Heavy metal removing by modified bentonite and study of catalytic activity

Article abstract of DOI:10.1016/j.molstruc.2019.126989

Due to the high hydrophobicity and surface area, clays are efficient adsorbents for the removal of liquid impurities and purification of gases when they are modified. In this work, bentonite was modified with imidazole and imidazolium groups and resulting clays were characterized by different techniques such as ¹H NMR, ¹³C NMR, TEM, SEM, XPS, TG, and FT-IR. Applications of these clays were studied in the removal of Co, Cu, and Pb in the wastewater. Effects of contact time, pH, initial heavy metal ions concentration, and kinetic were investigated. The catalytic activity of the metals adsorbed by imidazole modified bentonite was studied in A³ coupling reactions of various amines, aldehydes, and alkynes.

Full text of DOI:10.1016/j.molstruc.2019.126989

Journal Pre-proof
Heavy metal removing by modified bentonite and study of catalytic activity
Saeed Kakaei, Elham Sattarzadeh Khameneh, Fardin Rezazadeh, Majid Haji
Hosseini
PII:
S0022-2860(19)31086-5
DOI:
https://doi.org/10.1016/j.molstruc.2019.126989
MOLSTR 126989
Reference:
To appear in: Journal of Molecular Structure
Received Date: 19 May 2019
Revised Date: 25 August 2019
Accepted Date: 26 August 2019
Please cite this article as: S. Kakaei, E.S. Khameneh, F. Rezazadeh, M.H. Hosseini, Heavy metal
removing by modified bentonite and study of catalytic activity, Journal of Molecular Structure (2019), doi:
https://doi.org/10.1016/j.molstruc.2019.126989.
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Heavy Metal Removing by Modified Bentonite and
Study of Catalytic Activity
Saeed Kakaei a*, Elham Sattarzadeh Khameneh b, Fardin Rezazadeh C, Majid Haji Hosseini b
aRadiation Application Research School, Nuclear Science and Technology Research Institute, P. O.
Box 11365-3486, Tehran, Iran.
bMaterials and Nuclear Fuel Research School, Nuclear Science and Technology Research Institute,
Tehran, Iran
cDepartment of Chemistry, Faculty of Science, Urmia University, Urmia, Iran.
*Corresponding author: Dr. S. Kakaei, Skakaei@aeoi.org.ir
Keywords: Imidazole, Imidazolium, Bentonite, Heavy metal removal, Catalytic activity
Abstract: Due to the high hydrophobicity and surface area, clays are efficient adsorbents for the
removal of liquid impurities and purification of gases when they are modified. In this work, bentonite
was modified with imidazole and imidazolium groups and resulting clays were characterized by
13
different techniques such as 1H NMR, C NMR, TEM, SEM, XPS, TG, and FT-IR. Applications of
these clays were studied in the removal of Co, Cu, and Pb in the wastewater. Effects of contact time,
pH, initial heavy metal ions concentration, and kinetic were investigated. The catalytic activity of the
metals adsorbed by imidazole modified bentonite was studied in A3 coupling reactions of various
amines, aldehydes, and alkynes.
1 INTRODUCTION
1

Numerous toxic heavy metals have and are being discharged to the environment as industrial
wastes, causing serious soil and water pollution. In recent years, various physicochemical and
biological methods were developed for toxic heavy metal removal. Especially, in the past two
decades, increasing attentions have been paid for using clays as sorbents to remove contaminants.
Compared to other sorbents such as activated carbon and zeolite, mineral clays are greener, cheaper
and more naturally available. Clays are widely applied in many fields of technology and science such
as the removal of liquid impurities and purification of gases [1-3]. Such a wide range of usefulness of
clays is due to their high specific surface area, high chemical and mechanical stability, and a variety
of surface and structural properties. The chemical nature and pore structure generally determine the
sorption ability of clay materials. For gas-phase sorption, the pore structure, the nature, and volume
of pores are predominant factors. In the case of liquid-phase sorption, the chemical properties of
surface groups influence the extent of sorption. However, for increasing removal capacity of clay, in
the most of the cases, it is required modifying clay structure with ligands. Along this line, from
standpoint to green chemistry, using nitrogen based ligands instead of toxic and expensive
phosphorus ligands is highly desirable for modification of clays and preparing of sorbents.
Presently, the design of new heterogeneous catalysts comprising cheap, sustainable and eco-
friendly materials is important from sustainable chemistry standpoints [4-6]. Considering the
excellent properties of mineral clays, these soils can be considered as outstanding support for
designing heterogeneous catalysts. Different applications of propargylamines in synthetic organic
chemistry, therapeutic drug molecules, and agriculture chemicals recognize these compounds as
important building blocks in natural products and industry [7-15]. The classic method for preparation
of propargylamines included the addition of lithium acetylides or Grignard reagents to imine
derivatives under stoichiometric condition [16-18]. In recent years A3 coupling reaction which is a
2

