Evaluation of corrosion inhibition performance of a novel ionic liquid based on synergism between cation and anion

Article abstract of DOI:10.1039/d0nj00745e

A novel ionic liquid, 1-butyl-1H-imidazol-1-ium 3-carboxy-2-((2-carboxylatoethyl)thio)propanoate ([Bhim]CETSA), was synthesized as an environmentally friendly and efficient corrosion inhibitor, and its corrosion inhibition performance on A3 steel in 1 M HCl solution was investigated by using the weight loss method, and the results indicated that the inhibition efficiency reached up to 90.11% when the concentration of [Bhim]CETSA was 10 mM at 298 K. There was a synergistic effect between anion and cation, and the anion played a major role in the corrosion inhibition of [Bhim]CETSA. The adsorption of ionic liquid on the A3 steel surface followed a Langmuir adsorption model and was proved by using infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM), and the relevant thermodynamic parameters were calculated and discussed. Moreover, the existence of the hydrophobic film on the A3 steel was proven by contact angle measurement, and the corrosion inhibition mechanism of [Bhim]CETSA was further studied by quantum chemical calculation.

Full text of DOI:10.1039/d0nj00745e

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March 2018
Pages 3963-4776
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DOI: 10.1039/D0NJ00745E
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Evaluation of Corrosion Inhibition Performance of a Novel Ionic
Liquid Based on Synergism Between Cation and Anion
Received 00th January 20xx,
Accepted 00th January 20xx
a
a
a
b
c
a
a
Huajing Gao , Ning Xie , Hong Wang , Maolong Chen , Jianlin Zhang , Jian Sun *, Zhaohui Jin
DOI: 10.1039/x0xx00000x
A novel ionic liquid 1-butyl-1H-imidazol-1-ium 3-carboxy-2-((2-carboxylatoethyl)thio)propanoate ([Bhim]CETSA) was
synthesized as an environmentally friendly and efficient corrosion inhibitor, and its corrosion inhibition performance for
A3 steel in 1M HCl solution was investigated by using weight loss method, the results indicated that the inhibition
efficiency reached up to 90.11% when the concentration of [Bhim]CETSA was 10 mM at 298 K. There was a synergistic
effect between anion and cation, and anion played a major role in the corrosion inhibition of [Bhim]CETSA. The adsorption
of ionic liquid on the A3 steel surface was a Langmuir adsorption model and had been proved by infrared spectroscopy (IR),
X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM), the relevant thermodynamic parameters
were calculated and discussed. Moreover, the existence of hydrophobic film on the A3 steel was proved by contact angle
measurement, and the corrosion inhibition mechanism of [Bhim]CETSA was further studied by quantum chemical
calculation.
2
1-23
surface.
Ionic liquids have attracted wide attention in
Introduction
recent years due to their many advantages. Although the
thermal and chemical stability of some ionic liquids is not
satisfactory, which is mainly determined by their anions and
cations and their interactions, there is no doubt that ionic
In the production of chemical industry, metal has become an
essential material, especially carbon steel, it has been widely
used in chemical equipment because of its high strength and
low cost. Pickling technology is the process of removing oxide
scale on metal surface by using acid solution, and hydrochloric
2
4,25
1
liquids play an important role in various fields.
Ionic liquids
containing heteroatoms, such as P, S, N and O, have become
important green substitute for traditional corrosion inhibitors,
because of its low biological harm to the environment and
acid is more commonly used than other inorganic acids
2-4
because of its economy and practicality.
However, metal
26-29
effective interaction with metal surface.
At present, most
materials will be corroded in the acid solution, which can be
5,6
of the quaternary ammonium ionic liquids were reported as
solved by adding corrosion inhibitors. Corrosion inhibitor can
30-34
inhibitors,
the inhibition of these ionic liquids is mainly
protect metal materials from corrosion with only a small
amount of addition. In the early stage, traditional inhibitors
are mainly inorganic salts, such as chromate, nitrite and
phosphate, which are toxic and pollute the environment.
With the increasing awareness of environmental protection,
traditional toxic corrosion inhibitors are gradually eliminated.
Therefore, it is of great significance to study environment-
friendly, sustainable and efficient corrosion inhibitors.
dependent on the action of cations, and anions are usually
simple ions that do not have corrosion inhibition properties
-
-
7-10 such as Cl and Br , which there are no synergism between
cations and anions. Therefore, the design of an ionic liquid that
both cation and anion have corrosion inhibition performance
will maximize the utilization efficiency of the two ions.
Carboxyethylthiosuccinic acid (CETSA) is a kind of versatile
monomer which may have corrosion inhibition, meanwhile, it
can be used as anion to form ionic liquid. So far, there is no in-
depth study on CETSA as an inhibitor. Thus, CETSA as an anion
In recent years, some organic inhibitors have been developed
and reported in order to replace the toxic inorganic salt
11-16
inhibitors.
