-1S spectrometer in the range solutions used in the glass cell was 50 mL. Prior to the experi-
ꢁ
1
1
of 400–4000 cm . The measurement of the H-NMR (400 MHz) ments, the potential of the working electrode was stabilized for
1
3
and C-NMR (100 MHz) spectra was performed with a Bruker 30 min until it achieved a stable open circuit potential. The
ꢁ1
spectrometer (400 MHz). Elemental analyses were performed polarization curves were carried out with a scan rate of 1 mV s
using a GmbH-Vario EL III Elementar Analyzer.
with a potential range of ꢃ250 mV according to the open circuit
Synthesis and characterization of ethyl 2-(4-phenyl-1H-1,2,3- potential (OCP). The inhibition efficiency (h %) was calculated
pp
26
triazol-1-yl)acetate (3). A mixture of phenylacetylene (1) (10 from the corrosion current density values using eqn (1).
ꢀ
À
ꢂ
corr
Áꢁ
mmol), CuSO $5H O (0.20 g), sodium ascorbate (0.30 g), and
4
2
i
ꢁ icorr
corr
ethylazidoacetate (1) (12 mmol) in t-BuOH : H
2
O (1 : 1, v/v) (20
hpp% ¼
ꢀ 100
(1)
ꢂ
i
mL) was stirred at room temperature for 4 h. Aer completion of
the reaction, ice cold water (100 mL) was added to the reaction where i
ꢂ
and icorr are the values of the corrosion current
corr
mixture. The formed precipitate was collected by ltration, densities in the absence and presence of inhibitors,
washed with a saturated solution of ammonium chloride, and respectively.
recrystallized from ethanol to give the targeted 1,2,3-triazole (3).
On the other hand, the EIS technique were performed in the
ꢂ
ꢁ1
Yield: 96%, mp: 101–102 C, IR (n, cm ): 1550 (C]C), 1740 frequency range from 100 kHz to 100 mHz with 10 points per
ꢁ
1
1
(
C]O), 2985 (C–H ), 3060 cm (C–H ). H-NMR (400 MHz, decade. In this case, the Nyquist plots were plotted and analyzed
al ar
DMSO-d
6
): d
H
¼ 1.24 (3H, t, J ¼ 4.0 Hz, CH
3
), 4.18–4.22 (2H, q, using a suitable equivalent circuit. The inhibition efficiency was
27
OCH
2
), 5.14 (s, 2H, NCH
2
), 7.32–7.40 (m, 3H, Ar–H), 7.82–7.90 calculated using eqn (2).
1
3
(
m, 2H, Ar–H), 8.50 (s, 1H, CH-1,2,3-triazole). C-NMR (100
MHz, DMSO-d ): d ); 51.31 (NCH ); 63.40 (OCH );
¼ 14.78 (CH
22.57, 125.70, 127.89, 128.31, 130.98, 146.45 (Ar–C), 166.24
ꢀ
0
ꢁ
R
p
ꢁ R
p
6
C
3
2
2
himp% ¼
ꢀ 100
(2)
R
p
1
0
(C]O). Calcd for C H N O : C, 62.33; H, 5.67; N, 18.17. where R and R are the polarization resistance of the mild steel
12 13 3 2
p
p
Found: C, 62.50; H, 5.59; N, 18.06.
electrode in the presence and absence of inhibitors,
Synthesis and characterization of 2-(4-phenyl-1H-1,2,3- respectively.
triazol-1-yl)acetohydrazide (4). Compound (3) (10 mmol) was
dissolved in ethanol (30 mL) containing hydrazine hydrate (12
mmol). The mixture was heated under reux for 4 h. Aer cool-
2
.4. Theoretical approach
ing, the crude product was collected by ltration and recrystal-
lized from ethanol to afford the targeted acid hydrazide (4).
Several reactivity descriptors were extracted, such as the highest
occupied molecular orbital (HOMO), lowest unoccupied
molecular orbital (LUMO), dipole moment (m), and energy gap
ꢂ
ꢁ1
Yield: 90%, mp: 185–186 C, IR (n, cm ): 1540 (C]C), 1710
ꢁ
1
1
(
C]O), 2960 (C–H ), 3080 (C–H ), 3080 cm (N–H). H-NMR
al ar
(DEgap), etc. In addition, the reactive sites from electrophilic or
(
400 MHz, DMSO-d ): dH ¼ 4.62 (s, 2H, NH ), 5.08 (s, 2H,
6
2
nucleophilic attacks were extracted using Fukui indices calcu-
lations. These calculations were performed using the Gaussian
2
NCH ), 7.33–7.45 (m, 3H, Ar–H), 7.84–7.87 (m, 2H, Ar–H), 8.54
1
3
(
s, 1H, CH-1,2,3-triazole), 9.58 (s, 1H, NH). C-NMR (100 MHz,
DMSO-d ): d ); 123.14, 125.45, 128.12, 129.45,
30.98, 146.97 (Ar–C), 165.15 (C]O). Calcd for C10 O: C,
28
09 program at the DFT/(B3LYP) level with the 6-311G (d,p)
6
C
¼ 51.24 (NCH
2
basis set.
