The Qualitative And Quantitative Determination Of REEs Based On Multiple Fluorescence Techniques Using Quantum Dots Derived From Three Raw Carbon Materials

Rare Earth Elements(REEs),are indispensable elements in many modern industries,has become a crucial strategic resource for the 21st century.Their applications involve optics,lasers,renewable energy,energy storage,magnetism,catalysts,alloys,nuclear radiation and many other fields.However,their similar physical and chemical properties make their mining,extraction,purification and analysis great challenges.This thesis focused on the qualitative distinguish and the quantitative analysis of REEs,via the multiple fluorescence techniques with the assistance of multiple carbon or graphene quantum dots(CQDs and GQDs)based on three raw carbon materials including the folic acid(FA),the commercial graphene oxide and coal.The study covered material synthesis,characterizations,fluorescence techniques,and mechanical exploration,mainly contributing on the simplicity in raw materials and preparation methodology,the functionality in the quantum fluorescence efficiency,and the creativity in the qualitative distinguish and the quantitative analysis of REEs to some extent.This thesis includes five chapters.Chapter one had an overview of physical,chemical properties,electronic structures and applications of REEs,the development of CQDs and GQDs,as well as the basic aspect of fluorescence mechanisms of carbon dots(CDs)and REEs.Chapters two,three and four are three major components on studies of three CQDs and GQDs through three raw carbon materials and their fluorescence properties.Two fluorescence mechanisms were explored,which were the fluorescence quenching effect and the fluorescence sensitizing or antenna effect.Many material characterizations methods have been involved,such as SEM/TEM,XRD,XPS,FTIR,Raman and the Zeta potential,reveling the important contribution surface carboxyl function groups on applied CQDs or GQDs.Many fluorescence techniques involved the fluorescence intensity,the fluorescence lifetime and the quantum conversion efficiency of fluorescence.In the last chapter,which is Chapter five,an overview of major conclusions was given,as below,(1)A facile and one-step hydrothermally prepared,FA derived NCDs emitted the unique bright blue fluorescence in a high fluorescence quantum yield,and were effective in the determination of REEs' concentrations.Significantly,this as-received NCDs can also distinguish two groups of REEs with significantly different electronic structures,which were Group I REEs:La3+,Y3+,Lu3+,and Group ? REEs:Pr3+,Nd3+,Sm3+,Eu3+,Gd3+,Tb3+,Dy3+,Ho3+,Er3+,Tm3+,Yb3+.Taking examples of the selected La3+and Sm3+,their detection limit were found to be 0.045 ?M(the linear range of 0-6?M,R2=0.998)and 0.29 ?M(the linear range of 0-10 ?M,R2=0.9930),respectively.(2)A simple one-step chemical oxidation was applied for the preparation of the GQDs starting from the regular multilayer graphene oxide(GO)via the refluxing in the concentrated strong acids.The highly selective antenna effect of GQDs on one REE its aqueous media,which was Terbium(?)was identified.The excited terbium ions emitted their long-living fluorescence based on its own characteristic line-typed f-f transition,which was impossible to be investigated in the Tb3+ion in the aqueous solution.The linear range of the terbium ion concentration was within 0-30 ?M(R2=0.9960)with a detection limit of 0.3 ?M,based on the optimal fluorescence wavelength at 546 nm,excited at 230 nm.(3)N,P,S co-doped graphene quantum dots(NPS-GQDs)were prepared via a one-step wet chemical plus dialysis method directly using anthracite coal as raw material.The local doping of N,P and S on GQDs can reach high levels as 5.6%,3.7%and 3.7%(by atomic)during XPS detection,respectively.The effect of graphitizing degree of applied coals(varied coal ranks)on the formation of GQDs implied that raw coals with too high or too low graphitizing degree were not optimizing for the formation of high-quality GQDs.The prepared NPS-GQDs showed excellent properties on the excitation-dependent fluorescence and the quench by some trace metals.Thus,the NPS-GQDs were applied to detect of Pb2+in both DI water and a multa-elements analysis matrix,exhibited wide linear detection range(1-20 ?M)and a detection limit of 0.75?M.Similar results,as presented in 2),on the determination of Tb3+was obtained with a detection of limit of 0.2 ?M.To our best knowledge,there were almost no literatures reporting on distinguishing and detecting rare earth ions using CDs.