Refinements to the structure of graphite oxide: absolute quantification of functional groups via selective labelling

Abstract

Chemical modification and functionalization of inherent functional groups within graphite oxide (GO) are essential aspects of graphene-based nano-materials used in wide-ranging applications. Despite extensive research, there remains some discrepancy in its structure, with current knowledge limited primarily to spectroscopic data from XPS, NMR and vibrational spectroscopies. We report herein an innovative electrochemistry-based approach. Four electroactive labels are chosen to selectively functionalize groups in GO, and quantification of each group is achieved by voltammetric analysis. This allows for the first time quantification of absolute amounts of each group, with a further advantage of distinguishing various carbonyl species: namely ortho- and para-quinones from aliphatic ketones. Intrinsic variations in the compositions of permanganate versus chlorate-oxidized GOs were thus observed. Principal differences include permanganate-GO exhibiting substantial quinonyl content, in comparison to chlorate-GO with the vast majority of its carbonyls as isolated ketones. The results confirm that carboxylic groups are rare in actuality, and are in fact entirely absent from chlorate-GO. These observations refine and advance our understanding of GO structure by addressing certain disparities in past models resulting from employment of different oxidation routes, with the vital implication that GO production methods cannot be used interchangeably in the manufacture of graphene-based devices.

sp amorphous carbons in view of multianalytical consideration: Normal, expeсted and new

“…Addition of a sterically cumbersome carboxylic unit at any stage of oxidation significantly increases making the reaction not favorable even for (e) and (f) models, for which the change is minimal. As was shown [65], carboxyls actually are not friendly addends of graphene molecules due to energetic reason, the fact of which is supported experimentally by a number of reduced graphene studies (see review [66]) pointing to a very small contribution of the latter. "C=O" Shungite carbon The performed analysis does not allow making a clear conclusion which namely models are realized in the case of shungite carbon in practice since the energy is a characteristic of a potential ability only while the nature of empirical observations lies in the chemical kinetics rather than the thermodynamic stability of the products.…”

Brodie vs Hummers graphite oxides for preparation of multi-layered materials

“…For example, Brodie graphite oxides (BGO) exhibit 50-100 degrees higher temperature of exfoliation [26,27], phase transition between one and two layered solvate phases [28,29] absent in HGO [19], selective intercalation of methanol or ethanol from binary mixtures with water [30]. The nature of the difference between the Brodie and Hummers graphite oxides remains poorly understood and only few studies are available on this subject [27,31,32]. It should be noted that a quantitative estimation for the relative numbers of various functional groups using reactions of GO with various chemicals was available for HGO already in 1960-s reporting hydroxyls and ether groups as the two most abundant ones with carbonyls, enols and carboxyls present in smaller amounts [33].…”

Cyanographene and Graphene Acid: Emerging Derivatives Enabling High-Yield and Selective Functionalization of Graphene

“…For instance, the widely used derivative graphene oxide is prepared by harsh oxidation, and the oxidation conditions profoundly affect its stoichiometry, structure and properties without selectivity. 24 Consequently, there is a need for new strategies that permit selective and high yielding graphene functionalization under more controlled conditions.…”

“…It should be noted that while graphene oxide does contain carboxyl groups, they are attached to edges and defects, and their content is low (or even absent). 24 Moreover, they are accompanied by many other oxygen-containing groups. Here we present a two-step process, whereby FG is transformed into the fluorine-free cyanographene (G-CN, or graphene-nitrile) and subsequently hydrolyzed to graphene acid (G-COOH).…”