1
5
11 5
H N
5.29; H, 5.10; N, 32.24. Found: C, 55.05; H, 5.18; N, 32.13.
DEgap ¼ ELUMO ꢁ EHOMO
(3)
(4)
1
2.2. Materials preparation
c ¼ ðEHOMO þ ELUMO
Þ
2
The steel used in the present paper is a mild steel composed of
Fe (99.21), C (0.21), Mn (0.05), Si (0.38), S (0.05), P (0.09), and Al
1
h ¼ ðEHOMO ꢁ ELUMO
Þ
(5)
(6)
(0.01). Prior to each experiment, the steel samples were polished
2
with emery paper (until 1500 grid size), washed with distilled
water, degreased with acetone, and dried. The molar hydro-
chloric acid solution was prepared by dilution of analytical
grade 37% HCl. The concentration of the studied inhibitors
1
s ¼
h
ꢁ
5
ꢁ3
ranged from 5.0 ꢀ 10 M to 1.0 ꢀ 10 M.
The fraction of electrons transferred (DN110) from the
inhibitor to the (110) surface of the metal was evaluated as re-
ported by Pearson theory:
29
2.3. Electrochemical study
The electrochemical tests were performed using a potentiostat
type VersaSTAT 4, controlled with versa studio analyses soware.
The various electrochemical experiments were conducted using
c
ꢁ c
Feð110Þ
inh
F ꢁ cinh
inh
DN110 ¼ 2
¼
(7)
ðhFeð110Þ þ hinh
Þ
2h
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3
0
ꢁ
k
a molecule. Generally, electrophilic (f
) and nucleophilic
+
(
f ) attacks are calculated using eqn (8) and (9):
k
Nucleophilic attack
+
k
f
¼ P
k
(N + 1) ꢁ P
k
(N)
(8)
(9)
Electrophilic attack
ꢁ
f
k
¼ P
k
(N) ꢁ P (N ꢁ 1)
k
k
where P is the natural population for the atom k site in the
cationic (N ꢁ 1), anionic (N + 1), or neutral molecule (N).
3
. Results and discussion
Fig. 1 Evolution of the open circuit potential (OCP) versus time for
mild steel in 1.0 M HCl at the highest-tested concentration of [Tria-
CO Et] and [Tria-CONHNH ] at 298 K.
2 2
3
.1. Concentration effect of the studied triazole derivatives
.1.1. Open circuit potential. The variation of the mild steel
potential versus the elapsed time during 30 min for the unin-
3
where the work function (F) is the theoretical value of the hibited solution and the highest-tested concentration of the
electronegativity on the (110) surface and it presents a dense [Tria-CO Et] and [Tria-CONHNH ] inhibitors is illustrated in
2
2
surface package (F ¼ c
¼ 4.82 eV). The global hardness Fig. 1.
Fe(110)
corresponding to the metallic bulk is h
¼ 0 eV.
It was noticed that the addition of the studied molecules
Fe(110)
The Fukui indices indicate a tendency of the molecule to give induces a shi in OCP (i.e., the corrosion potential Ecorr). Based
or obtain electrons. Therefore, these functions have been on the plots presented in Fig. 2, it can be observed that the mild
modeled to detect the most nucleophilic interactions in steel sample could achieve a quasi-stable open circuit potential
in under 30 min. Therefore, 30 min of OCP measurement was
Fig. 2 Polarization curves of mild steel immersed in 1.0 M HCl without and with various concentrations of [Tria-CO
98 K.
2
Et] and [Tria-CONHNH
2
] at
2
Table 3 Polarization parameters for mild steel in 1.0 M HCl without and with various concentrations of [Tria-CO
2
Et] and [Tria-CONHNH
2
]
ꢁ
2
ꢁ1
Medium
Conc. (M)
ꢁEcorr (mV vs. Ag/AgCl)
i
corr (mA cm
)
ꢁb
c
(mV dec
)
PP
h %
1
.0 M HCl
—
413
435
427
402
388
440
431
414
402
944
230
109
29
139
138
138
136
130
138
138
137
137
—
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
5
[
Tria-CO Et]
2
5.0 ꢀ 10
75.6
88.4
96.9
97.3
72.3
88.2
96.9
97.1
4
4
3
5
4
4
3
1
5
1
.0 ꢀ 10
.0 ꢀ 10
.0 ꢀ 10
25
[
Tria-CONHNH
2
]
5.0 ꢀ 10
261
111
29
1
5
1
.0 ꢀ 10
.0 ꢀ 10
.0 ꢀ 10
27
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2 2
Fig. 3 Nyquist and Bode plots for mild steel in 1.0 M HCl with and without various [Tria-CO Et] and [Tria-CONHNH ] concentrations.
