Sonocatalytic performance of magnetic flower-like CoFe2O4 nanoparticles prepared from a heterometallic oxo-centered trinuclear complex under microwave irradiation

Article abstract of DOI:10.1016/j.poly.2018.08.028

In this work, CoFe₂O₄ nanoparticles were prepared successfully under microwave irradiation (MW-CoFe₂O₄) using a heterometallic oxo-centered trinuclear [CoFe₂O(CH₃COO)₆(H₂O)₃]·2H₂O complex as precursor and compared with conventional thermal method (CT-CoFe₂O₄). The nanoparticles of MW-CoFe₂O₄ and CT-CoFe₂O₄ were characterized by physicochemical methods. The X-ray diffraction results revealed that both MW-CoFe₂O₄ and CT-CoFe₂O₄ nanoparticles adopt a cubic spinel structure. The SEM images of MW-CoFe₂O₄ and CT-CoFe₂O₄ show flower-like morphology with average diameter size 9 and 33 nm, respectively. The MW-CoFe₂O₄ as a sonocatalyst was used for degradation of methylene blue and Rhodamine-B with conversion percent of 98% and 90%, respectively, which is up to fifty percent more than what recorded for CT-CoFe₂O₄ activity. The higher catalytic activity of MW-CoFe₂O₄ is related to its smaller particle size and higher porosity compared to CT-CoFe₂O₄ nanoparticles. These magnetic sonocatalysts were easily separated from reaction mixture by a magnet and reused without significant loss of activity. Also, a plausible mechanism through hydroxyl radical path was postulated.

Full text of DOI:10.1016/j.poly.2018.08.028

Accepted Manuscript
Sonocatalytic performance of magnetic flower-like CoFe O nanoparticles pre-
2
4
pared from a heterometallic oxo-centered trinuclear complex under microwave
irradiation
Mahdieh Ghobadifard, Saeed Farhadi, Sajjad Mohebbi
PII:
S0277-5387(18)30494-7
https://doi.org/10.1016/j.poly.2018.08.028
POLY 13351
DOI:
Reference:
To appear in:
Polyhedron
Received Date:
Revised Date:
Accepted Date:
13 March 2018
30 July 2018
10 August 2018
Please cite this article as: M. Ghobadifard, S. Farhadi, S. Mohebbi, Sonocatalytic performance of magnetic flower-
like CoFe O nanoparticles prepared from a heterometallic oxo-centered trinuclear complex under microwave
2
4
irradiation, Polyhedron (2018), doi: https://doi.org/10.1016/j.poly.2018.08.028
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1
Sonocatalytic performance of magnetic flower-like CoFe O nanoparticles
2
4
prepared from a heterometallic oxo-centered trinuclear complex under
microwave irradiation
a
b,
a
Mahdieh Ghobadifard , Saeed Farhadi* Sajjad Mohebbi*
a
Department of Chemistry, University of Kurdistan, Sanandaj, Iran P.O.Box 66179-415,
Tel: +98(87)33624133, Fax: +98(87)336660075.
b
Department of Chemistry, Lorestan University, Khoramabad 68135-465, Iran,
Tel.: +98 6633120611; fax: +98 6633120618.
*
Corresponding authers. E-mail: sfarhadi1348@yahoo.com and E-mail: smohebbi@uok.ac.ir
_____________________________________________________________________________________
Abstract. In this work, CoFe
MW-CoFe ) using a heterometallic oxo-centered trinuclear [CoFe
complex as precursor and compared with conventional thermal method (CT-CoFe
of MW-CoFe and CT-CoFe were characterized by physicochemical methods. The X-ray diffraction
results revealed that both MW-CoFe and CT-CoFe nanoparticles adopt a cubic spinel structure.
The SEM images of MW-CoFe and CT-CoFe show flower-like morphology with average diameter
size 9 and 33 nm, respectively. The MW-CoFe as a sonocatalyst was used for degradation of
methylene blue and Rhodamine-B with conversion percent of 98% and 90%, respectively, which is up to
fifty percent more than what recorded for CT-CoFe activity. The higher catalytic activity of MW-
CoFe is related to its smaller particle size and higher porosity compared to CT-CoFe nanoparticles.
O
2 4
nanoparticles were prepared successfully under microwave irradiation
O(CH COO) (H O) ]·2H
). The nanoparticles
(
2
O
4
2
3
6
2
3
2
O
2
O
4
2
O
4
O
2 4
2
O
4
2
O
4
2
O
4
2
O
4
O
2 4
2
O
4
2
O
4
2
O
4
These magnetic sonocatalysts were easily separated from reaction mixture by a magnet and reused
without significant loss of activity. Also, a plausible mechanism through hydroxyl radical path was
postulated.
Keywords: Flower-like; CoFe
2
4
O nanoparticles; MW irradiation; Conventional method; trinuclear
complex.
_
____________________________________________________________________________________
. Introduction
Spinel ferrite MFe O (M = Co, Mn, Mg, Ni, or Zn) nanoparticles are an attractive topic for scientists
1
2
4
due to their potential applications in a broad range from basic research to industrial usage [1]. Spinel
nanoparticles are widely considered as one of the most important inorganic nanomaterials due to their
1

