Fluorescence Sensing Of Metal Ions In Aqueous Solution Based On Water-stable MOFs

Metal-organic framework compounds?MOFs?are a new class of multifunctional crystalline materials with good stability,high porosity and specific surface area.They have a better application in gas storage,chemical separation,catalysis and fluorescence sensing.In this paper,six novel complexes were synthesized by carboxylic acid ligands and triazole derivative ligands.Because of their open metal sites,Lewis acids or basic sites,they can be used to detect different analytes.So fluorescence sensing in metal ions and other aspects has potential application value.The specific research content is divided into the following parts:1.The 5-?3,5-dipyridin-4-yl-[1,2,4]triazol-1-ylmethyl?-isophthalic acid?DPTMIA?was as an organic linker to synthesize a novel luminescent complex{[Zn?DPTMIA?]·?H₂O?₂?DMF?_0.5}_n?MOF-1?with d¹⁰ transition metal ion Zn²⁺via solvothermal reaction.The structure and basic properties of MOF-1 were characterized by X-ray single crystal diffraction,XRD,IR,elemental analysis and thermogravimetric analysis.The fluorescence properties of MOF-1 and its application in the detection of metal ions were investigated in detail.The experimental results show that MOF-1 has good thermal stability and can exist stably in the aqueous phase.And MOF-1 has strong fluorescence emission at 450 nm under excitation at 350 nm,which can realize the selective and sensitive identification of Fe³⁺in aqueous solution by fluorescence quenching.It has good application in detecting heavy metal ions of sewage environment.In addition,the fluorescent MOF is also capable of detecting sensitive and selective detection of nitrophenolic compounds in aqueous solution,especially 2,4-DNP.2.By using DPTMIA as an organic ligand,a three-dimensional luminescent Cd-MOF{[Cd?DPTMIA?]₂?H₂O?·3?CH₃CN?·2?DMF?}n?MOF-2?was formed,which exhibited fluorescence emission at 450 nm under excitation at 350 nm.It was found that MOF-2 can selectively recognize Fe³⁺,but this single fluorescence detection accompanied by a single fluorescent color change,concentration change of sensor sample or the environmental impact will reduce the sensitivity of the probe.Therefore,a composite material based dual-emission probe for Fe³⁺was prepared by the hybridization of MOF-2 with CdSe/ZnS quantum dots?QDs?-doped silica nanoparticles.CdSe/ZnS@MOF-2 showed characteristic fluorescence emission of MOF-2 and CdSe/ZnS at 450 nm?blue?and 650 nm?red?under excitation at 350 nm respectively.When the Fe³⁺in the solution was detected,the blue fluorescence of MOF-2 was quenched,while the red fluorescence of the CdSe/ZnS quantum dots remained.This eliminates errors caused by instrument,sample background and source instability,improving measurement selectivity and sensitivity.3.A novel luminescent terbium complex Tb-CP Tb?HL??EtOH?₂?NO₃?₂?MOF-3?was synthesized by using 2,6-bis-?5-pyridin-4-yl-1H-[1,2,4]triazol-3-yl?-pyridine?H₂L?as a organic ligand.When excited at 350 nm,MOF-3 exhibited green fluorescence with emission peaks at 490 nm,545 nm,584 nm,and 620 nm respectively,and the strongest emission at 545 nm.When encountering Zn²⁺ions in aqueous,the characteristic emission fluorescence of MOF-3 at 545 nm is weakened and strong fluorescence emission is generated at 427 nm which is the fluorescence of the newly formed complex2HL^--Zn²⁺,when encountering Cd²⁺,the fluorescence emission of 2HL^--Cd²⁺occurs at403 nm.The ratio fluorescence detection can realize the visual sensing of the target analyte.By establishing the internal standard,the interference of the probe concentration,the ambient temperature and the excitation intensity are greatly weakened,so that the result is more accurate and the response range is wider.Based on these experiments,it can also achieve"cascade recognition"of H₂PO₄^-,causing fluorescence of 2HL^--Zn²⁺and 2HL^--Cd²⁺to weaken until it disappears.In addition,MOF-3 can selectively detect 2,4-DNP by"switching"the fluorescent signal.4.A rigid triazole derivative,3-?5-Amino-1H-pyrazol-4-yl?-5-?3-amino-1H-Pyrazol-4-yl?-3,5-dihydro-[1,2,4]triazol-4-ylamine?APAPT?,was as a ligand to form three new types of frame materials?MOF-4^MOF-6?from 0D to 3D with CdI₂,MnSO₄·H₂O and ZnSO₄·7H₂O respectively under solvothermal conditions.The materials were then characterized by X-ray single crystal diffraction,thermogravimetric analysis,etc.,and their luminescence properties and catalytic properties were analyzed.