Increasing the functionality of graphene-based materials: pathways to carboxyl enrichment of Graphene Oxide

In the last two decades, the interest in graphene oxide (GO) has grown significantly due to the discovery of the wet chemical route to graphene. GO is a non-stoichiometric, 2D, carbon-based nanomaterials with outstanding properties and quivering chemistry. It is usually produced via the Hummers method, a wet chemical synthesis from bulk graphite [1]. GO can be described as a graphene layer decorated with islands of various oxygen-based functional groups (OFGs) such as: hydroxyls and epoxides in the basal plane and carbonyls, carboxyls, and phenols on the edges and defects [2]. Since the coexistence of these two domains, graphene oxide can be functionalized either covalently or non-covalently through a plethora of different reactions. Additionally, GO and functionalized GO can be reduced to partially restore the π-aromatic network and obtain properties similar to graphene. These unique assets make GO the perfect starting point for the synthesis of new functional materials [3]. Due to the very low abundance of carboxyl groups in graphene oxide, various attempts have been made in order to increase their quantity. In this work, two different functionalization reactions to obtain carboxyl-rich graphene oxide are presented. The first reaction is an O-acylation reaction with succinic anhydride in N,N-dimethylformamide (DMF) which involves alcohol and phenols-like [4]. An alternative approach is a nucleophilic substitution on the epoxide rings with γ-aminobutyric acid (GABA) in water. All the nanomaterials submitted have been fully characterized via various spectroscopic techniques such as: x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, UV-Vis spectroscopy, solid-state nuclear magnetic resonance (SS-NMR), and cyclic voltammetry (CV). The obtainment of a carboxyl-rich GO points to fostering the implementation of graphene-based materials in various fields such as: proton exchange membranes (PEM) in low-temperature fuel cells (LTFCs), removal of heavy metal ions from wastewaters, and amide-coupling with various amine-rich nanomaterials [4]. References: [1] Halbig C. A., Mukherjee B., Eigler S., Garaj S. J. Am. Chem. Soc., 2024, 146, 7431-7438. [2] Ferrari I., Motta A., Zanoni R., Scaramuzzo F.A., Amato F., Dalchiele E.A., Marrani A.G. Carbon, 2023, 203, 29-38. [3] Guo S., Garaj S., Bianco A., Ménard-Moyon C. Nat. Rev. Phys., 2022, 4, 247-262. [4] Amato F., Motta A., Giaccari L., Di Pasquale R., Scaramuzzo F. A., Zanoni R., Marrani A. G. Nanoscale Adv., 2023, 5, 893-906.