A novel CuO NPs/AgZSM-5 zeolite composite adsorbent: Synthesis, identification and its application for the removal of sulfur mustard agent simulant

Article abstract of DOI:10.1016/j.jallcom.2018.03.239

In this investigation, the parent NaZSM-5 zeolite has been successfully fabricated by the hydrothermal route and then to enhance the catalytic performance of this zeolite, silver ions (Ag⁺) and copper oxide nanoparticles (CuO NPs) were loaded in its structure through the ion exchange and impregnation methods to attain the novel CuO NPs/AgZSM-5 zeolite composite adsorbent. The parent and modified samples were comprehensively analyzed and identified by using the FESEM-EDX, TEM, XRD, and FTIR techniques. This is the first time that the CuO NPs/AgZSM-5 (containing 3.4 wt% Ag and 12.6 wt% CuO) has been utilized for the removal (adsorption and degradation) of 2-chloroethyl phenyl sulfide (2-CEPS) as a toxic sulfur mustard agent simulate, and its applicability was proved according to the GC-FID, GC-MS, and FTIR results. Moreover, the consequences of several experimental factors such as contact time, initial concentration, adsorbent dose, and adsorbent type on the removal efficiency of 2-CEPS were also surveyed. The GC-FID analysis data confirmed that the maximum removal yield of 2-CEPS was 100%. Besides, the parameters of contact time (120 min), initial concentration (25 mg/L), and adsorbent dose (0.3 g) were perused and optimized for the subsequent reaction. The reaction kinetic status was also studied employing first order model. The quantities of the half-life (t_1/2) and rate constant (k) were indicated as 26.25 min and 0.0264 min^?1, respectively. The product obtained from the degradation and hydrolysis reaction between the 2-CEPS and CuO NPs/AgZSM-5 was 2-hydroxy ethyl phenyl sulfide (2-HEPS) which is substantially less toxic than original pesticide.

Full text of DOI:10.1016/j.jallcom.2018.03.239

Accepted Manuscript
A novel CuO NPs/AgZSM-5 zeolite composite adsorbent: Synthesis, identification and
its application for the removal of sulfur mustard agent simulate
Meysam Sadeghi, Sina Yekta, Daryoush Mirzaei
PII:
S0925-8388(18)31109-5
10.1016/j.jallcom.2018.03.239
JALCOM 45469
DOI:
Reference:
To appear in: Journal of Alloys and Compounds
Received Date: 11 December 2017
Revised Date: 17 March 2018
Accepted Date: 19 March 2018
Please cite this article as: M. Sadeghi, S. Yekta, D. Mirzaei, A novel CuO NPs/AgZSM-5 zeolite
composite adsorbent: Synthesis, identification and its application for the removal of sulfur mustard agent
simulate, Journal of Alloys and Compounds (2018), doi: 10.1016/j.jallcom.2018.03.239.
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ACCEPTED MANUSCRIPT
Graphical abstract

ACCEPTED MANUSCRIPT
A novel CuO NPs/AgZSM-5 zeolite composite adsorbent: synthesis,
identification and its application for the removal of sulfur mustard agent
simulate
a
b*
a
Meysam Sadeghi , Sina Yekta , Daryoush Mirzaei
a
Department of Chemistry, Lorestan University, Khorramabad, Iran
b
Department of Chemistry, Payame Noor University, P.O. BOX. 4693179573, Ramsar, Iran
*
E-mail: sina.yekta.chem@gmail.com
Tel: +98-09039841109
Fax: +98-01155254021
Orcid ID: https://orcid.org/0000-0001-5249-0855
Abstract
In this investigation, the parent NaZSM-5 zeolite has been successfully fabricated by the
+
hydrothermal route and then to enhance the catalytic performance of this zeolite, silver ions (Ag ) and
copper oxide nanoparticles (CuO NPs) were loaded in its structure through the ion exchange and
impregnation methods to attain the novel CuO NPs/AgZSM-5 zeolite composite adsorbent. The
parent and modified samples were comprehensively analyzed and identified by using the FESEM-
EDX, TEM, XRD, and FTIR techniques. This is the first time that the CuO NPs/AgZSM-5
(
containing 3.4 wt.% Ag and 12.6 wt.% CuO) has been utilized for the removal (adsorption and
degradation) of 2-chloroethyl phenyl sulfide (2-CEPS) as a toxic sulfur mustard agent simulate, and
its applicability was proved according to the GC-FID, GC-MS, and FTIR results. Moreover, the
consequences of several experimental factors such as contact time, initial concentration, adsorbent
dose, and adsorbent type on the removal efficiency of 2-CEPS were also surveyed. The GC-FID
analysis data confirmed that the maximum removal yield of 2-CEPS was 100%. Besides, the
parameters of contact time (120 min), initial concentration (25 mg/L), and adsorbent dose (0.3 g) were
perused and optimized for the subsequent reaction. The reaction kinetic status was also studied
employing first order model. The quantities of the half-life (t ) and rate constant (k) were indicated
1
/2
-1
as 26.25 min and 0.0264 min , respectively. The product obtained from the degradation and
hydrolysis reaction between the 2-CEPS and CuO NPs/AgZSM-5 was 2-hydroxy ethyl phenyl sulfide
(
2-HEPS) which is substantially less toxic than original pesticide.
Keywords: CuO NPs/AgZSM-5, 2-CEPS, removal, adsorption, degradation.
. Introduction
1
The major perspective of science and scientific advances should be providing solutions for numerous
complex problems with which human beings have been struggling for long time now. But,
1

