Oxidative Degradation of Amoxicillin in Aqueous Solution with Contact

Article pubs.acs.org/IECR

Oxidative Degradation of Amoxicillin in Aqueous Solution with Contact Glow Discharge Electrolysis Xinglong Jin,*,† Xiaoyan Wang,‡ Yu Wang,† and Hongxia Ren§ †

School of Environmental Science and Safety Engineering, Tianjin University of Technology, Tianjin, 300384, China College of Environmental Science and Engineering, Nankai University, Tianjin, 300071, China § College of Chemistry, Nankai University, Tianjin 300071, China ‡

ABSTRACT: Degradation of amoxicillin (AMXL) in aqueous solution induced by contact glow discharge electrolysis (CGDE) was investigated in this paper. Experimental results demonstrated that the higher initial concentration resulted in the lower degradation rate, but the higher amount of AMXL was removed. The addition of Fe2+ or Fe3+ efficiently accelerated the degradation of AMXL. Similarly, stainless steel wire was also used as the anode in CGDE to enhance the degradation of AMXL, taking advantage of the iron ion diffused from the anode to solution. It was found that the degradation rate increased with the increasing anode diameter and anode number. Furthermore, the energy efficiency for AMXL degradation was also calculated. The energy efficiency increased with the increasing anode’s diameter and decreased with the anode’s number.

1. INTRODUCTION The presence of pharmaceutical compounds, namely, antibiotics, in the aquatic environment has received considerable attention during the last decades. Antibiotics have been produced and extensively used to prevent diseases and improve health since last century. Their continuous input into the environment through anthropogenic sources results in an increasing potential risk for aquatic and terrestrial organisms, because antibiotics may cause resistance in bacterial populations, making them ineffective for treatment of several diseases in the near future.1,2 The recalcitrant nature of the effluents containing antibiotics residues makes it difficult to eliminate these compounds by traditional treatments.3 Various advanced oxidation processes (AOPs) have been investigated with the aim of antibiotics removal from water, such as ozonation,4 Fenton and photo-Fenton processes,5,6 photocatalysis,7 irradiation,8 and dielectric barrier discharge (DBD).9 These processes are aimed at in situ generation of strong oxygenbased oxidizers, especially hydroxyl radicals, which are among the strongest oxidizers and can react nonselectively with various types of organic pollutants. Contact glow discharge electrolysis (CGDE) generates glow discharge plasma around the anode between the gas−liquid interface, which also leads to the formation of oxidizing species such as ·OH, H2O2, etc.10 Since a large amount of H2O2 accumulates in the anolyte, iron salts are usually added into the solution to enhance the degradation process. A variety of organic pollutants can be efficiently oxidized by means of CGDE and its combined process with Fe2+ and Fe3+.11−14 CGDE has attracted increasing attention as a technique for wastewater treatment, due to its lower applied voltage and simple equipment. To our knowledge, the degradation of antibiotic induced by CGDE has not been reported so far. Therefore, this paper investigates the degradation of antibiotic by means of CGDE and its combined process with Fe2+ and Fe3+. Amoxicillin (AMXL) is employed as the model pollutant, since AMXL is a © 2013 American Chemical Society

broad-spectrum antibiotic. The molecular formula of AMXL is C16H19N3O5S·3H2O, and its molecular weight is 419.46. Its chemical structure is shown in Figure 1.

Figure 1. Molecular structure of amoxicillin (AMXL).

2. EXPERIMENTAL SECTION The experimental apparatus with a single anode was similar to our previous study.15 The anode was a platinum wire (0.3 mm) or stainless steel wire (0.3−1.0 mm) held in the brass support sealed into a glass tube. The cathode was a stainless steel stick placed in another glass tube, which was covered at the bottom by a sinter glass disk of medium porosity. The anode was immersed into the solution to a depth of approximately 1.0 mm. The reactor with multianodes was similar to that in ref 14. Stainless steel wires (1.0 mm) were used as anode and evenly distributed around the cathode. The distance between the anode and the cathode was 2.5 cm. The solution in a jacked reaction vessel was maintained at 30 ± 1 °C by circulating water. Electrolytic solutions with certain conductivity were prepared by dissolving AMXL and sodium sulfate in the distilled water. The solution was gently stirred with a magnet bar during the reaction. The pressure in the reactor was atmospheric. The voltage was applied through a direct current power supply (0−1 kV, 0−1 A). Received: Revised: Accepted: Published: 9726

February 14, 2013 June 4, 2013 June 27, 2013 June 27, 2013 dx.doi.org/10.1021/ie400498f | Ind. Eng. Chem. Res. 2013, 52, 9726−9730

