Shenoy, joined by Brown graduate student Akbar Bagri and colleagues from Rutgers University and the University of Texas–Dallas, used molecular dynamic simulations to observe the atomic configuration of the graphene lattice and figure out why the remaining oxygen atoms remained in the structure. They found that the holdout oxygen atoms had formed double bonds with carbon atoms, a very stable arrangement that produces irregular holes in the lattice.
The oxygen atoms that form double bonds with carbon "have very low energy," Shenoy said. "They're unreactive. It's hard to get them out."
Now that they understand the configuration of the resistant oxygen atoms in the graphene, the researchers say adding hydrogen atoms in prescribed amounts and at defined locations is the best way to further reduce the graphene oxide. One promising technique, they write in the paper, is to introduce hydrogen where the oxygen atoms have bonded with the carbon atoms and formed the larger holes. The oxygen and hydrogen should pair up (as hydroxyls) and leave the lattice, in essence "healing the hole," Shenoy said.
Another approach is to remove the oxygen impurities by focusing on the areas where carbonyls — carbon atoms that are double-bonded to oxygen atoms — have formed. By adding hydrogen, the researchers theorize, the oxygen atoms can be peeled away in the form of water.
The researchers next plan to experiment with the hydrogen treatment techniques as well as to investigate the properties of graphene oxide "in its own right," Shenoy said.
Atoms of oxygen create distortions in a graphene sheet. The key to removing them is to apply hydrogen in exactly the right places.
(Photo Credit: Shenoy Lab, Brown University)
Engineering professor Vivek Shenoy (right) and graduate student Akbar Bagri have explored the atomic configuration of graphene oxide, showing how defects in graphene sheets can be located and treated.
(Photo Credit: Mike Cohea, Brown University)
Source: Brown University