Cu Doped ZIF-8 Nanocrystals:Mechanical Grinding Synthesis And Catalytic Performance Research

On account of permanent pores,high surface area and excellent stability of zeolitic imidazolate frameworks(ZIFs),much effort has been devoted to their synthesis and property study.Recently,ZIF-8 as one kind of ZIF material has got much attention for the catalytic application.Researchers found that doping other metal ion in ZIF-8 is an effective method for the synthesis of functional materials,as the doped metal can play as the catalytic active site in catalytic reaction.In this work,we successfully synthesized Cu doped ZIF-8 nanocrystals by liquid assisted mechanical chemistry method and applicated it to the dehydrogenative coupling of silanes and alcohols.The main research methods and results are as follow:(1)Cu doped ZIF-8 nanocrystals were synthesised by liquid assisted mechanical chemistry method.We optimized the synthesis strategy in three aspects: the role of liquid,the choice of metal precursors and the effect of metal-ligand ratio on product yield.The XRD,UV-Visible spectrum,BET method,EPR and XPS analysis were used to characterize the structure of Cu doped ZIF-8 nanocrystals.From the EPR and XPS characterization we found the coexist of Cu(I)and Cu(Ⅱ)in this material,which is different with generally thinking that only Cu(Ⅱ)existed in Cu doped ZIF-8.We speculated that the ligand(2-methylimizole)may play as a reducer to induce the reduction of Cu(Ⅱ)during synthesis process.(2)To investigate the catalytic performance of Cu doped ZIF-8 for dehydrogenative coupling of silanes with alcohols,dimethylphenylsilane(Ph Me2 Si H)and n-butanol were selected as model substrates for this reaction.Take Cu85%ZIF-8 for example,Cu85%ZIF-8 exhibited excellent catalytic activity,selectivity(Siloxanes)and stability for this reaction.We also tested the catalytic performance of other Cu-based MOF materials.The results made us to speculate that the proper ratio of Cu(I)to Cu(Ⅱ)play a key role for the excellent catalytic performance of Cu doped ZIF-8 nanocrystals.In conclusion,we synthesized Cu doped ZIF-8 nanocrystals by liquid assisted mechanical chemistry method.This synthesis strategy greatly reduced the amount of solvent used and was easy for large-scale synthesis.Further catalytic property research indicated that Cu doped ZIF-8nanocrystals exhibited excellent catalytic performance for dehydrogenative coupling of silanes with alcohols.We believe that the synthesis strategy reported here will open an avenue for the synthesis of multi-metal zeolitic imidazolate frameworks.