Preparation, characterization and catalytic potential of γ-Fe2O3@AC mesoporous heterojunction for activation of peroxymonosulfate into degradation of cyfluthrin insecticide

Accepted Manuscript Preparation, characterization and catalytic potential of γ-Fe2O3@AC mesoporous heterojunction for activation of peroxymonosulfate into degradation of cyfluthrin insecticide Ramin Khaghani, Babak Kakavandi, Khashayar Ghadirinejad, Emad Dehghani Fard, Anvar Asadi PII:

S1387-1811(19)30213-6

DOI:

https://doi.org/10.1016/j.micromeso.2019.04.013

Reference:

MICMAT 9417

To appear in:

Microporous and Mesoporous Materials

Received Date: 26 January 2019 Revised Date:

13 March 2019

Accepted Date: 8 April 2019

Please cite this article as: R. Khaghani, B. Kakavandi, K. Ghadirinejad, E.D. Fard, A. Asadi, Preparation, characterization and catalytic potential of γ-Fe2O3@AC mesoporous heterojunction for activation of peroxymonosulfate into degradation of cyfluthrin insecticide, Microporous and Mesoporous Materials (2019), doi: https://doi.org/10.1016/j.micromeso.2019.04.013. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Graphical abstract

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Preparation, characterization and catalytic potential of γ-Fe2O3@AC mesoporous heterojunction for activation of peroxymonosulfate into degradation of cyfluthrin insecticide

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Ramin Khaghani1, Babak Kakavandi 2, 3, *, Khashayar Ghadirinejad4, Emad Dehghani Fard3, Anvar Asadi5 1

Department of Military Health, Faculty of Medicine, Aja University of Medical Sciences, Tehran, Iran Aja University of Medical Sciences, Tehran, Iran 3 Research Center for Health, Safety and Environment, Alborz University of Medical Sciences, Karaj, Iran 4 College of Science and Engineering, Flinders University, Clovelly Park, SA 5042, Australia 5 Research Center for Environmental Determinants of Health (RCEDH), Kermanshah University of Medical Sciences, Kermanshah, Iran

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Abstract

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A novel application of maghemite nanoparticles embedded activated carbon (γ-Fe2O3@AC), as a mesoporous heterojunction composite, coupled with UV light was used for enhanced activation of peroxymonosulfate (PMS) for degradation of cyfluthrin insecticide. The performance of γFe2O3@AC/UV/PMS system was assessed as affected by different concentrations of PMS,

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catalyst and pollutant, pH of aqueous media, reaction time, co-exiting water matrix components and trapping agents. A tentative mechanism was proposed for the PMS decomposition and reactive species production in both solid and liquid phases. Catalytic activity of γ-Fe2O3@AC in

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the PMS decomposition was enhanced significantly when it coupled with UV light. In optimal conditions (pH 4.0, PMS 4.0 mM, 0.4 g/L catalyst, C0= 60 mg/L and time 80 min), the efficiency

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rates of 88.5 and 52.4 were achieved for degradation and mineralization of cyfluthrin, respectively. The degradation rate affected by matrix anions was reduced in order of HCO3– > NO3– > Cl– > SO42–. Cycling tests displayed the negligible iron leaching and high recyclability for γ-Fe2O3@AC within 5 times use. A strong synergistic effect was observed between applied

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Corresponding author: Aja University of Medical Sciences, Tehran, Iran. E-mail address: [email protected] (B. Kakavandi). 1

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agents in the activation of PMS. Pseudo-first-order kinetic model represented a significant correlation with the experimental data of degradation process. Among detected free radicals, SO4•− species had a conquer role in catalytic oxidative degradation process. γ-

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Fe2O3@AC/UV/PMS system showed an excellent performance in treatment of simulated real water and wastewater samples. Generally, coupling of γ-Fe2O3@AC and UV for improving PMS activation can be introduced as a successful and efficient approach to catalytic degradation of

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organic matters owing to tremendous catalytic activity, easy recovery, high stability and

Keywords:

Peroxymonosulfate;

Heterogeneous catalyst.

Cyfluthrin;

Insecticide

degradation;

Sulfate

radicals;

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1. Introduction

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reusability potential and the generation of various reactive free species simultaneously.

Over the last decades, consumption of insecticides has been widely increased in all commercial, industrial and household applications in the world. Cyfluthrin (usually called solfac) is a

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complex organic compound with chemical formula of C22H18Cl2FNO3 is known as the most common pyrethroid household insecticides [1, 2]. In household applications, it is used

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extensively to control a wide variety of both indoor and outdoor insects [3]. For commercial applications, it is employed as a 10-25 % solution concentrate and in outbuilding and agricultural uses it is in spray form. Recently, it found in coastal sediments collected in California as reported by researchers [4, 5]. Cyfluthrin has a high stability in the environment, accordingly its residues are accumulated in aquatic organisms, which can threaten seriously the aquatic food safety and human health [6]. It is noticeable that insecticides can enter aquatic environment via both direct

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and indirect discharge within disposal of effluents of wastewater treatment plants [6]. Environmental quality standard of 0.001 µg/L has been recommended for the toxicity of cyfluthrin to aquatic invertebrates and fishes [1]. Considering the environmental and human

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hazards of cyfluthrin, it is necessary for ongoing and accurate assessment of these contaminants in aqueous media and also the urgent attention for developing technologies of treatment and elimination.

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In recent decades, advanced oxidation processes (AOPs) have been introduced as most effective

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methods for degradation and complete mineralization of refractory pollutants. Among AOPs, systems on the basis of sulfate radicals (SO4–•) are more efficient than hydroxyl radicals (•OH) into degradation of organic matters [7, 8]. This superiority is associated with some properties such as independence to solution pH and strong oxidant of SO4•− (E⁰ = 2.5–3.1 V for SO4–• and E⁰ = 1.8-2.7 V for •OH), in comparison with •OH. SO4•− mostly produced through activation of

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peroxymonosulfate (PMS) and persulfate (PS) by using ultrasound and UV irradiations, carbonbased materials, semi-conductors and transition metals and heat [9-11]. The activation of PMS

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by these agents to generate SO4•− radicals is shown below (Eqs. 1-8):

HSO5− + hv → SO •4− + • OH

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(1)

HSO 5− + ))) → SO •4− + • OH

(2)

HSO 5− + heat → SO •4− + • OH

(3)

HSO 5− + AC → SO •4− + HO − + AC+

(4)

HSO 5− + AC →• OH + SO 24− + AC+

(5)

HSO 5− + e CB− → SO •4− (ads) + OH − or •OH + SO 24−

(6)

