Plasmonic enhancement of photocatalytic decomposition of methyl orange under visible light

By integrating strongly plasmonic Au nanoparticles with strongly catalytic TiO₂, we observe enhanced photocatalytic decomposition of methyl orange under visible illumination. Irradiating Au nanoparticles at their plasmon resonance frequency creates intense electric fields, which can be used to increase electron-hole pair generation rate in semiconductors. As a result, the photocatalytic activity of large bandgap semiconductors, like TiO₂, can be extended into the visible region of the electromagnetic spectrum. Here, we report a 9-fold improvement in the photocatalytic decomposition rate of methyl orange driven by a photocatalyst consisting of strongly plasmonic Au nanoparticles deposited on top of strongly catalytic TiO₂. Finite-difference time-domain (FDTD) simulations indicate that the improvement in photocatalytic activity in the visible range can be attributed to the electric field enhancement near the metal nanoparticles. The intense local fields produced by the surface plasmons couple light efficiently to the surface of the TiO₂. This enhancement mechanism is particularly effective because of TiO₂'s short exciton diffusion length, which would otherwise limit its photocatalytic efficiency. Our electromagnetic simulations of this process suggest that enhancement factors many times larger than this are possible if this mechanism can be optimized.