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Accepted Manuscript
Synthesis of pumice-TiO2 nanoflakes for sonocatalytic degradation of famotidine
Tannaz Sadeghi Rad, Alireza Khataee, Berkant Kayan, Dimitrios Kalderis, Sema
Akay
PII:
S0959-6526(18)32508-3
DOI:
10.1016/j.jclepro.2018.08.165
Reference:
JCLP 13949
To appear in:
Journal of Cleaner Production
Received Date: 17 April 2018
Revised Date:
24 July 2018
Accepted Date: 16 August 2018
Please cite this article as: Rad TS, Khataee A, Kayan B, Kalderis D, Akay S, Synthesis of pumiceTiO2 nanoflakes for sonocatalytic degradation of famotidine, Journal of Cleaner Production (2018), doi:
10.1016/j.jclepro.2018.08.165.
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ACCEPTED MANUSCRIPT
Graphical abstract
Synthesis and characterization of pumice-TiO2 and its application in the heterogeneous
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sonocatalytic process
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Synthesis of pumice-TiO2 nanoflakes for sonocatalytic degradation of
famotidine
Akay c
a
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Tannaz Sadeghi Rad,a Alireza Khataee,a,b,* Berkant Kayan,c Dimitrios Kalderis,d Sema
Research Laboratory of Advanced Water and Wastewater Treatment Processes, Department of
b
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Applied Chemistry, Faculty of Chemistry, University of Tabriz, 51666-16471 Tabriz, Iran
Department of Materials Science and Nanotechnology Engineering, Faculty of Engineering,
c
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Near East University, 99138 Nicosia, North Cyprus, Mersin 10, Turkey
Department of Chemistry, Art and Science Faculty, Aksaray University, 68100 Aksaray,
Turkey
d
Department of Environmental and Natural Resources Engineering, School of Applied Sciences,
* Corresponding author:
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Technological and Educational Institute of Crete, 73100 Chania, Crete, Greece
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E–mail address: a_khataee@tabrizu.ac.ir
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Tel.: +98 41 33393165; Fax: +98 41 33340191
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Abstract
Pumice-TiO2 was synthesized through simple sol-gel method. The successful synthesis of the
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catalyst was verified by SEM, EDS, XRF, FT-IR and BET techniques. Then, a sonocatalytic
process was performed to degrade famotidine in the presence of the synthesized catalyst and
under ultrasonic irradiation. The removal efficiency of the sonocatalytic process with pumice‒
TiO2, TiO2, pumice and sonolysis within 70 min was 71.1%, 33.9%, 31.1% and 8.9%,
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respectively. The main operational parameters which were examined in this study were catalyst
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dosage, pH, famotidine concentration and ultrasonic power which were optimized as 1.5 g/L, 5,
20 mg/L and 150 W, respectively. Moreover, the addition of radical scavengers (EDTA, Na2SO4
and 1, 4–benzoquinone) and enhancers (H2O2 and K2S2O8) which can affect the removal
efficiency were investigated. Diverse degradation by-products were identified using GC‒MS
analysis. Eventually, the reusability tests confirmed that the synthesized pumice‒TiO2 catalyst
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had significant stability after 5 consecutive runs.
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Keywords: Sonocatalytic degradation; Pumice; Pumice‒TiO2; Pharmaceutical.
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1. Introduction
Pharmaceuticals are a wide group of substances prepared to improve public health. In recent
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years, pharmaceutical industries have released diverse toxicological compounds to municipal
wastewater without further treatments, which have been identified as primary contaminants with
unfavorable consequences on environmental systems (Mondal et al., 2018). The majority of
pharmaceuticals are non–biodegradable and their degradation intermediates are more hazardous,
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therefore they should be eliminated from aquatic media or decreased to permissible levels (Jelic
et al., 2011). Famotidine (FMT), known as a H2 blocker drug, is commonly used for
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gastroesophageal reflux disease. Various studies reported that FMT remained intact in the urine
after usage and has been traced in wastewater effluents. Accordingly, particular treatment
approaches are required for the removal and degradation of FMT from municipal and industrial
wastewaters (Murphy et al., 2012).
