Preparation And Application Of Bismuth-based Quantum Dots

With the rapid development of nanotechnology,quantum dots(QDs)materials had broad application in biological markers,photoelectric materials,sensors,solar cells,etc.in recent years due to their unique properties.However,there was relatively few reports about the application of QDs materials in environment.Owing to the biological toxicity of traditional quantum dot materials such as Cd S?Cd Se and Cs Pb X₃(X=Cl,Br,I),their application in the environment were rarely reported.As an environmentally-friendly,non-toxic and non-carcinogenic green element,bismuth-based materials have been widely used in environmental fields such as catalysis and adsorption in recent years.However,there are few reports on bismuth-based QDs.In this thesis,Bi₂X₃(X=O,S,Se)QDs were prepared by simple method in aqueous solution,and their fluorescence properties were determined by UV-vis absorbance spectra,fluorescence spectra.By utilizing the law of fluorescence quenching of Bi₂X₃(X=O,S,Se)QDs,the concentration of Fe³⁺and humic acid in water could be determined.Moreover,the mechanism of Fe³⁺and humic acid determinatio by QDs was analyzed.The main works are summarized as follows:1.Bi₂O₃ QDs was synthesized from Bi(NO₃)₃·5H₂O by using water-soluble polyethylene glycol 400 as passivator under alkaline condition.Bi₂S₃ QDs was synthesized from Bi(NO₃)₃·5H₂O via hydrothermal reaction by using glutathione as sulfur source and passivator via hydrothermal reaction.Bi₂Se₃ QDs was prepared from bulk bismuth selenide materials in ethanol-water solution,which was synthesized from bismuth oxide and selenium in ethylene glycol.The fluorescence properties of three kinds of QDs were measured by UV-vis absorption and fluorescence spectra.The influence of reaction temperature and reaction time on the fluorescence properties of Bi₂X₃(X=O,S,Se)QDs were investigated to obtain the optimal reaction conditions,respectively.The effects of p H value and co-existing ions on the fluorescence properties of Bi₂X₃(X=O,S,Se)QDs were also discussed,respectively.The results showed that the Bi₂X₃(X=O,S,Se)QDs had good stability in the p H range of 3-12,and the coexistence of Fe³⁺in solution could result in the fluorescence quenching of QDs.While other metal ions and anions had little influence on the fluorescence properties of QDs.Bi₂X₃(X=O,S,Se)QDs maintained more than 90%fluorescence activity after being stored in the dark for 60 days.2.The influence of Fe³⁺concentrations on the fluorescence properties of Bi₂X₃(X=O,S,Se)QDs were investigated.Through the linear relationship between the concentration of Fe³⁺and the fluorescence intensity of QDs,the concentration of Fe³⁺in solution could be determined.The linear correlation coefficient R² between the fluorescence intensity of Bi₂O₃ QDs and the concentration of Fe³⁺,is 0.9877 in the Fe³⁺concentration range of 0-280?mol/L.At low Fe³⁺concentration(0-40?mol/L),R² is0.9937 and the detection limit(LOD)is 1.9?mol/L.For Bi₂S₃ QDs,R² is 0.9945 in the Fe³⁺concentration range of 0-520?mol/L,and R² is 0.9903 in the low Fe³⁺concentration(0-36?mol/L),and the LOD is 2.8?mol/L.For Bi₂Se₃ QDs,R² is 0.9955 in the Fe³⁺concentration range of 0-340 mol/L,and R² is 0.9973 in the low Fe³⁺concentration(0-120?mol/L),and the LOD is 3.8?mol/L.It was found that F^-ions could complex with Fe³⁺to form hexafluoride complexes in acidic condition,resulting in the recover of quenched fluorescence,thereby affecting the determination of Fe³⁺.Under the simulated actual water environment,the influence of Cu²⁺,Zn²⁺,Mn²⁺and Mg²⁺metal ions on the determination of Fe³⁺concentration by Bi₂X₃(X=O,S,Se)QDs were investigated.It was found that the co-existing ions had relatively little influence on the determination of Fe³⁺concentration.When the concentration of Cu²⁺was more than 50?mol/L,it would affect the determination of low concentration Fe³⁺(0-40 mol/L).3.The influence of the humic acid concentration in the solution on the fluorescence properties of the Bi₂X₃(X=O,S,Se)QDs was investigated,and the corresponding linear relationship was established for the determination of the concentration of humic acid in the solution.It was found that there was a good linear relationship between the fluorescence intensity of Bi₂X₃(X=O,S,Se)QDs and the humic acid concentration in the different range of 0-35 mg/L(Bi₂O₃ QD),0-30 mg/L(Bi₂S₃ QD)and 0-50mg/L(Bi₂Se₃ QD),respectively.The linear correlation coefficient R² and the LOD value for Bi₂X₃(X=O,S,Se)QDs was also determined to be 0.9952 and 0.3 mg/L(Bi₂O₃ QD),0.9854 and 1.3 mg/L(Bi₂S₃ QD),0.9924 and 0.5 mg/L(Bi₂Se₃ QD),respectively.It was found that the mechanism of fluorescence quenching caused by humic acid was different from that of Fe³⁺due to the weak fluorescence of humic acid,which might be a dynamic complexation.Therefore,the fluorescence intensity between Bi₂X₃(X=O,S,Se)QDs and humic acid would varied to be enhanced fluorescence or quenching according to the concentration of QDs and humic acid.Only when the QDs concentration is more than 0.6mmol/L,the the concentration of humic acid could be determined base on the linear relationship between the fluorescence intensity of QDs and humic acid concentration.