Immobilization of copper nanoparticles on perlite: Green synthesis, characterization and catalytic activity on aqueous reduction of 4-nitrophenol

Article abstract of DOI:10.1016/j.molcata.2015.01.032

We report the facile synthesis of environmentally benign Cu NPs/perlite composites without employing any toxic reductants or capping agents. Renewable natural Euphorbia esula L. not only functioned as a reductant, but also served as a stabilizer for the f

Full text of DOI:10.1016/j.molcata.2015.01.032

Accepted Manuscript
Title: Immobilization of copper nanoparticles on perlite:
Green synthesis, haracterization and catalytic activity on
aqueous reduction of 4-nitrophenol
Author: Mahmoud Nasrollahzadeh S.Mohammad Sajadi
Akbar Rostami-Vartooni Mojtaba Bagherzadeh Reza Safari
PII:
S1381-1169(15)00047-3
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.molcata.2015.01.032
MOLCAA 9415
To appear in:
Journal of Molecular Catalysis A: Chemical
Received date:
Revised date:
Accepted date:
12-12-2014
29-1-2015
30-1-2015
Please cite this article as: Mahmoud Nasrollahzadeh, S.Mohammad Sajadi, Akbar
Rostami-Vartooni, Mojtaba Bagherzadeh, Reza Safari, Immobilization of copper
nanoparticles on perlite: Green synthesis, haracterization and catalytic activity on
aqueous reduction of 4-nitrophenol, Journal of Molecular Catalysis A: Chemical
http://dx.doi.org/10.1016/j.molcata.2015.01.032
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Immobilization of copper nanoparticles on perlite: Green synthesis,
characterization and catalytic activity on aqueous reduction of 4-
nitrophenol
Mahmoud Nasrollahzadeh,*,a S. Mohammad Sajadi, Akbar Rostami-Vartooni, Mojtaba
b
a
Bagherzadeh and Reza Safaria
c
aDepartment of Chemistry, Faculty of Science, University of Qom, Qom 3716146611, Iran
bDepartment of Petroleum Geoscience, Faculty of Science, Soran University, PO Box 624, Soran, Kurdistan Regional
Government, Iraq
cMaterial Research School, NSTRI, 81465-1589, Isfahan, I. R. Iran
ABSTRACT
We report the facile synthesis of environmentally benign Cu NPs/perlite composites without
employing any toxic reductants or capping agents. Renewable natural Euphorbia esula L. not only
functioned as a reductant, but also served as a stabilizer for the formation of Cu NPs. Cu NPs
synthesized using aqueous extract of the leaves of Euphorbia esula L. was immobilized on perlite by a
very simple and inexpensive method. The structural investigation was performed using XRF, XRD,
SEM, EDS, TEM, TG-DTA, BET and FT-IR. The Cu NPs/perlite shows favorable activity and
separability on the catalytic reduction of 4-nitrophenol, and can be reused several times without a
decrease in the catalytic activity. Their reaction rate constant was calculated according to the pseudo-
first-order reaction equation.
Keywords: Green synthesis; Perlite; Copper nanoparticles; Reduction; 4-Nitrophenol
1
. Introduction
The homogeneous Cu catalyst is known as one of the most efficient catalytic systems for various
organic reactions [1-4]. However, homogeneous catalysts suffer from certain disadvantages such as
metal aggregation and precipitation which cause catalyst decomposition and a considerable loss of
catalytic activity, and are difficult to purify and reuse after chemical reactions which leads to a loss of
expensive metal and ligands and contamination to the products [1-4]. Catalyst separation is a
1

