导电LSCF/PES复合多孔膜的可控制备及其在电场辅助条件下的离子脱除机理研究

Organic/Inorganic composite membrane can enhance the membrane mechanical properties, improve the thermal stability, optimize the membrane pore structure and distribution, adjust the hydrophilic/hydrophobic balance, increase membrane permeability and separation selectivity by introducing inorganic particles into organic network. PES is used as substrate of the composite microporous membrane, conductive lanthanum strontium cobalt iron (LSCF) nano-particles are used as inorganic filler and coupling agent as surface modification agent for the preparation of LSCF/PES composite membrane. Effect of polymer concentration, the content of LSCF, modification conditions on the pore structure and permeability of composite membrane are studied. Low voltage electric field is applied in the both sides of the conductive composite membrane. The relation among the conductive LSCF/PES composite microporous membrane, permeate solution and auxiliary electric field is studied. Effect of membrane pore structure, surface charge density, permeate concentration, ionic charge type, electric field direction and strength are studied to demonstrate the influence on migration in the process of ion penetration. On the basis of charged membrane separation model, the ion rejection mechanism will be revealed. The separation mechanism of composite membrane prepared by ion optimization of process parameters under the weak electric field are researched. With low energy consumption, significantly improvement of selectivity of the membrane, has important theoretical significance and practical value to reduce the processing cost of seawater desalination and ion containing waste water.

有机无机复合膜通过在有机网络中引入无机质点，可提高膜的机械性能和热稳定性、改善和修饰膜的孔结构和分布，并提高膜的渗透性能和分离选择性。以聚醚砜（PES）为复合膜基体、导电镧锶钴铁（LSCF）纳米粒子为无机填充剂、硅烷偶联剂为表面改性剂制备LSCF/PES复合多孔膜。研究聚合物浓度、LSCF含量及偶联剂改性条件等参数对复合膜孔结构和渗透选择性能的影响规律。通过施加低压直流电场，研究导电LSCF/PES复合多孔膜与渗透液及辅助电场间的协同作用。详细考察膜孔结构、表面电荷密度、渗透液浓度、离子荷电类型、电场方向及强度等参数对渗透过程中的离子迁移及截留的影响规律。在荷电膜分离模型的基础上，揭示复合多孔膜的离子截留机理。通过优化复合膜制备工艺参数和弱电场作用下的离子分离机理，在低能耗的条件下，实现分离膜的渗透选择性的显著提高，对于降低海水淡化及含离子废水的处理成本具有重要的理论意义和实际价值。

纳滤膜由于其分离选择性高、渗透通量大而得到了广泛的研究。其选择性高的主要原因是纳滤膜表面含有可电离的功能基团，对溶液中的离子产生静电排斥，从而在膜孔较为疏松的条件下具有较高的截留能力。本项目通过研究外加辅助电场对膜表面的电荷密度进行强化，在不降低膜渗透能力的条件下，提高膜的分离选择性。实验研究表明，使用正向外加电场时，外加辅助电场对膜孔较大且膜表面电荷密度较高的膜作用显著，可以显著提高膜的截留率。使用8V直流电压的条件下，膜的截留率可以提高三倍以上。而使用外加反向电场时，电场作用对膜的分离选择性有抑制作用。在此基础上我们利用荷电膜的特征探索了新型MXene以及新型单体进行界面聚合制备的复合膜，使得复合纳滤膜的分离选择性得到了显著提升。电场辅助纳滤过程不仅丰富了纳滤膜分离过程的分离机理，也提高了纳滤膜的分离选择性，对于膜法水处理具有极高的理论和实际价值。