Facile Edge Functionalization of Graphene Layers with a Biosourced 2-Pyrone

Edge functionalization of graphene layers is of great interest in the field of materials chemistry: the properties of graphene are substantially unaltered and its compatibility and chemical reactivity with various environments can be tuned. In this work, edge functionalization of graphene layers was performed with a 2-pyrone, ethyl 3-hydroxy-2-oxo-2H-pyran-6-carboxylate (Pyr-COOEt). 2-Pyrones are C-6 unsaturated heterocyclic sugar derivatives and are intriguing building blocks for the preparation of innovative chemical structures. Sodium 3-acetoxy-2-oxo-2H-pyran-6-carboxylate was prepared starting from mucic acid, in a one-pot synthesis with a yield of about 74%, and was then transformed into the acid and then into ethyl ester derivatives. The adduct of Pyr-COOEt with a high surface area graphite (HSAG) was obtained by simply mixing and donating energy, either thermal or mechanical. The functionalization yield was estimated from thermogravimetric analysis (TGA) data and was found to be up to 91%. The adducts were characterized by Fourier transform infrared and Raman spectroscopies and wide-angle X-ray diffraction. The presence of pyrone in the adduct was clearly detected in the IR spectra, and the bulk structure of the graphitic substrate was found to be substantially unaltered by the functionalization reaction. The experimental findings suggest that the edge functionalization of the graphene layers occurred. Stable water dispersions of HSAG/Pyr adducts were prepared and studied through ultraviolet-visible analysis. Aggregates of few-layer graphene were obtained by mild sonication and centrifugation, as revealed by high-resolution transmission electron microscopy. This paper shows that a biobased molecule can be used for selectively decorating the edges of graphene layers, with oxygenated functional groups having a defined chemical structure and avoiding the use of oil-based, dangerous, and even noxious ingredients. The most plausible interpretation for the formation of the HSAG adduct with 2-pyrone seems to be the cycloaddition reaction between the edges of the graphitic substrate and the unsaturated biomolecule. Such a functionalization appears to be suitable for a scale up and paves the way for the preparation of a variety of derivatives.