Preparation and characterization of nano-CaO based on eggshell waste: Novel and green catalytic approach to highly efficient synthesis of pyrano[4,3-b]pyrans

Article abstract of DOI:10.1016/S1872-2067(12)60755-4

A general and efficient catalytic system for Pd/C-catalyzed ligand-free aerobic Suzuki cross-coupling reactions was developed. The reaction tolerated a wide range of aryl bromides with a hydrophilic group or a hydrophobic group without any additives in wa

Full text of DOI:10.1016/S1872-2067(12)60755-4

Chinese Journal of Catalysis 35 (2014) 351–356
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
Article
Preparation and characterization of nano‐CaO based on eggshell
waste: Novel and green catalytic approach to highly efficient
synthesis of pyrano[4,3‐b]pyrans
Elaheh Mosaddegh*, Asadollah Hassankhani
Department of New Materials, Institute of Science and High Technology and Environmental Sciences, Graduate University of Advanced Technology, PO
Box 76315‐117, Kerman, Iran
A R T I C L E I N F O
A B S T R A C T
Article history:
Nano‐CaO was prepared by calcination of ball‐milled chicken eggshell waste. This novel, bioactive,
heterogeneous catalyst, which had high catalytic activity and reusability, was used in the green
synthesis of pyrano[4,3‐b]pyrans via condensation of various aromatic aldehydes, malononitrile,
and 4‐hydroxy‐6‐methyl‐2H‐pyran‐2‐one at 120 °C under solvent‐free conditions. The reaction
proceeded to completion within 5–45 min in 93%–98% yield. The nano‐CaO was fully characterized
by scanning electron microscopy, X‐ray powder diffraction, infrared spectroscopy, X‐ray fluores‐
cence spectroscopy, and thermal gravimetric, surface area, and elemental analyses.
© 2014, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Received 11 October 2013
Accepted 22 November 2013
Published 20 March 2014
Keywords:
Nano‐calcium oxide
Eggshell waste
Biocatalyst
Published by Elsevier B.V. All rights reserved.
Pyrano[4,3‐b]pyrans
Ball‐mill
1. Introduction
cause it has no traditional uses [9]. The eggshell structure is
mesoporous, with the ability to form a nanoporous structure
Recently, there has been increasing interest in the develop‐
ment of clean technology to replace the use of hazardous rea‐
gents and catalysts with relatively environmentally benign
compounds. Additionally, “green chemistry” emphasizes the
optimization of synthetic methodologies to reduce pollution,
costs, and tedious work‐ups [1–3]. This new challenge has led
to a growing interest in the use of natural and bio compounds
for organic and inorganic application. Eggs, an abundant natu‐
ral food source, are consumed worldwide because they contain
essential amino acids, vitamins, and minerals. Chicken eggshell
is totally biodegradable, recyclable, and biocompatible, with
good osteoconductivity [4]. It consists of more than 90% CaCO3
and has emerged as a novel bone substitute in its natural form
[5–8]. This natural solid waste is non‐hazardous, and is com‐
monly disposed of in landfills without any pretreatment be‐
[10]. Substrates with nanostructures, dense nanopores, and
high surface areas have found many application in biosensors,
proteomics, light‐emitting diodes [4,11–14], and tissue engi‐
neering [15–17]. We previously reported the first ultrason‐
ic‐assisted preparation of nano‐CaCO3 based on eggshell waste,
and its use as a heterogeneous catalyst in the green synthesis of
2‐aminochromenes [16]. Eggshells have previously been used
to synthesize nanoparticle apatite, hydroxyapatite nanopow‐
ders, and nano‐CaCl2, but these require sintering or the use of
acidic and hazardous solvents to make porous scaffolds
[18–20]. In this paper, we report a green, simple, and cheap
approach to making nano‐CaO based on chicken eggshell waste.
We also characterized the nano‐CaO structure and investigated
its use as a catalyst in the green synthesis of pyra‐
no[4,3‐b]pyrans.
