Pd/CoFe2O4/chitosan: A highly effective and easily recoverable hybrid nanocatalyst for synthesis of benzonitriles and reduction of 2-nitroaniline

Article abstract of DOI:10.1016/j.jpcs.2020.109772

In this study, a novel catalyst system with high activity and easy recoverability was successfully prepared through the deposition of Pd nanoparticles (NPs) onto designed sustainable hybrid beads containing magnetic cobalt ferrite and chitosan (Pd/CoFe₂O₄/chitosan). The catalytic potential of Pd/CoFe₂O₄/chitosan hybrid nanocatalyst was then assessed in i) preparation of benzonitriles via aryl halides cyanation and ii) reduction of 2-nitroaniline (2-NA). Various aryl iodides and bromides were successfully cyanated by Pd/CoFe₂O₄/chitosan hybrid nanocatalyst with excellent reaction yields within 3 h. In addition to the production of benzonitriles, the hybrid nanocatalyst showed excellent activity by reducing 2-NA in 65 s. It was proved that the Pd/CoFe₂O₄/chitosan hybrid nanocatalyst outperformed many catalysts used in the cyanation of aryl halides and catalytic reduction of 2-NA previously reported in the literature. Moreover, it was found that the designed Pd/CoFe₂O₄/chitosan hybrid nanocatalyst was easily and effectively separated from the reaction mixture using an external magnet and reused several times in catalytic reactions without considerable loss of catalytic activity.

Full text of DOI:10.1016/j.jpcs.2020.109772

Journal Pre-proof
Pd/CoFe O /chitosan: A highly effective and easily recoverable hybrid nanocatalyst
2 4
for synthesis of benzonitriles and reduction of 2-nitroaniline
Talat Baran, Mahmoud Nasrollahzadeh
PII:
S0022-3697(20)32022-9
https://doi.org/10.1016/j.jpcs.2020.109772
PCS 109772
DOI:
Reference:
To appear in: Journal of Physics and Chemistry of Solids
Received Date: 2 August 2020
Revised Date: 5 September 2020
Accepted Date: 19 September 2020
Please cite this article as: T. Baran, M. Nasrollahzadeh, Pd/CoFe O /chitosan: A highly effective and
2 4
easily recoverable hybrid nanocatalyst for synthesis of benzonitriles and reduction of 2-nitroaniline,
Journal of Physics and Chemistry of Solids (2020), doi: https://doi.org/10.1016/j.jpcs.2020.109772.
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Graphical Abstract
Pd/CoFe2O4/chitosan: A highly effective and easily recoverable hybrid
nanocatalyst for synthesis of benzonitriles and reduction of 2-nitroaniline
Talat Baran and Mahmoud Nasrollahzadeh*
*Corresponding author.
E-mail address: mahmoudnasr81@gmail.com, m.nasrollahzadeh@qom.ac.ir (M. Nasrollahzadeh)

1
Pd/CoFe2O4/chitosan: A highly effective and easily recoverable
2 hybrid nanocatalyst for synthesis of benzonitriles and reduction of
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2-nitroaniline
Talat Barana, Mahmoud Nasrollahzadeh*
,b
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aDepartment of Chemistry, Faculty of Science and Letters, Aksaray University, 68100,
Aksaray, Turkey
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b Department of Chemistry, Faculty of Science, University of Qom, 3716146611, Qom, Iran
Abstract
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In this study, a novel catalyst system with high activity and easy recoverability was
successfully prepared through the deposition of Pd nanoparticles (NPs) onto designed
sustainable hybrid beads containing magnetic cobalt ferrite and chitosan
(Pd/CoFe2O4/chitosan). The catalytic potential of Pd/CoFe2O4/chitosan hybrid nanocatalyst
was then assessed in i) preparation of benzonitriles via aryl halides cyanation and ii) reduction
of 2-nitroaniline (2-NA). Various aryl iodides and bromides were successfully cyanated by
Pd/CoFe2O4/chitosan hybrid nanocatalyst with excellent reaction yields within 3 h. In addition
to the production of benzonitriles, the hybrid nanocatalyst showed excellent activity by
reducing 2-NA in 65 s. It was proved that the Pd/CoFe2O4/chitosan hybrid nanocatalyst
outperformed many catalysts used in the cyanation of aryl halides and catalytic reduction of
2-NA previously reported in the literature. Moreover, it was found that the designed
*Corresponding author.