The molecular structures of these organic
is used to design an ionic liquid which have synergistic effect
with cation, which will provide a new design method for ionic
liquid as an inhibitor. In this paper, CETSA was synthesized by
thiol-ene Click reaction, and a novel ionic liquid was
synthesized by CETSA as anion and 1-butylimidazole as cation,
the corrosion inhibition performance of [Bhim]CETSA for the
A3 steel in 1M HCl solution was investigated by using weight
loss method, IR, XPS, SEM and contact angle measurements,
and its adsorption behavior and mechanism on steel surface
were revealed by adsorption isotherms and quantum
chemistry.
inhibitors usually contain heteroatoms, heterocycles and
because heteroatoms have lone
electron pairs which are easy to adsorb on the metal
17-20
unsaturated bonds,
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dried and weighed for test. The weight-loss test was carried
Experimental
Materials
View Article Online
DOI: 10.1039/D0NJ00745E
out in 1 M HCl solution with or without [Bhim]CETSA at 298-
3
18 K, and the corrosion time was 24 h; the calculation
The composition of A3 steel used in the experiments (wt%) formula of corrosion rate (V), corrosion inhibition rate (η) and
was Mn (1.400%), Si (0.350%), C (0.220%), S (0.050%), P surface coverage (θ) were as follow
：
(0.0450%), and Fe for balance. The corrosive solution 1 M HCl
ꢁꢂ
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solution was prepared using analytical grade HCl and distilled
water, hydrochloric acid was purchased from Beijng Chemical
Works. Maleic acid, β-mercaptopropionic acid, trimethylamine
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ꢉꢆꢊꢈꢀ
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ꢌ
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(
NEt ) and 1-butylimidazole were purchased from Energy
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3
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Chemical.
Syntheses
Where ∆m is the mass loss of the A3 steel sample after the
weight loss measurements (g), t represents the corrosion time
2
The synthesis of CETSA and [Bhim]CETSA were shown in
Scheme 1.
Synthesis of CETSA
(
h), s is the surface area of sample (m ), V and V are the
0
inh
corrosion rates without and with [Bhim]CETSA respectively
-
2
-1
(g·m ·h ).
0.22 mol maleic acid was dissolved in 50 mL water and mixed Surface Analysis
with 0.2 mol β-mercaptopropionic acid, 5 mol% NEt3 was
IR Spectroscopy
added as catalyst. The reaction mixture was stirred and heated
The Fourier transform infrared spectra measurements were
carried out on the A3 steel surface (10 mm×10 mm×1 mm)
after its immersion in 1M HCl solution with 10 mM
o
to 90 C for 3 h. The mixed reaction solution was cooled to
o
crystallize at 8 C. The crude product of CETSA as the white
crystal was obtained by decompression and filtration. After
recrystallization, the product was dried to remove moisture. H
NMR (400 MHz, D O) δ 2.63 (m, 2H), 2.73 (m, 1H), 2.87 (m, 3H),
3.68 (dd, 1H, J=5.6, 9.4 Hz). IR (KBr, cm ): 2671(O-H),
1693(C=O), 1419(O=C-O), 1311(H-C-H), 670(C-S-C), 618(CH-S).
Synthesis of [Bhim]CETSA
[
Bhim]CETSA for 24 h using a Nicolet iS5 FTIR spectrometer in
1
ATR mode, the FTIR spectrum of [Bhim]CETSA sample was
obtained to use as a reference and the specimen was
measured in the KBr pallets.
2
-1
XPS Analysis
The size of A3 steel sample used for XPS measurement was 15
mm×15 mm×1 mm. The A3 steel sample was immersed in 1M
HCl solution with 10 mM [Bhim]CETSA for 24 h, and washed
with distilled water, then the sample was used for XPS
measurement after natural air drying to analyze the surface
composition of sample.
0
.01 mol CETSA was dissolved in 10 mL water, meanwhile, 0.03
mol 1-butylimidazole was dripped. The reaction mixture was
stirred and heated to 50 C for 2 h. The chloroform was added
to extract surplus 1-butylimidazole. Aqueous mixture was
o
distilled under vacuum to remove water and obtain products.
1
H NMR (400 MHz, CD OD) δ 0.99 (t, 6H, J=7.6 Hz), 1.35 (m,
3
SEM Characterization
4
H), 1.83 (m, 4H), 2.65 (m, 3H), 2.92 (m, 3H), 3.64 (dd, 1H,
J=5.29, 9.01 Hz), 4.12 (t, 4H, J=7.19 Hz), 7.17 (s, 2H), 7.31 (s,
H), 8.08 (s, 2H).
The surfaces of A3 steel specimens (5 mm×5 mm×1 mm) that
immersion in 1M HCl solution without and with 10 mM
Bhim]CETSA for 24h at 298K were measured using JSM6490LV
SEM instrument at high vacuum to observe the surface
morphology.
