Contents lists available at ScienceDirect

Ultrasonics - Sonochemistry

journal homepage: www.elsevier.com/locate/ultson

Sonocatalytic activity of biochar-supported ZnO nanorods in degradation ofgemifloxacin: Synergy study, effect of parameters and phytotoxicityevaluation

Peyman Gholamia,b, Laleh Dinpazhohb, Alireza Khataeeb,c,⁎, Yasin Oroojia,⁎

a College of Materials Science and Engineering, Nanjing Forestry University, No. 159, Longpan Road, Nanjing, 210037 Jiangsu, People's Republic of Chinab Research Laboratory of Advanced Water and Wastewater Treatment Processes, Department of Applied Chemistry, Faculty of Chemistry, University of Tabriz, 51666-16471 Tabriz, Iranc Department of Materials Science and Nanotechnology Engineering, Faculty of Engineering, Near East University, 99138 Nicosia, Mersin 10, Turkey

A R T I C L E I N F O

Keywords:Zinc oxideSonocatalysisNanocatalystBiocharZnO-biochar nanocomposite

A B S T R A C T

This study focuses on the facile preparation of ZnO-biochar (ZnO-BC) nanocomposite prepared by the hydro-thermal approach as an efficient sonocatalyst for degradation and mineralization of gemifloxacin (GMF).Morphological and textural characteristics of bare biochar (BC), ZnO nanorods (ZnO NRs) and ZnO-BC nano-composite were investigated using TEM, SEM and BET analyses. Moreover, XRD, FTIR, EDX and UV–vis DRSanalyses were performed to study the crystalline structure, functional groups, elemental composition and opticalproperties of the samples, respectively. ZnO-BC nanocomposite showed better sonocatalytic performance thanBC and ZnO NRs owing to its huge surface area, narrow band gap and enhanced sonoluminescence phenomenon.These properties led to the synergetic ability of ultrasonic irradiation and catalytic activity of ZnO-BC to generatereactive species and subsequent radical reactions. In addition, the effect of the addition of various gases andscavengers on the removal of GMF was evaluated. The GC–MS analysis was used to verify the generation of someintermediates and a possible pathway was proposed accordingly. 83.7% COD removal efficiency was observedwithin 90min treatment confirming efficient mineralization of GMF solution. The phytotoxicity test was carriedout using Lemna minor and the results proved that after the treatment process, a considerable toxicity removal ofthe GMF solution had occured.

1. Introduction

Antibiotics are very efficient pharmaceuticals used for preventing/treating illnesses and are widely consumed by human beings [1]. Owingto their wide application, the residue of antibiotics has been detected ingroundwater, surface water and soil as emerging pollutants over the lastyears [2]. Gemifloxacin (GMF) belongs to a class of medicines known asfluoroquinolones (FQs) which is used to treat bacterial infections bykilling the bacteria or hindering their growth [3]. Based on the WorldHealth Organization (WHO) report in 2014, the main concern asso-ciated with the antibiotic pollution is genotoxicity and the possibility ofprogressive increment in the prevalence of antibiotic resistance even atconcentrations as low as 0.20 μg L−1 [4]. As a result, finding a pros-perous method for removal of these pharmaceutics from aqueousmedium is an essential necessity. Of all the advanced oxidation pro-cesses (AOPs) available for this purpose, ultrasound irradiation has

been widely used for complete removal of pharmaceuticals, since itdoes not produce extra waste streams and is not restricted by thetoxicity or low biodegradability of pollutants [5].

The effect of sonication eventuates from the implosive collapse ofmicroscopic bubbles that are formed during the introduction of ultra-sound waves [6]. These waves exert cyclic sequences of compressionand decompression phases in the aqueous solution [7]. When pressuremagnitude exceeds the tensile strength of liquid, cavitation bubbles areproduced. The generated bubbles that have very short life time of aboutmicro seconds, grow by ultrasound frequency and eventually collapseafter reaching a critical size [8]. The consequence of this implosion isthe generation of localized hot spots with high temperature and pres-sure. The extreme condition of transient hot spots can produce hy-drogen and hydroxyl reactive radicals by homolytic cleavage of watermolecules [9]. These %OH radicals are strong oxidizing agents that arecapable of destroying and converting nearly all persistent organic

https://doi.org/10.1016/j.ultsonch.2019.03.001Received 28 July 2018; Received in revised form 20 February 2019; Accepted 2 March 2019

⁎ Corresponding authors at: Research Laboratory of Advanced Water and Wastewater Treatment Processes, Department of Applied Chemistry, Faculty of Chemistry,University of Tabriz, 51666-16471 Tabriz, Iran (A. Khataee).

E-mail addresses: a_khataee@tabrizu.ac.ir (A. Khataee), yasin@njfu.edu.cn (Y. Orooji).

Ultrasonics - Sonochemistry 55 (2019) 44–56

Available online 04 March 20191350-4177/ © 2019 Elsevier B.V. All rights reserved.

T

pollutants (POPs) to CO2 and H2O through their complete mineraliza-tion [10]. However, this process is considered to be merely time-con-suming and requires a lot of energy. Among various methods availableto improve the performance of sonolysis, extensive research has beendevoted to the application of catalysts [11]. Introduction of a solidcatalyst into the solution improves the generation of •OH radicals, sinceit enhances the formation of hot spots by increasing the number ofnuclei that are available for production of cavitational bubbles [12].

According to the available literature, various nano-sized semi-conductors such as ZnO [13,14], TiO2 [15], ZrO2 [16,17], FeCeOx [18],etc. have been reported to increase the performance of ultrasound indegradation of different organic pollutants. Among these, ZnO nanos-tructures have gained considerable attention due to their physical andchemical properties such as low cost, non-toxicity and chemical stabi-lity [19,20]. Moreover, it is well known that single-bubble sonolumi-nescence (SBSL) flushes contain intense ultraviolet (UV) light which canexcite ZnO by bubble implosion in the ultrasonic system [14,21].However, in order to prevent the fast recombination of generatedelectron-hole pairs and to increase specific surface area, ZnO nano-particles have been composited with different types of carbon-basedmaterials including graphene [22], graphene oxide [23], reduced gra-phene oxide [24], etc.

Pyrolyzation of biomass in an oxygen depleted atmosphere yields ablack carbon-rich product known as biochar (BC). Because of the car-bonaceous porous structure, increased specific surface area comparedto the precursor, as well as its abundant and inexpensive feed stock,biochar based nanocomposites have been widely used in water andwastewater treatment processes. Biochar-supported reduced grapheneoxide composite has been synthesized for the adsorption of lead ionsand atrazine [25]. Simultaneous removal of Cd (II) and Sb (III) has beenstudied by adsorption onto a MnFe2O4–BC nanocomposite. CeO2-BCnanocomposite has been synthesized to assess the sonocatalytic de-gradation of a textile dye [26]. Wang et al. also reported microwave-assisted preparation of N-doped biochar by activation of ammoniumacetate for adsorption of acid red 18 [27]. The application of ZnCl2-activated biochar for removal of aqueous As(III) has been investigatedby Xia et al [28].

The aims of this research are to (a) synthesize and incorporate ZnOnanorods (NRs) onto BC surface by a simple hydrothermal method, (b)evaluate the physical and chemical characteristics of ZnO NRs, BC andZnO-BC nanocomposite using XRD, EDX, FESEM, TEM, BET and FT-IRanalyses, (c) study the sonocatalytic degradation of GMF using ZnO-BCnanocomposite, (d) investigate the effect of some important operationalparameters, namely GMF concentration, ZnO-BC dosage, pH of solu-tion, ultrasonic power, addition of scavengers and gas bubbling, andfinally (e) determine the mineralization efficiency and the possible

degradation pathway using GC-MS.

