Sono-photo-Fenton oxidation of bisphenol-A over a LaFeO3 perovskite catalyst

Ultrasonics - Sonochemistry xxx (xxxx) xxx–xxx

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Sono-photo-Fenton oxidation of bisphenol-A over a LaFeO3 perovskite catalyst Meral Dükkancı Ege University, Engineering Faculty, Chemical Engineering Department, 35100, Bornova, Izmir, Turkey

A R T I C L E I N F O

A B S T R A C T

Keywords: Bisphenol-A Sono-photo-Fenton Perovskite catalyst Energy consumption

In this study, oxidation of bisphenol-A (IUPAC name – 2,2-(4,4-dihydroxyphenyl, BPA), which is an endocrine disrupting phenolic compound used in the polycarbonate plastic and epoxy resin industry, was investigated using sono-photo-Fenton process under visible light irradiation in the presence of an iron containing perovskite catalyst, LaFeO3. The catalyst prepared by sol–gel method, calcined at 500 °C showed a catalytic activity in BPA oxidation using sono-photo-Fenton process with a degradation degree and a chemical oxygen demand (COD) reduction of 21.8% and 11.2%, respectively. Degradation of BPA was studied by using individual and combined advanced oxidation techniques including sonication, heterogeneous Fenton reaction and photo oxidation over this catalyst to understand the effect of each process on degradation of BPA. It was seen, the role of sonication was very important in hybrid sono-photo-Fenton process due to the pyrolysis and sonoluminescence effects caused by ultrasonic irradiation. The prepared LaFeO3 perovskite catalyst was a good sonocatalyst rather than a photocatalyst. Sonication was not only the effective process to degrade BPA but also it was the cost effective process in terms of energy consumption. The studies show that the energy consumption is lower in the sonoFenton process than those in the photo-Fenton and sono-photo- Fenton processes.

1. Introduction

systems through various Advanced Oxidation Processes (AOPs) [7–32] which offer several particular advantages in terms of unselective degradation of BPA into a final mineralized form with the production of a highly oxidative hydroxyl radicals (OH%). Among the available AOPs, Fenton reaction is based on the electron transfer between H2O2 and a transition metal ion (iron is the most common one) acting as a catalyst. However, homogeneous Fenton reactions have some disadvantages such as, limited pH range for the reaction, production of iron containing sludge and difficulty of regeneration of catalyst. The drawbacks of homogeneous Fenton reactions can be overcome by using heterogeneous catalysts. Photo-Fenton process is a hybrid technique that uses Fenton reagent together with light (in this study visible light, λ > 400 nm) for the oxidation. Photoreactions often require the use of a photocatalyst. The most known photocatalyst is TiO2 [33] however it is not a good photocatalyst under the visible light. Nevertheless, perovskite based catalysts show good photocatalytic activity under visible light. Because they have lower band gap than semi-conductor catalysts such as TiO2. The other AOPs used in this study is sonication which is based on the acoustic cavitation created in the presence of ultrasound. Acoustic cavitation can be defined as the formation, growth and implosive collapse of microbubbles at very small time intervals which release large magnitudes of energy over a small area but at millions of places in the reactor [34]. The collapse of these micro-

Bisphenol A (BPA) is a commercial product and is the primary material for polycarbonate and epoxy resins fabrication. It is an organic synthetic compound with the chemical formula of C15H16O2 belonging to the group of diphenylmethane derivatives and bisphenols, with two hydroxyphenyl groups [1]. BPA is released into the ground water through sewage treatment effluent, landfill leachate, or discharge of effluent from wastewater and washwater of plants which produce material containing BPA. BPA can also be found in food and drinking water, and in living organisms (especially in fatty tissues). Since it is a synthetic hazardous compound, it affects the endocrine system primarily, plays a role in thyroid hormone dysfunctions, central nervous system function disorder and immune suppression above a certain limit [2–4]. BPA contamination became a real threat for human health even at low dose of 0.05 mg per kg body weight. Research on BPA as environmental contaminant has now major regulatory implications towards ecosystem health [5,6]. Acute toxicity of BPA for aquatic organisms was about 1–10 mg/L in fresh and marine species [1]. Due to the reasons mentioned above BPA must be treated before discharged to environment. A wide range of studies are reported on BPA removal from aqueous

E-mail address: [email protected]. http://dx.doi.org/10.1016/j.ultsonch.2017.04.040 Received 19 September 2016; Received in revised form 23 March 2017; Accepted 27 April 2017 1350-4177/ © 2017 Elsevier B.V. All rights reserved.

Please cite this article as: Dükkanci, M., Ultrasonics - Sonochemistry (2017), http://dx.doi.org/10.1016/j.ultsonch.2017.04.040

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surface. The amount of the BPA adsorbed by the catalyst was determined by measuring the BPA concentration after 30 min. The experiment in the presence of H2O2 was performed with an initial concentration of H2O2 of 2.38 mM, under a stirring speed of 500 rpm with an initial BPA pH of around 6.7. Two visible light lamps (high pressure Na lamps, each 150 W of two lamps, Philips) were used as a light source. An ultrasonic probe of 20 kHz with an output power of 40 W (Bandelin HD3200) was used as a source of ultrasound. Each run took 3 h. The reaction temperature was kept constant at 298 ± 2 K by circulating cooling water (PolyScience, MX07R-20-A12E) around the reactor to avoid the significant overheating of the reaction media. The reaction vessel was maintained in a box to prevent photochemical reactions excited by natural light. Samples were periodically drawn from the vessel and reaction was stopped by keeping the samples in iced-bed. Then the samples were centrifuged and filtrated with 0.45 μm PTFE syringe filters. The catalyst free samples were analyzed with a HPLC (Agilent 1200 series) with a ZORBAX Eclipse Plus C18 (4.6 × 150 mm, 5 µm) column. Detection was achieved with an UV detector at 278 nm, with a 20 μL sampling loop. The mobile phase, ultrapure water/acetonitrile (50/50, v/v) was run in an isocratic mode with a flow rate of 0.5 ml/min. The column oven was maintained at 25 °C. In addition to these measurements, the chemical oxygen demand (COD) removal of the BPA solution was determined by measuring initial COD and final COD (at the end of the run) of the BPA solution with a COD device (Lovibond Checkit Direct). Sono-Fenton, photo-Fenton and sono-photo-Fenton reactions were also performed in pure water in the presence of 0.5 g/dm3 LaFeO3 perovskite catalyst to investigate the formation of H2O2 in each process in order to establish a relationship between the H2O2 production and degradation of BPA in related process. The formed H2O2 was measured with Lovibond PCCHECKIT H2O2 device by using hydrogenperoxide LR Tablets (Lovibond).

