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

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.

Mo-BiVO4/Ca-BiVO4 Homojunction Nanostructure-Based Inverse Opals for Photoelectrocatalytic Pharmaceutical Degradation under Visible Light

“…The metal doped-BiVO 4 PCs were accordingly evaluated on the photoelectrocatalytic degradation of SA as well as TC and CIP antibiotics under visible light at +1.0 V versus Ag/AgCl (Figure ). SA PEC degradation obeyed first-order kinetics with the homojunction PCs exhibiting greatly improved reaction rates r vis (Figure a–c), which followed closely the corresponding photocurrent variations under visible light (Figure a), indicating that SA degradation proceeds via photogenerated holes at acidic conditions similar to TiO 2 PCs . On the other hand, Ca-BiVO 4 and Mo–Ca–Mo PC films showed the highest performance in TC photoelectrocatalytic degradation (Figure d–f), though Mo-doping had a weak detrimental effect compared to pristine BiVO 4 PC films.…”

Light concentration and electron transfer in plasmonic–photonic Ag,Au modified Mo-BiVO4 inverse opal photoelectrocatalysts

“…However, the observed splitting was considerably moderated and less resolved for all Mo-BiVO 4 films, indicating that the introduction of molybdenum dopants substituting for vanadium in the BiVO 4 lattice, leads to the averaging of the ms low-symmetry toward the tetragonal scheelite structure. 39 In addition, no sign of metallic Au and Ag NPs could be traced in the XRD patterns of the Ag,Au-modified PC films, indicative of their relatively low loading amount. Micro-Raman spectra for the Ag,Au-modified Mo-BiVO 4 films at 785 nm, displayed in all cases the characteristic vibrational modes of single-phase monoclinic scheelite (ms) BiVO 4 with no sign of the tetragonal scheelite or zircon polymorphic phases.…”

“…Then, liquid infiltration of the opal films was carried out by dip-coating in a complex metal salt precursor based on ammonium vanadate (NH 4 VO 3 ) (ACS, 99.0% min) and bismuth(III) nitrate pentahydrate, Bi(NO 3 ) 3 •5H 2 O (99.999% trace metals basis) with the addition of ammonium molybdate tetrahydrate (NH 4 ) 6 Mo 7 O 24 •4H 2 O (BioUltra, ≥99.0%) as source of molybdenum (Mo) dopants at Mo : V molar ratios of 3%, followed by drying for 1 h at 70 °C. 39 After repeating the dipcoating process for three times, calcination was performed at 400 °C to remove the PS opal template and crystallize the amorphous precursor in the Mo-BiVO 4 inverse opal structure. The fabricated PC films were labelled as Mo-BiVO 4 PCXXX with XXX being the templating sphere diameter.…”

Co-assembled MoS2–TiO2 Inverse Opal Photocatalysts for Visible Light-Activated Pharmaceutical Photodegradation

“…This was further corroborated by the corresponding pore size distribution determined from nonlocal density functional theory (NLDFT) analysis using the N 2 −silica desorption branch kernel (equilibrium model) at 77 K (Figure 3b). 58 Markedly increased mesopore volume (V meso ) of 0.499 cm 3 /g was thus derived by the NLDFT pore size distribution with a maximum at 4.89 nm mesopore width, which can be related to the small anatase nanoparticle size. 46 Further improvement of surface area that reached 347 m 2 /g was derived for 0.3 MoS 2 -PC425, while the mesopore volume showed a relatively small decrease to 0.444 cm 3 /g indicating that the integration of the relatively bulkier MoS 2 nanosheets in the nanocrystalline anatase walls mainly affected the inverse opal macroporosity compared to the mesopore distribution.…”

“…Photocatalytic activity screening of the MoS 2 −TiO 2 PC films was performed using SA as a model pollutant under visible light at pH = 3 (Figure 5), where direct oxidation by valence band holes takes place. 59 SA is a colorless pharmaceutical water contaminant that, unlike dyes, absorbs well below the PC film stop bands in the visible range (Figure S6a) and thus precludes any slow photon contribution via spectral overlap with the molecular electronic absorption. Blank experiments in the absence of photocatalytic films as well as in the presence of unmodified PC425 films showed negligible SA degradation under visible light (Figure 5a).…”