Hydrothermal self - sacrificing growth of polymorphous MnO2 on magnetic porous - carbon (Fe3O4@Cg/MnO2): A sustainable nanostructured catalyst for activation of molecular oxygen

Article abstract of DOI:10.1016/j.mcat.2021.111603

Novel core-shell carbon coated-magnetic (Fe₃O₄@C_g) nanoparticles supported MnO2 nanosheets (with α- and β-type structure) (Fe₃O₄@C_g/MnO₂) are synthesized through a self-sacrificing templet method. The new hybrid material was fully characterized with Fourier transformed infrared spectroscopy, energy-dispersive X-ray spectroscopy, scanning electron microscopy, X-ray diffraction analysis (XRD), N₂ adsorption/desorption analysis, and transmission electron microscopy; XRD and SEM results affirmed that α- and β-MnO₂ nanosheets polymorphs onto the Fe₃O₄@C_g. The catalytic activity of the as-prepared nanostructured catalyst Fe₃O₄@C_g/MnO₂ has been evaluated in O₂ activation for the selective oxidation of benzyl alcohol to benzaldehyde with high conversion; it stability being confirmed by the recycling of the nanostructured catalyst with no obvious loss even after six repeated runs.

Full text of DOI:10.1016/j.mcat.2021.111603

Molecular Catalysis 509 (2021) 111603
Contents lists available at ScienceDirect
Molecular Catalysis
journal homepage: www.journals.elsevier.com/molecular-catalysis
Hydrothermal self - sacrificing growth of polymorphous MnO2 on magnetic
porous - carbon (Fe3O4@Cg/MnO2): A sustainable nanostructured catalyst
for activation of molecular oxygen
Zohreh Bakhtiarzadehb, Shamila Rouhanic, Ziba Karimib, Sadegh Rostamniaa *, Titus A.
,b,
,
*
M. Msagatic, Dokyoon Kimd, Ho Won Jange, Seeram Ramakrishnaf, Rajender S. Varmag
,
,
*
Mohammadreza Shokouhimehre
a Organic and Nano Group (ONG), Department of Chemistry, Iran University of Science and Technology (IUST), PO Box 16846-13114, Tehran, Iran
b Organic and Nano Group (ONG), Department of Chemistry, Faculty of Science, University of Maragheh, PO BOX 55181-83111, Maragheh, Iran
c Institute for Nanotechnology and Water Sustainability (iNanoWS), College of Science, Engineering and Technology, University of South Africa, Johannesburg 1709,
South Africa
d Department of Bionano Engineering, Hanyang University, Ansan 15588, Republic of Korea
e Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul, 08826, Republic of Korea
f Department of Mechanical Engineering, Center for Nanofibers and Nanotechnology, National University of Singapore, Singapore, 119260, Singapore
g
ˇ
Regional Center of Advanced Technologies and Materials, Czech Advanced Technology and Research Institute, Palacky University, Slechtitelů 27, 783 71 Olomouc,
Czech Republic
A R T I C L E I N F O
A B S T R A C T
Keywords:
Novel core-shell carbon coated-magnetic (Fe3O4@Cg) nanoparticles supported MnO2 nanosheets (with α- and
MnO2
β-type structure) (Fe3O4@Cg/MnO2) are synthesized through a self-sacrificing templet method. The new hybrid
material was fully characterized with Fourier transformed infrared spectroscopy, energy-dispersive X-ray spec-
troscopy, scanning electron microscopy, X-ray diffraction analysis (XRD), N2 adsorption/desorption analysis, and
Magnetic nanoparticles
Alcohol oxidation
Nanostructured catalyst
transmission electron microscopy; XRD and SEM results affirmed that α- and β-MnO2 nanosheets polymorphs
onto the Fe3O4@Cg. The catalytic activity of the as-prepared nanostructured catalyst Fe3O4@Cg/MnO2 has been
evaluated in O2 activation for the selective oxidation of benzyl alcohol to benzaldehyde with high conversion; it
stability being confirmed by the recycling of the nanostructured catalyst with no obvious loss even after six
repeated runs.
1. Introduction
In recent years, heterogeneous catalytic system for the oxidation of
benzyl alcohol (BzOH) over both, the noble and non-noble transition
Nowadays, intensive efforts have been made to meet the ever-
growing demands for the development of greener catalytic protocols
with high-efficiency and high-selectivity [1,2]. Presently, the prepara-
tion of aldehydes by selective alcohol oxidation is a pivotal chemical
transformation for the synthesis of a variety of vital intermediates for the
fine chemicals [3]. Traditionally, the alcohol oxidation procedures are
performed with stoichiometric amounts of high-cost inorganic oxidants
which leads to the formation of environmentally harmful by-products
[4]. Hence, the development of green, efficient and economic hetero-
geneous catalytic aerobic oxidation systems exploiting the low-cost O2
or air as a terminal oxidant would be ideally suited for such significant
chemical transformations [5–7].
metal oxides have been studied extensively; deployment of non-noble
metal oxides has remarkable advantageous over noble metals due to
their inexpensive nature and high availability [8]. Among the various
non-noble transition metal oxides, manganese oxides have attracted
increasing attention due to the earth-abundant sources, high catalytic
activity, rich structures and morphologies, low-cost and environmental
friendliness, therefore, they have been widely applied in the fields of
lithium batteries, oxidants, and in catalysis arena [9–12].
Manganese oxide exits in various crystal structure forms such as α, β
and λ - types which differ in the arrangement of the basic octahedral
[MnO6] unit [13]. Recently, much attention has been directed toward
the synthesis of polymorphs of MnO2 with different morphology owing
* Corresponding author.