Table 4 EIS parameters obtained for mild steel in 1.0 M HCl with and without inhibitors
CPE
2
2
nꢁ1
ꢁ2
Medium
Conc (M)
R
s
(U cm )
R
p
(U cm )
Q (mF S
)
n
dl
Cdl (mF cm
)
q
imp
h %
1
.0 M HCl
—
1.7
1.7
1.6
1.7
1.6
1.7
1.8
1.8
2.1
33.0
114.2
237.0
627.8
702.7
105.0
214.9
607.5
660.9
312.7
160.7
116.4
64.8
0.784
0.828
0.838
0.854
0.855
0.824
0.831
0.848
0.866
89.1
70.1
58.3
37.5
34.3
69.8
64.3
34.6
34.5
—
—
ꢁ
5
4
4
3
5
4
4
3
[
Tria-CO Et]
2
5.0 ꢀ 10
0.711
0.860
0.947
0.953
0.685
0.846
0.945
0.950
71.1
86.0
94.7
95.3
68.5
84.6
94.5
95.0
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
1
5
1
.0 ꢀ 10
.0 ꢀ 10
.0 ꢀ 10
58.9
[
Tria-CONHNH
2
]
5.0 ꢀ 10
165.5
132.5
62.3
1
5
1
.0 ꢀ 10
.0 ꢀ 10
.0 ꢀ 10
57.2
31
assumed prior to performing all electrochemical measurements hydrogen evolution mechanism. In other words, the studied
in this work. molecules can reduce the hydrogen ions by covering the active
.1.2. PDP polarization curves. The polarization curves for reaction sites at the steel surface forming, therefore, a protective
the mild steel in the presence and absence of [Tria-CO Et] and lm. Moreover, the cathodic slope (b ) values did not show
3
2
c
[
Tria-CONHNH ] in 1.0 M HCl at 298 K are presented in Fig. 2. a large change with the increase of the inhibitor concentration,
2
Tafel parameters such as the corrosion potential (Ecorr), corro- which indicates that the reduction of hydrogen reaction is
32
c
sion current density (icorr), cathodic Tafel slope (b ), and investigated according to the pure activation mechanism.
percentage inhibition efficiencies (hPP%) are summarized in
Table 3.
It can be seen from this gure that the cathodic Tafel slope in
the presence of inhibitors decreased obviously to lower values
compared to the blank cathodic branches. Also, all curves rise to
parallel lines, indicating that our inhibitors do not alter the
Fig. 4 Electrochemical equivalent circuit used to fit the EIS data.
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Table 5 Percentage inhibition efficiency for different heterocyclic compounds in 1.0 M HCl (the concentration used is 1.0 ꢀ 10ꢁ3 M)
a
Heterocyclic compound
Highest inhibition efficiency (%) Metal exposed Reference
9
9
5.3
5.0
Mild steel
This work
2
Ethyl 2-(4-phenyl-1H-1,2,3-triazol-1-yl)acetate (Tria-CO Et)
Mild steel
This work
2
2
-(4-Phenyl-1H-1,2,3-triazol-1-yl)acetohydrazide (Tria-CONHNH )
92.4
Mild steel
39
2
,3-Diphenylquinoxaline (Q-H)
8
8
6.3
8.0
Mild steel
Mild steel
40
41
Benzo[d]thiazole-2-thiol
N-(1-Methyl-2,4-dioxo-1,2,3,4-tetrahydroquinazoline-3-carbonothioyl)propionamide
94.0
Mild steel
42
2
-(1,4,5-Triphenyl-1H-imidazol-2-yl)phenol (P1)
84.2
Mild steel
43
2
-(Phenylthio)phenyl-1-(o-tolyl)methanimine (PTM)
The inhibition efficiency values were determined using EIS measurements aer 1 h of immersion.
