Pumice-modified cellulose fiber: An environmentally benign solid state hybrid catalytic system for the synthesis of 2,4,5-triarylimidazole derivatives

Article abstract of DOI:10.1016/j.jpcs.2020.109443

In this study, we developed an instrumental hybrid catalytic system comprising cellulose fiber and volcanic pumice powder, which was applied as a suitable organic–inorganic hybrid catalyst for the synthesis of 2,4,5-triarylimidazole derivatives. High reaction yields (97%) were obtained in short reaction times (20 min) using this catalytic system. In physical terms, the high porosity of pumice provides an extremely high active surface area for electronic interactions among the components. Moreover, the most distinctive properties of this catalytic system are high biodegradability, simple separation of the catalyst, and good reusability. The natural pumice can be recovered easily using an external magnet and reused with no significant decline in the catalytic activity. The structural characteristics of this efficient catalytic system were assessed using various analytical methods.

Full text of DOI:10.1016/j.jpcs.2020.109443

Journal Pre-proof
Pumice-modified cellulose fiber: An environmentally benign solid state hybrid catalytic
system for the synthesis of 2,4,5-triarylimidazole derivatives
Ali Maleki, Saideh Gharibi, Kobra Valadi, Reza Taheri-Ledari
PII:
S0022-3697(19)32490-4
https://doi.org/10.1016/j.jpcs.2020.109443
PCS 109443
DOI:
Reference:
To appear in: Journal of Physics and Chemistry of Solids
Received Date: 9 November 2019
Revised Date: 3 March 2020
Accepted Date: 4 March 2020
Please cite this article as: A. Maleki, S. Gharibi, K. Valadi, R. Taheri-Ledari, Pumice-modified
cellulose fiber: An environmentally benign solid state hybrid catalytic system for the synthesis of
2,4,5-triarylimidazole derivatives, Journal of Physics and Chemistry of Solids (2020), doi: https://
doi.org/10.1016/j.jpcs.2020.109443.
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S1

Graphical Abstract

Pumice-modified cellulose fiber: An environmentally benign solid state hybrid
catalytic system for the synthesis of 2,4,5-triarylimidazole derivatives
Ali Maleki*, Saideh Gharibi, Kobra Valadi, Reza Taheri-Ledari
Catalysts and Organic Synthesis Research Laboratory, Department of Chemistry, Iran University of
Science and Technology, Tehran 16846-13114, Iran
*Corresponding author. E-mail: maleki@iust.ac.ir; Fax: +98-21-73021584; Tel: +98-21-
77240540-50
Abstract
In this study, we developed an instrumental hybrid catalytic system comprising cellulose fiber and
volcanic pumice powder, which was applied as a suitable organic–inorganic hybrid catalyst for the
synthesis of 2,4,5-triarylimidazole derivatives. High reaction yields (97%) were obtained in short reaction
times (20 min) using this catalytic system. In physical terms, the high porosity of pumice provides an
extremely high active surface area for electronic interactions among the components. Moreover, the most
distinctive properties of this catalytic system are high biodegradability, simple separation of the catalyst,
and good reusability. The natural pumice can be recovered easily using an external magnet and reused
with no significant decline in the catalytic activity. The structural characteristics of this efficient catalytic
system were assessed using various analytical methods.
Keywords: Biodegradable material; Catalytic system; Heterogeneous catalyst; Natural composite;
Organic catalysis.
1. Introduction
1

