Abstract

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