电解质环境中陶瓷纳滤膜对染料的截留机理研究

Ceramic nanofiltration (NF) membranes show great prospect in the purification of dyes and salts from printing and dyeing wastewater streams. However, there are key challenges in accurately describing the purification processes at various operational conditions, owing to the complex coupling interaction between microporous membranes and multi-components wastewater. This proposal is devoted to investigate the transport behaviors of water and micromolecular dyes in nanopores, and the performance of ceramic NF membrane to treat high-temperature, electrolyte-contained wastewater. By performing experimental measurements and molecular dynamics simulations, we will investigate the variation of water properties before and after entering the nanopores and the water permeability of the ceramic membranes at various operating conditions. In addition, the effects of concentration gradient and pressure gradient on water permeability and dyes rejection will be comprehensively studied based on non-equilibrium thermodynamics, and compared with those obtained from experimental measurements, to obtain the relation among NF performance, the structure of nanopores, solution properties and operating conditions. Furthermore, the effects of several key factors on the water peameability and the solute rejections of NF membrane will be investigated for dyes purification from high-temperature electrolyte-contained wastewater, including membrane surface properties, effective solute size, solution properties and ionic charge effects. The achievements in this work will contribute to perfecting porous membrane transport theory, integrating seamlessly the oriented design of NF membrane material and the optimization of operating conditions, and accelerating the design and development of NF technology for the treatment of dye wastewater.

基于陶瓷纳滤膜的印染废水处理技术具有良好的应用前景。然而体系中膜微结构-溶液特性-操作参数之间的相互作用非常复杂，使得现有的纳滤分离机理无法很好解释印染废水的截留过程。项目围绕陶瓷纳滤膜微结构对水/小分子染料的限域传递行为及高温电解质存在对截留性能的影响展开研究。通过实验测量与分子动力学模拟结合，研究水进入陶瓷纳米孔道中的性质变化，以及在不同操作和膜结构参数下的传递性能；利用非平衡热力学方程，分析水透过通量和染料截留率与浓度/压力差的关系，并与实验测量结果对比，获得膜结构特征和染料截留性能的关系；研究高温电解质环境下膜表面性质、溶质有效尺寸、溶液性质以及离子的电荷效应等对纳滤过程的影响，明确电解质存在对陶瓷纳滤膜截留染料的影响。通过本项目的研究，期望进一步改善膜结构特性和流体性质耦合作用下的纳滤传递机理，实现膜材料定向设计和操作条件优化的匹配，加快陶瓷纳滤膜处理印染废水技术的开发。

以电解质环境下，纳滤膜对染料的分离机理为研究目标，研究膜材料微结构及表面性质的精密调控方法，并考察其在染料/电解质分离中的应用。首先考察了陶瓷膜微结构对活性染料截留性能的影响，结果证实随着膜孔径的减小，活性染料的截留率也随之增加。其次，考察了膜表面性质对电解质的分离性能影响，以孔径5 nm的管式Al2O3膜为基膜，利用PDA和PEI的共聚物包裹住陶瓷膜分离层表面的Al2O3颗粒，当PEI浓度2 g/L，PDA/PEI沉积时间2 h，制得的膜表面电荷强度40 mV，截留分子量为220 Da的PDA/PEI/ Al2O3纳滤膜。在高温下测试复合Al2O3纳滤膜对MgCl2和MgSO4的截留性能，料液温度从室温逐渐升高至70 °C，复合Al2O3纳滤膜对MgCl2和MgSO4的截留性能呈下降趋势，MgSO4的截留率从84%下降到59%，对MgCl2的截留率从93%下降到71%。.在此基础上，提出了面向含活性染料印染废水分离的陶瓷纳滤膜的制备方法，通过考察溶胶与底膜的匹配性，制得截留分子量为816 Da的ZrO2纳滤膜，采用超声辅助溶胶-凝胶法制得截留分子量为3.9 kDa，纯水渗透率100 L m-2 h-1 bar-1的CeO2纳滤膜。考察了温度对电解质环境中的活性染料截留性能影响，在60 ℃下，CeO2膜对直接红80的截留率稳定在99%，渗透通量为194 L m-2 h-1，对刚果红的截留率稳定在95.5%，渗透通量为192 L m-2 h-1，对电解质的截留率低于2%。ZrO2纳滤膜对活性蓝KN-R截留率稳定在90%以上，电解质截留率低于4%。.由于阳离子染料分子量偏小且其分散性更好，而陶瓷膜表面电荷偏弱，本身具备的电荷效应不足以排斥截留阳离子。因此以截留分子量2300 Da的ZrO2膜为基膜，采用氨基硅烷偶联剂化学接枝增强膜表面的正电性，同时ZrO2膜截留分子量减小至1750 Da。室温下，改性后的ZrO2膜对单一亚甲基蓝的截留率78.5%，远高于未改性ZrO2膜的截留率15%。加入NaCl后，当料液温度从室温升高至60 ℃，改性后的ZrO2膜渗透通量从12.2 升高至21.4 L m-2 h-1，改性膜对亚甲基蓝的截留率从56%降低33.5%，对NaCl的截留率始终保持在10%，为阳离子染料的分离提供了指导。