a
2
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Usually, when the Ecorr displacement is larger than 85 mV,
Table 5 reports the percentage inhibition efficiency for some
corresponding to that of the uninhibited solution, the inhibitor selected heterocyclic compounds used as corrosion inhibitors
is regarded as a cathodic- or anodic-type inhibitor. On the other in 1.0 M HCl compared with our compounds (Tria-CO Et and
2
hand, when the displacement is less than 85 mV, the inhibitor Tria-CONHNH ). The values of inhibition efficiency, given in
2
33
is classied as a mixed-type one. In the present paper, the Table 5, were obtained using EIS measurement aer 1/2 h of
ꢁ
3
maximum Ecorr displacements were 25 mV with [Tria-CO
2
Et] immersion in 1.0 M HCl solution containing 1.0 ꢀ 10 M of
], suggesting that both inhibi- other derivatives. By comparing these data, we can show that
our triazole derivatives, Tria-CO Et and Tria-CONHNH , are the
and 27 mV with [Tria-CONHNH
tors acted as mixed-type.
2
2
2
3.1.3. EIS measurements. To gain more information about most effective inhibitors in 1.0 M HCl. Moreover, triazole deriva-
the corrosion mechanisms and conrm the previous results tives Tria-CO Et and Tria-CONHNH remain effective against the
2
2
obtained from polarization measurements, EIS measurements corrosion of steel at high temperatures (90% at 328 K).
were performed. Thus, the Nyquist plots and Bode diagrams 3.1.4. Isotherm adsorption. In order to comprehend the
experimental and t) of the samples in 1.0 M HCl in the adsorption mechanism of [Tria-CO Et] and [Tria-CONHNH
presence and absence of the [Tria-CO Et] and [Tria-CONHNH onto the mild steel surface in the inhibited medium, various
(
2
2
]
2
2
]
inhibitors are shown in Fig. 3. In addition, the electrochemical isotherm models were tested (Langmuir, Temkin, and Freund-
parameters obtained from this technique, and grouped in Table lich) using the electrochemical spectroscopy impedance data
4, were extracted aer a good simulation in the EC-Lab V10.02 (Fig. 5). The linear equations of various isotherms are as
soware using the electrical equivalent circuit presented in follows:
Fig. 4. It can be observed that the presented circuit has a CPE
instead of a pure capacitance element since the obtained plots
showed a depressed semicircle, non-ideal with their center
located below the real axis, which is related to different physical
Langmuir isotherm:
C
inh
1
C
inh
¼
þ Cinh
;
vs: Cinh
(10)
(11)
(12)
q
K
q
34
phenomena such as surface heterogeneity.
Freundlich isotherm:
Moreover, it is clear from Fig. 3 that all of the Nyquist tted
diagrams show a single capacitive loop and the size of these
plots increased with the rise of inhibitor concentration, indi-
cating that the corrosion reaction is principally controlled by
1
ln q ¼ ln K þ ln Cinh; lnðqÞvs: lnðCinh
Þ
n
35
a charge transfer process. Therefore, this phenomenon is
generally shown when we have the dispersal frequency attrib-
uted to the surface heterogeneity and roughness of the steel
surface.
Temkin isotherm:
ꢁ
1
1
q ¼
lnðKÞ ꢁ
lnðCinhÞ; q vs: lnðCinhÞ
2
a
2a
On the other side, the EIS measurements are presented also where: q ¼ the degree of surface coverage. C ¼ the inhibitor
inh
in Bode diagrams. The Bode phase angle plots show a single concentration. K ¼ the equilibrium constant of the adsorption/
peak at intermediate frequencies, indicating the presence of desorption process. a ¼ the molecular lateral interactions: (a >
one time constant. Moreover, the Bode plots obtained in the 0; attraction), (a < 0; repulsion).
presence of our inhibitors displayed only one phase maximum,
indicating only one relaxation process. Thus, the charge trans- adsorption, DG , was calculated using eqn (13)
The expression for the standard Gibb's free energy of
ꢂ
44
ads
fer process could have taken place at the metal/electrolyte
interface. It is also observed from the Bode plots that
ꢂ
ads
DG ¼ ꢁRT lnð55:5KÞ
(13)
36
a linear relationship between log|Z| vs. log(f) was shown in the where 55.5 is the molar concentration of H O in solution, R is
2
ꢁ
1
ꢁ1
intermittent frequency region, indicating that the phase angle is the universal gas constant (8.314 J mol
K ), T is the absolute
ꢂ
less than ꢁ90 and the slope value is close to ꢁ1. These results temperature, and K is the equilibrium constant of adsorption/
37
justied the equivalent circuit obtained.
From Table 4, it can be observed that the R values increased
desorption.
p
Firstly, it is clear from Table 6 that both [Tria-CO Et] and
2
with an increase in the [Tria-CO
2
Et] and [Tria-CONHNH
2
]
[Tria-CONHNH ] obey the Langmuir adsorption isotherm, since
2
concentration, as well as the inhibition efficiency, which ach- they achieve the best regression coefficient (0.999) and a slope
45
2
2 2
ieved a maximum value of 95.3% for [Tria-CO Et] and 95.0% for close to 1 (1.032 for [Tria-CO Et], and 1.033 for [Tria-CONHNH ]).
