Abstract
Graphene quantum dots (GQDs) containing N atoms were successfully synthesized using a facile, inexpensive, and environmentally friendly hydrothermal reaction of urea and citric acid, and the effect of the GQDs’ C–N configurations on their photoluminescence (PL) properties were investigated. High-resolution transmission electron microscopy (HR-TEM) images confirmed that the dots were spherical, with an average diameter of 2.17 nm. X-ray photoelectron spectroscopy (XPS) analysis indicated that the C–N configurations of the GQDs substantially affected their PL intensity. Increased PL intensity was obtained in areas with greater percentages of pyridinic-N and lower percentages of pyrrolic-N. This enhanced PL was attributed to delocalized π electrons from pyridinic-N contributing to the C system of the GQDs. On the basis of energy electron loss spectroscopy (EELS) and UV-Vis spectroscopy analyses, we propose a PL mechanism for hydrothermally synthesized GQDs.
Highlights
Our group has reported a similar synthesis of Graphene quantum dots (GQDs) by reacting citric acid and urea via a hydrothermal method[11]
To the best of our knowledge, the literature contains no reports regarding the role of these three C–N configurations or their relationship to the PL intensity of GQDs derived from citric acid and urea precursors with hydrothermal method
Atomic force microscopy (AFM) imaging (Fig. 2e) revealed a typical topographic height of 0–8.22 nm, with an average height of 1.89 nm (Fig. 2f); these results suggest that the average particle size was 1.89 nm, which is very similar to the average size observed by transmission electron microscopy (TEM) (2.17 nm)
Summary
Our group has reported a similar synthesis of GQDs by reacting citric acid and urea via a hydrothermal method[11]. Consistent with the results of Dong et al.[10] the prepared samples exhibited colour changes as the reaction between the citric acid and urea progressed. The sample prepared in the absence of the urea precursor exhibited no luminescence, indicating that nitrogen from the urea played an important role in the observed photoluminescence (PL) effect. Because the C–N configurations, i.e., pyrrolic-N, graphitic-N, and pyridinic-N, affected the electronic structure of GQDs13–15, elucidating the role of N configurations in GQDs is important for understanding their PL mechanism. To the best of our knowledge, the literature contains no reports regarding the role of these three C–N configurations or their relationship to the PL intensity of GQDs derived from citric acid and urea precursors with hydrothermal method. On the basis of these results, we propose a GQD PL mechanism that accounts for the effects of the C–N configurations
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
