New Epoxy sugar based glucose derivatives as eco friendly corrosion inhibitors for the carbon steel in 1.0 M HCl: Experimental and theoretical investigations

Article abstract of DOI:10.1016/j.jallcom.2020.154949

In this study, we chose to synthesize new sugar based glucose derivatives as ecological corrosion inhibitors for carbon steel in acidic medium. The products obtained in the form of syrupy liquids, and the purity of obtained compounds was characterized by NMR spectroscopy analysis. The corrosion inhibition activities for both compounds were evaluated by electrochemical and rheological methods. Thus, the results of the experimental tests have been confirmed by theoretical studies (DFT, MC and MD simulations). The surface study of carbon steel has been characterized by the scanning electron spectroscopy (SEM). The gravimetric solutions were identified using UV-Vis spectroscopy and Inductively Coupled Plasma-Optical Spectroscopy (ICP-OES).

Full text of DOI:10.1016/j.jallcom.2020.154949

Journal Pre-proof
New Epoxy sugar based glucose derivatives as eco friendly corrosion inhibitors for
the carbon steel in 1.0ꢀM HCl: Experimental and theoretical investigations
M. Rbaa, P. Dohare, A. Berisha, O. Dagdag, L. Lakhrissi, M. Galai, B. Lakhrissi, M.
Ebn Touhami, I. Warad, A. Zarrouk
PII:
S0925-8388(20)31312-8
DOI:
https://doi.org/10.1016/j.jallcom.2020.154949
JALCOM 154949
Reference:
To appear in: Journal of Alloys and Compounds
Received Date: 29 January 2020
Revised Date: 24 March 2020
Accepted Date: 25 March 2020
Please cite this article as: M. Rbaa, P. Dohare, A. Berisha, O. Dagdag, L. Lakhrissi, M. Galai, B.
Lakhrissi, M.E. Touhami, I. Warad, A. Zarrouk, New Epoxy sugar based glucose derivatives as eco
friendly corrosion inhibitors for the carbon steel in 1.0ꢀM HCl: Experimental and theoretical investigations,
Journal of Alloys and Compounds (2020), doi: https://doi.org/10.1016/j.jallcom.2020.154949.
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CRediT authorship contribution statement
M. Rbaa
: Investigation, Writing - original draft.
P. Dohare : Investigation, Writing - original draft.
A. Berisha : Investigation, Writing - original draft.
O. Dagdag : Investigation, Writing - original draft.
L. Lakhrissi : Investigation, Writing - original draft.
M. Galai
: Investigation, Writing - original draft.
B. Lakhrissi : Conceptualization, Writing - original draft, Writing - review &
editing.
M. Ebn Touhami: Conceptualization, Writing - original draft, Writing - review
& editing.
I. Warad
: Conceptualization, Writing - original draft, Writing - review &
editing.
A. Zarrouk : Conceptualization, Writing - original draft, Writing - review &
editing.

New Epoxy sugar based glucose derivatives as eco friendly
corrosion inhibitors for the carbon steel in 1.0 M HCl:
Experimental and theoretical investigations
a
b
c
a
a
d
M. Rbaa , P. Dohare , A. Berisha O. Dagdag , L. Lakhrissi , M. Galai , B.
,
Lakhrissi a, M. Ebn Touhami d, I. Warad e, A. Zarrouk f
aLaboratory Agro-Resources, Polymers and Process Engineering, Department of Chemistry, Faculty
of Sciences, Ibn Tofail University, PO Box 133, 14000, Kenitra, Morocco.
bDepartment of Chemistry, Indian Institute of Technology (BHU), Varanasi-221005, India.
cDepartment of Chemistry, Faculty of Natural and Mathematics Science, University of Prishtina,
10000 Prishtina, Kosovo.
dLaboratory of Materials Engineering and Environment: Modeling and Application, Faculty of
Science, Ibn Tofail University BP. 133-14000, Kenitra, Morocco.
eDepartment of Chemistry and Earth Sciences, PO Box 2713, Qatar University, Doha, Qatar.
fLaboratory of Materials, Nanotechnology and Environment, Faculty of Sciences, Mohammed V
University, Av. Ibn Battuta. B.P 1014, Rabat, Morocco.
✉Corresponding authors
Prof. Abdelkader ZARROUK
E-mail: azarrouk@gmail.com
Phone: 00212665201397
http://orcid.org/0000-0002-5495-2125
Dr. Mohamed Rbaa
E-mail: mohamed.rbaa10@gmail.com.
Phone: 00212682988498
http://orcid.org/0000-0003-1235-890X
1

Abstract
In this study, we chose to synthesize new sugar based glucose derivatives as ecological
corrosion inhibitors for carbon steel in acidic medium. The products obtained in the form of
syrupy liquids, and the purity of obtained compounds was characterized by NMR
spectroscopy analysis. The corrosion inhibition activities for both compounds were evaluated
by electrochemical and rheological methods. Thus, the results of the experimental tests have
been confirmed by theoretical studies (DFT, MC and MD simulations). The surface study of
carbon steel has been characterized by the scanning electron spectroscopy (SEM). The
gravimetric solutions were identified using UV-Vis spectroscopy and Inductively Coupled
Plasma-Optical Spectroscopy (ICP-OES).
Keywords: Synthesis; Rheological methods; Eco friendly corrosion inhibitors;
Electrochemical techniques; SEM; MD simulations.
2