bubbles induces the phenomenon of sonoluminescence and generates local hot spots with pressures higher than 500 atm and temperatures as high as 5200 K in cavitation bubble and about 1900 K in the interfacial region between the solution and the collapsing bubble. Under such conditions species such as OH%, H%,OOH%, and O are created from H2O and O2 dissociation and their associate reactions in the bubble [35–39]. The intensity of cavity implosion, and hence the nature of reaction are controlled by frequency of sonication, acoustic intensity (amount of power dissipated per square cm of the emitter area), bulk temperature, and static pressure [40]. The collapse of cavitation bubbles also initiates physical effects which include the production of shear forces and shock waves [41]. It is known that volatile organic compounds are degraded by pyrolysis inside the cavitation bubble by high temperature or at the bubble liquid interface by oxidation with OH% radicals, whereas nonvolatile compounds are degraded by oxidation with hydroxyl radicals at the bulk liquid. When the photocatalytic reaction accomplished with sonication, oxidation rate increases by the increased generation of OH% radicals and the mass transfer limitations are reduced by the turbulence created by sonication [42]. Also sonication helps in cleaning of the catalyst surface which increases its efficiency. In this study, sono-photo-Fenton oxidation of BPA was studied over the LaFeO3 perovskite catalyst in the presence of visible light irradiation. Degradation of BPA was investigated by individual and several combinations of AOPs including sonication, Fenton reaction and photo oxidation to understand the effect of each process on oxidation of BPA. A simple energy consumption analysis was done for the processes using sonication and/or light irradiation. Up to now, no study was reported in the literature for degradation of BPA by sono-photo-Fenton oxidation in the presence of LaFeO3 perovskite catalyst and by the individual and combined advanced oxidation processes of Fenton reaction, photo degradation and sonication. In addition to this, applying energy consumption analysis on the individual and combined processes of sonication and photo oxidation reactions is considered to be a significant contribution to the related literature.

3. Results and discussion 3.1. Sono-photo-Fenton oxidation of BPA over perovskite catalysts

2. Experimental study In the previous study [43], the degradation of BPA was performed by sono-photo-Fenton oxidation over perovskite catalysts, prepared by sol–gel method, calcined at different temperatures of 500, 700 and 800 °C in order to determine the most effective catalyst. The prepared samples were denoted as LaFeO3-500, LaFeO3-700, and LaFeO3-800, respectively. The sono-photo-Fenton experiments were carried out

Experimental set-up is shown in Fig. 1. A typical experiment was performed with 0.5 dm3 of 15 ppm of BPA aqueous solution in a cylindrical reactor. In the experiments containing catalyst at an amount of 0.5 g/dm3, the suspension was left for 30 min in the dark to establish the adsorption-desorption equilibrium of the BPA on the catalyst

Fig. 1. Experimental set-up used for the oxidation of BPA.

2

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16

(a)

15

LaFeO3+H2O2+US+visible light

14 13

C/C0

21.8 %

LaFeO3 +US+visible light

20.8 %

LaFeO3 +H2O2+US

12

LaFeO3 +US

11

US+H2O2

10

Only US

9

Only H2O2

8

only visible light 0

50

100

150

21.4 % 17.0 % 13.5 % 5.5 % 10.0 %

200

only LaFeO3

Time, min

5.8 % 0

Fig. 2. Sono-Photo-Fenton oxidation of BPA over the prepared LaFeO3 perovskite catalyst (calcined at 500 °C) [43].

5

10

15

20

25

DegradaƟon, %

(b)

under the conditions given in Part “2.Experimental Study”. LaFeO3-500 with a BET surface area of 15.4 m2/g and with a crystal size of 19.69 nm was found to be the most effective catalyst. The catalyst characterization studies were given in the previous study in detail [43]. Then, the activity of LaFeO3-500 catalyst was compared with the activity of Fe/TiO2 catalyst in the sono-photo- Fenton oxidation of BPA. However, in the present study, the individual and different combinations of advanced oxidation processes of Fenton reaction, photo oxidation and sonication were investigated in the presence of LaFeO3-500 (denoted as LaFeO3 in the present study) perovskite catalyst to understand the effect of each process on oxidation of BPA. Fig. 2 presents degradation of BPA by sono-photo-Fenton reaction over the LaFeO3 catalyst. As seen from Fig. 2, the degradation degree of 21.8% and the COD reduction of 11.2% were obtained in the presence of LaFeO3 catalyst after 3 h of oxidation.

H2O2 + US + visible light

19.8 %

LaFeO3 + H2O2 + visible light

12.7 %

Visible light + US

21.0 %

LaFeO3 + visible light

7.0 %

H2O2+LaFeO3

3.5 %

H2O2 + visible light

6.8 %

LaFeO3 +H2O2+US+visible light

21.8 % 0

5

10

15

20

25

DegradaƟon, % Fig. 3. Degradation percentage of BPA after 3 h of oxidation in the process of a) Only LaFeO3, Only visible light, Only H2O2, Only US, US + H2O2, LaFeO3 + US, LaFeO3 + H2O2 + US, LaFeO3 + US + visible light, LaFeO3 + H2O2 + US + visible light, b) H2O2 + visible light, H2O2 + LaFeO3, LaFeO3 + visible light, visible light + US, LaFeO3 + H2O2 + visible light, H2O2 + US + visible light.

