Cobalt oxide NPs immobilized on environmentally benign biological macromolecule-derived N-doped mesoporous carbon as an efficient catalyst for hydrogenation of nitroarenes

Article abstract of DOI:10.1016/j.jssc.2020.121645

Highly nitrogen-doped mesoporous carbon (N-mC) material incorporated cobalt oxide nanoparticles was synthesized through simple pyrolysis of environmentally friendly chitosan-polyaniline-Co(OAc)₂ precursor in one-step. The as-prepared catalyst named CoO&at;N-mC with 14.65 ?wtpercent nitrogen content was characterized by different analysis techniques. The heterogeneous catalyst exhibits outstanding catalytic activity for the reduction of a variety of nitroaromatic compounds in the presence of NaBH₄ as a reducing agent in water as a green solvent at 75 ?°C. Utilization of natural biological macromolecules such as chitosan as green and cheap starting material with harmless aniline and earth-abundant cobalt salt, facile synthesis, excellent product yield, short reaction time, high chemoselectivity, sustainable and mild reaction condition, and reusability of catalyst for at least five cycles without any significant decline in the catalytic efficiency are some prominent merits of this new nanocatalyst.

Full text of DOI:10.1016/j.jssc.2020.121645

Journal Pre-proof
Cobalt oxide NPs immobilized on environmentally benign biological macromolecule-
derived N-doped mesoporous carbon as an efficient catalyst for hydrogenation of
nitroarenes
Zahra Soleimani Nanadegani, Firouzeh Nemati, Ali Elhampour, Yalda Rangraz
PII:
S0022-4596(20)30475-8
DOI:
https://doi.org/10.1016/j.jssc.2020.121645
YJSSC 121645
Reference:
To appear in: Journal of Solid State Chemistry
Received Date: 6 June 2020
Revised Date: 21 July 2020
Accepted Date: 2 August 2020
Please cite this article as: Z.S. Nanadegani, F. Nemati, A. Elhampour, Y. Rangraz, Cobalt oxide NPs
immobilized on environmentally benign biological macromolecule-derived N-doped mesoporous carbon
as an efficient catalyst for hydrogenation of nitroarenes, Journal of Solid State Chemistry (2020), doi:
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Cobalt oxide NPs immobilized on environmentally benign biological
macromolecule-derived N-doped mesoporous carbon as an efficient
catalyst for hydrogenation of nitroarenes
Zahra Soleimani Nanadegani (Investigation, Data Curation, Visualization)
Firouzeh Nemati (Conceptualization; Validation, Resources, Writing - Review & Editing,
Supervision, Project administration, Funding acquisition)
Ali Elhampour (Conceptualization, Supervision)
Yalda Rangraz(Conceptualization, Methodology, Data Curation, Writing - Original Draft)

Cobalt oxide NPs immobilized on environmentally benign biological
macromolecule-derived N-doped mesoporous carbon as an efficient
catalyst for hydrogenation of nitroarenes
Zahra Soleimani Nanadegani,a Firouzeh Nemati,a* Ali Elhampoura, Yalda Rangraz*b
aDepartment of Chemistry, Semnan University, Semnan, Iran. Tel: (+982331532831); E-mail:
fnemati@semnan.ac.ir
bLecturer, Semnan University, Semnan, Iran. Email: yrangraz@semnan.ac.ir
Abstract: Highly nitrogen-doped mesoporous carbon (N-mC) material incorporated cobalt oxide
nanoparticles was synthesized through simple pyrolysis of environmentally friendly chitosan-
polyaniline-Co(OAc)2 precursor in one-step. The as-prepared catalyst named CoO@N-mC with
14.65 wt% nitrogen content was characterized by different analysis techniques. The
heterogeneous catalyst exhibits outstanding catalytic activity for the reduction of a variety of
nitroaromatic compounds in the presence of NaBH4 as a reducing agent in water as a green
solvent at 75 °C. Utilization of natural biological macromolecules such as chitosan as green and
cheap starting material with harmless aniline and earth-abundant cobalt salt, facile synthesis,
excellent product yield, short reaction time, high chemoselectivity, sustainable and mild reaction
condition, and reusability of catalyst for at least five cycles without any significant decline in the
catalytic efficiency are some prominent merits of this new nanocatalyst.
Keywords: Chitosan, Nitrogen-doped carbon, Cobalt oxide nanoparticles.
1. Introduction