2
excellent electrical, magnetic, optical and catalytic properties. For example, CoFe
2
O is well-known as a
4
hard magnetic material, crystalline anisotropy, high magneto, coercively, moderate saturation
magnetization and a suitable candidate for microwave devices [2]. Various wet chemical methods such as
hydrothermal, co-precipitation, sol-gel, combustion solution and other chemical solution methods have
been developed to prepare advanced inorganic materials [3]. One of the most promising techniques for the
prepation of inorganic materials to be the use of microwave irradiation. However, microwave (MW)
irradiation as a new synthetic strategy has developed in a broad research area. The molecular structure of
materials will not be affected by MW due to low energy irradiation comparing to typical bond energies. In
fact, the electronic structure around atoms does not change when interacted with MW and this provide
important applications [4]. The microwaves could interact with dielectric materials through polarization
mechanism. The main difference between microwave with conventional methods is the kind of heating
mechanism [5]. In the microwave heating method, the inner part of materials will be overheated while the
surface is cooler.
In recent years, the application of sonochemical method for the degradation of dyes [6], halogenated
hydrocarbons [7], pesticide components [8] and wastewater treatment has been reported. Because of the
need for higher amount of energy and longer time for an effective degradation, ultrasound alone is not
efficient for the degradation of the goal organic pollutant. To overcome this problem, sonocatalyst which
are active under ultrasonic irradiation can be used for demolition of organic pollutants in the aqueous
phase [9]. In recent years, CoFe
2
O nanoparticles with different structures have been used as a
4
photocatalyst for degradation of organic dye pollutants under different conditions.
As a new method, in this paper we report a fast, simple and clean route to prepare CoFe
2
O
4
nanoparticles in pure phase through microwave-induced solid-state decomposition of a heterometallic
oxo-centered trinuclear, [CoFe
2
O(CH
3
COO)
6
(H
2
O)
3
]·2H
2
O, as a novel precursor. The use of such a method
) has been explored for the first time. The product
nanoparticles has been used
to synthesize the CoFe nanoparticles (MW-CoFe
2
O
4
2
O
4
was identified by various analyses. In addition, the as-prepared MW-CoFe
2
O
4
as a noval sonocatalyst for the degradation of organic dyes such as methylene blue (MB), rhodamine B
2

