Synthesis And Characterization Of Graphene Quantum Dots By Ultraviolet Irradiation Method

Graphene quantum dots?GQDs?represent single-layer to tens of layers of graphene of a size less than 30 nm.Due to quantum confinement effect and edge effect,electrons in GQDs are limited in three-dimensional space,which lead to a non-zero generation gap and optical and electronic properties different with large size graphene.Because of the attractive futures in the fields of electrochemistry,physics,photoelectricity and biomedicine,the controllable preparation and mechanism of GQDs have been studied by lots of scientists.This research is aiming to explore an efficient production method of GQDs,to produce GQDs with uniform size and high quality.By adopting ultrasonic hummers method to produce graphene oxide?GO?,which were regarded as raw material,we produced GQDs by applying both ultrasonic wave and ultraviolet radiation.Then,the influences of technological parameter on the quality of GQDs were discussed,as well as the size,thickness,microstructure of GQDs.Both the GO produced by improved hummers and ultrasonic hummers methods own more disordered carbon and less order carbon,which proved the presence of GO.The raman intensities ratio I_D/I_G of GO produced by improved hummers method is 0.86,because strong phosphoric acid prevents the generation of defects in GO.While the raman intensities ratio I_D/I_G of GO produced by ultrasonic hummers method is 0.90 because of the presence of more oxygen containing functional groups and defects.What's more,GO produced by ultrasonic hummers method is good crystalline and more flat,which processes two dimensional size of 300-800nm and thickness of 1-3 layers.Using GO produced by ultrasonic hummers method as raw material,GQDs were produced by applying ultraviolet radiation.The size and thickness of GQDs decrease gradually with the increase of time and the intensity of ultraviolet radiation.In addition,the thesis is also to find the optimum process parameters,such as ultraviolet radiation,concentration of GO,concentration of H₂O₂,concentration of FeCl₃,pH value,and time.The size of GQDs is about 13-17 nm.Using GO produced by ultrasonic hummers method as raw material,GQDs were produced by applying ultraviolet radiation and ultrasonic wave at the same time.The size and thickness of GQDs decrease gradually with the increase of time and the intensity of ultraviolet radiation together with ultrasonic wave.Also the process parameters,including ultrasonic wave,ultraviolet radiation,concentration of GO,concentration of H₂O₂,concentration of FeCl₃,pH value,and time have been optimized.Finally,the produced GQDs have the size of about 3-5 nm,and the yield of GQDs is discovered.This research put forward a method of producing GQDs by applying both ultrasonic wave and ultraviolet radiation.By studying the influence of concentration of H₂O₂,FeCl₃,GO,pH,intensity of ultrasonic wave and ultraviolet radiation and reaction time to the size,microstructure of GQDs,we got the optimum process parameters to produce small sized GQDs,which is of great significance for large-scale preparation of GQDs.