Mono-transition-metal-substituted polyoxometalate intercalated layered double hydroxides for the catalytic decontamination of sulfur mustard simulant

Article abstract of DOI:10.1039/c9dt00395a

The Keggin-type mono-transition-metal-substituted [PW₁₁M(H₂O)O₃₉]^5? (PW₁₁M, M = Ni, Co, Cu) were intercalated into Zn₂Cr-based layered double hydroxide (Zn₂Cr-LDH) by an exfoliation-reassembly method and the synthesized Zn₂Cr-LDH-PW₁₁M composites were thoroughly characterized by Fourier transform infrared (FT-IR) spectroscopy, powder X-ray diffraction (PXRD), solid state ³¹P nuclear magnetic resonance (³¹P NMR) spectroscopy, thermogravimetric analysis (TGA), inductively coupled plasma atomic emission spectroscopy (ICP-AES), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The three composites can be used as heterogeneous catalysts to promote the oxidative decontamination of the sulfur mustard simulant 2-chloroethyl ethyl sulfide (CEES). Interestingly, a cooperative effect between the PW₁₁M cluster and Zn₂Cr-LDH is evidenced by the fact that the composites have a higher catalytic performance than either of the individual constituents alone. The catalytic activity of Zn₂Cr-LDH-PW₁₁M is significantly influenced by the substituted transition metals, showing the order: Zn₂Cr-LDH-PW₁₁Ni > Zn₂Cr-LDH-PW₁₁Co > Zn₂Cr-LDH-PW₁₁Cu. Under ambient conditions, the Zn₂Cr-LDH-PW₁₁Ni composite can convert 98% of CEES in 3 h using nearly stoichiometric 3% aqueous H₂O₂ with the selectivity of 94% for the nontoxic product 2-chloroethyl ethyl sulfoxide (CEESO). Moreover, the decontaminating material, Zn₂Cr-LDH-PW₁₁Ni, is stable to leaching and can be readily reused for up to ten cycles without obvious loss of its activity.

Full text of DOI:10.1039/c9dt00395a

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Efficient extraction of sulfate from water using
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DOI: 10.1039/C9DT00395A
ARTICLE
Mono-Transition-Metal-Substituted Polyoxometalate Intercalated
Layered Double Hydroxides for the Catalytic Decontamination of
Sulfur Mustard Simulant
Received 00th January 20xx,
Accepted 00th January 20xx
Xiangrong Sun, Jing Dong, Zhen Li, Huifang Liu, Xiaoting Jing, Yingnan Chi*, Changwen Hu
DOI: 10.1039/x0xx00000x
5
-
The Keggin-type mono-transition-metal-substituted [PW11M(H
based layered double hydroxide (Zn Cr-LDH) by an exfoliation-reassembly method and the synthesized Zn
composites were thoroughly characterized by Fourier transform infrared (FT-IR), powder X-ray diffraction (PXRD), solid state
2
O)O39] (PW11M, M = Ni, Co, Cu) were intercalated into Zn
2
Cr-
2
2
Cr-LDH-PW11
M
3
1
31
P nuclear magnetic resonance ( P NMR), thermogravimetric analysis (TGA), inductively coupled plasma atomic emission
spectroscopy (ICP-AES), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The three
composites can be used as heterogeneous catalysts to promote the oxidative decontamination of the sulfur mustard
simulant, 2-chloroethyl ethyl sulfide (CEES). Interestingly, a cooperative effect between PW11M cluster and Zn
evidenced by the fact that the composites have a higher catalytic performance than either of the individual constituents
alone. The catalytic activity of Zn Cr-LDH-PW11M is significantly influenced by the substituted transition metals, showing the
order: Zn Cr-LDH-PW11Ni > Zn Cr-LDH-PW11Co > Zn Cr-LDH-PW11Cu. Under the ambient conditions, Zn Cr-LDH-PW11Ni
composite can convert 98% of CEES in 3 h using nearly stoichiometric 3% aqueous H with the selectivity of 94% for
2
Cr-LDH is
2
2
2
2
2
2 2
O
nontoxic product, 2-chloroethyl ethyl sulfoxide (CEESO). Moreover, the decontaminating material, Zn
2
Cr-LDH-PW11Ni, is
stable to leaching and can be readily reused for up to ten cycles without obvious lose of its activity.
is still as toxic as sulfur mustard. Until now, several kinds of
catalysts for sulfur mustard degradation have been studied
Introduction
Bis(2-chloroethyl) sulfide, commonly called sulfur mustard or
HD, is a powerful vesicant that can directly damage tissue cells,
cause local inflammation, and lead to systemic poisoning even
1
5-18
6, 7, 19
including metal oxides
, polyoxometalates (POMs)
, and
coordination polymers20-22.
