Enhancement of corrosion inhibition of mild steel in acidic media by green-synthesized nano-manganese oxide

Abstract

In this study, extracts of withered flower petals such as rose petal (RP) and lotus petal (LP) were used as sources for natural antioxidants, namely anthocyanins, flavonols, phenolic compounds, and pectin to prepare nano-manganese oxide through the ultrasonic wave assisted green synthesis method, which is cost-effective and eco-friendly. The prepared nano-manganese oxides were used for enhancement of corrosion inhibition behavior of mild steel (MS) in acid medium (1 M HCl). The structural properties of the prepared nano samples were studied using X-ray powder diffraction studies (XRD). Functional groups and thermal behaviour of the prepared metal oxides were tested through Fourier transform infrared spectra (FTIR) and thermogravimetric (TG) analysis. Transmission electron microscope (TEM) showed the nanosized structure of the prepared manganese oxide. The specific surface areas were found to be 27.914 and 39.438 m 2 g À1 for the sample prepared from the RP and LPs extract, respectively by BET surface area analysis. Improved electrochemical properties were observed for LPM and the corrosion inhibition efficiency of LPM (72.63%) and RPM (51.50%) was higher compared to the bare MS plate under 1 M HCl medium.

Full text

Enhancement of corrosion inhibition of mild steel in acidic media by
green-synthesized nano-manganese oxide
Y.A. Syed Khadar
a,
⇑
, S. Surendhiran
b
, V. Gowthambabu
c
, S Halimabi Alias Shakila Banu
d
, V. Devabharathi
e
,
A. Balamurugan
f,
⇑
a
Department of Physics K.S.R College of Arts and Science for Women, Tiruchengode 637215, Tamilnadu, India
b
Centre for Nanoscience and Technology, KS Rangasamy College of Technology, Tiruchengode 637 215, Tamilnadu, India
c
Department of Physics, Dr N. G. P. Arts and Science College, Coimbatore 641 048, Tamilnadu, India
d
Department of Chemistry, Government Arts and Science College, Avinashi 641654, Tamilnadu, India
e
Department of Physics, KSR Institute for Engineering and Technology, Tiruchengode 637 215, Tamilnadu, India
f
Department of Physics, Government Arts and Science College, Avinashi 641654, Tamilnadu, India
article info
Article history:
Received 20 February 2021
Received in revised form 8 April 2021
Accepted 21 April 2021
Available online xxxx
Keywords:
Manganese oxide
Ultrasonication-assisted green synthesis
Mild steel
Corrosion inhibition
abstract
In this study, extracts of withered flower petals such as rose petal (RP) and lotus petal (LP) were used as
sources for natural antioxidants, namely anthocyanins, flavonols, phenolic compounds, and pectin to
prepare nano-manganese oxide through the ultrasonic wave assisted green synthesis method, which is
cost-effective and eco-friendly. The prepared nano-manganese oxides were used for enhancement of
corrosion inhibition behavior of mild steel (MS) in acid medium (1 M HCl). The structural properties of
the prepared nano samples were studied using X-ray powder diffraction studies (XRD). Functional groups
and thermal behaviour of the prepared metal oxides were tested through Fourier transform infrared
spectra (FTIR) and thermogravimetric (TG) analysis. Transmission electron microscope (TEM) showed
the nanosized structure of the prepared manganese oxide. The specific surface areas were found to be
27.914 and 39.438 m
2
g
1
for the sample prepared from the RP and LPs extract, respectively by BET
surface area analysis. Improved electrochemical properties were observed for LPM and the corrosion
inhibition efficiency of LPM (72.63%) and RPM (51.50%) was higher compared to the bare MS plate under
1 M HCl medium.
Ó2021 Elsevier Ltd. All rights reserved.
Selection and peer-review under responsibility of the scientific committee of the International e-Confer-
ence on Advancements in Materials Science and Technology.
