Sustainable chitosan/starch composite material for stabilization of palladium nanoparticles: Synthesis, characterization and investigation of catalytic behaviour of Pd@chitosan/starch nanocomposite in Suzuki–Miyaura reaction

Article abstract of DOI:10.1002/aoc.4075

We fabricated a green chitosan/starch composite as support material for stabilization of palladium nanoparticles for the first time. The chemical structure of the sustainable palladium nanocomposite was investigated using various techniques. Characterization studies showed that the average dimensions of the palladium nanocomposite ranged between 16 and 21?nm. The synthesized palladium nanocomposite was employed in the synthesis of a series of biphenyl compounds via Suzuki–Miyaura cross-coupling reactions with an unconventional technique. All coupling reactions were conducted in very short reaction time and excellent biphenyl yields were obtained in the presence of the nanocomposite. The palladium catalyst was tolerant to a wide range of functional groups. We also investigated the recyclability and reusability of the palladium nanocomposite, and found that it could be used for seven successive cycles.

Full text of DOI:10.1002/aoc.4075

Received: 30 June 2017
DOI: 10.1002/aoc.4075
Revised: 11 August 2017
Accepted: 12 August 2017
F U L L P A P E R
Sustainable chitosan/starch composite material for
stabilization of palladium nanoparticles: Synthesis,
characterization and investigation of catalytic behaviour of
Pd@chitosan/starch nanocomposite in Suzuki–Miyaura
reaction
Talat Baran1
| Nuray Yılmaz Baran2
| Ayfer Menteş1
1 Faculty of Science and Letters,
Department of Chemistry, Aksaray
University, 68100 Aksaray, Turkey
2 Technical Vocational School,
Department of Chemistry Technology,
Aksaray University, 68100 Aksaray,
Turkey
We fabricated a green chitosan/starch composite as support material for stabi-
lization of palladium nanoparticles for the first time. The chemical structure
of the sustainable palladium nanocomposite was investigated using various
techniques. Characterization studies showed that the average dimensions of
the palladium nanocomposite ranged between 16 and 21 nm. The synthesized
palladium nanocomposite was employed in the synthesis of a series of biphenyl
compounds via Suzuki–Miyaura cross‐coupling reactions with an unconven-
tional technique. All coupling reactions were conducted in very short reaction
time and excellent biphenyl yields were obtained in the presence of the
nanocomposite. The palladium catalyst was tolerant to a wide range of func-
tional groups. We also investigated the recyclability and reusability of the
palladium nanocomposite, and found that it could be used for seven succes-
sive cycles.
Correspondence
Talat Baran, Department of Chemistry,
Faculty of Science and Letters, Aksaray
University, 68100 Aksaray, Turkey.
Email: talatbaran_66@hotmail.com
KEYWORDS
chitosan, nanocomposite, reusability, starch
1 | INTRODUCTION
leaching of metal ions and (3) size of particles.[4] To solve
these problems, the synthesis of metallic nanoparticles on
Biopolymers are promising materials as supports for cata-
lytic reactions because of their high thermal stability, high
interaction capacity with metal ions and readily enabling
chemical modifications.[1] Additionally, these materials
have attracted increasing attention when compared to
conventional synthetic supports due to their eco‐friendly
nature.[2] Recently, researchers have prepared a variety
of catalysts derived from various materials such as chito-
san, starch, silica and cellulose, and have studied their
activities in catalytic reactions.[3] However, some bio‐
based catalysts show lower catalytic activity in reactions
due to certain problems as follows: (1) aggregation, (2)
solid materials such as silica, zeolite, carbon and
graphene has received great attention for catalytic systems
because of their easy separation, low cost and low
waste.[5] Among them, carbohydrate polymer composites
are regarded as some of the most promising support mate-
rials for catalytic systems because of their high surface
area and high metal binding capacity.[6] In the last
decade, various metallic nanoparticle catalysts such as sil-
ver, gold and platinum on solid materials have been syn-
thesized and their applications have been studied in
various fields.[7] Among these catalysts, palladium
nanocatalysts on composites are extraordinarily
Appl Organometal Chem. 2017;e4075.
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Copyright © 2017 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4075