Recently, multicomponent reactions (MCRs) have attracted much attention as one-pot, safe, and logical
methods. The excellent features of MCRs include their high efficiency, minimal number of synthetic
steps, ready availability of raw materials, environmental safety, short reaction time, and low costs [1,2].
The synthesis of imidazole derivatives is one of the most important MCRs where heterocyclic compounds
are produced with medicinal applications. Various methods have been developed to prepare these
substances [3]. In particular, the use of various functionalized organic–inorganic hybrid catalytic systems
has been widely reported [4,5]. Magnetized polymeric and fibrous composites such as polyvinyl alcohol
and cellulose have been used in many studies because they are simple to apply in isolation and separation
processes [2,6,7]. Iron oxide nanoparticles (Fe3O4 NPs) have frequently been employed for magnetization
in the catalytic and drug delivery systems [8─10]. Fe3O4 NPs have several advantages such as super-
paramagnetic behavior, nontoxicity, and surface functionalization capability, but this chemical agent is
produced from iron chloride salts. In previous studies, we designed nanosized catalytic systems and
applied Fe3O4 NPs in their structures [11−14]. In the present study, we utilized volcanic pumice powder
as a natural magnetic agent for preparing a substantial biocompatible and biodegradable catalytic system
with high porosity [15]. In addition, cellulose was used as another natural component in the proposed
system as the main catalytic active ingredient. Pumice is a porous stone formed from volcanic eruptions.
After a volcanic eruption, the rapid evaporation of gases and cooling lead to the formation of a porous
structure in natural pumice [16]. In the present study, granulated pumice stone was ground and powdered
by ball milling and using a mortar and pestle. Natural pumice was selected because of its highly porous
structure, availability, abundance, magnetic properties, and low cost [17]. In general, iron-based catalysts
such as pumice powder have been used widely and their applications have been reviewed in the field of
catalysis. For instance, Alver et al. employed volcanic pumice to design instrumental catalytic systems for
various catalytic applications [17−19]. This catalytic system can be readily separated from the reaction
mixture by an external magnet because of its magnetic properties. In general, magnetic purification is
2

greatly preferred compared with other methods, which are usually time consuming, difficult, and
expensive.
Among the various composite matrices, polymers are considered an important class of materials, which
are divided into natural and synthetic categories. Cellulose has various advantages, such as good
biodegradability, high availability, inexpensiveness, nontoxicity, and the presence of a large number of
hydroxyl functional groups that can activate the carboxylic groups in MCRs [20,21]. Similarly, natural
pumice powder has useful properties, including high stability and thickness, a porous structure with
cavities of different sizes, and remarkable magnetic properties [22]. The main disadvantages of using
catalytic systems in industry are their low efficiency, high cost, and toxicity, which represent severe
obstacles that hinder the scaling up of processes. The separation of the catalytic system after completing
the reaction is the main concern in catalytic applications. Various materials with different properties have
been used to solve this problem. Thus, in the present study, the natural pumice powder made it easier to
separate the catalyst because of its intrinsic magnetic properties, which together with its low price and
availability make it an ideal agent for industrial applications. The reactions of the desired imidazole
derivatives were catalyzed using the proposed organic–inorganic hybrid catalyst. High reaction yields
(97%) were obtained in a short reaction time (20 min) using a small amount (0.03 g) of the
cellulose@pumice catalytic system. Excellent reusability was demonstrated for this catalytic system by
magnetic isolation, washing, and drying.
2. Results and discussion
2.1. Characterization
In this study, a natural cellulose/pumice composite was prepared via an in situ method [23]. The
successful formation of the composite was confirmed using various analytical techniques. Finally, the
catalytic efficiency of the fabricated cellulose@pumice composite was investigated in MCRs to
synthesize imidazole derivatives.
3

Fourier transform-infrared (FT-IR) spectroscopy was used to study the chemical bonds and chemical
structures within the organic and inorganic materials. The FT-IR absorption spectra obtained for the
natural volcanic pumice and hybrid cellulose@pumice samples at wavelengths from 400 to 4000 cm–1 are
shown in Figure 1. According to previous studies, the sharp peak at ca. 1100 cm–1 was related to the
stretching vibrations of Si-O-Si in the silica network of the structure of the natural pumice (spectrum a)
[19]. The intensity of the sharp broad peak attributed to hydroxyl groups at ca. 3400 cm–1 was enhanced
after combining with cellulose fiber (spectrum b). In addition, stretching vibrations were observed at 1526
and 2036 cm–1, which correspond to oxygen-hydrogen and carbon-hydrogen bonds in the microcrystalline
cellulose matrix, respectively. The stretching vibrations of C-H bonds (with hybridization sp3) in
cellulose were observed at ca. 2900 cm–1. The absorption peak at 590 cm–1 was related to the bending
vibrations of hydroxyl groups [23,24].
Figure 1. Fourier infrared spectra obtained for (a) cellulose@pumice organic–inorganic hybrid catalyst,
(b) pumice powder, and (c) cellulose powder.
4