3.2. The degradation of BPA by individual and combined advanced oxidation processes

H2 O2))) → 2OH%

In this part of the study, the individual and combined use of sonication, Fenton oxidation and photocatalytic oxidation were studied to degrade BPA in the presence of LaFeO3 perovskite catalyst calcined at 500 °C. Experiments were performed with 15 ppm of 0.5 dm3 BPA aqueous solution (66 μM), initial BPA pH of around 6.7, catalyst amount of 0.5 g/dm3, H2O2 concentration of 2.38 mM, stirring speed of 500 rpm, temperature of 298 K, reaction duration of 3 h, an ultrasonic probe of 20 kHz and each of 150 W two visible light lamps. The selected concentration of H2O2 is the stoichiometric amount to achieve complete mineralization of BPA according to the equation below:

C15H16 O2 + 36H2 O2 → 15CO2 + 44H2 O

19.9 %

(2)

where))) refers to ultrasound (sonication). The obtained degradation was 21.4% in the combined process of LaFeO3 + US (sonocatalytic) process. The degradation mechanism of sonocatalytic reactions can be explained by means of hot spot theory and sonoluminescence. Ultrasonic irradiation in the presence of LaFeO3 catalyst can generate various active species on the surface of catalyst. According to the hot spot theory, heat energy is produced by ultrasonic cavitation and this energy breaks H2O molecules through pyrolysis into H. and OH% radicals. At the same time, the light energy, sonoluminescence, with a relatively wide range of wavelengths (below 375 nm) caused by ultrasonic irradiation can excite LaFeO3 particles to act as a photocatalyst and then photo-generated hole-electron pairs are formed (Eq. (3)) [38,39,46,47]. OH% radicals are produced by the reaction of electrons with O2 and H+ (Eq. (4)). The generated holes react with OHand/or H2O to produce hydroxyl radicals (Eqs. (5) and (6)) which react with BPA molecules (Eq. (7)):

(1)

Each run was repeated at least 2 times and the standard deviation of the average of independent runs changed in the range of ± 0.1 and ± 1.2. The studied processes and obtained results are given in Fig. 3a and b with the standard deviations of each run. As seen in Fig. 3a, when the individual processes were compared with each other, the highest degradation, 13.5%, was obtained in the presence of US only. Addition of the H2O2 to US oxidation increased the degradation to 17%. BPA is a hydrophobic compound at the pH under the pKa values of BPA (9.6 and 10.2) and hydrophobic compounds degrade in the cavitation bubble by direct pyrolysis or at cavitation bubble-liquid interface by OH% radical attack [36]. It is known that sonication leads to breakdown of the H2O2 to OH% radicals (Eq. (2)) which exhibit a high oxidation potential and can directly degrade organic pollutants. Hence the degradation of BPA is increased in the presence of ultrasound and H2O2 together [1,44,45].

LaFeO3 + ultrasonic irradiation(sonoluminescence) → LaFeO3 (e−,h+) 3e−

+ O2 +

h+

OH−

h+

2H+

→

→

OH%

+ H2 O→

OH%

+

OH%

OH%

+

OH−

(3) (4) (5)

+

H+

+ BPA → degradation products[39,46]

(6) (7)

In addition to these, according to nitrogen adsorption measurements given in the previous study of the author [43], after the sono-photoFenton oxidation process of BPA over the LaFeO3 perovskite catalyst calcined at 500 °C, a decrease in catalyst pore size from 11.6 to 3

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11.2 nm, an increase in external surface area from 9.4 to 14.2 m2/g because of the reduction in particle size and an increase in total pore volume from 0.0052 to 0.0362 cm3/g were observed due to the presence of sonication and this result was also confirmed by the SEM images of the LaFeO3 perovskite catalyst. This effect of sonication provides additional nuclei for the cavitation phenomena and hence the number of cavitation events occurring in the reactor are enhanced [34,36]. On the other hand, as mentioned in Part “1. Introduction”, sonication reduces the mass transfer limitations by the created turbulence. Also sonication helps in the cleaning of the catalyst surface which increases its efficiency [42]. In addition to this, the formed H2O2 via reaction (10) in sonication can react with Fe2+ in the catalyst to form OH% radicals. All these effects increase the activity of LaFeO3 perovskite catalyst in the sonication process. Addition of 2.38 mM H2O2 (LaFeO3 + H2O2 + ultrasound, Fig. 3a) to US + LaFeO3 binary oxidation process decreased slightly the degradation of BPA from 21.4% to 19.9%. This negative effect of H2O2 may be explained as follows: H2O2 in aqueous solution decomposes to generate OH% radicals under the light energy (sonoluminescence) produced during ultrasonic irradiation below 375 nm (Eq. (8)). At the same time during the sonolysis, water molecules are directly decomposed leading to generation of OH% and H% radicals (Eq. (9)). As the OH% radicals have a very short lifetime, they tend to combine with each other to produce H2O2 (Eq. (10)) or produced OH% radicals may react with H2O2 (Eq. (11)) to form other radical species such as perhydroxyl radicals (HO2%) which are less reactive than OH% radicals. These two effects decreased the degradation of BPA due to the decrement in the amount of OH% radicals available to oxidize BPA [47].

