Biosynthesis of Au nanoparticles by Gymnocladus assamicus and its catalytic activity

•Green synthesis of Au nanoparticles by G. assamicus pod extract.•The formation of nanoparticles is possibly facilitated by phenolic acids.•Au nanoparticles showed suitable catalytic activity.•Rate of catalytic reaction depends on the concentration of nanoparticles.•The method may be used for reduction of 4-nitrophenol to 4-aminophenol.

Here we first report synthesis of gold (Au) nanoparticles by using Gymnocladus assamicus pod extract in aqueous medium. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis revealed that the Au nanoparticles predominantly formed planar structure and size range 4.5±0.23–22.5±1.24 nm with 2θ values at 38.22°, 44.38°, 64.34°, 77.6° and 81.24° for lattice plane. The formation of pure metallic nanoparticles by reduction of the metal ions is possibly facilitated by reducing by phenolic acids like gallic acid, protocatechuic acid and kaempferol present in the G. assamicus pod extract. The Au solution shows potential catalytic activity in reduction of 4-nitrophenol to 4-aminophenol.