Energy-dispersive X-ray (EDX) spectroscopy was employed to monitor the elements present in the
samples and the weight percentage of each atom [25]. The results obtained by EDX analysis using the
neat natural pumice and the prepared cellulose@pumice composite are shown in Figure 2. The elements
in pumice comprised iron, carbon, silicon, aluminum, calcium, sodium, and oxygen, and a sharp signal
was also present for carbon after combining with cellulose fiber [19].
Figure 2. Energy-dispersive X-ray spectra obtained for (a) neat volcanic pumice powder and (b)
cellulose@pumice organic–inorganic hybrid catalyst (x-axis: energy (keV); and y-axis: intensity (a. u.)).
The size, shape, and composition of the product were studied by scanning electron microscopy (SEM), as
shown in Figure 3. The images of the neat natural volcanic pumice after grinding (Figures 3a and 3b)
5

showed that a very large active surface area was provided by the pumice laminates in a range of 0.3-0.5
µm diameter. Numerous pores were present between the laminates and in the pumice’s structure, which
could capture the reactants in chemical reactions for catalytic purposes. According to the Figure 3c,
porous micro-sheets of pumice were evenly distributed between the cellulose strands. Thus, a large
surface area was provided by this natural composition. The carbon elemental mapping results (as
measures of the composition) for the natural pumice powder before and after combining with the cellulose
fiber are illustrated in Figures 3c and 3d, respectively. As expected, the amount of elemental carbon
increased significantly after modifying the pumice with cellulose fiber due to the high abundance of
carbon in the structure of the cellulose.
Figure 3. Scanning electron microscopy images obtained for (a) the neat pumice powder and (b)
fabricated cellulose@pumice. Carbon elemental mapping results obtained for (c) the neat pumice powder
and (d) fabricated cellulose@pumice organic–inorganic hybrid catalyst.
One of the most important parameters that increase the efficiency of a catalyst is magnetism, which
allows it to be readily separated from the reaction mixture and reused several times. Therefore, as shown
in Figure 4a, the magnetic behavior of the neat pumice and the cellulose-modified pumice composite were
investigated by using a vibrating sample magnetometer (VSM). Magnetic-hysteresis (M–H) curves I and
6

II in Figure 4a show that the magnetic strength of the pumice decreased from 49.8 to 34.2 emu/g after it
was combined with cellulose. The reduced magnetic strength of the composite demonstrated that the
pumice was correctly loaded on the surfaces of the cellulose fiber [26].
Thermogravimetric analysis (TGA) was conducted to determine the thermal stability of the prepared
cellulose@pumice catalyst in the temperature range from 20–600°C at a rate of 10°C/min, as shown in
Figure 4b. A small shoulder was observed below 120°C due to the adsorption and desorption of the
physically adsorbed moisture in the air onto the hot surfaces of the particles. A gradual decrease in the
weight ratio was observed up to 250°C, which could be attributed to separation of the water molecules
absorbed on the cellulose fibers, and a weight lost of ~0.5% occurred in this stage. Subsequently, a steep
decrease in the relative mass percentage (~2%) was observed up to 270°C, which was probably due to the
removal of the water molecules trapped in the underlying layers of the silica network in the volcanic
pumice powder [27]. Next, a gradual decrease occurred due to the separation of the hydroxyl groups in
cellulose during the dehydration process [28], and there was a weight loss of ~5% up to 480°C in this
stage. Subsequently, fracturing occurred at above 500°C because of the destruction of the structure of the
pumice [29].
The structures and crystalline profiles of the natural pumice powder and fabricated cellulose@pumice
composite were confirmed by X-ray diffraction (XRD) analysis, as shown in Figure 4c. The two peaks at
2θ = 23 and 29° were related to dihydrate minerals, and the peak at a diffraction angle of 2θ = 26.65°
demonstrated the presence of the amorphous structure of pumice (pattern I) [17−19]. Moreover, the
presence of microcrystalline cellulose was indicated by the peak observed at 2θ = 22° (pattern II) [30]. In
general, the XRD pattern (II) exhibited a significant shift (~5°) after combining the pumice with cellulose
as shown by the distinct shifts in the areas of the peaks that appeared at 33° and 37° in pattern II, which
may be attributed to the surface of pumice laminates being coated by cellulose fibers. This change in the
lattice composition may be the main explanation for the change in the XRD patterns [31,32].
7

