Light induced coarsening of metal nanoparticles

Abstract

We report a novel metal particle coarsening mechanism that is controlled by exposure of the substrate to light. Pt nanoparticles on TiO₂ are observed to undergo enhanced coarsening during light illumination under conditions associated with photocatalytic water splitting. The average Pt particle size changed from 1.7 to 2.1 nm over 12 hours of photoreaction conditions whereas control experiments in the dark showed no change in Pt particle size. The coarsening is thermodynamically driven by the Gibbs–Thompson effect but is kinetically controlled by photon illumination conditions. These effects accelerate electron transport between particles on the substrate of differing sizes and dramatically increase the rate of Ostwald ripening. This enhanced coarsening mechanism will operate in other metal particle systems supported on semiconductors which harvest light and inject electrons into the conduction band. The kinetic rate of ripening is related to the degree to which the substrate conductivity and photovoltage is enhance during light illumination.