Catalytic dechlorination of 2,4-dichlorophenol by Ni/Fe nanoparticles prepared in the presence of ultrasonic irradiation

Article abstract of DOI:10.1016/j.ultsonch.2014.03.002

In this study, nickle/iron (Ni/Fe) nanoparticles were synthesized by liquid phase reductive method in the presence of 20 kHz ultrasonic irradiation to improve nanoparticles' disparity and avoid agglomeration. The characterized results showed that this method has obviously modified most of the particles in term of sizes and specific surface areas. Meanwhile, the improved nanoscale Ni/Fe particles were employed for the reductive dechlorination of 2,4-dichlorophenol (2,4-DCP) as a function of some influential factors (Ni content, Ni/Fe nanoparticles dosage, reaction temperature and initial pH values) and degradation path. Experimental results showed that 2,4-DCP was first adsorbed by Ni/Fe nanoparticles, then quickly reduced to o-chlorophenol (o-CP), p-chlorophenol (p-CP), and finally to phenol (P). The application of ultrasonic irradiation for Ni/Fe nanoparticles synthesis was found to significantly enhance the removal efficiency of 2,4-DCP. Consequently, the phenol production rates increased from 68% (in the absence of ultrasonic irradiation) to 87% (in the presence of ultrasonic irradiation) within 180 min. Nearly 96% of 2,4-DCP was removed after 300 min reaction with these optimized conditions: Ni content over Fe⁰ 3 wt%, initial 2,4-DCP concentration 20 mg L^-1, Ni/Fe dosage 3 g L^-1, initial pH value 3.0, and reaction temperature 25 °C. The degradation of 2,4-DCP followed pseudo-first-order kinetics reaction and the apparent pseudo-first-order kinetics constant was 0.0737 min ^-1. This study suggested that the presence of ultrasonic irradiation in the synthesis of nanoscale Ni/Fe particles could be a promising technique to enhance nanoparticle's disparity and avoid agglomeration.

Full text of DOI:10.1016/j.ultsonch.2014.03.002

Ultrasonics Sonochemistry xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Ultrasonics Sonochemistry
journal homepage: www.elsevier.com/locate/ultson
Catalytic dechlorination of 2,4-dichlorophenol by Ni/Fe nanoparticles
prepared in the presence of ultrasonic irradiation
Deming Zhao , Yiya Zheng , Min Li , Shams Ali Baig , Donglei Wu , Xinhua Xu b,
a
a
a,c
b
b,
⇑
⇑
a
College of Chemical Engineering and Materials Science, Zhejiang University of Technology, Hangzhou 310032, People’s Republic of China
College of Environmental and Resource Sciences, Zhejiang University, Hangzhou 310058, People’s Republic of China
Ningbo Research and Design Institute of Chemical Industry, Ningbo 315040, People’s Republic of China
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
In this study, nickle/iron (Ni/Fe) nanoparticles were synthesized by liquid phase reductive method in the
presence of 20 kHz ultrasonic irradiation to improve nanoparticles’ disparity and avoid agglomeration.
The characterized results showed that this method has obviously modified most of the particles in term
of sizes and specific surface areas. Meanwhile, the improved nanoscale Ni/Fe particles were employed for
the reductive dechlorination of 2,4-dichlorophenol (2,4-DCP) as a function of some influential factors (Ni
content, Ni/Fe nanoparticles dosage, reaction temperature and initial pH values) and degradation path.
Experimental results showed that 2,4-DCP was first adsorbed by Ni/Fe nanoparticles, then quickly
reduced to o-chlorophenol (o-CP), p-chlorophenol (p-CP), and finally to phenol (P). The application of
ultrasonic irradiation for Ni/Fe nanoparticles synthesis was found to significantly enhance the removal
efficiency of 2,4-DCP. Consequently, the phenol production rates increased from 68% (in the absence of
Received 17 December 2013
Received in revised form 5 March 2014
Accepted 5 March 2014
Available online xxxx
Keywords:
2
,4-dichlorophenol (2,4-DCP)
Catalytic dechlorination
Ni/Fe nanoparticles
Ultrasound
Kinetics
ultrasonic irradiation) to 87% (in the presence of ultrasonic irradiation) within 180 min. Nearly 96% of
0
2
,4-DCP was removed after 300 min reaction with these optimized conditions: Ni content over Fe
ꢀ1
ꢀ1
3
wt%, initial 2,4-DCP concentration 20 mg L , Ni/Fe dosage 3 g L , initial pH value 3.0, and reaction
temperature 25 °C. The degradation of 2,4-DCP followed pseudo-first-order kinetics reaction and the
ꢀ1
apparent pseudo-first-order kinetics constant was 0.0737 min . This study suggested that the presence
of ultrasonic irradiation in the synthesis of nanoscale Ni/Fe particles could be a promising technique to
enhance nanoparticle’s disparity and avoid agglomeration.