Mn+ + HSO5−→ Mn+1 + SO4•− + OH−

(7) 3

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Mn+1 + HSO5− → Mn+ + SO5•− + H+

(8)

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Metal ions have been attracted attentions of many environmentalists for using in AOPs as promising activators, because of their high availability and efficiency and cost-effectiveness. However, application of metal ions in homogeneous form has been restricted, because of the generation of metal hydroxide sludge, the difficulties in reusability, causing secondary pollution

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and require further chemicals or treatment [12, 13]. To overcome these problems, the application

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of metal ions-based heterogeneous catalysts have been presented as most efficient alternative approach due to the cost-effectiveness, stable physiochemical structure and feasible in recycling [14, 15]. In this regards, magnetic nanoparticles (MNPs) (e. g. maghemite (γ-Fe2O3), hematite (α-Fe2O3) and magnetite (Fe3O4)) showed the excellent performance in activation of PMS and production of sulfate radicals owing to the Fe3+-Fe2+ redox cycles [16, 17]. But, as reported in the

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literature [18, 19], MNPs have low surface catalytic activity and also low degradation rate, because of strong tendency towards agglomeration and subsequently low surface/volume ratio. In this regards, coating MNPs on some supporting materials like activated carbon (AC), zeolite,

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polymer and chitosan to overcome these limitations has been recommended as a promising

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technique [14, 16, 20]. This approach, as proved, enhances the catalytic potential of MNPs effectively in oxidation processes thereby uniformly deposition of them and efficient adsorption of both target contaminant and oxidant. It is worth to mention that the degradation/mineralization performance of oxidation systems improved significantly when various agents were employed simultaneously for activation of PMS. In recent years, various combinations of activators including Fe2+/UV [21], Co2+/US [22], N-doped TiO2/LED [23], Fe3O4 and US [24], and TiO2@CuFe2O4/UV [19] have been applied in 4

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the oxidation systems for efficient PMS decomposition and production of additional reactive species. With this background, as a first study, we coupled several agents including heterogeneous catalyst γ-Fe2O3, AC and UV light for activation of PMS simultaneously into

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degradation of cyfluthrin. Herein, UV light can play a critical role in enhancement of the degradation efficiency of organic pollutants thereby either direct (Eq. (1)) or indirect production of reactive oxidizing species via regeneration of Fe2+ (Eq. (9)).

Fe(OH) + hν → Fe2+ + • OH

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2+

(9)

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Up to the present time, no research is published about UV-assisted decomposition of PMS coupled with heterogeneous γ-Fe2O3@AC catalyst into degradation of cyfluthrin insecticide. Therefore, in the present work, we focused on coupling γ-Fe2O3@AC and UV as PMS activators for the efficient mineralization of organic matters. According to the literature, this is the first

2.1. Materials

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2. Materials and methods

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study on cyfluthrin removal by hybrid γ-Fe2O3@AC/UV/PMS system.

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In this study, all chemicals were of analytical-laboratory grade and applied as received without further purification, as illustrated in Supporting Information. 2.2. Synthesis and properties of catalyst γ-Fe2O3 NPs were synthesized via in-situ chemical co-precipitation approach, as reported in our previously published paper [25]. For γ-Fe2O3 NPs, a mixture containing FeCl3. 6H2O (2.02 g) and FeCl2. 4H2O (0.75 g) was prepared in 150 mL DI-water. The whole mixture was sonicated 5

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for 15 min at 70±1 ̊C and then stirred at 80±1oC for 30 min using a mechanical mixer. Afterwards, in order to precipitate hydrated iron oxides, 20 mL NH3 aliquot (8 mM) was added drop-wise into the mixture to adjust pH to 10.0-11.0. After 45 min stirring and subsequent

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cooling, a black solid precipitate was obtained from the solution within magnetic separation which rinses sequentially via DI-water/ethanol until the pH reached to the neutral state and then oxidized in an oven at 250±1̊C for 60 min. In a similar procedure, γ-Fe2O3@AC with a weight

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ratio of iron ions to AC: 1:1 was synthesized, with the difference that a certain amount of AC (3.0 g) was added into the Fe2+/Fe3+ mixture before the addition of NH3. In this work, several

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techniques including XRD, FESEM, TEM, BET, EDS and VSM were employed to determine the textural, structural, size and shape of nanoparticles, physicochemical and magnetic properties of prepared catalysts. Further information for these techniques are presented in Table 1.

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2.3. Experimental design and procedure

All experiments related to cyfluthrin degradation by γ-Fe2O3@AC/UV/PMS process were conducted in a 500 mL cylindrical quartz vessel at ambient temperature of 25±2 ºC. In the first

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step, some control experiments with different systems were performed under the same

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operational conditions to determine the most efficient process for elimination of cyfluthrin. The batch oxidation tests were conducted at different experimental variables like solution pH, catalyst dosage, PMS loading, cyfluthrin concentration and reaction time to determine the optimum operational conditions using central composite design (CCD) approach in response surface methodology (RSM) of Design-Expert V10.0 software, as illustrated in Table 2. After optimization, the effect of co-exiting water matrix components and scavenger agents as well as reusability, stability and mineralization degree were also evaluated.

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In each test, after adjustment of pH, the specific amounts of catalyst and PMS were added to the reactor containing cyfluthrin solution and oxidation reactions were begun by emitting UV light. Herein, the light source was a UV-C lamp (PHILIPS) with intensity of 6W and λ = 254 nm and

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100 cm2 illuminated area, that placed vertically near the reactor at distance of 1.0 cm. Thereafter, the samples were mixed using a mechanical mixer at 250 rpm for 90 min. At the end of each run, aliquots were withdrawn from the reactor, quenched immediately with 0.1 mL Na2S2O3 (0.2 M)

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for prevention of additional side reactions, then analyzed using a high-performance liquid chromatography (HPLC) to measure the residual concentrations of cyfluthrin. The error bars in

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the figures were omitted for graphic simplicity, except for the cases where they were necessary. The degradation efficiency was calculated via the equations below:

(10)

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 C − Ct  Degradation (%) =  0  × 100  C0 

where, Co and Ct represent cyfluthrin concentrations (mg/L) at initial and time t of the oxidation

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reaction, respectively.

