Ultra-thin carbon nanotubes can separate salt from seawater

Washington : Scientists have developed carbon nanotubes over 50,000 times thinner than a human hair which can separate salt from seawater, an advance that may help solve the global water crisis. Increasing demands for fresh water pose a global threat to sustainable development, resulting in water scarcity for four billion people, researchers said.

Current water purification technologies can benefit from the development of membranes with specialised pores that mimic highly efficient and water selective biological proteins.

Scientists, including those from Northeastern University in the US, developed carbon nanotube pores that can exclude salt from seawater. The team found that water permeability in carbon nanotubes (CNTs) with diameters of 0.8 nanometre significantly exceeds that of wider carbon nanotubes.

The nanotubes, hollow structures made of carbon atoms in a unique arrangement, are more than 50,000 times thinner than a human hair. The super smooth inner surface of the nanotube is responsible for their remarkably high water permeability, while the tiny pore size blocks larger salt ions.

Computer simulations and experimental studies of water transport through CNTs with diameters larger than one nanametre showed enhanced water flow, but did not match the transport efficiency of biological proteins and did not separate salt efficiently, especially at higher salinities.

The key breakthrough achieved by the LLNL team was to use smaller-diameter nanotubes that delivered the required boost in performance. "Carbon nanotubes are a unique platform for studying molecular transport and nanofluidics," said Alex Noy principal investigator at LLNL.