2
[
Contact Angle Measurements
The A3 steel sample was immersed in 1M HCl solution without
and with 1, 2, 5, 10 mM [Bhim]CETSA for 24 h, and washed
with distilled water, then contact angle measurements were
carried out on these samples using JC2000C optical contact
angle measuring instrument to determine the hydrophobicity
of [Bhim]CETSA film on the surface of A3steel sheet.
Quantum Chemical Study
Scheme 1 The synthesis of CETSA and [Bhim]CETSA
Thermo gravimetric Analysis (TG)
The molecular structures of the CETSA were geometrically
optimized by using density functional theory (DFT) /B3LYP-
D3BJ method with the basis set 6-31G(d) on the Gaussian
09.D.01. Quantum chemical parameters such as the energy of
the highest occupied molecular orbital (HOMO), the lowest
unoccupied molecular orbital (LUMO), the energy gap
between ELUMO and EHOMO (ΔE=ELUMO−EHOMO), dipole moment (μ)
TG measurement of [Bhim]CETSA was carried out. For
comparison, CETSA and 1-butylimidazole also were tested
using Q35 instrument. These samples were loaded in a
platinum crucible and heated under N at a heating rate of
2
-1
1
0 °C·min from 20 to 300 °C.
Weight loss measurements
The size of A3 steel sample used for weight loss measurement were calculated.
was 50 mm×50 mm×1 mm. Before the test, the steel pieces
are polished with sandpaper, then cleaned and deoiled with
Result and Discussion
deionized water, anhydrous ethanol and acetone, and finally
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 2
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Thermal Stability Analysis of [Bhim]CETSA
Bhim]CETSA was a viscous liquid at room temperature, this
temperatures can significantly slow down the corrosion rate of
View Article Online
DOI: 10.1039/D0NJ00745E
the sample, increase the corrosion inhibition efficiency and
[
surface coverage (θ), which indicates that [Bhim]CETSA has
outstanding corrosion inhibition for A3 steel in acid medium,
and the corrosion inhibition effect depends on the amount of
shows that it accords with the characteristics of ionic liquid
with low melting point. Ionic liquid and its synthetic materials
are characterized by TG and the result is shown in Fig. 1.
Significantly, this result is obtained by ramped temperature
analysis and may have an error compared to the isothermal
temperature analysis, which caused by the temperature
increased rapidly at a fixed rate in the experiment. As Fig. 1
shown, decomposition process of [Bhim]CETSA includes three
stages, a small weight loss peak appeared before 100 C, which
[
Bhim]CETSA. The inhibition efficiency increases with the
increase of concentration, and reached up to 90.11% when the
concentration of [Bhim]CETSA is 10 mM at 298 K. However,
with the increase of temperature, the inhibition efficiency of
0
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[
Bhim]CETSA to A3 steel decreases slightly, which intensifies
o
the thermal movement of [Bhim]CETSA molecule and reduces
the viscosity of the interface between metal and solution,
accelerates the movement frequency of reaction particles,
decreases the contact probability between a molecule and A3
steel surface, and promotes the diffusion of corrosion products
to the solution, so the protective film which formed by
was may be caused by the volatilization of the combined water
in the product. There are two strong weight loss peaks in the
o
o
range of 110-120 C and 160-170 C, which may be caused by
the decomposition of cations and anions respectively
according to the thermo gravimetric curve of raw materials.
The results indicate that [Bhim]CETSA has good thermal
stability and can be used as corrosion inhibitor when the
[
Bhim]CETSA molecule becomes difficult to from and reduces
3
6-38
the protection ability to A3 steel.
o
Ionic liquid [Bhim]CETSA completely ionizes in aqueous
solution to give 1-butylimidazole cation and CETSA anion. In
order to study the contribution and synergistic effect of cation
and anion on corrosion inhibition performance, the relevant
corrosion parameters and synergistic coefficient (S) are
temperature is less than 100 C.
39,40
calculated and shown in Table 2. S is calculated as follows:
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ꢇꢌꢓꢖꢙꢗ
Where θ , θ , and θ are the surface coverage of CETSA, 1-
1
2
1+2
butylimidazole, and [Bhim]CETSA, respectively.
As can be seen from Table 2, the value of S are greater than 1
when the concentration is 1 mM at 298 K or 1, 2 and 5 mM at
08K, that indicates the interaction between CETSA and 1-
butylimidazole is a synergistic effect. The value of S are less
than 1 when the concentration is 10 mM at 308 K or 2, 5 and
0 mM at 298K, that means an antagonistic effect occurs
3
1
between 1-butylimidazole and CETSA, which may be related to
the competitive adsorption of 1-butylimidazole and CETSA on
Fig. 1 TG analysis of [Bhim]CETSA and its synthetic materials
Weight Loss Measurements
32,39
the A3 steel surface.
The result of Table 2 indicates that
The results of weight loss measurements for A3 steel in 1M HCl the synergistic effect of 1-butylimidazole and CETSA enhance
solution are shown in Table 1. The results show that adding with the increase of temperature or the decrease of
[
Bhim]CETSA to the corrosion solution at different concentration.