H2 O2 + ultrasonic irradiation(sonoluminescence) → 2OH%

(8)

H2 O))) → OH% + H%

(9)

OH% + OH% → H2 O2

OH%

+ H2 O2 → H2 O+

reaction (LaFeO3 + H2O2 + visible light (Fig. 3b)) increased the degradation from 7.0% to 12.7%. Considering the degradation (21.8%) obtained in the overall process of LaFeO3 + H2O2 + US + visible light (sono-photo-Fenton oxidation) it can be said that US plays a crucial role in the oxidation and LaFeO3 is a good sonocatalyst rather than a photocatalyst under the experimental conditions studied. The catalytic activity of LaFeO3 perovskite catalyst in sono-Fenton process was higher than that in photo-Fenton process. When the efficiency of each process was discussed in terms of COD reductions, it could be seen that COD reductions were obtained only when US was employed in the processes. The COD reductions of 4.8%, 9.1%, 7.9%, 5.6% and 8.0% were achieved in the combined processes of LaFeO3 + US, Visible light + US, LaFeO3 + US + visible light, LaFeO3 + H2O2 + US, H2O2 + US + visible light irradiation processes, respectively. However, the highest COD reduction (11.2%) was achieved in the overall process of sono-photo-Fenton oxidation as well as the highest degradation degree (21.8%). 3.3·H2O2 formation in Sono-Fenton, Photo-Fenton and Sono-photo-Fenton reactions As known well, AOPs rely on the production of OH% radicals for the destruction of organic pollutants. And these highly oxidative radicals may recombine into H2O2. Thus, production of H2O2 in AOPs shows the yield of OH% formation. In this part of the study, sono-Fenton, photo-Fenton and sono-photoFenton reactions were performed in pure water in the presence of 0.5 g/ dm3 LaFeO3 perovskite catalyst to investigate the formation of H2O2 in each process. Relationship between the H2O2 production and degradation of BPA in related process was tried to establish. The formed H2O2 was measured with Lovibond PCCHECKIT H2O2 device by using hydrogenperoxide LR Tablets (Lovibond). The results are given in Fig. 4. As seen from Fig. 4, 0.35 mg/dm3 H2O2 was formed in sono-Fenton reaction at the end of 3 h of reaction. The formation of OH% in sonoFenton oxidation can be explained according to Eqs. (3)(6) and (9). These OH% radicals can recombine with each other to produce H2O2. The amount of formed H2O2 was 0.1 mg/dm3 in photo-Fenton reaction after the 3 h of reaction. In photo-Fenton reaction OH% radicals formation was expected via reactions (12)(16). And similar with sonoFenton oxidation, the produced OH% radicals can recombine with each other that yield to formation of H2O2.

(10)

HO%2

(11)

When sonocatalytic process was conducted in the presence of visible light irradiation (Fig. 3a), a degradation of 20.8% was achieved at the end of 3 h of oxidation, whereas, a degradation of 21.4% was obtained in sonocatalytic reaction. Almost the same degradation degree obtained shows that there is no positive oxidation effect of visible light in the triple process of LaFeO3 + US + visible light. Namely, it might be that, it was hard to excite the LaFeO3 perovskite catalyst with visible light irradiation (> 400 nm) whereas in sonocatalytic reaction the light energy, sonoluminescence, with a relatively wide range of wavelenghts (below 375 nm) caused by ultrasonic irradiation excited the catalyst. However, in the sonophotolytic (visible light + US, Fig. 3b) process the degradation was 21.0% which was very similar to the one obtained in LaFeO3 + US + visible light triple process, but higher than when the US was used alone. This might mean that visible light irradiation tolerated negative effect of recombination OH% radicals. The processes in the absence of US, such as H2O2 + visible light (Fig. 3b) the degradation of 6.8% was obtained due to the low efficiency of decomposition of H2O2 to hydroxyl radicals under visible light irradiation. In the dual process of H2O2 + LaFeO3 catalyst (heterogeneous Fenton reaction, Fig. 3b) very low degradation of 3.5% was obtained. It might be that LaFeO3 was not a very active Fenton catalyst due to its small external surface area of 9.4 m2/g [43] where the most Fenton reactions take place. In LaFeO3 + visible light (photocatalytic reaction, Fig. 3b) only a degradation of 7.0% was achieved. As explained previously LaFeO3 was not a good photocatalyst under the visible light irradiation. But its efficiency was higher in the presence of sonication. Being a comparatively effective sonocatalyst of LaFeO3 might be explained by the excitation of the LaFeO3 samples by sonoluminescence, by the change in physical nature of the catalyst due to the presence of ultrasound and all the other positive effects of sonication mentioned above. Addition of H2O2 to the photocatalytic

hν

Fe3+ + H2 O→ Fe2+ + OH% + H+

(12)

hν

LaFeO3 → LaFeO3 (e−,h+) 3e−

+ O2 +

2H+

→

OH%

+

(13)

OH−

(14)

0.4

H2O2 amount, mg/dm3

0.35 0.3 0.25 0.2 0.15 0.1 0.05 0 0

30

60

90

120

150

180

Time, min Pure water+LaFeO3+US pure water+LaFeO3+US+visible light

pure water+LaFeO3+visible light

Fig. 4. H2O2 formation as a function of time in pure water in the presence of LaFeO3 catalyst (T = 298 K).

4

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h+ + OH− → OH% h+

+ H2 O→

OH%

(15)

+

H+

Table 1 Required parameters for the calculation of external mass transfer resistance.

