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Formation mechanism and optimization of highly luminescent N-doped graphene quantum dots.

Qu D, Zheng M, Zhang L, Zhao H, Xie Z, Jing X, Haddad RE, Fan H, Sun Z - Sci Rep (2014)

Bottom Line: The intramoleculur dehydrolysis between neighbour amide and COOH groups led to formation of pyrrolic N in the graphene framework.N-doping results in a great improvement of PL quantum yield (QY) of GQDs.The obtained N-doped GQDs exhibit an excitation-independent blue emission with single exponential lifetime decay.

View Article: PubMed Central - PubMed

Affiliation: 1] State Key Laboratory of Luminescence and Applications, Changchun Institute of Optics, Fine Mechanics and Physics, Changchun 130033, Jilin, P. R. China [2] University of Chinese Academy of Science, Beijing 100000, P. R. China.

ABSTRACT
Photoluminescent graphene quantum dots (GQDs) have received enormous attention because of their unique chemical, electronic and optical properties. Here a series of GQDs were synthesized under hydrothermal processes in order to investigate the formation process and optical properties of N-doped GQDs. Citric acid (CA) was used as a carbon precursor and self-assembled into sheet structure in a basic condition and formed N-free GQD graphite framework through intermolecular dehydrolysis reaction. N-doped GQDs were prepared using a series of N-containing bases such as urea. Detailed structural and property studies demonstrated the formation mechanism of N-doped GQDs for tunable optical emissions. Hydrothermal conditions promote formation of amide between -NH₂ and -COOH with the presence of amine in the reaction. The intramoleculur dehydrolysis between neighbour amide and COOH groups led to formation of pyrrolic N in the graphene framework. Further, the pyrrolic N transformed to graphite N under hydrothermal conditions. N-doping results in a great improvement of PL quantum yield (QY) of GQDs. By optimized reaction conditions, the highest PL QY (94%) of N-doped GQDs was obtained using CA as a carbon source and ethylene diamine as a N source. The obtained N-doped GQDs exhibit an excitation-independent blue emission with single exponential lifetime decay.

No MeSH data available.


Related in: MedlinePlus

Characterizations of GQDs-G and GQDs-T.(A) Representative TEM images of GQDs-G. Inset: HR-TEM and particle size distribution. (B) Representative TEM images of GQDs-T. Inset: HR-TEM and particle size distribution. (C) UV-Vis spectra (dash line) and PL spectra (solid lines) of GQDs-G and (D) GQDs-TRIS.
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f7: Characterizations of GQDs-G and GQDs-T.(A) Representative TEM images of GQDs-G. Inset: HR-TEM and particle size distribution. (B) Representative TEM images of GQDs-T. Inset: HR-TEM and particle size distribution. (C) UV-Vis spectra (dash line) and PL spectra (solid lines) of GQDs-G and (D) GQDs-TRIS.

Mentions: We synthesized GQDs using other carbon sources such as glucose and TRIS under the same hydrothermal route. Figure 7 shows the TEM images of GQDs prepared from glucose (GQDs-G) and TRIS (GQDs-TRIS) as carbon source. The graphite lattice fringes also are observed in the HR-TEM images. Different optical properties are observed. The GQDs-G exhibits two absorption bands at 300 nm and 350 nm in the UV-Vis spectrum. There is a relative broad emission band at 445 nm under excitation of 360 nm. The emission band shifts to 510 nm when excitation wavelength changes to 420 nm. The lifetime (Supplementary Figure S10) is not a single exponential decay anymore. It can be fitted as double exponential decay, where τ1 is 7.9 ns (64.5%) and τ2 is 1.8 ns (25.5%) (the numbers in parentheses are the percentages of each lifetime). GQDs-TRIS also exhibits an excitation-dependent PL emission and double exponential lifetime decay (τave = 6 ns). Both GQDs-G and GQDs-T show relative low PL QY of 6% and 16%, respectively. From above results, citric acid is a better carbon source in the preparation of GQDs through hydrothermal routes.


