Catalyst for the degradation of 1,1-dimethylhydrazine and its by-product N-nitrosodimethylamine in propellant wastewater

Article abstract of DOI:10.1039/c5ra20481j

A three-component metal catalyst was prepared and used in the process of catalytic wet peroxide oxidation (CWPO) for the degradation of unsymmetrical dimethylhydrazine (UDMH) in propellant wastewater with H₂O₂. It was structurally characterized using scanning electron spectroscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDX), and its catalytic activity was evaluated using indexes such as the efficiency of UDMH degradation and chemical oxygen demand (COD) removal and the concentrations of ammonia (NH₃-N), formaldehyde (HCHO), total nitrogen (TN), total organic carbon (TOC) and N-nitrosodimethylamine (NDMA). Besides, the reaction system was monitored using UV-Vis full wavelength scanning spectroscopy and liquid chromatography-mass spectroscopy (LC-MS). As a result, it was observed that the degradation mechanism involved OH attacking the amino group and homocoupling in UDMH with the simultaneous transformation of the active component Cu^II/I. Based on investigation of the reaction factors (H₂O₂ dosage, temperature, catalyst dosage, pH and initial concentration of UDMH) focusing on the removal of NDMA, the optimal conditions for CWPO with a three-component metal catalyst were determined. The high treatable concentration of UDMH (500 mg L^-1), rapid rate and good reusability with a high efficiency of UDMH degradation and COD removal (99.9% in 10 min and 94.6% in 30 min, respectively) and the low concentration of NDMA are merits of the present catalyst.

Full text of DOI:10.1039/c5ra20481j

View Article Online
View Journal
RSC Advances
This article can be cited before page numbers have been issued, to do this please use: M. L. Liang, M.
Wu, H. ni, W. J. LI, Q. Qi, P. C. Zeng, Y. C. Zhou and Y. Zheng, RSC Adv., 2015, DOI: 10.1039/C5RA20481J.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. This Accepted Manuscript will be replaced by the edited,
formatted and paginated article as soon as this is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/advances

Page 1 of 29
RSC Advances
View Article Online
DOI: 10.1039/C5RA20481J
Catalyst for the Degradation of 1,1ꢀdimethylhydrazine and its Byꢀproduct
NꢀNitrosodimethylamine in Propellant Wastewater
Meiling Liang, Weijie Li, Qi Qi, Pingchuan Zeng, Yucheng Zhou, Yingping zheng,
Min Wu*, Henmei Ni*
School of Chemistry and Chemical Engineering, Southeast University, Nanjing
2
11189, P. R. China
Eꢀmail: Min WU, wuminnj@163.com, Henmei_ni@hotmail.com

RSC Advances
Page 2 of 29
View Article Online
DOI: 10.1039/C5RA20481J
Abstract
The threeꢀcomponent metal catalyst was prepared and used in the process of
catalytic wet peroxide oxidation (CWPO) for the degradation of unsymmetrical
dimethylhydrazine (UDMH) in propellant wastewater with H O . It was structurally
2
2
characterized by scanning electron spectroscopy (SEM), Xꢀray diffraction (XRD),
Xꢀray photoelectron spectroscopy (XPS) and energyꢀdispersive Xꢀray (EDX), and its
catalytic activity was evaluated with the indexes such as the efficiency of UDMH
degradation and chemical oxygen demand (COD) removal, the concentration of
ammonia (NH ꢀN), formaldehyde (HCHO), total nitrogen (TN) , total organic carbon
3
(TOC) and NꢀNitrosodimethylamine (NDMA). Besides, the reaction system was
traced by UVꢀVis full wavelength scanning spectroscopy and liquid
chromatographyꢀmass spectroscopy (LCꢀMS). As a result, it was observed that the
degradation mechanism was created by ·OH attacking the amino group and
II/I
homocoupling in UDMH with the mutual transformation of active ingredient Cu
.
Based on the investigation of reaction factors(H O dosage, temperature, catalyst
2
2
dosage, pH and the initial concentration of UDMH) focusing on the removal of
NDMA, the optimal conditions for CWPO with threeꢀcomponent metal catalyst were
determined. The high treatable concentration of UDMH (500 mg/L), rapid rate and
good reusability with the high efficiency of UDMH degradation and COD removal
(99.9 % in 10 min and 94.6 % in 30 min, respectively) and the low concentration of
NDMA were the plausible performance of present catalyst.
Keywords: High concentration of UDMH, Threeꢀcomponent metal catalyst, CWPO,

Page 3 of 29
RSC Advances
View Article Online
DOI: 10.1039/C5RA20481J
Degradation mechanism, NDMA.
. Introduction
As the principal component of liquid rocket propellant, unsymmetrical
1
dimethylhydrazine (1,1ꢀdimethylhydrazine, UDMH) is widely used in the launching
tests of missiles and satellites due to its good thermal stability, large combustion heat
1, 2
and high specific impulse . With the rapid development of aerospace industry, the
huge consumption of UDMH unfortunately results in a large amount of waste water.
In the past, it was discharged without any treatment because UDMH is readily
oxidized in the air. However, nowadays it is found that the possible compounds
derived from the degradation of UDMH are suspected to be harmful to the
3
environment and human health . As an example, among them,
NꢀNitrosodimethylamine (NDMA) is extremely dangerous because it is a potent
4
, 5
carcinogen . Numerous methods have been tried to deplete it, including physical and
chemical treatment, and photocatalytic degradation. However, the degradation
1, 2,
efficiency is still unsatisfactory, let alone many shortcomings of those approaches
6
ꢀ10
.
For example, the traditional physical techniques known for the UDMH removal
6
such as the adsorption by activated carbon, ion exchange and incineration are not
appropriate for the treatment of UDMH wastewater due to the regeneration issues of
activated carbon and ion exchange resins as well as the pollution problems caused by
incineration. Chemical treatment with chloramines, fenton, ozone, heterogeneous
2
, 7ꢀ9
catalytic oxidation may be used for the removal of UDMH from water
. However,
these methods are mainly disadvantageous to generate Nꢀnitrosodimethylamine

RSC Advances
Page 4 of 29
View Article Online
DOI: 10.1039/C5RA20481J
10
(
NDMA), an intermediate of UDMH oxidation . It is even more toxic than UDMH.
Photocatalysis, such as O
3
/UV and H
2
O
2
/UV, is reported as an efficient method for the
1
degradation of UDMH with the merit minimizing the formation of NDMA . A
mechanism of degradation of UDMH by H
2 2
O is suggested as following (Eq. 1～17),
H O → 2
OH
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
2
2
H O +
OH →
OOH + H O
2
2
2


