Visible Light Trapping against Charge Recombination in FeO_x-TiO₂ Photonic Crystal Photocatalysts

Tailoring metal oxide photocatalysts in the form of heterostructured photonic crystals has spurred particular interest as an advanced route to simultaneously improve harnessing of solar light and charge separation relying on the combined effect of light trapping by macroporous periodic structures and compositional materials' modifications. In this work, surface deposition of FeO_x nanoclusters on TiO₂ photonic crystals is investigated to explore the interplay of slow-photon amplification, visible light absorption, and charge separation in FeO_x-TiO₂ photocatalytic films. Photonic bandgap engineered TiO₂ inverse opals deposited by the convective evaporation-induced co-assembly method were surface modified by successive chemisorption-calcination cycles using Fe(III) acetylacetonate, which allowed the controlled variation of FeO_x loading on the photonic films. Low amounts of FeO_x nanoclusters on the TiO₂ inverse opals resulted in diameter-selective improvements of photocatalytic performance on salicylic acid degradation and photocurrent density under visible light, surpassing similarly modified P25 films. The observed enhancement was related to the combination of optimal light trapping and charge separation induced by the FeO_x-TiO₂ interfacial coupling. However, an increase of the FeO_x loading resulted in severe performance deterioration, particularly prominent under UV-Vis light, attributed to persistent surface recombination via diverse defect d-states.