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随着现代社会工业化的高速发展,天然水中砷的含量迅速增加[1]。水中砷污染已成为全社会亟待解决的重要环境问题之一[2]。目前,常用的除砷方法主要有混凝沉淀法、离子交换法、膜分离法、吸附法[3-6]等。混凝沉淀法中预氧化过程会增加后续污水处理的问题[3];离子交换法须采用特殊材料,工艺流程较繁琐[4];膜分离法易出现膜污染等问题,该法适用于处理量相对较少的砷污染水[5]。因此,吸附法在处理效率高、操作简单和适用性强等方面的优势越来越受到人们的重视[6]。
多壁碳纳米管(CNTs)具有比表面积大、孔隙结构丰富、表面易于被修饰等特点,近年来在制备复合吸附材料方面已有诸多的应用[7]。IBRAHIM等[8]研究了深共熔溶剂(DESs)功能化CNTs对水中甲基橙的吸附性能;李德云等[9]在研究改性CNTs吸附水中亚甲基蓝过程时提到Cu/CuO改性CNTs对亚甲基蓝的吸附效果优于原始CNTs;杨爱丽等[10]在研究臭氧氧化改性CNTs对铀的吸附去除时提到,含氧量的增加会显著提高改性CNTs对铀的去除率。
目前,对水中砷去除的研究多集中在吸附剂的氧化改性以及对As(Ⅴ)的吸附去除上,对As(Ⅲ)的削减效果分析和去除机制等方面的研究相对较少[11]。本研究从活化CNTs管壁接枝点位、负载高活性基团的酰胺类材料的角度出发,采用强酸氧化和酰胺化等方法制备了酰胺化/氧化碳纳米管-聚苯胺(NMCNTs-PANI),并探究该复合材料对水中As(Ⅲ)的吸附性能。
酰胺化/氧化碳纳米管-聚苯胺吸附三价砷
Adsorption of As(Ⅲ) from aqueous solution by amidated/oxidized carbon nanotube-polyaniline
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摘要: 为探讨改性碳纳米管(CNTs)对砷的吸附特性,采用化学修饰对CNTs进行了改性。将CNTs先后进行氧化和酰胺化处理,并与聚苯胺反应,得到酰胺化/氧化碳纳米管-聚苯胺(NMCNTs-PANI),利用SEM观察、比表面积测定、含氧含氮官能团和分子结构分析对改性前后CNTs进行了表征;研究了NMCNTs-PANI在不同反应体系对As(Ⅲ)的吸附效果。结果表明:NMCNTs-PANI总孔容和平均孔径均有所增加;表面含氧含氮基团增加;初始pH对吸附量影响较显著;共存阴离子对吸附量影响可忽略不计;吸附过程符合准一级动力学和准二级动力学方程,证实该过程主要以化学吸附为主;吸附等温线符合Langmuir模型。NMCNTs-PANI通过表面吸附-化学诱导作用可较好地去除水中As(Ⅲ),是一种优良的含砷污染水的吸附剂。Abstract: To promote the As(Ⅲ) adsorption capacity of carbon nanotubes (CNTs), the modification of CNTs was conducted in this study. Firstly, CNTs were modified with oxidation and amidation, followed by reaction with polyaniline to obtain amidated/oxidized carbon nanotube-polyaniline (NMCNTs-PANI). Both the modified and pristine carbon nanotubes were observed by scanning electron microscope to compare their morphological differences. Their specific surface, functional groups and molecular structure were also determined. The adsorption behavior of As(Ⅲ) on NMCNTs-PANI was further studied. The results show that the total pore volume and average pore size of NMCNTs-PANI increased, as well as the surface oxygen and nitrogen-containing groups. The initial pH had significant effects on the adsorption capacity, while the coexisting anions had a negligible effect on As(Ⅲ) adsorption. The kinetic data fitted well with the pseudo-first-order and pseudo-second-order kinetic model, which demonstrated that chemical adsorption was the main mechanism. The adsorption isotherms of NMCNTs-PANI fitted well with the Langmuir model. The good performance on As(Ⅲ) removal by NMCNTs-PANI was completed through surface adsorption-chemical induction actions. The high As(Ⅲ) removal efficiency of the NMCNTs-PANI makes it to be an excellent adsorbent for arsenic-contaminated water treatment.
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Key words:
- trivalent arsenic /
- modified carbon nanotube /
- polyaniline(PANI) /
- adsorption
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表 1 CNTs原粉、NMCNTs-PANI和吸附后材料的物理性质
Table 1. Physical characteristics of CNTs, NMCNTs-PANI and post-adsorption composite
改性前后的材料 比表面积/(m2·g−1) 孔容/(cm3·g−1) 平均孔径/nm CNTs原粉 156.59 0.58 3.58 NMCNTs-PANI 134.97 0.99 13.84 吸附后材料 120.80 0.87 12.85 表 2 不同动力学模型拟合参数
Table 2. Fitting parameters for various kinetic models
qe,exp/(mg·g−1) 准一级动力学方程 准二级动力学方程 k1 qe,cal R2 k2 qe,cal R2 14.50 0.12 14.78 0.983 0.006 18.37 0.994 注:qe,exp和qe,cal依次为平衡吸附量实验值和拟合值。 表 3 不同吸附等温线主要拟合参数
Table 3. Main fitting parameters for various adsorption isotherms
Langmuir Freundlich qm/(mg·g−1) kL R2 kF n−1 R2 15.08 4.60 0.927 10.68 0.20 0.885 -
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