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Accepted Manuscript
Excellent corrosion inhibition performance of novel quinoline
derivatives on mild steel in HCl media: Experimental and
computational investigations
Lu Jiang, Yujie Qiang, Zulei Lei, Jianing Wang, Zhongjian Qin,
Bin Xiang
PII: S0167-7322(17)33980-6
DOI: https://doi.org/10.1016/j.molliq.2018.01.133
Reference: MOLLIQ 8587
To appear in: Journal of Molecular Liquids
Received date: 30 August 2017
Revised date: 25 December 2017
Accepted date: 23 January 2018
Please cite this article as: Lu Jiang, Yujie Qiang, Zulei Lei, Jianing Wang, Zhongjian Qin,
Bin Xiang , Excellent corrosion inhibition performance of novel quinoline derivatives
on mild steel in HCl media: Experimental and computational investigations. The address
for the corresponding author was captured as affiliation for all authors. Please check if
appropriate. Molliq(2017), https://doi.org/10.1016/j.molliq.2018.01.133
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Excellent Corrosion Inhibition Performance of Novel Quinoline Derivatives on Mild
Steel in HCl media: Experimental and Computational Investigations
Lu Jianga,b, Yujie Qianga,b, Zulei Leia,b, Jianing Wanga,b, Zhongjian Qina,b, Bin Xianga*,b
a School of Chemistry and Chemical Engineering, Chongqing University, Chongqing 400044, PR China.
b National-municipal Joint Engineering Laboratory for Chemical Process Intensification and Reaction,
Chongqing University, Chongqing 400044, PR China
. * Corresponding authors: E-mail: [email protected] TEL: [phone]
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Abstract: The inhibition performance of two synthesized quinoline derivatives: 6-benzylquinoline (BQ) and
6-(quinolin-6-ylmethyl) benzene-1,2,3,4,5-pentasulfonic acid (QBPA) on mild steel in 1 M HCl has been
investigated through weight loss, electrochemical measurements, scanning electron microscopy (SEM), and
atomic force microscopy (AFM). All experimental results indicated that BQ and QBPA extremely enhanced
the corrosion resistance of mild steel and QBPA showed a better inhibitive performance than BQ. The results
of potentiodynamic polarization illustrated that BQ and QBPA performed as mixed-type inhibitors. Langmuir
adsorption isotherm was well fitted for the adsorption of BQ and QBPA on mild steel surface with a
competitive physisorption and chemisorption mechanism. The results of quantum chemical calculations and
molecular dynamic simulations showed that benzene rings of both BQ and QBPA adsorbed on the metal
surface in distinct gradient direction and quinoline ring of both BQ and QBPA adsorbed nearly parallel on
the steel surface.
Key words: mild steel; inhibition corrosion; adsorption; electrochemistry; molecular modeling
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1 Introduction
Mild steel, which has excellent physical properties, affordability in economy and simple smelting
process, extensively applies in industrial field [1]. The main problem of mild steel is that it is easy to be
corroded in acid pickling process, causing severely financial and industrial losses. An effective way of anti-
corrosion for mild steel is the addition of corrosion inhibitors.
Many inorganic and synthetic organic compounds have been proved to be excellent corrosion inhibitors
in recent years, such as chromate [2], polyphosphates [3] and benzothiazole [4]. However, these inhibitors
often have a negative effect to both human and environment, which hinders their application. Ghulamullah
khan et al. [5] stated that toxic inhibitors may cause temporary or permanent damage like kidney or liver or
disturbing biochemical or enzyme system in body and often arise during synthesis or its applications, causing
severely security risks and economic losses. Hence, the development of environmental-friendly inhibitors is
becoming a widely discussed issue. Quinoline derivatives are crucial ingredients of anti-malarial drugs and
have special pharmacological properties [6], which has no significant toxicity to environment [7] .They are
also easy to be synthesized and cost-efficient with high inhibition performance [8]. So, quinoline derivatives
harbor remarkably practical applicability in metal anti-corrosion field.
Some scientific studies on quinoline derivatives as corrosion inhibitors have been reported in recent
years. Achary et al.[9] stated 8-Hydroxy quinoline (HQ) and 3-formyl-8-hydroxy quinoline (FQ) to be two
effective corrosion inhibitors on mild steel in 1 M HCl. Gerengi al. [10] concluded the corrosion inhibition
performance of 8-Hydroxyquinoline on copper in 0.1 M HCl and the best inhibition efficiency was only 79%
at optimal concentration 0.016M. Singh et al. [7] successfully applied a series of 1, 4-dihrdroquinoline
derivatives as corrosion inhibitors for mild steel and demonstrated that methoxy group enhanced the
corrosion inhibition efficiency. However, to the best of author’s knowledge, most investigated quinoline
derivatives exhibit low corrosion inhibition efficiencies.
