UC Berkeley

In this thesis, the potential applications of typical nanoporous material (including Graphene Oxide (GO), Carbon Nanotube (CNT) and molybdenum disulfide (MoS_2)) in water and ion separation are systematically investigated. Different computational methods (including Molecular Dynamics (MD), Density functional theorem (DFT), Transport theorem in membrane) are introduced to study the mechanical and chemical properties of these materials; Depending on the corresponding experiments to be simulated, hundreds of models are built to explore properties in the process and compared with experimental results.

Several independent conclusions from different models are made and described in different chapters, whose main application is for desalination. Desalination is one of the most promising approaches to provide fresh water in the face of growing water demand. Currently, commercial reverse osmosis (RO) techniques still suffer from important drawbacks, including high energy consuming and serious fouling. In order for this method can be really used to solve the water challenges of this century, a step-change is needed in RO membrane technology. Because of significant advances in the field of nanotechnology and computational material and chemical science in the past decade, it is becoming possible to develop a new generation of RO membranes.

We show that all these nanoporous materials possess exceptional physical and mechanical properties, which allow for water passage while rejecting salt ions if it possessed nanometer-sized pores. By using computer simulations (Both DFT and MD) from the atomic scale to the engineering scale, we first investigated the relationship between the atomic structure of nanoporous material and its membrane properties in RO applications. Then we studied the thermodynamics, chemistry and mechanics of each material and

the water and salt surrounding it. Finally, we establish the system-level implications of promising membrane properties for desalination plants, which can act as an RO membrane with several orders of magnitude higher water permeability than traditional polymer membranes as long as the size of nanopores is well controlled.

Besides of desalination, in chapter 6, we also investigate diffusion and selectivity of carbon nanotube embedded in the cell membrane to $Na^+$ and $K^+$ ions, in order to find the minimum diameter for different ions to pass through, and compare with the so called biological selectivity filters. The present work is a systematic study of ion and water transport through CNT embedded in cell membrane.

Overall, our efforts on this issue are of importance for future simulation studies investigating water and ion conduction through nanoscopic channels. This dissertation might also prove useful in designing more efficient nanoscopic conduits for future experimental studies, and even highlights a path for the development of next-generation membranes for clean water production in the 21st century.