Ó 2014 Elsevier B.V. All rights reserved.
1
. Introduction
The presence and widespread use of chlorinated aromatic sol-
rather than via electron transfer [8,9]. However, high expense of
Pd, Pt, Ag catalysts may restrict its wide application. Thus, it is
highly desirable to investigate more cost-effective catalysts to
cater this problem. In the present scenario, Ni is one of the better
choices. A rapid and complete reductive dechlorination technology
of chloroaromatics involving the use of bimetallic Ni/Fe nanoparti-
cles has also been reported in literature [4,6,10–13].
vents, chemical cleaning agents, biocides, preservatives and pesti-
cides in the environment represents a serious problem because of
their toxicity, persistence and accumulation potential in plants and
animal tissues [1,2]. Most of the chlorophenols are listed as priority
pollutants by the USEPA [3,4].
2
Ni can utilize the produced H from ZVI corrosion and acceler-
0
Zero valent iron (Fe , ZVI) is a mild reducing agent with reduc-
ate the rates of catalytic dechlorination reaction [12,13]. In
addition, bimetallic nanoparticles, when compared to the conven-
tional particles have some advantages due to possessing larger spe-
cific surface area and higher surface reactivity [12]. In order to
obtain the stabilized and high reactive nanoscale Ni/Fe bimetallic
particles and decrease their agglomeration and accumulation in
the effluent, ultrasound technique is applied to synthesis the nano-
scale Ni/Fe bimetallic particles. Ultrasound has been very useful in
the synthesis of a wide range of nanostructured materials includ-
ing high surface area transition metals, alloys, carbides, oxides,
and colloids. Sono-chemistry arises from acoustic cavitation; the
formation, growth, and implosive collapse of bubbles in a liquid.
tion potential of ꢀ0.440 V. Treatment of recalcitrant chemicals
using ZVI has been a main focus of research in recent years [4–
7
]. Compared with iron alone, bimetallic particles have shown
higher efficiencies for the dechlorination of many chlorinated com-
pounds. It has been suggested that feeding a second catalytic metal
such as Pd, Pt, Ag or Ni could prevent toxic byproduct formation by
dechlorinating chlorinated pollutants via hydrogen reduction
⇑
Corresponding authors. Tel./fax: +86 571 88982031.
E-mail addresses: wudl@zju.edu.cn, xuxinhua@zju.edu.cn (X. Xu).
http://dx.doi.org/10.1016/j.ultsonch.2014.03.002
350-4177/Ó 2014 Elsevier B.V. All rights reserved.
1
Please cite this article in press as: D. Zhao et al., Catalytic dechlorination of 2,4-dichlorophenol by Ni/Fe nanoparticles prepared in the presence of ultra-
sonic irradiation, Ultrason. Sonochem. (2014), http://dx.doi.org/10.1016/j.ultsonch.2014.03.002

2
D. Zhao et al. / Ultrasonics Sonochemistry xxx (2014) xxx–xxx
The collapse of cavitation bubbles generates localized hot spots
with transient temperature of about 10,000 K, pressures of about
medium was simultaneously stirred using mechanical stir at
25 °C by external cold water circulation. The ferrous iron was
reduced to zero-valent iron according to the following reaction,
Eq. (1):
1
000 atm or higher and cooling rates in excess of 109 K/s. Under
such extreme conditions, various chemical reactions and physical
changes occur and numerous nano-structured materials such as
metals, alloys, oxides and biomaterials can be effectively synthe-
sized with required particle size distribution. In the past the
sonochemical method has been applied to prepare various nano-
materials and the catalytic activity has been evaluated by different
researchers [14–16].
The objective of this study was to investigate the feasibility to
enhance reductive dechlorination of 2,4-DCP by coupling Ni–Fe
bimetallic nanoparticles prepared in the presence of ultrasonic
irradiation. In addition, other influential factors contributing to
2
6
þ
ꢀ
FeðH
2
OÞ þ 2BH4 ! Fe # þ2BðOHÞ þ 7H
2
"
ð1Þ
3
The Fe0 nanoparticles were then rinsed several times with
deoxygenated deionized water. Subsequently, Ni/Fe nanoparticles
were synthesized by reacting with the wet nanoscale Fe particles
0
in an aqueous solution of nickle sulfate hexahydrate
ꢀ1
(
8.41 mmol L ) under stirring according to the following equation,
Eq. (2):
2
þ
0
2þ
Ni þ Fe ! Fe þ Ni
.3. Batch experimental procedures
Batch experiments of 2,4-DCP dechlorination were performed
ð2Þ
2
,4-DCP catalytic reduction such as nanoscale Ni/Fe particles dos-
0
age, Ni content over Fe , initial 2,4-DCP concentration, reaction
temperature, mechanical stirring speed and initial pH values were
also examined.