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Advanced oxidation processes (AOPs) are introduced as more promising techniques due to
their high potential for mineralization and degradation of refractory organic pollutants by in situ
formation of reactive oxygen species (ROSs), specially hydroxyl radicals (•OH) (Atalay and
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Ersöz, 2016; Chong et al., 2012). Ultrasonic process as an environmentally friendly AOP,
extensively applied for removal of pharmaceuticals from contaminated aquatic areas (Chong et
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al., 2017; Khataee et al., 2016c). The mechanism of the sonolysis process is mainly related to the
effect of acoustic cavitation and free radical generation. Acoustic cavitation is the formation of
tiny microbubbles which grow and eventually collapse by generating great localized pressure and
temperature. H⦁ and ⦁OH are produced by water molecules splitting that occurs via hot spots at
the interface of the bubble–liquid (Chong et al., 2017; Khataee et al., 2018). Nevertheless, the
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main obstacle for application of sonolysis process is energy consumption in thermal form and
increasing operational cost (Dinesh et al., 2015).
Combination of sonication with nanocatalysts to develop heterogeneous sonocatalytic process
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boosts the removal efficiency (RE%) to a great extent (Porhemmat et al., 2017). Sonocatalysts
cause enhanced mass transfer among contaminants in the solution medium and the surface of the
catalyst. Moreover, active sites for bubble nucleation are increased in the presence of catalysts.
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Diverse semiconductors including CdSe (Khataee et al., 2018), ZnO (Khataee et al., 2015b),
ZrO2 (Khataee et al., 2017b), TiO2 (Wang et al., 2010) and FeCeOx (Chong et al., 2017) have
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been applied as catalyst in heterogeneous sonocatalytic processes. Amongst, titanium dioxide
(TiO2) has been recommended as a suitable catalyst for utilization in wastewater and water
treatment procedures due to low toxicity, low-price and specific chemical and physical
properties.
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Various synthesis methods have been used in order to provide TiO2 based catalysts, for
instance: electrochemical (Mo et al., 2014), precipitation (Haldorai and Shim, 2014),
sonochemical (Bhagwat et al., 2017) and sol–gel (Khataee et al., 2017a). Among these methods,
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sol-gel is the more attractive technique due to low-temperature requirement, short treatment time
and superb control on catalyst size and morphology (Danks et al., 2016).
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In order to enhance the stability and performance of TiO2 in sonocatalytic process, different
porous substrates are applied and diverse elements are doped to TiO2 structure. Pumice is a
textural volcanic silicate material, which is widely utilized as adsorbent, support and catalyst in
water–based treatment processes due to superb stability and mechanical strength, porous
structure and catalytic efficiency (Yuan et al., 2016). To date, there is no study based on
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immobilization of TiO2 on pumice by sol–gel method and using it as sonocatalyst in
heterogeneous sonocatalytic process.
This study has focused on the synthesis and immobilization of TiO2 on pumice surface and its
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application for degradation of FMT via a heterogeneous sonocatalytic process. Different methods
such as: scanning electron microscopy (SEM), energy‒dispersive X‒ray spectroscopy (EDS), X‒
ray fluorescence (XRF), Fourier transform infrared spectroscopy (FT‒IR), photoluminescence
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(PL) and Brunauer‒Emmett‒Teller (BET) analysis were performed in order to specify the
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characterization of pumice and pumice‒TiO2 samples. Afterwards, the performance of pumice‒
TiO2, TiO2 and plain pumice was compared in sonocatalytic process for the degradation of FMT.
The impact of working parameters including pumice‒TiO2 dosage, pH, initial FMT concentration
and ultrasonic power on the RE% of FMT were evaluated. Furthermore, the effect of various
scavengers and enhancers was studied. Eventually, the generated intermediates were
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distinguished by gas chromatography‒mass spectrometry (GC–MS) method.
2.1. Materials
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2. Experimental details
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The entire analytical grade reagents and chemicals were utilized as received. Hydrochloric
acid (HCl, 38%), Ethylenediamine tetra acetic acid (C10H16N2O8, EDTA, ≥99%), 1, 4–
benzoquinone (BQ, C6H4O2, 99%), Sodium sulfate anhydrous (Na2SO4, 99 %), Sodium
hydroxide (NaOH, 99%), Sulfuric acid (H2SO4, 98%), Titanium dioxide (TiO2), Titanium
butoxide (Ti(OBu)4, 98%), Hydrogen peroxide (H2O2, 30 %), Potassium persulfate (K2S2O8,
98%) were procured from Merck company. Absolute Ethyl alcohol (C2H5OH, 99.6 % v/v) was
purchased from Jahan Alcohol Teb Arak company (JATA, Iran). Pumice sample was obtained
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from the Hasandagi volcanic mountain zone (Aksaray, Turkey). Famotidine (FMT) as a model
pollutant, was obtained from Pursina pharmaceutical company (Iran). The chemical composition
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of FMT is illustrated in Fig. 1.