E-mail address: mahmoudnasr81@gmail.com, m.nasrollahzadeh@qom.ac.ir (M. Nasrollahzadeh).
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Pd/CoFe2O4/chitosan hybrid nanocatalyst was easily and effectively separated from the
reaction mixture using an external magnet and reused several times in catalytic reactions
without considerable loss of catalytic activity.
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Keywords: Pd catalyst, Chitosan, Benzonitrile, 2-Nitroaniline
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1. Introduction
Recently, generation of noble metal nanocatalysts has attracted the attention of scientists due
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to their excellent catalytic performance, nanosized structures, good electronic/optical
properties and huge surface areas [1, 2]. Therefore, different noble metals have been designed
as homogeneous or heterogeneous nanocatalysts for different organic reactions [3, 4].
Although homogeneous catalysts are highly effective and selective, they suffer from
separation problems and usually need costly and specific separation techniques [5, 6]. To
address this problem, preparation of heterogeneous catalysts on various organic/inorganic
support materials has recently received significant attention due to the facile separation of
catalysts [7-9]. However, in most cases, the recovery of heterogeneous catalysts from the
reaction medium via simple traditional methods such as filtration and centrifugation is a
tedious and time consuming task. These problems can be eliminated by the preparation of
catalysts on the modified magnetic composites as catalyst supports to obtain easily separable
catalyst [9, 10]. Additionally, catalysts with magnetic nature can be reused several times due
to retaining their initial activity, which makes them sustainable and ideal catalysts in organic
reactions. Modified magnetic composites are usually prepared on a magnetic core and then
modified with various compounds to obtain different stabilizers/supports [11, 12].
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The development of magnetically recoverable catalytic systems from the reaction media
without using conventional costly and tedious work-up methods plays a crucial role in both
organic reactions and industrial applications. Among magnetic NPs, cobalt spinel ferrites
(CoFe2O4) have superior properties such as high magnetization, excellent mechanical and
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chemical stability as well as easily modified surfaces [13, 14]. Therefore, various compounds
can be combined with CoFe2O4 to synthesize catalyst supports. Chitosan, which is a versatile
and renewable biopolymer obtained from natural sources, has outstanding properties such as
biocompatibility, low cost, abundance and high thermal stability [15, 16]. More importantly, it
has free hydroxyl and amine functional groups, which can provide coordination of transition
metals on the polymer backbone [17]. Additionally, chitosan hydrogel beads can be easily
obtained via these functional groups to improve the metal binding capacity of chitosan [18].
There are several reports concerning the application of chitosan based magnetic catalysts in
organic synthesis [19-21]. Therefore, chitosan can be modified with CoFe2O4, followed by the
preparation of CoFe2O4/chitosan hybrid beads as stabilizers. Afterwards, different metallic
nanoparticles can be immobilized on the designed support and their catalytic role in various
organic reactions can be investigated.
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Benzonitriles are important structural moieties of several valuable compounds such as
agrochemicals, biologically active compounds, natural products and dyes [4,22]. Moreover,
these versatile compounds can be readily transformed into different functional groups such as
aldehydes, amides, acids, amines and ketones [4,22]. For more than a century, benzonitriles
have been synthesized by Rosenmund-von Braun and Sandmeyer reactions [23-26]. However,
these traditional methods suffer from some disadvantages such as i) high reaction
temperatures, ii) large quantities of heavy metal wastes and iii) use of stoichiometric amounts
of CuCN [27, 28]. Therefore, transition metal catalyzed aryl halide cyanation reactions have
been developed as a new methodology for the synthesis of benzonitriles using cyanating
agents such as Cu(CN)2, NaCN, KCN, TMSCN, Zn(CN)2 etc. [4,29-31]. However, the
application of many cyanide agents is generally limited in in the industry due to their highly
toxic nature [4, 30]. Therefore, there is a need for a low toxic cyanation source in this
reaction. Recently, K4[Fe(CN)6] has been utilized as a cyanation agent by researchers due to
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its inexpensiveness, non-toxicity, safety, simplicity of handling and commercial availability
[27, 32]. Different metal catalysts have been designed and utilized in the aryl halide cyanation
in the presence of K4[Fe(CN)6] [33, 34]. Owing to their high catalytic activity and excellent
functional group tolerance, Pd catalysts play an important role in this reaction compared to the
other metal catalysts [30, 35]. Pd catalysts with efficient catalytic performance are thus highly
desired in the cyanation of aryl halides.