3
(RhB) and methyl orange (MO) organic dyes under ultrasound irradiation. Furthermore, the sonoactivity
of MW-CoFe
thermal decomposition of the precursor und.
. Experimental
2
O
4
was compared with the CoFe
O
2 4
nanoparticles (CT-CoFe
2
O ) prepared via conventional
4
2
2
.1. Materials
Iron(III) nitrate nonahydrate (Fe(NO
3
)
3
.9H
2
O, 99%), cobalt nitrate hexahydrate (Co(NO
, 30%) were
S), methyl orange (MO,
) were prepared from Merck chemical company.
ethanol was distilled and deionized water was consumed. All other chemicals were used as received.
3
)
2
.6H
2
O,
9
9%), sodium acetate trihydrate )C₂H₃NaO₂.3H₂O, 99%) and hydrogen peroxide (H
purchased from Sigma-Aldrich. methylene blue (MB, C16
NaO S), and Rhodamine B (RhB, C28
2
O
2
H18ClN
3
C
14 14
H N
3
3
H
31ClN
2
O
3
2
.2. Characterization techniques
XRD was recorded by Rigaku D-max C III, Ni-filtered Cu Ka radiation (40 kV, 30 mA, k = 1.5406 Å).
FT-IR spectra were recorded on a Shimadzu system 160 spectrophotometer using KBr pellets. The
morphology was identified by a scanning electron microscope imaging (FE-SEM= Mira3 Tescan)
equipped with a link energy-dispersive X-ray spectroscopy (EDX) analyzer. Vibrating sample
magnetometer (VSM, Daneshpajoh Kashan Co, Iran) was employed to measure the magnetic properties
of the CoFe
2
O
4
nanoparticles at room temperature. The sonocatalytic activity of the CoFe
2
O
4
nanoparticles was monitored on a UV–Vis (Cary 100, Varian Company, USA) with the wavelength range
of 300–800 nm at room temperature. An ultrasonic device operating at 37 kHz (James 6MX, England)
was used for the degradation of dye solutions.
2
.3. Preparation of [CoFe
2
O(MeCO
2
)
6
(H
2
O)
3
].2H
2
O
The modified Weinland and Holtmeier method was applied [10]. In a synthetic procedure, a solution
of 25 g sodium acetate trihydrate (0.31 mol) in 50 mL of deionized water (50 ml) was added to a stirred
solution of 29 g cobalt nitrate (0.1 mol) and 8 g iron(III) nitrate nonahydrate (0.02 mol) in 50 ml of
3

4
deionized water. The resulted brown precipitate was filtered, washed with ethanol and water and finally
dried in air.
2
.4. Preparation of MW-CoFe
2
O
4
nanoparticles
O(MeCO
In a synthetic procedure, the [CoFe
2
)
2 6
2
(H O)
3
].2H O complex which synthesized in the
2
previous section were placed inside a microwave oven under different conditions: (800 W, 5 min), (800
W, 10 min), (800 W, 15 min), (900 W, 5 min), (900 W, 10 min) and (900 W, 15 min). Among of these,
applying 900 W power for 10 min is the best conditions for preparation of the CoFe
2
O
4
nanoparticles. In
).
this way, a black CoFe powder was obtained by calcination under MW irradiation (MW-CoFe
2
O
4
2
O
4
2
.5. Preparation of CT-CoFe
2
O
4
nanoparticles
O complex was also decomposed by a conventional heating method in
The [CoFe O(MeCO (H O) ].nH
2
2
)
6
2
3
2
an electric furnace under different conditions: (300 °C, 1.5 h), (300 °C, 2 h), (350 °C, 1.5 h), (350 °C, 2
h), (400 °C, 1.5 h) and (400 °C, 2 h). The furnace temperature 400 °C for 2 h was the best conditions for
the preparation of the CoFe
O
2 4
2
nanoparticles. The [CoFe O(MeCO
2
)
6
(H
2
O)
3
].nH
2
O complex was
decomposed by reaction with oxygen to produce the black CoFe
2
O
4
nanoparticles (CT-CoFe
O
2 4
).
2
.6. Sonocatalytic degradation of organic dyes
Sonocatalytic degradation of the aqueous solutions of dyes was performed in the presence of the
CoFe nanoparticles (MW-CoFe and CT-CoFe ) using an ultrasonic bath (Sonic 6MX, 100 W,
England) under an output frequency of 37 kHz. In a typical experiment, 50 mg CoFe catalyst was
2
O
4
2
O
4
2
O
4
O
2 4
added to 50 mL (25 mg/L) of MB, RB and MO to perform the sonocatalytic degradation, respectively.
Before ultrasonic irradiation the solution was stirred for 15 min in the dark condition to gain adsorption–
desorption balance between the dye and sonocatalyst. In next step, 2ml H
2
O (1 M) was added to the
2
mixture and irradiated by ultrasound. At regular time period, 2 mL aliquots of the reaction solution were
sampled, and the catalyst was instantly separated from the suspension by magnet. The progress of
reaction was monitored by UV–Vis spectrophotometry via concentration determination of MB, RB and
4