2
in the same three-necked flask into which Ni/Fe nanoparticles
were added. 2,4-DCP stock solution and a certain amount of deox-
ygenated deionized water was added into the flask containing
freshly prepared Ni/Fe nanoparticles. The reaction solution was
stirred under nitrogen flow to simulate anaerobic environment at
25 °C. Aliquots of samples were periodically collected with glass
syringes and the reaction was quenched by passing through
2
. Experimental
2.1. Chemicals
Iron sulfate heptahydrate (AR grade), 2,4-DCP (AP grade), o-CP
(
CP grade), p-CP (CP grade), phenol (CP grade) were purchased
from the Sinopharm Group Chemical Reagent Co., Ltd., China, and
nickle sulfate hexahydrate (99%) obtained from Aladdin-Reagent.
Sodium borohydride (AR grade) purchased from Tianjin Chemical
Reagent Research Institute. All chemicals were used as received
without further purification. 2,4-DCP was dissolved in deionized
water and stored at 4 °C. Ni/Fe nanoparticles were synthesized
immediately before use.
0.22 lm polyether sulphone (PES) membrane filters.
2.4. Methods of analysis
Prior to the characterization, all the freshly synthesized Ni/Fe
nanoparticles (with a Ni bulk loading of 3%) were immersed in
absolute ethyl alcohol and dispersed by an ultrasonator. Transmis-
sion electron microscope (TEM) images of the particles were
obtained with a JEOL JEM 200CX microscope (JEOL Electronics
Co., JP) performed at a voltage of 160 kV for morphological mea-
surements. Brunauer–Emmett–Teller (BET) specific surface area
of all the synthesized Ni/Fe nanoparticles were measured using
nitrogen adsorption method with a surface analyzer (ASAR2020M+,
Micromeritics Instrument Corp., US). Before the analysis, the parti-
cles were dried in vacuum at 25 °C for 24 h and then hydrogen flow
at 260 °C for further 4 h.
2.2. Synthesis
Fig. 1 presents the experimental setup used in this study. In
the presence or absence of 20 kHz and 150 W KQ-3200DB rectan-
gular type of ultrasonic elutriation apparatus (dimensions
3
00 mm ꢁ 150 mm ꢁ 150 mm) with effective volume of 2000 mL
purchased from Kunshan ultrasonic apparatus Co., Ltd., China;.
The Ni/Fe bimetallic nanoparticles were synthesized in a 500 mL
three-necked flask under nitrogen gas. Nanoscale Fe0 particles
were synthesized by drop wise addition of the stoichiometric
Organic compounds such as 2,4-DCP, p-CP, o-CP and phenol
were analyzed by SHIMADZU High Performance Liquid Chroma-
tography. Agilent C18 Column, 150 mm ꢁ 4.6 mm, mobile phase:
ꢀ
1
amounts of NaBH
taining FeSO
4
(0.50 mol L ) aqueous solution into a flask con-
ꢀ1
ꢀ
1
MeOH/H
2
O (60/40, v/
v), flow rate: 1.0 mL min , detector: UV at
4
ꢂ7H
2
O (0.25 mol L ) aqueous solution. The aqueous
2
80 nm, sample size: 20 lm.
3
. Results and discussion
3.1. Ni/Fe nanoparticles characterization
The BET specific surface area of the synthesized Ni/Fe nanopar-
ticles in the presence and absence of 20 kHz ultrasonic irradiation
2
ꢀ1
2
ꢀ1
were 38.28 m g and 19.97 m g , respectively. Fresh nanoscale
Ni/Fe particles were black in color. Since the size of nanoscale par-
ticles is smaller than the wavelength of visible light, therefore, they
display perfect black body for light absorbance. Fig. 2(a–d) shows
TEM images and particle size distributions of the fresh Ni/Fe nano-
particles prepared in the presence and absence of 20 kHz ultra-
sonic irradiation, and TEM images of the reacted (after 300 min)
Ni/Fe nanoparticles prepared in the presence of ultrasonic irradia-
tion. The fresh Ni/Fe nanoparticles prepared in the absence of
ultrasonic irradiation were spherical in shape with particle size
ranging from 20 to 100 nm (Fig. 2(d)), and appeared to aggregate
together (Fig. 2(a)). However, nanoscale Ni/Fe particles prepared
Fig. 1. Schematic diagram of experimental appartus used in this study.
