Singlet Oxygen- and Hole-Mediated Selective Oxidation of Arylethylenes to Aryltetralones by Ag/Ag3PO4 under Visible Light Irradiation

Conventional semiconductor photocatalysts produce superoxide and hydroxyl radicals as the major reactive oxygen species (ROS). Here, we report that Ag/Ag3PO4 catalyst efficiently generates singlet oxygen (1O2) without other ROS under visible light irradiation. Ag/Ag3PO4 was prepared simply through photo-reduction of Ag+ under visible light irradiation. Formation of 1O2 was probed by a set of evidences such as electron spin resonance and quenching experiments. Ag/Ag3PO4 was efficient in the selective oxidation of styrenes to 4-aryltetralones with good selectivity and yield under very mild conditions without extra additives, and the photocatalyst could be facilely recycled for reuse. Mechanism studies indicate that both the photo-generated holes and 1O2 are the keys for the success of the transformation. The electron-rich surface of Ag nanoparticles and the low conduction band potential of Ag3PO4 are the reasons to produce 1O2 rather than superoxide by dioxygen activation. This is the first report on heterogeneous silver salt to produce large amounts of 1O2 at a multiphase interface under visible light irradiation.