Comparison for Cu(Ⅱ) and Cr(Ⅵ) adsorption behavior onto chitosan hydrogel beads

doi:10.16085/j.issn.1000-6613.2017.02.043

Abstract

Abstract: To facilitate the separation of chitosan powder after adsorption process,we adopted the sol-gel and freeze-drying method for the synthesis of millimeter-scale chitosan hydrogel beads(2.8 to 3mm),and further revealed the different adsorption behavior for Cu(Ⅱ) and Cr(Ⅵ) ions. Results showed that the optimum pH value for the adsorption of Cr(Ⅵ) and Cu(Ⅱ) ions was 3.0 and 5.5,respectively;The adsorption equilibrium achieved in 2h for Cr(Ⅵ) and 25h for Cu(Ⅱ) ions;The adsorption process for Cu(Ⅱ) ions was spontaneous and endothermic reactions with the increase of entropy. In a contrary,the adsorption process for Cr(Ⅵ) ions was spontaneous and exothermic reactions with the decrease of entropy;Desorption efficiency for Cu(II)-loaded CHBs(Cu-CHBs) was relatively low,while the desorption of Cr(Ⅵ)-loaded CHBs(Cr-CHBs) was conducted easily. Additionally,based on the results of FTIR and five models,including Langmuir isotherm,Freundlich isotherm,pseudo-first order kinetics,pseudo-second order kinetics,and intra-particle diffusion model. the adsorption process onto CHBs was monolayer chemisorptions for Cu(Ⅱ) ions and adsorption-reduction process for Cr(Ⅵ) ions mainly including monolayer chemisorptions together with multilayer physisorptions. The maximal adsorption capacities for Cu(Ⅱ) ions and Cr(Ⅵ) ions were 155.67mg/g and 185.08mg/g,respectively. This indicates that freeze-drying medthod enhanced adsorption capacity of CHBs are promising to solve the separation of chitosan powders.

Key words: chitosan hydrogel beads(CHBs), freeze-drying, Cu(Ⅱ) and Cr(Ⅵ) ions, adsorption, reduction, kinetic modeling

摘要： 为使壳聚糖粉末吸附后易于固液分离，采用溶胶-凝胶-冷冻干燥法制备毫米级（2.8~3mm）壳聚糖凝胶球，比较了Cu（Ⅱ）和Cr（Ⅵ）吸附行为。结果表明，壳聚糖凝胶球对Cu（Ⅱ）和Cr（Ⅵ）吸附行为不同：Cu（Ⅱ）和Cr（Ⅵ）最佳吸附pH分别为5.5和3.0；达到吸附平衡Cu（Ⅱ）和Cr（Ⅵ）分别需要25h和2h；Cu（Ⅱ）的吸附反应是自发、吸热、熵增过程，而Cr（Ⅵ）吸附反应为自发、放热、熵减过程；吸附Cu（Ⅱ）后的壳聚糖凝胶球不易脱附，而吸附Cr（Ⅵ）后凝胶球脱附率相对较高。借助红外表征及Langmuir、Freundlich等温模型、拟一级、拟二级动力学、颗粒内扩散模型对吸附过程拟合表明，Cu（Ⅱ）吸附机理为单层化学吸附，而Cr（Ⅵ）是单层化学吸附与多层物理吸附共同作用的吸附-还原过程。壳聚糖凝胶球对Cu（Ⅱ）和Cr（Ⅵ）的最大吸附量分别为155.67mg/g和185.08mg/g，说明冷冻干燥法可以强化壳聚糖的吸附量，同时毫米级的壳聚糖凝胶球改善了壳聚糖粉体吸附剂难分离的问题。

关键词: 壳聚糖凝胶球, 冷冻干燥, Cu (Ⅱ)和Cr (Ⅵ), 吸附, 还原, 动力学模型

CLC Number:

X703

ZHANG Yizhong, LIU Shan, LIU Zhiwen, WU Wencheng, DENG Dongyang, JU Yongming. Comparison for Cu(Ⅱ) and Cr(Ⅵ) adsorption behavior onto chitosan hydrogel beads[J]. Chemical Industry and Engineering Progree, 2017, 36(02): 712-719.

张艺钟, 刘珊, 刘志文, 吴文成, 邓东阳, 鞠勇明. 壳聚糖凝胶球对Cu(Ⅱ)和Cr(Ⅵ)吸附行为的对比[J]. 化工进展, 2017, 36(02): 712-719.

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