2. Experimental

2.1. Reagents and materials

The biochar was prepared from wheat husks and paper sludgewhich was obtained from Sonnenerde GmbH (Riedlingsdorf, Austria)and then it was used as received. The sample was prepared throughconventional pyrolysis at 500 °C at a residence time of 20min and noinert gas was used in order to drive off pyrolyic vapors. The biochar wasgiven 5min to gas out and then it was quenched with water to reach30% water content. Detailed explanation on full characterization of thematerials and production conditions can be found in a publication byBachmann et al. [29]. Gemifloxacin (GMF) was obtained from AminPharmaceutical Co. (Iran). Zn(NO3)2·4H2O (98%) was purchased fromSigma-Aldrich (USA). All of the other materials were supplied by Merck(Germany). All reagent-grade chemicals were used as purchasedwithout any further purification and Millipore water was used in thepreparation of all aqueous solutions.

2.2. Preparation of ZnO-BC nanocomposite

On the BC, ZnO NRs were grown using a facile, simple and lowtemperature hydrothermal procedure. Typically, 1 g of the BC powderwas dispersed into deionized water (80mL) by sonicating for 20minbefore adding Zn(NO3)2·4H2O (20mM); 1.8mL NH3 (32%) wasdropped into the solution to adjust pH to 11. After transferring thisalkaline solution into a Teflon coated stainless steel autoclave, it washeated at 90 °C for a duration of 2 h. The resulting precipitate wascollected, filtered using a filtration paper, and rinsed three times withdeionized water and dried at 40 °C for 12 h [30]. This process was re-peated for the production of pure ZnO NRs without adding BC to thesynthesis medium. Schematic representation of ZnO-BC synthesis pro-cedure is given in Fig. 1.

2.3. Characterization

PANalytical X’Pert PRO (Germany) diffractometer (Cu Kα radiation:0.15406 nm; 45 kV, 40mA) in 2θ ranging from 20 to 80° was used torecord the X-ray powder diffraction data. In order to determine theaverage size of the ZnO crystallites, Scherrer's formula was used at themost intense diffraction peak of ZnO and ZnO-BC patterns (2θ: 36.25°)[26]. The FT-IR spectra were collected on a Bruker Tensor 27 (Ger-many) spectrophotometer. N2 adsorption-desorption isotherms at 77 Kwere measured using a Belsorp Mini II (Japan) equipment. TEM images

Fig. 1. Schematic diagram of the preparation of ZnO-BC nanocomposite.

P. Gholami, et al. Ultrasonics - Sonochemistry 55 (2019) 44–56

45

of ZnO NRs were acquired using a JEOL JEM-2200FS (Japan) micro-scope operating at 200 kV. FESEM images and EDX spectra were re-corded using a field-emission scanning electron microscope (Mira3Tescan, Czech Republic) equipped with an EDX analyzer at an accel-erating voltage of 20 kV. UV–vis DRS spectra of the samples were ob-tained with a Sinco S-4100 (Korea) to determine the band gap of theZnO and ZnO-BC.

2.4. Sonocatalytic activity

Sonocatalytic performance of as-prepared catalysts was studied inthe GMF degradation. In a typical experiment, 100mL of GMF solution(20–50mg L−1) was transferred to a 250mL Erlenmeyer flask andcertain amount of the sonocatalyst was added to the solution. In orderto adjust the pH of the solution, NaOH and HCl aqueous solutions wereused. Ultrasonic bath (EP S3, Sonica, Italy) with inside dimensions of140mm width, 230mm length, 100mm height, with an operatingfrequency of 40 kHz and power of 300W was used to sonicate the so-lution. During the course of the ultrasound irradiation, the temperatureof the ultrasonic bath was controlled by adding ice-water to the bathwater. The Erlenmeyer flask was fixed at 10mm from the bottom of thebath, while the water level was kept constant at 80mm inside the bath.At regular intervals of 5min, 3mL treated solution was withdrawn andthen remnant GMF concentration was determined using an ultraviolet-visible (UV-vis) spectrophotometer (SU–6100, Philler scientific, USA) ata maximum wavelength of 343 nm. The degradation efficiency (DE%)of GMF was defined as follows:

⎜ ⎟= ⎛⎝

− ⎞⎠

×DE A AA

% 100t0

0 (1)

where A0 represents the absorbance of GMF solution before irra-diation and At is the absorbance of GMF solution degraded within acertain period of time. To determine the concentration of the dissolvedzinc in the solution, an atomic absorption spectroscopy (AAS) equip-ment (Novaa 400, Analytikjena, Germany) was applied.

To determine the intermediates generated during the initial steps ofthe degradation, GMF solution was treated under sonocatalytic de-gradation process using ZnO-BC nanocomposite (US/ZnO-BC process)for 10min, and then the treated solution was analyzed by an Agilent6890 GC system coupled to an Agilent 5973 MS instrument. A detaileddescription of the sample preparation and method used for the de-termination of the intermediates was presented in our previous work[31]. Mineralization of GMF solution before and after sonodegradationwas determined by chemical oxygen demand (COD) analysis. The CODanalyses were performed using Palintest (United Kingdom) instrument,based on standard method 5220 [32]. The concentration of NH+

4 , NO−3

and NO−2 ions generated from mineralization of GMF solution were

determined by an ion chromatography system (930 compact IC flex,Metrom, Switzerland).

For the phytotoxicity assessment, pigment contents of L. minor suchas total carotenoids, total chlorophyll, chlorophyll a, and chlorophyll bwere determined for the L. minor fronds which were subjected to GMFsolution, treated GMF solution and water based on the procedure sug-gested by Lichtenthaler [33]. Measurement of the pigment contents ofplants was carried out after 10 days to investigate the toxicity of solu-tions.

3. Results and discussion

3.1. Characterization of BC, ZnO, and ZnO-BC nanocomposite

BC, ZnO and ZnO-BC nanocomposite were characterized by XRDanalysis and the obtained data are presented in Fig. 2a. The XRD pat-tern of pure BC presents some weak peaks associated with the presenceof CaCO3 [34] and SiO2 [35] phases. As shown in Fig. 2a, wurtzite ZnO

structure is the only detectable crystallographic phase in the XRD pat-tern of ZnO NRs, which is in good agreement with the JCPDS No. 36-1451 [19]. On the other hand, the XRD pattern of ZnO-BC nano-composite shows that all detected peaks can be excellently matched tothe mixture of ZnO and BC samples and no other phases are detected.

The particle size of ZnO NRs for the ZnO-BC samples were estimatedto be 27 and 22 nm, respectively, by the X-ray line broadening methodusing the Scherrer formula (Eq. (2)) at the strongest peak of ZnO andZnO-BC patterns (2θ: 36.25°).

=D Kλβ θcosXRD

(2)

where K is the Scherrer constant, λ is the X-ray wavelength, β refers tothe half-width of the strongest diffraction peaks, and θ represents theBragg angle.

The FT-IR analysis was employed to identify some characteristicfunctional groups on the samples. The obtained results are representedin Fig. 2b. For all the samples, the relatively intense bands observed at1650 and 3440 cm−1 are ascribed to the bending vibration of HeOeHand OeH and the peaks located from 2850 to 2940 cm−1 originate fromthe symmetric and asymmetric stretching mode of vibration of CeHbond, respectively [36]. Also, the band at 1037, 1124, 1325, 1417 and1452 cm−1 can be attributed to the stretching vibration of SieOeSi,CeO stretch coupled to CeC, stretching vibration of C]C group,bending vibration of CH2 group and stretching vibration of COO−

[37–39]. The appearance of a broad band at 626 cm−1 is attributed tothe stretching mode of CO3

2− in BC [40]. Interestingly, a strong peak at524 cm−1 is observed in the ZnO and ZnO-BC nanocomposite that canbe ascribed to the ZneO stretching [41]. However, any signal related toZnO is not detected in the BC spectrum. An additional peak at 580 cm−1

is observed in ZnO-BC nanocomposite which belongs to the ZnO vi-bration and makes it clear that ZnO NRs were attached on the surface ofBC [42].

