石墨烯垂直阵列膜的构建及其表面化学调控增强分离性能机理研究

As an emerging water treatment technology with many advantages, membrane separation technology has found important applications, for example, the efficient removal of refractory pollutants. However, current membranes always suffer the compromise between permeability and selectivity, which is a main technical bottleneck limiting their further development. The compromise can be theoretically alleviated by lowering interfacial friction, increasing pore channels, decreasing pore tortuosity and increasing surface charge density. Considering the atomically smooth surface and good electric conductivity of graphene which can be used to construct high-permeability and -selectivity nanochannels by coupling with electrochemistry, this project will develop a graphene-based vertically aligned membrane with high porosity and liner pore channels, and investigate the relationship between their structural characteristics and permeability. Additionally, this project will also investigate the separation performance of vertically aligned graphene membranes with various chemical groups towards various refractory pollutants and clarify the underlying separation mechanism, as well as explore the mechanism underlying electrochemistry-induced improved selectivity of vertically aligned graphene membranes. This project will provide theoretical and technical supports for the efficient removal of refractory pollutants and the development of high-performance membranes.

膜分离技术由于其诸多优点而成为一种新兴水处理技术，已在难降解污染物的高效去除等方面发挥着重要作用。目前，分离膜所具有的渗透性和选择性之间的矛盾关系是限制其进一步推广应用的主要技术瓶颈，理论上可通过降低界面摩擦力、增加水传输孔道数、降低孔道曲折率以及增加膜表面电荷密度等方面来缓解。石墨烯具有原子级光滑的表面和良好的导电性，可通过耦合电化学来构建具有高渗透速率的选择性纳米通道。鉴于此，本申请项目拟基于石墨烯，构建一种具有高孔隙率和直线形孔结构的垂直阵列纳滤膜，并考察其结构特性与膜渗透性之间的内在关系；考察不同化学官能团修饰的石墨烯垂直阵列膜对不同类型难降解污染物的分离性能，阐明其分离机理；探究电化学增强石墨烯垂直阵列膜选择性的机理。该项目的实施可为难降解污染物的高效去除和高性能分离膜的开发提供理论和技术支持。

石墨烯分离膜具有良好的选择性和透过性，具有潜在和广阔的应用前景。如何进一步提高其性能(如分离性能、机械强度、抗污染能力)以及污染后如何再生的问题仍然是限制其实际应用的瓶颈问题。鉴于此，本项目开展了以下研究：(1)制备了一种磺化石墨烯垂直阵列膜，具有垂直贯通的孔道结构，可以大幅度减小水传质阻力，其水通量是常见层状氧化石墨烯分离膜水通量的3~10倍。强电离磺酸根基团可以增加膜表面电荷密度，强化道南排斥效应，使得磺化石墨烯垂直阵列膜对离子的分离性能明显高于常见层状氧化石墨烯分离膜。(2)构建了一种新型的石墨烯分离膜，利用碳纳米管作为保护层把石墨烯分离层机械束缚在其与支承层之间，从而提高其结构稳定性。利用碳纳米管层的逐级预截留和预吸附减少到达石墨烯分离层的污染物的量，进而显著提高石墨烯分离膜的抗污染能力。在同样条件下，具有碳纳米管保护层的石墨烯分离膜的归一化通量(0.82-0.92)要明显高于无碳纳米管保护层的石墨烯分离膜的归一化通量(0.42-0.53)。(3)利用电化学引发的静电排斥效应和氧化降解作用，并在反冲洗辅助下强化污染物从膜上的去除，从而实现其高效再生。当给污染后的石墨烯分离膜-0.9 V vs. SCE的阴极电势时，其可以通过反冲洗再生，通量恢复率可达~96%。把石墨烯分离膜作为阳极，利用2.5 V的槽压原位清洗20分钟后，石墨烯分离膜的纯水透过速率可以从污染后的<3.0 L m-2 h-1 bar-1恢复到>9.2 L m-2 h-1 bar-1。该项目的实施可推动石墨烯分离膜的实际应用，并提供相关理论和技术支持。