Heterostructured CoO_x–TiO₂ Mesoporous/Photonic Crystal Bilayer Films for Enhanced Visible-Light Harvesting and Photocatalysis

• Main Authors: Stelios Loukopoulos, Alexia Toumazatou, Elias Sakellis, Evangelia Xenogiannopoulou, Nikos Boukos, Athanasios Dimoulas, Vlassis Likodimos
• Format: Article
• Language: English
• Published: MDPI AG 2020-09-01
• Series: Materials
• Subjects: photonic crystals; titanium dioxide; cobalt oxides; visible light; photocatalysis; slow photons
• Online Access: https://www.mdpi.com/1996-1944/13/19/4305

Heterostructured bilayer films, consisting of co-assembled TiO₂ photonic crystals as the bottom layer and a highly performing mesoporous P25 titania as the top layer decorated with CoO_x nanoclusters, are demonstrated as highly efficient visible-light photocatalysts. Broadband visible-light activation of the bilayer films was implemented by the surface modification of both titania layers with nanoscale clusters of Co oxides relying on the chemisorption of Co acetylacetonate complexes on TiO₂, followed by post-calcination. Tuning the slow photon regions of the inverse opal supporting layer to the visible-light absorption of surface CoO<i>_x</i> oxides resulted in significant amplification of salicylic-acid photodegradation under visible and ultraviolet (UV)–visible light (Vis), outperforming benchmark P25 films of higher titania loading. This enhancement was related to the spatially separated contributions of slow photon propagation in the inverse opal support layer assisted by Bragg reflection toward the CoO<i>_x</i>-modified mesoporous P25 top layer. This effect indicates that photonic crystals may be highly effective as both photocatalytically active and backscattering layers in multilayer photocatalytic films.