Surface plasmon resonance of gold nanocrystals coupled with slow-photon-effect of biomorphic TiO2 photonic crystals for enhanced photocatalysis under visible-light

• A high visible-light harvesting capability is achieved in biomorphic Au/TiO2 photonic crystal.
• A sol–gel method is introduced in synthesis of Au/TiO2-BMPC.
• SPR intensity of gold nanocrystals is enhanced by slow-photon-effect of the potonic crystals.
• The photocatalysis efficiency of methyl orange (MO) can be significantly improved.

The slow photon effect in a photonic crystal (PC) can lead to delay and storage of light in the PC and has an immense potential for improving solar-to-energy efficiency. A series of biomorphic TiO2 photonic crystal (TiO2-BMPC) structures are fabricated through a sol–gel method by using butterfly wings as templates, and subsequently gold nanoparticles (Au NPs) with an average size of about 9 nm are deposited in situ into the TiO2-BMPC. Varying structural characteristics of the PCs by choosing different butterfly wings, the slow photon region of the photonic band gap could be purposely tuned to overlap with strong localized surface plasmon resonance (SPR) region of the Au NPs. The matching slow photon of the TiO2-BMPC templated from the butterfly wings of Euploea mulciber intensifies the SPR responses (central at 550 nm) of the Au NPs. Consequently, the visible-light harvesting capability of the Au/TiO2-BMPC is significantly improved due to this unique biomorphic architecture. As a result, the designed photocatalyst exhibits a photocatalytic activity that is several time higher than conventional Au/TiO2-P25 material, as illustrated by the example of the photocatalytic decomposition of methyl orange (MO) under visible-light illumination.

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