5
MO at wavelength of 665, 554 and 465 nm, respectively. The degradation percent was calculated using
the Eq. 1 [11]:
Degradation efficiency (%) = [((C
0
-C))/C
0
] × 100%
(1)
Where C is the concentration of the reactant after irradiation at time (min) and C is the concentrations
0
of the MB, RB and MO after adsorption–desorption balance.
3
3
. Results and discussion
.1. Characterization of MW-CoFe
2
O
4
and CT-CoFe
2
4
O nanoparticles
The MW-CoFe
CoFe O(MeCO
view in the [CoFe
2
O
4
and CT-CoFe
(H O) ].2H O with high purity and homogeneous characters. From schematic point of
O(MeCO (H O) ].2H O complex has a µ -oxo anion in the center with donor-
2
O
4
nanoparticles were formed by thermal decomposition process of
[
2
2
)
6
2
3
2
2
2
)
6
2
3
2
3
acceptor interaction with metal ions. The carboxylate groups have coordinated to the neighboring metal
ions as bidentate bridge ligands (Fig. S1) [12–19]. The FT-IR spectroscopy describe the position of the
ions present in the crystal plexus through their vibration modes (Figure 1a). The CoFe
was formed by the thermal decomposition process of [Fe CoO(MeCO (H O) ].nH O complex. As shown
in Figure 1b and 1c, the infrared spectra patterns of decomposition products confirm their nature in
comparing with the precursor complex. The FT-IR spectra for both MW-CoFe and CT-CoFe
nanoparticles exhibited two main absorption bands below 1000 cm which referred to the crystal
vibrations of MeO bonds in the cubic spinel ferrites. The higher frequency band (ν ) is defined to the
vibrations of the bond between the tetrahedral metal ion and the oxygen ion. The lower frequency band
) is defined to vibrations of the bond between octahedral metal ion and oxygen ion [20]. The one band
2
O
4
nanoparticles
2
2
)
6
2
3
2
2
O
4
2
O
4
-
1
1
(ν
2
-
1
in the range 410-430 cm referred to the natural stretching vibrations in the octahedral sites and the band
-1
in the range 550-600 cm is due to the natural stretching vibrations of the metal ions in the tetrahedral
sites. The octahedral stretching vibrations were observed at a lower wave number as compared to the
tetrahedral stretching vibrations because the M-O bond length in the octahedral site is higher than that of
5

6
tetrahedral site [21]. The absence of organic bands in the FTIR spectrum MW-CoFe
2
O
4
and CT-CoFe
2
O
O
4
4
nanoparticles could be ascribed to the decomposition of organic compounds and formation CoFe
ferrite.
2
2
Fig. 1. FT-IR spectra of (a) complex [Fe CoO(MeCO
2
)
6
(H
2
O)
3
].nH
2
O (b) MW-CoFe
2
O and (c) CT-
4
CoFe O .
2
4
EDS element mapping display homogeneous distribution of Co, Fe and O from in both MW-CoFe
and CT-CoFe
Cobalt and Oxygen peaks, with no other elements or impurity. The element percentages of Fe, Co and O
were found to be 12.95%, 4.77% and 82.28% for MW-CoFe and 14.22%, 6.40 % and 79.38% for CT-
CoFe , respectively. This result further confirms that the final product consist highly pure CoFe
nanoparticles.
2
O
4
2
O (Fig. 2). The EDX spectrum of the product in Fig. 3 reveals the presence of only Iron,
4
2
O
4
2
O
4
2
O
4
6

7
Fig. 2. EDS element mapping of Co, Fe and O (a-d) for MW-CoFe
O
2 4
and (e-h) for CT-CoFe
2
4
O .
Fig. 3. The EDX spectrum of (a) MW-CoFe
2
O
4
and (b) CT-CoFe
2
O .
4
The XRD patterns of the analysis products are shown in Fig. 4. The X-ray diffraction patterns for
MW-CoFe and CT-CoFe nanoparticles confirmed the cubic spinel phases (JCPDS card: 02-1045)
2
O
4
2
O
4
as indicated by the (220), (311), (400), (422), (511), (440), (531) and (620) reflection peaks. The broad
peaks width is suggestive low crystallite while the sharpness of peaks related to high crystallite of
7