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unfortunately one of the most hideous facts of these scientific developments is to turning them to the
opposite side and against humanity and moral values which is due to embracing more domination and
power on other parties. Another serious concern which has been obsessing minds toward itself is what
happens if these opposite scientific advances become available for terrorist groups or organizations
around the world. In this matter, the Chemical Warfare Agents (CWA) can be named as one of the
malicious outcomes of those mentioned shameful and dark corners of scientific developments. These
agents were fabricated and designed to negatively impact the crowd by any route of exposure and to
be effective even at slight doses. The CWAs are intended to be used in military aspects for mass
killing purposes, or incapacitate people owing to their highly disastrous physiological effects [1, 2].
Also, their release impacts the environment and contaminates the ground waters. Thus, it is of great
significance to find applicable approaches for their destruction and disposal. The sulfur mustard is
recognized as one of the main sorts of these chemical weapons. Sulfur mustard, bis-(2-chloroethyl)
sulfide, also known as HD, S-mustard, HS, etc smells as garlic or mustard. But on the other hand, its
disabling vapor concentration is likely to have trivial odor that one will not be able to sense until the
first aftereffect appears. Further, it is tasteless and colorless, which makes it extremely dangerous
since its detection become considerably impossible by the senses. Besides, HD has been known as a
human carcinogen which obligates harmful consequences to the body by interfering chemical
reactions with cellular constituents. The nicotinamide adenine dinucleotide (NAD) depletion,
prevention of mitosis, reduced tissue respiration and eventually death are the results of such implied
biochemical reactions [3-5]. It is also notable that World War I, Syria, and Iran-Iraq war are some
irrefutable examples when the HD agent released for calamitous massacre. The 2-chloroethyl phenyl
sulfide (2-CEPS) is a known simulate of sulfur mustard which has been frequently used in numerous
researches as the less toxic sort of this chemical agent [6]. Considering a high yield adsorption-
degradation, it is essential to synthesis an applicable adsorbent. ZSM-5 (MFI-type zeolite), first
introduced by Argauer and Landolt in 1972 [7], is a zeolite comprising three-dimensional channels
designated by 10-membered rings with average pore size of 6Å. ZSM-5 offers particular properties
such as unexampled channel structure, shape selectivity, thermal stability, acidity which make them
superior to be utilized as catalyst and sorbent in several fields like fine chemical production, liquid
and gas separation, and petrochemical processing [8,9]. Recently growing attention has been devoted
to synthesis procedure, characteristics and numerous applications of ZSM-5 zeolites. Meanwhile,
different templates have been defined for the synthesis process of ZSM-5 zeolites, namely
tetrapropylamine bromide. In this regard, the substance used as template, the quality of the reagents,
and the gel composition, are some of major parameters that may affect the physicochemical
characteristics of ZSM-5 zeolites. Thereupon, it is of great significance to consider and use an
appropriate template for the synthesis of ZSM-5 [10-12]. In fact, MFI-type zeolite with those above
mentioned 10-membered oxygen rings and equal pore structure is effectively able to display a host
behavior and entrap the guest molecules into the micropores. On the other hand, considering the
2