Table 1 Corrosion rate of A3 steel and inhibition efficiency of various concentrations of [Bhim]CETSA in 1 M HCl at different temperatures obtained from weight loss measurements
-
2
-1
T(K)
C(mM)
V(g·m ·h )
4.6100
0.8092
0.6592
0.5342
0.4558
15.3050
3.2767
2.3375
1.6775
1.6092
30.5433
9.4725
7.3067
7.1333
6.3550
η (%)
θ
blank
1
2
5
82.45
85.70
88.41
90.11
0.8245
0.8570
0.8841
0.9011
2
3
3
98
08
18
1
0
blank
1
2
5
10
blank
1
2
5
78.59
84.73
89.04
89.49
0.7859
0.8473
0.8904
0.8949
68.99
76.08
76.65
79.19
0.6899
0.7608
0.7665
0.7919
1
0
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View Article Online
DOI: 10.1039/D0NJ00745E
Table 2 Corrosion parameters and synergistic coefficient obtained from weight loss measurements for A3 steel in 1 M HCl without (Blank) and with different concentrations of
corrosion inhibitor at 298 and 308 K
CETSA
1-butylimidazole
[Bhim]CETSA
T(K)
C(mM)
S
-
2
-1
-2 -1
-2 -1
V(g·m ·h )
4.6100
1.2683
1.0675
0.8758
0.5900
15.3050
9.6825
7.4158
5.2000
2.3533
η (%)
V(g·m ·h )
η (%)
V(g·m ·h )
η (%)
blank
4.6100
3.9533
2.3108
2.1258
1.9408
15.3050
14.2150
13.3092
12.9908
10.1108
4.6100
0.8092
0.6592
0.5342
0.4558
15.3050
3.2767
2.3375
1.6775
1.6092
1
2
5
72.49
76.84
81.00
87.20
14.24
49.87
53.89
57.90
82.45
85.70
88.41
90.11
1.34
0.81
0.76
0.54
2
98
0
1
2
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9
0
1
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0
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0
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0
1
2
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0
1
0
blank
1
2
5
45.26
58.07
70.60
86.69
19.63
24.75
26.55
42.84
78.59
84.73
89.04
89.49
2.05
2.07
1.97
0.72
308
1
0
Adsorption Isotherm
sharing of electrons or electron transfer between iron atoms
on the steel surface and corrosion inhibitor molecules to form
in Table 3 show that
ads
the adsorption of [Bhim]CETSA on the steel surface is a mixed
adsorption.
The corrosion inhibitors block the corrosion of metals in acidic
media due to the adsorption capacity on the metal surface.
The adsorption thermodynamic parameters can be used to
explain the interaction between inhibitors and metal surfaces,
and coverage is considered to be the most effective parameter
to study the adsorption behavior of inhibitors. Langmuir studied compound in 1 M HCl at different temperatures
isotherm is one of the most classical adsorption models, and
its adsorption isotherm is as follows:
4
3,44
0
4
0
covalent bonds.
The value of ΔG
Table 3 Adsorption parameters obtained from weight loss measurements for the
41
0
0
0
K
ads
ΔG ads
ΔH ads
ΔS ads
T(K)
-
1
-1
-1
-1 -1
(
L·mol )
(kJ·mol )
-32.02
(kJ·mol )
(J·mol ·K )
56.70
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ꢜꢝꢞꢟ
ꢀ
ꢘꢛꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢆꢠꢈ
2
3
3
98
08
18
7380
6477
5020
-32.76
-33.15
-15.12
57.27
56.69
Where C is the concentration of corrosion inhibitor; θ is
surface coverage; Kads is the adsorption equilibrium constant.
0
ads
-1
The standard enthalpy change (ΔH , kJ·mol ) in adsorption
process can be obtained from Van’t Hoff equation (7) and the
The relationship between K
and adsorption Gibbs free
ads
0
42
energy ΔG is as follows:
ads
ꢋ
slope of the fitting line in Fig. 3, and the standard entropy
ꢇ
ꢠꢠꢡꢠ
ꢁꢥ
ꢝꢞꢟ
)ꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢆꢨꢈ change (ΔS0 J·mol ·K ) can be obtained from the classical
-1 -1
ꢜꢝꢞꢟ
ꢀ
ꢢꢣꢤ(ꢌ
ads,
ꢦꢧ
4
5
thermodynamic relationship (8) respectively.
Where 55.5 is the molar concentration of water in the solvent
-1
-1 -1
(mol·L ); R is the gas constant (8.314 J·mol ·K ) and T is the
0
ads
absolute temperature (K), fit data of Kads and ΔG are listed in
Table 3.