* Corresponding author. Tel: +98‐342‐6226611; Fax: +98‐342‐6226617; E‐mail: emosaddegh@gmail.com
DOI: 10.1016/S1872‐2067(12)60755‐4 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 35, No. 3, March 2014

Elaheh Mosaddegh et al. / Chinese Journal of Catalysis 35 (2014) 351–356
gravimetric analysis‐differential thermal analysis (TGA‐DTA)
X
experiments were carried out using an STA 409 PC Luxx ther‐
mal analysis instrument (NETZSCH, Germany) under a flow of
nitrogen. The sample mass used was about 20 mg, and the
temperature ranged from 25 to 900 °C, with a rising rate of 10
°C/min. The film cross‐section morphology was examined us‐
ing field‐emission scanning electron microscopy (FESEM) after
fracturing in liquid nitrogen. Dried samples were coated with
gold ions using an ion coater for 150 s. The surface structure
was visualized using FESEM (Hitachi S4160) at an accelerating
voltage of 15 kV. Transmission electron microscopy (TEM)
images were obtained using a LEO912‐AB (LEO, Germany)
transmission electron microscope with an accelerating voltage
of 120 kV. Particles were deposited on carbon foil supported by
a copper grid. Energy‐dispersive X‐ray analysis (EDX) was per‐
formed using an Oxford instruments EDX detector (UK) with an
accelerating voltage of 10.0 kV. Milling was carried out in a
planetary ball‐mill using a hardened chromium steel vial (250
mL) at room temperature in an argon atmosphere. The
ball‐to‐powder mass ratio and the rotation speed of the vial
were 10:1 and 350 r/min, respectively.
CHO
O
O
O
CN
CN
CN
Nano CaO
120 oC, solvent-free
O
+
+
OH
X
O
NH2
Scheme 1. Synthesis of 2‐amino‐7‐methyl‐5‐oxo‐4‐phenyl‐4,5‐dihy‐
dropyrano[4,3‐b]pyran‐3‐carbonitrile derivatives.
It is known that many pyran derivatives exhibit a wide
spectrum of pharmacological and biological activity [21–23].
Moreover, they have been shown to have important medicinal
properties such as antimicrobial [24], antiviral [25,26], antipro‐
liferative [27], antitumor [28], anticancer [29], anti‐HIV, an‐
tituberculosis, anti‐inflammatory, and antifungal activity
[30–35]. Despite their wide range of pharmacological and in‐
dustrial application, the synthesis of pyrano[4,3‐b]pyrans has
received little attention. Recently, members of this important
class of pyran derivatives have been synthesized via one‐pot
multicomponent condensation reactions of aryl aldehydes,
malononitrile, and 4‐hydroxy‐6‐methyl‐2H‐pyran‐2‐one in the
presence of different reagents. Various reagents such as
KF‐Al2O3 [36], [bmim]BF4 [28], piperidine [37], and NH4OAc
[38] have been used to accomplish this transformation. How‐
ever, in spite of their potential utility, all of these methods suf‐
fer from one or more disadvantages, such as unsatisfactory
yields, very prolonged reaction time, and the use of organic
solvents. So, in a continuation of our efforts to develop new
green chemistry methods [39,40], we decided to explore the
green synthesis of 2‐amino‐7‐methyl‐5‐oxo‐4‐phenyl‐4,5‐di‐
hydropyrano[4,3‐b]pyran‐3‐carbonitrile derivatives in the
presence of nano‐CaO based on eggshell waste as a novel and
green biocatalyst, under solvent‐free and thermal conditions
(Scheme 1).
2.2. Catalyst preparation
Empty chicken eggshells were collected from household
waste and washed with warm tap‐water. The adhering mem‐
branes were separated manually. The eggshells were then
washed with distilled water and dried at 120 °C for 1 h. The
eggshells were milled in a planetary ball‐mill for 2 h, and the
eggshell powder was calcined at 900 °C for 1 h. The resulting
material was denoted by nano‐CaO.