Aniline derivatives play an important role in organic synthesis, especially in fine chemicals,
biological, and pharmaceutical materials [1, 2]. Conventionally, anilines can be synthesized by
reduction of nitroarenes in the presence of different catalysts containing noble metals such as Pd,
Pt, Ag along with alloys like PdCu, AuCu, and PtNi with a convenient hydrogen source [3-6].
However, the application scope of these metals is still restricted in the industry because of
moderate availability, high price, and secondary pollution causes by metal leaching. Therefore,
some researches have spurred interest in catalysis with more earth-abundant alternatives,
especially Fe, Co, and Ni metals [2, 7, 8].
Although, the non-noble metals endure from the oxidation, sintering, and leaching problems.
Therefore, the development of greener and more effective heterogeneous non-noble catalysts is
highly imperative to synthesize functionalized nitroarenes under benign reaction conditions for
large-scale production.
It has been found that, among the non-noble metals, cobalt nanoparticles exhibit unexpectedly
high catalytic activity toward hydrogenation of nitro compounds [9].
In recent years, many attempts have been made to design different heterogeneous cobalt catalysts
for reduction reactions [10-13].
Recently, N-doped carbon metal-based catalysts were found as a novel strategy for improving
the performance of the heterogeneous catalyst [14-16].
A key issue for the catalytic activity of these materials is the synergistic combination of metal
nanoparticles with the N-doped carbon matrix, which results from the pyrolysis of the original
organic ligand [17].
One of the suitable organic ligand for the preparation of N-doped carbon material is chitosan [17,
18]. This non-toxic biomass-derived product has some interesting properties including

sustainability biodegradable and low-cost as well as a high binding affinity for transition-metal
ions. Furthermore, increasing the nitrogen content in N-doped carbon materials can largely
improve the physicochemical properties of these carbonaceous skeletons because of the strong
interaction between the lone-pair electrons of doped N-atoms and exotic species [19].
Considering the aforementioned background and our endeavors in the design and synthesis of the
novel heterogeneous catalyst [20-28], herein, the cobalt oxide incorporated in N-rich-
mesoporous carbon material (CoO@N-mC) was synthesized by a facile one-pot pyrolysis
method. The starting material prepared from in situ polymerization of polyaniline (PANI) in the
presence of chitosan (CS), and then grafting to cobalt acetate. The pyrolysis of CS/PANI-
Co(OAc)2 as precursor at three different temperatures (600, 700 and 800 °C) showed that the
CoO@N-mC composite, which prepared at 600 °C exhibited efficient catalytic activity as a
catalyst in the reduction of nitro compounds with NaBH4 as reducing agent, in H2O as a green
solvent at 600 °C.
2. Experimental
2.1 Materials
All chemicals Chitosan, Aniline, Ammonium persulfate (APS), Cobalt(II) acetate tetrahydrate
CO(OAc)2.4H2O, sodium borohydride (NaBH4), Acetic acid, solvents, and various nitroarenes
were purchased from chemical corporations and exploited without purification.
2.2 Characterization Techniques
To analyze functional groups, Fourier transform infrared (FT-IR) spectra were recorded by using
a Shimadzu 8400s spectrometer in the range of 4000-400 cm−1 with pressed KBr discs. The
crystalline structure of the material was surveyed by a Philips X-ray diffractometer (XRD) using
Cu Ka as the irradiation source (λ=1.5418 Å) in the range of 2θ = 10°-80°.