Based on the experimental results of the weight loss
measurement, the (C/θ) - C in the temperature range of 298-
318 K is plotted and fitted linearly, and the results are shown
in Fig. 2. There is an excellent linear relationship between C/θ
and C at different temperatures, and the correlation
2
coefficient (R ) is almost equal to 1, which is in agreement with
the Langmuir isotherm. As can be seen from Table 3, with the
increase of temperature, the adsorption equilibrium constant
Kads gradually decreases, indicating that high temperature will
lead to partial desorption of [Bhim]CETSA molecules on the
steel surface and decrease of the corrosion inhibition
efficiency, which is consistent with the conclusion of the
weight loss measurement, and the negative value of ΔG
indicates that the adsorption of [Bhim]CETSA on the steel
surface is spontaneous. Generally, when ΔG
0
ads
0
-1
> -20 kJ·mol ,
ads
Fig. 2 Langmuir absorption isotherm fitting for [Bhim]CETSA on the A3 steel surface
it is the electrostatic interaction between charged molecules
ꢋ
0
ꢁꢫꢝꢞꢟ
and charged metals, which is physical adsorption; when ΔG
ꢩꢪꢜꢝꢞꢟ ꢀꢌ
ꢘꢛꢬꢭꢃꢄꢮꢭꢄꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢆꢯꢈ
ads
-
1
ꢦꢧ
ꢀꢁꢫꢋ ꢌꢧꢁꢰ ꢝꢋ ꢞꢟꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢆꢱꢈ
< -40 kJ·mol , it is chemical adsorption, which is caused by the
ꢋ
ꢁ
ꢥ
ꢝꢞꢟ
ꢝꢞꢟ
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1
1
1
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2
2
2
2
2
2
2
2
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3
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4
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4
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6
Where Constant is antiderivative constant. The result obtained corrosion effect. There is a theory that if η decreases with
View Article Online
DOI: 10.1039/D0NJ00745E
from equations 7 and 8 are also listed in Table 3.The negative increasing temperature, E (presence of inhibitor)>E (absence
a
a
0
ads
value of ΔH
in Table 3 indicates that the adsorption of of inhibitor), otherwise, if η increases with increasing
[
Bhim]CETSA is an exothermic process, which is due to temperature, Ea(presence of inhibitor)< Ea(absence of
5
3,54
combined action of chemical adsorption and physical inhibitor),
which is in agreement with the calculation
in Table 3 are positive at results of activation energy and the relationship between
ads
4
6,47
0
adsorption.
The values of ΔS
different temperatures, and the difference is not significant, corrosion inhibition rate and temperature in weight loss
indicating that adsorption is accompanied by the process of
entropy increase. The process of increasing entropy implies an
increase in disorder because the corrosion inhibitor adsorbs
the substance on the metal surface as a replacement for H O
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
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7
8
9
0
1
2
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9
0
1
2
3
4
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9
0
1
2
3
4
5
6
7
8
9
0
2
Fig. 4 The relationship between lnV and 1/T
measurements.
Surface Analysis
-
1
Fig. 3 lnKads -T curve fitting for A3 steel in 1M HCl solution in the presence of 10
IR Spectroscopy
mM [Bhim]CETSA
The IR spectrometer was employed to analyze the
molecules, and the volume of H O molecules is much smaller
than that of [Bhim]CETSA molecule. Therefore, the adsorption
of a single [Bhim]CETSA molecule will lead to the desorption of
2
multiple H O molecules, so the overall adsorption is a process
2
48,49
of entropy increase.
Activation Parameters
In order to further study the interaction process between
[
Bhim]CETSA and A3 steel surface, Arrhenius formula (9) was
50
used to analyze.
ꢴꢝ
ꢀ
ꢲꢢꢣꢤꢳꢌ ꢵꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢅꢆꢶꢈ
ꢦꢧ
-
2
-1
Where V is corrosion rate (g·m ·h ); E is activation energy
a
-
1
(
(
kJ·mol ); A is pre-exponential factor; R is the gas constant
-1
-1
8.314 J·mol ·K ) and T is the absolute temperature (K). E can
a
be obtained from the slope of the fitting curve between lnV
and 1/T in Fig. 4, and the calculated values of Ea are
summarized in Table S1 (Supporting Information). It can be
seen from equation (9) that high activation energy (E ) will
reduce the corrosion rate. The results of Table S1 show that
the activation energy of blank group is lower than that of
a
Fig. 5 IR spectra of (a) the [Bhim]CETSA sample and (b) the the A3 steel samples
which was immersed in 1 M HCl containing 10 mM [Bhim]CETSA for 24 h at 298 K
[
Bhim]CETSA group, indicating that blank group is more prone
5
1
to corrosion. However, in the acid solution containing
Bhim]CETSA, as [Bhim]CETSA molecules form an adsorption
film on the steel surface, the system needs to obtain more
[
Bhim]CETSA sample (a) and the A3 steel samples which was
[
immersed in 1 M HCl containing 10 mM [Bhim]CETSA for 24 h
at 298 K (b), and the IR spectra are shown in Fig. 5.
