NSF/DMR-BSF: Understanding transport in biomimetic carbon nanotube porin membranes for water treatment and osmotic energy harvesting

University Of California - Merced, Merced CA

Investigators

Abstract

Non-Technical: While most of the world is made up of water, water for human consumption nearly always requires some form of purification before use. Given the ever-increasing global demand, access to clean water is a world-wide problem that requires novel technologies to keep up with demand at reduced costs. Since the ocean remains the only truly inexhaustible water source, reverse osmosis seawater desalination will remain a vital component of a sustainable water solution in the US and beyond. Moreover, in places with scarce freshwater resources, such as Israel, Middle East, or Western US, desalination becomes a critical component. While desalination solutions have been on the market for more than 50 years, most of commercial reverse osmosis desalination installations still rely on decades-old membrane technology that has likely reached its useful limit years ago. In this joint US/Israel project, the investigators will develop a new kind of membrane that efficiently and quickly removes salt from water by passing water molecules through very small carbon nanotubes with diameters less than one-millionth of a human hair. Nanotubes are not only small, but also extraordinarily efficient, passing water faster than any other known pore. The propose studies also will take a radically-different approach that imitates the structure of the best membrane biological membrane 'the outer membrane of a live cell' and should deliver significant improvements over existing cell membranes for water purification. A vital part of this investigation will involve educational outreach to undergraduate and K-12 students on the importance of water technologies, training US and Israeli graduate students in the state of the art biomimetic technologies, and developing a joint US-Israel summer school in which the students can learn from global leaders in water purification research. Technical: This collaborative project, which brings together two US-based biomaterials/nanopores groups (Noy, Wanunu) and an Israeli membrane science group (Freger), will develop a robust biomimetic membrane platform that mimics hierarchical organization of a cell membrane and exploits highly-efficient and selective transport in carbon nanotube porins. Specifically, membranes that comprise carbon nanotube porins (CNTPs) embedded in a thin matrix layer resting on a permeable membrane support will be designed and fabricated. These components mimic the three main structural elements of a cell membrane: (i) membrane pore channels, (ii) lipid bilayer, and (iii) cytoskeleton. This study will characterize water and ion transport in these membranes on ensemble and single-pore scales, focusing mainly on the physical principles by which nanopore confinement enables efficient and selective transport. This research will also use chemical modification to alter selectivity of the carbon nanotube porins. These membranes should enable enhanced membrane performance for reverse osmosis (RO) water purification and osmotic power generation using reverse electrodialysis (RED). They will also allow us to explore fundamental questions in modern membrane science, such as the physics of water transport and ion exclusion, the role of confinement in nanopores, effects of fixed charges, and limitations imposed by concentration polarization. Finally, outreach efforts in this project will allow us to highlight the importance of basic research and disruptive technological advances for ensuring future availability of clean water. This will be achieved through a) creation of a joint US-Israel summer school that would be focused on new water technologies and fundamentals of water-related science, b) training US graduate and undergraduate students about water research in the global context.