Ni nanoparticles

Chemosphere 103 (2014) 80–85

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Enhancement of catalytic degradation of amoxicillin in aqueous solution using clay supported bimetallic Fe/Ni nanoparticles Xiulan Weng a, Qian Sun b, Shen Lin c, Zuliang Chen a,d,⇑, Mallavarapu Megharaj d, Ravendra Naidu d a

School of Environmental Science and Engineering, Fujian Normal University, Fuzhou 350007, Fujian Province, China Key Laboratory of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, Fujian Province, China c School of Chemistry and Chemical Engineering, Fujian Normal University, Fuzhou 350007, Fujian Province, China d Centre for Environmental Risk Assessment and Remediation, University of South Australia, Mawson Lakes, SA 5095, Australia b

h i g h l i g h t s  Amoxicillin in aqueous solution was degraded using B–Fe/Ni.  More than 93.67% of AMX was removed only 60 min.  B–Fe/Ni were used for characterization.  The degradation mechanism of amoxicillin was proposed.

a r t i c l e

i n f o

Article history: Received 15 July 2013 Received in revised form 5 November 2013 Accepted 9 November 2013 Available online 17 December 2013 Keywords: Bimetallic Fe/Ni Nanoparticles Bentonite Amoxicillin Degradation

a b s t r a c t Despite bimetallic Fe/Ni nanoparticles have been extensively used to remediate groundwater, they have not been used for the catalytic degradation of amoxicillin (AMX). In this study, bentonite-supported bimetallic Fe/Ni (B–Fe/Ni) nanoparticles were used to degrade AMX in aqueous solution. More than 94% of AMX was removed using B–Fe/Ni, while only 84% was removed by Fe/Ni at an initial concentration of 60 mg L1 within 60 min due to bentonite serving as the support mechanism, leading to a decrease in aggregation of Fe/Ni nanoparticles, which was confirmed by scanning electron microscopy (SEM). The formation of iron oxides in the B–Fe/Ni after reaction with AMX was confirmed by X-ray diffraction (XRD). The main factors controlling the degradation of AMX such as the initial pH of the solution, dosage of B–Fe/Ni, initial AMX concentration, and the reaction temperature were discussed. The possible degradation mechanism was proposed, which was based on the analysis of degraded products by liquid chromatography-mass spectrometry (LC–MS). Ó 2013 Elsevier Ltd. All rights reserved.

1. Introduction Amoxicillin is one of the world’s most important commercial antibiotics due to its high bacterial resistance and large spectrum against a wide variety of microorganisms (Elmoll and Chaudhuri, 2009). The presence of antibiotics in wastewater has increased in recent years (Watkinson et al., 2007) and it is a challenge to remove antibiotics residue from the wastewaters (Homem et al., 2010). Several methods are currently employed for this purpose such as adsorption (Putra et al., 2009), membrane filtration (Li et al., 2004), Fenton oxidation (Homem et al., 2010) and photocatalytic degradation (Dimitrakopoulou et al., 2012). Advanced oxidation technologies such as Fenton oxidation and photocatalytic ⇑ Corresponding author at: Centre for Environmental Risk Assessment and Remediation, University of South Australia, Mawson Lakes, SA 5095, Australia. Fax: +61 08 83025057. E-mail address: [email protected] (Z. Chen). 0045-6535/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.chemosphere.2013.11.033

degradation are often used for amoxicillin degradation. However, emerging large volumes of iron sludge is a major problem of the process of the Fenton oxidation and photocatalytic degradation likes low quantum yields which restrict its widespread acceptance as a practical remediation technology (Bokare et al., 2008). Hence, it is necessary to explore new technologies that remove AMX effectively from water. Iron-based bimetallic nanoparticles has received attention for remediating groundwater contaminants (Schrick et al., 2002) because of its small particle size, large specific surface area, high density and great intrinsic reactivity regarding reactive surface sites (Zhang et al., 2011). However, the aggregation of these nanoparticles into chain-like structures is one of their well-known characteristics, which is responsible for reducing the reactivity. The stability of iron nanoparticles against aggregation can be improved by the use of organic surfactants, or by utilizing capping agents (Sun et al., 2007). Another approach is to synthesize iron

