Amoxicillin as Corrosion Inhibitor for Cast Steel

Vol.:(0123456789)
1 3
Journal of Solid State Electrochemistry
https://doi.org/10.1007/s10008-023-05788-0
ORIGINAL PAPER
Expired amoxicillin asaneco‑friendly corrosion inhibitor forcast
steel insulfuric acid environment: electrochemical, surface
andthermodynamic studies
AyoubElAloua1 · MohammedOubahou2· AbdeslamElBouari1· OmarTanane1
Received: 2 October 2023 / Revised: 11 December 2023 / Accepted: 18 December 2023
© The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2023
Abstract
During the acid pickling process, the corrosion of cast steel in acidic solutions is difficult to avoid. Thus, the utilization
of inhibitors has emerged as an effective strategy for reducing the corrosion rate of cast steel. However, the conventional
use of both organic and inorganic corrosion inhibitors raises environmental concerns due to their harmful properties. As a
result, there is a growing interest among researchers in exploring pharmaceutical drugs as a more environmentally friendly
approach to corrosion mitigation. In this study, we investigate the corrosion inhibition of cast steel using expired amoxicil-
lin (AMXL) in a 0.5 M sulfuric acid medium. Our analysis employs gravimetric, electrochemical, and scanning electron
microscopy (SEM) techniques. Electrochemical assessments conducted on cast steel electrodes indicate an increase in charge
transfer resistance, and a decrease in current density when amoxicillin is introduced into the corrosive environment. Weight
loss studies further confirm that amoxicillin reduces the corrosion rate of cast steel. Moreover, we observe that the inhibi-
tion effectiveness rises with increasing amoxicillin concentration but decreases with higher temperatures. Our findings also
reveal that the adsorption of amoxicillin on the cast steel surface follows the Langmuir isotherm. SEM analysis is employed
to visually confirm the impact of amoxicillin on the cast steel surface. The presented paper supported the effective use of
outdated medications, such as amoxicillin, as corrosion inhibitors for metals, offering broad industrial applications while
addressing environmental concerns.
Keywords Cast steel· AMXL· Corrosion inhibition· Adsorption· H2SO4
Introduction
Corrosion is a widespread and persistent problem that affects
a wide range of industries and infrastructures, posing sub-
stantial economic and safety concerns worldwide [1–4]. Due
to its massive usage in manufacturing, transportation, build-
ing, and other industries, steel in particular plays a crucial
role among the materials susceptible to corrosion especially
when it is in direct contact with aggressive solutions (sul-
furic and hydrochloric acid media) during acid pickling or
acid descaling [5, 6]. The progressive deterioration of met-
als by corrosion leads to financial losses through repair and
replacement as well as environmental problems [7].
In recent years, researchers and engineers have been tire-
lessly exploring innovative strategies to combat corrosion
and preserve the longevity of steel structures. One promising
approach that has gained considerable attention is the use of
corrosion inhibitors [8–11]. Corrosion inhibition techniques
involve the application of chemical compounds to the metal
surface to mitigate the destructive electrochemical processes
that cause corrosion [12]. These inhibitors form a protective
layer, hindering the interaction between the metal surface
and corrosive agents, thus slowing down or preventing the
corrosion process altogether [13].
Chemical inhibitors have historically been used exten-
sively to reduce corrosion by creating protective coat-
ings on metal surfaces and reducing the electrochemical
reactions. However, the growing demand for corrosion
inhibitors has given rise to a new frontier: the search for
* Ayoub El Aloua
[e-mail]
1 Laboratory ofPhysical Chemistry ofApplied Materials,
Faculty ofSciences Ben M’Sick B.P.7955, Hassan II
University ofCasablanca, Casablanca20670, Morocco
2 Laboratory ofPhysical Chemistry ofMaterials, Faculty
ofSciences Ben M’Sick B.P.7955, Hassan II University
ofCasablanca, Casablanca20670, Morocco