2.2. Synthesis of pumice‒TiO2
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A simple modified sol–gel synthesis method was carried out to prepare pumice‒TiO2:
(1) 1 g of pumice was added to ethanol (40 mL) and was well dispersed by ultrasonication
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during 15 min, (2) as the TiO2 precursor, Ti(OBu)4 (8 mL) was added to the previous solution,
(3) the resultant suspension was magnetically stirred (60 min) at ambient temperature, (4) a
solution containing HCl (38%, 8 mL) and ethanol (99%, 20 mL) was inserted dropwisely into the
prepared suspension and agitated for 1 h, (5) the pumice‒TiO2 particles were filtered and finally
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dried for 24 h at 100 °C.
It should be mentioned that, the similar synthesis method was studied by other papers (Wang
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et al., 2008). Thus, authors try to use similar amounts of TiO2 as reported before.
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2.3. Characterization instruments
SEM micrographs (Tescan, Mira3, Czech Republic) accompanied with an EDS microanalysis
were carried out to determine the morphology of surface and chemical structure of the pumice
and pumice‒TiO2, respectively. XRF analysis was performed by a Bruker S4 Explorer Rigaku
ZSX Primus II instrument (Japan) to evaluate the composition of the catalysts. FT‒IR
spectrophotometer (Tensor 27, Bruker, Germany) was applied to recognize the FT–IR spectra
using KBr pellet technique. The surface characteristics of the pumice and pumice‒TiO2 such as;
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specific surface area and porosity were studied utilizing the BET technique, which is obtained by
a Micromeritics Gemini VII, according to N2 adsorption–desorption isotherm data. In order to
and recorded by a spectrometer (Perkin Elmer LS45, USA).
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investigate the electron–hole recombinations, PL emission spectra of the samples were analyzed
To recognize the final byproducts during sonocatalytic degradation of FMT, GC–MS was
utilized. For this aim, FMT solution (40 mg/L) treatment was performed under the obtained
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optimum conditions. In order to extract the organic compounds 20 mL of diethyl ether was added
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twice. After volatilization, N, O-bis-(trimetylsilyl)-acetamide (100 µL) was used to dissolve
residual solid under stirring for 15 min and heating at 60 °C. The generated silylated products
were analyzed by GC–MS (Hewlett Packard (HP) 6890 gas chromatography, Hewlett Packard
(HP) 5973 mass spectrometer; Palo Alto, CA, USA). HP-5MS capillary column, 30 m × 0.25
mm i.d., 0.25 µm film thickness was used to separate analytes. The temperature program is as
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follows: 50 °C for 3 min, heating at 10 °C/min up to 270 °C and a hold time of 4 min. The
electron energy was 70 eV and the inlet and transfer line temperatures were 270 °C and 250 °C,
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respectively.
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2.4. Heterogeneous sonocatalytic process for the degradation of FMT
The degradation efficiency of FMT was investigated in the presence of certain amounts of
pumice‒TiO2 employing an ultrasonic bath (Ultra 8060, 36 kHz, 150 W, England). In this study,
distinct amounts of pumice‒TiO2 were added to the FMT solution (100 mL) in an Erlenmeyer
flask (250 mL). The solution pH was controlled by HCl and NaOH (0.1 mol/L). Afterwards, the
Erlenmeyer flask was placed in the ultrasonic bath for 70 min in order to perform heterogeneous
sonocatalytic process. To prevent the photocatalytic reactions, all tests in ultrasonic bath were
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done at room temperature in the dark. During the procedure, 3 mL of the treated solution was
sampled at particular time intervals. The absorbance of the samples was recorded (λmax = 288
nm) utilizing UV–vis spectrophotometer (Analytik Jena, Specord 250, Germany). The RE% is
RE%=
A0-A
×100
A0
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calculated by Eq. (1):
(1)
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where A0 and A are initial FMT absorbance and absorbance after distinct reaction time,
3. Results and discussion
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respectively.
3.1. Characterization of pumice and pumice‒TiO2
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Fig. 2 (a-c) and (d-f) illustrate the SEM figures of pumice and pumice-TiO2 with different
magnifications, respectively. The SEM images of plain pumice show a bulky, irregular and
rough structure. However, pumice-TiO2 images indicate the formation of uniform nanoflakes on
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the pumice surface. Figure 2f indicates the thickness of the flakes which are in the nano size
ranges. It can be concluded that TiO2 nanoflakes were synthesized and immobilized successfully
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on pumice surface. Liu et al. reported the nanoflake morphology of TiO2 in Ag species/TiO2
catalyst, which is in accordance with the SEM analysis of this paper (Liu et al., 2011).
