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Mg-based amorphous alloys for decolorization of azo dyes
Accepted Manuscript Microarticle Mg-based amorphous alloys for decolorization of azo dyes Changqin Zhang, Zhengwang Zhu, Haifeng Zhang PII: DOI: Reference:
S2211-3797(17)30539-9 http://dx.doi.org/10.1016/j.rinp.2017.06.031 RINP 746
To appear in:
Results in Physics
Received Date: Accepted Date:
29 March 2017 19 June 2017
Please cite this article as: Zhang, C., Zhu, Z., Zhang, H., Mg-based amorphous alloys for decolorization of azo dyes, Results in Physics (2017), doi: http://dx.doi.org/10.1016/j.rinp.2017.06.031
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.
Mg-based amorphous alloys for decolorization of azo dyes Changqin Zhang 1 , Zhengwang Zhu 2, Haifeng Zhang 2 1 2
School of Materials Science and Engineering, Shandong Jianzhu University, Jinan 250101, China Shenyang National Laboratory for Materials Science, Chinese Academy of Sciences, Shenyang 110016, China Abstract The authors recently found that Mg-based amorphous ribbons had a prominent effect on the decolorization of azo dyes. Direct Blue 2B and Acid Orange II solutions of 100 mg/L could be decolorized nearly completely by the ribbons within 30 min. Decolorization mechanism was discussed briefly, and kinetic analysis based on the experimental data indicated that physical adsorption and reductive degradation for the azo dye solutions mediated by Mg63Cu16.8Ag11.2Er9 amorphous ribbons could proceeded in an elegant and rapid manner. This new finding seems attractive, valuable and promising for the raw effluent generated by textile dye manufacturing company in the future. Keywords: Mg-based amorphous alloys, decolorization, azo dyes
1. INTRODUCTION Water pollution caused by effluent discharge from textile dye manufacturing and textile dyeing mills is one of the major environmental concerns in the world today. Among these, degradation of azo dye effluents has received increasing attention because of their extensive use in the textile, leather and dyestuff industries [1,2]. Various physical and/or chemical methods, such as biological treatment, flocculation, adsorption and advanced oxidation processes, have been tried to treat azo dye wastewater [3-6]. However, the above removal methods have several shortcomings such as high cost, limited applicability and/or generation of chemical sludge. Therefore, new treatment methods that are cost effective and eco-friendly should be developed to decolorize azo dyes efficiently. Magnesium–palladium system was found to be a potential method that could efficiently decolorize azo dyes such as reactive black 5, sunset yellow FCF and tartrazine dyes [7]. There was complete loss of visible range absorption peaks and the color removal rate exceeded 95% within 24 h of reaction. However, corrosion of pure Mg in water reduced its endurance since a large amount of Mg could be consumed by water. At a rough estimate, total cost of the integrated process using this method was about 0.6 US dollar for 1L of solution containing 100mg of dye due to the addition and loss of Pd0, which was too high for the application. Although solid solution alloying with nonnoble metals is an effective way to improve the corrosion behavior of crystalline Mg alloys, in many cases, this method is highly limited by the low solubility of the desired alloying elements. Recently, a few studies have been carried out on the degradation of organic pollution in aqueous solution by Mg-based amorphous alloys [8-10]. However, these alloys are usually in powder state or troubled by the tedious preparation process. Power state of the alloys can bring a high decolorization rate, but the corrosion consumption during the decolorization process is huge, which
Corresponding author. Tel.: +0086-0531-86361832; fax: +00860531-86361832. E-mail address: [email protected] (C. Zhang)
decreases the utilization rate of Mg element. In this paper, based on our previous work [11-13], we introduced alloy vetrification technique to change the form of zero-valent magnesium into glassy ribbons, and obtained Mg rich amorhous ribbons through one-step method. The prepared Mg-based amorphous ribbons exhibit prominent effect on the decolorization of Direct Blue 2B and Acid Orange II solutions.
