化学学报 ›› 2013, Vol. 71 ›› Issue (04): 625-633.DOI: 10.6023/A12110910 上一篇    下一篇

研究论文

磁性多壁碳纳米管对水中三种硝基咪唑类药物的吸附行为

任晓东a,b, 熊振湖a,b   

  1. a 天津城市建设学院 环境与市政工程学院 天津 300384;
    b 天津城市建设学院 天津市水质科学与技术重点实验室 天津 300384
  • 收稿日期:2012-11-13 出版日期:2013-04-14 发布日期:2013-02-06
  • 通讯作者: 熊振湖 E-mail:zhenhu.xiong@126.com
  • 基金资助:

    项目受国家自然科学基金(No. 50878138)资助.

Adsorption Behavior of Three Nitroimidazoles in Aqueous Solutions to Magnetic-modified Multi-walled Carbon Nanotubes

Ren Xiaodonga,b, Xiong Zhenhua,b   

  1. a Collage of Environmental and Municipal Engineering, Tianjin Institute of Urban Construction, Tianjin 300384, China;
    b Collage of Environmental and Municipal Engineering, Tianjin Key Laboratory of Water Quality Science and Technology, Tianjin 300384, China
  • Received:2012-11-13 Online:2013-04-14 Published:2013-02-06
  • Supported by:

    Project supported by the National Natural Science Foundation of China (No. 50878138).

在制备磁性多壁碳纳米管(MWCNTs)并且对其表征的基础上, 将磁性MWCNTs用于吸附水溶液中的三种硝基咪唑类药物(甲硝唑、奥硝唑、替硝唑). 研究了溶液pH值、吸附剂量、吸附时间和温度对吸附过程的影响. 结果表明, 当磁性MWCNTs投加量为5 g·L-1, 溶液pH值为7, 吸附时间为300 min时, 甲硝唑、奥硝唑、替硝唑的去除率分别达到92.86%, 94.44%, 94.91%. 吸附动力学分析证实准二级模型准确地反映了吸附过程的动力学, 而Freundlich模型很好地描述了不同温度下的吸附等温线. 吸附过程的总速度受到外部质量传递和粒子内扩散的影响, 但主导因素是粒子内扩散. 吸附机理可能是由MWCNTs和硝基咪唑类化合物之间的静电引力及π-π堆积作用产生的. 对热力学参数(ΔH0, ΔS0, ΔG0)的计算揭示, 在实验的温度范围, 硝基咪唑类药物的吸附是自发、放热的物理过程. 最后考察了吸附材料中Fe的溢出情况, 发现在中性pH下Fe的溢出仅是0.96 mg·L-1, 表明磁性MWCNTs在中性水体中是相当稳定的.

关键词: 磁性多壁碳纳米管, 硝基咪唑类药物, 吸附, 动力学, 热力学

The magnetic multi-walled carbon nanotubes (MWCNTs) were synthesized by wet chemical treatments. Firstly, an amount of 1.0 g of purified MWCNTs was suspended in 200 mL of mixed solution containing 1.7 g of ammonium ferrous sulfate and 2.5 g of ammonium ferric sulfate, which was followed by a slow addition of 10.0 mL of 8 mol·L-1 NH4OH solution at constant temperature of 50 ℃, under nitrogen atmosphere, with the aid of ultrasonic stirring for 10 min. The pH of the final mixture was controlled in the range of 11~12. The reaction was allowed to continue for 30 min, which results in the color of the suspension changing from black to brown. After the completion of the reaction, the suspension was allowed to cool at room temperature. The magnetic MWCNTs was isolated from the mixture by a permanent magnet, afterwards dried under vacuum. The size and morphology of the synthesized magnetic MWCNTs were characterized by transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy and vibrating sample magnetometer. The magnetic MWCNTs was used to adsorbing the three nitroimidazoles,—metronidazole, ornidazole and tinidazole—in aqueous solutions. The adsorption kinetic (or isotherms) experiments were carried out by adding 250 mg of magnetic MWCNTs to a 50 mL flask which containing a solution made up of one or three nitroimidazoles with known initial concentration (10 mg·L-1) at natural pH, then agitating in a temperature-controlled shaker at (25±1) ℃ for different time intervals (1~480 min). The effect of pH was performed by dispersion of 250 mg of magnetic MWCNTs in 50 mL aqueous solution which containing 10 mg·L-1 of three nitroimidazoles of each. The results showed that the removal of metronidazole, ornidazole and tinidazole reached 92.86%, 94.44%, 94.91% respectively when the dosage of magnetic MWCNTs was 5 g·L-1, the pH values was 7 and the time of adsorption was 300 min. Adsorption kinetic analysis demonstrated that pseudo-second order model could interpret the kinetics of the adsorption process, and Freundlich model could better explains the isotherm for adsorption process under different temperatures. The overall adsorption rate appeared to be influenced by both the external mass transfer and the intraparticle diffusion, and mainly governed by the intraparticle diffusion. The adsorption mechanism could be explained by electrostatic attraction between MWCNTs and nitroimidazoles, and by π-π stacking interaction. The obtained thermodynamic parameters (ΔH0, ΔS0, ΔG0), calculated from adsorption process revealed that 1) ΔG0<0 indicated that the adsorption of nitroimidazoles on magnetic MWCNTs was spontaneous; 2) ΔG0 indicated that the adsorption is physical process; 3) ΔH0<0 indicated that the absorption reaction was exothermic and that low temperatures were favorable for adsorption, and 4) ΔS0>0 indicated that the adsorption process was an entropy enhancing process in the experimental temperature range. Finally, the leaching of Fe from adsorbent into the treated water was tested, which found that the leaching of Fe was as low as 0.96 mg·L-1. It indicated that the magnetic MWCNT was very stable in neutral aqueous solution.

Key words: magnetic multi-walled carbon nanotubes, nitroimidazoles, adsorption, kinetics, thermodynamics