Green synthesis of Ag@Au bimetallic regenerated cellulose nanofibers for catalytic applications

Abstract

The green synthesis of nanocomposites has attracted huge consideration in recent years due to its positive environmentally friendly impact. The present study reports the first bimetallic Ag–Au cellulose nanofiber composite (Ag@Au/CNCs) prepared via a very simple green preparation method. An aqueous leaves extract of Moringa oleifera was used to obtain the bimetallic Ag@Au/CNC nanocomposite. High-resolution transmission electron microscopy (HRTEM) observations revealed the successful formation of triangle, hexagonal, and spherical shapes of well-combined Ag–Au nanoparticles on the regenerated cellulose nanofiber surface. Further, the formation of Au–Ag bimetallic nanostructures was confirmed by X-ray photoelectron spectroscopy (XPS) and X-ray crystallography (XRD) results. The resultant bimetallic Ag@Au/CNC catalyst was found to perform remarkably well in the reduction of nitrophenols. The bimetallic Ag@Au/CNC catalyst gave excellent k_app values of 15.59 and 22.83 × 10⁻³ s⁻¹ for the 2- and 4-nitrophenol reduction process, respectively. To our delight, the Ag@Au/CNC catalyst was found to perform well in the aza-Michael reaction. The catalytic activity of Ag@Au/CNCs was compared with mono-metallic Ag/CNCs, Au/CNCs, and other reported catalysts. Based on the results obtained, the high synergy of Ag@Au/CNCs was explained. A possible mechanism is proposed for the Ag@Au/CNC-catalyzed nitrophenol reduction and aza-Michael reactions.