Application Of In Situ Modified Metal-organic Framework Materials In Fluorescence Sensing

With the development of scientific and technological level and industrial technology,people’s quality of life has been greatly improved,but also the demand for living environment is getting higher and higher.Environmental pollution,especially water pollution,has been troubling people and has brought many negative effects to people’s life.The concentration of metal ions in water can be harmful to organisms,even fatal.Therefore,it is very important to monitor the concentration of metal ions in water in real time.In addition,small molecular polypeptides regulate the normal life activities of organisms,and the p H value of the environment also affects the activity of biological enzymes,which have more or less impact on the health level of organisms.And the fluorescence sensor is an efficient and simple detection method,which can be applied to the sensing of metal ions,biological small molecules and p H.Therefore,the selection and design strategy of fluorescence sensor materials are worth further study.Metal-organic skeleton materials（MOFs）are porous crystal materials coordinated by metal nodes and organic linkers,which are good main materials for fluorescent sensors.Because of its variable pore size and controllable pores,it also provides the possibility for the composite of fluorescent guest molecules.Its rigid frame structure can protect the guest materials from external environment interference.In addition,the high specific surface area of MOFs also has a strong ability to enrich detected substances.Therefore,MOFs based fluorescence sensor has a certain application prospect.In this paper,two kinds of MOFs matrix composites were prepared and their fluorescence properties and practical detection ability as fluorescence sensors were investigated.The research work is as follows:（1）The BER@ZIF-8 composite was synthesized using a one-pot method.Structural characterization confirmed the successful synthesis of the composite material and demonstrated that ZIF-8 successfully encapsulated berbertin（BER）into the pore.And BER@ZIF-8 combines bright solid and liquid luminescence at 534 nm for excellent fluorescence performance.Further testing revealed that BER@ZIF-8 was a specific fluorescence sensor for Fe³⁺in water,It has no response to common metal ions such as Cr³⁺,Co²⁺,Cu²⁺,Zn²⁺,Ni⁺,Mg²⁺,Ca²⁺,Na⁺,K⁺,Al³⁺and anions such as Cl^-,HCO₃^-,NO₃^-,NO₂^-,SO₄^2-,etc.,and has excellent time stability and p H stability.The fluorescence intensity ratio of I₅₃₄（H₂O）/I₅₃₄(Fe³⁺)increased linearly with the increase of Fe³⁺concentration,and the detection limit was 3.23μM.（2）MnO₂ nanoparticles were grown on the surface of UiO-66 by in-situ growth method to form UiO-66@MnO₂ composite material.A series of characterization tests were carried out to demonstrate the successful preparation of UiO-66@MnO₂ and that the MnO₂ nanoparticles were loaded on the UiO-66 surface.UiO-66@MnO₂ showed a yellow-green fluorescence of564 nm in the presence of o-phenylene diamine.Because cysteine in glutathione（GSH）contains sulfhydryl group,which is strongly reducing,and can undergo oxidation reduction reaction with MnO₂ to reduce the oxidation ability of UiO-66@MnO₂ and quench fluorescence,UiO-66@MnO₂ is used as a sensing detection of GSH.Further studies showed that UiO-66@MnO₂ had a specific recognition of GSH and good anti-interference performance,and the fluorescence quenching ratio（F₀-F）/F₀ has a good linear relationship with GSH concentration,and the detection limit of GSH reaches 1.20μM.In addition,UiO-66@MnO₂ also has protonation/deprotonation properties,under acidic conditions（p H=1～7）,with the enhancement of acidity,fluorescence quenching is more obvious,fluorescence quenching curve shows a“λ”characteristic;However,under the alkaline environment（p H=8～14）,the fluorescence quenching was more obvious with the increase of alkaline,and the fluorescence quenching ratio increases linearly with the increase of p H value.