Preparation Of Functional Zirconium-based Porphyrin Metal-Organic Frameworks And Applications In Electrochemical Sensing

Metal-organic frameworks(MOFs)formed by the coordination of metal ions/clusters with organic ligands are a research hotspot in the material field in recent years.MOFs possess large specific surface area,permanent porosity and adjustable physicochemical properties.In addition,MOFs are similar in structure to the homogeneous catalysts,and they also have the characteristics of easy recovery after catalysis of heterogeneous catalysts.These features give them great advantages in applications of catalysis.However,the application of MOFs in the field of electrocatalysis is limited due to their poor electroconductivity.So we combined redox-active Zr-based porphyrin MOFs with highly conductive carbon materials to improve their electrical conductivity.For Zr-based porphyrin MOFs,different topologies are formed from the different coordination of Zr(Ⅳ)and porphyrin,and the topologies may affect their catalytic performances.Therefore,we selected three Zr-based porphyrin MOFs with different topologies and combined them with conductive polymers to study the catalytic differences of three composites.In this paper,Zr-based porphyrin MOFs/macroporous carbon(MPC)composites and Zr-based porphyrin MOFs/polypyrrole(PPy)composites were synthesized by using MPC and PPy as carriers.The morphology and composition of the composites were studied by various methods.At the same time,Zr-based porphyrin MOFs/MPC composites were used for detecting luteolin and m-nitrophenol(m-NP)to evaluate their electrocatalytic performances,and caffeic acid(CA)was selected as probe molecule to study the electrocatalytic activities and compare electrocatalytic differences of the Zr-based porphyrin MOFs/PPy composites.The specific work of the paper is as follows:1.Zr-based porphyrin MOFs(MOF-525)/MPC composites were successfully prepared by solvothermal reaction for the first time.Structural characteristics and experimental studies show that MOF-525/MPC composites combine the advantages of MOF-525 and MPC,which possess high catalytic activity and excellent conductivity.A novel electrochemical sensor based on MOF-525/MPC was fabricated.The sensor presents superior electrocatalytic activity to the oxidation of luteolin and the reduction of m-NP,such as wide linear range,high sensitivity and low detection limit.The reaction mechanisms of luteolin and m-NP on the sensor were researched.Moreover,the proposed sensor was also used for the determination of luteolin and m-NP in samples,and the results are satisfactory.2.We prepared MOF-525/PPy,PCN-224/PPy and PCN-222/PPy composites by using simple synthetic and highly conductive PPy as carrier to load three kinds of Zr-based porphyrin MOFs with different topologies: MOF-525(ftw),PCN-224(she)and PCN-222(csq).We studied the structures and electrocatalytic properties of the samples through various measurements.It is found that there are distinct differences in electrocatalytic activities of these three composites,which may be mainly affected by the topological structure of three Zr-based porphyrin MOFs.The MOF-525 with a topological structure of ftw shows larger surface area and pore volume,which can expose more active sites.In addition,the charge-transfer resistance of MOF-525/PPy modified electrode is smaller than PCN-224/PPy and PCN-222/PPy modified electrode.Thus MOF-525/PPy possesses the best electrocatalytic performance in three composites.Moreover,we studied the reaction mechanisms of CA on MOF-525/PPy,PCN-224/PPy and PCN-222/PPy modified electrode.It is discovered that they show the same catalytic mechanisms,which is related to the same catalytic sites of porphyrin of three Zr-based porphyrin MOFs.This study provides a new idea for the selection of Zr-based porphyrin MOFs used as electrocatalysts.