one-pot reaction of amines, aldehydes and alkynes via metal C-H bond activations of terminal
alkynes was developed as an efficient and atom-economic method for preparation of
propargylamines [19-23]. This reaction can be catalyzed by different transition-metals [24-39],
however from economic stand point using cheap and naturally available transition metals and
catalysts are highly desirable.
To the best of our knowledge, there is no report on the removal of heavy metals from water and
subsequently, use of removed metal as a catalyst in the A3 coupling reaction. In this work, we studied
bentonite as naturally abundant clay as well as imidazole and imidazolium groups functionalized
bentonite as cheap, simple and stable materials in the resulted in removal of metals from water and
used for the first time resulted in materials as a catalyst in the preparation of propargylamines via A3
coupling reaction.
2 Experimental Section
2.1 Materials and methods
All materials were pure and purchased from Sigma-Aldrich, Across and Merck Millipore. Sodium
type bentonite was purchased from Daneshmand chemical trading co (Iran). Reactions were
1
monitored by gas chromatography in a Varian CP-3800 apparatus. H NMR and 13C NMR spectra
were recorded at 400 MHz and 100 MHz, respectively on a Bruker Avance HD apparatus in CDCl3.
Chemical shifts are given on the δ-scale in ppm, and residual solvent peaks were used as internal
standards. The TEM and SEM mapping images were captured by EOL JEM-2010 and Hitachi
S3000N. XPS analyses were performed using a K-alpha spectrometer. The weight loss of samples
was measured using a thermo gravimeter NETZSCH STA 409 under an O2 flow rate of 20 ml/min
with a heating rate of 10 °C·min-1 from 30 to 800 °C. Digital images of the samples were acquired
with Hitachi S4160 FE-SEM apparatus operating at 20 kV. FT-IR studies of samples were performed
3

using a FT-IR spectrophotometer Bruker vector 22 where the prepared KBr pellets ranged from 400
to 4000 cm-1.
2.2 Synthesis of imidazolium ionic liquid (IL).
Benzyl bromide (0.12 mL, 1 mmol) and vinyl imidazole (0.18 mL, 2 mmol) were dissolved in dry
o
THF (10 mL) and the mixture was stirred under an argon atmosphere at 40 C for 24 h. Then the
resulting mixture was centrifuged to remove the solvent. The residue was washed with THF (3 × 10
1
mL) and hexane (3 × 10 mL) and the resulting solid dried under vacuum. H NMR (DMSO, 400
MHz): δ 10 (s, 1H), 8.38 (s, 1H), 8.09 (s, 1H), 7.55 (d, 2H. J=4), 7.37-7.41 (m, 5H), 6.05-6.09 (m,
1H), 5.59 (s, br, 2H), 5.42 (s, br, 1H), 3.53 (s, br, 2H). 13C NMR (DMSO, 100 MHz):δ 136.20,
135.21, 129.43, 129.28, 129.11, 123.73, 120.10, 109.27, 52.32, 40.43 (Figures S1 and S2).
2.3 Preparation of Ben@S:
Bentonite (1 g) was sonicated in dried toluene (30 mL) followed by dropwise addition of (3-
mercaptopropyl)triethoxysilane (12 mmol, 2.3 mL). The reaction mixture was refluxed for 24 h under
argon gas atmosphere. Then, the reaction mixture was subjected to centrifugation and the obtained
solid was washed with ethanol (3×10 mL) rinse and dried under vacuum at 60 °C.
2.4 Preparation of Ben@S-Im:
A mixture of 10 min. sonicated Ben@S (0.5 g) in dry ethanol (15 mL), vinyl imidazole (2.5
mmol, 0.23 mL) and AIBN (0.7mmol, 115mg) as an initiator was added to the reaction system.
The reaction mixture was refluxed for 24 h under argon atmosphere. Then the solid was separated
with centrifugation and the resulting vinyl imidazole functionalized bentonite was washed with
ethanol (3×10 mL) and dried under vacuum at 60 °C.
4

