Lanthanide Organic Frameworks For The Luminescent Recognition And Detection Of Ions In Aqueous Solution

The field of metal-organic frameworks(MOFs) has undergone explosive growth over the past decades.MOFs-a kind of highly crystalline material-are linked with metal ions and multidentate organic ligands through various chemical bonds.MOFs can be used for gas storage,exchange of ions,luminescent sensor and etc.For the purpose of the application in aqueous solution,two Lanthanide MOFs which are stable in water have been synthesized.The frameworks Eu₂(Fuma)₂(Oxa)·8H₂O(EuFO1),Tb(NTA)(H₂O)(TbNTA1) (Fuma=fumarate,Oxa=oxalate,NTA=nitrilotriacetate anion) were synthesized by hydrothermal method.The studies on the PXRD,TGA,EA and Photo-Luminescent Spectroscopic indicated that the derived MOFs can be potential sensors for cations and anions.The activated framework EuFO1a was investigated for the cation sensing.Metal ions such as Na⁺,Cu²⁺,Co²⁺,Al³⁺,Fe³⁺ and ere were introduced into EuFO1a.The resulted EuFO1a-x(x=immersed ion) show different kind of luminescent quench effect for Cu²⁺,Co²⁺,Fe³⁺,Cr³⁺ and Ni²⁺,especially in ⁵D₀→⁷F₂ transition.The mechanism for this is mainly due to the overlap of spectra between cations and Eu³⁺. The energy of radiative transition of Eu³⁺ was absorbed by metal ions which decreased photoluminescent intensity.The framework TbNTA1 was investigated for sensing of the anion in aqueous solution.Results show that after being immersed in the anion solution(F^-,Cl^-,Br^-,I-, NO₃^3-,CO₃^2-,SO₄^2-,PO₄^3- and etc),only the resulted TbNTA1-PO₄^3-show significant quench effect for photoluminescent intensity,especially with ⁵D₄→⁷F₅ transition.This is mainly due to the binding manner and possible structure formed between TbNTA1 and tetrahedron shaped PO₄^3-,therefore decreased photoluminescence intensity.Those experiments showed that the preparation of water-stable MOFs can be achieved with elaborately selected lanthanide ions and organic ligands.MOFs can be candidates of luminescent sensor with the modification of spectra and coordination module.