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2.4. Analytical methods

The mineralization degree was evaluated in terms of total organic carbon (TOC) abatement using a TOC analyzer (Shimadzu VCHS/CSN, Japan). An atomic absorption spectrometer (AAS) instrument (Analytikjena vario 6, Germany) was used to measurement of the quantity of leached Fe. A HPLC (Agilent 1200 Infinity Series) equipped with ultraviolet (UV) detector using a LiChrosorb Si 60 column (4.6 mm × 250 mm, 5µm) was applied to measure the residual cyfluthrin concentrations following the procedure of Vodeb et al, [26]. The wavelength of UV 7

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detector was set at 265 nm and the temperature of column hold was kept constant at 25 °C. To identify cyfluthrin, a mobile phase containing mixture of n-hexane and dichloromethane with

3. Results and discussion

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3.1. γ-Fe2O3@AC characterization techniques

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and the limit of detection were 20.0 µL and 10 µg/L, respectively.

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ratio of 40:60 (v/v %) was used at the flow rate of 1.5 mL/min. The sample volume to injection

According to XRD analysis (Fig. 1), all XRD patterns of samples (i.e., γ-Fe2O3, AC, γFe2O3@AC) were quite consistent with the patterns of standards based on their JCPDS cards. In the XRD spectra of AC, a broad peak at 2θ value of 25̊ is observable clearly which is related to carbon. For γ-Fe2O3, six intense peaks at 2θ values of 30.26o, 35.6o, 43.34o, 53.8o, 57.36o, and

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62.96o belonged to the diffraction of crystalline phase of γ-Fe2O3 (JCPDS No. 39- 1346) [25]. From the XRD pattern of γ-Fe2O3, a high purity can be confirmed for maghemite NPs, because no characteristic peaks of impurities were observed, indicating that γ-Fe2O3 was successfully

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synthesized. As shown in γ-Fe2O3@AC spectra, all diffraction peaks assigned to both maghemite

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NPs and carbon were detected with lack of considerable changes in their XRD patterns, demonstrating the successful crystallization degree of γ-Fe2O3@AC without destroying the structure of its components. Moreover, based on Scherrer equation, the average diameter of γFe2O3 was determined 32 nm. More details on this equation are described in Supporting Information. The external surface of AC was porous, smooth and have some cavities (Fig. 2a) which can provide a high adsorption capacity for the removal of pollutants. FESEM analysis (Fig. 2b) 8

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shows a high agglomeration for pristine γ-Fe2O3 MNPs, while the intensity shows a significant decrease after coating onto the surface AC, as presented in Fig. 2b. Compared to virgin AC, the external surfaces of γ-Fe2O3@AC were much irregular, which come from the agglomeration

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status and also uniform distribution of γ-Fe2O3 on carbon surfaces. Meanwhile, this feature can provide extra several reactive sites on the catalyst and improve its catalytic performance in the oxidation/degradation processes. In EDS spectrum (Fig. 2c), the main peaks attributing carbon

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(C, 38.5%), oxygen (O, 20.4%) and iron (Fe, 41.1%) elements were detected observably for asprepared catalyst, confirming the presence of Fe and O, as dominant elements of preparation

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process, in structure of γ-Fe2O3@AC. As observed, EDS analysis did not represent any peak related to the impurity, which shows that the catalyst is highly pure. From TEM image of γFe2O3@AC (Fig. 2d), a coating layer of maghemite NPs on the AC surface was detected with a relatively spherical or cubical structure and the average side length of 15 – 25 nm, which is in

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excellent agreement with the results of XRD analysis. This analysis proved that γ-Fe2O3 was synthesized with a nano diameter and then successfully loaded over AC surfaces. Table 3 shows the findings of BET analysis of physico-chemical features of sample.

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Accordingly, the specific surface area of 56.8, 745.2 and 584.6 m2/g were obtained respectively

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for γ-Fe2O3, AC and γ-Fe2O3@AC based on the N2 adsorption/desorption measurement. It was noticeable that the coating of MNPs led to decreasing the specific surface area of AC, which can be alluded to the blocking of AC pores by the maghemite NPs. The N2 adsorption/desorption isotherm in Fig. 3a exhibits a typical Langmuir type IV isotherm for γ-Fe2O3@AC, which depicts the mesoporous structure of as-synthesized catalyst with a hysteresis loop [19]. Classification of as-prepared catalyst into mesopores group also is verified by the pore size distribution (insert Fig. 3a), that was in the range of 2 < d > 50 nm based on IUPAC category

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[27]. The magnetic hysteresis loops of VSM analysis related to γ-Fe2O3 and γ-Fe2O3@AC are shown in Fig. 3b. Accordingly, the highest magnetization saturation of γ-Fe2O3@AC (Ms = 25.1 emu/g) was obtained lower than bare γ-Fe2O3 (Ms = 64.6 emu/g) ones, which can be attributed to

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the presence of non-magnetic AC in texture of as-synthesized catalyst. Meanwhile, the separation and recovery of γ-Fe2O3@AC from solution phase was quick and lasted in 30 s, after exposure to the magnetic field, as shown in Fig. 3b. Hence, this rectifying feature makes γ-

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Fe2O3@AC a feasible catalyst in practical applications owing to easy separation and to prevent

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the environment and/or secondary pollutions.

3.2.Various system performance on cyfluthrin removal

Herein, some series of experiments were performed to comparison of various processes (i.e., γFe2O3, AC, γ-Fe2O3@AC, γ-Fe2O3/UV, γ-Fe2O3/PMS, UV, PMS, UV/PMS and γ-

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Fe2O3@AC/UV/PMS) for enhancement of cyfluthrin removal under same input variables within 60 min treatment (conditions: pH 5.5 ± 0.5, 4.0 mM PMS, 20 mg/L cyfluthrin, 0.3 g/L catalyst (AC, γ-Fe2O3 and γ-Fe2O3@AC)). Herein, regarding Fig. 4, a minimal removal efficiency was

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achieved for UV (6.8%) and PMS (12.4%) only, implying that they could not degrade cyfluthrin effectively. However, a better performance into cyfluthrin degradation (32.7 %) was observed

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when UV light coupled with PMS owing to the generation free radicals (e.g., •OH and SO4•−) in systems which contributes in destroy of organic pollutants. For solid materials of γ-Fe2O3, AC and γ-Fe2O3@AC without UV and PMS, the removal rates of 10.6, 24.8 % and 30.5% were obtained, respectively, through adsorption process. A little efficiency for γ-Fe2O3 comes from its low specific surface area (60.5 m2/g), compared to AC and γ-Fe2O3@AC. For γ-Fe2O3@AC, although specific surface area of composite was lower than that of pristine AC, the removal percentage of cyfluthrin by γ-Fe2O3@AC was much greater than that AC. It was worth to 10

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mention that the γ-Fe2O3 loaded on AC surface creates additional available reactive surface sites for γ-Fe2O3@AC composite which enhance the adsorptive removal of pollutants.

