Chemical reactivity of graphene oxide towards amines elucidated by solid-state NMR

Abstract

Graphene oxide (GO) is an attractive nanomaterial for many applications. Controlling the functionalization of GO is essential for the design of graphene-based conjugates with novel properties. But, the chemical composition of GO has not been fully elucidated yet. Due to the high reactivity of the oxygenated moieties, mainly epoxy, hydroxyl and carboxyl groups, several derivatization reactions may occur concomitantly. The reactivity of GO with amine derivatives has been exploited in the literature to design graphene-based conjugates, mainly through amidation. However, in this study we undoubtedly demonstrate using magic angle spinning (MAS) solid-state NMR that the reaction between GO and amine functions occurs via ring opening of the epoxides, and not by amidation. We also prove that there is a negligible amount of carboxylic acid groups in two GO samples obtained by a different synthesis process, hence eliminating the possibility of amidation reactions with amine derivatives. This work brings additional insights into the chemical reactivity of GO, which is fundamental to control its functionalization, and highlights the major role of MAS NMR spectroscopy for a comprehensive characterization of derivatized GO.

Improved Biocompatibility of Amino‐Functionalized Graphene Oxide in Caenorhabditis elegans

“…Thermogravimetric profile of GO (Figure S1E, Supporting Information) shows a typical trend with a first mass loss below 100 °C ascribed to the desorption of adsorbed water and unstable oxygenated groups, a second loss around 200 °C due to the decomposition of more stable oxygenated groups . GONH 2 presents a less significant thermal loss, which has been attributed to the instability of some oxygenated group present on the GO surface that are depleted during the amination reaction . The Kaiser test confirmed the presence of free amines on the GO surface.…”

Modular Preparation of Graphene‐Based Functional Architectures through Two‐Step Organic Reactions: Towards High‐Performance Energy Storage

“…Figure 2d isplays the N1s XPS spectrao fb oth GO and ethylenediamine-modifiedG O. Pristine GO exhibits mostlyn oisy N1ss pectrum, which indicates an egligible nitrogen content( Figure 2a). [47] Furthermore, two peaks can be deconvoluted in the N1ss pectrum ( Figure 2b): the former at about 399 eV can be assigned to CÀN, and the latter at about 401 eV can be attributed to the formation of imineb onds. [47] Furthermore, two peaks can be deconvoluted in the N1ss pectrum ( Figure 2b): the former at about 399 eV can be assigned to CÀN, and the latter at about 401 eV can be attributed to the formation of imineb onds.…”

“…[47] Furthermore, two peaks can be deconvoluted in the N1ss pectrum ( Figure 2b): the former at about 399 eV can be assigned to CÀN, and the latter at about 401 eV can be attributed to the formation of imineb onds. [47] The high degree of functionalization of ethylenedi- The thermal stability of both GO and ethylenediamine-modified GO wass tudied by means of thermogravimetric analysis (TGA). [47] The high degree of functionalization of ethylenedi- The thermal stability of both GO and ethylenediamine-modified GO wass tudied by means of thermogravimetric analysis (TGA).…”

Functionalization of graphene: does the organic chemistry matter?

“…The epoxides’ opening by nucleophiles can therefore act as a competing side reaction in many coupling processes with the inclusion of graphene-family materials [9,16]. In other words, opening graphene-family material’s epoxides should be taken into account even when the crosslinker-based amidation or esterification approach is performed.…”

“…For example [24], it is not clear whether the word “amination” refers to the formation of the amide (NH–CO) bond or to the reaction that the amine component has with the epoxy groups of GO, as divergent notes are included in this study’s results. The reaction of GO with diamines is a well-documented process (i.e., a nucleophilic attack on GO’s epoxides) [16,27], so the unexpected presence of an amide bond in the material, obtained via the reaction between p -phenylenediamine and graphene oxide with no additive (heating at 80 °C for 24 h), should be directly observed using IR spectroscopy. In this case, benzene rings were claimed to be introduced to GO via the presence of a strong absorption band located at ca.…”