Detection Of Heavy Metal Ions Based On Graphene Oxide Fluorescence Sensor

Since the discovery of graphene materials,which have attracted many scientific researchers due to their stable fluorescence properties,good water solubility,excellent resistance to bleaching and easy functionalization.Graphene materials are low toxicity and environmental friendliness,which have shown a great value in many applications such as chemical sensors,biosensors,biological imaging and tracing catalysis etc.In this paper,three kinds of fluorescence systems based on graphene were constructed,and a new fluorescence analysis method for the determination of heavy metal ions was established.Besides,the actual samples were successfully analyzed and determined.The method is simple,and it has a strong operability,high sensitivity and wide application range.The main content of the paper is as follows:1.Determination of bismuth ion by fluorescence spectrophotometry with GO/L-tryptophan systemGraphene oxide（GO）was prepared by a modified Hummers method,and it was characterized by scanning electron microscopy（SEM）,energy dispersive X-ray spectroscopy（EDS）,Fourier infrared spectroscopy（FTIR）,ultraviolet absorption and fluorescence spectroscopy.Based on GO’s fluorescence quenching of L-Trp,a new fluorescence analysis method to determine the content of Bi³⁺was established.The linear range for the determination of Bi³⁺is 0.5-100μmol·L^-1,the linear regression equation isΔI=8.081C+20.817（R²=0.9995）,and the detection limit is 0.5×10^-6mo L·L^-1.Compared with other analytical techniques,this method is simple and has ahigh sensitivity,and has realizedrealizes the determination of Bi³⁺content in a certain mine wastewater.2.Preparation of PPy/graphene oxide quantum dots and its application in silver ion analysisPolypyrrole（PPy）was prepared by chemical oxidation method,which was used as a modified material,and then the PPy/graphene oxide quantum dot（GQDs）system was synthesized by a one step hydrothermal method.They were mainly distributed between 50-60nm and with a good dispersibility.A new fluorescence analysis method for the determination of Ag⁺content has been established under the conditions of an excitation wavelength of 365 nm and an emission wavelength of 465 nm,by using silver ions quenching the fluorescence of the system,.The linear range of Ag⁺is 0～140μM,the linear regression equation isΔI=11.968C+1.328（R²=0.9996）,and the detection limit is 0.14×10^-6mo L·L^-1.Compared with other fluorescence analysis methods,this method has the advantages of wide linear range and low detection limit,and has successfully realized the fluorescence detection of Ag⁺in tailings wastewater.3.Preparation and application of graphene quantum dot materials co-doped with sulfur and nitrogen and its application in lead ion analysisSulfur and nitrogen co-doped graphene quantum dots（S,N-GQDs）were prepared by a hydrothermal method with citric acid as carbon source,thiourea and N,N-dimethylformamide as sulfur source and nitrogen source.The results of the characterization of surface morphology,showed that the S,N-GQDs were mainly distributed in the range of 10～20nm.N-H bond,N=C=O,S=O and C=O were successfully introduced.The optimal excitation wavelength of the system was 360 nm and the optimal emission wavelength was 436 nm by fluorescence spectrum analysis.The fluorescence quenching of S,N-GQDs was quenched in the presence of mercury ions,and the system was basically restored by adding sodium sulfide.After the addition of Pb²⁺,the fluorescence intensity of the system decreases with the increased concentration of Pb²⁺.Based on this,a novel switched fluorescence sensor for determination of Pb²⁺has been established.The linear range of Pb²⁺is 0～70μm,and the linear equation isΔI=9.248C+0.54（R²=0.9998）.The detection limit was 0.3×10^-6mo L·L^-1.This method has the advantages of good selectivity,low detection limit and high sensitivity,and has successfully realized the fluorescence detection of Pb²⁺in the wastewater of polymetallic sulfide ore flotation process with high ionization and high alkaline.