[
1
Tria-CONHNH
2
] at the highest-tested concentration (1.0 ꢀ In addition, the adsorption constant values Kads for the Freundlich
ꢁ3
0
M). On the other hand, the values of Q and Cdl decreased as isotherm are too small to show any signicance. Thus, these
the concentration of both compounds increased, indicating inhibitors disobey the Freundlich isotherm model. On the other
adsorption on the mild steel surface. Moreover, the ndl values side, the high value of Kads in the Temkin model led us to propose
obtained are less than unity in both the inhibited and unin- that our compounds might be exhibiting a repulsive interaction,
hibited solutions, which indicates that the CPE element acts as since they have a negative value of the parameter (a) but the
38
a pseudo capacitor. From these results, it can be seen that regression coefficient is too small compared to those obtained in
both studied inhibitors showed a close efficiency despite the the Langmuir isotherm, which allowed us to report that [Tria-
46
replacement of the CO
2
Et group by CONHNH
2
.
2 2
CO Et] and [Tria-CONHNH ] disobey the Temkin isotherm.
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2 2
Fig. 5 Langmuir, Freundlich, and Temkin adsorption isotherms of [Tria-CO Et] and [Tria-CONHNH ] on the mild steel surface.
Many studies have reported that electrostatic interaction 3.2. Temperature effect of the studied triazole derivatives
happens between charged molecules and charged metals
Temperature is a valuable parameter in studying the metal
ꢁ1
(
physical adsorption) when DGads is around ꢁ20 kJ mol
.
corrosion behavior because it can change the electrode/
electrolyte interface, such as the dissolution of the adsorbed
Meanwhile, a coordinated bond (chemisorption) is achieved
ꢁ
1
47,48
when the DGads values are around ꢁ40 kJ mol or more.
In
49
molecule barrier. Therefore, the effect of temperature on the
ꢁ
1
the present work, the DGads values are ꢁ37.5 kJ mol for [Tria-
corrosion inhibition of mild steel in 1.0 M HCl in the absence
ꢁ
1
CO
2
Et] and ꢁ37.2 kJ mol for [Tria-CONHNH
2
], indicating that
ꢁ3
and presence of 1.0 ꢀ 10 M [Tria-CO
2 2
Et] and [Tria-CONHNH ]
our inhibitors adsorbed onto the steel surface by creating
a strong barrier lm. It has previously been demonstrated that
the tested triazole compounds have good corrosion inhibition
performances due to their ability to form signicant interac-
tions with the iron atoms. It can also be highlighted that in an
acidic solution, the surface of the steel electrode takes a positive
charge. These actions imply three types of interaction: (i) the
interaction of the non-bonding electron pairs on the hetero-
atoms with the vacant d-orbitals of the Fe-atoms and hence
responsible for chemical adsorption. (ii) The interaction
has been investigated at temperatures ranging from 298 K to
3
28 K using the polarization curve technique. The polarization
ꢁ3
curves at the highest-tested concentration (1.0 ꢀ 10 M) are
presented in Fig. 6, and the various electrochemical parameters
are listed in Table 7.
From the temperature analysis, it can be seen that the icorr
values in the presence of the studied inhibitors are less than
those obtained in the blank solution, signifying that these
compounds have considerably inhibited the corrosion reaction
of mild steel. As shown in Table 7, when the temperature is
ꢁ
occurring between the negatively charged Cl ions on the mild
increased from 298 to 328 K, the i
values are increased from
corr
steel surface and the positively charged protonated forms of
ꢁ2
ꢁ2
2
5 mA cm to 270 mA cm for [Tria-CO
2
Et] and from 27 mA
[
Tria-CONHNH ] and [Tria-CO Et]. (iii) p-electron clouds on the
ꢁ2
ꢁ2
2
2
cm to 216 mA cm for [Tria-CONHNH
2
]. In addition, it can be
aromatic ring also participating in the donor–acceptor kind of
interaction (retro-donation) with the ionized Fe atoms on the
surface. These interactions result in the minimization of metal
dissolution in the acidic medium by protective lm formation
of the inhibitor molecules on the mild steel surface.
noted that the inhibition efficiency decreases slightly in the
presence of the inhibitors, so that the two inhibitors remain
effective against the corrosion of the steel in hydrochloric acid.
Thus, the examined compounds still show superior inhibition
performance to protect mild steel from corrosion by forming
49,50
a rm adsorption lm on the steel surface.
