Synthesis,photocatalysis And Mercury Ion Adsorption Properties Of Zirconium-Based Metal-Organic Cages

Metal-organic cages（MOCs）are discrete supramolecules which are made up of metal clusters and organic groups（such as carboxylic acid pyridine and pyrimidine,etc.）.Zirconium metal-organic cages（Zr-MOCs）have high chemical stability,thermal stability and permanent porosity.What’s more,the reasonable solubility also expands their applications based on solution.A series of Zr-MOCs constructed by different linking organic groups have been applied in various fields,such as gas separation,catalysis and biological imaging.In recent years,environmental problems have attracted wide attention,including global climate warming caused by excessive CO₂ emissions as well as Hg pollution that threatens public health for a long time.Based on this,in this paper,two functional Zr-MOCs were synthesized by one-pot method for photocatalytic reduction of CO₂and adsorption of toxic Hg²⁺in wastewater,respectively.1.Herein,single crystals of Ir^III-MOC-NH₂ were synthesized by mix-and-match strategy from a mixture of zirconocene dichloride,H₂-bpdc-NH₂ and H₂Ir-ppyc.Single molecular cage Ir^III-MOC-NH₂ shows high reactivity and selectivity in converting CO₂ into CO under visible light.The selectivity is of 99.5%and turnover frequency reaches～120 h^-1 which is 3.4-fold higher than that of bulk Ir^III-MOC-NH₂and two orders of magnitude higher than that of classical MOF counterpart(Ir^III-Uio-67-NH₂).The apparent quantum yield is up to 6.71%that ranks among the highest value of reported crystalline porous materials.Moreover,aggregation-induced deactivation of Ir^III complex is restrained after incorporating into MOC-NH₂.The DFT calculations disclose Ir^III complex is the catalytic center and-NH₂ in the framework plays the synergetic effect in the stabilization of the transition state and CO₂ adducts.2.A thiol-functionalized zirconium MOC（MOC-（SH）₂）with excellent dispersion was synthesized,displaying ideal properties for Hg²⁺capture.MOC-（SH）₂exhibits the ability of removing Hg²⁺in aqueous solutions with a capacity of 335.9mg _Hg2+/g _{MOC-（SH）2},which surpasses that of classical Zr-based MOF Uio-66-（SH）₂ by1.89 folds.Additionally,99.6%of Hg²⁺can be effectively captured by MOC-（SH）₂with the concentration decreased from 5 to 0.02 ppm reaching the emission standard of Hg²⁺,outperforming the performance of Uio-66-（SH）₂.The excellent absorption property of MOC-（SH）₂ is also achieved in terms of superior selectivity under the presence of competitive metal ions.Meanwhile,the regenerated MOC-（SH）₂ can be reused without apparent loss of Hg²⁺loading capacity.UV-vis absorption spectra,IR spectra and emission spectra further verified the strong chemical affinity between Hg²⁺and the thiol of MOC-（SH）₂.