Surface Plasmon Catalytic Aerobic Oxidation of Aromatic Amines in Metal/Molecule/Metal Junctions

The surface plasmon catalytic selective aerobic oxidation of aromatic amines to aromatic azo compounds in metal/molecule/metal junctions was explored by density functional theory. The overall reaction could be divided into the initial plasmon-induced oxygen activation and the subsequent photothermal-driven dehydrogenation process. The activation of oxygen on silver and gold surfaces is proposed through a surface plasmon-mediated hot electron injection mechanism at solid/gas interface. Resonance absorption of incident light by metal nanostructures generates energetic electron-hole pairs. Time-dependent density functional theory calculations illustrate that the excited hot electrons created on metal surfaces can transfer to the antibonding 2 pi* orbital of adsorbed oxygen, which facilitates the dissociation of O-2 on metal surfaces. Silver shows better catalytic performance for the oxygen activation due to its stronger surface plasmon resonance absorption intensity and higher hot electron energy level. Aromatic amines adsorbed on the metal surfaces can be selectively oxidized to the corresponding azo compounds by the activated surface oxygen species. The aerobic oxidations of p-aminothiophenol in the nanogaps between metal substrate and three different nanoparticles (Ag, Au, and Au@SiO2) are compared. The activated oxygen species on silver surfaces exhibits the strongest oxidation ability for its lowest reaction barriers of dehydrogenations. This work demonstrates that silver catalyst should be an excellent candidate for the heterogeneous photocatalysis, which can concurrently enhance oxygen dissociation and oxidative dehydrogenation reactions.