The results of nitrogen adsorption-desorption analysis for pure BC,ZnO NRs and ZnO-BC nanocomposite show type IV isotherms with widehysteresis loops typical of mesoporous materials Fig. 2c. Table 1 dis-plays the textural characteristics of the samples, calculated from Bru-nauer–Emmett–Teller (BET) methods. According to Table 1, the BETspecific surface area and the total pore volume of the ZnO NRs(183.41m2 g−1 and 0.24m3 g−1, respectively) are remarkably higherthan those of BC sample (68.19m2 g−1 and 0.07m3 g−1, respectively).Accordingly, as expected, incorporation of ZnO NRs onto the surface ofBC enhanced the characteristics of BC in terms of specific surface area(119.5 m2 g−1) and pore volume (0.16 cm3 g−1).

The optical characteristics of the ZnO NRs and ZnO-BC nano-camposite were determined by applying UV–vis DRS spectroscopy.Extrapolation of the linear portion of the plot of (Ahv)2 versus (hv) wascarried out to calculate the band gap of the samples (Fig. 2d), based onEq. (3).

=υ υ(αh ) K(h - E )2g (3)

where α, hυ, K, and Eg are absorption coefficient, photon energy (eV),absorption index, and band gap energy, respectively. The band gap ofZnO NRs and ZnO-BC nanocomposite were estimated as 3.04 and2.77 eV, respectively. ZnO-BC sample exhibits lower band gap valuecompared to ZnO NRs. This can be attributed to the BC introduction. Asit has been demonstrated in previous studies, doping a semiconductoronto the graphite-like carbon matrix can create vacancies, which leadsto band gap narrowing [43].

The morphology of the synthesized ZnO RDs was studied by FESEMand TEM images. Fig. 3a–f show the FESEM images of the bare BC athigh and low magnifications. The structural characteristic of BC de-monstrates its potential to act as excellent support for immobilization ofnano-sized catalyst (Fig. 3a–c). Channel-like microstructure proliferatethe biochar surface, revealing partial retention of the initial biomassmorphology. The porous structure of the BC is produced through the

P. Gholami, et al. Ultrasonics - Sonochemistry 55 (2019) 44–56

46

generation of volatile materials during pyrolysis. As the materials es-cape, cracks and pores begin to form on the biochar surface. Fig. 3g–ishow a well-defined rod shaped morphology of ZnO NRs fabricated byhydrothermal technique. The TEM images also clearly confirm thesynthesis of nano-sized ZnO in rod shape with uniform diameters aspresented in Fig. 4. All the zinc oxide NRs have diameters about20–40 nm. On the other hand, according to the SEM images of ZnO-BCnanocomposite, the zinc oxide nanorods were grown in uniform size,high density, and randomly distributed (Fig. 3j–l).

Elemental composition of ZnO, bare BC, and ZnO-BC samples weredetermined by EDX microanalysis. Fig. 5a–c reveals that the BC samplecontains O, C, Si, Ca, Al, K, Na, Mg and P elements. Furthermore, theEDX spectrum of ZnO sample shows an intense peak of Zn, demon-strating successful synthesis of ZnO NRs using hydrothermal method.By comparing the EDX spectrum of ZnO-BC with those of pure ZnO andbare BC, it can be concluded that ZnO NRs were successfully in-corporated onto the BC surface.

In consequence, the results obtained from characterization of bareBC, ZnO NRs and ZnO-BC nanocomposite clearly confirm the growth ofZnO nanorods on the porous surface of biochar.

3.2. Comparative study on GMF removal by different processes

A comparative investigation on removal of GMF with US, ZnO, ZnO-BC, BC, US/BC, US/ZnO and US/ZnO-BC systems was performed for45min and the results are illustrated in Fig. 6a. The GMF degradationefficiency under identical conditions showed the following order; US(10.4%) < ZnO (12.2%) < ZnO-BC (15.1%) < BC (23.4%) < US/BC (46.8%) < US/ZnO (64.6%) < US/ZnO-BC (96.1%). Due to thelow production rate of hydroxyl radicals by using sonolysis alone, thelowest DE% was achieved by ultrasound waves. On the other hand,adsorption capacity of the BC and ZnO-BC samples transcend that ofZnO, which could be ascribed to the difference in hydrophobicity of thesamples. The functional groups on the surface of catalyst do not play thekey role in degradation of pollutant molecules in advanced oxidationprocesses and do not have a significant effect on the catalytic activity.However, the presence of some functional groups on the surface ofcatalyst affects its ability in the absorption of pollutant molecules. Ac-cording to the results of FT-IR analysis, some peaks such as those thatappear at 1650, 1452, 1325, 1124, 1037, and 626 cm-1 are responsiblefor the hydrophobicity of BC. Whilst Zn–O stretching that appears forZnO and ZnO-BC, but not in BC, is responsible for the hydrophilicity ofZnO. Generally, the relatively hydrophobic GMF molecules show higheraffinity for adsorption on the BC and ZnO-BC samples which are morehydrophobic adsorbent than ZnO [44]. When solid particles were in-troduced to the sonication medium, the relatively porous particles ac-celerated the cavitation bubble nucleation in the system which led to anincrease in the DE%. The possible mechanisms by which this could beexplained are (a) the decrease in the threshold energy for the bubbles

Fig. 2. (a) XRD patterns, (b) FT-IR spectra, (c) N2 adsorption/desorption isotherms of BC, ZnO and ZnO-BC samples and (d) (Ahυ)2–hv curves of the ZnO and ZnO-BCsamples.

Table 1Textural characteristics of the samples.

Sample Surface area (m2/g) Pore volume (cm3/g)

Pure BC 68.19 0.07ZnO NRs 183.41 0.24ZnO-BC 119.15 0.16

P. Gholami, et al. Ultrasonics - Sonochemistry 55 (2019) 44–56

47

generation [45], (b) the increase in nucleation sites [46] and (c) theincrease in mass-transfer efficiency [9] which results in formation ofmore •OH radicals. The enhanced degradation efficiency achieved byZnO/US and ZnO-BC/US processes can be ascribed to the sonolumi-nescence phenomenon. The intense UV light that is the result of theaforementioned mechanism leads to the excitation of ZnO or ZnO-BCwhich subsequently play the role of an efficient photocatalyst duringsonolysis [47,48]. The higher DE% in US/ZnO-BC process may also beattributed to the electron-trapping ability of BC. The recent studies[49–51] on the redox characteristics of chars has proposed this property

as a potential reason for various chemical processes. Studies haveshown that biochar is able to accept significant amounts of electrons intheir environment. Klüpfel et al. used electrochemical measurements inorder to assess the electron accepting capacity (EAC) of biochar; themaximum amount of electrons that a particular char can accept from anadequet reductive environment is defined as EAC. Klüpfel et al. [51]have shown that the EAC of biochar attained a maximum of 0.54mmol(e−).gbiochar−1. The vacant d-orbitals in metals like Si and Al that existin Biochar gallery can act as electron acceptors and thus enhance theelectron transfer between biochar and ZnO interface by hampering the

Fig. 3. SEM micrographs of BC (a–f), ZnO (g–i) and ZnO-BC (j–l) samples.

P. Gholami, et al. Ultrasonics - Sonochemistry 55 (2019) 44–56

48

recombination of electron-hole pairs. Afterward, reactive species suchas H2O2, %OH and O2

%− are produced as a result of the reactions thatoccur between electrons trapped in ZnO conduction bond (CB) and theadsorbed oxygen molecules through Eqs. (4)–(9). Accordingly, thestability of electron-hole pairs is expanded, and thus the number ofgenerated •OH radicals increases through Eqs. (10) and (11) [52].Moreover, as can be seen from Fig. 2d, ZnO-BC nanocomposite has alower band gap (2.77 eV) than that of ZnO NRS (3.04 eV) and as ex-pected, acts as a more efficient sonocatalyst.