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Table 6 Parameter results from different isotherm models tested
2
DG ðkJ molꢁ1
ꢂ
Isotherms
Langmuir
Freundlich
Temkin
Inhibitors
R
Parameters
K
Þ
ads
4
4
[Tria-CO
2
Et]
0.999
0.999
0.907
0.908
0.920
0.923
Slope
1.032
1.033
11.19
9.98
6.65 ꢀ 10
5.90 ꢀ 10
1.83
ꢁ37.5
ꢁ37.2
ꢁ11.4
ꢁ11.6
ꢁ59.5
ꢁ56.5
[
Tria-CONHNH
2
2
2
]
]
]
[Tria-CO
2
Et]
n
a
[
Tria-CONHNH
[Tria-CO Et]
Tria-CONHNH
1.97
8
8
2
ꢁ6.68
4.88 ꢀ 10
[
ꢁ6.06
1.46 ꢀ 10
The Arrhenius plots of Ln(icorr) vs. 1000/T and Ln(icorr/T) 1000/T, while the DH* and DS* values were obtained from linear
vs. 1000/T of mild steel in 1.0 M HCl medium containing square ts of ln Icorr/T vs. 1000/T (Fig. 7).
ꢂ
ꢃ
[
Tria-CO Et] and [Tria-CONHNH ] are presented in Fig. 7.
2 2
ꢁ
Ea
RT
The corrosion kinetic parameters, such as activation energy
(
*
a
i
corr ¼ Ae
(14)
E
a
), enthalpy of activation ðDH Þ, and entropy of activation
*
a
ðDS Þ for the corrosion of mild steel in acidic solution
ꢂ
ꢃ ꢂ
ꢃ
DS*
R
DH*
RT
without and with the highest-tested concentration of the
RT
ꢁ
3
i
corr
¼
e
e
(15)
inhibitors (1.0 ꢀ 10 M) at temperatures ranging from 298
Nħ
K to 328 K were calculated from the Arrhenius eqn (14) and
5
1
where N is Avogadro's number, T is the absolute temperature, R
is the gas constant, and ħ is Plank's constant. From the activa-
tion parameter results, it can be seen that the E
solution containing [Tria-CO Et] and [Tria-CONHNH ] are
higher than those in the case of the uninhibited solution, which
the transition state eqn (15). The activation parameters for
MS in 1.0 M HCl with and without the studied triazole
derivatives are presented in Table 8.
a
values of the
2
2
The activation parameters for mild steel in 1.0 M HCl solu-
tion without and with the [Tria-CO
compounds were obtained from linear square ts of ln Icorr vs.
2 2
Et] and [Tria-CONHNH ]
may be attributed to the formation of a compact barrier lm on
] (1.0 ꢀ 10ꢁ
3
Fig. 6 Polarization curves for steel surfaces without and with the highest-tested concentration of [Tria-CO
M) at various temperatures.
Et] and [Tria-CONHNH
2 2
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Table 7 Electrochemical parameters for steel surfaces with and without the studied inhibitors at temperatures ranging from 298 K to 328 K
ꢁ2
ꢁ1
Medium
.0 M HCl
Temp. (K)
298
ꢁEcorr (mV vs. Ag/AgCl)
i
corr (mA cm
)
ꢁb
c
(mV dec
)
PP
h %
1
413
410
411
412
388
410
416
428
402
417
418
428
944
139
137
126
120
130
136
121
117
137
137
125
119
—
—
—
—
97.3
97.2
92.6
92.0
97.1
97.1
96.3
93.6
3
3
3
08
18
28
1690
2328
3387
25
[
Tria-CO
2
Et]
298
3
3
3
08
18
28
46
170
270
27
49
86
[
Tria-CONHNH
2
]
298
3
3
3
08
18
28
216
52
the mild steel surface. The higher energy barrier for the using the natural populations in order to nd the most reactive
corrosion process in the case of the inhibited solutions suggests sites of the studied molecules.
that the adsorbed inhibitor lm prevents the charge/mass
From the HOMO and LUMO, the orbital distribution is
53,54
transfer reaction occurring on the surface,
thus protecting localized principally in the aromatic and triazole rings showing
the metal from dissolution. The positive values for the activa- that [Tria-CO Et] and [Tria-CONHNH ] inhibitors can create
2
2
*
tion enthalpy DH reect the endothermic nature of the mild bonds with the vacant orbital of iron because they have many
a
55
steel dissolution process.
reactive sites distributed along the inhibitors' structures.
*
a
The value of activation entropy ðDS Þ increases and is Moreover, the ESPM distributions show that the total density (in
59,60
negative in the presence of the inhibitor [Tria-CONHNH
2
], red color) is located on the oxygen and nitrogen atoms.