2.3. General procedure for synthesis of pyrano[4,3‐b]pyrans
A mixture of 4‐chlorobenzaldehyde (0.14 g, 1 mmol), malo‐
nonitrile (0.07 g, 1 mmol), and 4‐hydroxy‐6‐methyl‐2H‐py‐
ran‐2‐one (0.126 g, 1 mmol) was stirred thoroughly at 120 °C
under solvent‐free conditions in the presence of a catalyst
amount of nano‐CaO (0.1 g) to afford the corresponding pyra‐
no[4,3‐b]pyran in excellent yield. After completion of the reac‐
tion (thin‐layer chromatography), hot EtOH was added and the
reaction mixture was stirred for 5 min. Then the solid catalyst
was filtered from the soluble products and washed with hot
EtOH. After cooling, the crude products were precipitated. Pure
pyrano[4,3‐b]pyrans were obtained in high yields without fur‐
ther purification. All compounds were known in the literature
[28,36–38] and the NMR and IR spectra of the products were in
agreement with earlier data [28,36–38].
Spectra data of two selected compounds are as following.
2‐amino‐7‐methyl‐5‐oxo‐4‐(4‐chlorophenyl)‐4H,5H‐pyrano
[4,3‐b]pyran‐3‐carbonitrile (Table 2, Entry 2): pale‐yellow
crystals, mp 227–229 °C. IR (KBr, cm−1): 3383, 3324, 3195,
2201, 1710, 1674, 1645, 1597, 1488, 1445, 1414, 1384, 1261,
1141, 1092, 1015, 981, 854, 830, 807, 777, 511. 1H NMR (400.2
MHz, DMSO, ): 2.23 (s, 3H, CH3), 4.33 (s, 1H, CH), 6.29 (s, 1H,
=CH), 7.23 (d, 2H, J = 8.4 Hz, ArH), 7.26 (s, 2H, NH2), 7.38 (d, 2H,
J = 8.4 Hz, ArH). 13C NMR (400.2 MHz, DMSO, ): 19.8, 36.2,
2. Experimental
2.1. Materials and Instruments
All chemicals were of analytical grade, purchased from
Merck, and used as received. Melting points were determined
using a Gallenkamp melting‐point apparatus and are uncor‐
rected. Nuclear magnetic resonance (NMR) spectra were rec‐
orded at 500 (1H) and 125.77 (13C) MHz using a Bruker
DRX‐500 Avance spectrometer. Fourier‐transform infrared
(FT‐IR) spectra were obtained using a MATSON 1000 FT‐IR
spectrophotometer. X‐ray diffraction (XRD) was performed
using a D8 Bruker diffractometer (40 kV and 40 mA) with Cu Kα
radiation (λ = 0.154 nm) to analyze the crystal structure of the
milled powders. The XRD patterns were recorded in the 2θ
range 20°–80° with a step size of 0.01°. The mean size and size
distribution of the eggshell powder were measured using a
dynamic laser light scattering apparatus (FRITSCH Analysette
22 NanoTec Laser Particle Sizer). The chemical composition of
the catalyst was determined using X‐ray fluorescence (XRF)
spectroscopy (Microanalyser Unisantis XMF‐104, Germany)
operated at 40 kV and 300 mA, with Mo radiation. Thermo‐

Elaheh Mosaddegh et al. / Chinese Journal of Catalysis 35 (2014) 351–356
57.9, 98.4, 100.7, 119.6, 128.8, 129.9, 132.1, 143.0, 158.5, 158.7,
161.8, 163.6.