1
death in high doses. Since it was first used effectively in World
War I, sulfur mustard becomes the most produced, stored and
used chemical warfare agent (once known as the “King of the
2
Battle Gases”). Although an international treaty prohibiting the
production and use of sulfur mustard has been signed in 1992,
this compound was still repeatedly used in recent terrorist
attacks. In general, sulfur mustard can be neutralized by three
3
-7
8-10
Scheme 1. The three decontamination pathways of sulfur mustard.
pathways:
oxidation ,
dehydrohalogenation
,
and
hydrolysis1 (Scheme 1). However, the slow degradation rate
of dehydrochlorination and hydrolysis limits their practical
application. In comparison, the selective oxidation is a highly
attractive way, especially using molecular oxygen or hydrogen
peroxide as oxidant. During the decontamination, the selectivity
is very important because the partially oxidation product,
sulfoxide, is less toxic but the over-oxidation product, sulfone,
1-14
POMs are a family of discrete polyanionic clusters, which are
mainly composed of Mo, W, V, Nb centers and oxo ligands.
Owing to their excellent multi-electron redox property, POMs
2
3, 24
2
5-29
can effectively catalyze a series of oxidation reactions.
The
investigations in Hill’s group indicate that transition metal
3
0-35
36
containing POMs, such as {PV
2
Mo10
O
40
}
, {FePW11
O
O
39} ,
III
37, 38
39
{(Fe (OH
2 2 3 9 34 2
) ) (PW O ) }
, and {(FeOH
2
2
) Fe (P
2
2
W
15
56
)
2
}
are active catalysts for the oxidative decontamination of sulfur
Photoelectronic/Electrophotonic Conversion Materials, School of Chemistry and mustard and its simulants. Since POMs have high solubility in
Key Laboratory of Cluster Science Ministry of Education, Beijing Key Laboratory of
Chemical Engineering
Beijing Institute of Technology
Beijing, 100081 (P.R. China)
water and other polar solvents, the reusability of them after
catalysis remains a great challenge. From the practical point of
E-mail: chiyingnan7887@bit.edu.cn
Footnotes relating to the title and/or authors should appear here.
Electronic Supplementary Information (ESI) available: [details of any supplementary
information available should be included here]. See DOI: 10.1039/x0xx00000x
view, the development of personal protective equipment needs
materials that not only can catalytically decompose sulfur
mustard but also can be integrated into suits, gloves, and
†
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boots.40 Therefore, several POM-based decontamination (SEM, JOEL JSE-7500F) and transmission electron microscopy
View Article Online
3
3,
DOI: 10.1039/C9DT00395A
materials were synthesized by immobilizing POMs on carbon
(TEM, JOEL JEM-2010) were used to observe the morphology
, metal organic frameworks (MOFs) 35, 43, or and microstructure of the samples. The BET specific surface
nanoparticles44-46.
areas were measured at 77 K by using a Belsorp-max surface
4
1
30, 32, 42
,
fibers
Layered double hydroxides (LDHs) are assembled from area detecting instrument. The X-ray photoelectron
positively charged layers and interlayer anions by electrostatic spectroscopy (XPS) W4f spectrum was performed on ESCALAB
4
7
31
and hydrogen bonding interactions. The good interlayer 250Xi. Solid state P NMR were performed at room
anion-exchange ability and the tunable charge density and temperature on 700 MHz Bruker Ascend spectrometer. The
acid/base property make LDH an excellent host to immobilize degradation of CEES was monitored by gas chromatograph
2 28
POMs. The first reported LDH-POM material is Zn Al-LDH-V10O , (Shimadzu GC-2014C) equipped with a flame ionization
which shows enhanced photocatalytic activity in the oxidation detector (FID) and a HP-5 ms capillary column.
of isopropanol.48 Subsequently, a series of LDH-POM materials
Synthesis of Zn
2
Cr-LDH-PW11M(H
2
O)O39 Composites
have been prepared and used in catalytic transformations of
II
II
II
4
9,
50
51-54
Synthesis of K
5
PW11M(H
2
II
O)O39 (M = Ni , Co , and Cu ).
