The Preparation And Application Research Of Nitrogen And Sulfur Co-doped Carbon Quantum Dots With High Fluorescence Quantum Yield

Carbon quantum dots(CQDs)are carbon-based nanomaterials with a spherical shape and a size within 10 nm,are similar to carbon nanotubes,graphene,and fullerene.The unique structure and properties of CQDs make it one of the most attractive materials in nanoscale.Compared with semiconductor quantum dots,CQDs have better biocompatibility due to their carbon-based structure,which is more in line with the demand and development of green chemistry.In addition,CQDs have great application potential in biomedicine,sensing and detection,optical devices and other fields due to the abundant raw materials,simple and diverse preparation methods,excellent fluorescence performance and strong chemical stability.In this paper,one-step solvothermal method is used to prepare heteroatoms-nitrogen and sulfur co-doped red/orange dual-emitting carbon quantum dots(N,S-CQDs)and nitrogen and sulfur co-doped multi-color fluorescent emission carbon quantum dots.The synthesis method,fluorescence performance,morphology and structure were explored and analyzed,and the fluorescence mechanism was analyzed in depth using simulation analysis techniques,and its applications were studied using its fluorescence properties.The main contents are as followed:1.Using L-cystine and o-phenylenediamine as precursors and ethanol as a solvent,red/orange dual-emission CQDs with photoluminescence quantum yield(PLQY)up to35.7%was synthesized,and the maximum emission peaks were at 595 nm and 648 nm.Through FTIR,XPS,Raman and other advanced characterization techniques,it was found that the doped N and S elements play an important role in the formation of high quantum yield CQDs.N,S-CQDs have unique reversible pH fluorescence performance,and the fluorescence intensity has a good linear relationship with pH value when pH value was between 1.0 to 3.0.Fluorescence quenching of N,S-CQDs occurred in the presence of Ag~+,which made them useful as fast and ultrasensitive pH and Ag~+probe sensor.In addition,low cell toxicity and good biocompatibility made N,S-CQDs useful for biological imaging research.2.Multicolor fluorescent carbon quantum dots-blue,yellow,and red CQDs(B-CQDs,Y-CQDs,R-CQDs)were synthesized from the same precursors,toluic acid and o-phenylenediamine,by changing the reaction conditions,reaction temperature,and other reaction conditions,the PLQY were50.8%,25.4%and 65.1%,respectively.This is the first report of N and S co-doped CQDs with red fluorescent with the fluorescence quantum yield more than 50%.The prepared CQDs have uniform size and similar morphology,so the effect of quantum size effect on the fluorescence emission wavelength was ruled out.The detailed characterization analysis results showed the fluorescence emission wavelength of N,S-CQDs in different solvents were different,which is attributed to the different degrees of oxidation on the surface of CQDs.CQDs were developed into fluorescent hydrogels for precise remote force measurement and WLEDs with CIE color coordinates of(0.31,0.32).