Holes would typically be considered unwanted defects, but the MIT team has found that certain defects in graphene can be an advantage in fields such as dialysis. Typically, much thicker polymer membranes are used in laboratories to filter out specific molecules from solution, such as proteins, amino acids, chemicals, and salts. If it could be tailored with selectively-sized pores that let through certain molecules but not others, graphene could substantially improve separation membrane technology.
The researchers also found that simply turning down the temperature during the normal process of growing graphene will produce pores in the exact size range as most molecules that dialysis membranes aim to filter. The new technique could thus be easily integrated into any large-scale manufacturing of graphene, such as a roll-to-roll process that the team has previously developed.
“If you take this to a roll-to-roll manufacturing process, it’s a game changer,” says lead author Piran Kidambi, formerly an MIT postdoc and now an assistant professor at Vanderbilt University. “You don’t need anything else. Just reduce the temperature, and we have a fully integrated manufacturing setup for graphene membranes.”
Kidambi and his colleagues previously developed a technique to generate nanometer-sized pores in graphene, by first fabricating pristine graphene using conventional methods, then using oxygen plasma to etch away at the fully formed material to create pores. Other groups have used focused beams of ions to methodically drill holes into graphene, but Kidambi says these techniques are difficult to integrate into any large-scale manufacturing process.
“Scalability of these processes are extremely limited,” Kidambi says. “They would take way too much time, and in an industrially quick process, such pore-generating techniques would be challenging to do.”