1. Introduction
Nanomaterials have been used for achieving proficiency,
durability, and viability. Such materials are ordinarily used in med-
ical, physical, chemical, drug, designing, and ecological applica-
tions because of their improved surface-area-to-volume ratio [1].
Nanoparticles (NPs) can be synthesized by using various physical
and chemical techniques. In general, such techniques are unde-
pendable to the environment, less proficient, more expensive,
and risks to human wellbeing. Green syntheses are preferred over
traditional strategies. The plant extract-based amalgamation of
inorganic NPs is exceptionally effective, easy, and harmless. The
natural biological compounds present in plant extracts can act as
reducing and capping agents to prepare nanomaterials [2]. They
have gained attention because of their broad applications in sev-
eral fields, for example, catalysis, secondary batteries, sensors,
microelectronics, optoelectronics, and surface-oriented applica-
tions [1,2].
Reports on the green synthesis of manganese oxide nanoparti-
cles using leaf/peel extracts of Aloe vera, Datura stramonium, Yucca
gloriosa, and orange peel are available in the literature [1,3–5].In
this report, developing a naturally benevolent route for the synthe-
sis of biomolecule-covered manganese oxide NPs using rose petal
(RP) and lotus petal (LP) hot water extract as reducing and capping
agents and their erosion-restraint property was evaluated.
Mild steel (MS) plate is widely used in structural and engineer-
ing developments because of its accessibility, reasonable cost, and
physical properties. However, the use of the MS plate can be
https://doi.org/10.1016/j.matpr.2021.04.335
2214-7853/Ó2021 Elsevier Ltd. All rights reserved.
Selection and peer-review under responsibility of the scientific committee of the International e-Conference on Advancements in Materials Science and Technology.
⇑
Corresponding author.
E-mail addresses: dryaskh@gmail.com (Y.A. Syed Khadar), bala.snr@gmail.com
(A. Balamurugan).
Materials Today: Proceedings xxx (xxxx) xxx
Contents lists available at ScienceDirect
Materials Today: Proceedings
journal homepage: www.elsevier.com/locate/matpr
Please cite this article as: Y.A. Syed Khadar, S. Surendhiran, V. Gowthambabu et al., Enhancement of corrosion inhibition of mild steel in acidic mediaby
green-synthesized nano-manganese oxide, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2021.04.335

restricted because of the conditions where it must be utilized.
These can be natural conditions that can prompt the deterioration
of the metal surface by corrosion or other conditions such as wear
intensity [6].
One of the ways being investigated in the field of surface engi-
neering to improve the surface properties of metals is coating and
alloying. The coating of other metal oxides on metal surfaces as
defensive layers can be done by different strategies in the particu-
lar spin coating, dip coating, and electrodeposition. In any case,
spin coating is one of the cost-effective and proficient strategies
for uniform coating on the metal surface. It is preferred as it
enables researchers to control the thickness of the coating and
requires working conditions at room temperature. The metal coat-
ing on a superficial level should have the desired qualities and
properties. The properties that can be upgraded by spin coating
include corrosion resistance, surface hardness, wear resistance,
and surface morphology. Spin coating of manganese oxide onto
MS plate was considered as one of the primary techniques used
for the corrosion protection of MS plate utilized in modern applica-
tions [7]. The NPs exert good effects including erosion resistance
for a substrate. Mostly, NPs give improved protection from oxida-
tion, corrosion, disintegration, and wear to the composite layer [8].
2. Experimental section
2.1. Preparation of rose and lotus petal extracts
The withered rose and lotus petals were grounded well with the
help of a domestic mixer (mixie) to get a fine powder. Then, 10 g of
each petal powder was mixed separately with 100 mL double-
distilled (DD) water in an Erlenmeyer flask and boiled at 70 °C
for 30 min. afterwards, the boiled solution was allowed to room
temperature without any disturbances and the resulting aqueous
solution was filtered using Whatman No. 1 filter paper. Further,
the resultant RP and LP petal extracts were used for experimental
purpose.
