Ultrathin material provides productive desalination

Engineers at MIT have found that a single sheet of graphene is exceptionally sturdy. It remains intact under applied pressures of at least 100 bars. The key to withstanding such high pressures is pairing graphene with a thin underlying support substrate that is pocked with tiny holes, or pores. The smaller the substrate’s pores, the more resilient the graphene is under high pressure.

Such a sheet can be used as a membrane for desalination in which filtration membranes must withstand high-pressure flows to efficiently remove salt from seawater. The research is published in Nano Letters.

Many commercial existing membranes desalinate water under applied pressures of about 50 to 80 bars, above which they tend to get compacted or otherwise suffer in performance. If membranes were able to withstand higher pressures, 100bars or greater, they might also be able to purify extremely salty water.

Researchers grew the sheets of graphene using a technique called chemical vapor deposition. This graphene sheet is placed on thin sheets of porous polycarbonate. Each sheet was designed with pores of a particular size, ranging from 30 nanometers to 3 microns in diameter.

The team placed the graphene-polycarbonate membranes in the middle of a chamber, into the top half of which they pumped argon gas, using a pressure regulator. The researchers also measured the gas flow rate in the bottom half of the chamber, to monitor if parts of the graphene membrane had failed, or “burst,” from the pressure.