1. Introduction
The assessment of corrosion of steel and the presentation of the solutions has been a question
of great interest in most of the metal industrial sectors [1]. Therefore, improving the
mechanical properties of these metals is of great interest in a wide range of disciplines. For a
long time, researchers presenting solutions for this unwanted phenomenon, among the most
cost-effective proposals presented are the protection from the organic or inorganic chemical
inhibitors. In addition, the chemical inhibitors are very profitable for the corrosion inhibition
of steel, especially in acidic media, like hydrochloric acid and sulfuric acid medium [2-10].
By way of example, we have found heterocyclic inhibitors which are effective in inhibiting
corrosion of steel in an acid medium, such as 8-hydroxyquinoline and its derivatives,
benzimidazole derivatives, quinoxaline derivatives [11-13]. However, the problem of these
heterocycles presents a little signs of both toxicity for the environment [14]. Also, the
application of synthetic compounds as corrosion inhibitors is limited because of the increasing
ecological awareness and strict environmental regulations as most of the traditional corrosion
inhibitors are synthesized using expensive and toxic chemicals and solvents. In view of this,
recently, Glucose and their derivatives are being used as corrosion inhibitors as they are
available at the economic and commercial level [15]. Because of the natural and biological
origin, they can be regarded as one of the greenest sources of the chemical compounds used as
corrosion inhibitors. More so, the presence of numerous polar functional groups such as –OH
further enhance their corrosion inhibition effectiveness by increasing their molecular size as
well as increase solubility in the polar electrolytes. These polar functional groups can also
serve as adsorption centers during the meta-inhibitor interactions. Looking the greenness of
glucose and their derivatives along with their high protection efficiency, the synthesis,
characterization and utilization in all fields of science and technology, including in the area of
metallic corrosion inhibition should be further explored [16]. The ecological inhibitors have
3

been the subject of many published studies for corrosion inhibition in acidic medium. In
addition, the ecological inhibitors have two major advantages, the first effective corrosion
inhibition and the second do not affect the environment [17]. The ecological inhibitors are of
natural in origin, such as oils and seeds of medicinal plants, or of synthetic origin, such as
glucose, mannose and fructose [18,19]. However, the advantage of sugar-based compounds
remains the best ecological inhibitors because their degradations in the media always give
basic molecules, which is the simple sugar (glucose, mannose or fructose). According to the
literature, glucose and its derivatives are not toxic to nature and living beings. In addition,
glucose is widely used in the hospitals field as a potential drug, especially in the form of
syrup. In addition, glucose is used to prevent the crystallization of sugar, nougatine, boiled
sweets, soft caramels, fruit pastes, gums and marshmallows [20,21].
In this work, we focused on the synthesis and presentation of newly synthesized glucose
derivatives as ecological inhibitors of carbon steel in molar hydrochloric acid. The study of
corrosion inhibiting power is approved using the rheological methods and electrochemical
methods (impedance spectroscopy and potentiodynamic polarization). The experimental
results have been confirmed by theoretical studies (calculates DFT, MC and MD simulations).
The surface study of the carbon steel after the corrosion was characterized by the scanning
electron spectroscopy (SEM). The gravimetric solutions were analyzed using UV-Vis
spectroscopy and Inductively Coupled Plasma-Optical Spectroscopy (ICP-OES).
2. Material and methods
2.1. Chemical study
All instruments, reagents, and the used solvent for the preparation of these compounds have
been published in a previous work [22]. The NMR spectra were carried out on a BRUKER
1
AM 300 spectrometer operating in Fourier transform at the frequency of 300.13 MHz for H
4

13
NMR and 75.47 MHz for C NMR. The associated calculator is an Aspect 3000 using the
BRUKER 1986 software (DI6R 861). The compound is dissolved in a proportion of 40 to 100
mg in 0.2 to 0.5 ml of deuterated solvent (DMSO). Tetramethylsilane (TMS) is used as a
fictitious reference, different control tubes used to regularly calibrate the apparatus by fixing
the SR (Spectrum Reference).
The synthesis of glucose-derived inhibitors was performed under specific conditions in five steps
(Figure 1).
Figure 1. Synthesis of 5,6-anhydro-3-O-dodecyl-1,2-O-isopropylidene-α-D-glucofuranose (G-
C12) and 5,6-anhydro-3-O-hexadecyl-1,2-O-isopropylidene-α-D-glucofuranose (G-C6)
General procedure for organic synthesis
To a solution of tosylated substrates (5 a, b) (220 g L-1) in the dioxane-water mixture (9: 1)
were added 2.4 equivalent of sodium hydroxide. The reaction mixture is stirred for 1 h at
room temperature and TLC monitors the reaction. After filtration, the reaction mediums are
neutralized with a saturated aqueous solution of ammonium chloride and extracted twice with
toluene. The combined organic phases are dried over sulfate of anhydrous sodium, filtered
5