2.5 Preparation of Ben@S-Im-IL
In a 25 mL flask, Ben@S (0.5 g) was sonicated in dry ethanol (15 mL) for 10 min. Then,
imidazolium IL (3 mmol) and AIBN (0.7 mmol, 115mg) were added and stirring reaction mixture
was refluxed under argon atmosphere for 24 hrs. After subsequently the reaction mixture was
subjected to centrifugation and the obtained isolated solids were washed with ethanol (2×15 mL)
and then dried in an oven at 70 °C.
2.6 Adsorption experiments
For the adsorption experiment, initially, adsorbents (5 mg) were treated with separately prepared
Cu(OAc)2, Pb(OAc)2, and Co(OAc)2. (20 mg/L). For reaching the equilibrium adsorption capacity
(qe), the adsorbents were added to the heavy metal ion solutions (15 mL) and stirred for 4 h at
room temperature. The equilibrium was achieved after 2 h. After collecting adsorbents by
centrifugation, the initial heavy metal ion concentration effects on the qe values were also
investigated. In this regard, a series of samples containing 5 mg of the support, dissolved in 15 mL
of metal solutions, were used. The adsorptions capacities were measured for five different
concentrations (10, 20, 40, 60 and 100 mM). The water solutions of metal ions were buffered to
pH 5 (acetic acid/ sodium acetate buffer). The solutions were stirred for 2 h at room temperature.
The starting (C0; mmol/L) and post-equilibration (Ceq; mmol/L) concentrations of metal ions were
measured by atomic absorption spectrophotometry. The amount of metal adsorbed (qe; mmol/g)
after equilibration was calculated from the difference between C0 and Ceq:
ꢇ
ꢈ
ꢆ
ꢀꢁ = ꢂ
(1)
ꢃ ꢅ ꢃ
ꢄ
ꢉ
Where m is the mass of support (0.005 g) and V is the volume of aqueous solution (L). For the
adsorption kinetic studies, 5 mg of the support was dissolved in 15 mL of buffered (pH=5) metal
5

solution with the initial concentration of 20 mM and were stirred at room temperature. The
aqueous samples were taken at preset time intervals and the concentrations of metal ions were
measured by atomic absorption spectrophotometry. The amount of adsorption at time t, qt
(mmol/g), was calculated from:
ꢇ
ꢈ
ꢋ
ꢀꢊ = ꢂ
(2)
ꢃ ꢅ ꢃ
ꢄ
ꢉ
Where m is the mass of support (0.005 g), C0 (mmol/L) is the initial metal ion concentration, Ct
(mmol/L) is the metal ion concentration at time t, V is the volume of aqueous solution (L). The
relations between the sorption properties of the support and the pH of the solution were studied in
the pH range from 2 to 7. The pH of the solutions was adjusted with the buffers containing
KCl/HCl (pH=2), acetic acid/sodium acetate (pH=3–6) and HEPES (4-(2-hydroxyethyl)-1-
piperazineethanesulfonic acid) buffer (pH=7). The measurements were made for 20 mM metal
concentration. The starting and final concentrations of metal ions in aqueous phases were
measured by atomic absorption spectrophotometry. Experiments with real wastewater samples
were performed by adding 2 mL of wastewater sample to a solution of adsorbents (20 mg) in
deionized water (20 mL). The solutions were stirred for 2 h. The starting and final concentrations
of metal ions in aqueous phases were measured by atomic absorption spectrophotometry.
2.7 General procedure for the synthesis of propargylamines:
To a 5 mL flask containing heavy metal treated clay (containing 2 mol% of metal), aldehyde (1
mmol), phenylacetylene (1.5 mmol), amine (1.5 mmol) and H2O/THF (10:1, 2 mL) were added and
o
the mixture was stirred at 40 C for 24h under argon atmosphere. Progress of reactions was
1
monitored by TLC or H NMR. After completion of the reaction, the crude products were extracted
using ethyl acetate (3×5 mL). Further purification was performed by column chromatography on
6

silica gel using hexane and ethyl acetate as eluents. All products were known and characterized by 1H
NMR and 13C NMR.
3
RESULTS AND DISCUSSIONS
3.1
Synthesis of supports and their characterization
For modification of bentonite, initially, the raw bentonite 1 was treated with (3-mercaptopropyl)
triethoxysilane to afford mercapto functionalized bentonite (Scheme 1) 2 (Ben@S). Then, 2 was
allowed to react with vinyl imidazole in dry ethanol under argon atmosphere and reflux conditions to
achieve imidazole modified bentonite 3 (Ben@S-Im). Also, the composition of ionic liquid modified
bentonite 4 (Ben@S-Im-IL) was obtained from the reaction of Ben@S with imidazolium ionic liquid
in ethanol solvent and reflux conditions. At the final step, these compounds were used as adsorbents
for the removal of heavy metal ions and after adsorption, these compounds were used as a catalyst for
the preparation of propargylamines.
Scheme 1. Preparation of supports
7