2.2. Synthesis of manganese oxide nanorods
The manganese oxide NPs were produced by the ultrasonic
wave-assisted green synthesis process [9]. First, 0.1 M manganese
(II) acetate was added with 100 mL of RP and LP extracts separately
and constantly stirred for 24 h at ambient temperature. Then, the
aqueous solution was subjected to ultrasonic wave’s irradiation
process at 40 kHz (Advanced Sonicator; Lark, New Delhi, India)
for 120 min and the resultant product was dehydrated using a
hot plate. The resulting powder was calcinated at 500 °C for 3 h
to get ultrafine manganese oxide nanorods.
2.3. Electrode preparation for electrochemical corrosion studies
In this study, a 1 cm
2
MS plate was used as an active material to
investigate the electrochemical corrosion inhibition properties. Ini-
tially, the MS plate was polished with silicon carbide (SiC) grid
paper and washed well with acetone. Then, 15 mg synthesized
LPM and RPM were separately mixed with 5 mg polyvinylidene flu-
oride (PVDF) and 8 mL N-Methyl-2-pyrrolidone (NMP) to make a
uniformity slurry. Then, the slurry was coated on MS plate using
the spin coating technique.
2.4. Characterization techniques
The thermal behaviour of the synthesized material was ana-
lyzed through TG/DTA (Exstar TG/DTA 6300; Hitachi, Tokyo,
Japan). The structural properties were characterized by XRD (X’Pert
PRO; PANalytical, Almelo, the Netherlands). The microstructural
properties were analyzed by HRTEM (JEOL, Japan). The functional
groups and particle size distribution (PSD) were investigated with
the help of Fourier transform infrared (FTIR) spectrophotometer
(Spectrum 100; PerkinElmer, USA) and a particle size analyzer
(Nanophox; Sympatec, Germany), respectively. The specific surface
area (SSA) was calculated using the Brunauer–Emmett–Teller (BET)
process using a BET surface area analyzer (Autosorb AS-1MP;
Quantachrome, Boynton Beach, FL). The experiment to study the
corrosion inhibition properties of bare MS and LPM- and RPM-
coated MS plate was carried out by linear sweep voltammetry
(LSV) in 1 M HCL electrolyte with a three-electrode setup through
an electrochemical workstation (PGSTAT302N; Metrohm Autolab,
the Netherlands) at room temperature.
3. Results and discussions
3.1. Thermogravimetric analysis
Fig. 1(a) shows the TGA curves of both manganese oxide nanor-
ods synthesized using LP and RP extracts, which show the two
stages of decomposition. The first stage of decomposition occurs
due to coordinated H
2
O molecule and the second stage of decom-
position occurs due to the formation of manganese oxide nanorods
[10]. The overall weight loss (%) can be found to be 50.8% and 31.4%
for RPM and LPM nanorods, respectively. Comparatively, the man-
ganese oxide nanorods synthesized using LP had higher thermal
stability than RP.
3.2. XRD analysis
The X-ray powder diffraction (XRD) pattern of prepared man-
ganese oxide nanorods (RPM and LPM), which shows the presence
of two phases such as b-Mn
2
O
3
and Mn
3
O
4
was shown in Fig. 1(b).
Here, the major phase b-Mn
2
O
3
possess a body-centred cubic
structure and the minor phase Mn
3
O
4
possess a tetragonal crystal
structure with the crystallographic space group of Ia (2 0 6) and
I41/and (14 1), respectively. All diffraction peaks perfectly matched
with JCPDS file numbers 65-7467 (a = 9.408 Å) and 01-1127 (a = 5.
75 Å and c = 9.42 Å). The average crystallite size was brought into
being to be 19 and 12 nm for RPM and LPM, respectively, which
was calculated by Debye–Scherrer formula [11,12]. The sharp
intense diffraction peaks seen in manganese oxide NPs synthesized
using LP are due to smaller crystallite size.