thiophene oxidation
,
olefin epoxidation
,
II
II
esterification5 , and so on. Although POMs inserted LDH
5-57
5 11 2 39
K PW M(H O)O (M = Ni , Co , and Cu ) were prepared
according to the reported methods.62
3
H PW12O40 were
materials have been proven to be active for the oxidation of
5
8-60
sulfides in the presence of H
O
2 2
by Song et al,
such kind of dissolved in deionized water (80 °C) and the pH of the solution
CO solution. To this, the
material is rarely used in the oxidative decontamination of was adjusted to 4.8 by adding Li
2
3
6
1
chemical warfare agents or their simulants.
In this work, three decontaminating composites, Zn
PW11M(H
been successfully prepared by intercalating mono-transition-
metal-substituted Keggin-type tungstophosphate into Zn Cr-
LDH-NO and thoroughly characterized by Fourier transform
infrared (FT-IR), powder X-ray diffraction (PXRD), solid state P
nitrate salts of Ni, Co, or Cu and KCl powder were added and the
Cr-LDH- mixture was filtered while hot. The filtrates were placed in a
O)O39 (for 1, M = Ni; for 2, M = Co; for 3, M = Cu) have refrigerator overnight and then crystals were observed and
2
2
collected. The crystals were dissolved in a small amount of hot
water for recrystallization.
Synthesis of Zn
synthesized according to literature by the conventional co-
precipitation method.63 A 20 mL solution containing 0.66 M of
2
3
2
Cr-LDH-NO
3
.
The Zn
2
Cr-LDH-NO
3
was
3
1
3
1
nuclear magnetic resonance ( P NMR), thermogravimetric
analysis (TGA), inductively coupled plasma atomic emission
spectroscopy (ICP-AES) and Brunauer-Emmett-Teller (BET). The
three composites can catalyze the selective oxidation of sufur
mustard simulant, 2-chloroethyl ethyl sulfide (CEES), in the
presence of nearly stoichiometric 3% hydrogen peroxide and
the catalytic performance of 1 is better than those of 2 and 3.
Using 1 as heterogeneous catalyst, 98% CEES was converted in
Zn(NO
simultaneously dropped into a 150 mL boiled deionized water
with vigorous stirring under N atmosphere and the final pH of
the solution was controlled to about 5.5. After aging at 80 °C for
2 h, the light purple precipitate (Zn Cr-LDH-NO ) was filtered
3 2 3 3
) and 0.33 M of Cr(NO ) and 50 mL NaOH (2M) were
2
1
2
3
and washed by deionized water and ethanol, respectively, and
dried at 60 °C for 12 h.
3
2
h with 94% selectivity under ambient conditions. The Zn Cr-
Synthesis of Zn
2
Cr-LDH-PW11M composites. In order to obtain
Cr-LDH-NO
3
LDH-PW11Ni (1) is robustness and can be reused for ten cycles
without significant loss of its activity.
exfoliated Zn Cr-LDH nanosheets, the prepared Zn
2
2
was dispersed into 20 mL formamide to form a colloidal
suspension.63 To this, the aqueous solution of
K PW11M(H O)O39 was added dropwise and the mixture was
5 2
Experimental
stirred for 30 min under ambient conditions. The crude product
was washed with water and ethanol, respectively, and dried
under vacuum at 80 °C for 12 h.
Materials and methods
H
3
PW12
O
40 and the nitrate salts of Ni, Co, Cu, Zn, Cr were
purchased from Sinopharm Chemical Reagent Co., Ltd.. NaOH,
KCl, Li CO , aqueous H , and CEES were purchased from
2
3
2 2
O
Catalytic oxidation of CEES.
