Preparation,Characterization And Fluorescence Detection Performances Of Lanthanide Organic Frameworks

Metal-organic frameworks(MOFs)have attracted more and more attention due to their structural designability and pore size tunability.Especially,luminescent MOFs(LMOFs)with the superiorities of inherent crystallinity,definite structure,tunable pore,and multiple functionalizations,have been widely used in sensing field.Among them,the most prominent luminescent materials in LMOFs are lanthanide metal-organic frameworks(Ln-MOFs).The luminescence of Ln-MOFs comes from the Ln3+f-f electron transition of the inner layer,so it has more outstanding advantages and characteristics than general transition metal-organic frameworkss,such as high optical purity,large stokes-shift,high quantum yield,clear emission peaks,visible color change to the naked eye,long luminescence lifetimes and so on.In this thesis,some luminescent lanthanide organic frameworks were successfully prepared and their luminescent characteristics and relative influence factors were studied in detail.As a result,some noval fluorescent sensing systems based on Ln-MOFs were developed and their analytical applications in environmental samples were investigated.The main content are as follows:(1)A pillar-like 3D europium organic framework(Eu-MOF)material with good luminescence properties was synthesized by a hydrothermal method using 3,3',4,4'-biphenyltetracarboxylic acid as ligand and europium ion as metal source and its analytical performance as a fluorescent sensing material was studied.The results showed that the Eu-MOF exhibited excellent luminescence and structural stability in the aqueous solution or other organic solvents and good pH-independent luminescence stability in the pH range of 5-11.By exploiting strong quenching effects of Fe3+,Al3+and nitrobenzene(NB)three noval fluorescence analytical methods based on turn-off mode were developed,the detection limits were respectively 0.39 ?M for Fe3+ 0.084 ?M for Al3+and 0.013?M for NB.In addition,their fluorescent quenching mechanisms were also clarified.(2)A new Eu3+-based strontium-organic framework(Eu3+@Sr-MOF)was prepared by selecting 2D network structure Sr-MOF containing uncoordinated carbonyl groups as the parent framework,Eu3+cations were successfully introduced into the pores of Sr-MOF by a postsynthetic modification(PSM)strategy.The obtained material was fully characterized,and the luminescent properties of Eu3+@Sr-MOF sample were investigated in detail.The results displayed that Eu3+@Sr-MOF not only possessed excellent water stability and chemical stabilities in a wide pH range(3-11),but also could be employed as a highly selective and highly sensitive fluorescent probe for sensing Cr(?)and Cr(?)via "turn off" mode.The detection limits for Cr3+ and CrO42-were down to 0.15?and 0.17?M and linear ranges were 0.6-150 ?M and 0.1-200 ?M with high quenching constants Ksv of 1.56×104 and 1.19×104,respectively.(3)Sm-MOF was successfully prepared from 2-amino-terephthalic acid(H2ATPA)and Sm(NO3)3·6H2O under solvothermal condition.Since "hard acid" Ln3+does not have affinity with "soft base" N atom,the amino N atom in ATPA2-does not participate in coordination when ATPA2-reacts with Ln3+.The "free" amino group is just a strong complexing agent for common heavy metal ions.The study has showed that it is just the strong interaction between Hg2+ and the amino groups of Sm-MOF that induced quenching of charge transfer emission and enhancement of Sm3+ characteristic fluorescence,which could be employed to specifically determine Hg2+.At the same time,the Sm-MOF also showed high adsorption capacity for Hg2+ and could be used to remove Hg2+ in water.