M. Karaca et al. / Ultrasonics Sonochemistry 31 (2016) 250–256
251
considerable interest due to its unique physical, chemical and opti-
cal characteristics such as high UV absorption potential, wide band
gap (3.37 eV) and low cost [18,19]. Various methods have been
reported to increase the catalytic activity of ZnO such as semicon-
ductor coupling, metal doping, non-metal doping and immobiliza-
tion of ZnO on the materials surface with large surface area [3].
In this paper, ZnO nanoparticles, as a sonocatalyst, have been
synthesized and immobilized on the surface of montmorillonite
K10 (MMT) for the degradation of a drug. To the best of our knowl-
edge, there is no detailed report on the sonocatalytic performance
of ZnO/MMT nanocomposite for the removal of naproxen. The
effect of different key factors on the sonocatalytic degradation of
naproxen, such as initial concentration of naproxen, ZnO/MMT
dosage, pH of the solution, the presence of organic and inorganic
anions and the power of ultrasonic generator have been studied.
GC–MS analysis was also used to identify the intermediates
produced during sonocatalysis of naproxen.
mass spectrometer (Canada) was used to identify produced inter-
mediates during sonocatalysis of naproxen.
2.3. Sonocatalytic degradation experiments
The sonocatalytic degradation of naproxen was carried out in an
ultrasonic apparatus (WUC-D10H, 40 kHz, 665 W, Korea) under air
atmosphere. In a typical approach, 100 mL of naproxen solution
with known initial concentration containing desired amount of
catalyst was sonicated with a frequency of 60 kHz and output
power of 650 W at natural pH. At desired time intervals, a required
volume of sample was taken out and the remaining naproxen con-
centration was determined using Varian Cary 100 UV–Vis spec-
trophotometer (Australia) at a maximum wavelength of 230 nm.
UV–Vis spectral changes of naproxen in the presence of ZnO/
MMT nanocomposite as a function time under ultrasonic irradia-
tion were studied and the results are presented in Fig. 1. The max-
imum peak observed at the wavelength of 230 nm decreased
gradually as the time increased, and it almost disappeared after
the irradiation time of 120 min, revealing the sonocatalytic degra-
dation of naproxen on the surface of the ZnO/MMT nanocomposite.
2
. Materials and methods
2.1. Materials
3
. Results and discussion
14 3
Naproxen (C14H O , 98%) was purchased from Sigma–Aldrich,
(
USA) and dissolved in distilled water. Characteristics and chemical
3.1. Characterization of ZnO/MMT nanocomposite
structure of naproxen are shown in Table 1. ZnCl , HCl and NaOH
2
were purchased from Merck, Germany. Cetyltrimethylammonium
bromide (CTAB) and montmorillonite K10 (MMT) were purchased
from Sigma–Aldrich Co. (USA). All other chemicals were of analyt-
ical grade.
Fig. 2 shows the SEM images of MMT and synthesized ZnO/
MMT nanoparticles. When the SEM images of the MMT (Fig. 2(a))
and the ZnO/MMT (Fig. 2(b)) samples compared with each other,
it is clearly seen that the ZnO particles immobilized on the porous
surface of MMT. Fig. 3 shows the HR-TEM images of synthesized
ZnO nanoparticles on MMT. Fig. 3((a) and (b)) shows the HR-TEM
images of bare MMT with a porous surface. Fig. 3((c) and (d))
shows the HR-TEM images of ZnO/MMT nanocomposite. Plate-
like ZnO particles are obvious in HR-TEM images indicating the
proper synthesis of nanosized ZnO on porous surface of MMT.
These images show the shape and particle size distribution of
ZnO–MMT sample indicating that the ZnO–MMT particles are
within the nanoscale (6100 nm).
2.2. Catalyst synthesis and characterization
ZnO/MMT nanocomposite was prepared through synthesis of
ZnO nanoparticles on the surface of MMT. In order to reach a
homogenous suspension of MMT, 1 g of MMT was dissolved in
1
00 mL distilled water and stirred for 24 h. Then the desired
amount of CTAB was added to the MMT solution with stirring.
Then, 1 g of ZnCl was added to 20 mL distilled water. 1 M NaOH
2
solution was added drop wise to the above solution until the pH
reached to 12.5. The prepared zinc chloride was added to CTAB/
MMT suspension and the mixture was stirred for 6 h. Finally, the
obtained precipitate was washed with distilled water and ethanol
and dried at 90 °C for 3 h.
The XRD pattern of the synthesized ZnO/MMT nanocomposite
(Fig. 4) exhibited dominant peaks at 2h value of 31.71°, 34.41°,
36.21°, 47.51°, 56.61°, 63.0°, 66.08°, 68.0°, 68.28°, 71.64°, and
75.96° which corresponded to the (100), (002), (101), (102),
(110), (103), (200), (112), (201), (004), and (202) planes of
Scanning electron microscope (SEM) model (MIRA3 FEG-SEM
Tescan, Czech) and high-resolution transmission electron micro-
scope (HR-TEM) model JEM 2100F, JEOL (Japan) operated at
2
.5
2
0
min
15 min
0 min
45 min
1
00 k were used to investigate the surface morphology of the
MMT particles and ZnO/MMT composite. Crystal structures of pure
MMT, ZnO particles and ZnO/MMT composite were determined
using X-ray powder diffraction (XRD) measurements by P analyti-
cal X’Pert PRO diffractometer (Germany). The Brunauer–Emmett–
Teller (BET) equation was used to measure the total specific surface
areas (SBET). An Agilent 6890 gas chromatograph with a 30 m to
3
1.5
1
60 min
75 min
90 min
120 min
0
.25 mm HP-5MS capillary column coupled with an Agilent 5973
0
.5
0
Table 1
Characteristics of naproxen.
Chemical structure
Molecular formula
k
max (nm)
M
w
(g/mol)
200
250
300
14 14 3
C H O
230
230.259
Wavelength (nm)
2
CO H
Fig. 1. The changes in the UV–vis spectrum of 10 mg/L of naproxen during different
treatment time (experimental conditions: [Catalyst] = 0.5 g/L, pH = 4.5 and US
Power = 650 W/L).
O