Figure 4. (a) Magnetic-hysteresis curves obtained for the pumice powder (I) and cellulose@pumice (II) at
room temperature. (b) Thermogravimetric analysis curve obtained for the cellulose@pumice organic–
inorganic hybrid catalyst. (c) X-ray diffraction pattern obtained for the pumice powder (I) and
cellulose@pumice (II) composite.
To further clarify the combination of the composite, X-ray photoelectron spectroscopy (XPS) was
conducted for the natural pumice and fabricated cellulose@pumice composite (Figure 5). The peak
intensities determined for carbon and oxygen were considered the two main criteria for assessing the
8

addition of the cellulose fibers. Significant increases in the intensities of these two peaks were observed at
~300 and 580 eV after adding cellulose, which is structurally rich in these two elements.
Figure 5. X-ray photoelectron spectra obtained for (a) the neat natural pumice powder and (b) the
fabricated cellulose@pumice organic–inorganic hybrid catalyst.
2.2. Application of the cellulose@pumice organic–inorganic hybrid catalyst for the synthesis of 2,4,5-
triarylimidazoles derivatives
To obtain the best reaction conditions for the synthesis of triarylimidazole derivatives, several control
reactions were conducted using different conditions and the results obtained are summarized in Table 1.
The synthesis of product 4a was selected as a model reaction (Scheme 1). Under catalyst-free conditions,
the reaction’s progress was not acceptable (entry 1 in Table 1). The model reaction was then optimized by
using various amounts of the organic–inorganic hybrid catalyst under different conditions, where various
9

media and different temperatures were tested to obtain the most appropriate conditions. The reaction’s
progress was monitored by thin-layer chromatography (TLC).
Scheme 1. Catalytic application of cellulose@pumice organic–inorganic hybrid catalyst in the synthesis
of 2,4,5-triaryl-1H-imidazoles.
Table 1. Optimization of the reaction to synthesize 4a catalyzed by the cellulose@pumice organic–
inorganic hybrid catalyst.
Entry
Solvent
Catalytic system
Cat. a (g) Conditions
Temp.
Time (min) Yield b (%)
(°C)
1
2
3
4
5
6
7
8
9
10
Water
EtOH
EtOH
EtOH
EtOH
EtOH
DMF
Cellulose@pumice
Cellulose@pumice
Cellulose@pumice
Cellulose@pumice
Cellulose@pumice
Cellulose@pumice
Cellulose@pumice
Cellulose@pumice
Cellulose
-
Reflux
Reflux
100
70
40
40
20
20
20
20
20
20
20
20
Trace
Trace
72
-
0.01
0.03
0.05
0.03
0.03
0.03
0.03
0.03
Reflux
70
Reflux
70
98
Reflux
70
98
Stirring
Reflux
25
97*
95
110
130
25
DMSO
EtOH
EtOH
Autoclave
Stirring
Stirring
93
81
Pumice
25
69
a
b
Cellulose@pumice organic–inorganic hybrid catalyst; isolated yield; *optimum conditions; benzaldehyde 1 (1.0 mmol),
ammonium acetate 2 (2.0 mmol), and benzyl 3 (1.0 mmol) were used for the synthesis of 4a.
10

Table 2 shows some previously reported catalytic systems based on natural volcanic powder and their
disadvantages compared with our system. Intense reaction conditions and long reaction times were the
two main disadvantages of these catalytic systems. By contrast, out natural catalytic system allows the
synthesis of imidazole derivatives via reactions with high yields and short reaction times under very mild
reaction conditions. The reusability without loss of catalytic activity was demonstrated for the pumice
powder because of its inherent magnetism. The catalytic performance of the cellulose@pumice composite
was evaluated by obtaining 15 different imidazole derivatives with high yields (Table 3).
Table 2. Previously reported catalytic systems with different natural bases and .
Entry
Catalytic System
Pumice-Pd/Cu
Pumice-Pd
Catalytic purpose
Disadvantages
High temperature
Long reaction time
Ref.
[33]
[34]
1
2
3
Reduction of nitrates
Hydrogenation of phenylacetylene
Oxidation of CO and benzyl alcohol
Pumice-Pd/Ag
High temperature and long [35,36]
reaction time
4
Natural pumice
Ozonation degradation of p-
chloronitrobenzene
High temperature and low
efficiency
[37]
5
6
Fe(TDFSPP)-HNTa
Fe3O4-HNT-SO3H
Oxidation of alkanes
Low efficiency
[38]
[39]
Synthesis
High temperature
of dihydropyrimidinones
7
Poly(N-IPA)-HNTb
Thermoresponsive curcumin release
Long reaction time
[40]
a Iron(III) porphyrin [Fe(TDFSPP)] immobilized on raw halloysite nanotubes (HNTs)
b Poly(N-isopropylacrylamide)-HNTs
Table 3. Synthesis of 2,4,5-triarylimidazoles derivatives 4a–n under optimized conditions.
11