E-mail addresses: rostamnia@iust.ac.ir (S. Rostamnia), varma.rajender@epa.gov (R.S. Varma), mrsh2@snu.ac.kr (M. Shokouhimehr).
https://doi.org/10.1016/j.mcat.2021.111603
Received 22 December 2020; Received in revised form 8 April 2021; Accepted 23 April 2021
Available online 28 May 2021
2468-8231/© 2021 Elsevier B.V. All rights reserved.

Z. Bakhtiarzadeh et al.
Molecular Catalysis 509 (2021) 111603
Fig. 1. Schematic preparation of MnO2 on CHC substrate by hydrothermal method.
to the varied applications of polymorphism in the chemical industry [9,
reused for six runs without any significant loss of catalytic activity. The
advantage of this aerobic oxidation method includes the simple opera-
tion, easy catalyst separation and reusability, and high selectivity.
14–17]. Among MnO2 phases, α- and β-MnO2 are less active catalytically
in comparison to γ-phase which lead to the formation of desirable
oxidation products [18]; MnO2 has been reported as a selective
oxidizing catalyst in the aerobic oxidation of BzOH with high reactivity
and selectivity [19–24].
2. Experimental
Overall, the nanoparticles (NPs) exhibit excellent catalytic perfor-
mances due to the size effect and their large surface area. However, the
use of NPs as a catalyst is associated with some limitations as it suffers
from aggregations and low stability [18,25]. The aforementioned chal-
lenges for NPs need viable solutions and not surprisingly, researchers
have suggested that immobilizing active species onto an ideal support
could solve the lingering problem [22,26–28]. Recently, Hu et al. re-
ported the synthesis of ultrafine MnO2 NPs supported on graphene
oxide, which was applied as a catalyst in selective aerobic oxidation of
BzOH [8]. Wu and co-workers utilized the supported manganese oxide
on MCM-41 zeolite as a catalyst to oxidize BzOH [29]. Another study
was reported by Kadam et al., where λ -MnO2/GO composite was
employed for the oxidation of BzOH [18].
2.1. Materials
All chemicals including iron (III) chloride hexahydrate
(FeCl3•6H2O), potassium permanganate (KMnO4), poly(vinyl-
pyrrolidone) (PVP), ethylene glycol, benzyl alcohol, sodium acetate and
glucose were obtained from Merck and used without further purifica-
tion. All other chemicals were of analytical grade purity and used
without further purification.
2.2. Synthesis of carbon-coated Fe3O4 NPs (Fe3O4@Cg)
The Fe3O4 NPs were first synthesized via a modified hydrothermal
method. FeCl3. 6H2O (1.5 g), polyvinyl pyrrolidine (PVP) (1 g) and so-
dium acetate (2 g) were dissolved in ethylene glycol (30 mL) and stirred
for 1 h. Then the mixture was transferred into a Teflon-lined stainless-
Core-shell magnetic NPs have garnered considerable attention lately
due to their multi-functional properties such as large accessible surface
area, biocompatibility, low toxicity, easy surface decoration, high sta-
bility and easy separation which render them as ideal materials for
catalytic applications [30,31].
◦
steel autoclave and heated at 200 C for 10 h. After cooling to room
temperature, the Fe3O4 NPs were separated by using an external magnet,
washed with distilled water and ethanol several times and dried under
reduced pressure. In the next stage, the synthesis of magnetite-carbon
core-shell NPs was accomplished through sonicating the as-fabricated
Fe3O4 NPs with 5 g glucose in 30 mL deionized water. Next, the above
mixture was transferred into a Teflon-lined stainless-steel autoclave,
sealed and kept at a temperature of 200 ◦C for 12 h. After the reaction
system was cooled to ambient temperature, the ensuing black precipi-
tate was separated by a magnetic field, washed with distilled water and
methanol, and finally dried in a vacuum oven.
Therefore, in continuation of our research interest in exploring effi-
cient catalysts [32–35], the preparation of core-shell carbon-coated
magnetic NPs via a facile hydrothermal method is described that could
be utilized as a support for the immobilization of α- β- and δ-MnO2
(Fe3O4@Cg/MnO2). Subsequently, it was employed as a recyclable
catalyst for selective aerobic oxidation of BzOH into the corresponding
aldehyde. Furthermore, a controlled oxidation of alcohols was accom-
plished with no over-oxidation to carboxylic acid (ArCOOH) which can
be related to the presence of α- and β-MnO2 polymorphs. The synthesis
of MnO2 nanosheets have been generally performed using KMnO4 and
MnCl2/MnS as a metal source [13,9]. It is worth mentioning that the
Fe3O4@Cg/MnO2 was prepared by in-situ growing method via
self-sacrificing carbon shell layer as reducing agent with KMnO4
providing a Mn-source [9,36]. Moreover, Fe3O4 NPs were simply pre-
pared using iron (III) chloride as the only ferric ion single resource
(Scheme 1).
2.3. Synthesis of Fe3O4@Cg/MnO2
MnO2 nanosheets supported onto the Fe3O4@Cg NPs were assembled
by dispersing the Fe3O4@Cg (0.3 g) in 75 mL aqueous solution of KMnO4
(0.03 M) with ultrasonication for 1 h. Then, the resulting mixture was
transferred into a Teflon-lined stainless-steel autoclave and heated at
180 ◦C for 6 h. The obtained product was separated, and washed thor-
oughly with water and methanol before being dried in an oven,
providing the Fe3O4@Cg/MnO2 nanostructured catalyst.