Journal of Solid State Electrochemistry
1 3
alternative and sustainable sources. This environmental
concern has therefore been transformed into an exciting
opportunity, as scientists have embarked on an intriguing
adventure to investigate the potential use of out-of-date
drugs in corrosion inhibition [14].
Researchers want to use expired medications in new ways
in order to reduce pharmaceutical waste and, at the same
time, protect important metal infrastructure in a sustainable
and affordable way. The active chemical components found
in expired pharmaceuticals are the basis for the idea of using
them as corrosion inhibitors. According to reports, organic
compounds with S, O, or N atoms are thought to be the most
efficient corrosion inhibitors due to their higher efficacies
[15, 16]. This category of molecules can be adsorbed on
the metal surface by transferring the lone pair of electrons
from an S, O, or N atom to an open orbital on the surface
of the metal [17]. The use of outdated medications as effec-
tive corrosion inhibitors for certain metals in acidic medium
has recently become common. Soltaninejad etal. tested the
corrosion inhibition ability of penicillin for mild steel in
phosphoric acid solution, which gives an efficiency of 95%
at maximum concentration [18]. In another work, Rana and
his collaborators found that etoricoxib was a powerful envi-
ronmentally benign corrosion inhibitor for carbon steel in
0.5 M H3PO4 [19]. According to Fouda etal., an unused
meropenem drug was investigated as a powerful corrosion
inhibitor for Cu in acidic solution [20]. The use of outdated
antibacterial medications as corrosion inhibitors will be the
answer to waste management even though their effective-
ness is not noticeably better than that of traditional inhibitors
[14]. Based on that, AMXL has the potential to be applicable
as an inhibitor for steel against electrochemical corrosion.
In this work, AMXL was applied as a corrosion inhibi-
tor for cast steel in the H2SO4 (0.5 M) solution. Impedance
and polarization curves were utilized to explore the inhibi-
tion effectiveness of AMXL. Simultaneously, weight loss
technique was utilized to evaluate how the protection pro-
vided by this product changed the rate of cast steel corro-
sion. Besides, scanning electron microscopy was utilized to
examine the surface protection.
Experimental procedure
Working electrode andtest solution
The cast steel utilized in the current work is composed of
the following elements (by weight): C (0.23), Si (0.41),
Mn (0.68), Ni (0.04), P (0.01), S (0.006), and Fe (balance).
The steel rod was mounted with Teflon to leave a 0.07
cm2 surface in contact with the test solutions. Before each
experiment, the sample was mechanically abraded using
different grades of sand paper ended with 2000 grade grift,
then washed using distilled water and dried at room tem-
perature. The acidic medium (0.5 mol/L) was made from
95% H2SO4 solution of Sigma-Aldrich by diluting it with
deionized water. Amoxicillin product, where its molecular
structure is presented in Scheme1, was dissolved to create
the inhibiting solution with various concentrations (10−4,
5 × 10−4, 10−3, and 10−2 mol/L).
Electrochemical studies
Electrochemical assessments were done using a standard
three-electrode cell, employing cast steel sample as work-
ing electrode, a platinum wire as counter electrode, and
Ag/AgCl electrode as reference electrode. These studies
were executed using the PGZ100 potentiostat piloted with
Voltamaster 5 analysis program. Electrochemical imped-
ance spectroscopy (EIS) studies were done after the sub-
mersion of the electrodes in the tested solutions for 30 min
to reach a stable potential. The frequency range varied
from 100 kHz to 10 mHz and the signal amplitude was 10
mV. After that, the polarization curves were performed
with a scan rate of 1 mV/s in the potential range of − 700
to − 300 mV.
Gravimetric method
Gravimetric measurement of cast steel specimens in H2SO4
(0.5 M) medium in the presence and absence of varying
doses of AMXL were performed according to the American
Society for Testing and Materials (ASTM G 31–72) rules
[4]. The cast steel samples of 25 × 10 × 10 mm3 dimensions
were weighed and immersed in 0.5M H2SO4 for 1 day with
and without various AMXL concentrations at the tempera-
ture range of 298–328 K. After that, the specimens were
removed from test solutions after the appropriate immersion
time, and corrosion products were removed using a sharp
brush, followed by washing with distilled water and acetone,
drying, and reweighing with a balance. Equations1 and 2
were utilized to determine the corrosion rate
v
and the inhi-
bition performance ηWL, respectively [21]:
HO
H
N
O
NH
2
N
O
S
H
O
OH
Scheme1 Chemical formula of AMXL

Journal of Solid State Electrochemistry
1 3
where W means the weight loss in (g), S represents the sur-
face of the specimen exposed to the test solution in (cm2), t
is the incubation time in (h), and ν0 and ν are the corrosion
rates of the uninhibited and inhibited media, respectively,
measured in (mg cm2 h−1).
Surface characterization
The effect of AMXL on the morphology of cast steel was
investigated with scanning electron microscopy (SEM)
(1)
v
=
W
St
(2)
𝜂
WL =
v
0
−v
v
0
×
100
technique. The images were taken using SH-4000M model.
The cast steel specimen were submerged in the test electro-
lyte in the absence and presence of AMXL for 1 day, then
they were taken from the test media, rinsed with distilled
water, and dried using filter paper before surface evaluation.
Results anddiscussion
EIS study
EIS assessments were performed to study the behavior of
cast steel electrode in sulfuric acid in the absence and pres-
ence of AMXL. Nyquist curves obtained from the EIS stud-
ies were depicted in Fig.1.
Fig. 1 Nyquist diagrams of cast steel/H2SO4 system with and without c (AMXL)