(16) Parameters

where hv represents visible light irradiation. However no H2O2 was measured in sono-photo-Fenton reaction of pure water. In sono-photo-Fenton reaction of water in the presence of LaFeO3 catalyst, H2O2 was formed through the reactions (3)(6) and (9) (10) but the formed H2O2 was consumed by the following reactions:

Fe2+ + H2 O2 → Fe3+ + OH− + OH%

(17)

Fe3+ + H2 O2 → Fe2+ + HOO% + H+

(18)

DAB dp ρb ε ρc μc ρsolution Nsc n R

So no H2O2 was measured in sono-photo-Fenton reaction. The results of H2O2 formation complied with the results obtained in sono-Fenton (LaFeO3 + US) and photo-Fenton (LaFeO3 + light) degradation of BPA. As given in Fig. 3a and b, 21.4% and 7.0% degradation of BPA were observed in sono-Fenton (LaFeO3 + US) and photo-Fenton (LaFeO3 + light) oxidations, respectively. As the formation of H2O2 in sono-Fenton reaction of water was higher than that photo-Fenton reaction, the higher degradation of BPA was observed in sono-Fenton oxidation. This result shows that activity of LaFeO3 catalyst in sonoFenton oxidation was higher than that in photo-Fenton oxidation. Although no H2O2 formation was measured in sono-photo-Fenton (LaFeO3 + US + Light) reaction of water, 20.8% degradation of BPA was achieved after a reaction time of 3 h (Fig. 3a). As mentioned above, H2O2 was consumed through the Eqs. (17) and (18), but OH% radical production persists to oxidize BPA molecules before recombination with each other.

3.5. Energy consumption evaluation of the processes The efficiency of the process in terms of degradation degree and COD reductions is important but not enough to answer the question whether the used process is economical in terms of energy consumption. The energy consumed in the process should be considered and a simple economic analysis from the point of energy consumption was performed in the present study, as well. For this purpose, the electric energy consumed per kg of BPA (EEM) was calculated. This parameter is defined as the electric energy in kilowatts hours (kWh) required to degrade 1 kg of BPA in water. The EEM value (kWh kg−1) can be calculated as follows:

3.4. External mass transfer resistance in Sono-photo-Fenton oxidation of BPA

−rA′ ρb Rn k m CAb

(19)

where -r′A = reaction rate per unit mass of catalyst (mol/g s), n = reaction order (in this study n = 2), R = catalyst particle radius (m), ρb = bulk density of catalyst (g/dm3), ρb = (1-ε) ρc, ε = catalyst porosity, ρc = catalyst solid density, CAb = bulk concentration of BPA (mol/dm3), and km = mass transfer coefficient (m/s). Mass transfer coefficient, km, was estimated from Eq. (20) which was derived from Dwidevi-Upadhyay [48].

km =

⎛ Δρμ g ⎞1/3 2DAB c ⎟ + 0.31Nsc−2/3 ⎜⎜ 2 ⎟ dp ⎝ ρc ⎠

E= [P t ]/60

(21)

EEM = [E]/[(C 0−C)V]

(22)

where E is the electric energy consumption in each experiment (kWh), P is the related power (kW) of the used system, t (min) is the time in which the power is supplied to the BPA aqueous solution, V is the volume (dm3) of the treated BPA aqueous solution, and C0 and C are the initial and final (at the end of 3 h of oxidation) concentrations (mg/ dm3) of BPA, respectively [51]. The power of the two visible lights are 300 W (each is 150 W). However, the actual power of sonication is different from the output power (40 W) of ultrasonic generator. Actual power of ultrasonic generator can be measured by calorimetric method. It is assumed that, in a pure liquid, mechanical energy from ultrasonic generator produces heat and so, via calorimetry, acoustic power entering the system can be obtained. In calorimetry, the temperature (T) is recorded against time (t), using a thermocouple placed into the reactor. The ultrasonic power actually entering the system is obtained according to Eq. (23):

As mentioned in present manuscript the mass transfer limitations are reduced by the turbulence created by sonication. To prove this, external mass transfer resistance was investigated theoretically by calculating the dimensionless Mears parameter (Cm). Mears parameter is the ratio of the rate of reaction to the external diffusion rate. If this dimensionless parameter is less than 0.15, the external mass transfer resistance is low and can be neglected, Eq. (19) [48,49]:

Cm =

5.88x10−6 cm2/s 10x10−6 m 280 g/dm3 (measured) Vvoid/(VTotal) = 0.0101 (from BET data) [43] 283 g/dm3 Dynamic μc = 0.0089 g/cms, Kinematic μc = 0.008926 cm2/s 997 g/dm3 (taken as water) μc/DAB 2 5 × 10−6 m

Power = (dT/dt) Cp M

(23) −1 −1

where Cp = heat capacity of water (4.187 kJ kg K at 20 °C) and M = mass of water used. Actual power of sonication was calculated to be 23 W according to calorimetric method. Table 2 shows the results of electric energy consumed per kg of BPA (EEM) in different combinations of AOPs. As can be seen from Table 2 the best cost effective process for the degradation of BPA was LaFeO3 + US binary process. It was followed by the processes of LaFeO3 + H2O2 + US, H2O2 + US and only US. In summary it can be concluded that presence of US in the oxidation process not only gave the higher degradation degrees and COD reductions but also had better electrical efficiency as compared with the other individual or combined processes investigated in this study. But it must be kept in mind that, ultrasonic power should be optimized in order to avoid unnecessary loss of energy in sonochemical treatment. Because the maximum radius of cavitation bubble varies with square root of the power. As the power increases intensification of the violence of the collapse increases which increases degradation of organic pollutant. But after an optimum value no further increase is

(20) 2

where DAB = the diffusivity of BPA in water (cm /s), dp = diameter of the catalyst particle (m), Nsc = Schmidt number (μc/DAB), Δρ = the difference between density of solution and catalyst (g/dm3), g = gravitational acceleration (9.81 m/s2), and ρc = catalyst solid density (g/ dm3). The required data needed in Eqs. (19) and (20) are given in Table 1. The Mears parameter, Cm, is calculated as 6.1 × 10−4. So, it could be concluded that since the Mears parameter is much smaller than 0.15, the extremal mass transfer resistance could be neglected in sono-photoFenton oxidation of BPA. In addition to this, according to Hougen C −C criterion, AbC As = 1.50 × 10−5 < 0.1 was found, which also shows the Ab negligible external mass transfer resistance [50]. 5

