Mechanisms and applications of plasmon-induced charge separation at TiO₂ films loaded with gold nanoparticles

Plasmon-induced photoelectrochemistry in the visible region was studied at gold nanoparticle-nanoporous TiO₂ composites (Au-TiO₂) prepared by photocatalytic deposition of gold in a porous TiO₂ film. Photoaction spectra for both the open-circuit potential and short-circuit current were in good agreement with the absorption spectrum of the gold nanoparticles in the TiO₂ film. The gold nanoparticles are photoexcited due to plasmon resonance, and charge separation is accomplished by the transfer of photoexcited electrons from the gold particle to the TiO ₂ conduction band and the simultaneous transfer of compensative electrons from a donor in the solution to the gold particle. Besides its low-cost and facile preparation, a photovoltaic cell with the optimized electron mediator (Fe^2+/3+) exhibits an optimum incident photon to current conversion efficiency (IPCE) of 26%. The Au-TiO₂ can photocatalytically oxidize ethanol and methanol at the expense of oxygen reduction under visible light; it is potentially applicable to a new class of photocatalysts and photovoltaic fuel cells.