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The Fluorescent Quenching Mechanism of N and S Co-Doped Graphene Quantum Dots with Fe3+ and Hg2+ Ions and Their Application as a Novel Fluorescent Sensor

1
Department of Physics, Yunnan University, Kunming 650091, China
2
School of Materials Science and Engineering, Yunnan University, Kunming 650091, China
3
Key Lab of Quantum Information of Yunnan Province, Yunnan University, Kunming 650091, China
*
Author to whom correspondence should be addressed.
Nanomaterials 2019, 9(5), 738; https://doi.org/10.3390/nano9050738
Received: 22 April 2019 / Revised: 8 May 2019 / Accepted: 9 May 2019 / Published: 13 May 2019
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Abstract

The fluorescence intensity of N, S co-doped graphene quantum dots (N, S-GQDs) can be quenched by Fe3+ and Hg2+. Density functional theory (DFT) simulation and experimental studies indicate that the fluorescence quenching mechanisms for Fe3+ and Hg2+ detection are mainly attributed to the inner filter effect (IFE) and dynamic quenching process, respectively. The electronegativity difference between C and doped atoms (N, S) in favor to introduce negative charge sites on the surface of N, S-GQDs leads to charge redistribution. Those negative charge sites facilitate the adsorption of cations on the N, S-GQDs’ surface. Atomic population analysis results show that some charge transfer from Fe3+ and Hg2+ to N, S-GQDs, which relate to the fluorescent quenching of N, S-GQDs. In addition, negative adsorption energy indicates the adsorption of Hg2+ and Fe2+ is energetically favorable, which also contributes to the adsorption of quencher ions. Blue fluorescent N, S-GQDs were synthesized by a facile one-pot hydrothermal treatment. Fluorescent lifetime and UV-vis measurements further validate the fluorescent quenching mechanism is related to the electron transfer dynamic quenching and IFE quenching. The as-synthesized N, S-GQDs were applied as a fluorescent probe for Fe3+ and Hg2+ detection. Results indicate that N, S-GQDs have good sensitivity and selectivity on Fe3+ and Hg2+ with a detection limit as low as 2.88 and 0.27 nM, respectively. View Full-Text
Keywords: N and S co-doped graphene quantum dots; fluorescence quenching; DFT; non-radiative electron transfer; inner filter effect; fluorescence sensor N and S co-doped graphene quantum dots; fluorescence quenching; DFT; non-radiative electron transfer; inner filter effect; fluorescence sensor
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Yang, Y.; Zou, T.; Wang, Z.; Xing, X.; Peng, S.; Zhao, R.; Zhang, X.; Wang, Y. The Fluorescent Quenching Mechanism of N and S Co-Doped Graphene Quantum Dots with Fe3+ and Hg2+ Ions and Their Application as a Novel Fluorescent Sensor. Nanomaterials 2019, 9, 738.

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