Chemosphere 103 (2014) 80–85
Contents lists available at ScienceDirect
Chemosphere journal homepage: www.elsevier.com/locate/chemosphere
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
X. Weng et al. / Chemosphere 103 (2014) 80–85
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 (
Contents lists available at ScienceDirect
Chemosphere journal homepage: www.elsevier.com/locate/chemosphere
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
X. Weng et al. / Chemosphere 103 (2014) 80–85
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.
81
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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X. Weng et al. / Chemosphere 103 (2014) 80–85
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 (