3.3. Fourier transforms infrared spectroscopic analysis
Fig. 2(a) shows the FTIR spectra of manganese oxide NPs, which
were noted in the range from 4000 to 400 cm
1
. The two sharp
identical peaks observed around ~475 and ~602 cm
-1
are attribu-
ted to asymmetric Mn–O–Mn vibration and Mn–O stretching
modes of vibration, respectively [13]. Interestingly, no hydroxyl
(OH) group was observed in synthesized manganese oxide NPs
because petals of rose and lotus have excellent hydrophobic beha-
viour in nature. It is evidence of the incorporation of biomolecules
in manganese oxide NPs.
3.4. Particle size distribution analysis
The average particle size of the prepared LPM and RPM nanor-
ods was analyzed by using the dynamic light-scattering method.
Fig. 2(b) shows the PSD curves of the prepared materials, and the
average particle size was found to be 21.1 and 26.5 nm for LPM
Y.A. Syed Khadar, S. Surendhiran, V. Gowthambabu et al. Materials Today: Proceedings xxx (xxxx) xxx
2

and RPM, respectively, which revealed that the prepared nanorods
were in the nano-size range. These results are matched well with
those of the XRD analysis.
3.5. High-resolution transmission electron microscopic analysis
The microstructural properties of the prepared manganese
oxide nanorods were analyzed by HRTEM analysis. HRTEM micro-
graphs clearly show the formation of manganese oxide nanorods in
both LP and RP samples (Fig. 3a & c). The HRTEM images are shown
in Fig. 3(b & d), and the d-spacing values 0.301 and 0.314 nm
marked in the pattern correspond to (314) crystal plane of man-
ganese oxide, which is also in good agreement with the XRD anal-
ysis. The corresponding SAED pattern is shown in insets of Fig. 3(b
& d), which also shows highly crystalline manganese oxide nanor-
ods with appropriate lattice fringes [14].
3.6. BET specific surface area studies
The specific surface area (SSA) and porous nature of green-
synthesized manganese oxide nanorods were investigated by N
2
adsorption and desorption measurements (Fig. 4(a)). The SSA, pore
size, and pore volume were found to be 39.438 m
2
g
1
, 1.72 nm,
and 0.243 m
2
g
1
and 27.914 m
2
g
1
, 2.06 nm, and 0.130 m
2
g
1
for manganese oxide NPs synthesized using LP and RP,
respectively, by adopting BET and Barrett–Joyner–Halenda analy-
ses. Hence, this analysis confirmed the formation of porous man-
ganese oxide [15].
3.7. Electrochemical corrosion studies
The electrochemical corrosion inhibition properties of MS/RPM
and MS/LPM were characterized by linear sweep voltammetry
analysis under 1 M HCL medium. The corresponding potentiody-
namic polarization curve and Tafel plot are shown in Fig. 4(b). Ini-
tially, the potential was functionalized at 1.0 V and the rust
started at the MS at the anode and its potential tended to be in
motion toward 0 V through the gap of ~5 m/V. According to the
potentiodynamic polarization curve, the corrosion potential of
MS/RPM and MS/LPM move toward the positive region compared
with the bare MS. The calculated electrochemical parameters such
as corrosion current; corrosion rate, polarization resistance, and
improved corrosion inhibition (%) are shown in Table 1. The dimin-
ish in corrosion current and enhancement in polarization resis-
tance of MS/LPM show a better corrosion rate of about
0.24529 mm/yr compared to MS/RPM and bare MS having corro-
sion rates of 0.43472 and 0.89651 mm/yr, respectively. Hence,
the MS/LPM shows a higher improved corrosion inhibition of
Fig. 1. (a) TGA curve of RPM and LPM; (b) XRD profile of RPM and LPM.
Fig. 2. (a) FTIR spectra, and (b) PSD curves of LPM and RPM.
Y.A. Syed Khadar, S. Surendhiran, V. Gowthambabu et al. Materials Today: Proceedings xxx (xxxx) xxx
3

Fig. 3. (a & c) TEM, (b & d) HRTEM, and (insets) SAED patterns of LPM and RPM.