In order to study the constituent elements of pumice and pumice‒TiO2 samples, EDS analysis
was performed. Results exposed that the both samples contain C, N, O, Na, Mg, Al, Si, S, Cl, K,
Ca and Fe elements (Fig. 3a and 3b). Fig. 3b indicates a strong peak and some weak peaks for Ti,
which confirm the modification of pumice with TiO2.
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Table 1 provides the information on chemical composition of the catalysts which were
obtained by XRF analysis. The major compounds such as SiO2, TiO2, Al2O3, Fe2O3, MnO, MgO,
CaO, Na2O and K2O are present in pumice and pumice‒TiO2. The weight percentages of TiO2 in
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pumice and pumice‒TiO2 samples were 0.087 and 7.673 %, respectively. It can be deduced that,
TiO2 was formed well on pumice surface.
The surface functional groups of pumice (Fig. 4a) and pumice‒TiO2 (Fig. 4b) were
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determined by FT‒IR analysis. The wide peak around 3440 1/cm associates with the water
molecules stretching vibration in the lattice (moisture) and ‒OH groups (Sepehr et al., 2013;
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Stevens Jr et al., 2008). The stretching vibration of the hydroxyl groups of H2O absorbed from
the environment is at about 1630 1/cm. The stretching modes of Al‒O and Si‒O bonds are
observed around 1075 1/cm and the bending vibrations of these groups are considered to be
between 500 and 550 1/cm. Around 785 1/cm, the stretching vibration of Si‒O‒Al is recorded
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(Sepehr et al., 2013). By comparing the pumice and pumice‒TiO2, the new absorbance peak for
pumice‒TiO2 appears at around 1460 1/cm and the peak at 940 1/cm is sharpened which can be
attributed to Ti‒O‒Ti and Ti‒O‒Si, respectively (Hassani et al., 2017). Eventually, FT‒IR results
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support the growth of Ti containing groups by pumice‒TiO2 synthesis.
The PL spectra were utilized to study the fate of electron–hole pairs recombination in the
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synthesized catalysts. The PL emission spectra of TiO2 and pumice‒TiO2 were examined in the
range of 355‒455 nm (Fig. 5). In comparison with TiO2, the PL intensity is decreased in pumice‒
TiO2 sample which confirms a lower recombination rate of generated electrons and holes. Thus,
TiO2 modification improves the separation of charge carrier, which could lead to higher removal
efficiency. Similar results have also been observed in previous research papers (Hajjaji et al.,
2014; Zhang et al., 2013).
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The pore volume and specific surface area of samples were studied by the BET model, which
are reported to be 0.234 cm3/g and 1.0211 m2/g for pumice and increased to 0.377 cm3/g and
1.9435 m2/g for pumice‒TiO2, respectively. It should be considered that, pumice is a volcanic
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sand and its surface area varies widely, from 0.12 m2/g (Yuan et al., 2016) to more than 32.2
method of post-collection processing.
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3.2. Comparing different processes for removal of FMT
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m2/g (Liu et al., 2014)). This depends on the location from which pumice is obtained and the
The performance of the diverse procedures including; sonolysis, adsorption and sonocatalytic
processes in the presence of pumice, TiO2 and pumice‒TiO2 is shown in Fig. 6. The RE% is
8.9% in sonolysis process after 70 min of reaction, which is insufficient for FMT degradation.
(2).
•
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H2O →
OH + •H
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During sonolysis process, water molecules generate hydroxyl radicals with low rate through Eq.
(2)
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The adsorption of FMT on catalyst surface of TiO2, pumice and pumice‒TiO2 is 3.5, 14.0 and
19.3%, respectively. It should be mentioned that, pumice as a porous support can prepare a site
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for adsorption of FMT on catalyst surface (Heibati et al., 2015). The results reveal that, the RE%
is about 31.1, 33.9 and 71.1% for sonocatalysis with pumice, TiO2 and pumice‒TiO2,
respectively. The observed increment in sonocatalytic process can be attributed to the generation
of vast numbers off cavitation bubbles on the surface of the solid catalyst, which result in
production of more hydroxyl radicals by water cleavage. The higher RE% in the presence of
pumice‒TiO2 is due to the production of electron–hole pairs by using TiO2 as semiconductor.