The aerobic oxidation of BzOH and its derivatives by Fe3O4@Cg/
MnO2 show that the corresponding aldehydes can be obtained in high
yield as the main products. The Fe3O4@Cg/MnO2 catalyst could also be
2

Z. Bakhtiarzadeh et al.
Molecular Catalysis 509 (2021) 111603
Fig. 2. (a) FTIR spectra of Fe3O4, Fe3O4@Cg, and Fe3O4@Cg/MnO2. (b) VSM magnetization curves of Fe3O4 and Fe3O4@Cg/MnO2. (c) XRD patterns of Fe3O4@Cg and
Fe3O4@Cg/MnO2.
observed at 1024 cmꢀ 1 can be attributed to the C O stretching vibra-
tion. Peaks at 1646 and 1679 cmꢀ 1 frequencies represent the stretching
vibration of C = C and COOH groups, respectively [39]. In addition, the
peak signals at 2850 and 2921 cmꢀ 1 correspond to the asymmetric and
–
2.4. A typical procedure for O2-activation for selective oxidation of BzOH
in the presence of Fe3O4@Cg/MnO2
BzOH (1 mmol) and Fe3O4@Cg/MnO2 (0.05 g) were dissolved in 10
mL of toluene under continuous purging of dry air. Then, the reaction
was stirred at 120 ◦C for 4 h. After completion of the reaction, the
catalyst was separated from the solution using an external magnet,
washed, and dried under reduced pressure. The conversion of the
products was calculated as follows:
–
symmetric C H vibration. These numerous absorption bands indicate
the amount of various carbon and oxygen-containing functional groups
on the surface of the Fe3O4@Cg have been obtained from the glucose
during the hydrothermal synthesis [40]. Moreover, for the
Fe3O4@Cg/MnO2, the peaks at 765, 621 and 530 cmꢀ 1 are associated to
the Mn-O stretching vibration which affirms the presence of poly-
morphous MnO2.
(
)
Co ꢀ Cy
Conversion (%) =
× 100
Co
The superparamagnetic behavior of magnetic NPs is favourable for
the magnetic separation. Hence, the magnetic properties of Fe3O4 and
Fe3O4@Cg/MnO2 were investigated using a vibrating sample magne-
tometer (VSM) at room temperature; the hysteresis curves in Fig. 2b
shows the saturation magnetization of Fe3O4 NPs to be ~64 emu/g,
while Fe3O4@Cg/MnO2 has a magnetization of ~18 emu/g. The
decreased saturation magnetization value of Fe3O4@Cg/MnO2 is
attributed to the surface modification of the NPs. Nonetheless, it is still
good enough for facilitating the magnetic separation of particles.
To confirm the polymorphous phases of the as-obtained Fe3O4@Cg/
MnO2, X-ray diffraction analysis (XRD) analysis was performed (Fig. 2c)
which shows a series of characteristic peaks at 30.3, 35.4, 43.6, 53.4,
57.3, and 63.2◦ (2θ) which are in good consistent with the cubic spinel
phase of Fe3O4 (JCPDS card No. 19–0629). Moreover, arising broad peak
(19.5◦) beside the iron oxide peak can be ascribed to the specific
reflection of amorphous carbons [41]. In Fe3O4@Cg/MnO2, by
where, Co is the initial concentration of alcohols. Cy is the concentrations
of alcohols at a certain reaction time. The yields of products were
calculated via the normalization method based on the GC–MS analysis.
Turnover number (TON) represents the average number of substrate
molecules converted into the product per molecule of the catalyst
(Table 2).
3. Result and discussion
The preparation of Fe3O4@Cg/MnO2 is implemented via an effective
strategy as depicted in Fig. 1. The superparamagnetic Fe3O4@Cg was
first fabricated via a solvothermal route by applying ferric ion as a single
iron source. Then, polymorphous MnO2 nanosheets were grown in the
presence of Fe3O4@Cg through self-sacrificing redox reaction between
carbon shell layer and KMnO4 [37]. The oxidation/reduction reaction is
described in the equation shown in Fig. 1.
comparing to the XRD patterns of the standard α- and β-MnO2 (JCPDS
card No. 44–0141 and No. 24–0735) samples, it can be realized that the
hydrothermally in-situ growing manganese oxide were polymorphs of
Fig. 2a shows the Fourier transform infrared (FTIR) spectrums of
Fe3O4, Fe3O4@Cg, and Fe3O4@Cg/MnO2. The sharp intense band at 570
cmꢀ 1 is assigned to the vibration of the Fe–O group which confirms the
presence of the Fe3O4. The broad peaks at 3420 cmꢀ 1 can be assigned to
O–H stretching vibration arising from hydroxyl groups [38]. The band
MnO2 with α, β and δ phase structures. In addition, on the basis of these
results, it is revealed that the core-shell carbon-coated Fe3O4 NPs has not
changed during growth process of MnO2 nanosheets.
3

Z. Bakhtiarzadeh et al.
Molecular Catalysis 509 (2021) 111603
The morphology and nanostructure of Fe3O4@Cg NPs and
Fe3O4@Cg/MnO2 were studied by scanning electron microscopy (SEM)
and transmission electron microscopy (TEM) analysis. The SEM images
displays that the Fe3O4@Cg NPs, prepared via solvothermal method,
have spherical structure and uniform sizes with the diameter of
200–220 nm (Fig. 3a,b). Fig. 3c-f reveal that the polymorphous MnO2
may be formed by several MnO2 nanosheets overlapping together on the
surfaces of Fe3O4@Cg.
As is clear from the TEM image with higher magnification (Fig. 4a-e),
the Fe3O4@Cg NPs have a core-shell structure comprising aggregated
Fe3O4 (dark core) encapsulated with amorphous carbon shell of 21.69
nm of thickness (light area) which is less dense than the core structure.
The results from the TEM image of Fe3O4@Cg/MnO2 (Fig. 4d,e)
confirmed that MnO2 nanosheets are located on the surface of spherical
Fe3O4@Cg NPs.
