Photoreductive synthesis and analytical performance of silver nanoparticles stabilized with humic acids for selective and sensitive colorimetric detection of mercury (II) ions.

This study presents the one-step photoreductive synthesis and characterization of humic acid-stabilized silver nanoparticles (AgNP@HA) via the reduction of Ag+ ions by ketyl radicals generated by UVA-light using the water-soluble photoinitiator Irgacure® 2959 (I-2959) as a function of pH and HA concentration. The formation and properties of the AgNP@HA were characterized by several techniques, including UV-Vis, FTIR, and Raman spectroscopies, as well as transmission electron microscopy (TEM) and dynamic light scattering (DLS). The UV-Vis absorption spectrum changes occurring during the formation of the AgNP@HA were modeled with the multivariate curve fitting using alternating least squares (MCR-ALS) method. The kinetic profiles of each observed species suggested that AgNP@HA are produced through a mechanism of nucleation and aggregation. The AgNP@HA solutions were evaluated as colorimetric sensors for the selective detection of Hg2+ ions at different pH. The changes in the surface plasmon band absorbance of AgNP@HA induced by Hg2+, irrespective of the presence of other interfering ions and pH, indicated that AgNP@HA specifically interacts with Hg2+ to form an amalgam with silver, with remarkable analytical performance, detecting Hg2+ in the sub ppm range. These results indicate that AgNP@HA prepared by photoreduction with I-2959 can be used as a suitable, simple, economical, and environmentally friendly plasmonic sensor for the detection of mercury in water samples.