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According to Fig. 4, the removal rate of cyfluthrin increased to 42.9 and 38.6 % respectively for γ-Fe2O3/PMS and AC/PMS systems during 60 min reaction. These results demonstrate that both AC and γ-Fe2O3 NPs were more efficient in decomposition of PMS molecules in comparison with UV light owing to the catalytic reaction between PMS and catalysts. According to Eqs. (4

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and 5), AC could decompose PMS molecules effectively to convert into SO4•− radicals. In

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addition, both adsorption and catalytic degradation processes were involved in cyfluthrin elimination during AC/PMS system. For γ-Fe2O3/PMS process, the presence of redox-active centers of γ-Fe2O3 (i.e., Fe2+ and Fe3+ ions) leads to PMS decomposition and reactive oxidizing species generation, as described in Eqs. (9 and10) [28]. A degradation rate of 28.4% was obtained for γ-Fe2O3 coupled with UV, indicating prepared maghemite NPs have photocatalytic

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activity in conjunction with UV into derogation of organic matters. However, when γFe2O3@AC applied simultaneously along with UV and PMS, a rapid improvement was observed in degradation rate of cyfluthrin and reached 98.4% after 60 min reaction, which was

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significantly greater than those of other studied processes. The possible reason for this

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enhancement is associated with use several simultaneous activators (i.e., AC, Fe and UV) in PMS decomposition and efficient production of free oxidizing radicals. It also proved the synergistic effect between the employed factors on the PMS activation and improve system performance. Generally, the results reveal that decontamination efficiencies of individual processes are remarkably lower compared to simultaneous systems. To conclude, heterogeneous γ-Fe2O3@AC catalyst not only has a proper adsorption efficiency, but also possess an excellent catalytic performance in PMS activation. Therefore, γ-Fe2O3@AC/UV/PMS hybrid system, as

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efficient process, chosen for subsequent tests of cyfluthrin degradation optimization, in this study.

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3.3.Effect of operational factors On the basis of CCD approach in RSM, 48 batch runs were proposed for investigation of the role of five input experimental variables on the cyfluthrin removal and then determination of optimal

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operating conditions, as illustrated in Table S-1. The responses were added to this table and then evaluated by analysis of variance (ANOVA) for assessment of the significance and adequacy of

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the model. Herein, quadratic model was suggested by Design-Expert as best model according to results presented in Table S-2. Further details for development of the model reliability and statistical analysis are explained in Supporting Information. Regarding the quadratic model, the polynomial equation for the cyfluthrin removal (%) was obtained in terms of coded factors as

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follows:

Cyfluthrin removal (%) = + 46.68 - (4.25X1) + (4.08X2) - (8.15X3) + (2.39X4) + (5.01X5) + (2.16X1.X2) – (1.54X1.X3) - (0.21X1.X4) – (1.25 X1.X5) – (2.02X2.X3) + (1.51X2.X4) + (1.94

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X2.X5) - (1.64X3.X4) – (2.19 X3.X5) + (1.27 X4.X5) – (0.47X12) - (1.93X22) + (8.21X32) +

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(0.72X42) + (0.72 X52) (11)

The equation shows both the negative and positive effects of experimental variables on the response parameter. X3 and X4 showed the maximum and minimum coefficients, respectively, meaning that the initial cyfluthrin concentration and PMS dosage have the highest and lowest effect on the performance of γ-Fe2O3@AC/UV/PMS process in comparison with the other independent factors. 12

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In catalytic oxidation systems, pH of solution played a critical role in the process performance, because of its effects on the ionization degree of either pollutant or oxidant, generating free

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radicals and transition metals, catalyst surfaces feature, activity and solubility of oxidant and the kinetics of reactions [29, 30]. In this work, the efficiency of γ-Fe2O3@AC/UV/PMS system for degradation of cyfluthrin affected the solution pH which was evaluated in the range of 2.0-10.0.

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Fig. 5a shows that the degradation efficiency was significantly dependent on the solution pH and PMS loading. The better performance was observed at acidic conditions than neutral and alkaline

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ones. Under same operated conditions, the decontamination rate was reduced with increasing the pH of solution, so that the degradation efficiency decreased substantially from 48.6 to 38.4%, when the initial pH value was increased from 2.0 to 10.0, respectively. High performance at acidic media, in fact, results from dissolving additional fraction of iron ions and increasing the

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reaction rate between PMS and iron species, leading to more generation of reactive species [31]. It was worth to mention that more SO4•− radicals can be produced at acidic environments, whereas higher concentration of •OH radicals than sulfate one can be observed in alkaline

•

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conditions [32, 33]. Therefore, since SO4•− radicals have higher values of oxidation potential than OH ones, the higher degradation efficiency in acidic than alkaline pH values are expected.

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Similar results have been published in the literature about the sulfate radical-based radicals’ heterogeneous oxidation studies [12, 13]. In contrast, at higher pH values (alkaline media), reaction rate between iron species and PMS molecules was decreased, due to the both precipitation of iron and formation of ferric hydroxide complexes, and subsequently decreasing the decontamination efficiency [19]. Another reason for this phenomenon is transforming SO4•− radicals to •OH species with lower oxidation potentials via reaction with OH- (Eq. (12)) and

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decomposition of PMS molecules in a non-radial way. Besides, the electrostatic repulsion forces between oxidant (SO52− and HSO5− molecules) and catalyst with negative surface charge at

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strong alkaline environment, led to reducing the generation of free radicals in system [33-35]. •

SO •4− + OH − → SO 24− + OH

(12)

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The 3D plot in Fig.5a indicated the gradual degradation of cyfluthrin with enhancing PMS concentration. As observed, the maximum degradation rate occurred in high level of PMS

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dosage (5.0 mM). In accordance with similar studies [10, 36], extra HSO5− molecules are available to the active sites of γ-Fe2O3@AC at higher dosages of PMS, which accelerated the degradation rate of pollutant through formation of additional SO4•− radicals. At lower PMS concentrations, however, the sufficient quantity of sulfate radicals is not produced to destruct contaminant effectively. In fact, by increasing ratio of PMS to pollutant molar, more free radicals

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are provided for attacking organic matters that promotes the mineralization efficiency [37]. In many studies, researchers proved that further enhancement in the loading of PMS did not

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caused an improvement in decontamination process, because of the recombination of free oxidizing radicals (Eqs. 13 and 14), the reactions between produced radicals (Eq. (15)) and the

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scavenging of PMS, based on reactions (16 and 17) [38-42].

