A 3D lattice made from graphene oxide and ice. Photo: University at Buffalo.
A 3D lattice made from graphene oxide and ice. Photo: University at Buffalo.

Discovered in 2004, graphene is an atom-thick sheet of carbon that is is one million times thinner than a human hair, 300 times stronger than steel, and a highly efficient conductor of heat and electricity. These qualities could, among other things, make computers faster, batteries more powerful and solar panels more efficient. But the material is tough to manipulate beyond its normal two-dimensional form.

Recently, scientists have poured graphene oxide suspension, a gel-like form of the material, into freezing molds to create three-dimensional (3D) objects. This process works, but only with simple structures that have limited commercial applications.

Another option is to use a 3D printer. In this scenario, scientists typically mix graphene with a polymer or other thickening agent. This helps keep the structure from falling apart, but removing the polymer via a thermal process can damage the delicate structure.

A research team made up of engineers from the University at Buffalo (UB), Kansas State University and the Harbin Institute of Technology in China may now have solved this problem.

In a paper in Small, they report using a modified 3D printer and frozen water to create lattice-shaped cubes and a three-dimensional truss with overhangs using graphene oxide. These structures could be an important step toward making graphene commercially viable in electronics, medical diagnostic devices and other industries.

"Graphene is notoriously difficult to manipulate, but the structures we built show that it's possible to control its shape in three-dimensional forms," said Chi Zhou, assistant professor of industrial and systems engineering at UB's School of Engineering and Applied Sciences, and a corresponding author of the paper. Zhou is a member of the Sustainable Manufacturing and Advanced Robotic Technologies (SMART), a UB Community of Excellence launched in 2015; he also is a member of UB's New York State Center of Excellence in Materials Informatics.

In their experiments, the engineers mixed the graphene oxide with water. They then printed the lattice framework on a surface cooled to -25°C. The graphene is sandwiched between the layers of frozen ice, which act as a structural support.

After the process is completed, the lattice is dipped in liquid nitrogen, which helps to form even stronger hydrogen bonds. The lattice is then placed in a freeze dryer, where the ice is transformed into gas and removed. The end result is a complex, three-dimensional structure made of graphene aerogel that retains its shape at room temperature.

"By keeping the graphene in a cold environment, we were able to ensure that it retained the shape we designed. This is an important step toward making graphene a commercially-viable material," said Dong Lin, assistant professor of industrial and manufacturing systems engineering at Kansas State University, and the paper's other corresponding author.

The researchers now plan to build on their findings by investigating how to create aerogel structures made from multiple materials.

This story is adapted from material from the University at Buffalo, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.