Aladdin Industrial Corporation. CAUTION: The simulant of HD,
CEES, is highly toxic and the decontamination experiments
should be performed carefully by the trained personnel in a
hood under good ventilation. PXRD data were collected on a
Bruker instrument (D8 Venture) equipped with graphite-
monochromatized Cu Kα radiation ( λ = 0.154 nm; scan speed =
The selective oxidation (decontamination) of CEES using
different catalysts were carried out as follows. Catalyst (0.0015
mmol) was dispersed in acetonitrile (4 mL), followed by addition
of CEES (0.5 mmol) and 1,3-dichlorobenzene (internal standard,
0
3
.25 mmol). After stirring for 2 minutes at room temperature,
% aqueous H (0.525 mmol) was added dropwise. The
2 2
O
−
1
5
° min ; 2θ = 5-70°) at room temperature. The FT-IR spectra
reaction was monitored by gas chromatography at various time
intervals and the products were qualitatively analyzed by GC-
MS. In the recycle experiments, the catalyst 1 was filtered after
the reaction and washed with ethyl acetate and dried under
vacuum at 50 °C and used for the next cycle.
were measured on a Nicolet 170SXFT-IR spectrophotometer in
−
1
the range 400-4000 cm . The elemental analyses of Zn, Cr and
W were performed by a ThermoiCAP 6000 atomic emission
spectrometer. Thermogravimetric data were collected on a
Shimadzu DTG-60AH thermal analyzer under air atmosphere
−
1
with a heating rate of 10 °C min . Scanning electron microscopy
2
| J. Name., 2012, 00, 1-3
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vibrations of the P-O
terminal oxygen atoms), W-O
atoms) and W-O
The Zn Cr-LDH-NO
to the vibration of NO
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a d
(a: tetrahedral oxygen atoms), W-O (d:
Results and discussion
Synthesis and Characterization of Zn Cr-LDH-PW11M.
2
DOI: 10.1039/C9DT00395A
b
-W (b: corner-shared oxygen
c
(c: edge-shared oxygen atoms), respectively.
-1
2
3
host shows a strong peak at 1385 cm due
As transition metal containing POMs have been proven to be
active in the selective oxidation of sulfur mustard and/or its
simulants, in our experiment three mono-transition-metal-
-
3
anion. Compared with LDH host and
POM precursors, the synthesized three composites have all the
characteristic peaks of mono-substituted POMs but the
II
II
II
substituted Keggin-type PW11M (M = Ni , Co , and Cu ) were
used to combine with LDH. Zn Cr-LDH-NO was chosen as the
host based on the following considerations. First, Zn Cr-LDH-
NO is formed under weak acidic conditions, which is more
compatible with the working pH range of polyanion PW11M than
other basic LDH, such as Mg Al-LDH-NO and Zn Al-LDH-NO
Second, we found that the activity of Zn Cr-LDH-NO
heterogeneous catalysts is better than those of Zn
and Mg Al-LDH-NO
1). As shown in Scheme 2, Zn
an exfoliation-reassembly method. The Zn
synthesized by the co-precipitation of Zn(NO
solution with NaOH under N atmosphere. After aging at 80 °C
for 12 h, the resulting precipitate was washed with deionized
water and dried at 60 °C. The Zn Cr-LDH-NO was exfoliated by
-
absorption band of NO
spectra further confirms successful intercalation of PW11M into
Zn Cr-LDH. Compared with POM precursors, the characteristic
absorption bands of POMs in Zn Cr-LDH-PW11M are slightly
3
anion is much weaker. The FT-IR
2
3
2
2
3
2
redshifted, which might be caused by the electrostatic and
hydrogen bonding interactions between polyanions and the
host.
2
3
2
3
.
2
3
host as
Al-LDH-NO
3
2
2
3
in the oxidation of CEES (Table 1, entry 9-
Cr-LDH-PW11M was prepared by
Cr-LDH-NO was first
and Cr(NO
1
2
2
3
3
)
2
3 3
)
2
2
3
formamide to form colloidal nanosheet suspension and to this
PW11M solution was added dropwise. After 30 min stirring,
Zn Cr-LDH-PW11M composite was obtained.
2
2
Scheme 2. The synthesis process of Zn Cr-LDH-PW11M by an exfoliation-
reassembly method.
The PXRD patterns of three synthesized composites and
Cr-LDH-NO are shown in Figure 1a. For LDH, the (003)
Zn
2
3
diffraction peak is related to the layer spacing. When small
nitrate is replaced by large PW11M, the spacing layers are
enlarged and the (003) peak correspondingly shifts to lower
Figure 1. (a) The PXRD patterns of Zn
2 2 3
Cr-LDH-PW11M and Zn Cr-LDH-NO ; (b) FT-
2
position. For three Zn Cr-LDH-PW11M composites, the
IR spectra of Zn Cr-LDH--NO , Zn Cr-LDH-PW11Ni, and PW11Ni.
