Preparation and Optical Properties of Graphene Quantum Dots Containing Nitrogen

doi:10.15541/jim20160227

Abstract

Abstract:

Graphene quantum dots containing nitrogen (NGQDs) were synthesized by the hydrothermal method. AFM, TEM and XPS were employed to investigate the morphology and composition of NGQDs, and their optical properties were studied by UV-Vis and photoluminescent (PL) spectroscopy. AFM and TEM images showed that NGQDs were about 8.9 nm in size and 0.6-2.0 nm in thickness (1-3 layers graphene). The result of XPS showed that nitrogen content in NGQDs was ~17% and nitrogen existed mainly in the form of "pyrrolic N". Spectroscopy experiments indicated that excitation spectra of NGQDs were similar to their absorption spectra, and their emission spectra were excitation-independent. In addition, quantum yield of NGQDs was calculated to be ~18%, increasing with the content of nitrogen in NGQDs increase. Furthermore, the lifetime decay curve was well fitted to a double exponential decay curve (τ₁=2.93 ns, τ₂=9.00 ns), which indicates that there are two feature chromophores in NGQDs. The chromophores are sp² clusters with oxygen groups and pyrrolic ring.

Key words: graphene quantum dots, hydrothermal method, nitrogen doped, optical properties

CLC Number:

TQ174

ZHANG Dong-Mei, TIAN Lei, GUO Hui-Lin. Preparation and Optical Properties of Graphene Quantum Dots Containing Nitrogen[J]. Journal of Inorganic Materials, 2016, 31(10): 1123-1128.

Figures/Tables 11

Table 1 Elements analysis and quantum yield of NGQDs

Sample	C/wt%	N/wt%	H/wt%	Quantum yield (QY)
NGQDs-1	32.90	13.41	6.318	8.50%
NGQDs-2	32.28	15.87	6.469	12.59%
NGQDs-3	35.27	17.29	6.270	18.11%
NGQDs-4	36.52	17.76	6.133	18.24%

Fig. 1 AFM image of NGQDs-3 and the height profiles along the line (a) and corresponding TEM image (b)

Fig. 2 XPS survey spectrum (a), C1s spectra (b) and N 1s spectra of NGQDs-3

Fig. 3 FT-IR spectrum of NGQDs-3

Fig. 4 UV-Vis spectra of NGQDs

Fig. 5 Excitation spectra (a) and emmision spectra (b) of NGQDs

Fig. 6 Emmision spectra of NGQDs-3 at different excitation wavelengths

Fig. 7 PL spectra and intensities of NGQDs-3 at different pH

Fig. 8 PL spectra of NGQDs-3 before and after irradiating in 365 nm UV lamp for 1 h (a) and before and after placing for 1 month (b)

Fig. 9 PL decay curves of NGQDs-3

Fig. 10 Schematic diagram of photoluminescence of NGQDs

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