Formation mechanism and optimization of highly luminescent N-doped graphene quantum dots.

Qu D, Zheng M, Zhang L, Zhao H, Xie Z, Jing X, Haddad RE, Fan H, Sun Z - Sci Rep (2014)

Characterizations of GQDs-G and GQDs-T.(A) Representative TEM images of GQDs-G. Inset: HR-TEM and particle size distribution. (B) Representative TEM images of GQDs-T. Inset: HR-TEM and particle size distribution. (C) UV-Vis spectra (dash line) and PL spectra (solid lines) of GQDs-G and (D) GQDs-TRIS.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4061557&req=5

f7: Characterizations of GQDs-G and GQDs-T.(A) Representative TEM images of GQDs-G. Inset: HR-TEM and particle size distribution. (B) Representative TEM images of GQDs-T. Inset: HR-TEM and particle size distribution. (C) UV-Vis spectra (dash line) and PL spectra (solid lines) of GQDs-G and (D) GQDs-TRIS.
Mentions: We synthesized GQDs using other carbon sources such as glucose and TRIS under the same hydrothermal route. Figure 7 shows the TEM images of GQDs prepared from glucose (GQDs-G) and TRIS (GQDs-TRIS) as carbon source. The graphite lattice fringes also are observed in the HR-TEM images. Different optical properties are observed. The GQDs-G exhibits two absorption bands at 300 nm and 350 nm in the UV-Vis spectrum. There is a relative broad emission band at 445 nm under excitation of 360 nm. The emission band shifts to 510 nm when excitation wavelength changes to 420 nm. The lifetime (Supplementary Figure S10) is not a single exponential decay anymore. It can be fitted as double exponential decay, where τ1 is 7.9 ns (64.5%) and τ2 is 1.8 ns (25.5%) (the numbers in parentheses are the percentages of each lifetime). GQDs-TRIS also exhibits an excitation-dependent PL emission and double exponential lifetime decay (τave = 6 ns). Both GQDs-G and GQDs-T show relative low PL QY of 6% and 16%, respectively. From above results, citric acid is a better carbon source in the preparation of GQDs through hydrothermal routes.

Bottom Line: The intramoleculur dehydrolysis between neighbour amide and COOH groups led to formation of pyrrolic N in the graphene framework.N-doping results in a great improvement of PL quantum yield (QY) of GQDs.The obtained N-doped GQDs exhibit an excitation-independent blue emission with single exponential lifetime decay.

View Article: PubMed Central - PubMed

Affiliation: 1] State Key Laboratory of Luminescence and Applications, Changchun Institute of Optics, Fine Mechanics and Physics, Changchun 130033, Jilin, P. R. China [2] University of Chinese Academy of Science, Beijing 100000, P. R. China.

ABSTRACT
Photoluminescent graphene quantum dots (GQDs) have received enormous attention because of their unique chemical, electronic and optical properties. Here a series of GQDs were synthesized under hydrothermal processes in order to investigate the formation process and optical properties of N-doped GQDs. Citric acid (CA) was used as a carbon precursor and self-assembled into sheet structure in a basic condition and formed N-free GQD graphite framework through intermolecular dehydrolysis reaction. N-doped GQDs were prepared using a series of N-containing bases such as urea. Detailed structural and property studies demonstrated the formation mechanism of N-doped GQDs for tunable optical emissions. Hydrothermal conditions promote formation of amide between -NH₂ and -COOH with the presence of amine in the reaction. The intramoleculur dehydrolysis between neighbour amide and COOH groups led to formation of pyrrolic N in the graphene framework. Further, the pyrrolic N transformed to graphite N under hydrothermal conditions. N-doping results in a great improvement of PL quantum yield (QY) of GQDs. By optimized reaction conditions, the highest PL QY (94%) of N-doped GQDs was obtained using CA as a carbon source and ethylene diamine as a N source. The obtained N-doped GQDs exhibit an excitation-independent blue emission with single exponential lifetime decay.

No MeSH data available.


Related in: MedlinePlus