Green synthesis of gold nanoparticles using Pogestemon benghalensis (B) O. Ktz. leaf extract and studies of their photocatalytic activity in degradation of methylene blue

•Gold nanoparticles were biosynthesized using leaf extract of P. benghalensis (B) O. Ktz.•Powder XRD showed face-centered cubic structure of gold having average crystallite size 13.07 nm.•The TEM images revealed the material to be predominantly spherical and triangular in shape with sizes 10–50 nm.•Gold nanoparticles showed pronounced photocatalytic activity.

Biosynthesis of gold nanoparticles has been accomplished via reduction of aqueous chloroauric acid solution with the leaf extract of Pogestemon benghalensis (B) O. Ktz., as both reductant and stabilizer. The synthesized nanoparticles were characterized by UV–visible, powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier transform infrared (FT-IR) studies. The UV–visible spectrum of the synthesized gold nanoparticles showed surface plasmon resonance (SPR) around 555 nm after 12 h. The powder XRD pattern furnished evidence for the formation of face-centered cubic structure of gold having average crystallite size 13.07 nm. The shapes of synthesized gold nanoparticles are mostly spherical and triangular with sizes 10–50 nm. The photocatalytic degradation of methylene blue dye was monitored spectrophotometrically using gold nanoparticles as catalyst under visible light illumination.