Paul Rincon of the BBC writes of a new report of a “Graphene-based sieve turns seawater into drinking water” . He is justifiably excited by this long sought possibility of desalinization via filtration. If this can be made to work cheaply at large scales, it is a huge, huge deal for the parched coast of California and everywhere else.
But the technology is actually cooler than that. Jijo Abraham and colleagues working in Manchester describe it as “Tunable sieving of ions using graphene oxide membranes.” 
“Tunable”. I like the sound of that. (Almost as good as “programmable” :-))
Their technique attacks the problem that Grapheme (actually Graphene Oxide) filters expand when wet, which causes any pores or channels to open up, negating the desired effect. I.e., when immersed in salt water, they swell up and let salt through. Bummer.
Their technique prevents this by sandwiching GO with tiny pores into an epoxy matrix which prevents it from expanding. By creating GO of whatever granularity you desire, you can “tune” the resulting composite.
They make use of the tuning to investigate how this filtration works. They find that the rejection of the salt (NaCl) by small pores (around 10 microns) is not solely due to geometry, but also due to the interaction of the salt ions eith the barrier.
“In this regime, the capillary size is smaller than the hydrated diameters of ions and their permeation is exponentially suppressed with decreas- ing d. The suppression mechanism can be described in terms of additional energy barriers that arise because of the necessity to par- tially strip ions from their hydrated shells so that they can fit inside the capillaries. Water transport is much less affected by d.” (, p. 4)
This is nice work, and quite promising. In light of the excitement exemplified by Rincon, it is important to note that there is a long way to go before this concept can be manufactured and used in realistic scales.
“Even though scalable production of such membranes is difficult, one can envisage using alternative fabrication techniques to control d in GO laminates.” (p. 4)
Very nice work, and likely to inspire more advances in the future. But still at the “one can envisage” stage.
- Jijo Abraham, Kalangi S. Vasu, Christopher D. Williams, Kalon Gopinadhan, Yang Su, Christie T. Cherian, James Dix, Eric Prestat, Sarah J. Haigh, Irina V. Grigorieva, Paola Carbone, Andre K. Geim, and Rahul R. Nair, Tunable sieving of ions using graphene oxide membranes. Nat Nano, advance online publication 04/03/online 2017. http://dx.doi.org/10.1038/nnano.2017.21
- Paul Rincon Graphene-based sieve turns seawater into drinking water. BBC News.April 3 2017, http://www.bbc.co.uk/news/science-environment-39482342