Industrial & Engineering Chemistry Research

Article

The concentration of AMXL was measured by high performance liquid chromatography (HPLC, Com 6000) coupled with a C18 reversed-phase column (150 mm × 4.6 mm I.D., 5 μm) at 30 °C. The mobile phase was methanol− water (10/90, V/V) at a flow rate of 1.0 mL/min. Detection was performed with an ultraviolet (UV) detector at a wavelength of 254 nm. The degradation rate was calculated with the following equation: degradation rate = 100% × (C0 − Ct )/C0

(1)

where C0 stands for the initial concentration of AMXL and Ct denotes the concentration of AMXL after a t min CGDE treatment. The concentration of total Fe was determined by a colorimetrical method with 1,10-phenanthroline as the color reagent.16 The determination of H2O2 was based on the reaction of H2O2 with titanyl ions giving a yellow-colored complex of pertitanic acid:17 Ti4 + + H 2O2 + 2H 2O → TiO2 ·H 2O2 + 4H+

Figure 3. Change of pH and conductivity of solution during CGDE treatment (voltage: 510 V; electrolyte: 2 g/L Na2SO4; anode: 0.3 mm platinum wire).

(2)

3. RESULTS AND DISCUSSION 3.1. AMXL Degradation under Different Initial Concentrations. The degradation of AMXL with CGDE was conducted under the following conditions: 510 V; 300 mL; pH 5.3; 2.0 g/L Na2SO4 (3.0 mS/cm). Under this condition, the degradation of AMXL with different initial concentration (20−120 mg/L) was investigated and results were shown in Figure 2. The higher initial concentration resulted in lower

tration of AMXL is 80 mg/L. It can be found that the pH value of the solution dropped rapidly and the conductivity increased rapidly. The decrease of pH resulted from the increasing concentration of H+, which led to the increase of the conductivity of solution. The electrolysis of water molecule accounted for the change of pH. In addition, the molecule of AMXL could decompose to some organic acids which also contributed to the decrease of pH. Figure 4 lists the concentration of H2O2 in anolyte with and without AMXL in solution. As shown in Figure 4, the

Figure 2. AMXL degradation under different initial concentrations after 90 min CGDE treatment (voltage: 510 V; electrolyte: 2 g/L Na2SO4; anode: 0.3 mm platinum wire).

Figure 4. Concentration of H2O2 during CGDE treatment (voltage: 510 V; electrolyte: 2 g/L Na2SO4; anode: 0.3 mm platinum wire).

AMXL degradation rate, but the higher amount of AMXL removed. For example, when the initial AMXL concentration was 20 mg/L, more than 90% of AMXL was removed after a 90 min treatment and the amount of AMXL removed was 5.91 mg. When the initial AMXL concentration increased to 120 mg/L, about 50% of AMXL could be removed within the same treatment time, and the amount of AMXL removed increased to 19.56 mg. This phenomenon can be explained by the fact that more AMXL molecules are available for oxidative degradation at the higher AMXL concentration. Figure 3 displays the change of pH and conductivity of solution during CGDE treatment, when the initial concen-

concentration of H2O2 increased linearly with the increase of CGDE treatment time with and without AMXL in solution. The concentration of H2O2 with AMXL as substrate was slightly lower than that without AMXL. As seen from Figure 4, there was still a large amount of H2O2 accumulating in anolyte during CGDE treatment. And the anolyte remained acidic during CGDE treatment, shown in Figure 3. Therefore, it was desirable to convert H2O2 to ·OH, by adding iron salts into the solution, in order to increase the degradation of AMXL through Fenton reactions. 3.2. Effect of Iron Salts on AMXL Degradation. Figures 5 and 6 display the effect of Fe2+ and Fe3+ with different 9727

dx.doi.org/10.1021/ie400498f | Ind. Eng. Chem. Res. 2013, 52, 9726−9730


Article

3.3. AMXL Degradation with Stainless Steel Wire as the Anode. In most cases, platinum was usually used as the anode material in CGDE. In our previous study, platinum wire was replaced with stainless steel wire, due to its lower cost.14 In addition, Fe ion diffused into the solution due to the electrode corrosion during CGDE treatment, which could also accelerate the degradation of substrate. This paper also employed the stainless steel wire as the anode material for AMXL degradation in CGDE. Figures 7 and 8 list the degradation rate of AMXL

Figure 5. Effect of Fe2+ on AMXL degradation (voltage: 510 V; electrolyte: 2 g/L Na2SO4; anode: 0.3 mm platinum wire; AMXL: 80 mg/L).