+ → −− −metals e metals eCB (4)

metals− e−+O2→metals+O2%− (5)

O2%−+H+→HO2

% (6)

HO2%+O2

%−+H+→H2O2+O2% (7)

H2O2+ eCB−→ %OH+OH− (8)

H2O2+O2%−→ %OH+OH−+O2 (9)

H2O+ hVB+→ %OH+H+ (10)

OH−+ hVB+→ %OH (11)

In order to compare the degradation rate of GMF using the studiedsystems, both pseudo-first and pseudo-second order kinetic modelswere used to analyze the experimental data by applying linear regres-sion analysis to the data plots of ln (A0/At) and [(1/At) − (1/A0)],respectively, as a function of time [16]. The results showed that thecorrelation coefficient (R2) values for the pseudo-first-order model(> 0.98) (Fig. 6b) were higher than those for the pseudo-second-ordermodel (< 0.87) (for which detailed data were not reported). Therefore,it can be concluded that the degradation rates of all studied systemsfollowed the pseudo-first-order kinetic. The rate constants (kapp) weredetermined graphically and Fig. 6c represents the comparison of thekapp values for GMF degradation using the combined and individualprocesses. kapp of the US/ZnO-BC system is far higher than those of theothers. For the better interpretation, the synergy factors for the US/BC,US/ZnO and US/ZnO-BC systems were determined as 1.7, 4.1 and 10.7,applying Eqs. (12)–(14), respectively.

=+

Synergy factork

k kUS BCUS BC

US BC/

/

(12)

Fig. 4. TEM images of ZnO nanorods.

Fig. 5. EDX spectra of BC (a), ZnO (b) and ZnO-BC (c) samples.

P. Gholami, et al. Ultrasonics - Sonochemistry 55 (2019) 44–56

49

=+

Synergy factork

k kUS ZnOUS ZnO

US ZnO/

/

(13)

=+−

−

−Synergy factor

kk kUS ZnO BC

US ZnO BC

US ZnO BC/

/

(14)

3.3. Sonocatalytic degradation of GMF over ZnO-BC nanocomposite

3.3.1. Effect of working parameters on sonocatalysis processSince the pollutant concentration plays a significant role in water

treatment, the impact of initial GMF concentration was studied over therange of 20–50mg L−1 while the catalyst dosage, pH, ultrasonic powerand thus the number of generated reactive radicals remained constantduring the experiments. As a result, the ZnO-BC nanocomposite was notsuccessful in providing enough active sites for the production of re-active species which are responsible for degradation of GMF molecules[14,53]. Hence, as demonstrated in Fig. 7a, the degradation efficiencydecreased remarkably from 96.1% to 35.5% as the pollutant con-centration increased from 20mg L−1 to 50mg L−1.

GMF degradation using US/ZnO-BC process was studied in solutionswith various pH values. The sonocatalytic performance of ZnO-BC wasnot significantly affected by the value of solution pH in the range of3.5–9.5. It should be mentioned that pH does not have any influence onthe cavitational phenomenon regarding the number of cavitation col-lapses or the temperature/pressure formed during cavity collapse [54].However, the change in solution pH may cause negative or positive

charges on the surface of catalyst and affect the interaction betweencatalyst surface and pollutant molecules [55]. But in the case of sono-catalytic degradation of GMF, the effect of solution turbulence is moreconsiderable than the effect of electrostatic interaction between ZnO-BCsurface and non-charged GMF molecules. At lower pH values the DE%was slightly higher as represented in Fig. 7b. This is mainly because atlow pH values, the oxidation potential of •OH radicals is higher than thealkaline condition [56]. Since the solution pH did not remarkably affectDE%, degradation experiments were conducted in natural pH of GMFsolution (5.5), unless otherwise stated.

In order to study the effect of ZnO-BC dosage on degradation effi-ciency, a series of experiments were conducted with various con-centrations of the catalyst. Results demonstrated that DE% increasedconcurrent with increasing the sonocatalyst dosage (Fig. 7c). Themaximum degradation efficiency was found to be 96.1% with 1.5 g L−1

of sonocatalyst. This is attributed to the increased number of availablecatalytic active sites and hence the number of produced reactive radi-cals in solution [57].

Fig. 7d shows the sonocatalytic degradation of GMF under differentultrasonic irradiation powers of 150, 300 and 450W. As the ultrasoundpower increased from 150 to 450, the DE% enhanced from 85.7% to97.4%. An increase in ultrasonic power results in an increment in ul-trasound amplitude that favors more violent transient cavitation bubblecollapse. In addition, when ultrasound is subjected to the solution, itwould cause greater turbulence and pulsation of the liquid phase andthis mechanical effect increases the mass transfer coefficient. Moreover,

Fig. 6. (a) Comparison of GMF degradation efficiency in different processes; (b) the kinetic analysis using pseudo-first-order model; (c) comparison of the kapp valuesfor the combined and individual processes; Experimental conditions: pH=5.5, [GMF]0=20mg/L, [catalyst]= 1.5 g/L and ultrasonic power= 300W.

P. Gholami, et al. Ultrasonics - Sonochemistry 55 (2019) 44–56

50

owing to the cleaning effect of sonolysis, more active sites would beavailable on the surface of solid catalyst. Eventually, the number ofcavitational bubbles increases which leads to the production of morehydroxyl radicals and rapid degradation rate of pollutant molecules[58,59].

3.3.2. Effects of gas addition on sonocatalysis processGas sparging can ease the initialization of new cavitational events

since the dissolved gasses can act as new nucleation sites and trigger thefree radical formation. While gas purging can enhance degradation rate,the efficiency is solely dependent on the nature of the gas [7]. To in-vestigate the effect of gas sparging on the sonocatalytic degradation, thesolution of 20mg L−1 GMF containing 1 g L−1 catalyst with pH of 5.5was taken and the experiments were conducted by introducing thesolution to corresponding gases including argon, oxygen and air during45min of sonication process at the flow rate of 15 L h−1. The findingsshowed that the maximum removal efficiency of 95.3% was reportedfor argon sparged solution, while the oxygen and air purged solutionsshowed a lower degradation rate of 90.9% and 82.1%, respectively. Thehighest degradation efficiency observed in argon bubbled solution isrelated to its high solubility (0.056mLmL−1 water) [60], polytropicratio (1.67) [61], and low thermal conductivity (0.018Wm−1 K−1)[61]. The high solubility of a gas in liquid phase affects the free radicalproduction by increasing nucleation sites in aqueous medium whichfacilitates the cavitation phenomena and increases the number of gen-erated •OH radicals [60]. Furthermore, high polytropic ratio and lowthermal conductivity result in high pressure and temperature of

cavitational bubbles during their collapse which leads to increased so-nochemical activity [61]. Oxygen and air have lower solubility (0.049and 0.029mLmL−1 water, respectively) and polytropic ratio (1.40) andhigher thermal conductivity (0.026 and 0.025Wm−1 K−1, respec-tively) than those of argon. Therefore, lower DE% were observed asoxygen and air were bubbled into the sonication medium (Fig. 8). Si-milar results have been reported by Hapeshi et al. [62].

3.3.3. Determining the main species that are involved in the sonocatalyticdegradation of GMF with the use of scavengers

In order to elucidate the role of main reactive species involved indegradation of GMF, benzoquinone (BQ), ethylenediaminetetraaceticacid (EDTA) and t-butanol were added to solution and the solution wassonicated for 45min. The corresponding results are shown in Fig. 9a.Among these, BQ which is an O2

%− scavenger showed only a subtleeffect as quencher on degradation efficiency, suggesting that O2

%− doesnot play a significant role in removal of GMF [63]. On the other hand,the DE% diminished to 62.9% in presence of EDTA, because it restrainsthe GMF removal by decreasing the number of formed h+ which canreact with OH− and H2O molecules to generate %OH radicals (Eq. (15)).However, still a copious amount of hydroxyl radicals were produced byhot spots [64]. In this case of study, t-butanol demonstrated a greaterquenching effect on pollutant degradation, proving that the %OH radi-cals are the major reactive species [65].

