In situ biogenic synthesis of Pd nanoparticles over reduced graphene oxide by using a plant extract (Thymbra spicata) and its catalytic evaluation towards cyanation of aryl halides

Abstract

An eco-friendly biosynthesized Pd NP anchored Thymbra spicata extract-modified graphene oxide (Pd NPs/rGO-T. spicata) nanohybrid material has been introduced. Initially, the herb, Thymbra spicata extract was immobilized on the surface of GO via their natural adhering capability. The polyphenolic function grafted in situ prepared RGO acted as the natural reductant of Pd precursor. The as-prepared nanocomposite (Pd NPs/rGO-T. spicata) was characterized using Fourier transform infrared (FTIR), UV-vis, X-ray diffraction (XRD), inductively coupled plasma (ICP), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), high resolution transmission electron microscopy (HRTEM), Fast Fourier Transform (FFT), Raman spectroscopy and EDX elemental mapping techniques. It has been observed that the Pd NPs with perfect crystal structure, uniform shape and size were dispersed homogeneously on the rGO surface. The material showed excellent water dispersibility due to the hydrophilicity of biomolecules attached over them, which is very essential in heterogeneous catalysis. The T. spicata contained biomolecules served as effective capping, reducing and stabilizing agents for the uniform immobilization of Pd precursors on graphene sheet surface without aggregation. The catalytic activity of this nano hybrid was assessed comprehensively in the cyanation of aryl halides with a wide range of substrates using K₄[Fe(CN)₆] as a cheap source of cyanide. The model reaction resulted outstanding catalytic performance with a great reusability of the catalysis.

Keywords: Cyanation; Graphene oxide; Nanocatalyst; Palladium; Plant extract.