There is a lot of water in the ocean. The problem is…it’s a bit salty.
Researchers from MIT use NERSC to show that nanometer-scale pores in single-layer freestanding graphene can effectively filter salt from water. The results indicate that the membrane’s ability to prevent the salt passage depends critically on pore diameter with adequately sized pores allowing for water flow while blocking ions.
Overall, the results indicate that the water permeability of this material is several orders of magnitude higher than conventional reverse osmosis membranes, and that nanoporous graphene may have a valuable role to play for water purification.
Guided by advanced molecular modeling at the National Energy Research Supercomputing Center, Massachusetts Institute of Technology scientists are investigating how to turn atom-thick carbon layers into membranes for a new and improved desalination method in places with inadequate fresh water. “Without any actual experimental demonstration, what our calculations tell us is that the performance of the graphene membrane for water desalination would be very high,” says Jeffrey Grossman, a materials scientist who is MIT’s Carl Richard Soderberg, associate professor of power engineering and leader of the investigation. Graphene, first described in 1962 and the focus of a 2010 Nobel Prize in physics, is a chicken-wire mesh of carbon atoms that provide the underpinnings for graphite, charcoal, carbon nanotubes and buckyballs.
What has sparked Grossman’s group’s interest is graphene’s phenomenal structural strength and chemical attributes that might make it ideal for filtering salt from seawater. The goal is to drill just-the-right-width, billionth-of-a-meter nanopores into graphene’s normally impenetrable surface so pressurized water alone could get through without damaging the ultrathin structure. That might make it more efficient than the reverse osmosis process that now offers the best performance of all seawater desalination options. The problem is reverse osmosis has comparatively high costs and energy use. Those faults mean that although seawater is widely available, “dramatically new technologies” are needed to make desalination “a sustainable water supply option,” Grossman and graduate student David Cohen-Tanugi reported earlier this year in the journal Nano Letters. Computer modeling is increasingly essential to modern-day chemistry and materials science because, according to Grossman “it sits in between theory and experiment,” so that “we can do actually what an experiment would have a hard time doing, which is to peel away the levels of complexity one by one.”
Professor Jeffrey C. Grossman
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