Biosynthesis of Palladium Nanoparticles Using Delonix regia Leaf Extract and Its Catalytic Activity for Nitro-aromatics Hydrogenation

This work presents the biosynthesis of palladium nanoparticles (Pd-NPs) using Delonix regia (D. regia) leaf extract, and their catalytic activity was evaluated for 2-nitrophenol (2-NP) and 2-nitroaniline (2-NA) hydrogenation reactions. The appearance of a broad continuous absorption spectrum in the visible ultraviolet region in UV-visible spectra confirmed the synthesis of Pd-NPs. The crystalline structure of Pd-NPs (with size range of 2-4 nm) was confirmed by X-ray diffraction and transmission electron microscopy analysis, respectively. The appearance of an optical absorption peak at 2.80 keV in energy dispersive spectra further confirmed the presence of Pd-NPs. Fourier transform infrared analysis suggested the role of water-soluble polyols present in the D. regia leaf extract in mediating the synthesis of Pd-NPs. Moreover, the catalytic activity of Pd-NPs for hydrogenation reactions was studied by UV-visible spectroscopy. Pd-NPs showed catalytic activity through electron relay effect. The hydrogenation reactions followed pseudo-first-order kinetics with respect to the substrates.