Investigations On The Spectral Properties Of Boron-Doped Graphene Quantum Dots And Applications

As a kind of novel carbon material,graphene is a single layer of carbon atoms in a honeycomb structure.Due to the quantum confinement and edge effects,graphene nanosheets of size less than 100 nm,known as graphene quantum dots（GQDs）,usually display outstanding optical properties.In chapter 1,brief reviews are given to the properties,preparation approachs and the modifications of GQDs,and their applications in the fields of sensing and bio-imaging as well.In chapter 2,the boron-doped graphene quantum dots（B-GQDs）are prepared and characterized.A microwave one-pot approach for the synthesis of B-GQDs has been proposed using graphene oxide（GO）and borax as source materials.The results of high resolution transmission electron microscopy（HRTEM）indicate that the obatined GQDs are of uniform distribution,with size of ca.3-8 nm.X-ray photoelectron spectroscopy（XPS）reveals that boron atoms have been successfully doped into graphene structures,and the atom percentage of B in GQDs is measured to be 1.44%.The existence of boron-carbon bond in fourier transform infrared spectra（FT-IR）further confirms the successfull doping of B into the strcuture of GQDs.Raman spectra suggests that the doping of boron atoms into the conjugated carbon framework restores some defect of GQDs structures,resluting in the decreasing of the defect level.As a result,a broad D band is observed in the Raman spectra of B-GQDs,with an I_D/I_G value of 1.04.In chapter 3,the photoluminescence（PL）properties of the as-prepared B-GQDs are investigated.The obtained B-GQDs exhibit excitation-independent PL behavior in a certain range,and the excitation/emission maximum is 320 nm/430 nm,respectively.The quantum yield of B-GQDs is up to 21.1%.The PL intensity of B-GQDs keeps virtuall stable in the pH range of 4.0～11.0,and an ionic strength high to 2.0 mol L^-1 KCl and irritating time 2 h hardly pose any effect on the PL of B-GQDs.The standard MTT assay results suggest that the obtained B-GQDs are of low cytotoxicity and excellent biocompatibility,and a cell viability of 87%is even obtained under a B-GQD concentration of 4 mg mL^-1.The B-GQDs are applied in the imaging of live HeLa cells,and excellent imaging results are obtained.