2. EXPERIMENTAL DETAILS The alloy ingot with nominal compositions of Mg63Cu16.8Ag11.2Er9 alloy was produced by induction melting a mixture of Mg, Cu, Ag and Er alloy under an Ar atmosphere. The ingot was then remelted in a quartz tube by induction melting, followed by roller spinning to obtain ribbons. These as-prepared ribbons were analyzed by X-ray Diffraction (XRD) to obtain the information of their structures. Scanning electron microscope (SEM) was employed to observe the surface morphology of the prepared ribbons. Direct Blue 2B and Acid Orange II powders were dissolved in distilled water respectively to get water solutions of 100 mg/L. Two batches of beakers (marked as Beaker A and Beaker B, containing Direct Blue 2B solutions and Acid Orange II solutions respectively) containing 150 mL dye solutions were placed in the controllable constant temperature water–bath trough, and mild mechanical agitation of 200 r/min was executed to ensure the mass transport in the beakers. The glassy ribbons were cut into pieces of ~2×20 mm2, and put into the beakers respectively after the temperature reached to the scheduled values. The nominal area of the ribbons put into Beaker A and Beaker B was both about 0.003 m2. About 4 mL solution was taken from the beaker at intervals, and UV-vis spectrum of the solution was recorded from 200 to 600 nm using a UV-visible spectrophotometer (JASCO V-550) after filtered through 0.45 μm membrane filter. The concentrations of the dye solutions were quantified by measuring the absorption intensity at λmax.
3. RESULTS AND DISCUSSION
The amorphous nature of the ribbons can be verified by the broad peak that appears in its XRD pattern as Fig. 1 shows. According to previous studies on the decolorization properties of amorphous alloys [8-13], the excellent capabilty of various amorphous alloys in decolorizing azo dyes can be attributed to their amorphous nature and the thermodynamic state, which lie at a higher energy level that is conducive to the reduction of –N=N- bonds. The nominal composition of the alloy that we chose has a high glass forming ablity, so that the amorphous ribbons can be obtained conviniently.
Fig. 1. XRD pattern of Mg63Cu16.8Ag11.2Er9 ribbons.
Fig. 2. Images of (a) Direct Blue 2B and (b) Acid Orange II solutions processed by Mg63Cu16.8Ag11.2Er9 ribbons for different times. Fig.2 presents the images of Direct Blue 2B and Acid Orange II solutions treated by the ribbons for different times at 40 °C. It can be seen that, after only 5 min, the chromaticity of both Direct Blue 2B and Acid Orange II solutions can be decreased significantly; 15 min later, there is basically no chromaticity for both two solutions. It is obvious that these two solutions can be decolorized by the ribbons nearly completely within 30
min. For the ribbons, their specific surface area is too low and out of the range of the BET analysis with nitrogen. Considering that the ribbons are quite smooth, it is reasonable to assume that they are cuboids as was done in previous studies. Based on this assumption, the specific surface area of the ribbons can be considered approximately equal to their nominal area. The UV–vis spectrum changes of Acid Orange II solutions as a function of reaction time at 30°C and 50°C are illustrated in Fig. 3a. The strong absorbance peak at λmax = 484 nm in the visible region originates from a conjugated structure formed by the azo bonds, the intensity of which denotes the dye concentration in the solution [11, 12]. The bands at λmax become weaker, revealing the decrement of Acid Orange II in the solution. Along with that, all absorbance peaks become weaker and weaker at the primary stage. After reacting at 30°C for 10 min, no obvious absorbance peaks appears at the UV-vis spectrum, indicating there is no Acid Orange II or new reaction products in the solution. However, during the subsequent reaction, some new products may form and come into the solution, which can be verified by the appearance of the absorbance peak at ~250 nm in the UV–vis spectrum of 15 min. This new peak is considered to be corresponding to the –NH2 groups, and its appearance proves that the degradation of Acid Orange II occurred after the primary physical adsorption. Similar phenomenon could be observed for the reaction at 50°C, but the declorization process was slower than that of the reaction at 30°C. Fig. 3b shows the Ct normalized by C0 dependence on the reaction time, where C0 and Ct are the current and initial dye concentration, respectively. By nonlinear curve fit, it is deduced that the process fits very well with first order exponential decay kinetics proposed by Nam and Tratnyek [13] as follows: Ct/C0=exp(−kobst) (1) where kobs (min−1) is the observed rate constant, and t is the reaction time. Thus, kobs of the process by Mg63Cu16.8Ag11.2Er9 at 30°C and 50°C are 0.249 min -1 and 0.202 min-1, respectively. These observed rate constants should be normalized by the surface area when the decolorization rates of different systems were compared. Here, we used surface area normalized rate constant (kSA) to compare the decolorization rates of different systems, where kSA is defined as kobs divided by the surface area of the ribbons per liter of dye solutions, namely kSA = kobs / (0.010/0.15) = 15kobs. Hence, kSA of the process by Mg63Cu16.8Ag11.2Er9 at 30°C and 50°C are 3.73 L m-2 min-1 and 3.03 L m-2 min-1, respectively. These values are sinificantly higher than that of zero-valent iron [16] or Mg-Pd system [7], and comparable to that of Fe77.2Mo0.8Si9B13 amorphous ribbons [13] or MgZnbased amorphous alloys [8, 10].