Figure 7. Effect of different anode diameter on AMXL degradation (voltage: 510 V; electrolyte: 2 g/L Na2SO4; anode: stainless steel wire).

Figure 6. Effect of Fe3+ on AMXL degradation (voltage: 510 V; electrolyte: 2 g/L Na2SO4; anode: 0.3 mm platinum wire; AMXL: 80 mg/L).

concentrations on the degradation rate of AMXL (80 mg/L). Both Fe2+ and Fe3+ ions showed remarkable catalytic effects on AMXL removal. For example, the degradation rate of AMXL was just 25.56% after 30 min CGDE treatment without the addition of iron salts. When the concentration of Fe2+ was 1, 2, 3, 4, 5, and 6 mg/L, the degradation rate of AMXL increased to 55.14%, 70.50%, 82.62%, 89.95%, 95.30%, and 97.63% after a 30 min CGDE treatment, respectively. With 1, 2, 3, 4, and 5 mg/L Fe3+ in the solution, the degradation rate of AMXL increased to 28.96%, 52.83%, 74.48%, 92.55%, and 96.92% after a 30 min CGDE treatment, respectively. It was because both Fe2+ and Fe3+ can decompose H2O2 to ·OH and HO2·, due to the following reactions: H 2O2 + Fe 2 + → Fe3 + + ·OH + OH−

Fe

3+

+ H 2O2 → Fe

2+

+ HO2 ·+H 2+

+

Figure 8. Concentration of total Fe in anolyte without substrate during CGDE treatment (voltage: 510 V; electrolyte: 2 g/L Na2SO4; anode: stainless steel wire).

and total Fe in anolyte with different diameter stainless steel wire as anode. When the diameter was 0.3, 0.5, 0.8, 0.9, and 1.0 mm, the degradation rates of AMXL after a 90 min CGDE treatment were 66.38%, 79.20%, 90.30%, 99.69%, and 99.69%, respectively. The concentration of Fe was trace with 0.3 mm stainless steel wire as the anode, and the degradation rate of AMXL was close to that (67.27%) of platinum wire, which similar to that in our previous study.14 The application of stainless steel wire improved the AMXL degradation rate when the anode diameter was 0.5, 0.8, 0.9, and 1.0 mm. On the one

(3) (4)

3+

Therefore, the addition of Fe and Fe efficiently enhanced the degradation of AMXL due to Fenton reactions. 9728



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hand, the increase of anode diameter slightly increased the current, which enhanced the degradation of AMXL. On the other hand, the amount of Fe diffusing into anolyte due to anode corrosion in CGDE also improved the degradation of AMXL. The concentration of total Fe increased with the increasing diameter of stainless steel wire, which can efficiently decompose H2O2 to ·OH. 3.4. AMXL Degradation with Multiple Anodes. In our previous study, it has been demonstrated that multianode CGDE can efficiently improve the degradation of organic substrate, especially in higher concentrations.14 This paper also employed multianode CGDE for the degradation of AMXL with 500 mg/L as its initial concentration. Figure 9

Figure 10. Effect of anode number on the concentration of Fe ion in anolyte (voltage: 510 V; electrolyte: 2 g/L Na2SO4; anode: 1.0 mm stainless steel wire).

As shown in Table 1, with the single anode, the energy efficiency with 0.3 mm stainless steel wire was 0.954 g/kWh, Table 1. Energy Efficiency of AMXL Degradation with CGDE (voltage: 510 V; electrolyte: 2 g/L Na2SO4) C0 (mg/L)

diameter (mm)

anode number

current (A)

energy efficiency (g/kWh)

platinum wire

80

0.3

1

0.0221

1.073

stainless steel wire

80 80 80 80 80

0.3 0.5 0.8 0.9 1.0

1 1 1 1 1

0.0246 0.0243 0.0248 0.0259 0.0262

0.954 1.200 1.506 1.574 1.842

stainless steel wire

500 500 500 500 500 500

1.0 1.0 1.0 1.0 1.0 1.0

1 2 3 4 5 6

0.0325 0.0507 0.0924 0.1201 0.1410 0.1578

6.025 5.119 4.949 4.734 4.652 4.649

anode material

Figure 9. Effect of stainless steel anode with different number of AMXL degradation (voltage: 510 V; electrolyte: 2 g/L Na2SO4; initial AMXL concentration: 500 mg/L; anode: 1.0 mm stainless steel wire).