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nanoparticles in the presence of supporting inorganic materials (Chen et al., 2011; Shi et al., 2011). Recently, our studies on synthesis of stable and dispersible ironbased nanoparticles using clays as a supporting inorganic material have been reported (Chen et al., 2011; Shi et al., 2011), where the reactivity and efficiency of clay-supported iron-based nanoparticles significantly proved superior to iron-based nanoparticles without support in the form of clay. Nowadays, nanoscale zero-valent iron (nZVI) used for AMX and ampicillin has been reported (Ghauch et al., 2009), where degradation of the antibiotics required 3 h due to nZVI having an intrinsic aggregation and oxidation that may limit its reaction rate. The decrease in iron reactivity over time is probably due to: firstly, the formation of oxide layers on the particle surface during the reaction; or secondly, the nZVI particles making contact with air (Schrick et al., 2002). To enhance the reactivity of nZVI particles in degrading b-lactam antibiotics, the advantages of bimetallic Fe/Ni nanoparticles are considered here since Fe acts as a reducing agent, whilst Ni acts as a catalyst with hydrogen generated from the reduction of water (Schrick et al., 2002). Additionally, the introduction of the metal Ni not only enhances the nanoparticles’ stability in air by inhibiting the oxidation, but also increases reactivity (Su et al., 2011). To date, Fe-based bimetallic nanoparticles have been widely used to remediate different organic compounds (Bokare et al., 2008; Fang et al., 2011; Su et al., 2011), while bimetallic Fe/Ni nanoparticles and bentonite supported Fe/Ni have not been reported for the catalytic degradation of amoxicillin. In this study, a new highly reactive bentonite-supported Fe/Ni nanoparticles (B–Fe/Ni) was used for the degradation of AMX to determine whether AMX was degraded by B–Fe/Ni. Hence, the following investigations included (1) comparing the removal of AMX using bentonite, Fe/Ni and B–Fe/Ni to understand their roles; (2) characterization of before and after B–Fe/Ni reacting with AMX to understand the change in surface and chemical species; (3) batch degradation experiments in various conditions; and (4) the analysis of degraded products by HPLC–MS to propose the degradation mechanism. 2. Experimental 2.1. Materials and chemicals Bentonite used in this experiment was supplied by Longyan Kaolin Co., Ltd., Fujian, China. After drying at 353 K overnight, raw bentonite was ground and sieved with a 200 mesh screen prior to use. All the chemicals used in this study were analytical reagent grade and did not undergo any further purification. A solution containing AMX was prepared by dissolving various amounts of AMX with distilled water to the desired initial concentrations. 2.2. Synthesis of bentonite-supported Fe/Ni particles Fe/Ni particles and B–Fe/Ni particles were synthesized describe elsewhere (Chen et al., 2011; Shi et al., 2011). A preparation of B–Fe/Ni contained bentonite and Fe/Ni mass ratio of 1:1; FeCl36H2O (9.65 g) and NiSO46H2O (0.90 g) was dissolved in 50 mL of miscible liquids (distilled water and absolute ethanol at a volume ratio of 1:4), and then the mixed solution added to three-necked flask, where contained 2.00 g benonite. This mixture was stirred with an electric rod for 15 min in a nitrogen atmosphere, and then an aqueous solution of NaBH4 (1.1 M, 100 mL) was added at the speed of 1– 2 drops per second and stirred vigorously and continuously under this nitrogen atmosphere. After adding all of the NaBH4 solution, the mixture was stirred under the nitrogen atmosphere continuously for another 20 min.