zero-valent metals frozen in atomic state in the ribbons [13-15]. Along with physical adsorption on the ribbon surface, chemical degradation is initiated by the ionization (corrosion) of reductive zero-valent metals such as magnesium by the reaction of Mg0 - 2e- = Mg2+ [7]. The electrons derived from the metal are captured by protons to generate nascent hydrogen [H], which induces the cleavage of azo bond (–N=N–). Thus, the chromophore group and conjugated system of the azo dye are destroyed [16]. The corresponding reduced products have no chromophore groups, so that their existence has no noticeable effect on the color of the solutions.
4. CONCLUSIONS Mg63Cu16.8Ag11.2Er9 amorphous ribbons Physical adsorption will facilitate rapid uptake and concentration of dye molecules on the surface of the ribbons. The dye molecules can subsequently be subjected to reductive decolorization process catalyzed by Mg-based amorphous ribbons, and the end products formed may be subjected to aerobic biodegradation process.
ost Magnesium–palladium system, and th Fig. 3. (a) UV-vis spectra of Acid Orange II solution and (b) Ct normalized by C0 dependence on the reaction time during the decolorization of the solution by Mg63Cu16.8Ag11.2Er9 ribbons. The observed decolorization effect of Mg63Cu16.8Ag11.2Er9 ribbons for Acid Orange II solution is the combination of physical adsorption and chemical degradation. At the primary stage of the reaction, physical adsorption of dye molecules on the ribbon surface is the dominant hand for the decolorization. After physical adsorption goes along for some time, chemical degradation starts and degradation products come into the solution. It can be seen from Fig. 3a that, the intensity of absorbance peak at 484 nm for the solution reacting at 30°C decreases much faster than that reacting at 50°C, while the intensity of absorbance peak at 250 nm for the former increases slower than that for the latter along with the reaction. For Mg63Cu16.8Ag11.2Er9 ribbons, lower temperature is beneficial to physical adsorption, and this leads to the larger kobs of the reaction at 30°C. However, for chemical degradation, higher temperature may accelerate the chemical reaction and more degradation products would be detected in the solution. The role of Mg63Cu16.8Ag11.2Er9 ribbons in the degradation process can be attributed to the reductive
Acknowledgments The authors gratefully acknowledge the financial support from the Doctor Fund of Shandong Jianzhu University (Grant No. XNBS1429), and A Project of Shandong Province Higher Educational Science and Technology Program (Grant No. J14LA54). REFERENCES
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Park, H., Choi, W. Visible light and Fe(III)mediated degradation of acid Orange 7 in the absence of H2O2 Journal of Photochemistry and Photobiology A, 159 2003: pp. 241-247. Van der Zee, F. P., Lettinga, G., Field, J. A. Azo dye decolorization by anaerobic granular sludge Chemosphere, 44, 2001: pp. 11691176. Mezohegyi, G., Kolodkin, A., Castro, U. I., Bengoa, C., Stuber, F., Font, J., Fabregat, A., Fortuny, A. Effective Anaerobic Decolorization of Azo Dye Acid Orange 7 in Continuous Upflow Packed-Bed Reactor Using Biological Activated Carbon System Industrial & Engineering Chemistry Research, 46, 2007: pp. 6788-6792. Dutta, K., Mukhopadhyay, S., Bhattacharjee, S., Chaudhuri, B. Chemical
