This is the first demonstration of an industrial, scalable method for manufacturing high-quality graphene that is tailored for use in membranes that filter a variety of molecules, including salts, larger ions, proteins, or nanoparticles.
"For several years, researchers have thought of graphene as a potential route to ultrathin membranes," says John Hart, associate professor of mechanical engineering and director of the Laboratory for Manufacturing and Productivity at MIT. "We believe this is the first study that has tailored the manufacturing of graphene toward membrane applications, which require the graphene to be seamless, cover the substrate fully, and be of high quality."
Graphene is often synthesised through chemical vapour deposition, heating a copper foil that acts as a substrate for a combination of carbon and other gases. If graphene membranes are ever to be used commercially they will have to be produced in large quantities, at high rates, and with reliable performance.
"We know that for industrialization, it would need to be a continuous process," said Hart. "You would never be able to make enough by making just pieces. And membranes that are used commercially need to be fairly big - some so big that you would have to send a poster-wide sheet of foil into a furnace to make a membrane."
The team used a roll-to-roll approach with CVD to manufacture high-quality graphene in large quantities and at a high rate. The system consists of two spools, connected by a conveyor belt that runs through a small furnace. The first spool unfurls a long strip of copper foil, less than 1cm wide. When it enters the furnace, the foil is fed through first one tube and then another, in a "split-zone" design.
While the foil rolls through the first tube, it heats up to a certain ideal temperature, at which point it is ready to roll through the second tube, where the scientists pump in a specified ratio of methane and hydrogen