果胶吸附重金属的作用机理及与分子结构间的关系研究

Heavy metal pollution damages the health of human being. It is meaningful to develop excellent biosorbents for heavy metal removal. Many studies have shown that pectin can strongly adsorb heavy metals. However, the effect of pectin structure on its adsorptive property remains unclear. The mechanism of adsorption of heavy metal by pectin is inconclusive. In this study, kinds of methods will be used to prepare pectins with different structures, which will be further characterized by modern instrumental analysis combing traditional chemical methods. After that, Pb2+ will be used as a model heavy metal. The interaction between pectin and Pb2+ will be studied by molecular simulation using sofewares such as Hyperchem. Then experiments of adsorbing Pb2+ by pectin will be carried out. The adsorption capacities, isotherms, kinetics, and thermodynamic parameters of pectin will be investigated. Rate equation, activation energy, adsorption equilibrium constant, free energy, entropy, changes of electric potential and pH, as well as changes of functional groups and morphological structure before and after adsorption will be determined. The effect of molecular structure on adsorption properties of pectin will be analyzed using kinds of statistical analysis, and the relationship between structure and adsorption properties can be established. Combing with the results of molecular simulation, the adsorption mechanism will be deduced. This study can provide theoretical reference for elaborating the mechanism of heavy metals adsorbed by pectin, and offer an academic support for preparing excellent pectin biosorbent using goal-directed modification.

重金属污染危害人体健康，研究对重金属有良好吸附性能的生物吸附剂对解决该问题具有重要意义。众多研究表明果胶具有优良的重金属吸附性能。然而果胶分子结构对其吸附性能的影响尚不明晰，果胶吸附重金属的作用机制也尚无定论。本项目拟采用多种手段制备具有不同分子结构的果胶，采用现代仪器分析结合传统化学表征果胶分子结构。以Pb2+为重金属模型，采用Hyperchem等软件进行分子模拟，预测果胶和Pb2+间的相互作用。进行果胶吸附Pb2+实验，考察果胶的吸附容量、吸附等温方程、吸附动力学和热力学特性，测定速率方程、活化能、吸附平衡常数、pH和电位变化、以及吸附前后果胶官能团和形貌的变化等。采用多种数理统计分析果胶结构对吸附性能的影响规律，建立分子结构与吸附机理间的相关性。结合分子模拟结果，推导果胶的吸附机理。本项目为阐述果胶吸附重金属的作用机理提供理论参考，为针对性地修饰果胶，制备优质果胶吸附剂提供理论支持。

众多研究表明果胶具有优良的重金属吸附性能，然而果胶分子结构对其吸附性能的影响尚不明晰，果胶吸附重金属的作用机制也尚无定论。本项目以Pb2+为重金属模型，分析了果胶结构对Pb2+吸附的影响，表明果胶对Pb2+的吸附能力主要受果胶的酯化度，分子量和酰胺化度分子结构的影响，其与酯化度和分子量呈负相关，与酰胺化度呈正相关。果胶吸附Pb2+的过程主要受pH，温度，吸附时间和Pb2+溶液初始浓度的影响。采用吸附动力学模拟了果胶对Pb2+的吸附过程，表明吸附过程符合准二级动力学方程，吸附速率受化学吸附控制。结合果胶对Pb2+吸附前后红外光谱图、pH值，Zeta电位以及X射线光电子能谱的变化探究了果胶对Pb2+的吸附机制，表明吸附过程主要是羧基和氨基参与了反应，Pb2+与H+之间存在离子交换，与酰胺基团存在螯合作用。在上述基础上,本项目还制备了乙二胺改性果胶磁性微球和果胶/聚间苯二胺复合微球两种果胶基吸附剂，采用粒子扩散模型和吸附等温线模型模拟了果胶基吸附剂对Pb2+的吸附过程，表明颗粒内扩散是吸收速率的决定性步骤，Langmuir模型可以较好的拟合实验结果，表明吸附是单分子层的。解吸和再生实验表明果胶基微球具有良好的可循环利用性。这些结果表明果胶基吸附剂不仅提高了果胶对Pb2+的吸附能力，也解决了果胶吸附Pb2+后无法分离以及再生循环利用的问题。本项目为阐述果胶吸附重金属的作用机理提供理论参考，为针对性地修饰果胶制备优质果胶吸附剂提供理论支持。