Refining the Structure of Graphite Oxide through Selective Labeling of Functional Groups

Abstract

The various inherent functional groups within graphite oxide (GO) are of significant interest for numerous research applications exploiting their reactivity. While there has been much advance in the research of graphenes and GO over the years, our current understanding of GO structure is primarily derived using spectroscopic techniques such as XPS, NMR, FTIR and Raman spectroscopies. In contrast, we report an alternative electrochemical approach to investigate the composition of GO, previously developed to study surface functionalities within other carbon-based materials. In separate reactions, four electroactive labels were first employed to selectively label the various functional groups in GO, followed by their subsequent quantification using cyclic voltammetry. Distinct functional group compositions were consequently found depending on the choice of GO oxidation method, either via chlorate or permanganate oxidations. An additional advantage of the method is the ability to distinguishing the types of carbonyl groups such as quinonyl species over isolated ketones. Thus, we noted that permanganate oxidation produced GO with its carbonyls mainly existing as 1,2-quinones, while chlorate oxidation resulted primarily in aliphatic ketones. Furthermore, carboxylic groups that were erstwhile thought to be responsible for the acidic nature of GO were observed to be low in permanganate-GO and non-existent in chlorate-GO. We also deduced that epoxides likely exist as the main functionality within permanganate-GO, and discuss that the relatively low labelled-hydroxyl content may be due to previously proposed disproportionation reactions which result in formation of other groups. Overall, this selective labelling and electrochemical detection method has provided an improved and refined understanding of GO structures.