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Table 2 Estimation of Electric Energy for different combinations of AOPs. Processes

Electrical power, kW

Time, min

(C0-C), mg/dm3

E, (kWh)

EEM, kWh kg−1

Only visible light Only US H2O2 + visible light H2O2 + US Visible light + US LaFeO3 + US LaFeO3 + visible light LaFeO3 + H2O2 + visible light LaFeO3 + H2O2 + US LaFeO3 + US + visible light H2O2 + US + visible light LaFeO3 + H2O2 + US + visible light

0.3 0.023 0.3 0.023 0.323 0.023 0.3 0.3 0.023 0.323 0.323 0.323

180 180 180 180 180 180 180 180 180 180 180 180

1.50 2.03 1.02 2.55 3.14 3.20 1.05 1.90 2.99 3.12 2.97 3.27

0.90 0.07 0.90 0.07 0.97 0.07 0.90 0.90 0.07 0.97 0.97 0.97

1.20 × 106 6.81 × 104 1.76 × 106 5.41 × 104 6.16 × 105 4.31 × 104 1.71 × 106 9.66 × 105 4.62 × 104 6.21 × 105 6.53 × 105 5.93 × 105

References

expected. In addition to this, formation of large bubbles may disturb the sound waves transmitted between the reaction vessel walls and transducer tips [52–54]. However, considering the efficiency of sonication (when it was compared with heterogeneous Fenton and photoFenton oxidation), the effects of different parameters such as US power, amounts of H2O2 and catalyst, and pH of BPA solution on the degradation of BPA by sono-Fenton oxidation will be investigated in future in detail in order to increase degradation of BPA and decrease energy consumption.

[1] E. Nikfar, M.H. Dehghani, A.H. Mahvi, N. Rastkari, M. Asif, I. Tyagi, S. Agarwal, V.K. Gupta, Removal of Bisphenol A from aqueous solutions using ultrasonic waves and hydrogen peroxide, J. Mol. Liq. 213 (2016) 332–338. [2] D.A. Crain, M. Erıksen, T. Iguchi, S. Jobling, H. Laufer, G.A. Leblanc, L.J. Guıllette, An ecological assessment of bisphenol-A: evidence from comparative biology, Reprod. Toxicol. 24 (2007) 225–239. [3] B. Er, B. Sarımehmetoğlu, The assessment of bisphenol A presence in Foods, Vet. Hekim Derg. 82 (2011) 69–74. [4] L. Luo, Y. Yang, A. Zhang, M. Wang, Y. Liu, L. Bian, F. Jiang, X. Pan, Hydrothermal synthesis of fluorinated anatase TiO2/reduced graphene oxide nanocomposites and their photocatalytic degradation of bisphenol A, Appl. Surf. Sci. 353 (2015) 469–479. [5] C.Y. Kuo, H.M. Hsiao, Preparation of iodine doped titanium dioxide to photodegrade aqueous bisphenol A under visible light, Process. Saf. Environ. 95 (2015) 265–270. [6] J. Sharma, I.M. Mishra, V. Kumar, Degradation and mineralization of Bisphenol A (BPA) in aqueous solution using advanced oxidation processes: UV/H2O2 and UV/ S2O82- oxidation systems, J. Environ. Manage. 156 (2015) 266–275. [7] C. Petrier, R. Torres-Palma, E. Combet, G. Sarantakos, S. Baup, C. Pulgarin, Enhanced sonochemical degradation of Bisphenol-A by biocarbonate ions, Ultrason. Sonochem. 17 (2010) 111–115. [8] Y. Son, M. Lım, J. Khım, L.H. Kım, M. Ashokkumar, Comparison of calorimetric energy and cavitation energy for the removal of Bisphenol-A: the effects of frequency and liquid height, Chem. Eng. J. 183 (2012) 39–45. [9] R.A. Torres, F. Abdelmalek, E. Combet, C. Petrıer, C. Pulgarin, A Comparative study of ultrasonic cavitation and Fenton’s reagent for Bisphenol A degradation in deionized and natural waters, J. Hazard. Mater. 146 (2007) 546–551. [10] D.P. Mohapatra, S.K. Brar, R.D. Tyagı, R.Y. Surampallı, Concominant degradation of Bisphenol A during ultrasonication and Fenton oxidation and production of biofertilizer from wastewater sludge, Ultrason. Sonochem. 18 (2011) 1018–1027. [11] R. Huang, Z. Fang, X. Yan, W. Cheng, Heterogeneous sono-Fenton catalytic degradation of Bisphenol A by Fe3O4 magnetic nanoparticles under neutral condition, Chem. Eng. J. 197 (2012) 242–249. [12] H. Katsumata, S. Kawabe, S. Kaneco, T. Suzuki, K. Ohta, Degradation of Bisphenol A in water by the photo-Fenton reaction, J. Photochem. Photobiol. A. 162 (2004) 297–305. [13] K. Lin, J. Ding, H. Wang, X. Huang, J. Gan, Goethite-mediated transformation of Bisphenol A, Chemosphere 89 (2012) 789–795. [14] D. Zhou, F. Wu, N. Deng, W. Xıang, Photooxidation of Bisphenol A (BPA) in water in the presence of ferric and carboxylate salts, Water Res. 38 (2004) 4107–4116. [15] M. Neamtu, F.H. Frımmel, Degradation of endocrine disrupting Bisphenol A by 254 nm irradiation in different water matrices and effect on yeast cells, Water Res. 40 (2006) 3745–3750. [16] C. Kuo, C. Wu, H. Lin, Photocatalytic degradation of Bisphenol A in a visible light/ TiO2 system, Desalination 256 (2010) 37–42. [17] X. Wang, T. Lim, Solvothermal synthesis of C-N codoped TiO2 and photocatalytic evaluation for Bisphenol A degradation using a visible-light irradiated led photoreactor, Appl. Catal. B 100 (2010) 355–364. [18] Z. Qing, L. Jınhua, C. Hongchong, C. Quanpeng, Z. Baoxue, S. Shuchuan, C. Weımın, Characterization and mechanism of the photoelectrocatalytic oxidation of organic pollutants in a thin-layer reactor, Chinese J. Catal. 32 (2011) 1357–1363. [19] J. Yang, J. Dai, J. Li, Characterization and degradation of Bisphenol A using Pr, N co-doped TiO2 with highly visible light activity, J. Appl. Surf. Sci. 257 (2011) 8965–8973. [20] S. Irmak, O. Erbatur, A. Akgerman, Degradation of 17 β-estradiol and Bisphenol A in aqueous medium by using ozone and ozone/UV techniques, J. Hazard. Mater. B126 (2005) 54–62. [21] M. Deborde, S. Rabouan, P. Mazellier, J.P. Duguet, B. Legube, Oxidation of Bisphenol A by ozone in aqueous solution, Water Res. 42 (2008) 4299–4308. [22] T. Garoma, S. Matsumoto, Ozonation of aqueous solution containing Bisphenol A: effect of operational parameters, J. Hazard. Mater. 167 (2009) 1185–1191. [23] R.A. Torres-Palma, J.I. Nieto, E. Combet, C. Petrıer, C. Pulgarın, An innovative ultrasound, Fe2+ and TiO2 photoassisted process for Bisphenol A mineralization,

