Mechanistic Insights into Free Chlorine and Reactive Oxygen Species Production on Irradiation of Semiconducting Silver Chloride Particles

Silver halide based plasmonic absorbers are excellent photocatalysts under visible light irradiation. In this work we have investigated the kinetics and mechanism of generation of free chlorine and reactive oxygen species (ROS), both of which may play a role in organic degradation, on irradiation of AgCl(s). Our work shows that generation of free chlorine occurs via oxidation of Cl by photogenerated holes in the valence band. Photogenerated electrons in the conduction band reduce Ag+ to form Ag-0 atoms which coalesce and aggregate to form silver nanoparticles (AgNPs). Superoxide and its more stable disproportionation product hydrogen peroxide (H2O2) are also presumably formed as a result of the reduction of dioxygen by photogenerated electrons; however, H2O2 was not detected, possibly as a result of its reaction with free chlorine and AgNPs. Confirmation that this reaction in all likelihood occurred was provided by quantification of the formation of singlet oxygen (O-1(2)), a product of this reaction. On the basis of our experimental observations, we have developed a kinetic model that adequately describes the generation of free chlorine, ROS, and AgNPs on irradiation of AgCl(s).