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Nowadays, water and environmental pollution caused by various organic pollutants;
especially nitro compounds, has become an important issue [36, 37]. Among nitro
compounds, 2-nitroaniline (2-NA) is one of the most dangerous compounds for aquatic and
human life due to its potential mutagenic and carcinogenic effects [38]. Therefore, 2-NA
poses a great threat to both environmental and public health even at very low concentrations
in water [39]. Hence, the removal of 2-NA from environmental waters is vital to protect
human health. Up till now, different strategies such as thermal decomposition, photocatalytic
degradation, adsorption and catalytic reduction have been developed to remove nitro
compounds [36, 40-42]. Among these, catalytic reduction is one of the most preferable
processes since it provides easy operation, high performance and cost effectiveness [43, 44].
Additionally, catalytic reduction products can be used in various areas. For example, o-
phenylenediamine, which is the reduction product of o-NA, has been widely utilized in the
synthesis of different products such as surfactants, polymers and dyes [45-47]. Therefore, the
reduction of o-NA to o-phenylenediamine in the presence of catalysts is also of great
importance both in terms of environmental and industrial issues and catalysts with high
performance are greatly desired in this reaction.
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In this study, a new heterogeneous Pd nanocatalyst was prepared on magnetic hybrid
microbeads consisting of CoFe2O4/chitosan as the support and its chemical structure was
characterized by FT-IR, FE-SEM, EDS, TEM and XRD. Based on the characterizations,
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Pd/CoFe2O4/chitosan was homogeneously dispersed with a particle size of about 25 nm. The
catalytic behavior of Pd/CoFe2O4/chitosan hybrid nanocatalyst was then investigated in i) aryl
halide cyanation and ii) 2-NA reduction. Pd/CoFe2O4/chitosan hybrid nanocatalyst showed
high catalytic performance in the halide cyanation with a high reaction yield of up to 98%.
Pd/CoFe2O4/chitosan hybrid nanocatalyst developed also successfully converted o-NA to o-
phenylenediamine within a very short reaction time (65 s). More importantly,
Pd/CoFe2O4/chitosan hybrid nanocatalyst displayed high reusability in both aryl halide
cyanation and o-NA reduction due to its magnetic recoverability.
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3. Results and discussion
2. Experimental
2.1. Tools and reagents
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Chitosan (De-acetylation degree: 78%, low molecular weight), FeCl3.6H2O, CoCl2.6H2O,
glutaraldehyde, PdCl2, 2-nitroaniline, K4[Fe(CN)6], NaBH4, Na2CO3, KOH, NaOH, Cs2CO3,
K2CO3, DMF, DMSO, NMP, toluene and aryl halides were purchased from Sigma-Aldrich
Chemical Co. The FT-IR spectra of CoFe2O4/chitosan and Pd/CoFe2O4/chitosan nanocatalyst
were recorded on a Perkin Elmer Spectrum 100 FT-IR spectrophotometer. The XRD patterns
of CoFe2O4, CoFe2O4/chitosan and Pd/CoFe2O4/chitosan hybrid nanocatalyst were obtained
using a Rigaku smart lab system. The FE-SEM micrograms and EDS images of
CoFe2O4/chitosan and Pd/CoFe2O4/chitosan hybrid nanocatalyst were obtained using a
QUANTA-FEG 250ESEM. The TEM images of Pd/CoFe2O4/chitosan hybrid nanocatalyst
were recorded by a TEM JEOL JEM-2100 (UHR) instrument. The reduction of 2-NA was
followed by UV-Vis spectroscopy (Genesys 10S UV-Vis spectrophotometer). Benzonitriles
were characterized using a GC-MS Agilent GC-7890 A-MS 5975 instrument.
