Green Chemistry in action: towards sustainable production of Gold nanoparticles

Abstract

Abstract This study reports the synthesis of gold nanoparticles from a gold precursor salt (HAuCl4·3H2O) using Moringa oleifera bark broth, a cheap renewable material, without adding external surfactant, capping agent or template. Biomolecules responsible for reducing Au3+ to Au0 and stabilization of the resulting nanoparticles were extracted from the bark, and the synthesis was monitored for precursor concentration, percentage broth, pH of reaction media and reaction time. The biosynthesized nanoparticles were characterized using spectroscopic (FTIR and UV-Vis) techniques, advanced microscopic imaging (HRTEM, SEM/EDS), and Zeta potential measurements. Distinct color change from yellow to wine red was observed, indicative of the formation of gold particles at nanoscale. The SPR band was found at around 550 nm, in agreement with conventional synthetic protocols. The particles were stable with a net negative surface charge (–20 mV), a contribution associated with the protein nature of the broth. Addition of Pb2+ to the polydisperse nanoparticle suspension resulted in a color shift, to a faint blue color, coupled with a corresponding SPR shift to higher wavelengths, depending on the concentration of Pb2+ added. This color change is attributed to the aggregation of the colloidal particles due to complexation effects of the metal ions with the biomolecules on the surface of the nanoparticles.