critically important issue, and catalysts that are active but difficult to recycle/recover from the reaction
mixture are generally not preferred in the chemical industry.Thus, the use of heterogeneous copper
catalysts is often desirable from the perspective of process development due to their easy handling,
simple recovery, and recycling.
Since catalysis takes place on metal surface, nanoparticles (NPs) are much more reactive than the
particulate metal counterpart due to their small sizes and large surface areas [5]. So, heterogeneous
catalysts are more and more used in the form of nanoparticles. Unfortunately, the agglomeration of
metal NPs is inevitable due to their small size, resulting in a remarkable reduction in their catalytic
activities [6]. To prevent the agglomeration of metal nanoparticles (MNPs) and the over-
stoichiometric use of Cu reagents, the catalytically active metal NPs are usually immobilized on/into
less expensive solid supports such as polymers, carbon, metal oxides, grapheme, gum and zeolite
regarded as ideal supports for heterogeneous catalyst due to their excellent stability, high surface area,
tunable pore size, and robust surface chemistry [2-4,7-11]. However, most of these supports suffer
from inefficiency to achieve highly distributed and stable noble metal NPs. Therefore, it is desirable to
develop an efficient and new support for the immobilization of metal NPs.
Perlite is a naturally occurring dense glassy volcanic rock and can be expanded up to 10-20 times
its original volume when heated rapidly at 700-1200 °C [12]. Perlite is generally chemically inert and
has a pH of approximately 7. It contains silica (greater than 70%), aluminum, potassium, sodium and
3
-5% water and is used filler in various processes such as paint, enamels, glazes, plastics, and resins
[
13]. Since perlite granules are highly porous media, they can naturally act as an excellent support. So
far of our knowledge, there is no report of using of perlite as a support for the preparation of new
catalysts. This study considers perlite could be used as a support for the immobilization of copper
NPs. The purpose of this study was to evaluate the catalytic activity of Cu NPs/perlite composites for
reduction of 4-nitrophenol in water. Copper (Cu) is relatively cheap compared to other noble metals
such as gold (Au), palladium (Pd) and platinum (Pt).
2
. Experimental
2
.1. Instruments and reagents
High-purity chemical reagents were purchased from the Merck and Aldrich chemical companies. All
materials were of commercial reagent grade. Melting points were deter-mined in open capillaries
2

1
13
using a BUCHI 510 melting point apparatus and are uncorrected. H NMR and C NMR spectra were
recorded on a Bruker Avance DRX spectrometer at 400 and 100 MHz, respectively. The element
analyses (C, H, N) were obtained from a Carlo ERBA Model EA 1108 analyzer carried out on Perkin-
Elmer 240c analyzer. X-Ray diffraction (XRD) was performed at 25 °C (D/Max-2550 PC, RIGAKU,
Japan) in reflection mode using Cu Ka radiation. Fourier transform infrared (FT-IR) spectra were
recorded using a Nicolet 5700 spectrometer (Thermo Nicolet Corporation, US) at the wavenumber
-1
range 4000-400 cm at ambient conditions. Morphologies of catalyst were observed using a scanning
electron microscope (JSM-5600LV, JEOL Ltd., Japan) with an operating voltage of 15 kV. The
elemental composition of catalyst was analyzed using an X-ray energy dispersive spectroscopy (EDS)
detector (IE 300X, Oxford, UK) attached to the SEM. Thermogravimetric-differential thermal
analysis (TG-DTA) was performed using STA 1500 Rheometric Scientific (England). The flow rate of
o
air was 120 ml/min and the ramping rate of sample was 2 C/min. The shape and size of Cu NPs
crystals were identified by transmission electron microscope (TEM) using a Philips EM208
microscope operating at an accelerating voltage of 90 kV. The Brunauer-Emmett-Teller (BET)
specific surface areas (SBET) and the porosity of the samples were evaluated on the basis of nitrogen
adsorption isotherms measured at 77 K using a BELSORP-max nitrogen adsorption apparatus (Japan
Inc.). Ultraviolet-visible (UV-vis) absorption spectra were recorded by a Shimadzu UV 2100 PC UV-
visible spectrophotometer.
2
.2. Preparation of extract of the leaves of Euphorbia esula L.
5
0 g of dried powder of the leaves of Euphorbia esula L. was extracted using boiling in 300 mL
double distillated water for 20 min and aqueous extract was centrifuged in 7000 rpm to obtain the
supernatant as extract [14]. According the literatures, the most important phytochemicals inside this
genus are mainly terpenoids, flavonoids, phenolic acids, tannins, sterols, skin-irritating and tumor
promoting latexes and also their active ingenol diterpenoids in different parts of the plant [15-17].
2
.3. Green synthesis of copper nanoparticles using Euphorbia esula L. leaves extract
The copper nanoparticles were synthesized by the following process. In a 250 mL conical flask, 10
3