2‐amino‐7‐methyl‐5‐oxo‐4‐(3‐nitrophenyl)‐4H,5H‐pyrano[4,
3‐b]pyran‐3‐carbonitrile (Table 2, Entry 3): pale‐yellow crys‐
tals, mp 230–232 °C. IR (KBr, cm−1): 3400, 3327, 2198, 1716,
1615, 1526, 1448, 1385, 1263, 1200, 1144, 1024, 978, 817,
759, 733. 1H NMR (400.2 MHz, DMSO, ): 2.24 (s, 3H, CH3), 4.53
(s, 1H, CH), 6.75 (s, 1H, =CH), 7.35 (s, 2H, NH2), 7.67 (t, J = 8.0
Hz, 1H, ArH), 7.72 (tt, J = 8.0 Hz, J = 1.2 Hz, 1H, ArH), 8.15 (t, J =
2.0 Hz, 1H, ArH), 8.17(dd, dd, J = 8.0 Hz, J = 2.0 Hz, J = 1.2 Hz, 1H,
ArH). 13C NMR (400.2 MHz, DMSO, ): 19.9, 36.4, 58.2, 98.3,
100.6, 119.7, 128.6, 129.8, 132.2, 143.1, 158.7, 159.0, 162.3,
163.7.
(1)
(2)
(3)
30
40
50
2/(o )
60
70
3. Results and discussion
Fig. 2. XRD patterns of calcined commercially available CaCO3 (1),
nano‐CaO (2), and commercially available CaCO3 (3).
The characterization results showed that the CaO was the
most abundant component (98.6%) in the nanocatalyst; this
was associated with the presence of CaCO3. The nano‐eggshell
catalyst also contained small amounts of Mg (0.39%), P
(0.35%), Sr (0.3%), Si (0.3%), K (0.014%), Na (0.023%), and Zn
(0.003%). Waste eggshell can therefore be considered chemi‐
cally to be a relatively pure, natural carbonate‐based material.
Figure 1(3) shows the IR spectra of commercially available
CaCO3. The broad transmission band at approximately 3436
cm−1 can be attributed to OH stretching vibration from residual
water. The weak band at 1632 cm−1 corresponds to C=O bonds
from carbonate. Two well‐defined IR bands at 1426, 873, and
700 cm−1 are attributed to asymmetric C–O stretching and
out‐of‐plane and in‐plane bending modes, respectively, for
CO32− molecules.
Figure 1(2) shows the spectrum of calcined commercially
available CaCO3. The presence of a peak at 3647 cm−1 is at‐
tributable to OH in Ca(OH)2 formed during adsorption of water
by CaO. The wide and strong band at around 500 cm−1 corre‐
sponds to the Ca–O bond. The IR spectrum of the nano‐CaO
(Fig. 1(1)) had peaks at the same wavenumbers as that of cal‐
cined CaCO3, indicating that the nano‐CaO based on eggshells
and the calcined commercially available CaCO3 are chemically
very similar. Our results regarding uncalcined and calcined
eggshells agree with those reported in the literature [5].
The XRD patterns of the raw eggshell powder and commer‐
cially available CaCO3 were identical, with peaks at 2θ = 29.4°,
indicating that calcite (CaCO3) is the major phase in the waste
eggshell (Fig. 2(3)). The XRD pattern of the nano‐eggshell cal‐
cined at 900 °C for 1 h had a peak at 2θ = 34.2° (Fig. 2(2)). The
major peak of the calcite phase (2θ = 29.4) was not observed in
the XRD pattern of the nano‐CaO, implying that the CaCO3
phase was completely transformed to the CaO phase (Fig. 2(2)).
The XRD pattern of calcined commercially available CaCO3 (Fig.
2(1)) had a peak at the same 2θ angle as that of the calcined
eggshell.
The CaO crystallite size was calculated using the Scherrer
equation. The calcined eggshell generated nanocrystalline CaO
with a crystallite size of 40 nm, whereas the calcined commer‐
cially available CaCO3 showed a very high degree of crystallinity
with a crystallite size of more than 100 nm.
A suitable eggshell calcination temperature was determined
using TGA‐DTA. As shown in Fig. 3, calcination below 600 °C
did not lead to the formation of CaO. Complete conversion was
obtained for calcination temperatures above 600 °C, and nano‐
crystalline CaO was the major phase. The mass loss between
600 and 867 °C is 47.2% and is caused mainly by decomposi‐
tion of calcite, with the formation of CaO and CO2.
Release of CO2 led to the creation of nanocrystalline CaO.