The energy-dispersive X-ray spectroscopy (EDX) shows the presence
of the expected elements in the structure of the catalyst, comprising
oxygen, carbon, iron and manganese in the Fe3O4@Cg/MnO2 (Fig. 5a).
The investigation of the specific surface area for Fe3O4@Cg was per-
formed using BET measurement as presented in Fig. 5b. It can be seen
that carbon-coated Fe3O4 NPs have the BET surface area of 12 m2/g.
The catalytic performance of Fe3O4@Cg/MnO2 was evaluated in the
selective oxidation of BzOH to benzaldehyde (BzCHO) with O2 as an
oxidant for 4 h in various solvents, under different reaction temperature
and the amounts of the nanostructured catalyst; obtained results are
summarized in Table 1. As seen in Table 1, the conversion of BzOH to
Fig. 3. SEM images of (a,b) Fe3O4@Cg, (c,d) Fe3O4@Cg/MnO2, and (e,f)
Fe3O4@Cg and MnO2.
Fig. 4. High magnification TEM images of (a) Fe3O4, (b,c) Fe3O4@Cg, and (d,e) Fe3O4@Cg/MnO2.
Fig. 5. (a) EDX spectra of Fe3O4@Cg/MnO2 and Fe3O4@Cg. (b) N2 Adsorption–desorption isotherms of Fe3O4@Cg/MnO2 and Fe3O4@Cg.
4

Z. Bakhtiarzadeh et al.
Molecular Catalysis 509 (2021) 111603
Table 1
BzOH oxidation by Fe3O4@Cg/MnO2 under various reaction conditionsa.
Entry
Catalyst (mg)
Solvent
Temperature ( ◦C)
Conversion/Yieldb (%)
1
5
Toluene
Toluene
Toluene
Toluene
CH2Cl2
CHCl3
110
110
110
70
40/38
82/76
96/92
64/60
50/48
30/28
70/45
10/-
2
10
20
30
20
20
20
20
20
20
20
3
4
5
100
100
100
r.t
6
7
H2O
8
Toluene
Toluene
Toluene
Toluened
9
30
25/-
10
50
60/54
-/trace
11
110
aReaction conditions: BzOH (1 mmol), Fe3O4@Cg/MnO2, solvent (10 mL), 110 ◦C, 4 h.
bBased on GC–MS.
cSealed tube.
dWithout BzOH for oxidation evaluation of toluene to BzCHO.
Table 2
Results of selective benzylic alcohols oxidation over Fe3O4@Cg/MnOa2.
Entry
Substrate
Convb. (%)
Yieldb (%)
TONc
TOFd (hꢀ 1
)
1
4-Br
88
91
90
78
81
94
95
96
76
65
89
86
88
90
74
76
92
92
92
73
58
86
–
–
2
4-Cl
48
–
12
3
4-Me
3-NO2
2-Cl
–
4
–
–
5
–
–
6
4-MeO
3,4,5-MeO
H
–
–
7
–
–
8
53
–
13.25
9
2-Me
2-Cl
–
–
–
10
–
–
11
3-Cl
aReaction conditions: BzOH (1 mmol), Fe3O4@Cg/MnO2 (20 mg), Toluene (10 mL), 110 ◦C, 4 h with O2 balloon.
bBased on GC–MS.
cTurnover number represents the average number of substrate molecules converted into the product per molecule of catalyst.
dTurnover frequency per hour.
BzCHO was gradually enhanced with the increase of the amount of
catalyst (Table 1, entries 1–3). Indeed, 20 mg of Fe3O4@Cg/MnO2
showed the highest conversion (94%). In order to study the effect of the
solvents, the reaction was conducted in various solvents such as CH2Cl2,
CHCl3, toluene and H2O under the same reaction conditions. Among the
applied solvents, the highest conversion was observed in toluene
(Table 1, entry 8). The influence of reaction temperature was studied for
the optimized catalyst system. As indicated in Table 1, at a lower tem-
perature (<50 ◦C) conversion were rather low (< 60%), whereas at the
elevated temperature of 120 ◦C, the BzOH conversion was markedly
increased (up to 96%); hence it was found that the high temperature was
favourable for the oxidation of BzOH. Furthermore, the corresponding
5

Z. Bakhtiarzadeh et al.
Molecular Catalysis 509 (2021) 111603
Fig. 6. (a) Leaching test of Fe3O4@Cg/MnO2. (b) XRD pattern of the recovered Fe3O4@Cg/MnO2 catalyst. (c) Recycling of Fe3O4@Cg/MnO2 catalyst for the oxidation
of BzOH to BzCHO in toluene under oxygen atmosphere at 110 ◦C for 4 h.
Scheme 1. Procedure for the synthesis of Fe3O4@Cg/MnO2.
aldehyde could be obtained as the only desirable product with yield of
21%, 15% and 12% by using MnO2, Fe3O4, and Fe3O4@Cg as a catalyst
under the same reaction conditions, respectively. When we did not
charge the reaction mixture with BzOH to check oxidation of toluene, no
formation of formation of BzOH or BzCHO could be detected (Table 1,
entry 11).
benzyl alcohols to the corresponding aldehydes, without any detectable
over-oxidation to their carboxylic acids.
