▎ 摘　　要

Lewis acidic chlorostannate(IV)-based imidazolium ionic liquid ([PmimCl][SnCl4](x) IL) was post-grafted on graphene oxide (GO) nanosheets through a 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 (BV) oxidation in water due to the high water-dispersion, diminished diffusion limitation, enriched surface acid sites, as well as the concerted effects between Bronsted 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. (C) 2016 Elsevier B.V. All rights reserved.