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BARAN ET AL.
important in homogeneous and heterogeneous catalytic
systems for increasing the selectivity and reaction yield.[8]
Therefore, palladium nanoparticles stabilized on biopoly-
mers are suitable candidates for Suzuki–Miyaura coupling
reactions.
halides, toluene, ethanol and acetic acid were purchased
from Sigma‐Aldrich.
2.2 | Instrumentation
Palladium‐catalysed Suzuki–Miyaura coupling reac-
tions represent one of the most important organic synthe-
sis methods, where different unconventional techniques
such as microwave and ultrasound irradiations, grinding
and photo‐activated processes have been applied success-
fully.[9] Following a green chemistry approach, environ-
mentally benign Suzuki–Miyaura coupling reactions give
a variety of biphenyl compounds which are widely used
in cosmetics, pharmacology, drug discovery, agricultural
compounds, etc.[10] Suzuki–Miyaura reactions have high
tolerance for various functional groups when compared
to other cross‐coupling reactions.[11] Therefore,
researchers have made continuing efforts to develop new
homogeneous and heterogeneous catalysts or catalyst sys-
tems for Suzuki–Miyaura reactions since the discovery of
these reactions.[12] Considering excellent catalytic activity
and selectivity, researchers have showed greater interest
in heterogeneous catalysts than homogeneous ones for
Suzuki–Miyaura coupling reactions.[13]
In the study reported here, (1) we produced a new chi-
tosan/starch (CS/ST) composite as support material for
palladium nanoparticles and its structure was investigated
using various analytical tools, (2) a Pd@chitosan/starch
nanocomposite was designed using the CS/ST composite
and (3) the catalytic behaviour of the Pd@chitosan/starch
nanocomposite was investigated in Suzuki–Miyaura
cross‐coupling reactions using the direct interaction of
electromagnetic irradiation with molecules in the reaction
mixture with very short reaction times under solvent‐free
conditions. Characterization studies showed CS/ST and
Pd@chitosan/starch nanocomposite were successfully
prepared. We found that the novel palladium nanocom-
posite showed excellent catalytic performance towards
the coupling reactions of phenylboronic acid with a series
of aryl halides, and desired biphenyl products were pro-
duced in yields of up to 99%. Moreover, reusability inves-
tigation revealed that the palladium nanocomposite was
easily recovered from reaction media and showed supe-
rior stability for several successive cycles without signifi-
cant loss of its activity.
Fourier transform infrared (FT‐IR) spectra of CS/ST and
Pd@chitosan/starch nanocomposite were obtained with
a PerkinElmer Spectrum 100 FT‐IR spectrophotometer.
X‐ray diffraction (XRD) patterns were recorded using a
Rigaku Smart Lab system (at 40 kV, 30 mA; and 2θ scan
angle of 10–70°). Thermal and mechanical durability of
CS/ST and Pd@chitosan/starch nanocomposite were
studied with an EXSTAR S11 7300 (nitrogen atmosphere;
30–650 °C heating range). The surface properties of sam-
ples were determined using scanning electron microscopy
(SEM) with a QUANTA‐FEG 250 ESEM by coating sam-
ples with platinum. The analysis of Pd ions on CS/ST
was conducted using energy‐dispersive X‐ray (EDX) anal-
ysis with an EDAX‐Metek. Palladium ion content of the
Pd nanocomposite was determined using a PerkinElmer
Optima 2100 DV inductively coupled plasma (ICP) optical
emission spectrometer (OES). GC–MS analysis of biphe-
nyl compounds was performed with an Agilent GC‐
7890A‐MS 5975. 1H NMR spectra of biphenyl compounds
were recorded with an Agilent 600 MHz spectrometer
using acetone‐d6 as solvent. A domestic microwave oven
was used in the catalytic tests.
2.3 | Production of palladium
nanoparticles on CS/ST
Chitosan (1 g) was dissolved in a solution of 2% acetic acid
(100 ml). Starch (1 g) was added to the reaction media,
which was stirred overnight at room temperature to
obtain the CS/ST composite. Then, 0.2 g of Na2PdCl4 in
10 ml of water was added dropwise to the reaction mix-
ture and stirred for 3 h. Subsequently, freshly prepared
NaBH4 solution (0.8 M, 10 ml in water) was added to
the reaction media to reduce Pd(II) to Pd(0) and we
immediately observed that the light yellow colour of the
solution turned dark grey. The resulting mixture was
stirred for 30 min. Finally, the pH of the reaction solution
was adjusted to neutral pH with NaOH solution, and the
Pd@chitosan/starch nanocomposite was filtered and
washed with distilled water and allowed to dry at room
temperature (Scheme 1).
2 | EXPERIMENTAL
2.1 | Materials
2.4 | Optimal conditions for Suzuki–
Miyaura coupling reactions
To find the optimal reaction conditions for Suzuki–
Miyaura reactions, we investigated the effect of parame-
ters such as base, catalyst loading and reaction time on
Chitosan, starch, Na2PdCl4, KOH, NaHCO3, NaOH,
Cs2CO3, K2CO3, MgSO4, NaBH4, phenylboronic acid, aryl