In the hot filtration leaching test, the Fe3O4@Cg/MnO2 nano-
structured catalyst was removed in the middle of the reaction (2 h) and
the reaction was continued with the reaction mixture without the
nanostructured catalyst. It was observed that there is no enhancement in
the conversion to aldehyde yield, thus indicating that no active species
were leached during the reaction mixture (Fig. 6a). The recovery and
reusability experiments for the selective oxidation of BzOH was also
performed by six successive cycles under the optimum conditions to
evaluate the stability of the Fe3O4@Cg/MnO2 nanostructured catalyst
(Fig. 6c). After the completion of the reaction, the nanostructured
catalyst was separated using an external magnet, washed thoroughly
with methanol, and then dried for the next run. Then, the remaining
magnetic nanostructured catalyst was also deployed under the same
experimental reaction conditions. It is worth pointing out that the
Fe3O4@Cg/MnO2 could be reused at least six times without appreciable
reduction in conversions of BzOH to BzCHO. As depicted in Fig. 6b, the
XRD pattern of the recovered Fe3O4@Cg/MnO2 catalyst ascertained that
no change in the phase composition occurred compared to fresh nano-
structured catalyst. These findings confirm that the structure of the
To demonstrate the applicability of the as-fabricated nanostructured
catalyst, the optimized reaction conditions (20 mg of Fe3O4@Cg/MnO2,
Toluene, 110 ◦C) were chosen for a further study of the catalyst in the
oxidation of various benzylic alcohols with different electron-
withdrawing and electron-donating substituents (Table 2). The results
revealed that electronic properties of substitutes on benzyl group have
an impact on the oxidation reaction. In presence of electron-donating
groups (Table 2, entries 3,6,7), the corresponding BzCHO products
were obtained in higher conversions than the electron-withdrawing
groups (Table 2, entries 1,2,4) over 4 h. The effect of the position
(meta, ortho and para) of electron-withdrawing substituents on this
reaction was also assessed; higher conversion was obtained for meta-
position because of the apparent steric hindrance and electronic na-
ture of ortho and para position, respectively (Table 2, entries 3–5). It
should be noted that this method is highly selective for the oxidation of
6

Z. Bakhtiarzadeh et al.
Molecular Catalysis 509 (2021) 111603
sacrificing template route for the growth of polymorphous
α- and
Table 3
Catalytic activity of various Mn-based catalysts for the oxidation of BzOH.
β-MnO2 nanosheets onto the core-shell carbon-coated Fe3O4 NPs. The
ensuing catalyst was characterized by various technique including FTIR,
EDX, SEM, TEM, XRD, and BET. Then, the Fe3O4@Cg/MnO2 was applied
as a highly active and efficient catalyst for the selective oxidation of
BzOH to BzCHO using oxygen as a green oxidant. The results showed
that the products were obtained in high conversion over 4 h. The newly
developed nanostructured catalyst could also be recycled and reused for
six runs without any significant loss of catalytic activity and stability.
The significant advantages of this method include the simplicity in
operation, simply work-up, excellent selectivity and the reusability.
Entry
Catalyst
Conditions
Temperature
Time
(h)
Yield
(%)
(◦C)
[Refs.]
1
2
Ni2Mn-LDH
(0.2 mg)
BzOH1 mmol,
120
70
1.7
2
99 [24]
O2 (1 atm)
Ce/MnOx
(450 mg)
BzOH 10 mM,
O2 flow (60 mL/
min)
81 [42]
3
MnO2
BzOH 100 mM,
air flow (200
mL/min)
110
2
83 [8]
NPs@GO
(200 mg)
Au/MnO2
(20 mg)
Co3O4/
4
5
BzOH 2 g, O2 1
bar
120
100
2
6 [43]
Declaration of Competing Interest
BzOH 100 Mm,
12
92 [44]
MnO2
O2 flow (20 mL/
We wish to confirm that there are no known conflicts of interest
associated with this publication and there has been no significant
financial support for this work that could have influenced its outcome.
(25 mg)
Pd@Mn5O8
(80 mg)
min)
6
7
BzOH 100 mM,
TBHP
80
4
4
89 [19]
89 [20]
–
MnO2 Co
BzOH Toluene
110
(67 mg/
mmol)
O2 aerobic
Acknowledgements
8
Fe3O4@Cg/
MnO2
BzOH 1 mmol,
Toluene, O2
aerobic
110
4
92 [This
work]
This research was supported by the National Research Foundation of
Korea (NRF) funded by the Ministry of Science and ICT
(2020M2D8A206983011). Furthermore, the financial supports of the
Basic Science Research Program (2017R1A2B3009135) through the
National Research Foundation of Korea is appreciated .
(20 mg)
Supplementary materials
Supplementary material associated with this article can be found, in
the online version, at doi:10.1016/j.mcat.2021.111603.
References
[1] A.G. Moaser, A. Ahadi, S. Rouhani, B.B. Mamba, T.A.M. Msagati, S. Rostamnia,
T. Kavetskyy, S. Dugheri, S. Khaksar, A. Hasanzadeh, M. Shokouhimehr, Curbed of
molybdenum oxido-diperoxido complex on ionic liquid body of mesoporous Bipy-
PMO-IL as a promising catalyst for selective sulfide oxidation, J. Mol. Liq. 312
(2020), 113388, https://doi.org/10.1016/j.molliq.2020.113388.
[2] S. Rostamnia, B. Gholipour, X. Liu, Y. Wang, H. Arandiyan, NH2 -coordinately
immobilized tris ( 8-quinolinolato ) iron onto the silica coated magnetite
nanoparticle : Fe3O4 @ SiO2 -FeQ3 as a selective fenton- like catalyst for clean
oxidation of sulfides, J. Colloid Interface Sci. 511 (2018) 447–455, https://doi.org/
10.1016/j.jcis.2017.10.028.
[3] M. Guan, C. Wang, J. Zhang, Y. Zhao, Practical organic solvent-free Cu(OAc)2/
DMAP/TEMPO-catalyzed aldehyde and imine formation from alcohols under air
atmosphere, RSC Adv 4 (2014) 48777–48782, https://doi.org/10.1039/
c4ra09851j.
