The Design Of Ionic Liquid Modified Graphene Oxide Catalysts For Catalytic Oxidation In Wate

With the deterioration of energy resources and environment,green chemistry has been attached extensive attention.Efficient catalytic systems with reusable catalysts have drawn much attention in the field of catalysis.Based on the hydrophilicity of graphene oxide(GO),as well as the positive effect of ionic liquid(IL)on catalytic sites,IL-modified GO was designed as the supports for several catalytic sites in this work.The resultant GO-based catalysts could circumvent the mass transfer limitation in aqueous oxidation system and also could be facilely recovered for efficient reuse.(1)Chiral salen Ti(?)compelx was grafted on imidazolium-based IL functionalized GO through covalent linkage.Hydrophilicity of GO sheets together with well compatibility of IL modifier made the resultant chiral salen Ti(?)catalyst(GO-IL-salen Ti(?))highly dispersive in water.The heterogeneous GO-IL-salen Ti(?)behaved as pseudo-homogeneous catalyst in asymmetric sulfoxidation in water using H2O2(30 wt.%)as an oxidant,exhibiting excellent catalytic activity,selectivity and reusability in the aqueous oxidation system.(2)Lewis acidic chlorostannate(?)-based imidazolium IL([PmimCl][SnCl4]x IL)was post-grafted on GO nanosheets througha silylation process.Characterization results suggested the coexistence of intrinsic carboxylic acid on GO edges and the post-grafted Lewis acidic IL on GO planes in the catalysts.The Bronsted-Lewis acidic combined catalysts of GO/[PmimCl][SnCl4]were highly efficient and universal in Baeyer-Villiger(BY)oxidation in water due to the highwater-dispersion,diminished diffusion limitation,enriched surface acid sites,as well as the concerted effects between Br(?)nsted and Lewis acid sites.Only 3.0 mol%of GO/[PmimCl][SnCl4]x(x=0.5,1.0,1.5)was sufficient for affording almost quantitative yield of a wide range of lactones in water without the need of any organic solvents and cocatalysts,whereas Lewis acidic IL of[PmimCl][SnCl4]1.0 itself was far less efficient.More importantly,the heterogeneous catalysts were perfectly stable and could be reused several times without significant loss of activity and selectivity.(3)Lewis acidic ferric(?)-based imidazolium IL[PmimCl]FeCl3]was grafted on GO though silylation process.Due to the excellent hydrophilicity of GO,the resultant catalyst of GO/[PmimCl][FeCl3]could be highly dispersed in water.As a heterogeneous catalyst,the GO/[PmimCl][FeCl3]exhibited comparable catalytic performance to the homogeneous[PmimCl][FeCl3]in hydroxylation of phenol in water.More importantly,GO/[PmimCl][FeCl3]could be facilely recovered from aqueous system for efficient reuse by filtration.