In an article published in the scientific journal Nature Chemistry, researchers from Brown University explain how they are able to precisely locate different carbon atoms that cause defects during the preparation of the material graphene in a process known as the reduction of graphene oxide.
Despite its inherent ability, graphene and its derivatives "are materials about which we understand very little," said lead researcher Vivek Shenoy, a professor of engineering at Brown University. "The better we understand their properties, the more technological possibilities will open up to us."
The researcher and a team of American scientists obtained new insights into these mysterious substances. The research team was able to pinpoint the atomic configuration of non-carbon atoms that cause defects during the preparation of graphene in a process known as graphene oxide reduction. As a conclusion from this study, the scientists recommend how to optimize this method through a detailed description in which hydrogen gas is used – instead of heat – to remove the impurities/defects on the graphene surface.
The surfaces produced in the process of reducing graphene oxide are two-dimensional and look like honeycomb-like carbon planes. Most of the atoms in the crystal lattice are carbon, which is the desired material for scientists. However, within the structure, oxygen and hydrogen atoms are also woven into them, which impair the uniformity of the structure of the surface. By applying enough heat to the crystal, some of these oxygen atoms bind to the hydrogen atoms and are removed in the form of water. However, some of these oxygen atoms are more stubborn and they still remain inside the structure.
The researchers used molecular dynamics simulations to observe the atomic configuration of the graphene lattice and determine why the remaining oxygen atoms nevertheless remained within the structure. They found that the "reluctant" oxygen atoms formed double bonds with carbon atoms - a very stable chemical arrangement that gives rise to irregular complexes in the lattice. The oxygen atoms that form double bonds with the carbon atoms "have a very low energy," explains the lead researcher. "They are inactive, so it is difficult to keep them away from the building."
Now that the researchers have understood the characteristics of the stubborn oxygen atoms in graphene, they recommend adding hydrogen atoms in fixed amounts and in defined areas and claim that this is the best way to recycle more and more graphene oxide. One such promising method, the researchers explain in their article, is to flow hydrogen to those points where the oxygen atoms have bonded to the hydrogen atoms and created wide niches. In the next step, the hydrogen and oxygen atoms are supposed to join together to form hydroxyl groups and leave the crystal, that is, "fix the hole," according to the main researcher's article. Another approach is to remove the oxygen impurities by focusing on the areas where carbonyls were formed - carbon atoms connected by a double bond to oxygen atoms. Following the introduction of hydrogen, the researchers believe, the oxygen atoms will be able to break away from the structure in the form of water droplets.
In the next step, the researchers plan to test their hydrogen approaches as well as examine the properties of graphene oxide themselves in more detail.
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Anyone else feel cognitive dissonance when looking at the picture? 😛