52
-1
energy to overcome the obstacles of the film, thus, the
corrosion rate is reduced, which has an excellent anti-
As shown in Fig. 5 (a), the absorption peak at 3121 cm
belongs to the stretching vibration peak of N-H bond. The peak
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-1
+
at 2362 cm belongs to the absorption peak of -NH in the Fig. 6 (c), N 1s was fitted and two peaks appeared at 399.7
View Article Online
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DOI: 10.1039/D0NJ00745E
and 399.75eV, which correspond to N-C, N-Fe bonds,
imidazole cation, and the peaks at 2960, 2934 and 2874 cm
belong to the stretching vibration of C-H (-CH , -CH ), the band respectively. After the coordination between N element and
2
3
-1
at 1712 cm is corresponding to the stretching vibration peak Fe occurs, the electron cloud density of N transfers to Fe,
-
1
-1
of C=C bond, the peak located at 1229 cm and 1088 cm are resulting in the decrease of the electron cloud density of N.
attributed to the stretching vibration of C-N bond. In the IR due to the perturbation of the valence state on the inner
spectrum, the C-S band of sulfur ether usually appears electrons, the electron excitation of the energy layer becomes
-
1
55
between 720-570 cm , where the absorption peak of CH -S: difficult, and the binding energy increases. In the Fig. 6 (d),
0
1
2
3
4
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0
1
2
3
4
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0
1
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0
1
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-1
-1
6
90-630 cm , the absorption peak of CH-S: 650-600 cm . The the S 2p region only can be fitted into one peak at 168.1eV,
-1
-1
absorption peaks at 662 cm and 629 cm in Fig. 5 (a) which may correspond to S-Fe bond. Therefore, the above XPS
correspond to the above two functional groups. It can be seen results further prove the adsorption of [Bhim]CETSA on the
from Fig. 5 (b) that the same absorption peak (2962, 2947, steel surface.
-
1
2
882, 2360, 1606, 1035, 678 and 648 cm ) can be found by IR SEM Characterization
spectrum analysis on the surface of A3 steel which was treated In order to explore the corrosion inhibition performance of
by [Bhim]CETSA as in Fig. 5 (a), indicating that ionic liquid has [Bhim]CETSA from the microscopic perspective, the
been adsorbed on the surface of A3 steel during the corrosion microstructure of the steel surface was observed by using SEM.
inhibition process. The results of IR spectroscopy can be The surface morphology of A3 steel immersed in 1M HCl
further demonstrated by XPS characterization.
XPS Analysis
solution without or with the added concentration of 10mM
Bhim]CETSA for 24 h at 298K was shown in Fig. 7.
[
In order to further determine whether the corrosion inhibitor
molecules adsorbed on the surface of the A3 steel sheet, The
surface compositions of the A3 steel treated by immersion in 1
M HCl containing 10 mM [Bhim]CETSA for 24 h at 298 K are
analyzed using XPS, and the result is shown in Fig. 6.
Fig. 7 SEM images of A3 steel after immersion in 1 M HCl without (a) and with (b) 10
mM [Bhim]CETSA for 24 h at 298K
As can be seen from Fig. 7(a), when [Bhim]CETSA was not
added, the A3 steel sheet was severely eroded by HCl, and the
surface became uneven with many grooves. However, in the
hydrochloric acid solution with [Bhim]CETSA (b), the surface of
A3 steel became smooth and flat without obvious corrosion
pits or trenches, and even signs of sandpaper polishing could
be clearly seen, indicating that A3 steel was effectively
protected by [Bhim]CETSA, which further confirmed the
previous experimental results.
Contact Angle Measurements
The hydrophilicity and hydrophobicity of the surface can
directly reflect the adsorption effect of [Bhim]CETSA on A3
steel surface. The optical contact angle measuring instrument
was used to test the hydrophobicity of the steel surface after
corrosion in 1M HCl solution without and with corrosion
inhibitor. Fig. 8 shows the water contact angle on the steel
surface after immersion in 1M HCl solution with different
concentration of [Bhim]CETSA. As shown in Fig. 8, after
immersion in hydrochloric acid solution without adding
Fig. 6 XPS spectra (a: survey, b: C 1s, c: N 1s, d: S 2p) from the surface of A3 steel which
was immersed in 1 M HCl containing 10 mM [Bhim]CETSA for 24 h at 298 K
Untreated A3 steel does not contain element N, and contains
only trace element of S that is not sufficient to be detected.
