Hydrothermal functionalization of graphene quantum dots extracted from cellulose

Abstract

Functionalization is a promising approach to modify the physical and chemical properties of graphene quantum dots (GQDs). However, the synthesis of functionalized GQDs (F-GQDs) is usually conducted with strong acids. Thus, the sustainable synthesis route of F-GQDs remains a challenge. This is important for suitable optimization of GQDs to be applied in sustainable photovoltaic applications, especially dye-sensitized solar cells owing to the strong attachment of functional group elements. This study presents a detailed study of optical, structural, and chemical changes that occurred in GQDs during the functionalization process by adding an ionic liquid, 1-ethyl-1-methylpyrrolidium bis(trifluoromethylsulfonyl)imide via hydrothermal synthesis approach using an eco-friendly route comprising only cellulose and deionized (DI) water. The presence of ionic liquid provides fundamental elements (nitrogen (N), fluorine (F), and sulfur (S)), which are added to GQDs producing F-GQDs. The optimum result shows that the 20 wt% N, F, S functionalized GQDs have the largest UV–vis absorption and photoluminescence emission. The F-GQDs also revealed a single crystalline hexagonal graphene-like honeycomb structure in transmission electron microscopy and increased roughness relatively from atomic force microscopy. Moreover, the Fourier transform infrared and x-ray photoelectron spectroscopy have also confirmed the presence of C-N, C=S, C-F, and N-H functional groups in the F-GQDs produced.