Infrared spectrum of graphene oxide explained by KFU scientists

The paper was published in Carbon.

The study was conducted under the project New approaches to deciphering the structure and chemical properties of graphene oxide, supported by a grant from the Russian Science Foundation.

Graphene oxide is a nano-material based on carbon, oxygen, and hydrogen. It represents two-dimensional sheets of graphene with oxygen-containing functional groups attached to carbon atoms – epoxy, hydroxyl, carboxyl and others.

"Graphene oxide has attracted the attention of researchers since the first half of the twentieth century. It was then that active work began to study the structure and chemical properties of this material," says the first author of the article, Senior Research Associate of the Laboratory of Prospective Carbon Nanomaterials Vasily Brusko. "After the discovery of the unique conducting properties of graphene in 2006, a new golden era in the field of graphene oxide began. Today it is one of the most studied materials of the last decade. Its applications range from selective membranes to electrodes of chemical energy sources, from filler of polymer composites to theranostics."

In aqueous solutions, graphene oxide is able to delaminate into individual sheets just one atom thick.

"This gives unlimited possibilities for its modification and incorporation into polymer matrices," Brusko explains. "At the same time, the polymer is structured with the latter acquiring a number of interesting properties: rheological, conductive, optical and others. It is also possible to obtain graphene from graphene oxide."

According to the project lead, Lead Research Associate of the Laboratory of Prospective Carbon Nanomaterials Ayrat Dimiev, many fundamental issues related to the chemical structure of graphene oxide remain unresolved today.

"In particular, the most important issue is the characterization and standardization of this material," he stresses. "One popular method of characterization is infrared spectroscopy. Although the first infrared spectrum of graphene oxide was published back in 1955, to date it has not been fully deciphered. In particular, there is no understanding of where the absorption bands associated with graphene oxide's basic oxygen groups, epoxides, and tertiary alcohols are located. This leads to massive misinterpretation of the spectra. Interestingly, even absorption bands that were previously unambiguously and convincingly assigned to specific groups are now massively misinterpreted."

During the study, KFU chemists synthesized several dozen modified graphene oxide samples and recorded their infrared spectra. The graphene oxide samples were modified with alkaline reagents, amines and hydrogen bromide. Partially oxidized graphene oxide samples were also prepared.

"I fell in love with this material back in 2010, when I synthesized it for the first time in the laboratory of Professor James Tour at Rice University, then I paid attention to its very interesting properties which are difficult to explain from the point of view of a chemist, and the fact that the literature is full of illogical interpretations of the properties of graphene oxide and direct errors in the interpretation of experimental data." shares Dimiev.

A number of unique properties, according to the scientist, are characteristic of aqueous dispersions of graphene oxide, the rheological properties of which depend on its concentration.

"These systems cannot be unambiguously attributed to any classical type of liquid systems. Aqueous solutions of graphene oxide exhibit anomalously high acidic properties and cation exchange capacity, which cannot be explained in terms of a generally recognized structural model. In addition, well-knownb reactions, targeting the functional groups present in it, do not run well with graphene oxide," continues the researcher.

The scientist reports that the decoded infrared spectra were recorded by Artur Khannanov, Associate Professor of the Department of Inorganic Chemistry, and NMR spectra obtained for independent confirmation of changes in the structure of graphene oxide – by graduate and former employee of Kazan University Aydar Rakhmatullin.

More information:
Unraveling the infrared spectrum of graphene oxide
www.sciencedirect.com/science/ … ii/S0008622324007267

Provided by Kazan Federal University