8
product. The average size of the CoFe
2
O
4
crystallites (D) was measured by the XRD peaks width using
the Debye–Scherer (Eq. 2):
ꢀ
ꢁꢂꢃꢄ
D = ꢅ
(2)
ꢆꢇꢈꢉꢊꢋꢌ
Where θ is the Bragg angle, λ is the wavelength of the X-ray radiation (0.154056 nm), and h1/2 is the peak
◦
width at half of maximum intense. For MW-CoFe
2
O
4
based on a line width of 1.65 for the diffraction
peak positioned at 2θ = 18.55
CoFe . Also, for CT-CoFe
positioned at 2θ = 30.07
So, the size of the MW-CoFe
ꢀ
2
O
4
2
O
4
ꢀ
2
O
4
Fig. 4. The XRD patterns of the analysis products (a) MW-CoFe
2
O
4
and (b) CT-CoFe
2
O .
4
The morphologies of CoFe
SEM images shows the MW-CoFe
With close approach, ones can conclude that the nanoparticles with flower-like morphology form from
individual nanoplates/sheets moieties. In Fig. 5b, the structure of MW-CoFe is clearly exhibit the joint
O
2 4
nanoparticles were investigated by FESEM. As shown in Fig. 5a-d, the
2
O
4
and CT-CoFe nanoparticles almost adopt uniform morphology.
2
O
4
2
O
4
8

9
of nanoplates to form flower-like structures. Average edge length of nanosheets for the synthesized MW-
2
CoFe O
4
and CT-CoFe
O
2 4
nanoparticles are in the range of 60–300 nm with 9 and 33 nm thickness,
respectively. However, the formation mechanism of flower-like structure from nanosheets is not clear yet.
Fig. 5. SEM micrographs of the surface of (a,b) MW-CoFe
2
O
4
and (c,d) CT-CoFe
2
O .
4
Fig. 6 shows the magnetization verses practical magnetic field curve for MW-CoFe
2
4
O and CT-
CoFe nanoparticles at room temperature. The fine shape of the hysteresis loops is a characteristic of a
2
O
4
weak ferromagnetic behavior. It is well-known that the magnetic behavior of the nanoparticles strongly
depends on the particle shape, distribution, sizes and interaction of magnetic hardness phases [22,23]. The
hysteresis loop shows a ferromagnetic behavior for the MW-CoFe
of 3.26 emu/g. The coercive field (Hc) and the saturation magnetization (Ms) are about 237 Oe and 23.88
emu/g, respectively. The hysteresis loop shows a weak ferromagnetic behavior for the CT-CoFe with a
remnant magnetization (Mr) of 1.52 emu/g. Because the CT-CoFe nanoparticles are made of small
2
O
4
with a remnant magnetization (Mr)
O
2 4
2
O
4
9

10
magnetic domains and each magnetic domain is characterized by its own magnetic moment that oriented
randomly. The coercive field (Hc) and the saturation magnetization (Ms) are about 162 Oe and 23.65
emu/g, respectively. So, the hysteresis loops for the MW-CoFe
2
O shows stronger magnetic properties
4
than CT-CoFe
2
O .
4
Fig. 6. Magnetic hysteresis loops at room temperature of (a) MW-CoFe
2
O
4
and (b) CT-CoFe
2
4
O .
Generating various canted spin structures and unfix the collinear spin arrangement at the surface,
caused the low values of Ms for the MW-CoFe and CT-CoFe nanoparticles could be ascribe to
surface distortion. This effect, especially for MW-CoFe particles, is prominent due to large surface to
volume ratio. The other reason for low values of magnetization MW-CoFe and CT-CoFe particles is
due to the magneto crystalline anisotropy, which depends on the degree of crystallinity of the MW-
CoFe and CT-CoFe nanoparticles. Furthermore, the magnetic properties of nanomaterials have been
believed dependent on the sample shape and so on [24].
2
O
4
2
O
4
2
O
4
2
O
4
O
2 4
2
O
4
O
2 4
10