mL solution of CuCl
2
2
⋅2H O 5 mM was mixed with 100 mL of the aqueous plant extract (100 g dried
leaves of the plant extracted using 500 mL of deionized water while heating at 80 °C and pH 9 for 30
min then filtered) along with vigorous shaking until gradually changing the color of the mixture
during 20 min from yellow to dark indicating the formation of Cu nanoparticles (as monitored by UV-
vis and FT-IR spectra of the solution). The well shaked mixture then filtered and centrifuged at 6500
rpm for 30 min and obtained precipitation washed with absolute ethanol and double distillated water,
respectively. Then, the nano zero valent copper was calcined at 600 ˚C [14].
2
.4. Preparation of Cu NPs/perlite
The Cu NPs/perlite was fabricated by immobilization of Cu NPs synthesized using aqueous extract of
the leaves of Euphorbia esula L on perlite. Approximately, 1.0 g of perlite was dispersed in 15 mL of
an aqueous Cu NPs solution (0.05 M) and stirred for 15 h at 100 ˚C. Then, the mixture was cooled
down to room temperature, filtered, washed with water, and dried.
2
.5. Reduction of 4-nitrophenol by Cu NPs/perlite
A 0.25 M solution of freshly prepared NaBH (25 mL) was added to the stirred mixture of 2.5 mM 4-
4
nitrophenol solution (25 mL) and 10 mg of the Cu NPs/perlite catalyst. The mixture was stirred at
room temperature until the deep yellow solution became colorless. The reaction progress was
monitored by UV-vis spectroscopy at a wavelength of 400 nm. 1.0 mL of the solution was extracted
and diluted to 25 mL for further UV-vis absorption analysis at certain intervals. After completion of
reaction, the catalyst was simply separated by simple filtration and washed successively with ethanol
and water, and then dried and was used for successive cycles. The product was confirmed by their
1
melting points and H NMR spectroscopy.
3
. Results and discussion
Most of the routes for the synthesis of metal nanoparticles use chemical reduction routes which pose
high environmental risk because of chemical toxicity and biological hazards. The green synthesis
techniques are generally synthetic routes that utilize relatively nontoxic solvents such as water,
4

biological extracts, and biological systems [18,19]. Due to our ongoing interest on the green synthesis
of metal NPs [20-23], we wish to report a new and rapid protocol for preparation of Cu NPs by using
Euphorbia esula L. [24,25] leaf extract as a reducing and stabilizing agent.
The Euphorbia esula L. [24,25] leaf extract which is rich in terpenoids, flavonoids, tannins, sterols
and other aromatic compounds may possibly responsible for reduction of Cu2+ metal ions and effective
stabilization of synthesized NPs. Of course the formation of copper NPs is mainly affected using the
reduction of metal ions by antioxidant constituents such as flavonoids present in the extract of the
leaves of Euphorbia esula L. to nano zero valent (NZV) metallic particles (Figure 1).
Figure 1. Bioreduction of metallic ions using the flavonoids as potent antioxidants in aqueous extract
of the leaves of Euphorbia esula L.
5

The synthesized nanoparticles have been well characterized by XRD, TEM and UV-vis
spectroscopy [14].
UV-vis spectroscopy is an important technique to determine the formation and stability of metal
NPs in aqueous solution. Figure 2 shows the UV-vis spectra of Cu NPs formation. Our results showed
that the maximum absorbance of green synthesized Cu NPs was at 580 nm due to the surface plasmon
absorption of nanosized Cu particles.
Figure 2. UV-vis spectrum of Cu NPs synthesized using aqueous extract of the leaves of Euphorbia
esula L) .A; 20 min and B; 30 min.(
The Cu NPs/perlite was prepared by a simple procedure, via the immobilization of Cu NPs
synthesized using aqueous extract of the leaves of Euphorbia esula L. and was thoroughly
characterized by various sophisticated analytical techniques such as XRF, XRD, SEM, EDS, TEM,
TG-DTA, FT-IR and BET specific surface area studies.
The chemical compositions of the perlite were determined with XRF (Table 1). It is noteworthy
2 2 3
that the perlite is a natural alumino-silicate; rich in SiO and Al O .
Table 1
Typical approximate composition analysis of perlite.
Constituent
SiO
Al
Na
Typical, %
60-75
12-16
5-10
2
2
O
3
2
O
K
2
O
2-5
6