SO•4− + SO•4− → 2SO24− or S2O82− •

(13)

OH+• OH→ H2O2

(14)

SO•4− +• OH→ HSO−4 +1/2O2

(15)

HSO5− + SO•4− → SO5•− + SO24− + H+

(16) 14

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HSO5− +• OH → SO•5− + H2O or HSO−4 + HO•2

(17)

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Fig. 5b exhibits the interactive effect of catalyst dosage and reaction time on decontamination of γ-cyfluthrin over γ-Fe2O3@AC/UV/PMS. As shown, an enhancement in catalyst dosage has a favorable effect on the efficiency of system and the maximum degradation rate was achieved in 0.5 g/L of γ-Fe2O3@AC. Cyfluthrin degradation efficiency was increased considerably from 30.6

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to 46.8 %, as catalyst dosage promoted from 0.1 to 0.5 g/L, respectively during 50 min reaction. This increase can be resulted from: (i) increasing the accessibility of redox-active centers (γ-

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Fe2O3) and the Fe2+/Fe3+ ions for activation of PMS molecules and (ii) accelerating the adsorption process of both PMS and cyfluthrin molecules through existence of higher specific surface area, which in turn boost more reactive oxidizing species [21, 43]. According to Fig. 5b, it is clear that that degradation percentage was increased by passing the reaction time, which can

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be alluded to the production of extra reactive species in system during treatment. The simultaneous effects of initial cyfluthrin concentration and reaction time on performance of

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γ-Fe2O3@AC/UV/PMS system are shown in Fig. 5c. Accordingly, the removal efficiency has an indirect relationship with initial pollutant concentrations which would be expressed through

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some facts: (i) catalyst surface sites coverage and consequently hampering the reaction of PMS at centers of redox-active, (ii) the fixed PMS amount and so the number of free reactive species would not be enough for entire degradation of the total compounds, (iii) limitation of the penetration amount of UV light, which caused declining the formed free radicals via interaction between UV light and PMS molecules, and (iv) powerful competition between parent substances and intermediations for reaction with oxidizing species at higher concentrations of pollutant [44,

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45]. Similar observations have been mentioned in previous studies for photo-oxidation processes of various organic compounds using sulfate radicals [9, 10, 46].

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From Figs. 5 b and d it is clear that the further enhancement in the quantity of catalyst from 0.4 to 0.5 g/L led to a remarkable decrease in decontamination efficiency. This trend was observed for tests related to interactive effect of catalyst dosage with other studied variables. This phenomenon can be explained by: i) self-binding and aggregates of catalyst particles that decline

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the number of catalyst reactive sites at high concentrations, ii) the scavenging influence of SO4−•

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with presence of excesses iron ions (Eq. 18) [47] and decreasing the light penetration and number of photons, leading to declining the photo-decomposition of PMS. Therefore, increase of catalyst dosage until a certain amount has favorable effect on the efficiency of γFe2O3@AC/UV/PMS system, and then it dropped dramatically at the excessive dosages of

SO4−• + Fe2+ → Fe3+ + SO24−

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catalyst, which is in a good consistent with similar studies [19, 48, 49]. (18)

3.4.Optimum conditions of γ-Fe2O3@AC/UV/PMS

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The optimum operating conditions for cyfluthrin removal by γ-Fe2O3@AC/UV/PMS system was

AC C

determined using a numerical technique in the Design-Expert software. Herein, removal efficiency (%) of cyfluthrin, as a response, set at “maximum”, while the intended purpose for the operational factors was “in range”. Based on this scenario, the optimum values of studied factors were pH 4.0, 0.4 g/L catalyst dosage, 4.0 mM PMS concentration and 80 min reaction for 40 mg/L of cyfluthrin. Under these conditions, the predicted and observed maximum removal efficiencies were 86 and 88.3%, respectively, with a high desirability (0.87). A negligible

16

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difference was observed between the values of predicted and observed which suggests the high

3.5.Effects of co-existing water matrix anions

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accuracy of applied model and the reliability of CCD approach in RSM.

In actual environment, the co-existing components, especially anions might affect the process

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performance into efficient elimination of the target pollutant. In this regards, the ability of γFe2O3@AC/UV/PMS system in decontamination of cyfluthrin was assessed in the presence of

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some water matrix anions such as nitrate (NO3−), sulfate (SO42−), chloride (Cl−) and bicarbonate (HCO3−) species under optimum operating conditions. From Fig. 6a, it is clear that an inhibition effect in the cyfluthrin degradation took place for all above-mentioned anions. The degradation percentages of cyfluthrin dropped from 87.6 to 82.4, 86.8, 85 and 58.7 after adding 50 mM nitrate, sulfate, chloride and bicarbonate anions, respectively, during 80 min reaction. Generally,

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the inhibitory effect was in sequence of HCO3−>NO3−>Cl−>SO42−. For all anions, inhibition effects were originated from their act as scavenger of the reactive species and they were

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transformed to less oxidative radicals like Cl2•−, ClOH•−, Cl•, NO3•, NO2•, and CO3•, according to Eqs. (19-24) [19, 50]. Furthermore, the influence of UV light in solution reaction decreased, due

AC C

to turbidity caused by the existence of anions. Another reason for this observation can be justified by the adsorption of anions on the catalyst surface and subsequently pore blocking, which caused declining both the adsorption ability and surface catalytic activity of γ-Fe2O3@AC. In addition, herein, anions can be competed with the organic substances for reaction with the formed active radicals, leading to hindering the degradation of pollutant [51, 52]. Among studied anions, however, the strong inhibition effect was belonged to bicarbonate ions and chloride and sulfate showed lower effect, which is in accordance well with those reported in previous studies. 17

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For bicarbonate ions, the significant inhibitory effect can be described from two ways: i) quenching both •OH and SO4•− to generate carbonate (CO3•−) and bicarbonate (HCO3•−) radicals with lower reactivity (E0 = 1.78 V) (Eqs. 23 and 24) [39] and ii) decreasing oxidation potentials

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of reactive species through increasing the pH of solution [53]. As reported in the literature, reaction rate constant between organic matters and CO3•− is 2 to 3 orders of magnitude lower than for the reaction of •OH and SO4•− radicals with pollutants [19]. Hence, the degradation

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efficiency of cyfluthrin was declined significantly through both consumption and quenching of

Cl− + •OH/SO4•− → ClOH•−/SO42−/Cl• Cl• + Cl- → Cl2•– NO3−+ •OH/SO4•−→ NO3• + OH−/SO42−

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NO3• + H2O + e−aq → NO2• + 2OH−

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reactive oxidizing radicals and PMS decomposition in a non-efficient way.