OH +
OOH → O + H O
2
2
2
H O → 2H O + O
2
2
2
2
(
CH3 )2 NNH +
OH →
(
CH3 )2 NN
H + H O
2
2
(
CH3 )2 NN
H +
OOH →
CH3 )2 NN OOH →
CH3 )2 NN OOH →
(
CH3 )2 NN
(
H OOH
)
−
+
(
(
H
)
(
CH3 )2 NN OOH + H
−
−
(
(
CH3 )2 NN = O + OH
CH3
CH3
H
CH3
N N O +¡ ¤O H
CH3
NH¡¤+ ¡ N¤ O
CH3
(9)
N
CH3
CH3
NO
NH¡¤+ ¡ ¤N O
CH3
H C NHCH + HNO
2
3
(10)
H C NHCH + H O
CH NH + HCHO + H
3 2
2
3
2
(11)
(
CH3 )2 NN
H +
OH →
CH3 )2 N = N ↔
CH3 )2 N = N → CH N = N +
CH3
(
CH3 )2 N = N + H O
(12)
2
2
(
(
CH3 )2 NN = NN
(
CH3 )2
(13)
(14)
(15)
(16)
(17)
(
3
CH N = N →
CH + N
3
3
2


CH +
OH → CH OH
3
3
CH OH +
OH → HCHO
3

Page 5 of 29
RSC Advances
View Article Online
DOI: 10.1039/C5RA20481J
However, for the largeꢀscale industrial applications, the low concentration of
UDMH in wastewater makes these methods inefficient. Therefore, the destruction of
the subꢀstandard UDMH becomes a very urgent task with a new catalytic system, and
also the main topic of this paper.
Comprehensively taking account of the factors such as the degradation
efficiency, byꢀproducts, cost and capacity of treatment, and also employing
2 2
ecoꢀfriendly H O as the oxidant, the catalytic wet peroxide oxidation (CWPO) is
considered as the most potential method for the practical applications and attractive to
11
II
many researchers . It is reported that Cu was an effective ion to promote UDMH
decomposition by homocoupling reaction of UDMH with the mutual transformation
II/I
12
II
of active ingredient Cu
(Eq. 18 and Eq. 19) . Moreover, the capacity of Cu for
breaking UDMH molecules down is significantly enhanced by increasing hydrogen
1
3
peroxide . On the other hand, it is wellꢀknown that amides can be reduced to the
II
corresponding inorganic amines in the presence of Zn
catalysts under mild
II
conditions, and Ni is a stronger hydrogenation catalyst to promote degradation of
14ꢀ16
NDMA(Eq. 20
～
22)
. Therefore, in order to promote the performance of catalyst
in the decomposition of UDMH, simultaneously the ability of decomposing NDMA,
II
II
II
it may be a good choice to combine Cu
with Ni
and Zn
to make a
II
II
II
multiꢀcomponent catalyst. Adding Zn and Ni into Cu catalyst, a possible
mechanism of degrading UDMH may be figured out as following,
2
+
+
2
+
+
5
(
CH3 )2 NNH +16Cu → 2(CH )NN = CH − N = N(CH ) +16Cu +14H + N (18)
2
3
3
2
+
+
2+
4
Cu + O + 4H → 4Cu + 2H O
(19)
2
2

RSC Advances
Page 6 of 29
View Article Online
DOI: 10.1039/C5RA20481J
CH3
CH3
N
(
20)
O
NiHads
N
O
Ni
Ni
+
N
N
H
CH3
CH3
CH3
CH3
O
O
(
21)
NiHads
N
Ni
+
N
Ni
N
H
N
H
H
CH3
CH3
CH3
CH3
NH
O
Ni
Ni
O
H
N
Ni
+
Ni
(22)
H
N
H
N
CH3
CH3
This is right the purpose of present research, in which the catalytic properties of
CuOꢀZnOꢀNiO/γꢀAl O were tested in the oxidation of UDMH with H O .
2
3
2
2
2
2
. Experimental
.1. Materials and reagents
2 4 3 2
Aluminium (Ⅲ ) sulphate decahydrate (Al (SO ) ·18H O), Dimethylamine
3 2 3
borane ((CH ) NHBH , DMAB), Polyethylene glycol (PEG200(1000), Copper(Ⅲ )
nitrate trihydrate (Cu(NO ) ·3H O), Zinc(Ⅲ ) nitrate hexahydrate (Zn(NO ) ·6H O),
3
2
2
3 2
2
3 2 2 2 2
Nickel(Ⅲ ) nitrate hexahydrate(Ni(NO ) ·6H O), hydrogen peroxide (H O , 30 %,
wt %), and ethanol (AR) were all purchased from Sinopharm Chemical Reagent Co.
Ltd, and used without any further treatment. Distilled water was used for all the
experiments.
2
.2. Preparation of γꢀAl
2
O
3
and CuO/ZnO/NiO/γꢀAl
2 3
O nanoparticles
γꢀAl and CuO/ZnO/NiO/γꢀAl O
2
O
3
2 3
nanoparticles were prepared in accordance
17
with Ref . Namely, 15.0 g PEG 1000 and 150 mL PEG 200 as a surfactant were
added into the aqueous solution consisted of Al (SO ) ·18H O (33.3 g), DMAB
2
4 3
2

Page 7 of 29
RSC Advances
View Article Online
DOI: 10.1039/C5RA20481J
(118.0 g) and 500 mL distilled water in a 1000 mL threeꢀnecked round bottom flask
with heat jacket. After stirring for 30 min with an anchorꢀtype mechanical stirrer, the
reaction was performed at 80 °C for 1 h, and then, rapidly cooled to room temperature
with flowing tap water. The resultant white precipitate was separated by
centrifugation and washed trice with distilled water and ethanol. After dried at 80 °C
for 12 h in air, the product was ground to powders and calcined at 950 °C for 2 h.
2 3
The same process was applied to prepare the CuO/ZnO/NiO/γꢀAl O
nanoparticles with the altered recipe. The aqueous solution was formulated with
Cu(NO ) ·3H O (0.32 g) , Zn(NO ) ·6H O (0.37 g) and Ni(NO ) ·6H O (0.39 g) in
3
2
2
3 2
2
3 2
2
water.
2
.3. Characterization of catalysts
Xꢀray diffraction (XRD, Rigaku Miniflex 600) using Cu K
α
was employed to
analyze the structure of catalyst at 2θ angle from 5° to 80°. The surface elements and
their states were analyzed by Xꢀray photoelectron spectroscopy (XPS, Thermo
ESCALABꢀ250) with Al Ka (1486.6 eV) irradiation source. A scanning electron
microscopy (SEM, Hitachi Sꢀ4800) was applied to discover the surface morphology
and energyꢀdispersive Xꢀray (EDX, Hitachi Sꢀ4800) to evaluate the chemical
composition on the catalyst surface.
2
.4. Catalytic wet peroxide oxidation
The catalytic oxidation of UDMH was carried out in a 250 mL threeꢀnecked
round bottom flask with 100 mL 500 mg/L of simulated UDMH wastewater, 1 g