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unprecedented features of the combination of microporous solid materials with nanoparticles
including high surface area along with the open framework and also the well-designated pore size, the
microporous solid materials loaded with nanoparticles have recently attracted significant attention.
The semiconductor nanoparticles are good example of this implied combination. In this matter, to
functionalize both surface area and microporous internal surface of the microporous materials and
their subsequent use as host materials, an appropriate modification process should be implemented
[
13,14]. Furthermore, in recent years, the perception of wide potential and applicability of metal oxide
nanoparticles has opened a new window toward synthesis and use of these nanomaterials for
multipurpose use in different scientific fields. The characteristics of nanomaterials are highly related
to the morphology, size and particular surface area of the synthesized nanomaterials [15]. Due to
having specific physical and chemical properties differing from bulk, they have been greatly
employed in several fields for instance optoelectronics, sensing, solar cells and catalysis. TiO [16,
2
1
7], CaO [18], Y O nanoparticles [19], MgO [5,20], ZnO [21], and Fe O [22] etc are some examples
2 3 3 4
of transition metal oxides which have been utilized in numerous scientific researches. Copper (II)
oxide (CuO) or known as cupric oxide is also one of the most applying metal oxides which have been
used for many applications in various fields. Besides, it represents a superior monoclinic tenorite
structure and also shows p-type semiconductor behavior with an indirect band gap of 1.21-1.51 eV
[
23, 24]. The semiconductor materials have been the center of attentions regarding to their substantial
role in electronic and optoelectronic devices. They have been considerably used in gas sensors [25],
magnetic storage systems [26], electro chemical cell [27], field emitters [28], nano fluid [29], super
conductors [30], and catalysts [31] etc. Moreover, CuO has been extensively employed as an
environmental catalyst for the degradation of environmental pollutants [32, 33]. To synthesis the CuO
nanoparticles, several methods can be considered including sol-gel [34], precipitation [35], thermal
+
decomposition [36], and alcothermal method [37]. Apart from what explained about CuO, Ag was
also applied because of its unique catalytic characteristics [38, 39]. From this combination basis, in
our previous studies, two different composite adsorbents of Pb-MCM-41/ZnNiO [40] and NiO
2
NPs/Ag-clinoptilolite [41] were synthesized and introduced for the first time for the adsorption and
degradation of CWAs. In the current study, to develop a much superior adsorbent for such lethal
chemical warfare with lesser time of reaction and applicability for higher concentrations of 2-CEPS
compared with those previously mentioned ones, the CuO NPs/AgZSM-5 as a novel zeolite
composite adsorbent synthesized via the impregnation method is represented and punctually
discussed.
2
. Experimental
The chemical reagents were all of analytical grade and utilized as received with no extra purification
process. Sodium hydroxide pellets (NaOH), sodium aluminate (NaAlO ), silicic acid (H SiO ), 2-
2
2
3
chloroethyl phenyl sulfide (2-CEPS), n-octane, n-decane, copper nitrate trihydrate (Cu(NO ) .3H O),
3
2
2
3

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silver nitrate (AgNO ), and hydrochloric acid (HCl) were all purchased from Sigma-Aldrich chemical
3
company. Further, the deionized water (D.W) was employed throughout the research.
2
.1. Instrumentation
The functional groups, morphology, crystalline structure, elemental composition, and structure
features are known as some physicochemical characteristics of the understudy samples which have
been investigated via several analytical techniques. To observe the morphology and elemental
composition analysis of the samples, a Field emission scanning electron microscopy‐energy dispersive
X‐ray spectroscopy (FESEM‐EDX) on a MIRA3 TESCAN was operated. The shape and size of the
samples were indicated by transmission electron microscopy (TEM) on an EM10C microscope
functioning at an advancing voltage of 100 Kv. Moreover, using a Philips X’pert Pro diffractometer
equipped with CoKα radiation at wavelength of 1.54056 Å (30 mA and 40 kV) at room temperature,
the powder X-ray diffraction (XRD) patterns were obtained. In this regard, the corresponded data
-1
were gathered over in the 2θ range of 4°-80° with a scanning speed of 2° min . The Fourier transform
infrared (FTIR) were acquired on a Schimadzu system FTIR 160 spectrophotometer in the wavelength
-1
scope of 400 to 4000 cm using KBr disks the technique. Besides, To monitor the hydrolysis
reactions of the 2-chloroethyl phenyl sulfide (2-CEPS), a Varian Star 3400CX series gas
chromatograph associated with flame ionization detector (GC-FID) and an OV-101CWHP 80/100
silica capillary column (30 m×0.25 mm inner diameter (i.d.), 0.25 ꢀm film thickness) was operated
and the related results were recorded. The gained products were investigated by a HP-Agilent gas
chromatograph-mass spectrometer fitted with a fused-silica capillary column (DB 1701, 30 m×0.25
mm inner diameter (i.d.), 0.25 ꢀm film thickness). Also, the GC utilized under the conditions of: the
-
1
column temperature was first set at 60°C for 5min and then adjusted at 20°C min to 200°C to reach
the ultimate temperature at which was held for 13 min. Plus, the injector, MS quad and source
temperatures were programmed at 60°C, 200°C and 230°C, respectively. Helium (99.999% purity)
-1
with the flow rate of 1 mL min was applied as the carrier gas.
.2. Synthesis of NaZSM-5
2
To synthesize the NaZSM-5 zeolite, the hydrothermal method was applied as a typical procedure. At
First, the values of 50 mmol sodium hydroxide pellets (NaOH) and 6 mmol sodium aluminate
(
NaAlO ) were added and subsequently dissolved in the deionized water (D.W) and then transferred
2
to a polypropylene bottle. Next, this mixture was undergone agitation on a shaker for overnight. After
the mentioned mixture was appropriately mixed, an adequate quantity of silica sol (40wt. %) was
gently introduced to the solution under rigorous stirring for 12h. Ultimately, 0.2% seed was added and
o
hydrothermally processed in an oven at 180 C for 32 h [42].
2
.3. Preparation of AgZSM-5
To gain the AgZSM-5 zeolite, the ion exchange route was utilized. In this matter, firstly, 5 g of the
NaZSM-5 zeolite which was prepared in before was introduced to a 50 mL of a 1 M silver nitrate
(
AgNO ) solution and this mixture was magnetically agitated at 60°C for 5 h. This agitation process
3
4