4. Conclusions In this study, sono-photo-Fenton oxidation of BPA was studied over a LaFeO3 perovskite catalyst in the presence of visible light irradiation, the efficiency of individual and combined processes of sonication, Fenton reaction and photo catalytic reactions was investigated in terms of degradation degrees and COD reductions in BPA oxidation and electrical energy consumption of the processes. It was observed that sonication plays an important role in the degradation of BPA due to the pyrolysis and sonoluminescence effect caused by ultrasonic irradiation. Also, it may be said that the prepared LaFeO3 perovskite catalyst was a good sonocatalyst rather than a photocatalyst. It was also proved by the H2O2 formation in sono-Fenton and photo-Fenton reaction of pure water in the presence of LaFeO3 perovskite catalyst. On the other hand, processes including sonication have better energy consumption efficiency as compared with the other individual or combined processes, as well. In the sono-photo-Fenton oxidation of BPA, a degradation of 21.8% and a COD reduction of 11.2% which are too low to be practical were achieved at the end of 3 h of reaction. The external mass transfer resistance was calculated theoretically and it can be said that it was negligible in sono-photo-Fenton oxidation of BPA. The energy analysis results show that in the photo-Fenton and sonophoto-Fenton oxidation of BPA, the energy consumptions are higher than that in sono-Fenton process. So, for this purpose, further studies are required on the sono-Fenton oxidation of BPA over perovskite LaFeO3 catalyst to optimize the ultrasonic power, amount of catalyst, amount of H2O2, and pH of the BPA solution. By this way, it is expected that the energy consumption can be decreased by increasing the degradation degree of BPA to a higher value than that in this study. Acknowledgement The author acknowledges the financial support from TUBİTAK (The Scientific and Technological Research Council of Turkey) under project number of 213M648 and Ege University Scientific Research Fund under project 15BİL009. The author also acknowledges the assistance and guidance of Professor Gönül Gündüz during this study. 6

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M. Dükkancı Water Res. 44 (2010) 2245–2252. [24] M. Lim, Y. Son, S. Na, J. Khim, Effect of TiO2 concentration for sonophotocatalytic degradation of Bisphenol A, in: Proceedings of Symposium on Ultrasonic Electronics, vol. 31, 2010, pp.103–104. [25] J. Poerschmann, U. Trommler, T. Goreckı, Aromatic intermediate formation during oxidative degradation of Bisphenol A by homogeneous sub-stoichiometric Fenton reaction, Chemosphere 79 (2010) 975–986. [26] M.Y. Leiw, G.H. Guai, X. Wang, M.S. Tse, N.C. Mang, O.K. Tan, Dark ambient degradation of Bisphenol A and Acid Orange 8 as organic pollutants by perovskite SrFeO3-x metal oxide, J. Hazard. Mater. 260 (2013) 1–8. [27] Y.B. Xie, X.Z. Li, Degradation of bisphenol A in aqueous solution by H2O2- assisted photoelectrocatalytic oxidation, J. Hazard. Mater. B38 (2006) 526–533. [28] C. Wang, L. Zhu, C. Song, G. Shan, P. Chen, Characterization of photocatalyst Bi3.84W0.16O6.24 and its photodegradation on Bisphenol A under simulated solar light irradiation, Appl. Catal. B 105 (2011) 229–236. [29] C. Wang, L. Zhu, M. Wei, P. Chen, G. Shan, Photolytic reaction mechanism and impacts of coexisting Substances on photodegradation of Bisphenol A by Bi2WO6 in water, Water Res. 46 (2012) 845–853. [30] R. Xing, L. Wu, Z. Fei, P. Wu, Mesopolymer modified with palladium phthalocyaninesulfonate as a versatile photocatalyst for phenol and Bisphenol A degradation under visible light irradiation, J. Environ. Sci. 25 (2013) 1687–1695. [31] L. Zhang, W. Wang, S. Sun, Y. Sun, E. Gao, Z. Zhang, Elimination of BPA endocrine disruptor by magnetic BiOBr@SiO2@Fe3O4 photocatalyst, Appl. Catal. B 148–149 (2014) 164–169. [32] C. Wang, Photocatalytic degradation of bisphenol A and dye by graphene-oxide/ Ag3PO4 composite under visible light irradiation, Ceram. Int. 40 (2014) 8061–8070. [33] M. Sivakumar, Y. Iida, K. Yasui, T. Tuziuti, Preparation of nanosized TiO2 supported on activated alumina by a sonochemical method: observation of an increased photocatalytic decolourisation efficiency, Res. Chem. Intermed. 30 (2004) 785–792. [34] P.R. Gogate, M. Sivakumar, A.B. Pandit, Destruction of Rhodamine B using novel sonochemical reactor with capacity of 7.5 l, Sep. Purif. Technol. 34 (2004) 13–24. [35] H. Ferkous, Q. Hamdaoui, S. Meruani, Sonochemical degradation of naphthol blue black in water: effect of operating parameters, Ultrason. Sonochem. 26 (2015) 40–47. [36] Y.A.J. Al-Hamadani, K.H. Chu, J.R.V. Flora, D.H. Kim, M. Jang, J. Sohn, W. Joo, Y. Yoon, Sonocatalytical degradation enhancement for ibuprofen and sulfamethoxazole in the presence of glass beads and single-walled carbon nanotubes, Ultrason. Sonochem. 32 (2016) 440–448. [37] D.K. Kim, Y. He, J. Jeon, K.E. O’Shea, Irradiation of ultrasound to 5-methylbenzotriazole in aqueous phase: degradation kinetics and mechanisms, Ultrason. Sonochem. 31 (2016) 227–236. [38] L.L. He, X.P. Liu, Y.X. Wang, Z.X. Wang, Y.J. Yang, Y.P Gao., B. Liu, X. Wang, Sonochemical degradation of methyl orange in the presence of Bi2WO6: effect of operating parameters and the generated reactive oxygen species, Ultrason. Sonochem. 33 (2016) 90–98. [39] M. Zhou, H. Yang, T. Xian, R.S. Li, H.M. Zhang, X.X. Wang, Sonocatalytic