(19) (20) (21) (22) (23)

HCO3− + • OH → H 2O + CO•3−

(24)

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HCO3− + SO •4− → SO 24− + H + CO •3−

(25)

HSO5- + Cl- → SO42- + HOCl

(26)

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SO42−+ •OH → SO4•−

HSO5- + 2Cl- + H+ → SO42- + Cl2 + H2O

(27)

In the case of sulfate ion, a minimal inhibiting effect on the process performance came from the generation of inevitable product of sulfate radical during γ-Fe2O3@AC/UV/PMS system, based on Eq. (25). A quenching impact on the oxidative degradation of cyfluthrin for nitrate can be related to the trapping of SO4•− radicals by NO3− anions to generate the free radicals with lower 18

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redox potential (i.e., NO3• (E0 =2.30 V) and NO2• (E0 =1.03 V)) (Eqs. (24) and (22)) [54] as well as the adsorption and reduction of nitrate ions on the catalyst surface [53]. During γFe2O3@AC/UV/PMS system, the degradation rate was reduced by addition of Cl− ions owing to

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the reaction between Cl− and PMS and formation of HOCl and Cl2, as described in Eqs. (26) and (27) [22]. Faint inhibiting effect for chloride ions can also be associated with production of

and SO4•− species.

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3.6. Scavenging agents and degradation mechanism

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reactive species of chlorine radicals (i.e., Cl2•−, ClOH•− and Cl•) with lower reactivity than •OH

In order to determine the degradation mechanism of cyfluthrin using γ-Fe2O3@AC/UV/PMS system, the understanding what free radicals are produced and contribute in decontamination process is necessary. In this work, three scavenger agents including tert-butyl alcohol (TBA),

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methanol (MeOH) and sodium azide (NaN3) were applied in the concentration of 50 mM to determine the reactive species [55]. Note the TBA was mostly used as a specific scavenger of •

OH, while MeOH known as a quenching agent of both •OH (9.7 ×108 M-1 s-1) and SO4•− (3.2

EP

×106 M-1 s-1) radicals. NaN3 can quench all the three free radicals, i.e. •OH, SO4•− and singlet oxygen (1O2), since has a high reactivity with •OH (1.2 ×1010 M-1 s-1) and SO4•− (2.5 ×109 M-1 s-1)

AC C

and dioxygen (2 ×109 M-1 s-1) species [56, 57]. For all studied quenched agents, the inhibiting effect on performance of γ-Fe2O3@AC/UV/PMS system was observed, as illustrated in Fig. 6b. The degradation efficiency of cyfluthrin was decreased to 82, 68.2 and 50.5 % when TBA, MeOH and NaN3 were added into system, respectively, whereas it was 88.6 % in the absence of any scavengers. These results depicted that •OH, SO4•− and 1O2 species have been existed and contributed during γ-Fe2O3@AC/UV/PMS system. The considerable hampering effect of MeOH indicates that it can significantly suppress PMS activation and the efficiency of system was 19

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influenced by SO4•− radicals. Reducing the degradation rate of cyfluthrin in γFe2O3@AC/UV/PMS system in the presence of NaN3 was higher than the other quenchers, confirming that 1O2 species also participated in the degradation process. Herein, 1O2 species can

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be generated via either recombination of formed superoxide (O2•–) anions (Eq. (28)) or reaction between •OH and O2•– (Eq. (29))

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O2•– + O2•– + 2H → H2O2 + 1O2 O2•– + HO• + 2H → OH- + 1O2

(28) (29)

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Scheme 1 shows tentative mechanism of cyfluthrin degradation in the γ-Fe2O3@AC/UV/PMS system based on findings of scavenging tests. Regarding to this mechanism, the reactions related to PMS decompositions and generation of free radicals were taken place in both the catalyst surface and the solution phase. Herein, reactive oxidizing species that produced on the catalyst

•

(ads),

while the ones are produced in solution phase signed

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surface marked •OH(ads) and SO4•−

OH(free) and SO4•−(free). In solid phase, firstly, some interactions were taken place on the catalyst

surface to form reactive species (i.e., SO5•−

(ads)

and SO4•−

(ads))

via reaction between adsorbed

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PMS molecules and Fe2+/Fe3+ ions assigned to γ-Fe2O3 NPs, according to Eqs. (30-31). Thereafter, generated free radical’s attacks adsorbed cyfluthrin on the catalyst surface for

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degradation. In this phase, PMS decomposition using AC thereby transfer of electrons from surface was taken place to produce active radicals (•OH(ads)), as illustrated in Eqs. (4) and (5) [56, 58]. In γ-Fe2O3@AC, therefore, both γ-Fe2O3 NPs and AC contribute in activation of PMS and the generation of free radicals effectively in solid phase. Thus, γ-Fe2O3@AC can have a significant catalytic activity in degradation of organic matters, owing to the efficient synergistic effect between adsorption and oxidation processes.

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In solution phase, similar to solid phase, PMS molecules were catalyzed by leached iron ions from the catalyst surface, leading to form •OH(free) and SO4•−

species (Eqs. 30 and 31). In

(free)

both solid and solution phases, meanwhile, PMS decomposition rate could be promoted

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remarkably under UV light to generate extra reactive species (Eq. (1)). In another rout, furthermore, SO5•- species, with a lower reactivity potential, could be both formed in aqueous media and on the surfaces of catalyst based on reactions (32) and (33) and can further self-react

≡Fe2+ + HSO5−→≡Fe3+ + SO4•− + OH− ≡Fe3+ + HSO5− →≡Fe2+ + SO5•− + H+

HSO5− + SO•4− → HSO4− + SO•5−

2SO•5− → S2O82− + O 2

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HSO 5− + • OH → H 2 O + SO •5−

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to generate PS (Eq. 34).

(30) (31) (32) (33) (34)

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In the following, oxidation of cyfluthrin molecules by SO4•− (free/ads) was occurred via the electron

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transfer mechanism to form cyfluthrin radical cation (cyfluthrin•+) (Eq. (35)) and then reaction between cyfluthrin•+ and H2O to generate (OH)cyfluthrin radicals (i.e., (OH)cyfluthrin•) (Eq. (36)). (OH)cyfluthrin• can also be produced through reaction between •OH and cyfluthrin (Eq. (37)). Finally, (OH)cyfluthrin• is degraded to intermediates, H2O and CO2 within further oxidation reaction, as explained in Eq. (38). During γ-Fe2O3@AC/UV/PMS system, as conclusion, three activators including γ-Fe2O3, AC and UV light participate in decomposition of PMS molecules, subsequently degradation and mineralization of organic compounds. Thus, a 21

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high degradation rate can have achieved from γ-Fe2O3@AC/UV/PMS hybrid system, because of the remarkable generation of •OH and SO4•− radicals simultaneously as well as multi PMS

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activator excitation.