The conduction–band electrons can interact well with oxygen molecules and generate reactive
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radicals and molecules such as HO2•, O2•–, •OH and H2O2, that can help the degradation of FMT
(Eqs. (3–8)). The generated holes on the catalyst surface are responsible for producing •OH by
hydroxyl anions and the adsorbed water oxidation (Eqs. 9 and 10) (Khataee et al., 2015a). Also,
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based on the PL analysis the recombination rate of electron–hole can be reduced by using
pumice‒TiO2, so the removal efficiency increases significantly. The small effect of the
sonoluminescence process should be considered during the sonication, when the semiconductor
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was activated like a photocatalyst (Selli, 2002).
O2 + e– → O2•–
H+ + O2•– → •OOH
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O2•– + •OOH + H+ → H2O2 + O2
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pumice‒TiO2 (h+ + e–)
pumice‒TiO2 →
(3)
(4)
(5)
(6)
O2•– + H2O2 → •OH + OH– + O2
(7)
e– + H2O2 → •OH + OH–
(8)
(9)
OH– + h+ → •OH
(10)
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H2O + h+ → •OH + H+
Based on the aforementioned facts, all remaining tests were done by pumice‒TiO2 as the
promising sonocatalyst and the effect of various operational parameters such as sonocatalyst
dosage, pH, FMT concentration and ultrasonic power were investigated.
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3.3. Effects of the working parameters on the degradation of FMT during sonocatalytic
process
The impact of various factors such as catalyst dosage, pH, FMT concentration and ultrasonic
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power were thoroughly evaluated on sonocatalytic degradation of FMT. The influence of
pumice‒TiO2 on the degradation efficiency of FMT is illustrated in Fig. 7a. The RE% is
enhanced by sonocatalyst increment up to 1.5 g/L due to the increase in accessible surface area
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of pumice‒TiO2, which resulted in the generation of more ROSs (Wang et al., 2009). By
enhancing the catalyst dosage to 2 g/L, the RE% declined due to the catalyst aggregation and the
the optimum sonocatalyst concentration.
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blockage of ultrasound waves in the solution media (Chen, 2009). Hence, 1.5 g/L was chosen as
Based on the earlier studies, pH is the most influential parameter in the heterogeneous
sonocatalytic process (Al-Hamadani et al., 2017; Sivakumar and Muthukumar, 2011).
To
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examine the impact of pH on the degradation efficiency of FMT, solution pH was set over a vast
range of values (3, 5, 7 and 9). As it can be seen from Fig. 7b, the FMT degradation was declined
from 75.5 to 34.8 % as the pH value raised from 3 to 9. As the pH increased from 0 to 14, the
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oxidation potential of hydroxyl radical decreased from 2.8 to 1.95 V. In addition, at high pH
values, smaller amounts of free hydroxyl radicals were produced due to the recombination of
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OH to generate H2O2 species (Das et al., 2017).
Fig. 7c demonstrates the effect of increasing FMT initial concentration (10‒50 mg/L) on the
degradation efficiency of sonocatalytic process treated by pumice‒TiO2 catalyst. As the
concentration of FMT was enhanced (10‒50 mg/L), the RE% decreased (82.1‒31.3 %). This can
be due to the following reasons: (i) The sonocatalyst surface area is occupied with numerous
FMT and intermediate molecules and (ii) limited number of ROSs is generated which is
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responsible for degradation of more FMT molecules; as a consequence, the RE% significantly
declines (Das et al., 2017; Sun and Lemley, 2011).
Fig. 7d depicts the influence of ultrasonic power on the degradation of FMT using pumice‒
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TiO2 as sonocatalyst. As the ultrasonic power improved from 150 W to 300 W, the RE%
increased from 71.1 to 80.2%, within a reaction time of 70 min. The result can be explained by
these facts; (i) great turbulence can be created in higher ultrasonic power, which can improve
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mass transfer of FMT, ROSs and degradation intermediates among the active surface of the
sonocatalyst and the bulk solution, (ii) in high ultrasound power, cavitation energy increased, the
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cavitation threshold decreased and finally the number of the produced cavitation bubbles
enhanced (iii) great number of ROSs are formed by increasing the number of collapsing bubbles
and (iv) cleaning performance of the ultrasonic irradiations can keep the active sites of pumice‒
TiO2 free and available (Das et al., 2017). It should be noted that, since the RE% didn’t notably
ultrasonic power.