ACCEPTED MANUSCRIPT
+
+
would be followed by an ion exchange by which Ag ions were located instead of Na ions. To
+
eliminate the surplus Ag ions from the zeolite framework, the resulted AgZSM-5 zeolite was
consecutively filtered and washed by using the deionized water (D.W) and 0.1 M hydrochloric acid
(
HCl) solution prior to be dried at 110°C for 16 h. The cleaned and dried AgZSM-5 zeolite powder
was then calcined at 400°C for 4 h. The demonstrated procedure was renewed thrice to approach
sufficient ion exchange.
2
.4. Preparation of CuO NPs/AgZSM-5
The CuO NPs/AgZSM-5 zeolite composite was prepared by the impregnation method. In a typical
experimental procedure, 4 g of the AgZSM-5 zeolite was introduced to a solution of 2 M of copper
nitrate trihydrate (Cu(NO ) .3H O) reactant in 150 mL deionized water (D.W). After that, the mixture
3
2
2
was rigorously stirred at room temperature for 6h. After accomplishment of the reaction, the obtained
sample were filtered, washed by the deionized water (D.W) several times and dried nightlong at
1
10°C before the next process. The acquired product was specified after calcination at 500°C and
being settled in air for 6h. Furthermore, the raw CuO NPs was also synthesized in the absence of the
AgZSM-5 zeolite under equal conditions.
2
.5. Removal reaction tests of 2-CEPS over CuO NPs/AgZSM-5
The removal (adsorption and degradation) reaction of 2-chloroethyl phenyl sulfide (2-CEPS) sulfur
mustard agent simulate on the CuO NPs/AgZSM-5 composite is comprehended according to the
following approach. In a typical manner, 10 mL of n-decane as the solvent, 200 µL of n-octnane as
the internal standard, and 25, 50, 75 and 100 mg/L of 2-CEPS were introduced to a 50 mL Erlenmeyer
flask which was toughly sealed to resist the solvent vaporization. More, the resulting samples were all
sufficiently stirred for 2 min to attain homogeneous mixture. Afterwards, the amounts of 0.1, 0.2, 0.3,
0
.4, 0.5, and 0.6 g of CuO NPs/AgZSM-5 composite were added to the above prepared solutions,
respectively. Further, no attempt was implemented to control surrounding ambient conditions for
instance humidity or light. Afterwards, all of the supplied samples were gently shaken for 15, 30, 45,
6
0, 75, 90, 115 and 120 min on a wrist-action shaker to attain a noticeable adsorption and a substantial
interaction between the CuO NPs/AgZSM-5 composite and 2-CEPS. These obtained solution samples
were then left to be settled until the precipitation process was fully completed. Finally, 10 µL of upper
solution of each sample was picked up via a micro-syringe and then injected to the GC-FID and GC-
MS devices to get further quantitative view.
3
. Results and discussion
3
.1. SEM
The characteristics such as morphology and crystalline size of the synthesized parent NaZSM-5
zeolite, AgZSM-5 zeolite, CuO NPs/AgZSM-5 zeolite composite and plus raw CuO NPs were
investigated via the Field emission scanning electron microscopy (FESEM) technique, and the related
results represented in Fig.1. The SEM micrographs display uniformly morphology of the NaZSM-5
(
Fig.1a) and AgZSM-5 (Fig.1b) zeolites as the hexagonal cubic and also quasi-spherical CuO NPs
5

