Preparation Of Nitrogen-doped Cane Molasses Graphene Quantum Dots And Their Detection Of Antibiotics And Metal Ions

With the rapid development of modern industry,antibiotics and metal ions are more and more widely used in daily life,so the detection of antibiotics and metal ions in food and water environment is particularly important.Graphene quantum dot fluorescent materials have been widely used in various fields such as sensors,biomedicine and energy due to their stable photoluminescence,good biocompatibility,excellent water solubility,low toxicity and easy surface modification.However,it also has the disadvantages of difficult operation,high cost,and incapability of large-scale preparation.Therefore,it is imminent to find a method that is simple to operate,low-cost,and capable of large-scale preparation of graphene quantum dots.Hydrothermal method is a simple method to prepare graphene quantum dots on a large scale,which can effectively meet the above requirements.In order to further realize the requirement of low cost,more and more researchers focus on natural biomass or biomass waste.Among them,cane molasses is a kind of biomass waste,which has a total sugar content of 50%and is rich in various functional groups,which also provides greater possibilities for doping and detection.Therefore,in this thesis,highly fluorescent nitrogen-doped graphene quantum dots（N-GQDs）were prepared by a one-pot hydrothermal method using cane molasses as the green carbon source and ethylenediamine as the nitrogen source,and its application in sensors was explored.The details of the study are as follows:（1）Using sugarcane molasses as a green carbon source,GQDs and N-GQDs were successfully prepared with quantum yields of 3.9%and 24.4%,respectively.Firstly,the morphology and structure information were characterized,which effectively proved the success of nitrogen doping.Then the effects of different reaction conditions as well as different testing conditions on the fluorescence performance of N-GQDs were also discussed to determine the optimal conditions.Finally,the stability of GQDs and N-GQDs was investigated in terms of zeta potential,storage time and sodium chloride concentration,and the results showed that the stability of N-GQDs was significantly better than that of GQDs.（2）A sensor for the detection of nitrofuran antibiotics was established based on N-GQDs.The response of N-GQDs to different antibiotics was first studied,and the results showed that N-GQDs are highly selective to nitrofuran antibiotics.The detection limits of N-GQDs for furazolidone,nitrofurantoin,nitrofurazone and furaltadone were 0.25μmol·L^-1,0.07μmol·L^-1,0.17μmol·L^-1 and 0.31μmol·L^-1,respectively,and the response time was only for 10 seconds.Secondly,the quenching mechanism was studied,and the results showed that the quenching mechanism between them was a dynamic quenching cooperative photo-induced electron transfer mechanism.Finally,the N-GQDs were used for the analysis and detection of furazolidone in a variety of real samples,and the results showed that the applicability of N-GQDs in practical applications was very good.（3）A sensor for detecting metal ions was established based on N-GQDs.Firstly,the response of N-GQDs to different metal ions was studied,and it was found that N-GQDs could be used to selectively detect Ag⁺,Mn²⁺,Co²⁺and Fe³⁺.Then,the masking effect of the masking agent on the response metal ions was studied,and different mixed masking agents were selected according to the masking effect of the masking agent on the response metal ions,and the separate detection of different metal ions was successfully realized.The detection limits of N-GQDs for Ag⁺,Mn²⁺,Co²⁺and Fe³⁺are 0.12μmol·L^-1,0.53μmol·L^-1,0.53μmol·L^-1 and 0.70μmol·L^-1,respectively.Finally,the quenching mechanisms of Ag⁺,Mn²⁺,Co²⁺,and Fe³⁺metal ions on N-GQDs are all static quenching by UV-Vis absorption spectra and fluorescence lifetime.