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2.2. Synthesis of CoFe2O4
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FeCl3.6H2O (8.2 mmol) and CoCl2.6H2O (4.1 mmol) were dissolved in 75 mL of water and
the solution obtained was stirred at room temperature (RT). 3 g of NaOH (15 mL) were then
added to the reaction mixture dropwise over a period of 10 min during which a black colored
precipitate was formed. Afterwards, the reaction temperature was increased to 90 °C and
stirring was continued for 2 h. Finally, the mixture was cooled to RT and magnetic particles
were then collected by an external magnet, rinsed with water, dried at 80 °C overnight and
calcined at 500 °C for 5 h (Scheme 1).
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2.3. Synthesis of CoFe2O4/chitosan hybrid beads as stabilizer
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1 g of chitosan was dissolved in acetic acid solution (100 mL, 2% v/v) at RT, followed by the
addition of 1 g of CoFe2O4 and stirring for 3 h. The resulting mixture was poured into an
alkaline solution containing NaOH (12 g), water (40 mL) and methanol (60 mL) to form
spherical gel beads. CoFe2O4/chitosan hydrogel beads were then recovered by filtration and
washed with water. Cross-linking was performed by stirring CoFe2O4/chitosan hydrogel beads
with glutaraldehyde (3 mL) in 50ꢀmL of methanol at 70ºC for 6 h. Finally, the cross-linked
CoFe2O4/chitosan beads were collected, washed with water and dried to use as a catalyst
support in the synthesis of Pd NPs (Scheme 1).
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2.3. Preparation of Pd/CoFe2O4/chitosan hybrid nanocatalyst
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1.5 g of the designed CoFe2O4/chitosan microcapsules and 0.3 g of PdCl2 were added into 30
mL of ethanol and the mixture obtained was stirred 70ꢀ°C for 4 h. At the end of this period,
Pd/CoFe2O4/chitosan nanocatalyst was collected using an external magnet, washed with
ethanol and dried to test its catalytic performance in both aryl halide cyanation and 2-NA
reduction (Scheme 1).
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Scheme 1. Preparation of Pd/CoFe2O4/chitosan hybrid nanocatalyst.
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2.4. Typical procedure for aryl halide cyanation using Pd/CoFe2O4/chitosan hybrid
nanocatalyst
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To a Schlenk tube, aryl halide (1.0 mmol), Na2CO3 (1.5 mmol), K4[Fe(CN)6] (0.2 mmol),
Pd/CoFe2O4/chitosan hybrid nanocatalyst (0.25 mol. %) and DMF (6 mL) were transferred
and the resulting mixture was stirred at 120 °C for 3 h. At the end of cyanation reaction,
Pd/CoFe2O4/chitosan hybrid nanocatalyst was separated by an external magnet from the
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reaction medium. The reaction mixture was then extracted using H2O: diethyl ether mixture
three times and the organic phase, which contained benzonitriles, was dried over Na2SO4.
Finally, the desired benzonitrile products were obtained by evaporating the solvents and
benzonitriles were characterized by FT-IR and GC-MS (Fig. S1-S7) analyses.
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2.5. Reduction of 2-NA catalyzed by Pd/CoFe2O4/chitosan hybrid nanocatalyst
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Freshly prepared NaBH4 (0.1 mL, 2.5ꢀ×ꢀ10-2ꢀM) was added to a 2-NA solution (1 mL,
1.25ꢀ×ꢀ10-4ꢀM) and the resulting mixture was stirred at RT for 2 min. Afterwards,
Pd/CoFe2O4/chitosan hybrid nanocatalyst (4 mg) was added to the mixture and stirring was
continued until completion of 2-NA reduction. The progress of the conversion of 2-NA to o-
phenylenediamine was monitored by UV-Vis spectroscopy. After the 2-NA reduction was
complete, Pd/CoFe2O4/chitosan hybrid nanocatalyst was easily separated using an external
magnet, washed with water and dried to use in recycling studies.
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3. Results and discussion
3.1 Characterization of Pd/CoFe2O4/chitosan hybrid nanocatalyst
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Fig. 1 shows the comparative FT-IR spectra of CoFe2O4/chitosan and Pd/CoFe2O4/chitosan
hybrid nanocatalyst. In the spectrum of CoFe2O4/chitosan, characteristic adsorption peaks
were observed at 3293 cm-1 (-OH stretching), 2923-2874 cm-1 (-CH stretching), 1556 cm-1 (-
NH bending vibration), 1403 cm-1 (-C-H stretching), 1012 cm-1 (-C-O-C stretching) [48].
