超快水传输石墨烯正渗透膜的分离机制研究

In recent years, forward osmosis has attracted growing attention in desalination and power generation from the mixing of fresh water and seawater in estuaries. The application of this technology, however, is limited due to the low water flux of forward osmosis membrane. Internal concentration polarization occurring in bulky support layers of membranes has been one of the most common and unavoidable phenomena in osmotically driven membrane processes, which accounts for the reduction of the water flux. That the active layer of the membrane is too thick is another major cause of flux reduction. On the advent of large scale monolayer graphene film and the precise technique for making pores, graphene, currently the world's thinnest and strongest material, might be used to prepare semipermeable membrane. Owing to its ultra-high strength, when large scale graphene is used as forward osmosis membrane, the use of support layer can be greatly reduced, or even unnecessary when the external pressure is not artificially applied on the system. As a result, the internal concentration polarization can be markedly reduced, even be removed. Besides, the mass transfer resistance of the membrane will be decreased significantly due to the ultrathin feature of graphene. In this program, functional graphene will be used as forward osmosis membrane. Density function theory, molecular dynamics simulations and experimental methods will be applied on various forward osmosis systems to study the interactions between the graphene membrane and the substances in the solutions, and to analyze the effects of the structural and environmental factors on the properties of the membrane. Then the relationship between the interactions in these systems and the properties of the membrane can be built. Finally, we try to disclose the separation mechanism of graphene forward osmosis membrane. The prospective results of the project can be provided as an analysis reference for preparing forward osmosis membrane with lower internal concentration polarization, lower mass transfer resistance and higher water flux.

近年来，正渗透技术在利用河流入海口处的渗透能发电和海水淡化方面受到广泛关注，然而，正渗透膜水通量低，严重地制约了该技术的应用。在膜支撑层内产生的内浓差极化现象和截留层过厚是水通量低的主要原因。石墨烯是目前发现的最薄和强度最高的材料。大面积石墨烯的问世以及精密的制孔技术使将石墨烯制备成半透膜成为可能。如果将石墨烯用作正渗透膜，其超高的强度可以极大地减少支撑层的使用，甚至在无外加压力的条件下，可无需支撑层，从而大幅度降低甚至消除内浓差极化。此外，其超薄的特性将使膜对水的传质阻力大大降低。本项目拟选用功能化石墨烯作为正渗透膜，采用密度泛函理论、分子动力学模拟以及实验方法，研究膜与溶液中各物质间的作用形式，明确各变量对膜分离性能的影响规律，建立物质间的作用形式与体系性能间的关系，进而揭示膜对溶液中水分子和盐离子的分离机制，为制备低内浓差极化、低传质阻力和高通量的正渗透膜提供理论参考。

近年来，正渗透技术在利用河流入海口处的渗透能发电方面备受关注，然而，正渗透膜水通量低，严重地制约了该技术的应用。本项目通过研究溶液的微观结构，膜与溶液中各物质的作用形式，各变量与膜性能的关系，膜对水分子和盐离子的分离机制等方面，发现超薄的石墨烯膜不但具有高的力学强度，而且具有高水通量和盐截留率，解决了目前正渗透膜内浓差极化现象严重的问题，也解决了不能同时改善正渗透膜水通量、盐截留率和机械强度的难题。此外本项目研究表明由于石墨烯膜的厚度极薄，远远低于传统正渗透膜的厚度，导致其传质机理与传统正渗透膜的差异显著，本项目为制备低内浓差极化、低传质阻力和高通量的正渗透膜提了供理论依据，对于高效利用渗透能资源具有一定的意义。