Fabrication And Application Of 3,4-Hydroxypyridinone-Modified Carbon Quantum Dots

Carbon Quantum Dots（CQDs）,a star material in carbon-based nanomaterials,have gained considerable attention owing to its excellent optical properties,good water-solubility,low toxicity and high fluorescence stability,etc.To date,the fluorescent probes based on CQDs have been applied to the detection of various metal ions harmful to the environment,such as Hg²⁺,Cu²⁺,etc.However,there are very few studies of CQDs as fluorescent sensor for detection of radionuclides.Uranium,one of the radionuclides,has posed a serious threat to the ecological environment and human health,because it not only possesses chemical toxicity,but also its radioactive toxicity.In addition,there are some shortcomings in the traditional detection technology for uranium,such as the time-consuming,complex pretreatment of samples,inconvenience in carrying,slow response time and so on,which hinder their application in nuclear emergency and practical detection.Therefore,this thesis aims to design a fluorescent probe with high selectivity,high sensitivity and rapid response time for uranyl ion(UO₂²⁺),which is based upon CQDs.Specific research contents and results are as follows:Firstly,we have been prepared CQDs rich in amino groups on the surface via low temperature pyrolyzation of citric acid and polyethylenimine.3,4-hydroxypyridone（HOPO）is a class of organic molecules showing a strong affinity for uranyl ions.We have successfully introduced HOPO molecule as the second functional group onto the surface of CQDs through the amidation reaction between the carboxyl groups of the HOPO unit and the amino groups of CQDs,the obtained CQDs possess a large amount of HOPO chelating groups on their surface.The results indicate that the HOPO-modified CQDs emit bright fluorescence under UV light and exhibit higher pH stability compared with unmodified CQDs.Secondly,by virtue of the high binding affinity of HOPO-modified CQDs toward uranyl and the excellent photoluminescence properties of CQDs in aqueous solution,the detection performance of modified-CQDs for uranyl ions was investigated.The selective experiments show that the modified-CQDs have high selectivity to uranyl ions,and other competing ions have little effect on the fluorescence intensity of CQDs.In order to comparison of detection performance toward uranyl ions between modified-CQDs and unmodified-CQDs,the relationship between fluorescence intensity and uranyl ions concentration were investigated respectively.The obtained results suggested that the modified-CQDs show better sensitivity and lower detection limit.In addition to this,we have compared our results with some representative detection methods,the response time（30 s）of this fluorescent probe is much shorter than the rest of uranyl detection,which opens up the possibility of on-site detection of uranium in the environment.Finally,a series of experiments were performed to explore the detection mechanism of the probe,the results showed that uranyl ions can induce aggregation of CQDs,leading to fluorescence quenching.