RSC Advances
Page 8 of 29
View Article Online
DOI: 10.1039/C5RA20481J
2 3 2 2
CuOꢀZnOꢀNiO/γꢀAl O catalyst and 4 mL H O (30 %, wt %). In order to avoid the
loss of volatile UDMH by evaporating in the experiments, and keep the reaction
temperature at constant as well, a total reflux system and thermostatic waterꢀbath
were employed. The reaction solution, 10 mL, sampled at given time intervals was
2 2 2
treated by adding MnO to remove the H O residual, and then centrifuging for 10
min at 3,000 rpm to separate the catalyst from the aqueous solution. Both of the
catalyst and aqueous solution were analyzed to evaluate the performance of catalyst
such as the percentage conversion of UDMH and removal efficiency of chemical
oxygen demand (COD). UDMH concentration was determined by spectrophotometry
with sodium amino ferrocyanide according to Chinese standard GB/T 14376ꢀ93,
whilst the COD was detected by a standard method using COD reagents. They were
calculated over the following equations:
(
C ꢀCt
)
×100%
0
UDMH deg radation efficiency
(
%
)
=
C0
(
COD ꢀCOD
)
×100%
0
t
COD deg radation efficiency
(
%
)
=
COD0
Where
UDMH wastewater
time
C
0
and COD
0
are the initial UDMH and COD concentration (mg/L) of the
and COD are the UDMH and COD concentration (mg/L) at
,
C
t
t
t.
The component variation of reaction system was monitored by a UVꢀvisible
spectrophotometer, where the solutions sampled at different time intervals and treated
with MnO were used. The amount of total nitrogen (TN), ammonia (NH ꢀN)
and formaldehyde (HCHO) in the reaction system were determined respectively
2
3

Page 9 of 29
RSC Advances
View Article Online
DOI: 10.1039/C5RA20481J
according to Chinese standard HJ 636ꢀ2012, HJ 535ꢀ2009 and HJ 601ꢀ2011. The
amount of main intermediate NDMA was detected by highꢀperformance liquid
18
chromatography (HPLC) and other intermediate products were evaluated by liquid
1
9
chromatography–mass spectrometry (LCꢀMS) . Total amount of organic carbon
2
0
（
TOC
）
was measured by TOC analyzer .
In the experiments of degrading UDMH, the effect of different variables
including H dosage (0ꢀ6 mL), reaction temperature (25ꢀ70 °C), catalyst dosage
0ꢀ1.5 g), initial pH value (4ꢀ10) and initial UDMH concentration (200ꢀ1000 mg/L)
2 2
O
(
were investigated. Catalyst recycling experiment was implemented to detect the
stability and reusability of the synthesized catalyst.
3
. Results and Discussions
First of all, it should be remarked that the components of catalyst were
II
determined by a series of preliminary experiments including single component (Cu ),
II
II
II
II
twoꢀcomponent (Cu ꢀZn and Cu ꢀNi ) and threeꢀcomponent catalysts. When
single component and twoꢀcomponent were supported on γꢀAl , the degradation
2
O
3
efficiency of UDMH and COD were not ideal, namely that couldn’t meet the national
emission standards of UDMH content and COD, in addition NDMA content was
relatively high. The efficiency of threeꢀcomponent was the best. Since those data were
regardless to the content of this paper, for succinctness and also the secrecy of patent,
they were excluded.
3
.1. Catalysts characteristics

RSC Advances
Page 10 of 29
View Article Online
DOI: 10.1039/C5RA20481J
In order to evaluate the effects of loading Cu, Zn and Ni, as an example, the
SEM images of γꢀAl and a typical CuO/ZnO/NiO/γꢀAl are presented
respectively in Figure 1 at different magnifications. The support, γꢀAl , appears as
O
2 3
2 3
O
2
O
3
irregular shape of alumina particles (a) and has a large gap (A) leading to a strong
adsorption. When copper, zinc and nickel oxides at low loadings were impregnated,
no significant change could be observed in the shape (b).
Figure 1. SEM images of γꢀAl
2 3
O (A, a) and
2C0nmuO/ZnO/NiO/γꢀAl (B, b) catalysts at different
2
O
3
magnification.
The surface distribution of elements was identified by EDX. As shown in
Figure 2, Cu, Zn and Ni peaks can be clearly seen from Fig. 2b. Moreover, the mass
fraction of these elements doped on γꢀAl
content. It indicated that copper zinc and nickel atoms are dominantly distributed on
the surface of γꢀAl
2 3
O is basically identical with the nominal
，
2
3
O .
Figure 2. EDX patterns of γꢀAl
2 3
O and
CuO/ZnO/NiO/γꢀAl catalysts.
2 3
O
2 3 2 3
The XRD patterns of γꢀAl O and CuO/ZnO/NiO/γꢀAl O are exhibited in

Page 11 of 29
RSC Advances
View Article Online
DOI: 10.1039/C5RA20481J
Figure 3. The characteristic peaks peculiar to γꢀAl
2
O
3
, i.e. 2θ=37.38°, 45.86° and
was prepared successfully. When
copper, zinc and nickel atoms were introduced into γꢀAl , as shown in Fig. 3, no
17, 21
6
7.16°, were observed
2 3
. It indicated that γꢀAl O
2
O
3
significant change was found in the XRD pattern. It indicated that the lattice of
γꢀAl O was not interfered with the addition of Cu, Zn and Ni. Additionally, the
2
3
diffraction from the crystalline CuO, ZnO and NiO was not observed in the spectrum.
All the above results evidenced that Cu, Zn and Ni were highly dispersed and
22
adsorbed on the surface of γꢀAl
2 3
O . The loading mass percentage was too low to
form the independent crystalline phase.
Figure 3. XRD patterns of γꢀAl
2 3
O and
CuO/ZnO/NiO/γꢀAl catalysts.
2
O
3
In order to evaluate the performance of metal ions during the reaction, XPS of
catalyst at proꢀ and
postꢀreaction were also carried
out. As shown in Fig. 4 that the
valence of three elements of
the catalyst have not changed
before and during reaction, the
2 3
Figure 4. XPS spectra of CuO/ZnO/NiO/γꢀAl O
catalyst at proꢀ and postꢀreaction.
binding energy at about 856.1 eV and 862.1 eV were observed, assigned to the main