Journal of Solid State Electrochemistry
1 3
It is very clear that the EIS spectra of cast steel in H2SO4
(0.5 M) in the presence and absence of AMXL exhibited iden-
tical characteristics, implying that the process of cast steel cor-
rosion in the acid was unaffected by the addition of AMXL.
This funding demonstrated that the investigated product pre-
vents the metal corrosion simply by adhering to its surface and
obstructing the active sites [22–25]. Furthermore, it is evident
that each impedance diagram exclusively displays a single
capacitive semicircle that is depressed in the high-frequency
region. Hence, the non-ideality of these semicircles could be
attributable to the cast steel surface’s heterogeneity, frequency
dispersion, and surface roughness [26]. An appropriate equiva-
lent circuit was used to fit the EIS data (Fig.2). The circuit
contains solution resistance (Rs), a constant phase element
(CPE), and charge transfer resistance (Rct). In our study, we
opted for employing a CPE in place of pure capacitance (Cdl)
to consider the impact of surface heterogeneity on the double-
layer capacitor. This choice enabled us to achieve a more pre-
cise and fitting representation of the system [27].
The following equation describes the impedance of CPE [4]:
Herein, Q refers to the CPE magnitude, i is the imaginary
unit, ѡ represents the angular frequency, and n is the phase
shift. For the proposed equivalent circuit model, Cdl was deter-
mined with Eq.4.
The inhibition effectiveness ηEIS for AMXL at different
concentrations was determined using the following expression:
In the above expression,
R0
ct
and
Ri
ct
represent respectively
the charge transfer resistance in the absence and presence
of AMXL.
(3)
Z
CPE =
1
Q(iw)
n
(4)
C
dl =n
√
Q×R1−n
ct
(5)
𝜂
EIS =
R
i
ct −R
0
ct
Ri
ct
×
100
The determined impedance parameters were given in
Table1. It can be observed from the calculated parameters
that the introduction of AMXL decreases the double-layer
capacity Cdl value and raises the value of Rct. Moreover,
the increase in the inhibitor concentration makes this effect
becomes more and more prominent. This demonstrates that
the selected inhibitor has been successfully adsorbed on the
metal surface [28, 29]. It can be further concluded that the
adhesion of organic molecules on the steel surface can alert
the electrical double layer, which leads to lower the attack
of the corrosive solution, and thus increasing the inhibiting
performance of AMXL [30]. The impedance assessments
confirm the rise in the inhibition ability of AMXL with
increasing concentration up to 96.10% when the concentra-
tion reaches 10−2 mol/L.
The Bode diagrams presented in Fig.3(a), (b) revealed
a consistent peak present in both inhibited and uninhibited
sample, providing confirmation for the validity of the equiv-
alent circuit model employed to fit the EIS outcomes. More-
over, the Bode plots indicate a single maximum phase, indi-
cating that charge transfer at the interface between the cast
steel and the solution governed the electrochemical process
[31]. Furthermore, as AMXL concentration increases, the
phase angle values rise up to 60° in comparison to the sul-
furic acid solution alone. This signifies an enhancement in
the inhibition performance due to the adsorption of AMXL
on the cast steel surface [32].
Fig. 2 Equivalent circuit cor-
responding to fitted EIS data
Rs
Q
dl
Rct
Table 1 Impedance data obtained for cast steel/H2SO4 system with-
out and with c (AMXL)
Inhibitor Rs(Ω.cm2)Rct (Ω. cm2)Cdl (µF.cm−2)n ηEIS (%)
Blank 4.09 16.2 139 0.83 -
10−44.92 71.1 57 0.81 77.21
5 × 10−45.05 81.5 47.5 0.77 80.12
10−34.41 203.6 37.5 0.75 92.04
10−25.06 415.9 20.2 0.78 96.10

Journal of Solid State Electrochemistry
1 3
Potentiodynamic polarization curves
Polarization curves for the electrochemical corrosion of cast steel
in H2SO4 (0.5 M) in the presence and absence of the selected
AMXL concentrations at 25 °C were presented in Fig.4.
It is clear from Fig.4 that the addition of AMXL to the
blank solution moved Tafel plots to lower current density.
This behavior indicates that the investigated product less-
ens the corrosion current density, which lowers the rate
of cast steel degradation in 0.5 M H2SO4 [33]. Related
electrochemical parameters including corrosion potential
(Ecorr), corrosion current density (icorr), and so on were
summarized in Table2. Additionally, the inhibition ability
was determined as follows:
Herein, icorr and i′corr signify respectively the corrosion
current density in the absence and presence of AMXL.
(6)
IE
PDP =
i
corr
−i
corr
i
corr
×
100
Fig. 3 Bode plots for cast steel in H2SO4 without and with AMXL at various concentrations
Fig. 4 Tafel plots for cast steel
in H2SO4 with and without
AMXL at various concentra-
tions