and the filtrate is evaporated under reduced pressure. The reaction crude is chromatographed
on a column of silica gel (eluent gradient: hexane acetone) to give the compounds G-C6 and
G-C12 in the form of syrupy liquids, whose structure and purity were later confirmed by 13C
and 1H NMR spectroscopic analyzes.
2.2. Electrochemical and rheological test
The corrosion inhibition effect of the G-C6 and G-C12 on carbon steel corrosion in 1.0 M HCl
first of all demonstrated using electrochemical methods. The electrochemical studies were
carried out using conventional three electrode system in which platinum rod, saturated
calomel and carbon steel specimen are used as a counter, reference and working electrodes,
respectively. The electrochemical impedance spectroscopic (EIS) studies were carried out at
OCP (Open Circuit Potential) in the frequency range of 100 KHz−100 mHz, with 10 points
per decade. The EIS data were fitted in a suitable equivalent circuit to get values of
polarization resistance (Rp).
Potentiodynamic polarization (PDP) studies on the corrosion of carbon steel in 1.0 M HCl
with and without G-C6 and G-C12 were carried out by recording the anodic and cathodic Tafel
curves in the potential range of -800 mV to -200 mV with respect to the potential of SCE
(saturated calomel electrode) with a scan rate of 0.5 mV s−1.
The inhibition efficiencies were calculated using following equations (1,2): respectively, for
the potentiodynamic polarization and electrochemical impedance spectroscopy techniques.
ic0orr −icorr
ηPP
=
×100
(1)
ic0orr
icorr and ic0orr are the corrosion current density with and without the addition of inhibitors (G-C6
and G-C12).
Rp − Rp0
ηEIS
=
×100
(2)
Rp
6

Rp and Rp0 are the polarization resistance with and without the addition of inhibitors (G-C6
and G-C12).
The material used in this study was a carbon steel with a chemical composition (in
wt%) of C, 0.11; Si, 0.24; Mn, 0.47; Cr, 0.12; Mo, 0.02; Ni, 0.1; Al, 0.03; Cu, 0.14; Co, <
0.012; V, < 0.003; W, 0.06; Fe, balance. The steel samples were pre-treated prior to the
experiments by grinding with emery paper SiC (120, 400, 600 and 1200); rinsed with distilled
water, degreased in acetone in an ultrasonic bath immersion for 5 min, washed again with
bidistilled water and then dried at room temperature before use. The acid solutions (1.0 M
HCl) were prepared by dilution of an analytical reagent grade 37 % HCl with double distilled
water. The concentration range of G-C6 and G-C12 employed in this study was 10-6 M to
10-3 M.
The rheological study has been detailed in another work that is already published [23].
2.3. Surface characterization
The surface morphology was studied using an SEM instrument (JOEL model JSM-5500
microscope). UV-Vis [Jenway ultraviolet-visible spectrophotometer (series 67)] technique
was utilized to investigate the formed complexes.
2.4. DFT, Monte Carlo and Molecular Dynamic Simulations
The DFT, Monte Carlo (MC) and Molecular Dynamics (MD) and calculation were performed
using Materials Studio 7.0 [24].
DFT calculations were performed using the DMol3 software (within the Materials Studio). All
electron calculations are employed for geometry optimization with the double numerical plus
polarization basis set (DNP) [25]. The exchange-correlation energy is described by the
Perdew–Burke–Ernzerhof functional within the generalized gradient approximation
(GGA/PBE). All energy minima were characterized by performing a vibrational analysis to
ensure the lack of imaginary frequencies [26].
7

For MC the interaction between iron surface and the inhibitor in the simulated corrosion
media is approximated using the slab model of Fe (110) with periodic boundary conditions
[using a Fe unit cell, cleaved at h k l (1 1 0) plane and expanded 10x10 with the addition of an
30 A vacuum layer at C axis) containing 700 water molecules/one inhibitor molecule (either
G-C6 or G-C12 /25 hydronium+25 chloride ions. The Metropolis Monte Carlo method was
used to evaluate the adsorption configurations [COMPASS II force field, (energy
convergence tolerance of 2 × 10−5 kcal/mol, force convergence tolerance of 0.001
kcal/mol/A)] of the interaction between the molecules and the substrates.
The MD simulations with the Forcite Module (Materials Studio) were accomplished using
COMPASS II (Condensed-phase Optimized Molecular Potentials for Atomistic Simulation
Studies) force field with the atom charges assigned from GGA/PBE calculations [27]. Prior
to the use of MD simulations, the slab model containing the corrosion media and the inhibitor
molecule is optimized using the Smart optimization algorithm with the energy convergence
criteria of 10−4 kcal/mol and force criteria of 5 × 10−3 kcal/mol/Å. MD was conducted using
an NVT (constant-temperature, constant-volume) canonical ensemble at 298 K. The time step
for MD was 1fs with a total simulation time of 500 ps (5 × 105 steps). The system temperature
was controlled using a Berendsen Thermostat (0.1 ps decay constant). For the Radial
Distribution Function (RDF) analysis, 500 ps of trajectory frames were used.
3. Result and discussion
3.1. Chemistry
3.1.2. Spectral data and physicochemical characterizations of compounds
5,6-anhydro-3-O-dodecyl-1,2-O-isopropylidene-α-D-glucofuranose (G-C12)
R (%) 89; Formula brute C21H38O5; M 370.54; 25 (CHCl
) -41.7 (c = 0.7).
[α]D
3
8