11
3
.2. Sonocatalytic degradation of dyes over the MW-CoFe
2
O
4
and CT-CoFe
2
O
4
nanoparticles
The sonocatalytic performance of MW-CoFe and CT-CoFe
2
O
4
2
O
4
nanoparticles by the degradation of
MB, RB and MO, as typical organic dyes pollutant in the textile industry were evaluated. The
sonocatalytic degradation process was monitored by measuring the absorption intensity at ꢍmax of MB,
RhB and MO at about 664, 554 and 465 nm. To the 50 mL aqueous 25 ppm of MB, RB or MO, 50 mg
nanomagnetic catalyst CoFe
mL H (1M). Figs. 7, 8 and 9 show the UV-Vis absorbance of MB, RB and MO aqueous solution in the
MW-CoFe /H /US and CT-CoFe /H /US systems, respectively. The efficiency of US,
/US, MW-CoFe /US, CT-CoFe /US, MW-CoFe /H /US and CT-CoFe /H /US
2
O
4
was added and exposed to ultrasonic (US) irradiation in the presence of 2
2
O
2
2
O
4
2
O
2
2
O
4
2
O
2
H O
2 2
2
O
4
2
O
4
2
O
4
2
O
2
O
2 4
2
O
2
systems for degradation of MB, RB and MO were evaluated. The intensity of the absorption bands was
decreased within the irradiation time, until completely was been colorless. These observations confirm the
efficiency of the MW-CoFe
2 4
O /H
2
O
2
/US and CT-CoFe
2
O
4
/H
2
O /US systems for successful degradation
2
of MB, RB and MO dyes. The results of MB, RB and MO degradation rate are shown in Fig. 10. As can
be seen, the ability of US alone for degrading MB, RB and MO were negligible. while in the absence of
catalyst the degradation of organic dyes through H
attributed to negligible producing of hydroxyl radicals through direct sono decomposition of H
25]:
2
O
2
/US process was decreased slightly which could be
2
O
2
(Eq. 3)
[
•
H O
2 2
+ US →2 OH
(3)
In Figs. 7-9, the UV–vis spectrum of the initial MB, RhB and MO dye solutions was dark blue, dark
Pink and dark orange, with the λmax at 665, 554 and 465 nm, respectively. By the time, the absorbance
intensity at λmax for MB, RhB and MO dyes was decreased and the solutions color turned. In addition, the
MW-CoFe
external magnet. MB was degraded 98% and 67% by MW-CoFe
respectively within 91 min, while degradation of the MB took 181 min by the CT-CoFe
2
O
4
and CT-CoFe
2
O nanoparticles were separated easily from the reaction solutions by
4
2
O
4 2
/H O
2
and CT-CoFe
2
O
4
/H
2
O
2
system
2
O
4 2
/H O
2
system.
11

12
In the case of RhB, in the presence of MW-CoFe
degradation, while 83% was degradation in the presence of CT-CoFe
Also, within 91 min only 60% of MO was degraded in the presence of MW-CoFe
0% in the presence of CT-CoFe /H system.
2
O
4
/H
2
O
2
system 90% of RhB within 91 min was
/H system after 121 min.
/H system and
O
2 4
O
2 2
O
2 4
O
2 2
4
2
O
4
2
O
2
Fig. 7. UV–vis spectra of MB dye solution oxidized by H
O
2 2
with the addition of (a) MW-CoFe
2
O and
4
(
b) CT-CoFe , at different intervals.
2
O
4
12

13
Fig. 8. UV–vis spectra of RhB dye solution oxidized by H
2
O
2
with the addition of (a) MW-CoFe
2
O and
4
(
b) CT-CoFe , at different intervals.
2
O
4
Fig. 9. UV–vis spectra of MO dye solution oxidized by H
O
2 2
with the addition of (a) MW-CoFe
2
O and
4
(
b) CT-CoFe , at different intervals.
2
O
4
Furthermore, the degradation efficiencies of MB with the US, H
2
O
2
/US, MW-CoFe
2
O /US, CT-
4
CoFe /US, MW-CoFe /H /US and CT-CoFe /H /US systems were 0%, 16%, 52%,41% ,
2
O
4
O
2 4
O
2 2
2
O
4
2
O
2
13

