Study On Synthesis Of Fluorescent Carbon Quantum Dots And Their Applications As Fluorescent Probes

Carbon quantum dots（CQDs）have huge-application prospects in chemical sensing,bio-sensing,bio-imaging and other fields due to their unique advantages,such as biocompatibility,photo-stability,small diameter and tunable photoluminescence（PL）,etc.This paper focuses on the synthesis of CQDs and explores their applications in chemical sensing.Firstly,the related literatures were reviewed.Then,three types of carbon quantum dots with surface functionlization were prepared by hydrothermal method using tryptone,peptone,and sodium polyphosphate,and their applications for detecting 2,4-dinitrophenol and oxalic acid were studied.The main research work is as follows:This work reports an easy one step synthesis of carbon quantum dots via pyrolysis of tryptone.The as-synthesized CQDs exhibit relatively high quantum yield of 18.3%and good photo-stability.The luminescence intensity of the CQDs shows a good linear correlation with p H（5～12）and ionic strength（0～5 mol/L）,respectively.The CQDs prepared using tryptone could be used as fluorescent probes for selective response of 2,4-dinitrophenol（2,4-DNP）.The mechanism of fluorescence quenching of 2,4-DNP to CQDs is related to a combination of inner filter effect（IFE）and static quenching effect.Calibration curve was linear within the range from 0.010 to 4.0μg/m L 2,4-dinitrophenol,and the detection limit was as low as 5.1μg/L.The CQDs were successfully applied to the analysis of water samples in real environment.Nitrogen and phosphorus co-doped carbon quantum dots were synthesized by hydrothermal method using tryptone and sodium polyphosphate.The as-prepared CQDs have a high quantum yield of 25.4%,and good stability in high ionic strength and ultraviolet light environment.The luminescence of the carbon quantum dots shows a linear correlation with p H,indicating that they have the potential for p H sensors application.In addition,the synthesized carbon quantum dots can be used as fluorescent probes for detecting 2,4-dinitrophenol.The fluorescence intensity of the probes showed a linear response to 2,4-DNP in the concentration range of 0.01～2.5μg/m L with a low detection limit of 3.6μg/L.The probes have excellent selectivity and high sensitivity,and were used to determine 2,4-dinitrophenol in river water,lake water and tap water.The recoveries were from 93.8%to 103%with RSD<0.74%.A single-step hydrothermal route was developed for the synthesis of carbon quantum dots by using peptone as carbon source.The prepared CQDs can be used as"off-on"fluorescence probes for oxalic acid（OA）.The fluorescence of CQDs is quenched effectively by Cu²⁺.Then,the fluorescence of the solution of CQDs-Cu²⁺is recovered in the presence of oxalic acid.The calibration plot was linear over the large concentration range of 8.9×10^-5～7.2×10^-4mol L^-1,and the detection limit was 2.0×10^-5mol L^-1.The fluorescence response mechanism was investigated by means of UV-vis absorption spectrum,fluorescence spectrum,fluorescence lifetime measurement and stern-volume equation.It was concluded that fluorescence of CQDs is significantly quenched by Cu²⁺ions via dynamic mechanism,then is recovered due to the interaction of Cu²⁺with oxalic acid to form insoluble copper oxalate.The proposed method was applied to the detection of oxalic acid in human urine and spinach.