Frontier | Uncovering the secrets of 3D graphene

Graphene is a new material that carries a lot of hope. Discovered in 2004, it is one million times thinner than a human hair and 300 times stronger than steel. It is known for its excellent electrical and thermal conductivity.

These unique properties could make it a promising material for faster computers, more powerful batteries and more efficient solar cells, but because the material is two-dimensional, processing is limited.

Recently, scientists have been pouring graphene oxide into a suspension, forming a gel form, and then freezing it to build 3D forms. Although this process works, it only forms simple structures, and the business model is greatly limited. Another option is to use a 3D printer. In this case, scientists usually mix graphene with polymers or other thickeners. This can prevent the molecular structure from being destroyed. However, when the polymer is removed by heating, its microstructure will also be destroyed.

A research team - consisting of engineers from the University at Buffalo, Kansas State University and Harbin Institute of Technology in China - may have solved this problem. A study published February 10 in the journal Small describes how the team used a modified 3D printer and chilled water to build a lattice cube and topped the three-dimensional framework with graphene oxide. The structure could be a key step in advancing graphene into commercial electronic devices and medical diagnostic equipment and even other industries.

"Graphene is notoriously difficult to manipulate, but the structures we built show that its three-dimensional shape can be controlled," said Chi Zhou, assistant professor of industrial and systems engineering in the Ulaanbaatar College of Engineering and Applied Sciences and co-author of the paper.

Zhou is a member of the Center for Sustainable Manufacturing and Advanced Robotics Technologies (SMART), which was established in Ulaanbaatar in 2015, and the New York State Center for Advanced Materials Research in Ulaanbaatar.

In their experiments, the team mixed graphene oxide with water. Then, at a surface temperature of -25°C, they printed the lattice structure. The graphene was sandwiched between layers of ice, which acted as a support structure. After the experimental process was completed, the lattice was soaked in liquid nitrogen, which helped to form stronger hydrogen bonds.

The lattice was then placed in a freeze dryer, which was used to sublime the ice into gas and remove it. The end result was a three-dimensional structure composed of graphene aerogel that was also stable at room temperature.

"By keeping graphene in a cold environment, we can ensure that it stays in the shape we designed. This is an important step toward making graphene a commercial material," said Dong Lin, associate professor in the Department of Industrial and Manufacturing Systems Engineering at Kansas State University and senior author of the study.

The researchers plan to further study how to make aerogel structures formed by multiple materials.