RSC Advances
Page 12 of 29
View Article Online
DOI: 10.1039/C5RA20481J
2+
23
line of Ni (2p3/2) and its satellite, respectively . The Figure 4 also displays the Cu
XPS spectra (930–970 eV) and the Zn XPS spectra (1016–1028 eV). The
2+
2+
characteristic peaks peculiar to Cu (2p3/2) and Zn (2p3/2) , i.e. BE=933.3 eV and
24, 25
1
021.9 eV, were observed
. This result suggests that the catalyst itself is not
changed and only plays the role in changing the reaction rate during the reaction.
3
.2. Trials of UDMH catalytic oxidation
As described in the section of introduction, the UDMH and COD are readily
removed from the wastewater by various means.
However, the removal of NDMA derived from the
decomposition of UDMH is hard. Therefore, in
order
to
test
the
performance
of
Figure 5. UVꢀvis full
wavelength scanning under
different times
CuO/ZnO/NiO/γꢀAl
2
O
3
catalyst,
a
preliminary
experiment was carried out by dropwise adding
H
2
O
2
with peristaltic pump. The conditions are: UDMH: 500 mg/L, H O : 4 mL,
2 2
catalyst: 1 g, pH: 8.5, 60 °C, and the UVꢀvis full wavelength scanning was carried out
to trace the reaction process. However, it should be remarked that, since no peak
appears from 500 to 800 nm, only the spectra in the range from 200 to 500 nm
wavelength is selected. As shown in Figure 5, it is characterized as the disappearance
of peak of 0 time at 215 nm within only 2 min, instead, the platform peak from 220
nm to 280 nm appeared during the catalyzed reaction. Moreover, the broadness of
platform peak gradually becomes small and smooth, companying with decrease of
absorbance strength from 5 to 30 minutes. Furthermore, a special peak in the vicinity

Page 13 of 29
RSC Advances
View Article Online
DOI: 10.1039/C5RA20481J
of 350 nm with high absorbance suddenly appears at the reaction time 2 min. In
addition, this peak becomes weak at 5 minutes, and finally disappears at 10 minutes.
This result qualitatively indicated that UDMH immediately reacted in the system,
turning into the unstable intermediate compounds.
In order to further clarify the intermediate compounds, ESI (+) mass
spectroscopy was carried out with
61.1
486
100
1
solution of UDMH oxidation sampled
at 5 minutes. As shown in Figure 6,
with the original UDMH solution, only
two substances, i.e. UDMH and NDMA,
were observed. However, a lot of
substances was found in the solution
sampled at 5 min. Among them, the
7
5.1
0
m/z
5
0
60
70
80
90 100 110 120 130 140 150 160 170 180 190 200
8
9.0
110
1
00
8
8.0
3
8
6.0
7
1.0
102.0 105.0
91.0
75.1
117.0 122.0
130.0
60.1
1
49.1
107.0
79.0
99.1
2.6
148.0
180.0
9
129.0 134.0
1
68.0 177.2
190.0196.6 202.2
5
6.0
109.0
136.1
163.0
0
5
m/z
0
60
70
80
90
100 110 120 130 140 150 160 170 180 190 200
Figure 6. ESI (+) mass spectra of
possible
products of UDMH reported in the
references were detected, such as Nꢀnitrosodimethylamine (NDMA),
oxidation
intermediate
original UDMH and products of UDMH
oxidation in 5 minutes.
1
1
,1ꢀdimethylguanidine (DMG), 1ꢀFormylꢀ2,2ꢀdimethylhydrazineand1(FDMH), and
12, 19, 26
,4,4ꢀtetramethylꢀ2ꢀtetrazene (TMT)
. The fragment intensity ratios are
presented in Table 1. These products further explained the emergence of platform and
special peak in Figure 5. Besides, it confirmed the mechanism of degradation that
hydroxyl radicals mainly attacked the amino group of UDMH molecule. Of course, all
of these substances would be further oxidized to the corresponding small molecules

RSC Advances
Page 14 of 29
View Article Online
DOI: 10.1039/C5RA20481J
which were not reflected in the mass spectrum because of small molecular weight. For
example NDMA and TMT were broken down into methylamine and formaldehyde
13, 27, 28
respectively by Eq. 9
～
11 and Eq. 12
～
17
. Additionally, reminiscent of Figure
5
, it can be conclude that UDMH and most of its subsequent intermediate products
could be thoroughly degraded by the present catalyst.
Table 1. Possible oxidation intermediate products of UDMH in 5 minutes
Precursor Fragment
Structural
formula
Molecular
weight
The substance name
ion
intensity
ratio
m/z
Nꢀnitrosodimethylamine
N
N
7
4.1
87.1
8.1
16.2
75.1
88
38.5
92.5
100
37
O
NH2
NH
1
,1ꢀdimethylguanidine
ꢀFormylꢀ2,2ꢀdimethylhydrazine
,1,4,4ꢀtetramethylꢀ2ꢀtetrazene
N
N
1
NH
8
89
O
1
N
N
1
117
N
N
On the basis of the unique amino group of UDMH, in order to further illustrate
the degradation of UDMH, the quality indexes of
wastewater treatment such as NH ꢀN, TN and TOC
3
were separately detected. The results are shown in
Figure 7, including the variation of main
byproducts of UDMH decomposition, NDMA (Eq.
Figure 7. The change of
NH ꢀN, HCHO, TN, TOC,
3
11ꢀ13
13, 27, 28
NDMA in the process of
5
～
8)
and HCHO(Eq. 9
～
17)
according
UDMH oxidation.
to the mechanism described in the part of
introduction. It is clear that, in general, all the indexes decreased as the reaction
proceeded, except that of NDMA. The content of NDMA increased from 0 to 5 min.
th
After leveled off in 5 min, it gradually decreased to a stable value at 30 min. The

