Graphene is a wonder material saddled with great expectations.
Discovered in 2004, it consists of a single layer of carbon atoms packed together in a honeycomb-like pattern. Among its unworldly properties, graphene is 1 million times thinner than a human hair, 300 times stronger than steel, the best-known conductor of heat and electricity, and, under certain conditions, lighter than air. These attributes could, among other things, help make computers faster, batteries more powerful and solar panels more efficient.
But the material has yet to reach its potential, in part because it’s hard to manipulate beyond its two-dimensional form. This conundrum has sent scientists around the world searching for a reliable way to make 3-D graphene. One approach—pouring graphene oxide, a gel-like form of graphene, into freezing molds—has met with partial success. The process works, but only with simple structures that have limited commercial use.
Some scientists have been working with a 3-D printer. In this scenario, graphene is mixed with a polymer or other thickening agent. The combination, when pushed out of the printer’s inkjets, creates three-dimensional objects. But when the polymer is removed later by heat, it damages the delicate structure, often rendering it useless.
Zhou, working with engineers from Kansas State University and the Harbin Institute of Technology in China, may have finally solved that problem.
Instead of injecting graphene with thickening agents, the team uses a modified 3-D printer to combine graphene oxide (graphene with extra oxygen atoms) and water. The printer deposits layers of the mixture on a surface cooled to minus 25 C. The graphene freezes instantly, creating three-dimensional structures, with ice acting as a support.
After the process is finished, engineers dip the structures—everything from lattice-shaped cubes to spiderweb-like orbs—in liquid nitrogen, which strengthens the bond between the ice and graphene. The structures are then placed in a freeze dryer, where the ice changes into gas and is removed. The end result is graphene aerogel, a porous and superlight material in which the liquid part of the gel is replaced by air, allowing it to retain its shape at room temperature.
“The structures we built show that it’s possible to control the shape of graphene in three-dimensional forms,” says Zhou, a native of China who arrived at UB in 2013. “What’s more exciting, though, is that this process could be an important step toward making graphene commercially viable.”
Zhou and his colleagues have made objects with densities as low as .5 kilograms per cubic meter—or less than half the weight of air. This near weightlessness could revolutionize the transportation industry, for one, with the production of cars and airplanes that are ultralight and thus much more fuel-efficient.
In addition to advancing electronics, batteries and medical diagnostic devices, graphene aerogel could have a profound impact on environmental cleanups. Studies show it can absorb up to 900 times its weight, making the material an incredible tool for sopping up oil spills.
Possibilities such as these have tantalized scientists since graphene’s discovery 12 years ago. Now, says Zhou, they may soon be realized. “We’re getting there,” he says. “Layer by layer.”