BARAN ET AL.
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B(OH)2
X
CS
O
Pd
O
O
CS
CS
ST
Pd
ST
CS
ST
O
Pd
ST
CS
ST
Pd
O
Pd
O
R
R
O
Pd
O
CS
ST
X: I,Br,Cl
biphenyl compounds
CH2OH
SCHEME
2
General synthesis scheme of Suzuki–Miyaura
O
O
reactions
CS:
OH
O
NH2
microwave irradiation for 6 min at 50 °C. After comple-
tion of the coupling reaction, the reaction mixture was
cooled to room temperature. Then the solid palladium
nanocomposite was separated by filtration. A mixture of
toluene (4 ml) and water (2 ml) was added to the reaction
solution and extracted three times. Finally, the organic
phase containing the desired biphenyl compounds was
subjected to GC–MS for characterization. Turnover num-
ber (TON) and turnover frequency (TOF; as mol product
CH2OH
O
O
ST:
OH
O
OH
SCHEME
nanocomposite
1
Synthesis pathway of Pd@chitosan/starch
the yield of 4‐methoxybiphenyl which was synthesized
from the coupling reaction of phenylboronic acid with 4‐
bromoanisole as model reaction. The model coupling
reaction was performed with various inorganic bases such
as NaOH, KOH, NaHCO3, Cs2CO3 and K2CO3 to deter-
mine the most suitable base system. We observed that
NaOH, KOH and NaHCO3 did not have a significant
influence on the biphenyl yields (17, 28 and 15%, respec-
tively). On the other hand, a moderately high reaction
yield was obtained with Cs2CO3 (80%). Among the bases,
K2CO3 gave the highest reaction yield (98%) and so we
decided to use K2CO3 as base system. The model coupling
reaction was carried out within 1–6 min to determine the
optimal time and we recorded a linear increase in the
reaction yield up to 5 min (1 min, 20% yield; 2 min, 35%
yield; 3 min, 68% yield; 4 min, 79% yield; 5 min, 88% yield;
6 min, 98% yield). However, biphenyl yield did not change
for longer reaction time (7 min, 98% yield), and so, based
on these experimental findings, we opted for 6 min as the
optimal reaction time. We also attempted to find an opti-
mal catalyst loading for the Suzuki–Miyaura reaction and
we conducted preliminary studies with various amounts
of catalyst. The optimum catalyst loading was determined
as 0.005 mol% (0.001 mol% catalyst, 25% yield; 0.002 mol%
catalyst, 58% yield; 0.003 mol% catalyst, 80% yield;
0.004 mol% catalyst, 88% yield; 0.005 mol% catalyst, 98%
yield; 0.006 mol% catalyst, 98% yield).
(mol catalyst)−1
calculated.[14]
h
−1) of all coupling reactions were
3 | RESULTS AND DISCUSSION
3.1 | Characterization of nanocomposite
3.1.1 | FT‐IR analysis
Figure 1 shows the FT‐IR spectra of CS/ST and
Pd@chitosan/starch nanocomposite. When the FT‐IR
spectrum of CS/ST was examined, we observed important
bands belonging to chitosan and starch. These include:
3294 cm−1 (―OH stretching of starch), 2930 cm−1
(―C―H stretching of starch), 1644 cm−1 (―C―O
stretching of chitosan), 1563 cm−1 (NH2 bending of chito-
san), 1150 cm−1 (C―O―C stretching of chitosan and
starch) and 1015 cm−1 (C―O stretching chitosan and
starch).[15, 3b] The presence of these peaks in the spectrum
showed that CS/ST was successfully formulated. We
observed that the FT‐IR spectrum of Pd@chitosan/starch
nanocomposite was similar to that of CS/ST. However,
peak intensities of Pd@chitosan/starch nanocomposite
decreased and the peaks shifted to lower wavenumbers
compared to CS/ST. These important changes can be
attributed to bonding interactions between the functional
groups of CS/ST and palladium ions.[16]
2.5 | General procedure for Suzuki–
Miyaura coupling reactions
3.1.2 | SEM/EDX analysis
A typical cross‐coupling reaction was carried out as fol-
lows (Scheme 2). A mixture of aryl halide (1.12 mmol),
phenylboronic acid (1.87 mmol), potassium carbonate
(3.75 mmol) and Pd@chitosan/starch nanocomposite
(0.005 mol%) was added to a Schlenk tube and the
resulting heterogeneous mixture was exposed to 400 W
Surface morphology and microstructure of CS/ST and
Pd@chitosan/starch nanocomposite were explored using
SEM analysis and the micrographs are shown in
Figure 2. From the SEM image, we observed that CS/ST
had coarse irregular morphology characteristics

