Insights into the formation of N doped 3D-graphene quantum dots. Spectroscopic and computational approach

Abstract

In this work, we utilize a top-down approach to synthesize nitrogen doped graphene quantum dots from a 3D-graphene precursor via an eco-friendly hydrothermal method. The nanoparticles obtained showed a 2–3 nm diameter and well dispersion behavior in aqueous media. The reaction mechanism of insertion of nitrogen from polyvinylpolypyrrolidone onto the 3D-graphene structure, via an esterification reaction, was studied by the density functional theory, in addition, the kinetic and thermodynamic magnitudes of the reaction was analyzed with the help of Eyring's transition state theory and statistical thermodynamics. After analysis by ss-NMR and XPS spectroscopies, the functional groups involved in this process were characterized, and N was found mainly as amide/amine groups. Fluorescence emission, which exhibited a red shift (552 nm) and an emission maximum at 512 nm when excited at 480 nm, demonstrated a low stoke shift (Δλ = 32 nm), explained by the proposed structural model.