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1 Materials and instruments All used reagents were prepared from analytical reagent grade chemicals and distilled water. sulfanilamide, urea, polyacrylamide and sodium hydroxide were used as received. Stock Pb2+, Ni2+, Cu2+, Zn2+ and Cd2+ solutions(1g/L) were prepared by lead nitrate, nickel nitrate, copper sulfate pentahydrate, zinc chloride and cadmium nitrate respectively. Used instruments in this study were as follows: Visible spectrophotometer VIS-7220. Fourier transform infrared spectrometer Nicolet 5700. Atomic absorption spectrophotometer TAS-986.
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2 Preparation of the chelating agent-PUS A mixture of polyacrylamide and water was kept at room temperature for 1 day to obtain a homogeneous gelatinous mass. The mixture was added to a three-necked flask containing urea and sulfanilamide and the contents were mixed uniformly using an electric stir bar. Then equal volume of sodium hydroxide was added into the stirred mixture. The mixture was stirred at a temperature for some hours until reaction was complete. Finally, heavy metal ions chelator was obtained.
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3 Properties of the heavy metal chelator The percentage removal of nickel was chosen as the qualities index to ensure the fittest reaction condition. In each experiment, the heavy metal chelator of known bulks from 0.5 to 3.0mL were added to 100mL Erlenmeyer with 20.0mL of Ni2+ solution of known concentrations 1g/L under constant stirring(200rpm), the reaction times used were those obtained from study as function of contact time that was 25min. The metal ion concentration of Ni2+ was determined by spectrophotometry, the metal ion concentration of Zn2+, Cu2+ and Cd2+ were determined by Atomic Absorption Spectrophotometer. Results and discussion
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1 Synthesis of PUS
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1.1 Effects of the sodium hydroxide In order to determine the optimal conditions of synthesis of PUS, the effect of four conditions including sodium hydroxide, reaction temperature, contact time and material ratio were investigated. The percentage removal of Ni2+ was chosen as the qualities index to ensure the fittest synthesis condition. The experiment, concerning the influence of the quantity of sodium hydroxide on synthesis of PUS, is carried out under the conditions that the reaction time is 2h, the reaction temperature is 50℃, the quantity of sulfanilamide and urea is 3g and 2g respectively. Fig. 1 presents the removal rates of Ni2+ by the four chelators were 64.6%, 82.0%, 99.7%, 89.1% at sodium hydroxide of 1.2g, 1.6g, 2.0g, 2.4g respectively. It is obviously that the heavy metal chelator is obtained by 2g sodium hydroxide can strongly affect the removing of Ni2+. Therefore, we can choose 2g as the proper quantity of sodium hydroxide according to the treatment requirements. Fig. 1 Effects of the sodium hydroxide Fig. 2 Effect of the material ratio
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1.2 Effects of the material ratio The experiment, concerning the influence of the quantity of sulfanilamide and urea on synthesis of PUS, is carried out under the conditions that the reaction time is 2h, the reaction temperature is 50℃, the quantity of sodium hydroxide is 2g, the quantity of sulfanilamide /urea (m/m) is 4/1, 3/2 and 2/3 respectively. That the removal rates of Ni2+ by the three chelators are presented in Fig. 2, especially highly increase when the quantity of sulfanilamide and urea is 3g and 2g respectively, Therefore, we can choose sulfanilamide and urea is 3g and 2g respectively as the proper quantity of sulfanilamide and urea according to the treatment requirements.
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1.3 Effect of temperature The experiment, concerning the influence of reaction temperature on synthesis of PUS, is carried out under the conditions that the reaction time is 2h, the quantity of sodium hydroxide is 2g, the quantity of sulfanilamide and urea is 3g and 2g respectively. The removal rates of Ni2+ by the three chelators are presented in Fig. 3, The chelation capacity increased from 0.5 to 3.0 mL when the temperature increases from 30 to 50℃, indicating the rise in adsorption capacity was due to the increase in collision frequency in the raw materials. While the removal rate of Ni2+ which the synthesis temperature is 50℃ is far greater than the removal rate of Ni2+ which is 70℃. So that we can choose 50℃ as the proper synthesis temperature. Fig. 3 Effects of the temperature Fig. 4 Effects of the reaction time
DOI: 10.1016/j.matlet.2005.10.046
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1.4 Effects of the reaction time The experiment, concerning the influence of reaction time on synthesis of PUS, is carried out under the conditions that the reaction temperature is 50℃, the quantity of sodium hydroxide is 2g, the quantity of sulfanilamide and urea is 3g and 2g respectively. The removal rates of Ni2+ by the three chelators are presented in Fig. 4. The removal rate of Ni2+ which the synthesis time is 2h is far greater than the removal rate of Ni2+ which is 3h. Therefore, we can choose 2h as the proper reactive time according to the treatment requirements.
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1.5 the preparation of PUS A mixture of polyacrylamide and water was kept at room temperature for 1 day to obtain a homogeneous gelatinous mass. The mixture was added to a three-necked flask containing urea of 2.0g and sulfanilamide of 3.0g, and the contents were mixed uniformly using an electric stir bar. Then equal volume of sodium hydroxide of 2.0g was added into the stirred mixture. The mixture was stirred at a 50℃ for 2 hours until reaction was complete. Finally, PUS was obtained.
