Visible-light photocatalytic degradation of dyes by TiO2–Au inverse opal films synthesized by Atomic Layer Deposition

TiO2–Au composite planar films and inverse opals were synthesized by Atomic Layer Deposition (ALD) using Direct Liquid Injection for TiO2 deposition and for the injection of preformed Au nanoparticles (NPs). A few nanometers thick layer of TiO2 was deposited after the Au NPs. Thermal annealing at 380 °C allowed to remove the polystyrene beads template and to form anatase TiO2. The obtained inverse opals have a layered structure of hollow TiO2 spheres interconnected by channels formed at the template beads contacts. Au NPs are homogeneously distributed on the surface. Their localized surface plasmon resonance (SPR) at 587 nm confirm that they are embedded in TiO2. These photocatalysts were tested for the degradation of methylene blue solutions under visible-light illumination. A significant photocatalytic effect is reported with a 95% degradation after 7 h of exposure only for the composite inverse opal. This results from the transfer of hot electrons from the NPs excited at their SPR to the conduction band of TiO2. They generate reactive oxygen species at the surface of TiO2 which are involved in the initial stage of MB degradation. These results highlight the potential of ALD for the fabrication of complex composite structures for application in photocatalysis.