Studies On CL Mechanisms Of Nitrate And Nitrosamines With Online UV Degradation And CQDs Sensitization And Their Applications

Nitrate is widely present in nature,it is one of the important reasons leading to eutrophication of water,and it will be reduced to more toxic nitrite in the natural environment or entering the human body,and further form nitrosamines（NAs）,endangering human health.NAs are the most important class of N-nitroso compounds.They are found in food and the environment.They are strong carcinogens and can induce tumors in various organs.Therefore,the development and establishment of detection methods for nitrate and NAs in water are of great significance for protecting the health of the population.Since nitrate and NAs are both small molecule compounds and do not have ideal optical properties,their detection methods are limited.UV photodegradation is one of the main forms of photodegradation and has been successfully used for the degradation and pretreatment of environmental pollutants.This study intends to start with a variety of active intermediates that nitrate and NAs can generate during the ultraviolet degradation process,and then use the unique advantages of carbon quantum dots（CQDs）to explore the mechanism of chemiluminescence（CL）,Successfully established a new method for chemiluminescence detection of nitrate and NAs.The full text mainly includes the following three parts:（1）Drawing on and improving the synthesis method of CQDs in the literature,citrate-urea CQDs and glycerin-hexadecyl trimethyl ammonium bromide（CTAB）-serine CQDs were prepared.The optical characteristics,morphology and particle size of the two CQDs were characterized by means of ultraviolet-visible absorption spectroscopy,fluorescence spectrophotometry,transmission electron microscopy and nanometer particle size analysis.（2）UV degradation of the samples in sulfite media,and based on the coexistence conditions of glycerol-CTAB-serineCQDs-H₂O₂,a new method for determining nitrate in water was constructed.The synthesis methods of CQDs and the influence conditions of chemiluminescence system were optimized.Under optimal conditions,the CL intensity of the system increases linearly with the increase in nitrate concentration(1.0×10^-7 mol/L^-11.0×10^-5 mol/L^-1),and the detection limit is 5.0×10^-8mol/L（S/N=3）.This method has been successfully applied to the determination of nitrate in tap water,packaged drinking water and mineral water.The intra-day relative standard deviation（RSD）was 4.77%and the inter-day relative standard deviation（RSD）was 2.07%.The test results of this method were compared with the test results of GB/T 5750.5-2006 method by paired t test,and no significant difference was found between the two（P>0.05）.（3）The results of this study indicate that in the presence of CQDs synthesized with citric acid-urea as raw materials and using phosphate as a degradation medium,the chemiluminescence intensity of NAs has increased significantly by more than 200times.On the basis of optimizing the conditions of degradation medium and its concentration,chemiluminescent reaction medium and its concentration,concentration and flow rate of CQDs,the detection of 7 common NAs was realized.And through a series of means such as ultraviolet absorption spectrum,fluorescence spectrum,chemiluminescence spectrum,free radical capture experiment,ion interference experiment and so on,the luminescence mechanism of the system was studied,and the chemiluminescence mechanism of the system was discussed and clarified.