Please cite this article in press as: D. Zhao et al., Catalytic dechlorination of 2,4-dichlorophenol by Ni/Fe nanoparticles prepared in the presence of ultra-
sonic irradiation, Ultrason. Sonochem. (2014), http://dx.doi.org/10.1016/j.ultsonch.2014.03.002

D. Zhao et al. / Ultrasonics Sonochemistry xxx (2014) xxx–xxx
3
(a)
(
d)
(
b)
(e)
(c)
Fig. 2. (a) TEM image of fresh Ni/Fe nanoparticles synthesized in the absence of 20 kHz ultrasound, (b) TEM image of fresh Ni/Fe nanoparticles synthesized in the presence of
0 kHz ultrasound, (c) TEM image of aged Ni/Fe nanoparticles synthesized in the presence of 20 kHz ultrasound, (d) Particle size distribution from TEM image for the fresh Ni/
2
Fe nanoparticles prepared in the presence and absence of 20 kHz ultrasonic irradiation, (e) XRD patterns of the fresh Ni/Fe nanoparticles prepared in the presence and absence
of 20 kHz ultrasonic irradiation and the reacted (after 300 min) Ni/Fe nanoparticles prepared in the presence of ultrasonic irradiation.
in the presence of ultrasonic irradiation were also spherical, but
the particle size ranges from 10 to 70 nm (Fig. 2(d)), and appeared
to be smaller particles diameter and better disparity (Fig. 2(b)).
Spherical particles aggregate to form dendrites due to magnetic
interactions between the primary metal particles, and also their
surface tension interactions [12,17,18]. A mucous layer was ad-
hered onto the surface of Ni/Fe nanoparticles prepared in the ab-
sence of ultrasonic irradiation, reflects the possibility of lowering
the dechlorination efficiency. A thick mucous layer showed on
the surface of the Ni/Fe nanoparticles prepared in the presence of
ultrasonic irradiation after 300 min of reaction (Fig. 2(c)). More or-
ganic components such as 2,4-DCP, p-CP, o-CP and phenol, as well
as metal hydroxides and carbonate passivating layers on the nano-
particles’ surface inhibited the particles’ active sites, likely leading
to lower the dechlorination efficiency [5,13]. These minerals on the
or lepidocrocite (c-FeOOH) [6,19]. For example, Huang and Zhang
[19] also suggested that a stratified ZVI corrosion coating would
form in water, for which the outer and middle layers comprised
both FeOOH and Fe
3 4
O , while the inner layer mainly consisted of
Fe . This can also be observed in XRD patterns. Fig. 2(f) shows
3 4
O
the XRD patterns of the fresh and the 300 min aged Pd/Fe nanopar-
ticles prepared in the presence of ultrasound. The XRD pattern for
the fresh sample presents a strong peak at 44.66°, which corre-
sponds to the body-centered cubic N–Fe0 at the (110) plane. The
peak in the XRD pattern of the aged sample shows evidence of iron
oxides, possibly Fe
mixture. This agrees with the fact that Fe /Fe
3
O
4
(magnetite) or Fe
2
O
3
0
(maghemite), or their
couple is more
3
O
4
thermodynamically favorable at pH 6.1 or above [20].
The importances of sonication over conventional methods for
the preparation of nanopartilces have been widely documented
in literature [5,19,21–23], and the above experimental and
nanoparticles’ surface were likely composed of goethite (a-FeOOH)
Please cite this article in press as: D. Zhao et al., Catalytic dechlorination of 2,4-dichlorophenol by Ni/Fe nanoparticles prepared in the presence of ultra-
sonic irradiation, Ultrason. Sonochem. (2014), http://dx.doi.org/10.1016/j.ultsonch.2014.03.002

4
D. Zhao et al. / Ultrasonics Sonochemistry xxx (2014) xxx–xxx
characterized results are also in agreement with earlier studies.
More uniform distribution/dispersion of the nanoparticles, higher
surface area, better thermal stability, and phase purity, are some
of the advantages of the synthesis process for nanomaterials in
the presence of ultrasound. The effects of introducing ultrasound
strongly depend on the input power into the reaction medium
and metal carbonates on the surface of nanoscale Ni/Fe particles.
This was also demonstrated by the fact that the 2,4-DCP concentra-
tion dropped quickly in the first 30 min, but the resultant phenol
concentration was much less than the maximum attainable con-
centration. The non-detected proportion of intermediates may be
0
related to the bimetallic Fe nanoparticles, which appear to serves
[
5,23]. Herein, in order to increase the surface area of the reactive
as non-reactive sorption sites for intermediates [5,13,19].