Fig. 4. (a) N2 adsorption and desorption measurements of LPM and RPM, (b) potentiodynamic polarization curves of MS, MS/RPM, and MS/LPM.
Table 1
Tafel polarization parameters of bare, LPM and RPM coated MS in 1 M HCL medium.
Subtract Ecorr (mV) icorr (A) Corrosion rate (mm/yr) Polarization (
X
) Improved efficiency (%)
Bare MS 652.280 68.5470 0.89651 167.800 –
MS/RPM 601.550 39.1330 0.43472 173.140 51.50
MS/LPM 778.190 26.2730 0.24529 734.960 72.63
Y.A. Syed Khadar, S. Surendhiran, V. Gowthambabu et al. Materials Today: Proceedings xxx (xxxx) xxx
4

approximately 72.63% compared to MS/RPM having 50.51% and
previously reported results [16–19]. The improvement in the cor-
rosion rate of MS coated with LPM was due to the hydrophobic nat-
ure of LPs. The comparative assessment on various nanomaterials,
synthesis methods, coating subtracts and their corrosion inhibition
efficiency with this present work are tabulated in Table 2.
4. Conclusion
In this investigation, highly crystalline manganese oxide nanor-
ods were successfully synthesized via an ultrasonic wave-assisted
green synthesis route using rose and lotus petals extracts. Their
physicochemical properties were extensively studied by various
characterization techniques. The improved corrosion inhibition
behaviour of MS/LPM (72.63%) was much higher than that of MS/
RPM (51.50%) at 1 M HCl aqueous medium, which might be due
to the hydrophobic nature of LPs. Hence, the LPM NPs showed bet-
ter results compared to RPM. It is hoped that in the future, the syn-
thesis of nano-metal oxides utilizing organic moiety of a range of
natural resources as capping agent’s means will find applications
in catalysis fields.
CRediT authorship contribution statement
Y.A. Syed Khadar: Writing - original draft, Data curation,
Methodology. S. Surendhiran: Formal analysis, Methodology,
Investigation, Software. V. Gowthambabu: Writing - original draft,
Methodology, Software. S Halimabi Alias Shakila Banu: Conceptu-
alization, Writing - review & editing. V. Devabharathi: Writing -
review & editing. A. Balamurugan: Writing - review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared
to influence the work reported in this paper.
Acknowledgements
The author expresses his sincere thanks to Dr R. Gopalakrish-
nan, Principal, K.S. Rangasamy College of Technology (Autono-
mous), Tiruchengode, Tamil Nadu, India, for his constant support
and encouragement for carrying out this work.
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Table 2
A comparative assessment of nanomaterial coating on different metal surfaces for improvement of corrosion inhibition behaviours.
S. No NPs Synthesis Method Subtract Medium Corrosion efficiency (%) Reference
1 CdS/MWCNT Opunica ficus Indicafruit extract Zn Plate 3.5% NaCl 76.25 [20]
Zn Plate 1 M HCl 45.19
Zn Plate 6 M KOH 51.68
2 NiO-Zn Chemical method MS plate 3.5% NaCl 49.70 [21]
3 SnO2 Green synthesis MS Plate 3.5% NaCl 64.20 [22]
4 NiO Delonix elata leaf extract Zn plate 3.5% NaCl 68.40 [23]
1 M HCl 75.70
1 M H2SO4 88.60
6 M KOH 56.80
NiO Delonix elata leaf extract Mg plate 3.5% NaCl 61.10 [23]
1 M HCl 71.90
1 M H2SO4 79.50
6 M KOH 55.90
5 MnO2 Rose petal extract MS Plate 1 M HCl 51.50 This work
Lotus petal extract 1 M HCl 72.63
Y.A. Syed Khadar, S. Surendhiran, V. Gowthambabu et al. Materials Today: Proceedings xxx (xxxx) xxx
5