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Vacuum filtration was employed to collect the B–Fe/Ni particles and these were quickly rinsed three times with absolute ethanol. Doing so prevented the B–Fe/Ni from oxidizing and it was then dried at 333 K under vacuum overnight. The theoretical mass of B–Fe/Ni was 4.00 g, bentonite was 2.00 g, and Ni was 0.200 g, the theoretical mass fraction of bentonite in synthesized B–Fe/Ni was 50%, and Ni in synthesized B–Fe/Ni was 5%, and Fe/Ni was prepared under identical conditions but without bentonite. 2.3. Characterizations and methods Scanning electron microscopy (SEM) images of bentonite, Fe/Ni, fresh and used B–Fe/Ni were acquired using a JSM-7500F (JEOL Ltd. Co., Tokyo, Japan). Images of samples were recorded at different magnifications at an operating voltage of 5 kV. X-ray diffraction (XRD) patterns of fresh and used B–Fe/Ni were performed using a Philips-X’Pert Pro MPD (Netherlands) with a high-power Cu Ka X-xay source (k = 0.154 nm) at 40 kV/40 mA. 2.4. Batch experiments To compare degradation efficiency of AMX in aqueous solution, an experiment was carried out using Fe/Ni (0.05 g), B–Fe/Ni (0.10 g) and bentonite (0.05 g) added to 25 mL solution of an initial AMX concentration of 60 mg L1 under anoxic conditions for the reaction system by pass nitrogen. The former two had the same mass as Fe/Ni, while the latter two had the same mass of bentonite. Mixed solutions were left at their initial pH level stirred at 250 r min1 at 298 K to the desired time intervals. Following this they were all filtered through 0.45 lm membranes to measure the residual concentration of AMX. The effect of various parameters affecting the degradation of AMX in aqueous solution by B–Fe/Ni particles was investigated. The initial pH values used in this study was 4–11 which was adjusted with concentrated hydrochloric acid/sodium hydroxide (1 mol L1), the dosage of B–Fe/Ni nanoparticles was 2–8 g L1, the initial concentration of AMX was 40–100 mg L1, and the reaction temperature was 290–308 K. The reuse of B–Fe/Ni for degradation of AMX was evaluated, where 0.1 g B–Fe/Ni was added to 60 mg L1 of AMX solution (25 mL). After 1 h, the solution was centrifuged with 3000 r min1 for 10 min to obtain solid–liquid separation. The used B–Fe/Ni was re-used to remove new mixed antibiotics solution for 3 times in succession. All these experiments were carried out in triplicate. The concentration of AMX solution was measured using a UVSpectrophotometer (722N, Shanghai, China) at k = 228.3 nm. Degradation efficiency of AMX by B–Fe/Ni particles was calculated using the following equation (Chen et al., 2011):

Rð%Þ ¼

C0  Ct  100% C0

ð1Þ

where R (%) represented the AMX removal efficiency, C0 (mg L1) was the initial concentration of AMX in the solution and Ct (mg L1) stood for the concentration of AMX at t min. Sample analysis was performed with liquid chromatography– mass spectrometry (HPLC/Q-TOF-MS, Bruker, Germany) using ESI interface in positive mode. A C18 analytical column (2.1  100 mm, 1.7 lm particle size) was used to determine AMX and AMX products. A gradient elution was performed with a mobile phase of methanol (A) and distilled water (B) at a flow rate 0.3 mL min1, i.e.: 0–1 min 10% A; 1–11 min 75% A; 11–14 min 10% A. The sample was used to perform 20 lL injections with the samples maintained at 303 K. The source conditions of MS were as follows: End Plate Offset: 500 V, 91 nA; Capillary: 4500 V, 4 nA; Nebulizer: 0.6B bar; mass range: 70–500 m/z; quadupole ion energy: 5.0 eV; drying gas: 6.0 L min1; dry temperature: 180 °C.

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3. Results and discussion 3.1. Degradation of AMX using various materials The removal of AMX in aqueous solution using various materials was investigated as shown in Fig. 1. It can be seen that 94% of AMX was removed from the solution within 60 min using B–Fe/Ni, while only 84% was degraded using Fe/Ni nanoparticles, and the degradation rate of AMX by B–Fe/Ni (kobs = 0.077) was higher than that of Fe/Ni (kobs = 0.050). It was due to the fact that the aggregation of Fe/Ni nanoparticles was reduced and hence the reactivity of Fe/Ni nanoparticles was enhanced when bentonite was employed as support. In addition, sorption of AMX onto the bentonite from the aqueous solution was insignificant (<1%). Consequently, it is indicated that bentonite had good dispersant and stabilizer for the supporting Fe/Ni nanoparticles as reported in our previous studies (Chen et al., 2011; Shi et al., 2011).

