Cr(Ⅵ) Removal from Water with Polyethyleneimine-Modified Magnetic Chitosan

Rui YUE; Hong-cheng CHEN; Yu-ming HUANG; Ping FENG

doi:10.13718/j.cnki.xdzk.2019.07.017

Magnetic chitosan (MCTS) nanoparticles were synthesized with a one-pot solvothermal method and then modified by polyethylenimide (PEI) to prepare magnetic PEI-MCTS for removing Cr(Ⅵ). The effects of the initial solution pH, PEI content, adsorbent dosage, ionic strength and adsorption time were systematically studied. The results showed that an acid condition favored Cr (Ⅵ) adsorption. Cr(Ⅵ) adsorption by PEI-MCTS could be described with the Langmuir model and the pseudo-second-order model, and the maximum adsorption capacity was 193. 57 mg/g. In conclusion, the PEI-MCTS composites developed in this study are stable and reusable and, therefore, are recommended for Cr(Ⅵ) removal.

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铬及其化合物是重要的化工原料，广泛用于制革、电镀和颜料生产等.由于其具有致癌、致突变性质，这些工业排放的含铬Cr(Ⅵ)废液对环境和人类健康产生了严重威胁.为此，建立了多种技术方法用于去除Cr(Ⅵ)，如化学还原、离子交换和吸附法^[1-3]等.吸附法具有简单、易操作、成本低等优点，受到广泛关注.目前，基于微生物细胞^[4]、壳聚糖^[5]和农业副产物^[6]的生物吸附剂已用于Cr(Ⅵ)去除，具有成本低、无毒和来源丰富等优点.壳聚糖(CTS)是一种很有潜力的生物吸附剂，因为CTS易生物降解，而且其分子链中含有丰富的功能基团(—NH₂和—OH)等^[7].然而，未修饰的CTS难以从废水中分离出来，因此，多种磁性CTS吸附剂应运而生，已用于去除Cr(Ⅵ)^[7-8].然而在多数情况下，这些MCTS合成过程复杂，至少包括三步：首先合成磁性Fe₃O₄纳米颗粒，其次对其表面进行修饰，最后再将CTS嫁接在其表面.而且，已经报道的MCTS对Cr(Ⅵ)的吸附容量有限，如Hu等^[9]用乙二胺修饰的交联CTS对Cr(Ⅵ)的最大吸附容量仅为51.81 mg/g，为改善其吸附容量，王文凤等通过一步热溶剂法简单快速地合成了200 nm左右的MCTS微球，该微球对Cu(Ⅱ)吸附容量可达129.6 mg/g，而且吸附在10 min内达到平衡^[10].聚乙烯亚胺(PEI)是具有支链结构的阳离子聚电解质，其分子链上富含大量氨基，在较宽的pH值范围内都可以质子化带正电荷，可与带负电荷的阴离子通过静电作用实现去除.本研究先通过一步热溶剂法合成纳米颗粒MCTS，再通过交联法将PEI修饰在其表面，从而进一步提高吸附剂对Cr(Ⅵ)的吸附能力.

1. 实验方法与材料

1.1. 仪器及试剂

所有化学试剂的使用都没有经过进一步的纯化.脱乙酰度为91.1%的CTS(平均分子量为3.0×10⁵ g/mol)购自南通兴成生物制品厂.聚乙烯亚胺(PEI)(Mw，18000)购自上海Sigma-Aldrich有限公司. NaAc购买于科龙化学试剂有限公司.其他试剂，如乙二醇、丙酮、乙醇等均购自重庆化学试剂有限公司. UV-2450型紫外-可见分光光度计(岛津公司，苏州)；ZHWY-2102C型恒温振荡培养箱(上海智城仪器制造有限公司，上海).

1.2. PEI-MCTS的制备

将2 g FeCl₃·6H₂O溶于60 mL乙二醇中，加入4 g NaAc后，磁力搅拌使其完全溶解后，再加入CTS 4 g，并搅拌12 h，之后将混合溶液转移至反应釜中加热到200 ℃，并在该温度下反应8 h后冷却至室温得到黑色材料，依次用去离子水和乙醇洗3遍，分离后的材料在60 ℃下干燥即得MCTS.为制备PEI-MCTS，将0.3 g MCTS加入到50 mL PEI溶液中，超声20 min后，在室温和300 r/min机械搅拌条件下逐滴加入25 mL体积分数为5%的戊二醛水溶液，继续搅拌30 min后，用超纯水冲洗材料直至上清液清澈，固体材料在50 ℃下干燥，即得PEI-MCTS.

1.3. 吸附实验

在一系列100 mL锥形瓶中，分别加入50 mL Cr(Ⅵ)溶液和5 mg吸附剂，置于摇床中以180 r/min转速摇一段吋间，吸附完成后，磁性分离，取上清液测定Cr(Ⅵ)的质量浓度.每一组实验均设置平行样，所有结果取两个平行样的平均值. Cr(Vl)溶液初始pH值用稀NaOH溶液或稀HCl溶液调节.上清液中Cr(Ⅵ)质量浓度采用二苯碳酰二肼分光光度法测定.计算吸附容量：

式中，q_e为吸附容量(mg/g)；C_o和C_e分别为Cr(Ⅵ)的初始质量浓度和平衡质量浓度(mg/L)；V(mL)是Cr(Ⅵ)溶液的体积；m(mg)是PEI-MCTS的质量(g).

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Cr(Ⅵ) Removal from Water with Polyethyleneimine-Modified Magnetic Chitosan

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Cr(Ⅵ) Removal from Water with Polyethyleneimine-Modified Magnetic Chitosan

Corresponding author: Yu-ming HUANG ;

Corresponding authors: Ping FENG