Synthetic Nanotubes Beat Nature at Water Purification

August 25, 2017

A new study published in the journal Science may have major implications for the future of water purification.

Professor Aleksandr Noy and his research team at Lawrence Livermore National Lab found that carbon nanotube porins (CNTPs) — hollow cylinders made of pure carbon that resemble microscopic drinking straws — can transport pure water across barriers while excluding impurities. The study also shows that CNTPs do this better than any material known to science.

Approximately 100,000 times thinner than a human hair, CNTPs are so narrow that liquid water has to rearrange itself into a single-file chain of water molecules in order to pass through. This helps CNTPs separate water from dissolved salts, even at salinities higher than seawater.

Materials that employ microscopic pores to separate water from contaminants are not new. Most technologies used for desalinization work on this principle. Even nature’s solution to the water purification problem, the aquaporin, works much the same way.

Aquaporins are cell-surface proteins found in everything from bacteria to humans. They’re nature’s water conduits, regulating the flow of water in and out of cells. Their unique chemical structure allows them to distinguish water molecules from other particles, resulting in highly selective water transport.

“Synthetic membranes used in water purification are a few orders of magnitude worse than aquaporins,” Noy said. “Aquaporins are the gold standard by which membranes are judged.”

Because of this, researchers have tried to design aquaporin-based water purification systems, largely without success. These technologies are difficult to scale. Plus, proteins degrade over relatively short time spans, making aquaporin-based technologies unstable.

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