1H NMR (300 MHz, DMSO-d6) (δppm): 0.87 (s, 3 H, CH3), 3.62-3.85 (m, 31 H, CH2-
carbon chain), 1.25-1.51 (d, 6 H, 2 CH3), 2.83-3.10-4.64-5.86 (d, 4 H, CH-glucose function).
13C NMR (75 MHz, DMSO-d6) (δppm): 110.84 (2 C(CH3)2), 22.07, 25.43 (2 C(CH3)2),
13.91 (CH3-carbon chain), 80.53-82.06 (CH-glucose function). 25.98-31.27 (CH-carbon
chain).
5,6-anhydro-3-O-hexyl-1,2-O-isopropylidene-α-D-glucofuranose (G-C6
)
R (%) 92; Formula brute C15H26O5; M 286.37; 25 (CHCl
[α]D
3
) -25.1 (c = 0.7). 1H: δppm 0.80 (s, 3
H, CH3-carbon chain), 1.19-2.45 (s, 6 H, CH2-carbon chain), 2.65-3.03 (s, 6 H, CH3- glucose
function), 3.42-3.80 (m, 4 H, CHglucose), 5.79 (s, 1 H, CH glucose function). 13C: δppm 13.86 (CH3-
carbon chain), 22.05-26.51 (CH2-carbon chain), 28.65-29.14 (CH3-glucose function), 45.57-
82.09 (CH-glucose function), 110.80 (C-OHglucose).
3.2. Rheological Study
The viscosities of the two compounds G-C6 and G-C12 as a function of shear rate in the
temperature range of 298-328 K as shown in Figure 2. The results derived from viscosity
measurements demonstrate that G-C6 and G-C12 work as Newtonian liquids and their
viscosities are independent to the shear rate from 0.01 to 200 s-1. The evolutions of the
viscosity for compounds G-C6 and G-C12 at different temperature permitted the estimate of the
viscosity activation energy (Ea (kJ/mol)). The Ea values for G-C6 and G-C12 were calculated as
follows [23].
Ea


η
T =
( )
η
0 exp −
(4)



RT

Where Viscosity (
η
) (Pa.s), η0 is a constant, R the gas constant (8.314 J/mol K) and T in K.
Arrhenius plots for the viscosity were given in Figure 3. Values of Ea for compound G-C6
and G-C12 were estimated from the slope of Ln ( ) vs. 1/T. The activation energy for
η
compounds G-C6 and G-C12 are respectively equal to 26.48 and 38.65, respectively. The
9

results show that, the Ea for G-C12 is the highest. These energies are then grouped together in
Table 1. We note that the higher the activation energy the higher the viscosity [23].
80
G-C12-298 K
60
G-C12-308 K
G-C12-318 K
G-C12-328 K
40
η
20
0
50
100
150
200
Shear rate (s-1)
50
40
30
20
10
G-C6-298 K
G-C6-308 K
G-C6-318 K
G-C6-328 K
η
50
100
150
200
Shear rate (s-1)
Figure 2. Viscosity measured as a function of shear for compounds G-C6 and G-C12 at
different temperature.
10

G-C6
4.2
3.9
3.6
3.3
3.0
2.7
2.4
G-C12
D Fittig data
η
3.00 3.05 3.10 3.15 3.20 3.25 3.30 3.35 3.40
1000/T (K-1)
Figure 3. The relationship between Ln (η) and 1/T for compounds G-C6 and G-C12 at different
temperature.
Table 1. Activation parameters for compounds G-C6 and G-C12
.
R2
Ea
(kJ/mol)
0.91948
0.99139
26.48
38.65
G-C6
G-C12
3.2. Electrochemical Study
3.2.1. PDP study
Polarization measurements have been carried out in order to gain knowledge concerning the
kinetics of the anodic and cathodic reactions. Typical potentiodynamic polarization curves of
the carbon steel in 1.0 M HCl solutions without and with the addition of different
concentrations of G-C6 and G-C12 are shown in Fig. 4. Electrochemical kinetic parameters
(corrosion potential (Ecorr), corrosion current density (icorr), cathodic and anodic Tafel slope
(βc and
β
a), determined from these experiments by extrapolation method, are reported in
Table 2
.
11

103
102
101
100
10-1
10-2
10-3
10-4
Blank solution
10-3 M of G-C12
10-4 M of G-C12
10-5 M of G-C12
10-6 M of G-C12
-0.8
-0.6
-0.4
-0.2
E (V/SCE)
103
102
101
100
10-1
10-2
10-3
10-4
10-5
Blank solution
10-3 M of G-C6
10-4 M of G-C6
10-5 M of G-C6
10-6 M of G-C6
-0.8
-0.6
-0.4
-0.2
E (V/SCE)
Figure 4. The polarization curves in the absence and in the presence of the compounds G-C6
and G-C12
Table 2. The values of the electrochemical parameters associated with the polarization study.
Medium Conc.
-Ecorr
(mV vs. SCE)
icorr
Tafel slopes
(mV dec-1)
ηpp
(%)
(M)
(µA cm-2)
-βc
βa
0
457.7
405.8
486.3
485.9
420.3
551.3
79.7
77.7
46.4
17.4
114.8
168.8
109.3
133.2
114.5
102.0
76.0
95.6
67.6
44.3
──
Blank
G-C12
10-6
10-5
10-4
10-3
85.5
85.9
91.6
96.8
12

