Among a number of critical uses of membrane separations for human existence, the use for water purification is exemplar. With water scarcity becoming more common, and as availability of cheap water becomes sparse for communities, the need for supplement sources of water becomes essential. This includes use of desalinated water from brackish water sources and seawater.
Meanwhile, researchers at Lawrence Livermore National Laboratory have created a carbon nanotube pores that are highly efficient in removing salt from water, and are comparable to commercial desalination membranes. The tiny pores are only 0.8 nanometers in diameter, when compared to the diameter of human hair that measures 60,000 nm across. The finding is published in the Sept 18 edition of the journal Science Advances.
Shortcomings of Reverse Osmosis necessitated New Method
Meanwhile, reverse osmosis – the leading technology for removing salt from water uses thin-film composite membranes. This involves use of membranes to separate water from the ions present in salinated feed streams. However, some basic performance issues remain. For example, thin-film composite membranes face constraints of permeability selectivity, and often leads to insufficient rejection of ions and trace micropollutants. Hence, this requires additional purification resulting in increased energy and cost.
Meanwhile, biological water channels provide a blueprint for structures that could provide increased performance. Biological water channels have an extremely small inner pore that squeezes down water to a single file configuration enabling very high water permeability. The rate of transport of water through each pore exceeds 1 billion water molecules per second.
For artificial water channels, carbon nanotubes are some of the most promising scaffold structures. This is because of low friction of water on the smooth inner surfaces of carbon nanotubes, which mimic biological water channels.