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improve in the ultrasonic powers of 150 and 300 W, 150 W was chosen as the optimum
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3.4. Effect of various scavengers on the degradation of FMT
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Diverse scavengers were used in order to assess the main ROSs and investigate the
importance of surface reactions in the heterogeneous sonocatalytic process (Fathinia and
Khataee, 2015; Khataee et al., 2016b). The effect of the adsorption process and different reactive
agents such as •OH, O2•‒ and h+ should be considered in this process. In this study, the removal
of FMT by the sonocatalytic process was evaluated in the presence of EDTA, BQ and Na2SO4
with molar ratios of [FMT]0:[scavenger]0 of 1:1, 1:10, and 1: 50.
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EDTA was applied to investigate the role of adsorption of FMT and scavenging the h+. As
shown in Fig. 8a, EDTA reduced the FMT degradation and the RE% was decreased from 71.1 to
63.0, 51.5 and 41.7 % in the molar ratios of 1:1, 1:10, and 1: 50, respectively. The obtained
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results can be described as follows; (i) the yield of hydroxyl radicals is hindered by the
scavenging effect of EDTA on h+ based on Eqs. 9 and 10, and (ii) EDTA has a competitive
adsorption ability on pumice‒TiO2 surface area that can inhibit the adsorption of FMT. Similar
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results were published by Fathinia et al. and Sun et al (Fathinia and Khataee, 2015; Sun et al.,
2013).
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The effect of Na2SO4 on the RE% of FMT was evaluated at the optimum condition which is
indicated in Fig. 8b. As the molar ratio of Na2SO4 increased from 1:1 to 1:50, the RE% was
remarkably reduced from 71.1 to 38.5 %. The results confirmed that the presence of Na2SO4 as a
hydroxyl radical inhibitor, had a great impact on the radical type interactions (Eq. 11) (Khataee
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et al., 2016a).
SO42‒ + •OH → SO4•‒ + OH‒
(11)
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Based on the earlier works, BQ is a highly reactive species toward O2•‒ (Khataee et al., 2017c;
Rodríguez et al., 2015). As it can be seen from Fig. 8c, the RE% was decreased in the presence
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of different molar ratios of BQ, which confirmed the negative effect of BQ on the degradation of
FMT. It can be deduced that the superoxide radical had noticeable effect on the removal of FMT
in sonocatalytic process.
3.5. Effect of various enhancers on the degradation of FMT
Hydrogen peroxide and potassium persulfate were inserted to the reaction media as enhancers
and the outcomes are illustrated in Fig. 9. The RE% was enhanced from 71.1 to 79.2 and 90.1 %
in the presence of H2O2 and K2S2O8, respectively. The improved degradation of FMT by addition
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of hydrogen peroxide is related to the production of more hydroxyl radicals with ultrasonic
irradiation and reduction of H2O2 at the conduction band (Eqs. 12 and 13) (Khataee et al.,
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2016d).
)))
2 •OH
H2O2 →
(12)
e− + H2O2 → OH− + •OH
(13)
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Based on the Eqs. (14 and 15), potassium persulfate addition could increase RE%, owing to
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S2O82− →
2 SO4•−
H2O + SO4•− → •OH + SO42− + H+
3.6. Reusability of the Pumice-TiO2
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the reaction of H2O with generated SO4•− which resulted in •OH formation.
(14)
(15)
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Reusability of the Pumice-TiO2 is a prominent factor specially from economic point of view
and industrial usage (Areerob et al., 2018). The stability and reusability of the sonocatalyst was
tested by using sonocatalyst in five consecutive runs. Fig. 10 exhibits the reduction of RE% from
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71.1 to 64.6 % during five cyclic tests. The results unveil that Pumice-TiO2 is a stable and
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durable catalyst for the treatment of pharmaceuticals.
3.7. FMT degradation intermediates
The final intermediates formed during the heterogeneous sonocatalytic process were
discovered by GC–MS analysis. Table 2 depicts 16 by–products that were obtained by
comparing them with commercial standards. Various acids and alcohols were formed by
aromatic ring and bond cleavages (C–N, C–S and C–C). However, some by–products cannot be
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identified due to the mineralization of them in short time and the GC–MS limitations (Chen,
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2009).
