Robust yet single-layer material with ‘nanopores’ can effectively filter salt from seawater

Material_Nanopores_Filters_Salt_Seawater_1A computer model of a nanopore in a single-layer sheet of MoS2 .

The ‘holy grail’ solution of water shortage has always pertained to filtration of salt from the massive quantities of seawater present in our planet. Of course, a few of these desalination techniques already exist in our contemporary technological scope. But this time around, researchers from the University of Illinois may have come up with a more effective method to filter salt from seawater – in the form of a new material with ‘nanopore’ arrangements. This material in question here pertains to a nanometre-thick sheet of molybdenum disulphide (MoS2) that is punctured with a set of nano-sized pores. So when high volumes of seawater passes through the material layer, salt and other contaminants are more effectively blocked by the minuscule-sized nanopores. In comparative terms, the scientists estimate that their contrived thin-film membrane technology can account for filtration of 70 percent more water than even graphene.

The question naturally arises – how is this tech different from the present-day desalination processes? Well in conventional terms, most desalination processes relate to reverse osmosis, where the water is forced through a thin plastic membrane. Now while normally these plastic membranes may seem to comprise ultra-thin layers, from the microscopic angle, their structure pertains more to tubular arrangements than 2D membranes. In essence, more pressure is required for the water to push through the material, which in turns equates to more energy expended in the process. Moreover, the tube-like nanometer funnels are susceptible to clogging (from both salt or dirt) that can further increase the operational costs.

Suffice it to say, the aforementioned molybdenum disulphide membrane eschews such problems, by allowing the passing of water with far lesser resistance (due to the prevalence of single-layer sheets). This is coupled with the fact that MoS2 is also a robust material that can take enormous pressure from the passing seawater volumes. However, beyond just its streamlined characteristics, it is intrinsic chemistry that proves to be an ultimate advantage in the case of this technology. As Mohammad Heiranian, first author of the study, makes it clear –

MoS2 has inherent advantages in that the molybdenum in the center attracts water, then the sulphur on the other side pushes it away, so we have much higher rate of water going through the pore. It’s inherent in the chemistry of MoS2 and the geometry of the pore, so we don’t have to functionalise the pore, which is a very complex process with graphene.

With all said and done, the technology is still in its nascent stage, with the researchers looking forward to collaborative efforts with other organizations, to field test the water desalination credentials of MoS2. And in spite of the novelty of this single-layer material, the scientists are quite confident of the effectiveness of MoS2 in actual commercial applications. As Amir Barati Farimani, one of the members of the team, said –

Nanotechnology could play a great role in reducing the cost of desalination plants and making them energy efficient. I’m in California now, and there’s a lot of talk about the drought and how to tackle it. I’m very hopeful that this work can help the designers of desalination plants. This type of thin membrane can increase return on investment because they are much more energy efficient.

The study was originally published in Nature Communications.

Source: University of Illinois

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