To study the thermal stability of the samples, thermogravimetric analysis (TG) was
accomplished on a DuPont 2000 thermo-analyzer instrument, rising from 30 to 800 °C under an
air atmosphere at a ramping rate of 10 °C/min.
The detailed morphology and elemental mapping of prepared samples were investigated using a
field emission scanning electron microscope (FESEM) (Tescanvega II XMU digital scanning
microscope), equipped with the energy dispersive X-ray spectroscopy (EDS).
Brunauer-Emmett-Teller (BET) measurement was performed on a Beckman Coulter SA3100
plane area analysis. Raman spectroscopy was applied to evaluate the graphitization of CoO@N-
mC nanocatalyst.
The content of Co in the nanocatalyst was determined with an atomic absorption spectrometer
(Shimadzu model AA-680) using air/acetylene flame atomizer.
Thin layer chromatography (TLC) on commercial aluminum-backed plates coated with silica gel
60 F254, by UV light was used for determinations of the progress of the reduction reaction.
2.3 Fabrication of CoO@N-mC Nanocatalyst
2.3.1 Fabrication of CS/PANI hybrid
The CS/PANI hybrid was prepared based on previous literature [29]. In a typical procedure,
0.754 g of aniline (8. 35 mmol) in 100 mL of 2 wt % acetic acid was added to a solution of
chitosan (1 g) in 2 wt % acetic acid (100 mL). Then, the mixture was cooled to 5 °C in an
ice/water bath under vigorous stirring. Afterward, 25 mL of 2 wt % acetic acid solution
containing 1.9 g of ammonium persulfate (8.35 mmol) was dropwise added to the above-cooled
mixture and stirred at 5 °C for 1 h, and then at ambient temperature for 3 h. Finally, the resulting
green sediment was centrifuged and washed several times with 2 wt % acetic acid solution to
remove completely oligomers of aniline and then dried at 80 °C for 12 h.

2.3.2 Fabrication of CS/PANI-Co(OAc)2
0.126 g of cobalt(II) acetate tetrahydrate (0.5 mmol) was first dissolved in 20 mL of ethanol in a
100 mL round-bottom flask. Second, 0.69 g of prepared CS/PANI hybrid was added to the above
mixture and refluxed at 70 °C with continuous stirring for 20 h. After the reaction mixture was
cooled to room temperature, ethanol evaporated on a rotary evaporator and then obtained brown
solid dried in an oven at 60 °C for 12 h.
2.3.3 Fabrication of CoO@N-mC
The obtained CS/PANI-Co(OAc)2 powder was transferred into a ceramic crucible and heated in
a muffle furnace at the appropriate temperature (e.g. 600, 700, and 800 °C) for 2 h under
nitrogen atmosphere. The ramping rate was 10 °C min−1. The resultant black material was
denoted as CoO@N-mC.
2.3.4 Synthesis of amines catalyzed using CoO@N-mC
To a 10 mL round-bottom flask equipped with a magnetic stirrer, CoO@N-mC nanocatalyst (30
mg), nitroarene (1.0 mmol), and H2O (3 mL) were added and the reaction mixture was stirred at
ambient temperature for 5 min, then NaBH4 (3 mmol) was added and the resulting mixture
heated in an oil bath at 75 °C for an appropriate time. After the finishing of the reduction
reaction that was followed by applying TLC, CoO@N-mC nanocatalyst was separated with the
centrifuge, rinsed with ethanol, dried at 60 °C to be ready for the next cycle without any
purification. After isolation of catalyst, the product was extracted with ethyl acetate and purified
by short column chromatography on silica gel, if necessary, to obtain the relevant compound in
desired purity.
3. Results and discussion
3.1. Preparation and characterization of the CoO@N-mC catalyst

The steps of the preparation process for the CoO@N-mC catalyst were schematically depicted in
Scheme 1. In the first step, the starting material was prepared by in situ oxidation polymerization
of aniline monomer in the presence of chitosan at 5 °C. Then cobalt acetate was immobilized
into the chitosan/PANI material in ethanol at 70 °C for 20h. Finally, the CS/PANI-Co(OAc)2 as
the brown powder was pyrolyzed at three different temperatures to generate CoO@N-mC
catalyst (for details see Experimental section). Among them, the as-prepared composite, which
had been prepared at 600 °C shows the best catalytic character. So, it was examined using
different techniques including XRD, FTIR, TGA, FE-SEM, EDX, Raman, and BET, which
discuss in detail in follow.
Scheme 1. The synthetic procedure of CoO@N-mC

