How do nitrogen-doped carbon dots generate from molecular precursors? An investigation of the formation mechanism and a solution-based large-scale synthesis

Abstract

A bottom-up method, using monoethanolamine (MEA) as both a passivation agent and a solvent, has been developed for rapid and massive synthesis of nitrogen-doped carbon dots (N-C-dots) from citric acid under heating conditions. This method requires relative mild temperature (170 °C) without special equipment, and affords one-pot large-scale production (39.96 g) of high-quality N-C-dots (quantum yield 10 of 40.3%) in a few minutes (10 minutes). Significantly, an interesting formation process of N-C-dots, for the first time, has been monitored by transmission electron microscopy, ultraviolet-visible absorbance spectroscopy, photoluminescence spectroscopy, Fourier transformed infrared spectroscopy, and thermogravimetric analysis, and a corresponding formation mechanism including polymerization, aromatization, nucleation, and growth, is proposed. It is important that the MEA-based synthesis of N-C-15 dots can be extended to various precursors, such as glucose, ascorbic acid, cysteine, and glutathione, which show general university. Furthermore, the N-C-dots with strong fluorescence, excellent optical stability, and low cytotoxicity, are successfully applied as fluorescent probes for bioimaging.

Nitrogen-doped Carbon Dots Mediated Fluorescent on-off Assay for Rapid and Highly Sensitive Pyrophosphate and Alkaline Phosphatase Detection

“…The XRD spectrum (Supplementary Fig. S2) exhibits a broad peak at around 23°, corresponding to a disordered carbon atoms 46 . The above facts suggest that the as-prepared CDs are N-doped and exhibit abundance hydrophilic groups on the surface.

Figure 1( a ) TEM image of N-CDs.

…”

Understanding the Photoluminescence Mechanism of Nitrogen‐Doped Carbon Dots by Selective Interaction with Copper Ions

“…The nearly white‐light‐emitting NCDs with an emission band centered at 460 nm show four peaks in the UV/Vis absorption spectrum, namely at 227, 265, 338 and 390 nm (Figure ). The peak at 227 nm might originate from the π–π* absorption of the C=C core whereas the peaks at 265 and 338 nm are ascribed to the absorption of the C=N and C=O functional groups, respectively . The band at ≈390 nm is attributed to the formation of J‐type self‐assemblies, which must have aroused from the π stacking of aromatic nucleus and due to the involvement of surface functional groups.…”

“…The peak at 227 nm might originate from the p-p*a bsorption of the C=C core whereas the peaks at 265 and 338 nm are ascribed to the absorption of the C=Na nd C=Of unctional groups, respectively. [34] The band at % 390 nm is attributed to the formation of Jtype self-assemblies, [35] which must have aroused from the p stacking of aromatic nucleus and due to the involvement of surfacefunctional groups. Figure 1s hows the broad PL spectra of NCDs under UV excitation, which covers al arge portion of the visible spectrum.…”

Upconverting Carbon Nanodots from Ethylenediaminetetraacetic Acid (EDTA) as Near‐Infrared Activated Phototheranostic Agents

“…The process typicallyp roceeds through an umber of sequential steps including polymerization and carbonization of organic precursors ( Figure 1a). Hu et al [43] suggested ad etailed mechanism proceeding through four stages, including dehydration, polymerization, carbonization, and passivation. They claimedi nt heir study that the molecules assembled as ar esult of hydrogen bonding.…”

“…In parallel, aromatic clusters are formed and when their concentrationr eaches ac ritical super-saturation point, nucleation of carbon nanodotst akes place after multiple aggregation events. [43] Finally,t he polymers disappear and CNDs remain. [43] TEMa nalysiss hows the presence of crystalline N-CNDs with clear lattice fringesa nd average sizes of 2.9 AE 0.5 nm (Figure1ba nd Figure S1 in the Supporting Information).…”