Preparation Of Palladium-based Metal-organic Framework Composites And Studies On Their Enzyme-like And Oxygen Reduction Activities

Metal organic framework(MOF)materials have inherent advantages,such as high specific surface area,high porosity and pore volume,when used as carriers of metal nanoparticles.They can stabilize metal nanoparticles and confine their growth to make them have a smaller size and a relatively high degree of dispersion.Therefore,MOF-supported metal nanoparticles cannot be underestimated in the field of catalysis.On the one hand,we synthesized the composite of metal nanoparticles and MOF to mimic biological enzymes by virtue of the catalytic effect of small-sized metal nanoparticles and the substrate enrichment effect of MOF.The as-synthesized compsite was applied in small molecule detection and the corresponding catalytic mechanism was also studied.Results show that the composite exhibits prospective application in sensing.On the other hand,by adjusting the content of metal nanoparticles,the types of metal cations in MOF,and pyrolysis conditions,we successfully adjusted the lattice size,composition,size and shape of the loaded metal nanoparticles.Therefore,the electrochemical catalysis performance of metal nanoparticles and MOF composite was improved,including the electrical conductivity,chemical stability and active sites,which broke the limitations of its application in the field of electrocatalysis.The specific research content of this paper is mainly divided into the following two parts:1.Through solution dipping method,highly dispersed sub-nano-scale palladium particles fixed in the pores of zeolite imidazole framework(ZIF-8)(Pd@ZIF-8)were successfully synthesized.Compared with horseradish peroxidase and reported palladium-based nanozymes,the as-synthesized Pd@ZIF-8 has a better affinity for the substrate 3,3',5,5'-tetramethylbenzidine/H₂O₂,which can be attributed to the great catalytical activity of small-sized Pd nanoparticles as well as the limiting effect and substrate accumulation effect of ZIF-8.A glucose/cholesterol sensor was successfully constructed by combining the Pd@ZIF-8 nanoenzyme with glucose oxidase/cholesterol oxidase.Compared with the literature report,the sensor we prepared showed a wider linear range and lower detection limit,indicating its potential in human blood glucose and cholesterol monitoring.2.Palladium metal nanoparitcles are confined and loaded in ZIF-8.Then,using the Pd nanoparticles and ZIF-8 as a precursor,a high crystallinity order Pd Zn alloy(o-Pd Zn)was prepared through pyrolysis process.The lattice spacing of the Pd nanoparticles is controlled by adjusting the content of the guest palladium in the precursor and the calcination temperature.At the same time,the transition metal Co doped in the MOF forms active sites,and catalyzes the pyrolysis of the MOF framework to generate nitrogen-doped carbon nanotubes,which serve as electron transfer channels and enhance the conductivity of the material.Through this host-guest co-regulation strategy,we successfully synthesized a composite material with two active sites(o-Pd Zn and Co nanoparticles)supported by nitrogen-doped carbon material.This material exhibits excellent catalytic performance for electrocatalytic oxygen reduction.