10-6
10-5
10-4
10-3
488.3
476.8
448.0
482.7
136.0
127.5
49.3
169.4
141.0
94.9
95.4
62.1
73.2
115.6
75.3
76.9
91.0
94.4
G-C6
30.9
114.1
As it can be seen, the anodic and cathodic reactions are affected by the addition of G-C6 and
G-C12. Thus, the addition of the inhibitor reduces the carbon steel dissolution as well as
retards the hydrogen evolution reaction. In addition, the parallel cathodic Tafel curves in Fig.
4 show that the hydrogen evolution is activation-controlled and the reduction mechanism is
not affected by the presence of the inhibitor [28]. The addition of the compounds causes a
slight change in the corrosion potential values (Ecorr) and the cathode slopes (βc). Also, the
difference between two successive values of corrosion potential lower than -85 (mV/SCE).
This explains that the two compounds act as inhibitors of the mixed type [28]. Meanwhile, the
inhibition degree for anodic reaction was lower than that for anodic reaction, implying the
cathodic reaction was principally restrained.
The addition of the inhibitors (G-C12 and G-C6.) causes a decrease in the corrosion current
densities, hence an increase in inhibition efficiencies. The inhibitory efficiency is of the order
of 96.8 %, 94.4 %, respectively for G-C12 and G-C6
.
The order of efficiency (G-C12 and G-C6) for the two compounds can be explained by the
carbon chain (-C12H25) carried on the compound G-C12
.
3.2.2. EIS study
Electrochemical impedance spectroscopy experiments were carried out on a newly polished
steel surface in acidic solution without and with the addition of G-C12 and G-C6at open circuit
potential at 298 K. Fig. 5 show impedance spectra, as Nyquist and Bode plots obtained for
carbon steel in the absence and the presence of different concentrations of G-C12 and G-C6
.
The Nyquist plots show a single depressed capacitive semicircle for both inhibited and
uninhibited solutions, with one capacitive time constant in the Bode-phase plots. The
13

depressed semicircle in Nyquist diagrams is characteristic of solid electrodes that exhibit
frequency dispersion due to the roughness and other inhomogeneities of the surface [29].
Also, the slopes of the Bode-modulus plots (Log|Z| vs Log f) are not equal to -1 (Fig. 5),
which are commonly observed for solid electrodes as a result of frequency dispersion of
interfacial impedance. As the increase of inhibitor concentration, the radius of capacitive arc
showed an uptrend, this was due to the surface of the steel was covered by more inhibitor
molecules. That is to say, the compactness of protective film was improved as the inhibitor
concentration increased.
3.0
Blank solution
600
450
300
150
0
(b)
0
G-C
(a)
10-3 M of G-C12
12
2.5
2.0
10-4 M of G-C12
10-5 M of G-C12
10-6 M of G-C12
-20
-40
0.4 Hz
1.5
1.0
0.5
100 KHz
2 Hz
Blank
10-6 M
10-5 M
10-4 M
-60
-80
10-3 M
Fittingcurves
0.0
-1
0
1
2
3
4
5
0
150
300
450
600
Log f (Hz)
Zre (&
cm2)
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Blank solution
600
(b)
G-C
0
-3
6
10 M of G-C6
(a)
-4
10 M of G-C6
-5
10 M of G-C6
7.93 Hz
-20
-40
-60
-80
450
300
150
0
-6
10 M of G-C6
2 Hz
Blank
100 KHz
10-6
10-5
10-4
10-3
M
M
M
M
0.1 Hz
Fitting curves
-1
0
1
2
3
4
5
0
150
300
450
600
Log f (Hz)
Zre (ꢀ
cm2)
14

Figure 5. The steel curves obtained by impedance spectroscopy without and with the addition
of G-C12 and G-C6 : Nyquist diagrams and : Bode and phase plots).
(a
b
The equivalent circuit model was fitted with a simple Rs(RpCPE) electrical model due to one-
time constant in the Bode phase plots and the result was shown in Figure SI2.
By statistics, the parameter was presented in Table 3. Among them, Rs was the solution
resistance, Rp denoted the polarization resistance. CPE was the constant phase angle element,
representing the capacitive property of electric double layer [30]. The CPE could be
calculated by equation 5 [31]:
1
ZCPE
=
(5)
n
Y jw
(
)
Thereinto, Y, w, j and n represent the CPE magnitude, angular frequency, imaginary root and
error parameter, respectively. When the n was -1, 0, 0.5 and 1, the CPE could represent an
inductor, resistor, Warburg impedance and capacitor, respectively. The Cdl was obtained from
the equation 6 [32]:
n−1
C = Y 2
π
f
(6)
(
)
dl
where f is the frequency at the maximum value of the imaginary part in EIS image. The n
value could be used to reflect the surface roughness.
Table 3. The values of the electrochemical parameters associated with the impedance
spectroscopy.
Comps
C
(M)
Rs
Rp
Cdl
ndl
Q
ȠEIS
%
θ
(ꢀ
cm2)
(ꢀ
cm2)
(µFcm-2 )
(µF Sn-1)
Blank
G-C12
00
1.22±0.02 034.85±0.43 117.1
0.82±0.06 315.1±2.8 ──
──
10-6 1.83±0.03 254.10±0.44 60.03
10-5 2.50±0.06 351.10±0.44 44.83
10-4 1.98±0.02 446.90±0.44 30.32
10-3 2.17±0.02 633.20±0.43 24.67
10-6 1.39±0.01 191.50±0.51 51.81
10-5 2.24±0.03 263.40±0.51 43.98
10-4 2.52±0.03 364.00±0.43 41.83
10-3 2.02±0.02 608.60±0.43 29.72
15
0.85±0.05 112.0±0.5 86.3 0.863
0.86±0.05 079.4±1.2 90.1 0.901
0.83±0.05 063.0±0.5 92.2 0.922
0.84±0.05 048.0±0.5 94.4 0.944
0.89±0.05 085.0±2.6 81.8 0.818
0.88±0.05 073.0±1.5 86.8 0.868
0.88±0.05 068.0±1.0 90.4 0.904
0.88±0.05 046.3±0.4 94.3 0.943
G-C6