Fig. 3(c and d) presents the generation and further degradation
process of p- and o-CP during the same reaction period with differ-
ent Ni/Fe nanoparticles prepared in the presence and absence of
ultrasound. The results suggested that 2,4-DCP was first adsorbed
by nanoscale Ni/Fe particles, then reduced to o-CP and p-CP, and la-
ter converted to phenol. Phenol was detected as the final organic
product in the dechlorination reaction. Meanwhile, the experimen-
tal results demonstrated that the generation of o-CP was more than
that of p-CP, although in the further reductive degradation process,
o-CP was easily reduced to phenol substantially than p-CP. So, the
concentration of o-CP was much higher than the concentration of
p-CP during the catalytic dechlorination of 2,4-DCP. But the con-
centrations of o-CP and p-CP were higher with the Ni/Fe nanopar-
ticles synthesized in the presence of ultrasound than that with the
absence of ultrasound within 240 min reaction. Obviously, the cat-
alytic reductive degradation process quickly proceeded with Ni/Fe
nanoparticles prepared in the presence of ultrasound than with the
absence of ultrasound. Therefore, nanoscale Ni/Fe particles were
synthesized in the presence of ultrasound during the following
experiments.
solids, decrease particle diameter and avoid the agglomeration, it
was necessary to apply ultrasound for preparing nZVI particles un-
der fixed input power 150 W during the course of whole reaction
time.
3
.2. Catalytic dechlorination of 2,4-DCP by Ni/Fe nanoparticles
synthesized in the presence and absence of ultrasonic irradiation
Influences of different Ni/Fe nanoparticles prepared in the pres-
ence and absence of ultrasonic irradiation on 2,4-DCP catalytic
dechlorination were performed at nanoscale Ni/Fe particles dosage
of 3 g L , Ni content of 3 wt%, initial 2,4-DCP concentration of
2
ꢀ1
ꢀ
1
0 mg L , an initial pH value of 3.0, reaction temperature of
2
5 °C and mechanical stirring speed of 600 rpm. Fig. 3 illustrates
the dechlorination of 2,4-DCP by different Ni/Fe nanoparticles.
The concentration of 2,4-DCP decreased rapidly and the re-
moval percentage reached 87% in 180 min, then further improved
to nearly 96% in 300 min for nanoscale Ni/Fe particles prepared
in the presence of ultrasound. In contrast, only 68% and 86% rem-
ovals were achieved for nanoscale Ni/Fe particles prepared in the
absence of ultrasound during the same reaction periods. Compared
to initial concentration (20 mg L 2,4-DCP), approximately 8–10%
carbon mass loss was observed. It showed that a proportion of or-
ganic compounds was absorbed or covered by surface passivating
layers, most likely due to the precipitation of metal hydroxides
ꢀ1
3.3. Effects of Ni content
It is considered that Fe0 can promote hydrogenolysis reaction
where the chlorine atom in chlorophenols can be replaced by a
20
16
12
8
4
0
12
(
a)
(b)
1
0
8
6
4
2
0
0
30
60
90 120 150 180 210 240 270 300
Time , min
0
30
60
90 120 150 180 210 240 270 300
Time , min
1
1
0
.5
.0
.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
(
c)
(d)
0.0
0
30
60
90 120 150 180 210 240 270 300
Time , min
0
30
60
90 120 150 180 210 240 270 300
Time , min
Ni/Fe nanoparticles synthesized in the presence of ultrasound
Ni/Fe nanoparticles synthesized in the absence of ultrasound
Fig. 3. Dechlorination of 2,4-DCP by Ni/Fe nanoparticles prepared in the presence and absence of ultrasound (T = 25 °C, pHin = 3.0, C2,4-DCP = 20 mg L 1, CNi/Fe=3 g L
ꢀ
ꢀ1
,
mechanical stirring speed = 600 rpm, Ni content = 3 wt%).
Please cite this article in press as: D. Zhao et al., Catalytic dechlorination of 2,4-dichlorophenol by Ni/Fe nanoparticles prepared in the presence of ultra-
sonic irradiation, Ultrason. Sonochem. (2014), http://dx.doi.org/10.1016/j.ultsonch.2014.03.002

D. Zhao et al. / Ultrasonics Sonochemistry xxx (2014) xxx–xxx
5
hydrogen atom. Nickle is a well-known catalyst for the hydrogen-
olysis. The co-existence of nickle and Fe in the particles has been
the dosage of Ni/Fe nanoparticles means the larger Ni/Fe nanopar-
ticles surface area that ultimately enhances the reaction rate. With
0
ꢀ1
proved to be very effective to accelerate the catalytic dechlorina-
tion reaction. Therefore, the Ni loading percentage on Ni/Fe nano-
particles may be one of the important influential factors on the
reductive dechlorination efficiency. The efficiencies of catalytic
dechlorination and phenol formations were obviously increased
as Ni content over Fe0 increased from 1 to 3 wt%, as shown in
Fig. 4. The removal percentage of 2,4-DCP reached from 54% to
the elevation of Ni/Fe nanoparticles dosage from 2 to 3 g L , obvi-
ous differences were observed and the removal percentage of 2,4-
DCP increased from 79% to 96% after 300 min of the reaction. The
removal percentage of 2,4-DCP was similar with the Ni/Fe nano-
ꢀ
1
particles dosage of 3–5 g L after 300 min of the reaction. This
indicated of insignificant final removal efficiency due to the excess
dosage of Ni/Fe nanoparticles. However, it may accelerate the ini-
tial reaction rate and provide more active sites of nanoscale Ni/Fe
particles for collision with 2,4-DCP during the reductive process.
