The Identification And Detection Of REEs Based On Fluorescence Method Using Doped Semiconductor Carbon Quantum Dots

Rare earth elements（REEs）are indispensable high-tech elements in the 21st century,which have been widely used in high-performance technologies such as electric vehicle batteries,lighting displays,wind turbine magnets,circuits and national defense systems.However,their similar chemical properties and symbiosis in nature make great challenges on their extraction,concentration,separation,detection and recovery.Fluorescence spectrophotometry has become a powerful analytical tool to detect REEs with its obvious advantage such as simple operation,quick response,low cost,high selectivity and sensitivity.The Carbon dots（CDs）in carbon nanomaterials family are one of the excellent materials to exhibit the fluorescence effect.This paper focused on the specific recognition of REEs by CDs,via using different carbon sources and preparation methods to change its structure to generate―CDs or REE-centered‖fluorescence response,so as to build fluorescence sensors for recognition and quantification of REEs.The thesis includes following four parts:Chapter 1:A brief review of characteristics of REEs and the luminescence mechanism of complex as well as the development of REEs fluorescence analysis.The properties,preparation and application in the analysis and detection of CDs are also introduced,so as to direct the core research contents of this thesis.Chapter 2:The Nitrogen-doped Graphene Quantum Dots（N-GQDs）were prepared by the chemical reduction method using Graphene oxide（GO）as carbon source,N-methyl-2-pyrrolidone（NMP）as solvent and nitrogen doping source.The doping amount of N atom is 11.4%.The morphology,structure and optical properties of the as-prepared N-GQDs were characterized by transmission electron microscopy（TEM）,infrared spectroscopy（FT-IR）,X-ray photoelectron spectroscopy（XPS）,UV-visible absorption spectroscopy（UV-Vis）,photoluminescence spectroscopy（PL）and other instruments.The results show that the as-prepared N-GQDs have excellent water solubility,dispersivity,excitation dependent blue emission fluorescence,and photostability.Due to the selective fluorescence quenching of N-GQDs caused by Ce⁴⁺ions,a based―N-GQDs-centered‖sensor for the Ce⁴⁺recognition was constructed with a detection limit of 0.8352μM in the detection range of 1-44μM.The sensor was applied to the rapid and accurate detection of Ce⁴⁺in real artificial samples（tap water and lake water）.Chapter 3:The Carbon dot（CD）with abundant oxygen-containing functional groups on its surface was prepared by the chemical oxidation method using anthracite with high degree of coalification as a carbon source.The morphology,structure and optical properties of the as-prepared CD was characterized by TEM,FT-IR,XPS,UV-Vis,PL and other instruments.The results show that the as-prepared CD has good water solubility,dispersibility,excitation dependent blue emission fluorescence and photostability.The as-prepared CD was sensitive to p H and thus has the potential to measure p H values of the liquid environment.Due to the as-prepared CD selectively transfered the absorbed energy to either Tb³⁺or Eu³⁺ions to enhance their characteristic fluorescence,a sensor recognizing Tb³⁺ion or Eu³⁺ion by the―REE-centered‖response mechanism was then established.The characteristic peak of terbium and europium at 616 nm or 546 nm was used to determine the the detection range and limit of Tb³⁺or Eu³⁺were 0.67-6.67 or 1-10μM and 0.10 or 0.79μM,respectively,and then applied to the rapid detection of these ions in real artificial samples.Chapter 4:The Silicon doped Carbon Dot（Si-CD）using rice husk as carbon and silica sources was prepared by the high temperature carbonization followed by the further chemical oxidation.The morphology,structure and optical properties of Si-CD were characterized in detail.The results show that the prepared Si-CD also has good water solubility,dispersibility and excitation dependent blue emission fluorescence.Due to that Si-CD and REEs combine to generate different fluorescence responses,the sensor based―Si-CD-centered‖response mechanism for qualitative recognition of REEs was established.Studies exhibited four REE groups:group 1 involves Y³⁺,Sc³⁺and Lu³⁺,group 2(La³⁺and Gd³⁺),group 3(Tb³⁺,Dy³⁺,Tm³⁺and Yb³⁺)and group 4(Ce³⁺,Pr³⁺,Nd³⁺,Sm³⁺,Eu³⁺,Ho³⁺and Er³⁺).Furtehrmore,Si-CD could transfered absorbed energy to Tb³⁺for its fluorescence enhancement and its own fluorescence emission was reduced.This helped to establish a new fluorescence sensor system for the ratio detection of Tb³⁺ions in a much higher sensitivity.The detection range and detection limit were 1-12μm and 3.24 n M,respectively.This sensor could also applicable in the detection of Tb³⁺ion in real artificial samples by matrix correction.Simultaneously,Si-CD could also transfer the absorbed energy to Eu³⁺or Dy³⁺to enhance its characteristic emission and a sensor for detection of Eu³⁺or Dy³⁺ions was constructed.The characteristic peak of Europium and Dysprosium at 616 nm and 575nm was used to determine the detection range and limit of was 1-16μM or 4-30μM and 0.15μM or 2.43μM,respectively.Chapter 5:Give conclusion and perspectives of this paper and propose feasible schemes and developments in the future.