PhD Defense by Haiping Gao

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School of Civil and Environmental Engineering


Ph.D. Thesis Defense Announcement

Membrane-based technologies for clean energy generation: Advanced membranes development



Haiping Gao



Dr. Yongsheng Chen (CEE)


Committee Members:

Dr. John Crittenden (CEE), Dr. Ching-Hua Huang (CEE), Dr. Xing Xie (CEE), Dr. Shuman Xia (ME), Dr. Zhaohui Tong (University of Florida)


Date & Time: Monday, August 5, 2019 – 2:00pm

Location: Capstone Building, Room 338 – 828 West Peachtree Street


Complete announcement, with abstract, is attached

Salinity gradients have emerged as a potential sustainable source for renewable energy. The free energy released from mixing two solutions of different salinities can be harvested by controlled mass transport through membrane - based technologies, reverse electrodialysis (RED) and pressure retarded osmosis (PRO). Salinity gradient power (SGP) has made remarkable progress in the past decade. However, it remains challenging to realize the practical application feasibility of the RED and PRO technologies. Since membranes are the heart of these technologies, it is therefore critical to develop membranes with highly anticipated properties for advancement of SGP as economically attractive sustainable energy. 
This study primarily focused on developing high - performance membranes for efficiently capturing SGP in RED and PRO systems. Additionally, a better understanding on the correlation of leading membrane properties, including permselectivity and ionic conductivity, with the underlying characteristics of the membrane was investigated through statistical simulation and experimental validation. The modeling and simulation results can potentially offer fine - tuning approaches for ion exchange membranes (IEMs) - based electrochemical systems like RED but not limited to RED system.
With respect to the RED system, monovalent - ion selective anion exchange membranes (AEMs) were fabricated by layer-by-layer (LBL) modification. The optimized membranes exhibited simultaneously enhanced monovalent-ion selectivity and anti-fouling potential due to the formation of a negatively charged surface layer. Consequently, higher energy efficiency and power density were achieved with monovalent-ion selective membrane than that achieved with standard commercial AEM. In terms of the PRO system, the freestanding hybrid thin membranes were developed using two - dimensional (2D) materials, MXene and graphene oxide (GO), as building blocks. The “limiting factor” internal concentration polarization (ICP) was remarkably mitigated in the support free MXene/GO hybrid membranes. Thus, the effective osmotic driving force for water permeation was largely increased, which contributed to a high water flux and anticipating PRO power output. The finds in this work highlight a new platform on the fabrication of advanced 2D materials assembled hybrid membranes and its promise in osmotic energy harvesting. 


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