Preparation Of Doped Graphene Quantum Dots And Application Of Photocatalysis

Graphene quantum dots（GQDs）,a derivant of graphene,possess stronger quantum confinement and edge effects,besides the excellent properties of graphene.Futhermore,GQDs have an extensive application prospect in the fields of catalysis,optoelectronic devices and biological imaging.As the most outstanding optical properties of GQDs,photoluminescence（PL）can be influence by both the quantum confinement and surface/internal functional groups.It exists great significance to further improve the performance of PL in the field of photoelectric catalysis,photovoltaic devices and electrochemical detection by modifying the doping of GQDs.In order to improve the PL properties of GQDs and develop its application,we study the preparation of doped GQDs,the tuning and mechanism of PL,photocatalysis.Specific content as follows:1.The fluorine doped graphene quantum dots（F-GQDs）with F/C atomic ratio of up to84.25%were prepared by solid phase reaction using GQDs as predecessor and XeF₂ as fluorine source.After analyzing the content and form of fluorine,we study the PL and photoluminescence emission（PLE）spectra of F-GQDs.Compared with that of GQDs,the PL emission peak of F-GQDs has an obvious blue-shift.Finally,we explain the blue-shift phenomenon by energy level transition.2.The nitrogen and sulfur co-doped graphene quantum dots（NS-GQDs）with a corresponding size of 2.5 nm,which is independent of excitation wavelength,were prepared by hydrothermal method using ammonia as nitrogen source and sulfur powder as sulfur source.Compared with the precursor GQDs,the PL emission peak of the NS-GQDs has a blue shift of 54 nm.Comparison of PL spectra with nitrogen doped graphene quantum dots（N-GQDs）,we conclude that the edge region of NS-GQDs carry more functional groups leading to the decrease of the central sp² region,and then the blue shift of the PL emission peak happen.3.A series of sulfur doped graphene quantum dots（S-GQDs）with different sulfur contents were prepared by a hydrothermal method using sulfur powder as sulfur source and GQDs as precursor.The average size of S-GQDs with high quantum yield（⁵7%）was mainly concentrated at 3 nm.The characterization indicates that the PL of S-GQDs exhibit independent of excitation wavelength and have a obvious blue-shift.Through studying the PL spectra of S-GQDs with different sulfur contents,the results show that the wavelength/intensity of the PL emission peak is closely related to the ratio of thiophene sulfur to sulfur dioxide4.With a simple hydrothermal method,S-GQDs/TiO₂ photocatalytic composite was prepared by carring S-GQDs nanoparticles on the surface of P25 TiO₂.The photocatalytic efficiency of S-GQDs/TiO₂ composites was measured by the degradation of methyl orange（MO）.The results showed that the photocatalytic efficiency of S-GQDs/TiO₂ composites was significantly higher than that of the conventional photocatalyst TiO₂ under the short time illumination.Photocatalytic mechanism was discussed preliminarily.During the photocatalytic activity,S-GQDs not only provide electrons to promote the formation of electron hole pair,S-GQDs generated reactive oxygen species(·O_2-),which is an indispensable role to enhance the photocatalytic efficiency.