Design, Synthesis And Catalytic Performance Of Zr-based Metal-organic Framework Composites

Since the 21st century,with the progress of science and technology and social development,people’s excessive use of fossil fuels leads to the shortage of fossil fuel resources,and the problem of environmental pollution is becoming more and more serious,and people’s demand for renewable energy is also increasing.As solar energy is rich in resources and has a wide range of uses,solar energy has become the best choice to replace traditional fossil fuels.However,the use of solar energy for photocatalysis or photothermal catalysis is still faced with some problems,such as low utilization,limited conversion efficiency,and so on.In recent years,semiconductor catalysts have been widely developed in the fields of photocatalysis,electrocatalysis,thermal catalysis,and photothermal catalysis.Metal-organic framework（MOFs）can also be called porous coordination polymer（PCPs）,which is a highly crystalline porous material assembled by metal ions/clusters and organic ligands.Because of their high crystallinity,porous structure,high editability,and ultra-high specific surface area,MOFs show excellent application prospects in a variety of catalytic reactions,chemical sensing,gas adsorption and separation,biomedicine,and other fields.Therefore,in the past two decades,it has received great attention and made great progress.Unfortunately,most MOFs have poor photoresponse in the visible region,which limits their application in photocatalytic reactions to a great extent.Therefore,it is promising to prepare MOF matrix composites with a wide spectral response to improve their photocatalytic activity under visible light irradiation.Therefore,we combined the typical UiO-66-NH2 with phosphorus-doped hexagonal carbon nitride to improve the photocatalytic activity of UiO-66-NH2.Firstly,under the hydrothermal condition assisted by phosphoric acid,melamine was hydrolyzed in situ to form cyanuric acid,then the supramolecular precursor was obtained by self-assembly,and then p-TCN was obtained by calcination at 500℃for4h.Then p-TCN@U6-X composites were prepared by in-situ loading of stable UiO-66-NH2,on p-TCN by solvothermal method.The high specific surface area and porosity of MOF are conducive to the accumulation of reactants and improve the catalytic kinetics;the presence of phosphorus in p-TCN narrows the bandgap of carbon nitride,thus improving the electrical conductivity;the tubular structure of p-TCN is conducive to enhance light scattering and play a catalytic role.The results show that the photocatalytic hydrogen production performance of p-TCN@U6-3 is up to 2628μmol g^-1 h^-l,which is 8.19 times and 5.36 times higher than that of p-TCN and UiO-66-NH2,respectively.At the same time,p-TCN@U6-3 also shows good catalytic performance for oxidative coupling of amines,with selectivity as high as99%and conversion as high as 98%.Zinc ferrite（ZnFe2O4）is loaded onto UiO-66-NH2 to the surface by the electrostatic assembly.In this part of the work,we first prepared ZnFe2O4 ultra-small nanoparticles.Spinel ZnFe2O4 with a narrow bandgap has attracted wide attention in solar energy conversion,photocatalysis,and electrocatalysis because of its good response to visible light,good photochemical stability,and low cost.Then,by the electrostatic assembly,ZnFe2O4 was loaded onto UiO-66-NH2 to the surface,and ZnFe2O4@UiO-66-NH2（ZFO@U6N）composites were prepared.The multi-empty structure and high specific surface area of UiO-66-NH2 make it a good carrier,which improves the dispersion of ZnFe2O4 and facilitates the exposure of more active sites.At the same time,the better photo responsiveness of ZnFe2O4 helps to improve the absorption and utilization of light in the composites,and the interaction and electron transfer between ZnFe2O4 and UiO-66-NH2 can better restrain the recombination of electron-hole pairs and improve the efficiency of charge transfer.Therefore,ZFO@U6N composites showed higher conversion（67%）and selectivity（99%）for photocatalytic conversion of benzyl alcohol to benzaldehyde.The semiconductor photocatalyst modified by metal can effectively improve the semiconductor light absorption range,narrow the bandgap,accelerate the migration of photogenerated carriers,and effectively restrain the electron-hole recombination.All these are beneficial to improve the photocatalytic activity of semiconductor photocatalysts.Therefore,using this point,the porous structure of Cu-doped UiO-66-NH2,UiO-66-NH2,and unsaturated coordination groups were prepared by the impregnation method.While maintaining the high specific surface area of MOF,the bandgap of UiO-66-NH2 was reduced and the visible light absorption range was improved.The results show that the conversion and selectivity of Cu-U6N for photocatalytic oxidation of benzyl alcohol to benzaldehyde are 63%and 99%,respectively.