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

Edge functionalization of graphene layers is of greatinterest in thefield of materials chemistry: the properties ofgraphene are substantially unaltered and its compatibility andchemical reactivity with various environments can be tuned. In thiswork, edge functionalization of graphene layers was performed witha 2-pyrone, ethyl 3-hydroxy-2-oxo-2H-pyran-6-carboxylate (Pyr-COOEt). 2-Pyrones are C-6 unsaturated heterocyclic sugarderivatives and are intriguing building blocks for the preparationof innovative chemical structures. Sodium 3-acetoxy-2-oxo-2H-pyran-6-carboxylate was prepared starting from mucic acid, in aone-pot synthesis with a yield of about 74%, and was thentransformed into the acid and then into ethyl ester derivatives. Theadduct 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 fromthermogravimetric analysis (TGA) data and was found to be up to 91%. The adducts were characterized by Fourier transforminfrared and Raman spectroscopies and wide-angle X-ray diffraction. The presence of pyrone in the adduct was clearly detected inthe IR spectra, and the bulk structure of the graphitic substrate was found to be substantially unaltered by the functionalizationreaction. The experimentalfindings suggest that the edge functionalization of the graphene layers occurred. Stable water dispersionsof HSAG/Pyr adducts were prepared and studied through ultraviolet-visible analysis. Aggregates of few-layer graphene wereobtained by mild sonication and centrifugation, as revealed by high-resolution transmission electron microscopy. This paper showsthat a biobased molecule can be used for selectively decorating the edges of graphene layers, with oxygenated functional groupshaving a defined chemical structure and avoiding the use of oil-based, dangerous, and even noxious ingredients. The most plausibleinterpretation for the formation of the HSAG adduct with 2-pyrone seems to be the cycloaddition reaction between the edges of thegraphitic substrate and the unsaturated biomolecule. Such a functionalization appears to be suitable for a scale up and paves the wayfor the preparation of a variety of derivatives