Facile one-step hydrothermal synthesis of monolayer and turbostratic bilayer n-doped graphene quantum dots using sucrose as a carbon source.

Graphene quantum dots (GQDs) have attracted attention from researchers owing to their outstanding properties, such as chemical inertness, stable photoluminescence (PL), biocompatibility, and low toxicity, which make them suitable for bioimaging, optoelectronic device, sensor, and others. At present, there are several studies that report the effect of the size of GQDs on their properties; however, but there is only a few studies that report the effect of the thickness of GQDs on their properties. It may be attributed to the difficulty to obtain the accurate information on the thickness of GQDs. In this study, we demonstrate the facile and one-step hydrothermal synthesis of monolayer and bilayer n-doped graphene quantum dots (NGQDs) using sucrose as a carbon source. UV-visible and PL spectra show the quantum yield of the NGQDs is 4.9 times higher than that of the GQDs. Besides, the NGQDs exhibit sensitive PL for Ag ions. In addition, the thickness distribution and interlayer spacing of NGQDs are revealed by X-ray diffraction (XRD) curve fitting, which is calculated using a simple and accurate equation. The information on the structure of the NGQDs from the XRD curve fitting is in a good agreement with the Raman results. This accurate estimation of the structure of GQDs by XRD curve fitting using the simple equation may extend the limits of GDQ study.