The structure of the prepared materials was studied by FT-IR spectroscopy (Figure 1). Generally, a
decrease of OH peak intensity at 3400-3600 cm−1 in (3) and (4), indicates successful modification
with imidazole and imidazolium groups. Also, results showed typical imidazole chain, (C–H/N–C–
H) peak at 2925 cm−1, ring vibration peak at 1098-1220 cm−1[24, 25] as well as peaks located at 835
and 1635 cm-1, related to the C-H of rings and bending vibration of the adsorbed water on the
surface, a weak peak at 3162 cm−1 could be related to C−H stretching vibrations of imidazole moiety
[25, 26]. A new peak in 1525 cm−1, could be due to the aromatic C=C or C=N stretching vibration
and bending vibration modes [27]. confirming the attachment of imidazole and imidazolium groups.
Fig. 1. FT-IR spectra of Bentonite, Ben@S-Im and Ben@S-Im-IL
Thermogravimetric analyses (TGA) of Ben@S, Ben@S-Im and Ben@S-Im-IL were studied
between 25 and 800 °C. Two small loss of weights in the Ben@S material between 25-150 °C and
120-800 °C, were related to the loss of physically adsorbed water and hydroxyl groups of Ben@S,
8

respectively. TGA measurements for Ben@S-Im showed increasing of main weight loss between
150-800 °C due to the addition of the imidazole group. Furthermore, the increase of weight loss in
Ben@S-Im-IL confirmed the successful attachment of higher weight imidazolium ionic liquid to the
Ben@S (Figure 2).
Fig. 2. TGA diagrams of Bentonite, Ben@S-Im and Ben@S-Im-IL.
3.2 Adsorption rate
3.2.1 Effect of contact time on Metal ions sorption
In order to study the equilibrium adsorption capacity, the adsorption capacities were determined at
different times (Figure 3). The results showed that the adsorption capacities of the adsorbents were
changed with time. As it can be seen, in the initial 30 minutes of the treatment, the sharp increases in
the adsorption capacity were obtained which may relate to the high complexion and geometric
attraction between functional imidazole groups and heavy metal ions. From 30 min to 120 min the
adsorption capacities did not have any significant changes. It can be concluded that the adsorption
9

capacities obtained in the 30 min are equilibrium adsorption capacities (qe). There are some
parameters which determine the adsorption rate, such as stirring (or flow) rate in the aqueous phase,
adsorbent structure (e.g. size, porosity, surface area), amount of adsorbent, metal ion properties (e.g.
hydrated ionic radius), concentration of metal ions, pH, temperature, chelate-formation rate, and of
course, the presence of other metal ions which may compete with the ions of interest for active
adsorption sites.
Fig. 3. Adsorption capacity of Co(II), Pb(II) and Cu(II) by Bentonite, Ben@S-Im and Ben@S-Im.
3.2.2 Effect of pH
The effect of pH on the equilibrium adsorption capacities was also examined. The results indicated
that for the pH value of 5, the highest qe were achieved (Figure 4). Using pH higher than 5, the qe
values decreased which may be related to the precipitation of heavy metal ions with OH- anions. For
the pH values 2-4, the qe was also decreased which may be related to the protonation of sulfur and
imidazole/imidazolium’s nitrogens. In the case using bentonite as an adsorbent, this decrement is
10

much lower than using imidazole or imidazolium as adsorbents. This may be related to the absence of
sulfur and nitrogen in the raw bentonite.
Fig. 4. Effect of pH on equilibrium adsorption capacity of a) Bentonite, b) Ben@S-Im and c)
Ben@S-Im-IL for adsorption of Cu(II), Co(II) and Pb(II).
3.2.3 Metal ions concentration effect
The effect of initial heavy metal ions concentration on the adsorption capacity was also studied. In
this regard, the two adsorption isotherms model, Langmuir, and Freundlich were calculated by
equations (3) and (4).
ꢃ
ꢍ
ꢃ
ꢆ
ꢆ
=
ꢒ ꢌ
(3)
ꢌ
ꢆ
ꢎꢍꢌ
ꢏꢐꢑ
ꢏꢐꢑ
11

log qe= log ꢓꢔ ꢒ ꢕꢍ log ꢖ
(4)
ꢁ
Where, Ce (mg/L), qe (mg/g), K1, qmax (mg/g), Kf and n are equilibrium concentration, equilibrium
adsorption capacity, Langmuir constant related to binding sites affinity, the maximum adsorption
capacity, Freundlich constants related to adsorption capacity and adsorption intensity, respectively.
The Langmuir and Freundlich isotherm models for three adsorbents were fitted in Figure 5.
Fig. 5. Langmuir (a) and Freundlich (b) isotherm models of Bentonite, Ben@S-Im and Ben@S-Im-
IL for adsorption of Cu(II), Co(II) and Pb(II).
12

