Chlorin-based Metal Organic Frameworks For The Detection Of Phosphate

Phosphate ions play an important role in the growth and reproduction of aquatic animals and plants.It can cause eutrophication of water bodies,the growth of algae and plankton,decrease of oxygen content,and eventually lead to the destruction of ecological balance when there is an excess of phosphate.In addition,excess of phosphate in the human body can cause diseases.Therefore,the detection of phosphate is important.Metal organic frameworks（MOFs）are a class of porous crystal materials formed by the coordination of organic ligands and inorganic metal clusters.Chlorin can be used as an organic ligand to construct chlorin-based MOFs due to excellent luminescent properties.However,the sensor based on chlorin MOFs are very few reported.In this work,chlorin-based MOF as a fluorescence sensing platform was developed for the detection of phosphate.Tetra（4-carboxyphenyl）chlorin was synthesized using methylterephthalaldehydate and pyrrole.And then TCPC-Zr was prepared by taking tetra（4-carboxyphenyl）chlorin as an organic ligand and Zr Cl₄as metal ions via solvothermal approach.The morphology,characteristic functional group,structure,thermal stability and optical properties of ligand and TCPC-Zr was characterized successively by scanning electron microscopy（SEM）,FT-IR spectroscopy,Power X-ray diffraction（PXRD）,thermogravimetric analysis（TGA）,UV-vis absorption spectroscopy and fluorescence spectroscopy.The fluorescence analysis results show that the fluorescence intensity of TCPC-Zr increases with the increase concentration of phosphate ion.The effects of reaction time,solvent and material concentration on the enhancement were investigated.It was found that TCPC-Zr solution with final concentration of 0.018 mg·m L^-1 prepared with acetonitrile reacted with phosphate for 1 h,which could achieve the maximum fluorescence enhancement.The fluorescence enhancement degree of TCPC-Zr showed a good linear relationship with the concentration of phosphate in the range of 0.5μM-10μM（R²=0.9959）under the optimal conditions.The limit of detection was calculated to be 0.012μM.Moreover,TCPC-Zr exhibits a good selectivity and anti-interference for phosphate ion.The fluorescence enhancement mechanism of TCPC-Zr induced by phosphate ion was investigated by X-ray photoelectron spectroscopy（XPS）.The results show that the fluorescence enhancement is caused by the strong affinity between metal Zr in TCPC-Zr and P-O in phosphate ion.Finally,TCPC-Zr was applied to the detection of phosphate ions in river water and milk samples.The spiked recoveries were in the range of 94.42%-114.65%,and the relative standard deviations（RSD）is lower than 5.44%.Therefore,the method established in this experiment potential for the detection of phosphate ions in actual samples in the future.