2
3
2
characteristic (003) diffraction peaks obviously shift left
compared with that of LDH host indicating the successful
intercalation of POMs. According to the basal spacing of d(003),
the gallery height value of 1.06 nm is calculated, which is in good
accordance with the diameter of Keggin-type cluster. In
2
The Zn Cr-LDH-PW11Ni, composite 1, was selected as a
representative example for the following characterizations.
Based on the SEM and TEM images (Figure 2a-2c), we found that
Zn Cr-LDH-PW Ni still has a typical LDH nanosheet morphology
2 11
2 3
and compared with the image of Zn Cr-LDH-NO no structure
o
addition, the (110) diffraction peaks (2θ = ~60 ) and a broad
o
hump diffraction peaks (2θ = ~32-42 ) are nearly unchanged
change is observed. Energy dispersive X-ray spectroscopy (EDS)
Figure S2) indicates that composite 1 contains Zn, Cr, P, W, Ni,
revealing that the layered structure of LDH is maintained after
the intercalation of PW11M.
(
and O elements and the tungsten and nickel are evenly
dispersed on the LDH layers, that is proven by elemental
mapping measurements (Figure 2d). The ICP-AES analyses
The FT-IR spectra of composite 1, LDH host, and POM
precursor are shown in Figure 1b. The three mono-substituted
PW11M exhibit similar characteristic peaks (Figure S1) at about
-1
indicate that the loading amount of PW Ni is 52 wt%
1
080 ， 940 ， 880 ， 807 cm , which are attributed to the
11
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-. The XPS W4f dichlorobenzene (internal standard, 0.25 mmol)VaienwdArtcicaletOanlylinset
3
corresponding to 60% exchange rate of NO
spectrum of Zn
well-resolved peaks at 37.7 and 35.6 eV correspond to W4f5/2 2 min under ambient conditions, and then 3 % aqueous H
and W4f7/2, respectively. (0.525 mmol) was added to initiate the reaction. As shown in
2
Cr-LDH-PW11Ni is shown in Figure S3, where two (0.0015 mmol) were mixed in acetonitrileD(O4I:m10L.1)0a3n9d/Cs9tDirTr0e0d39f5oAr
2 2
O
Figure 4b and Table 1, entry 1-3, all the composites as
heterogeneous catalysts can promote the oxidation of CEES and
7
6-98% CEES is converted in 3 h. The catalytic activity of
composite 1 with the conversion of 98% is better than that of 2
91%) or 3 (76%). In comparison, a negligible conversion of CEES
(
is provided in the blank experiment (without catalysts). In the
oxidation of CEES, the selectivity is an important parameter to
be considered. The partial oxidation product, nontoxic 2-
chloroethyl ethyl sulfoxide (CEESO), is more preferred than the
over oxidation product, toxic 2-chloroethyl ethyl sulfone
2
(CEESO ). In our case, very similar selectivity (94%) for CEESO is
given by three composites (Figure 4b and Table 1, entry 1-3).
Figure 2. (a) SEM image of Zn
2
Cr-LDH-NO
3
; (b) SEM image of Zn
2
Cr-LDH-PW11Ni;
Cr-LDH-PW11Ni.
(
c) TEM image of Zn Cr-LDH-PW11Ni; (d) Elemental mapping of Zn
2
2
Solid state 31P NMR of composite 1 (Figure 3a) shows that
the characteristic peak of PW11Ni at δ = -11.3 ppm still can be
found in the Zn Cr-LDH-PW11Ni. In addition, the N adsorption-
2
2
desorption isotherms of 1 were measured to assess its porosity.
As shown in Figure 3b, composite 1 exhibits the type IV isotherm
pattern with a clear hysteresis loop indicating the presence of
Figure 4. (a) Catalytic decontamination of CEES; (b) CEES oxidation using different
Zn
2
Cr-LDH-PW11M composites; (c) Time profile for CEES oxidative transformation
2
mesopores. Composite 1 has a BET surface area of 24.92 m /g,
using Zn
2
Cr-LDH-PW11Ni. Reaction conditions: Catalyst (0.0015 mmol), CEES (0.5
2
which is higher than that of LDH host (13.56 m /g) and average
2 2
mmol), and 1,3-dichlorobenzene (0.25 mmol), 3% aqueous H O (0.525 mmol) and
pore size of the composite (42.48 nm) is also larger than that of
host (14.14 nm). The results display that the intercalation of
POM leads to the increase of surface area and the increased
surface area might not only facilitates the exposure of catalyst
acetonitrile (4 mL) at room temperature.
