Arsenic Oxidation Kinetics with Plasmonic Nanocatalysts

Abstract

Arsenic is one of the most toxic elements present in natural waters, andprolonged ingestion causes severe damage to health. Its oxidation from highly toxic As(III) toless harmful species involving As(V) is a process included in most remediation methods. Thekinetics of this homogeneous redox reaction in the presence of hydrogen peroxide is veryslow. We propose the use of metal nanoparticles as plasmonic catalysts for this reactionassisted by solar illumination. In this work, we show that As(III) oxidation to As(V) isaccelerated by gold and silver nanoparticles through heterogeneous catalysis, and underplasmon excitation, hot charge carriers are generated that contribute to further increase in thereaction rate. We evaluate the efficiency of these nanocatalysts and their dependence on theexcitation wavelength, and we quantify the different contributions to the oxidation process.Our results show that gold nanoparticles are better heterogeneous catalysts than silvernanoparticles; however, the latter increase their efficiency 8 times under resonant illumination, with irradiation powers close to thatof sunlight, evidencing that the lower-cost material becomes a more efficient catalyst with light.