Page 15 of 29
RSC Advances
View Article Online
DOI: 10.1039/C5RA20481J
3
concentration of NH ꢀN, TN and TOC decreased rapidly at first 2 minutes, and then
declined slowly. Meanwhile HCHO suddenly appeared at 2 min. Its content decreased
gradually and finally reached equilibrium. These results indicated that UDMH was
degraded readily by present catalytic system. And also, the mechanism of degradation
as ours induced in the part of introduction was correct due to the generation of
NDMA in the process of degradation.
Figure 8 shows the variation of COD and degradation efficiency of UDMH in
the reaction. As shown in Figure 8, with the increase of reaction time, the degradation
efficiency of UDMH increased rapidly. It reached more than 98.7 % merely in 10
minutes. However, for the COD removal efficiency, it is fairly time expended. It
reached 95.0 % in 30 minutes until attained the national standard of emission level
which is as low as 50 mg/L. At a glimpse of the curve, three stages are obvious, i.e.
the rapid increase from 0 to 10 min, the leveled off
stage from 10 to 20 min and finally rapid increase
from 20 to 30 min. The first stage (rapid increase) is
likely ascribed to the removal of COD in the original
2 2
wastewater with a little amount of H O . The second
Figure 8. UDMH and COD
degradation efficiency under
different times
stage (leveled off) is possibly attributed to the
generation of intermediates. As discussed above,
UDMH was decomposed readily in a few minutes, but a large amount of various
intermediate compounds was produced in the system. Therefore, the leveled off stage
implies that, at least, the intermediate compounds are hard to be decompose such as

RSC Advances
Page 16 of 29
View Article Online
DOI: 10.1039/C5RA20481J
NDMA shown in Figure 7 under the present catalytic conditions. Certainly,
reminiscent of dropwise addition of H , it is also apparent that the inadequate
amount of H was a possible reason. As shown in Fig. 8, the efficiency of COD
removal rapidly increased from 20 to 30 min after this stage. This result indicated that
the concentration of H was the main factor to improve the COD removal efficiency.
2
O
2
2
O
2
2
O
2
Anyway, the level of COD was finally decreased to the level required by the standard.
This was a great result encouraging us to do the further research.
Summarizing all the data reflected by the figures, it is reasonable that with the
increase of concentration of H O and the reaction time, oxidation of ·OH from H O
2
2
2
2
improved increasingly. UDMH and the intermediate products could be relatively
1
thoroughly degraded. Moreover, compared with the fenton method and
2
9
photocatalysis method , the present process was advantageous to save time and
achieve the higher degradation efficiency. For example, by present process, it only
took 30 minutes to attain ca 98% of the degradation efficiency, whereas by the
aboveꢀmentioned methods, more than 1 h was needed and those degradation
efficiencies was lower than ours under the same concentration of UDMH wastewater.
2 3 2 2
Therefore, the combination of the CuO/ZnO/NiO/γꢀAl O catalyst and H O was a
good choice to treat the UDMH wastewater. The following optimization was carried
out to achieve more desirable results and meet emissions standards of NDMA.
3
.2.2 Effect of H
2 2
O dosage
The degradation efficiency of UDMH is closely related to the powerful
11
2 2
oxidization of ·OH derived from H O (Eq. 1) . Theoretically, the total amount of

Page 17 of 29
RSC Advances
View Article Online
DOI: 10.1039/C5RA20481J
H
2
O
2
is 0.75 mL for completely oxidizing 100 mL, 500 mg/L of UDMH to the
volatile substances. However, it is reported that the amount as much as more than
2 2
several times the stoichiometric ratio of H O was needed in most cases due to the
2
inadequate applicability . Figure 9 (a and b) presents the effects of H O dosage on
2
2
the catalytic degradation of UDMH in wastewater and the generation of intermediate
product (NDMA) by using our catalyst and CWPO process. It is clear that, with only
1
mL H
2
2
O , UDMH was completely degraded, but the COD removal efficiency (Fig.
9
a) was aggrandized gradually as the volume of H
2
O
2
increased from 0 to 6 mL. It
attained to a maximum value, 96.5%, as 6 mL H O was added. In contrast, as shown
2
2
in Fig. 9b, the concentration of NDMA attained to the maximum value only
expending 1 mL H . This result was coincident to the former shown in Fig. 8,
further confirming that the main product of UDMH oxidation was NDMA. However,
a problem arises that why the excessive H is needed. It is possibly ascribed to a
factor that the intermediate products of UDMH oxidation are much more difficult to
be oxidized than UDMH by H . Since the oxidation rate of intermediate products is
slow, the scavenging effect occurs as shown in Eq. 2
hydroxyl radicals reacted with H and UDMH to produce ·OOH (Eq. 2 and Eq. 5).
It quenches ·OH to form O (Eq. 3), giving rise to severe loss of H . Consequently,
excessive amount of H O is required to complement the loss of ·OH. This
2
O
2
2
O
2
2
O
2
1
1, 13
～
3 and Eq. 5
. Some of
2
O
2
2
2 2
O
2
2
explanation is supported by the oxidation of NDMA. As shown in Fig. 9b, with the
increase of H , NDMA content rose fleetly from 2.2 mg/L to 38.0 mg/L, and then
decreased gradually to a stable value of 2.4 mg/L. According to the mechanism, ·OH
2
O
2

RSC Advances
Page 18 of 29
View Article Online
DOI: 10.1039/C5RA20481J
1
, 27
attacks amino group of UDMH according to the reactions (Eq. 5
～8) , thereby
UDMH was transferred into NDMA. The concentration of NDMA reached the
maximum value, ca 40 mg/L, when 1 mL H was added. It indicated that UDMH
was mostly transferred into NDMA. Therefore, the excessive amount of H was
actually applied to oxidize NDMA. This result further confirmed that, as shown in Fig.
2
O
2
2
O
2
9
b, NDMA contributed the main part of COD after UDMH was exhausted.
Taking all the factors such as the efficiency of UDMH degradation and COD
removal as well as the generated content of NDMA into consideration,
comprehensively the optimal volume for CWPO of 100 mL, 500 mg/L of UDMH
wastewater was determined, i.e. 5 mL of H O , which was about 6.7 times as much as
2
2
the theoretical dosage.
Figure 9. Effect of H
CuO/ZnO/NiO/γꢀAl
efficiency; (b) NDMA concentration (UDMH: 500 mg/L; temperature:
0 °C; catalyst: 1 g; pH: 8.5; time:30 min).
2
O
2
dose on catalytic oxidation of UDMH by
2
O catalyst: (a) UDMH and COD degradation
3
6
3
.2.3. Effect of temperature
The generation of ·OH is restricted directly by the temperature. The effect of
temperature on degradation of UDMH and the generation of intermediate product
NDMA) was shown in Figure 10 (a and b). Obviously from 25 °C to 70 °C, both the
(