It can be seen that the n value in the blank solution was the lowest, indicating that the surface
roughness was the highest. As the increase of inhibitor concentration, the n value presented a
downtrend. This was due to the inhibitor adsorbed on the surface of steel and then decreased
the surface homogeneity [33].
The examination of the results in Table 3 indicating that the values of the polarization
resistance (Rp) increase with the addition of the inhibitor compounds G-C12 and G-C6 that are
attributed due to the adsorption of the compounds on to the metal surface [34]. Decreased in
double layer capacity (Cdl) values in the presence of G-C12 and G-C6 are attributed due to the
decrease in dielectric constant and the improvement of the thickness of the electrical double
layer or the combination of both [34]. The inhibition efficiencies obtained in the study of
impedance spectroscopy are of the following order of 94.4 % for the compound G-C12 and
94.3 % for the compound G-C6.The results obtained in the study of impedance confirm the
results found in the potentiodynamic polarization (G-C12 > G-C12)
.
3.2.3. Temperature effect, activation and adsorption parameters
The temperature is essential for the completeness of the studies of the carbon steel corrosion
in the acidic medium, especially in the hydrochloric acid at a range of 238-328 K [35]. The
results of the effect of temperature help us to calculate the several activation and adsorption
parameters such as, activation energy (Ea), activation enthalpy (
ꢀHa) entropy activation (ꢀSa)
and adsorption entropy (
∆
Ga°ds ). These activation and adsorption parameters give us more
important information on the adsorption mechanism and the adsorption mode [35]. Figure SI3
show polarization curves at different temperatures range (238-328 K) without and with the
addition of G-C12 and G-C6. Moreover, the parameters of temperature, activation and
adsorption are given in Table 4a
.
16

Table 4a. Temperature effect, activation and adsorption parameters
−∆Ga°ds
(kJ mol-1)
Temp
(K)
-Ecorr
icorr
-βc
βa
ƞPDP Ea
%
ꢀHa
ꢀSa
mV/SCE µA/cm² mV dec-1
mV dec-
kJ mol-1
kJ mol-1 J mol-1 K-1
1
Blank
298±2
308±2
318±2
328±2
G-C12
298±2
308±2
318±2
328±2
G-C6
496.3
491.0
475.0
465.0
551.3
1200
1450
2200
43.4
184.0
71.0
39.0
──
──
──
──
35.44
──
32.84
──
── ──
-81.24
──
──
112.0
124.0
118.0
161.0
──
──
──
-44.09
-42.68
420.3
481.2
464.4
512.2
17.4
94.4
120.5
352.9
114.5
141.7
158.9
139.0
44.3
101.1
73.9
96.8 75.57
92.1 ──
91.7 ──
84.0 ──
72.99
──
──
-25.90
──
──
117.7
──
──
298±2
308±2
318±2
328±2
482.7
475.0
504.2
471.0
30.9
114.1
149.0
139.8
151.9
115.6
93.0
79.7
94.4 72.33
91.4 ──
81.2 ──
80.5 ──
69.73
──
──
-18.70
──
──
103.2
272.2
428.5
139.6
──
──
Table 4a shows that the current density values increase with the addition of
G-C12 and G-C6 compounds. Hence, a slight decrease in inhibition efficacy for both
compounds, but still the two compounds remains effective at high temperature. The activation
and adsorption parameters such as, activation energy of corrosion (Ea), activation enthalpy of
corrosion (
ꢀ
Ha) entropy activation of corrosion (
ꢀSa) and the standard Gibbs free energy of
adsorption (
∆
Ga°ds ) are calculated by the following equations (7-10) [36-39]
−E


