Synthesis,Characterization And Fluorescent Properties Of Znic-based Coordination Polymer Micro/nanomaterials

In recent years,metal organic frameworks?MOFs?or coordination polymers?CPs?coordinated by metal ions and organic ligands have drawn much attention since the infinite probabilities in structures and properties originated from the combination of metal and polydentate ligands.With the improvement of nanoscience and technology,the nanomaterials with specific morphology and size display better physical and chemical properties than their bulk materials.Therefore,various coordination polymers nanostructures present extensively potential applications in many fields,such as gas adsorption and separation,catalysis,optical materials,biological imaging and drug delivery.In this paper,the ligands with various coordination sites,such as pyridinedicarboxylic acid?PDC?,trimellitic acid?H₃BTC?,bipyridine?BPY?and terephthalic acid?H₂BDC?,were employed for the synthesis of three zinc-based coordination polymer micro-nano materials.The main contents are as follows:1.Tb³⁺-doped zinc-based coordination polymer nanospindle bundles(Zn-PDC/Tb³⁺)were synthesized by a simple solution precipitation route at room temperature,employing Zn?NO₃?₂,Tb?NO₃?₃ and 2,5-Na₂PDC as the initial reactants,and a mixture of deionized water and absolute ethanol with the volume ratio of 10:10 as the solvent.The as-obtained nanostructures presented strong fluorescent emission under the excitation of 298 nm light,which was attributed to the characteristic emission of Tb³⁺ion.It was found that the abovementioned strong fluorescence of the nanostructures could be selectively quenched by Cefixime?CFX?in aqueous solution.The other common antibiotics hardly interfered.Thus,as-obtained Zn-PDC/Tb³⁺nanostructures could be prepared as a highly-sensitive fluorescence probe for selective detection of CFX in aqueous system.The corresponding detection limit reached 72 ppb.The theoretic calculation and UV-Vis absorption experiments confirmed that the fluorescence quenching of Zn-PDC/Tb³⁺nanostructures towards CFX should be attributed to the electron transfer and the fluorescence inner filter effect?IFE?between the fluorescent matter and the analyte.It is worth noting that this is the first report of a rare earth-doped coordination polymer for the selective detection of cefixime antibiotics.2.Zn-Hbtc-BPY/Ln³⁺fluorescent nanospheres were successfully synthesized via a two-step synthesis route.First,the spherical Zn-Hbtc-BPY nanomaterials were prepared employing zinc nitrate as the metal source,trimesic acid and bipyridine as the mixed ligands.Then,spherical Zn-Hbtc-BPY nanomaterials were sunk in an ethanol solution containing Ln³⁺ions(Ln³⁺=Eu³⁺,Tb³⁺,Eu³⁺/Tb³⁺)at room temperature to form Zn-Hbtc-BPY/Ln³⁺fluorescent nanospheres.Experiments showed that the obtained Zn-Hbtc-BPY/Ln³⁺nanospheres exhibited tunable optical properties under the excitation of the light with various wavelengths.This means that white light emission can be achieved by adjusting the excitation wavelength.It was found that L-tryptophan could cause the characteristic emission increase/decrease at 370/546 nm of the as-prepared Zn-Hbtc-BPY/Tb³⁺fluorescent nanospheres.As a result,the fluorescence intensity ratio between the above wavelengths(I_370/546)could be tuned by the concentration of L-tryptophan.Since the other amino acids did not interfere with the above phenomenon,as-obtained Zn-Hbtc-BPY/Tb³⁺nanospheres has potential application as a fluorescence probe for the selective detection of L-tryptophan in the aqueous system,with the detection limit of 17?M.3.The cationic metal-organic frameworks,MOF-5/Tb³⁺nanocubes were successfully synthesized employing zinc acetate,terbium nitrate and terephthalic acid as raw materials at room temperature.It was found that some parameters,such as the sort and amount of reactants,the sort and amount of solvents and the amount of the additive,could markedly affect the morphology and size of MOF-5/Tb³⁺nanomaterials.More importantly,the fluorescence of as-obtained MOF-5/Tb³⁺nanocubes could be selectively quenched by Cr?VI?ions in aqueous solution.The detection limit was in turn 2.29?M for deionized water,2.56?M for the Mirror Lake water and 2.99?M for Yangtze River water.Thus,the as-prepared MOF-5/Tb³⁺fluorescent probe presents potential application for the rapid detection of Cr?VI?ions in aqueous system.