Improving Visible Light Photocatalysis Using Optical Defects in CoO_x-TiO₂ Photonic Crystals

The rational design of photonic crystal photocatalysts has attracted significant interest in order to improve their light harvesting and photocatalytic performances. In this work, an advanced approach to enhance slow light propagation and visible light photocatalysis is demonstrated for the first time by integrating a planar defect into CoO_x-TiO₂ inverse opals. Trilayer photonic crystal films were fabricated through the successive deposition of an inverse opal TiO₂ underlayer, a thin titania interlayer, and a photonic top layer, whose visible light activation was implemented through surface modification with CoO_x nanoscale complexes. Optical measurements showed the formation of "donor"-like localized states within the photonic band gap, which reduced the Bragg reflection and expanded the slow photon spectral range. The optimization of CoO_x loading and photonic band gap tuning resulted in a markedly improved photocatalytic performance for salicylic acid degradation and photocurrent generation compared to the additive effects of the constituent monolayers, indicative of light localization in the defect layer. The electrochemical impedance results showed reduced recombination kinetics, corroborating that the introduction of an optical defect into inverse opal photocatalysts provides a versatile and effective strategy for boosting the photonic amplification effects in visible light photocatalysis by evading the constraints imposed by narrow slow photon spectral regions.