Removal efficiency / %

100 80 60 bentonite Fe/Ni(0.9:0.1) B-Fe/Ni(1:0.9:0.1)

40 20 0 0

10

20

30

40

50

60

Time / min Fig. 1. The degradation of AMX using various materials. Conditions: 25 mL; C0 = 60 mg L1; 298 K; dosage of B–Fe/Ni: 4.0 g L1; dosage of Fe/Ni: 2.0 g L1; dosage of bentonite: 2.0 g L1; pH = 6; under anoxic conditions.

In addition, bentonite as a support material stabilizing and dispersing Fe/Ni nanoparticles was also supported by measuring their specific surface area. The porosity of B–Fe/Ni as determined by nitrogen adsorption/desorption was 0.301 cm3 g1 and the mean specific surface area (SSA) of 41.4 m2 g1 for B–Fe/Ni was obtained, which was 6.9 times larger than bentonite alone (6.0 m2 g1). Fe/Ni nanoparticles were dispersed onto the surface of bentonite and consequently this enhanced the level of reactivity. Despite the Fe/Ni SSA (53.9 m2 g1) being larger than that of B–Fe/Ni (41.4 m2 g1), its reaction activity was lower than that of B–Fe/Ni due to aggregation. Similar results were observed in our previous study on the clay supported nZVI for the removal of Pb2+ (Zhang et al., 2011) and Cr (VI) (Shi et al., 2011) from wastewater.

3.2. Characterization Fig. 2 shows the SEM images of bentonite, Fe/Ni, and fresh and used B–Fe/Ni. Fig. 2(a) shows that the surface of the raw bentonite was smooth and small ravines among different interlaminations were observed, where bentonite provided a highly specific surface area (6.0 m2 g1) and enabled the Fe/Ni nanoparticles to be well dispersed as a support material (Chen et al., 2011; Shi et al., 2011). Fig. 2(b) indicates that the synthesized Fe/Ni nanoparticles were roughly globular and had a chain-like aggregation with a diameter in the range of 40–90 nm, which explains why the chain-like aggregation reduced the reactivity of Fe/Ni nanoparticles (see Fig. 1). Fig. 2(c) shows that the Fe/Ni nanoparticles were well distributed on the bentonite with a low agglomeration and a high dispersibility where the mass fraction of bentonite was 50% as previously documented (Chen et al., 2011; Shi et al., 2011). However, Fig. 2(d) shows the sizes of used B–Fe/Ni increased significantly and the surface became scabrous after reacting with AMX in aqueous solution, which gradually became covered with B–Fe/Ni on the surface. This is attributed to the formation of iron oxide layers such as Fe3O4 and Fe2O3 (Chen et al., 2011) on the surface of the used B–Fe/Ni and confirmed by the following section of XRD.

Fig. 2. SEM images of laboratory synthesized Fe/Ni particles with and without a support material. (a) Bentonite; (b) Fe/Ni; (c) fresh B–Fe/Ni; and (d) used B–Fe/Ni.

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apparent peak of Fe0 compared to the XRD patterns of fresh B–Fe/Ni. It could be concluded that the iron oxides formed and Fe0 of B–Fe/Ni decreased when B–Fe/Ni came into contact with AMX in aqueous solution (Cheng et al., 2010).

Intensity (counts)

Fe3O4 Fe2O3

c

Fe O Fe2O3 2 3

0

Fe

0

Ni

0

Fe

3.3. Parameters affecting the degradation of AMX

0

Ni

b

0

Ni

0

Ni

a 20

40

60

80

2 theta (degrees) Fig. 3. XRD pattern. (a) Bentonite; (b) fresh B–Fe/Ni; and (c) used B–Fe/Ni.