Moreover, a new peak was observed at 1638 cm-1, which corresponded to the stretching of the
imine group, confirming the formation of CoFe2O4/chitosan beads. Although the FT-IR
spectrum of Pd/CoFe2O4/chitosan is similar to that of its support CoFe2O4/chitosan), it was
observed that the peaks corresponding to the functional groups of CoFe2O4/chitosan shifted to
lower wavelengths because of interaction of palladium with CoFe2O4/chitosan microbeads.
On the other hand, the FT-IR analysis of samples was carried out using ATR-FT-IR (4000-
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650 cm-1). The characteristic Fe bands, which generally occur at low wavenumbers (<600 cm-
1), were not observed in the spectrum. Therefore, the presence of Fe peaks confirmed the
results of XRD and EDS analyses.
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Fig. 1. FT-IR spectra of CoFe2O4/chitosan (a) and Pd/CoFe2O4/chitosan hybrid nanocatalyst
(b).
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The XRD patterns of CoFe2O4, CoFe2O4/chitosan and Pd/CoFe2O4/chitosan hybrid
nanocatalyst are shown in Fig. 2. The XRD spectrum of CoFe2O4 displayed typical diffraction
peaks at 18.25º, 30.14º, 35.55º, 43.11º, 53.75º, 57.06º and 62.68º, which are assigned to [111],
[220], [311], [400], [422], [511] and [440] planes of CoFe2O4, respectively [49, 50]. These
peaks confirmed the successful fabrication of CoFe2O4. Following the synthesis of
CoFe2O4/chitosan microbeads, a new broad peak was observed at 20.06º, which was due to
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chitosan [17]. As for the XRD pattern of Pd/CoFe2O4/chitosan hybrid nanocatalyst, five new
diffraction peaks were clearly observed at 40.15°, 46.66°, 68.12º, 82.06º and 86.50°, which
are attributed to (111), (200), (220), (311) and (222) crystalline planes of face-centered
palladium, respectively, confirming the fabrication of Pd NPs on CoFe2O4/chitosan
microbeads [51].
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Fig. 2. XRD patterns of CoFe2O4 (a), CoFe2O4/chitosan (b) and Pd/CoFe2O4/chitosan
hybrid nanocatalyst (c).
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Fig.
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demonstrates the SEM images of the CoFe2O4/chitosan and
Pd/CoFe2O4/chitosan hybrid nanocatalysts, respectively. SEM images evidently indicated that
both CoFe2O4/chitosan and Pd/CoFe2O4/chitosan hybrid nanocatalyst had spherical
morphologies, confirming the formation of their microbead form (Fig. 3a, c). Additionally,
the surface morphologies of CoFe2O4/chitosan and Pd/CoFe2O4/chitosan hybrid nanocatalyst
beads were investigated at higher magnifications. The images showed that both cobalt ferrite
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and Pd NPs were fabricated (Fig. 3b,d). On the other hand, the elemental compositions of
CoFe2O4/chitosan and Pd/CoFe2O4/chitosan hybrid nanocatalyst beads were studied by EDS
analysis (Fig. 4). The EDS spectrum of CoFe2O4/chitosan beads showed the presence of C, N,
O, Fe and Co peaks (Fig. 4a). In the EDS spectrum of Pd/CoFe2O4/chitosan hybrid
nanocatalyst, Pd element was clearly observed, indicating the production of Pd nanocatalyst
on the support (CoFe2O4/chitosan) (Fig. 4b)
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Fig. 3. SEM micrograms of CoFe2O4/chitosan (a,b) and Pd/CoFe2O4/chitosan hybrid
nanocatalyst (c,d).
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Fig. 4. EDS spectra of CoFe2O4/chitosan (a) and Pd/CoFe2O4/chitosan hybrid nanocatalyst
(b).
