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

Stelios Loukopoulos,Alexia Toumazatou,Nikos Boukos,Evangelia Xenogiannopoulou,Elias Sakellis,Athanasios Dimoulas,Vlassis Likodimos

doi:10.3390/ma13194305

Stelios Loukopoulos, Alexia Toumazatou + Show 5 more

Open Access

https://doi.org/10.3390/ma13194305

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Abstract

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 CoOx 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 CoOx 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 CoOx-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.

Highlights

Shaping photocatalytic materials in the form of photonic crystals (PCs) has become a competent structural modification that exploits the unique capabilities for slow photon-assisted light harvesting, pore interconnectivity, and surface accessibility of periodic macroporous structures, such as inverse opals [1]
Materials 2020, 13, 4305 applied to enhance the light-harvesting efficiency of dye-sensitized solar cells by coupling a TiO2 inverse opal layer on a conventional nanoparticulate titania photoelectrode [11], exploiting the back reflection in the photonic band gap (PBG) region of the PC layer that acts as a dielectric mirror and the excitation of localized slow photon modes within the nanocrystalline mesoporous film [12,13]
Activation of the bilayer films over a broad spectral range was performed via the surface modification

Summary

Introduction

Shaping photocatalytic materials in the form of photonic crystals (PCs) has become a competent structural modification that exploits the unique capabilities for slow photon-assisted light harvesting, pore interconnectivity, and surface accessibility of periodic macroporous structures, such as inverse opals [1] These distinctive structural features can be effectively combined with rational compositional tuning of the materials’ properties for charge separation and visible-light activation (VLA) leading to efficient visible-light photocatalysts [2,3]. In addition to single-layer, monolithic inverse opals, PCs have attracted attention as photocatalytically inert supports for thin-film photocatalysts, where their strong PBG (Bragg) reflection is tuned to the catalysts’ electronic absorption edge [6,7,8,9,10] It should be noted that all films all films exhibited similar C 1s signals due to adventitious carbon that varied weakly after CoOx exhibited similar C 1s signals due to adventitious carbon that varied weakly after CoOx deposition or deposition or PMMA template removal, indicating that organic residues in the film pores are rather

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