Optical Detection Of Phosphate/mercury Ions Based On Zr-MOFs Materials With Simulated Enzyme Properties

Phosphate ion is usually considered as an important index of eutrophication in water,and can cause great harm to water ecological environment.Mercury ion is known to be a kind of toxic heavy metal ions,having potential ecological risks.Thus,it is of great importance to develop a rapid,simple and sensitive method for phosphate ion and mercury ion determination in the environment.Compared to other methods,optical methods,especially colorimetric and fluorometric assays have been attracted more attention in the detection field due to their advantages such as distinct visualization,fast response and easy operation.Among the synthesis methods for colorimetric detection,the enzyme colorimetric sensors have better advantages,such as high catalytic efficiency,good specificity and mild reaction conditions.In recent years,some MOFs and noble metal nanoparticles have shown good simulated enzyme activity.Therefore,this article is based on the metal-organic framework materials combined with optical analysis methods for rapid detection of phosphate ion and mercury ion in environment.The experiment is divided into the following two parts:1.In this work,MOF-808（Zr/Ce）was simply synthesized for phosphate detection and removal.Ce⁴⁺/Ce³⁺sites in MOF-808（Zr/Ce）offer high oxidase-mimicking catalytic activity,can catalyze TMB,meanwhile Zr⁴⁺sites provide the specificity due to the high affinity between phosphate and Zr⁴⁺.Colorimetric sensing for phosphate was achieved based on the enhancement of oxidase-like activity of MOF-808（Zr/Ce）.The linear detection range for phosphate detection was 11μM-581μM,and the detection limit（LOD）was 3.7μM.MOF-808（Zr/Ce）/CNFs（cellulose nanofibers）flexible film synthesized by filtration method also enables rapid identification of phosphate.Besides,the phosphate adsorption performance of MOF-808（Zr/Ce）was also investigated.The adsorption capacity is 54.88,65.14,and 68.54 mg g^-1 at 298,308,and 318 K,respectively.The results show that MOF-808（Zr/Ce）has considerable potential for phosphate detection and removal.2.A colorimetric and ratiometric fluorescent dual-mode assay is constructed for sensitive and specific Hg²⁺sensing based on Ui O-66-NH₂@Au.The addition of Hg²⁺stimulates the peroxidase-like activity of Ui O-66-NH₂@Au by the formation of Au-Hg amalgam,promoting the oxidizing of chromogenic substrate OPD to DAP with the aid of H₂O₂,which lead to the change of colorimetric and fluorescent signals.The absorbance of the sensing system at 450nm is linear positive correlation with Hg²⁺concentration of 30-1400 n M and the color of the solution under visible light shaded from light yellow to dark yellow.With the increase of Hg²⁺concentration,the fluorescence signal at 570 nm increased whereas that at 455 nm（intrinsic fluorescence of Ui O-66-NH₂）decreased due to inner filter effect,the fluorescence intensity ratio(F₄₅₅/F₅₇₀)decreasing linearly with Log[Hg²⁺]over the range 60-1700 n M;the fluorescence emission of sensing system under UV excitation changed from blue to yellow.The results indicate that the colorimetric and ratiometric fluorescent dual-mode assay based on Ui O-66-NH₂@Au realized visual determination of Hg²⁺rapidly and reliably,revealed application prospect in Hg²⁺monitoring.