| Mercury,it is one of the most toxic heavy metals.The mercury-rising(divalent mercury)in inorganic mercury has a highly toxic.Mercury pollution is mainly composed of water as a medium.Crops are exposed to the atmosphere all the year round,rooted in the soil and grow with the help of natural nutrients and water.As a link in the food chain of crops,the accompanying pollution also accumulates with the food chain and finally enters the human body.After mercury ions enter the human body,they can accumulate in human organs,destroy the central nervous system and cause metabolic disorders.Therefore,supervising the content of mercury ions in the environment is of great importance to the human health.However,the current detection of mercury ions mainly relies on large instruments and complicated operation process,so the real-time on-site detection of mercury ions still faces great challenges.With the emergence of nanomaterials,fluorescence sensor analysis technology has been greatly developed in the past decade.By synthesizing fluorescent nanomaterials,such as quantum dots,fluorescence analysis sensor with higher sensitivity and stronger anti-interference ability can be constructed.In addition,a suitable substrate material can be selected according to the performance of the fluorescent probe to further prepare the paper-based chip and realize the visual detection of Hg(Ⅱ)in the field.Therefore,in this paper,four kinds of fluorescence probes were designed,and fluorescence sensor with high stability and high selectivity was constructed to realize rapid visual detection of Hg(Ⅱ).Specific research work is as follows:(1)Fluorescence nitrogen-doped carbon quantum dots(N-CQDs)were synthesized by one-pot hydrothermal method using catechol and ethylenediamine.The N-CQDs were characterized by transmission electron microscopy,X-ray diffraction and infrared spectroscopy to analyze the size,element composition and functional group types.A fluorescence sensor was constructed based on the fluorescent probe,and the material had stable fluorescence signal by virtue of the unsaturated group of benzene ring.Hg(Ⅱ)reacts with the fluorescent probe to form the ground state compound,which induces the charge transfer(LMCT)effect from the ligand to metal ions,leading to fluorescence quenching.The fluorescent probe showed a good response to Hg(Ⅱ),and optimized the related factors such as p H and time.Under the optimal conditions,the detection limit of Hg(Ⅱ)was as low as 8 n M with a wide linear range of 15 n M-10 μM.The carbon quantum dots have been successfully used in the detection of divalence mercury ions in environmental water,sorghum and rice,and successfully modified to paper based chip recognition to semiquantitative detection of Hg(Ⅱ),indicating that the fluorescent probe has great application value in the field visual detection of Hg(Ⅱ).(2)Although the carbon quantum dot fluorescence sensor based on a single benzene ring group has good stability,the high detection limit affects the monitoring of trace mercury ions.Therefore,folic acid was used to react with m-phenylenediamine and pphenylenediamine respectively,coordination with benzene using folic acid conjugated heterocyclic glow,due to the changes of amino location on the benzene ring,forming the two kinds of compound Ⅰ(phenylene diamine + folic acid)and Ⅱ(para-phenylene diamine+ folic acid)have different response of mercury ion effect,fluorescence quenching and enhancement.Compound Ⅰ within 5 n M to 200 n M linear detection limit as low as 0.8n M;Compound Ⅱ has a wide linear range(100 n M to 5000 n M).Both kinds of fluorescence sensors show the ability of visual detection of Hg(Ⅱ).They are integrated into PVDF thin films to construct paper-based chips,which have good effect on Hg(Ⅱ)detection,low cost and more potential for large-scale application.(3)Considering the introduction of excellent properties of folic acid to synthesize carbon quantum dots,then on the basis of it,add new element-silicon,explore the fluorescent sensor has better detection performance,3-ammonia propyl silane as silicon source and the top three oxygen radicals folic acid by one step synthesis method,in order to build the nitrogen and silicon doped carbon quantum dots(N,Si-CQDs),the sensor detection range in both the stability and mercury ions have greatly ascend.In addition,the paper based chip constructed can not only realize specific recognition detection of Hg(Ⅱ),but also realize the quantitative detection of Hg(Ⅱ)due to the good linear relationship between the size of the fluorescence quenching ring and the concentration of mercury ions in a certain range,which is more important significance for rapid visual detection on site and a larger step towards practical application. |
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