Here, two quinoline-based inhibitors namely, 6-benzylquinoline (BQ) and 6-(quinolin-6-ylmethyl)
benzene-1, 2, 3, 4, 5-pentasulfonic acid (QBPA) were synthesized and identified by Fourier Transform
Infrared Spectroscopy (FT-IR) and Hydrogen Nuclear Magnetic Resonance Spectroscopy (1H NMR).
Afterwards, weight loss and electrochemical measurements were implemented to investigate the performance
of the inhibitors on the corrosion of mild steel in 1 M HCl. The surface morphologies of samples were
analyzed utilizing scanning electron microscopy (SEM) and atomic force microscope (AFM) technique.
Quantum chemical calculations and molecules dynamics (MD) simulations were implemented to explain the
inhibition mechanism of these two organic molecules.
2. Experimental
2.1. Synthesis and characterization of corrosion inhibitors
Fig. 1 shows the synthetic route of the studied inhibitors. The intermediate product 6-benzylquinoline
(BQ) was prepared by an ice-water bath added quinoline and benzyl chloride (molar ratio 1:1). After 1 hour
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reaction, the reagents were washed with 10 mL ethyl acetate and a small amount of sodium iodide, then
heated to room temperature (298K) for 9 h and then heated to 338K for 27 h. The resulting solution was
purified by washing, filtering with ethyl acetate and dried in vacuum.
6-(Quinolin-6-ylmethyl) benzene-1,2,3,4,5-pentasulfonic acid (QBPA) was synthesized by reacting the
mixture of intermediate product BQ and concentrated sulfuric acid (molar ratio 1:5) in an ice-water bath for
2 h and then heated to 338K for 4 h. The product was percolated, swashed with ethyl acetate and desiccated
in vacuum.
Fig. S1 shows the FT-IR and 1H NMR spectrums of BQ and QBPA. For BQ: light red, solid, yield =
82%. 1H NMR (400 MHz), δ (ppm) (Fig. 2a): 3.5144 (m, 2H, ArCH2), 7.1918 (t, 2H, ArCH2CCHCH),
7.2924 (d, 2H, ArCH2CCH and NCHCH), 7.8075 (t, 1H, Ar-H), 7.9603 (m, 2H, Ar-H), 8.2243 (d, 2H, Ar-
H), 9.0438 (d, 1H, NCHCHCH-), 9.2104 (d, 1H, NCH-). FT-IR (KBr pellet) (Fig. 2c): 2922.9 and 2852.0
cm-1 (ν C-H, aliphatic fatty chain), 1032.6-1230.6 cm-1 (ν C-N, fatty amines) and 3060.1-3254.2 cm-1 (ν C-H,
aromatic). For QBPA: red, liquid, yield= 63%. 1H NMR (400 MHz), δ (ppm) (Fig. 2b): 3.3532 (m, 5H, SO3H),
3.9652 (m, 2H, ArCH2), 7.1901 (t, 2H, ArCH2CCHCH), 7.2903 (t, 2H, ArCH2CCH and NCHCH) 9.0481
(d, 1H, NCHCHCH-), 9.2019 (d, 1H, NCH-). FT-IR (KBr pellet) (Fig. 2d): 1355.2 and 1192.8 cm-1 (νR-SO2-
OH), 1022.8 cm-1 (ν C-N, fatty amines), 2920.6 and 2850.5 cm-1 (ν C-H, aliphatic fatty chain), 2976.6-3260.9
cm-1 (ν C-H, aromatic).
2.2. Materials and reagents for inhibition tests
The size of mild steel was 3 cm ×2 cm ×1 cm for weight loss measurements and 0.5 cm ×0.5 cm ×0.5
cm for surface analysis while the exposed area of electrochemical experiments was 1 cm2. Before the tests,
all specimens were carefully polished by a sequence of emery papers of grade Nos. 400, 800, 1200 and 2000,
and then rinsed with distilled water, degreased with absolute ethyl alcohol and finally dried at room
temperature.
Analytical grade HCl (37.5%, purchased in Chongqing Chuandong Chemical Co., LTD) was diluted
with distilled water to acquire the test solution.
2.3. Weight loss experiments
In this study, weight loss experiments were taken according to the standard methods [11]. The corrosion
parameters (corrosion rate CRW, the surface coverage θ, corrosion inhibition efficiency ηW) were calculated
using the following equations [12, 13]:
St WW St
ΔW
C21
RW 
(1)
ο
RW
RW
ο
RW
CCC
θ
(2)
100
CCC
%ηο
RW
RW
ο
RW
W
(3)
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