(1)
100
2.0
90
1.5
(2)
(3)
80
1.0
70
0.5
60
0.0
4000 3500 3000 2500 2000 1500 1000 500
Wavenumber (cm1)
50
0
100 200 300 400 500 600 700 800 900
Temperature (oC)
Fig. 1. FT‐IR spectra of nano‐CaO (1), calcined commercially available
CaCO3 (2), and commercially available CaCO3 (3).
Fig. 3. TGA‐DTA curves of nano‐CaO based on eggshell.

Elaheh Mosaddegh et al. / Chinese Journal of Catalysis 35 (2014) 351–356
Table 1
(a)
(b)
Effect of average particle size of catalysts on the synthesis of 2‐amino‐
7‐methyl‐5‐oxo‐4‐(4‐chlorophenyl)‐4H,5H‐pyrano[4,3‐b]pyran‐3‐carbo
nitrile.
Ball milling Average particle Time Yieldb
Catalyst
Time (h)
size a (µm)
(min)
45
(%)
96
75
20
35
Nano‐CaO
2
11
23
47
26
Calcined eggshell
Calcined eggshell
Calcined CaCO3
1
300
300
300
0.5
2
(d)
(c)
a Determined by laser particle sizer.
b Yield refers to isolated pure product.
Table 2
Nano‐CaO‐catalyzed synthesis of 2‐amino‐7‐methyl‐5‐oxo‐4‐phenyl‐
4H,5H‐pyrano[4,3‐b] pyran‐3‐carbonitrile derivatives.
Entry
Ar
Time (min)
Yield a (%)
1
2
3
4
5
6
7
8
9
10
C6H5
4‐Cl‐C6H4
5
45
35
25
25
5
20
20
30
15
94
96
93
95
94
97
98
94
93
96
Fig. 4. FESEM images of nano‐CaO (a), raw eggshell (b), calcined com‐
mercially available CaCO3 (c), and TEM image of nano‐CaO (d).
3‐NO2‐C6H4
2,4‐Cl2‐C6H4
4‐Br‐C6H4
2‐OH‐C6H4
4‐OH‐C6H4
4‐CH3O‐C6H4
4‐CH3‐C6H4
4‐(CH3)2N‐C6H4
The specimens also had high apparent porosities as a result of
decomposition of CaCO3 with evolution of CO2 outside the egg‐
shell powder structure. The effect of carbonate decomposition
is clearly observed in the TEM and FESEM images of the sin‐
tered specimens, as shown in Fig. 4. The FESEM images of raw
eggshell, nano‐CaO obtained by thermal decomposition of egg‐
shell, and calcined CaCO3 were compared. The images show
that the porosity of the nano‐CaO is higher than that of raw
eggshell because of release of CO2 from inside the structure as a
result of calcination. The mesoporous nature of the nanocata‐
lyst, compared with the low porosity of the calcined CaCO3 sur‐
face, is responsible for the catalytic effect of the nano‐eggshell.
This effect is a result of the larger contact area resulting from
the large number of pores and pits distributed over the entire
eggshell surface.
Nitrogen physisorption analysis was performed to compare
the surface areas of the nanocatalyst and calcined commercially
available CaCO3. Brunauer‐Emmett‐Teller surface area analysis
showed a high surface area of 8.0142 m2/g, with an average
particle size of 11 µm, for the nanocatalyst, whereas the values
were 3.5421 m2/g and 23 µm for eggshell that was only cal‐
cined. This is because ball‐milling reduced the eggshell particle
size. As shown in Table 1, the low surface area (1.7364 m2/g)
and larger particle size (26 µm) of the calcined CaCO3 led to low
porosity and low catalytic activity.
We then explored the catalytic activity of nano‐CaO in the
green synthesis of pyrano[4,3‐b]pyran derivatives, using con‐
densation reactions of various aromatic aldehydes (1 mmol),
4‐hydroxy‐6‐methyl‐2H‐pyran‐2‐one (1 mmol), and malono‐
nitrile (1.2 mmol) under solvent‐free conditions. Without the
addition of a catalyst, no pyrano[4,3‐b]pyrans were formed,
even after 10 h, under the reaction conditions used.