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oxidation of methylene blue using a Fenton-like reaction Journal of Hazardous Materials, 84, 2001: pp. 57-71. Chen, J., Zhu, L. Heterogeneous UV-Fenton catalytic degradation of dyestuff in water with hydroxyl-Fe pillared bentonite Catalysis Today, 126, 2007: pp. 463-470. Ozer, R. R., Ferry, J. L. Investigation of the photocatalytic activity of TiO2-polyoxometalate systems Environment Science & Technology, 35, 2001: pp. 3242-3246. Patel, R., Suresh, S. Decolourization of azo dyes using magnesium-palladium system Journal of Hazardous Materials, 137, 2006: pp. 1729-1741. Wang, J.-Q., Liu, Y.-H., Chen, M.-W., Louzguine-Luzgin, D. V., Inoue, A., Perepezko, J. H. Excellent capability in degrading azo dyes by MgZn-based metallic glass powders Scientific Reports, 2, 2012: pp. Luo, X., Li, R., Zong, J., Zhang, Y., Li, H., Zhang, T. Enhanced degradation of azo dye by nanoporous-copper-decorated Mg-Cu-Y metallic glass powder through dealloying pretreatment Applied Surface Science, 305, 2014: pp. 314-320. Ramya, M., Karthika, M., Selvakumar, R., Raj, B., Ravi, K. R. A facile and efficient single step ball milling process for synthesis of partially amorphous Mg-Zn-Ca alloy powders for dye degradation Journal of Alloys and Compounds, 696, 2017: pp. 185-192. Zhang, C., Zhang, H., Lv, M. Decolorization of azo dye solution by Fe–Mo–Si–B amorphous alloy Journal of Non-Crystalline Solids, 356, 2010: pp. 1703-1706.
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Zhang, C., Zhu, Z., Zhang, H., Hu, Z. Rapid reductive degradation of azo dyes by a unique structure of amorphous alloys Chinese Science Bulletin, 56, 2011: pp. 3988-3992. Zhang, C., Zhu, Z., Zhang, H., Hu, Z. Rapid decolorization of Acid Orange II aqueous solution by amorphous zero-valent iron Journal of Environmental Sciences, 24, 2012: pp. 1015-1021. Cao, J., Wei, L., Huang, Q., Wang, L., Han, S. Reducing degradation of azo dye by zerovalent iron in aqueous solution Chemosphere, 38, 1999: pp. 565-571. Fan, J., Guo, Y., Wang, J., Fan, M. Rapid decolorization of azo dye methyl orange in aqueous solution by nanoscale zero-valent iron particles Journal of Hazardous Materials, 166, 2009: pp. 904-910. Nam, S., Tratnyek, P. G. Reduction of azo dyes with zero-valent iron Water Research, 34, 2000: pp. 1837-1845. Saxe, J. P., Lubenow, B. L., Chiu, P. C., Huang, C. P., Cha, D. K. Enhanced biodegradation of azo dyes using an integrated elemental iron-activated sludge system: I, Evaluation of system performance Water Environment Research, 78, 2006: pp. 19-25. Hou, M., Li, F., Liu, X., Wang, X., Wan, H. The effect of substituent groups on the reductive degradation of azo dyes by zerovalent iron Journal of Hazardous Materials, 145, 2007: pp. 305-314. K.Sohn, S.W. Kang, S. Ahn, M. Woo, Yang, S. K. Fe(0) nanoparticles for nitrate reduction: stability, reactivity, and transformation Environment Science & Technology, 40, 2006: pp. 5514-5519.
S2211-3797(17)30539-9 http://dx.doi.org/10.1016/j.rinp.2017.06.031 RINP 746
To appear in:
Results in Physics
Received Date: Accepted Date:
29 March 2017 19 June 2017
Please cite this article as: Zhang, C., Zhu, Z., Zhang, H., Mg-based amorphous alloys for decolorization of azo dyes, Results in Physics (2017), doi: http://dx.doi.org/10.1016/j.rinp.2017.06.031
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.
