(7ds) Advanced Materials and Nanotechnologies for Water-Energy Applications

My research interest is to develop advanced materials and nanotechnologies for energy and environment including resource mining from seawater, desalination, wastewater resource recovery, water/wastewater treatment, and fuel production from wastewater. Earth water system including the ocean, surface water, and groundwater provide tremendous resources including fresh water, food, minerals and so on. To preserve the water system and at the same time withdraw valuable resources and energy in an eco-friendly manner is extremely important and challenging.

During my postdoc, I have developed several technologies for resource mining/recovery from seawater and wastewater. One of such technologies is uranium extraction from seawater. In total there is hundreds of times more uranium in sea water than on land, but extracting it for use in nuclear power generation is challenging due to its low concentration and the high salinity background. Current approaches based on sorbent materials are limited due to their surface-based physicochemical adsorption nature. I have developed a half-wave rectified alternating current electrochemical (HW-ACE) method for uranium extraction from seawater based on an amidoxime-functionalized carbon electrode. The amidoxime functionalization enables surface specific binding to uranyl ions, while the electric field can migrate the ions to the electrode and induce electrodeposition of uranium compounds, forming charge-neutral species. Extraction is not limited by the electrode surface area, and the alternating manner of the applied voltage prevents unwanted cations from blocking the active sites and avoids water splitting. The HW-ACE method achieved the highest reported capacity for uranium extraction which is nine-fold higher than conventional physicochemical methods. The HW-ACE method also shows much faster kinetics with great selectivity and reusability.

Besides, I have also worked on water/wastewater treatment during my Ph.D. Point-of-use water disinfection is extremely important for public health, especially for developing areas with limited energy supply and insufficient infrastructures. I have developed two types of point-of-use water disinfection technologies for rapid and effective pathogen inactivation. In the first technology, I have developed a new photocatalyst, few layered vertically aligned MoS₂ nanofilms (FLV-MoS₂), to harvest not only UV light but also visible light for photocatalytic water disinfection. By decreasing the domain size of MoS₂ to few layers, its bandgap was increased from 1.3 to 1.55 eV which allowed the FLV-MoS₂ to harvest both UV and visible light to generate reactive oxygen species for bacterial inactivation. FLV-MoS₂ showed much better photocatalyst water disinfection performance comparing to the most adopted photocatalyst TiO₂. In the second technology, I have invented a new technology, one-dimensional nanowire-assisted electroporation (1D-NE), for pathogen inactivation. High electric field (>10⁶ V/m) was built by introducing 1D nanomaterial electrode under a small and safe voltage of less than 10V. Bacteria and viruses were electroporated under high electric field. Since electroporation occurs on the scale of nanosecond to microsecond, the 1D-NE based filtration achieved a speed that was several orders of magnitude faster than traditional filtration technologies with comparable disinfection efficiency.

In the future research, I will take the advantages of nanotechnologies and electrochemical methods to bring in a new perspective and better solutions for water research that can contribute to the water-energy-food security nexus.

Teaching Interests:

I am interested in teaching most of the major courses for Chemical Engineering including thermodynamics, spectroscopy, catalysis, separation process, nanoscale fabrication, and electrochemistry. I have experience as guest lecturers for both graduate and undergraduate level courses related to nanotechnologies at Stanford.

Selected Publications:

C. Liu, P.-C. Hsu, J. Xie, J. Zhao, T. Wu, H. Wang, W. Liu, J. Zhang, S. Chu, Y. Cui. A Half-Wave Rectified Alternating Current Electrochemical Method for Uranium Extraction from Sea Water. Nature Energy, 2017, 2, 17007.

C. Liu, D. Kong, P.-C. Hsu, H. Yuan, H. W. Lee, Y. Liu, H. Wang, S. Wang, K. Yan, D. Lin, P. Maraccini, K. Parker, A. B. Boehm, Y. Cui. Rapid water disinfection by vertically aligned MoS₂ nanofilms and visible light. Nature Nanotechnology, 2016, 11, 1098–1104.

C. Liu*, P.-C. Hsu*, H. W. Lee, M. Ye, G. Zheng, N. Liu, W. Li, Y. Cui. Transparent air filter for high-efficiency PM_2.5 capture. Nature Communications, 2015, 6, 6205.

C. Liu, X. Xie, W. Zhao, J. Yao, D. Kong, A. B. Boehm, and Y. Cui. Static electricity powered copper oxide nanowire microbicidal electroporation for water disinfection. Nano Letters, 2014, 14, 5603–5608.

C. Liu, X. Xie, W. Zhao, N. Liu, P. A. Maraccini, L. M. Sassoubre, A. B. Boehm, and Y. Cui. Conducting nano-sponge electroporation for affordable and high-efficiency disinfection of bacteria and viruses in water. Nano Letters, 2013, 13, 4288–4293.