a
i
= Aexp
(7)
(8)
corr




RT












RT
∆
Sa
∆
Ha
icorr
=
exp
exp
Nh
R
RT
°




1
−∆Gads
(9)
Kads
=
=
exp


55.5
RT
Cinh
1
+ C inh
(10)
θ
Kads
17

The activation energy (Ea) was calculated by the variation of Ln (icorr) = f (1 / T) (Figure SI4).
Ha and Sa are also calculated by extrapolation of the Arrhenius equation and the variation
of Ln (icorr / T) = 1000 / T (Figure SI5). To obtain the best model to describe the adsorption of
the inhibitor studied, the Cinh/ curve as a function of the Cinh concentration of G-C12 and G-
ꢀ
ꢀ
θ
C6 must be linear, this shows an adsorption of G-C12 and G-C6 on the surface of steel. in 1.0
M HCl with a correlation coefficient greater than 0.9999 (Figure SI6).
From Table 4a, the activation energy values (Ea) for both compounds are larger than those of
1.0 M HCl. This explains the presence of an energy barrier involved after the addition of the
compounds [40]. In addition, the positive values of the activation enthalpy (ꢀHa) in the
presence of the glucose-derived compounds indicates inhomogeneity of the surface after
addition of the compounds. Also, that the reaction is endothermic [40]. The most positive
values of the entropy of activation (ꢀSa) show that the two inhibitors are well absorbed on the
surface of the steel [41]. The standard Gibbs free energy of adsorption ( ∆Ga°ds ) values for both
compounds are greater than -40 kJ/mol. According to the literature, these two compounds are
adsorbed on the surface of the steel by chemical mode of adsorption (chemisorption) [41].
Table 4b reports the type and corrosion mechanism inhibition for some selected
8-hydroxyquinoline derivatives recently used as corrosion inhibitors in hydrochloric acid
medium compared with two newly syntheses compounds.
Table 4b. Inhibitors performance of novel quinoline derivatives used as corrosion inhibitors
for mild steel in 1.0 M HCl medium from impedance spectroscopy measurements.
Compounds
Materials
Inhibition
Efficiency (*)
94.4 %
Adsorption
isotherm
Inhibitor
type
Ref.
3-((8-hydroxyquinolin-5-
yl)-methyl)-2-
Langmuir
Mixed
type
[20]
phenylquinazolin-4(3H)-
one
18

3-((8-hydroxyquinolin-5-
yl)-2-(4-nitrophenyl)-
95.9 %
Langmuir
Langmuir
Mixed
type
[20]
[11]
quinazolin-4(3H)-one
5-((4, 5-dihydro-oxazol-2-
yl) methyl) quinolin-8-ol
(QDO)
97.40 %
anodic
type
5-((4, 5-dihydro-imidazol-
2-yl) methyl) quinolin-8-ol
(QIM)
91.82 %
94.4 %
Langmuir
Langmuir
[11]
anodic
type
5,6-anhydro-3-O-
hexadecyl-1,2-O-
Mixed
type
This work
isopropylidene-α-D-
glucofuranose (G-C6)
5,6-anhydro-3-O-
dodedecyl-1,2-O-
96.8 %
Langmuir
Mixed
type
This work
isopropylidene-α-D-
glucofuranose (G-C12)
The glucose derivatives used in this study are ecological non-toxic and biodegradable because
it is a natural origin (Glucose). In addition, our compound is more effective compared to the
other compounds which is already published (Table 4b). However, the compounds used in
this study are resistant to high temperature, which gives authorization for use in the industrial
field.
4. Characterization of the metal surface
4.1. SEM study
19

We performed an SEM analysis to analyze and characterize the metal surface of the carbon
steel after corrosion in molar hydrochloric acid with and without of the compounds. The SEM
image in 1.0 M HCl alone shows that the surface is destroyed by corrosion (Figure 6A). The
observation of the SEM images in the case of the presence of the glycoside compounds
(Figure 6B, C) shows that the surface of the steel was protected by a layer of organic
compounds in the form of a deposit [42,43].
Figure 6. SEM image of CS before (A) and after immersion for 6 h in 1.0 M HCl with 10-3 M
of (B) G-C12 and (C) G-C6.
4.2. UV-visible spectroscopy
In order to study the complexing property of the two compounds with iron we have carried
out a study by UV-visible spectroscopy (UV-vis) [44]. The UV-visible spectra shows that the
maximum wavelengths move from 260.22 to 312.41 nm for the G-C12 compound and from
254.52 to 340.45 nm for the G-C6. This result reveals that the these two compounds are
capable of making bonds with iron ions dissolved in 1.0 M HCl (Figure SI6).
4.3. ICP-OES analysis
To measure iron dissolution in HCl with and without inhibitors we performed an ICP-OES
analysis. The analysis shows that there is an amount of iron of 259.939 mg/L in the case of
carbon steel in 1.0 HCl alone. After the addition of the two compounds G-C12 and G-C6 it is
observed that the amount of iron dissolved in HCl is of the order of 6.297 mg/L for the
compound G-C12 and 6.312 mg/L for the compound G- C6.These results explain that the
20

glycoside compounds decrease the iron dissolution in HCl, proves that the these two
compounds have an inhibitory effect on the dissolution of the carbon steel in 1.0 M HCl [45].
5. Theoretical study
5.1. DFT
The adsorptive behavior of the Epoxy Sugar derivatives bearing a longer (-C12H25) or a
shorter (-C6H13) alkyl chains can be evaluated through the shape and symmetry of the Highest
Occupied Molecular Orbitals (HOMO) and Lowest Unoccupied Molecular Orbitals (LUMO),
by analyzing [42,45]. HOMO designates the regions prone to electron donation (to
electrophilic species), whereas LUMO the regions that have an affinity to accept the electrons
(from nucleophile species). The distribution of HOMO in the studied Epoxy sugar derivatives
(Figure 7) is delocalized mainly through the oxygen atoms of the sugar moiety, the similar
distribution is observed also for LUMO, meaning that this part of molecule is where the
interaction with the metals surface (iron) takes place by an electron donation from molecule
toward the surface [46]. Electrostatic potential maps (ESP) presented in the Figure 7c, are
helpful to pinpoint the rich (red color) or poor (blue) regions of electron density in the
molecule. The regions with the high electron density are concentrated nearby oxygen atoms
whereas the electron density distribution is low at the –C and –H atoms [47].
21