100

100

a

Removal efficiency / %

Removal efficiency / %

To further understand the formation of iron oxides and their distribution patterns on the B–Fe/Ni, the XRD patterns of bentonite, fresh B–Fe/Ni and used B–Fe/Ni are revealed in Fig. 3. Comparing Fig. 3(a) and (b), the apparent diffraction peaks appeared at 2h = 26.6° and 19.8°, which were the characteristic peak of bentonite (Yuan et al., 2008) as well as some small peaks representing the intrinsic structure of bentonite. However, the XRD patterns of fresh B–Fe/Ni (Fig. 3(b)) show that an apparent peak of Fe0 (2h = 44.9°) was reached, indicating that Fe0 and Ni0 were present in B–Fe/Ni (Schrick et al., 2002; Zhang et al., 2011). The XRD patterns for used B–Fe/Ni are shown in Fig. 3(c), where the peaks relative to the presence of Fe3O4 (2h = 35.5°) and Fe2O3 (2h = 30.3°, 57.8°, 62.8°) appears in the used B–Fe/Ni (Chen et al., 2011). A similar result was reported in corrosion products resulting from dechlorination of pentachlorophenol using nanoscale Fe/Ni particles (Cheng et al., 2010). These Fe (II) and Fe (III) corrosion products indicated that the formation of Fe (II) constituted an intermediate step in the transformation process. Furthermore, a decrease was noted in the

80 60 pH= 4 pH= 6 PH= 7 pH= 9 PH= 11

40 20 0 0

The degradation of AMX by B–Fe/Ni was conducted at initial pH values of 4, 6, 7, 9 and 11 as presented in Fig. 4(a). The degradation efficiency was 96%, 94%, 91%, 88% and 60% after 60 min when the initial pH value rose from 4 to 11, respectively. It can be seen that degradation efficiency increased as the pH value decreased, and a maximum level of degradation efficiency was observed at pH value of 4. This is explained by the low solution pH value favouring the corrosion of iron in aqueous solution, including the formation of atomic hydrogen and subsequently molecular hydrogen at the Ni surface (Bokare et al., 2008). It is important for the degradation of AMX through its hydride because it reductively degrades so that the b-lactam bond of AMX can be cleaved. In the alkaline solution, in contrast, slow production of H2 limited the degradation of AMX, and precipitation of metal hydroxides also formed the passivating layers on the catalyst surface and deactivated the B–Fe/Ni bimetallic nanoparticles (Zhou et al., 2010). Hence, the degradation of AMX decreased significantly when pH increased, suggesting that optimal AMX reduction occurs under acidic conditions. Dosage of B–Fe/Ni nanoparticles affecting the degradation efficiency of AMX is presented in Fig. 4(b). The degradation efficiency of AMX was 87% using B–Fe/Ni at 2.0 g L1 for 60 min, but was nearly 94%, 96% when the dosage of B–Fe/Ni was 4.0 g L1, 8.0 g L1, respectively. The degradation efficiency of AMX was improved with increasing of the dosage of B–Fe/Ni. This is mainly due to that an increase in the amount of B–Fe/Ni can lead to an increase in total surface area and available active sites for AMX (Bokare