14
9
8% and 65%, respectively (Figure 10 a). Also, the degradation efficiencies of RhB with the US,
/US, MW-CoFe /US, CT-CoFe /US, MW-CoFe /H /US and CT-CoFe /H /US
systems were 0%, 14%, 48%, 39%, 94% and 71%, respectively (Figure 10 b). The degradation
efficiencies of MO with the US, H /US, MW-CoFe /US, CT-CoFe /US, MW-CoFe /H /US
and CT-CoFe /H /US systems were 0%, 9%,21%, 19%, 59% and 38%, respectively (Figure 10 c).
The sono degradation of MB, RhB or MO were varied due to their different sizes and surface electric
charges [26]. The above results confirmed that ultrasonic irradiation, H , MW-CoFe and CT-
CoFe are essential factor for the complete degradation of MB, RhB or MO.
H
O
2 2
2
O
4
2
O
4
2
O
4
2
O
2
2
O
4
2
O
2
2
O
2
O
2 4
2
O
4
2
O
4
2
O
2
O
2 4
2
O
2
2
O
2
2
O
4
2
O
4
Fig.10. The relative concentration change of (a) MB, (b) RhB and (c) MO in the presence and without
presence of the nanoparticles of MW-CoFe and CT-CoFe
2
O
4
2
O .
4
3
.2.1. Effect of H
The amount of H
CT-CoFe
MB was degraded while by increasing the amount of H
2
O
2
2
O
2
was optimized to run efficient degradation of MB using both of MW-CoFe
, less than 41% of
up to twice, the degradation efficiency
2
O and
4
O
2 4
under ultra sound irradiation. As could be seen in Fig. 11, without H
2
O
2
2
O
2
14

15
remarkably was increased up to 98% for MW-CoFe
2
O
4
and 65% for CT-CoFe
2
O
4
. However more addition
of H not only was not further boosted on the degradation effectiveness but also decreases the
2
O
2
•
degradation yield. Because the high amount of the H
2
O act as OH radicals scavenger that generates
2
•
HOO radicals with lower oxidation potential [27–29].
Fig. 11. Effect of the different amount of H
2
O
2
on the sonocatalytic degradation of MB in present of the
and (b) CT-CoFe
(a) MW-CoFe
2
O
4
2
O .
4
3.2.2. Effect of catalyst dosage
The catalyst dosage was optimized for MB degradation in oxidation condition and under ultrasound
irradiation. As shown in Fig. 12, the degradation performance of MB is depended on catalyst amount. By
the increasing the catalyst dosage up to 50 mg the degradation yield was increased but higher dosage
catalyst from 50 to 75 mg lead to a reduction in degradation efficiency of MB. This phenomenon could be
related to aggregation of particles and the bereavement in active surface area. Also, increasing the amount
of catalyst, might be causes the active reaction sites [30] and so, affected the area of cavitation
phenomenon.
15

16
Fig. 12. Effect of the different amount of (a) MW-CoFe
2
O
4
and (b) CT-CoFe
2
O on the sonocatalytic
4
degradation of MB.
3.2.3. Mechanism of sonocatalytic degradation
To further determine the sonocatalytic process over CoFe
2
O
4
nanoparticles, t-BuOH, ammonium
•
+
•−
2
oxalate (AO) and benzoquinone (BQ) as scavenger for OH, h and O
were added to the reaction
mixture. As demonstrated in Fig.13, when BQ is added to the reaction system, sono degradation process
•
2
−
of organic dyes is close to the reaction in the absence of O
scavengers. While the t-BuOH and AO can
•
+
greatly prevent the sono degradation, which mentions that the OH and h played the important role in the
sono degradation process.
16

17
Fig. 13. Effects of the addition scavenger on the sono degradation process of organic dyes over CoFe
nanoparticles.
2
O
4
Based on the above results, a feasible mechanism under US irradiation for the degradation of dyes by
MW-CoFe and CT-CoFe nanoparticles was proposed. The probable sonocatalytic degradation
mechanism could be based on a process known as “cavitations” (Eq. 4). The first, sonoluminescence by
2
O
4
O
2 4
31,32
ultrasonic cavitation effect could generate light has a relatively wide range of wavelengths.
Under this
condition the MW-CoFe and CT-CoFe nanoparticles should be excited to execute the degradation.
2
O
4
2
O
4
Second, by ultrasonic cavitation effect in an aqueous medium, the temperature of the ‘‘hot spot” produced
could reach a very high temperature (about more than 1000 °C). Such high temperature, to produce
•
32-34
hydroxyl radicals (OH ) on the surface of the catalyst, could enough break down H
These heat energies of ‘‘hot spot” Similar to light, could also excite the prepared MW-CoFe
CoFe nanoparticles (Eq. 5). The electrons are excited to the conduction band (CB) of CoFe
nanoparticles, from valence band (VB) and the surface or the inner of CoFe nanoparticles, electron-
hole pairs are formed (Eq. 6). The generated electrons of CoFe reacted with H
2
O
2
molecules.
O
2 4
and CT-
2
O
4
2
O
4
O
2 4
2
O
4
O
2 2
to produce hydroxyl
•
-
radicals (OH ), to degrade MB, RhB and MO (Eq. 7). The generated holes oxidized the OH or H
2
O
17

