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

• Main Authors: Yue Yang, Tong Zou, Zhezhe Wang, Xinxin Xing, Sijia Peng, Rongjun Zhao, Xu Zhang, Yude Wang
• Format: Article
• Language: English
• Published: MDPI AG 2019-05-01
• Series: Nanomaterials
• Subjects: N and S co-doped graphene quantum dots; fluorescence quenching; DFT; non-radiative electron transfer; inner filter effect; fluorescence sensor
• Online Access: https://www.mdpi.com/2079-4991/9/5/738
• ISSN: 2079-4991

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.