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The TEM analysis of Pd/CoFe2O4/chitosan hybrid nanocatalyst beads was performed
for further characterization and the obtained TEM images are shown in Fig. 5. The TEM
images showed that Pd NPs were successfully immobilized on CoFe2O4/chitosan and their
average diameter were around ~20ꢀnm.
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The content of the Pd within Pd/CoFe2O4/chitosan, as determined by ICP-OES
(Inductively coupled plasma-optical emission spectrometry), was found to be 9.36 wt%.
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Fig. 5. TEM images of Pd/CoFe2O4/chitosan hybrid nanocatalyst.
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3.2. Investigation of catalytic activity of Pd/CoFe2O4 chitosan hybrid nanocatalyst
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The catalytic behavior of Pd/CoFe2O4/chitosan hybrid nanocatalyst was first evaluated in aryl
halide cyanation in the presence of K4[Fe(CN)6], which is a cyanide source with low toxicity,
cost effectiveness and ready availability. To optimize the reaction parameters, the cyanation
of p-NO2C6H4Br by Pd/CoFe2O4/chitosan hybrid nanocatalyst was chosen as the model
reaction. Preliminary experiments were then performed under various reaction conditions and
the isolated yields are listed in Table 1. Based on the results of the control experiment, the
optimal reaction conditions were as follows; catalyst loading: 0.25 mol. %, base: Na2CO3,
solvent: DMF, reaction temperature: 120 °C and reaction time: 3 h. The scope of activity of
Pd/CoFe2O4/chitosan hybrid nanocatalyst was then studied in the cyanation of a range of aryl
halides under optimal conditions and the results are summarized in Table 2. The results
showed that both aryl iodide and bromide cyanation reactions proceeded smoothly with good
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reaction yields in the presence of Pd/CoFe2O4/chitosan nanocatalyst. In addition,
Pd/CoFe2O4/chitosan was an effective nanocatalyst with a broad range of substrates in aryl
halide cyanation. Additionally, the catalytic efficacy of Pd/CoFe2O4/chitosan hybrid
nanocatalyst was compared to that of other reported catalysts in the cyanation of p-CH3C6H4I
and the results are given in Table 3. As observed in the Table, the developed catalyst system
(Pd/CoFe2O4/chitosan hybrid nanocatalyst) is superior to the other reported systems in terms
of yield, amount of catalyst and reaction time.
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Table 1. The optimization of reaction conditions for cyanation of p-NO2C6H4Br using
K4[Fe(CN)6].
Entry Catalyst (mol%) Solvent
Base
K2CO3
K2CO3
K2CO3
K2CO3
KOH
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
9
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.1
Toluene
DMF
NMP
DMSO
DMF
DMF
DMF
DMF
DMF
DMF
DMF
2
2
2
2
2
2
2
3
3
3
3
70
82
65
45
45
52
88
98
78
98
0
NaOH
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
10
11
0.3
0
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Reaction conditions: p-NO2C6H4Br (1.5 mmol), K4Fe(CN)6 (0.2 mmol), base (1.8 mmol), DMF (6.0 mL), 120
°C.
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Table 2. Catalytic role of Pd/CoFe2O4/chitosan hybrid nanocatalyst in the synthesis of
benzonitriles.
Entry
R
X
I
I
I
I
Yielda (%)
1
2
3
4
m-NO2
p-CH3O
p-CH3
m-CH3
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5
6
7
8
9
10
11
12
o-CH3
m-NO2
p-NO2
p-CH3O
p-CN
p-CH3
m-CH3
o-CH3
I
90
96
98
94
99
92
89
88
Br
Br
Br
Br
Br
Br
Br
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Reaction conditions: aryl halides (1.5 mmol), K4Fe(CN)6 (0.2 mmol), Na2CO3 (1.8 mmol), Pd/CoFe2O4/chitosan
hybrid nanocatalyst (0.25 mol %), DMF (6.0 mL), 3h, 120 °C.
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a Isolated yields.
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Table 3. Comparison of Pd/CoFe2O4/chitosan hybrid nanocatalyst with other reported
catalysts in the cyanation of p-NO2C6H4Br.
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Entry
Catalyst
Pd@CuFe2O4
Pd-CD-PU-NS
Time Yield (%)
Ref.
