Metal-organic frameworks(MOFs)hold great promise as porous matrixes for the incorporation of Au NPs because of their rationally designed framework structures.Unfortunately,the as-synthesized bulk MOFs usually vary in the range of micron-or submicron-size,rendering extremely longer molecular diffusion distance of chemical species.Two-dimensional(2D)MOF nanosheets with extended lateral dimensions and nanometer thickness are expected to implement fast kinetics and effectively lower mass-transfer barriers during embedding Au NPs process and sequential catalytic reactions.In this study,a novel 2D nanosheet of mixed-ligand Ni(Ⅱ)MOF(referred to NMOFNi)was successfully fabricated.With the merits of well-defined micropores and functional oxygen-decorated inner walls,the incorporation of quite monodisperse ultra-small Au nanoparticles of around 1 nm into NMOF-Ni has been achieved for the first time.The resulting nanocomposites exhibit remarkable catalytic performance and good size selectivity toward aqueous reduction reactions of nitrophenol,taking advantage of ultra-small Au and 2D nanosheet nature,as well as the intact microporosity of host matrix.The present encouraging findings might shed light on new ways to develop high-performance heterogeneous catalysts by using of 2D MOF nanosheets with functional cavities as hosts for homogeneous distribution of ultra-small Au NPs.