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which were desirably supported on the AgZSM-5 zeolite surface (Fig.1c). Besides, the SEM
+
micrographs prove the assumption that Ag ion exchange and CuO NPs loading processes had no
sensible negative impact on the morphology and the crystallinity of the structures. The mediocre
crystalline size of the synthesized AgZSM-5 zeolite and CuO NPs in the CuO NPs/AgZSM-5
composite framework was estimated to be 2 micron and less than 20 nm, respectively.
3
.2. EDX
To investigate the elemental composition of the pre-prepared parent NaZSM-5 zeolite, CuO
NPs/AgZSM-5 zeolite composite and raw CuO NPs, more study was implemented in detail by the
energy dispersive X-rays (EDX) analysis technique and the affiliated outcome was collected in Fig.2.
From Fig.2, it can be undoubtedly inferred that the Na, O, Al, and Si elements are present in the
NaZSM-5 and CuO NPs/AgZSM-5 structures. In the provided EDX spectra, the emerged peaks in the
ranges of nearly 0.5 to 2 are respectively attributed to the binding energies of O, Na, Al, and Si which
are referred to the main elements of the ZSM-5 zeolite (Fig.2a). Moreover, in spectrum (Fig.2b), the
two emerged peaks in the ranges of 2.92 and 3.21 keV are attributed to the binding energies of Ag and
three observed peaks in the ranges of 0.93, 8.04 and 9.03 keV are corresponded to the binding
energies of Cu. This confirms the existence of Cu in the synthesized composite. On the other hand,
the obtained information also reveals the coexistence of 3.4 wt.% Ag and 12.6 wt.% CuO in the
synthesized composite structure, respectively. As can be seen, the Fig.3 depicts an instance SEM
image of the synthesized composite with the related EDX elemental mappings. The major
concentration of the related element has been indicated by a brighter area in the elemental map. In this
regard, each of the various elements has been depicted in different color in order to simplify the
identification of their positions within the nanomaterials. As it has been represented in Fig.3, the
related elemental dot-mappings clearly point the presence of O, Al, Si, Ag, and Cu. According to
maps, the homogeneity of the sample can be proved by the uniform distribution of elements over the
composite.
3
.3. TEM
The shape and size of the pre-synthesized CuO NPs/AgZSM-5 zeolite composite (Fig.3a) and raw
CuO NPs (Fig.3b) were meticulously surveyed by the transmission electron microscopy (TEM) as the
corresponding images have been depicted in Fig.3. Besides, the high magnification TEM micrograph
in Fig.3a displays the loaded dark particles of CuO NPs with mediocre particle size of 16 nm on the
bright surface of AgZSM-5 zeolite. The gained results were in good consistency with the mediocre
particle size calculated via the Debye-Scherer formula from the XRD pattern.
3
.4. XRD
Fig.4 comprises the typical powder X-ray diffraction (XRD) patterns of the parent NaZSM-5 zeolite,
AgZSM-5 zeolite, CuO NPs/AgZSM-5 zeolite composite, and raw CuO NPs, respectively. As can be
observed in the patterns, the six obvious main and narrow peaks relating to the NaZSM-5 zeolite
emerged at 2θ of 7.1945°, 8.9836°, 14.4871°, 22.8369°, 23.1653°, and 46.5112° (Fig.4a) were
6

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referred to the diffraction planes of (101), (200) (301), (511), (303), and (503), respectively and are in
accordance with those of the NaZSM-5 zeolite with JCPDS Card No. 025-1349 which are marked
with orange circle symbols. The NaZSM-5 zeolite framework was undergone no change even after
+
Ag ion exchange process which led to form the expected AgZSM-5 (Fig.4b). Meantime, the
synthesized CuO NPs playing the role of guest material were loaded as a 12.6 wt.% onto the AgZSM-
5
zeolite which was considered as the host material. This momentous phenomenon dictates a series of
new appeared peaks gained at 2θ of 41.5541°, 45.3006°, and 57.2789° referring to the diffraction
planes of (002), (111), and (202) respectively which are marked with black square symbols.
Furthermore, there was no identified characteristic peak implying the impurities during the loading
process of CuO species. Also, the particle size of the synthesized CuO NPs included on the AgZSM-5
was further explored by XRD technique and line broadening of the peak at 2θ=4°-80° as measured by
ꢄ.ꢅ ꢆ
the Debye-Scherrer equation: ꢀꢁꢂꢃ
=
. In the noted equation, DXRD is corresponded to the
ꢇ ꢈꢉꢊ ꢋ
mediocre crystallite size, λ refers to the wavelength of CoK radiation, β is known as the full width at
α
half maximum (FWHM) of the selected diffraction peak and θ is defined as the Bragg diffraction
angle. The peaks related to the raw CuO NPs appeared at scattering angles 2θ= 37.9235°, 41.5511°,
4
5.2733°, 57.2749°, 62.982°, 68.8817°, 72.9301° and 78.8443° affiliating to the diffraction planes of
100), (002), (111), (202), (113), (220), (311), and (222), respectively which crystallized in the
monoclinic phase and were in good consistency with those of CuO NPs with the literature values
JCPDS Card No. 05-0661). From the above specified equation, the mediocre particle size for CuO
(
(
NPs in the CuO NPs/AgZSM-5 zeolite composite is calculated 16.2 nm. The calculated particle size
from XRD measurement is in good agreement with the attained results from the SEM analysis.
3
.5. FTIR
The Fourier transform infrared (FTIR) was used to determine the functional groups and the typical
bands of the parent NaZSM-5 zeolite, AgZSM-5 zeolite, CuO NPs/AgZSM-5 zeolite composite, raw
CuO NPs, and 2-CEPS-CuO NPs/AgZSM-5 zeolite composite, and resulting are recorded in Fig.5. It
is also notable that the peak positions are approximately the same for all four ZSM-5 zeolite samples.
All these pre-synthesized particular samples, including NaZSM-5, AgZSM-5, and CuO NPs/AgZSM-
-1
-1
5
show representative sharp peaks about 451 cm and 545 cm which are attributed to the bending
vibrations of the insensitive internal SiO or AlO tetrahedral units and plus double five-member rings
4
4
in the pentasil framework of ZSM-5(MFI) type zeolite, respectively. The peaks occurred about 796
-
1
-1
-1
cm , 1093 cm and 1224 cm are assigned to the internal tetrahedral symmetrical and asymmetrical
stretching vibrations of Si-O-Si linkages of the ZSM-5 zeolite framework, respectively. Besides, the
-1
-1
peaks emerged about 1633 cm and 3649 cm can be referred to the H-O-H bending O-H bonding
vibrations and physically adsorbed H O molecules of the ZSM-5, respectively. Delving into the Figs.
2
5
a-5c verifies the assumption that no phenomenal variation has observed in the bands of AgZSM-5
zeolite and CuO NPs/AgZSM-5 zeolite composite compared with the parent NaZSM-5 zeolite. This
7

