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. 2016 May 27:7:758-66.
doi: 10.3762/bjnano.7.67. eCollection 2016.

Facile synthesis of water-soluble carbon nano-onions under alkaline conditions

Gaber Hashem Gaber Ahmed  1 , Rosana Badía Laíño  2 , Josefa Angela García Calzón  2 , Marta Elena Díaz García  2
Affiliations

Facile synthesis of water-soluble carbon nano-onions under alkaline conditions

Gaber Hashem Gaber Ahmed et al. Beilstein J Nanotechnol. .

Abstract

Carbonization of tomatoes at 240 °C using 30% (w/v) NaOH as catalyst produced carbon onions (C-onions), while solely carbon dots (C-dots) were obtained at the same temperature in the absence of the catalyst. Other natural materials, such as carrots and tree leaves (acer saccharum), under the same temperature and alkaline conditions did not produce carbon onions. XRD, FTIR, HRTEM, UV-vis spectroscopy, and photoluminescence analyses were performed to characterize the as-synthesized carbon nanomaterials. Preliminary tests demonstrate a capability of the versatile materials for chemical sensing of metal ions. The high content of lycopene in tomatoes may explain the formation of C-onions in alkaline media and a possible formation mechanism for such structures was outlined.

Keywords: carbon dots; carbon onions; metal-ion sensing; photoluminescence; thermal carbonization.

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Figures

Figure 1
Figure 1
HRTEM images of C-dots obtained by carbonization in aqueous environment, using as carbon source a) tomatoes, b) carrots and c) tree leaves.
Figure 2
Figure 2
HRTEM images of C-dots obtained by carbonization in NaOH 30% (w/v), using as carbon source a) carrots, b) tree leaves.
Figure 3
Figure 3
a) HRTEM image of C-onions obtained by carbonization in NaOH 30% (w/v), using tomatoes as carbon source; b) intensity profile (arbitrary units) measured over the white arrow marked in a).
Figure 4
Figure 4
XRD patterns of C-NPs obtained from tomatoes through carbonization in aqueous (C-dots) and NaOH 30% (w/v) (C-onions) media.
Figure 5
Figure 5
FTIR spectra of C-dots and C-onions obtained by carbonization of tomatoes in aqueous solution and NaOH 30% (w/v), respectively.
Figure 6
Figure 6
Effect of some metals on the photoluminescence spectra of C-NPs at pH 6. a) C-onions measured at λex = 328 nm. Slit width of emission and excitation was 10 and 20, respectively. b) C-dots measured at λex = 362 nm. The slit widths of emission and excitation were both 20 nm. The concentration of metals was 10 ppm in all cases.
Figure 7
Figure 7
Hypothetical growth of carbon onions from lycopene.
See this image and copyright information in PMC

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