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BARAN ET AL.
FIGURE 1 FT‐IR spectra of (a) CS/CT
and (b) Pd@chitosan/starch
nanocomposite
FIGURE 2 SEM images of (a) CS/CT and (b) Pd@chitosan/starch nanocomposite
(Figure 2a). As seen from Figure 2(b), the Pd@chitosan/
starch nanocomposite had a spherical morphology
structure. The average diameters of Pd@chitosan/starch
nanocomposite particles were found to be between 16
and 21 nm. It is noteworthy that palladium ions were
homogeneously distributed on the CS/ST surface and no

BARAN ET AL.
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aggregation formation was observed in the micrograph of
the Pd@chitosan/starch nanocomposite. To confirm the
presence of palladium ions on the CS/ST matrix, we con-
ducted EDX analysis of the Pd nanocomposite (Figure 3).
The signal of Pd was clearly displayed in the EDX spec-
trum. This signal revealed that Pd@chitosan/starch nano-
composite was formed on the composite matrix. In
addition, Pd content on the CS/ST matrix was analysed
using both ICP‐OES and EDAX and found as 2.61 and
2.53%, respectively. These very close values revealed that
Pd nanoparticles were homogeneously dispersed on the
CS/ST surface.
the pattern of Pd@chitosan/starch nanocomposite
(Figure 4b), three characteristic peaks are observed at
40°, 46° and 68° which correspond to crystallographic
planes of Pd(0).[17] These peaks show that Pd(II) was
successfully reduced to Pd(0).
3.1.4 | Thermogravimetric (TG)/differen-
tial TG (DTG) analysis
TG/DTG analyses of CS/ST and Pd@chitosan/starch
nanocomposite were carried out to determine the thermal
stability of samples. The obtained curves are shown in
Figure 5. From Figure 5(a), maximum thermal decay of
CS/ST was found at 217.3 °C. In addition, we observed
four main degradation stages for CS/ST. The first degrada-
tion stage (6.09%) corresponds to the adsorbed water on
the composite. In the second major degradation step,
22.15% loss of mass can be related to degradation of chito-
san saccharide rings. The third step of 20.42% mass loss
can be due to degradation of starch saccharide rings.
The closeness of mass losses of these degradation steps
3.1.3 | XRD analysis
To evaluate the structure of CS/ST and Pd@chitosan/
starch nanocomposite, XRD analysis was carried out and
the patterns are shown in Figure 4. We observed two
strong and sharp peaks at 9.3° and 20.4° in the spectrum
of CS/ST (Figure 4a). These peaks can be attributed to sac-
charide peaks of chitosan and starch, respectively.[15, 3b] In
FIGURE 3 EDX spectrum of Pd@chitosan/starch nanocomposite

