Bio-functionalized anisotropic gold nanoparticles as efficient catalyst for nitrile hydration and hydrogenation of nitrophenol

The authors report a biogenic synthesis of anisotropic Au nanoparticles exploiting the advantages of the aqueous leaf extract of Garcinia pedunculata Roxb. The study also delved into the differences in anisotropy and catalytic activities of Au nanoparticles synthesized using leaf extract alone and in combination with 0.3% starch solution. UV–Visible spectroscopy showed the occurrence of surface plasmon resonance band of Au nanoparticles centered at 520–550 nm. The presence of Au crystallites was evidenced from the structural and surface analyses using XRD and XPS. HRTEM study vouched for the stability and shape-templating growth of anisotropic Au nanoparticles viz., a mixture of nanotriangles, nanohexagons, nanospheres and truncated nanotriangles. Furthermore, the nanomaterials were successfully employed as catalysts for two important reactions viz. hydration of nitriles to amides and reduction of 4-nitrophenol to aminophenol. In both the reactions, the starch-based AuNP catalyst exhibited superior activity over starch-free AuNP. The catalyst was found to be efficient, reusable up to four cycles without loss of activity and environmentally benign. Thus, we advocate the multifarious role of the leaf extract viz., bio-conjugating, capping, shape-directing, bio-stabilizing and bio-functionalizing agent in the biogenic synthesis of anisotropic Au nanoparticles.