Since N and S elements are contained in ionic liquid
[
Bhim]CETSA, the water contact angle of the steel surface is
[
Bhim]CETSA, this indicates that the corrosion inhibitor
small, showing hydrophilicity. With the increase of the
concentration of [Bhim]CETSA in 1 M HCl solution, the contact
angle of steel surface increases gradually. When the
concentration of [Bhim]CETSA in 1 M HCl solution is 10 mM,
the contact angle of steel surface is 90 , showing obvious
hydrophobicity, which suggests that a dense hydrophobic film
of [Bhim]CETSA has been formed on the surface of A3 steel
molecule forms a layer of adsorption film on the surface of
steel sheet, which inhibits the corrosion of metal. In the Fig. 6
(b), the C 1s region can be fitted into two peaks, which located
at 284.8eV and 288.1eV. The peak at 284.8eV is mainly
attributed to C-H or C-C bonds. Another peak is attributed to
the presence of carbon impurities in the A3 steel sample. In
o
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and effectively isolated the contact between the steel surface increase of the dipole moment may have intensified the
and the corrosive medium.
View Article Online
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DOI: 10.1039/D0NJ00745E
adsorption of corrosion inhibitor and metal surface.
Therefore, the adsorption process of CETSA on A3 steel can be
regarded as the process of replacing water molecules on the
steel surface with CETSA molecules in solution.
Table 4 Frontier orbital energies and dipole moment of CETSA and Fe
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0
Molecule
CETSA
Fe
EHOMO (eV) ELUMO (eV)
μ (D)
9.39
-
-8.33
-7.81
0.03
-0.25
Fig. 8 Contact angle for A3 steel after 24 h immersion in 1 M HCl with different
concentrations of [Bhim]CETSA
Quantum Chemical Study
The internal relationship between the molecular structure and
corrosion inhibition performance can be explained by
quantum chemical calculation, which is of great significance
for the structural design and mechanism research of corrosion
inhibitors. According to the front molecular orbital theory, any
chemical reaction is due to the electronic transition caused by
the interaction between the highest occupied orbit (HOMO)
and the lowest altitude orbit (LUMO) of reactants. According
to the experimental results in Table 2, anions in ionic liquids
play a key role in corrosion inhibition. Therefore, in-depth
research on CETSA was conducted through quantum chemical
calculation, and the optimized geometric structures and the
distributions of HOMO and LUMO for CETSA are given in Fig. 9,
whereas the calculated quantum chemical parameters
including EHOMO, ELUMO, and dipole moment (μ) are reported in
Table 4. The molecular reactivity is determined by the HOMO
and LUMO of the forward orbital. EHOMO is related to the ability
of molecule to supply electron, a high EHOMO value means a
strong electron-donating ability. ELUMO represents the
molecule's ability to receive electrons, and the lower value of
57
Fig. 9 Optimized geometric structure (a) and the distributions of HOMO
b) and LUMO (c) for CETSA
5
8-
(
E
LUMO, the much easier to accept electrons for the molecule.
60
Fig. 8 shows that HOMO is mainly distributed on sulfur atom
and two carboxyl groups in CETSA molecule, while LUMO is Mechanism of Corrosion Inhibition
distributed on another carboxyl group, corresponding to the
synthesis result of ionic liquid, which only two carboxyl groups
in CETSA molecule participate in the reaction.
In general, the mechanism of corrosion inhibition in acidic
media is thought to be the adsorption of inhibitor molecules
on the metal surface to block the contact between the
corrosive medium and the metal surface, which is proved by IR
spectroscopy, XPS analysis and contact angle measurements.
The adsorption types of ionic liquid on steel surface include
physical adsorption and chemical adsorption. On the one hand,
the O atoms with lone pair electrons in LUMO orbital of CETSA
The forward orbital energy of Fe in Table 4 comes from
41
literature. The (ELUMOFe - EHOMO) is larger than (ELUMO - EHOMOFe),
indicating that the CETSA molecule is more able to accept
electrons interacting with Fe than provide electrons interacting
with Fe. The μ can be used to evaluate the polarity of
6
1
3
8,64-66
molecules, and related to the inhibitive ability. In the Table 4,
the μ of CETSA molecule is 9.39 Debye(3.13×10 C m), which
is larger than that of water molecule (6.23×10 C m). The
are easy to be protonated in acidic solution.
HCl is
-
29
+
-
completely ionized into H and Cl in aqueous solution. Under
-30
62
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-
the electrostatic action, Cl will adsorb with positively charged
metal surface and generate negative charge at the interface of
Fe and HCl solution, which is conducive to the adsorption of
protonated CETSA on steel surface, and the presence of
Acknowledgements
View Article Online
DOI: 10.1039/D0NJ00745E
This work was supported by Jilin province science and
technology development plan project (20180201019SF), and
the Doctor Startup Foundation of Jilin Institute of Chemical
Technology.
+
cationic N in ionic liquid further strengthen the trend of the
6
7,68
electrostatic adsorption,
which corresponds to the result
that the inhibition rate of [Bhim]CETSA is higher than that of
CETSA. The above description belongs to physical adsorption.
