Preparation And Properties Of Several Doped Graphene Quantum Dots By Solution Method

Luminescent graphene quantum dots(GQDs) have received more and more attentions due to their excellent fluorescence properties. Theoretical and experimental studies have shown that GQDs exhibit more pronounced edge effect and stronger quantum confinement effect than graphene and therefore become a promising candidate for applications in the fields of optoelectronic devices, sensors and biological imaging. However, there are still some disadvantadges including less active sites, low fluorescence quantum yield and unsatisfactory selectivity, which severely limit their attractiveness and application. Research shows that doping with heteroatoms into the network of graphene could effectively introduce bandgap, defects and localized reactive sites into graphene, thus many special physical and chemical properties. Up to now, the preparation and mechanism of doped GQDs remains underinvestgated, therefore, to explore the preparation of doped GQDs and the ability to modulate their structural and properties of GQDs is of great scientific significance and application value.In this thesisl, the following studies have been performed:1、Using acetylene as carbon sources, we successfully fabricated monodispersed crystalline nitrogen-doped graphene quantum dots(N-GQDs) and sulfur-doped graphene quantum dots(S-GQDs) with a method namely reflux reaction. Under 254 nm and 365 nm ultraviolet light illumiation, the N-GQDs emit blue and green light, the S-GQDs emit violet and blue light respectively. By transmission electron microscopy(TEM) and atomic force microscopy(AFM), spherical quantum dots are observed with an average particle size of less than 5 nm(dN-GQDs = 3.3 nm, dS-GQDs = 4.3 nm). The X-ray photoelectron spectroscopies(XPS), Fourier transform infrared spectroscopy(FTIR) and X-ray diffraction(XRD) confirmed that N and S atoms have been successfully doped into the graphene structure. The photoluminescence experiments(PL or PLE) and ultraviolet-visible absorption spectrum(UV-vis) characterization showed that the introduction of N and S atoms effectively modulate the electronic structure and optical properties of GQDs.2 、Again using acetylene as carbon sources, we successfully fabricated monodispersed crystalline lithium-doped graphene quantum dots(Li-GQDs) and zinc-doped graphene quantum dots(Zn-GQDs) by hydrothermal method. Under 254 nm and 365 nm ultraviolet light illumination, the Li-GQDs emit violet and green light, the Zn-GQDs emit violet and blue light respectively. The TEM and AFM characterization showed a spherical particle in Li-GQDs and an ellipsoid particle in Zn-GQDs with a mean diameter of 3.5 nm for Li-GQDs and4.8 nm for Zn-GQDs. The XPS, FTIR, XRD and Raman characterization confirmed that the Li and Zn atoms have been successfully doped into the graphene structure. The PL, PLE and UV-vis characterizations indicate that the introduction of Li and Zn atoms has effectively modulate the electronic structure and optical properties of GQDs.