Cyfluthrin + SO4•−→ Cyfluthrin•+ + SO42–

(35)

Cyfluthrin•+ + H2O → (OH)Cyfluthrin• + H+

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(36)

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Cyfluthrin + •OH →(OH)Cyfluthrin• (OH)Cyfluthrin• → By-products → CO2 + H2O + Cl–

3.7. Degradation kinetic study

(37) (38)

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In this work, kinetic modelling of cyfluthrin degradation in γ-Fe2O3@AC/UV/PMS system was performed using pseudo first-order model under optimal conditions. Based on this model,

Ct = −kt C0

(39)

AC C

ln

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reaction rate constant (kobs) was determined using the following Eq.

where, Ct and C0 are the final and initial cyfluthrin concentrations (mg/L), kobs is the rate constant (1/min) and t is the contact time (min). The values of kobs can be determined from the linear relationship between ln (Ct/C0) and time. A good correlation coefficient (R2 > 0.92) was obtained between the experimental data using the pseudo first-order model (see Fig. S-1), suggesting that cyfluthrin degradation using γ-Fe2O3@AC/UV/PMS process was well explained by the pseudo first-order kinetic model. The reaction rate constant (kobs) was found to be 0.027 min-1 for the 22

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degradation of cyfluthrin over γ-Fe2O3@AC/UV/PMS system, which was much higher than those of reported in the literature for pollutants degradation by another sulfate radical-based

3.8. Recycling potential and mineralization studies

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AOPs [44, 59, 60].

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From economic aspects, the reusability and stability of the catalyst are the critical parameters in practical applications. In this work, the recycling potential of γ-Fe2O3@AC in activation of PMS

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and the degradation rate of cyfluthrin during γ-Fe2O3@AC/UV/PMS system was assessed continuously for 5 cycles with lack of chemical/physical modification. After finishing each step, the catalyst was separated, dried at 70 ºC for 1 h, and then applied for the next run. The durability of catalyst was also evaluated for each cycles via measurement of leached iron amount. The results of reusability/durability and mineralization studies are shown in Figs. 7a and

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b. Accordingly, the γ-Fe2O3@AC/UV/PMS process efficiency in both degradation and mineralization was decreased slightly with reused times. In optimum experimental factors, the

EP

removal efficiency and mineralization rates in the 1st cycle were 88.5 and 52.4 %, respectively, while they reduced to 79 and 38.4 %, respectively for fifth cycles. Several reasons can be

AC C

represented for reduction in the degradation/mineralization rate by increasing application runs: i) blocking pores of catalyst by pollutant molecules and its by-products after each use, which caused a gradual decline in both adsorption capacity and catalytic surface activity of catalyst, ii) losing mass of iron species on the catalyst surface during use cycles, iii) strong competition between produced by-products and pollutant molecules for reacting with reactive species, and iv) inactivation of the active catalytic sites on the surface of catalyst because of the consecutive washing and drying frequents. For all studied cycles, as shown in Fig. 7b, leaching amount of 23

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iron was < 0.25 mg/L, which is lower than the maximum acceptable Fe quantity in drinking water (i.e., 0.3 mg/L). These results elucidate a high physicochemical stability for γ-Fe2O3@AC

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as well as strong incorporation of γ-Fe2O3 NPs into the mesoporous texture of the AC. 3.9. Synergistic effect

Herein, some control experiments were performed in optimum conditions for determination of

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the synergistic effect of applied agents in γ-Fe2O3@AC/UV/PMS system using an enhancement factor (R), according to Eq. (40) [19]. More details for these tests and the values of R are

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expressed in Supporting information. Under same operating conditions, the decontamination efficiencies of 89, 45.6 and 27.4% was obtained for γ-Fe2O3@AC/UV/PMS, γ-Fe2O3@AC/PMS and UV/PMS processes. A higher degradation efficiency for γ-Fe2O3@AC/UV/PMS in comparison with other processes confirms a significant synergistic effect between UV light and catalyst in the efficient PMS activation and consequently degradation of cyfluthrin. Considering

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these results, the value of R was 1.22, indicating a synergistic effect between applied agents in γFe2O3@AC/UV/PMS system. This synergistic effect might be associated with the PMS

EP

decomposition by several activators simultaneously, which caused additional production of reactive species. These findings implied a high catalytic activity for as-prepared catalyst in

R=

AC C

coupling with UV light for enhanced activate PMS.

Removal efficiency of γ - Fe 2 O 3@AC/UV/PMS Removal efficiency of UV/PMS + Removal efficiency of γ - Fe 2 O 3 @AC/PMS (40)

3.10. Performance of γ-Fe2O3@AC/UV/PMS system in the real applications

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Herein, the performance of γ-Fe2O3@AC/UV/PMS process in cyfluthrin removal from real samples was evaluated for three samples including tap water, raw and treated wastewater samples from municipal wastewater treatment plant. The characteristics of these samples are

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illustrated in Table S-4. All the samples were simulated with a certain concentration of cyfluthrin (40 mg/L) and the tests were performed in optimum experimental factors. From Fig. 8 it is clear in all samples, the performance of γ-Fe2O3@AC/UV/PMS process showed lower performance

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than of DI-water. For raw and treated wastewater samples, a wide variety of ions and organic substances may be existed which could compete with cyfluthrin molecules for reaction with free

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radicals, leading to a decrease in process efficiency. The presence of high concentrations of TDS in tap water sample would intervene with reactive species and quenched them can be a rational reason for dropping in system. From these results, it can be concluded that γFe2O3@AC/UV/PMS system possess a high performance in treatment of actual contaminated

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waters and so would be applied as a promising and effective method for the

4. Conclusion

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degradation/mineralization of organic matters.

AC C

Catalytic activation of PMS molecules by γ-Fe2O3@AC heterojunction catalyst coupled with UV light, as a first report, was performed into cyfluthrin degradation. As-prepared catalyst showed an excellent ability in the PMS molecules decomposition and the generation of sulfate radicals. Over 88% cyfluthrin were degraded during 80 min of photocatalytic reaction by γFe2O3@AC/UV/PMS system at optimum conditions. According to scavenging tests, SO4•–, •OH and 1O2 species contributed in catalytic oxidation reactions of pollutant. Coupling of catalyst with UV irradiation elucidated a significant synergistic effect during degradation process of 25

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cyfluthrin. The process indicated a tremendous efficiency in the treatment of simulated real waters and wastewaters, demonstrating γ-Fe2O3@AC/UV/PMS hybrid system has a high

Acknowledgment

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potential for using in actual applications.