10

20

30

40

50

b

80 60 -1

40

2.0 g L -1 4.0 g L -1 8.0 g L

20 0 0

60

10

20

100

c

80 60

-1

40 mg L -1 60 mg L -1 100 mg L

40

30

40

50

60

Time / min

Removal efficiency / %

Removal efficiency / %

Time / min

20 0

100

d

80 60 290 K 298 K 308 K

40 20 0

0

10

20

30

40

Time / min

50

60

0

10

20

30

40

50

60

Time / min

Fig. 4. Parameters affecting the degradation of AMX. (a) Different initial solution pH on the degradation, conditions: 25 mL; C0 = 60 mg L1; 298 K; dosage of B–Fe/Ni: 4.0 g L1; pH = 4, 6, 7, 9, 11; under anoxic conditions. (b) Different dosage of B–Fe/Ni on the degradation, conditions: 25 mL; C0 = 60 mg L1; 298 K; dosage of B–Fe/Ni: 2.0 g L1, 4.0 g L1, 8.0 g L1; pH = 6; under anoxic conditions. (c) Different initial AMX concentration on the degradation, conditions: 25 mL; C0 = 40 mg L1, 60 mg L1, 100 mg L1; 298 K; dosage of B–Fe/Ni: 4.0 g L1; pH = 6; under anoxic conditions. (d) Different temperature on the degradation. Conditions: 25 mL; C0 = 60 mg L1; 290 K, 298 K, 308 K; dosage of B–Fe/Ni: 4.0 g L1; pH = 6; under anoxic conditions.

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et al., 2008; Liu et al., 2013). This is in accordance with the results observed by the studies of iron-nickel bimetallic nanoparticles used to degrade azo dye Orange G (Bokare et al., 2008). The effect of initial AMX concentration on degradation efficiency was investigated in the range 40–100 mg L1. As shown in Fig. 4(c), the degradation efficiency increased significantly as the initial AMX concentration decreased. 94% of AMX was degraded with the concentration of 40 mg L1 within 20 min, while it was only 72% within 20 min at an AMX concentration of 100 mg L1. Generally, the degradation of AMX in the B–Fe/Ni nanoparticles is a heterogeneous reaction, which involves adsorption of the AMX on the Ni surface and the subsequent surface reaction (Bokare et al., 2008; Fang et al., 2011). Increasing the initial concentration of AMX led to competitive adsorption among the AMX molecules when the adsorption reaction area of B–Fe/Ni was fixed (Fang et al., 2011). To assess the effect of different temperatures, batch experiments were conducted at 290, 298 and 308 K. As shown in Fig. 4(d), the results revealed that 93% of AMX was removed at 308 K, while only 60% AMX was removed at 290 K in 15 min. However, the degradation efficiency of AMX increased when the temperature was increased, and then successively reached equilib-

rium, where more than 90% AMX was removed after 60 min. This suggests that temperature’s impact on the degradation of AMX resulted from the mobility of AMX molecules from liquid phase transfer to the surface of nanoparticles increased as the temperature increased (Liu et al., 2013). 3.4. Analysis of degraded products and the possible degradation mechanism LC–MS analysis was carried out on AMX before and after reaction within 60 min using MS to verify their structures as shown in Fig. 5 and a potential degradation pathway of AMX using B– Fe/Ni is described in Fig. 6. As shown in Fig. 6, the degradation pathway of amoxicillin by nZVI started with the opening of the b-lactam ring and yielded the product amoxicillin penicilloic acid (m/z 383 C16H21N3O6S, Fig. 6(a)) (Ghauch et al., 2009), where nZVI in B–Fe/Ni was oxidized and provided hydrogen radicals and hydroxyl radical, and AMX molecule accepted hydrogen radicals and hydroxyl radical, two electrons were produced when one zero-valent iron reacted to the H2O after a given mass of Fe/Ni nanoparticles has been added, hydrogen ion was transferred from liquid phase near the surface of Fe0 to the surface of catalytic

Fig. 5. Mass spectra of AMX. (a) AMX before reaction; and (b) AMX after reaction.

Fig. 6. Proposed mechanism p for the degradation of AMX by B–Fe/Ni nanoparticles.

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Ni0. In the meantime, the AMX molecules were adsorbed onto the surface of the B–Fe/Ni nanoparticles and these made contact with each other, which is represented by Eqs. (2)–(7) (Bokare et al., 2008; Cheng et al., 2010; Fang et al., 2011). AMX exhibited the product ion (m/z 339) of C15H21N3O4S (Fig. 6(b)), (m/z 324) of C15H20N2O4S (Fig. 6(c)) and (m/z 314) of C15H26N2O3S (Fig. 6(d)) (Li et al., 2012) due to the generated intermediates of AMX reducing further and leading to the loss of COOH, NH3, and the carboxylreducing reaction and then opening the five-membered thiazolidine ring. Moreover a very weak peak of m/z at 383, 339, 324 and 314 is presented in Fig. 6(b) where C16H21N3O6S (m/z 383), C15H21N3O4S (m/z 339), C15H20N2O4S (m/z 324) and C15H26N2O3S (m/z 314) are intermediate products being immediately reduced by B– Fe/Ni. The structure of this degradation product was confirmed by the appearance of the characteristic fragment at m/z 300 (C14H24N2O3S) which is the product of a demethyl reaction (Fig. 6(e)).