To probe the role of two components: PW M and Zn Cr-
1
1
2
active sites (POMs), but also contribute to the improvement of LDH in the degradation of CEES, a series of control experiments
catalytic activity.
11
were conducted (Table 1). First, the potassium salts of PW M
were used and they can decontaminate CEES in homogeneous
system with the conversion of 81% for PW11Ni, 78% for PW11Co,
and 73% for PW11Cu, respectively (Table 1, entry 4-6). Under
otherwise identical conditions, the host, Zn
converts 30% of CEES, which is far lower than that of PW11
73-81%). The above results indicate that in the Zn Cr-LDH-
2
Cr-LDH, only
M
(
2
PW11M composites the inserted POM clusters are the main
catalytic active sites. More importantly the cooperative effect
between PW11M and Zn Cr-LDH is evident because the
2
composites have a higher catalytic performance than either of
the individual constituents alone. To assess the influence of
substituted transition metals on the decontamination process,
Figure 3. (a) Solid state 31P NMR spectra of Zn
Cr-LDH-NO
2
3 2
and Zn Cr-LDH-PW11Ni;
(b) The N adsorption-desorption isotherms of Zn Cr-LDH-PW11Ni.
2 2
plenary H
entry 7-8). Under the same conditions, the conversions of
40 (21%) and K 39 (58%) are lower than those of
PW11M (73-81%), indicating that both the tungstophosphate
and the substituted transition metals contribute to the catalytic
decontamination. It is interesting to note that the order of
3 7
PW12O40 and lacunary K PW11O39 were used (Table 1,
Decontamination of CEES
The catalytic performance of three Zn
composites 1-3 was evaluated in the oxidative decontamination
of CEES, which is a widely used simulant for sulfur mustard. In a
typical degradation reaction, CEES (0.5 mmol), 1,3-
H PW12O
3
7
PW11O
2
Cr-LDH-PW11M
2
catalytic activity for Zn Cr-LDH-PW11M composites (1 > 2 > 3) is
4
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consistent with that observed in homogeneous system (PW11Ni material is stable to leaching under turnover conditions and
View Article Online
DOI: 10.1039/C9DT00395A
>
2
PW11Co > PW11Cu) and that further confirms the important Zn Cr-LDH is an efficient host to immobilize PW11Ni. Moreover,
role of substituted transition metals in the oxidation of CEES. As the recyclability and stability of composite 1 were evaluated. As
the good performance, composite 1 with TON of 327 was used shown in Figure 5b, after 10 cycles only a slight decrease in
in the following experiments. To explore the influence of conversion and selectivity was found. In addition, the
catalyst or oxidant on the degradation of CEES, the catalytic comparison of FT-IR and PXRD spectra before and after the
reactions with different amount of catalyst or oxidant were recycle test confirms that the structure of Zn
performed. We find that the conversion of CEES increases with maintained during the recycle (Figure S7).
the dosage of composite 1 or oxidant (Figure S6).
2
Cr-LDH-PW11Ni is
Table 1. Decontamination of CEES using different catalysts
Entr
y
Catalyst
System
Conversi
on (%)
98
Selectivit
y (%)
94
1
Zn
2
Cr-LDH-PW11Ni
Heterogeneous
Heterogeneous
Heterogeneous
Homogeneous
Homogeneous
Homogeneous
Homogeneous
Homogeneous
Heterogeneous
Heterogeneous
Heterogeneous
2
Zn
2
Cr-LDH-PW11Co
91
93
3
Zn
2
Cr-LDH-PW11Cu
76
94
Figure 5. (a) Leaching test for CEES decontamination using Zn
Recycle test for CEES decontamination using Zn Cr-LDH-PW11Ni. Reaction
conditions: Catalyst (0.0015 mmol), CEES (0.5 mmol), and 1,3-dichlorobenzene
0.25 mmol), 3% aqueous H (0.525 mmol) and acetonitrile (4 mL) at room
temperature.