Figure 7. Optimized structures, distribution of orbitals (a. HOMO and b. LUMO) and ESP of
EpoxySugar G-C12 and G-C6 molecules.
5.2. Monte Carlo
In the Figure 8 are represented the resulting interaction energies curves for Fe (110) /G-C12 or
G-C6 /700 H2O/25 hydronium+25 chloride ions simulated corrosion media derived from
Monte Carlo calculations. In each MC step there is a tendency of the convergence of every
energy contribution (the total energy, the average total energy, the van der Waals energy, the
electrostatic energy and the intermolecular energy) in the course of the calculation steps
during the adsorption of the inhibitor molecule onto the Fe(110) surface [48].
22

Figure 8. Monte Carlo calculation resulting interaction energies curves for Fe (110)/G-C12
(a.) or G-C12 (b) /700 H2O/25 hydronium+25 chloride ions simulated corrosion media.
The distribution of the adsorption energies during the Monte Carlo Calculations for the
species that are used to simulate the corrosion media are represented in the Figure 9. The
negative energy values are an indication of spontaneity of the inhibitor adsorption toward the
Fe surface. The adsorption energy depending on the configuration of inhibitor onto the Fe
23

surface for a G-C12 molecule is in the range of -83.55 to -139.45 kcal/mol, whereas the
adsorption energy for G-C6 is in the range of -114.55 to -122.05 kcal/mol.
Figure 9. Adsorption energy distribution curves for Fe (110)/ G-C12 (a) or G-C6 (b) /700
H2O/25 hydronium+25 chloride ions simulated corrosion media obtained via Monte Carlo
calculations.
These relatively high adsorption energy values are accountable for the water displacement
from Fe(110) surface due to the interaction of the inhibitor by electron sharing of its oxygen-
24

sugar moiety and the metal surface. This interaction involves the overlap between the sharing
of electrons from –O atoms of the inhibitor compounds and the 3d electrons of the iron
surface [48].
5.6. Molecular Dynamics
In order to understand at the molecular level the interaction details of the studied inhibitor
with the Fe (110) surface the Molecular Dynamics simulations were accomplished. The most
stable geometry configurations (Figure 10 a. and b) jointly with the RDF poses (Figure 11
)
obtained from these simulations provided a in depth information regarding the corrosion
inhibition expressed by these epoxy sugar derivatives.
Figure 10. Side and top views of the most stable adsorption configuration for Fe (110)/G-C12
(a.) or G-C6 (b.) /700 H2O/25 hydronium+25 chloride ions in the simulated corrosion media
obtained by Molecular Dynamics simulations.
25

Both of the inhibitors are flat lying onto the Fe surface, and somewhat a greater extent of
adsorption energy (from MC) in the case of G-C12 compared to G-C6 is due to a greater
surface of the former one.
The RDF is frequently used in MD simulations to evaluate the interaction between the studied
inhibitors and the surface. When the peaks arise at the distances 1 Å up to 3.5 Å, it is
associated with chemisorption (for the physisorption the peaks arise at the distances larger
than 3.5 Å) [48]. The RDF value (Figure 11) for O atom of the both epoxy sugar derivatives
shows that the bond length of O atoms and the iron surface is less than 3.5 Å, pointing out to
chemisorptions through the inhibitors. This strong interaction leads to the protection of the
metal against dissolution – by a chemisorption process.
Figure 11. RDF of O atoms of the Epoxy Sugar derivatives on the Fe (110) surface.
6. Conclusion
In this study, we presented two ecological inhibitors as corrosion inhibitors of carbon steel.
These compounds have been characterized by the usual spectral, the NMR analyzes show that
26

it has good coherence between the spectral values and the assigned structures. In addition, the
result of the electrochemical and rheological study shows that these two compounds have a
remarkable corrosion inhibiting effect and that the inhibitory efficiency increases with the
increase in concentrations for the two inhibitors. The highest inhibition efficiency values at
10-3 M (optimum concentration) are 94.4 % and 94.3 % for G-C12 and G-C6, respectively.
Both inhibitors acting on the metal surface as inhibitors of the mixed type. The corresponding
values of the standard Gibbs free energy of adsorption (-44.09 to -42.68 kJ/mol) revealed that
the adsorption mechanism of the G-C12 and G-C6 are mainly due to chemisorption. While, the
increase in temperature causes a slight decrease in the values of the inhibitory efficiencies.
Thermodynamic studies show that both inhibitors acting on the metal surface according to the
Langmuir isotherm. Theoretical results DFT and MD simulation indicated that the both
inhibitors is efficient, which is completely agree with the experimental results.
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