Design, Preparation And Performances Of New Metal-organic Frameworks With Fluorescence Sensing Properties

With the rapid development of urbanization and industrialization,the emissions of drugs and personal care products（PPCPs）,organic small molecule compounds and heavy metals into the environment are increasing year by year,which have led to the increasingly serious impacts on the ecological environment,and caused a series of environmental problems,posing a great threat to human health.Therefore,the effective treatment of pollutants in the environment is an urgent problem to be solved.However,the premise of effective prevention and control of pollutants in the environment is to carry out real-time and effective large-scale monitoring of these pollutants,to achieve the targeted treatment for pollutants.At present,the detection methods for PPCPs,small organic molecules and heavy metals in the environment are still at the laboratory level,and the commonly used methods are high performance liquid chromatography,gas chromatography,inductively coupled plasma emission spectrum,etc.Although these testing techniques can accurately and effectively detect pollutants in environmental samples,the process of environmental sample collection,sample pretreatment and sample on-machine testing are tedious,time-consuming and costly,which greatly limits the large scope of environmental sample detection and get the real-time sample data of environmental.Therefore,the development of new sensing materials is one of the most important ways to improve the detection level of pollutants in the environment.Due to its adjustable structure and large specific surface area,metal organic frameworks（MOFs）have attracted wide attention in the fields of adsorption,catalysis,fluorescence sensing and drug loading.Through crystal engineering principles,this study choose 1,2,3,4,5,6-cyclohexane carboxylic acid（H₆clhex）and 2,6-naphthalene dicarboxylic acid（2,6-NDC）for ligands and synthesized eight kinds of new lanthanide based metal organic frameworks（Ln-MOFs）,and use them to fluorescent sense PPCPs in the environment,such as naproxen（NPX）,4-amino benzyl arsenic acid（p-ASA）,tetracycline（TC）and enrofloxacin（ENP）.The novel Ln-MOFs was characterized and their structure was analyzed.The fluorescence sensing performance of the materials in different detection environments was studied,and the sensing mechanism was explored.By adjusting the synthesis strategy,this study not only realized the sensing of PPCPs in organic phase,but also realized the sensing process in water phase.In addition,in order to further improve the accuracy of fluorescence sensing,2,6-NDC was selected as the organic ligand,and by coordination with europium ions,a new ratiometric fluorescence probe was obtained and used it for sensing ENP in water.The main research results of this paper are as follows.（1）Fluorescence probe of Ln-MOFs in sensing NPX in organic phase.According to the principle of crystal engineering,six new Ln-MOFs were designed and hydrothermally combined using the lanthanide metals ions terbium（Tb）,holmium（Ho）,neodymium（Nd）,erbium（Er）,samarium（Sm）and gadolinium（Gd）as metal nodes,[Ln₂（COO）（clhex）·2H₂O)]·2H₂O（Ln = Tb,Ho,Nd）,[Sm₂（clhex）·3H₂O)]·H₂O,[Ln₂（clhex）·3H₂O)]·3H₂O（Ln = Er,Gd）.Six Ln-MOFs exhibited typical two-dimensional and three-dimensional structures,and [Tb₂（COO）（clhex）·2H₂O)]·2H₂O（BUC-68）exhibited typical fluorescence emission characteristics of Tb3+.A comparative analysis of different PPCPs performance of BUC-68 in fluorescence sensing was carried out,and it was found that NPX can cause fluorescence quenching of BUC-68 in PPCPs with the same concentration（10-3 M）.Using BUC-68 as a fluorescent probe,the selectivity,minimum detection limit and recycling ability of BUC-68 for NPX were investigated.The results show that BUC-68 can be used as a high sensitivity and selectivity fluorescent probe for sensing NPX.By testing the UV-visible absorption spectrum of PPCPs and comparing the fluorescence life of BUC-68 before and after the test,the mechanism of BUC-68 sensing NPX was analyzed,and it was found that BUC-68 sensing NPX originated from the competitive absorption of ultraviolet light between NPX and BUC-68.（2）Fluorescence probe of Ln-MOFs in sensing p-ASA in aqueous phase.A novel three dimensional Ln-MOFs [Eu₂（clhex）·3H₂O)]·H₂O（BUC-69）was synthesized by hydrothermal method,and BUC-69 exhibited extremely high water stability（40 days）.BUC-69 was used as fluorescent probe for p-ASA in water.Through water stability analysis,ion interference experiment,lowest limit of detection and cyclicity experiment,the results showed that BUC-69 could not only high sensitivity and selectively sense of p-ASA,but also have good cyclic usability.The detection results of p-ASA wastewater used to detect the real lake configuration are basically consistent with the results of the laboratory test of inductively coupled plasma emission spectroscopy,indicating that BUC-69 has the potential of sensing p-ASA in the environment.The fluorescence sensing mechanism of BUC-69 was analyzed,and the results showed that the fluorescence quenching effect of BUC-69 was mainly caused by the competitive absorption of ultraviolet light between p-ASA and BUC-69.（3）Fluorescence probe of Ln-MOFs for ratiometric sensing ENP and selective sensing TC in water phase.A novel ratiometric fluorescent MOFs probe Eu（2,6-NDC）（COO）（BUC-88）was designed and synthesized.BUC-88 performed excellent water stability and fluorescence sensing properties,BUC-88 can be used for ratiometric sensing of ENP in water and selective sensing of TC in water.Furthermore,BUC-88 was prepared as a membrane device for cyclic detection of TC in water.Fluorescence lifetime test and UV-visible absorption spectrum test showed that the sensing mechanism for tetracycline was the competitive absorption of tetracycline to ultraviolet light.BUC-88 was prepared into a fluorescent film for sensing TC,and the results showed that the fluorescent film could be effectively used for sensing TC.The development of fluorescent sensor is beneficial to the practical application of fluorescent probe.