Lawrence Livermore National Laboratory (LLNL) scientists have created new carbon nanotube (CNT) pores to desalinate seawater and brackish water sources.
Said to be more efficient at removing salt from water when compared to commercial desalination membranes, these new pores represent some of the most promising scaffold structures for artificial water channels. They measure just 0.8 nanometers (nm) in diameter. In comparison, a human hair measures nearly 60,000 nm across.
Reverse Osmosis is the go-to-method for removing salt from water. It usually consists of thin-film composite (TFC) membranes that separate water from the ions present in saline feed streams.
It isn’t however infallible: TFC membranes are constrained by the permeability-selectivity trade-offs and often have insufficient rejection of some ions and trace micropollutants.
This calls for additional purification stages that are not only energy intensive but operation-wise costly too.
To create their new filtration pores, the LLNL team led by Alex Noy turned to biological water channels – also known as ‘aquaporins’ – for inspiration.
These structures have an extremely narrow inner pore that squeezes water down to a single-file configuration that enables extremely high water permeability.
They also boast of transport rates exceeding 1 billion water molecules per second through each pore.
Taking a cue from this, Noy’s team developed CNT porins (CNTPs) to form artificial water channels that mimic aquaporin channel functionality and intrachannel single-file water arrangement.
They then measured water and chloride ion transport through 0.8-nm-diameter CNTPs using fluorescence-based assays.
These showed enhanced flow and strong ion rejection through inner channels of carbon nanotubes.
Image and content: Ella Maru Studios/LLNL