Synthesis And Fluorescence Evaluation Of Metal-Organic Gels

Metal Organic gel（MOG）is a new kind of amorphous intelligent soft material self-assembled by Metal ions and organic ligands,which has the characteristics of high specific surface area,strong flexibility,abundant binding sites and low density.It is widely used in adsorption,catalysis and sensing.However,MOG-Al is still in its infancy and needs to be further expanded.As an essential element in human body,copper（Cu）plays an important role in the process of life activities.Water or food contaminated with copper ions will lead to the imbalance of Cu²⁺in human body after consumption,thus affecting human health.Therefore,it is of great significance to construct a Cu²⁺detection method.In this paper,a metal-organic gel material was prepared by using 1,2,4,5-tetra（4-carboxyphenyl）benzene and 2,5-pyrazine dicarboxylic acid dihydrate as ligand and trivalent aluminum ion(Al³⁺)as the central metal ion（MOG-Al）via solvothermal method.The surface morphology,characteristic functional groups and thermal stability of MOG-Al were investigated by scanning electron microscopy,Fourier transform infrared spectroscopy and thermogravimetry,respectively.The fluorescence performance of MOG-Al was evaluated.Furthermore,the effect of the buffer system,p H,MOG-Al concentration on detection of Cu²⁺by the fluorescence emission of MOG-Al.The results showed that under the p H=8.0 HEPES buffer system and MOG-Al concentration of 7.0 mg·L^-1 MOGG-Al showed the strongest fluorescence response to Cu²⁺and remained relatively stable within 8 h.Under the excitationwavelength of 270 nm,the quenching（F₀-F）degree at emission wavelength of390 nm increased with the increase of Cu²⁺concentration,with a linear range of 0.05-100μM and a detection limit of 45 n M.The interaction mechanism between MOG-Al and Cu²⁺was explored by X-ray photoelectron spectroscopy.The research results indicate that Cu²⁺coordinates with the carboxyl group and pyrazine N in MOG-Al,which leads to the transfer of electrons from the ligand to Cu²⁺,and further cause the fluorescence quenching of the material.Compared with 1,2,4,5-tetrakis（4-carboxy-phenyl）benzene and 2,5-pyrazinedicarboxylic acid dihydrate,the prepared MOG-Al has higher detection sensitivity for Cu²⁺.Through the selectivity experiment,the present fluorescence sensing platform exhibits a good selectivity.Finally,MOG-Al was applied to the detection of Cu²⁺in water resources and food,and the recoveries of Cu²⁺in seawater and river water were 101.68%and127.00%,respectively.The recoveries of Cu²⁺in rice,soybean milk powder and pig liver were 92.70%-99.60%,98.14%-113.00%and 98.14%-116.00%,respectively.In conclusion,MOG-Al demonstrates excellent fluorescence detection performance for Cu²⁺and has great prospects in food environment and biology.