On the other hand, the [Bhim]CETSA contains heteroatom (S,
N, O) with lone electron pair and π bond, which can provide
electron to form stable coordination bond through the empty
orbit on the Fe atom, so as to achieve the adsorption
0
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3
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2
3
4
5
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7
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9
0
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Notes and references
1
2
3
4
5
A. L. Chong, J. I. Mardel, D. R. MacFarlane, M. Forsyth and A.
E. Somers, ACS Sustainable Chem. Eng., 2016, 4, 1746-1755.
E. Barmatov, T. Hughes and M. Nagl, Corros. Sci., 2015, 92
,
85-94.
69,70
effect,
which is chemical adsorption. In addition, the
J. Zhang, X. L. Gong, H. H. Yu and M. Du, Corros. Sci., 2011, 53,
3
324-3330.
inhibitor molecule may coordinate with the oxidation product
2+
X. Ma, X. Jiang, S. Xia, M. Shan, X. Li, L. Yu and Q. Tang, Appl.
Surf. Sci., 2016, 371, 248-257.
B. Donnelly, T. C. Downie, R. Grzeskowiak, H. R. Hamburg
and D. Short, Corros. Sci., 1978, 18, 109-116.
Fe to form a chelate, and the water-insoluble chelate will be
deposited on the above-mentioned formed adsorption film,
which will be further improve density of adsorption
71
membrane.
6
7
J. Cui, R. Shi and Y. Pei, Appl. Surf. Sci., 2017, 416, 213-224.
A. M. Fekry and R. R. Mohamed, Electrochim. Acta, 2010, 55
,
1
933-1939.
8
9
G. Gece, Corros. Sci., 2011, 53, 3873-3898.
E. E. Oguzie, Mater. Lett., 2005, 59, 1076-1079.
Conclusions
In summary, the principal conclusions are as follows:
(1) CETSA was successfully synthesized by thiol-ene Click
reaction and was used as anion to neutralize with 1-
butylimidazole to produce ionic liquid [Bhim]CETSA. TG
analysis showed that the ionic liquid [Bhim]CETSA had
excellent thermal stability and the isothermal TG of 13 G. Avci, Colloids. Surf. A., 2008, 317, 730-736.
[Bhim]CETSA will be further studied in future work.
(2) A novel ionic liquid [Bhim]CETSA was investigated as an
environmentally friendly and efficient corrosion inhibitor, the
results of weight loss experiment indicate that the inhibition 16 X. H. Li, S. D. Deng and H. Fu, Electrochim. Acta, 2009, 54
efficiency of [Bhim]CETSA for A3 steel in 1 M HCl solution
reached up to 90.11% when its concentration was 10 mM at
298 K.
(3) There is a synergistic effect between anions and cations of
[Bhim]CETSA, which is different from some traditional ionic 19 I. Dehri and M. Ozcan, Mater. Chem. Phys., 2006, 98, 316-
liquid inhibitors, and anions play a major role in corrosion
inhibition of [Bhim]CETSA.
(4) The adsorption of [Bhim]CETSA on the A3 steel surface
conforms to the Langmuir adsorption isotherm and has been
demonstrated by IR spectroscopy, XPS and SEM 22 H. Abdollahi, A. Ershad-Langroudi, A. Salimi and A. Rahimi,
characterization. The results of contact angle test show that
the maximum contact angle is 90 , indicating that a dense
hydrophobic film of [Bhim]CETSA has been formed on the
surface of A3 steel.
(5) The result of quantum chemical calculation shows that the 25 Z. M. Xue, L. Qin, J. Y. Jiang, T. C. Mu, and G. H. Gao, Phys.
adsorption active sites of CETSA are distributed in the whole
molecular structure, and the ability of CETSA to get electron
with Fe is stronger than that of the donor.
(6) The inhibition mechanism of [Bhim]CETSA is to form
adsorption membrane on the steel surface to block the
contact between metal and acid solution, the type of 28 A. Ehsani, M. Mahjani, M. Hosseini, R. Safari, R. Moshrefi and
adsorption is mixed adsorption, including physical adsorption
10 Y. Li, P. Zhao, Q. Liang and B. Hou, Appl. Surf. Sci., 2005, 252
,
1
245-1253.
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1
,
2
2 R. Solmaz, G. Kardas, B. Yazlcl and M. Erbil, Colloids. Surf. A.,
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1
4 S. A. Hossain and A. I. Almarshad, Corros. Eng. Sci. Tech.,
006, 41, 77-81.
5 F. L. Zeng, X. Tan, J. F. Li and Z. Zhang, Corros. Eng. Sci. Tech.,
013 48: 108-115.
2
1
2
,
4089-4098.
7 M. Abdallah, E. A. Helal and A. S. Fouda, Corros. Sci., 2006, 48
639-1654.
8 M. Abdallah, H. E. Meghed and M. Sobhi, Mater. Chem. Phys.
009, 118, 111-117.
1
1
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New Journal of Chemistry
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View Article Online
DOI: 10.1039/D0NJ00745E
A dense hydrophobic film of [Bhim]CETSA has been formed on the
surface of A3 steel and effectively isolated the contact between the steel
surface and the corrosive medium.
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