Authors are sincerely appreciated Aja University of Medical Sciences, Tehran, Iran to support

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this research financially with 91000191 project number. References

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Tables

Table 1 Details of experimental equipment used to characterization of γ-Fe2O3@AC properties Application To X-ray powder of γ-Fe2O3, AC and γ-Fe2O3@AC diffraction pattern. FESEMb FESEM, Mira 3-XMU. To morphological features assessment of γ-Fe2O3, AC and γFe2O3@AC. EDSc Mira 3-XMU. For elemental analysis of γ-Fe2O3@AC. BETd Quantachrome, NOVA 2000, USA. To measure the specific surface area of γ-Fe2O3, AC and γFe2O3@AC. TEMe PHILIPS, EM, Netherlands To determine the size and shape of γ-Fe2O3. VSMf 7400, Lakeshare, USA. To analyze the magnetic properties of γ-Fe2O3 and γFe2O3@AC. a: X-ray diffraction; b: Field emission-scanning electron microscope; c: Energy Dispersive X-ray Spectrometer; d: Brunaeur, Emmett and Teller; e: Transmission electron microscope; f: Vibrating Sample Magnetometer.

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Equipment type D8-Advance, Bruker.

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Technique XRDa

Table 2. Independent parameters and their levels in the experimental design. Independent factors

Unit

Symbols

-α

X1 X2 X3 X4 X5

2.0 0.1 20 1.0 10

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g/L mg/L mM min

4.0 0.2 40 2.0 30

6.0 0.3 60 3.0 50

8.0 0.4 80 4.0 70

+α 10.0 0.5 100 5.0 90

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Soliton pH Catalyst dosage Initial contaminant concentration PMS loading Reaction time

Ranges and levels - 1 Level 0 +1 Level

AC C

Table 3. Physico-chemical features of γ-Fe2O3, AC and γ-Fe2O3@AC. Sample

SBET(m2/g)

Vta (cm3/g)

Vmb (cm3/g)

Dpc (nm)

Pore structure

Color

γ-Fe2O3 AC γ-Fe2O3@AC

56.8 745.2 584.6

0.005 0.52 0.32

42.5 160.8 122.7

2.36 3.85 3.7

Mesopore Mesopore Mesopore

Black Black Black

a

Vt denotes the total pore volume. Vm denotes the monolayer volume. c Dp denotes the average pore diameter. b

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Figures Figure 1. (a) The XRD patterns of AC, γ-Fe2O3 and γ-Fe2O3@AC.

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Figure 2. FESEM images of AC (a) and γ-Fe2O3@AC (b), EDS analysis for γ-Fe2O3@AC (c) and TEM image of the γ-Fe2O3 loaded on AC (d). Figure 3. (a) Adsorption/desorption isotherm of N2 on γ-Fe2O3@AC (insert: BJH pore size distribution) and (b) M-H hysteresis loops of γ-Fe2O3 and γ-Fe2O3@AC (insert: magnetic properties of γ-Fe2O3@AC in the presence an external magnetic field).

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Figure 4. The decontamination efficiency of cyfluthrin by the different processes (Conditions: pH 5.5 ± 0.5, 4.0 mM PMS, 20 mg/L cyfluthrin, 0.3 g/L catalyst (AC, γ-Fe2O3 and γ-Fe2O3@AC), and 60 min treatment time).

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Figure 5. Influence of operational variables on the performance of MPAC/US/UV/H2O2 system into cyfluthrin degradation: The combined effect of solution pH and PMS dosage (a), catalyst loading and reaction time (b), initial contaminant concentration and reaction time (c) and PMS dosage and catalyst loading (d) (Conditions: T:20 ±1oC; (a) 0.3 g/L catalyst, time 70 min, C0= 60 mg/L; (b) pH 6.0, PMS 3.0 mM, C0= 60 mg/L; (c) pH 6.0, PMS 3.0 mM, 0.3 g/L catalyst; (d) pH 6.0, time 70 min, C0= 60 mg/L). Figure 6. The effect of co-existing anions (a) and scavengers (b) on the degradation rate of cyfluthrin over γ-Fe2O3@AC/UV/PMS system at optimal conditions (pH 4.0, PMS 4.0 mM, 0.4 g/L catalyst, C0= 60 mg/L and time 80 min).

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Scheme 1. Proposed schemes for formation of reactive oxidizing species as well as cyfluthrin degradation during γ-Fe2O3@AC/UV/PMS system. Figure 7. (a) The recyclability (a) and the mineralization degree and Fe leaching (b) profiles of γFe2O3@AC in UV/PMS system within 5 consecutive cycles at optimal conditions (pH 4.0, PMS 4.0 mM, 0.4 g/L catalyst, C0= 60 mg/L and time 80 min).

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Figure 8. The performance of γ-Fe2O3@AC/UV/PMS system into cyfluthrin degradation from different samples under optimum conditions (pH 4.0, PMS 4.0 mM, 0.4 g/L catalyst, C0= 60 mg/L and time 80 min).

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2100

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1200

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γ-Fe2O3

900

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600

0 10

20

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40

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300

50

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Fig. 1

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(d)

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BJH-Plot

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Magnetic saturation (emu/g)

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60

dVp/drp

Quantity adsorbed (cm3/g STP)

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γ-Fe2O3

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γ-Fe2O3@AC

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-20 -40 -60

100

-80 -11 -9

1

-7

-5

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P/P0 Fig. 3

7

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11

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100 98.4

A B C D E F G H I K M

50.2

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42.9 38.6 32.7

30.5

10.6

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24.8

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H

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Fig. 4

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γ-Fe2O3 AC γ-Fe2O3@AC UV PMS PMS/UV γ-Fe2O3/UV γ-Fe2O3/PMS AC/PMS γ-Fe2O3@AC/PMS γ-Fe2O3@AC/PMS/UV

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Decontamination (%)

80

M

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(c)

Fig. 5

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82.4

58.7

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TE D

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Nitrate

Bicarbonate

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NaN3

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Scheme 1

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(a) 90 80

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Decontamination (%)

70 60 50 1st run

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Fe Con. (mg/L)

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0 2 3 Adsorbent dose (g/L)

Fig. 7

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5

Fe Con. (mg/L)

60

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88.4 82.3

79.6

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Cyfluthrin removal (%)

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Raw wastewater

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Tested sample

Treated wastewater

AC C

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Fig. 8

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Highlights 1. Photo-oxidative cyfluthrin degradation, as first study, was performed using PMS decomposition by γ-Fe2O3@AC.

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2. Coupling γ-Fe2O3@AC with UV indicates a significant synergistic effect in activate PMS. 3. The inhibitory effect followed the decreasing order: HCO3– > NO3– > Cl– > SO42–. 4. The process represents a good performance in treatment of simulated real water and wastewater samples.