For stronger, lighter, cheaper materials, scroll up
Water filters of the future may be made from billions of tiny, graphene-based nanoscrolls. Each scroll, made by rolling up a single, atom-thick layer of graphene, could be tailored to trap specific molecules and pollutants in its tightly wound folds. Billions of these scrolls, stacked layer by layer, may produce a lightweight, durable, and highly selective water purification membrane.
But there’s a catch: Graphene does not come cheap. The material’s exceptional mechanical and chemical properties are due to its very regular, hexagonal structure, which resembles microscopic chicken wire. Scientists take great pains in keeping graphene in its pure, unblemished form, using processes that are expensive and time-consuming, and that severely limit graphene’s practical uses.
Seeking an alternative, a team from MIT and Harvard University is looking to graphene oxide — graphene’s much cheaper, imperfect form. Graphene oxide is graphene that is also covered with oxygen and hydrogen groups. The material is essentially what graphene becomes if it’s left to sit out in open air. The team fabricated nanoscrolls made from graphene oxide flakes and was able to control the dimensions of each nanoscroll, using both low- and high-frequency ultrasonic techniques. The scrolls have mechanical properties that are similar to graphene, and they can be made at a fraction of the cost, the researchers say.
“If you really want to make an engineering structure, at this point it’s not practical to use graphene,” says Itai Stein, a graduate student in MIT’s Department of Mechanical Engineering. “Graphene oxide is two to four orders of magnitude cheaper, and with our technique, we can tune the dimensions of these architectures and open a window to industry.”
Stein says graphene oxide nanoscrolls could also be used as ultralight chemical sensors, drug delivery vehicles, and hydrogen storage platforms, in addition to water filters. Stein and Carlo Amadei, a graduate student at Harvard University, have published their results in the journalNanoscale.
Getting away from crumpled graphene
The team’s paper originally grew out of an MIT class, 2.675 (Micro/Nano Engineering), taught by Rohit Karnik, associate professor of mechanical engineering. As part of their final project, Stein and Amadei teamed up to design nanoscrolls from graphene oxide. Amadei, as a member of Professor Chad Vecitis’ lab at Harvard University, had been working with graphene oxide for water purification applications, while Stein was experimenting with carbon nanotubes and other nanoscale architectures, as part of a group led by Brian Wardle, professor of aeronautics and astronautics at MIT.