The Langmuir and Freundlich parameters were also collected in Table 1.
Table 1. Isotherm parameters of Langmuir and Freundlich models of Bentonite, Ben@S-Im and
Ben@S-Im-IL for adsorption of Cu(II), Co(II) and Pb(II).
Langmuir isotherm
Freundlich isotherm
Support
Metal ion
qmax(mg/g)
Kl
R2
Kf
n
R2
Co(II)
Cu(II)
Pb(II)
Co(II)
Cu(II)
Pb(II)
Co(II)
Cu(II)
Pb(II)
39.4
52.36
61.73
81.96
87.71
133.33
66.2
0.0675
0.0695
0.0684
0.127
0.0696
0.1226
0.1488
0.9990
0.9992
0.9975
0.9969 13.3291
0.9994 12.1088
6.4640
7.941
6.188
2.58
2.43
2.39
2.35
2.26
2.64
4.32
2.37
3.19
0.9718
0.9563
0.9620
0.9173
0.9655
0.9723
0.9749
0.9632
0.9510
Bentonite
Ben@S-Im
0.9993
0.9981 22.7248
27.252
Ben@S-Im-
IL
69.93
106.38
0.07299 0.9990 10.4858
0.1688 0.9979 28.63
In table 1, the qmax values for Bentonite, Ben@S-Im, and Ben@S-Im-IL for adsorbing heavy metal
ions such as Co(II), Cu(II) and Pb(II) ranged from 39.4 to 133.33 mg/g. The qmax values for Ben@S-
Im were much higher than Bentonite and Ben@S-Im-IL which may be related to better interaction of
sulfur and imidazole’s nitrogens with heavy metal ions [28]. Also, the Langmuir constant (Kl) for
three adsorbents ranged from 0.0675 to 0.1688. The Kl values for Bentonite, Ben@S-Im and Ben@S-
Im-IL all have positive values which made the adsorption process favorable. Also, the correlation
coefficients (R2) values for the Langmuir model ranged from 0.9969 to 0.9994 which are all close to
1. Study of the Freundlich parameters showed that the adsorption intensities (n) ranged from 2.26 to
4.32, and for values higher than 1 (1/n closer to 0) the adsorption process is more likely to be
heterogeneous. [29] Moreover, the Freundlich constants (Kf) ranged from 6.188 to 28.63. The Kf
values showed the interaction between metal ions and adsorbents, and the greater more this value, the
better adsorption will proceed. In this regard, the Kf values for Ben@S-Im and Ben@S-Im-IL are
greater than the Kf values of Bentonite which may be related to the effect of ligand addition on the
13

bentonite structures. The correlation coefficients (R2) for the three adsorbents on the Freundlich
equation ranged from 0.9173 to 0.9749 which are all lower values than the Langmuir model. It can be
concluded that the adsorption isotherm is very well modeled by the Langmuir model. The adsorption
capacity of adsorbents for Pb(II) was more than that for Cu(II) and Co(II). It could be attributed to
large atomic weight, ionic radius and electronegativity of Pb(II)[29].
3.3 Kinetic study
The effect of the time on the adsorption capacity was also examined by pseudo-first-order and
pseudo-second-order equations (equation 5 and 6).
lnꢂ ꢀꢁ − ꢀꢊꢇ = ln ꢀꢁ − ꢓꢍꢗ
(5)
(6)
ꢊ
ꢍ
ꢊ
=
ꢙ ꢒ ꢌ
ꢌ
ꢋ
ꢘ ꢌ
ꢙ
ꢆ
ꢆ
Where, k1 (1/min) and k2 (g/(mg
.
min)) are the pseudo-first-order and pseudo-second-order kinetic
rate constant, respectively. Using equation 5 and 6, the kinetic diagrams were fitted (Figure 6) and
the parameters were collected in Table 2.
14

Fig. 6. Pseudo-first-order (a) and Pseudo-second-order (b) kinetic models of Bentonite, Ben@S-Im
and Ben@S-Im-IL for adsorption of Cu(II), Co(II) and Pb(II).
Table 2. Kinetic parameters of Bentonite, Ben@S-Im and Ben@S-Im-IL for adsorption of Cu(II),
Co(II) and Pb(II).
Pseudo-first-order model
Pseudo-second-order model
K2
(mg/(g min))
0.9973
0.9898
Support
Metal ion
qe
K1
qe
R2
R2
(mg/g)
20.8130
32.8502
49.282
(1/min)
0.0919
0.0801
0.0802
(mg/g)
21.008
31.348
46.62
.
Co(II)
Cu(II)
Pb(II)
0.9999
0.9990
0.9981
0.0075
0.0039
Bentonite
0.00175 0.9833
15

