Abstract
Photo-Fenton-like oxidation of organic substances is one of the key advanced oxidation processes based on the reversible Fe2+↔Fe3+ transition and the generation of a strong oxidant ·OH in the presence of H2O2 and is currently considered as a promising method for the purification of polluted aqueous media. However, the absence of effective and stable photocatalysts of this process, operating under the action of visible light, necessitates the exploratory studies, mainly among iron oxides and ferrites of various compositions and structures. In this work, using the method of solution combustion followed by heat treatment in air the heterojunction nanocomposites based on ytterbium orthoferrite and cerium dioxide of the composition o-YbFeO3/h-YbFeO3/CeO2 (0–20 mol.%) with high absorption in the visible region and advanced photo-Fenton-like activity were obtained. The nanocomposites were studied by EDS, SEM, XRD, BET, and DRS methods. The photo-Fenton-like activity of the nanocomposites was investigated during the degradation of methyl violet under the action of visible (λmax = 410 nm) radiation. As a result, the formation of I-type heterojunction based on stable rhombic (55.4–79.0 nm) and metastable hexagonal (19.5–24.0 nm) modifications of ytterbium orthoferrite (o-YbFeO3 and h-YbFeO3, respectively) and cubic cerium dioxide CeO2 (13.2–19.2 nm) nanocrystals was established. It was shown that the obtained nanocomposites had foamy morphology and were characterized by a specific surface in the range of 9.1–25.0 m2/g, depending on the CeO2 content. It was found that nanocrystalline components were chemically and phase-pure, uniformly spatially distributed over the nanocomposite, and had multiple contacts with each other. Based on this fact and the established electronic structure of the nanocomposite components, the formation of I-type heterojunction with the participation of o-YbFeO3 (Eg = 2.15 eV), h-YbFeO3 (Eg = 2.08 eV), and CeO2 (Eg = 2.38 eV) was shown, the presence of which increased photocatalytic activity of the resulting nanocomposite. The optimal content of CeO2 in the nanocomposite was 5%, and the o-YbFeO3/h-YbFeO3/CeO2–5% sample was characterized by the highest rate constant of photo-Fenton-like degradation of methyl violet under the action of visible light equal to k = 0.138 min–1, which was 2.5 to 5 times higher than for nanocomposites based on ytterbium orthoferrite. The obtained results obtained indicate that the developed nanocomposites can be considered as a promising basis for the advanced oxidation processes for the purification of aqueous media from organic pollutants.
Highlights
The problem of water purification from organic pollutants is attracting more and more attention
We propose the preparation of the o-YbFeO3/h-YbFeO3/CeO2 nanocomposite by the method of solution combustion, carried out in a soft glow mode, followed by a heat treatment of amorphous products at moderate temperatures in air
The error of the determination method for heavy elements is about 0.5 wt.%, it was stated that the compositions of the composites for the main elements (Yb, Ce, Fe) were in good agreement with the composition specified during their synthesis
Summary
The problem of water purification from organic pollutants is attracting more and more attention. The classical homogeneous Fenton process has significant disadvantages, such as high specific cost, limited operating pH range, the formation of a large volume of iron sludge (which has a detrimental effect on the environment and leads to the loss of a large amount of catalytic metals), as well as difficulties in catalyst regeneration (Fe2+) To overcome these disadvantages the improved approaches based on the Fenton process are currently being developed and, in particular, a photoinduced Fenton-like heterogeneous process, which eliminates the known limitations. The formation of a heterojunction prevents the recombination of electron-hole pairs and thereby increases the overall photocatalytic efficiency of the nanocomposite material [15, 17], but does not significantly affect the characteristic region of radiation absorption To solve this problem, this work proposes the development of nanocomposite photocatalysts based on ytterbium orthoferrite and a co-catalyst, cubic cerium oxide (CeO2). We propose the preparation of the o-YbFeO3/h-YbFeO3/CeO2 nanocomposite by the method of solution combustion, carried out in a soft glow mode, followed by a heat treatment of amorphous products at moderate temperatures in air
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