Fe0 ! Fe2þ þ 2e

ð2Þ

Ni

2H2 O þ 2e ! 2H þ 2OH

ð3Þ

Ni þ H ! Ni—H

ð4Þ

Fe2þ ! Fe3þ þ e

ð5Þ

Fe3þ þ H2 O ! Fe2þ þ OH þ Hþ

ð6Þ

Ni  H þ AMX ! Ni þ AMXreduced þ H2 O

ð7Þ

0

In the reaction system, Ni played the role of catalysis and medium of electronic conduction, and it also acted as a micro battery for bimetallic Fe–Ni nanoparticles. Hence, the generation of electrons due to the corrosion of nZVI within the B–Fe/Ni nanoparticles was the rate limited reaction under the present study’s experimental conditions. 3.5. Reuse in degradation of AMX by B–Fe/Ni Repeated use of B–Fe/Ni nanoparticles for degrading AMX was investigated, which indicates that reactivity of B–Fe/Ni decreased when reuse increased. In the first degradation cycle, more than 94% AMX was degraded at a concentration of 60 mg L1. When the experiment reached its second, third and fourth cycle, the degradation efficiency declined to 74%, 23% and 5%, respectively. Therefore, the effective reuse of B–Ni/Fe for the degradation of AMX was 2 times. However, further improvements are needed to recycle and reactivate the catalyst after reaction thus prolongs its service life. 4. Conclusion This study has shown that bentonite played the role of dispersant and stabilizer, leading to an enhancement in the reactivity of B–Fe/Ni nanoparticles. The results obtained from SEM indicate that Fe/Ni loaded onto bentonite was well dispersed and this enhanced to decrease the aggregation of Fe/Ni. SEM and XRD, analyses were all demonstrated that Fe/Ni loaded onto bentonite and Fe in the B–Fe/Ni was oxidized to form iron oxide layers after reaction with AMX. In addition, the pH of the solution, the dosage B–Fe/ Ni, the initial AMX concentration and the reaction temperature are