[40]

[41] [42]

[43]

[44]

[45]

[46]

[47]

[48]

[49]

[50] [51]

[52]

[53] [54]

7

degradation of RhB over LuFeO3 particles under ultrasonic irradiation, J. Hazard. Mater. 289 (2015) 149–157. M. Sivakumar, P.A. Tatake, A.B. Pandit, Kinetics of p-nitrophenol degradation: effect of reaction conditions and cavitational parameters for a multiple frequency system, Chem. Eng. J. 85 (2002) 327–338. M. Sivakumar, A.B. Pandit, Wastewater treatment: a novel energy efficient hydrodynamic cavitational technique, Ultrason. Sonochem. 9 (2002) 123–131. A. Khataee, P. Gholami, B. Vahid, S.W. Joo, Heterogeneous sono-Fenton process using pyrite nanorods prepared by non-thermal plasma for degradation of an anthraquinone dye, Ultrason. Sonochem. 32 (2016) 357–370. M. Dükkancı, Degradation of bisphenol-a using a sonophoto Fenton-like hybrid process over a LaFeO3 perovskite catalyst and a comparison of its activity with a TiO2 photocatalyst, Turk. J. Chem. 40 (2016) 784–801. F.Z. Yehia, G. Eshaq, A.M. Rabie, A.H. Mady, A.E. ElMetwally, Phenol degradation by advanced Fenton process in combination with ultrasonic irradiation, Egypt. J. Pet. 24 (2015) 13–18. S. Manickam, N. Binti Zainal Abidin, S. Parthasarathy, I. Alzorqi, E. Huay Ng, T.J. Tiong, R.L. Gomes, A. Ali, Role of H2O2 in the fluctuating patterns of COD (chemical oxygen demand) during the treatment of palm oil mill effluent (POME) using pilot scale triple frequency ultrasound cavitation reactor, Ultrason. Sonochem. 21 (2014) 1519–1526. X. Chen, J. Dai, G. Shi, L. Li, G. Wang, H. Yang, Sonocatalytic degradation of Rhodamine B catalyzed by β-Bi2O3 particles under ultrasonic irradiation, Ultrason. Sonochem. 29 (2016) 172–177. H. Eskandarloo, A. Badiei, M.A. Behnajady, G.M. Ziarani, Ultrasonic-assisted degradation of phenazopyridine with a combination of Sm-doped ZnO nanoparticles and inorganic oxidants, Ultrason. Sonochem. 28 (2016) 169–177. E. Sert, A.D. Buluklu, S. Karakuş, F.S. Atalay, Kinetic study of catalytic esterification of acrylic acid with butanol catalyzed by different ion Exchange resins, Chem. Eng. Process. 73 (2013) 23–28. M. Mohagheghi, C. Bakeri, M. Saeedizadi, Study of the effects of external and internal diffusion on the propane dehydrogenation reaction over Pt-Sn/Al2O3 catalyst, Chem. Eng. Technol. 30 (2007) 1721–1725. J.M. Smith, Chemical Engineering Kinetics, third ed., McGraw-Hill, 1981, pp. 389–411. M. Dükkancı, M. Vinatoru, T.J. Mason, Sonochemical treatment of Orange II using ultrasound at a range of frequencies and powers, J. Adv. Oxid. Technol. 15 (2012) 277–283. M. Sivakumar, A. Towata, K. Yasui, T. Tuziuti, T. Kozuka, Y. Lida, Dependence of sonochemical parameters on the platinization of rutile titania- An observation of a pronounced increase in photocatalytic efficiencies, Ultrason. Sonochem. 17 (2010) 621–627. M. Sivakumar, A.B. Pandit, Ultrasound enhanced degradation of Rhodamine B: optimization with power density, Ultrason. Sonochem. 8 (2001) 233–240. S. Parthasarathy, R.R. Mohammed, C.M. Fong, R.L. Gomes, S. Manickam, A novel hybrid approach of activated carbon and ultrasound cavitation fort he intensification of palm oil mill effluent (POME) polishing, J. Cleaner Prod. 112 (2016) 1218–1226.