[4] A. Dijksman, I.W.C.E. Arends, R.A. Sheldon, Cu(II)-nitroxyl radicals as catalytic
galactose oxidase mimics, Org. Biomol. Chem. 1 (2003) 3232–3237, https://doi.
org/10.1039/b305941c.
Scheme 2. Proposed mechanism for the oxidation of BzOH by Fe3O4@Cg/
MnO2 catalyst.
[5] H. Alamgholiloo, S. Rostamnia, K. Zhang, T.H. Lee, Y.S. Lee, R.S. Varma, H.
W. Jang, M. Shokouhimehr, Boosting aerobic oxidation of alcohols via synergistic
effect between TEMPO and a composite Fe3O4/Cu-BDC/GO Nanocatalyst, ACS
Omega 5 (2020) 5182–5191, https://doi.org/10.1021/acsomega.9b04209.
[6] E. Doustkhah, S. Rostamnia, B. Gholipour, B. Zeynizadeh, A. Baghban, R. Luque,
Design of chitosan-dithiocarbamate magnetically separable catalytic
nanocomposites for greener aqueous oxidations at room temperature, Mol. Catal.
434 (2017) 7–15, https://doi.org/10.1016/j.mcat.2017.01.031.
Fe3O4@Cg/MnO2 has excellent stability under the reaction conditions
which are of great significance for practical applications.
Table 3 summarizes the catalytic activity studies of several previ-
ously published Mn-base catalysts. The Fe3O4@Cg/MnO2 catalyst
exhibited high catalytic activity with good yield in comparison with
those selective stipulated studies.
¨
¨
¨
[7] P.J. Figiel, A. Sibaouih, J.U. Ahmad, M. Nieger, M.T. Raisanen, M. Leskela, T. Repo,
Aerobic oxidation of benzylic alcohols in water by 2,2,6,6- tetramethylpiperidine-
1-oxyl(TEMPO)/Copper(II) 2-N-Arylpyrrolecarbaldimino complexes, Adv. Synth.
Catal. 351 (2009) 2625–2632, https://doi.org/10.1002/adsc.200900478.
[8] Z. Hu, Y. Zhao, J. Liu, J. Wang, B. Zhang, X. Xiang, Ultrafine MnO2 nanoparticles
decorated on graphene oxide as a highly efficient and recyclable catalyst for
aerobic oxidation of benzyl alcohol, J. Colloid Interface Sci. 483 (2016) 26–33,
https://doi.org/10.1016/j.jcis.2016.08.010.
A plausible mechanism for the selective oxidation of BzOH to the
corresponding BzCHO by Fe3O4@Cg/MnO2 is outlined in Scheme 2. The
process involves free radical mechanism as reported by Goldman [45].
–
In the first step, the O H group of the BzOH is added to MnO2 species to
generate a coordination complex. Subsequently, the hydrogen atom
transfers from benzylic carbon to oxygen of MnO2 to produce a stable
radical. Finally, by the reduction of the Mn (III) to the more stable Mn
(II), the aldehyde product is formed.
[9] S. Chen, G. Liu, H. Yadegari, H. Wang, S.Z. Qiao, Three-dimensional MnO2
ultrathin nanosheet aerogels for high-performance LiO2 batteries, J. Mater. Chem.
A. 3 (2015) 2559–2563, https://doi.org/10.1039/c5ta00004a.
[10] Y. Murashima, R. Ohtani, T. Matsui, H. Takehira, R. Yokota, M. Nakamura, L.
F. Lindoy, S. Hayami, Coexistence of electrical conductivity and ferromagnetism in
a hybrid material formed from reduced graphene oxide and manganese oxide, Dalt.
Trans. 44 (2015) 5049–5052, https://doi.org/10.1039/c5dt00299k.
4. Conclusions
[11] J. Qu, L. Shi, C. He, F. Gao, B. Li, Q. Zhou, H. Hu, G. Shao, X. Wang, J. Qiu, Highly
efficient synthesis of graphene/MnO2 hybrids and their application for ultrafast
In the present study, a novel methodology was designed via self-
7

Z. Bakhtiarzadeh et al.
Molecular Catalysis 509 (2021) 111603
oxidative decomposition of methylene blue, Carbon N. Y. 66 (2014) 485–492,
[30] S. Dai, N. Wang, C. Qi, X. Wang, Y. Ma, L. Yang, X. Liu, Q. Huang, C. Nie, B. Hu,
X. Wang, Preparation of core-shell structure Fe3O4@C@MnO2 nanoparticles for
efficient elimination of U(VI) and Eu(III) ions, Sci. Total Environ. 685 (2019)
986–996, https://doi.org/10.1016/j.scitotenv.2019.06.292.
https://doi.org/10.1016/j.carbon.2013.09.025.
[12] J. Lei, X. Lu, W. Wang, X. Bian, Y. Xue, C. Wang, L. Li, Fabrication of MnO2/
graphene oxide composite nanosheets and their application in hydrazine detection,
RSC Adv 2 (2012) 2541–2544, https://doi.org/10.1039/c2ra01065h.
[13] Y. Dong, K. Li, P. Jiang, G. Wang, H. Miao, J. Zhang, C. Zhang, Simple
[31] Z. Fathi, E. Doustkhah, S. Rostamnia, F. Darvishi, A. Ghodsi, Y. Ide, Interaction of
Yarrowia lipolytica lipase with dithiocarbamate modified magnetic carbon
Fe3O4@C-NHCS2H core-shell nanoparticles, Int. J. Biol. Macromol. 117 (2018)
218–224, https://doi.org/10.1016/j.ijbiomac.2018.05.156.
hydrothermal preparation of α-, β-, and γ-MnO2 and phase sensitivity in catalytic
ozonation, RSC Adv 4 (2014) 39167–39173, https://doi.org/10.1039/c4ra02654c.