Mg-based amorphous alloys for decolorization of azo dyes Changqin Zhang 1 , Zhengwang Zhu 2, Haifeng Zhang 2 1 2
School of Materials Science and Engineering, Shandong Jianzhu University, Jinan 250101, China Shenyang National Laboratory for Materials Science, Chinese Academy of Sciences, Shenyang 110016, China Abstract The authors recently found that Mg-based amorphous ribbons had a prominent effect on the decolorization of azo dyes. Direct Blue 2B and Acid Orange II solutions of 100 mg/L could be decolorized nearly completely by the ribbons within 30 min. Decolorization mechanism was discussed briefly, and kinetic analysis based on the experimental data indicated that physical adsorption and reductive degradation for the azo dye solutions mediated by Mg63Cu16.8Ag11.2Er9 amorphous ribbons could proceeded in an elegant and rapid manner. This new finding seems attractive, valuable and promising for the raw effluent generated by textile dye manufacturing company in the future. Keywords: Mg-based amorphous alloys, decolorization, azo dyes
1. INTRODUCTION Water pollution caused by effluent discharge from textile dye manufacturing and textile dyeing mills is one of the major environmental concerns in the world today. Among these, degradation of azo dye effluents has received increasing attention because of their extensive use in the textile, leather and dyestuff industries [1,2]. Various physical and/or chemical methods, such as biological treatment, flocculation, adsorption and advanced oxidation processes, have been tried to treat azo dye wastewater [3-6]. However, the above removal methods have several shortcomings such as high cost, limited applicability and/or generation of chemical sludge. Therefore, new treatment methods that are cost effective and eco-friendly should be developed to decolorize azo dyes efficiently. Magnesium–palladium system was found to be a potential method that could efficiently decolorize azo dyes such as reactive black 5, sunset yellow FCF and tartrazine dyes [7]. There was complete loss of visible range absorption peaks and the color removal rate exceeded 95% within 24 h of reaction. However, corrosion of pure Mg in water reduced its endurance since a large amount of Mg could be consumed by water. At a rough estimate, total cost of the integrated process using this method was about 0.6 US dollar for 1L of solution containing 100mg of dye due to the addition and loss of Pd0, which was too high for the application. Although solid solution alloying with nonnoble metals is an effective way to improve the corrosion behavior of crystalline Mg alloys, in many cases, this method is highly limited by the low solubility of the desired alloying elements. Recently, a few studies have been carried out on the degradation of organic pollution in aqueous solution by Mg-based amorphous alloys [8-10]. However, these alloys are usually in powder state or troubled by the tedious preparation process. Power state of the alloys can bring a high decolorization rate, but the corrosion consumption during the decolorization process is huge, which
Corresponding author. Tel.: +0086-0531-86361832; fax: +00860531-86361832. E-mail address: [email protected] (C. Zhang)
decreases the utilization rate of Mg element. In this paper, based on our previous work [11-13], we introduced alloy vetrification technique to change the form of zero-valent magnesium into glassy ribbons, and obtained Mg rich amorhous ribbons through one-step method. The prepared Mg-based amorphous ribbons exhibit prominent effect on the decolorization of Direct Blue 2B and Acid Orange II solutions.
2. EXPERIMENTAL DETAILS The alloy ingot with nominal compositions of Mg63Cu16.8Ag11.2Er9 alloy was produced by induction melting a mixture of Mg, Cu, Ag and Er alloy under an Ar atmosphere. The ingot was then remelted in a quartz tube by induction melting, followed by roller spinning to obtain ribbons. These as-prepared ribbons were analyzed by X-ray Diffraction (XRD) to obtain the information of their structures. Scanning electron microscope (SEM) was employed to observe the surface morphology of the prepared ribbons. Direct Blue 2B and Acid Orange II powders were dissolved in distilled water respectively to get water solutions of 100 mg/L. Two batches of beakers (marked as Beaker A and Beaker B, containing Direct Blue 2B solutions and Acid Orange II solutions respectively) containing 150 mL dye solutions were placed in the controllable constant temperature water–bath trough, and mild mechanical agitation of 200 r/min was executed to ensure the mass transport in the beakers. The glassy ribbons were cut into pieces of ~2×20 mm2, and put into the beakers respectively after the temperature reached to the scheduled values. The nominal area of the ribbons put into Beaker A and Beaker B was both about 0.003 m2. About 4 mL solution was taken from the beaker at intervals, and UV-vis spectrum of the solution was recorded from 200 to 600 nm using a UV-visible spectrophotometer (JASCO V-550) after filtered through 0.45 μm membrane filter. The concentrations of the dye solutions were quantified by measuring the absorption intensity at λmax.
3. RESULTS AND DISCUSSION
The amorphous nature of the ribbons can be verified by the broad peak that appears in its XRD pattern as Fig. 1 shows. According to previous studies on the decolorization properties of amorphous alloys [8-13], the excellent capabilty of various amorphous alloys in decolorizing azo dyes can be attributed to their amorphous nature and the thermodynamic state, which lie at a higher energy level that is conducive to the reduction of –N=N- bonds. The nominal composition of the alloy that we chose has a high glass forming ablity, so that the amorphous ribbons can be obtained conviniently.