demonstrates the degradation rate of AMXL with multiple stainless steel wire as the anodes. When the initial concentration of AMXL was 500 mg/L, the degradation rate of AMXL was 29.22%, 43.36%, 80.46%, 88.74%, 95.16%, and 95.58% after a 30 min CGDE treatment, with 1, 2, 3, 4, 5, and 6 anodes, respectively. Figure 10 lists the concentration of total Fe in anolyte without substrate. It can be found that the concentration of total Fe increased with the increasing number of anodes. With single anode, the concentration of total Fe was trace, which was similar to that in our previous study.14 When the anode number increased to 2, 3, 4, 5, and 6, the concentration of total Fe was 8.84, 10.95, 24.40, 24.99 and 28.77 mg/L after a 30 min CGDE treatment, respectively. Multiple anodes in CGDE also led to the increase of current in the circuit, which also enhanced AMXL degradation. 3.5. Energy Efficiency. Energy efficiency is an important parameter in practice. In this work, the energy efficiency for AMXL degradation (J) was calculated by the following equation.18 J=

close to that (1.073 g/kWh) with 0.3 mm platinum wire. When the diameter of stainless steel wire was 0.5, 0.8, 0.9, and 1.0 mm, the values of J were 1.200, 1.506, 1.574, and 1.842 g/kWh, respectively. It can be seen that the energy efficiency increased with the increasing diameter of stainless steel anode. When the initial concentration was 500 mg/L, the values of J were 6.025, 5.119, 4.949, 4.734, 4.652, and 4.649 g/kWh, with 1, 2, 3, 4, 5, and 6 anodes, respectively. The energy efficiency declined with the increase of anode number. The increase of anode number led to the increase of current and total Fe diffusing from the anode into the anolyte, which enhanced the degradation of AMXL. This also demonstrated that multiple stainless steel anodes in CGDE benefit the degradation of AMXL.

1 CV 2 0

UIt1/2

(5)

4. CONCLUSIONS This paper investigated AMXL degradation in aqueous solution with CGDE. The degradation rate of AMXL was 67.27% after a 90 min CGDE when the applied voltage was 510 V and

where C0 is the initial concentration of the AMXL in g/L, V is volume of treated solution in L, U is applied voltage in kV, I is the current in A, and t1/2 is the time in h required for 50% AMXL degradation. J is expressed in g/kWh. 9729



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electrolyte was 2 g/L Na2SO4. With the addition of Fe2+ or Fe3+, the degradation of AMXL was efficiently enhanced. When the concentration of Fe2+ or Fe3+ was 5 mg/L, the degradation rate of AMXL was 95.30% and 96.92% after a 30 min CGDE treatment, respectively. The degradation rate of AMXL increased with the diameter of stainless steel anode. Furthermore, multianode CGDE with stainless steel wire as anode can also accelerate the AMXL degradation process. The energy efficiency increased with the increasing anode’s diameter and decreased with the anode’s number. This work provided a possible way for the degradation of antibiotics in aqueous solution with CGDE.

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(13) Wang, L.; Jiang, X. Unusual catalytic effects of iron salts on phenol degradation by glow discharge plasma in aqueous solution. J. Hazard. Mater. 2009, 161, 926. (14) Jin, X.; Zhang, H.; Wang, X.; Zhou, M. An improved multianode contact glow discharge electrolysis reactor for dye discoloration. Electrochim. Acta 2011, 59, 474. (15) Jin, X.; Wang, X.; Yue, J.; Cai, Y.; Zhang, H. The effect of electrolyte constituents on contact glow discharge electrolysis. Electrochim. Acta 2010, 56, 925. (16) Harvey, A. E.; Smart, J. A., Jr.; Amis, E. S. Simultaneous spectrophotometric determination of iron(II) and total iron with 1,10phenanthroline. Anal. Chem. 1953, 26, 1854. (17) Eisenberg, G. M. Colorimetric determination of hydrogen peroxide. Ind. Eng. Chem. Anal. Ed. 1943, 15, 327. (18) Malik, M. A. Water purification by plasmas: Which reactors are most energy efficient? Plasma Chem. Plasma Process. 2010, 30, 21.

AUTHOR INFORMATION

Corresponding Author

*Tel:+8622 60214185. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors gratefully acknowledge financial support from the Tianjin Research Program of Application Foundation and Advanced Technology (No. 11JCZDJC25000), the National Natural Science Foundations of China (No. 201204039), and the Fundamental Research Funds for the Central Universities (No. 65011601).

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Oxidative Degradation of Amoxicillin in Aqueous Solution with Contact

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