用于贵金属回收的高性能壳聚糖纳米纤维膜的热致相分离法制备

Chitosan nanofiber membranes (CNMs) have outstanding adsorption properties and can be used to recover precious metals effectively from wastewaters. However, the preparation of CNMs and their application are limited by the difficult-to-scale-up electrospinning technology which also results in poor membrane mechanical property due to the solvent such as acetic acid used. In this work, thermal-induced phase separation (TIPS) method will be adopted to prepare the CNMs on the basis that raising temperature will induce the aggregation of polymer chains to form naturally nanofibers from the homogenous chitosan solution using alkali/urea as the solvent. This will be a far more convenient and effective way to obtain CNMs. Detailed implementations are as follows: (1) homogenous solution of chitosan will be prepared by directly dissolving chitosan at low temperature in alkali/urea aqueous solution and then phase separation will be induced by raising the temperature to construct the nanofibrous architecture. By doing so, CNMs with high mechanical strength and porosity will be expected. The influencing factors on nanofiber size, membrane pore size and porosity will be fully explored. (2) By introducing sulfuric groups on the chitosan chain, chemical modified CNMs (S-CNMs) will be obtained and their selectivity to Au (III) and Pt (IV) ions will be promoted. (3) Membrane chromatography composed of layered S-CNMs will be fabricated and its performance will be studied to recover precious metal ions at low concentrations from wastewaters by dynamic adsorption. This project will provide a new pathway and strategy to prepare and use CNMs more efficiently. It will also provide better theoretical insight and experimental support to explore the full potential of CNMs chromatography for the recovery of low concentration precious metals.

壳聚糖纳米纤维膜具有优异的吸附分离性能，可用来高效回收贵金属。然而目前只能通过难以放大应用的静电纺丝方法制备，且由于诸如醋酸等溶剂的使用导致膜的力学性能较差，制约膜的推广应用。本课题拟采用更简便、快捷、有效的热致相分离法，利用低温下壳聚糖溶解于碱/尿素的均相溶液，通过升温得到高孔隙率高强度的壳聚糖纳米纤维膜，用于贵金属的吸附回收。具体内容包括：（1）采用碱/尿素水溶液为溶剂，低温下制备壳聚糖均相溶液，升温使其相分离，得到具有天然纳米纤维结构的多孔纤维膜，研究控制纤维直径、孔径和孔隙率的因素；（2）将所得纳米纤维膜进行表面接枝，引入含硫基团，用于低浓度金、铂离子的回收，提高吸附选择性；（3）以堆膜的形式制备膜色谱，研究其对低浓度贵金属离子的动态吸附行为。本研究将为壳聚糖纳米纤维膜的制备和高效利用提供新的方法和思路；为壳聚糖纳米纤维膜色谱对贵金属离子回收的实际应用提供理论与实验依据。

壳聚糖纳米纤维膜具有优异的吸附分离性能，可用来高效回收贵金属。然而目前只能通过静电纺丝方法制备，且由于诸如醋酸等溶剂的使用导致膜的力学性能较差，制约膜的推广应用。本项目以碱/尿素水溶液体系为溶剂，低温下溶解壳聚糖得到均相溶液，通过升温使溶液发生热致相分离，得到壳聚糖纳米纤维膜，为壳聚糖纳米纤维膜的制备和高效利用提供新的方法和思路。本项目主要开展了以下四方面的研究工作：1）通过控制碱/尿素/水的比例，筛选出合适的壳聚糖溶剂，通过控制冷冻温度和冷冻时间，最终得到了壳聚糖的均相溶液。进一步研究不同温度下壳聚糖溶液的热稳定性，得到了壳聚糖溶液的凝胶化过程。2）通过选择不同的热处理方式，精细调控膜材料的结构。利用质量分数为4%的溶液，以40℃的80%的乙醇为凝固浴，制备出具有较好纳米纤维结构的壳聚糖膜材料。3）以铀离子为研究目标，开展吸附实验研究。壳聚糖纳米纤维膜对铀吸附量为114.66 mg/g，纳米纤维膜三维纤维状网络结构使得铀离子可以很容易进入样品的内部，加速了扩散速率，提高了吸附容量。拟二级动力学模型更好地描述了铀的吸附动力学模型，铀的吸附过程主要受化学吸附的控制，相互连接的网络结构加速了吸附过程。4）通过XPS分析手段研究壳聚糖分子中不同元素特征峰在吸附前后的变化，分析其与配合物铀离子相互作用的官能团，考察了壳聚糖纳米纤维膜吸附铀离子的机理。氨基和羟基同时参与了吸附反应，铀的吸附机理可归结为与胺基的螯合反应和与羟基的配位作用。总之，通过本项目的研究，探索了热致相分离的方法制备壳聚糖纳米纤维膜的可行性和应用性，为壳聚糖纳米纤维膜对铀离子回收的实际应用提供理论与实验依据。