Page 19 of 29
RSC Advances
View Article Online
DOI: 10.1039/C5RA20481J
efficiency of UDMH degradation and COD removal (Fig. 10a) increased, whilst the
concentration of intermediate product (NDMA) declined gradually (Fig. 10b) with the
increase of temperature. For example, at 25 °C, the efficiency of UDMH degradation
was only 80 %, whilst the percentage of COD removal was about 46 %. The
concentration of NDMA was as high as 75 mg/L. It indicated that, at low
temperatures, neither UDMH nor intermediate products such as NDMA were not
2 2
completely degraded for H O not being converted to ·OH. At 40 °C, UDMH was
almost completely degraded, whereas efficiency of COD removal was only 63.8 %.
Meanwhile, the concentration of NDMA decreased to a half concentration of NDMA
as that at 25 °C because of part of intermediate product(NDMA) being oxidized to
27, 28
methylamine and formaldehyde by extra ·OH (Eq. 9
～
11)
. When the temperature
rose to 65 °C and 70 °C, all indexes such as the efficiency of UDMH degradation,
COD removal and NDMA content were satisfied according to the standard. This is
due to the fact that the generation of ·OH by H O (Eq. 1) is much easier and faster at
2
2
higher temperature, resulting in the improvement of the oxidation efficiency of
UDMH and intermediate product (Eq. 9 11) . Therefore, higher temperature was
～
beneficial to the degradation of UDMH. But too much high temperature didn’t
necessarily contributed to the improvement of the degradation performance because
the thermal decomposition of H O (Eq. 4) was severe , leading to a low utilization of
2
2
1
2
1
H
2
O
. In order to achieve less energy consumption, resources saving and the
excellent degradation effect, 65 °C should be the best temperature for catalytic
degradation of UDMH wastewater by CuO/ZnO/NiO/γꢀAl with H as oxidant.
2
O
3
2 2
O

RSC Advances
Page 20 of 29
View Article Online
DOI: 10.1039/C5RA20481J
9
Compared with Cu
x
Mg1ꢀxCr
2
O
4
/
γꢀAl
2
O
3
catalyst system , the UDMH molecular can be
completely transformed into the deep oxidation products CO
2
, H O and N and don’t
2
2
produce secondary pollutants. However, the low concentration of UDMH in
wastewater and harsh conditions such high temperature makes this method inefficient.
Therefore, the mild reaction condition of the catalyst is necessary for the industrial
requirements.
Figure 10. Effect of temperature on catalytic oxidation of UDMH by
CuO/ZnO/NiO/γꢀAl O catalyst: (a) UDMH and COD degradation
2 3
efficiency; (b) NDMA concentration (UDMH: 500 mg/L; H
2 2
O : 5 mL;
catalyst: 1 g; pH: 8.5; time:30 min).
3
.2.4 Effect of catalyst dosage
The effect of catalyst dosage on the catalytic degradation of UDMH wastewater
and the generation of intermediate product (NDMA) are shown in Figure 11 (a and b).
It was inferred that catalyst dosage was of great importance for the efficiency of
UDMH degradation and COD removal. When the catalyst dosage was increased from
0
6
g to 1.0 g, the efficiency of UDMH degradation and COD removal increased from
9.1 % to nearly 100 % and 54.6 % to 97.5 %, respectively (Fig. 11a). Meanwhile, the
concentration of NDMA decreased from 30 to 2.4 mg/L. These results proved that the
present catalyst was effective in CWPO to degrade UDMH and its main intermediate
product, NDMA, by H O . 1.0 g CuO/ZnO/NiO/γꢀAl O catalyst was appropriate in
2
2
2
3

Page 21 of 29
RSC Advances
View Article Online
DOI: 10.1039/C5RA20481J
II
II
the present system. Since the present catalyst containing Zn and Ni , amides were
1
6
reduced to the corresponding amines under the mild conditions . Furthermore, nickel
is a stronger hydrogenation catalyst, attacking the NꢀN bond of NDMA to form DMA
15
(Eq. 20
～
22)
and ·NO, which subsequently converted to methylamine,
formaldehyde (Eq. 11) and ammonia through sequential electron transfer steps. Two
important aspects of the copperꢀfacilitated reaction are changed in copper oxidation
2+
14
sites and the relative accessibility of the Cu LUMO orbital , thereby leading copper,
zinc and nickel to be more accessible to the NDMA molecules in the solution.
Therefore, catalyst dosage was an considerably important factor for the catalytic
degradation of UDMH wastewater due to forming strong oxidizing ·OH by catalytic
2 2
decomposition of H O (Eq. 1) and generating coupling reaction through the
2
+
12
generation and disappearance of active ingredient Cu (Eq. 18 and Eq. 19) .
Figure 11. Effect of catalyst dosage on catalytic oxidation of UDMH by
2 3
CuO/ZnO/NiO/γꢀAl O catalyst: (a) UDMH and COD degradation
efficiency; (b) NDMA concentration (UDMH: 500 mg/L; H O : 5.0 mL;
2
2
temperature: 65 °C; pH: 8.5; time: 30 min).
3
.2.5. Effect of initial pH
The simulation of initial pH of UDMH wastewater ranging from 4 to 10 was
carried out by adding the diluted solutions of sulfuric acid and sodium hydroxide for
the purpose to evaluate the influence of pH on the degradation performance. The

RSC Advances
Page 22 of 29
View Article Online
DOI: 10.1039/C5RA20481J
results are reflected in Figure 12 (a and b). An apparent feature was that the
generation of NDMA was greatly affected by pH values (Fig. 12b). The optimal
degradation efficiency was obtained at the pH of 7.5, the UDMH conversion and
COD removal reached 99.9 % and 94.6 %, meanwhile NDMA content was about 0.45
mg/L after 30 minutes. Lower and higher pH values were not beneficial to the
degradation of UDMH. When the initial pH of UDMH solution was sour, the COD
and UDMH degradation efficiency generally showed an andante upward trend. Under
heavily acidic conditions the degradation of UDMH was severely prevented which
2
+
could be attributed to inhibition of reaction of Cu and UDMH (Eq. 18) and relative
stability of H which was not easily decomposed into hydroxyl radicals. However,
acidic conditions was favorable to restrain the transformation of UDMH to NDMA
2
O
2
30, 31
(Eq. 7)
.
In addition, the strong alkaline circumstance was also not suitable for the
degradation of UDMH wastewater and inhibiting formation of NDMA. It was
explained that zinc oxide and aluminium oxide reacting with sodium hydroxide
2
ꢀ
ꢀ
became the ZnO
catalyst and breaking support of catalysts. Moreover H
sodium hydroxide generated H O. What’s more alkaline conditions promoted the
2
and AlO
2
which resulted in significantly reducing activity of the
2
O
2
readily reacting with
2
generation of NDMA. Heavily acidic and alkaline conditions were not only beneficial
to the degradation of UDMH and recovery of catalyst. Thus, nearꢀneutral pH
conditions were more suitable for catalytic oxidation of UDMH wastewater. It turned
out that the pH 7.5 was the optimum for the total UDMH oxidation since the reaction