[21]
[52]
[53]
[54]
1
2
3
4
5
6
7
24 h
10 h
12 h
7h
78
89
85
85
93
95
98
Pd-LHMS-3
Pd NPs
Pd/PPy nanocomposite
Pd NPs@CAP
6h
8h
[31]
[55]
Pd/CoFe2O4/chitosan hybrid nanocatalyst
3h
Present study
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On the other hand, the catalytic performance of Pd/CoFe2O4/chitosan hybrid
nanocatalyst was also investigated in 2-NA reduction in water at room temperature using
NaBH4 as the hydrogen source. 2-NA reduction in the presence of Pd/CoFe2O4/chitosan
nanocatalyst was followed by UV-Vis spectroscopy. It is known that 2-NA has typical UV-
Vis bands of λmax at about 283 nm and 410 nm [56]. It was reported that following the
reduction of 2-NA i) the band at 410 nm diminished and ii) the band at 2 3 nm shifted to
higher wavelength due to the formation of o-phenylenediamine [57]. In this study, as
observed in Fig. 6a, 2-NA gave two characteristic absorption bands at 283 nm and 400 nm in
the absence of Pd/CoFe2O4/chitosan hybrid nanocatalyst. After adding the prepared
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Pd/CoFe2O4/chitosan hybrid nanocatalyst into the reaction mixture containing 2-NA and
NaBH4, the adsorption band of 2-NA at 410 nm gradually decreased as the catalytic reaction
proceeded and completely disappeared within 65 s. Additionally, it was observed that the
yellow color of the reaction mixture solution converted into colorless as the reaction
continued. Moreover, the band at 283 nm shifted to 292 nm, confirming the formation of o-
phenylenediamine. These observations showed that 2-NA was successfully converted to o-
phenylenediamine by Pd/CoFe2O4/chitosan hybrid nanocatalyst within 65 s. On the other
hand, the control experiment was performed in the absence of Pd/CoFe2O4/chitosan hybrid
nanocatalyst and no reduction product was observed at extended period of time in the UV-Vis
spectrum. This indicated that Pd/CoFe2O4/chitosan hybrid nanocatalyst was critically
important in the 2-NA reduction.
273
274
275
276
Fig. 6b displayed shows a linear correlation between ln (c/c0) and reaction time (t) for
2-NA reduction using Pd/CoFe2O4/chitosan hybrid nanocatalyst. Since NaBH4 concentration
is higher than that of 2-NA, the catalytic system follows pseudo first order kinetics. The rate
constant was calculated as 0.0131s-1 using the following equation:
277
ln (c/c0)ꢀ=ꢀ-kt
278
279
where, c0 and c are the initial concentrations of 2-NA at tested reaction time (t), and
also k (s-1) is the reaction rate.
280
281
282
283
284
285
It has been reported that ferrites NPs are important magnetic materials, which are used
for various applications such as drug delivery, magnetothermal therapy, microwave absorbent
sensors, and as catalysts in for many organic transformations [58,59]. However, among the
nanoparticles, Pd NPs stand out as effective catalysts due to their high activity and stability in
different organic reactions. For further investigation, the activity of Pd/CoFe2O4/chitosan
nanocatalyst was compared to that of CoFe2O4/chitosan nanocatalyst. Cyanation of p-
16

286
287
288
289
290
291
NO2C6H4Br, which was selected as the model reaction, was carried out in the presence of
CoFe2O4/chitosan nanocatalyst under optimal reaction conditions (Na2CO3, DMF, 120 °C, 3 h
etc.) and a very low yield was obtained (~3%). On the other hand, the reduction of 2-NA in
the presence of CoFe2O4/chitosan nanocatalyst was complete after 15 min. These results show
that the designed Pd/CoFe2O4/chitosan nanocatalyst is critically significant in the cyanation of
aryl halides and 2-NA reduction.
292
293
294
295
To show the superiority of Pd/CoFe2O4/chitosan hybrid nanocatalyst, its catalytic
efficiency was compared with that of some reported catalysis in 2-NA reduction (Table 4).
According to the results, Pd/CoFe2O4/chitosan is a more effective catalyst than other catalysts
in terms of reaction time and catalyst amount.