ACCEPTED MANUSCRIPT
fact encourages the opinion that the ion exchange and loading procedures of NaZSM-5 zeolite by the
+
Ag ion and CuO shows a negligible effect on the chemical structure of the zeolite structure. Fig.5c
displays a new occurred peak corresponding to the loaded CuO NPs. The absorption peak appeared at
-1
9
29 cm is attributed to Cu-O-Al and Cu-O-Si bonds which uncovers the trapped CuO in the zeolite
framework structure. On the other hand, Fig.5e shows the FTIR spectrum of the raw synthesized CuO
-1
-1
NPs. The broad absorption peaks observed around 3675 cm and 1620 cm are corresponded to the
-
1
–1
adsorbed H O molecules. Also, three recognized peaks at 482 cm and 525 cm are assigned to the
2
stretching vibrations of Cu-O bonding. Besides, to provide much more intelligible demonstration
about the adsorption process of 2-CEPS on the synthesized adsorbent composite, the FTIR analysis
was applied after the reaction and the corresponding spectrum were precisely recorded. As can be
-
1
-1
observed in Fig.5d, two new substantial absorption peaks spotted at 1276 cm and 1508 cm are
assigned to the S-C and C=C bonds, respectively.
3
3
.6. Removal of 2-CEPS on the CuO NPs/AgZSM-5
.6.1. Effect of contact time
The gas chromatograph-flame ionization detector (GC-FID) analysis was operated to study and
monitor the performance of the synthesized CuO NPs/AgZSM-5 zeolite composite adsorbent for the
removal (adsorption and degradation) of 2-CEPS in aqueous solution. To gain the highest reaction
efficiency, the important factors like reaction time were surveyed by employing n-decane as the
o
solvent, a 120 min time considered as the shaking time and also the temperature of 25 C, respectively.
Figs.6 and 7 illustrate the so-called area under curve (AUC) data under above defined conditions of
GC-FID chromatograms. From the GC-FID chromatograms it is brightly comprehended that 2-CEPS
displays a retention time around 15.3 min. Further, to acquire the degradation quantity, the integrated
AUC data of two samples of 2-CEPS and n-octane as the internal standard were computed for all
variables and its ratio (integrated AUC of CEPS/integrated AUC of n-octane) was determined.
Several time intervals were selected for various respective experiments to reach to the optimum time
of reaction for the removal of 2-CEPS on the synthesized CuO NPs/AgZSM-5 composite. The
mentioned experiments uncover the apparent relationship between removal characteristic of adsorbent
and different time intervals. In this matter, Figs. 6-8 depict the changes in the removal (%) against
stirring time and the obtained product% (2-HEPS%, with retention time about 17.9 min) at different
initial 2-CEPS concentration and plus the correlation between removal efficiency of 2-CEPS on the
synthesized CuO NPs/AgZSM-5 composite to the contact time. Therefore, the reaction time was
surveyed in the scope of 0 to 120 min. To reach the most appropriate reaction time and subsequently
the highest removal efficiency, 120 min was approved as an optimum value for the posterior
sequential experiments. Additionally, in Fig.6, the GC-FID spectra and affiliated data have been
shown.
8

