The Preparation Of Phenylendiamine-based Carbon Quantum Dots And Application Of Fluorescence Analysis And Detection

As a new type of fluorescent material,carbon quantum dots?CQDs? are attracted the attention of researchers due to their low biotoxicity,low cost,high stability and good water solubility.They are widely used in biosensing,drug carrier,cell imaging,fluorescence probes,photoelectrocatalysis and other fields.However,the development of carbon quantum dots?CQDs? is still restricted because of the low quantum yield of carbon quantum dots?CQDs?,and the photoluminescence mechanism still restrict its development,which had become the research hotspots of researchers.In this paper,phenylenediamine was used as raw material,and carbon quantum dots?CQDs? with higher quantum yield and multicolor luminescence were obtained by doping modification with different methods.The morphology and optical properties for the synthetic carbon quantum dots?CQDs? were characterized by UV-visible absorption spectroscopy?UV-vis?,fourier transform infrared spectroscopy?FTIR?,fluorescence spectroscopy?FL?,X-ray photoelectron spectroscopy?XPS?,transmission electron microscopy?TEM?,Raman,etc.Its performance is further optimized.Carbon quantum dots?CQDs? with stable properties were found for the analysis and detection of metal ions and small organic molecules.The main research work of this paper was as follows:1.Nitrogen-doped carbon quantum dots?N-CQDs-1? with long emission wavelengthwerepreparedbyhydrothermalsynthesismethodusing o-phenylenediamine?oPD? as carbon source and urea as nitrogen source.The average particle size of N-CQDs-1 was 3.04 nm.It had stable chemical properties and could be used for cell imaging.The carbon quantum dots had high selectivity and ultra-sensitivity for Fe³⁺,and the detection limit for Fe³⁺ was 39 nM.The mechanism of N-CQDs-1 detecting Fe³⁺ was discussed.It was found that the UV-vis absorption peak shifted greatly after addition of Fe³⁺ and the fluorescence lifetime changes little before and after the addition of Fe³⁺.Therefore,we speculate that the mechanism of fluorescence quenching for N-CQDs-1 by Fe³⁺ was a static quenching mechanism.The coordinate interaction between Fe³⁺ and O,N of amide bond on the surface of N-CQDs-1 to form a stable complex leads to a large accumulation of N-CQDs-1 and quenching the fluorescence.2.Nitrogen-sulfur co-doped carbon quantum dots?N,S-CQDs? with green fluorescencewerepreparedbyone-stephydrothermalmethodusing o-phenylenediamine?oPD? as carbon source and brilliant red X-3B as nitrogen source and sulfur source.It was found that an average particle size of N,S-CQDs was only 1.36nm and was highly selective to CF with a detection limit of 65nM.N,S-CQDs were successfully used in the detection of caffeine in water,cell imaging,detection and estimation of caffeine content in actual samples.The obtained caffeine content was basically consistent with the literature data,indicating that N,S-CQDs have practical application potential.3.Nitrogen-doped carbon quantum dots?N-CQDs-2? with strong bright blue-green fluorescenceweresynthesizedbysolvothermalmethodusing m-phenylenediamine?mPD? as raw material and ethanol as solvent.In this process,m-phenylenediamine?mPD? was used as carbon source and nitrogen source.The synthesis process is completed simultaneously with doping and passivation processes.It was avoided the subsequent modification process of nitrogen-doped carbon quantum dots?N-CQDs-2?.Among various metal ions,N-CQDs-2 had a high selectivity and ultra-sensitivity to Cr⁶⁺ with the detection limit of 13nM.N-CQDs-2-Cr⁶⁺ had a good selective recognition for AA.We had successfully designed N-CQDs-2 as an"off-on"switch-type fluorescent probe for the detection of hexavalent chromium(Cr⁶⁺)ions and ascorbic acid?AA? in water,and the pharmaceuticals.In the further mechanism discussion,it was found that the fluorescence quenching of N-CQDs-2 by Cr⁶⁺ was dynamic quenching,and may be non-radiative electron transfer between Cr⁶⁺ and N-CQDs-2.