→ +H O OH H2))) % % (15)

Numerous amount of natural inorganic anions exist along with

Fig. 7. Effect of operation parameters on degradation efficiency of GMF in the US/ZnO-BC process; (a) effect of pollutant concentration (pH=5.5,[Catalyst]= 1.5 g/L and ultrasonic power= 300W); (b) effect of pH ([GMF]0=20mg/L, [Catalyst]= 1.5 g/L and ultrasonic power= 300W); (c) effect of ZnO-BCdosage ([GMF]0=20mg/L, pH=5.5 and ultrasonic power= 300W) and (d) effect of ultrasonic power ([GMF]0= 20mg/L, pH=5.5 and [Catalyst]= 1.5 g/L).

P. Gholami, et al. Ultrasonics - Sonochemistry 55 (2019) 44–56

51

antibiotics in natural water sources. Therefore, considering the utili-zation of sonocatalytic degradation for ecological specimens, the effectof inorganic scavengers was also studied by adding different salts in US/ZnO-BC process. The obtained results are depicted in Fig. 9b. When20mg L−1 of inorganic salts, namely, Na2SO4, Na2CO3 and NaCl wereadded to the solutions, the DE% decreased from 96.1% to 84.1%, 70.8%and 58.6%, respectively. This can be explained by two reasons: first, theoxidation potentials of the radicals produced from reaction betweenhydroxyl radicals and the anions that take part in degradation of pol-lutant molecules (Eqs. (16)–18)) are lower than that of hydroxyl radi-cals; second, the active sites on ZnO-BC catalyst may be clogged by theanions that are present in the solution [66]. The relatively lowscavenging effect of sulfate anions on degradation efficiency of GMFmay be attributed to the higher oxidation potential of sulfate radicalsthan others [66,67].

SO42−+ %OH→ SO4

%−+OH− (16)

CO32−+ %OH→ CO3

%−+OH− (17)

Cl−+ %OH→ %Cl+OH− (18)

The comparative effect of these salts has been investigated by Shahet al. [66] on sonophotocatalytic degradation efficiency of two textiledyes in presence of Cu-ZnO as catalyst and the same reactivity order of

NaCl > Na2CO3 > Na2SO4 has been reported.

3.4. Reusability of ZnO-BC nanocomposite

One of the critical points of heterogeneous catalytic systems is thestability and reusability of the catalyst, especially for long term usage.Therefore, to evaluate the reusability of the catalyst, 1.5 g L−1 of ZnO-BC was used in five consecutive sonocatalytic runs. Fig. 10 indicatesthat almost 10% loss of degradation efficiency was observed after fiveruns. Moreover, after sonocatalytic process, the total leached Zn con-centration was 0.53mg L−1 in the presence of ZnO-BC catalyst andunder the studied pH condition (pH=5.5), which is lower than WorldHealth Organization (WHO) standard permissible limit (3.0 mg L−1)[68]. After the reaction, the SEM images of the sonocatalyst were re-corded to further study the stability of the ZnO-BC nanocomposite(Fig. 11a–c). According to Fig. 11a–c, there is no noticeable change inthe morphology of ZnO-BC sample after the photocatalytic processes. Inaddition, the Zeta potential values of fresh and used ZnO-BC suspendedin water were recorded as +20.7 and +21.4mV at pH 5.5 (natural pHof GMF solution), which depicts that no significant change had occurredin the surface charge of the catalyst after five consecutive runs. All inall, the obtained results strongly confirm the stability of the catalystover several applications.

Fig. 8. Effect of gas sparging on degradation efficiency of GMF; Experimentalconditions: pH=5.5, [GMF]0= 20mg/L, [catalyst]= 1 g/L, gas flowrate= 15 L/h and ultrasonic power= 300W.

Fig. 9. The effect of organic (a) and inorganic (b) scavengers on the GMF degradation by US/ZnO-BC process; Experimental conditions: pH=5.5, [GMF]0= 20mg/L, [Catalyst]= 1.5 g/L, ultrasonic power=300W and [scavenger]0= 20mg/L.

Fig. 10. Degradation efficiency for five consecutive sonocatalytic runs.Experimental conditions: pH=5.5, [GMF]0= 20mg/L, [catalyst]= 1.5 g/Land ultrasonic power=300W.

P. Gholami, et al. Ultrasonics - Sonochemistry 55 (2019) 44–56

52

3.5. Transformation products and degradation pathway

The intermediates generated in GMF solution treated through US/ZnO-BC process were identified using GC-MS analysis after 10min so-nocatalysis, and accordingly a reasonable degradation pathway wasproposed. The details of the main intermediate products produced from

GMF degradation and proposed degradation pathway are shown inTable 2 and Fig. 12, respectively. From Fig. 12, 1,8-Naphthyridin-4-one,2-amino-1-piperazin-1-ylethanone and 2-propen-1-ol were detected asthree dominant intermediate products in the early steps of the reaction.It must be pointed out that there might be other compounds resultedfrom GMF dissociation before the formation of these compounds that

Fig. 11. SEM images of ZnO-BC after sonocatalytic process with different magnifications.

Table 2Identified intermediate compounds during sonochemical degradation of GMF.

No. Compound name Structure Retention time (min) Main fragments

1 1,8-Naphthyridin-4-one 18.145 63 (24.31%), 78 (39.62%), 118 (51.27%), 146 (100%)

2 3-(Pyridin-2-ylamino)prop-2-enal 13.048 51 (15.81%), 78 (34.98%), 119 (100%), 148 (27.69%)

3 2-Amino-1-piperazin-1-ylethanone 23.659 44 (100%), 56 (19.56%), 85 (35.73%), 114 (19.08%)

4 N-[2-(Dimethylamino)ethyl]glycinamid 11.207 32 (22.74%), 42 42.92%), 58 (71.84%), 86 (100%)

5 N-(6-Aminohexanoyl)glycine 16.372 30 (27.43%), 44 (29.46%), 72 (67.19%), 86 (100%)

6 2-Propen-1-ol 8.634 29 (51.79%), 31 (41.20%), 39 (24.95%), 57 (100%)

7 1,2-Propanediol 5.861 27 (38.61%), 31 (51.37%), 45 (100%), 61 (17.09%)

Fig. 12. Proposed degradation pathway of GMF.

P. Gholami, et al. Ultrasonics - Sonochemistry 55 (2019) 44–56

53

were not identified. The further oxidation of 2-propen-1-ol on ZnO-BCnanocomposite generated 1,2-propanediol. Evidently, subsequent oxi-dation of 1,8-naphthyridin-4-one resulted in the generation of 3-(pyr-idin-2-ylamino)prop-2-enal as one of the first ring cleavage products.The attack of reactive species lead to the cleavage of pyridine ring of 3-(pyridin-2-ylamino)prop-2-enal to generate N-(6-Aminohexanoyl)gly-cine. On the other hand, N-[2-(Dimethylamino)ethyl]glycinamid wasproduced through ring-opening of 2-amino-1-piperazin-1-ylethanone.Eventually, all the aliphatic compounds could be mineralized into H2O,CO2 and inorganic ions. The mineralization of an organic contaminantthat contain N heteroatom proceeds via production of different by-products such as amides and carboxylic acids, which are eventuallymineralized to H2O and CO2 and release inorganic ions. Hence, a de-crease in COD concentration as well as an increase in inorganic ionsconcentration in the treated solution could be reasonable indicators formineralization of the pollutant [69]. Thus, the COD and IC analysesunder the optimized values of the operational parameters were used toevaluate the efficiency of US/ZnO-BC process. 58.3% and 83.7% CODremoval efficiencies were observed within 45 and 90min treatment,respectively. In addition, the results obtained from IC analysis revealedthat upon degradation of GMF molecules, the N atoms were released asNO−

3 anions and NH+4 cations. The initial concentration of NO−

3 andNH+

4 ions in the GMF solution were 0.09 and 0.05mg L−1 which in-creased to 8.4 and 5.7 mg L−1 within 45min treatment.