Page 23 of 29
RSC Advances
View Article Online
DOI: 10.1039/C5RA20481J
rate was relatively high as well as the UDMH mineralization degree. As we know,
1, 8
with the fenton method , the catalyst was efficient under the acidic conditions. In the
alkaline solution, the fenton reagents would be deactive. Therefore, the catalyst
developed in this paper is necessarily a complement for the industrial requirements.
Figure 12. Effect of pH value on catalytic oxidation of UDMH by
CuO/ZnO/NiO/γꢀAl
efficiency; (b) NDMA concentration (UDMH: 500 mg/L; H
temperature: 65 °C; catalyst: 1 g; time:30 min).
2
O
3
catalyst: (a) UDMH and COD degradation
2
O
2
: 5.0 mL;
3
.2.6. Effect of initial concentration of simulated UDMH wastewater
The initial concentration of UDMH was adjusted within the range of 200–
000 mg/L and the experiments were performed to meet the emission Standards by all
1
kinds of industries. As shown in Figure 13a, both the efficiency of UDMH
degradation and COD removal ware inversely proportional to their initial
concentrations. As the initial concentration increased from 200 to 1000 mg/L, they
decreased from ca 100 % to 95.5 % and 96.5 % to 85.4 %, respectively. However, the
concentration of NDMA increased constantly (Fig. 13b). These results were natural
since the concentration of H O was constant. Anyway, comprehensively considered
2
2
all the indexes, when the initial concentration of UDMH was lower than 500 mg/L,
the reaction conditions presented in Figure 13 were relatively appropriate to treat
UDMH wastewater. It meant that, by the present catalyst and CWPO, the treatable

RSC Advances
Page 24 of 29
View Article Online
DOI: 10.1039/C5RA20481J
maximum concentration of UDMH in wastewater was 500 mg/L. It was much higher
29
than the upper limitation by photocatalysis , 200 mg/L, let alone the highest
efficiency of photocatalysis was less than 90%. Anyway, this value, 500mg/L, is
satisfactory industrially in most cases as we know.
Figure 13. Effect of initial concentration of UDMH on catalytic
oxidation of UDMH by CuO/ZnO/NiO/γꢀAl
COD degradation efficiency; (b) NDMA concentration (H
temperature: 65 °C; catalyst: 1 g; pH:7.5; time:30 min).
2
O
3
catalyst: (a) UDMH and
2
O
2
: 5 mL;
4
2 3
. Reusability of CuO/ZnO/NiO/γꢀAl O
3
2
Reusability of catalyst is a key factor to determine the feasibility of a catalyst .
Hence, in order to investigate the reusability of catalyst, the experiments were
designed as follows. The catalyst powder after each reaction was recycled by
centrifugation, and then dried. Five runs were conducted to evaluate the longꢀterm
2 3
reusability of CuO/ZnO/NiO/γꢀAl O with the optimal conditions discussed above.
The results are listed in Table 2. It is clear that the little decrease of both efficiency of
UDMH degradation and COD removal were observed after five runs reaction, but the
values were acceptable. The concentration of NDMA remained in the water slightly
increased (Table 2). Two reasons are cited to explain the above conditions. At first, it
can be speculated that a thimbleful of catalyst was lost inevitably in the process of
recycling catalyst. Secondly, a portion of elements was leached in aqueous solution,

Page 25 of 29
RSC Advances
View Article Online
DOI: 10.1039/C5RA20481J
2
+
resulting in lower activity. The content of main active ingredient Cu was detected. It
was observed that it was less than 5% of copper loadings after twenty runs reaction,
indicating a negligible leaching. Although these factors somehow influenced the
catalytic activity, the synthesized CuO/ZnO/NiO/γꢀAl O kept relatively high activity
2
3
at least in five runs and the catalytic efficiency was satisfactory. It is plausible
2
, 12
compared with the methods using ion as a catalyst
.
Table 2. The indicators of the UDMH oxidation after reusing.
Repeating times
1
2
3
4
5
UDMH conversion (%)
COD removal (%)
99.9
94.6
0.45
99.5
93.8
1.26
99.0
92.4
2.04
98.7
91.1
3.05
98.1
90.7
3.92
NDMA content (mg/L)
5
. Conclusions
Threeꢀcomponent metal catalyst (CuO/ZnO/NiO/γꢀAl
method of impregnationꢀcalcination. The structural analysis by XRD, SEM and EDX
indicated that the surface morphology of γꢀAl nanoparticles was maintained at preꢀ
and postꢀtreatment, whilst CuO, ZnO and NiO were dispersed on the surface of
γꢀAl nanoparticle without any aggregation. It was firstly used as a catalyst in the
2 3
O ) was prepared by the
2
O
3
2
O
3
process of catalytic wet peroxide oxidation (CWPO) for the degradation of
unsymmetrical dimethylhydrazine (UDMH) in propellant wastewater with H O . As a
2
2
result, UDMH was degraded rapidly and efficiently due to the highly active ·OH
derived from H . However, a key problem in the process arose from the removal of
2
O
2
COD. Tracing the process of CWPO with the full scan UVꢀVis and ESI (+) mass
spectroscopy, it was found that a hard degradable compound, NDMA, was created by

RSC Advances
Page 26 of 29
View Article Online
DOI: 10.1039/C5RA20481J
the degradation of UDMH. The path of NDMA generation was suggested that the
2
+
hydroxyl radical (·OH) attacked mainly amino group of UDMH and Cu . UDMH
generated coupling reaction through the generation and disappearance of active
2+
ingredient Cu . Based on the investigation of reaction factors, i.e. H O dosage,
2
2
temperature, pH of wastewater, catalyst dosage and the initial concentration of
UDMH. The optimal conditions for CWPO with CuO/ZnO/NiO/γꢀAl were
determined, namely for the wastewater containing 500 mg/L UDMH, the H dosage
was 5 mL, catalyst, 1.0 g, pH 7.5, temperature, 65 . Under these conditions, the
2
O
3
2
O
2
℃
maximal treatable concentration of UDMH was 500 mg/L, with which the high
efficiency of UDMH degradation and COD removal (99.9 % in 10 min and 94.6 % in
3
0 min, respectively) and the low concentration of NDMA (0.45 mg/L) were obtained.
Moreover, the catalyst activity less changed after recycling for 5 times, indicating a
good reusability. According to the Chinese standards for wastewater emission, by the
present catalyst and CWPO process, the levels of UDMH and COD were qualified,
but the concentration of NDMA was still a little higher than that of standards. Hence,
the further improvement of this catalyst is required in the future.
Acknowledgements
The manuscript was perceived and revised by Prof. Henmei Ni.
References
1
.
.
M. T. Angaji and R. Ghiaee, Ultrason. Sonochem., 2015, 23, 257ꢀ265.
2
O. A. Makhotkina, E. V. Kuznetsova and S. V. Preis, Appl. Catal. B-Environ
,
2
006, 68, 85ꢀ91.