The XRD pattern of as-prepared catalyst, CoO@N-mC, is shown in Fig. 1. The characteristic
peak of N-mC material has appeared as a broad peak at 25º, which can be indexed to (0 0 2)
plane of the graphitic carbon [30].
The absence of another broad peak at 2θ = 44º (1 0 0 plane), demonstrates the more defects
because of the incorporation of more additional nitrogen atoms into the carbon skeleton [31].
Also, the other diffraction peaks at 35º (1 1 1), 42º (2 0 0), and 61º (2 2 0) were matched with the
cubic phase of CoO particles in nanocomposite [32]. Using the Debye-Sherrer formula from the
full width at half maximum (FWHM), the mean size of the CoO nanoparticles has been estimated
around 18 nm.
Fig. 1. XRD pattern of CoO@N-mC
The functional groups were identified by FT-IR spectra of CS-PANI, CS-PANI/Co(OAc)2 and
CoO@N-mC, and they displayed in Fig. 2. The FTIR spectrum of the CS-PANI presents
distinctive vibrational bands of both CS and PANI segments; The broad bands centered at 3159

and 3417 cm-1 can be attributed to the stretching vibrations of the hydroxyl and amine groups as
well as the H-bonding interaction between CS and PANI [33]. The obvious peaks appearing at
1575 and 1446 cm−1 correspond to the stretching vibrations of C=N (quinoid ring) and C=C
(benzenoid ring) of PANI, respectively [34]. Also, the adsorption bands located at 1400, 1064,
and 696 cm-1 can be assigned to the stretching vibrations of C-N, C-O (related to CS), and γ(C-
H) in the aromatic ring, respectively [35] (Fig. 2a). These overcomes illustrate that a strong steric
electrostatic interaction happens between CS and PANI, indicating the generation of a
copolymer.
In the FTIR spectrum of the CS-PANI/Co(OAc)2, the intensity of the quinoid and benzenoid
bands has decreased. This result displays that nitrogen atoms of amine (-NH-) and imine (-N=)
have bonded with Co2+ through either complexation or protonation [36](Fig. 2b).
In the FTIR spectrum of the CoO@N-mC, the presence of adsorption peak at 1398 cm-1 related
to the stretching vibrations of the C-C bond affirms the successful conversion of the precursor to
synthesized nanocatalyst as well as the well-carbonized structure of the CoO@N-mC (Fig. 2c).

Fig. 2. FT-IR spectra of (a) CS-PANI, (b) CS-PANI/Co(OAc)2 and (c) CoO@N-mC
The thermal behavior of the CS-PANI/Co(OAc)2 and CoO@N-mC was investigated using
thermogravimetric analysis (TGA) (Fig. 3). The thermogram of the CS-PANI/Co(OAc)2 shows
three weight loss stages. The first mass loss in the range of 30-150 °C is ascribed to the
evaporation of guest molecules, such as H2O and EtOH solvent, trapped in the polymeric
framework. Rapid weight loss (about 33%) at approximately 150-300 °C corresponds to the
deacetylation and depolymerization of CS [35]. The final mass loss (about 40%) that occurred in
the range of 350-550 °C can be attributed to the residual decomposition reactions, degradation of
acetate counter anion, and the decomposition and degradation of the polymer backbone [17, 33]
(Fig. 3a). The TGA curve of CoO@N-mC exhibits that the thermal decomposition of the catalyst
starts from higher temperature compared with the precursor (about 400 °C), indicating pyrolysis
can significantly enhance the thermal stability of the prepared nanocatalyst. The residual mass

percent of the sample at 800 °C was estimated at around 20% that related to the content of cobalt
oxide in the composite(Fig. 3b).
Fig. 3. TGA diagrams of (a) CS-PANI/Co(OAc)2 and (b) CoO@N-mC
The morphology, structure, and elemental composition of CoO@N-mC were characterized by
FE-SEM and EDX analyses (Fig. 4 and 5). CoO@N-mC indicates a sponge-like morphology
with a rough surface and abundant mesopores. Cobalt oxide NPs were uniformly distributed in
the N-rich-mesoporous carbon matrix after pyrolysis at 600 °C (Fig. 4). Besides, the EDX
spectrum of CoO@N-mC clearly exhibits that the nanocatalyst was composed of C, N, O, and
Co elements.
The appearance of the S element in the EDX pattern of catalyst is due to the use of ammonium
persulfate in the chitosan-polyaniline polymerization process (Fig. 5). The amount of cobalt
obtained from EDX analysis was nearly 11.45 wt%.