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BARAN ET AL.
FIGURE 4 XRD patterns of (a) CS/CT
and (b) Pd@chitosan/starch
nanocomposite
can be explained by the fact that the composition of the
composite is nearly 1:1. The last degradation step can be
attributed to the thermal decay of the glucosamine resid-
uals of chitosan and starch. We observed a slightly higher
degradation temperature for Pd@chitosan/starch nano-
composite (263.3 °C), indicating that it is suitable for cat-
alytic reactions (Figure 5b). This difference of thermal
stabilities between composite and catalyst provides impor-
tant an evidence for the formation of palladium
nanocatalyst on CS/ST.
or para‐bromonitrobenzene and phenylboronic acid.
Outstanding product yield was also obtained with aryl
bromide containing electron‐withdrawing group ―CN
(90%). Aryl bromides with meta‐ and para‐substituted
―NH2 gave good product yields of 72 and 83%. However,
moderately high reaction yields of 55 and 72%
were obtained with aryl bromides which contain
electron‐donating ortho‐ and para‐substituted ―CH3
group, respectively. We also tested the effectiveness of
the palladium nanocomposite in the reactions of aryl
chlorides which generally have poor reactivity in
Suzuki–Miyaura reactions and obtained good reaction
yields (entries 17–23).[18] For example, the Pd nanocom-
posite produced good results in the presence of electron‐
withdrawing ―NO2 and ―CN substituent groups on aryl
chlorides: 73 and 75% yields, respectively. Additionally,
we also obtained good product yields with ortho, meta
and para ―OCH3 group on the substrate (48, 60, 70%,
respectively). On the other hand, the lowest product
yields were reached with aryl chlorides having ortho, meta
and para ―CH3 group which shows electron‐donating
characteristics. Taking into account the obtained results,
the novel palladium nanocomposite showed excellent
catalytic behaviour in Suzuki–Miyaura cross‐coupling
reactions. These findings reveal that the palladium
catalyst is tolerant to a wide range of functional groups
in Suzuki–Miyaura cross‐coupling reactions.
3.2 | Catalytic behaviour of palladium
nanocomposite in Suzuki reactions
Using the optimized conditions mentioned in Section 1.4,
we examined the catalytic performance of the palladium
nanocomposite in the synthesis of 23 different biphenyl
compounds via Suzuki–Miyaura coupling reactions. The
results are summarized in Table 1. Excellent biphenyl
product yields were obtained with aryl iodides (entries
11–16). The coupling reaction of the aryl iodide with para
―OCH3 group produced excellent biphenyl yield of 99%.
Aryl iodide bearing electron‐withdrawing ―NO2 group
at the meta position gave excellent reaction yield of 90%.
The 4‐NH2 aryl iodide also gave good biphenyl yield
(88%). Electron‐withdrawing group ―CH3 at ortho, meta
and para positions of aryl iodides gave good reaction
yields of 55, 70 and 75%, respectively (entries 14–16). Also,
we observed that the cross‐coupling reactions of aryl
bromides with phenylboronic acid provided excellent
biphenyl yields (entries 1–10). For example, high reaction
yields were reached with aryl bromides containing
―OCH3 at the ortho, meta and para position: 82, 87 and
98%, respectively. Excellent biphenyl yields of 80 and
95% were reached with the coupling reactions of meta‐
TON and TOF values of any catalyst play a crucial role
in its industrial applicability. So, we calculated the TON
and TOF values for all coupling reactions and the findings
are presented in Table 1. High TONs (19 800) and TOFs
(198 000) were reached using very small amount of
Pd@chitosan/starch nanocomposite. These findings
showed the catalyst can be used in different industrial
applications due to the high TONs TOFs. In addition,

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FIGURE 5 TG/DTG curves of (a) CS/CT and (b) Pd@chitosan/starch nanocomposite

