Study Of Metal Ions Detections Based On CdTe Quantum Dots And Carbon Nanodots Preparation

Quantum dots(QDs) are semiconductor nanoparticles that are of specialstructure, unique optical and electronic properties, which studies have been foucusedby more and more researchers in recent years. In this thesis, the sensitive and selectivedetection methods for two metal ions, Cu²⁺and Ag⁺, were studied using QDs. Then,carbon QDs were synthesized directly from citric acid by a one-step pyrolysis, andtheir fluorescence and ECL charactenstics were studied.This thesis includes four chapters as follows:In chapter I, the definition, properities and applications of QDs are introduced. Inaddition, the advances and applications of carbon QDs are also introduced.In chapter II, based on the principle of colorimetric sensor, the results ofcolorimetric determination were directly resolved by changing the light intensity oftwo luminescence materials. In the experiments, we developed a rapid, stable andsimple colorimetric sensor for Cu²⁺detection. The fluorescence of CdTe QDs was bequenched by Cu²⁺, but Ru(bpy)3Cl2in PAV membrane contained stable fluorescence.Moreover, CdTe QDs and Ru(bpy)3Cl2could be excited using a same excitationwavelength. The color of the sensor was recorded by a CCD camera and the result scould be obtained and identified using a colorimetric card.In chapter III, CdTe QDs capped with glutathione were synthetized bymicrowave assisted treatment. The effects of pH, temperature and reaction time, wereinvestigated. Then, based on the visible light absorption of CdTe QDs and the colorchange after adding Ag⁺, we developed a semiquantitative visual method for Ag⁺detection. The assay allows for the sensing of Ag⁺in the range from10^-7to10^-4mol/Lby naked eyes. In addtion, we developed a fluorescent method for Ag+detectionwhich based on CdTe QDs in the present of sequestrant. Meanwhile, the possiblemechanism of fluorescence quenching was studied. A excellent linear relationship(R²=0.9987) is obtained from1.0×10^-6to2.0×10^-5mol/L Ag⁺with a detection limit aslow as8.8×10^-7mol/L (S/N=3). In chapter Ⅳ, In this study, carbon QDs were made from by heating citric acid inoil bath, and characterized by fluorescence and electrochemiluminescence(ECL). Theresults showed that the obtained carbon QDs were uniform in size, wide excitationwavelength (320⁴20nm), good stability in wide pH range and under radiation, andhigh fluorescence quantum yield (12.2%) without surface passivation. The ECLcharacteristics of carbon QDs were also investigated. In addition, citric acid isinnoxious and uses as a food additive. It is friendly to environment and easy operation.Carbon QDs show good prospects in application due to good fluorescence and ECLproperties carbon dots, as well as environment friendly.