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3
.6.2. Effect of adsorbent dose
Using the least amount of adsorbent to obtain the highest rate of removal is an undeniable key
parameter that cannot be connived. It grants much more authenticity to the proposed method for
further future development and investigations. In present research, to evaluate the best applicable
quantity of adsorbent, a range of 0.1 to 0.6 g of the synthesized CuO NPs/AgZSM-5 adsorbent was
applied for the removal of 2-CEPS. As has been represented in Fig.9, the increase in the adsorbent
quantity is caused to higher degradation efficiency. Thenceforth, as this increase continued no
substantial change recognized and the curve slope showed a linear behavior implying the constant
values. Eventually, the value of 0.3 g of CuO NPs/AgZSM-5 adsorbent was denoted as the optimum
value to conquer the high yield adsorption and subsequent degradation reaction.
3
.6.3. Effect of adsorbent type
To compare the influence of adsorbent type on the removal efficiency, NaZSM-5 zeolite, AgZSM-5
zeolite, CuO NPs/AgZSM-5 zeolite composite and raw CuO NPs were prepared as four segregated
adsorbents for the adsorption and degradation process of 2-CEPS molecule. These series of
experiments were designed and fulfilled under the similar conditions for the assigned adsorbents.
Raw NaZSM-5 zeolite does not have high catalytic performance and that is why the loading process
+
by Ag and CuO NPs was applied to increase the catalytic role, respectively. It is also acknowledged
that the raw CuO NPs represent the lower adsorption-degradation for 2-CEPS compared with
NaZSM-5. Based on the Fig.10, it can be vividly deduced that the highest rate of adsorption and
degradation of 2-CEPS observed for the CuO NPs/AgZSM-5 composite adsorbent which
demonstrates the efficacious combination of CuO NPs with AgZSM-5 zeolite.
3
.6.4. Reaction kinetics
As can be seen in Fig.11, the removal kinetics was investigated employing the plots of Ln
concentration versus reaction time. The parameter k which is defined as the removal rate constant or
in other word "slope", was calculated from the first order equation as follows: Ln C /C =kt. In this
o
t
equation, parameter C is specified as the concentration of the 2-CEPS at time t, parameter C is
t
o
corresponded to the initial concentration and k is referred to the removal rate constant. Furthermore,
the half-life (t ) can be computed by t = 0.693/k. Also, 0.3 g of CuO NPs/AgZSM-5 composite
1
/2
1/2
was introduced into the discrete containers including 25 mg/L of 2-CEPS at definite time intervals to
study the reaction kinetics. The respective results have been represented in Table 1.
3
.6.5. GC-MS
The compound originated from the degradation and hydrolysis of 2-CEPS on the CuO NPs/AgZSM-5
composite adsorbent was identified by gas chromatography coupled with mass spectrometry (GC-MS)
analysis. Fig.12 exhibits four significant peaks at various retention times. The peaks about 9.5 and
1
0.5 min are assigned to the n-octane internal standard and n-decane solvent, respectively. Besides,
two other sharp peaks about 15.3 and 17.9 min are identified which is attributed to the 2-CEPS and its
degraded product namely 2-HEPS, respectively. Further, the detector was programmed to scan a mass
9

ACCEPTED MANUSCRIPT
range of 28, 45, 65, 77, 91, 109, 123 and 172 m/z (Fig.12a), and 28, 45, 59, 77, 85, 131 and 154 m/z
(
Fig.12b) for 2-CEPS, and 2-HEPS, respectively.
.6.6. Mechanism of the 2-CEPS removal
3
According to the provided information from GC-FID and GC-MS analyses, the proposed mechanism
schemes for the adsorption and degradation (removal) procedure of the 2-CEPS on the CuO
NPs/AgZSM-5 composite adsorbent and beside the formation of degradation product have been
+
shown in (Scheme 1a and 1b). In the assigned scheme, the role of both silver (Ag ) and copper oxide
(
CuO) species on the removal reactions have been separately reviewed. It should be also assumed that
both of the represented routes are conceivable and may proceed simultaneously. In route (Scheme 1a)
first, the Cl atom of 2-CEPS molecule undergoes a nucleophilic attack by the Bronsted acid sites
(
hydroxyl groups (Cu-OH)) which are present through the CuO of the CuO NPs/AgZSM-5 composite
structure. During this phenomenon, an intermediate of cyclic sulfonium ion is expected to be formed
but it is the nonvolatile form of the corresponding compound so that its extraction and subsequent
detection by the GC-FID is not possible. Then after a short interval, de-halogenation reaction causes
the elimination of the chlorine atom from 2-CEPS molecule. Meanwhile, whether the H O molecule is
2
present or not, various reactions are probable to proceed and hydrolysis originated substance will be
2
+
revealed on the surface of Cu species (Cu ) as the Lewis acid sites. The hydrolysis process goes on
until 2-hydroxyl ethyl phenyl sulfide (2-HEPS) as the major removal product of 2-CEPS is emerged.
In contrast, in route (Scheme 1b) the chlorine and sulfur atoms of sulfur mustard agent simulate
+
undergo an electrophilic attack by positive silver (Ag ) from the zeolite structure and as a results
forces 2-CEPS molecule to be adsorbed on the surface and pores of the composite. The transition
+
states for the creation of S-Ag -Cl bonds will also lead to form cyclic sulfonium ion which is
recognized as an intermediate. These impermanent intermediates, in the presence of H O, change into
2
2
-hydroxyl ethyl phenyl sulfide (2-HEPS) which is known as the hydrolysis product on the surface of
+
silver species (Ag ) as the Lewis acid sites of the synthesized CuO NPs/AgZSM-5 composite.
4
. Conclusion
In the current research, the synthesis and application of CuO NPs/AgZSM-5 zeolite composite as a
novel adsorbent for the adsorption and degradation of 2-chloroethyl phenyl sulfide (2-CEPS, a sulfur
mustard agent simulate) was evaluated via the GC-FID analysis. Furthermore, the effect of several
operative variables such as contact time, initial concentration, adsorbent dose and adsorbent type on
the removal efficiency were meticulously surveyed and discussed. Afterwards the significant
structural, morphological and crystalline size of the CuO NPs/AgZSM-5 composite synthesized by the
impregnation method was proved via different characterization studies. Considering the GC-FID
analysis results, it can be clearly inferred that the 2-CEPS was significantly removed by the
synthesized composite adsorbent with 100% yield under defined optimized conditions namely:
contact time (120 min), initial concentration (25 mg/L), and adsorbent dose (0.3 g). The reaction
kinetic study was also exerted by using the first order model and the related quantity of the half-life
1
0