[14] Z. Li, Y. Ding, Y. Xiong, Q. Yang, Y. Xie, One-step solution-based catalytic route to
[32] A. Ahadi, H. Alamgholiloo, S. Rostamnia, X. Liu, M. Shokouhimehr, D.A. Alonso,
R. Luque, Layer-wise titania growth within dimeric organic functional group
viologen periodic mesoporous organosilica as efficient photocatalyst for oxidative
formic acid decomposition, ChemCatChem 11 (2019) 4803–4809, https://doi.org/
10.1002/cctc.201900486.
fabricate novel α-MnO2 hierarchical structures on a large scale, Chem. Commun.
(2005) 918–920, https://doi.org/10.1039/b414204g.
[15] Z. Li, Y. Ding, Y. Xiong, Y. Xie, Rational growth of various α-MnO2 hierarchical
structures and β-MnO2 nanorods via a homogeneous catalytic route, Cryst. Growth
Des. 5 (2005) 1953–1958, https://doi.org/10.1021/cg050221m.
[33] A. Baghban, M. Heidarizadeh, E. Doustkhah, S. Rostamnia, P.F. Rezaei, Covalently
bonded pancreatic lipase onto the dithiocarbamate/chitosan-based magnetite:
stepwise fabrication of Fe3O4@CS/NHCS-Lip as a novel and promising
nanobiocatalyst, Int. J. Biol. Macromol. 103 (2017) 1194–1200, https://doi.org/
10.1016/j.ijbiomac.2017.05.159.
[16] J. Wu, H. Huang, L. Yu, J. Hu, Controllable hydrothermal synthesis of MnO&lt;
sub&gt;2&lt;/sub&gt; nanostructures, Adv. Mater. Phys. Chem (2013) 201–205,
https://doi.org/10.4236/ampc.2013.33029, 03.
[17] F. Cheng, J. Zhao, W. Song, C. Li, H. Ma, J. Chen, P. Shen, Facile controlled
synthesis of MnO2 nanostructures of novel shapes and their application in batteries,
Inorg. Chem. 45 (2006) 2038–2044, https://doi.org/10.1021/ic051715b.
[18] M.M. Kadam, K.B. Dhopte, N. Jha, V.G. Gaikar, P.R. Nemade, Synthesis,
characterization and application of γ-MnO2/graphene oxide for the selective
aerobic oxidation of benzyl alcohols to corresponding carbonyl compounds, New J.
Chem. 40 (2016) 1436–1442, https://doi.org/10.1039/c5nj03140k.
[34] H. Karimi-Maleh, F. Karimi, S. Malekmohammadi, N. Zakariae, R. Esmaeili,
S. Rostamnia, M.L. Yola, N. Atar, S. Movaghgharnezhad, S. Rajendran, A. Razmjou,
Y. Orooji, S. Agarwal, V.K. Gupta, An amplified voltammetric sensor based on
platinum nanoparticle/polyoxometalate/two-dimensional hexagonal boron nitride
nanosheets composite and ionic liquid for determination of N-hydroxysuccinimide
in water samples, J. Mol. Liq. (2020) 310, https://doi.org/10.1016/j.
molliq.2020.113185.
¨
˘
[19] R.B. Tosun, K.O. Hamaloglu, P.A. Kavaklı, C. Kavaklı, A. Tuncel, A synergistic
catalyst based on a multivalence monodisperse-porous microspheres with oxygen
vacancies for benzyl alcohol oxidation, Mol. Catal. 497 (2020), 111227, https://
doi.org/10.1016/j.mcat.2020.111227.
[35] E. Doustkhah, M. Heidarizadeh, S. Rostamnia, A. Hassankhani, B. Kazemi, X. Liu,
Copper immobilization on carboxylic acid-rich Fe3O4-Pectin: Cu2+@Fe3O4-Pectin
a superparamagnetic nanobiopolymer source for click reaction, Mater. Lett. 216
(2018) 139–143, https://doi.org/10.1016/j.matlet.2018.01.014.
[20] A. Kamimura, Y. Nozaki, M. Nishiyama, M. Nakayama, Oxidation of benzyl
alcohols by semi-stoichiometric amounts of cobalt-doped birnessite-type layered
MnO2 under oxygen atmosphere, RSC Adv. 3 (2013) 468–472, https://doi.org/
10.1039/c2ra22117a.
[36] Z. Li, Y. Yao, Y. Zheng, T. Gao, Z. Liu, G. Zhou, Fabrication of core-shell Fe3O4
@C@MnO2 microspheres and their application in supercapacitors, J. Electrochem.
Soc. 165 (2018), https://doi.org/10.1149/2.0961802jes. E58-E63.
[37] B. Duan, D. Wang, H. Wu, P. Xu, P. Jiang, G. Xia, Z. Liu, H. Wang, Z. Guo, Q. Chen,
Core-Shell Structurized Fe3O4@C@MnO2 nanoparticles as pH responsive T1-T2*
dual-modal contrast agents for tumor diagnosis, ACS Biomater. Sci. Eng 4 (2018)
3047–3054, https://doi.org/10.1021/acsbiomaterials.8b00287.
[21] J. Bu, W. Wang, H. Zhang, C. Wu, B. Zhang, Y. Cao, F. Zhou, Q. Zhang, X. Zhang,
Efficient synthesis of imine from alcohols and amines over different crystal
structure MnOX catalysts, Mol. Catal. 459 (2018) 46–54, https://doi.org/10.1016/
j.mcat.2018.08.016.
[22] Q. Tang, X. Huang, Y. Chen, T. Liu, Y. Yang, Characterization and catalytic
application of highly dispersed manganese oxides supported on activated carbon,
J. Mol. Catal. A Chem. 301 (2009) 24–30, https://doi.org/10.1016/j.
molcata.2008.11.003.
