Synthesis,Characterization And Application Of Graphene Quantum Dots

Graphenequantum dots(GQDs),as a new kind of quantum dots,have emerged and ignited tremendous research interests.Due to the pronounced quantum confinement and edge effects,GQDs display numerous novel chemical/physical properties,such as excellent solubility,chemical inertia,stable photoluminescence,which makes them promising in photoelectrondevices,sensors,bioimaging,etc.In this thesis,we synthesized GQDs by a facile one-step solvothermal method using graphene oxide as precursors,and the structure of the GQDs was further characterized.Subsequently,we explored the electrochemiluminescence and fluorescence properties of GQDs.The main contents and results are included asfollow:1.Preparation and characterization of GQDsWe synthesized GQDs by a solvothermal methodusing GO as precursor.The quantum yield of acquired GQDs was about 6.26%.The structure and fluorescence properties of GQDs were characterized by scanning electron microscopy(SEM),atomic force microscopy(AFM),fourier transform infrared spectroscopy(FT-IR),fluorescence spectroscopy(FL)and UV-vis spectroscopy.The resulting GQDs had a surface rich in oxygen-containing functional groups such as-COOH?-OH,and were relatively uniform in size with a size distribution between 29nm and 37nm,an average diameter of 34 nm,and a typical topographic height of 1.0?3.8nm.The aqueous dispersion of GQDs displayed an absorption band at about 330 nm,and maximum excitation and emission wavelengths at 370 nm and 520 nm,respectively.Meanwhile,the FL emission peak 520 nm changed with the change of excitation wavelengths.The excitation-dependent emission was supposed to be related to the size of GQDs.2.Study and application of electrochemiluminescence properties of GQDsWe found that GQDs could be used as coreactant to enhance the electrochemiluminescence of Ru(bpy)₃²⁺and the mechanismwas discussed.Upon the addition of L-alanine to Ru(bpy)₃²⁺,the ECL signal of GQDs-Ru(bpy)₃²⁺was further increased.The relative ECL intensity(I-I₀)/I₀ exhibited a good linearity with the concentrations of L-alanine in the range of 1?600?g/m L with the detection limit of 0.51?g/m L.Combining with sequential injection technique,we established a GQDs-SIA-ECL method for L-alanine determination.It is expected to be applied to the determination of L-alanine in biological samples.3.The interaction between GQDs and Mo S₂ nanosheetsWe found that Mo S₂nanosheets could efficiently quench the fluorescence of GQDs.With the addition of H₂O₂ to the mixture of GQDs and Mo S₂nanosheets,the quenched fluorescence could be recovered and the FL enhancement displayed a good linear relationship with the concentration of H₂O₂ in the range of 0.1?4.0 mmol/L.Moreover,we further investigated the effect of BSA?Hb and metal ions on the fluorescence properties of GQDs.The results showed Fe³⁺and Hb had the most significant quenching impacts on GQDs,which are expected to be used for their quantitative detection.