Time
(min)
Yield a
(%)
Melting point (°C)
Obtained
Entry
Aldehyde
Product
Ref.
Reported
234–236
210–211
226–228
183–186
250–252
180–182
230–232
236–238
220–222
201–203
280–281
208–210
239–240
this work
1
Benzaldehyde
2,4-Dichlorobenzaldehyde
2-Nitrobenzaldehyde
9
97
95
93
93
90
88
94
87
92
88
96
95
95
98
235–237
210–212
225–227
184–186
248–250
180–181
230–232
236–237
221–223
200–201
279–281
207–209
238–240
157–159
[41]
[42]
[41]
[43]
[43]
[42]
[43]
[42]
[41]
[41]
[44]
[44]
[45]
-
4a
4b
4c
4d
4e
4f
2
10
10
10
10
10
7
3
5
3-Hydroxybenzaldehyde
2-Chlorobenzaldehyde
6
7
4-Chlorobenzaldehyde
8
3,4-Dimethoxybenzaldehyde
4-Methoxybenzaldehyde
2,5-Dimethoxybenzaldehyde
3-Nitrobenzaldehyde
4g
4h
4i
9
8
10
11
12
13
14
15
10
10
10
10
10
10
4j
4-Nitrobenzaldehyde
4k
4l
4-Methylbenzaldehyde
4-Dimethylaminobenzaldehyde
3,4,5-Trimethoxybenzaldehyde
4m
4n
a Reaction conditions: 0.03 g of catalytic system with stirring for 20 min at room temperature.
2.3. Proposed mechanism for the synthesis of 2,4,5-triarylimidazoles derivatives
The raw imidazole synthesis materials reacted according to the mechanism proposed in Scheme 2, and
finally the cellulose@pumice product was also recovered. Initially, the hydroxyl cellulose functional
groups present in the catalyst activated carbonyl aldehyde 1 and benzyl 2. Next, ammonia molecules
reacted with aldehyde, which was activated by the acidic catalyst to form intermediate I. Intermediate I
then further reacted with benzyl, which was already activated by the catalyst, to form intermediate II.
12

Finally, the catalyst was separated using an external magnet and washed several times. The synthesized
product was prepared for identification [46].
Scheme 2. Proposed mechanism for the synthesis of 4a–n by using the cellulose@pumice organic–
inorganic hybrid catalyst.
2.4. Reusability of cellulose@pumice organic–inorganic hybrid catalyst
One of the most important parameters for a catalytic system is its recyclability and simple separation from
the reaction medium without reducing its activity. Thus, in order to investigate the recyclability of our
fabricated catalytic system, the recycled catalyst was reused 10 times after completing the synthesis
reaction (for 4a) and the synthesized product was evaluated (Figure 6). According to the results, no
significant change in the catalytic activity was observed after reusing the catalyst 10 times.
13

Figure 6. Recycling of the cellulose@pumice organic–inorganic hybrid catalyst when producing 4a.
3. Materials and methods
3.1. Materials & equipment
All the chemicals, reagents, and equipment used in this study are listed in Table 4.
Table 4. Chemicals and equipment used in this study.
Materials and Equipment
Pumice stone
Purity and Brand
Granulated – Sigma Aldrich
Microcrystalline - Sigma Aldrich
Sigma Aldrich – 97% and 98%
Sigma Aldrich – 98%
Sigma Aldrich – 98%
Merck, 97%
Cellulose
Benzaldehyde derivatives
Ammonium acetate
Benzyl
Sodium hydroxide
Urea
Sigma Aldrich – 98%
Sigma Aldrich – 97%
Ethanol
14