Fig. 1. XRD pattern of Mg63Cu16.8Ag11.2Er9 ribbons.
Fig. 2. Images of (a) Direct Blue 2B and (b) Acid Orange II solutions processed by Mg63Cu16.8Ag11.2Er9 ribbons for different times. Fig.2 presents the images of Direct Blue 2B and Acid Orange II solutions treated by the ribbons for different times at 40 °C. It can be seen that, after only 5 min, the chromaticity of both Direct Blue 2B and Acid Orange II solutions can be decreased significantly; 15 min later, there is basically no chromaticity for both two solutions. It is obvious that these two solutions can be decolorized by the ribbons nearly completely within 30
min. For the ribbons, their specific surface area is too low and out of the range of the BET analysis with nitrogen. Considering that the ribbons are quite smooth, it is reasonable to assume that they are cuboids as was done in previous studies. Based on this assumption, the specific surface area of the ribbons can be considered approximately equal to their nominal area. The UV–vis spectrum changes of Acid Orange II solutions as a function of reaction time at 30°C and 50°C are illustrated in Fig. 3a. The strong absorbance peak at λmax = 484 nm in the visible region originates from a conjugated structure formed by the azo bonds, the intensity of which denotes the dye concentration in the solution [11, 12]. The bands at λmax become weaker, revealing the decrement of Acid Orange II in the solution. Along with that, all absorbance peaks become weaker and weaker at the primary stage. After reacting at 30°C for 10 min, no obvious absorbance peaks appears at the UV-vis spectrum, indicating there is no Acid Orange II or new reaction products in the solution. However, during the subsequent reaction, some new products may form and come into the solution, which can be verified by the appearance of the absorbance peak at ~250 nm in the UV–vis spectrum of 15 min. This new peak is considered to be corresponding to the –NH2 groups, and its appearance proves that the degradation of Acid Orange II occurred after the primary physical adsorption. Similar phenomenon could be observed for the reaction at 50°C, but the declorization process was slower than that of the reaction at 30°C. Fig. 3b shows the Ct normalized by C0 dependence on the reaction time, where C0 and Ct are the current and initial dye concentration, respectively. By nonlinear curve fit, it is deduced that the process fits very well with first order exponential decay kinetics proposed by Nam and Tratnyek [13] as follows: Ct/C0=exp(−kobst) (1) where kobs (min−1) is the observed rate constant, and t is the reaction time. Thus, kobs of the process by Mg63Cu16.8Ag11.2Er9 at 30°C and 50°C are 0.249 min -1 and 0.202 min-1, respectively. These observed rate constants should be normalized by the surface area when the decolorization rates of different systems were compared. Here, we used surface area normalized rate constant (kSA) to compare the decolorization rates of different systems, where kSA is defined as kobs divided by the surface area of the ribbons per liter of dye solutions, namely kSA = kobs / (0.010/0.15) = 15kobs. Hence, kSA of the process by Mg63Cu16.8Ag11.2Er9 at 30°C and 50°C are 3.73 L m-2 min-1 and 3.03 L m-2 min-1, respectively. These values are sinificantly higher than that of zero-valent iron [16] or Mg-Pd system [7], and comparable to that of Fe77.2Mo0.8Si9B13 amorphous ribbons [13] or MgZnbased amorphous alloys [8, 10].
zero-valent metals frozen in atomic state in the ribbons [13-15]. Along with physical adsorption on the ribbon surface, chemical degradation is initiated by the ionization (corrosion) of reductive zero-valent metals such as magnesium by the reaction of Mg0 - 2e- = Mg2+ [7]. The electrons derived from the metal are captured by protons to generate nascent hydrogen [H], which induces the cleavage of azo bond (–N=N–). Thus, the chromophore group and conjugated system of the azo dye are destroyed [16]. The corresponding reduced products have no chromophore groups, so that their existence has no noticeable effect on the color of the solutions.
