Synthesis Of Eu And Zn Based Fluorescent MOFs And Their Fluorescence Sensing Properties For Organic Small Solvents And Nitroaromatic Compounds

Metal-organic framework?MOFs?are a new class of hybrid porous materials composed of secondary structure units?SBUs?,namely metal ions/clusters and organic linkers that are linked into a three-dimensional lattice.MOFs are derived from polyhedral or small cluster coordinated polymers,and gradually expand into one-dimensional chains,two-dimensional layers and final three-dimensional frameworks.With their novel topologies,they have a wide range of applications in separation,catalysis,sensing,biomedicine and so on.In recent years,due to their advantages,such as high sensitivity,low cost and short response time,fluorescence sensors have received a great deal of attention from researchers.Along with the appearance of fluorescent MOFs,greater possibilities have been provided for exploring novel fluorescent materials and detecting small molecules and organic substances.Accordingly,two kinds of fluorescent MOFs were designed and synthesized in this thesis.The fluorescence sensing properties of synthetic materials for organic small molecules and nitroaromatic compounds were studied respectively,and their potentials of application in detection and other aspects were explored.The main researches are as follows:The first part:The characteristics,recent development and applications of metal-organic framework?MOFs?were outlined briefly.In addition,the classification,emitting mechanism and application of luminescent MOFs were introduced.Finally,the significance of this research was proposed.The second part:Through DMF solvent heating and ethanol solvent refluxing,which are simple and rapid,the material[Eu?BTC?·?H₂O?₆]was synthesized respectively,composing of rare earth element Eu as the metal skeleton and trimellitic acid?H₃BTC?as the organic ligand.XRD,FT-IR,TG,SEM,PL and nitrogen adsorption analysis were used to characterize the morphology,particle size,thermal stability,and fluorescence properties.The results showed that the morphology of MOFs synthesized by the ethanol solvent refluxing method was regular and well-dispersed.The MOFs had a length of 4?m,a width range of 50¹00 nm,and a relatively high thermal stability.Interacted with nine organic small molecules respectively,the fluorescence intensity of MOFs was significantly different,which indicated that MOFs can selectively recognize different organic small molecules.It is further speculated that the binding force between the Eu³⁺open site and organic small molecules is different,because of the micro-environment of the pore structure of MOFs;energy transfer occurs between the organic small molecule and the ligand.The combination of the two causes a change in the fluorescence intensity.This high sensitivity and specificity indicated that the material can be applied to identify organic small molecules.The third part:The surface active agent cetyltrimethylammonium bromide?CTAB?was used as a soft template to design and synthesize a fluorescent MOFs[Zn?BDC?·?H₂O?_0.75].The amount of CTAB and the reaction time on the morphology of MOFs were investigated in detail.The results showed that the optimal amount of CTAB was 1.0 g and the best reaction time was 2 h.Then the structure and properties of the as-synthesized product were characterized by XRD,FT-IR,TG,SEM,PL and nitrogen adsorption analysis.The results showed that the morphology of Zn?BDC?·?H₂O?_0.75 was rod-like,with a length of 2?m,a width range of 50²00 nm.Besides,it has high thermal stability and good fluorescence performance,and it can be used as a potential fluorescence detection material.The fourth part:The fluorescence properties of the interaction between Zn?BDC?·?H₂O?_0.75 and nitroaromatic compounds?NACs?were studied.The nitroaromatic compounds included 1,3-dinitrobenzene?1,3-DNB?,O-nitrotoluene?ONT?,m-nitrotoluene?MNT?,p-nitrotoluene?PNT?,o-nitrophenol?ONP?,p-nitrophenol?PNP?.Zn?BDC?·?H₂O?_0.75had a sensitive fluorescence response to NACs.When the structure and concentration of NACs were changed,different fluorescence quenching properties were exhibited:in the same concentration range of 2⁵00 mg·L^-1,PNP and ONP had the strongest quenching ability to Zn?BDC?·?H₂O?_0.75 with a annihilation efficiency as high as 91⁹4%,followed by ONT,MNT and PNT,and 1,3-DNB had the weakest one.For all the substances in a certain concentration range,the concentration and the corresponding relative fluorescence intensity showed a good linear correlation,in which the correlation coefficient was up to 0.99,and detection limit was as low as 2 mg·L^-1.The mechanism of fluorescence quenching can be explained by the donor-acceptor charge transfer mechanism.When Zn?BDC?·?H₂O?_0.75 was recycled five times,its XRD pattern and fluorescence intensity had almost no change,indicating that the structure of Zn?BDC?·?H₂O?_0.75 was stable and had excellent performance.It can be used as fluorescent sensors for recycling and can identifiy nitroaromatic compounds accurately and sensitively.