CaO
0-2
0-1
0-1
1-2
MgO
Fe O
2 3
Combined H
2
O
The FT-IR spectra of Cu NPs/perlite is shown in Figure 3, the broad peak around 3400 cm1-
1
-
indicates the O-H bond vibrations. An O-H deformation vibration was observed near 1630 cm. The
1
-
remaining peaks at 1355, 1035, 782, and 453 cm correspond to the stretching bands of Si-O and Si-
O-Si groups, and deformation bands of Si-O group and Al-O-Si groups of perlite, respectively. The
FT-IR studies of Cu NPs/perlite confirm that there was no change in functional group after the
immobilization of Cu NPs on perlite.
Figure 3. FT-IR spectrum of Cu NPs/perlite and perlite.
Figure 4 shows the XRD pattern of Cu NPs/perlite. The broad peak centered at 2θ = 25° was
assigned to the characteristic peak of perlite, indicating its amorphous nature. Notably, no reflections
assignable to metallic Cu were present in the XRD pattern of Cu NPs/perlite, possibly due to the poor
crystallinity of the Cu particles in Cu NPs/perlite. In order to confirm the presence of a metallic Cu
component in Cu NPs/perlite, the chemical composition of the products was further analyzed by the
7

Energy Dispersive X-ray Spectroscopy (EDS) spectrum. It further confirmed that Cu NPs/perlite was
composed of Si, Al, Cd, Fe, Cu and oxygen (Figure 5).
The size and shape of the Cu NPs/perlite was examined by scanning electron microscopy (SEM)
and transmission electron microscopy (TEM). Figure 5 shows typical large-scale FE-SEM images of
the as-produced Cu NPs/perlite. It is clearly observed that the Cu NPs have various sizes less than 32
nm.
The size of as-prepared Cu NPs/perlite was further examined by TEM (Figure 5). The particles
exhibited spherical morphology with low tendency to agglomeration.
Figure 4. XRD powder pattern of Cu NPs/perlite.
8

Figure 5. EDS spectrum, FE-SEM and TEM images of Cu NPs/perlite.
The specific surface areas and pore volume of Cu NPs/perlite was determined by BET (Brunauer-
9

2
Emmett-Teller). The N adsorption-desorption isotherm and Barrett-Joyner-Halenda (BJH) pore size
distribution plot of Cu NPs/perlite showed in Figure 6. The results indicate that the specific surface
area, pore volume, and average pore diameter of perlite were increased after immobilization of copper
nanoparticles. Based on isotherm curve, the measured BET surface area of Cu NPs/perlite was 3.8
2
2
m /g, whereas the surface area of perlite is 1.73 m /g [26]. It is clear that number of pores on the
surface of perlite fairly increased after immobilization of copper nanoparticles. Moreover, the Barrett-
Joyner-Halenda (BJH) analysis showed that the average pore diameter is 8.1 nm and the pore volume
-3
is 7.7×10 cc/g, whereas the average pore diameter and pore volume of perlite is 1.9 nm and 2.29 ×
-3
1
0 cc/g, respectively [26].
1
0

Figure 6. The N
2
adsorption-desorption isotherm and Barrett-Joyner-Halenda (BJH) pore size
distribution plot of catalyst.
Figure 7 shows the TG/DTA curves measured for Cu NPs/perlite. In the TG/DTA data of Cu
NPs/perlite a gradual weight decreasing (about 4.0 wt %) was only observed between 180 and 300 °C
corresponding to desorption of surface water.
Figure 7. TG/DTA data measured for Cu NPs/perlite.
1
1