4. CONCLUSIONS Mg63Cu16.8Ag11.2Er9 amorphous ribbons Physical adsorption will facilitate rapid uptake and concentration of dye molecules on the surface of the ribbons. The dye molecules can subsequently be subjected to reductive decolorization process catalyzed by Mg-based amorphous ribbons, and the end products formed may be subjected to aerobic biodegradation process.
ost Magnesium–palladium system, and th Fig. 3. (a) UV-vis spectra of Acid Orange II solution and (b) Ct normalized by C0 dependence on the reaction time during the decolorization of the solution by Mg63Cu16.8Ag11.2Er9 ribbons. The observed decolorization effect of Mg63Cu16.8Ag11.2Er9 ribbons for Acid Orange II solution is the combination of physical adsorption and chemical degradation. At the primary stage of the reaction, physical adsorption of dye molecules on the ribbon surface is the dominant hand for the decolorization. After physical adsorption goes along for some time, chemical degradation starts and degradation products come into the solution. It can be seen from Fig. 3a that, the intensity of absorbance peak at 484 nm for the solution reacting at 30°C decreases much faster than that reacting at 50°C, while the intensity of absorbance peak at 250 nm for the former increases slower than that for the latter along with the reaction. For Mg63Cu16.8Ag11.2Er9 ribbons, lower temperature is beneficial to physical adsorption, and this leads to the larger kobs of the reaction at 30°C. However, for chemical degradation, higher temperature may accelerate the chemical reaction and more degradation products would be detected in the solution. The role of Mg63Cu16.8Ag11.2Er9 ribbons in the degradation process can be attributed to the reductive
Acknowledgments The authors gratefully acknowledge the financial support from the Doctor Fund of Shandong Jianzhu University (Grant No. XNBS1429), and A Project of Shandong Province Higher Educational Science and Technology Program (Grant No. J14LA54). REFERENCES
1.
2.
3.
4.
Park, H., Choi, W. Visible light and Fe(III)mediated degradation of acid Orange 7 in the absence of H2O2 Journal of Photochemistry and Photobiology A, 159 2003: pp. 241-247. Van der Zee, F. P., Lettinga, G., Field, J. A. Azo dye decolorization by anaerobic granular sludge Chemosphere, 44, 2001: pp. 11691176. Mezohegyi, G., Kolodkin, A., Castro, U. I., Bengoa, C., Stuber, F., Font, J., Fabregat, A., Fortuny, A. Effective Anaerobic Decolorization of Azo Dye Acid Orange 7 in Continuous Upflow Packed-Bed Reactor Using Biological Activated Carbon System Industrial & Engineering Chemistry Research, 46, 2007: pp. 6788-6792. Dutta, K., Mukhopadhyay, S., Bhattacharjee, S., Chaudhuri, B. Chemical
5.
6.
7.
8.
9.
10.
11.
oxidation of methylene blue using a Fenton-like reaction Journal of Hazardous Materials, 84, 2001: pp. 57-71. Chen, J., Zhu, L. Heterogeneous UV-Fenton catalytic degradation of dyestuff in water with hydroxyl-Fe pillared bentonite Catalysis Today, 126, 2007: pp. 463-470. Ozer, R. R., Ferry, J. L. Investigation of the photocatalytic activity of TiO2-polyoxometalate systems Environment Science & Technology, 35, 2001: pp. 3242-3246. Patel, R., Suresh, S. Decolourization of azo dyes using magnesium-palladium system Journal of Hazardous Materials, 137, 2006: pp. 1729-1741. Wang, J.-Q., Liu, Y.-H., Chen, M.-W., Louzguine-Luzgin, D. V., Inoue, A., Perepezko, J. H. Excellent capability in degrading azo dyes by MgZn-based metallic glass powders Scientific Reports, 2, 2012: pp. Luo, X., Li, R., Zong, J., Zhang, Y., Li, H., Zhang, T. Enhanced degradation of azo dye by nanoporous-copper-decorated Mg-Cu-Y metallic glass powder through dealloying pretreatment Applied Surface Science, 305, 2014: pp. 314-320. Ramya, M., Karthika, M., Selvakumar, R., Raj, B., Ravi, K. R. A facile and efficient single step ball milling process for synthesis of partially amorphous Mg-Zn-Ca alloy powders for dye degradation Journal of Alloys and Compounds, 696, 2017: pp. 185-192. Zhang, C., Zhang, H., Lv, M. Decolorization of azo dye solution by Fe–Mo–Si–B amorphous alloy Journal of Non-Crystalline Solids, 356, 2010: pp. 1703-1706.
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19.
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