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the main factors that influence degradation efficiency, while the works concerning influences of various ions in wastewater will be discussed further. The LC–MS analysis of degraded products shows that the degradation of AMX through its hydride reductively degraded to a cleaving of the AMX’s b-lactam bond and then led to the degradation of AMX. Acknowledgement The financial support of the Fujian ‘‘Minjiang Fellowship’’ from Fujian Normal University is gratefully acknowledged. References Bokare, A.D., Chikate, R.C., Rode, C.V., Paknikar, K.M., 2008. Iron–nickel bimetallic nanoparticles for reductive degradation of azo dye Orange G in aqueous solution. Appl. Catal. B: Environ. 79, 270–278. Chen, Z.X., Jin, X.Y., Chen, Z.L., Megharaj, M., Naidu, R., 2011. Removal of methyl orange from aqueous solution using bentonite-supported nanoscale zero-valent iron. J. Colloid Interface Sci. 363, 601–607. Cheng, R., Zhou, W., Wang, J.L., Qi, D.D., Guo, L., Zhang, W.X., Qian, Y., 2010. Dechlorination of pentachlorophenol using nanoscale Fe/Ni particles: role of nano-Ni and its size effect. J. Hazard. Mater. 180, 79–85. Dimitrakopoulou, D., Rethemiotaki, I., Frontistis, Z., Xekoukoulotakis, N.P., Venieri, D., Mantzavinos, D., 2012. Degradation, mineralization and antibiotic inactivation of amoxicillin by UV-A/TiO2 photocatalysis. J. Environ. Manage. 98, 168–174. Elmoll, E.S., Chaudhuri, M., 2009. Degradation of the antibiotics amoxicillin, ampicillin and cloxacillin in aqueous solution by the photo-Fenton process. J. Hazard. Mater. 172, 1476–1481. Fang, Z.Q., Qiu, X.H., Chen, J.H., Qiu, X.Q., 2011. Debromination of polybrominated diphenyl ethers by Ni/Fe bimetallic nanoparticles:Influencing factors, kinetics, and mechanism. J. Hazard. Mater. 185, 958–969. Ghauch, A., Tuqan, A., Assi, H.A., 2009. Antibiotic removal from water: elimination of amoxicillin and ampicillin by microscale and nanoscale iron particles. Environ. Pollut. 157, 1626–1635. Homem, V., Alves, A., Santos, L., 2010. Amoxicillin degradation at ppb levels by Fenton’s oxidation using design of experiments. Sci. Total Environ. 408, 6272– 6280. Li, S., Li, X., Wang, D., 2004. Membrane (RO–UF) filtration for antibiotic wastewater treatment and recovery of antibiotics. Sep. Purif. Technol. 34, 109–114. Li, X.M., Shen, T.T., Wang, D.B., Yue, X., Liu, X., Yang, Q., Cao, J.B., Zheng, W., Zeng, G.M., 2012. Photodegradation of amoxicillin by catalyzed Fe3+/H2O2 process. J. Environ. Sci. 24, 269–275. Liu, X.W., Chen, Z.X., Chen, Z.L., Megharaj, M., Naidu, R., 2013. Remediation of Direct Black G in wastewater using kaolin-supported bimetallic Fe/Ni nanoparticles. Chem. Eng. J. 223, 764–771. Putra, E.K., Pranowo, R., Sunarso, J., Indraswati, N., Ismadji, S., 2009. Performance of activated carbon and bentonite for adsorption of amoxicillin from wastewater: mechanisms, isotherms and kinetics. Water Res. 43, 2419–2430. Schrick, B., Blough, J.L., Jones, A.D., Mallouk, T.E., 2002. Hydrodechlorination of trichloroethylene to hydrocarbons using bimetallic nickel–iron nanoparticles. Chem. Mater. 14, 5140–5147. Shi, L.N., Zhang, X., Chen, Z.L., 2011. Removal of Chromium (VI) from wastewater using bentonite-supported nanoscale zero-valent iron. Water Res. 45, 886–892. Su, J., Lin, S., Chen, Z.L., Megharaj, M., Naidu, R., 2011. Dechlorination of pchlorophenol from aqueous solution using bentonite supported Fe/Pd nanoparticles: synthesis, characterization and kinetics. Desalination 280, 167– 173. Sun, Y.P., Li, X.Q., Zhang, W.X., Wang, H.P., 2007. A method for the preparation of stable dispersion of zero-valent iron nanoparticles. Colloids Surf. A 308, 60–66. Watkinson, A.J., Murbyc, E.J., Costanzo, S.D., 2007. Removal of antibiotics in conventional and advanced wastewater treatment: implications for environmental discharge and wastewater recycling. Water Res. 41, 4164–4176. Yuan, P., Annabi-Bergaya, F., Tao, Q., Fan, M.D., Liu, Z.W., Zhu, J.X., He, H.P., Chen, T.H., 2008. A combined study by XRD, FTIR, TG and HRTEM on the structure of delaminated Fe-intercalated/pillared clay. J. Colloid Interface Sci. 324, 142–149. Zhang, X., Lin, S., Chen, Z.L., Megharaj, M., Naidu, R., 2011. Kaolinite-supported nanoscale zero-valent iron for removal of Pb2+ from aqueous solution: reactivity, characterization and mechanism. Water Res. 45, 3481–3488. Zhou, T., Li, Y.Z., Lim, T.T., 2010. Catalytic hydrodechlorination of chlorophenols by Pd/Fe nanoparticles: comparisons with other bimetallic systems, kinetics and mechanism. Sep. Purif. Technol. 76, 206–214.