Silver nanoparticles synthesized in tetraalkylphosphonium ionic liquids are found to be excellent catalysts for borohydride-induced reductive degeneration of Eosin-Y, a dye that has been classified as a Class 3 carcinogen by the International Agency for Research on Cancer. TEM images indicated that the size of the Ag nanoparticles was significantly influenced by heat-induced sintering. A strategy was devised to redisperse smaller Ag nanoparticles from their aggregated/sintered counterparts via a two-step protocol that involved oxidative etching of Ag nanoparticles, followed by a re-reduction step. This protocol led to a reduction in the sintered Ag nanoparticle size from 15.7 +/- 6.1 nm to 3.7 +/- 0.8 nm, which was consistent with the size of the as-synthesized nanoparticles. The as-synthesized and the redispersed Ag nanoparticles were found to catalyze the bleaching of Eosin-Y with comparable efficiencies; first order rate constants for Eosin Y reduction were similar to 8 times higher for smaller Ag nanoparticles compared to their sintered counterparts. An examination of the kinetics of Ag nanoparticle etching was performed via temperature-controlled UV-vis spectroscopy. Changes in the oxidation state of Ag during this sequence of events were also followed by in situ X-ray absorption spectroscopy of Ag nanoparticles in the ionic liquid. (C) 2014 Elsevier B.V. All rights reserved.