Scientists have created a device which incorporated the smallest possible manmade perforations to enable salt water to be desalinated and made drinkable.
Researchers at the University of Manchester’s National Graphene Institute assembled ultra fine materials into a device on which they were then able to create these perforations just several angstroms (0.1 nanometre) wide to study how ions pass through them.
The slits are made from graphene, hexagonal boron nitride (hBN) and molybdenum disulphide (MoS2). The scientist discovered that ions with diameters larger than the size of the slit can pass through.
“When we looked more carefully, we found that bigger ions moved through more slowly than smaller ones like potassium chloride” said Gopi Kalon, a postdoctoral researcher who led the experimental effort.
Ali Esfandiar, the first author of the paper in which the findings are detailed, added “The classical viewpoint is that ions with a diameter larger than the slit size cannot permeate, but our results show that this explanation is too simplistic. Ions in fact behave like soft tennis balls rather than hard billiard ones, and large ions can still pass – either by distorting their water shells or maybe shedding them altogether.”
These size-exclusion studies allow for a better understanding of how similar scale biological filters such as aquaporins work and so will help in the development of high-flux filters for water desalination and related technologies, said the institute.
In April this year graphene-oxide based membranes developed at the NGI attracted attention as promising candidates for new filtration technologies.
This investigation, published in Science magazine, using the membranes ”demonstrates the real-world potential of providing clean drinking water from salt water”, researchers said.