Blue and green luminescent carbon nanodots from controllable fuel-rich flame reactors

Abstract

The continuous synthesis in controlled gas flame reactors is here demonstrated as a very effective approach for the direct and easy production of structurally reproducible carbon nanodots. In this work, the design of a simple deposition system, inserted into the reactor, is introduced. A controlled flame reactor is employed in the present investigation. The system was optimized for the production of carbon nanoparticles including fluorescent nanocarbons. Blue and green fluorescent carbon could be easily separated from the carbon nanoparticles by extraction with organic solvents and characterized by advanced chemical (size exclusion chromatography and mass spectrometry) and spectroscopic analysis. The blue fluorescent carbon comprised a mixture of molecular fluorophores and aromatic domains; the green fluorescent carbon was composed of aromatic domains (10-20 aromatic condensed rings), bonded and/or turbostratically stacked together. The green-fluorescent carbon nanodots produced in the flame reactor were insoluble in water but soluble in N-methylpyrrolidinone and showed excitation-independent luminescence. These results provide insights for a simple and controlled synthesis of carbon nanodots with specific and versatile features, which is a promising pathway for their use in quite different applicative sectors of bioimaging.

Figure 1

(a) Scheme of the experimental setup for carbon particulate matter sampling from premixed flames and solvent treatment, (b) photos of the heavily sooting (HSF) and lightly sooting (LSF) reactors.

Figure 2

TEM images of flame-synthesized carbon particulate matter.

Figure 3

UV-Visible absorption, excitation and emission fluorescence spectra of blue CDs (a) (λ_exc = 315 nm and λ_em = 440 nm), and green CDs (b) (λ_exc = 340 nm and λ_em = 505 nm), extracted from carbon particulate matter sampled at 6 mm of the HSF reactor. The photos of blue and green fluorescent sample solutions and the optical band gap values measured on the UV-Visible spectra are inserted in the respective figures.

Figure 4

Normalized fluorescence spectra of blue CDs (left) and green CDs (right) excited at different wavelengths. The photos of blue and green fluorescent sample solutions are inserted in the respective figures. The reported spectra refer to CDs sampled at 6 mm of flame height in heavily sooting (HSF) reactor.

Figure 5

Synchronous emission spectra (Δλ = 10 nm) of blue and green CDs extracted from carbon particulate matter sampled at 6 mm of flame height in heavily sooting (HSF) reactor. The photos of blue and green fluorescent sample solutions are inserted in the figure.

Figure 6

Molecular weight distribution of the blue and green CDs as measured by SEC analysis. The reported distributions refer to the CDs sampled at 6 mm of the HSF reactor.