碳纳米复合膜微观结构与其抗污染性能的构-效关系研究

Carbonaceous nanocomposite membranes (CNM) are a novel type of water treatment membranes that have drawn broad attentions around the world. These nanocomposite membranes can possess greater removal efficiencies for contaminants and lower energy consumption than traditional membranes, due to the integration of carbonaceous nanomaterials (e.g., carbon nanotube, graphene, and carbon nanofiber) into traditional membrane materials during the membrane fabrication processes. However, like existing membranes for water treatment, successful engineering applications of CNM are still dependent upon the possibility of overcoming the technical bottleneck of membrane fouling that ubiquitously exist during membrane water treatment. Therefore, the overarching goal of the proposed study is to investigate the fundamental relationship between the structural properties of nanocomposite membranes and their anti-fouling behaviors. The study will be conducted with three inter-related major tasks: preparation of CNM and determination of their nano-structures, assessment of the fouling potential of CNM and the fouling modes of different fouling materials, and molecular dynamic (MD) simulation of foulant transport at membrane-water interfaces. Specifically, we will first prepare representative types of CNM and then identify their nanostructures using comprehensive analytical approaches. Furthermore, the antifouling ability of these membranes will be determined under conditions commonly encountered during membrane water treatment; also, major foulants and their corresponding fouling modes will be identified using state-of-arts analytical methods. After the relationship between the nanostructure of CNM and their anti-fouling behavior is established, the experimentally determined structural properties of CNM and their fouling potentials will be used as the model inputs for MD simulation of the transport behaviors of membrane foulants inside membrane nanostructures. The modeling results will be compared to experimental results in order to reveal the underlying mechanisms of the structure-antifouling behavior relationship, from the perspective of interfacial sciences. The outcome of the study will provide useful scientific supports important to the advances of membrane water treatment technologies in China.

碳纳米复合膜是一种广受关注的新型水处理膜材料。通过复合功能碳纳米材料（如碳纳米管、石墨烯和纳米碳纤维）和传统膜材料，可制备出具有不同微观纳米结构的复合膜，提高膜过滤效果、降低过滤能耗。然而，类似于传统膜材料，碳纳米复合膜的工程应用也必须跨越膜污染这个技术瓶颈。因此，本项目试图从应用基础研究的角度，深入探究碳纳米复合膜微观结构与其抗膜污染性能间的构-效关系这个基本科学问题，并开展复合膜制备与微观结构表征、复合膜污染评价，及污染物在膜-水界面的分子动力学模拟三个方面研究。在深入认知复合膜微观纳米结构的基础上，系统考察典型膜污染物在模拟地表水条件下对不同结构复合膜的污染情况，分析并确定主要膜污染物及污染模式，进而在构-效关系实验研究基础上，利用分子动力学模型模拟污染物在碳纳米膜结构中的传质规律，揭示复合膜污染构-效关系的界面化学原理。本项目研究成果将为我国膜法水处理技术进步提供必要理论支持。

以碳纳米管、石墨烯为代表的碳纳米材料在新型膜法水处理技术领域得到了日益广泛的重视。然而，纳米复合膜材料微观结构与其抗膜污染性能之间的构效关系原理仍有待确定。针对该科学问题，本项目综合采用膜过滤实验与分子动力学模拟的研究手段，并结合各种分析表征技术，初步辨识了复合膜纳米材料自身结构与其堆积结构的区别，发现影响膜孔结构和膜抗污染性能的主要因素是纳米材料的堆积结构。同时，纳米复合膜的抗污染性能还受水体污染物与膜材料的界面作用影响，因此与纳米材料的表面特性、水体污染物性质和水化学条件紧密联系。其中，羧基化碳纳米材料能够通过形成较小的膜孔通道，降低孔缩作用对膜透水率的影响，并通过抑制界面憎水作用和pi-pi键作用，延缓不可逆有机膜污染。在膜污染物方面，与以往研究认识不同，发现多糖类污染物可以直接与碳材料表面发生较强的氢键或配位键，或与腐殖质或蛋白偶合，造成不可逆膜污染。在各种水化学因素中，Ca离子是关键，较低浓度的Ca离子就能够通过屏蔽碳材料表面电荷、与有机物形成复合配位体等形式，强化有机物去除，并形成可逆膜污染。上述研究发现为新型碳纳米复合膜的设计和应用提供了重要参考。