Research On Fabrication Of Luminescent Carbon Dots By Solution Process And Their Properties

As one of the most important topics of carbon materials,carbon dots have drawn intensive attention and triggered substantial investigation since their discovery in 2004 due to their excellent fluorescent properties.Besides ease of preparation and low-cost synthesis,carbon dots manifest superior merits including resistance to photobleaching,outstanding chemical inertness,water solubility,easy surface functionalization,excellent biocompatibility to replace conventional unsatisfactory fluorescent materials.Carbon dots have already exhibited many versatile applications in the field of fluorescence sensors,photocatalysis,drug delivery,optoelectronic devices and bioimaging.At present,the actual mechanism of CDs photoluminescence is still an open debate among researchers because of their diversity in structure.Therefore in this thesis,the following work is carried out based on the synthesis,luminescent mechanism and applications :First of all,the water-soluble fluorescent carbon dots were synthesized by microwave-assisted method,and the effects of different carbon sources,urea and different solvents on the fluorescent properties were studied.The results showed that the synthesized carbon dots were excitation wavelength-dependent.The absorption peaks,strongest PL peaks and corresponding excitation peaks of carbon dots synthesized by different organic molecules were at different wavelengths and had different PL quantum yield,indicating that the molecular structure of carbon source had an important influence on the properties of carbon dots.After adding urea as nitrogen source,the UV-Vis spectra and PL spectra of the carbon dots changed to some extent.On the other hand,using urea could increase or decrease the products yield synthesized from different molecule carbon sources and increase the PL quantum yield of the carbon dots.The fluorescent properties of carbon dots synthesized with different organic solvents were different with those synthesized with water.Secondly,multicolor fluorescent carbon dots synthesized by hydrothermal/solvothermal treatment of different solvent had PL peaks at blue(470 nm),green(500 nm),yellow(539 nm)and red(595 nm)wavelength and different absorption peaks.Through experiments,it was found that amide solvent was the key to get red fluorescence in carbon dots,while acetic acid could enhance red emission.Due to the inner filter effect and FRET effect,the intensity of the PL spectra of the carbon dots would vary with the solution concentration,and the emissions would gradually red-shift or blue-shift.On the other hand,the absorption spectra of the synthesized carbon dots would change with the increase of p H,and the emission showed p H-dependent PL.The fluorescent properties of carbon dots were greatly changed by reduction with sodium borohydride.It was convinced that the carbon dots synthesized by hydrothermal/solvothermal treatment had a surface states related luminescent mechanism.TEM,XRD,FTIR,Raman,XPS and other methods were used to characterize the structure,size and chemical composition of carbon dots.The solid state luminescence of carbon dots was realized by combining carbon dots with sodium chloride,and the fluorescence emission peaks were located at 460 nm,496 nm,564 nm and 585 nm respectively.