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

Abstract

A simple, clean, and efficient synthesis method has been developed for deposition of ∼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 (A³-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.