| Carbon quantum dots are one of most important novel fluorescent nanomaterials. There are a number of advantages, such as water-soluble, light stability, low toxicity, green, light bleach, easy function and so on. It has an important application in the detection field. The main methods of detecting heavy metals contain atomic absorption spectrometry, spectrophotometry, fluorescent analysis and electrochemical analysis. Most methods are so expensive equipment or extremely fussy processes to support operation. However, electrochemical analysis method has high sensitivity, simplicity, low cost and so on. Carbon quantum dots / thiol acetic acid modified electrode was prepared by self assembly method based on polyethylenimine functionalized carbon quantum dots with high selectivity to copper ions, and a new electrochemical analysis method for determination of copper ions was established. Carbon precursors have no special requirements for purity and wide selection range. Carbon precursors have citric acid, glucose, activated carbon, waste paper, carotenes and so on. However, silicon doped carbon quantum dots are synthesized using 3-aminopropyl trimethoxysilane(APTMS) and glutaraldehyde(GA) as mixed carbon precursors.This new method has not yet been reported. The work of this paper includes several parts as follows:(1) Preparation and optical characterization of polyethylenimine functionalized carbon quantum dots were investigated. Polyethylenimine functionalized carbon quantum dots had been synthesized using saturated citric acid as carbon source and polyethyleneimine as stabilizer by one-step hydrothermal method. Absorption wavelength, excitation wavelength and emission wavelength were 358, 365 and 460 nm, respectively.The result showed that linear between excitation wavelength and maximum emission wavelength, and it emitted high blue light under the ultraviolet lamp.(2) Carbon quantum dots / thiol acetic acid / gold electrode modified electrode was prepared by self-assembly method, and a new electrochemical analysis method was established for the determination of copper ions. Electrochemical behavior of copper ions at the modified electrode and the effects of supporting electrolytes, scan rates, pH value and concentrations of NaAc-HAc buffer solution on the peak current were discussed. The results showed that modified electrode accumulated copper ions in the standard copper ions solution under 0.2 mol/L(pH=4.2) NaAc-HAc buffer solution with scan rate of 20 m V/s, resulting in obvious oxidation reduction peak, showing the characteristics of irreversible electrode reactions. The good linear between copper ions with the concentration range of 9.41 nmol/L- 111.11 nmol/L and the reduction peak current was investigated. Correlation coefficient was 0.9756 and the detection limit was 3.24 nmol/L. The method could be applied to the detection of copper ions in environmental water samples with recoveries of 98.85%- 99.98%.(3) The synthesis, characterization and factors of silicon doped carbon quantum dots were investigated. A novel silicon doped carbon quantum dot was synthesized from APTMS and GA as carbon precursor by hydrothermal method based on Schiff's base reaction. The particle sizes, composition and optical properties of carbon quantum dot were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, ultraviolet spectrophotometer, fluorescence spectrophotometer. Effects of reaction temperature, reaction time, molar ratio of APTMS to GA, solvents, pH value and measuring temperature on the growth process and fluorescent properties were investigated. The results showed that the silicon doped carbon quantum dot was spherical with a diameter of about 1- 2 nm and rich in azomethine group and silicon-hydride bond. Absorption wavelength, excitation wavelength and maximum emission peak were 258, 350 and 400 nm, respectively. The fluorescence quantum yield was up to 13.6%. The carbon quantum dot solution was synthesized from molar ratio of 1 : 2 with APTMS and GA by heating at 180 degrees for 8 hours in phosphate buffer( pH=6.0) exhibited maximum fluorescence intensity. In addition, the fluorescence intensity decreased with the increase of the measuring temperature from 273 K to 303 K.(4) Copper ions in water samples were detected by fluorescence-quenching method with silicon doped carbon quantum dots. The fluorescent intensity of silicon doped carbon quantum dot was quenched by copper ions. The developed method was applied to the determination of copper ions in water samples by using silicon doped carbon quantum dot fluorescent probe on the basis of the relationship between fluorescence quenching ratio and the concentrations of copper ions. But other metal ions had no function of quenching. Good recoveries of 91.36%- 100.80%, a detection limit of 0.13 ?mol/L and relative standard deviations of 0.20%- 0.93% were evaluated, respectively.(5) Silicon doped carbon quantum dots-rhodamine B(RhB@QDs) as fluorescent probe was prepared and the optimum conditions of the FRET system were identified. The fluorescence resonance transfer was investigated by using silicon doped carbon quantum dots as a donor and rhodamine B as an acceptor. Effects of the pH value, the concentrations of the silicon doped carbon quantum dots and rhodamine B on the energy transfer system were investigated. Experimental results showed that the optimum condition of the resonance energy of RhB@QDs were the concentration of silicon doped carbon quantum dots of 0.26 mmol/L and the concentration of rhodamine B of 83.33 mg/L in the phosphate buffer solution( pH=7.8). Then fluorescence resonance energy transfer efficiency achieved maximum. In other word, the energy transfer effect of RhB@QDs was the best. |
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