296
297
298
299
Fig. 6. UV-Vis spectrum of the product of 2-NA reduction in the presence of
Pd/CoFe2O4/chitosan hybrid nanocatalyst (a) and linear dependence graph between ln(c/c0)
and time (b)
300
301
Table 4. Comparison of Pd/CoFe2O4/chitosan hybrid nanocatalyst with some reported
catalysts in 2-NA reduction.
Entry
Catalyst
Amount of catalyst
10 mg
Time
150 s
6 min
8 min
Ref.
[38]
[60]
[61]
1
2
3
SiO2@CuxO@TiO2
MMT@Fe3O4@Cu MNPs
Fe-Cu@MCC system
20 mg
0.05g
17

4
5
6
Fe3O4@SiO2@Cu-Ni-Fe-Cr LDH
NiFe2O4@Cu NPs
0.01g
0.15g
6 mg
13 min
1 min
1.5 h
[62]
[63]
[64]
Pd NPs/RGO
7
Ag/mNC nanocatalyst
5 mg
3 h
[65]
8
9
10
Fe3O4‐ Glu‐ Ag nanocatalyst
Fe3O4@EDTA-Pd
Pd/CoFe2O4/chitosan hybrid nanocatalyst
60 mg
20 mg
4 mg
12 min
10 min
65 s
[66]
[67]
Present
study
302
303
3.3. Recyclability of Pd/CoFe2O4/chitosan hybrid nanocatalyst
304
305
306
307
308
309
310
311
312
313
314
Recyclability/recoverability is one of the significant properties of catalyst systems from
economic, practical and sustainability aspects. Therefore, the reusability of
Pd/CoFe2O4/chitosan hybrid nanocatalyst was tested in both p-NO2C6H4Br cyanation and 2-
NA reduction. To reuse Pd/CoFe2O4/chitosan nanocatalyst, it was readily recovered using an
external magnet after each catalytic test, rinsed with water and dried for further tests. The
recyclability tests indicated that Pd/CoFe2O4/chitosan hybrid nanocatalyst successfully
catalyzed both cyanation of p-NO2C6H4Br and reduction of 2-NA for five successive times.
The SEM and TEM analyses of Pd/CoFe2O4/chitosan hybrid nanocatalyst after five cycles
indicated that its particle size, shape and morphology were almost the same as that of the fresh
catalyst (Fig. 7), confirming the excellent chemical stability of Pd/CoFe2O4/chitosan hybrid
nanocatalyst.
315
18

316
317
Fig. 7. SEM and TEM images of recycled Pd/CoFe2O4/chitosan hybrid nanocatalyst after the
5 runs.
318
4. Conclusion
319
320
321
322
323
324
325
326
327
328
329
330
331
332
In conclusion, a new heterogeneous palladium nanocatalyst system was successfully
fabricated on CoFe2O4/chitosan beads as a stabilizer and characterized. Characterization
studies showed that Pd NPs were immobilized on CoFe2O4/chitosan hybrid beads and their
particle size was about 20 nm. The catalytic potential of Pd/CoFe2O4/chitosan hybrid
nanocatalyst was then tested in the aryl halide cyanation and 2-NA reduction. Different
benzonitriles were successfully generated with excellent yields using Pd/CoFe2O4/chitosan
hybrid nanocatalyst. Additionally, Pd/CoFe2O4/chitosan hybrid nanocatalyst converted 2-NA
to o-phenylenediamine within only 65 s. Furthermore, it was found that Pd/CoFe2O4/chitosan
hybrid nanocatalyst can be reused up to five cycles in both reactions. To sum up, the designed
catalytic system exhibited valuable characteristics such as facile recoverability, high stability,
easy work-up, long life, and excellent catalytic activity within a short reaction time.
Considering the unique properties of Pd/CoFe2O4/chitosan hybrid nanocatalyst, it can be
utilized in the degradation of environmental pollutants such as organic dyes/nitroarenes and
production of different benzonitriles.
333
334
335
Conflict of Interest: Authors declare no conflict of interest.
336
Acknowledgments
337
338
We gratefully acknowledge Aksaray University and the University of Qom for the support of
this work.
19

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341
Appendix A. Supplementary data
Contains information about the GC-MS spectra of synthesized benzonitriles.
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345
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347
348
349
350
351
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353
354
355
356
357
358
359
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361
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