Therefore, the optimal Ni/Fe nanoparticles dosage is chosen to be
9
7% within 300 min. Correspondingly, the production rate of phe-
nol increased from 39% to 76%, respectively. Increasing in the Ni
0
content over Fe from 3 to 4 wt% only caused slight improvement
ꢀ1
to the catalytic dechlorination 2,4-DCP. The slight improvement
3 g L for 2,4-DCP catalytic dechlorination.
0
in the removal efficiency at Ni content over Fe > 3 wt% could be
the accumulation of excessive hydrogen gas, which hinders the
contact between target organic pollutants and metal nanoparticles,
and that resultantly decreases the available surface area for
3
.5. Effects of reaction temperature
The influence of reaction temperature on 2,4-DCP catalytic
2
,4-DCP dechlorination. This phenomenon is consistent with the
dechlorination was also investigated, as shown in Fig. 6. The degra-
dation and dechlorination efficiency of 2,4-DCP and the production
rates of phenol increased dramatically with an increased of reac-
tion temperature. Raising the reaction temperature from 10 to
previously reported studies [5,13,20,23]. In order to promote the
cost-effective use of nickel and efficient 2,4-DCP dechlorination,
3
wt% nickel content was selected for this study.
3
5 °C, the final removal percentage of 2,4-DCP increased from
3
.4. Effects of Ni/Fe nanoparticles dosage
77% to 97%, which resulted of an increased in phenol production
ꢀ1
from 5.01 to 9.25 mg L in 300 min. At 10 °C reaction tempera-
ture, the catalytic dechlorination of 2,4-DCP was incomplete and
the final removal percentage only reached to 77% after 300 min.
Effects of Ni/Fe nanoparticles dosage on the catalytic dechlori-
nation of 2,4-DCP were investigated, as shown in Fig. 5. Increasing
20
16
12
8
4
0
1
0
8
6
4
2
0
0
Ni Content over Fe
wt.%
2 wt.%
1
3
4
wt.%
wt.%
0
Ni Content over Fe
1
2
3
4
wt.%
wt.%
wt.%
wt.%
0
30 60 90 120 150 180 210 240 270 300
0
30 60 90 120 150 180 210 240 270 300
Time , min
Time , min
0
Fig. 4. Effects of Ni content over Fe in Ni/Fe nanoparticles on 2,4-DCP dechlorination by Ni/Fe nanoparticles prepared in the presence of ultrasound (T = 25 °C, pHin = 3.0,
ꢀ
1
ꢀ1
C
2,4-DCP = 20 mg L , CNi/Fe=3 g L , mechanical stirring speed = 600 rpm).
1
0
8
6
4
2
0
2
1
1
0
6
2
8
4
0
Ni/Fe nanoparticles dosage
-1
2
3
4
5
g L
g L
g L
g L
-1
-1
-1
Ni/Fe nanoparticles dosage
-
1
2
3
4
5
g L
-1
g L-
1
g L-
1
g L
0
30 60 90 120 150 180 210 240 270 300
0
30 60 90 120 150 180 210 240 270 300
Time , min
Time , min
Fig. 5. Effects of Ni/Fe nanoparticles dosage on 2,4-DCP dechlorination (T = 25 °C, C2,4-DCP = 20 mg L 1, mechanical stirring speed = 600 rpm, pHin = 5.0, the Ni content = 3
ꢀ
wt%).
Please cite this article in press as: D. Zhao et al., Catalytic dechlorination of 2,4-dichlorophenol by Ni/Fe nanoparticles prepared in the presence of ultra-
sonic irradiation, Ultrason. Sonochem. (2014), http://dx.doi.org/10.1016/j.ultsonch.2014.03.002

6
D. Zhao et al. / Ultrasonics Sonochemistry xxx (2014) xxx–xxx
20
16
12
8
4
0
12
Reaction Temperature
Reaction Temperature
O
O
O
O
15
25
35
C
C
C
15
25
35
C
C
C
10
8
O
O
6
4
2
0
0
30 60 90 120 150 180 210 240 270 300
0
30 60 90 120 150 180 210 240 270 300
Time , min
Time , min
Fig. 6. Effects of reaction temperature on 2,4-DCP dechlorination (C2,4-DCP = 20 mg L 1, mechanical stirring speed = 600 rpm, pHin = 5.0, CNi/Fe=3 g L , Ni content = 3 wt%).