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-1
(
t ) and rate constant (k) were measured as 26.25 min and 0.0264 min , respectively. Besides, the
1/2
obtained characterizations information confirmed the substantial, applicability and particular potential
of the synthesized adsorbent for high yield adsorption and degradation of 2-CEPS. Consequently, 2-
hydroxy ethyl phenyl sulfide (2-HEPS) as the less-toxic degradation and hydrolysis product of 2-
CEPS on the CuO NPs/AgZSM-5 composite adsorbent was detected and verified.
Acknowledgments
The authors give their sincere thanks to the Payame Noor University, Ramsar, Iran for all sincere
supports.
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Table1. First order kinetic parameters for the removal of 2-CEPS over CuO NPs/AgZSM-5 at
different initial concentration.
Initial concentration
-1
Half-life (t , min)
Rate constant (k, min )
First order kinetic equation
Ln C /C = 0.0264t-0.1135
1
/2
(
mg/L)
2
5
7
5
0
5
26.25
55.44
0.0264
0.0125
0.0064
0.0046
o
t
Ln C /C = 0.0125t-0.0045
o
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150.65
Ln C /C = 0.0064t+0.0477
o t
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00
Ln C /C = 0.0046t+0.0463
o t

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Fig.1. SEM micrographs of: a) parent NaZSM-5, b) AgZSM-5, c) CuO NPs/AgZSM-5, and d) raw
CuO NPs.
1

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Fig.2. EDX analyses of: a) parent NaZSM-5, b) CuO NPs/AgZSM-5, c) raw CuO NPs, and d) SEM
micrograph of the CuO NPs/AgZSM-5 with relating EDX dot-mappings which specifies the positions
of various elements over the composite framework.
2

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Fig.3. TEM micrographs of: a) CuO NPs/AgZSM-5, and b) raw CuO NPs.
Fig.4. XRD patterns of: a) parent NaZSM-5, b) AgZSM-5, c) CuO NPs/AgZSM-5, and d) raw CuO
NPs.
3

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Fig.5. FTIR spectra of: a) parent NaZSM-5, b) AgZSM-5, c) CuO NPs/AgZSM-5, d) CuO
NPs/AgZSM-5 after adsorption of 2-CEPS, and e) raw CuO NPs.
4

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Fig.6. GC-FID chromatograms for the 2-CEPS-CuO NPs/AgZSM-5 sample at different contact times:
a) 0, b) 15, c) 30, d) 45, e) 60, f) 75, g) 90, h) 115, and i) 120 min.
5

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Fig.7. Effect of contact time on the removal of 2-CEPS over CuO NPs/AgZSM-5 at different initial
concentrations.
Fig.8. Plot of the obtained 2-HEPS% against initial concentration on the removal of 2-CEPS over
CuO NPs/AgZSM-5(optimum conditions: adsorbent dose: 0.3 g, and contact time: 120 min).
Fig.9. Effect of adsorbent dose on the removal of 2-CEPS over CuO NPs/AgZSM-5 (optimum
conditions: initial concentration: 25 mg/L, and contact time: 120 min).
6

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Fig.10. Effect of adsorbent type on the removal of 2-CEPS (optimum conditions: initial concentration:
25 mg/L, contact time: 120 min, and adsorbent dose: 0.3 g).
Fig.11. Plot of Ln C /C against contact time on the removal of 2-CEPS over CuO NPs/AgZSM-5
0
t
composite at different initial concentrations.
7

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Fig.12. GC-MS analysis and mass spectra of the degradation and hydrolysis product of the CuO
NPs/AgZSM-5 composite reaction with 2-CEPS: a) 2-CEPS, and b) 2-HEPS.
8

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Scheme 1. Reaction mechanisms for the removal of 2-CEPS over CuO NPs/AgZSM-5.
9

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Highlights:
•
The CuO NPs/AgZSM-5 adsorbent composite was synthesized via the impregnation
method.
•
•
•
The CuO NPs/AgZSM-5 was applied for the high yield removal of 2-CEPS.
The reaction kinetic status was also studied employing first order model.
2-hydroxy ethyl phenyl sulfide (2-HEPS) as the degradation product was attained.