Co(II)
Cu(II)
Pb(II)
Co(II)
Cu(II)
Pb(II)
80.7008
97.23
100.26
83.8305
95.06
0.0651
0.0916
0.0995
0.0865
0.0834
0.1157
0.9887
0.9714
0.9876
0.9869
0.9785
0.9888
93.46
99.01
0.00128 0.9979
0.00153 0.9974
Ben@S-Im
123.46 0.00184 0.9990
81.32
86.96
98.04
0.00142 0.9961
0.00126 0.9955
0.00231 0.9987
Ben@S-Im-
IL
95.98
The equilibrium adsorption capacity (qe) values for Ben@S-Im are higher than the other two
adsorbents, ranging from 80.70, 97.23 and 100.26 for Co(II), Cu(II) and Pb(II), respectively. This
may be related to the better interaction of sulfur and imidazole’s nitrogen with heavy metal ions.
These values were decreased when using Ben@S-Im-IL as adsorbent. This can be relevant to the
congestion of proton ion (H+) on the imidazolium structure and also the existence of the positive
charge on the structure which may make some repulsion between metal ions and positive charge of
imidazolium [30]. The pseudo-first-order constant (K1) for adsorbing of Co(II), Cu(II) and Pb(II) by
Bentonite, Ben@S-Im and Ben@S-Im-IL ranged from 0.0651 to 0.1157. The k1 value for Ben@S-Im
is higher than the other two adsorbents. Investigation of R2 values for the pseudo-first-order equation
showed that the R2 values for Bentonite as adsorbent ranged from 0.9981 to 0.9999 which are all
close to 1. On the other two adsorbents, these values ranged from 0.9714 to 0.9888. The study of the
correlation coefficients revealed that the mechanism of the adsorption for using bentonite as an
adsorbent is more likely to be physical than chemical adsorption. The study of the pseudo-second-
order model showed that the qe values for Ben@S-Im and Ben@S-Im-IL as adsorbents are higher
than Bentonite. This may be related to the addition of organic groups to the bentonite structure [31].
The study of the pseudo-second-order constant (K2) indicated that all values are in the same range
(0.00128 to 0.0075). Also, the R2 values for Ben@S-Im and Ben@S-Im-IL are much closer to 1 than
Bentonite. These results showed that the mechanism for adsorbing of heavy metal ions by Ben@S-Im
and Ben@S-Im-IL is much like pseudo-second-order and in this regard, the adsorption process is
more likely to be chemical adsorption than physical [32].
16

3.4 Adsorption of heavy metals in the wastewater
The application of the Ben@S-Im was studied in the adsorption of Co(II), Cu(II) and Pb(II) in the
wastewater. The results are collected in table 3. Using 20 mg of Ben@S-Im as adsorbent, removal
efficacy of 84%, 87% and 90% were gained for Co(II), Cu(II) and Pb(II), respectively. An increment
of adsorbent weight to 60, 120 and 200 lead to higher removal efficacy for adsorbing of heavy metal
ions. The removal efficacy of almost 100% was achieved for using 200 mg of Ben@S-Im. The
results indicated that the Ben@S-Im has good potential for using in the industrial wastewater.
Table 3. Amount of adsorbent (Ben@S-Im), equilibrium concentration of heavy metal ions and
removal efficiencies of Ben@S-Im adsorbing Co(II), Cu(II) and Pb(II).
Co(II)
Cec
(mg/L) (mg/L)
Cu(II)
Ce
(mg/L)
3.9
2.4
1.2
Pb(II)
Ce
(mg/L)
3.0
2.1
0.9
a
b
AA
C0
Red
(%)
84
89
93
C0
(mg/L)
30
Re
(%)
87
92
96
C0
(mg/L)
30
Re
(%)
90
93
97
(mg)
20
60
120
200
30
30
30
30
4.8
3.3
2.1
0.6
30
30
30
30
30
30
98
0.3
99
0.0
100
a Amount of Adsorbent (Ben@S-Im)
b Initial ion concentration of heavy metal ion solution
c Concentration of heavy metal ion after equilibrium
d The removal efficacy was calculated by the following equation: Re = (C0 – Ce)/C0
3.5 Catalytic performance
For widespread the adsorbents applications, the catalytic activity of the Bentonite, Ben@S-Im and
Ben@S-Im-IL were also studied. For this purpose and initially, the reaction of benzaldehyde with
piperidine and phenylacetylene was selected as a model reaction and the effect of different factors
such as different metals, catalyst loading, solvent effect, reaction temperature and time of reaction
were studied. Using 1 mol% of catalyst (Pb, Co, Cu) in three different supports at room temperature,
17

very low yields were obtained in 24 h (Table 4a, 4b, 4c, and entries 1-3). With increasing the catalyst
to 2 mol%, yields were improved (Table 4a, 4b, 4c, entries 4-6). Also, with increasing the
temperature to 40 °C and using H2O/THF as a solvent, yields of reactions were significantly
increased and the best results were obtained using Ben@S-Im supported metals, especially Ben@S-
Im@Cu. (Table 4a, 4b, 4c, entries 7-9). It should be noted that by reducing the reaction time to 12h,
the yield of reaction were noticeably decreased (Tables 4a-c, entries 10-12). Also, performing the
reaction in the absence of bentonite@metal (Table 4a-c, entry 13) or using metal salts without
bentonite gave lower yields (Table 4a, entries 14-16).
Table 4a. Optimization of the reaction conditions for the reaction of benzaldehyde, piperidine and
phenylacetylene catalyzed by Bentonite@metal.
Cat
(mol%)
Temp
(oC)
Time
(h)
Yield
(%)b
Entry
Metal
Pb
Solvent
H2O
1
2
1
1
r.t
r.t
24
24
0
5
Co
H2O
3
4
5
6
Cu
Pb
Co
Cu
H2O
H2O
H2O
H2O
1
2
2
2
r.t
r.t
r.t
r.t
24
24
24
24
10
0
14
20
18

