Preparation Of Carbon Quantum Dots And Their Application In Electroanalytical Chemistry

In recent years, quantum dots(QDs) have widely applied in the fields of electrochemistry, biochemistry and medical treament due to their excellent optical property and major specific surface area. However, semiconductor QDs have blink phenomenon and abvious metal ion cytotoxicity. Therefore semiconductor QDs have a certain extent constraint in their practical application. Carbon quantum dots(CQDs), acts as a new-style carbon nanomaterials, have many advantages such as excellent optical property, small size features and low toxicity, whitch is more safe than the past electrochemiluminescence material. CQDs can not only overcome the blink phenomenon but also have lower cytotoxicity. Therefore CQDs may be a well select to replace the semiconductor QDs.In this work, firstly, we explored a better way to synthesis the CQDs. The experimental conditions were simpleness and the preparation was rapid. The raw CQDs material was economically and environment friendly and have good properties. Secondly, the CQDs doped with other element was synthesised which can enhance the ECL performance of the CQDs. The obtained CQDs were applied to the detection of some ions and the related mechanism were discussed. Specific work is as follows: 1. The synthesis of CQDs?Ag@CQDs?NCQDsThe glucose as the raw material, we synthesised CQDs by hydrothermal method. The synthesised CQDs have good electrochemiluminescence, fluorescence, aiti-bleach characters,and also have good saltresistance, water solubility and hypotoxicity. From the TEM image, we can see that the CQDs were uniform distributed and the particle size were in the range of 7.0 ± 0.5 nm. From the ultraviolet spectrum, we find that the CQDs have an obvious absorption peak at the wavelength of 260 nm. From the fluorescence of the CQDs, we can see that the emission wavelength at 425 nm when the excitation wavelength was 335 nm. From the FTIR of the CQDs, we know there are a mount of carboxyl group and carbanyl group on the surface of the CQDs. On the base of CQDs, we introduced Ag NO3 in the solution, and then Na OH was added. with the reducing action of Na OH, the Ag@CQDs were successfully synthesized. From the TEM image, we know that the Ag@CQDs were uniform distribution in solution. The particle size range is about 30 ± 2.0 nm. From the ultraviolet spectrum, we find that Ag@CQDs has two obvious absorption peaks at the wavelength of 260 nm and 430 nm, respectively. From the fluorescence of Ag@CQDs we see that the emission wavelength at 425 nm when the excitation wavelength was 335 nm. The fluorescence intensity of CQDs was stronger than the Ag@CQDs under the same concentration. We also used alanine as the carbon and nitrogen source, with the hydrothermal method to synthesize the nitrogen doped CQDs(NCQDs). From the ultraviolet spectrum, we find that NCQDs has an obvious absorption peak at the wavelength of 320 nm. From the fluorescence of NCQDs, we see that the emission wavelength at 440 nm when the excitation wavelength was 360 nm. 2. The electrochemiluminescence of Ag@CQDs and its application in high sensitive test of chloridionWe take advantage of the Nafion to make the Ag@CQDs modificate to the electrode.Compared to the CQDs/GCE, the electrochemiluminescence of Ag@CQDs/GCE was more stable and the intensity was nearly ten times the CQDs/GCE. In the 0.1M, PBS(p H=7.4) solution, K2S2O8 acted as the coreaction reagent. Due to the Cl- can effectively quench the electrochemiluminescence of the Ag@CQDs, we established a new method to detecte the Cl-, the method has a good selectivity and a high sensitivity. We also explored the mechanism of quench. The result indicated that when the concentration of Cl- at the range of 0.99-450 n M, the concentration of the Cl- and the analysis signal(I0-I)/ I0 has a good linear relation. The detection limit was 0.33 n M(S/N=3). 3. The electrochemiluminescence of NCQDs and its application in high sensitive detectionof copper ion.In 0.1 M PBS(p H=7.0) solution, K2S2O8 acted as the coreaction reagent, we studied the the electrochemiluminescence of NCQDs. Because Cu2+ can effectively quench the electrochemiluminescence of the NCQDs, we established a new method to detect the Cu2+, the method has a good selectivity and a high sensitivity. The result indicated that the analysis signal(I0-I)/I0, and has a good linear relation to the concentration of Cu2+ in the range of 0.20-30 ?M With the detection limit of 30 n M(S/N=3).