Construction Of Fluorescent MOFs For Selective Detection Of Pollutants In Water

Metal-Organic Frameworks（MOFs）,as a kind of crystalline porous material,are constructed by coordination bonds between organic ligands and metal ions or metal ion clusters.MOFs have the advantages of rich composition and structure,large specific surface area,high porosity,adjustable pore environment and easy functionalization.Therefore they have great prospects in the application fields of adsorption and separation,catalysis and sensing,which have attracted extensive attention and research.In this thesis,two In（Ⅲ）-MOFs（BUT-128 and BUT-129）with the similar structure were constructed by solvothermal method.Both of these two MOFs have good fluorescence properties and water stability.Antibiotic pollutants with different levels of toxicity in water can be specifically identified by combing the changes of different fluorescence signals of the two MOFs.In addition,BUT-128 and BUT-129 also have the potential to detect metal ion pollutants(Fe³⁺,Ag⁺and Cr₂O₇^2-)in water.Using water stabilized MOFs as fluorescence sensor to detect residual antibiotics in agricultural wasterwater has the advantages of high sensitivity,simple operation and short time-consuming.In the thesis,two isomorphic In（Ⅲ）-MOFs are synthesized by solvothermal method.The molecular formulas are In₅（BTETA）_11/3（OH）₄（H₂O）[H₃BTETA=4,4’,4’’-（benzene-1,3,5-triyltris（ethyne-2,1-diyl））tribenzoic acid]（BUT-128）andIn₅（TTETA）_11/3（OH）₄（H₂O）[H₃TTETA=4,4’,4’’-（（2,4,6-trimethylbenzene-1,3,5-triyl）tris（ethyne-2,1-diyl））tribenzoic acid]（BUT-129）respectively.The single crystal structure analysis shows that BUT-128 and BUT-129 crystallized in hexagonal R3c space group,with octahedral cage structure with inner diameter of about 15（?）,and the BET specific surface areas are 1998 and1626 m²g^-1 respectively.In addition,BUT-128 and BUT-129 can still maintain the integrity of the structural framework after water treatment,which provides the prerequisite for the detection of antibiotics in the water medium.Furthermore,we explored the fluorescence properties of BUT-128 and BUT-129,and found that although the two MOFs share the same structure,they have different fluorescence properties because of the three more extra methyl structures on the central benzene ring of the ligand of BUT-129 over BUT-128.Through the fluorescence titration experiment,it was found that nitrofuran antibiotics have a highly sensitive fluorescence quenching response towards both BUT-128 and BUT-129.Besides,chloramphenicol also has a highly sensitive fluorescence quenching response towards BUT-128.The limits of detection could reach ppb levels.In addition,the fluorescent sensor array based on two MOFs can be used to specifically identify the antibiotics with different levels of toxicity.This detection method has advantages of high selectivity and strong anti-interference.In addition to the residual antibiotics in agricultural wastewater,various metal ions in industrial wastewater are also one of the main reasons of environmental pollution.The author continued to explore the detection performance of metal ions in water by using BUT-128 and BUT-129 as the fluorescent probes.Due to the strong inner filter effect,BUT-128 has high fluorescence quenching efficiency for Fe³⁺and Ag⁺,and the limit of detection are 62 and 253 ppb respectively.In addition,the fluorescence of both BUT-128 and BUT-129 can be highly quenched by Cr₂O₇^2-.The two MOFs have high selectivity for the detection of Cr₂O₇^2-.After being recycled for4 times,the quenching efficiency of Cr₂O₇^2-towards BUT-128 and BUT-129 remains at high level,which proves their good stability as fluorescence material for metal ions.In addition,the reasons for the different fluorescence quenching properties of the two MOFs are explained through mechanism exploration,which provides theoretical guidance for the screening or design of fluorescence materials for metal ions detection with high sensitivity and selectivity.