3.6. Phytotoxicity assessment

Lemna minor (L. minor) is a rapidly spreading aquatic plant andbecause of its small and widespread genome size, it is an appropriatespecies for investigation of pollutant phytotoxicity [70]. In order tostudy the phytotoxicity of GMF solution, fifty fully-grown fronds of L.minor were placed in a 500mL beaker containing 4mL of culturemedium and 200mL of the solution. Water, GMF solution (20mg L−1)and treated GMF solution were chosen as testing solutions. Eq. (19) wasused to calculate the Relative Frond Number (RFN) [71].

= −Relative Frond Number (RFN) (Frond N Frond N )Frond N

10 0

0 (19)

where N0 and N10 demonstrate the frond numbers at the beginning andafter 10 days, respectively. The RFN was measured as 1.44, 1.24 and0.16 for water, treated GMF solution and untreated GMF solution, re-spectively (Fig. 13a–c). These results imply that the toxicity of GMFsolution is remarkably higher than that of all the other samples. Aftertreatment of GMF solution through US/ZnO-BC process, the RFN in-creases from 0.16 to 1.24 demonstrating the reduction in toxicity. Itshould be mentioned that the solutions with higher toxicity have lowerpigment contents because of the plants death. The phytotoxicity of GMFsolution was proved by its lower pigment contents. The pigment con-tents significantly increased after GMF degradation, revealing that thelow toxic by-products and products were produced through the US/ZnO-BC process (Fig. 13d).

4. Conclusions

Zinc oxide nanorods supported on biochar were successfully syn-thesized by facile and low temperature hydrothermal method. The re-sults obtained from the characterization of ZnO-BC nanocomposite byXRD, EDX, FESEM, TEM, BET and FT-IR analyses clearly confirmed thegrowth of ZnO nanorods on the porous surface of biochar. The ZnO-biochar nanocomposite showed greater sonocatalytic performance ascompared to pure ZnO nanorods and bare biochar. The influence of thedifferent parameters including the catalyst dosage, initial GMF con-centration, pH and ultrasonic power on the sonocatalytic efficiencywere studied. For 45min ultrasonic irradiation, 1.5 g L−1 ZnO-bio-char addition amount, pH=5.5 and 20mg L−1 GMF concentrationconditions, the sonocatalytic degradation efficiency could reach 96.1%.

Based on the results of GC–MS, COD and IC analyses it could be con-cluded that GMF was first decomposed to aromatic and aliphatic in-termediates in the early stage of the reactions and then mineralized toCO2, H2O and inorganic ions. Addition of gases enhanced the GMFdegradation efficiency by increasing the nucleation sites in aqueousmedium and enhancing pressure and temperature of cavitational

Fig. 13. Macroscopic images of L. minor in (a) water, (b) treated GMF solutionand untreated GMF solution (c) and (d) evaluation of total chlorophyll, chlor-ophyll a, chlorophyll b and total carotenoides in the samples.

P. Gholami, et al. Ultrasonics - Sonochemistry 55 (2019) 44–56

54

bubbles. Finally, the phytotoxicity tests showed that the sonodegrada-tion of GMF solution significantly reduced the solution toxicity com-pared to the untreated solution.

Acknowledgements

The authors appreciate all the support provided by the University ofTabriz and Nanjing Forestry University.

References

[1] Y. Zhou, N. Zhu, W. Guo, Y. Wang, X. Huang, P. Wu, Z. Dang, X. Zhang, J. Xian,Simultaneous electricity production and antibiotics removal by microbial fuel cells,J. Environ. Manage. 217 (2018) 565–572.

[2] C. Kim, H.-D. Ryu, E.G. Chung, Y. Kim, J.-K. Lee, A review of analytical proceduresfor the simultaneous determination of medically important veterinary antibiotics inenvironmental water: sample preparation, liquid chromatography, and mass spec-trometry, J. Environ. Manage. 217 (2018) 629–645.

[3] R. Wilson, J.J. Schentag, P. Ball, L. Mandell, A comparison of gemifloxacin andclarithromycin in acute exacerbations of chronic bronchitis and long-term clinicaloutcomes, Clin. Ther. 24 (2002) 639–652.

[4] L. Jiang, X. Hu, T. Xu, H. Zhang, D. Sheng, D. Yin, Prevalence of antibiotic re-sistance genes and their relationship with antibiotics in the Huangpu River and thedrinking water sources, Shanghai, China, Sci. Total Environ. 458 (2013) 267–272.

[5] V. Belgiorno, L. Rizzo, D. Fatta, C. Della Rocca, G. Lofrano, A. Nikolaou, V. Naddeo,S. Meric, Review on endocrine disrupting-emerging compounds in urban waste-water: occurrence and removal by photocatalysis and ultrasonic irradiation forwastewater reuse, Desalination 215 (2007) 166–176.

[6] S. Houtmeyers, J. Degrève, K. Willems, R. Dewil, L. Appels, Comparing the influ-ence of low power ultrasonic and microwave pre-treatments on the solubilisationand semi-continuous anaerobic digestion of waste activated sludge, Bioresour.Technol. 171 (2014) 44–49.

[7] R.J. Wood, J. Lee, M.J. Bussemaker, A parametric review of sonochemistry: controland augmentation of sonochemical activity in aqueous solutions, Ultrason.Sonochem. 38 (2017) 351–370.

[8] F. Soumia, C. Petrier, Effect of potassium monopersulfate (oxone) and operatingparameters on sonochemical degradation of cationic dye in an aqueous solution,Ultrason. Sonochem. 32 (2016) 343–347.

[9] K.H. Chu, Y.A. Al-Hamadani, C.M. Park, G. Lee, M. Jang, A. Jang, N. Her, A. Son,Y. Yoon, Ultrasonic treatment of endocrine disrupting compounds, pharmaceu-ticals, and personal care products in water: a review, Chem. Eng. J. 327 (2017)629–647.

[10] Y. Bessekhouad, R. Brahimi, F. Hamdini, M. Trari, Cu2S/TiO2 heterojunction ap-plied to visible light Orange II degradation, J. Photochem. Photobiol. A: Chem. 248(2012) 15–23.

[11] N. Pokhrel, P.K. Vabbina, N. Pala, Sonochemistry: science and engineering,Ultrason. Sonochem. 29 (2016) 104–128.

[12] P. Sathishkumar, R.V. Mangalaraja, S. Anandan, Review on the recent improve-ments in sonochemical and combined sonochemical oxidation processes – a pow-erful tool for destruction of environmental contaminants, Renew. Sust. Energ. Rev.55 (2016) 426–454.

[13] L. Zhang, H. Qi, Z. Yan, Y. Gu, W. Sun, A.A. Zewde, Sonophotocatalytic inactivationof E. coli using ZnO nanofluids and its mechanism, Ultrason. Sonochem. 34 (2017)232–238.

[14] S.-B. Hu, L. Li, M.-Y. Luo, Y.-F. Yun, C.-T. Chang, Aqueous norfloxacin sonocatalyticdegradation with multilayer flower-like ZnO in the presence of peroxydisulfate,Ultrason. Sonochem. 38 (2017) 446–454.

[15] D. Marković, Z. Šaponjić, M. Radoičić, T. Radetić, V. Vodnik, B. Potkonjak,M. Radetić, Sonophotocatalytic degradation of dye CI Acid Orange 7 by TiO2 and Agnanoparticles immobilized on corona pretreated polypropylene non-woven fabric,Ultrason. Sonochem. 24 (2015) 221–229.

