Synthesis Of Carbons Dots With Tunable Optical Properties And Their Applications

As a new type of zero-nanomaterial,carbon dots have attracted researchers’ interests due to their excellent physical and chemical properties,and have been applied in many fields.In terms of their synthesis,carbon dots can be synthesized by cheap reactants and simple methods.In terms of structure,carbon dots are composed of graphitized carbon cores and amorphous parts.There are many functional groups in carbon dots’ surface.The shape of carbon dots is usually spherical and the particle size is in the range of 1?10 nm.In the terms of property,carbon dots have outstanding fluorescence,easy modification,low toxicity and good biocompatibility.In terms of application,carbon dots are widely used in bioimaging,sensing,catalysis and other fields.Although carbon dots have made great progress after more than ten years of development,there are still many issues that have not been solved.The main aspects are as follows:(1)The mechanism of the fluorescence of carbon dots is so complicated that we cannot control fluorescence through synthesis.(2)Long-wavelength luminescent carbon dots are favored in biological application,but there are not many reports on water-soluble carbon dots which are red or near-infrared emissive.(3)Carbon dots have been applied in more and more fields based on their physicochemical properties.Developing other properties is necessary.The contribution of our work to the carbon dots can be described as below:(1)By adjusting the ratio of reactants and reaction temperature,the graphitization degree of synthesized carbon dots and the content of surface functional groups are changed to achieve the tunable optical properties of carbon dots;(2)Based on the concept of semiconductor doping,boron and other elements are doped into carbon dots,causing the changes in the optical properties of the carbon dots,and we synthesized red-emitting carbon dots successfully;(3)We explored the applications of different optical properties of carbon dots in LED devices,ion detection,bioimaging and and photothermal field.The concrete contents of our work can be described in detail as follows:First of all,using citric acid as the carbon source,urea as the nitrogen source,and N,N-dimethylformamide as solvent,a series of multi-color fluorescent carbon dots were synthesized at different temperatures with different ratios.The fluorescence spectrum of carbon dots covered the visible spectrum from 430 nm to 630 nm.Through the characterization of the structure and optical properties of carbon dots,we found that the red shift of the fluorescence emission wavelength appeared with the increase of the graphitization degree;at the same time,as the reaction temperature increases,the content of functional groups such as carboxyl groups on the surface of carbon dots increased.This is also an important factor in the red-shift of fluorescence emission of carbon dots.Secondly,in order to further explore the ways of controlling the emission of carbon dots,we tried to dope other elements into carbon dots,hoping to change the emission of carbon dots.With citric acid as the carbon source,ethylenediamine as the nitrogen source,mixed with boron,phosphorus,sulfur,selenium and other elements to obtain heteroatom-doped carbon dots.Elements such as boron created new defect levels and functional groups,changing the optical properties of carbon dots.We also synthesized sulfur,nitrogen co-doped carbon dots by using thiourea as the sulfur source and nitrogen source,and successfully regulated the emission wavelength to the red light region.Using dopamine as the carbon source and nitrogen source,we synthesized carbon dots whose absorption spectrum extended into the visible light region,and this carbon dots had photothermal conversion property.Finally,we applied the carbon dots in different fields to expand their applications.(1)We applied multi-color fluorescent carbon dots to light-converting LEDs.By adjusting the type and content of carbon dots,we successfully prepared LEDs of different colors.The color coordinates of white LEDs was(0.33,0.34),and the color rendering index was 92.(2)We detected glucose by using borate groups on boron,nitrogen co-doped carbon dots successfully;using carboxyl and thiocyanate groups on the surface of sulfur,nitrogen co-doped carbon dots,ferric ions and ascorbic acid were detected.At the same time,the excellent red fluorescence of sulfur,nitrogen co-doped carbon dots has great application advantages in the biomedical field.We have successfully applied it to drug loading and bioimaging.(3)The carbon dots synthesized by using dopamine extended the absorption in the visible light region,and had photothermal conversion property.The carbon dots with dual properties of fluorescence and photothermal had a great application in biomedical imaging and photothermotherapy field.