18
ꢀ
molecules from H
hydroxyl radicals with active types oxidized the dye molecules to products (H
6]. So, the suggested schematic mechanism for the sonogenerated electron−hole separation process of
MW-CoFe and CT-CoFe is illustrated in Fig. 14. Ultrasoun would help faster mass transfer to/from
the surface of nanoparticles and hydogenperoxide activation. The possible process should be as following:
O
2 2
adsorbed on the surface of CoFe
O
2 4
particles to produce OH (Eq. 8). Finally, these
2
O, CO , etc) (Eq. 9) [31–
2
3
2
O
4
2
O
4
Ultrasonic irradiation (cavitation effect) → heat + light
(4)
(5)
(6)
(7)
*
2
[CoFe O
4
] + light or heat → [CoFe
2
O ]
4
*
+
-
2
[CoFe O
4
] → [CoFe
2
O
4
] + h + e
-
-
ꢀ
e
CB + H O
2 2
→ OH + OH
+
ꢎꢏꢃꢐ
ꢀ
h
VB + ꢏꢑꢎꢃ→ OH
(8)
(9)
ꢀ
dye + OH → degradation products (H
2
O, CO , etc)
2
Fig. 14. Schematic drawing the separation of generated electrons and holes on the interface of the MW-
CoFe (1.35 ev) and CT-CoFe (1.36 ev) under ultrasonic irradiation.
2
O
4
2
O
4
3.2.4. Reusability test
In order to evaluate the performance of the MW-CoFe
2
O
4
and CT-CoFe
2
O nanoparticles sonocatalyst,
4
it was separated from the reaction mixture by a magnet, washed with deionized water several times and
again reused for degradation of MB, RhB and MO. The catalyst performance was examined 6 times
without significant loss in activity. As shown in Fig. 15, the FT-IR spectra of the recovered MW-CoFe
2
O
4
18

19
and CT-CoFe
catalysts (see Figure 1b and c). This finding confirms that the structure of the MW-CoFe
CoFe nanoparticles are stable under the reaction conditions.
2
O
4
nanoparticles do not show significant changes after the six run comparing to the unused
2
O
4
and CT-
2
O
4
Fig. 15. (a) Recyclability of MW-CoFe
2
O
4
and CT-CoFe
2
4
O nanoparticles, and (b) FT-IR of recovered
MW-CoFe and CT-CoFe
2
O
4
O
2 4
nanoparticles after the sixth run.
4. Conclusions
The catalytic and properties of CoFe
2
O nanoparticles that obtained by using MW irradiation and
4
conventional thermal methods were compared. As conclusion, the particle size was well controlled using
microwave irradiation method with advantages of monodispersity and small particle size less than 10 nm.
These nanoparticles were shown higher sonocatalytic activity of toward degradation of organic cationic
dyes such as MB and RhB. Also, the magnetic behavior of CoFe
separation of catalyst from reaction solution by an external magnet. The MW-CoFe
sonocatalytic efficiencies as high as 98% and 90%, for MB and RhB degradation that are up to 50 % more
than what obtained for CT-CoFe . In contrast, low degradation percentages were recorded for MOdue
to its anionic nature. The higher catalytic reactivity of MW-CoFe should be related to their smaller
particle size (9 nm) than CT-CoFe (33 nm), and obviously higher active surface area. This facile and
O
2 4
nanoparticles provides facile
O
2 4
shows the
O
2 4
2
O
4
2
O
4
19

20
inexpensive synthesis by MW irradiation methods could be extended for fabrication of other MFe
Mn, Ni, and Zn) nanomaterials with high reactivity.
2
O (M
4
=
Acknowledgments:
We gratefully acknowledge University of Kurdistan and University of Lorestan for their support.
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Table of content:
The easily reusable high efficiency of magnetic flower-like CoFe
decomposition of [CoFe O(CH COO) (H O) ]·2H O in very short reaction time and using them as
sonocatalyst for degenerated of organic dyes.
2
O nanoparticles prepared through
4
2
3
6
2
3
2
23