Construction Of Metal-organic Framework Electrochemical Sensors And Their Application

Metal-organic frameworks?MOFs?,as a new class of porous coordination polymers?PCPs?,which are synthesized by assembling metal ions with organic ligands.With the progress of MOF research,MOFs have received considerable attention because of their high surface area,high porosity,tunable structures,large pore volumes and open metal sites.The special textural properties endow MOFs with great promises in the fields of biological and chemical sensing applications.Nevertheless,the applications of MOFs materials are limited in electrochemical sensing due to the poor conductivity,less selectivity and lack of modification sites.In order to satisfy the realistic applications of MOFs,it is desirable to further enhance the properties and introduce new functionalities.In this regard,integrating MOFs and a variety of functional materials into a single structure has been proposed recently to combine the merits and mitigate the shortcomings of both the components.Up to now,various MOFs composites-based electrochemical sensors have been successfully developed to apply in the areas of environmental monitoring,food safety and health monitoring.With the development of the society,more and more analytes need to be detected.Therefore,it is imperative to construct a series of effective and sensitive MOFs composites-based electrochemical sensors and expand its application areas.Herein,in order to develop the novel MOFs composites-based electrochemical sensor,some well-defined MOFs composites were designed and synthesized to build several kinds of sensor systems.Some environmental contaminations and disease markers were chosen as target analytes.By implementing some innovations to the sensor system,the sensitivity and stability of the electrochemical sensor are enhanced while detecting these analytes.The main results of this dissertation are as following:1. A new electrochemical method based on a metal-organic framework composite was developed for simultaneous detection of multiple heavy-metal ions in aqueous solutions.In this study,a graphene aerogel?GA?and MOF?Ui O-66-NH₂?composite was designed and synthesized for the first time.The GA-Ui O-66-NH₂ composite were synthesized via the in-situ growth of the Ui O-66-NH₂ crystal on the GA matrix.GAs not only serves as the backbone for Ui O-66-NH₂ but also enhances the conductivity of the composite by accelerating the electron transfer in the matrix.Ui O-66-NH₂ worked as a binding site for heavy-metal ions because of the interaction between hydrophilic groups and metal cations.The detection performance of the GA-Ui O-66-NH₂ composite-modified electrodes was determined.The developed electrochemical method can be successfully applied for individual and simultaneous detection of heavy-metal ions,namely,Cd²⁺,Pb²⁺,Cu²⁺and Hg²⁺,in aqueous solutions with high sensitivity and selectivity.The limit of detection?LOD?for simultaneously detecting multiple metal ions were 9 n M for Cd²⁺,1 n M for Pb²⁺,8 n M for Cu²⁺,and 0.9 n M for Hg²⁺.The method can also be used for simultaneous detection of Cd²⁺,Pb²⁺,Cu²⁺,and Hg²⁺in river water and the leaching solutions of soil and vegetable with high accuracy and reliability.The recovery of Cd²⁺,Pb²⁺,Cu²⁺,and Hg²⁺was between 86.7 and 104.7%.2. A novel MOF@MOF composite-based electrochemical sensor was constructed for nonenzymatic glucose sensing in alkaline media.In this study,a well-defined core-shell MOF@MOF?Ui O-67@Ni-MOF?composite was firstly synthesized.The Ui O-67@Ni-MOF composites were synthesized by internal extended growth of shell Ni-MOF on the core Ui O-67 under polyvinylpyrrolidone?PVP?regulation.In the sensor system,Ui O-67 with large specific surface area and good conductivity was used to accelerate the rate of electron transfer of Ui O-67@Ni-MOF composites.Ni-MOF served as an electrocatalytic material due to excellent electrochemical activity toward glucose oxidation.To demonstrate the detection performance of the Ui O-67@Ni-MOF composite-based sensor,it was successfully used for nonenzymatic glucose sensing.The results indicated that Ui O-67@Ni-MOF composites exhibited high electrocatalytic activity toward glucose oxidation compared with individual Ui O-67 and Ni-MOF.Moreover,the sensor possessed high sensitivity and selectivity for real-time amperometric detection of glucose.The result of amperometry under optimal conditions displayed that the sensor had a fast response?<5 s?,wide linear range?5?M to 3.9 m M?,and low LOD?0.98?M?.It performed glucose level detection in human serum samples with acceptable reliability and accuracy.3. New type of metal-organic framework composite-based electrochemical sensor was fabricated for sensitive and selective detection of glyphosate.In this study,we designed and synthesized a graphene nanosheets?GNS?and MOF?Ui O-67?composite.The Ui O-67/GNS composite was prepared by the in-situ growth of Ui O-67 on the graphene nanosheets.GNS with high specific surface area and excellent conductivity was used to enhance the conductivity of the composite.Ui O-67 containing Zr-OH groups exhibited high affinity for phosphate groups,endowing the composites with a high adsorption property for glyphosate.Meanwhile,the addition of Ui O-67 can avoid the aggregation of GNS.The GNS-Ui O-67composite-modified electrodes were employed as a sensor to detect the glyphosate in an electrolyte solution containing Cu²⁺ion by an electrochemical method.Because of the strong interaction between glyphosate and Cu²⁺ion forms a complex,the detection of glyphosate was performed by an indirect method.The results showed that the fabricated electrochemical sensor possessed superior sensitivity for glyphosate sensing.The linear ranges for the detection were 0.01?M?5.5?M.The limit of detection was 0.3 n M.To demonstrate the practical applicability of the sensor system,it was successfully applied to test the glyphosate in the different real samples.In summary,we had successfully designed and synthesized a variety of metal-organic framework composites and fabricated electrochemical sensors for the detection of different analytes.These researches provide a novel idea and method for the application of metal-organic framework composites in the area of electrochemical sensors.