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1.6 Characterization of PUS Characterization of PUS and PUS-nickel complex were carried out (KBr discs) in the range 500-4000cm-1 using Fourier Transform Infrared Spectrometer. The FT-IR spectrums were presented in Fig. 5 and it exhibited many alterations after ion chelation. The major differences were:(1) In the spectrum of PUS, the wide peak at The band at 3378cm-1, corresponding to the stretch vibration absorption peak of N–H2 group, shifted to higher wave number(3436cm-1) significantly after Ni2+ chelation[[] Zhong-Biao Wu, Wei-Min Ni, Bao-Hong Guan: J. Hazard. Mater. Vol. 152 (2008), 757 ]. (2) The absorb band at 1600cm-1 attributed to the axial deformation of the carbonyl of the amide function and the angular deformation of the N-H bond[[] Osvaldo Karnitz Jr., Leandro Vinicius Alves Gurgel, Júlio César Perin de Melo, Vagner Roberto Botaro, Tânia Márcia Sacramento Melo, Rossimiriam Pereira de Freitas Gil and Laurent Frédéric Gil: Bioresour. Technol. Vol. 98 (2007), 1291 ] of the amine function shifted to higher wave number(1635cm-1) significantly after Ni2+ chelation. (3)The adsorption band near 1313cm-1 was caused by the stretching vibrations of the C=S[[] XiaoSheng Jing, FuQiang Liu, Xin Yang, PanPan Ling, LanJuan Li, Chao Long and AiMin Li: J. Hazard. Mater. Vol. 167(2009) , 589 ]. (4) The weak peak at 1385cm-1 for C-N stretching vibration indicate the presence of the organic moiety[[] K.A. Venkatesan, T.G. Srinivasan, P.R. Vasudeva Rao: Physicochemical and Engineering Aspects Vol. 180 (2001), 277. ]. (5) The peaks were observed 3436cm-1, which was ascribed to the stretching vibrations of C=O group in hydroxyl (-OH)[[] C.-Y. Chen, C.-L. Chiang, C.-R. Chen: Sep. Purif. Technol. Vol. 54 (2007), 396 ] was carried out successfully. The appearances of these absorption bands show that some new groups have been formed and PUS could favor the uptake of metal ions by formation of complexes with them. Fig. 5 FT-IR spectrum of PUS and PUS-nickel complex with an effective frequency range of 500-4000 cm-1
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2 Study on characteristics of PUS
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2.1 Effects caused by the individual metal ions on treatment effectiveness the concentration of Ni2+, Zn2+, Cu2+, Cd2+ is 1.0, 6.5, 0.5, 0.1g/L respectively. Get each solution of 20mL in six small beakers and the addition of PUS is 1mL, 2mL, 3mL, 4mL, 5mL, 6mL in sequence. Filter them at room temperature after stirred the samples with magnetic stirring apparatus 25min later and measured the ion concentration of heavy metals by Atomic Absorption Spectrophotometer. The result is presented in the Fig. 6. It was found that the removal rate increased with increasing dosage of PUS. This revealed the characteristic of chelation mechanism and might be attributed to the higher insignificant competitive chelation of heavy metal ions at higher dosage of PUS. It shows that 99.7% of Ni2+, 98.8% of Zn2+, 100.0% of Cu2+ and 99.9% of Cd2+ were removed when the dosage of PUS was 3.0g, 4.0g, 5.0g and 6.0g respectively, and the treated wastewater can meet pollutant emission standards for plating GB21900–2008.
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2.2 Effects caused by the coexistence of metal ions on treatment effectiveness A Simulate wastewater containing primarily Cu2+, Cd2+, Ni2+, Pb2+ and Zn2+ ions was measured by Atomic Absorption Spectrophotometer(AAS), The initial metal concentration is 200mg/L, 40mg/L, 200mg/L, 13mg/L and 130mg/L respectively. After 100mL of the wastewater reacted with 20mL of PUS under the room temperature 25min later, the suspensions were separated by centrifuge for instrumental analysis. The result is presented in the Fig. 7. It showed that 100.0% of Cu2+, 95.5% of Cd2+, 100.0% of Ni2+, 99.9% of Pb2+ and 99.9% of Zn2+ were removed. Therefore, it has a high removal efficiency of Cu2+, Ni2+, Pb2+ and Zn2+, the quality of treated concentration of heavy metal ions can meet pollutant emission standards for plating GB21900–2008. Although the removal rate of Cd2+ was 99.1%, but it did not meet the emission standards. The possible reason that Cd2+ had low removal efficiency could attributed to the five kinds of metal ions compete the coordination group. Fig. 6 Effects caused by the individual metal ions on Fig. 7 Effect caused by the coexistence of metal ions on treatment effectiveness treatment effectiveness Conclusion In this study, a novel heavy metal ions chelator-PUS was easily prepared by reaction with sulfanilamide and urea for the adsorptive removal of heavy metals from aqueous solutions. FT-IR suggestted the successful nucleophilic addition. High chelation affinity for aqueous Cu2+, Cd2+, Ni2+, Pb2+ and Zn2+ was achieved through the chelate of metal ions by amino groups(N-C-S, N-H, C=O) of PUS, and the chelation was not much impacted by the environment. Thus PUS exhibits an excellent ability to remove Cu2+, Ni2+, Pb2+ and Zn2+ from aqueous solutions. It may be promising in the field of the removal of heavy metals from wastewaters.
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