4. Conclusion
Pumice and Pumice-TiO2 were synthesized by sol–gel method and characterized by SEM,
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EDS, XRF, FT‒IR, PL and BET analysis. Pumice–TiO2 showed high sonocatalytic performance
in comparison with pumice and TiO2 for degradation of FMT. At the optimum conditions of
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Pumice–TiO2 dosage of 1.5 g/L, pH of 5, FMT concentration of 20 mg/L and ultrasonic power of
150 W, the removal efficiency of 71.1 % was obtained in 70 min. The effect of diverse
scavengers (EDTA, Na2SO4 and BQ) and enhancers (H2O2 and K2S2O8) on the RE% were
thoroughly studied. GC–MS technique was employed to recognize the major by–products
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produced during the FMT degradation by sonocatalytic process. Results revealed that FMT can
be successfully degraded to short chain aliphatics, acids and alcohols. Eventually, Pumice-TiO2
was introduced as a promising sonocatalyst with high stability and durability, which can treat
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FMT solution with high efficiency within a short time.
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Acknowledgement
The authors would like to appreciate the University of Tabriz (Iran) for all the supports
prepared.
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Figure captions
Fig. 1. Chemical structure of FMT.
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Fig. 2. SEM images of (a‒c) pumice and (d‒f) pumice‒TiO2 samples.
Fig. 3. EDS spectra of (a) pumice and (b) pumice‒TiO2.
Fig. 4. FT‒IR spectra of pumice and pumice‒TiO2.
Fig. 5. The PL emission spectra of TiO2 and Pumice‒TiO2.
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Fig. 6. Comparison of the removal efficiency of FMT in the different processes: (a): TiO2, (b):
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US, (c): Pumice, (d): Pumice-TiO2, (e): Pumice/US, (f): TiO2/US and (g): Pumice-TiO2/US,
(Experimental conditions: [Pumice]0 =1.5 g/L, [TiO2]0 =1.5 g/L, [Pumice-TiO2]0 =1.5 g/L, pH =
5, ultrasonic power = 150 W and [FMT]0 = 20 mg/L).
Fig. 7. The influences of working parameters on the removal efficiency of FMT; (a) effect of
pumice‒TiO2 dosage (pH = 5, [FMT]0 = 20 mg/L and ultrasonic power = 150 W); (b) effect of
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pH ([FMT]0 = 20 mg/L, [pumice‒TiO2]0 = 1.5 g/L and ultrasonic power = 150 W); (c) effect of
FMT concentration (pH = 5, [pumice‒TiO2]0 = 1.5 g/L and ultrasonic power = 150 W); and
effect of ultrasonic power (pH = 5, [FMT]0 = 20 mg/L and [pumice‒TiO2]0 = 1.5 g/L).
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Fig. 8. The influences of (a) EDTA, (b) Na2SO4 and (c) BQ on the removal efficiency of FMT
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([Pumice-TiO2]0 =1.5 g/L, pH = 5, ultrasonic power = 150 W and [FMT]0 = 20 mg/L).
Fig. 9. The Influence of H2O2 and K2S2O8 on the removal efficiency of FMT, ([Pumice-TiO2]0 =
1.5 g/L, pH = 5, ultrasonic power = 150 W, [FMT]0 = 20 mg/L, [H2O2]0 = 4 mmol/L and
[K2S2O8]0 = 4 mmol/L).
Fig. 10. Reusability behavior of Pumice-TiO2 in sonocatalytic degradation ([Pumice-TiO2]0 =1.5
g/L, pH = 5, ultrasonic power = 150 W and [FMT]0 = 20 mg/L).
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Table 1. The chemical composition (%) of the Pumice and pumice-TiO2 samples.
TiO2
0.087
7.673
Al2O3
7.967
6.820
Fe2O3
1.219
1.136
MnO
0.109
0.102
MgO
0.347
0.254
CaO
0.634
0.527
Na2O
0.962
0.772
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Pumice-TiO2
SiO2
46.982
40.959
K2O
2.998
2.845
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Table 2. Generated intermediates during sonocatalytic process of FMT
(40 mg/L) at pH of 5 and Pumice-TiO2 concentration of 1.5 g/L.