Page 27 of 29
RSC Advances
View Article Online
DOI: 10.1039/C5RA20481J
3
.
.
L. Carlsen, O. A. Kenesova and S. E. Batyrbekova, Chemosphere, 2007, 67,
108ꢀ1116.
1
4
W. A. Mitch, J. O. Sharp, R. R. Trussell, R. L. Valentine, L. AlvarezꢀCohen
and D. L. Sedlak, Environ. Eng. Sci., 2003, 20, 389ꢀ404.
5
.
.
C. K. Schmidt and H. J. Brauch, Environ. Sci. Technol., 2008, 42, 6340ꢀ6346.
X. L. Gou, X. M. Lv, H. Cui and X. Li, Appl. Mech. Mater., 2013, 295ꢀ298,
6
1
486ꢀ1489.
7.
8.
9.
I. M. Schreiber and W. A. Mitch, Environ. Sci. Technol., 2005, 39, 3811ꢀ3818.
H. Y. Xu, M. Prasad and Y. Liu, J. Hazard. Mater., 2009, 165, 1186ꢀ1192.
Z. R. Ismagilov, M. A. Kerzhentsev, I. Z. Ismagilov, V. A. Sazonov, V. N.
Parmon, G. L. Elizarova, O. P. Pestunova, V. A. Shandakov, Y. L. Zuev, V. N.
Eryomin, N. V. Pestereva, F. Garin and H. J. Veringa, Catal. Today, 2002, 75,
2
77ꢀ285.
1
0.
D. D. Yifru and V. A. Nzengung, Environ. Sci. Technol., 2006, 40, 7374ꢀ7380.
K. Huang, Y. Xu, L. G. Wang and D. F. Wu, RSC Adv., 2015, 5, 32795ꢀ32803.
O. P. Pestunova, G. L. Elizarova, Z. R. Ismagilov, M. A. Kerzhentsev and V. N.
Parmon, Catal. Today, 2002, 75, 219ꢀ225.
11.
1
2.
1
3.
G. Y. Zhang, L. Wang, Y. F. Xu, C. H. Fan and R. S. Xue, Procedia Environ.
Sci., 2011, 10, 703ꢀ708.
1
4.
5.
C. H. Huang and A. T. Stone, Environ. Sci. Technol., 2003, 37, 1829ꢀ1837.
L. Gui, R. W. Gillham and M. S. Odziemkowski, Environ. Sci. Technol., 2000,
1
3
4, 3489ꢀ3494.

RSC Advances
Page 28 of 29
View Article Online
DOI: 10.1039/C5RA20481J
1
6.
7.
S. Das, D. Addis, S. Zhou, K. Junge and M. Beller, J. Am. Chem. Soc., 2010,
32, 1770ꢀ1771.
H. M. Wang, S. X. Pu, J. W. Li, L. Zhu and J. G. Li, Mater. Lett., 2014, 124,
96ꢀ298.
1
1
2
1
8.
9.
J. Nawrocki and P. Andrzejewski, J. Hazard. Mater., 2011, 189, 1ꢀ18.
A. D. Smolenkov, I. A. Rodin, A. V. Shpak and O. A. Shpigun, Int. J. Environ.
Anal. Chem., 2007, 87, 351ꢀ359.
1
2
0.
1.
G. StꢀJean, Rapid Commun. Mass Spectrom., 2003, 17, 419ꢀ428.
B. Y. Jibril, A. Y. Atta, Y. M. AlꢀWaheibi and T. K. AlꢀWaheibi, J. Ind. Eng.
Chem., 2013, 19, 1800ꢀ1804.
2
2
2.
3.
S. K. Kim, K. H. Kim and S. K. Ihm, Chemosphere, 2007, 68, 287ꢀ292.
D. Srinivas, C. V. V. Satyanarayana, H. S. Potdar and P. Ratnasamy, Appl.
Catal. A-Gen., 2003, 246, 323ꢀ334.
2
24.
25.
26.
M. FernandezꢀGarcia, I. RodriguezꢀRamos, P. FerreiraꢀAparicio and A.
GuerreroꢀRuiz, J. Catal., 1998, 178, 253ꢀ263.
T. Q. Ye, L. X. Yuan, Y. Q. Chen, T. Kan, J. Tu, X. F. Zhu, Y. Torimoto, M.
Yamamoto and Q. X. Li, Catal. Lett., 2009, 127, 323ꢀ333.
D. S. Kosyakov, N. V. Ul'yanovskii, K. G. Bogolitsyn and O. A. Shpigun, Int.
J. Environ. Anal. Chem., 2014, 94, 1254ꢀ1263.
2
7.
8.
M. T. Angaji and R. Ghiaee, J. Taiwan Inst. Chem. Eng., 2015.
C. Lee, W. Choi, Y. G. Kim and J. Yoon, Environ. Sci. Technol., 2005, 39,
2
2
101ꢀ2106.

Page 29 of 29
RSC Advances
View Article Online
DOI: 10.1039/C5RA20481J
2
9.
0.
P. A. Kolinko, D. V. Kozlov, A. V. Vorontsov and S. V. Preis, Catal. Today
,
2
007, 122, 178ꢀ185.
3
L. Lin, B. Xu, Y. L. Lin, L. Yan, K. Y. Shen, S. J. Xia, C. Y. Hu and R. Rong,
Water Air Soil Pollut., 2013, 224.
3
1.
2.
M. Selbes, D. Kim and T. Karanfil, Water Res., 2014, 66, 169ꢀ179.
W. Ding, M. Wu, M. L. Liang, H. M. Ni and Y. Li, Anal. Lett., 2015, 48,
3
1
551ꢀ1569.