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

Martha Pylarinou,Athanasios Dimoulas,Vlassis Likodimos,Evangelia Xenogiannopoulou,Spiros Gardelis,Nikos Boukos,Alexia Toumazatou,Elias Sakellis

doi:10.3390/ma14237117

Abstract

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 FeOx nanoclusters on TiO2 photonic crystals is investigated to explore the interplay of slow-photon amplification, visible light absorption, and charge separation in FeOx–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 FeOx loading on the photonic films. Low amounts of FeOx 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 FeOx–TiO2 interfacial coupling. However, an increase of the FeOx loading resulted in severe performance deterioration, particularly prominent under UV-Vis light, attributed to persistent surface recombination via diverse defect d-states.

Highlights

These Raman bands are close to the characteristic Raman modes of hematite a-Fe2 O3 [67], as shown in the reference spectra of Figure S4a [68]. They could be identified during laser heating experiments on maghemite (γ-Fe2 O3 ) nanoparticles, as shown in Figure S4b, while the same laser-induced transformation to hematite has been previously reported for the less crystalline ferrihydrite and wüstite phases [67,69]. These results suggest that poorly crystallized or even amorphous FeOx nanoclusters are deposited on the anatase walls of the surface-modified photonic crystals (PCs) films, consistent with the TEM
Surface modification of co-assembled TiO2 inverse opals by variable amounts of FeOx nanoclusters was implemented by successive chemisorption-calcination cycles of Fe(III)
Distinctive diameter-dependent improvements of the salicylic acid (SA) photocatalytic degradation rates and photocurrent density were obtained under visible light for low loading amounts of FeOx nanoclusters, which outperformed benchmark P25 films subjected to the same treatment

Summary

Introduction

A promising, though the challenging approach to intensify light-matter interactions and amplify photon capture is based on the fabrication of photocatalytic photonic crystals (PCs), i.e., periodically ordered structures, whose refractive index is spatially modulated on the scale of light’s wavelength [14,15,16,17]. Substantial research has been devoted to exploiting these advantageous characteristics in combination with materials’ compositional properties in order to develop visible light-activated (VLA) photonic photocatalysts [26], including coupling PCs with plasmonic [27,28,29,30] and graphene nanomaterials [31,32,33] as well as metal-oxide (MO) nanoclusters [34,35,36]

Methods

Results

Conclusion