Study On Preparation, Luminescence Mechanism And Application Of Carbon Quantum Dots

As a new type of fluorescent carbon nanomaterials,carbon quantum dots?CDs?have unique optical properties compared with traditional nanomaterials and have attracted much attentions.However,the luminescent mechanism of CDs is still not clear,and its low fluorescence intensity limits its applications in a wider area.In this thesis,CDs were synthesized by a microwave method and the luminescence mechanism of CDs was investigated by surfactant modification and regulation of carbon sources.In addition,the fluorescence intensity of CDs was further enhanced by localized surface plasmon resonance?LSPR?of silver?Ag?nanoparticles.Finally,CDs were applied in metal ion sensing and antibiotic detection.Firstly,the effects of surface states and carbon nucleus on the fluorescence spectra of CDs were investigated.Red emitting CDs?R-CDs?were modified by surfactants with different electroneg ativities.The results indicated that pyrrole nitrogens were related to the blue emission,graphite nitrogen was correlated with the emission of green light,and oxygen related bonds were contributed to the red emission.In addition,blue emitting CDs were synthesized by a series of amino acids with different carbon and nitrogen contents.The results disclosed that the emission of 305 nm and 355 nm was originated from intrinsic carbon and graphite nitrogen of carbon nucleus,respectively.The pyridine nitrogen,amino nitrogen,and carbon-oxygen double bonds affected the emission of the surface states for CDs centerd at 410 nm,445 nm,and 500 nm,respectively,which were further verified by theoretical calculations.Secondly,the fluorescence enhancement and Raman enhancement of CDs were achieved by the LSPR effects of Ag nanoparticles.The surface of Ag nanoparticles was coated with a certain thickness of silica layer and coupled with CDs with different emission wavelengths,which successfully enhanced the fluorescence intensity of green and yellow emitting CDs.When the thickness of the silica layer is 15 nm,the enhancement factor can be up to 5-6times.In addition,with the increased size of the uncoated Ag nanoparticles,the fluorescence intensity of the CDs gradually decreases,but the uncoated Ag nanoparticles have a significant Raman enhancement effect as they are loaded with blue emitting CDs.Therefore,it is suggested that there is an electron transfer process between the Ag nanoparticles and the CDs.When the electrons are transferred from the Ag nanoparticles to the CDs,the CDs can realize fluorescence enhancement,while the electrons are transferred from the CDs to the Ag nanoparticles,Raman enhancement can be achieved.Finally,the application of CDs in fluorescence sensing was developed.Based on the fluorescence inner filter effects,a fluorescence sensor for selective detection of Fe³⁺ions was developed.The detection range of Fe³⁺ions is 12.5-500?mol/L and the detecton limit is 12.5?mol/L.In addition,owing to combination of fluorescence inner filter effect and static quenching,and the unique complexation of metal Al³⁺ions with antibiotics,a two-step approach was proposed to selectively detect seven antibiotics?tetracycline,oxytetracycline,chlortetracycline,doxycycline,metronidazole,sulfadiazine,and chloramphenicol?,which has a detection limit of 50 nmol/L and a detection range of0.05-250?mol/L.