羧化二氧化钛/海藻酸钙杂化水凝胶纳滤膜构建及截留染料性能与机理研究

For the fouling problem of traditional membranes resulted from its hydrophobicity, in this project, a free-standing carboxylated titanium dioxide/calcium alginate (TiO2-COOH/CaAlg) hybrid hydrogel nanofiltration membrane was fabricated through ionic cross-linking method using sodium alginate as membrane substrate, carboxylated titanium dioxide (TiO2-COOH) nanoparticles as reinforcing agent and polyethylene glycol (PEG) as pore-forming agent for removal of dyes. Based on the potentiation of nano-inorganic particles and the cross-linking interaction of Ca2+ ion on the –COOH of TiO2-COOH nanoparticles and alginates, the mechanical strength of hydrogel membrane was enhanced. The problems of hydrogel membrane with poor stability, high swelling degree and deform pores were solved. The assembly and entanglement between TiO2-COOH and alginate was discussed. The influences of molecular weight and dosage of PEG on the membrane pore structure were investigated. The pore structure and charges of membranes were controlled. The structure-function relationships between the structure of hydrogel nanofiltration membrane and the rejection ratio of dyes were investigated. The action mechanisms of TiO2-COOH and CaAlg on the removal of dyes were discussed. The rejection mechanism and anti-fouling mechanism of hydrogel nanofiltration membrane for dyes were revealed. This project realized the separation of blended dyes and provided a new idea for the fabrication of a green separation membrane, which had the good anti-fouling property and filtration performance.

针对传统疏水膜易污染的问题，本项目以海藻酸钠(NaAlg)为成膜基材，纳米羧化二氧化钛(TiO2-COOH)为增强剂，聚乙二醇(PEG)为致孔剂，通过离子交联制备自支撑羧化二氧化钛/海藻酸钙(TiO2-COOH/CaAlg)杂化水凝胶纳滤膜去除染料。利用无机纳米粒子的增强作用和钙离子对羧化二氧化钛上-COOH与海藻酸钠上-COOH的协同交联作用，提高水凝胶膜的机械强度，解决海藻酸钙水凝胶过滤膜稳定性差、易溶胀、膜孔易变形问题。探究TiO2-COOH与海藻酸钠的组装及相互缠绕作用，考察PEG分子量及用量对膜孔结构的影响，实现水凝胶纳滤膜膜孔结构和膜体电荷的可控；研究水凝胶纳滤膜结构与截留染料性能的构效关系，探讨羧化二氧化钛与海藻酸钙在截留染料中的作用机制，揭示水凝胶纳滤膜对染料的截留机理及抗染料污染机理，实现混合染料的分离，为开发绿色环保、高抗污染、具有良好过滤性能的新型分离膜提供思路。

印染废水因有机物含量高、成分复杂、色度深、水质变化大而成为国内外公认的难处理废水之一。纳滤膜分离技术能从印染废水中回收有用的染料和盐类，处理后的水可直接回用。但是传统纳滤膜孔径小、结构致密，回收的染料盐度高，高离子强度影响染料的稳定性，而且疏水的膜材料易受有机物的污染。针对此问题，本项目开发一种具有优良抗污染性能的疏松纳滤膜用于染料脱盐。. 项目中以海藻酸钠（NaAlg）为成膜基材，海藻酸钠是一种从褐藻中提取的线型嵌段共聚物，价格低廉，无毒，可以通过Ca2+交联成水凝胶膜，但是纯海藻酸钙水凝胶过滤膜机械性能差，在无机盐溶液中易溶胀。因此，在铸膜液中添加羧化二氧化钛（TiO2-COOH）纳米粒子作为增强剂，利用羧化二氧化钛的增强作用和钙离子对TiO2-COOH上羧基与NaAlg上羧基的协同交联作用，提高水凝胶膜的机械性能，降低膜的溶胀度。同时利用羧化二氧化钛羧基之间的电荷排斥作用，以及羧基的亲水性，提高TiO2-COOH在水凝胶膜中的分散性。项目中采用红外光谱、扫描电镜和能量色散X射线光谱对水凝胶膜的化学组成和形貌结构进行表征，测试水凝胶膜的孔径分析、zeta电位、力学性能、溶胀性能、抗污染性以及染料截留和染料脱盐性能。获得羧化二氧化钛含量与水凝胶膜结构和性能之间的关系，实现水凝胶纳滤膜的可控制备，揭示对染料和无机盐的截留机理。制备的水凝胶膜对考马斯亮蓝G250(Mw 858.1 Da)、直接黑38(Mw 781.7 Da)、刚果红(Mw 696.7 Da)和酸性红66(Mw 556.5 Da)四种阴离子染料的截留率分别为98.4%、96.8%、95.9%和90.2%，对无机盐的截留率为RNaCl (9.0%) < RMgCl2 (12.3%) < RNa2SO4 (15.6%) < RMgSO4 (16.1%)，实现了染料与无机盐的高效分离。