ꢀ
ꢀ1
20
16
12
8
4
0
10
8
pH=3
pH=5
pH=7
pH=9
pH=11
pH=3
pH=5
pH=7
pH=9
pH=11
6
4
2
0
0
30 60 90 120 150 180 210 240 270 300
0
30 60 90 120 150 180 210 240 270 300
Time , min
Time , min
Fig. 7. Effects of solution initial pH on 2,4-DCP dechlorination (T = 25 °C, C2,4-DCP = 20 mg L 1, mechanical stirring speed = 600 rpm, pHin = 3.0, Ni content = 3 wt%, CNi/Fe = 3 g
ꢀ
ꢀ
1
L
).
+
When the reaction temperature increased to 25 °C, 2,4-DCP could
completely be reduced into phenol. At 35 °C, the catalytic dechlo-
rination of 2,4-DCP was much faster and the mobility of 2,4-DCP
from solution to nanoparticles increased at higher temperature,
or the activation energy for electron transfer or the formation of
a reactive surface complex increased. Based on the above analyses
and experimental evidences, the subsequent experiments were
performed at 25 °C.
2,4-DCP. It indicates that the presence of H largely enhances the
2,4-DCP reductive dechlorination efficiency, which is an agreement
with the evidences reported in previous studies [13,26].
3.7. Effects of initial 2,4-DCP concentration
Four different initial concentrations of 2,4-DCP (20, 30, 40 and
0 mg L ) were employed in our study. Fig. 8 shows the reductive
ꢀ1
5
dechlorination of 2,4-DCP with different initial 2,4-DCP concentra-
tions at T = 25 °C, initial pH value 3.0, mechanical stirring speed
3
.6. Effects of initial pH value
6
00 rpm, the Ni content 3 wt%, and the nanoscale Ni/Fe particles
ꢀ1
dosage of 3 g L . The removal percentages of 2,4-DCP reached
4%, 72%, 69% and 72% each after 15 min, and then the final re-
The pH is considered an important factor in reductive dechlori-
7
nation of chlorinated organic compounds using zero-valent iron
6]. Low pH allows more of the iron surface to remain available
moval percentages of 2,4-DCP reached 97%, 98%, 97%, and 92%,
respectively, after 300 min of the reaction. Though the final
removal percentage of 2,4-DCP was similar to each other, the
absolute removal amount increased with increasing of the initial
[
for reaction with the chlorinated molecules or at least assists iron
corrosion. At higher pH values, carbonate and hydroxide coatings
undoubtedly come out, which hinder access to the Fe0 surface
2
,4-DCP concentrations.
[
24,25]. As a result, the catalytic activity decreases at higher pH
values. Fig. 7 shows the effect of different initial pH values on
the catalytic dechlorination of 2,4-DCP by Ni/Fe nanoparticles.
When the initial pH values increased from 3, 5, 7 to 9, the removal
percentages of 2,4-DCP dropped from 96%, 89%, 82% to 68%, respec-
tively, in 300 min. The increase of initial pH values of the reactant
solutions from 7 to 9, leads to transform from acidic to alkaline
condition, which obviously dropped the removal percentages of
3.8. Kinetics of 2,4-DCP catalytic dechlorination with Ni/Fe
nanoparticles freshly prepared in the presence of ultrasonic irradiation
The transformations of 2,4-DCP to phenol using Ni/Fe nanopar-
ticles in the presence of ultrasonic irradiation are shown in Fig. 3.
The products consist of phenol (P), p-CP and o-CP (Fig. 9). Previous
Please cite this article in press as: D. Zhao et al., Catalytic dechlorination of 2,4-dichlorophenol by Ni/Fe nanoparticles prepared in the presence of ultra-
sonic irradiation, Ultrason. Sonochem. (2014), http://dx.doi.org/10.1016/j.ultsonch.2014.03.002

D. Zhao et al. / Ultrasonics Sonochemistry xxx (2014) xxx–xxx
7
50
40
30
20
10
0
30
Initial 2,4-DCP Concentration
Initial 2,4-DCP Concentration
-1
-1
2
3
4
5
0 mg L
20 mg L
-1
-
1
25
0 mg L
30 mg L
-1
-
1
0 mg L
mg L
40 mg L
-1
-1
5 mg L
20
15
10
5
0
0
30 60 90 120 150 180 210 240 270 300
0
30 60 90 120 150 180 210 240 270 300
Time , min
Time , min
Fig. 8. Effects of initial 2,4-DCP concentrations on 2,4-DCP dechlorination (T = 25 °C, pHin = 3.0, mechanical stirring speed = 600 rpm, Ni content = 3 wt%, CNi/Fe=3 g L 1).