Fig. 4. SEM images of CoO@N-mC at disparate magnifications
Fig. 5. EDX spectrum of CoO@N-mC

To figure out the distribution of elements in CoO@N-mC, the EDX-mapping analysis was
conducted. As depicted in Fig. 6, elements of C, N, O, and Co are uniformly distributed in
CoO@N-mC nanocomposite.
For measuring the cobalt amount in CoO@N-mC, atomic absorption spectroscopy (AAS)
analysis was exploited. The cobalt content was calculated to be 13.45 wt %, which is consistent
with the data of EDX analysis.
Fig. 6. Elemental mapping data of CoO@N-mC

Raman spectroscopy is a sensitive and informative technique to determine the degree of
graphitization of the carbon matrix in the synthesized catalyst. The Raman spectrum of the
CoO@N-mC nanocatalyst (Fig. 7) displays two strong peaks at around 1582 cm-1 (G-bond) and
1372 cm-1 (D-band) that can be assigned to the sp2-bonded graphitic carbon sheets (the in-plane
vibration of the sp2 carbon atoms) and the disordered or defective graphitic carbon [37],
respectively. The presence of these two peaks affirms the graphitic carbon structure for CoO@N-
mC. Furthermore, the attendance of the 2D band at 2681 cm−1 is another evidence to confirm the
degree of graphitization at a good level [38, 39]. The ID/IG value was found to be 1.06,
indicating plenty of disordered or more defective graphitic structures due to the doping of N
atoms to the carbon matrix [40].
Fig. 7. Raman spectrum of CoO@N-mC

The porosity parameters of CoO@N-mC were investigated by the nitrogen adsorption-desorption
technique. As displayed in Fig. 8a, the isotherm of nanocatalyst reveals a type-IV curve based on
the IUPAC nomenclature, thereby authenticates the existence of the mesopores structure. The
specific surface area and total pore volume of the CoO@N-mC are determined to be 32.96 m2 g-1
and 0.051 cm3 g-1. Also, according to the BJH method, the distribution of pore size shows that
the nanocatalyst has uniform mesopores of 6.32 nm (Fig. 8b).
Fig. 8. N2 adsorption-desorption isotherm (a) and BJH pore size distribution graph (b) of CoO@N-mC
3.2. Catalytic studies of CoO@N-mC nanocomposite as a heterogeneous catalyst in the synthesis
of amines
To examine the catalytic potential of the CoO@N-mC, the reduction of 4-nitroaniline in the
presence of NaBH4 was chosen as a test reaction and the influence of different parameters
(dosage of the catalyst and reductant, solvent and temperature) was surveyed in detail for the
optimization of the reaction conditions and the outcomes were summarized in Table 1. Primarily,

the effect of catalyst quantity was examined with the conduction of the benchmark reaction in
different dosages of the as-prepared nanocatalyst. As listed in Table 1, Entry 2, 30 mg of
CoO@N-mC was found to be the best result. By decreasing the nanocomposite loading to 20 mg,
the conversion of the target product decreased to 70% (Table 1, Entry 1) and increase the amount
of nanocomposite from 30 to 40 mg did not either appreciable influence on the product yield or
rate of reaction (Table 1, Entry 3). In the next step, the NaBH4 loading was investigated. Sodium
borohydride is an effective and widely used reducing agent. The relatively low cost and the ease
with which it can be handled contribute to its popularity [41]. The best yield was attained with 3
mmol of NaBH4 (Table 1, Entry 6). The reaction was also performed in the absence of the
NaBH4 and an only trace amount of 4-nitroaniline was formed (Table 1, Entry 4). Subsequently,
to analyze the role of the solvent, the model reaction was fulfilled in miscellaneous solvents
(Table 1, Entries 7-11) The product yield was very low in non-polar and aprotic solvents like
toluene and THF, while by employing protic solvents such as H2O, CH3OH, EtOH, and EtOH:
H2O, the desired product was achieved in high yield. Among protic solvents, H2O as an
inexpensive, sustainable, green, and the environmentally friendly solvent was selected as the
most suitable solvent for this transformation. The possible explanation for increasing its catalytic
performance in water could be that CoO@N-mC with high N-doping content has high
hydrophobic properties, which resulted better exposure to the reactant systems due to well
dispersion of the catalyst in the water [7]. Eventually, temperature screening was done and the
best yield was achieved at 75 °C. With the temperature reduction to 55 °C, the conversion
percentage of the product reduced to 80% (Table 1, Entry 12) and as shown in (Table 1, Entry
13), the increment of the temperature to higher one was not impressive on the yield of the amine.

