Fluorescent Sensing Analysis Based On Metal/Covalent Organic Frameworks

Metal organic frameworks?MOFs?are high crystallinity materials formed by the coordination of inorganic metal ions and organic bridging ligands with periodic network structure.Covalent organic framework?COFs?is a kind of porous organic material with crystallinity and periodic structure,which is formed by covalent bonds of light elements.Both MOFs and COFs have the advantages of high porosity,large specific surface area,adjustable structure and so on.They have potential huge application value in terms of gas adsorption,heterogeneous catalysis,sensing detection,energy storage,biological imaging and so on.In this paper,fluorescence metal-organic framework and covalent organic framework were prepared for the sensing analysis of ionic contaminants.The main research about this work is as follows:?1?Strong fluorescence ZnMOF-74 and weak fluorescence CuMOF-74 were synthesized by 2,5-dihydroxy-1,4-benzenedicarboxylic acid via solvothermal method with Zn?NO₃?₂ and Cu?NO₃?₂,respectively.Fluorescence of ZnMOF-74 decreased on account of complexation between Zn²⁺and S^2-.Fluorescene of CuMOF-74 recoveried which was result from the formation of CuS precipitation.ZnMOF-74 probe was applied to detect S^2-in water samples with a detection limit of 6.527 nM and a linear range from 19.6 nM to 90?M.CuMOF-74 probe was applied to detect S^2-in water samples with a detection limit of 1.5 nM and a linear range from 4.5 nM to 125?M.Different fluorescence signals with the two kinds of sensors for sulfur ion based on two kinds of MOF-74 for different sensing mechanisms,but both ZnMOF-74 and CuMOF-74 could realize sulfur ion sensing.?2?A two-dimensional COF synthesized by amine-aldehyde condensation reaction between 4,4',4''-?1,3,5-triazine-2,4,6-triyl?trianiline and 2,5-dihydroxy terethaldehyde?TAPT-DHTA-COF?was used as a host to encapsulate N-doped carbon dots?NCDs?and Rhodamine B?RhB??NCDs-RhB@COF?.NCDs and RhB were uniformly assembled into the pores of TAPT-DHTA-COF based on the hydrogen bond.The as-prepared NCDs-RhB@COF nanocomposites exhibited double emission peaks both of NCDs at 440 nm and RhB at 570 nm under the excitation of 340 nm.After the addition of Hg²⁺,the emission at 440 nm decreased while the fluorescence at570 nm increased due to the strong coordination between NCDs-RhB@COF and Hg²⁺.The“on-off”fluorescence probe was applied to detect Hg²⁺in water samples with a detection limit of 15.9 nM and a linear range from 47.7 nM to 10?M.Furthermore,NCDs-RhB@COF also showed high sensitivity,good selectivity and stability,which was expected to apply in quality testing of industrial goods and further biological cell experiments.?3?The PTDA-DATA-SBP was first synthesized by amine-aldehyde condensation reaction between 1,10-Phenanthroline-2,9-dicarboxaldehyde?PTDA?and 2,5-Diaminoterephthalicacid?DATA?.PTDA-DATA-SBP was utilized to build sensor for copper ion and showed one emission at 565 nm under the excitation of 338nm.Copper ion was able to coordinate with nitrogen atom on the imide bond and the oxygen atom on the carboxyl group so that fluorescence of PTDA-DATA-SBP quenched.The sensor was applied to detect Cu²⁺in water samples with a detection limit of 1.15 nM and a linear range from 3.45 nM to 8?M.