Following Charge Separation on the Nanoscale in Cu2O-Au Nanoframe Hollow Nanoparticles

Cu2O-Au nanoframes with different nanolayer thicknesses of Cu2O were prepared, and their photocatalytic properties in aqueous solutions were studied. Cu2O semiconductor excitation leads to electron-hole separation. In aqueous solution, the hole is known to oxidize water to produce hydroxyl radicals whose concentration (and that of the holes) can be monitored by the rate of the degradation of dissolved methylene blue dye. The exciton lifetime is determined by femtosecond techniques and is determined by electron-hole recombination which depends on the rates of a number of competing processes such as, electron or hole transfer to an acceptor such as a gold nanoframe and/or the electron or hole trapping processes at the Cu2O-Au nanoframe interface. We measured the exciton lifetime as a function of the average Cu2O-Au layer separation. A good correlation was found between the rate of the photocatalytic degradation of methylene blue and the exciton lifetime. The exciton lifetime is found to increase as the Cu2O thickness is increased. This leads to an increase in the electron-hole separation time and thus an increase in the hole (and so the hydroxyl radical) concentration leading to an observed enhanced rate of the dye degradation.