2
Cr-LDH-PW11Ni; (b)
4
K
5
PW11Ni(H
2
O)O39
81
93
2
5
K
5
2
PW11Co(H O)O39
78
89
6
K
5
2
PW11Cu(H O)O39
73
90
(
2 2
O
7
K
PW11O
7 39
58
92
8
H PW12O
3 40
21
91
For the oxidation reaction with hydrogen peroxide as
oxidant, both radical and nonradical processes could be
9
Mg
Zn
Zn
2
Al-LDH-NO
Al-LDH-NO
Cr-LDH-NO
3
<10
<10
30
99
1
1
0
1
2
3
99
involved. To reveal the mechanism of the reaction, several
−
96
radical scavengers including p-benzoquinone for •O
2
/•O
2
H and
2
3
tert-butyl alcohol and diphenylamine for •OH were used in the
oxidative detoxification of CEES. As shown in Table S1, the
conversion of CEES is nearly unchanged after adding radical
scavengers, indicating that it’s not a radical reaction process.
Therefore, we proposed a possible nonradical mechanism:
hydrogen peroxide is activate by the intercalated PW11M cluster
to form active peroxo-species, which subsequently oxidize CEES
to CEESO. Our speculation is supported by previous
investigations that both the polyoxotungstates and the
substituted transition metals on POMs can react with hydrogen
Reaction conditions: Catalyst (0.0015 mmol), CEES (0.5 mmol), and 1,3-
2 2
dichlorobenzene (0.25 mmol), 3% aqueous H O (0.525 mmol) and acetonitrile (4
mL) at room temperature.
The degradation profile for Zn
is shown in Figure 4c, where about 50% of CEES is converted in
0 min. The undesired product, toxic CEESO , is formed in the
2
Cr-LDH-PW11Ni, composite 1,
4
2
first 30 min but during the following 2.5 h its amount is nearly
unchanged even though the concentration of CEESO is greatly
increased. This is different from the phenomenon reported in
niobium saponite clay, where the selectivity for CEESO is
dramatically decreased when the conversion of CEES reached
6
4-66
peroxide to form active peroxo-species.
3
maximum. Compared with the reported catalytic materials,
Conclusions
2
Zn Cr-LDH-PW11Ni composite has the following two advantages:
1
) exhibiting a higher selectivity for nontoxic CEESO (94%); 2) In summary, three novel decontaminating composites, Zn Cr-
2
using green dilute H
saponite clay gave a selectivity of 71% by using 5 equiv. 30% intercalating Keggin-type PW M into Zn Cr-LDH host and
2 2
11
O (3%) as oxidant. For example, niobium LDH-PW M (M = Ni, Co, Cu), were successfully fabricated by
1
1
2
H
2
O
2
and PW12@NU-1000 formed by incorporating H
into MOF has a selectivity of 57% in the presence of 1.5 equiv. oxidative degradation of CEES (a sulfur mustard simulant),
0% H , and H PV 40 supported on porous carbon Zn Cr-LDH-PW Ni exhibits a better catalytic performance
3
PW12O
40 thoroughly characterized by routine techniques. In the
3
O
2 2
5
2
Mo10O
2
11
materials oxidize sulfur mustard simulant by tert- (conversion: 98%, selectivity: 94%) than other two
butylhydroperoxide.3
, 32, 43
2 2
In addition, the efficiency of H O
counterparts. Notably, Zn Cr-LDH not only acts as an excellent
2
utilization in the composite 1 system is as high as 98.9%.
host for the stable immobilization of PW M polyanions but also
1
1
A leaching test was performed to check the heterogeneous contributes to the enhancement of catalytic activity. The Zn Cr-
2
2
11
nature of Zn Cr-LDH-PW11Ni. When the reaction was carried out LDH-PW Ni with stable structure and good recyclability is a
for 0.5 h with the conversion of about 43%, the catalyst was promising catalytic material for the effective decontamination
filtered off and the filtrate continued to react under the same of sulfur mustard and has potential application in the
conditions for 2.5 h giving a negligible conversion of CEES fabrication of personal protective equipment.
(Figure 5a). The result displays that the synthesized catalytic
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ARTICLE
Journal Name
2
7 N. Mizuno, K. Kamata and K. Yamaguchi, Top CaVtiaewl,A2rt0ic1le0O,n5lin3e,
Conflicts of interest
There are no conflicts to declare.
8
76-893.
DOI: 10.1039/C9DT00395A
28 H. N. Miras, J. Yan, D. L. Long and L. Cronin, Chem Soc Rev,
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