[16] A. Khataee, B. Kayan, P. Gholami, D. Kalderis, S. Akay, L. Dinpazhoh, Sonocatalyticdegradation of Reactive Yellow 39 using synthesized ZrO2 nanoparticles on biochar,Ultrason. Sonochem. 39 (2017) 540–549.

[17] P. Bansal, G.R. Chaudhary, S. Mehta, Comparative study of catalytic activity of ZrO2

nanoparticles for sonocatalytic and photocatalytic degradation of cationic and an-ionic dyes, Chem. Eng. J. 280 (2015) 475–485.

[18] S. Chong, G. Zhang, Z. Wei, N. Zhang, T. Huang, Y. Liu, Sonocatalytic degradationof diclofenac with FeCeOx particles in water, Ultrason. Sonochem. 34 (2017)418–425.

[19] R. Darvishi, Cheshmeh Soltani, S. Jorfi, M. Safari, M.-S. Rajaei, Enhanced sonoca-talysis of textile wastewater using bentonite-supported ZnO nanoparticles: responsesurface methodological approach, J. Environ. Manage. 179 (2016) 47–57.

[20] Y. Areerob, J.Y. Cho, W.K. Jang, W.-C. Oh, Enhanced sonocatalytic degradation oforganic dyes from aqueous solutions by novel synthesis of mesoporous Fe3O4-gra-phene/ZnO@SiO2 nanocomposites, Ultrason. Sonochem. 41 (2018) 267–278.

[21] N. Shimizu, C. Ogino, M.F. Dadjour, T. Murata, Sonocatalytic degradation of me-thylene blue with TiO2 pellets in water, Ultrason. Sonochem. 14 (2007) 184–190.

[22] Y. Areerob, J.Y. Cho, W.K. Jang, W.-C. Oh, Enhanced sonocatalytic degradation oforganic dyes from aqueous solutions by novel synthesis of mesoporous Fe3O4-gra-phene/ZnO@ SiO2 nanocomposites, Ultrason. Sonochem. 41 (2018) 267–278.

[23] S.O. Oppong, W.W. Anku, S.K. Shukla, P.P. Govender, Synthesis and

characterisation of neodymium doped-zinc oxide–graphene oxide nanocomposite asa highly efficient photocatalyst for enhanced degradation of indigo carmine inwater under simulated solar light, Res. Chem. Intermed. 43 (2017) 481–501.

[24] L. Nirumand, S. Farhadi, A. Zabardasti, A. Khataee, Synthesis and sonocatalyticperformance of a ternary magnetic MIL-101 (Cr)/RGO/ZnFe2O4 nanocomposite fordegradation of dye pollutants, Ultrason. Sonochem. 42 (2018) 647–658.

[25] Y. Zhang, B. Cao, L. Zhao, L. Sun, Y. Gao, J. Li, F. Yang, Biochar-supported reducedgraphene oxide composite for adsorption and coadsorption of atrazine and leadions, Appl. Surf. Sci. 427 (2018) 147–155.

[26] A. Khataee, P. Gholami, D. Kalderis, E. Pachatouridou, M. Konsolakis, Preparationof novel CeO2-biochar nanocomposite for sonocatalytic degradation of a textile dye,Ultrason. Sonochem. 41 (2018) 503–513.

[27] L. Wang, W. Yan, C. He, H. Wen, Z. Cai, Z. Wang, Z. Chen, W. Liu, Microwave-assisted preparation of nitrogen-doped biochars by ammonium acetate activationfor adsorption of acid red 18, Appl. Surf. Sci. 433 (2018) 222–231.

[28] D. Xia, F. Tan, C. Zhang, X. Jiang, Z. Chen, H. Li, Y. Zheng, Q. Li, Y. Wang, ZnCl2-activated biochar from biogas residue facilitates aqueous As(III) removal, Appl.Surf. Sci. 377 (2016) 361–369.

[29] Hans Jörg Bachmann, Thomas D. Bucheli, Alba Dieguez-Alonso, Daniele Fabbri,Heike Knicker, Hans-Peter Schmidt, Axel Ulbricht, Roland Becker,Alessandro Buscaroli, Diane Buerge, Andrew Cross, Dane Dickinson, Akio Enders,Valdemar I. Esteves, Michael W.H. Evangelou, Guido Fellet, Kevin Friedrich,Gabriel Gasco Guerrero, Bruno Glaser, Ulrich M. Hanke, Kelly Hanley, Isabel Hilber,Dimitrios Kalderis, Jens Leifeld, Ondrej Masek, Jan Mumme, MarinaPaneque Carmona, Roberto Calvelo Pereira, Frederic Rees, Alessandro G. Rombolà,José Maria de la Rosa, Ruben Sakrabani, Saran Sohi, Gerhard Soja,Massimo Valagussa, Frank Verheijen, Franz Zehetner, Toward the standardizationof biochar analysis: the COST Action TD1107 interlaboratory comparison, J. Agric.Food Chem. 64 (2) (2016) 513–527, https://doi.org/10.1021/acs.jafc.5b05055.

[30] K. Gurav, M. Gang, S. Shin, U. Patil, P. Deshmukh, G. Agawane, M. Suryawanshi,S. Pawar, P. Patil, C. Lokhande, Gas sensing properties of hydrothermally grownZnO nanorods with different aspect ratios, Sens. Actuator B-Chem. 190 (2014)439–445.

[31] A. Khataee, B. Kayan, P. Gholami, D. Kalderis, S. Akay, Sonocatalytic degradation ofan anthraquinone dye using TiO2-biochar nanocomposite, Ultrason. Sonochem. 39(2017) 120–128.

[32] American Public Health Association, American Water Works Association, WaterEnvironment Federation, Standard Methods for the Examination of Water andWastewater, 19th ed., Washington, 1995.

[33] H.K. Lichtenthaler, [34] Chlorophylls and carotenoids: Pigments of photosyntheticbiomembranes, Methods in Enzymology, Academic Press, 1987, pp. 350–382.

[34] M. Karimi, A. Jodaei, A. Khajvandi, A. Sadeghinik, R. Jahandideh, In-situ captureand conversion of atmospheric CO2 into nano-CaCO3 using a novel pathway basedon deep eutectic choline chloride-calcium chloride, J. Environ. Manage. 206 (2018)516–522.

[35] K.L. Lin, W.C. Chang, D.F. Lin, H.L. Luo, M.C. Tsai, Effects of nano-SiO2 and dif-ferent ash particle sizes on sludge ash–cement mortar, J. Environ. Manage. 88(2008) 708–714.

[36] C.-C. Chu, K.L. White, P. Liu, X. Zhang, H.-J. Sue, Electrical conductivity andthermal stability of polypropylene containing well-dispersed multi-walled carbonnanotubes disentangled with exfoliated nanoplatelets, Carbon 50 (2012)4711–4721.

[37] K.-W. Jung, B.H. Choi, C.M. Dao, Y.J. Lee, J.-W. Choi, K.-H. Ahn, S.-H. Lee,Aluminum carboxylate-based metal organic frameworks for effective adsorption ofanionic azo dyes from aqueous media, J. Ind. Eng. Chem. 59 (2018) 149–159.

[38] T.A. Saleh, S.O. Adio, M. Asif, H. Dafalla, Statistical analysis of phenols adsorptionon diethylenetriamine-modified activated carbon, J. Clean. Prod. 182 (2018)960–968.

[39] L. Ayed, A. Mahdhi, A. Cheref, A. Bakhrouf, Decolorization and degradation of azodye Methyl Red by an isolated Sphingomonas paucimobilis: biotoxicity and meta-bolites characterization, Desalination 274 (2011) 272–277.