8 of 11
BARAN ET AL.
TABLE 1 Suzuki–Miyaura reactions of aryl halides and phenylboronic acid in the presence of Pd@chitosan/starch nanocompositea
Entry
Phenylboronic acid
Aryl halide
Product
Biphenyl yield (%)
TON
TOF
1
98
19 600
196 000
2
3
87
82
17 400
16 400
174 000
164 000
4
5
83
72
16 600
14 400
166 000
144 000
6
7
8
90
95
80
18 000
19 000
16 000
180 000
190 000
160 000
9
72
55
14 400
11 000
144 000
110 000
10
11
12
13
99
88
90
19 800
17 600
18 000
198 000
176 000
180 000
14
15
75
70
15 000
14 000
150 000
140 000
16
55
11 000
111 000
(Continues)

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TABLE 1 (Continued)
Entry
Phenylboronic acid
Aryl halide
Product
Biphenyl yield (%)
TON
TOF
17
70
14 000
140 000
18
19
60
48
12 000
9 600
120 000
96 000
20
21
75
73
15 000
14 600
150 000
146 000
22
23
45
35
9 000
7 000
90 000
70 000
aReaction conditions: 1.12 mmol aryl halide, 1.87 mmol phenylboronic acid, 3.75 mmol K2CO3, 0.005 mol% Pd@chitosan/starch nanocomposite, 50 °C, 0.1 h,
microwave irradiation.
TABLE 2 Comparison of catalytic performance of Pd@chitosan/starch nanocomposite with that of other catalysts in Suzuki cross‐coupling
reactions
Catalyst
Yield (%)
Time
Temperature (°C)
Ref.
[19]
Fe3O4@CS‐Schiff base Pd catalyst
97
20 min
80
[1]
CS‐g‐mPEG350 Pd(0) catalyst
Pd‐NPs@chitosan
92
96
95
96
96
97
99
0.33 h
5 h
150
70
[20]
[2]
Chitosan‐supported palladium(0) catalyst
CMC‐NHC‐Pd
15 min
3 h
150
60
[3c]
[21]
[22]
Cell‐Pd(0)
5.5 h
30 min
6 min
100
80
Nano‐Pd
Pd@chitosan/starch nanocomposite
50
Present study
we compared the catalytic activity of Pd@chitosan/starch
nanocomposite with that of other catalysts reported in the
literature (Table 2). In terms of high reaction yields
obtained in very short reaction times, very low catalyst
loading and tolerance to a broad range of functional
groups on the substrate, Pd@chitosan/starch nanocom-
posite is advantageous compared to the other catalysts.
In addition, characterization of obtained biphenyl com-
pounds was performed using GC–MS and 1H NMR analy-
sis. The results are given in the supporting information.
3.3 | Reusability of Pd@chitosan/starch
nanocomposite
From the viewpoint of industrial usability, a major
property for any catalyst is its ability to be recycled.[3b]
Therefore, we decided to investigate the sustainability
of Pd@chitosan/starch nanocomposite on the model
coupling reaction under determined optimal conditions.
After the first recycling test, the catalyst was filtered and
rinsed with hot methanol and water for subsequent

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BARAN ET AL.
ORCID
Talat Baran http://orcid.org/0000-0003-0206-3841
Nuray Yılmaz Baran
http://orcid.org/0000-0001-9725-
3458
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4 | CONCLUSIONS
In summary, a sustainable Pd@chitosan/starch nano-
composite was synthesized for the first time, and its
chemical characterization was carried out using FT‐IR,
TG/DTG, SEM/EDX, XRD and ICP‐OES analytic tools.
Spectroscopic studies showed that Pd@chitosan/starch
nanocomposite was immobilized successfully on the
CS/CT surface and the average size of Pd@chitosan/
starch nanocomposite particles was determined as 16–
21 nm. The designed novel Pd@chitosan/starch nano-
composite showed superior catalytic behaviour for the
synthesis of biphenyl compounds via Suzuki–Miyaura
cross‐coupling reactions using the microwave irradiation
technique which is an alternative source of energy for
organic synthesis. Production of biphenyls was carried
out under solvent‐free conditions and in very short reac-
tion times. Moreover, the prepared palladium nanocom-
posite showed good reusability in Suzuki–Miyaura
reactions due to its ease of recovery from reaction
media. The developed catalyst offered many advantages
such as high conversion, TONs and TOFs and tolerance
to a broad range of functional groups in Suzuki
reactions.
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How to cite this article: Baran T, Yılmaz Baran
N, Menteş A. Sustainable chitosan/starch
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