Naked Au nanoparticles monodispersed onto multifunctional cellulose nanocrystal-graphene hybrid sheets: towards efficient and sustainable heterogeneous catalysts

A simple, clean, and efficient synthesis method has been developed for deposition of similar to 3 nm monodisperse naked'' gold nanoparticles (Au NPs) onto cellulose nanocrystal-graphene (CNC-G) hybrid sheets without the use of additional reducing and capping agents. The as-prepared catalysts (Au@CNC-G) were examined using FT-IR spectroscopy, thermogravimetric analysis (TGA), atomic force microscopy, electron microscopy, wide-angle X-ray diffraction, and X-ray photoelectron spectroscopy (XPS). After some optimization, the Au@CNC-G catalyst exhibited robust catalytic activity, impressive stability, and good flexibility for the one-pot'' reaction of an alkyne, an amine, and an aldehyde (A(3)-coupling) in water. The catalytic activity of the Au@CNC-G catalyst could be attributed to the synergistic effect derived from the coexistence of CNC and graphene. The Au3+ ions could be in situ reduced to create fine Au NPs and simultaneously anchored on the surface of CNC-G hybrid sheets through coordination, leading to the uniform dispersion of the Au NPs. Moreover, the Au@CNC-G catalyst could be conveniently recycled and reused many times, thus lowering the cost and minimizing the environmental pollution caused by organic solvents and heavy metal ions.