Synthetic Nanotubes Beat Nature at Water Purification

These shortcomings inspired Noy and colleagues to search for synthetic pores that were just as selective with none of the drawbacks. Carbon nanotubes seemed an obvious choice.

“We created something that looks and works like a protein, but it’s stable since it’s a carbon nanotube,” Noy said.

Other groups previously synthesized carbon nanotubes that could transport water, but none were as effective. That’s partly because earlier generations of nanotubes had diameters in excess of 1 nanometer. CNTPs, with a diameter of 0.8 nanometers, are much closer to the 0.3 nanometer aquaporin channel.

This structural similarity leads to functional similarity, with CNTPs behaving a lot like aquaporins. Both require water to pass through in a single-file chain, and both exploit structural properties to deny passage to salts and small molecules.

But CNTPs are more than just an improvement over larger, less selective nanotubes.

“We finally created a synthetic nanopore that beats aquaporin at water transport and desalinization,” Noy said. “This is the first synthetic pore that beats nature.”

CNTPs are six times more effective than aquaporins at water transport. That’s because aquaporins produce friction between water molecules and the channel walls. CNTPs, on the other hand, have very low friction.

CNTPs have another unusual property. Under certain conditions they can transport charged particles, with researchers controlling the direction of the current. This means CNTPs can be induced to behave a lot like an artificial nerve signal. However, Noy and colleagues emphasize that much remains to be studied.

“We’re continuing to study the mechanism of water transport through CNTPs,” Noy said. “Our goal is to achieve transport that is truly without friction. We want perfectly effortless, perfectly selective water transport.”

UC Merced graduate student Yun-Chiao Yao Opens a New Window. co-authored the study. Additional co-authors include Ramya Tunuguntla of LLNL, Robert Henley of LLNL and Northeastern University, Tuan Anh Pham of LLNL, and Meni Wanunu of Northeastern University Opens a New Window. .

Funding was provided by the U.S. Department of Energy Opens a New Window. Office of Basic Energy Science Opens a New Window. .

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