Study On Surface Modification By Amine Group And Application Of Graphene Quantum Dots

Graphene quantum dots(GQDs)have many advantages,such as excellent tunable luminescence,good water solubility,easy surface functionalization,low cytotoxicity and a wide range of raw materials.They are widely used in photoelectric,biological imaging,anti-counterfeiting,catalysis and sensing fields.However,there are still some problems with GQDs.For example,the preparation of GQDs usually requires strong acid,and the subsequent process of removing acid is very complicated.In addition,the prepared GQDs generally have low fluorescence quantum efficiency and need to be further improved.In this paper,GQDs with uniform size were prepared by acid-free solvothermal method.The average size of GQDs is only 1.70 nm,and the thickness is between 1.1 and 1.6 nm.It emits blue-green light under irradiation of 365 nm ultraviolet light,the fluorescence quantum efficiency is 26 %,and the fluorescence lifetime is 5.32 ns.In order to further improve the performance of GQDs,GQDs were modified by amino group,o-phenylenediamine modified GQDs(o-GQDs)and p-phenylenediamine modified GQDs(p-GQDs)were prepared.The average size of o-GQDs is 2.40 nm,and the thickness is between 1.7 and 1.8 nm.it emits yellow light under blue light excitation at 440 nm,the fluorescence quantum efficiency is 54 % and the fluorescence lifetime is 5.40 ns.The average size of p-GQDs is 2.56 nm,and the thickness is between 1.5 and 3.0 nm.It emits pink light under irradiation of 365 nm ultraviolet light,the fluorescence quantum efficiency is 67 % and the fluorescence lifetime is 5.67 ns.It was found that the quantum efficiency of graphene quantum dots modified by surface functional groups has been greatly improved,and the fluorescence lifetime has also been improved to a certain extent.In order to achieve solid-state light emission of GQDs,yellow-emitting o-GQDs gel glass and white-emitting p-GQDs gel glass were prepared by dispersing a certain amount of o-GQDs and p-GQDs in a gel solution.At the same time,the thermogravimetric analysis of o-GQDs and p-GQDs gel glasses was performed.The mass loss of the two kinds of gel glasses before 103 ? is not very large,which indicates that it is relatively stable at normal operating temperatures of white LEDs(WLEDs)devices,such gel glass is very suitable as a light conversion material for WLEDs devices.The o-GQDs and p-GQDs gel glasses were respectively assembled with blue chips and ultraviolet chips to obtain WLEDs devices.With the increase of current,the color coordinates of o-GQDs and p-GQDs gel glass LEDs devices gradually shift to the white center.When the current is 1000 m A,the color coordinates of o-GQDs and p-GQDs gel glass LEDs devices are(0.398,0.346)and(0.343,0.239),both of which can be used for WLEDs devices.In addition,we also designed three different fluorescent anti-counterfeiting schemes based on GQDs fluorescent inks,including handwriting,stamping and inkjet printing.By handwriting,stamping,or inkjet printing the patterns on the filter paper,the patterns on the filter paper are invisible under visible light,but the pattern can be clearly displayed under irradiation of 365 nm ultraviolet light.