[38] I.J. Bruce, T. Sen, Surface modification of magnetic nanoparticles with
alkoxysilanes and their application in magnetic bioseparations, Langmuir 21
(2005) 7029–7035, https://doi.org/10.1021/la050553t.
[39] Y. Li, X. Xu, D. Qi, C. Deng, P. Yang, X. Zhang, Yan Li, † Xiuqing Xu, † Dawei Qi,
Chunhui Deng, *Pengyuan Yang, Xiangmin Zhang*, J. Proteome Res. 7 (2008)
2526–2538.
[23] Y. Li, A. Sabbaghi, J. Huang, K.C. Li, L.S. Tsui, F.L.Y. Lam, X. Hu, Aerobic oxidation
of benzyl alcohol: influence from catalysts basicity, acidity, and preparation
methods, Mol. Catal. 485 (2020), 110789, https://doi.org/10.1016/j.
mcat.2020.110789.
[40] Y. Li, T. Leng, H. Lin, C. Deng, X. Xu, N. Yao, P. Yang, X. Zhang, Preparation of
Fe3O4@ZrO2 core - shell microspheres as affinity probes for selective enrichment
and direct determination of phosphopeptides using matrix-assisted laser desorption
ionization mass spectrometry, J. Proteome Res. 6 (2007) 4498–4510, https://doi.
org/10.1021/pr070167s.
[24] A. Wang, W.Y. Zhou, Z. Sun, Z. Zhang, Z. Zhang, M.Y. He, Q. Chen, Mn(III) active
site in hydrotalcite efficiently catalyzes the oxidation of alkylarenes with molecular
oxygen, Mol. Catal. 499 (2021), 111276, https://doi.org/10.1016/j.
mcat.2020.111276.
[41] X. Bao, Z. Qiang, J.H. Chang, W. Ben, J. Qu, Synthesis of carbon-coated magnetic
nanocomposite (Fe3O4 at C) and its application for sulfonamide antibiotics removal
from water, J. Environ. Sci. (China). 26 (2014) 962–969, https://doi.org/10.1016/
S1001-0742(13)60485-4.
[25] D. Wu, X. Xie, Y. Zhang, D. Zhang, W. Du, X. Zhang, B. Wang, MnO2/carbon
composites for supercapacitor: synthesis and electrochemical performance, Front.
Mater. 7 (2020) 1–16, https://doi.org/10.3389/fmats.2020.00002.
[26] H. Alamgholiloo, S. Rostamnia, N.N. Pesyan, Anchoring and stabilization of
colloidal PdNPs on exfoliated bis-thiourea modified graphene oxide layers with
super catalytic activity in water and PEG, Colloids Surfaces A Physicochem. Eng.
Asp. 602 (2020), 125130, https://doi.org/10.1016/j.colsurfa.2020.125130.
[27] V.M. Shinde, E. Skupien, M. Makkee, Synthesis of highly dispersed Pd
nanoparticles supported on multi-walled carbon nanotubes and their excellent
catalytic performance for oxidation of benzyl alcohol, Catal. Sci. Technol. 5 (2015)
4144–4153, https://doi.org/10.1039/c5cy00563a.
[42] F. Arena, B. Gumina, A.F. Lombardo, C. Espro, A. Patti, L. Spadaro, L. Spiccia,
Nanostructured MnOx catalysts in the liquid phase selective oxidation of benzyl
alcohol with oxygen: part I. Effects of Ce and Fe addition on structure and
reactivity, Appl. Catal. B Environ. 162 (2015) 260–267, https://doi.org/10.1016/j.
apcatb.2014.06.054.
[43] M. Alhumaimess, Z. Lin, Q. He, L. Lu, N. Dimitratos, N.F. Dummer, M. Conte, S.
H. Taylor, J.K. Bartley, C.J. Kiely, G.J. Hutchings, Oxidation of benzyl alcohol and
carbon monoxide using gold nanoparticles supported on MnO2 nanowire
microspheres,, Chem. A Eur. J. 20 (2014) 1701–1710, https://doi.org/10.1002/
chem.201303355.
[28] H. Alamgholiloo, S. Rostamnia, A. Hassankhani, X. Liu, A. Eftekhari,
A. Hasanzadeh, K. Zhang, H. Karimi-Maleh, S. Khaksar, R.S. Varma,
M. Shokouhimehr, Formation and stabilization of colloidal ultra-small palladium
nanoparticles on diamine-modified Cr-MIL-101: synergic boost to hydrogen
production from formic acid, J. Colloid Interface Sci. 567 (2020) 126–135, https://
doi.org/10.1016/j.jcis.2020.01.087.
[44] V.G. Reddy, D. Jampaiah, A. Chalkidis, Y.M. Sabri, E.L.H. Mayes, S.K. Bhargava,
Highly dispersed cobalt oxide nanoparticles on manganese oxide nanotubes for
aerobic oxidation of benzyl alcohol, Catal. Commun. 130 (2019), 105763, https://
doi.org/10.1016/j.catcom.2019.105763.
[29] G. Wu, Y. Gao, F. Ma, B. Zheng, L. Liu, H. Sun, W. Wu, Catalytic oxidation of benzyl
alcohol over manganese oxide supported on MCM-41 zeolite, Chem. Eng. J. 271
(2015) 14–22, https://doi.org/10.1016/j.cej.2015.01.119.
[45] I.M. Goldman, Observation of a large isotope effect in the manganese dioxide
oxidation of benzyl alcohol, J. Org. Chem. 34 (1969) 3289–3295, https://doi.org/
10.1021/jo01263a015.
8