To identify the optimum conditions, first, the effect of tem‐
perature on the reaction rate was studied for the preparation of
pyrano[4,3‐b]pyrans (Table 2). At 120 °C, the reaction over
nano‐CaO proceeded to completion very rapid. Decreasing the
a Yield refers to isolated pure product.
temperature led to decreased product yields and reaction rates.
Next, the optimum amount of nanocatalyst in the range
0.02–0.2 g was evaluated. The highest yield was obtained with
0.1 g of catalyst. A further increase in the amount of catalyst up
to 0.2 g did not have any significant effect on the product yield
or reaction time.
To investigate the effect of particle size on the catalytic ac‐
tivity, calcined eggshells ball‐milled for different time were
used in the reaction. As shown in Table 1, the catalytic activity
increased with decreasing particle size. The highest yield was
obtained with nano‐CaO of average particle size 11 µm. In addi‐
tion, a comparison reaction was carried out to show that the
nano‐CaO was a better catalyst than commercially available
CaCO3. As the data in Table 1 show, the reaction proceeded to
completion in 45 min, with a product yield of 96% over the
nano‐CaO, whereas the corresponding values were 5 h and
35% over calcined CaCO3. Since the catalytic activity of the cat‐
alysts agreed well with the specific surface areas and catalyst
particle size, it is logical to conclude that mesoporous CaO with
crystals of reduced size is a more effective catalyst than cal‐
cined CaCO3 with a larger particle size and low porosity.
The generality of this reaction was examined using different
aldehydes (Table 2). In all cases, the reactions gave the corre‐
sponding products in good to excellent yields (93%–98%) in
very short reaction time (5–45 min). This method offers signif‐
icant improvements with regard to the scope of the transfor‐
mation, simplicity, and green aspects, by avoiding expensive,
hazardous, or corrosive catalysts.
A possible mechanism for the formation of the products is
shown in Scheme 2. The reaction occurs via the initial for‐

Elaheh Mosaddegh et al. / Chinese Journal of Catalysis 35 (2014) 351–356
OH
O
tion of nano‐CaO based on eggshell waste was explored. Also, a
X
H
green, rapid, and highly efficient protocol for the one‐pot syn‐
thesis of pyrano[4,3‐b]pyrans under thermal solvent‐free con‐
ditions, using an inexpensive and green catalyst, was devel‐
oped. The nano‐CaO was reused several times without any loss
of catalytic activity and reusability. This green catalyst is a nov‐
el and biocompatible nanocatalyst based on eggshell waste; it
can catalyze organic transformations and reduce environmen‐
tal problems. This is the first use of eggshell waste material as a
nano‐sized natural CaO catalyst in organic synthesis.
4
O
O
CN
O
C
N
O
CN
CN
X
H
3
X
CN
Acknowledgments
O
H
CN
O
CN
NH
O
The financial support of the Iran National Science Founda‐
tion (INSF) and support of the Graduate University of Advanced
Technology are gratefully acknowledged (project 91004279).
2
H
O
2
X
1
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In summary, the easy and rapid ball‐mill‐assisted prepara‐

Elaheh Mosaddegh et al. / Chinese Journal of Catalysis 35 (2014) 351–356
Graphical Abstract
Chin. J. Catal., 2014, 35: 351–356 doi: 10.1016/S1872‐2067(12)60755‐4
Preparation and characterization of nano‐CaO based on eggshell
waste: Novel and green catalytic approach to highly efficient
synthesis of pyrano[4,3‐b]pyrans
Nano eggshell waste
(Nano-CaO)
Eggshell
∆, solvent-free
Elaheh Mosaddegh*, Asadollah Hassankhani
Graduate University of Advanced Technology, Iran
Calcination
The ball‐mill‐assisted preparation by thermal decomposition of
nano‐CaO derived from chicken eggshell waste was reported as a
novel, bioactive, and heterogeneous catalyst with high catalytic ac‐
tivity and reusability in the green synthesis of pyrano[4,3‐b]pyrans.
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