Main fragments (m/z) / (percent)
1
13.357
207.10 (100.00%), 73.10 (95.37%),
246.10 (83.27%), 147.10 (48.88%),
57.10 (46.66%)
2
9.588
3
8.425
4
7.237
5
9.420
6
5.069
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73.10 (100%), 75.10 (51.81%), 191.10
(43.68%), 207.00 (42.33%), 147.10
(30.22%)
98.10 (100%), 73.10 (26.36%), 75.10
(11.12%), 99.10 (10.68%), 221.00
(7.66%)
75.10 (100%), 116.10 (97.55%), 73.10
(26.39%), 117.10 (16.79%), 76.10
(14.63%)
73.10 (100%), 147.10 (50.43%), 75.10
(46.08%), 231.10 (36.32%), 116.00
(34.50%)
73.10 (100%), 75.10 (98.46%), 59.10
(71.10%), 100.10 (47.48%), 128.10
(33.93%)
207.00 (100%), 123.00 (57.45%), 57.10
(35.09%), 73.00 (32.53%), 165.00
(31.29%)
147.10 (100%), 73.10 (86.40%), 232.10
(57.72%), 207.00 (53.80%), 75.10
(52.00%)
131.10 (100%), 73.10 (90.82%), 246.10
(56.96%), 147.00 (55.17%), 75.10
(39.33%)
75.10 (100%), 207.10 (94.33%), 73.10
(36.26%), 208.00 (21.77%), 45.10
(14.93%)
75.10 (100%), 73.10 (93.94%), 59.10
(63.35%), 100.10 (42.69%), 128.10
(31.51%)
147.10 (100%), 189.10 (62.79%), 73.10
(17.67%), 148.10 (16.40%), 190.10
(11.68%)
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13.771
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12.797
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4.703
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5.022
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11.106
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5.933
15
12.273
16
9.734
207.00 (100%), 57.10 (34.17%), 55.10
(28.65%), 75.00 (26.19%), 73.10
(24.91%)
75.10 (100%), 116.10 (86.19%), 73.10
(15.34%), 117.10 (9.46%), 76.10
(8.80%)
207.00 (100%), 73.00 (47.20%), 75.10
(43.77%), 147.10 (34.10%), 57.10
(33.84%)
207.00 (100%), 206.10 (69.69%), 73.10
(67.28%), 75.10 (67.25%), 147.10
(63.88%)
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17.944
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Fig. 1. Chemical structure of FMT.
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Fig. 2. SEM images of (a‒c) pumice and (d‒f) pumice‒TiO2 samples.
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Fig. 3. EDS spectra of (a) pumice and (b) pumice‒TiO2.
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Fig. 4. FT‒IR spectra of pumice and pumice‒TiO2.
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TiO2
100
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Pumice-TiO2
60
20
0
355
365
375
385
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40
395
405
415
425
435
Wavelength (nm)
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Fig. 5. The PL emission spectra of TiO2 and Pumice‒TiO2.
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(g)
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RE (%)
70
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40
50
60
(f)
(e)
(d)
(c)
(b)
(a)
70
80
Time (min)
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Fig. 6. Comparison of the removal efficiency of FMT in the different processes: (a): TiO2, (b):
US, (c): Pumice, (d): Pumice-TiO2, (e): Pumice/US, (f): TiO2/US and (g): Pumice-TiO2/US,
(Experimental conditions: [Pumice]0 =1.5 g/L, [TiO2]0 =1.5 g/L, [Pumice-TiO2]0 =1.5 g/L, pH =
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Fig. 7. Influence of working parameters on the removal efficiency of FMT; (a) effect of pumice‒
TiO2 dosage (pH = 5, [FMT]0 = 20 mg/L and ultrasonic power = 150 W); (b) effect of pH
([FMT]0 = 20 mg/L, [pumice‒TiO2]0 = 1.5 g/L and ultrasonic power = 150 W); (c) effect of FMT
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concentration (pH = 5, [pumice‒TiO2]0 = 1.5 g/L and ultrasonic power = 150 W); and effect of
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ultrasonic power (pH = 5, [FMT]0 = 20 mg/L and [pumice‒TiO2]0 = 1.5 g/L).
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Fig. 8. The influences of (a) EDTA, (b) Na2SO4 and (c) BQ on the removal efficiency of FMT
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Fig. 9. The Influence of H2O2 and K2S2O8 on the removal efficiency of FMT, ([Pumice-TiO2]0 =
1.5 g/L, pH = 5, ultrasonic power = 150 W, [FMT]0 = 20 mg/L, [H2O2]0 = 4 mmol/L and
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Fig. 10. Reusability behavior of Pumice-TiO2 in sonocatalytic degradation ([Pumice-TiO2]0 =1.5
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Highlights:
Synthesis of pumice‒TiO2 by modified sol-gel method.
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Application of pumice‒TiO2 nanoflakes in sonocatalytic degradation of FMT.
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Examining the effects of radical scavenger and reaction enhancer on RE% of FMT.
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Identifying sixteen FMT degradation intermediates by GC‒MS.
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