Sulfuric acid
Merck, 99%
Melting point
Electrothermal 9100, Made in UK
Shimadzu IR-470 spectrometer
Numerix DXP–X10P
FT-IR analysis
EDX analysis
SEM analysis
XRD analysis
Ultrasound cleaning bath
VSM analysis
TGA analysis
Sigma-Zeiss microscope
JEOL JDX–8030 (30 kV, 20 mA)
KQ-250 DE (40 kHz, 250 W)
Lakeshore 7407
STA504 device
3.2. Preparation of the cellulose@pumice organic–inorganic hybrid catalyst
First, a solution was prepared containing NaOH, urea, and deionized water with weight ratios of 7, 12,
and 81, respectively, before adding 4.0 g of microcrystalline cellulose. The reaction mixture was then
stirred in an ice bath at –8°C until the cellulose dissolved completely and a gel solution was obtained.
Next, 1.0 g of pumice powder was added and stirred at ambient temperature for 24 h. The resulting
product was then washed several times with deionized water and finally dried.
3.3. General procedure for synthesizing imidazole derivatives 4a–n in the presence of the nanostructure
catalyst
First, 1.0 mmol of aromaromatic aldehyde derivatives, 1.0 mmol of benzyl, 2.0 mmol of ammonium
acetate, and 0.03 g of the catalyst were dispersed in ethanol as a polar solvent by ultrasonication. The
progress of the reaction was monitored by TLC. After completing the reaction, the cellulose@pumice
catalyst was separated using a magnet and the precipitate was washed several times with ethanol and hot
water, before drying in an oven. The anti-solvent method and flash-column chromatography were used to
purify the products. After purification of the products, the reaction yields were calculated by determining
the pure weights of the products and the molar percentages of the reactants.
3.4. Spectral data for selected products
15

1
2,4,5-Triphenylimidazole (4a): Infrared (
IR) (KBr tablet) cm–1: 3432, 1660, 1550, 1486, 1462. H-nuclear
magnetic resonance (NMR), in dimethyl sulfoxide (DMSO-d6) d: 12.55 (1H, br s), 7.50–7.90 (15H, m).
13C NMR (DMSO-d6) d: 125.1, 126.4, 127.0, 127.7, 128.1, 128.2, 128.3, 128.4, 130.3, 131.0, 135.1,
137.1, 145.3.
1
2,4-Dichlorophenyl-4,5-diphenylimidazole (4b): IR (KBr) cm–1: 3405, 3060, 1603, 1485, 1448, 1433. H
NMR (DMSO-d6) d: 12.79 (1H, br s), 7.21–7.56 (12H, m), 8.11 (2H, d, J 8.8 Hz). 13C NMR (DMSO-d6)
¼
d: 126.5, 126.2, 127.0, 128.1, 128.3, 128.5, 128.4, 128.7, 129.1, 129.1, 130.81, 130.8, 132.5, 134.9, 137.2,
144.3.
1
2-(4-Methylphenyl)-4,5-diphenylimidazole (4l): IR (KBr) cm–1: 3405, 3033, 1602, 1493, 1449. H NMR
(DMSO-d6) d: 12.60 (1H, br s), 7.98 (2H, d, J¼8.4 Hz), 7.20–7.56 (12H, m), 2.23 (3H, s). 13C NMR
(DMSO-d6) d: 20.8, 125.3, 126.4, 127.0, 127.6, 127.6, 127.6, 128.3, 128.3, 128.6, 129.2, 131.1, 135.2,
136.8, 137.6, 145.5.
4. Conclusions
In this study, we prepared a natural product-based cellulose/pumice magnetic organic-inorganic hybrid
catalyst as an efficient catalytic system for the synthesis of 2,4,5-triarylimidazole derivatives. This
efficient catalytic system was characterized by FT-IR spectroscopy, SEM, EDX spectroscopy, XRD
spectroscopy, TGA, and VSM. The nanoscale catalyst system has several advantages such as convenient
separation, amenable synthesis reactions (97% yield after 20 min at room temperature), and the use of low
amounts of the heterogeneous catalyst (0.03 g). A large active surface area was provided due to the high
porosity of the pumice according to SEM. VSM analysis demonstrated the super-paramagnetic behavior
of the nanoscale catalytic system, thereby allowing the simple separation of the organic–inorganic hybrid
catalyst and its recovery from further reactions with no losses. The organic–inorganic hybrid catalyst was
readily recovered in an external magnetic field and reused efficiently without any significant decrease in
16

its catalytic activity. Moreover, synthesis reactions were catalyzed via the synergistic effect of ultrasound
waves and the cellulose/pumice organic–inorganic hybrid catalyst.
Acknowledgments
The authors gratefully acknowledge partial support from the Research Council of the Iran University of
Science and Technology (IUST).
Conflict of Interest
The authors declare no conflict of interest.
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Highlights
‹
‹
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Efficient natural product-derived catalytic system presented.
Cellulose/pumice composite suitable for use as a catalyst in organic synthesis.
Natural magnetic powder immobilized on cellulose fibers.
High reaction yields obtained for triarylimidazole derivatives.

Competing interest statement
The authors whose names are listed in this article have no competing interests or other conflict of
interests that might be perceived to influence the results and/or discussion reported in this paper.
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