Role of C–N Configurations in the Photoluminescence of Graphene Quantum Dots Synthesized by a Hydrothermal Route

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.

A detailed investigation on the performance of dye-sensitized solar cells based on reduced graphene oxide-doped TiO2 photoanode

“…p* and 1s ? r* transitions, respectively, shows typical spectra of graphitic carbon materials [37]. In addition, the C K-edge appeared in EELS of TiO 2 in Fig.…”

Oxidant mediated one-step complete conversion of multi-walled carbon nanotubes to graphene quantum dots and their bioactivity against mammalian and bacterial cells

“…The absence of bismuth or any other metal ion peak in the 12 h treated GQDs shows that the as-synthesized GQDs were free from the oxidants used to break it down. [49][50][51][52] The O1s spectrum showed a broad peak at the binding energy of ~532 eV which may be due to C=O and C-O bonds (Figure 2c). In N1s spectrum, two peaks were observed at ~401 eV and ~406 eV.…”

“…Here, we have reported a one-step, low-cost, aqueous-phase, simple approach for the complete conversion of multiwalled carbon nanotubes into the water-dispersible GQDs with an average size ~3 nm using sodium bismuthate (NaBiO 3 ) as a strong oxidant. [49][50][51][52] The O1s spectrum showed a broad peak at the binding energy of ~532 eV which may be due to C=O and C-O bonds (Figure 2c). The cytotoxicity studies of GQDs against mammalian NIH 3T3 (mouse embryo fibroblast cells) and HEK 293T (human embryonic kidney cells) cells showed that the as-synthesized GQDs were non-cytotoxic up to the concentration of ~200 µg mL -1 .…”

A collagen based cryogel bioscaffold coated with nanostructured polydopamine as a platform for mesenchymal stem cell therapy

“…These spectra included a C–C, C=C peak with a binding energy of ~284 eV [Fig. 3(b);] 39–41 which is observed in collagen spectra. 42 The atomic structure of collagen (that is, the material of our bioscaffolds) was confirmed with its three characteristic footprint signatures at 1630 cm −1 (corresponding to the amide I due to carbonyl stretching—C–H), 1551 cm −1 (corresponding to the amide II due to vibrations on the plane of the N–H bond and C–N stretching) and 1232 cm −1 (corresponding to vibrations on the plane of amide III due to C–N stretching and N–H deformation).…”