Preparation Of Functional Metal Organic Framework Materials And Its Application In Water Pollutant Detection

Since entering the 21st century,China’s economy has ushered in a stage of rapid development.More and more attention has been paid to environmental protection and governance,and people are more and more looking forward to a better living environment.How to solve various environmental problems has increasingly become the focus of public attention,especially water environmental problems(pollutants),which not only have a wide variety,but also will continue to penetrate into people’s lives.Therefore,it is an inevitable trend for the development of analytical technology to detect it efficiently,simply and quickly.As a new kind of crystalline porous materials,metal organic frameworks(MOFs)have the characteristics of tunable chemical structure,ultra-high porosity,super large specific surface area,adjustable pore size/shape and internal and external surfaces.They have broad application prospects in the fields of gas adsorption,catalysis,luminescence,biological imaging,energy storage and conversion.In this paper,three different MOFs materials were designed and synthesized based on their catalytic colorimetric and luminescent properties,which were successfully used for the colorimetric detection of dissolved hydrogen sulfide,the fluorescence detection of copper ion and the colorimetric ratio fluorescence detection of mercury ion.(1)High concentration of dissolved hydrogen sulfide in water can not only poison aquatic animals and plants,but also destroy the ecosystem and make the water body stink.Therefore,it is necessary to find a method that can sensitively and quickly detect hydrogen sulfide in water environment.Colorimetry is one of the classical rapid detection methods.The incomplete catalytic activity of single component MOF as a simulated enzyme may limit its application in colorimetric sensor.The potential of bimetallic MOFs as mimetic enzymes is rarely used to assess H2S levels,Therefore,this section propose a hybrid node Cu-Fe MOF as a simulated enzyme for rapid colorimetric detection of H2S based on target induced inactivation effect.Mixed metal Cu-Fe MOF with high density open metal sites was synthesized by a simple one pot method.The mixed Cu-Fe MOF consists of a well-known paddle wheel like[Cu2(COO)4]dimer and[Fe3(μ3-O)(COO)6]trimer cluster.In the presence of H2O2,it can catalyze the oxidation of 3,3’,5,5’-tetramethylbenzidine(TMB)to produce blue oxtmb,and the dissolved H2S will inactivate the simulated enzyme,so that the blue disappears.The working mechanism of the sensor is discussed through steady-state dynamic analysis.The experimental conditions were optimized.When the optimal concentrations of TMB,H2O2 and MOF were 1.4 mM,0.56 mM,0.30 mg/mL and 0.1 M NaAc-HAC buffer(pH=3.5),the UV absorption at 652 nm decreased and the concentration of H2S was 0-80 μM showed a good linear relationship in the concentration range,and its detection limit was 1.6 μmol/L.In addition,some potential substances in the water sample have no interference.The method has the advantages of low cost,high sensitivity,good selectivity and visible to the naked eye.It has been successfully applied to the determination of H2S in industrial wastewater.(2)Cu2+ plays an important role in the water environment and in the human body.When the concentration of copper ions in the water environment reaches the human body through the food chain,it will cause various serious diseases,such as Alzheimer’s disease and Parkinson’s disease.Therefore,it is of great significance to detect its concentration efficiently and sensitively in the water environment.MOF based on colorimetric sensor is simple and rapid for the detection of water environmental pollutants,but its sensitivity is not high.Therefore,it is particularly important to increase its sensitivity by changing the coordination between a variety of mixed organic bridging ligands and metal nodes.This section propose a Zr based MOF with mixed double ligand structure for highly sensitive detection of Cu2+ based on fluorescence quenching effect.This MOFs material uses 2,5-dimercaptoterephthalic acid(SH-BDC)and racemic tetra(4-carboxyphenyl)porphyrin(TCPP)as double ligands,zirconium chloride as the central metal ion,and uses the coupling between Cu2+,SH-BDC and TCPP to achieve highly sensitive detection of Cu2+.The experimental conditions were optimized.When the optimal concentration of MOF was 0.27 mg/mL,20 mM Tris HCl buffer(pH=5.5)and Ex/Em=446 nm/686 nm,the difference ratio of fluorescence intensity at 686 nm to Cu2+ concentration was 0-14 μM that showed a good linear relationship in the concentration range,and its detection limit was 250 nM.The method has the advantages of low cost,high sensitivity and good selectivity.It has been successfully applied to the determination of Cu2+in water environment.(3)Hg2+ is a common heavy metal in the water environment.Its abnormal concentration does great harm to the environment and human body,such as Minamata disease,one of the eight public hazards in the world.Therefore,it is necessary to detect its concentration with high sensitivity and fast in water environment.MOF based on colorimetric sensor is simple and rapid for the detection of water environmental pollutants,but its sensitivity is not high.Although the fluorescence method has high sensitivity,it is not easy to observe quickly.In order to complement the advantages of the two,this section propose a composite of Zr based MOF with mixed double ligand structure and fluorescein,which is used for the highly sensitive and rapid detection of Hg2+based on colorimetric and ratio fluorescence effect.The complex combines zirconium based MOFs with fluorescein isothiocyanate(FITC)with terephthalic acid(BDC)and 5,10,15,20-tetra(4-pyridyl)porphyrin(TPP)as double ligands,and realizes the colorimetric effect and ratio fluorescence effect of changing color from gray white to yellow green through the coupling effect between Hg2+,fluorescein isothiocyanate and TPP.The experimental conditions were optimized.Under the conditions of optimal concentration of MOF 0.24 mg/mL,50 mM Tris-HCl buffer(pH=2.5)and Ex=420 nm,the ratio of fluorescence intensity at 713 nm to fluorescence intensity at 513 nm and the concentration of Hg2+were 0-40μM that showed a good linear relationship in the concentration range,and its detection limit was 800 nM.The method has the advantages of clear visibility,good selectivity and high sensitivity.It has been successfully applied to the determination of Hg2+ in water environment.