It
which means a decrease in the disorder during the trans- could be concluded that the present inhibitors can favor the
56
formation of the reagents into an activated complex; in the adsorption phenomenon onto the surface of mild steel. The
*
a
2 2
case of [Tria-CO Et] the value of DS was high and positive values of the theoretical descriptors obtained for [Tria-CO Et]
53,57
meaning an increase in the disorder.
are close to those obtained with [Tria-CONHNH ]. These nd-
2
ings are in good agreement with the experimental results.
1
3.3. DFT study
DFT has been mainly useful to correlate the electronic proper-
Table 8 Thermodynamic parameters of the activation parameters for
ties to the inhibition performance obtained experimentally, i.e. [Tria-CO Et] and [Tria-CONHNH ]
2
2
understanding the adsorption mechanism of the molecules
used. Quantum descriptor calculations were extracted using
the DFT method at the B3LYP/6-311G (d,p) level (Table 9). The
58
Activation parameters 1.0 M HCl [Tria-CO
2
2
Et] [Tria-CONHNH ]
ꢁ1
E
a
(kJ mol
)
33.8
31.2
68.7
66.1
55.1
52.5
optimized geometries of [Tria-CO
2
Et] and [Tria-CONHNH
2
], as
ðDH Þ ðkJ molꢁ1Þ
*
a
*
well as their frontier molecular orbitals (LUMO and HOMO), are
shown in Fig. 8. The Fukui functions have also been calculated
ꢁ1
ꢁ1Þ
ꢁ82.7
3.0
ꢁ42.1
ðDH Þ ðJ mol
K
a
Fig. 7 Arrhenius and transition state plots for mild steel in 1.0 M HCl solution with and without the optimum concentration (1.0 ꢀ 10ꢁ3 M) of the
studied inhibitors.
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6
2
Table 9 Quantum chemical descriptors for [Tria-CO
2
Et] and [Tria- the corrosion rate of mild steel for both inhibitors.
2
CONHNH ] in the gas and aqueous phases
According to the literature, small electronegativity values
cause molecules to easily reach electron equilibrium so that
the molecules get more reactive. In contrast, high electro-
[
Tria-CO Et]
2
[Tria-CONHNH
2
]
Parameters
Gas
Aqueous
Gas
Aqueous negativity values show the opposite. In this study, the
electronegativity value of [Tria-CO Et] calculated in the gas
phase is the lowest (3.45 eV) compared to the electronega-
tivity value for [Tria-CONHNH ], which is 3.76 eV. Based on
2
E
E
HOMO (eV)
LUMO (eV)
ꢁ6.1183
ꢁ0.7997
5.3185
0.3760
2.6592
3.4590
5.2803
0.2558
2.2496
0.4445
ꢁ6.4269
ꢁ1.0482
5.3787
0.3718
2.6893
3.7375
7.3222
0.2012
2.5971
0.3850
ꢁ6.4427
ꢁ1.0792
5.3634
0.3728
2.6817
3.7609
2.6494
0.1974
2.6372
0.3791
ꢁ6.3763
ꢁ1.0242
5.3520
0.3736
2.6760
3.7002
6.3022
0.2092
2.5582
0.3908
2
DEgap (eV)
ꢁ1
s (eV
)
the dipole moment values in the corrosion eld, some
authors reported that the dipole moment increases with the
efficiency but others say the opposite. In our case, we found
that the dipole moment increases with the inhibition
h (eV)
c (eV)
m (D)
DN
6
3,64
efficiency.
U
3
The most active sites of the Fukui indices for the studied
molecules have been extracted in the gas and aqueous
phases and are listed in Table 10. It can be seen from these
þ
results that the calculated values of f for [Tria-CO
2
Et] are
k
According to the obtained EHOMO and DEgap values (Table 9), it
typically localized on C11, C5, C6, and O16. While, O16,
O14, and N4 are the most active sites for electrophilic
can be observed that [Tria-CO Et] is very reactive in the gas
2
phase, while it is less reactive in the aqueous phase. In addition,
it can be suggested that the similar inhibition proprieties of the
investigated compounds create this contradiction between the
two studied phases. Also, the lower values of ELUMO obtained for
both studied molecules indicate the ability of these molecules
ꢁ
65,66
attack, since the highest values of fk were recorded.
For
+
[
Tria-CONHNH
2
], the highest values of f
k
are situated on the
C15, C10, and C5 atoms, which further suggests that these
atoms are responsible for forming a back bond by accepting
the electron coming from the mild steel surface. However,
61
to accept electrons in the aqueous phase.
