Green synthesis of gold nanoparticles under sunlight irradiation and their colorimetric detection of Ni2+ and Co2+ ions

The present work describes the preparation of gold nanoparticles (AuNPs) under natural sunlight irradiation and their use in colorimetric detection of heavy metal ions. The AuNPs were prepared by an environmentally benign method using N-cholyl-l-valine (NaValC) as a self-reducing as well as stabilizing agent in aqueous medium. The size and shape of the particles were systematically controlled by varying the ratio of NaValC and Au3+ ions. The pH of the solution medium, sunlight irradiation and reaction time also influence the size and shape selectivity. The prepared NPs were thoroughly characterized by using UV-visible spectroscopy, TEM, DLS, EDX, XRD, XPS, FT-IR, cyclic voltammetry and TGA techniques. Natural solar energy acting as a driving force for the generation of AuNPs in aqueous medium makes the process eco-friendly, attractive and economical. As these NPs are highly reactive towards the surrounding environment the prepared AuNPs were effectively utilized for the colorimetric detection of Co2+ and Ni2+ ions in environmental samples.