ꢀ
k
1
ꢀ
k
1
ꢀ
2
; 4-DCP ! CP þ Cl ! P þ 2Cl
ð3Þ
Oxide shell
Fe
Ni
where CP represents the total molecules of o-CP and p-CP in the
reaction. k and k refer the corresponding reaction rate for the dis-
appearance of 2,4-DCP and CP. The corresponding reaction rate
equations for the disappearance of 2,4-DCP, the resultant formation
of CP (including o-CP and p-CP) intermediates, and the accumula-
tion of P in the batch system are shown in Eqs. (4)–(6):
-
e
-
1
2
-
H
H
2
O/H
2
2
H
2
O/H
2
Fe0
core
2,4-DCP
e-
e-
H
2
O/H
2
2
O/H
o-CP
p-CP
-
-
e-
ꢀ
dC2;4-DCP
dt
¼
k
1
C
2;4-DCP
ð4Þ
ð5Þ
ð6Þ
P
2 2
H O/H
dCCP
dt
¼
k
1
C
2;4-DCP ꢀ k
2 CP
C
Fig. 9. Mechanism for dechlorination of 2,4-DCP by Ni/Fe nanoparticles.
d½Pꢃ
studies have shown that the degradation rate of chlorinated sol-
vents by Ni/Fe nanoscale particles follows a pseudo-first-order
reaction, if the Ni/Fe nanoscale particles dosage increased in the
reaction [5,6,13,27]. Chlorines in 2,4-DCP might be removed from
the benzene ring in the following sequence steps, Eq. (3).
¼ k C
2
CP
dt
The above simultaneous rate equations are integrated, leading
to the following molar fractions, Eqs. (7)–(9):
k
1
t
a
2;4-DCP ¼ eꢀ
ð7Þ
Table 1
k Values at different experimental conditions.
/min 1
ꢀ
R
ꢀ1
R
Reaction conditions
1 ꢀ a
k
1
2
k /min
Ni/Fe nanoparticles
Prepared method
Ni content over Fe
In the absence of ultrasound
In the presence of ultrasound
1 wt%
0.9863
0.9089
0.9159
0.9787
0.9863
0.9966
0.950
0.9863
0.9915
0.9953
0.9372
0.9863
0.9848
0.9863
0.9292
0.9396
0.9160
0.9457
0.9863
0.9779
0.9689
0.9650
0.07372
0.00626
0.00261
0.06718
0.07372
0.09651
0.00555
0.07372
0.08858
0.10339
0.00483
0.07372
0.07802
0.07372
0.00664
0.00536
0.00492
0.00331
0.07372
0.06345
0.06964
0.05927
0.92
0.91
0.94
0.96
0.92
0.96
0.96
0.92
0.93
0.97
0.98
0.92
0.98
0.92
0.98
0.96
0.97
0.96
0.92
0.97
0.92
0.94
0.0633
0.95
0.98
0.96
0.98
0.95
0.93
0.91
0.95
0.93
0.94
0.94
0.95
0.93
0.95
0.99
0.97
0.99
0.97
0.95
0.93
0.98
0.92
0.00405
0.00535
0.00535
0.0633
0
2
3
4
wt%
wt%
wt%
0.0833
ꢀ
1
1
1
1
Ni/Fe dosage
2 g L
0.01282
0.06329
0.08695
0.09338
0.00106
0.06329
0.04219
0.06329
0.00818
0.00285
0.00100
0.00081
0.06329
0.03677
0.09259
0.0769
ꢀ
ꢀ
ꢀ
3
4
5
g L
g L
g L
Reaction temperature
Initial pH values
15 °C
3
4
0 °C
5 °C
3
5
7
9
1
1
ꢀ
ꢀ
ꢀ
ꢀ
1
1
1
1
Initial 2,4-DCP concentration
20 mg L
3
4
5
0 mg L
0 mg L
0 mg L
Note: 1 ꢀ a represents the molar fraction of the total organic compounds in solution; k
1 2
and k refer the corresponding reaction rate for the disappearance of 2,4-DCP and CP,
respectively; R denotes the correlation coefficient between the experimental data can match the calculated number.
Please cite this article in press as: D. Zhao et al., Catalytic dechlorination of 2,4-dichlorophenol by Ni/Fe nanoparticles prepared in the presence of ultra-
sonic irradiation, Ultrason. Sonochem. (2014), http://dx.doi.org/10.1016/j.ultsonch.2014.03.002

8
D. Zhao et al. / Ultrasonics Sonochemistry xxx (2014) xxx–xxx
k
ꢀ k
1
ðeꢀk ꢀ eꢀk t
1
t
2
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aCP ¼ k
Þ
ð8Þ
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ꢀ1
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0
The authors are thankful for the financial support provided by
Zhejiang Provincial Natural Science Foundation of China (No.
Y5100075), and the Science and Technology Plan Project of Zhe-
jiang Province (No. 2012C23044).
2
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Please cite this article in press as: D. Zhao et al., Catalytic dechlorination of 2,4-dichlorophenol by Ni/Fe nanoparticles prepared in the presence of ultra-
sonic irradiation, Ultrason. Sonochem. (2014), http://dx.doi.org/10.1016/j.ultsonch.2014.03.002