Tuning and transferring slow photons from TiO photonic crystals to BiVO nanoparticles for unprecedented visible light photocatalysis.

Periodic structures with alternating refractive indices such as inverse opal photonic crystals are capable of reducing the group velocity of light such that this slowed light can be more efficiently harvested for highly enhanced solar energy conversion. However, the generation, the manipulation and, in particular, the practical applications of these slow photons remain highly challenging. Here, we report the first proof of concept on the ability to control, in an inverse opal TiO-BiVO hetero-composite, the transfer of slow photons generated from the inverse opal photonic structure to the photocatalytically active BiVO nanoparticles for highly enhanced visible light photoconversion. Tuning the slow photon frequencies, in order to accommodate the electronic band gap of BiVO for slow photon transfer and for significantly improved light harvesting, was successfully achieved by varying the structural periodicity (pore size) of inverse opal and the light incidence angle. The photocatalytic activity of BiVO in all inverse opal structures, promoted by slow photon effect, reached up to 7 times higher than those in the non-structured compact films. This work opens new avenues for the practical utilization of slow photon effect under visible light in photocatalytic energy-related applications like water splitting and carbon dioxide reduction and in photovoltaics.