[40] A. Bakr, N. Sayed, T. Salama, I.O. Ali, R.A. Gayed, N. Negm, Potential of Mg–Zn–Allayered double hydroxide (LDH)/montmorillonite nanocomposite in remediation ofwastewater containing manganese ions, Res. Chem. Intermed. 44 (2018) 389–405.

[41] N. Batra, M. Tomar, V. Gupta, Realization of an efficient cholesterol biosensor usingZnO nanostructured thin film, Analyst 137 (2012) 5854–5859.

[42] T. Arfin, S.N. Rangari, Graphene oxide-ZnO nanocomposite modified electrode forthe detection of phenol, Anal. Methods 10 (2018) 347–358.

[43] H. Li, J. Hu, X. Zhou, X. Li, X. Wang, An investigation of the biochar-based visible-light photocatalyst via a self-assembly strategy, J. Environ. Manage. 217 (2018)175–182.

[44] A. Zielińska, P. Oleszczuk, Evaluation of sewage sludge and slow pyrolyzed sewagesludge-derived biochar for adsorption of phenanthrene and pyrene, Bioresour.Technol. 192 (2015) 618–626.

[45] J. Kim, B. Park, Y. Son, J. Khim, Peat moss-derived biochar for sonocatalytic ap-plications, Ultrason. Sonochem. 42 (2018) 26–30.

[46] N. Zhang, G. Zhang, S. Chong, H. Zhao, T. Huang, J. Zhu, Ultrasonic impregnationof MnO2/CeO2 and its application in catalytic sono-degradation of methyl orange, J.Environ. Manage. 205 (2018) 134–141.

[47] A. Khataee, H. Marandizadeh, B. Vahid, M. Zarei, S.W. Joo, Combination of pho-tocatalytic and photoelectro-Fenton/citrate processes for dye degradation usingimmobilized N-doped TiO2 nanoparticles and a cathode with carbon nanotubes:central composite design optimization, Chem. Eng. Process. 73 (2013) 103–110.

[48] I.V. Lightcap, T.H. Kosel, P.V. Kamat, Anchoring semiconductor and metal nano-particles on a two-dimensional catalyst mat. Storing and shuttling electrons withreduced graphene oxide, Nano Lett. 10 (2010) 577–583.

P. Gholami, et al. Ultrasonics - Sonochemistry 55 (2019) 44–56

55

[49] L. Yu, Y. Yuan, J. Tang, Y. Wang, S.J.S.r. Zhou, Biochar as an electron shuttle forreductive dechlorination of pentachlorophenol by Geobacter sulfurreducens, Sci.Rep. 5 (2015) 16221.

[50] A. Kappler, M.L. Wuestner, A. Ruecker, J. Harter, M. Halama, S. Behrens, Biochar asan electron shuttle between bacteria and Fe(III) minerals, Environ. Sci. Technol.Lett. 1 (2014) 339–344.

[51] L. Klüpfel, M. Keiluweit, M. Kleber, M. Sander, Redox properties of plant biomass-derived black carbon (Biochar), Environ. Sci. Technol. 48 (2014) 5601–5611.

[52] T. Paul, M.C. Dodd, T.J. Strathmann, Photolytic and photocatalytic decompositionof aqueous ciprofloxacin: transformation products and residual antibacterial ac-tivity, Water Res. 44 (2010) 3121–3132.

[53] L. Gan, L. Xu, K. Qian, Preparation of core-shell structured CoFe2O4 incorporatedAg3PO4 nanocomposites for photocatalytic degradation of organic dyes, Mater.Des. 109 (2016) 354–360.

[54] A.G. Chakinala, P.R. Gogate, A.E. Burgess, D.H. Bremner, Intensification of hy-droxyl radical production in sonochemical reactors, Ultrason. Sonochem. 14 (2007)509–514.

[55] E. Kordouli, K. Bourikas, A. Lycourghiotis, C. Kordulis, The mechanism of azo-dyesadsorption on the titanium dioxide surface and their photocatalytic degradationover samples with various anatase/rutile ratios, Catal. Today 252 (2015) 128–135.

[56] A. Babuponnusami, K. Muthukumar, A review on Fenton and improvements to theFenton process for wastewater treatment, J. Environ. Chem. Eng. 2 (2014)557–572.

[57] R. Das, M. Bhaumik, S. Giri, A. Maity, Sonocatalytic rapid degradation of Congo reddye from aqueous solution using magnetic Fe0/polyaniline nanofibers, Ultrason.Sonochem. 37 (2017) 600–613.

[58] Z. Boutamine, O. Hamdaoui, S. Merouani, Probing the radical chemistry and thereaction zone during the sono-degradation of endocrine disruptor 2-phenox-yethanol in water, Ultrason. Sonochem. 41 (2018) 521–526.

[59] E. Kuna, R. Behling, S. Valange, G. Chatel, J.C. Colmenares, Sonocatalysis: a po-tential sustainable pathway for the valorization of lignocellulosic biomass and de-rivatives, Top. Curr. Chem. 375 (2017) 41.

[60] D.E. Kritikos, N.P. Xekoukoulotakis, E. Psillakis, D. Mantzavinos, Photocatalyticdegradation of reactive black 5 in aqueous solutions: effect of operating conditions

and coupling with ultrasound irradiation, Water Res. 41 (2007) 2236–2246.[61] L.H. Thompson, L.K. Doraiswamy, Sonochemistry: science and engineering, Ind.

Eng. Chem. Res. 38 (1999) 1215–1249.[62] E. Hapeshi, I. Fotiou, D. Fatta-Kassinos, Sonophotocatalytic treatment of ofloxacin

in secondary treated effluent and elucidation of its transformation products, Chem.Eng. J. 224 (2013) 96–105.

[63] X. Liu, L. Huang, D. Zhang, T. Yan, J. Zhang, L. Shi, Light driven fabrication ofhighly dispersed Mn-Co/RGO and the synergistic effect in catalytic degradation ofmethylene blue, Mater. Des. 140 (2018) 286–294.

[64] T. Zhou, X. Zou, J. Mao, X. Wu, Decomposition of sulfadiazine in a sonochemicalFe0-catalyzed persulfate system: parameters optimizing and interferences of was-tewater matrix, Appl. Catal. B-Environ. 185 (2016) 31–41.

[65] Y.L. Pang, A.Z. Abdullah, S. Bhatia, Review on sonochemical methods in the pre-sence of catalysts and chemical additives for treatment of organic pollutants inwastewater, Desalination 277 (2011) 1–14.

[66] J. Shah, M.R. Jan, F. Khitab, Sonophotocatalytic Degradation of Textile dyes overCu impregnated ZnO catalyst in Aqueous Solution, Process Saf. Environ. Prot.(2018).

[67] A. Khataee, P. Gholami, M. Sheydaei, S. Khorram, S.W. Joo, Preparation of na-nostructured pyrite with N2 glow discharge plasma and the study of its catalyticperformance in the heterogeneous Fenton process, New J. Chem. 40 (2016)5221–5230.

[68] World Health Organization, Overview of the environment and health in Europe inthe 1990s, (1999).

[69] H. Lin, J. Niu, J. Xu, Y. Li, Y. Pan, Electrochemical mineralization of sulfa-methoxazole by Ti/SnO2-Sb/Ce-PbO2 anode: kinetics, reaction pathways, and en-ergy cost evolution, Electrochim. Acta 97 (2013) 167–174.

[70] W. Drost, M. Matzke, T. Backhaus, Heavy metal toxicity to Lemna minor: studies onthe time dependence of growth inhibition and the recovery after exposure,Chemosphere 67 (2007) 36–43.

[71] R. Wang, J.H. Xin, Y. Yang, H. Liu, L. Xu, J. Hu, The characteristics and photo-catalytic activities of silver doped ZnO nanocrystallites, Appl. Surf. Sci. 227 (2004)312–317.

P. Gholami, et al. Ultrasonics - Sonochemistry 55 (2019) 44–56

56