H2O/THF
H2O/THF
H2O/THF
H2O/THF
H2O/THF
H2O/THF
H2O/THF
H2O/THF
H2O/THF
H2O/THF
2
2
7
Pb
Co
40
40
40
40
40
40
40
40
40
40
24
24
24
12
12
12
24
24
24
24
0
45
63
0
8
2
9
Cu
2
10
11
12
13
14
15
16
Pb
2
Co
32
50
0a
2
Cu
---
2
---
Pb(OAc)2
Co(OAc)2
Cu(OAc)2
2b
15b
38b
2
2
a Reaction performed in the absanse of Bentonite@metal
b Reactions performed using metal salts in the absence of bentonite.
Table 4b. Optimization of the reaction conditions for the reaction of benzaldehyde, piperidine and
phenylacetylene catalyzed by Ben@S-Im@metal.
Cat (mol%) Temp (oC)
r.t
Yield (%)b
0
Time (h)
Entry Metal
Pb
Solvent
H2O
24
1
1
19

24
24
24
24
24
24
24
24
12
12
12
24
2
3
Co
Cu
Pb
Co
Cu
Pb
Co
Cu
Pb
Co
Cu
---
H2O
H2O
1
1
r.t
r.t
r.t
r.t
r.t
40
40
40
40
40
40
40
12
18
0
2
4
H2O
2
5
H2O
35
52
0
2
6
H2O
H2O/THF
H2O/THF
H2O/THF
H2O/THF
H2O/THF
H2O/THF
H2O/THF
2
7
2
8
78
92
0
2
9
2
10
11
12
13a
2
70
75
0
2
---
a Reaction performed in the absanse of Bentonite@metal
Table 4c. Optimization of the reaction conditions for the reaction of benzaldehyde, piperidine and
phenylacetylene catalyzed by Ben@S-Im-IL@metal.
Solvent Cat (mol%) Temp (oC)
Yield (%)b
Time (h)
Entry Metal
20

24
24
1
2
Pb
H2O
H2O
1
1
r.t
r.t
0
Co
21
24
24
24
24
24
24
24
12
12
12
12
3
4
Cu
Pb
Co
Cu
Pb
Co
Cu
Pb
Co
Cu
---
H2O
1
2
r.t
r.t
20
0
H2O
2
5
H2O
r.t
40
54
0
2
6
H2O
r.t
2
7
H2O/THF
H2O/THF
H2O/THF
H2O/THF
H2O/THF
H2O/THF
H2O/THF
40
40
40
40
40
40
40
2
8
65
83
0
2
9
2
10
11
12
13d
2
45
61
1d
2
---
a
Reaction conditions: benzaldehyde (0.5 mmol), piperidine (0.75 mmol), phenylacetylene (0.75 mmol) Solvent (2
mL), and catalyst (see, column).
b Yields were determined by 1H NMR
c H2O/THF (10:1)
d Reaction performed in the absanse of Bentonite@metal
Ben@S-Im treated metals were selected as an efficient and cheap catalyst and characterized
structures. The structure of Ben@S-Im after treating with Pb, Co, and Cu was studied using X-ray
photoelectron spectroscopy (XPS) (Figure 7). The XPS spectra in C1s region showed four peaks
centered at 284.5, 285.6, 286.6 and 288.5 eV, which are related to C-C or C=C, C-N or C-O, C=O or
21

C=N forms of carbon, respectively (Figure 7-a) [33]. The XPS spectra in N1s showed two peaks at
399 and 400 eV, which are attributed to the neutral amine and positively charged quaternary nitrogen
species respectively (Figure 7-b)[35]. In Figure 7-c, the two regions are 162.8 and 164.1 eV and are
related to S2p3/2 and S2p1/2, respectively. The XPS spectrum was observed in the 138.3 and 143.1 eV,
for Pb4f7/2 and Pb4f5/2, respectively, which are related to the oxidation state of Pb(II) (Figure 7-
d)[36]. The peaks of (781 and 783.5 eV) and (796.8 and 799.5 eV) are related to Co (2p3/2) and Co
(2p1/2), respectively which is related to Co2+. In addition, Co3+ peaks appeared in the areas of 786.1
and 802.1 eV. Also, two additional peaks in the 788.5 and 804.1 eV regions are related to the Co
Satellites (shake-off and shake-up) and are due to a sudden change in Coulombic potential as the
photo ejected electron passes through the valence band (Figure 7-e)[37].
The XPS spectrum in Cu (2p) region showed eight peaks. The two-peak at 932.9 and 952.9 eV are
related to Cu (2p3/2) and Cu (2p1/2) in CuO, respectively. Also, the peak of 935 eV is related to the
Cu2+ species. Except for the main peaks, three additional signals were observed at 940.5, 943.9, and
954.3 eV which could be attributed to Cu(II) states in CuO and Cu(OAc)2. The results also showed
two small peaks at 961.3 and 963.5 eV, which are related to Cu2O or Cu(0). Because the binding
energy of the Cu(0) and Cu2O are very close and only 0.1 eV, it is very difficult to prove they are
correct species using the binding energy of this region (Figure 7-f)[38].
22