Evaluation of the catalytic activity of Cu NPs/perlite through the reduction of 4-nitrophenol in water
-Nitrophenol (4-NP) is carcinogenic and genotoxic to human beings and wildlife, which can damage
4
the central nervous system, liver, kidney and blood of humans and animals. Degradation of the
compound to nondangerous product is difficult because of its high stability and low solubility in water
[
27]. The reduction or conversion of 4-NP acquires great importance both environmentally and
industrially. Its reduction product, 4-aminophenol (4-AP), is an important industrial intermediate for
manufacturing analgesic and antipyretic drugs, anticorrosion lubricants, and hair dying agents [28].
Therefore, developing an efficient, durable and eco-friendly method to produce 4-AP is a major
4
challenge in catalysis research. The reduction of 4-NP with sodium borohydride (NaBH ) as reducing
agent in the presence of Cu NPs has been extensively investigated in our previous work [29].
However, the catalytic performance of Cu NPs/perlite in the reduction of 4-NP to 4-AP has not been
well examined. In the present work, the catalytic performance of the synthesized Cu NPs/perlite was
4
evaluated by the reduction of 4-NP with NaBH to 4-AP (Scheme 1).
The UV-vis spectra of the reaction mixture were monitored with the progress of the catalytic
reduction of 4-NP (Figure 8a and 8b). As shown in Figure 8, there was a red shift of the peak of 4-NP
from 317 to 400 nm, observed immediately after the addition of NaBH
4
. This was due to the formation
(Scheme 2) [30].
of 4-nitrophenolate ions under alkaline conditions caused by the addition of NaBH
4
The absorption of 4-NP at 400 nm decreases with a concomitant increase in the peak at about 300 nm,
which is attributed to the reduced product, 4-aminophenol. The absorption peak at 400 nm is fully
disappeared after about 2.5 min in the presence of 10 mg of Cu NPs/perlite catalyst. Without catalyst,
1
2

no significant color change was observed within the reaction time and the peak at 400 nm remained
unaltered for a long duration. This suggests that even an excessive concentration of NaBH cannot
4
reduce 4-nitrophenolate ions completely in the absence of catalysis. Also, the loss of catalytic activity
was not observed after the catalyst was recycled for three times, indicating high stability of the Cu
NPs/perlite catalyst.
Figure 8. (a) UV-visible spectra of 4-NP in the absence of NaBH
4
, (b) Time-dependent UV-visible
] = 0.25 M;
absorption spectra for the reduction of 4-NP, Conditions: [4-NP] = 2.5×10−3 M; [NaBH
4
t 0
catalyst = 10 mg, (c) Plot of ln(A /A ) versus time for the reduction of 4-NP with Cu/perlite.
Conditions: [4-NP] = 2.5×10−3 M; [NaBH
] = 0.25 M; catalyst = 10 mg.
4
Due to the presence of large excess of NaBH
independent of the concentration of NaBH , and the reduction of 4-NP to 4-AP can be treated as a
pseudo-first-order reaction. As the absorbance of 4-NP is proportional to its concentration in the
medium, the ratio of A /A is proportional to the ratio of C /C (A is the absorbance at any time t, A
is the absorbance at time t = 0, C is the concentration of 4-NP in the reaction time t and C is the
initial concentration of 4-NP). Pseudo-first-order rate constant could be calculated by the following
4
compared to 4-NP, the rate of reduction is
4
t
0
t
0
t
0
t
0
1
3

rate law equation [31]:
ln(C
t
/C
0
) = ln(A
t
/A
0
) = -kt
/A
the rate constant for this reaction is 0.027 s , which is comparable to those reported previously
32,33].
To show the advantages of proposed method in comparison with other reported methods, we
where, k is the rate constant. From the linear relations of ln(A
t
0
), shown in Figure 8c, we found that
-1
[
summarized some of results for reduction of 4-NP in Table 2, which shows that Cu NPs/perlite is an
equally or more efficient catalyst with respect to reaction time and yield than previously reported ones.
Compared with the other literature works on the reduction of 4-NP, the notable features of our
method are:








The reaction system is clean;
Elimination of toxic reagents and homogeneous catalysts;
The conversion and yield of the product is very high;
The use of plant extract as an economic and effective alternative represents an interesting,
fast and clean synthetic route for the large scale synthesis of Cu NPs;
Avoidance of the high reaction temperature;






Natural and highly efficient heterogeneous catalyst activity;
Ease of handling and cost efficiency of the catalyst;
Avoidance of the non-green solvents application and by-products preparation;
Higher yields and purity, shorter reaction time and milder conditions;
The Cu NPs/perlite can be easily recovered.
Table 2
Comparison present methodology with other reported methods in the reduction of 4-NP.
Entry
Conditions (yield, %)
O, H
Ref.
1
2
3
4
5
6
7
GA-Pt NPs, H
Resin-Au NPs, MeOH/H
NAP-Mg-Au(0), H O, NaBH
Ni-PVAm/SBA-15, H O, NaBH
TiO O, oxalic acid, ultraviolet light (16W), N
Fe @C@Pt, EtOH, H , r.t., 60 min (98)
Cu NPs, THF/H O, NaBH , 50 °C, 2 h (66)
2
2
, r.t., 8 h (82)
O, NaBH
, r.t., N
, r.t., 85 min (98)
34
35
36
37
38
39
40
2
4
, 40 °C, 20 min (82)
, 7 min (98)
2
4
2
2
4
2
-G1%,H
2
2
, 60 min (95)
3
O
4
2
2
4
1
4

8
9
1
1
1
1
1
1
1
1
1
1
2
HMMS-NH
Polymer-anchored Pd(II) complex, DMF, H
PdCu/graphene, EtOH/H O, NaBH , 50 °C, 1.5 h (98)
KCC-1/Au, H O, NaBH , r.t., 12 min
Au-GO, H O, NaBH , r.t., 30 min
Au/graphene hydrogel, H O, NaBH
Au@PZS@CNTs, H O, NaBH , r.t., 16 min
Ag/KCC-1, H O, NaBH , r.t., 510 s
Cu NPs, H O, NaBH , r.t., 50 min
Pd-FG, H O, NaBH , r.t., 12 min
p(AMPS)-Ni composite, H O, NaBH
p(AMPS)-Co composite, H O, NaBH
Cu NPs/perlite, H O, NaBH , r.t., 2.5 min (99)
2
-Pd, EtOH, H
2
, r.t., 60 min (98)
41
2
, 30 °C, 5.5 h (84)
42
0
1
2
3
4
5
6
7
8
9
0
2
4
43
2
4
44
2
4
45
2
4
, r.t., 720 s
46
2
4
47
2
4
48
2
4
49
2
4
50
2
4
, 30 °C, 60 min
, 30 °C, 28 min
51
2
4
52
2
4
This work
It is important to point out that the Cu NPs/perlite composites show relatively higher catalytic
activity than Cu NPs alone. We investigated the effects of the perlite support on the catalytic activity.
Reduction of 4-NP with NaBH was carried out respectively in the absence of a catalyst, the presence
4
of Cu NPs, the presence of perlite, and the presence of Cu NPs/perlite composite to investigate the
catalytic effect of the as-prepared Cu NPs/perlite on the reaction. According to the results, no
appreciable reaction took place after 30 min without a catalyst or in the presence of perlite. A reaction
4
time of 580 s was required to achieve the full reduction of 4-NP by NaBH using Cu NPs alone as
catalysts. But when the Cu NPs/perlite composite was used as the catalyst, the reaction proceeded
much faster and completed in 2.5 min. Such observation indicates that the perlite support may play an
active part in the catalysis, yielding a synergistic effect. The synergistically enhanced catalytic activity
may be explained as follows: given that 4-NP is π-rich in nature, it is expected that 4-NP can be
adsorbed onto perlite via π–π stacking interactions. Such adsorption provides a high concentration of
4
-NP near to the Cu NPs on perlite, leading to highly efficient contact between them. In contrast,
without a highly adsorbent perlite support, 4-NP must collide with Cu NPs by chance, and remains in
contact for the catalysis to proceed. When this is not achieved, 4-NP will pass back into solution and
can only react further when it collides with Cu NPs again [33].
Finally, the focus of on the experimental study of catalysis (such as Cu NPs/perlite) effects on
immobilization of copper NPs on perlite, the obtained results can be demonstrated by computational
studies, in which intra-molecular catalyst affects the nano-sized organic systems. As our current work
1
5

