Even though the majority of the Earth is covered in water, a surprising number of people around the world don’t have easy access to clean drinking water. The oceans of course are full of salt, and it is difficult to filter that salt out. Researchers at the University of Manchester have found a way to improve a graphene-based filter mechanism that could help convert sea water to potable water.
Pure graphene can do the job, but it is difficult to manufacture in commercial quantities. In addition, the membrane requires the creation of tiny holes, further complicating the production. The new method uses graphene oxide, which is very simple to make and deploy.
Graphene oxide membranes have been used before to filter out small particles, but they swell a bit in the presence of water and that change in properties is enough for salt to get through. The new research shows that constraining the membrane with a wall made from epoxy resin stops the expansion and allows the membrane to block salt.
Traditional graphene oxide membranes can’t block particles smaller than about 9 angstroms. The filter mechanism relies on spacing between layers of the filter which can be as broad as 13.5 angstroms in water. Not only does the new technique allow a spacing as low as 6.4 angstroms, but the spacing can be tuned for different purposes. The new filters can reject up to 97% of the salt in water.