ꢁ
superior values of f
k
are on O16, N2, N1, and C15. It can be
Furthermore, the value of DN110 < 3.6 according to
Lukovist's study, signifying the increase in electron-
donating ability to the metal surface and this can decrease
observed that these responsible sites are also remarked in
the aqueous phase and suitable for donor–acceptor
2 2
Fig. 8 Optimized structures, HOMO and LUMO and ESP maps for [Tria-CO Et] and [Tria-CONHNH ] in neutral form.
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+
ꢁ
k
k 2 2
Table 10 Most active sites of f , f for [Tria-CO Et] and [Tria-CONHNH ] in the gas and aqueous phases
+
ꢁ
Molecule
[Tria-CO
Atoms
N 1
N4
Phase
P(N)
P(N ꢁ 1)
P(N + 1)
f
k
f
k
2
Et]
G
A
G
A
G
A
G
A
G
A
G
A
G
A
G
A
G
A
G
A
G
A
G
A
G
A
7.265
7.308
7.157
7.144
6.097
6.071
6.069
6.077
6.205
6.211
8.568
8.562
8.540
8.588
7.266
7.311
7.022
7.051
6.097
6.072
6.069
6.076
6.206
6.212
8.574
8.631
7.175
7.221
7.144
7.132
6.014
5.968
6.023
6.017
6.099
6.103
8.520
8.529
8.446
8.499
7.176
7.218
6.903
6.915
6.019
5.983
6.033
6.046
6.108
6.136
8.458
8.472
7.298
7.343
7.161
7.155
6.178
6.170
6.140
6.216
6.318
6.388
8.598
8.573
8.615
8.611
7.296
7.346
7.051
7.078
6.186
6.168
6.145
6.235
6.324
6.408
8.6200
8.6373
0.033
0.034
0.003
0.011
0.081
0.099
0.070
0.139
0.113
0.177
0.029
0.011
0.075
0.022
0.030
0.034
0.029
0.026
0.088
0.095
0.076
0.158
0.118
0.196
0.0458
0.0059
0.090
0.087
1.270
0.011
C5
ꢁ1.046
0.103
0.055
0.059
0.032
0.108
3.392
0.033
2.500
0.089
0.089
0.093
0.118
0.135
0.078
0.088
0.035
0.029
0.097
0.075
0.115
0.158
C6
C 11
O14
O16
N 1
N2
[
2
Tria-CONHNH ]
C 5
C 10
C15
O 16
interactions, and thus facilitate the adsorption of the
inhibitor on the metal surface.
3 A. Mohagheghi and R. Arenia, Corrosion inhibition of
carbon steel by dipotassium hydrogen phosphate in
alkaline solutions with low chloride contamination, Constr.
Build. Mater., 2018, 187, 760–772.
4
. Conclusion
4
C. Verma, E. E. Ebenso and M. A. Quraishi, Ionic liquids as
green and sustainable corrosion inhibitors for metals and
alloys: An overview, J. Mol. Liq., 2017, 233, 403–414.
In the present study, the corrosion inhibition and adsorption
characteristics of two triazole derivatives ([Tria-CO Et] and [Tria-
2
CONHNH ]) in 1.0 M HCl solution were investigated by various
5 R. Salim, E. Ech-chihbi, H. Oudda, F. El Hajjaji, M. Taleb and
S. Jodeh, A review on the assessment of imidazole [1,2-a]
pyridines as corrosion inhibitor of metals, J Bio Tribo.
Corros., 2019, 13, 5–11.
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Corrosion Inhibitors: Principles and Applications, Elsevier
Inc. Amsterdam, 2020.
2
electrochemical techniques and a theoretical approach. The
polarization curves display that these compounds acted as
a mixed-type inhibitor. The electrochemical impedance spec-
troscopy results indicate that the inhibition efficiency reaches
2
a maximum value of 95.3% for [Tria-CO Et] and 95% for [Tria-
CONHNH ]. The temperature study did not show a remarkable
2
effect of the two studied inhibitors in the range of 298–328 K. The
adsorption behavior shows that these triazole derivatives suit the
Langmuir isotherm model. The obtained global and selective
descriptors are in good correlation with the experimental part.
7 F. El-Hajjaji, M. Messali, M. V. Mart ´ı nez de Yuso,
E. Rodr ´ı guez-Castell ´o n, S. Almutairi, T. J. Bandosz and
M. Algarra, Effect of 1-(3-phenoxypropyl) pyridazin-1-ium
bromide on steel corrosion inhibition in acidic medium, J.
Colloid Interface Sci., 2019, 541, 418–424.
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Conflicts of interest
There are no conicts to declare.
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