Therefore, Entry 6 of Table 1 was selected as the optimum condition in the hydrogenation
reaction of nitro compounds.
Table 1. Optimization of the amount of the catalyst and reductant, solvent, and temperature for
reduction of 4-nitroaniline as a model reaction using CoO@N-mC as catalysta
NaBH4
(mmol)
Temp.(oC)
Entry Catalyst (mg)
Solvent
Time(min) Yield(%)b
1
2
3
4
5
6
7
8
9
10
11
12
13
20
30
40
30
30
30
30
30
30
30
30
30
30
4
4
4
-
2
3
3
3
3
3
3
3
3
H2O
H2O
H2O
H2O
H2O
75
75
75
75
75
75
75
75
75
75
75
55
95
25
25
25
25
25
25
25
25
25
25
25
25
25
75
98
98
Trace
70
98
85
75
98
35
H2O
EtOH
MeOH
H2O:EtOH
THF
Toluene
H2O
30
80
98
H2O
aReaction condition: substrate (1.0 mmol), solvent (3 mL), NaBH4.
bIsolated yield.
After elucidating the favorable reaction conditions, the generality and scope of the reaction were
investigated using several structurally different nitroarenes. Results indicate that nitroarenes
bearing electron-donating substituents such as OH, NH2, NHNH2, and CH2OH as well as
reducible electron-withdrawing substituents such as CN, COCH3, CHO, and COOH were
efficiently reduced to corresponding products in excellent yields and sensitive functional groups

remained intact during the hydrogenation process. Also, nitrobenzenes with halogen groups
including Cl, Br, and I were successfully converted into the relevant aniline derivatives without
dehalogenation.
Table 2. The reduction reaction of nitroarenes in the presence of CoO@N-mC nanocatalysta
TOFc
(h-1)
Time
(min)
Yield
(%)b
Entry
Substrate
Product
3196
1
2
3
20
25
25
96
98
94
4307
4104
6725
HO
NO2
HO
NH2
4
5
10
30
98
90
1978
1978
6
7
30
60
90
75
824
3163
8
20
95

6730
6730
9
10
10
98
98
10
6730
1978
11
12
10
30
98
90
3130
3956
989
13
14
20
25
94
90
15
16
60
90
824
60
75
areaction conditions: substrate (1 mmol), nanocatalyst (30 mg, 0.091 mol%), NaBH4 (3 mmol), solvent (3 mL,
H2O), 75 °C
bIsolated yield; c mol (product) mol-1(catalyst) h-1
3.3 Proposed mechanism route for the amine synthesis in the presence of CoO@N-mC
nanocomposite
Based on the previous reports [42-44], a tentative mechanism for the hydrogenation of
nitroarenes by applying as-fabricated Co nanocatalyst in the attendance of sodium borohydride is
pictorially demonstrated in Scheme 2.

The present reduction process consists of several successive steps as displayed in the schematic
-
diagram: (1) reaction of NaBH4 with H2O to produce BO2 and activation hydrogen (H2), (2) the
cleavage of H-H bond in the presence of cobalt oxide NPs and formation of cobalt hydride
complex (3) the adsorption of nitroarene to the surface of cobalt active sites, (4) hydride transfer
from cobalt hydride complex to the nitroarene and reduction of the nitro group to the nitroso,
hydroxylamine and next aniline derivative in the rate determining step, and (5) finally desorption
of product from the surface of the nanocatalyst.

