Inverse opal TiO₂-based heterocomposite photonic structures for slow photon-assisted visible light photocatalysis

Manipulation of light was proved to be an efficient strategy to improve light harvesting efficiency in solar energy conversion. Inverse opal (IO) photonic structures are among the most promising materials, which permit light manipulation, thanks to their ability to slow down light at specific wavelengths and localize it within the dielectric structure. However, the generation, the control and, in particular, the practical utilization of these narrow spectral range ‘slow photons’ remain highly challenging and relatively underexplored. In this work, we report the ability not only to generate slow photons in the visible range by synthesizing highly ordered IO TiO₂ photonic structures, but also to control and tune their wavelengths, by varying lattice parameters (pore sizes), such that they can be efficiently utilized by the composite bismuth (Bi)-based semiconductor for visible light photocatalysis. Photocatalytic experiments revealed a 70% increase in efficiency in all IO structures compared to the corresponding non-structured compact film. In addition, a 20% increase in efficiency was observed when the photonic stop band gap as well as its blue and red edges were accurately tuned to match the electronic absorption of the Bi-based photocatalyst. Our choice of IO synthesis parameters and tuning strategies enabled us to generate, control and transfer the energy of slow photons from IO TiO₂ to the composite visible light-responsive photocatalyst for highly amplified photoactivity. This work opens new possibilities for the practical utilization of slow photon effect under visible light in various solar energy conversion applications.