Fig. 7. XPS spectra of Ben@S-Im@Metal at a) C1s, b) N1s, c) S2p, d) Pb4f , e) Co2p , f) Cu2p
regions.
An element mapping images show the spatial distribution of elements in a sample which are a very
useful method for displaying compositional zonation. Resulting SEM-Map and overlay map images
of Ben@S-Im confirmed the presence of C, N, Pb, Co, and Cu, which are uniformly distributed in the
structure [39](Figures 8 and 9).
23

Fig. 8. a) SEM and b-f) Map images of Ben@S-Im [b) C, c) N, d) Pb, e) Co and f) Cu].
24

Fig. 9. Overlay map images of Ben@S-Im@metals with a) Pb, b) Co and c) Cu.
Furthermore, EDX analysis showed the presence of different elements such as Pb, Co, Cu, N, Si,
Al, and C in the structure of Ben@S-Im@metal (Figure 10).
25

Fig. 10. EDS spectrum of the Ben@S-Im with a) Pb, b) Co and c) Cu.
26

Using the above optimized - conditions (Table 4b, entries 8-9), these catalysts were then explored
for A3 coupling reaction of a variety of aldehydes, amines, and alkynes (Table 5). Results indicated
very good yields for various aromatic aldehydes containing electron-deficient and donating groups
(Table 5, entries 2-5). As well as, the reaction of heterocyclic 3-thiophenecarbaldehyde with
piperidine and phenylacetylene with Co and Cu were performed efficiently, giving 62% and 88%
yields, respectively (Table 5, entry 6). Reactions of 1-octyne as aliphatic alkyne with benzaldehyde
and piperidine and also heptanal as an aliphatic aldehyde with phenylacetylene and piperidine
proceeded well (Table 5, entries 7 and 8). Different amines such as piperidine, morpholine,
pyrrolidine and dimethylamine reacted in A3 coupling reaction in the presence of both of the metals,
successfully affording desired products in very good to excellent yields.
Table 5. Reactions of different aldehydes, amines and alkynes in the presence of Ben@S-
Im@Metal.
(1) Co: 78%, Cu: 92%
(3) Co: 55%, Cu: 68%
(2) Co: 58%, Cu: 70%
27

(4) Co: 70%, Cu: 88%
(5) Co: 63%, Cu: 79%
(6) Co: 57%, Cu: 88%
(9) Co: 78%, Cu: 95%
(7) Co: 50%, Cu: 71%
(8) Co: 38%, Cu: 86%
(11) Co: 81%, Cu: 93%
(10) Co: 70%, Cu: 90%
a Reaction conditions: aldehyde (1 mmol), amine (1.5 mmol), alkyne (1.5 mmol), H2O/THF (2 mL), and catalyst (2
mol % Metal). Isolated yields.
4 Recycling of the catalysts
Finally, recycling of the Ben@S-Im@Cu and Ben@S-Im@Co was studied for the A3 coupling
reaction of benzaldehyde, piperidine and phenylacetylene under the optimized reaction
conditions. For this purpose, after completion of the reaction, a mixture of reaction washing with
28

ethyl acetate was reused in another batch. Results indicated that the catalysts were recyclable up
to 3 consecutive runs with a small decrease in activity. However, yields were dropped to 43 and
39 % in run 4 for Ben@S-Im@Cu and Ben@S-Im@Co, respectively (Figure 11).
Fig. 11. Recycling of the catalysts (Ben@S-Im@Cu and Co) for the A3 coupling reaction.
The catalytic activity of Ben@S-Im@metal is compared with some of the reported catalysts in A3
coupling reaction with benzaldehyde, piperidine and phenylacetylene, as a common substrate
(Table 6). Results indicated a relatively good activity of the presented catalyst. It should be noted
that compared to other catalysts, the most advantage of ben@S-Im@metal is its subsequent
application and activity after heavy metal removal as a catalyst.
Table 6. Comparison catalytic activity of Ben@S-Im@metal with other reported catalysts in A3
coupling reaction.
Entry
Catalyst
T ( °C)
T (h)
Cu or Co
Yield
29