we investigate the intra-molecular electronic transport mechanisms in organic systems, induced by
surface/catalyst effect, using quantum theory of atoms-in-molecule (QTAIM). The QTAIM that can be
utilized to determine the chemical behaviour of organic molecular systems as an expansion of
quantum mechanics to proper the open molecular systems in terms of the topology of such systems or
local electron density
, Laplacian
, atomic electronic energy
, molecular
Virial/potential force
and bonding characteristics [53-55]. Using the QTAIM, the contour
-
maps of the electron density and its Laplacian and Virial force of the NO
Ph-OH molecules and -C-NO
demonstrated in Figures 9 and 10. Analysis of computational results (not reported here for brevity)
shows that the oxygen atoms of the NO functional group have different local electronic properties
such as electron density, atomic basins and atomic boundary surfaces). Also, atomic scale analyses of
the results demonstrate that the hydrogen and carbon atoms of the rings are generally the weakest
responses to catalyst nature and in which its effects on the NO group is larger than OH functional
group. It is also predicted that the interaction (or absorption) between nano-size Cu particles of the Cu
NPs/perlite catalyst and NO functional group of the molecule (-Cu-NO -) play a dominant role in the
intra-molecular electronic transport for the reduction of NO . Moreover, it is possible to predict and
2
-Ph-OH, NO
2
-Ph-O , NH
2
-
2
-Cu-O- bonding plan, in the molecular planes are calculated and results
2
(
2
2
2
2
study the molecular/submolecular energy and charge transfers to determine atoms and functional
groups with lower or higher sensitivity to surface/catalyst effect as an important factor for effective
designing the actual molecular systems and intelligent control of their environmental behaviour.
1
6

1
7

2

(r)) and its Laplacian (   (r)
Figure 9. The contour maps of the electron density (
) and Virial
force
of the NO
2
2
-Ph-OH (left) and NH -Ph-OH (right) molecules, in the molecular planes, are
calculated using QTAIM.
1
8

1
9

2

(r)) and its Laplacian (   (r)
Figure 10. the contour maps of the electron density (
) and Virial force
-
of the NO
2
-Ph-O (left) molecule and -C-NO
2
-Cu-O- bonding plan (right), in the molecular planes,
in the molecular planes, are calculated using QTAIM.
Catalyst recyclability
The reusability, which is an important factor for a catalyst, was investigated by recovering the Cu
NPs/perlite catalyst from the reaction mixture by filtration and reusing it in the next reaction. The
perlite supports not only enhance the catalytic activity of Cu NPs via a synergistic effect, but also lend
the Cu NPs/perlite the easiness of separation and recovery for practical catalytic applications. After
completion of the reaction, the catalyst was separated by simple filtration and was washed with
ethanol and water, dried in a hot air oven at 100 °C for 2 h and the recycled catalyst was saved for the
next round. The slight yield loss was observed after three cycles. Meanwhile, EDS observation after
the repeated catalytic tests was also carried out to check the stability of the as-prepared catalyst. It was
found that the Cu content of the Cu NPs/perlite was scarcely changed, suggesting the good stability of
the materials.
2
0

4
. Conclusions
In conclusion, Cu NPs/perlite with good catalytic activity has been successfully fabricated by
immobilization of Cu NPs on perlite. Cu NPs was prepared using aqueous extract of the leaves of
Euphorbia esula L. The as-prepared Cu NPs/perlite catalyst exhibits excellent catalytic activity and
recyclability for the reduction of 4-NP to 4-AP. The rate constant and the reaction yield calculated for
the reduction of 4-nitrophenol is comparable to the best reported in the literature.
Acknowledgments
We gratefully acknowledge the Iranian Nano Council and the University of Qom for the support of
this work.
References
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