Scheme 2. The plausible mechanism for the reduction of nitroarenes by CoO@N-mC
3.4 Comparison between catalytic efficiency of CoO@N-mC and other reported catalysts in the
hydrogenation reaction
In this step of work, the advantage and applicability of CoO@N-mC in the hydrogenation
reaction of nitroarenes were compared with several reported homogeneous and heterogeneous
cobalt catalysts in the literature and the results are summarized in Table 3. Although each of
these catalytic systems has its own advantages, it is evident that the current approach displays
superiority in terms of reaction conditions such as solvent, reductant, temperature, recovery and
reusability, loading of catalyst as well as time and product yield.

Table 3. Comparison between catalytic activity of CoO@N-mC and other catalysts in the
hydrogenation of 4-nitroaniline
Entry
Catalyst [ref]
Reaction conditions
Time(h) Yield(%)
1
2
3
4
5
6
7
8
9
Co3S4 (5 mol%) [45]
n-CeO2 (15 mg) [46]
EtOH, NaBH4, 25 °C
N2H4.H2O, EtOH, 80 °C
EtOH, HCO2NH4, r.t
EtOH, H2, 140 °C
1
58
39
8
Pd/C (5 wt%) [47]
12
99
Ni/C-300 (50 mg) [48]
Fe-500-1 ha ( 0.025 mmol) [49]
0.5
95
EtOH, N2H4.H2O, 85 °C
EtOH/H2O, NaBH4, r.t
EtOH, H2, 120 °C
4
100
90
b
Pd@CQD@Fe3O4 (0.008 mol%) [50]
4
Co/mCN-900c (10 mg) [11]
Co@NMC-800d (40 mg) [2]
Present work (30 mg)
4
2
99.9
97.8
96
EtOH, H2, 80 °C
H2O, NaBH4, 75 °C
25 (min)
a nanofibers γ-Fe2O3 NPs encapsulated in porous carbon
b Pd anchored on magnetic NPs modified with carbon quantum dots
c Cobalt NPs immobilized on N-doped mesoporous carbon
d Co-based N-doped mesoporous carbon
3.5 Reusability of CoO@N-mC
Catalysts recovery and reproducibility are very important factors from the viewpoint of green
chemistry, especially for industrial and commercial applications. In this regard, the reusability of
the CoO@N-mC catalyst was checked in the model reaction under the optimum reaction
situations. At the end of the first run, the catalyst was recovered from the reaction media and
reused in the next cycles after washing several times with acetone and ethanol and drying in an
oven. As illustrated in Fig. 9, CoO@N-mC can be reused for 5 runs with only a negligible loss in
yield and its catalytic activity.

Fig. 9. Recycling experiment of CoO@N-mC
Likewise, the XRD pattern of the used nanocatalyst indicates that the crystalline structure and
phase composition of the CoO@N-mC were maintained well without change (Fig. 10).

Fig. 10. XRD patterns of (a) fresh and (b) recycled CoO@N-mC
4. Conclusion
In this research, in-situ cobalt oxide nanoparticles supported on nitrogen-doped mesoporous
carbon material (CoO@N-mC) were successfully synthesized through simple one-pot pyrolysis
of environmental friendly chitosan-polyaniline-Co(OAc)2 as a new precursor. The as-fabricated
CoO@N-mC nanocomposite was then exploited as a recent and impressive catalyst for the
hydrogenation of nitroarenes and indicated an outstanding efficiency in the synthesis of the vast
range of amines under mild condition. Also, this cobalt nanocatalyst exhibited good stability and
could be easily separated and reused five times with a slight decrease in its activity. We hope that
this study can be provided enormous opportunities for the design and preparation of other metal
nanoparticles based heteroatom-doped mesoporous carbon catalysts for the reduction reaction of
nitroarenes with challenging substrates.
Notes

The authors declare no competing financial interest.
Acknowledgments
The authors gratefully acknowledge the financial support of this work by the Chemistry Faculty
of Semnan University.
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